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SpaceX Vehicles and Missions => SpaceX Starship Program => Topic started by: Slarty1080 on 04/26/2020 01:01 pm

Title: Starship heat shield
Post by: Slarty1080 on 04/26/2020 01:01 pm
Seems there has been some discussion concerning the nature and geometry of the tiles to be used on Starship.
https://forum.nasaspaceflight.com/index.php?topic=50620.msg2073268#msg2073268 (https://forum.nasaspaceflight.com/index.php?topic=50620.msg2073268#msg2073268)

Moving this to a separate thread as requested

Here's my take on what the  tile layout might be. I know that everyone is trying to minimise the number of tiles, but I think there is a trade off and if they need to have a few dozen tile types to make a reliable and uniform surface then so be it. In my design the tiles get narrower as you move towards the apex. At some point depending on the degree of curvature relative to the size of the tiles it might also be necessary to decrease their height as well.
Title: Re: Starship heat shield
Post by: Eylrid on 04/26/2020 01:08 pm
Having a large number of intricate tile shapes might not be a problem by itself as long as they don't require a manual repairs. Unlike on the Shuttle there is no chance of getting hit by debris during launch.

For tiling a rounded cone they could do it using the same slightly warped hexagon at each height point.

But they might eventually go for unique shapes of varying thickness anyway in order to optimize mass.

It's actually mathematically impossible to tile a rounded cone with any sort of uniform warped hexagon.  If you try it, you'll find that it works alright at the beginning, but as the surface continues curving, your hexagons will become more and more distorted until you're forced to add pentagons to the mix.  This is a direct consequence of the Euler Identity.

There's just no way to avoid requiring a large number of different tile shapes when trying to tile a surface with non-zero curvature.  (A cylinder has, mathematically speaking, zero curvature, just to be clear on this.  Not so for a rounded cone)

Mathematically you're correct.

But engineers like to cheat ;D

1 type of tile in 2 forms, whole and cut in half.

PS: I'd like to emphasize that only 200deg of SS needs to be tiled.

Long straight lines like that are problematic.

In the words of Elon when asked why hexagons:

Quote
No straight path for hot gas to accelerate through the gaps

https://twitter.com/elonmusk/status/1107379727302451200
Title: Re: Starship heat shield
Post by: rakaydos on 04/26/2020 01:15 pm
If I was back at my parents' place, I would have a practical project, using some of the model rocket nose cones in the attic, and an old settlers of Catan game. The idea being to minimize the number of off-regular shapes to tile half the cone.

Intuitively, I would think the best approach involves a line of custom tiles at the base of the curve, and a custom nose cap. The edges of the tile set would twist in an interesting way.
Title: Re: Starship heat shield
Post by: DusanC on 04/26/2020 01:17 pm
Having a large number of intricate tile shapes might not be a problem by itself as long as they don't require a manual repairs. Unlike on the Shuttle there is no chance of getting hit by debris during launch.

For tiling a rounded cone they could do it using the same slightly warped hexagon at each height point.

But they might eventually go for unique shapes of varying thickness anyway in order to optimize mass.

It's actually mathematically impossible to tile a rounded cone with any sort of uniform warped hexagon.  If you try it, you'll find that it works alright at the beginning, but as the surface continues curving, your hexagons will become more and more distorted until you're forced to add pentagons to the mix.  This is a direct consequence of the Euler Identity.

There's just no way to avoid requiring a large number of different tile shapes when trying to tile a surface with non-zero curvature.  (A cylinder has, mathematically speaking, zero curvature, just to be clear on this.  Not so for a rounded cone)

Mathematically you're correct.

But engineers like to cheat ;D

1 type of tile in 2 forms, whole and cut in half.

PS: I'd like to emphasize that only 200deg of SS needs to be tiled.

Long straight lines like that are problematic.

In the words of Elon when asked why hexagons:

Quote
No straight path for hot gas to accelerate through the gaps

https://twitter.com/elonmusk/status/1107379727302451200
I agree that is a problem, every solution has its trade offs.
There are two extremes for solving SS tiling problem:
1. Different tiles for each row
2. Universal tile with trade offs

I presume the answer is in between, probably universal tile for large radii and special tiles (like Slarty's excellent idea above) for small radii.
Title: Re: Starship heat shield
Post by: Karloss12 on 04/26/2020 01:23 pm
Having a large number of intricate tile shapes might not be a problem by itself as long as they don't require a manual repairs. Unlike on the Shuttle there is no chance of getting hit by debris during launch.

For tiling a rounded cone they could do it using the same slightly warped hexagon at each height point.

But they might eventually go for unique shapes of varying thickness anyway in order to optimize mass.

It's actually mathematically impossible to tile a rounded cone with any sort of uniform warped hexagon.  If you try it, you'll find that it works alright at the beginning, but as the surface continues curving, your hexagons will become more and more distorted until you're forced to add pentagons to the mix.  This is a direct consequence of the Euler Identity.

There's just no way to avoid requiring a large number of different tile shapes when trying to tile a surface with non-zero curvature.  (A cylinder has, mathematically speaking, zero curvature, just to be clear on this.  Not so for a rounded cone)

Mathematically you're correct.

But engineers like to cheat ;D

1 type of tile in 2 forms, whole and cut in half.

PS: I'd like to emphasize that only 200deg of SS needs to be tiled.

Long straight lines like that are problematic.

In the words of Elon when asked why hexagons:

Quote
No straight path for hot gas to accelerate through the gaps

https://twitter.com/elonmusk/status/1107379727302451200
I think there will be near ideal hexagonal throughout, however they will get smaller in width and height as the cone hoop diameter gets smaller (as you go up the cone).
When the tiles get too small and fiddly there will need to be a step change, where there is a row of half tiles to end the existing pattern so that a new pattern can start from scratch with larger tiles. 
It would look aesthetically pleasing if the new pattern on top had the first row of tiles twice the size of the last row of tiles on the first pattern.
Title: Re: Starship heat shield
Post by: SteveU on 04/26/2020 01:27 pm
Seems there has been some discussion concerning the nature and geometry of the tiles to be used on Starship.
https://forum.nasaspaceflight.com/index.php?topic=50620.msg2073268#msg2073268 (https://forum.nasaspaceflight.com/index.php?topic=50620.msg2073268#msg2073268)

Moving this to a separate thread as requested

Here's my take on what the  tile layout might be. I know that everyone is trying to minimise the number of tiles, but I think there is a trade off and if they need to have a few dozen tile types to make a reliable and uniform surface then so be it. In my design the tiles get narrower as you move towards the apex. At some point depending on the degree of curvature relative to the size of the tiles it might also be necessary to decrease their height as well.
[bolding mine]
As long as there are multiples of each shape, whole rows for example, I wholeheartedly agree with this. We have to remember that there will be hundreds of these ships, so having different shapes, as long as they aren’t “one offs” shouldn’t be a problem.  This applies to initial construction and repairs (both on Earth or Mars).  Biggest issue with the shuttle was that almost every single tile was slightly different.
Title: Re: Starship heat shield
Post by: DusanC on 04/26/2020 01:38 pm
I have a questions based on excellent BCG's photos https://forum.nasaspaceflight.com/index.php?topic=48895.msg2072270#msg2072270

There are indications that some tiles on SS SN4 are made by coating bent sheet metal. There are even some areas where there is small surface damage to the coating. Is there any other explanation?
Title: Re: Starship heat shield
Post by: Karloss12 on 04/26/2020 01:43 pm
Seems there has been some discussion concerning the nature and geometry of the tiles to be used on Starship.
https://forum.nasaspaceflight.com/index.php?topic=50620.msg2073268#msg2073268 (https://forum.nasaspaceflight.com/index.php?topic=50620.msg2073268#msg2073268)

Moving this to a separate thread as requested

Here's my take on what the  tile layout might be. I know that everyone is trying to minimise the number of tiles, but I think there is a trade off and if they need to have a few dozen tile types to make a reliable and uniform surface then so be it. In my design the tiles get narrower as you move towards the apex. At some point depending on the degree of curvature relative to the size of the tiles it might also be necessary to decrease their height as well.
[bolding mine]
As long as there are multiples of each shape, whole rows for example, I wholeheartedly agree with this. We have to remember that there will be hundreds of these ships, so having different shapes, as long as they aren’t “one offs” shouldn’t be a problem.  This applies to initial construction and repairs (both on Earth or Mars).  Biggest issue with the shuttle was that almost every single tile was slightly different.
If there are 100 rows, each with indentical tiles, and each tile has the same fastening arrangement, then every tile on the SS can be cut from the same identical raw tile (using a water jet cutter).
It would be to much weight to take 100-200 spare tiles to mars. Instead they will just take half a dozen or so of these raw tiles as spares and use simple hand tools to cut them to any of the 100 or so different shapes (corresponding to 100 different rows).
They would have to get some practice in custom making tiles before they left for Mars.
Title: Re: Starship heat shield
Post by: Karloss12 on 04/26/2020 01:58 pm
I have a questions based on excellent BCG's photos https://forum.nasaspaceflight.com/index.php?topic=48895.msg2072270#msg2072270

There are indications that some tiles on SS SN4 are made by coating bent sheet metal. There are even some areas where there is small surface damage to the coating. Is there any other explanation?
The Shuttle had thin high temperature pads which would be inserted in the gaps between tiles to prevent heat getting under the tile.
Elon is trying to avoid having to do this by using hexagonal tiles, however he may have to resign himself to there being a need for something to be positioned between the tiles.
Title: Re: Starship heat shield
Post by: wannamoonbase on 04/26/2020 02:36 pm
Will the tiles be flat and approximate the 9 meter curved shape of SS? 

Or will the tiles themselves have That 9M curve made into them?

The forward end of the nose will need to be curved, probably in 2 dimensions the closer to the nose.

Once flying the heat shield could easily be a multi year improvement project. 

Edit: There will be plenty of specialty pieces around and on the control surfaces as well.
Title: Re: Starship heat shield
Post by: rakaydos on 04/26/2020 02:42 pm
Will the tiles be flat and approximate the 9 meter curved shape of SS? 

Or will the tiles themselves have That 9M curve made into them?

The forward end of the nose will need to be curved, probably in 2 dimensions the closer to the nose.

Once flying the heat shield could easily be a multi year improvement project. 

Edit: There will be plenty of specialty pieces around and on the control surfaces as well.
flat is probably significantly cheaper, and good enough to do the job.
Title: Re: Starship heat shield
Post by: joek on 04/26/2020 04:01 pm
I have a questions based on excellent BCG's photos https://forum.nasaspaceflight.com/index.php?topic=48895.msg2072270#msg2072270

There are indications that some tiles on SS SN4 are made by coating bent sheet metal. There are even some areas where there is small surface damage to the coating. Is there any other explanation?

Don't see indication of sheet metal.  Looks like a coating on the underlying material (white stuff), which is showing through in a couple areas.[1]  In any case, doubt those "defects" will matter for near-term tests as unlikely to stress TPS-related thermal properties.  Near-term test more likely focused on mechanical properties of tiles and attachment.  Leaving those "defects" may also be, if not intentional, "so they're not all prefect... let's see what happens?... does it spread, start peeling off or...?"


[1] That would be consistent with similar TPS construction.
edit: p.s. see attached as example; snip from Thermal Protection Materials and Systems: Past and Future (https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160001151.pdf), Sylvia M. Johnson, NASA Ames Research Center, 25-Jan-2015.
Title: Re: Starship heat shield
Post by: joek on 04/26/2020 04:11 pm
Will the tiles be flat and approximate the 9 meter curved shape of SS? 
...
flat is probably significantly cheaper, and good enough to do the job.

Likely depends on fabrication technique(s).  Molded or stamped? Make it most any shape/curvature at similar cost.  Milled-machined?  More expensive.  Cut from larger sheets or molds? ... ?

In any case, commonality will be key to reducing costs (including attachment mechanisms)--notwithstanding that there will likely be some specialty pieces.
Title: Re: Starship heat shield
Post by: livingjw on 04/26/2020 04:13 pm
I have a questions based on excellent BCG's photos https://forum.nasaspaceflight.com/index.php?topic=48895.msg2072270#msg2072270

There are indications that some tiles on SS SN4 are made by coating bent sheet metal. There are even some areas where there is small surface damage to the coating. Is there any other explanation?

- The tiles look similar to how the Shuttle tiles were made. Molded white rigid insulation (AETB or similar) with a hard outer coating for protection and control of emissivity. I don't know how you would mechanically attach such a tile since the rigid insulation have very little strength. Perhaps structural inserts molded into the insulation.

- Rigid insulation is easily milled to any shape, then the coating is applied.

John
Title: Re: Starship heat shield
Post by: WormPicker959 on 04/26/2020 04:56 pm
I have a questions based on excellent BCG's photos https://forum.nasaspaceflight.com/index.php?topic=48895.msg2072270#msg2072270

There are indications that some tiles on SS SN4 are made by coating bent sheet metal. There are even some areas where there is small surface damage to the coating. Is there any other explanation?

<WAG> It could be that these are manufacturing rejects? They're not going to perform entry heating tests, so likely these are tests of stability/fastening to ship. For that, you don't need a perfect tile, and can use the ones that didn't pass QC. </WAG>
Title: Re: Starship heat shield
Post by: xvel on 04/26/2020 05:24 pm
I have a questions based on excellent BCG's photos https://forum.nasaspaceflight.com/index.php?topic=48895.msg2072270#msg2072270

There are indications that some tiles on SS SN4 are made by coating bent sheet metal. There are even some areas where there is small surface damage to the coating. Is there any other explanation?

- The tiles look similar to how the Shuttle tiles were made. Molded white rigid insulation (AETB or similar) with a hard outer coating for protection and control of emissivity. I don't know how you would mechanically attach such a tile since the rigid insulation have very little strength. Perhaps structural inserts molded into the insulation.

- Rigid insulation is easily milled to any shape, then the coating is applied.

John

so maybe many different types of tiles will be viable and for repairing (on mars for example) they'll just have blanks and cut it with a small cnc milling machine (it shouldn't be heavy at all)
Title: Re: Starship heat shield
Post by: samgineer on 04/26/2020 05:28 pm
I have a questions based on excellent BCG's photos https://forum.nasaspaceflight.com/index.php?topic=48895.msg2072270#msg2072270

There are indications that some tiles on SS SN4 are made by coating bent sheet metal. There are even some areas where there is small surface damage to the coating. Is there any other explanation?

Interesting idea, in fact musk newer said about something about TUFROC or other kind of ceramic TPS, as I know last mention of TPS was last year video tweet from testing hex steel tiles. Before that there was another video from testing metal sheet on similar white (probably ceramic fibre) wool. Maybe they really are black, high temperature ceramics powder coated (like this used in exhaust systems (https://www.itccoatings.com/blog/2018/4/24/top-4-benefits-of-high-temp-ceramic-coating-for-your-cars-exhaust-system)), high temp resistant steel sheet hexagons. It is easy to made on production line, only few stampings and some kind of powder ceramics coating hardened in furnace everything simple, easy to mass produce and durable. Also in this case, mechanical attachment is much, much easier. 
Title: Re: Starship heat shield
Post by: livingjw on 04/26/2020 05:32 pm
I have a questions based on excellent BCG's photos https://forum.nasaspaceflight.com/index.php?topic=48895.msg2072270#msg2072270

There are indications that some tiles on SS SN4 are made by coating bent sheet metal. There are even some areas where there is small surface damage to the coating. Is there any other explanation?

- The tiles look similar to how the Shuttle tiles were made. Molded white rigid insulation (AETB or similar) with a hard outer coating for protection and control of emissivity. I don't know how you would mechanically attach such a tile since the rigid insulation have very little strength. Perhaps structural inserts molded into the insulation.

- Rigid insulation is easily milled to any shape, then the coating is applied.

John

so maybe many different types of tiles will be viable and for repairing (on mars for example) they'll just have blanks and cut it with a small cnc milling machine (it shouldn't be heavy at all)

Yes, the tiles are  ~-05% fiber and binder and 95% void.

John
Title: Re: Starship heat shield
Post by: Coastal Ron on 04/26/2020 05:40 pm
Yes, the tiles are  ~-05% fiber and binder and 95% void.

For attachment points, maybe when they are casting/molding the tiles, they insert a fiber matrix that terminates in one or more attachment points?

Or they could glue an attachment plate onto the bottom of each tile, but that could add a lot of weight.
Title: Re: Starship heat shield
Post by: livingjw on 04/26/2020 05:47 pm
Yes, the tiles are  ~-05% fiber and binder and 95% void.

For attachment points, maybe when they are casting/molding the tiles, they insert a fiber matrix that terminates in one or more attachment points?

Or they could glue an attachment plate onto the bottom of each tile, but that could add a lot of weight.

I'm thinking the former. You could mold ceramic matrix composite straps or fingers into the cavity which terminate at the attachment points.

John
Title: Re: Starship heat shield
Post by: joek on 04/26/2020 06:06 pm
Yes, the tiles are  ~-05% fiber and binder and 95% void.

For attachment points, maybe when they are casting/molding the tiles, they insert a fiber matrix that terminates in one or more attachment points?

Or they could glue an attachment plate onto the bottom of each tile, but that could add a lot of weight.

Likely those attachment points are what we are seeing in a couple photos--they appear to go directly from the airframe to the the TPS.  That appears to be one possible difference between previous applications of, e.g., TUFROC on X-37B; to my knowledge we have never seen what the airframe attachment looks like.  However, public presentations show attachment between two layers of the underlying TPS (see previous post), which might be similar to the airframe attachment.

That said, it is unclear if the types of attachments shown are semi-permanent and difficult to easily replace, or require substantive work to replace.

Think that difference is worth noting: How much time-cost-effort-$ does it require to initially fabricate-install , versus how much time-cost-effort-$ does it require to maintain-replace?  Obviously robustness of solution affects cost of both.  Guess is that SpaceX would prefer a more robust solution that decreases maintenance.

Which is why we are seeing what appears to be a base level airframe-to TPS pin-based (pop-on, pop-off) arrangement.  All they need to do is reduce the heat transfer/flux from the lower level TPS to the airframe to an acceptable level.[1]


[1] edit: p.s. Not to minimize the problem; certainly a challenge.  But has to be considered as a whole.  For example, Starship's "fluffiness" should help reduce TPS demands.
Title: Re: Starship heat shield
Post by: envy887 on 04/26/2020 07:01 pm
In my design the tiles get narrower as you move towards the apex. At some point depending on the degree of curvature relative to the size of the tiles it might also be necessary to decrease their height as well.

It looks to me like the radius in the in that direction is constant, so you would not need to decrease the height. Getting narrower is enough.
Title: Re: Starship heat shield
Post by: aero on 04/26/2020 07:27 pm
In my design the tiles get narrower as you move towards the apex. At some point depending on the degree of curvature relative to the size of the tiles it might also be necessary to decrease their height as well.

It looks to me like the radius in the in that direction is constant, so you would not need to decrease the height. Getting narrower is enough.

Are you considering that the heat shield only needs to be on one side? That is, they only go ~halfway around. That means that the ends of a row of tiles need not align with the previous row. Does that mean that the same sized tiles could be used for adjacent tile rows? Maybe not, but it is an additional degree of freedom to consider.
Title: Re: Starship heat shield
Post by: john smith 19 on 04/26/2020 07:33 pm
I have a questions based on excellent BCG's photos https://forum.nasaspaceflight.com/index.php?topic=48895.msg2072270#msg2072270

There are indications that some tiles on SS SN4 are made by coating bent sheet metal. There are even some areas where there is small surface damage to the coating. Is there any other explanation?
The Shuttle had thin high temperature pads which would be inserted in the gaps between tiles to prevent heat getting under the tile.
Elon is trying to avoid having to do this by using hexagonal tiles, however he may have to resign himself to there being a need for something to be positioned between the tiles.
They were called "gap fillers"  and were put in to stop rentry plasma hitting the aluminum skin.

Then the tiles were glued to thin nylon fabric layers (AIU like the stuff womens tights are made out of) to handle the contraction and expansion.

But steels TCE is substantially less than aluminiums so such a support pad should be redundant.

Also is it my impression that each tile is on a single point mounting? In principle each tile could tip and tile (slightly) in the airstream. This might be enough to avoid flow separation and any need to curve every tile to match the underlying surface.

But this is the easy part.

Wrapping that TPS around the wings/drag surfaces/whatever is likely to prove much trickier.

Title: Re: Starship heat shield
Post by: DusanC on 04/26/2020 07:46 pm
I have a questions based on excellent BCG's photos https://forum.nasaspaceflight.com/index.php?topic=48895.msg2072270#msg2072270

There are indications that some tiles on SS SN4 are made by coating bent sheet metal. There are even some areas where there is small surface damage to the coating. Is there any other explanation?
The Shuttle had thin high temperature pads which would be inserted in the gaps between tiles to prevent heat getting under the tile.
Elon is trying to avoid having to do this by using hexagonal tiles, however he may have to resign himself to there being a need for something to be positioned between the tiles.
They were called "gap fillers"  and were put in to stop rentry plasma hitting the aluminum skin.

Then the tiles were glued to thin nylon fabric layers (AIU like the stuff womens tights are made out of) to handle the contraction and expansion.

But steels TCE is substantially less than aluminiums so such a support pad should be redundant.

Also is it my impression that each tile is on a single point mounting? In principle each tile could tip and tile (slightly) in the airstream. This might be enough to avoid flow separation and any need to curve every tile to match the underlying surface.

But this is the easy part.

Wrapping that TPS around the wings/drag surfaces/whatever is likely to prove much trickier.
SS SN04 tiles have 2 types of snap mounting:
1. On all 6 sides
2. On 3 studs
Title: Re: Starship heat shield
Post by: john smith 19 on 04/26/2020 07:51 pm
Think that difference is worth noting: How much time-cost-effort-$ does it require to initially fabricate-install , versus how much time-cost-effort-$ does it require to maintain-replace?  Obviously robustness of solution affects cost of both.  Guess is that SpaceX would prefer a more robust solution that decreases maintenance.
Indeed.

Shuttle tile replacement costs were listed (on the TPSX database, now defunct) as $12000/m^2

However SS/SH will be radically cheaper as it is clear (unlike with shuttle) there will be a substantial amount of commonality, rather than the Shuttle, where nearly every tile was unique in size, shape and thickness (thinking this was a good idea may have been the design teams biggest failure. Actually building it was possibly the greatest triumph of the manufacturing team).
Title: Re: Starship heat shield
Post by: Slarty1080 on 04/26/2020 07:53 pm
Having a large number of intricate tile shapes might not be a problem by itself as long as they don't require a manual repairs. Unlike on the Shuttle there is no chance of getting hit by debris during launch.

For tiling a rounded cone they could do it using the same slightly warped hexagon at each height point.

But they might eventually go for unique shapes of varying thickness anyway in order to optimize mass.

It's actually mathematically impossible to tile a rounded cone with any sort of uniform warped hexagon.  If you try it, you'll find that it works alright at the beginning, but as the surface continues curving, your hexagons will become more and more distorted until you're forced to add pentagons to the mix.  This is a direct consequence of the Euler Identity.

There's just no way to avoid requiring a large number of different tile shapes when trying to tile a surface with non-zero curvature.  (A cylinder has, mathematically speaking, zero curvature, just to be clear on this.  Not so for a rounded cone)

Mathematically you're correct.

But engineers like to cheat ;D

1 type of tile in 2 forms, whole and cut in half.

PS: I'd like to emphasize that only 200deg of SS needs to be tiled.

Long straight lines like that are problematic.

In the words of Elon when asked why hexagons:

Quote
No straight path for hot gas to accelerate through the gaps

https://twitter.com/elonmusk/status/1107379727302451200
All of the verticals are the same size as the standard hex tile and the other lines are shorter.
Title: Re: Starship heat shield
Post by: john smith 19 on 04/26/2020 07:57 pm
SS SN04 tiles have 2 types of snap mounting:
1. On all 6 sides
2. On 3 studs
Thanks for that detail.


Title: Re: Starship heat shield
Post by: joek on 04/26/2020 07:57 pm
...
Also is it my impression that each tile is on a single point mounting? In principle each tile could tip and tile (slightly) in the airstream. This might be enough to avoid flow separation and any need to curve every tile to match the underlying surface.
...

Not sure I see that... Would guess it depends on required heat load transferred to (or isolated from) tiles to airframe.  If heat load can be limited to tiles (no xfer to airframe), would not matter; if heat load is required to be transferred to airframe, then likely does matter as those attach points will need to xfer heat load.  Then we are all into guessing about what level of heat load can be transferred or can or should be transferred from tiles to airframe through those points.... I have no idea.
Title: Re: Starship heat shield
Post by: joek on 04/26/2020 08:05 pm
SS SN04 tiles have 2 types of snap mounting:
1. On all 6 sides
2. On 3 studs
Please provide a definitive reference?  We have conjecture as to attachment for both.  Caution that what we have seen is not necessarily indicative of final configuration.  Thanks.
Title: Re: Starship heat shield
Post by: DusanC on 04/26/2020 08:18 pm
SS SN04 tiles have 2 types of snap mounting:
1. On all 6 sides
2. On 3 studs
Please provide a definitive reference?  We have conjecture as to attachment for both.  Caution that what we have seen is not necessarily indicative of final configuration.  Thanks.
Only true reference except EM

BCG

https://forum.nasaspaceflight.com/index.php?topic=48895.msg2070295#msg2070295
2nd and 3rd pic, zoom in.

Also, I said SS SN04 so OFC not final configuration.
Title: Re: Starship heat shield
Post by: Bananas_on_Mars on 04/26/2020 08:18 pm
If there are 100 rows, each with indentical tiles, and each tile has the same fastening arrangement, then every tile on the SS can be cut from the same identical raw tile (using a water jet cutter).
It would be to much weight to take 100-200 spare tiles to mars. Instead they will just take half a dozen or so of these raw tiles as spares and use simple hand tools to cut them to any of the 100 or so different shapes (corresponding to 100 different rows).
They would have to get some practice in custom making tiles before they left for Mars.

For „field repairs“ on mars they could easily use dissimilar materials (for example ablative materials). AFAIK Elon also said mars ships might have a heatshield that‘s different from what your average daily-use starship will have. Most Starships flying to mars might only use their heatshield once.
Title: Re: Starship heat shield
Post by: john smith 19 on 04/26/2020 08:24 pm
BTW

A few years ago DLR ran a sounding rocket test with the Brazilian space agency.

They built a nose cone out of standard sized RCC tiles, mostly triangles, pentagons etc.

The key development was the software to confirm despite the segments being flat that the aerodynamics were OK and the flow was smooth enough to avoid turbulent flow (which multiplies heat transfer between 4x and about 6x).
Title: Re: Starship heat shield
Post by: Slarty1080 on 04/26/2020 08:24 pm
In my design the tiles get narrower as you move towards the apex. At some point depending on the degree of curvature relative to the size of the tiles it might also be necessary to decrease their height as well.

It looks to me like the radius in the in that direction is constant, so you would not need to decrease the height. Getting narrower is enough.

Are you considering that the heat shield only needs to be on one side? That is, they only go ~halfway around. That means that the ends of a row of tiles need not align with the previous row. Does that mean that the same sized tiles could be used for adjacent tile rows? Maybe not, but it is an additional degree of freedom to consider.
The problem is that each tile needs to align with those in front and behind it. On a curved surface this means the angles on the hexagons have to change (see my diagram at the top of page 1) unless the intention is for tile overlap, in which case regular  hexagons might be tried, but I think it would be very messy. The areas of overlap would change and the zig-zag peaks and troughs between layers of tiles would run out of phase and wouldn't line up.
Title: Re: Starship heat shield
Post by: wes_wilson on 04/26/2020 09:41 pm
Is the flow over the tiles uni-directional enough to do overlapping tiles?  If the tile was thickest at the front where it attached and tapered towards the overlapped portion (like a wedge) you could keep the actual surface fairly close to smooth and use a fish dragon scale shape. 

https://www.featurepics.com/FI/Thumb300/20090104/Big-Carp-Scales-1022424.jpg
Title: Re: Starship heat shield
Post by: john smith 19 on 04/26/2020 09:55 pm
The problem is that each tile needs to align with those in front and behind it. On a curved surface this means the angles on the hexagons have to change (see my diagram at the top of page 1) unless the intention is for tile overlap, in which case regular  hexagons might be tried, but I think it would be very messy. The areas of overlap would change and the zig-zag peaks and troughs between layers of tiles would run out of phase and wouldn't line up.
Practically there are 2 issues here.
1) Finding the minimum number of tile type and sizes that map the surface. Kind of like how you render a CAD image with the minimum number (and type) of polygons.
2) How the edges of those polygons line up.

1) is relatively simple (for simple shapes)
2) Gets much more complex. The real question is how good does the polygonal approximation to the underlying surface need to be?

Because an exact match would imply thick tiles that can be machined to a curve (which is how they did it with the shuttle, and part of the very high cost of maintenance).

My instinct (and the work of DLR sounding rocket test) is that is not necessary provided the discontinuities are a fairly small part of the boundary layer thickness

If so you can get away with flat files of the same shape, but multiple sizes, all machined from a standard size billet.

That problem gets a lot trickier on the fin leading edges, with high curvature, needing a lot of small (but IMHO still standard shaped) tiles to handle the leading edge.  The area between the body and the control surfaces being exceptionally tricky.
Title: Re: Starship heat shield
Post by: Slarty1080 on 04/27/2020 10:18 am
The problem is that each tile needs to align with those in front and behind it. On a curved surface this means the angles on the hexagons have to change (see my diagram at the top of page 1) unless the intention is for tile overlap, in which case regular  hexagons might be tried, but I think it would be very messy. The areas of overlap would change and the zig-zag peaks and troughs between layers of tiles would run out of phase and wouldn't line up.
Practically there are 2 issues here.
1) Finding the minimum number of tile type and sizes that map the surface. Kind of like how you render a CAD image with the minimum number (and type) of polygons.
2) How the edges of those polygons line up.

1) is relatively simple (for simple shapes)
2) Gets much more complex. The real question is how good does the polygonal approximation to the underlying surface need to be?

Because an exact match would imply thick tiles that can be machined to a curve (which is how they did it with the shuttle, and part of the very high cost of maintenance).

My instinct (and the work of DLR sounding rocket test) is that is not necessary provided the discontinuities are a fairly small part of the boundary layer thickness

If so you can get away with flat files of the same shape, but multiple sizes, all machined from a standard size billet.

That problem gets a lt trickier on the fin leading edges, with high curvature, needing a lot of small (but IMHO still standard shaped) tiles to handle the leading edge.  The area between the body and the control surfaces being exceptionally tricky.
Can they make a special tile type that totally covers the leading edge on one side and keys in with the hexagon tiles on the other? If the curvature of the wings was constant it would only require one such tile... that said I'm thinking the curvature won't be the same will it? in which case it means unique tiles all along leading edge or at least on the variable curvature bits...
Title: Re: Starship heat shield
Post by: Eylrid on 04/27/2020 11:43 am
Having a large number of intricate tile shapes might not be a problem by itself as long as they don't require a manual repairs. Unlike on the Shuttle there is no chance of getting hit by debris during launch.

For tiling a rounded cone they could do it using the same slightly warped hexagon at each height point.

But they might eventually go for unique shapes of varying thickness anyway in order to optimize mass.

It's actually mathematically impossible to tile a rounded cone with any sort of uniform warped hexagon.  If you try it, you'll find that it works alright at the beginning, but as the surface continues curving, your hexagons will become more and more distorted until you're forced to add pentagons to the mix.  This is a direct consequence of the Euler Identity.

There's just no way to avoid requiring a large number of different tile shapes when trying to tile a surface with non-zero curvature.  (A cylinder has, mathematically speaking, zero curvature, just to be clear on this.  Not so for a rounded cone)

Mathematically you're correct.

But engineers like to cheat ;D

1 type of tile in 2 forms, whole and cut in half.

PS: I'd like to emphasize that only 200deg of SS needs to be tiled.

Long straight lines like that are problematic.

In the words of Elon when asked why hexagons:

Quote
No straight path for hot gas to accelerate through the gaps

https://twitter.com/elonmusk/status/1107379727302451200
All of the verticals are the same size as the standard hex tile and the other lines are shorter.

I wasn't refuting your idea, but DusanC's, which has long horizontal cuts: https://forum.nasaspaceflight.com/index.php?topic=50620.msg2073315#msg2073315. I cross quoted from the prototype thread to this one where the discussion is on topic.

As for your idea, I think it's one of the better ones. It seems like a good compromise between covering the curved surface and keeping the number of unique shapes down.
Title: Re: Starship heat shield
Post by: livingjw on 04/27/2020 04:21 pm
Then the tiles were glued to thin nylon fabric layers (AIU like the stuff womens tights are made out of) to handle the contraction and expansion.

In more detail:

- Shuttle Tiles are attached using high temperature silicone RTV adhesive. Similar to high temperature silicone adhesive from auto store.

- Tiles are bonded to a ~4 mm thick Strain Isolation Pad, SIP, made from Nomex felt. Nomex is related to Nylon.

- The SIP is, in turn, bonded to the aluminum Shuttle Skin with another layer of Silicone RTV adhesive.

John

Title: Re: Starship heat shield
Post by: LF on 04/27/2020 06:55 pm
BTW

A few years ago DLR ran a sounding rocket test with the Brazilian space agency.

They built a nose cone out of standard sized RCC tiles, mostly triangles, pentagons etc.

The key development was the software to confirm despite the segments being flat that the aerodynamics were OK and the flow was smooth enough to avoid turbulent flow (which multiplies heat transfer between 4x and about 6x).

Oh, this seems super super cool -- I was googling to try to learn more, and to clarify, are you talking about these tests or something else? https://en.wikipedia.org/wiki/Sharp_Edge_Flight_Experiment

From looking at it, it makes me think that the most obvious applications (and maybe obvious reasons it was funded) are hypersonic missiles, and that one of the hard jobs a hypersonic missile would be expected to do (zipping through atmosphere at high speed without burning up) can be aerodynamically similar to lobbing something nearly into orbit and having it re-enter.

It also makes me wonder how much interesting stuff is out there that we can read and draw conclusions about. Some cursory googling brings up stuff not much more interesting than the wikipedia entry.
Title: Re: Starship heat shield
Post by: john smith 19 on 04/28/2020 06:49 am
For „field repairs“ on mars they could easily use dissimilar materials (for example ablative materials). AFAIK Elon also said mars ships might have a heatshield that‘s different from what your average daily-use starship will have. Most Starships flying to mars might only use their heatshield once.
That opens up the field considerably

What people may not realize is that NASA developed conformable variants of both PICA and SIRCA ablators.

This stuff is like stiff foam sheet that can be cut. This can radically simplify TPS as normal materials are hard and rigid. So if you've got a surface with significant curvature to wrap round you either
a) Mfg a thick billet and machine it to shape
b) Thin smallish tiles that conform to the shape but need gap fillers.
IRL most objects will need gap fillers (IIRC Stardust was able to do the heat shield with a single piece, but that was right on the limit of the size they could mfg)
Putting an opening in these materials (for a door) needs serious pre-planning.

OTOH with the flexible version it's more like laying a carpet and cutting a flap to access floor mounted power or data sockets.

I'll also note that ablator panels were looked at for STS. They decided it could be viable provided you didn't have to gun the stuff into a honeycomb one cell at a time, although it would need stiffener walls, with the ablative making continuous channels between them.
Title: Re: Starship heat shield
Post by: Vemaster on 04/28/2020 09:15 am
The actual thickness of the tiles is ~9mm and they are placed on the sides/spikes with a height of ~37 mm:

(https://i.imgur.com/572IhiN.jpg)
Title: Re: Starship heat shield
Post by: spacexfanatic on 04/28/2020 11:48 am
Any data about the weight of the heatshield materials per square meter on SS. thanks.
Title: Re: Starship heat shield
Post by: rsdavis9 on 04/28/2020 01:14 pm
Any data about the weight of the heatshield materials per square meter on SS. thanks.

there is a thread for that. Rafael did a great job.

https://forum.nasaspaceflight.com/index.php?topic=50049.0

Is there a thread somewhere that gives the raptor specs. I know there is a post somewhere in the raptor thread that has it but it is very hard to find? I think livingjw did a very good post in there?
Title: Re: Starship heat shield
Post by: Crispy on 04/28/2020 01:27 pm
Hi, i'm new in this forum

i have notice this article from "the nextbig future" :
'Magnet Enhanced Aerocapture Would Enable 39 Day Mars Crewed Flights' (my enhanced)
I think it will be useful for Starship, someone could explain how it works

Welcome to NSF! There's a good thread on magnetoshells here:
https://forum.nasaspaceflight.com/index.php?topic=29912.0
Title: Re: Starship heat shield
Post by: spacexfanatic on 04/28/2020 01:38 pm
Any data about the weight of the heatshield materials per square meter on SS. thanks.

there is a thread for that. Rafael did a great job.

https://forum.nasaspaceflight.com/index.php?topic=50049.0

Is there a thread somewhere that gives the raptor specs. I know there is a post somewhere in the raptor thread that has it but it is very hard to find? I think livingjw did a very good post in there?

10 tons of heatshielding tiles for SS, a lot of work ahead for weight saving.
Title: Re: Starship heat shield
Post by: rsdavis9 on 04/28/2020 02:15 pm
Any data about the weight of the heatshield materials per square meter on SS. thanks.

there is a thread for that. Rafael did a great job.

https://forum.nasaspaceflight.com/index.php?topic=50049.0

Is there a thread somewhere that gives the raptor specs. I know there is a post somewhere in the raptor thread that has it but it is very hard to find? I think livingjw did a very good post in there?

Here is the best I can come up to answer my own question:

https://forum.nasaspaceflight.com/index.php?topic=47506.600


Title: Re: Starship heat shield
Post by: livingjw on 04/28/2020 03:50 pm
Any data about the weight of the heatshield materials per square meter on SS. thanks.

there is a thread for that. Rafael did a great job.

https://forum.nasaspaceflight.com/index.php?topic=50049.0

Is there a thread somewhere that gives the raptor specs. I know there is a post somewhere in the raptor thread that has it but it is very hard to find? I think livingjw did a very good post in there?

Here is the best I can come up to answer my own question:

https://forum.nasaspaceflight.com/index.php?topic=47506.600

I don't know what chamber pressure they have demonstrated now. It wouldn't surprise me if they have increased chamber pressure somewhat. 270 bar chamber pressure would give them 1.83 MN SL, 1.96 MN vac.

John
Title: Re: Starship heat shield
Post by: livingjw on 04/28/2020 04:05 pm
The actual thickness of the tiles is ~9mm and they are placed on the sides/spikes with a height of ~37 mm:

(https://i.imgur.com/572IhiN.jpg)

- The ~9 mm you are measuring might just be the depth to the lip. I speculated that the lip is there to hold gap filler. The outer coating, if similar to AETB shuttle tile, is very thin, ~.25 mm.

- If what we are seeing is an ablative outer cover it would be thicker. Might be 9 mm.

- Many mysteries yet to sorted out. Thanks for the estimates.

John
Title: Re: Starship heat shield
Post by: livingjw on 04/28/2020 04:13 pm
Having just done some TPS mass estimation work, my latest estimations are leaning to an average areal density of ~13 kg/m^2

John
Title: Re: Starship heat shield
Post by: northstar on 04/28/2020 06:15 pm
Having just done some TPS mass estimation work, my latest estimations are leaning to an average areal density of ~13 kg/m^2

John

So a total mass of about 8700 kg for one half the Starship
Title: Re: Starship heat shield
Post by: oiorionsbelt on 04/28/2020 07:29 pm
Having just done some TPS mass estimation work, my latest estimations are leaning to an average areal density of ~13 kg/m^2

John
Does this include the studs or sheet metal surround mounting system?
Title: Re: Starship heat shield
Post by: john smith 19 on 04/28/2020 08:43 pm
Any data about the weight of the heatshield materials per square meter on SS. thanks.

there is a thread for that. Rafael did a great job.

https://forum.nasaspaceflight.com/index.php?topic=50049.0

Is there a thread somewhere that gives the raptor specs. I know there is a post somewhere in the raptor thread that has it but it is very hard to find? I think livingjw did a very good post in there?

10 tons of heatshielding tiles for SS, a lot of work ahead for weight saving.
Not necessarily.

It depends if that's within the allocated mass for this subsystem.

If it is then that's good enough to be going on with.

Get something flying then measure it, then see what (if) level of optimization is needed.
Title: Re: Starship heat shield
Post by: livingjw on 04/29/2020 02:29 am
Having just done some TPS mass estimation work, my latest estimations are leaning to an average areal density of ~13 kg/m^2

John
Does this include the studs or sheet metal surround mounting system?

It would include the weight of short attachment studs. I have not done an analysis of a sheet metal edge support system. I think it would be a little heavier.

John
Title: Re: Starship heat shield
Post by: aceshigh on 04/29/2020 02:57 am
Couldn´t they just use some material painted... like Starlite? It seems a chemist guy rediscovered the formula and posted it on Youtube... that, or something else.

Even if they are all the same hexagonal tiles, won´t they have to check them all after each landing? Won´t that and replacing any damaged tile still be expensive and labor intensive?
Title: Re: Starship heat shield
Post by: rsdavis9 on 04/29/2020 02:05 pm
Couldn´t they just use some material painted... like Starlite? It seems a chemist guy rediscovered the formula and posted it on Youtube... that, or something else.

Even if they are all the same hexagonal tiles, won´t they have to check them all after each landing? Won´t that and replacing any damaged tile still be expensive and labor intensive?

I would think a visual check with camera would be enough.

Now the real question is what would a missing tile(fell off early in reentry) look like for damage.
1. heat would burn through the 4mm steel.
2. heat would permanently weaken steel but no hole.

So if just weakened it could be cut out and patched.

So for a hole and the fact that they have header tanks would this doom the landing? Maybe the depressurized tank would not be able to handle the aero forces?

Title: Re: Starship heat shield
Post by: envy887 on 04/29/2020 02:56 pm
Couldn´t they just use some material painted... like Starlite? It seems a chemist guy rediscovered the formula and posted it on Youtube... that, or something else.

Even if they are all the same hexagonal tiles, won´t they have to check them all after each landing? Won´t that and replacing any damaged tile still be expensive and labor intensive?

I would think a visual check with camera would be enough.

Now the real question is what would a missing tile(fell off early in reentry) look like for damage.
1. heat would burn through the 4mm steel.
2. heat would permanently weaken steel but no hole.

So if just weakened it could be cut out and patched.

So for a hole and the fact that they have header tanks would this doom the landing? Maybe the depressurized tank would not be able to handle the aero forces?

I doubt they would cut into the tank wall, that just unnecessarily weakens it further.. They could weld a doubler sheet over that spot, and then put a (slightly thinner) tile over the whole mess.
Title: Re: Starship heat shield
Post by: SteveU on 04/29/2020 03:04 pm
Couldn´t they just use some material painted... like Starlite? It seems a chemist guy rediscovered the formula and posted it on Youtube... that, or something else.

Even if they are all the same hexagonal tiles, won´t they have to check them all after each landing? Won´t that and replacing any damaged tile still be expensive and labor intensive?

I would think a visual check with camera would be enough.

Now the real question is what would a missing tile(fell off early in reentry) look like for damage.
1. heat would burn through the 4mm steel.
2. heat would permanently weaken steel but no hole.

So if just weakened it could be cut out and patched.

So for a hole and the fact that they have header tanks would this doom the landing? Maybe the depressurized tank would not be able to handle the aero forces?

I doubt they would cut into the tank wall, that just unnecessarily weakens it further.. They could weld a doubler sheet over that spot, and then put a (slightly thinner) tile over the whole mess.
Why not cut out the bad section - no different than the square access holes they are using now.
Title: Re: Starship heat shield
Post by: envy887 on 04/29/2020 03:18 pm
Couldn´t they just use some material painted... like Starlite? It seems a chemist guy rediscovered the formula and posted it on Youtube... that, or something else.

Even if they are all the same hexagonal tiles, won´t they have to check them all after each landing? Won´t that and replacing any damaged tile still be expensive and labor intensive?

I would think a visual check with camera would be enough.

Now the real question is what would a missing tile(fell off early in reentry) look like for damage.
1. heat would burn through the 4mm steel.
2. heat would permanently weaken steel but no hole.

So if just weakened it could be cut out and patched.

So for a hole and the fact that they have header tanks would this doom the landing? Maybe the depressurized tank would not be able to handle the aero forces?

I doubt they would cut into the tank wall, that just unnecessarily weakens it further.. They could weld a doubler sheet over that spot, and then put a (slightly thinner) tile over the whole mess.
Why not cut out the bad section - no different than the square access holes they are using now.

Still need the doubler around the cutout, so what does it gain?
Title: Re: Starship heat shield
Post by: Slarty1080 on 04/29/2020 03:45 pm
Looking at the possibilities for tiling the flippers it seems the more curves the more tiles required. If they can keep the edges relatively straight it will help minimise the number of tiles required. That said in the battle between aerodynamics and tile count I think aerodynamics wins.

One other thing, with the standard tiles which is the best configuration for the main tile type? Hexagon flat sides aligned upwards or hexagon vertices pointing upwards? Currently the test patch is installed flat side aligned upwards, but I would have thought the other orientation would provide less vertical tile gaps.
Title: Re: Starship heat shield
Post by: john smith 19 on 04/29/2020 09:31 pm
Looking at the possibilities for tiling the flippers it seems the more curves the more tiles required. If they can keep the edges relatively straight it will help minimise the number of tiles required. That said in the battle between aerodynamics and tile count I think aerodynamics wins.

One other thing, with the standard tiles which is the best configuration for the main tile type? Hexagon flat sides aligned upwards or hexagon vertices pointing upwards? Currently the test patch is installed flat side aligned upwards, but I would have thought the other orientation would provide less vertical tile gaps.
TBH at this stage in the game these are early test patches. This articles not likely to go very high or very far.

You're right that wrapping these tiles around a flipper will be tougher if the flipper is curved but the real issue is the edge of the flipper, rather than the acreage.  The question becomes at what scale do yo have a size that can wrap round the edges well enough to not disturb the boundary and not need a massive amount of machining to get a smooth enough OML.
Title: Re: Starship heat shield
Post by: SteveU on 04/30/2020 01:51 am
Couldn´t they just use some material painted... like Starlite? It seems a chemist guy rediscovered the formula and posted it on Youtube... that, or something else.

Even if they are all the same hexagonal tiles, won´t they have to check them all after each landing? Won´t that and replacing any damaged tile still be expensive and labor intensive?

I would think a visual check with camera would be enough.

Now the real question is what would a missing tile(fell off early in reentry) look like for damage.
1. heat would burn through the 4mm steel.
2. heat would permanently weaken steel but no hole.

So if just weakened it could be cut out and patched.

So for a hole and the fact that they have header tanks would this doom the landing? Maybe the depressurized tank would not be able to handle the aero forces?

I doubt they would cut into the tank wall, that just unnecessarily weakens it further.. They could weld a doubler sheet over that spot, and then put a (slightly thinner) tile over the whole mess.
Why not cut out the bad section - no different than the square access holes they are using now.

Still need the doubler around the cutout, so what does it gain?
Sorry - just now able to get back to this.

Besides leaving the damaged material offending my sense of aesthetics - not really sure.

The only possible reason would be if the damaged section might generate cracks.  The cracks may propagate, or cause a section to break off, but that’s pure speculation - don’t know the material properties well enough.
Title: Re: Starship heat shield
Post by: spacexfanatic on 04/30/2020 07:47 am
Couldn´t they just use some material painted... like Starlite? It seems a chemist guy rediscovered the formula and posted it on Youtube... that, or something else.

Even if they are all the same hexagonal tiles, won´t they have to check them all after each landing? Won´t that and replacing any damaged tile still be expensive and labor intensive?

I'm thinking about an indepent one piece heatshield that could be bolt to SS and removed easily so they wont be a lot of time consumming checks. (I think it should be the same for engines).
Title: Re: Starship heat shield
Post by: sebk on 04/30/2020 11:35 am
Couldn´t they just use some material painted... like Starlite? It seems a chemist guy rediscovered the formula and posted it on Youtube... that, or something else.

Even if they are all the same hexagonal tiles, won´t they have to check them all after each landing? Won´t that and replacing any damaged tile still be expensive and labor intensive?

I'm thinking about an indepent one piece heatshield that could be bolt to SS and removed easily so they wont be a lot of time consumming checks. (I think it should be the same for engines).

One large piece doesn't make checks easier. And large single piece would be heavy and close to impossible to manufacture (the only viable option would be soft blanket like material, but no such tech for the temperatures involved has been developed (soft blankets are good for ~1000K like Shuttle leeward, but Stainless steel doesn't need protection against 1000K, it needs protection against 1400-1600K on windward side). Also shield penetrating bolts add difficulty and failure points -- the current small tiles have a smart solution for tat problem: non penetrating snap-on studs.
Title: Re: Starship heat shield
Post by: spacexfanatic on 04/30/2020 11:45 am
Couldn´t they just use some material painted... like Starlite? It seems a chemist guy rediscovered the formula and posted it on Youtube... that, or something else.

Even if they are all the same hexagonal tiles, won´t they have to check them all after each landing? Won´t that and replacing any damaged tile still be expensive and labor intensive?

I'm thinking about an indepent one piece heatshield that could be bolt to SS and removed easily so they wont be a lot of time consumming checks. (I think it should be the same for engines).

One large piece doesn't make checks easier. And large single piece would be heavy and close to impossible to manufacture (the only viable option would be soft blanket like material, but no such tech for the temperatures involved has been developed (soft blankets are good for ~1000K like Shuttle leeward, but Stainless steel doesn't need protection against 1000K, it needs protection against 1400-1600K on windward side). Also shield penetrating bolts add difficulty and failure points -- the current small tiles have a smart solution for tat problem: non penetrating snap-on studs.

I was suggesting multiple heatshields that are interchanged so we don't lose time checking while ideling SS.
(https://www.lockheedmartin.com/content/dam/lockheed-martin/space/photo/feature/2016/orion/orion-heatshiled-ksc.jpg.pc-adaptive.1920.medium.)
Source:courtesy of https://www.lockheedmartin.com
Title: Re: Starship heat shield
Post by: Nevyn72 on 04/30/2020 12:03 pm
Couldn´t they just use some material painted... like Starlite? It seems a chemist guy rediscovered the formula and posted it on Youtube... that, or something else.

Even if they are all the same hexagonal tiles, won´t they have to check them all after each landing? Won´t that and replacing any damaged tile still be expensive and labor intensive?

I'm thinking about an indepent one piece heatshield that could be bolt to SS and removed easily so they wont be a lot of time consumming checks. (I think it should be the same for engines).

One large piece doesn't make checks easier. And large single piece would be heavy and close to impossible to manufacture (the only viable option would be soft blanket like material, but no such tech for the temperatures involved has been developed (soft blankets are good for ~1000K like Shuttle leeward, but Stainless steel doesn't need protection against 1000K, it needs protection against 1400-1600K on windward side). Also shield penetrating bolts add difficulty and failure points -- the current small tiles have a smart solution for tat problem: non penetrating snap-on studs.

I was suggesting multiple heatshields that are interchanged so we don't lose time checking while ideling SS.


How much time and infrastructure would be required to change out the heat shields on something the size of a Starship?  :o
Title: Re: Starship heat shield
Post by: spacexfanatic on 04/30/2020 12:15 pm
Couldn´t they just use some material painted... like Starlite? It seems a chemist guy rediscovered the formula and posted it on Youtube... that, or something else.

Even if they are all the same hexagonal tiles, won´t they have to check them all after each landing? Won´t that and replacing any damaged tile still be expensive and labor intensive?

I'm thinking about an indepent one piece heatshield that could be bolt to SS and removed easily so they wont be a lot of time consumming checks. (I think it should be the same for engines).

One large piece doesn't make checks easier. And large single piece would be heavy and close to impossible to manufacture (the only viable option would be soft blanket like material, but no such tech for the temperatures involved has been developed (soft blankets are good for ~1000K like Shuttle leeward, but Stainless steel doesn't need protection against 1000K, it needs protection against 1400-1600K on windward side). Also shield penetrating bolts add difficulty and failure points -- the current small tiles have a smart solution for tat problem: non penetrating snap-on studs.

I was suggesting multiple heatshields that are interchanged so we don't lose time checking while ideling SS.


How much time and infrastructure would be required to change out the heat shields on something the size of a Starship?  :o

 10 tons for heatshield  any respectable overhead crane could manage such a weight.
Title: Re: Starship heat shield
Post by: john smith 19 on 04/30/2020 12:16 pm
How much time and infrastructure would be required to change out the heat shields on something the size of a Starship?  :o
Indeed.

I don't think some people realize just how staggeringly big this thing is.

For those who don't go out to an airport and look at a 777 or an airbus 380. the Shuttle was about DC9 sized. Bigger than any previous vehicle, but still quite small.
Title: Re: Starship heat shield
Post by: rakaydos on 04/30/2020 12:25 pm
You guys find it easy to colonize Mars and hard to interchange a heatshield? ;D if so I would prefer being more down to earth and let talk about how to put the american flag on the red planet soil before chinese do the same it's more interesting for me than the aspirationals goals (dreams) of EM.
Not just any heat shield, you want a single unitary heat shield, that is also swappable. While being made out of materials chosen for their thermal characteristics, not their durability.

There's a reason the shuttle used tiles, and starship is also using hexagonal tiles.
Title: Re: Starship heat shield
Post by: RoboGoofers on 04/30/2020 12:28 pm
10 tons for heatshield  any respectable overhead crane could manage such a weight.
it would be a sail so a building would be needed. And it'd be nearly as flexible as sail cloth. It'd need lots of hands and eyes to apply and verify it was installed properly.
Title: Re: Starship heat shield
Post by: spacexfanatic on 04/30/2020 12:31 pm
You guys find it easy to colonize Mars and hard to interchange a heatshield? ;D if so I would prefer being more down to earth and let talk about how to put the american flag on the red planet soil before chinese do the same it's more interesting for me than the aspirationals goals (dreams) of EM.
Not just any heat shield, you want a single unitary heat shield, that is also swappable. While being made out of materials chosen for their thermal characteristics, not their durability.

There's a reason the shuttle used tiles, and starship is also using hexagonal tiles.

Those hexagonal tiles could be fixed to a structure that could be disassembled or fixed to SS, if you won't to operat quickly you won't be able to aford ideling all the spacecraft just because one tile has been damaged and need time to get repaired.

10 tons for heatshield  any respectable overhead crane could manage such a weight.
it would be a sail so a building would be needed. And it'd be nearly as flexible as sail cloth. It'd need lots of hands and eyes to apply and verify it was installed properly.

Please refere to the above response, it must be as easy as interchanging an airliner engine.
Title: Re: Starship heat shield
Post by: rakaydos on 04/30/2020 12:40 pm
Rapid inspection of tiles and replacement of only the defective ones is a solvable problem in an era of computer vision.
Title: Re: Starship heat shield
Post by: Nevyn72 on 04/30/2020 12:51 pm
Please refere to the above response, it must be as easy as interchanging an airliner engine.

Do you know what it takes and how long to change out an airliner engine?  :o

https://blog.virginatlantic.com/change-aircraft-engine/ (https://blog.virginatlantic.com/change-aircraft-engine/)
Title: Re: Starship heat shield
Post by: spacexfanatic on 04/30/2020 01:07 pm
Please refere to the above response, it must be as easy as interchanging an airliner engine.

Do you know what it takes and how long to change out an airliner engine?  :o

https://blog.virginatlantic.com/change-aircraft-engine/ (https://blog.virginatlantic.com/change-aircraft-engine/)

I saw a documentary on National Geographic it was too easy.
https://www.youtube.com/watch?v=lU4mXljJRC8
Title: Re: Starship heat shield
Post by: rakaydos on 04/30/2020 01:25 pm
Please refere to the above response, it must be as easy as interchanging an airliner engine.

Do you know what it takes and how long to change out an airliner engine?  :o

https://blog.virginatlantic.com/change-aircraft-engine/ (https://blog.virginatlantic.com/change-aircraft-engine/)

I saw a documentary on National Geographic it was too easy.
You'll notice they swap one engine, not an entire wing at once.

Tiles are the smart way of doing heat shields.
Title: Re: Starship heat shield
Post by: spacexfanatic on 04/30/2020 01:29 pm
Please refere to the above response, it must be as easy as interchanging an airliner engine.

Do you know what it takes and how long to change out an airliner engine?  :o

https://blog.virginatlantic.com/change-aircraft-engine/ (https://blog.virginatlantic.com/change-aircraft-engine/)

I saw a documentary on National Geographic it was too easy.
You'll notice they swap one engine, not an entire wing at once.

Tiles are the smart way of doing heat shields.

I was also suggesting swaping all the heat shield.
Title: Re: Starship heat shield
Post by: rakaydos on 04/30/2020 01:31 pm
Please refere to the above response, it must be as easy as interchanging an airliner engine.

Do you know what it takes and how long to change out an airliner engine?  :o

https://blog.virginatlantic.com/change-aircraft-engine/ (https://blog.virginatlantic.com/change-aircraft-engine/)

I saw a documentary on National Geographic it was too easy.
You'll notice they swap one engine, not an entire wing at once.

Tiles are the smart way of doing heat shields.

I was also suggesting swaping all the heat shield.
Why swap the whole heat shield if only a few tiles are damaged?
Title: Re: Starship heat shield
Post by: spacexfanatic on 04/30/2020 01:35 pm
Please refere to the above response, it must be as easy as interchanging an airliner engine.

Do you know what it takes and how long to change out an airliner engine?  :o

https://blog.virginatlantic.com/change-aircraft-engine/ (https://blog.virginatlantic.com/change-aircraft-engine/)

I saw a documentary on National Geographic it was too easy.
You'll notice they swap one engine, not an entire wing at once.

Tiles are the smart way of doing heat shields.

I was also suggesting swaping all the heat shield.
Why swap the whole heat shield if only a few tiles are damaged?

To make SS ready to fly as quickly as possible.
Title: Re: Starship heat shield
Post by: rakaydos on 04/30/2020 01:37 pm
Please refere to the above response, it must be as easy as interchanging an airliner engine.

Do you know what it takes and how long to change out an airliner engine?  :o

https://blog.virginatlantic.com/change-aircraft-engine/ (https://blog.virginatlantic.com/change-aircraft-engine/)

I saw a documentary on National Geographic it was too easy.
You'll notice they swap one engine, not an entire wing at once.

Tiles are the smart way of doing heat shields.

I was also suggesting swaping all the heat shield.
Why swap the whole heat shield if only a few tiles are damaged?

To make SS ready to fly as quickly as possible.
Swapping a 10 ton heat shield is going to be MUCH slower than scanning the shield, then swapping 4-5 tiles.
Title: Re: Starship heat shield
Post by: sebk on 04/30/2020 01:38 pm
You guys find it easy to colonize Mars and hard to interchange a heatshield? ;D if so I would prefer being more down to earth and let talk about how to put the american flag on the red planet soil before chinese do the same it's more interesting for me than the aspirationals goals (dreams) of EM.
Not just any heat shield, you want a single unitary heat shield, that is also swappable. While being made out of materials chosen for their thermal characteristics, not their durability.

There's a reason the shuttle used tiles, and starship is also using hexagonal tiles.

Those hexagonal tiles could be fixed to a structure that could be disassembled or fixed to SS, if you won't to operat quickly you won't be able to aford ideling all the spacecraft just because one tile has been damaged and need time to get repaired.

Such structure would be heavier than the tiles together.

But anyway, you got it backwards
Replacing one damaged tile is 15 minutes operation. They are "click on".

Replacing entire shield structure because of a single dent would take hours.

Better just replace the one tile.

10 tons for heatshield  any respectable overhead crane could manage such a weight.
it would be a sail so a building would be needed. And it'd be nearly as flexible as sail cloth. It'd need lots of hands and eyes to apply and verify it was installed properly.

Please refere to the above response, it must be as easy as interchanging an airliner engine.

Replacing airplane engine takes hours.
Title: Re: Starship heat shield
Post by: spacexfanatic on 04/30/2020 01:46 pm
I counted NASA wireless scanner is 3 seconds per tiles for space shuttle I counted 20 hours for scanning all tiles but don't know how much time to process the data nor to change any tiles, for me it's more safe to get a well checked and maintained heat shield and this require time. to close the drame of the shuttle.

Anyway whatever less expensive and rapid methode to keep SS operable ans most important safe is welcome.
Title: Re: Starship heat shield
Post by: sebk on 04/30/2020 01:54 pm
Please refere to the above response, it must be as easy as interchanging an airliner engine.

Do you know what it takes and how long to change out an airliner engine?  :o

https://blog.virginatlantic.com/change-aircraft-engine/ (https://blog.virginatlantic.com/change-aircraft-engine/)

I saw a documentary on National Geographic it was too easy.
https://www.youtube.com/watch?v=lU4mXljJRC8

Do you realize this was multiple hour operation? Hint: the movie is not real time  ;D See, that lighting is changed in the later phases of the operation? That's because hours have passed in the mean time.

Anyway, replacing dented tile is a fast operation. Replacing entire shield is not.

To replace a single tile:
1. remove the damaged one
2. place gap filler
3. click on the new tile
4. safety inspector checks the tile is properly placed

Done.

To replace entire shield structure:
1. Roll the vehicle to a building (50m tall structure is a huge sail, it has no rigidity, it will get damaged by wind when not firmly attached to either rocket body or a special stand; edit: 4m/s wind would exert a literal ton of force on such 500m^2 structure, if the structure weights 20t it would be pushed ~18° off vertical -- good luck doing any precise fastening work in such conditions; hence building is a must)
2. Undo few hundreds fasteners
3. Remove the structure
4. Put it on a special stand for detailed work
5. Hoist replacement structure
6. Carefully replace hundreds of fasteners
7. Safety inspector verifies hundreds of fasteners
8. Roll the vehicle back to the pad

Uffff. Hours have passed.

TL;DR:
The idea is completely wrong. Give it up.
Title: Re: Starship heat shield
Post by: Oersted on 04/30/2020 02:20 pm
I saw a documentary on National Geographic it was too easy.
https://www.youtube.com/watch?v=lU4mXljJRC8

These forums are populated with engineers and industry-level experts. Please don't argue with them by referencing TV documentaries. There is a lot to be learnt just by reading the forums and not posting.
Title: Re: Starship heat shield
Post by: livingjw on 04/30/2020 02:49 pm
- Heat shields have very little strength. They usually have a thin outer shell, or ablator, with insulation underneath. The insulation may be either rigid, like the Shuttle tile, or in the form of felt or batting. The whole has very little strength because you are trying to make it as light and as insulating as possible.

- There is also going to be thermal expansion mismatch between the heat shield and the underlying structure. Because of this tile or panels can only be so large before expansion joints have to be incorporated into the heat shield.

- A large heat shield would not be self supporting. It would rip apart of its own weight. Adding reinforcements to it only makes it heavier. Not good.

John
Title: Re: Starship heat shield
Post by: john smith 19 on 04/30/2020 03:42 pm
Rapid inspection of tiles and replacement of only the defective ones is a solvable problem in an era of computer vision.
It would have been a solved problem in the 90's if Marshall had let CMU install their shuttle inspection robot but apparently it was too risky as it might crash into the vehicle it was scanning (despite CMU's plan to use a very slow moving vehicle to carry the arm carrying the sensor package).

I'm guessing that would have made several hundred staff surplus to requirement as well.
Title: Re: Starship heat shield
Post by: john smith 19 on 04/30/2020 04:25 pm
- There is also going to be thermal expansion mismatch between the heat shield and the underlying structure. Because of this tile or panels can only be so large before expansion joints have to be incorporated into the heat shield.
True. In the case of the Shuttle tiles versus aluminum skin it was something like 3:1 in favor of the skin.

But

SS301 is substantially  lower in TCE.

As I also noted in another thread NASA solved this problem (and patented it, which has been expired for a decade) in the 80's. In principle large single pieces of TPS with substantial TCE (and anisotropic TCE) are viable.

Personally I  think it's a trade off. Replace a single piece the size of a whole half cylinder for any damage to that piece? That sounds excessive to me. OTOH too small and you end up with a huge jigsaw of pieces.

Ideally (and let's be clear this is a total fantasy) you want pattern to line up so that when a tile is damaged it only ever happens to a single tile and never crosses over and damages the edge of an adjacent tile as well.

Which is a total fantasy, given the surface area and number of tiles involved.  :(

IRL some times you'll get lucky, some times you won't. I think it's too early to say with any certainty what an optimal tile size (or placement) is

This is not a problem. It just means that know that SX have a scope of the problem it's time to start the field tests.  I strongly doubt what we are seeing now will be what finally goes to orbit. But it is a start.
Title: Re: Starship heat shield
Post by: Barley on 04/30/2020 06:49 pm
Ideally you want a thermal protection system that never gets damaged, then you don't care how long it takes to repair.

That's a fantasy, but the toughness of the tiles and gentleness of operations is an important part of the engineering.
Title: Re: Starship heat shield
Post by: rakaydos on 04/30/2020 06:51 pm
Ideally you want a thermal protection system that never gets damaged, then you don't care how long it takes to repair.

That's a fantasy, but the toughness of the tiles and gentleness of operations is an important part of the engineering.

That fantasy might apply to an individual flight, but it's better to plan for least expence for the lifetime of the vehical. Cheap repairs AND a durable shield is better than just a durable shield.
Title: Re: Starship heat shield
Post by: Slarty1080 on 04/30/2020 06:59 pm
Assuming that a single tile has been damaged and needs to be replaced, how would they do this? Do they have to use the narrow gap between tiles to get underneath or do they do something from the front of the damaged tile to remove it?
Title: Re: Starship heat shield
Post by: rakaydos on 04/30/2020 07:04 pm
Assuming that a single tile has been damaged and needs to be replaced, how would they do this? Do they have to use the narrow gap between tiles to get underneath or do they do something from the front of the damaged tile to remove it?
Well, the tile is damaged already, so it's already written off. Shatter it with a hammer, pry off the remains, straighten the pins, and attach a new tile?
Title: Re: Starship heat shield
Post by: Slarty1080 on 04/30/2020 07:08 pm
Assuming that a single tile has been damaged and needs to be replaced, how would they do this? Do they have to use the narrow gap between tiles to get underneath or do they do something from the front of the damaged tile to remove it?
Well, the tile is damaged already, so it's already written off. Shatter it with a hammer, pry off the remains, straighten the pins, and attach a new tile?
Seems reasonable, but when attaching the new tile won't the face of the tile insulate the studs from their needed electrical connection for the weld?
Title: Re: Starship heat shield
Post by: livingjw on 04/30/2020 07:16 pm
Assuming that a single tile has been damaged and needs to be replaced, how would they do this? Do they have to use the narrow gap between tiles to get underneath or do they do something from the front of the damaged tile to remove it?
Well, the tile is damaged already, so it's already written off. Shatter it with a hammer, pry off the remains, straighten the pins, and attach a new tile?
Seems reasonable, but when attaching the new tile won't the face of the tile insulate the studs from their needed electrical connection for the weld?

We are assuming that the tile are held on to the studs with clips. Short studs welded to the skin would probably not be damaged. If the studs are damaged, the skin in the area is probably also, so that is a separate problem.

John
Title: Re: Starship heat shield
Post by: JamesH65 on 04/30/2020 09:02 pm
I wonder what the optimal tile size is? There must be some cross over point as you get larger where it starts to become less easy to manufacture, install or handle, likewise getting smaller. Too small, too many and hence heavy, too large, need to be curved.

I suspect there will have to have some 'custom' tiles rather than hexagons for things like leading edgers and the nose.
Title: Re: Starship heat shield
Post by: livingjw on 04/30/2020 09:06 pm
I wonder what the optimal tile size is? There must be some cross over point as you get larger where it starts to become less easy to manufacture, install or handle, likewise getting smaller. Too small, too many and hence heavy, too large, need to be curved.

I suspect there will have to have some 'custom' tiles rather than hexagons for things like leading edgers and the nose.

Well, since SpaceX has hired really smart engineers to work out the details of its TPS system, my guess would be, about the size of the tiles we have seen.  :^)

John
Title: Re: Starship heat shield
Post by: Shrike DeCil on 04/30/2020 10:26 pm
For those who don't go out to an airport and look at a 777 or an airbus 380. the Shuttle was about DC9 sized. Bigger than any previous vehicle, but still quite small.

My quip not quite right (It won't be carrying a 747!) but:

NASA has planes that carry spacecraft, SpaceX will have spacecraft that could carry a plane.
Title: Re: Starship heat shield
Post by: Jorge on 05/01/2020 12:45 am
Rapid inspection of tiles and replacement of only the defective ones is a solvable problem in an era of computer vision.
It would have been a solved problem in the 90's if Marshall had let CMU install their shuttle inspection robot but apparently it was too risky as it might crash into the vehicle it was scanning (despite CMU's plan to use a very slow moving vehicle to carry the arm carrying the sensor package).

I'm guessing that would have made several hundred staff surplus to requirement as well.

RMS/OBSS won because it really was the best solution for reducing risk, despite being heavier than all the free-flyer solutions, including CMU's (and AERCam).
Title: Re: Starship heat shield
Post by: GregTheGrumpy on 05/01/2020 03:14 am
- Heat shields have very little strength. They usually have a thin outer shell, or ablator, with insulation underneath. The insulation may be either rigid, like the Shuttle tile, or in the form of felt or batting. The whole has very little strength because you are trying to make it as light and as insulating as possible.

- There is also going to be thermal expansion mismatch between the heat shield and the underlying structure. Because of this tile or panels can only be so large before expansion joints have to be incorporated into the heat shield.

- A large heat shield would not be self supporting. It would rip apart of its own weight. Adding reinforcements to it only makes it heavier. Not good.

John

John,

I like your answers & responses.  You provide information that I certainly don't have so I learn a lot.  You are generally patient and kind in your answers & I really appreciate that.

-g
Title: Re: Starship heat shield
Post by: john smith 19 on 05/01/2020 05:51 am
RMS/OBSS won because it really was the best solution for reducing risk, despite being heavier than all the free-flyer solutions, including CMU's (and AERCam).
I suspect we're talking at cross purposes.  The CMU project I am referring to was for a robot to inspect shuttle TPS on the ground during refurbishment in the hangar. 
Title: Re: Starship heat shield
Post by: Jorge on 05/01/2020 06:03 pm
RMS/OBSS won because it really was the best solution for reducing risk, despite being heavier than all the free-flyer solutions, including CMU's (and AERCam).
I suspect we're talking at cross purposes.  The CMU project I am referring to was for a robot to inspect shuttle TPS on the ground during refurbishment in the hangar. 

Fair enough. I mistook it for one of the in-flight robotic proposals.
Title: Re: Starship heat shield
Post by: john smith 19 on 05/01/2020 08:16 pm
Fair enough. I mistook it for one of the in-flight robotic proposals.
No. On the ground refurb.  The sensor package was designed to use multiple sensors to detect both surface visible damage and sub surface damage brought on by over temperature stressing of the tiles. In principle with every tile bar coded it could detect a damage one and issue the re-order immediately.

In the context of SS/SH you would probably have a second arm equipped to handle the actual replacement in near real time.

We'll see how SX actually do it.
Title: Re: Starship heat shield
Post by: JamesH65 on 05/03/2020 07:59 am
I wonder what the optimal tile size is? There must be some cross over point as you get larger where it starts to become less easy to manufacture, install or handle, likewise getting smaller. Too small, too many and hence heavy, too large, need to be curved.

I suspect there will have to have some 'custom' tiles rather than hexagons for things like leading edgers and the nose.

Well, since SpaceX has hired really smart engineers to work out the details of its TPS system, my guess would be, about the size of the tiles we have seen.  :^)

John

I guess so, but wonder if they are still prototyping. Get the techniques right, then scale up.
Title: Re: Starship heat shield
Post by: spacexfanatic on 05/03/2020 09:50 am
The idea of a removal single heat shield comes to me as an overall compartmentalization strategy for SS (engines, heat shield, resevoirs, cabin,..............), it may allow futur developement without having to rethink or redesign all the ship, it may also make it easier and quicker to maintain.

 If we are aiming for reusability, compartmentalization is the path to follow.

I was also thinking about converting the energy of the heat generated during re-entry to brake and reduce the speed of the vehicle to temperitures that could easily be sustained without heavy heat shield, a kind of gas turbine that is fueled with the hot air of the friction. is it physically possible (quantification of the forces and energy)? has the idea been suggested before? thanks.
Title: Re: Starship heat shield
Post by: volker2020 on 05/03/2020 10:12 am
I get the feeling, that a lot people here assume that the heat tilds are based on the shuttle design. They are not. They don't have to protect so much (steel, not aluminum below), and they can weight more.
This is starship, so they won't optimize to the end to save weight. When the equation is 2 tons less capacity for a more robust heat shield, they will take the 2 tons. Because it is still cheaper to start it 101 instead of 100 times, than to have an intensive checkup, every time it landed. 
Title: Re: Starship heat shield
Post by: spacexfanatic on 05/03/2020 10:27 am
I get the feeling, that a lot people here assume that the heat tilds are based on the shuttle design. They are not. They don't have to protect so much (steel, not aluminum below), and they can weight more.
This is starship, so they won't optimize to the end to save weight. When the equation is 2 tons less capacity for a more robust heat shield, they will take the 2 tons. Because it is still cheaper to start it 101 instead of 100 times, than to have an intensive checkup, every time it landed.

But still 10 tons or so (more than F9 payload to GTO) of weight to escape earth and mars gravity is a huge payload loss and fuel consumming burden.
Title: Re: Starship heat shield
Post by: volker2020 on 05/03/2020 11:05 am
I get the feeling, that a lot people here assume that the heat tilds are based on the shuttle design. They are not. They don't have to protect so much (steel, not aluminum below), and they can weight more.
This is starship, so they won't optimize to the end to save weight. When the equation is 2 tons less capacity for a more robust heat shield, they will take the 2 tons. Because it is still cheaper to start it 101 instead of 100 times, than to have an intensive checkup, every time it landed.

But still 10 tons or so (more than F9 payload to GTO) of weight to escape earth and mars gravity is a huge payload loss and fuel consumming burden.
Mars, exactly. They want to land this thing on mars, and the thermal envelop for loosing speed on mars will be not much apart from earth reentry. And what they clearly can not do, it trying to fix the heat shield on mars. It has to be rock solid, and I am sure, they knew that from day one.
Title: Re: Starship heat shield
Post by: Slarty1080 on 05/03/2020 04:54 pm
I get the feeling, that a lot people here assume that the heat tilds are based on the shuttle design. They are not. They don't have to protect so much (steel, not aluminum below), and they can weight more.
This is starship, so they won't optimize to the end to save weight. When the equation is 2 tons less capacity for a more robust heat shield, they will take the 2 tons. Because it is still cheaper to start it 101 instead of 100 times, than to have an intensive checkup, every time it landed.

But still 10 tons or so (more than F9 payload to GTO) of weight to escape earth and mars gravity is a huge payload loss and fuel consumming burden.
Mars, exactly. They want to land this thing on mars, and the thermal envelop for loosing speed on mars will be not much apart from earth reentry. And what they clearly can not do, it trying to fix the heat shield on mars. It has to be rock solid, and I am sure, they knew that from day one.
There's always a plan B if the heat shield is damaged fly them home and transfer to another starship for return to Earth, then repair in orbit if possible else park in a high orbit for posterity or let it burn up after all samples and crew have been transfered out.
Title: Re: Starship heat shield
Post by: livingjw on 05/03/2020 05:23 pm
I get the feeling, that a lot people here assume that the heat tilds are based on the shuttle design. They are not. They don't have to protect so much (steel, not aluminum below), and they can weight more.
This is starship, so they won't optimize to the end to save weight. When the equation is 2 tons less capacity for a more robust heat shield, they will take the 2 tons. Because it is still cheaper to start it 101 instead of 100 times, than to have an intensive checkup, every time it landed.

- If you know they are not based on ANY Shuttle technology, what are they based on? If you don't know, then you don't know that they are not.

- I don't assume they will be based solely on Shuttle tile. I suspect that they will make use of the NASA research in this area and may add some novel twists of their own.

- We are pretty sure they would like to mechanically fasten their tile. Shuttle tile bonding probably won't work for their interface temperature and anyway bonding was a pain in the neck.

- Steel vs aluminum just decreases the thickness of insulation required for the same total heat flux.

- Tile mass is always important, but, as you point out, so is robustness, inspectability and maintainability.

- It will be interesting.

John
Title: Re: Starship heat shield
Post by: Nomadd on 05/03/2020 05:29 pm
I get the feeling, that a lot people here assume that the heat tilds are based on the shuttle design. They are not. They don't have to protect so much (steel, not aluminum below), and they can weight more.
This is starship, so they won't optimize to the end to save weight. When the equation is 2 tons less capacity for a more robust heat shield, they will take the 2 tons. Because it is still cheaper to start it 101 instead of 100 times, than to have an intensive checkup, every time it landed.

But still 10 tons or so (more than F9 payload to GTO) of weight to escape earth and mars gravity is a huge payload loss and fuel consumming burden.
Mars, exactly. They want to land this thing on mars, and the thermal envelop for loosing speed on mars will be not much apart from earth reentry. And what they clearly can not do, it trying to fix the heat shield on mars. It has to be rock solid, and I am sure, they knew that from day one.
There's always a plan B if the heat shield is damaged fly them home and transfer to another starship for return to Earth, then repair in orbit if possible else park in a high orbit for posterity or let it burn up after all samples and crew have been transfered out.
Doesn't work too well if you're depending on aerocapture or braking to get into orbit.
Title: Re: Starship heat shield
Post by: rakaydos on 05/03/2020 06:03 pm
I get the feeling, that a lot people here assume that the heat tilds are based on the shuttle design. They are not. They don't have to protect so much (steel, not aluminum below), and they can weight more.
This is starship, so they won't optimize to the end to save weight. When the equation is 2 tons less capacity for a more robust heat shield, they will take the 2 tons. Because it is still cheaper to start it 101 instead of 100 times, than to have an intensive checkup, every time it landed.

But still 10 tons or so (more than F9 payload to GTO) of weight to escape earth and mars gravity is a huge payload loss and fuel consumming burden.
10 tons sounds like a lot, but the current design assumes a loaded dry weight (ship dry weight+payload) of 270 tons- so the heat shield is less than 5%, close to 3% of that number. Starship has a ROUNDING ERROR on it's lift capacity bigger than some launcher's max capacity.
Title: Re: Starship heat shield
Post by: Slarty1080 on 05/03/2020 06:05 pm
I get the feeling, that a lot people here assume that the heat tilds are based on the shuttle design. They are not. They don't have to protect so much (steel, not aluminum below), and they can weight more.
This is starship, so they won't optimize to the end to save weight. When the equation is 2 tons less capacity for a more robust heat shield, they will take the 2 tons. Because it is still cheaper to start it 101 instead of 100 times, than to have an intensive checkup, every time it landed.
But still 10 tons or so (more than F9 payload to GTO) of weight to escape earth and mars gravity is a huge payload loss and fuel consumming burden.
Mars, exactly. They want to land this thing on mars, and the thermal envelop for loosing speed on mars will be not much apart from earth reentry. And what they clearly can not do, it trying to fix the heat shield on mars. It has to be rock solid, and I am sure, they knew that from day one.
There's always a plan B if the heat shield is damaged fly them home and transfer to another starship for return to Earth, then repair in orbit if possible else park in a high orbit for posterity or let it burn up after all samples and crew have been transfered out.
Doesn't work too well if you're depending on aerocapture or braking to get into orbit.
True, I had forgotten about that. How tough are aerocapture requirements vs re-entry requirements?
Title: Re: Starship heat shield
Post by: rsdavis9 on 05/04/2020 01:09 pm
I have a question.

If we have a moon SS launched from the moon surface to the earth LEO.
No heat shield.
Aerocapture doesn't need to be done because you have less than earth escape velocity.
So you still need to slow down slowly because we don't have a heat shield.
How many passes are needed to slow down to a LEO orbit?
Does the time needed to do this greatly increase radiation exposer?

Asking in this thread because this thread has to do with heat loads and protection for planetary entry.

Title: Re: Starship heat shield
Post by: eriblo on 05/04/2020 02:36 pm
I have a question.

If we have a moon SS launched from the moon surface to the earth LEO.
No heat shield.
Aerocapture doesn't need to be done because you have less than earth escape velocity.
So you still need to slow down slowly because we don't have a heat shield.
How many passes are needed to slow down to a LEO orbit?
Does the time needed to do this greatly increase radiation exposer?

Asking in this thread because this thread has to do with heat loads and protection for planetary entry.
To recap my quick estimates in the Moon Starship mission profile thread:

Excess energy of a 100 t Starship going from 11 km/s to say 8 km/s at perigee is 1/2*100 t*((11 km/s)^2-(8 km/s)^2) = 2.9 TJ

This will be dissipated through thermal black-body radiation from the skin. Lets assume 623 K (350 °C, maxium temperature of Space Shuttle top TPS blankets) evenly over the whole Starship area (BBQ roll).

Stefan-Boltzmann with 623 K, emissivity=1: 8.5 kW/m^2.  Times 1300 m^2 = 11 MW of thermal radiation.

2.9 TJ/11 MW = 260 000 s or very close to 3 days.

This would take many years considering that the orbital period starts out at many days and the time at maximum drag is at most a few minutes and it completely neglects incoming heat from the Sun and Earth during aerobraking.
Title: Re: Starship heat shield
Post by: rakaydos on 05/04/2020 03:06 pm
I have a question.

If we have a moon SS launched from the moon surface to the earth LEO.
No heat shield.
Aerocapture doesn't need to be done because you have less than earth escape velocity.
So you still need to slow down slowly because we don't have a heat shield.
How many passes are needed to slow down to a LEO orbit?
Does the time needed to do this greatly increase radiation exposer?

Asking in this thread because this thread has to do with heat loads and protection for planetary entry.
To recap my quick estimates in the Moon Starship mission profile thread:

Excess energy of a 100 t Starship going from 11 km/s to say 8 km/s at perigee is 1/2*100 t*((11 km/s)^2-(8 km/s)^2) = 2.9 TJ

This will be dissipated through thermal black-body radiation from the skin. Lets assume 623 K (350 °C, maxium temperature of Space Shuttle top TPS blankets) evenly over the whole Starship area (BBQ roll).

Stefan-Boltzmann with 623 K, emissivity=1: 8.5 kW/m^2.  Times 1300 m^2 = 11 MW of thermal radiation.

2.9 TJ/11 MW = 260 000 s or very close to 3 days.

This would take many years considering that the orbital period starts out at many days and the time at maximum drag is at most a few minutes and it completely neglects incoming heat from the Sun and Earth during aerobraking.
You look like you are running a steady-state calculation. But what about a thermal mass one? An eliptcal orbit would give starship plenty of time to dissapate reentry heating before the next pass. So how much thermal energy can Starship hold without letting the structure pass 1000 degrees?
Title: Re: Starship heat shield
Post by: eriblo on 05/04/2020 04:05 pm
I have a question.

If we have a moon SS launched from the moon surface to the earth LEO.
No heat shield.
Aerocapture doesn't need to be done because you have less than earth escape velocity.
So you still need to slow down slowly because we don't have a heat shield.
How many passes are needed to slow down to a LEO orbit?
Does the time needed to do this greatly increase radiation exposer?

Asking in this thread because this thread has to do with heat loads and protection for planetary entry.
To recap my quick estimates in the Moon Starship mission profile thread:

Excess energy of a 100 t Starship going from 11 km/s to say 8 km/s at perigee is 1/2*100 t*((11 km/s)^2-(8 km/s)^2) = 2.9 TJ

This will be dissipated through thermal black-body radiation from the skin. Lets assume 623 K (350 °C, maxium temperature of Space Shuttle top TPS blankets) evenly over the whole Starship area (BBQ roll).

Stefan-Boltzmann with 623 K, emissivity=1: 8.5 kW/m^2.  Times 1300 m^2 = 11 MW of thermal radiation.

2.9 TJ/11 MW = 260 000 s or very close to 3 days.

This would take many years considering that the orbital period starts out at many days and the time at maximum drag is at most a few minutes and it completely neglects incoming heat from the Sun and Earth during aerobraking.
You look like you are running a steady-state calculation. But what about a thermal mass one? An eliptcal orbit would give starship plenty of time to dissapate reentry heating before the next pass. So how much thermal energy can Starship hold without letting the structure pass 1000 degrees?
Yes, I neglected that since Moon Starship will be well insulated (it is supposed to support humans and store cryogens in LLO and on the lunar surface) and each aerobraking session is just minutes long.

Even so: Lets assume that you minimize the profile towards the sun and super cold soak it in preparation and then let it go from say -100 °C to 500 °C (hot enough to ruin everything that is not stainless steel and quite possibly that as well - 1000 degrees is way more than it should tolerate unless those are degrees Rankine which would still be bad for the interior). Heat capacity of stainless is about 500 J/kg/K:

100 t*500 J/kg/K*600 K = 30 GJ

That is "only" 100 passes instead of >1000. With the assumptions above the radiated heat would of course also be much greater and the amount of energy deposited directly into the atmosphere might become important but I would still say that you need a heat shield if you want to use the atmosphere.
Title: Re: Starship heat shield
Post by: rsdavis9 on 05/04/2020 04:40 pm
I have a question.

If we have a moon SS launched from the moon surface to the earth LEO.
No heat shield.
Aerocapture doesn't need to be done because you have less than earth escape velocity.
So you still need to slow down slowly because we don't have a heat shield.
How many passes are needed to slow down to a LEO orbit?
Does the time needed to do this greatly increase radiation exposer?

Asking in this thread because this thread has to do with heat loads and protection for planetary entry.
To recap my quick estimates in the Moon Starship mission profile thread:

Excess energy of a 100 t Starship going from 11 km/s to say 8 km/s at perigee is 1/2*100 t*((11 km/s)^2-(8 km/s)^2) = 2.9 TJ

This will be dissipated through thermal black-body radiation from the skin. Lets assume 623 K (350 °C, maxium temperature of Space Shuttle top TPS blankets) evenly over the whole Starship area (BBQ roll).

Stefan-Boltzmann with 623 K, emissivity=1: 8.5 kW/m^2.  Times 1300 m^2 = 11 MW of thermal radiation.

2.9 TJ/11 MW = 260 000 s or very close to 3 days.

This would take many years considering that the orbital period starts out at many days and the time at maximum drag is at most a few minutes and it completely neglects incoming heat from the Sun and Earth during aerobraking.

I must have missed that.
Thanks
Is that the "moon starship" thread?
Title: Re: Starship heat shield
Post by: Keldor on 05/04/2020 05:46 pm
I have a question.

If we have a moon SS launched from the moon surface to the earth LEO.
No heat shield.
Aerocapture doesn't need to be done because you have less than earth escape velocity.
So you still need to slow down slowly because we don't have a heat shield.
How many passes are needed to slow down to a LEO orbit?
Does the time needed to do this greatly increase radiation exposer?

Asking in this thread because this thread has to do with heat loads and protection for planetary entry.
To recap my quick estimates in the Moon Starship mission profile thread:

Excess energy of a 100 t Starship going from 11 km/s to say 8 km/s at perigee is 1/2*100 t*((11 km/s)^2-(8 km/s)^2) = 2.9 TJ

This will be dissipated through thermal black-body radiation from the skin. Lets assume 623 K (350 °C, maxium temperature of Space Shuttle top TPS blankets) evenly over the whole Starship area (BBQ roll).

Stefan-Boltzmann with 623 K, emissivity=1: 8.5 kW/m^2.  Times 1300 m^2 = 11 MW of thermal radiation.

2.9 TJ/11 MW = 260 000 s or very close to 3 days.

This would take many years considering that the orbital period starts out at many days and the time at maximum drag is at most a few minutes and it completely neglects incoming heat from the Sun and Earth during aerobraking.

Thankfully, the vast majority (something on the order of 99% IIRC) of reentry heating/energy loss occurs in the shockwave ahead of the vehicle and is never actually absorbed.  Also, since SS is steel, the body can accept much higher temperatures than the shuttle, on the order of 1000C.  This means that even without a heatshield, you can aerobrake pretty aggressively, and thermal emission occurs much faster.

Finally, you can use evaporative cooling by letting the heat boil your propellant, and just venting the gas.  Assuming only 1% of the reentry heat is actually absorbed by the vehicle, your 2.9 TJ number requires around 150-200kg of propellant to be vaporized (assuming I got my math right), which is trivial.

Since heat can be shedded so easily by vaporizing a small amount of fuel, the only question remaining is how many aerobraking passes must occur.

If we handwave internal heat transfer during reentry and just assume the vehicle can accept enough energy to heat 30 tons worth of steel on the windward side to 1000C, then assuming 1% of reentry energy is accepted by the vehicle, then the specific heat of steel of 0.5 J/K suggests that 2 aerobraking passes are sufficient.  Since the lunar return trajectory has a high eccentricity, it only takes a small amount of energy loss at perigee to greatly lower apogee.  Thus, the intermediate orbit between brakings can be expected to be fairly low and only slightly eccentric, with a period on the order of hours and not days.  It might even slip below Van Allen belt entirely, which means the radiation exposure during this time would be quite low.
Title: Re: Starship heat shield
Post by: ValmirGP on 05/04/2020 06:02 pm
I have a question.

If we have a moon SS launched from the moon surface to the earth LEO.
No heat shield.
Aerocapture doesn't need to be done because you have less than earth escape velocity.
So you still need to slow down slowly because we don't have a heat shield.
How many passes are needed to slow down to a LEO orbit?
Does the time needed to do this greatly increase radiation exposer?

Asking in this thread because this thread has to do with heat loads and protection for planetary entry.
To recap my quick estimates in the Moon Starship mission profile thread:

Excess energy of a 100 t Starship going from 11 km/s to say 8 km/s at perigee is 1/2*100 t*((11 km/s)^2-(8 km/s)^2) = 2.9 TJ

This will be dissipated through thermal black-body radiation from the skin. Lets assume 623 K (350 °C, maxium temperature of Space Shuttle top TPS blankets) evenly over the whole Starship area (BBQ roll).

Stefan-Boltzmann with 623 K, emissivity=1: 8.5 kW/m^2.  Times 1300 m^2 = 11 MW of thermal radiation.

2.9 TJ/11 MW = 260 000 s or very close to 3 days.

This would take many years considering that the orbital period starts out at many days and the time at maximum drag is at most a few minutes and it completely neglects incoming heat from the Sun and Earth during aerobraking.

Thankfully, the vast majority (something on the order of 99% IIRC) of reentry heating/energy loss occurs in the shockwave ahead of the vehicle and is never actually absorbed.  Also, since SS is steel, the body can accept much higher temperatures than the shuttle, on the order of 1000C.  This means that even without a heatshield, you can aerobrake pretty aggressively, and thermal emission occurs much faster.

Finally, you can use evaporative cooling by letting the heat boil your propellant, and just venting the gas.  Assuming only 1% of the reentry heat is actually absorbed by the vehicle, your 2.9 TJ number requires around 150-200kg of propellant to be vaporized (assuming I got my math right), which is trivial.

Since heat can be shedded so easily by vaporizing a small amount of fuel, the only question remaining is how many aerobraking passes must occur.

If we handwave internal heat transfer during reentry and just assume the vehicle can accept enough energy to heat 30 tons worth of steel on the windward side to 1000C, then assuming 1% of reentry energy is accepted by the vehicle, then the specific heat of steel of 0.5 J/K suggests that 2 aerobraking passes are sufficient.  Since the lunar return trajectory has a high eccentricity, it only takes a small amount of energy loss at perigee to greatly lower apogee.  Thus, the intermediate orbit between brakings can be expected to be fairly low and only slightly eccentric, with a period on the order of hours and not days.  It might even slip below Van Allen belt entirely, which means the radiation exposure during this time would be quite low.

I remember in the movie 2010 (I know, it's fiction) they used an inflatable cocoon to do an aerobrake in Jupiter. Since NASA has already been experimenting with this concept, I wonder if something like that could be done on SS to help matters in returning form LLO to LEO this way.

Only link to the afore mentioned scene I have found is here... https://youtu.be/mMw9W7hI5yM?t=20
Title: Re: Starship heat shield
Post by: eriblo on 05/04/2020 07:12 pm

To recap my quick estimates in the Moon Starship mission profile thread:

[...]

I must have missed that.
Thanks
Is that the "moon starship" thread?
The Starship Moon mission profile (https://forum.nasaspaceflight.com/index.php?topic=50817.0) tread, but it was the same analysis just a slightly different formulation.
Title: Re: Starship heat shield
Post by: eriblo on 05/04/2020 08:43 pm
I have a question.

If we have a moon SS launched from the moon surface to the earth LEO.
No heat shield.
Aerocapture doesn't need to be done because you have less than earth escape velocity.
So you still need to slow down slowly because we don't have a heat shield.
How many passes are needed to slow down to a LEO orbit?
Does the time needed to do this greatly increase radiation exposer?

Asking in this thread because this thread has to do with heat loads and protection for planetary entry.
To recap my quick estimates in the Moon Starship mission profile thread:

Excess energy of a 100 t Starship going from 11 km/s to say 8 km/s at perigee is 1/2*100 t*((11 km/s)^2-(8 km/s)^2) = 2.9 TJ

This will be dissipated through thermal black-body radiation from the skin. Lets assume 623 K (350 °C, maxium temperature of Space Shuttle top TPS blankets) evenly over the whole Starship area (BBQ roll).

Stefan-Boltzmann with 623 K, emissivity=1: 8.5 kW/m^2.  Times 1300 m^2 = 11 MW of thermal radiation.

2.9 TJ/11 MW = 260 000 s or very close to 3 days.

This would take many years considering that the orbital period starts out at many days and the time at maximum drag is at most a few minutes and it completely neglects incoming heat from the Sun and Earth during aerobraking.

Thankfully, the vast majority (something on the order of 99% IIRC) of reentry heating/energy loss occurs in the shockwave ahead of the vehicle and is never actually absorbed.  Also, since SS is steel, the body can accept much higher temperatures than the shuttle, on the order of 1000C.  This means that even without a heatshield, you can aerobrake pretty aggressively, and thermal emission occurs much faster.

Finally, you can use evaporative cooling by letting the heat boil your propellant, and just venting the gas.  Assuming only 1% of the reentry heat is actually absorbed by the vehicle, your 2.9 TJ number requires around 150-200kg of propellant to be vaporized (assuming I got my math right), which is trivial.

Since heat can be shedded so easily by vaporizing a small amount of fuel, the only question remaining is how many aerobraking passes must occur.

If we handwave internal heat transfer during reentry and just assume the vehicle can accept enough energy to heat 30 tons worth of steel on the windward side to 1000C, then assuming 1% of reentry energy is accepted by the vehicle, then the specific heat of steel of 0.5 J/K suggests that 2 aerobraking passes are sufficient.  Since the lunar return trajectory has a high eccentricity, it only takes a small amount of energy loss at perigee to greatly lower apogee.  Thus, the intermediate orbit between brakings can be expected to be fairly low and only slightly eccentric, with a period on the order of hours and not days.  It might even slip below Van Allen belt entirely, which means the radiation exposure during this time would be quite low.
Yes, that is the secret to why reentry and aerocapture is possible at all - forming a shock wave at some distance from the surface which dumps almost all of the energy into the air. The role of the TPS is to make the proximity to that super heated air survivable.

For aerobreaking without a dedicated TPS the maximum temperature is much lower which means that you can not go as low into the atmosphere and (as I understand it) the density will not be enough to form a significant shock wave. The incoming air molecules will therefore heat the surface directly and a much larger portion of the total energy must be dissipated by the spacecraft itself.

1000 °C is much to high for 301 stainless steel, that is roughly the annealing treatment temperature. It will start loosing the cold hardening long before that (it is a function of temperature, time and stress and I do not think I have seen any definitive numbers for maximum allowable hull temperature). Even without hardening a quick look at some charts gives <30% of room temperature strength at 750 °C.

What numbers are you using for transpiration cooling? I get a mass that is one or two orders of magnitude larger.
Title: Re: Starship heat shield
Post by: john smith 19 on 05/07/2020 07:20 am
- I don't assume they will be based solely on Shuttle tile. I suspect that they will make use of the NASA research in this area and may add some novel twists of their own.
Definitely. Especially the later stuff like ROCCI.

Quote from: livingjw
- We are pretty sure they would like to mechanically fasten their tile. Shuttle tile bonding probably won't work for their interface temperature and anyway bonding was a pain in the neck.
The key parameter would be the tile back face temperature.

But what's the point of going SS in the first place if you can't run the back face hotter than Al alloy?
On the upside SS much lower TCE probably means you could could dispense with those "strain isolating" pads (sort of like a nylon sock) that they were glued to.

Which good because the company that made them shut the line years ago.  :(
Title: Re: Starship heat shield
Post by: john smith 19 on 05/07/2020 07:41 am
I remember in the movie 2010 (I know, it's fiction) they used an inflatable cocoon to do an aerobrake in Jupiter. Since NASA has already been experimenting with this concept, I wonder if something like that could be done on SS to help matters in returning form LLO to LEO this way.

Almost certainly not.

Such large expendable components don't fit in with SX's long term goals of fully reusable systems.
Title: Re: Starship heat shield
Post by: sebk on 05/07/2020 05:34 pm
I get the feeling, that a lot people here assume that the heat tilds are based on the shuttle design. They are not. They don't have to protect so much (steel, not aluminum below), and they can weight more.
This is starship, so they won't optimize to the end to save weight. When the equation is 2 tons less capacity for a more robust heat shield, they will take the 2 tons. Because it is still cheaper to start it 101 instead of 100 times, than to have an intensive checkup, every time it landed.
But still 10 tons or so (more than F9 payload to GTO) of weight to escape earth and mars gravity is a huge payload loss and fuel consumming burden.
Mars, exactly. They want to land this thing on mars, and the thermal envelop for loosing speed on mars will be not much apart from earth reentry. And what they clearly can not do, it trying to fix the heat shield on mars. It has to be rock solid, and I am sure, they knew that from day one.
There's always a plan B if the heat shield is damaged fly them home and transfer to another starship for return to Earth, then repair in orbit if possible else park in a high orbit for posterity or let it burn up after all samples and crew have been transfered out.
Doesn't work too well if you're depending on aerocapture or braking to get into orbit.
True, I had forgotten about that. How tough are aerocapture requirements vs re-entry requirements?

Capture from Hohmann transfer to HEEO (sth like 400000x200km) is ~11.6km/s vs 11km/s. This energy difference is ~7.4MJ/kg so it's like breaking form 3.7km/s to standstill.

Capture from an accelerated transfer (6.9km/s dV from Mars surface) to HEEO is 13.85km/s vs 11km/s. The energy difference is pretty like LEO reentry (8.4km/s to standstill TBE).

Capture from Hohmann to LEO is 11.6 vs 7.8km/s is like 8.6km/s to standstill. Now it should be clear why Elon was talking 2 skips before final reentry.
Title: Re: Starship heat shield
Post by: Nevyn72 on 05/07/2020 09:31 pm
That's two static fires for SN4 so far......

Have any of the test-fit heat tiles (3 sets) fallen off or broken?
Title: Re: Starship heat shield
Post by: Nevyn72 on 05/09/2020 03:11 am
That's two static fires for SN4 so far......

Have any of the test-fit heat tiles (3 sets) fallen off or broken?

Well at least there's an answer to my question thanks to Nomadd and his wanderings!

Looks like they have survived so far intact.
Title: Re: Starship heat shield
Post by: john smith 19 on 05/09/2020 06:26 am
That's two static fires for SN4 so far......

Have any of the test-fit heat tiles (3 sets) fallen off or broken?

Well at least there's an answer to my question thanks to Nomadd and his wanderings!

Looks like they have survived so far intact.
So with 3 engines they can stay attached through 2 engine startup/shutdown cycles.

That was not a guaranteed outcome.

So should the next big milestone be the first hop off the ground? Full loading of the tanks to thermally stress the TPS mounting hardware?
Title: Re: Starship heat shield
Post by: Nevyn72 on 05/09/2020 06:39 am
That's two static fires for SN4 so far......

Have any of the test-fit heat tiles (3 sets) fallen off or broken?

Well at least there's an answer to my question thanks to Nomadd and his wanderings!

Looks like they have survived so far intact.
So with 3 engines they can stay attached through 2 engine startup/shutdown cycles.

That was not a guaranteed outcome.

So should the next big milestone be the first hop off the ground? Full loading of the tanks to thermally stress the TPS mounting hardware?

Only 1 engine so far.......
Title: Re: Starship heat shield
Post by: john smith 19 on 05/09/2020 11:34 am
That's two static fires for SN4 so far......

Have any of the test-fit heat tiles (3 sets) fallen off or broken?

Well at least there's an answer to my question thanks to Nomadd and his wanderings!

Looks like they have survived so far intact.
So with 3 engines they can stay attached through 2 engine startup/shutdown cycles.

That was not a guaranteed outcome.

So should the next big milestone be the first hop off the ground? Full loading of the tanks to thermally stress the TPS mounting hardware?

Only 1 engine so far.......
Oops.

Then onward to 3 engines.
Title: Re: Starship heat shield
Post by: Stimbergi on 05/12/2020 02:39 pm
So, we have tiles in three sizes.
Сredit: BocaChicaGal (Mary)
Title: Re: Starship heat shield
Post by: steveleach on 05/12/2020 05:39 pm
Back in Jan 2019, EM tweeted that 60% of Starship wouldn't need any heat shield at all for a LEO reentry.

Quote
~1750K is peak heating expected on about 20% of Starship for LEO entry, ~1600K on 20%. Rest drops below 1450K, so no heat shield needed. Radiative cooling at T^4 takes care of 60% of the ship. Another reason for steel.

a) have we seen any updates since then that contradict this?

b) what would this look like? I assume nose and fins would need TPS; where else would?
Title: Re: Starship heat shield
Post by: rsdavis9 on 05/12/2020 07:08 pm
Back in Jan 2019, EM tweeted that 60% of Starship wouldn't need any heat shield at all for a LEO reentry.

Quote
~1750K is peak heating expected on about 20% of Starship for LEO entry, ~1600K on 20%. Rest drops below 1450K, so no heat shield needed. Radiative cooling at T^4 takes care of 60% of the ship. Another reason for steel.

a) have we seen any updates since then that contradict this?

b) what would this look like? I assume nose and fins would need TPS; where else would?

The whole centerline should be the highest. Nose slightly higher depending in Angle of Attack.
At 90deg nose and centerline should be close to the same temp. If not make the nose blunter.
Title: Re: Starship heat shield
Post by: steveleach on 05/12/2020 07:54 pm
Back in Jan 2019, EM tweeted that 60% of Starship wouldn't need any heat shield at all for a LEO reentry.

Quote
~1750K is peak heating expected on about 20% of Starship for LEO entry, ~1600K on 20%. Rest drops below 1450K, so no heat shield needed. Radiative cooling at T^4 takes care of 60% of the ship. Another reason for steel.

a) have we seen any updates since then that contradict this?

b) what would this look like? I assume nose and fins would need TPS; where else would?

The whole centerline should be the highest. Nose slightly higher depending in Angle of Attack.
At 90deg nose and centerline should be close to the same temp. If not make the nose blunter.
Not disputing, just trying to understand, but why is the centreline the highest temp?
Title: Re: Starship heat shield
Post by: rsdavis9 on 05/12/2020 08:04 pm
This is the first part of the ship to slow and divert the supersonic flow therefore the flow comes closer. The peak heat is mostly radiation which is determined by the temp and observable half sphere. I am totally guessing here as I try to imagine myself as an air molecule travelling at 6km/s at an immovable barrier. On the edges you have flow coming from the centerline that can divert the flow away from the body. The edge also sees less angle of hot stuff.

You can also see this with like the shuttle temp map.

https://en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_system#/media/File:STS-3_infrared_on_reentry.jpg

remember the AoA of the shuttle was about 30-40? so the edges of the wings are first in line for heat.

Is there a temp map of the dragon?

EDIT added shuttle heat map
Title: Re: Starship heat shield
Post by: steveleach on 05/12/2020 10:55 pm
This is the first part of the ship to slow and divert the supersonic flow therefore the flow comes closer. The peak heat is mostly radiation which is determined by the temp and observable half sphere. I am totally guessing here as I try to imagine myself as an air molecule travelling at 6km/s at an immovable barrier. On the edges you have flow coming from the centerline that can divert the flow away from the body. The edge also sees less angle of hot stuff.

You can also see this with like the shuttle temp map.

https://en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_system#/media/File:STS-3_infrared_on_reentry.jpg

remember the AoA of the shuttle was about 30-40? so the edges of the wings are first in line for heat.

Is there a temp map of the dragon?

EDIT added shuttle heat map
I've been struggling to find reentry temperature maps of capsules myself. The shuttle ones I've found (including the one you posted) certainly suggest that the main body is (comparatively) cool, but I know the angle of attack for Starship is very different.

My, probably naive, assumption was that peak heating would be where the shock wave rapidly changes direction, so on the edges of the fins, etc.
Title: Re: Starship heat shield
Post by: rsdavis9 on 05/13/2020 01:19 pm
This is the first part of the ship to slow and divert the supersonic flow therefore the flow comes closer. The peak heat is mostly radiation which is determined by the temp and observable half sphere. I am totally guessing here as I try to imagine myself as an air molecule travelling at 6km/s at an immovable barrier. On the edges you have flow coming from the centerline that can divert the flow away from the body. The edge also sees less angle of hot stuff.

You can also see this with like the shuttle temp map.

https://en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_system#/media/File:STS-3_infrared_on_reentry.jpg

remember the AoA of the shuttle was about 30-40? so the edges of the wings are first in line for heat.

Is there a temp map of the dragon?

EDIT added shuttle heat map
I've been struggling to find reentry temperature maps of capsules myself. The shuttle ones I've found (including the one you posted) certainly suggest that the main body is (comparatively) cool, but I know the angle of attack for Starship is very different.

My, probably naive, assumption was that peak heating would be where the shock wave rapidly changes direction, so on the edges of the fins, etc.

General principal. Blunt is best. Near the roots of the fins/whatever is where the flow should be quite hot.
Title: Re: Starship heat shield
Post by: livingjw on 05/13/2020 01:53 pm
This is the first part of the ship to slow and divert the supersonic flow therefore the flow comes closer. The peak heat is mostly radiation which is determined by the temp and observable half sphere. I am totally guessing here as I try to imagine myself as an air molecule travelling at 6km/s at an immovable barrier. On the edges you have flow coming from the centerline that can divert the flow away from the body. The edge also sees less angle of hot stuff.

You can also see this with like the shuttle temp map.

https://en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_system#/media/File:STS-3_infrared_on_reentry.jpg

remember the AoA of the shuttle was about 30-40? so the edges of the wings are first in line for heat.

Is there a temp map of the dragon?

EDIT added shuttle heat map
I've been struggling to find reentry temperature maps of capsules myself. The shuttle ones I've found (including the one you posted) certainly suggest that the main body is (comparatively) cool, but I know the angle of attack for Starship is very different.

My, probably naive, assumption was that peak heating would be where the shock wave rapidly changes direction, so on the edges of the fins, etc.

General principal. Blunt is best. Near the roots of the fins/whatever is where the flow should be quite hot.

Simple Newtonian hypersonic flow approximation is pretty good at determining pressure and heating.

John
Title: Re: Starship heat shield
Post by: steveleach on 05/13/2020 10:41 pm
Simple Newtonian hypersonic flow approximation is pretty good at determining pressure and heating.

John
Simple what now? ???
Title: Re: Starship heat shield
Post by: john smith 19 on 05/14/2020 06:08 am
I've been struggling to find reentry temperature maps of capsules myself. The shuttle ones I've found (including the one you posted) certainly suggest that the main body is (comparatively) cool, but I know the angle of attack for Starship is very different.

My, probably naive, assumption was that peak heating would be where the shock wave rapidly changes direction, so on the edges of the fins, etc.

General principal. Blunt is best. Near the roots of the fins/whatever is where the flow should be quite hot.
The fun starts when you get shock/shock interference and the heat transfer can raise between 4x and 10x.

This is sometimes called Edney type III or Edney type IV. It's the phenomena the X15 discovered when it carried a dummy scramjet and the shocks from it's nose with that from the fin carrying it sliced it clean off the fin.
Title: Re: Starship heat shield
Post by: john smith 19 on 05/14/2020 06:13 am
Simple Newtonian hypersonic flow approximation is pretty good at determining pressure and heating.

John
Simple what now? ???
Newton used a model for airflow that assumed air molecules travel in straight lines, like beams of light.

At the altitudes involved the air pressure is low enough (the Knusden number is high) that this approximation is valid and you can talk of "shadow" effects and being in the shadow of the wing (why the rudder on Shuttle was quite ineffective during this part of the flight). Here air pressure is not in psi, it's in pounds per sq foot
Title: Re: Starship heat shield
Post by: livingjw on 05/14/2020 06:16 am
Simple Newtonian hypersonic flow approximation is pretty good at determining pressure and heating.

John
Simple what now? ???

Reference Anderson, Hypersonics and High Temperature Gas Dynamics, 2nd ed. pg 311:
Newtonian impact theory: Cp=2*cos(phi)^2  where phi is the angle between the surface normal and freestream. This equation gives you pressure over the entire windward side of the vehicle. With the pressure you can get the velocities over the windward surface. With this and equation 6.106 and figure 6.17 you can get heating rate.

John

Title: Re: Starship heat shield
Post by: enbandi on 05/14/2020 09:46 am
There is a closeup of the latest test batch in the updates from BCG.

The gap between the rows can be symmetric and what we see as a bigger/white in one direction and close fit for the other two are only optical illusion.

But they still have the two separate style: one with the mounting holes (or whatever those white dots in a triangle pattern) and another, where the black cover seems continuous. No sign of the welded mounting pads however.

Title: Re: Starship heat shield
Post by: john smith 19 on 05/14/2020 11:23 am

But they still have the two separate style: one with the mounting holes (or whatever those white dots in a triangle pattern) and another, where the black cover seems continuous. No sign of the welded mounting pads however.
Intriguing.

You'd expect different tile types to be different sizes as well.

We know SX will need to make a lot of these so cost is definitely a factor.

The uniform colored ones could have multiple layers of protective skin over the mounting holes while the others have a simpler (faster and cheaper) single layer 

It'd be interesting to find out if the three rings correspond to surface changes, like bumps or indentations in the tiles.
Title: Re: Starship heat shield
Post by: livingjw on 05/14/2020 04:08 pm
I like the runt of the litter. Can't seem to fit in.  ;^)

John
Title: Re: Starship heat shield
Post by: Slarty1080 on 05/14/2020 08:32 pm
I like the runt of the litter. Can't seem to fit in.  ;^)

John
Yes it seems they are testing a smaller tile that is a little twisted of centre. Perhaps they want to see how well it holds up if the air can get under it and how much room they have to play with concerning gaps.
Title: Re: Starship heat shield
Post by: awests on 05/14/2020 08:42 pm
Could it be that the placement of the runt tile was aligned with the group at first. And now we are seeing it in a state where the fastening method has somewhat failed?
Title: Re: Starship heat shield
Post by: Aeneas on 05/14/2020 08:47 pm
Does anybody know, how much the heat shield weighs? kg/m²?
Title: Re: Starship heat shield
Post by: rsdavis9 on 05/14/2020 08:57 pm
Does anybody know, how much the heat shield weighs? kg/m²?

Rafael gives some estimates here:
https://forum.nasaspaceflight.com/index.php?topic=50049.0
Title: Re: Starship heat shield
Post by: enbandi on 05/14/2020 09:03 pm
Could it be that the placement of the runt tile was aligned with the group at first. And now we are seeing it in a state where the fastening method has somewhat failed?

That would be quite a serious mistake. Those tiles (and fastening) are designed to hold through a reentry/aerocapture. Multiple times, with small to no maintenance. This batch is mostly static as we know since their installation. Even not experienced a static fire....
Title: Re: Starship heat shield
Post by: Keldor on 05/14/2020 09:50 pm
Interestingly enough, it looks like the bottom of the white insulating layer DOES in fact fit perfectly, even though the black cap is twisted.  Could it have been ground into this shape during installation?

Steel has a much higher temperature before they start having problems than aluminum, like the Shuttle's air frame (and I believe the adhesives they used to connect the tiles had lower heat tolerance still?)  If gaps like this between the tiles are acceptable (remember, even the bottom of a crack is partially shielded by the adjacient tiles), then having them can greatly reduce the number of slightly different shapes needed to tile areas of non-zero curvature, such as the nose cone.  It also makes installation more forgiving if the workers can just shave off a little bit here or there to counteract accumulated error.

The next question is to what extent they can replicate the conditions of reentry without Super Heavy.  Remember, energy is proportional to velocity squared!  Perhaps tossing it on a long suborbital trajectory at a drone ship would be sufficient? 

RTLS would be a problem since near orbital velocity is much too fast for straight up, straight down to be survivable.  At these speeds, you traverse the thickness of the entire atmosphere in mere seconds, and going from a near orbital 7500 m/s to 0 in 30 seconds needs 25Gs of constant accelleration.  Of course, since most of that atmosphere is very thin, the bulk of your decelleration will occur much faster toward the end!  This leaves flying way out over the ocean and turning around.  It's hard to imagine how they'd get going more than maybe 3000-4000m/s this way, which, due to the square law, is an order of magnitude less energy than orbital reentry. 

The only reason F9 can get away with RTLS is because it's dumping off 100 tons worth of second stage before turning around, meaning that staging occurs at only around 2000 m/s.  This also means it's not as far down range, and still moving upward, further cutting into the velocity it has to reverse to get back home.  Nevertheless, this maneuver cuts 1/3 off of it's payload capability.
Title: Re: Starship heat shield
Post by: rsdavis9 on 05/15/2020 12:22 pm

The next question is to what extent they can replicate the conditions of reentry without Super Heavy.  Remember, energy is proportional to velocity squared!  Perhaps tossing it on a long suborbital trajectory at a drone ship would be sufficient? 

RTLS would be a problem since near orbital velocity is much too fast for straight up, straight down to be survivable.  At these speeds, you traverse the thickness of the entire atmosphere in mere seconds, and going from a near orbital 7500 m/s to 0 in 30 seconds needs 25Gs of constant accelleration.  Of course, since most of that atmosphere is very thin, the bulk of your decelleration will occur much faster toward the end!  This leaves flying way out over the ocean and turning around.  It's hard to imagine how they'd get going more than maybe 3000-4000m/s this way, which, due to the square law, is an order of magnitude less energy than orbital reentry. 


Would straight up and down at 2km/s be enough to simulate peak heating?
It wouldn't give the duration of heating that they want. So maybe straight up and down to do peak and maybe one out and back to do an approximation of duration albeit at a reduced temp. That way using data from both you can extrapolate the real thing.
Title: Re: Starship heat shield
Post by: envy887 on 05/15/2020 02:10 pm
This leaves flying way out over the ocean and turning around.  It's hard to imagine how they'd get going more than maybe 3000-4000m/s this way, which, due to the square law, is an order of magnitude less energy than orbital reentry.

Increasing the entry angle increases the heat flux, so they can match orbital entry at much lower velocity. By instrumenting the heat shield for this exercise and inspecting it afterward, they can validate their models which predict performance in a longer duration entry. That will probably establish enough confidence to go for an orbital attempt.

Matching heat flux gets rid of most of those annoying cubes and 8th powers that come with only varying velocity, so the model is less sensitive to minor errors. Adding more total energy is simply increasing time, which is linear and much easier to account for in a model.
Title: Re: Starship heat shield
Post by: Nomadd on 05/15/2020 02:21 pm
 I wasn't even looking at the tiles, and just found this in a wide shot. I'm not sure if I'd seen this angle before.
 I need to remember that if SN4 is still there next time I go wading where things are making way too big a splash four feet from me. (Yes, it gets closer every time I remember)
Title: Re: Starship heat shield
Post by: steveleach on 05/15/2020 02:30 pm
Simple Newtonian hypersonic flow approximation is pretty good at determining pressure and heating.

John
Simple what now? ???

Reference Anderson, Hypersonics and High Temperature Gas Dynamics, 2nd ed. pg 311:
Newtonian impact theory: Cp=2*cos(phi)^2  where phi is the angle between the surface normal and freestream. This equation gives you pressure over the entire windward side of the vehicle. With the pressure you can get the velocities over the windward surface. With this and equation 6.106 and figure 6.17 you can get heating rate.

John
Thanks John, I've started trying to get my head around that. If the current lockdown continues for another 8 or 9 years I might understand it all  :)

As I understand it though, the primary driver for heating is the angle of the surface to the air flow, so for a cylinder at 90% the greatest heating is a line down the centre of the vehicle.

For the shuttle, with its flat bottom, the entire base was essentially at the same angle, so other effects dominated, which is why we see it cooler in the centre, correct?
Title: Re: Starship heat shield
Post by: enbandi on 05/21/2020 04:07 pm
Did SN4 shake off a few heatshield tiles? (screenshots taken from bocachicagal photos)

First photo was from 5/15, second is from this morning.

Interesting observation regarding the SN4 test tiles. My bet however those are removed and not shaken down. (Those tiles are already went through 3 static fires, so inspection on two of them may worth the effort)

The more interesting parts are the studs: under the normal removed tile (in the patrern) there are 3 of them as we speculated.
But the other, external tile seems to had only 1 stud, maybe two if that is behind the adjacent tiles edge. But not the similar triangle pattern.
Title: Re: Starship heat shield
Post by: aceshigh on 05/22/2020 03:50 am
Did Musk ever said anything about even considering Magnetoshell Aerocapture.

NASA tests in 2014 already showed it was feasible, it was getting NIAC grants...

I am sure most of you know something about it, but for those that may never have heard...

https://www.nasa.gov/directorates/spacetech/niac/2012_Phase_I_magnetoshell/
Quote
. A NASA DRA 5.0 manned mission to Mars can be accomplished with 225 MT is mass savings and decreased programmatic and technical risk. Deep space planetary orbiters can be launched on rapid, direct trajectories decreasing trip times by more than 70%. And, with the same launch mass, a mission can be accomplished with significantly less trip time and thus, less solar and cosmic ray radiation exposure.



I know that SpaceX is not much into using unproven tech... they are more into maximizing efficiency of proven concepts rather than anything really novel. But having those Tesla batteries would already be interesting for creating a magnetoshell. And in the end, the mass savings seem significant as it allows less propellant being burnt to decrease reentry speed.
Title: Re: Starship heat shield
Post by: philw1776 on 05/23/2020 06:59 pm
Lots of discussion best under Advanced Concepts on this topic

https://forum.nasaspaceflight.com/index.php?topic=29912.msg2067052#msg2067052

Following posts aren't encouraging.

Nothing from SpaceX
Title: Re: Starship heat shield
Post by: SkyRate on 05/24/2020 11:17 pm
bocachicagal's latest and greatest pictures of the SN4 failed/removed heat shield tiles show that they were attached trough some kind of coarse-threaded screw that looks a lot like a shallow version of a self-drilling drywall anchor. I guessing it was drilled into the tile which was then pushed onto the protruding studs, locking in place.
Title: Re: Starship heat shield
Post by: hallmh on 05/25/2020 08:33 am
bocachicagal's latest and greatest pictures of the SN4 failed/removed heat shield tiles show that they were attached trough some kind of coarse-threaded screw that looks a lot like a shallow version of a self-drilling drywall anchor. I guessing it was drilled into the tile which was then pushed onto the protruding studs, locking in place.

Those photos, if you zoom in reeeally close, show a hex shape to the central hole, and a hint of a crosshead screw inside.

I think the 'drywall anchor' (good analogy btw) is screwed into a hole in the white insulation layer using a hex key, and that assembly is attached to the welded-on stud with a screw. Finally, the black ceramic layer is placed on top, secured (I assume) with high-temperature cement.

Title: Re: Starship heat shield
Post by: CorvusCorax on 05/25/2020 10:07 am
To get maximum of data, it might make sense to do flight tests with deliberately incorrectly or incompletely attached tiles ... ommit one or two bolts, see if the method can tolerate partial attachment failures. Also what happens if a tile is missing, can the airstream get underneath adjacent tiles and lift them off - like roof shingles in a storm - causing a chain reaction.

So seeing tiles fail during tests might not necessarily be a failure per se, it could have been "supposed to fail" or "fail as expected". importance at this point is gathering lotsa data

Title: Re: Starship heat shield
Post by: john smith 19 on 05/25/2020 10:20 am
To get maximum of data, it might make sense to do flight tests with deliberately incorrectly or incompletely attached tiles ... ommit one or two bolts, see if the method can tolerate partial attachment failures. Also what happens if a tile is missing, can the airstream get underneath adjacent tiles and lift them off - like roof shingles in a storm - causing a chain reaction.

So seeing tiles fail during tests might not necessarily be a failure per se, it could have been "supposed to fail" or "fail as expected". importance at this point is gathering lotsa data
Good point.

Collecting as much data as possible as early as possible lets you put tighter boundaries on everything else.

The real joker with mounting tiles is actually how do you dismount them?

This depends on the the type of tile and how it's mounted in the first place. Metallic tiles have assumed some kind of fastening, so how access it without a hole in the tile that is directly exposed to the airflow?

OTOH so far ceramic tiles have been bonded. the interesting option is to just crack the tiles off of what appear to be a set of studs (or in this context I'd call them "spigots").

Another interesting question. Could they just be a press fit cap over the studs/spigots on the skin? Then you'd just need a suction cup to pull them off.

Which of course raises the question "Are there any flight stages where the tile could be subjected to a negative surface pressure?"  The answer should be "No, never."
Title: Re: Starship heat shield
Post by: envy887 on 05/25/2020 12:27 pm
bocachicagal's latest and greatest pictures of the SN4 failed/removed heat shield tiles show that they were attached trough some kind of coarse-threaded screw that looks a lot like a shallow version of a self-drilling drywall anchor. I guessing it was drilled into the tile which was then pushed onto the protruding studs, locking in place.

Those photos, if you zoom in reeeally close, show a hex shape to the central hole, and a hint of a crosshead screw inside.

I think the 'drywall anchor' (good analogy btw) is screwed into a hole in the white insulation layer using a hex key, and that assembly is attached to the welded-on stud with a screw. Finally, the black ceramic layer is placed on top, secured (I assume) with high-temperature cement.

The black coating wraps around the tile into the gap, where it would be extremely hard to consistently apply in the field, so I'm sure that they come that way from the tile production facility.

As for the fastener, I see 2 square-ish things around a center dark spot. The alignment of the squares is consistent, pointing always to the center of the tile. I think the squares are the ends of spring tabs, and they snap over the little sphere on the end of the studs we previously saw welded to the tank walls.

The radial alignment is important because it would allow the tile to remain centered in its intended location as it expands at high temperature. The snap fit onto the sphere-tipped stud allows easy installation and allows some location tolerance between the stud positions and the anchors.

Edit: two of the weld studs are visible in the same photo, but it's difficult to make out the round tip. It looks like they wanted to test out a single centered mount, but couldn't be bothered to weld on one more stud outside the triangular pattern :D
Title: Re: Starship heat shield
Post by: Lars-J on 05/25/2020 06:45 pm
Another interesting question. Could they just be a press fit cap over the studs/spigots on the skin? Then you'd just need a suction cup to pull them off.

Which of course raises the question "Are there any flight stages where the tile could be subjected to a negative surface pressure?"  The answer should be "No, never."
Well there is that pesky vacuum that these Starships are supposed to spend a lot of time in... no greater negative pressure than that. ;)
Title: Re: Starship heat shield
Post by: Redclaws on 05/25/2020 07:09 pm
Isn’t that “zero surface pressure”, for this purpose?  There’s nothing *pulling* from a vacuum, it’s matter spreading out that gives the “sucking” effect we perceive.  And the surface the tile is attached to isn’t going anywhere, we hope.
Title: Re: Starship heat shield
Post by: SkyRate on 05/25/2020 08:15 pm
If there is a vacuum behind the tile, there can be no pressure outwards, but there could be problems if, say, water ice forms on the cold tank and then rapidly melts and vaporizes during reentry.
Title: Re: Starship heat shield
Post by: Coastal Ron on 05/25/2020 08:31 pm
Another interesting question. Could they just be a press fit cap over the studs/spigots on the skin? Then you'd just need a suction cup to pull them off.

Which of course raises the question "Are there any flight stages where the tile could be subjected to a negative surface pressure?"  The answer should be "No, never."
Well there is that pesky vacuum that these Starships are supposed to spend a lot of time in... no greater negative pressure than that. ;)

It's not the vacuum that is a concern, it would be a pressure differential caused by a vacuum. And for the tiles there should not be any areas that have pockets of contained air from the time of launch.

As to replacing tiles, unless you are on Earth using a vacuum to suction off tiles won't likely work since there would no or little air pressure. So hopefully they are planning for a mechanical means of removing and replacing tiles.
Title: Re: Starship heat shield
Post by: john smith 19 on 05/26/2020 06:21 am

It's not the vacuum that is a concern, it would be a pressure differential caused by a vacuum. And for the tiles there should not be any areas that have pockets of contained air from the time of launch.
Exactly. As long as the air from behind the tiles vents fast enough that should not be a problem.
Quote from: Coastal Ron
As to replacing tiles, unless you are on Earth using a vacuum to suction off tiles won't likely work since there would no or little air pressure. So hopefully they are planning for a mechanical means of removing and replacing tiles.
Good point. I was only considering tile replacement on earth. I'd forgotten possible on orbit and mars replacement scenarios.

That said a press fit onto 3 studs does look like a simple, cheap (and easily automated) way to mount them.

Which is what you need if you're going to be building SS by the 100s.
Title: Re: Starship heat shield
Post by: OTV Booster on 05/26/2020 02:23 pm
bocachicagal's latest and greatest pictures of the SN4 failed/removed heat shield tiles show that they were attached trough some kind of coarse-threaded screw that looks a lot like a shallow version of a self-drilling drywall anchor. I guessing it was drilled into the tile which was then pushed onto the protruding studs, locking in place.

Those photos, if you zoom in reeeally close, show a hex shape to the central hole, and a hint of a crosshead screw inside.

I think the 'drywall anchor' (good analogy btw) is screwed into a hole in the white insulation layer using a hex key, and that assembly is attached to the welded-on stud with a screw. Finally, the black ceramic layer is placed on top, secured (I assume) with high-temperature cement.

The black coating wraps around the tile into the gap, where it would be extremely hard to consistently apply in the field, so I'm sure that they come that way from the tile production facility.

As for the fastener, I see 2 square-ish things around a center dark spot. The alignment of the squares is consistent, pointing always to the center of the tile. I think the squares are the ends of spring tabs, and they snap over the little sphere on the end of the studs we previously saw welded to the tank walls.

The radial alignment is important because it would allow the tile to remain centered in its intended location as it expands at high temperature. The snap fit onto the sphere-tipped stud allows easy installation and allows some location tolerance between the stud positions and the anchors.

Edit: two of the weld studs are visible in the same photo, but it's difficult to make out the round tip. It looks like they wanted to test out a single centered mount, but couldn't be bothered to weld on one more stud outside the triangular pattern :D


I think the two ‘naked’ studs are just locator pins to keep the tile from rotating about the experimental single mount point. This tile was, IIRC, added almost as an afterthought and was not aligned with the other tiles. Iron workers with gastric distress from Corey’s Taco Dome.


I’m not sure I see the “2 square-ish things around a center dark spot.” Are you talking about in the center of each drywall anchor?


One thing I’m fairly certain about is the drywall anchors screw into the back of the tile. The large threads are to distribute the load to a material with miserable tinsel strength. Sort of like drywall or a foamy ceramic. The question is, are they screwed into the tile then the wall anchors mounted to the surface in some way or are they free spinning on the stud and the tile, with three small holes for a hex key, mounted and screwed onto them?


I think for now they’re doing both for now - with sub variations. Some tiles show vestiges of three small holes and some don't.


I wonder what the wall anchors are made of. Titanium? Stainless would be really heavy. How do stainless and titanium interact?


Phil
Title: Re: Starship heat shield
Post by: Nomadd on 05/26/2020 03:14 pm

One thing I’m fairly certain about is the drywall anchors screw into the back of the tile. The large threads are to distribute the load to a material with miserable tinsel strength. Sort of like drywall or a foamy ceramic. The question is, are they screwed into the tile then the wall anchors mounted to the surface in some way or are they free spinning on the stud and the tile, with three small holes for a hex key, mounted and screwed onto them?

I wonder what the wall anchors are made of. Titanium? Stainless would be really heavy. How do stainless and titanium interact?

Phil
  I know the material of the tile isn't that sturdy, but I'm sure it's stronger than tinsel.
 Hollow stainless screws shouldn't be too heavy. Maybe a six sided hole for driving in the back.  Welding titanium needs a lot more perfect conditions, as in a pretty much pure Argon or He environment. (Not an expert by any definition disclaimer) A lot of extra trouble and expense to save a couple hundred pounds.

Title: Re: Starship heat shield
Post by: envy887 on 05/26/2020 07:17 pm

One thing I’m fairly certain about is the drywall anchors screw into the back of the tile. The large threads are to distribute the load to a material with miserable tinsel strength. Sort of like drywall or a foamy ceramic. The question is, are they screwed into the tile then the wall anchors mounted to the surface in some way or are they free spinning on the stud and the tile, with three small holes for a hex key, mounted and screwed onto them?

I wonder what the wall anchors are made of. Titanium? Stainless would be really heavy. How do stainless and titanium interact?

Phil
  I know the material of the tile isn't that sturdy, but I'm sure it's stronger than tinsel.
 Hollow stainless screws shouldn't be too heavy. Maybe a six sided hole for driving in the back.  Welding titanium needs a lot more perfect conditions, as in a pretty much pure Argon or He environment. (Not an expert by any definition disclaimer) A lot of extra trouble and expense to save a couple hundred pounds.

If the spiral anchor is titanium, it wouldn't need to be welded to anything. It would mechanically attach to both the tile and the stud. The stud is probably stainless and stud welded to the outside of  the tank.

So the question is whether there is any adverse interaction between the titanium anchor and the stainless stud.
Title: Re: Starship heat shield
Post by: Lotick on 05/26/2020 10:53 pm

One thing I’m fairly certain about is the drywall anchors screw into the back of the tile. The large threads are to distribute the load to a material with miserable tinsel strength. Sort of like drywall or a foamy ceramic. The question is, are they screwed into the tile then the wall anchors mounted to the surface in some way or are they free spinning on the stud and the tile, with three small holes for a hex key, mounted and screwed onto them?


Can't agree more, the threaded thing resembles dowels for aerated concrete and other porous foamy materials. Most likely the 'dowel' screwed into the tile first, and then put on the pin welded to the ss skin. The center of the 'dowel' has a clamping mechanism that holds the pin. The only way to take the tile off is by breaking it and release the 'dowel' clamps.

To save weight the 'dowel' can be made from titanium. Titanium in pair with stainless steel used in medical implants, so there is probably no significant galvanic interaction between them.
Title: Re: Starship heat shield
Post by: OTV Booster on 05/27/2020 02:53 am
I'm sure I've seen this discussed but I don't remember the upshot. How practical would it be to 3D print a tile?  Not for production but for repair in a far away place. Wouldn't need to be the same material as a production tile, just good enough one earth EDL.
Title: Re: Starship heat shield
Post by: oiorionsbelt on 05/27/2020 05:35 am
Basically just need a caulking gun. In NASA speak TileRepair Ablator Dispenser, or T-RAD was developed for the shuttle.
Title: Re: Starship heat shield
Post by: john smith 19 on 05/27/2020 05:56 am
  I know the material of the tile isn't that sturdy, but I'm sure it's stronger than tinsel.
On the off chance you're not joking he means tensile.  Ceramics are typically -10x stronger in compression than tension.
Quote from: Nomadd
Hollow stainless screws shouldn't be too heavy. Maybe a six sided hole for driving in the back.  Welding titanium needs a lot more perfect conditions, as in a pretty much pure Argon or He environment. (Not an expert by any definition disclaimer) A lot of extra trouble and expense to save a couple hundred pounds.
Titanium is quite reactive in air in a way that SS simply isn't.

Let's keep in mind all of the design constraints for these tiles to avoid "local optimums."

Protect against earth re-entry from LEO.
Protect against earth re-entry from GEO (or at least GTO)
Protect against earth re-entry from mars
All of the above should be possible multiple (TBD) times.
At some point installation has to be capable of automation, ideally fairly simple and high speed. Hand placement on 100s of SS's won't cut it.
Tiles should be fairly easy//quick to inspect. Ideally you should be able to look at them and say "Yes, those are all good. That one's marginal and those two need replacing now" while inside a pressure suit.  :)
Has to be capable of repair while in a pressure suit (but could be straight swap out from a stock of spares rather than some clever single use repair foam like the shuttle)

It's that total combination that makes this design and development task so tough.  :(

Which suggest (regardless of how they are implemented)

Tiles self align WRT to each other, possibly with some compliance in the mounts to accommodate slightly misaligned placement.
No hand cut/sized/installed gap fillers (like on shuttle)
Limited number of sizes and shapes. Complex areas are done using more smaller (but standard) tiles.
Eliminate any special case areas, otherwise you have to either a) Carry special repair materials for them or b) Assume they never fail. With enough vehicles flying over a long enough period (and they definitely will be if Musks goals are to be met) this is very wishful thinking.  :(



Title: Re: Starship heat shield
Post by: OTV Booster on 05/27/2020 12:50 pm
  I know the material of the tile isn't that sturdy, but I'm sure it's stronger than tinsel.
On the off chance you're not joking he means tensile.  Ceramics are typically -10x stronger in compression than tension.
Quote from: Nomadd
Hollow stainless screws shouldn't be too heavy. Maybe a six sided hole for driving in the back.  Welding titanium needs a lot more perfect conditions, as in a pretty much pure Argon or He environment. (Not an expert by any definition disclaimer) A lot of extra trouble and expense to save a couple hundred pounds.
Titanium is quite reactive in air in a way that SS simply isn't.

Let's keep in mind all of the design constraints for these tiles to avoid "local optimums."

Protect against earth re-entry from LEO.
Protect against earth re-entry from GEO (or at least GTO)
Protect against earth re-entry from mars
All of the above should be possible multiple (TBD) times.
At some point installation has to be capable of automation, ideally fairly simple and high speed. Hand placement on 100s of SS's won't cut it.
Tiles should be fairly easy//quick to inspect. Ideally you should be able to look at them and say "Yes, those are all good. That one's marginal and those two need replacing now" while inside a pressure suit.  :)
Has to be capable of repair while in a pressure suit (but could be straight swap out from a stock of spares rather than some clever single use repair foam like the shuttle)

It's that total combination that makes this design and development task so tough.  :(

Which suggest (regardless of how they are implemented)

Tiles self align WRT to each other, possibly with some compliance in the mounts to accommodate slightly misaligned placement.
No hand cut/sized/installed gap fillers (like on shuttle)
Limited number of sizes and shapes. Complex areas are done using more smaller (but standard) tiles.
Eliminate any special case areas, otherwise you have to either a) Carry special repair materials for them or b) Assume they never fail. With enough vehicles flying over a long enough period (and they definitely will be if Musks goals are to be met) this is very wishful thinking.  :(


It's Nomadd! Joking? Heavens to mergatroid. Between my crappy spelling and my phones automatic 'corrections' the English language is facing stress never before envisioned.


Of all Musks goals, fast turnaround, at least after interplanetary EDL, may be the least realistic. The heat shield has a rough job. If it needs TLC after a high energy EDL, that's part of the cost of doing business.


When installing a high rpm grinding wheel it is standard to give it a tap. If there is a hidden crack somewhere it will give a characteristic dead thump. This got me thinking.


The SS has every promise of being a boom box. There is the possibility that many if not all failure modes will have acoustic signatures that a pickup array could narrow down to a few tiles making detailed inspection much easier. An inspection tool, essentially an acoustic pickup and a pinger, would be placed on a tile to be checked. Lots of moving parts here and maybe not practical. If it can be made to work it both makes inspection easier and lends itself to automation.


Phil
Title: Re: Starship heat shield
Post by: Lotick on 05/27/2020 01:39 pm
The clamps that hold pin can be designed to be able released by applying the strong magnetic field. Just like security tags for clothes.
This way the tile can be removed for inspection or replacement with ease.
Title: Re: Starship heat shield
Post by: rsdavis9 on 05/27/2020 03:53 pm
The clamps that hold pin can be designed to be able released by applying the strong magnetic field. Just like security tags for clothes.
This way the tile can be removed for inspection or replacement with ease.

I would think snap and snap off like the interior panels of a car would be sufficient and hold enough even in a strong airflow.
Very simple.
Title: Re: Starship heat shield
Post by: john smith 19 on 05/27/2020 04:19 pm
When installing a high rpm grinding wheel it is standard to give it a tap. If there is a hidden crack somewhere it will give a characteristic dead thump. This got me thinking.


The SS has every promise of being a boom box. There is the possibility that many if not all failure modes will have acoustic signatures that a pickup array could narrow down to a few tiles making detailed inspection much easier. An inspection tool, essentially an acoustic pickup and a pinger, would be placed on a tile to be checked. Lots of moving parts here and maybe not practical. If it can be made to work it both makes inspection easier and lends itself to automation.


Phil
What you're talking about is usually called "Acoustic emission" monitoring.  It's been proposed (used?) for COPV monitoring amongst other applications. That's when you listen for sounds. But if you excite the structure that's more like active ultrasound system.

In effect you hear "pings" as the material cracks, or crystals slide over each other.

Note.
"Acoustic" in this context is not "sound" but a mechanical vibration wave. The signals can have a bandwidth of Mega Hertz rather than less than 20KHz.

The sound spectrum from a structure this big and the network of attached sensors ("Microphones doesn't really do them justice somehow) is going to be very complex. However if there are certain key features of a failure signature then something much simpler (like a filterbank) could serve well enough as a continuous failure detection system.
Title: Re: Starship heat shield
Post by: envy887 on 05/27/2020 04:20 pm
Protect against earth re-entry from LEO.
Protect against earth re-entry from GEO (or at least GTO)
Protect against earth re-entry from mars
All of the above should be possible multiple (TBD) times.

Starship will probably use multiple entry passes to keep the total heat impulse per pass around that of a LEO entry. For GTO or TLI that probably mean 2 passes, for circularization in LEO and then for EDL. For Mars that probably means a capture pass, a circularization pass, and an EDL pass.

Quote
At some point installation has to be capable of automation, ideally fairly simple and high speed. Hand placement on 100s of SS's won't cut it.
Tiles should be fairly easy//quick to inspect. Ideally you should be able to look at them and say "Yes, those are all good. That one's marginal and those two need replacing now" while inside a pressure suit.  :)
Has to be capable of repair while in a pressure suit (but could be straight swap out from a stock of spares rather than some clever single use repair foam like the shuttle)

Hand installation is fine, as long as it quick per tile. If 2 or 3 guys in a lift can install 2 tiles per minute, then 2 crews working 3 shifts can tile a whole Starship in 2 days. That's only 150-200 man-hours. For 100 ships a year, that's probably not worth automating.

Inspection and repair is a whole different question, but they need to get it flying first so I highly doubt they are spending too much time optimizing inspection techniques. Worst case, they break off all the tiles and install all new ones, which should only take a couple days. Better case, they are able to visually identify problematic tiles, which could eventually be  automated with a high res photographic scanning system.
Title: Re: Starship heat shield
Post by: john smith 19 on 05/27/2020 04:42 pm
Of all Musks goals, fast turnaround, at least after interplanetary EDL, may be the least realistic. The heat shield has a rough job. If it needs TLC after a high energy EDL, that's part of the cost of doing business.

Phil
Well yes and no. 

As always the devils in the details.  :)

By Shuttle standards "fast" would be 1 month (has anyone compared Shuttle surface area to area of SS covered by TPS? Someone must have by now. And don't forget the aerosurface in that calculation).

It'll depend on what sort of margins he wants in it.
Something that can do a 100 re-etries from mars (with the odd tile replacement  :) )  would a very different beast from something that can do indefinite numbers of LEO re-entries but the whole TPS needs to be scrapped if it comes in from mars.

Right now I'd guess the goal is just "Get it into the air and see what that does to them."

I'm pretty sure what makes first EDL on mars will be a very different item (even it looks quite similar) to what's going on now.
Title: Re: Starship heat shield
Post by: OTV Booster on 05/27/2020 05:08 pm
When installing a high rpm grinding wheel it is standard to give it a tap. If there is a hidden crack somewhere it will give a characteristic dead thump. This got me thinking.


The SS has every promise of being a boom box. There is the possibility that many if not all failure modes will have acoustic signatures that a pickup array could narrow down to a few tiles making detailed inspection much easier. An inspection tool, essentially an acoustic pickup and a pinger, would be placed on a tile to be checked. Lots of moving parts here and maybe not practical. If it can be made to work it both makes inspection easier and lends itself to automation.


Phil
What you're talking about is usually called "Acoustic emission" monitoring.  It's been proposed (used?) for COPV monitoring amongst other applications. That's when you listen for sounds. But if you excite the structure that's more like active ultrasound system.

In effect you hear "pings" as the material cracks, or crystals slide over each other.

Note.
"Acoustic" in this context is not "sound" but a mechanical vibration wave. The signals can have a bandwidth of Mega Hertz rather than less than 20KHz.

The sound spectrum from a structure this big and the network of attached sensors ("Microphones doesn't really do them justice somehow) is going to be very complex. However if there are certain key features of a failure signature then something much simpler (like a filterbank) could serve well enough as a continuous failure detection system.
I wasn't very precise on my wording but it looks like I got the idea across. By 'ping' I meant going active. The frequencies of interest and character of the signal (musician speak) will be very different, passive and active.


On the passive side I figure a combination of band pass filter and DSP. It'll be a noisy (vibration rich) environment. Hard to pick out signal from noise. I wonder if SX is already building a vibration database during testing. Something like what is done with sonar. I'd be very surprised if they weren't doing this at least on the engines.
Title: Re: Starship heat shield
Post by: john smith 19 on 05/27/2020 09:21 pm
I wasn't very precise on my wording but it looks like I got the idea across. By 'ping' I meant going active. The frequencies of interest and character of the signal (musician speak) will be very different, passive and active.


On the passive side I figure a combination of band pass filter and DSP. It'll be a noisy (vibration rich) environment. Hard to pick out signal from noise. I wonder if SX is already building a vibration database during testing. Something like what is done with sonar. I'd be very surprised if they weren't doing this at least on the engines.
That's a tricky one.

Modern storage is so large and cheap it's possible to record a staggering amount of data. So you can store more or less as much data as you want (the usual issue is resolution. 8 bits at 2MHz. Piece of cake. 16bits at 2MHz. Much tougher)

But right now SS (even its engines) is a moving development target.

So what part(s) of that spectrum is down to the TPS operating normally? What part is due to a tile failure? What part to the rest of the system?

It's unclear how much of that data will be usable as raw material for diagnostic purposes.

But it's probably cheaper to collect it and not use it than vice versa.

Title: Re: Starship heat shield
Post by: john smith 19 on 05/27/2020 09:50 pm
Hand installation is fine, as long as it quick per tile. If 2 or 3 guys in a lift can install 2 tiles per minute, then 2 crews working 3 shifts can tile a whole Starship in 2 days. That's only 150-200 man-hours. For 100 ships a year, that's probably not worth automating.
You might like to re-consider that.

Musk has talked of a million people on mars by 2050.
With a launch window every 26 months and 9 support payloads for every 1 passenger carrier and even assuming only 200 000 actually go (the other 800 000 are born there) that's 1539 SS each launch window.   :o

So manual is fine for prototypes (and all of these are prototypes so far) but it won't be viable on that sort of scale.
Quote from: envy887
Inspection and repair is a whole different question, but they need to get it flying first so I highly doubt they are spending too much time optimizing inspection techniques. Worst case, they break off all the tiles and install all new ones, which should only take a couple days. Better case, they are able to visually identify problematic tiles, which could eventually be  automated with a high res photographic scanning system.

At this point no, just getting something into the air would be the immediate goal. But it does have to be factored in as part of the big picture.
Title: Re: Starship heat shield
Post by: wannamoonbase on 05/27/2020 09:51 pm
Hand installation is fine, as long as it quick per tile. If 2 or 3 guys in a lift can install 2 tiles per minute, then 2 crews working 3 shifts can tile a whole Starship in 2 days. That's only 150-200 man-hours. For 100 ships a year, that's probably not worth automating.

For tiles that are consistent and the uniform in shape and curvature placement might be somewhat routine.  It's the odd ones and terminating ones around the edges and ends and in and around the control surfaces.  Those will likely take more time.

Unless things are automated with AI robots or some such thing.  But the first SS' covered in tiles will very likely be 100% manual installation.  Expect the first one to take a month or longer.  Once they have a heat shield that works and has a flight history, you can bet Elon will want to reduce the labor required.

That's going to be an awful lot of tiles, like a lot.
Title: Re: Starship heat shield
Post by: OTV Booster on 05/28/2020 02:55 am
I wasn't very precise on my wording but it looks like I got the idea across. By 'ping' I meant going active. The frequencies of interest and character of the signal (musician speak) will be very different, passive and active.


On the passive side I figure a combination of band pass filter and DSP. It'll be a noisy (vibration rich) environment. Hard to pick out signal from noise. I wonder if SX is already building a vibration database during testing. Something like what is done with sonar. I'd be very surprised if they weren't doing this at least on the engines.
That's a tricky one.

Modern storage is so large and cheap it's possible to record a staggering amount of data. So you can store more or less as much data as you want (the usual issue is resolution. 8 bits at 2MHz. Piece of cake. 16bits at 2MHz. Much tougher)

But right now SS (even its engines) is a moving development target.

So what part(s) of that spectrum is down to the TPS operating normally? What part is due to a tile failure? What part to the rest of the system?

It's unclear how much of that data will be usable as raw material for diagnostic purposes.

But it's probably cheaper to collect it and not use it than vice versa.


Working around ceramic floor tile, it has a characteristic sound, as do most materials. Slide one tile across another, tap with a hammer or slide a nail across the face of a tile and while each will sound different, each will have a certain 'tileness' to it. Crack a tile and it has the same tile like component in the sound. This would suggest itself as a starting point for investigation.


I can see cracking as a common failure mode along with surface spawling. Possibly delamination between the black and white layers. There is melting too, but I don't know if there is much of a sound associated with it. Melting should be easily discovered visually so it needn't depend on acoustics for discovery. Spawling, the same.


Characterize The sound of 'tileness' by intentionally breaking tiles in different ways in the lab, then use the pickups in the ship to look for that sound. An array of pickups should be able to use intensity and timing to localize the source to within a few tiles.


Once a few tiles get dinged during testing they'll have real data to refine the procedure.
Title: Re: Starship heat shield
Post by: Slarty1080 on 05/28/2020 08:21 pm
Could they embed a loop of wire inside the tile when it was made? Any cracks might then break the wire loop which could then be detected by magnetic induction.
Title: Re: Starship heat shield
Post by: john smith 19 on 05/29/2020 05:45 am
Could they embed a loop of wire inside the tile when it was made? Any cracks might then break the wire loop which could then be detected by magnetic induction.

Neat idea. Now factor in

Will it detect surface damage, or will it be so deep for thermal protection it survives even when the surface is too compromised to survive?

What does the metal properties interacting to the tile material do to them?

Most very high temp metals are also very dense. How much extra mass would this add?

It's actually a very neat idea. No electronics. No batteries. But because of the extreme range of environments involved everything becomes a factor that has to be tested for interaction with everything else.  :(



Title: Re: Starship heat shield
Post by: OTV Booster on 05/31/2020 08:59 pm
Could they embed a loop of wire inside the tile when it was made? Any cracks might then break the wire loop which could then be detected by magnetic induction.

Neat idea. Now factor in

Will it detect surface damage, or will it be so deep for thermal protection it survives even when the surface is too compromised to survive?

What does the metal properties interacting to the tile material do to them?

Most very high temp metals are also very dense. How much extra mass would this add?

It's actually a very neat idea. No electronics. No batteries. But because of the extreme range of environments involved everything becomes a factor that has to be tested for interaction with everything else.  :(
Surface damage can be checked visually. Maybe a drone on mars.


I'm not quite getting the idea. Would there be an induction coil under each tile? Would the whole SS body carry an AC signal?  That sounds interesting. Can two AC signals be injected and phase shifted to act like a phased array to pinpoint the failure?
Title: Re: Starship heat shield
Post by: john smith 19 on 06/01/2020 06:03 am
Surface damage can be checked visually. Maybe a drone on mars.


I'm not quite getting the idea. Would there be an induction coil under each tile? Would the whole SS body carry an AC signal?  That sounds interesting. Can two AC signals be injected and phase shifted to act like a phased array to pinpoint the failure?

I read it as a loop of wire in the tile (not necessarily circular). An induction coil on some kind of carrier is passed over each tile and the assumption is that most damage processes would involve breaking the coil, so no signal. In principle that head could also carry a camera to check for visual damage which might not snap the wire.

But I could be wrong.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/01/2020 07:33 am
Surface damage can be checked visually. Maybe a drone on mars.


I'm not quite getting the idea. Would there be an induction coil under each tile? Would the whole SS body carry an AC signal?  That sounds interesting. Can two AC signals be injected and phase shifted to act like a phased array to pinpoint the failure?

I read it as a loop of wire in the tile (not necessarily circular). An induction coil on some kind of carrier is passed over each tile and the assumption is that most damage processes would involve breaking the coil, so no signal. In principle that head could also carry a camera to check for visual damage which might not snap the wire.

But I could be wrong.
Yes similar to the sort of thing you get in a library where each book that gets scanned out and scanned back in again. Although obviously with different materials.
Title: Re: Starship heat shield
Post by: SkyRate on 06/01/2020 10:16 pm
Surface damage can be checked visually. Maybe a drone on mars.

I'm not quite getting the idea. Would there be an induction coil under each tile? Would the whole SS body carry an AC signal?  That sounds interesting. Can two AC signals be injected and phase shifted to act like a phased array to pinpoint the failure?

I read it as a loop of wire in the tile (not necessarily circular). An induction coil on some kind of carrier is passed over each tile and the assumption is that most damage processes would involve breaking the coil, so no signal. In principle that head could also carry a camera to check for visual damage which might not snap the wire.

You could update this idea for the digital age. Put an RFID chip and and antenna loop in each tile, just like in a credit card. Then each tile has a separate unique ID and you can interrogate a bunch of them in parallel. You'd need to keep the loop some minimum distance away from the steel hull, of course.
Title: Re: Starship heat shield
Post by: Keldor on 06/01/2020 10:36 pm
Could they embed a loop of wire inside the tile when it was made? Any cracks might then break the wire loop which could then be detected by magnetic induction.

Neat idea. Now factor in

Will it detect surface damage, or will it be so deep for thermal protection it survives even when the surface is too compromised to survive?

What does the metal properties interacting to the tile material do to them?

Most very high temp metals are also very dense. How much extra mass would this add?

It's actually a very neat idea. No electronics. No batteries. But because of the extreme range of environments involved everything becomes a factor that has to be tested for interaction with everything else.  :(

My feeling is that the wire would survive many situations where the tile would not, making it useless as an indicator.  The wire would simply be stronger than the tile, and, even assuming a crack shifts enough to put force on the wire, the tile around the wire would crumble as the wire flexes to accept the load without breaking.  Think about the way rebar in concrete survives long after the concrete itself begins to crack and crumble.

A worse problem is that the weaknesses in tiles that are most worrying are hairline cracks, nearly invisible to the eye.  Such a crack would be unlikely to break the wire, since neither side actually moved.
Title: Re: Starship heat shield
Post by: Exastro on 06/01/2020 10:43 pm
Could they embed a loop of wire inside the tile when it was made? Any cracks might then break the wire loop which could then be detected by magnetic induction.

Neat idea. Now factor in

Will it detect surface damage, or will it be so deep for thermal protection it survives even when the surface is too compromised to survive?

What does the metal properties interacting to the tile material do to them?

Most very high temp metals are also very dense. How much extra mass would this add?

It's actually a very neat idea. No electronics. No batteries. But because of the extreme range of environments involved everything becomes a factor that has to be tested for interaction with everything else.  :(

My feeling is that the wire would survive many situations where the tile would not, making it useless as an indicator.  The wire would simply be stronger than the tile, and, even assuming a crack shifts enough to put force on the wire, the tile around the wire would crumble as the wire flexes to accept the load without breaking.  Think about the way rebar in concrete survives long after the concrete itself begins to crack and crumble.

A worse problem is that the weaknesses in tiles that are most worrying are hairline cracks, nearly invisible to the eye.  Such a crack would be unlikely to break the wire, since neither side actually moved.


How about using optical fibers instead of wire?
Title: Re: Starship heat shield
Post by: GregTheGrumpy on 06/01/2020 11:31 pm
I would also suggest that 'wire' is probably the wrong word.  I believe we'd be talking about a trace (like on a circuit board) that was thin, just enough to conduct electricity but easily broken by any crack.

If you have a back and forth trace (not overlaping) that ran for the length and width of the tile, if there was any real damage then the circuit would break.  The frequency response of the tile to RF interrogation would surely change.

This is what I would expect to see in this idea.

IANAEE.
-g
Title: Re: Starship heat shield
Post by: Coastal Ron on 06/01/2020 11:40 pm
How about using optical fibers instead of wire?

The same issue exists with wires and with optical fibers - the connectors. If each tile has a connector, that weight not only adds up, but connectors are points of failure.

OK, now you have collected the signals from one tile, but there are thousands of them. Do you run individual wire or optical cables for each of those into one central monitor, or do you group them into local collection boxes that then have to run wires up to the central monitor? And if you group them, where are those local connection boxes at, and how are they protected?

This is a lot of technology to put on the side of the Starship that will be experiencing extremely high temperatures.

So I'm thinking they won't put sensors on the tiles.
Title: Re: Starship heat shield
Post by: john smith 19 on 06/02/2020 05:41 am
You could update this idea for the digital age. Put an RFID chip and and antenna loop in each tile, just like in a credit card. Then each tile has a separate unique ID and you can interrogate a bunch of them in parallel. You'd need to keep the loop some minimum distance away from the steel hull, of course.
That was developed for the Shuttle programme in the early 90's.

Each one had a spring contact held closed by a plated solder link (a similar safety device was fitted in TV sets). They were designed to be dropped in the gaps between the tiles and warn of a tile overheat. IOW Needs further inspection/possible replacement.
How about using optical fibers instead of wire?
Also possible. Alumina (basically sapphire without metal ions to color it) FO is available and is good to somewhere around 1500-2000c

But this technique implies all those sensor heads lead somewhere. The mass for this could start racking up pretty quickly.   :(

The classic way to avoid individual connections is to string a fiber behind (or through?) multiple tiles and embed a "fiber Bragg grating" patter in each section. These can then be interrogated individually (at a slower pace).

They have been embedded in 80m carbon fiber ships masts and large power transformers.
The same issue exists with wires and with optical fibers - the connectors. If each tile has a connector, that weight not only adds up, but connectors are points of failure.
OP was the the design is passive, read by a moving read with an induction coil. Break in wire -->> no signal.

Continuous monitoring is only realistically worthwhile if when you sense an issue you can do something about it.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/02/2020 07:48 am
Could they embed a loop of wire inside the tile when it was made? Any cracks might then break the wire loop which could then be detected by magnetic induction.

Neat idea. Now factor in

Will it detect surface damage, or will it be so deep for thermal protection it survives even when the surface is too compromised to survive?

What does the metal properties interacting to the tile material do to them?

Most very high temp metals are also very dense. How much extra mass would this add?

It's actually a very neat idea. No electronics. No batteries. But because of the extreme range of environments involved everything becomes a factor that has to be tested for interaction with everything else.  :(

My feeling is that the wire would survive many situations where the tile would not, making it useless as an indicator.  The wire would simply be stronger than the tile, and, even assuming a crack shifts enough to put force on the wire, the tile around the wire would crumble as the wire flexes to accept the load without breaking.  Think about the way rebar in concrete survives long after the concrete itself begins to crack and crumble.

A worse problem is that the weaknesses in tiles that are most worrying are hairline cracks, nearly invisible to the eye.  Such a crack would be unlikely to break the wire, since neither side actually moved.


How about using optical fibers instead of wire?
Optical fibres won't allow an electrical current to be induced so wouldn't work
Title: Re: Starship heat shield
Post by: ZChris13 on 06/02/2020 09:38 am
How about using optical fibers instead of wire?

The same issue exists with wires and with optical fibers - the connectors. If each tile has a connector, that weight not only adds up, but connectors are points of failure.

OK, now you have collected the signals from one tile, but there are thousands of them. Do you run individual wire or optical cables for each of those into one central monitor, or do you group them into local collection boxes that then have to run wires up to the central monitor? And if you group them, where are those local connection boxes at, and how are they protected?

This is a lot of technology to put on the side of the Starship that will be experiencing extremely high temperatures.

So I'm thinking they won't put sensors on the tiles.
I believe there to be some confusion about the original proposal here, particularly on your part, Coastal Ron. The tiles are not connected. They are passive, they do no active reporting. If the wire is intact, an external robot can pass over it and get an inductive response. If the wire is broken, the external robot will get a different inductive response. This happens on the ground in post-flight checkout, or I guess one could do it in orbit.
Title: Re: Starship heat shield
Post by: waveney on 06/02/2020 11:12 am
How about using optical fibers instead of wire?

The same issue exists with wires and with optical fibers - the connectors. If each tile has a connector, that weight not only adds up, but connectors are points of failure.

OK, now you have collected the signals from one tile, but there are thousands of them. Do you run individual wire or optical cables for each of those into one central monitor, or do you group them into local collection boxes that then have to run wires up to the central monitor? And if you group them, where are those local connection boxes at, and how are they protected?

This is a lot of technology to put on the side of the Starship that will be experiencing extremely high temperatures.

So I'm thinking they won't put sensors on the tiles.
I believe there to be some confusion about the original proposal here, particularly on your part, Coastal Ron. The tiles are not connected. They are passive, they do no active reporting. If the wire is intact, an external robot can pass over it and get an inductive response. If the wire is broken, the external robot will get a different inductive response. This happens on the ground in post-flight checkout, or I guess one could do it in orbit.
I don't know if this is useful or not:

Optical fibres can be tested in other ways,  A small break will be reflective and using a OTDR (Optical Time Duration Reflectometer see https://en.wikipedia.org/wiki/Optical_time-domain_reflectometer (https://en.wikipedia.org/wiki/Optical_time-domain_reflectometer)) the location of the break(s) can be accurately located.   If all the tiles are optically linked in some way (presumably at the back) an OTDR could check the entire Heat shield in one operation, locating all the cracked tiles in a test taking only a few seconds.  It would be practical to have the equipment on board and done in flight as well as on the ground.   Optic fibres can be quiet heat tolerant, depeding on what their outer layer is. 

They could also be used to measure the heat as well.  Heating changes the timing properties of the fibres in well known ways and the OTDR can be used to measure lots of things. 

(In the distant past I remember dealing in their properties measured in pico-seconds per kilometre per second.  I was wanting to know the rate of change of apparent length, given the actual length - So I could work out how often the Telecoms System using them had to adjust the clocks - this was a system running at 10G+ over distances up to 200km.  My role was system design).
Title: Re: Starship heat shield
Post by: OTV Booster on 06/02/2020 02:12 pm
How about using optical fibers instead of wire?

The same issue exists with wires and with optical fibers - the connectors. If each tile has a connector, that weight not only adds up, but connectors are points of failure.

OK, now you have collected the signals from one tile, but there are thousands of them. Do you run individual wire or optical cables for each of those into one central monitor, or do you group them into local collection boxes that then have to run wires up to the central monitor? And if you group them, where are those local connection boxes at, and how are they protected?

This is a lot of technology to put on the side of the Starship that will be experiencing extremely high temperatures.

So I'm thinking they won't put sensors on the tiles.
I believe there to be some confusion about the original proposal here, particularly on your part, Coastal Ron. The tiles are not connected. They are passive, they do no active reporting. If the wire is intact, an external robot can pass over it and get an inductive response. If the wire is broken, the external robot will get a different inductive response. This happens on the ground in post-flight checkout, or I guess one could do it in orbit.
Ahh, thank you. Rube Goldberg was taking over. However it's done it has to be cheap and simple.
Title: Re: Starship heat shield
Post by: wes_wilson on 06/02/2020 02:55 pm
How about using optical fibers instead of wire?

The same issue exists with wires and with optical fibers - the connectors. If each tile has a connector, that weight not only adds up, but connectors are points of failure.

OK, now you have collected the signals from one tile, but there are thousands of them. Do you run individual wire or optical cables for each of those into one central monitor, or do you group them into local collection boxes that then have to run wires up to the central monitor? And if you group them, where are those local connection boxes at, and how are they protected?

This is a lot of technology to put on the side of the Starship that will be experiencing extremely high temperatures.

So I'm thinking they won't put sensors on the tiles.
I believe there to be some confusion about the original proposal here, particularly on your part, Coastal Ron. The tiles are not connected. They are passive, they do no active reporting. If the wire is intact, an external robot can pass over it and get an inductive response. If the wire is broken, the external robot will get a different inductive response. This happens on the ground in post-flight checkout, or I guess one could do it in orbit.
Ahh, thank you. Rube Goldberg was taking over. However it's done it has to be cheap and simple.

Basically, the proposal is to embed the equivalent of a passive rfid tag in each tile designed so that if the tile breaks the rfid circuit is broken right?
Title: Re: Starship heat shield
Post by: OTV Booster on 06/02/2020 08:44 pm
How about using optical fibers instead of wire?

The same issue exists with wires and with optical fibers - the connectors. If each tile has a connector, that weight not only adds up, but connectors are points of failure.

OK, now you have collected the signals from one tile, but there are thousands of them. Do you run individual wire or optical cables for each of those into one central monitor, or do you group them into local collection boxes that then have to run wires up to the central monitor? And if you group them, where are those local connection boxes at, and how are they protected?

This is a lot of technology to put on the side of the Starship that will be experiencing extremely high temperatures.

So I'm thinking they won't put sensors on the tiles.
I believe there to be some confusion about the original proposal here, particularly on your part, Coastal Ron. The tiles are not connected. They are passive, they do no active reporting. If the wire is intact, an external robot can pass over it and get an inductive response. If the wire is broken, the external robot will get a different inductive response. This happens on the ground in post-flight checkout, or I guess one could do it in orbit.
Ahh, thank you. Rube Goldberg was taking over. However it's done it has to be cheap and simple.

Basically, the proposal is to embed the equivalent of a passive rfid tag in each tile designed so that if the tile breaks the rfid circuit is broken right?
Gettin complex again. The original proposal was a simple loop of wire embedded in the tile. Nothing more. An inspection device with an active induction coil would pass over the tiles. A tile with an intact loop will experience an induced current flow and create a corresponding magnetic field. A tile with a broken loop will not. A magnetic field, or the lack, will tell the state of the tile.


TBD: will all non visible tile failures consistently break the wire?


If this works it's elegant. And simple.


Phil
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/02/2020 08:45 pm
Just to emphasise the idea is not to plug anything in but to detect a crack remotely using an induction scanner of a metallic loop embedded in the tile. No connectors on the tile.

There are some valid objections to this as people have been pointing out, but there might still be scope. Perhaps some very fine metallic fibres could be added to the tile mix or a very fine metallic mesh layer. They should produce a detectable signal by making a variety of different loops inside the tile. Changes to the frequency of detection might then be related to the degree of damage, so it doesn’t have to be one big loop of wire.

I should point out that I’m just wildly speculating here (as is my way). But if this is not possible or practical then IMO there needs to be some other method of detecting damage to tiles perhaps by x-ray?
Title: Re: Starship heat shield
Post by: OTV Booster on 06/02/2020 09:07 pm
Further thought on the wire loop. John smith brought up three important possible show stoppers (maybe more. I'm running on memory here). High temps, possible failure to sever under a hairline crack and chemical reactivity with the tile.

The finest whisker of tungsten comes to mind. It's fine with high temps. It's brittle, improving the odds of sensitivity to a hairline. I'd be blowing smoke if I claimed to know anything about chemical interactions.

Cons: it's expensive and it's natural high resistance might create enough internal losses that the induced field will be hard to detect.

The internal resistance thing is just speculation on a possibility. Got nothing hard. On cost, depending on minimum acceptable gauge, one gr. would surely do five tiles and hopefully more.

Phil

Edit to add: density is 19.3. Not a whole lot of wire from a gram.

Interesting thing on tungsten refining. https://www.tungsten.com/tips/tungsten-and-costs/ (https://www.tungsten.com/tips/tungsten-and-costs/)

Market price is $25-$2500/ kilo. The article explains why the large range.
Title: Re: Starship heat shield
Post by: enbandi on 06/02/2020 10:42 pm
Gettin complex again. The original proposal was a simple loop of wire embedded in the tile. Nothing more. An inspection device with an active induction coil would pass over the tiles. A tile with an intact loop will experience an induced current flow and create a corresponding magnetic field. A tile with a broken loop will not. A magnetic field, or the lack, will tell the state of the tile.


TBD: will all non visible tile failures consistently break the wire?


If this works it's elegant. And simple.


Phil

Maybe more simple. What you propose is quite similar how the anti theft gates/tags operate (or operated before RFID). One side of the gate emits a RF signal on a given frequency, the tag is a loop or a simple line ("antenna") tuned to that frequency. When a tag is between the gates, the antenna will absorb some power, which is measurable at the opposite part of the gate.
For Starship, each tile has a nice RF mirror directly behind, so for a transmitter-receiver pair directed to an area the response will be reverse correlated to how many tag/line/antenna are intact, as broken ones will absorb less/no power.

RFID however has some advantage: with the above mentioned method, you have to scan through the surface, moving your detector along, and broken tiles will be where you got a different measurements. With RFID the response can carry data part (identifiers, unique for each tile), so with one "ping" you can get all the response from active/intact tiles without the scanning part (or can do RF/identifier based scanning instead of physical detector movements). Of course RFID need a tiny chip embedded, which will be more sensitive to the extreme heating.


A bit different topic: somewhere Elon mentioned/tweeted that the tiles itself will be the detectors/inspection system. I always imagined that as something physical, like a white layer beneath the black, which became visible when the top layer damaged. Or something like the car-brake-pads where can be hidden etches/grooves under the top layer, exposed only when the top layer wear out.
Title: Re: Starship heat shield
Post by: wes_wilson on 06/03/2020 12:31 pm
Healthcare and automotive industries have OTC "high-temp" RFID chips that are good into the 300-400 C range.  My earlier thought was that if you took the OPs original idea of the metal strands through the tile for break detection and formed those strands into an antenna shape connected to an embedded RFID chip you'd then be able to use cheap over the counter RFID scanning gear to rapidly scan the entire shield. 

Working tiles would self identify and tiles with broken antennas won't answer.

Edit: With the OP I was left with the impression that because you're just looking at continuity within the tile you'd need to scan each tile individually.  The RFID addition was to allow scanning large numbers of tiles simultaneously and know which specific tiles didn't answer.
Title: Re: Starship heat shield
Post by: OTV Booster on 06/03/2020 02:27 pm
Healthcare and automotive industries have OTC "high-temp" RFID chips that are good into the 300-400 C range.  My earlier thought was that if you took the OPs original idea of the metal strands through the tile for break detection and formed those strands into an antenna shape connected to an embedded RFID chip you'd then be able to use cheap over the counter RFID scanning gear to rapidly scan the entire shield. 

Working tiles would self identify and tiles with broken antennas won't answer.

Edit: With the OP I was left with the impression that because you're just looking at continuity within the tile you'd need to scan each tile individually.  The RFID addition was to allow scanning large numbers of tiles simultaneously and know which specific tiles didn't answer.
One informed opinion (livingjw) is that max acceptable skin temp is 600C. That would make a chip that fails at 400C a problem.


Theoretically the RFID could be stimulated and read from a distance but unless there is some mongo RF pumping out, even with a bit of an antenna and a half wave standoff from the skin, this will have some limitations. There needs to be a visual check anyhow so it seems simpler to just do both at the same time and go with a simple loop.


Despite defending the wire loop idea I think acoustic deserves some investigation.


Phil
Title: Re: Starship heat shield
Post by: enbandi on 06/03/2020 03:34 pm
Healthcare and automotive industries have OTC "high-temp" RFID chips that are good into the 300-400 C range.  My earlier thought was that if you took the OPs original idea of the metal strands through the tile for break detection and formed those strands into an antenna shape connected to an embedded RFID chip you'd then be able to use cheap over the counter RFID scanning gear to rapidly scan the entire shield. 

Working tiles would self identify and tiles with broken antennas won't answer.

Edit: With the OP I was left with the impression that because you're just looking at continuity within the tile you'd need to scan each tile individually.  The RFID addition was to allow scanning large numbers of tiles simultaneously and know which specific tiles didn't answer.
One informed opinion (livingjw) is that max acceptable skin temp is 600C. That would make a chip that fails at 400C a problem.


Theoretically the RFID could be stimulated and read from a distance but unless there is some mongo RF pumping out, even with a bit of an antenna and a half wave standoff from the skin, this will have some limitations. There needs to be a visual check anyhow so it seems simpler to just do both at the same time and go with a simple loop.


Despite defending the wire loop idea I think acoustic deserves some investigation.


Phil

Generally I am a bit skeptic about drone over usage (for every possible usage, even when more practical solutions are available), but inspection of tiles seems like a good task for drones. The required cameras, RFID or the suggested RF devices shall be well within the lift capacity, and in outdoor environment (possibly with reference GPS stations to differential measurements) positioning should not be a problem. (not sure about ultrasound however).

Replacement and repairs will need a scaffolding/cherry pickers anyhow. But a quick inspection can be done without that. And the platform (as a drone, positioning and guidance) can be COTS solution with marginal cost.
 
Title: Re: Starship heat shield
Post by: wes_wilson on 06/03/2020 06:09 pm
Healthcare and automotive industries have OTC "high-temp" RFID chips that are good into the 300-400 C range.  My earlier thought was that if you took the OPs original idea of the metal strands through the tile for break detection and formed those strands into an antenna shape connected to an embedded RFID chip you'd then be able to use cheap over the counter RFID scanning gear to rapidly scan the entire shield. 

Working tiles would self identify and tiles with broken antennas won't answer.

Edit: With the OP I was left with the impression that because you're just looking at continuity within the tile you'd need to scan each tile individually.  The RFID addition was to allow scanning large numbers of tiles simultaneously and know which specific tiles didn't answer.
One informed opinion (livingjw) is that max acceptable skin temp is 600C. That would make a chip that fails at 400C a problem.


Theoretically the RFID could be stimulated and read from a distance but unless there is some mongo RF pumping out, even with a bit of an antenna and a half wave standoff from the skin, this will have some limitations. There needs to be a visual check anyhow so it seems simpler to just do both at the same time and go with a simple loop.


Despite defending the wire loop idea I think acoustic deserves some investigation.


Phil

Generally I am a bit skeptic about drone over usage (for every possible usage, even when more practical solutions are available), but inspection of tiles seems like a good task for drones. The required cameras, RFID or the suggested RF devices shall be well within the lift capacity, and in outdoor environment (possibly with reference GPS stations to differential measurements) positioning should not be a problem. (not sure about ultrasound however).

Replacement and repairs will need a scaffolding/cherry pickers anyhow. But a quick inspection can be done without that. And the platform (as a drone, positioning and guidance) can be COTS solution with marginal cost.
 

I wasn't sure about the backside tile temperatures and 600C would be an issue.  Agree the idea is probably played out but one last thought before I retreat ;)  If the RFID readers were strategically positioned inside the Starship it would allow you to check the heat shield status dynamically on orbit and before you start your entry.  Knowing you'd taken no mmod damage after a 6 month journey and before landing would have some upsides.  Reading RFID through metal comes with additional challenges and specialized requirements so agree the idea is probably exhausted.

Edit:  This would also allow the captain to say "Status report on shields!".  "Shields are at 100% sir."  That makes it worth it right?
Title: Re: Starship heat shield
Post by: john smith 19 on 06/03/2020 07:07 pm
I wasn't sure about the backside tile temperatures and 600C would be an issue.  Agree the idea is probably played out but one last thought before I retreat ;)  If the RFID readers were strategically positioned inside the Starship it would allow you to check the heat shield status dynamically on orbit and before you start your entry.  Knowing you'd taken no mmod damage after a 6 month journey and before landing would have some upsides.  Reading RFID through metal comes with additional challenges and specialized requirements so agree the idea is probably exhausted.

Edit:  This would also allow the captain to say "Status report on shields!".  "Shields are at 100% sir."  That makes it worth it right?
Boom Boom  :) Very good.

Usual rule of thumb for silicon semiconductors (which is what all commodity electronics use) is semiconductor junctions fail at above 150c.

But you don't need active devices. Wire looks can be read with a magnetic field or tuned circuits can be fabricated.

At 150c+ in bulk the best technology is probably something called Low Temperature Cofired Ceramic (LTCC). It's used to make high quality chip carriers but it has lots of other potential uses. That "low" temperature part refers to the fact it's fired at 900c, not 1400c like it's cousin (High Temperature Cofired Ceramic). 900c means it can use high conductivity inks of copper and aluminum, rather than molybdenum and tungsten.

A passive design can incorporate a unique serial number in the same way passive RFID tags can.

Title: Re: Starship heat shield
Post by: philw1776 on 06/03/2020 10:02 pm
Think an acoustic scanner producing sonograms with advanced signal processing software.  Intact tiles have one signature.  Tiles with cracks or detached produce a variety of anomalous signatures. An analog (physical world) process that produces a digital signature capable of highly automated software processing and analysis.
Were I Elon, I'd assign the breadboard for this to interns.
Title: Re: Starship heat shield
Post by: enbandi on 06/03/2020 10:45 pm
Think an acoustic scanner producing sonograms with advanced signal processing software.  Intact tiles have one signature.  Tiles with cracks or detached produce a variety of anomalous signatures. An analog (physical world) process that produces a digital signature capable of highly automated software processing and analysis.
Were I Elon, I'd assign the breadboard for this to interns.

Definitely have advantages over the proposed RF or visual inspection, more subtle structural defects, even loosened studs/attachments shall be detectable this way if I am not mistaken.

But I am not familiar with this tech. Does it require mechanical proximity/attachments (like the emitter/microphone pushed against the tiles)? Or it is doable from a small distance (like several cm or something)? If former, that may define some procedural constraints, countering the advantages.
Title: Re: Starship heat shield
Post by: john smith 19 on 06/04/2020 06:10 am
But I am not familiar with this tech. Does it require mechanical proximity/attachments (like the emitter/microphone pushed against the tiles)? Or it is doable from a small distance (like several cm or something)? If former, that may define some procedural constraints, countering the advantages.
It's usually done with contact transducers but can be done with non -contact methods.  The higher the range the higher the power needed.

Note you need to consider the whole environment.

Can you do this on Mars after landing?
Title: Re: Starship heat shield
Post by: enbandi on 06/04/2020 08:42 am
Can you do this on Mars after landing?

Each method except RF readed from a distance (RFID) seems problematic on Mars, not enough air pressure for drones, or for sound propagation, no huge fixed structures to move inspection heads. Same for the Moon or in orbit inspections.

If they want to move any kind of inspection head along the surface, they will need a huge Canadarm or some kind of climbing robot for that. The climbing robot is very Sci-Fi, but far from a readily available solution, so less likely in my opinion.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/04/2020 09:18 am
Can you do this on Mars after landing?

Each method except RF readed from a distance (RFID) seems problematic on Mars, not enough air pressure for drones, or for sound propagation, no huge fixed structures to move inspection heads. Same for the Moon or in orbit inspections.

If they want to move any kind of inspection head along the surface, they will need a huge Canadarm or some kind of climbing robot for that. The climbing robot is very Sci-Fi, but far from a readily available solution, so less likely in my opinion.
Agreed. But if there is any significant damage to the heat shield when they need to leave Mars can the ship return to Earth using repeated aerocapture at lower temperature as an emergency measure? If it can then that might be a better fall back rather than attempt to repair on Mars.
Title: Re: Starship heat shield
Post by: john smith 19 on 06/04/2020 10:18 am
Can you do this on Mars after landing?

Each method except RF readed from a distance (RFID) seems problematic on Mars, not enough air pressure for drones, or for sound propagation, no huge fixed structures to move inspection heads. Same for the Moon or in orbit inspections.

If they want to move any kind of inspection head along the surface, they will need a huge Canadarm or some kind of climbing robot for that. The climbing robot is very Sci-Fi, but far from a readily available solution, so less likely in my opinion.
Keep in mind that unlike Shuttle you only need to check half of the structure, which I think makes the task a bit easier (not easy, easier).  They were looking at a frame the shuttle would pass through, but it's shape made that quite complex.  The sensor head could be quite light, no more than a few kilos, and SS has been getting shorter (I thought it was about 80m but IIRC it's now nearer 60m long).

However once you factor in a mars post-landing inspection they you'd like to do it from the inside.  Steel make magnetic field and RF sensors awkward (not impossible just more difficult) but something based on sound seems relatively viable.

A good point to consider is what are you going to do if you find tile damage after you're on mars?
Making the TPS out of a small number of different size (and thickness) tiles could mean you could get by with a small spares inventory (possibly with some on site machining). 

Keep in mind the shuttle repair foam was never actually tested to survive from orbit.  :(

Title: Re: Starship heat shield
Post by: john smith 19 on 06/04/2020 10:51 am
Agreed. But if there is any significant damage to the heat shield when they need to leave Mars can the ship return to Earth using repeated aerocapture at lower temperature as an emergency measure? If it can then that might be a better fall back rather than attempt to repair on Mars.
I think you're confused.

Aerocapture is a 1 pass flight through the atmosphere to shed all excess velocity and bring the vehicle into orbit. 

Aerocapture has never been tried except for Zond 6 and Zond 7.

Aerobraking is multi-pass but happens after your in a stable orbit to lower that orbit, normally down to full reentry.

Aerocapture is potentially a major game changer for speeding up interplanetary travel as you don't need the same amount of fuel to decelerate as you spent to accelerate.

Which did you have in mind?
Title: Re: Starship heat shield
Post by: rsdavis9 on 06/04/2020 12:07 pm
Can you do this on Mars after landing?

Each method except RF readed from a distance (RFID) seems problematic on Mars, not enough air pressure for drones, or for sound propagation, no huge fixed structures to move inspection heads. Same for the Moon or in orbit inspections.

If they want to move any kind of inspection head along the surface, they will need a huge Canadarm or some kind of climbing robot for that. The climbing robot is very Sci-Fi, but far from a readily available solution, so less likely in my opinion.

rope from top and robot that has wheels to move sideways. Maybe roll the rope so it moves sideways also.

EDIT: could be done in space with slight ullage acceleration.
Title: Re: Starship heat shield
Post by: enbandi on 06/04/2020 12:16 pm
Can you do this on Mars after landing?

Each method except RF readed from a distance (RFID) seems problematic on Mars, not enough air pressure for drones, or for sound propagation, no huge fixed structures to move inspection heads. Same for the Moon or in orbit inspections.

If they want to move any kind of inspection head along the surface, they will need a huge Canadarm or some kind of climbing robot for that. The climbing robot is very Sci-Fi, but far from a readily available solution, so less likely in my opinion.
Keep in mind that unlike Shuttle you only need to check half of the structure, which I think makes the task a bit easier (not easy, easier).  They were looking at a frame the shuttle would pass through, but it's shape made that quite complex.  The sensor head could be quite light, no more than a few kilos, and SS has been getting shorter (I thought it was about 80m but IIRC it's now nearer 60m long).

However once you factor in a mars post-landing inspection they you'd like to do it from the inside.  Steel make magnetic field and RF sensors awkward (not impossible just more difficult) but something based on sound seems relatively viable.

A good point to consider is what are you going to do if you find tile damage after you're on mars?
Making the TPS out of a small number of different size (and thickness) tiles could mean you could get by with a small spares inventory (possibly with some on site machining). 

Keep in mind the shuttle repair foam was never actually tested to survive from orbit.  :(

This process involve multiple challenges: how to inspect/detect? how to access (for repairs)? and how to repair (spares or backup material). Each may have a different solution, but for Mars none of them are easy. There were a longer discussion about possible spares, seems like we are now at the inspection part. And access is the next.

If you want to access the individual tiles (smooth surface, no mounting points) doesn't really matter if it is half of the ship or the whole, or if it is 60 or 80m tall. The closest mounting point will be 7m away (edge of the TPS). Far from human reach and too big for robotic arms (of normal size, if you want to move relevant load).

But for Mars I think conventional climbing equipment will do the job. I simple rope and harness from the top airlock (if there is any, like the Moonship), and you can easily access any part of your TPS (or the outer hull). Slow, unconvenient, but universal, and works at Mars or Moon as well on Earth. You can do both the repairs or the outer inspection this way.

As for sound and internal detection I have concerns. If you try to do that with a fixed acoustic system, for the whole ship (like 1-10-100 transducers/microphones) that sounds like a nightmare from the signal processing side. You will got response from 8000 tiles simultaneously, for 100 channels, while you still have to separate good signal from bad signal. I mean acoustic measurement of a single tile is OK. If you know which one, and have the response mainly from that.

But to do the same for the whole ship, while try to separate the signals from different tiles also: no way. Well maybe, they can came up with a very clever differential signal processing like phased arrays, transducers can be also timed or modulated but still a maybe, and not a trivial problem.

And internal inspection with a moving/handheld system doesn't make much sense. Half of the structure is a tank, which you may not want to access. And the rest is the crew compartment, where you are several layers away from the outer skin (hopefully: stiffeners, internal structure, insulation, furniture and equipment).

Title: Re: Starship heat shield
Post by: philw1776 on 06/04/2020 01:53 pm
On Mars consider an external acoustic test transducer where a long crane arm lifts and moves the transducer array touching (minimal atmosphere, or maybe not?) each tile or tile array to obtain a return signal for digital signal processing analysis.  A long crane arm lifting a not heavy transducer is relatively easy. If not an automated move & scan, move & scan, a video feed allows a Mars resident to move it around.  My guess is NOT automated. The human is there. Automation is engineering development time & resource intensive and fails fragile with unknown unknowns. 
The harder part is replacing the tile.  Maybe a human in a bucket lifted by a crane.
Crane stuff is a bit easier on Mars with ~38% gravity and sundry crane capability is needed for other applications.
Title: Re: Starship heat shield
Post by: rsdavis9 on 06/04/2020 02:41 pm
On Mars consider an external acoustic test transducer where a long crane arm lifts and moves the transducer array touching (minimal atmosphere, or maybe not?) each tile or tile array to obtain a return signal for digital signal processing analysis.  A long crane arm lifting a not heavy transducer is relatively easy. If not an automated move & scan, move & scan, a video feed allows a Mars resident to move it around.  My guess is NOT automated. The human is there. Automation is engineering development time & resource intensive and fails fragile with unknown unknowns. 
The harder part is replacing the tile.  Maybe a human in a bucket lifted by a crane.
Crane stuff is a bit easier on Mars with ~38% gravity and sundry crane capability is needed for other applications.

Replace in orbit. Easier to get around.
Title: Re: Starship heat shield
Post by: sebk on 06/04/2020 03:36 pm
On Mars consider an external acoustic test transducer where a long crane arm lifts and moves the transducer array touching (minimal atmosphere, or maybe not?) each tile or tile array to obtain a return signal for digital signal processing analysis.  A long crane arm lifting a not heavy transducer is relatively easy. If not an automated move & scan, move & scan, a video feed allows a Mars resident to move it around.  My guess is NOT automated. The human is there. Automation is engineering development time & resource intensive and fails fragile with unknown unknowns. 
The harder part is replacing the tile.  Maybe a human in a bucket lifted by a crane.
Crane stuff is a bit easier on Mars with ~38% gravity and sundry crane capability is needed for other applications.

Replace in orbit. Easier to get around.

Yep. Especially that more damage could happen on ascent. And still more on the way.

I'd guess the best time for inspection+repair EVA would be some couple of weeks before re-entry
Title: Re: Starship heat shield
Post by: sebk on 06/04/2020 03:56 pm
Can you do this on Mars after landing?

Each method except RF readed from a distance (RFID) seems problematic on Mars, not enough air pressure for drones, or for sound propagation, no huge fixed structures to move inspection heads. Same for the Moon or in orbit inspections.

If they want to move any kind of inspection head along the surface, they will need a huge Canadarm or some kind of climbing robot for that. The climbing robot is very Sci-Fi, but far from a readily available solution, so less likely in my opinion.
Agreed. But if there is any significant damage to the heat shield when they need to leave Mars can the ship return to Earth using repeated aerocapture at lower temperature as an emergency measure? If it can then that might be a better fall back rather than attempt to repair on Mars.

If you're doing Hohmann transfer from Mars, you have to slow down from ~11.7 to ~11.0 km/s to capture. Energy to lose is equivalent to kinetic energy at 4km/s. Can you do 4km/s re-entry without heatshield, just depending on stainless temperature resistance? Maybe, I don't know.

If you're doing fast transit using whole 6.9km/s dV available from Mars surface, you're coming in hot at 14.5km/s and capture is almost like GTO reentry. Heatshield required.


There's one more trick for Hohmann transfer. The ship would have about 370m/s dV worth of fuel in header tanks (meant to be used for landing). You could instead do a 0.3km/s retroburn just before the aerocapture and slow down to 11.5km/s. dE would be like 3km/s re-entry and on this one I'm pretty sure it could be survivable with heavily damaged heatshield. Once in HEEO there would be ~70m/s dV for maneuvering. Rescue ship could then arrive and evacuate the crew, refuel the damaged bird for landing, do more complex repairs, etc.
Title: Re: Starship heat shield
Post by: cdebuhr on 06/04/2020 04:12 pm
On Mars consider an external acoustic test transducer where a long crane arm lifts and moves the transducer array touching (minimal atmosphere, or maybe not?) each tile or tile array to obtain a return signal for digital signal processing analysis.  A long crane arm lifting a not heavy transducer is relatively easy. If not an automated move & scan, move & scan, a video feed allows a Mars resident to move it around.  My guess is NOT automated. The human is there. Automation is engineering development time & resource intensive and fails fragile with unknown unknowns. 
The harder part is replacing the tile.  Maybe a human in a bucket lifted by a crane.
Crane stuff is a bit easier on Mars with ~38% gravity and sundry crane capability is needed for other applications.

Replace in orbit. Easier to get around.

Yep. Especially that more damage could happen on ascent. And still more on the way.

I'd guess the best time for inspection+repair EVA would be some couple of weeks before re-entry
Lots of interesting ideas here for how to inspect/test/repair TPS.  I suspect most of then are probably unworkable, but that's OK, real gold comes from the Crazy Ideas Division, but only if there are enough crazy ideas!

Anyway, given the structure of likely TPS tiles, how likely is it really that we'll have hidden failure modes?  This is a legitimate question on my part (I'm not just making a rhetorical point ... I'm in no way well informed about the ins and outs of TPS).  ISTM that provided the attachment system is well designed (after they fly these things a few time they're going to have to strip the tiles and see how the attachments are doing), any trauma that would compromise a tile should leave a visible crack or crater.  I would think this would actually be a desirable design goal.  This would then reduce testing to a matter of optical inspection ... some combination of eyeballs (via HD video), machine vision, laser scanners, etc.  Ideally this could all go on a smallish free flyer that would be deployed to scan the TPS a couple weeks before re-entry.

As for actual repair, there's been a lot of talk about what shape tiles, how many types of spares, can they be fabbed locally, etc. but ISTM that it may be more practical to develop an emergency ablative patch material (sort of like what they had, but apparently never tested, for the shuttle ... definitely want to test it though!).  Leave tile replacement for Earth depot maintenance.  Eventually we'll have the deep-space infrastructure for off-world heat shield work, but for the first decade (at least) of Starships to Mars, it would be much simpler to just leave Mars with minor TPS damage and patch (with a well tested ablative patch material) before Earth arrival.  I'm really having a hard time imagining a practical system for doing TPS repair, even temporary patch work, on another planetary surface without a fair bit of infrastructure development happening first.

Edit: minor tyops
Title: Re: Starship heat shield
Post by: OTV Booster on 06/04/2020 05:26 pm
Think an acoustic scanner producing sonograms with advanced signal processing software.  Intact tiles have one signature.  Tiles with cracks or detached produce a variety of anomalous signatures. An analog (physical world) process that produces a digital signature capable of highly automated software processing and analysis.
Were I Elon, I'd assign the breadboard for this to interns.
When I introduced the idea of acoustic, it was intended to be a two step process with passive pickups inside the hull for rough localization and an active second pass of whatever process, to identify the specific tile.


The SS is going to be a big reverberating structure and I expect it to carry sound quite well. If a tile cracks it will give out a uniquely "tile like" sound. To give an example, I recently saw a water tumbler that looked as if it could have been glass or plastic. One tap with a fingernail and I knew it was plastic. Hard materials seem to have a characteristic sound signature independent of size or shape.


This would probably not need any very high frequency gymnastics. Most of the signature will probably be under 40khz (guess) but this would need some exploration. DSP to pull signal out of the background noise.


The fins can each have their own pickup array. Unless cryo rated pickup are used the tanks could be difficult. Bottom and top dome would be the closest the sensors could be to the middle. As 'boomy' as the SS is, I doubt it would be difficult to pick out a small array of tiles as the source of a signature.


Of course this is all speculation but it offers the potential for an inexpensive and easy to implement first line of defense. As a bonus, preliminary research looks to be inexpensive.


Phil
Title: Re: Starship heat shield
Post by: OTV Booster on 06/04/2020 05:42 pm
Can you do this on Mars after landing?

Each method except RF readed from a distance (RFID) seems problematic on Mars, not enough air pressure for drones, or for sound propagation, no huge fixed structures to move inspection heads. Same for the Moon or in orbit inspections.

If they want to move any kind of inspection head along the surface, they will need a huge Canadarm or some kind of climbing robot for that. The climbing robot is very Sci-Fi, but far from a readily available solution, so less likely in my opinion.
A canada arm would be a narrow use expensive solution that as currently built can not operate in 1g. Operation in .38g - unknown to me. If it were not for the external mounting points it would be a good solution for pre EDL inspection. IMO opinion a small free flyer would be better if inspection can be done without contact.


If a repair needs to be made after Martian landing a crane or lift of some sort will be needed. It can be used for inspection and will be useful for other tasks.


Phil
Title: Re: Starship heat shield
Post by: OTV Booster on 06/04/2020 05:53 pm
Can you do this on Mars after landing?

Each method except RF readed from a distance (RFID) seems problematic on Mars, not enough air pressure for drones, or for sound propagation, no huge fixed structures to move inspection heads. Same for the Moon or in orbit inspections.

If they want to move any kind of inspection head along the surface, they will need a huge Canadarm or some kind of climbing robot for that. The climbing robot is very Sci-Fi, but far from a readily available solution, so less likely in my opinion.
Keep in mind that unlike Shuttle you only need to check half of the structure, which I think makes the task a bit easier (not easy, easier).  They were looking at a frame the shuttle would pass through, but it's shape made that quite complex.  The sensor head could be quite light, no more than a few kilos, and SS has been getting shorter (I thought it was about 80m but IIRC it's now nearer 60m long).

However once you factor in a mars post-landing inspection they you'd like to do it from the inside.  Steel make magnetic field and RF sensors awkward (not impossible just more difficult) but something based on sound seems relatively viable.

A good point to consider is what are you going to do if you find tile damage after you're on mars?
Making the TPS out of a small number of different size (and thickness) tiles could mean you could get by with a small spares inventory (possibly with some on site machining). 

Keep in mind the shuttle repair foam was never actually tested to survive from orbit.  :(
In the parlance of 1960's US Army aviation, a missing tile would be a red X. Not flight worthy. A field repair (hopefully already tested and known to work) would be a circled red X. One time flight only. Field repair could be an array of small tiles, thermal caulking or ablative marshmallows. It only has to work for that one flight needed to get to a proper maintenance facility.
Title: Re: Starship heat shield
Post by: john smith 19 on 06/04/2020 06:07 pm
Lots of interesting ideas here for how to inspect/test/repair TPS.  I suspect most of then are probably unworkable, but that's OK, real gold comes from the Crazy Ideas Division, but only if there are enough crazy ideas!
The 3 key things people should take away from this discussion are

1) The problem is difficult if you want the solution to work both on earth and mars.
2) There are (fairly) obvious ways to deal with it but all of them have issues of one sort or another.
3) Those issues are solvable

Quote from: cdebuhr
Anyway, given the structure of likely TPS tiles, how likely is it really that we'll have hidden failure modes?  This is a legitimate question on my part (I'm not just making a rhetorical point ... I'm in no way well informed about the ins and outs of TPS).  ISTM that provided the attachment system is well designed (after they fly these things a few time they're going to have to strip the tiles and see how the attachments are doing), any trauma that would compromise a tile should leave a visible crack or crater.  I would think this would actually be a desirable design goal.  This would then reduce testing to a matter of optical inspection ... some combination of eyeballs (via HD video), machine vision, laser scanners, etc.  Ideally this could all go on a smallish free flyer that would be deployed to scan the TPS a couple weeks before re-entry.
Yes. The ideal  design would visibly change in a way that says "I can handle one more earth entry, but after that replace me."  I hope such a design is possible, but honestly have no idea. I keep thinking "Ok so there's a different color sub-surface layer that shows through if it's damaged, but won't that be hidden by the surface discoloration on entry?"
Quote from: cdebuhr
As for actual repair, there's been a lot of talk about what shape tiles, how many types of spares, can they be fabbed locally, etc. but ISTM that it may be more practical to develop an emergency ablative patch material (sort of like what they had, but apparently never tested, for the shuttle ... definitely want to test it though!).
Shuttle when with repair foam because NAA built a vehicle where nearly every single one of the 24 000 odd tiles (IIRC) was unique. Covering a surface with a limited number of different tile types (both in size, shape and thickness) means you can replace a part with a tested part. While a foam can accommodate any shape (as long as it's not too big) it's all down to the care and precision that it's applied and how closely the setting conditions match the nominal conditions the foam was tested in.
Title: Re: Starship heat shield
Post by: rsdavis9 on 06/04/2020 07:22 pm
Anybody have a WAG as to whether:
A tile on the centerline of windward which should be the hottest short of the fins
Is missing and would:
Burn through on reentry. Probably around melting of 1400C
Get so hot that the steel would be annealed and need replacement. Less than melting but more than 600C.
Not even get to the heat damage limit of 600C. This could happen because hot gases flow around single missing tile.
Title: Re: Starship heat shield
Post by: OTV Booster on 06/04/2020 11:02 pm
Anybody have a WAG as to whether:
A tile on the centerline of windward which should be the hottest short of the fins
Is missing and would:
Burn through on reentry. Probably around melting of 1400C
Get so hot that the steel would be annealed and need replacement. Less than melting but more than 600C.
Not even get to the heat damage limit of 600C. This could happen because hot gases flow around single missing tile.
I'm not sure if this even rises to the level of a WAG. Just running the cartoon simulation through my mind. IIRC 1400C is about the temp expected on the centerline. Most of this is heat from hypersonic shock compression with some radiative thrown in to keep it interesting.


Which a tile missing the I can think of nothing that would mitigate radiative impact. The raw skin would literally take the heat. Its not impossible that there might be an edge condition that would keep the shock compression from immediately entering the cavity. The operant word is 'immediately'. Closer to the center of the cavity the edge condition, whatever it is, will diminish until it just isn't there anymore and again, the skin is taking the heat. The rate of edge effect diminution would be impacted by tile thickness. In the hypersonic regime I'd expect it to be gone less than one tile thickness into the cavity.


So, after sober consideration and a bit of hot air, loose a centerline tile, loose the mission. It'll burn through.


Phil
Title: Re: Starship heat shield
Post by: OTV Booster on 06/04/2020 11:22 pm
On Mars consider an external acoustic test transducer where a long crane arm lifts and moves the transducer array touching (minimal atmosphere, or maybe not?) each tile or tile array to obtain a return signal for digital signal processing analysis.  A long crane arm lifting a not heavy transducer is relatively easy. If not an automated move & scan, move & scan, a video feed allows a Mars resident to move it around.  My guess is NOT automated. The human is there. Automation is engineering development time & resource intensive and fails fragile with unknown unknowns. 
The harder part is replacing the tile.  Maybe a human in a bucket lifted by a crane.
Crane stuff is a bit easier on Mars with ~38% gravity and sundry crane capability is needed for other applications.

Replace in orbit. Easier to get around.

Yep. Especially that more damage could happen on ascent. And still more on the way.

I'd guess the best time for inspection+repair EVA would be some couple of weeks before re-entry
Lots of interesting ideas here for how to inspect/test/repair TPS.  I suspect most of then are probably unworkable, but that's OK, real gold comes from the Crazy Ideas Division, but only if there are enough crazy ideas!

Anyway, given the structure of likely TPS tiles, how likely is it really that we'll have hidden failure modes?  This is a legitimate question on my part (I'm not just making a rhetorical point ... I'm in no way well informed about the ins and outs of TPS).  ISTM that provided the attachment system is well designed (after they fly these things a few time they're going to have to strip the tiles and see how the attachments are doing), any trauma that would compromise a tile should leave a visible crack or crater.  I would think this would actually be a desirable design goal.  This would then reduce testing to a matter of optical inspection ... some combination of eyeballs (via HD video), machine vision, laser scanners, etc.  Ideally this could all go on a smallish free flyer that would be deployed to scan the TPS a couple weeks before re-entry.

As for actual repair, there's been a lot of talk about what shape tiles, how many types of spares, can they be fabbed locally, etc. but ISTM that it may be more practical to develop an emergency ablative patch material (sort of like what they had, but apparently never tested, for the shuttle ... definitely want to test it though!).  Leave tile replacement for Earth depot maintenance.  Eventually we'll have the deep-space infrastructure for off-world heat shield work, but for the first decade (at least) of Starships to Mars, it would be much simpler to just leave Mars with minor TPS damage and patch (with a well tested ablative patch material) before Earth arrival.  I'm really having a hard time imagining a practical system for doing TPS repair, even temporary patch work, on another planetary surface without a fair bit of infrastructure development happening first.

Edit: minor tyops
A hidden failure mode would be a hairline crack. That might have no impact or be total disaster. I doubt Elon even knows but I expect he intends to have some engineers looking at all failure modes.


The tiles that have already been mounted were a laminate. The black surface layer, that I took to be glassy and the white layer underneath, that I took to be foamy. There might have been a metallic backing laminated into some samples. Stresses do things at material discontinuities. The white layer could conceivably have profound damage with nothing showing up on the black layer.


I think Elon mentioned a rope like material to be packed into the cracks to keep flow from entering. The white layer could be all but crumbling and the rope would hide it.


The tile might come slightly loose for some reason and the 'wall anchors' would hog out their recess in the tile leaving the tile free to cut loose at its earliest convenience.


I have to stop. I'm getting depressed.  :'(


Phil
Title: Re: Starship heat shield
Post by: Ionmars on 06/04/2020 11:44 pm
What is the effective difference between a crack in a tile and the small space between adjacent tiles? How close together can they be?
Title: Re: Starship heat shield
Post by: envy887 on 06/05/2020 12:41 am
Anybody have a WAG as to whether:
A tile on the centerline of windward which should be the hottest short of the fins
Is missing and would:
Burn through on reentry. Probably around melting of 1400C
Get so hot that the steel would be annealed and need replacement. Less than melting but more than 600C.
Not even get to the heat damage limit of 600C. This could happen because hot gases flow around single missing tile.
I'm not sure if this even rises to the level of a WAG. Just running the cartoon simulation through my mind. IIRC 1400C is about the temp expected on the centerline. Most of this is heat from hypersonic shock compression with some radiative thrown in to keep it interesting.


Which a tile missing the I can think of nothing that would mitigate radiative impact. The raw skin would literally take the heat. Its not impossible that there might be an edge condition that would keep the shock compression from immediately entering the cavity. The operant word is 'immediately'. Closer to the center of the cavity the edge condition, whatever it is, will diminish until it just isn't there anymore and again, the skin is taking the heat. The rate of edge effect diminution would be impacted by tile thickness. In the hypersonic regime I'd expect it to be gone less than one tile thickness into the cavity.


So, after sober consideration and a bit of hot air, loose a centerline tile, loose the mission. It'll burn through.


Phil

Heat transfer isn't that simple. The skin temp would rise from the equilibrium temp with the tile towards the equilibrium temp without it. However, that equilibrium temperature will likely not be the same as the stagnation temp of the gas flow.

For example, as the temperature of the skin approaches 1100 C, it will dump about 100 kW/m^2 via radiation to the cooler back walls of the tank. This goes up to 300 kW/m^2 at 1400 C. T^4 is your friend. The Shuttle TPS centerline flux peaked around 100 kW/m^2, so if the lost tile is over a tank or engine section, burn-through seems unlikely.

On the crew area, there will be insulation backing the skin, so that the crew compartment interior walls don't tend toward the 500+ degree skin temp. This is probably bad news for the skin, since it won't be able to dump heat radiatively to the interior. But that insulation might be able to handle the heat flux for long enough for the vehicle to finish reentry.
Title: Re: Starship heat shield
Post by: Ionmars on 06/05/2020 01:30 am
What is the effective difference between a crack in a tile and the small space between adjacent tiles? How close together can they be?
Because if the space between tiles is normally occupied with a filler to prevent inter-tile contact, then some types of cracks could be repaired in place rather than replaced. In this case the crack did not cause the tile to be dislodged, but is held in place by one or more pegs on each side of the crack.

First, use a laser cutter or router to widen the crack to the same width as the standard inter-tile gap. Then apply the same standard material to fill up the gap.

Added: This procedure may be appropriate in Space or on the Moon; In an Earth refurbishing facility it would probably be better to replace all cracked tiles.

Title: Re: Starship heat shield
Post by: john smith 19 on 06/05/2020 06:03 am
It's not about the damage to a tile..

It's about.

a) Can you detect that damage before it causes trouble.

b) Can you fix it somehow before it does damage to the mission.

Worst case you find yourself in a place where you absolutely need them to work but there is a hidden flaw in one or more of them that you cannot fix.

You're doomed, but you don't know it.

SX Know this. They know the consequences to public perception of space. They will move heaven and earth to never let it be an issue.
Title: Re: Starship heat shield
Post by: enbandi on 06/05/2020 12:40 pm

When I introduced the idea of acoustic, it was intended to be a two step process with passive pickups inside the hull for rough localization and an active second pass of whatever process, to identify the specific tile.


The SS is going to be a big reverberating structure and I expect it to carry sound quite well. If a tile cracks it will give out a uniquely "tile like" sound. To give an example, I recently saw a water tumbler that looked as if it could have been glass or plastic. One tap with a fingernail and I knew it was plastic. Hard materials seem to have a characteristic sound signature independent of size or shape.


This would probably not need any very high frequency gymnastics. Most of the signature will probably be under 40khz (guess) but this would need some exploration. DSP to pull signal out of the background noise.


The fins can each have their own pickup array. Unless cryo rated pickup are used the tanks could be difficult. Bottom and top dome would be the closest the sensors could be to the middle. As 'boomy' as the SS is, I doubt it would be difficult to pick out a small array of tiles as the source of a signature.


Of course this is all speculation but it offers the potential for an inexpensive and easy to implement first line of defense. As a bonus, preliminary research looks to be inexpensive.


Phil

This pickup system sounds like something that "cost nothing" and "can help" so definitely worth to implement. But I don not think that It can reach a fidelity level required to be used as a single method to restrict deeper scanning to specific areas. I mean, If it works, it can signal/pickup some tile failures, but I doubt that is good enough to detect all possible anomalies.

I interpret your idea as the passive checks should be done continuously, waiting for tiles to crack. No active pinging (like a man with hammer, knocking along the heatshield).

In this case the problem is the timing. The pickup system presumably will detect the cracking tiles in the coast phase/in orbit (if the crew does not party too loud at that time), if a spontaneous crack in coast phase ever happen. Those events are separated, one at a time, and no obvious external noise at that phase.

But I think tiles will fail more likely during the ascent/descent, maybe in groups (multiple at a time), in an environment where plenty of sound and resonance apply. And filtering out a tile cracking sound of the noise of reentry does not sounds that easy (needs quite big dynamic range).

PS: actually the man with hammer could work, just make no sense (if there is a hammer why not a more sophisticated inspection device).
Title: Re: Starship heat shield
Post by: OTV Booster on 06/05/2020 06:15 pm
Anybody have a WAG as to whether:
A tile on the centerline of windward which should be the hottest short of the fins
Is missing and would:
Burn through on reentry. Probably around melting of 1400C
Get so hot that the steel would be annealed and need replacement. Less than melting but more than 600C.
Not even get to the heat damage limit of 600C. This could happen because hot gases flow around single missing tile.
I'm not sure if this even rises to the level of a WAG. Just running the cartoon simulation through my mind. IIRC 1400C is about the temp expected on the centerline. Most of this is heat from hypersonic shock compression with some radiative thrown in to keep it interesting.


Which a tile missing the I can think of nothing that would mitigate radiative impact. The raw skin would literally take the heat. Its not impossible that there might be an edge condition that would keep the shock compression from immediately entering the cavity. The operant word is 'immediately'. Closer to the center of the cavity the edge condition, whatever it is, will diminish until it just isn't there anymore and again, the skin is taking the heat. The rate of edge effect diminution would be impacted by tile thickness. In the hypersonic regime I'd expect it to be gone less than one tile thickness into the cavity.


So, after sober consideration and a bit of hot air, loose a centerline tile, loose the mission. It'll burn through.


Phil

Heat transfer isn't that simple. The skin temp would rise from the equilibrium temp with the tile towards the equilibrium temp without it. However, that equilibrium temperature will likely not be the same as the stagnation temp of the gas flow.

For example, as the temperature of the skin approaches 1100 C, it will dump about 100 kW/m^2 via radiation to the cooler back walls of the tank. This goes up to 300 kW/m^2 at 1400 C. T^4 is your friend. The Shuttle TPS centerline flux peaked around 100 kW/m^2, so if the lost tile is over a tank or engine section, burn-through seems unlikely.

On the crew area, there will be insulation backing the skin, so that the crew compartment interior walls don't tend toward the 500+ degree skin temp. This is probably bad news for the skin, since it won't be able to dump heat radiatively to the interior. But that insulation might be able to handle the heat flux for long enough for the vehicle to finish reentry.
Much of that is over my head. While reading I was nodding my head and going ok, ok, and working towards a learning moment (for which I thank you). I do have a couple quibbles on what I did immediately understand.


Shuttle EDL temps inform for a LEO reentry but would be an underestimate of higher energy reentries. SS coming from afar will do at least one skip so maybe this is a non-issue.


Maybe more important, "might be able to handle the heat flux" is fine for an armchair discussion but is a bit uncomfortable for spam actually in the can. Ouch!


Overall, quite informative. I'm still rebuilding my mental cartoon simulation with this thought food.


Phil

Title: Re: Starship heat shield
Post by: Vanspace on 06/05/2020 10:12 pm
May I suggest a slightly different acoustic inspection approach. Instead of trying to pick cracking noises out of the whole sound stream, use an active test for the resonance of the tiles. Attach a tone generator to the hull to apply predefined vibrations to the system.

If the tiles are mounted on pins, when they are whole, they are going to behave acoustically like the resonator on a banjo or the bars on a xylophone. So vibrations propagated though the hull should resonate at predictable frequencies in the tile.

If the tile is broken or missing, that induced resonance will be missing or change due the changes in the physical structure of the tile. So any changes to the surface or structure of the tiles should stand out fairly easily as deviations from the known resonance.

During flight certification on a new ship run a series of test frequencies on the brand new TPS and record all the resonance patterns. Before EDL run it again to see if anything changed. With multiple tone generators and pickups it should be possible to identify the location of any identified bad tile or at least the general area.

I know that hand-waved away at lot difficulties but it would seem much simpler, faster and give a more Go/NoGo answer while in flight.

Title: Re: Starship heat shield
Post by: OTV Booster on 06/05/2020 11:43 pm

When I introduced the idea of acoustic, it was intended to be a two step process with passive pickups inside the hull for rough localization and an active second pass of whatever process, to identify the specific tile.


The SS is going to be a big reverberating structure and I expect it to carry sound quite well. If a tile cracks it will give out a uniquely "tile like" sound. To give an example, I recently saw a water tumbler that looked as if it could have been glass or plastic. One tap with a fingernail and I knew it was plastic. Hard materials seem to have a characteristic sound signature independent of size or shape.


This would probably not need any very high frequency gymnastics. Most of the signature will probably be under 40khz (guess) but this would need some exploration. DSP to pull signal out of the background noise.


The fins can each have their own pickup array. Unless cryo rated pickup are used the tanks could be difficult. Bottom and top dome would be the closest the sensors could be to the middle. As 'boomy' as the SS is, I doubt it would be difficult to pick out a small array of tiles as the source of a signature.


Of course this is all speculation but it offers the potential for an inexpensive and easy to implement first line of defense. As a bonus, preliminary research looks to be inexpensive.


Phil

This pickup system sounds like something that "cost nothing" and "can help" so definitely worth to implement. But I don not think that It can reach a fidelity level required to be used as a single method to restrict deeper scanning to specific areas. I mean, If it works, it can signal/pickup some tile failures, but I doubt that is good enough to detect all possible anomalies.

I interpret your idea as the passive checks should be done continuously, waiting for tiles to crack. No active pinging (like a man with hammer, knocking along the heatshield).

In this case the problem is the timing. The pickup system presumably will detect the cracking tiles in the coast phase/in orbit (if the crew does not party too loud at that time), if a spontaneous crack in coast phase ever happen. Those events are separated, one at a time, and no obvious external noise at that phase.

But I think tiles will fail more likely during the ascent/descent, maybe in groups (multiple at a time), in an environment where plenty of sound and resonance apply. And filtering out a tile cracking sound of the noise of reentry does not sounds that easy (needs quite big dynamic range).

PS: actually the man with hammer could work, just make no sense (if there is a hammer why not a more sophisticated inspection device).
MMOD is a danger at all times and should be acoustically detectable. There are many open questions and the answers will determine feasibility. It may not be viable but shouldn't take a lot of effort to explore.


My guess is that SS is going to be an acoustic zoo during EDL. The hull will boom and groan from differential heating and I don't have a clue what atmospheric flow will be like. During ascent (hadn't thought about that) engine noise will be added.


The questions here are the frequencies. I doubt, but don't really know, if it amounts to full spectrum white noise. It may be strong at some frequencies and low or even missing at others.


I've experience with ceramic floor tile and have handled fire brick but have no experience with heat tiles. My guess is firebrick is closer than floor tile and my experience there is literally 'I've handled it' and no more. If heat tiles crack like floor tile there will be a hard sharp transient that to my musician ears, is very distinct. It should stand out quite clearly even with moderate acoustic traffic in its frequency range.


Fire brick, I'm not so sure. I'd guess it wouldn't stand out as much, but I never broke one and don't really know.


The real idea killer is acoustic sensing can not afford false negatives. It's what alerts to a hidden problem. If other more sensitive means are needed to double check, just do them and be done with it.


It might work really well in conjunction with your 'man with a hammer' idea. In transit, a free flier with a low velocity BB gun. On the surface, a man lift with a BB gun. Maybe even do away with the man lift if the AI is a good shot.


It shouldn't take more than a few quick and dirties to see if there's anything to it.


Phil







Title: Re: Starship heat shield
Post by: envy887 on 06/06/2020 01:58 am
Heat transfer isn't that simple. The skin temp would rise from the equilibrium temp with the tile towards the equilibrium temp without it. However, that equilibrium temperature will likely not be the same as the stagnation temp of the gas flow.

For example, as the temperature of the skin approaches 1100 C, it will dump about 100 kW/m^2 via radiation to the cooler back walls of the tank. This goes up to 300 kW/m^2 at 1400 C. T^4 is your friend. The Shuttle TPS centerline flux peaked around 100 kW/m^2, so if the lost tile is over a tank or engine section, burn-through seems unlikely.

On the crew area, there will be insulation backing the skin, so that the crew compartment interior walls don't tend toward the 500+ degree skin temp. This is probably bad news for the skin, since it won't be able to dump heat radiatively to the interior. But that insulation might be able to handle the heat flux for long enough for the vehicle to finish reentry.
Much of that is over my head. While reading I was nodding my head and going ok, ok, and working towards a learning moment (for which I thank you). I do have a couple quibbles on what I did immediately understand.

Shuttle EDL temps inform for a LEO reentry but would be an underestimate of higher energy reentries. SS coming from afar will do at least one skip so maybe this is a non-issue.

Maybe more important, "might be able to handle the heat flux" is fine for an armchair discussion but is a bit uncomfortable for spam actually in the can. Ouch!

Peak heat flux is very strongly a function of hypersonic lift/drag ratio and ballistic coefficient, so we don't really have a good comparison other than Shuttle.

And I have no idea what the insulation between the crew capsule interior and the hot structure will be, so I can't say if it will survive reentry or not. It should be possible to design it to survive in the event of losing a tile and a burn-through of the hot structure. At least, for one entry as a fail-safe.

The reason one tile falling off a tank skin isn't necessary fatal, while the same tank with no tiles at all would burn up, is because of the total heat flux. Without the tiles shielding most of the tank, the entire windward surface would heat up and glow, radiating heat through the tank to the lee surface - which would then also heat up and stop absorbing much heat from the windward side. Once the whole thing is glowing hot, it can't radiate heat internally, and it would probably melt. But with only a single time missing, only a tiny fraction of the windward side is radiating heat to the whole lee side, which would not heat up much.
Title: Re: Starship heat shield
Post by: john smith 19 on 06/06/2020 09:54 am
Peak heat flux is very strongly a function of hypersonic lift/drag ratio and ballistic coefficient, so we don't really have a good comparison other than Shuttle.
And the ability to predict either hypersonic lift or drag from shape alone is still quite limited.

It also turns out the the L/D ratio narrows as the Mach number rises.

So your uncertainty rises just as margin of lift over drag falls. This is one of the things that has made designing SCramjets so hard.

Usually CFD types look to "anchor" the data with actual wind tunnel (or better yet flight) data. So the question is how closely does the SS design look like anything else in the database they have actual data on?

I would suggest the answer is "Not very."  :(

Obviously they'll do the best job possible but I'd expect significant design changes when an SS actually starts flying.
Title: Re: Starship heat shield
Post by: Oersted on 06/06/2020 11:48 am
Could they have some colouring material between tile layers that would show up in case of a crack? Or any kind of tracer material really; radioactive, colouring, "smell"... - something a detector can catch in case it slips out. 
Title: Re: Starship heat shield
Post by: Ionmars on 06/06/2020 03:29 pm
...
...
But I think tiles will fail more likely during the ascent/descent, maybe in groups (multiple at a time), in an environment where plenty of sound and resonance apply. And filtering out a tile cracking sound of the noise of reentry does not sounds that easy (needs quite big dynamic range).
...
...
When entering Earth atmosphere (EDL) detecting a crack may be too late anyway. Because what could you do about it until landing?
Title: Re: Starship heat shield
Post by: enbandi on 06/06/2020 05:20 pm
...
...
But I think tiles will fail more likely during the ascent/descent, maybe in groups (multiple at a time), in an environment where plenty of sound and resonance apply. And filtering out a tile cracking sound of the noise of reentry does not sounds that easy (needs quite big dynamic range).
...
...
When entering Earth atmosphere (EDL) detecting a crack may be too late anyway. Because what could you do about it until landing?

You are right. But with quick turnaround, a tanker reporting "no damage happened during EDL" can be relaunched without further inspection on the ground.

I bet it wont be the case in the first times.
Title: Re: Starship heat shield
Post by: OTV Booster on 06/06/2020 07:13 pm
Peak heat flux is very strongly a function of hypersonic lift/drag ratio and ballistic coefficient, so we don't really have a good comparison other than Shuttle.
And the ability to predict either hypersonic lift or drag from shape alone is still quite limited.

It also turns out the the L/D ratio narrows as the Mach number rises.

So your uncertainty rises just as margin of lift over drag falls. This is one of the things that has made designing SCramjets so hard.

Usually CFD types look to "anchor" the data with actual wind tunnel (or better yet flight) data. So the question is how closely does the SS design look like anything else in the database they have actual data on?

I would suggest the answer is "Not very."  :(

Obviously they'll do the best job possible but I'd expect significant design changes when an SS actually starts flying.
Interesting point on L/D narrowing as mach goes up. Between you and envy stuff is getting pounded into my noggin.


A slightly more than idle question: what is the largest radius ~spherical heat shield to do EDL with data available to us? Apollo?
Title: Re: Starship heat shield
Post by: OTV Booster on 06/06/2020 07:17 pm
...
...
But I think tiles will fail more likely during the ascent/descent, maybe in groups (multiple at a time), in an environment where plenty of sound and resonance apply. And filtering out a tile cracking sound of the noise of reentry does not sounds that easy (needs quite big dynamic range).
...
...
When entering Earth atmosphere (EDL) detecting a crack may be too late anyway. Because what could you do about it until landing?
Mars too.


That's why there's been a sub thread on in transit inspection.
Title: Re: Starship heat shield
Post by: wes_wilson on 06/06/2020 09:27 pm
Heat transfer isn't that simple. The skin temp would rise from the equilibrium temp with the tile towards the equilibrium temp without it. However, that equilibrium temperature will likely not be the same as the stagnation temp of the gas flow.

For example, as the temperature of the skin approaches 1100 C, it will dump about 100 kW/m^2 via radiation to the cooler back walls of the tank. This goes up to 300 kW/m^2 at 1400 C. T^4 is your friend. The Shuttle TPS centerline flux peaked around 100 kW/m^2, so if the lost tile is over a tank or engine section, burn-through seems unlikely.

On the crew area, there will be insulation backing the skin, so that the crew compartment interior walls don't tend toward the 500+ degree skin temp. This is probably bad news for the skin, since it won't be able to dump heat radiatively to the interior. But that insulation might be able to handle the heat flux for long enough for the vehicle to finish reentry.
Much of that is over my head. While reading I was nodding my head and going ok, ok, and working towards a learning moment (for which I thank you). I do have a couple quibbles on what I did immediately understand.

Shuttle EDL temps inform for a LEO reentry but would be an underestimate of higher energy reentries. SS coming from afar will do at least one skip so maybe this is a non-issue.

Maybe more important, "might be able to handle the heat flux" is fine for an armchair discussion but is a bit uncomfortable for spam actually in the can. Ouch!

Peak heat flux is very strongly a function of hypersonic lift/drag ratio and ballistic coefficient, so we don't really have a good comparison other than Shuttle.

And I have no idea what the insulation between the crew capsule interior and the hot structure will be, so I can't say if it will survive reentry or not. It should be possible to design it to survive in the event of losing a tile and a burn-through of the hot structure. At least, for one entry as a fail-safe.

The reason one tile falling off a tank skin isn't necessary fatal, while the same tank with no tiles at all would burn up, is because of the total heat flux. Without the tiles shielding most of the tank, the entire windward surface would heat up and glow, radiating heat through the tank to the lee surface - which would then also heat up and stop absorbing much heat from the windward side. Once the whole thing is glowing hot, it can't radiate heat internally, and it would probably melt. But with only a single time missing, only a tiny fraction of the windward side is radiating heat to the whole lee side, which would not heat up much.

Curious if you have any thoughts on how fast a missing tile would become an issue? Seconds?  A minute or two?

Over here, it was estimated that the heat shield was 10 tons.
https://forum.nasaspaceflight.com/index.php?topic=50049.0

It seems like there might be an opportunity for different approaches in the early design and the later designs by just adding redundancy.  Instead of shielding half the ship at 10 tons, shield the entire ship at 20 tons.  If an anomalous temp is detected beneath the tiles roll the ship to put good tiles into the heat.

Once tile inspection and repair mechanisms exist using them makes sense.  But it seems like the early trips might require two uses of the heat shield (mars edl, earth edl) before the shield can be practically inspected/repaired.  So maybe +1 redundancy on the shield is a solution for early trips.  Assuming an issue can be responded to through rotation quickly enough.

Title: Re: Starship heat shield
Post by: john smith 19 on 06/07/2020 07:59 pm
It seems like there might be an opportunity for different approaches in the early design and the later designs by just adding redundancy.  Instead of shielding half the ship at 10 tons, shield the entire ship at 20 tons.  If an anomalous temp is detected beneath the tiles roll the ship to put good tiles into the heat.
You do know that SS is going to have canard wings right?

And the passenger version will be part glazed on the nose.

does this still sound like a good idea to you?
Title: Re: Starship heat shield
Post by: wes_wilson on 06/07/2020 10:41 pm
It seems like there might be an opportunity for different approaches in the early design and the later designs by just adding redundancy.  Instead of shielding half the ship at 10 tons, shield the entire ship at 20 tons.  If an anomalous temp is detected beneath the tiles roll the ship to put good tiles into the heat.
You do know that SS is going to have canard wings right?

And the passenger version will be part glazed on the nose.

does this still sound like a good idea to you?

Cargo versions will precede passenger versions to Mars, so no issue there for early flights.

Canard wings are the prevailing speculation on the forums and Musk has said there are new designs coming soon.  I wasn't aware they'd become a certainty, have they?  And, I wasn't aware that canard wings prohibit inverted flight (or falling), do they? 
Title: Re: Starship heat shield
Post by: livingjw on 06/08/2020 02:12 am
It seems like there might be an opportunity for different approaches in the early design and the later designs by just adding redundancy.  Instead of shielding half the ship at 10 tons, shield the entire ship at 20 tons.  If an anomalous temp is detected beneath the tiles roll the ship to put good tiles into the heat.
You do know that SS is going to have canard wings right?

And the passenger version will be part glazed on the nose.

does this still sound like a good idea to you?

Cargo versions will precede passenger versions to Mars, so no issue there for early flights.

Canard wings are the prevailing speculation on the forums and Musk has said there are new designs coming soon.  I wasn't aware they'd become a certainty, have they?  And, I wasn't aware that canard wings prohibit inverted flight (or falling), do they?

 The skydiving reentry concept depends on moveable control surfaces. These are normally designed to operate with a defined hot side. The space shuttle, for example, would burn up if inverted during reentry. So would the Starship.

John
Title: Re: Starship heat shield
Post by: john smith 19 on 06/08/2020 06:24 am
Cargo versions will precede passenger versions to Mars, so no issue there for early flights.
It would invalidate any flight testing done by cargo flights, so yes there is an issue there.

Quote from: wes_wilson
Canard wings are the prevailing speculation on the forums and Musk has said there are new designs coming soon.  I wasn't aware they'd become a certainty, have they?  And, I wasn't aware that canard wings prohibit inverted flight (or falling), do they?
Canards are what musk has called them. He has also stated that SS will generate lift so what do you call an aero surface that generates lift?

I can see you're quite fond of this idea. But coming up with an idea and being fond of it doesn't make it viable.  :(
Title: Re: Starship heat shield
Post by: Lars-J on 06/08/2020 07:52 am
Cargo versions will precede passenger versions to Mars, so no issue there for early flights.
It would invalidate any flight testing done by cargo flights, so yes there is an issue there.

Quote from: wes_wilson
Canard wings are the prevailing speculation on the forums and Musk has said there are new designs coming soon.  I wasn't aware they'd become a certainty, have they?  And, I wasn't aware that canard wings prohibit inverted flight (or falling), do they?
Canards are what musk has called them. He has also stated that SS will generate lift so what do you call an aero surface that generates lift?

The movable surfaces on Starship are for adjusting drag, not lift. Yes drag can create lift, but at these high angles of attack (60-90 degrees) that will be a minor side effect at best. They LOOK like canards (and are therefore informally called canards) but will operate like air brakes. The vast majority of lift at re-entry angles will be coming from the body itself.
Quote
I can see you're quite fond of this idea. But coming up with an idea and being fond of it doesn't make it viable.  :(

I’m not going to touch that with a 10ft pole. ;)
Title: Re: Starship heat shield
Post by: wes_wilson on 06/08/2020 01:24 pm
Cargo versions will precede passenger versions to Mars, so no issue there for early flights.
It would invalidate any flight testing done by cargo flights, so yes there is an issue there.

Quote from: wes_wilson
Canard wings are the prevailing speculation on the forums and Musk has said there are new designs coming soon.  I wasn't aware they'd become a certainty, have they?  And, I wasn't aware that canard wings prohibit inverted flight (or falling), do they?
Canards are what musk has called them. He has also stated that SS will generate lift so what do you call an aero surface that generates lift?

The movable surfaces on Starship are for adjusting drag, not lift. Yes drag can create lift, but at these high angles of attack (60-90 degrees) that will be a minor side effect at best. They LOOK like canards (and are therefore informally called canards) but will operate like air brakes. The vast majority of lift at re-entry angles will be coming from the body itself.
Quote
I can see you're quite fond of this idea. But coming up with an idea and being fond of it doesn't make it viable.  :(

I’m not going to touch that with a 10ft pole. ;)

@johnsmith19 - That's actually quite funny.  It was an idea, a suggestion, and a question.  I'm ok with being wrong, learning why I'm wrong, and gaining knowledge.  Other people should be too.  So relax a bit, ok?  Your touchy/overly personal responses make the forum a less friendly place. 

Title: Re: Starship heat shield
Post by: wes_wilson on 06/08/2020 01:32 pm
It seems like there might be an opportunity for different approaches in the early design and the later designs by just adding redundancy.  Instead of shielding half the ship at 10 tons, shield the entire ship at 20 tons.  If an anomalous temp is detected beneath the tiles roll the ship to put good tiles into the heat.
You do know that SS is going to have canard wings right?

And the passenger version will be part glazed on the nose.

does this still sound like a good idea to you?

Cargo versions will precede passenger versions to Mars, so no issue there for early flights.

Canard wings are the prevailing speculation on the forums and Musk has said there are new designs coming soon.  I wasn't aware they'd become a certainty, have they?  And, I wasn't aware that canard wings prohibit inverted flight (or falling), do they?

 The skydiving reentry concept depends on moveable control surfaces. These are normally designed to operate with a defined hot side. The space shuttle, for example, would burn up if inverted during reentry. So would the Starship.

John

Hi John, appreciate the answer!  A follow up question if you don't mind?  My original thought was to shield both sides of the ship to provide heat shield redundancy for early flights before the ability to do external inspections/repairs exist.  Aside from the windows, I thought the designs floating around were symmetric so I'm still unclear why if both sides were shielded it couldn't re-enter with the bad side up and the good side down?    Something about the canards that only works in one orientation, or the ship isn't actually symmetrical, etc? 

Thanks
Title: Re: Starship heat shield
Post by: livingjw on 06/08/2020 02:55 pm
It seems like there might be an opportunity for different approaches in the early design and the later designs by just adding redundancy.  Instead of shielding half the ship at 10 tons, shield the entire ship at 20 tons.  If an anomalous temp is detected beneath the tiles roll the ship to put good tiles into the heat.
You do know that SS is going to have canard wings right?

And the passenger version will be part glazed on the nose.

does this still sound like a good idea to you?

Cargo versions will precede passenger versions to Mars, so no issue there for early flights.

Canard wings are the prevailing speculation on the forums and Musk has said there are new designs coming soon.  I wasn't aware they'd become a certainty, have they?  And, I wasn't aware that canard wings prohibit inverted flight (or falling), do they?

 The skydiving reentry concept depends on moveable control surfaces. These are normally designed to operate with a defined hot side. The space shuttle, for example, would burn up if inverted during reentry. So would the Starship.

John

Hi John, appreciate the answer!  A follow up question if you don't mind?  My original thought was to shield both sides of the ship to provide heat shield redundancy for early flights before the ability to do external inspections/repairs exist.  Aside from the windows, I thought the designs floating around were symmetric so I'm still unclear why if both sides were shielded it couldn't re-enter with the bad side up and the good side down?    Something about the canards that only works in one orientation, or the ship isn't actually symmetrical, etc? 

Thanks

- What we seen so far has an asymmetrical chine and control surfaces. This could be designed out of it, but you would still have to change the control arms as well as the air seals between the controls and the fixed structure. I am sure there are lots of other details that would have to be dealt with as well.

- I don't think it is worth it. TPS will be well tested before development is done.

John
Title: Re: Starship heat shield
Post by: Nomadd on 06/08/2020 03:06 pm
But I think tiles will fail more likely during the ascent/descent, maybe in groups (multiple at a time), in an environment where plenty of sound and resonance apply. And filtering out a tile cracking sound of the noise of reentry does not sounds that easy (needs quite big dynamic range).
When entering Earth atmosphere (EDL) detecting a crack may be too late anyway. Because what could you do about it until landing?
There could be profiles that might be sub optimal in other ways but easier on a damaged heat shield.
Title: Re: Starship heat shield
Post by: john smith 19 on 06/11/2020 06:39 am
But I think tiles will fail more likely during the ascent/descent, maybe in groups (multiple at a time), in an environment where plenty of sound and resonance apply. And filtering out a tile cracking sound of the noise of reentry does not sounds that easy (needs quite big dynamic range).
When entering Earth atmosphere (EDL) detecting a crack may be too late anyway. Because what could you do about it until landing?
There could be profiles that might be sub optimal in other ways but easier on a damaged heat shield.
Possible yes.  At that point you'd just want to get on the ground ASAP and figure everything else out later.

Logically you'd run monte carlo sims to see what happens if a tile gets destroyed and various flight paths get tried, seeing which ones lead to LOV, which lead to over temps on the tiles, which to overtemps on the structure etc, then see if you can find one that gets you all the way to the ground.

But be aware that it is not known if there is any profile that does get you to the ground. IOW tile failure at certain stations is unconditionally fatal to the vehicle. Possible outcome. Lots of sim work needed. Possible Koboyashi Maru situation.

[EDIT However I have just had a thought. 
If it's limited to a single tile (or small cluster) you could run a low pressure metal tube behind them all with gas inside (too hot for cryogen).  Pipe exposed airstream ruptures --> cloud of (lowish) temperature gas released, and continues exhausting till supply is shut off or vehicle lands.

Obviously if this is a serial pipe 2 hits will starve one of the sites of coolant leading to probable wall failure but it's simple, combines failure detection (sudden drop in pressure --> pipes burnt through) with instant action and if properly designed is adequate enough to get you on the ground.

The joker (as always) is mass. Hence my emphasis on low pressure and warm. A cryogenic flow would absorb a lot more energy through the flash boiling state change but defeats the point of allowing a hotter wall than an aluminum skin permits.

Oh, and then there's intumescent fire protection strategies.... ]
Title: Re: Starship heat shield
Post by: Morgun on 06/11/2020 06:34 pm
Could a thin layer of PICA-X under the tiles work as a fail-safe for a damaged tile? No idea how thick the layer would need to be or how much mass it would add.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/16/2020 09:22 am
Could a thin layer of PICA-X under the tiles work as a fail-safe for a damaged tile? No idea how thick the layer would need to be or how much mass it would add.
That might be a good idea. In fact looking at the tiles it looks like they are multi layer - presumably some insulation is needed to stop the contents of the Starship heating up. Perhaps the insulation might save them in an emergency
Title: Re: Starship heat shield
Post by: guckyfan on 06/16/2020 01:14 pm
Another question involving PicaX. Any idea if a PicaX heat shield would be cheaper or more expensive than the ceramic heat shield they are working on?

Background of my question is the possibility of permanently leaving cargo Starships on Mars. They would need to do only one Mars entry, no problem with reuse and water after launch. Would it make economic sense to use a PicaX heatshield for those flights?
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/17/2020 11:50 am
Another question involving PicaX. Any idea if a PicaX heat shield would be cheaper or more expensive than the ceramic heat shield they are working on?

Background of my question is the possibility of permanently leaving cargo Starships on Mars. They would need to do only one Mars entry, no problem with reuse and water after launch. Would it make economic sense to use a PicaX heatshield for those flights?
Not sure it would be worth the effort of developing a separate heatshield for this. But depending on cost it might make sense to coat the steel under the heat shield with it for insulation and emergency protection from loss of a tile
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 06/17/2020 12:16 pm
Another question involving PicaX. Any idea if a PicaX heat shield would be cheaper or more expensive than the ceramic heat shield they are working on?

Background of my question is the possibility of permanently leaving cargo Starships on Mars. They would need to do only one Mars entry, no problem with reuse and water after launch. Would it make economic sense to use a PicaX heatshield for those flights?
Not sure it would be worth the effort of developing a separate heatshield for this. But depending on cost it might make sense to coat the steel under the heat shield with it for insulation and emergency protection from loss of a tile

If you put PicaX between the tiles and the underlying metal you'd be asking PicaX to perform structural functions.  That's not really PicaX's forte.

Title: Re: Starship heat shield
Post by: Slarty1080 on 06/17/2020 12:47 pm
Another question involving PicaX. Any idea if a PicaX heat shield would be cheaper or more expensive than the ceramic heat shield they are working on?

Background of my question is the possibility of permanently leaving cargo Starships on Mars. They would need to do only one Mars entry, no problem with reuse and water after launch. Would it make economic sense to use a PicaX heatshield for those flights?
Not sure it would be worth the effort of developing a separate heatshield for this. But depending on cost it might make sense to coat the steel under the heat shield with it for insulation and emergency protection from loss of a tile

If you put PicaX between the tiles and the underlying metal you'd be asking PicaX to perform structural functions.  That's not really PicaX's forte.
Perhaps you're right, although I'm not sure what structural function it would serve as the titles would be supported through this layer on their studs. But if not PicaX then perhaps there's something else that might be suitable. Candidate materials need to be good insulators and also capable of providing so degree of last ditch emergency heat shield capability by ablation or any other mechanism to make tile loss a bit more survivable. The best part is no part, but they will need insulation anyway so this would just be added protection "for free".
Title: Re: Starship heat shield
Post by: livingjw on 06/17/2020 01:37 pm
I don't think this has been remarked on but it appears that SpaceX is testing yet another TPS attachment approach. This makes at least four types:

1) Tile, 3 stud mechanically attached with holes showing and what looks like a felt pad against the tank.
2) Tile without holes showing, probable mechanically attached, with felt pad.
3) Tile mechanically attached using welded metal frame
4) Tile which appears to be bonded with green adhesive of some sort. (Does not look like RTV. RTV probably could not handle the temperature.)

John
Title: Re: Starship heat shield
Post by: rsdavis9 on 06/17/2020 03:18 pm
How about stove cement?
I think it is some kind of water soluble silica
Title: Re: Starship heat shield
Post by: OTV Booster on 06/17/2020 05:15 pm
How about stove cement?
I think it is some kind of water soluble silica
Stove cement is IIRC more of a grout with good thermal characteristics than a glue. Here is one companies offerings for aerospace.


https://www.masterbond.com/industries/adhesive-systems-aerospace-industry?matchtype=b&network=g&device=m&adposition=&keyword=adhesives%20for%20aerospace&gclid=EAIaIQobChMIkoSCm6mJ6gIVDgCGCh1vUAayEAAYASAAEgI4LPD_BwE (https://www.masterbond.com/industries/adhesive-systems-aerospace-industry?matchtype=b&network=g&device=m&adposition=&keyword=adhesives%20for%20aerospace&gclid=EAIaIQobChMIkoSCm6mJ6gIVDgCGCh1vUAayEAAYASAAEgI4LPD_BwE)


I've skimmed through a couple of sites and seen references to 1800C but didn't dig. One approach would be a glue that insulates if a tile goes away. Another would be a glue that becomes an ablative. My gut says that glue adhesion and ablation go together easier than adhesion and insulation.


IIRC 800C is roughly where stainless (301?) starts to anneal and 600 or 650C was suggested as an acceptable limit. Any solution has to keep this in mind.


Phil
Title: Re: Starship heat shield
Post by: sebk on 06/22/2020 05:12 pm
I don't think this has been remarked on but it appears that SpaceX is testing yet another TPS attachment approach. This makes at least four types:

1) Tile, 3 stud mechanically attached with holes showing and what looks like a felt pad against the tank.
2) Tile without holes showing, probable mechanically attached, with felt pad.
3) Tile mechanically attached using welded metal frame
4) Tile which appears to be bonded with green adhesive of some sort. (Does not look like RTV. RTV probably could not handle the temperature.)

John

Or its some goo added for whatever purpose in addition to mechanical attachment.
Title: Re: Starship heat shield
Post by: OTV Booster on 06/23/2020 02:42 am
I don't think this has been remarked on but it appears that SpaceX is testing yet another TPS attachment approach. This makes at least four types:

1) Tile, 3 stud mechanically attached with holes showing and what looks like a felt pad against the tank.
2) Tile without holes showing, probable mechanically attached, with felt pad.
3) Tile mechanically attached using welded metal frame
4) Tile which appears to be bonded with green adhesive of some sort. (Does not look like RTV. RTV probably could not handle the temperature.)

John

Or its some goo added for whatever purpose in addition to mechanical attachment.
They went to considerable effort for the goo. It looks like they roughed up the surface for better bonding. Maybe a replacement for Johns call of a felt pad in 1 & 2 above, plus bonding.
Title: Re: Starship heat shield
Post by: john smith 19 on 06/23/2020 06:21 am
I don't think this has been remarked on but it appears that SpaceX is testing yet another TPS attachment approach. This makes at least four types:

1) Tile, 3 stud mechanically attached with holes showing and what looks like a felt pad against the tank.
2) Tile without holes showing, probable mechanically attached, with felt pad.
3) Tile mechanically attached using welded metal frame
4) Tile which appears to be bonded with green adhesive of some sort. (Does not look like RTV. RTV probably could not handle the temperature.)

John

Or its some goo added for whatever purpose in addition to mechanical attachment.
They went to considerable effort for the goo. It looks like they roughed up the surface for better bonding. Maybe a replacement for Johns call of a felt pad in 1 & 2 above, plus bonding.
The pads on shuttle were to deal with the thermal expansion coefficient of the aluminum being 3x that of the tile. AFAIK the mfg shut down the line and maybe out of business. It was some kind of nylon stocking material.

Glue and pads were the lightweight quick fix. SS TCE is lower than aluminum (not sure how much). I'd have guess low enough not to need pads. They were part of the reason shuttle tile replacement costs wer listed at $12000/m^2.

If you're definitely going tiles and cost is a factor (which it is) and mass not so much that points you in certain directions.

More "graded" materials, rather than any kind of very thin skin. Shifting the coating method on some high damage tiles lowered the repair rate by a factor of 10. IE 1 damaged for every 10 that had needed replacement.

No messing around with glue. It's called room temperature vulcanizing adhesive for a reason. Either go to a hotter formulation (which makes removal tricky) or don't do glue.

NASA solved ways  to mount materials not just with different TCE's but materials with different TCE's in different axes of the same material (RCC be the prime example) in the early 80's.

Obviously if you can break the tile into a couple of pieces, then remove those (like a spring driven center punch, but with a spade blade maybe?) then just remove the individual pieces.
Title: Re: Starship heat shield
Post by: envy887 on 06/23/2020 01:58 pm
I don't think this has been remarked on but it appears that SpaceX is testing yet another TPS attachment approach. This makes at least four types:

1) Tile, 3 stud mechanically attached with holes showing and what looks like a felt pad against the tank.
2) Tile without holes showing, probable mechanically attached, with felt pad.
3) Tile mechanically attached using welded metal frame
4) Tile which appears to be bonded with green adhesive of some sort. (Does not look like RTV. RTV probably could not handle the temperature.)

John

Or its some goo added for whatever purpose in addition to mechanical attachment.
They went to considerable effort for the goo. It looks like they roughed up the surface for better bonding. Maybe a replacement for Johns call of a felt pad in 1 & 2 above, plus bonding.
The pads on shuttle were to deal with the thermal expansion coefficient of the aluminum being 3x that of the tile. AFAIK the mfg shut down the line and maybe out of business. It was some kind of nylon stocking material.

Glue and pads were the lightweight quick fix. SS TCE is lower than aluminum (not sure how much). I'd have guess low enough not to need pads. They were part of the reason shuttle tile replacement costs wer listed at $12000/m^2.

If you're definitely going tiles and cost is a factor (which it is) and mass not so much that points you in certain directions.

More "graded" materials, rather than any kind of very thin skin. Shifting the coating method on some high damage tiles lowered the repair rate by a factor of 10. IE 1 damaged for every 10 that had needed replacement.

No messing around with glue. It's called room temperature vulcanizing adhesive for a reason. Either go to a hotter formulation (which makes removal tricky) or don't do glue.

NASA solved ways  to mount materials not just with different TCE's but materials with different TCE's in different axes of the same material (RCC be the prime example) in the early 80's.

Obviously if you can break the tile into a couple of pieces, then remove those (like a spring driven center punch, but with a spade blade maybe?) then just remove the individual pieces.

On previous iterations of tile attachment, It looked to me like SpaceX was trying to solve the differential thermal expansion via spring clips that allowed the tile to shrink and grow radially, with the gap between tiles taking up the difference.

The tiles are much hotter than the skin during entry, and also during fueling (attachment to a cryo tank skin during fueling was a design constraint hat the Shuttle TPS didn't have), so the tile might actually grow relative to the steel, despite having a lower coefficient of thermal expansion.
Title: Re: Starship heat shield
Post by: northstar on 07/10/2020 04:53 am
Interesting pictures today by Nomadd of a heat shield test ring, half filled with tile fastening studs.

Appear to be testing the application of the studs in a bulk situation, as they would do it on an actual install.
Title: Re: Starship heat shield
Post by: SteveU on 07/10/2020 10:21 am
There are two types of studs being applied to the test hull - A round version with flats milled on the outside and a hole in the center (threaded or not) and an 'open spring clip' (don't know how else to describe it).

Photo by Nomadd (cropped):
Title: Re: Starship heat shield
Post by: Twark_Main on 07/10/2020 06:00 pm
Interesting pictures today by Nomadd of a heat shield test ring, half filled with tile fastening studs.

Appear to be testing the application of the studs in a bulk situation, as they would do it on an actual install.

Link, since things tend to get rapidly buried around here: https://forum.nasaspaceflight.com/index.php?topic=51332.msg2105656#msg2105656
Title: Re: Starship heat shield
Post by: northstar on 07/26/2020 03:37 pm
There are two types of studs being applied to the test hull - A round version with flats milled on the outside and a hole in the center (threaded or not) and an 'open spring clip' (don't know how else to describe it).

Photo by Nomadd (cropped):

If you look at that crop and at this other attached here, clearly they have been experimenting with the right settings for weld current and duration for the best attachment of the studs.
Title: Re: Starship heat shield
Post by: john smith 19 on 08/01/2020 08:05 am
You could update this idea for the digital age. Put an RFID chip and and antenna loop in each tile, just like in a credit card. Then each tile has a separate unique ID and you can interrogate a bunch of them in parallel. You'd need to keep the loop some minimum distance away from the steel hull, of course.
IIRC this has already been mentioned in this thread.

It was tested by NASA for a Shuttle upgrade. The chips had a small pieced of solder that had been electroplated across contacts.  If the tile is over heated solder melts and contact goes open circuit.

Note it's not about the detailed failure, it's simply the need to flag "Something wrong here. Needs attention. Don't fly without replacing"
Title: Re: Starship heat shield
Post by: Poseidon on 08/01/2020 09:14 am
Hello

I have a question.
Since there is no thermal insulation of the tanks (well, not yet), how will they avoid the frost/ice formation to break the tiles apart?
Will the gap between the tiles be perfectly airtight insulated?
Title: Re: Starship heat shield
Post by: OTV Booster on 08/03/2020 02:58 pm
Hello

I have a question.
Since there is no thermal insulation of the tanks (well, not yet), how will they avoid the frost/ice formation to break the tiles apart?
Will the gap between the tiles be perfectly airtight insulated?
Great question. Nobody's replied yet so I'll take a shot. I doubt the tiles will be airtight and for an overall solution, well, I don't know.


Not much help :(


Phil
Title: Re: Starship heat shield
Post by: envy887 on 08/03/2020 03:06 pm
Hello

I have a question.
Since there is no thermal insulation of the tanks (well, not yet), how will they avoid the frost/ice formation to break the tiles apart?
Will the gap between the tiles be perfectly airtight insulated?

The frost on the tanks during propellant load is formed by continuous vapor deposition, which doesn't cause the expansion force associated with freezing liquid water.
Title: Re: Starship heat shield
Post by: wannamoonbase on 08/03/2020 03:07 pm
Hello

I have a question.
Since there is no thermal insulation of the tanks (well, not yet), how will they avoid the frost/ice formation to break the tiles apart?
Will the gap between the tiles be perfectly airtight insulated?
Great question. Nobody's replied yet so I'll take a shot. I doubt the tiles will be airtight and for an overall solution, well, I don't know.


Not much help :(


Phil

I don't think it's practical to seal the tiles airtight and have them properly serve their main function.

I'm most interested in the heat-shield and see that it's the biggest risk to the whole venture.  First concern is how well they endure the changing shape changing of the tanks when they pressurize and what will happen when the body of the vehicle encounters the pressure of re-entry. 

Then the transition from the pressurized tank section and the unpressurized sections fore and aft.

Seems like those would be significant, maybe each tile can handle it.  But we haven't seen it yet.  No doubt there is a lot of work going into it.
Title: Re: Starship heat shield
Post by: xanzi4096 on 08/03/2020 03:08 pm
Hello

I have a question.
Since there is no thermal insulation of the tanks (well, not yet), how will they avoid the frost/ice formation to break the tiles apart?
Will the gap between the tiles be perfectly airtight insulated?

As far as I can remember, hexagonal tiles were chosen so that there's no straight air channel along the gaps, and they aren't concerned about the tiles not being airtight as long as the majority of flow is across the outer surface. I could be misremembering though.
Title: Re: Starship heat shield
Post by: livingjw on 08/03/2020 03:14 pm
Hello

I have a question.
Since there is no thermal insulation of the tanks (well, not yet), how will they avoid the frost/ice formation to break the tiles apart?
Will the gap between the tiles be perfectly airtight insulated?
Great question. Nobody's replied yet so I'll take a shot. I doubt the tiles will be airtight and for an overall solution, well, I don't know.


Not much help :(


Phil

I don't think it's practical to seal the tiles airtight and have them properly serve their main function.

I'm most interested in the heat-shield and see that it's the biggest risk to the whole venture.  First concern is how well they endure the changing shape changing of the tanks when they pressurize and what will happen when the body of the vehicle encounters the pressure of re-entry. 

Then the transition from the pressurized tank section and the unpressurized sections fore and aft.

Seems like those would be significant, maybe each tile can handle it.  But we haven't seen it yet.  No doubt there is a lot of work going into it.

For all of the above stated reasons, I believe the tiles will be mounted on something like Nomex felt between the tile and the tank. Instead of bonding like the Shuttle did, it appears they will be attached using studs. This allow each tile to deal with vehicle deformations due to stresses applied throughout the mission. Between some tiles we may see filler material similar to that used on the Shuttle, but we have not seen any sign of that so far.

John
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/03/2020 03:15 pm
Hello

I have a question.
Since there is no thermal insulation of the tanks (well, not yet), how will they avoid the frost/ice formation to break the tiles apart?
Will the gap between the tiles be perfectly airtight insulated?
Great question. Nobody's replied yet so I'll take a shot. I doubt the tiles will be airtight and for an overall solution, well, I don't know.


Not much help :(


Phil

I don't think it's practical to seal the tiles airtight and have them properly serve their main function.

I'm most interested in the heat-shield and see that it's the biggest risk to the whole venture.  First concern is how well they endure the changing shape changing of the tanks when they pressurize and what will happen when the body of the vehicle encounters the pressure of re-entry. 

Then the transition from the pressurized tank section and the unpressurized sections fore and aft.

Seems like those would be significant, maybe each tile can handle it.  But we haven't seen it yet.  No doubt there is a lot of work going into it.
There seems to be a need to have a gap between the tiles to allow for expansion. Presumably this will be self correcting to a limited extent - the hotter the tiles get the less the gap and less heat seeps through. That said I'm not sure how much heat seepage is permissible or how much insulation there will be below the tiles?
Title: Re: Starship heat shield
Post by: dwheeler on 08/03/2020 03:37 pm
Hello

I have a question.
Since there is no thermal insulation of the tanks (well, not yet), how will they avoid the frost/ice formation to break the tiles apart?
Will the gap between the tiles be perfectly airtight insulated?

The frost on the tanks during propellant load is formed by continuous vapor deposition, which doesn't cause the expansion force associated with freezing liquid water.
So there's not the risk from expansion. But if the frost forms under the tiles, what happens to it during the launch. As it shakes free and drops off, (but still under the tiles), does it not risk damaging the tile mounts and or tiles? I know... SpaceX must know what they're doing and have some plan in place. I'm just wondering what that might be.

Title: Re: Starship heat shield
Post by: envy887 on 08/03/2020 04:04 pm
Hello

I have a question.
Since there is no thermal insulation of the tanks (well, not yet), how will they avoid the frost/ice formation to break the tiles apart?
Will the gap between the tiles be perfectly airtight insulated?

The frost on the tanks during propellant load is formed by continuous vapor deposition, which doesn't cause the expansion force associated with freezing liquid water.
So there's not the risk from expansion. But if the frost forms under the tiles, what happens to it during the launch. As it shakes free and drops off, (but still under the tiles), does it not risk damaging the tile mounts and or tiles? I know... SpaceX must know what they're doing and have some plan in place. I'm just wondering what that might be.

There's a rope seal is under the tile to keep hot gases out during reenty. Frost forms from atmospheric water vapor, and the rope seal should prevent air from entering the space under the tile.
Title: Re: Starship heat shield
Post by: Twark_Main on 08/03/2020 06:02 pm
Hello

I have a question.
Since there is no thermal insulation of the tanks (well, not yet), how will they avoid the frost/ice formation to break the tiles apart?
Will the gap between the tiles be perfectly airtight insulated?

As far as I can remember, hexagonal tiles were chosen so that there's no straight air channel along the gaps, and they aren't concerned about the tiles not being airtight as long as the majority of flow is across the outer surface. I could be misremembering though.

Your memory is good.

https://twitter.com/elonmusk/status/1107379727302451200
Title: Re: Starship heat shield
Post by: john smith 19 on 08/03/2020 09:18 pm
For all of the above stated reasons, I believe the tiles will be mounted on something like Nomex felt between the tile and the tank. Instead of bonding like the Shuttle did, it appears they will be attached using studs. This allow each tile to deal with vehicle deformations due to stresses applied throughout the mission. Between some tiles we may see filler material similar to that used on the Shuttle, but we have not seen any sign of that so far.

John
That makes no sense.

Firstly steel is about 1/10 the thermal conductivity of aluminum and IIRC it's expansion coefficient is about 1/3 that of aluminum.  So the tanks contents are easier to keep cool and the tank stresses caused by expansion and contraction are much reduced.

The key reason for the pads was that the tiles were bonded to the aluminum skin originally so as the skin expanded the tiles either cracked (reducing most of them to about 6" wide as the safe size) or peeled. The pads isolated the tiles excellent thermal but poor mechanical properties from the skins excellent mechanical but poor thermal properties.

But SS tiles are point mounted, which should simplify mounting them, although the reduced expansion should also reduce stress on the tiles anyway. 
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/03/2020 09:23 pm
Hello

I have a question.
Since there is no thermal insulation of the tanks (well, not yet), how will they avoid the frost/ice formation to break the tiles apart?
Will the gap between the tiles be perfectly airtight insulated?

The frost on the tanks during propellant load is formed by continuous vapor deposition, which doesn't cause the expansion force associated with freezing liquid water.
So there's not the risk from expansion. But if the frost forms under the tiles, what happens to it during the launch. As it shakes free and drops off, (but still under the tiles), does it not risk damaging the tile mounts and or tiles? I know... SpaceX must know what they're doing and have some plan in place. I'm just wondering what that might be.

There's a rope seal is under the tile to keep hot gases out during reenty. Frost forms from atmospheric water vapor, and the rope seal should prevent air from entering the space under the tile.
I hope that will work on Mars as well, because Starship will be on Mars with cryogenic propellant aboard for more than a year.
Title: Re: Starship heat shield
Post by: Nevyn72 on 08/03/2020 11:18 pm
Hello

I have a question.
Since there is no thermal insulation of the tanks (well, not yet), how will they avoid the frost/ice formation to break the tiles apart?
Will the gap between the tiles be perfectly airtight insulated?

The frost on the tanks during propellant load is formed by continuous vapor deposition, which doesn't cause the expansion force associated with freezing liquid water.
So there's not the risk from expansion. But if the frost forms under the tiles, what happens to it during the launch. As it shakes free and drops off, (but still under the tiles), does it not risk damaging the tile mounts and or tiles? I know... SpaceX must know what they're doing and have some plan in place. I'm just wondering what that might be.

There's a rope seal is under the tile to keep hot gases out during reenty. Frost forms from atmospheric water vapor, and the rope seal should prevent air from entering the space under the tile.
I hope that will work on Mars as well, because Starship will be on Mars with cryogenic propellant aboard for more than a year.

The atmosphere on Mars is so thin that any water that somehow forms on the surface of SS while it's sitting there will just sublimate away......
Title: Re: Starship heat shield
Post by: envy887 on 08/04/2020 03:00 am
Hello

I have a question.
Since there is no thermal insulation of the tanks (well, not yet), how will they avoid the frost/ice formation to break the tiles apart?
Will the gap between the tiles be perfectly airtight insulated?

The frost on the tanks during propellant load is formed by continuous vapor deposition, which doesn't cause the expansion force associated with freezing liquid water.
So there's not the risk from expansion. But if the frost forms under the tiles, what happens to it during the launch. As it shakes free and drops off, (but still under the tiles), does it not risk damaging the tile mounts and or tiles? I know... SpaceX must know what they're doing and have some plan in place. I'm just wondering what that might be.

There's a rope seal is under the tile to keep hot gases out during reenty. Frost forms from atmospheric water vapor, and the rope seal should prevent air from entering the space under the tile.
I hope that will work on Mars as well, because Starship will be on Mars with cryogenic propellant aboard for more than a year.

The atmosphere on Mars is so thin that any water that somehow forms on the surface of SS while it's sitting there will just sublimate away......

The problem on Mars is CO2 frost.
Title: Re: Starship heat shield
Post by: Nevyn72 on 08/04/2020 03:56 am
I'm actually more concerned about water between and under the tiles on Earth.

There will be small gaps between the tiles and a small space underneath the tiles.
These spaces may or may not have some form of padding or filling material....

The problem with small gaps and spaces are that they are great at drawing in water through capillary action. This water then is very hard to get out.

So....... The SS is sitting on the pad waiting for fueling and launch and it's raining.
Water is drawn between and below the tiles, largely filling the gaps.
You then add cryogenic fuel and oxidiser.
The water freezes, how much damage to the tiles does this cause?
How much additional weight is added to the vehicle from this trapped water? I would imagine it's non-trivial......

Do we know how the Space Shuttle was affected by this?
Title: Re: Starship heat shield
Post by: Faerwald on 08/04/2020 04:14 am
For all of the above stated reasons, I believe the tiles will be mounted on something like Nomex felt between the tile and the tank. Instead of bonding like the Shuttle did, it appears they will be attached using studs. This allow each tile to deal with vehicle deformations due to stresses applied throughout the mission. Between some tiles we may see filler material similar to that used on the Shuttle, but we have not seen any sign of that so far.

John
That makes no sense.

Firstly steel is about 1/10 the thermal conductivity of aluminum and IIRC it's expansion coefficient is about 1/3 that of aluminum.  So the tanks contents are easier to keep cool and the tank stresses caused by expansion and contraction are much reduced.

The key reason for the pads was that the tiles were bonded to the aluminum skin originally so as the skin expanded the tiles either cracked (reducing most of them to about 6" wide as the safe size) or peeled. The pads isolated the tiles excellent thermal but poor mechanical properties from the skins excellent mechanical but poor thermal properties.

But SS tiles are point mounted, which should simplify mounting them, although the reduced expansion should also reduce stress on the tiles anyway.

Stainless steel's youngs modulus is also about 3 times larger than aluminium so the force it exerts on parts trying to constrain either one is about the same.
Title: Re: Starship heat shield
Post by: _MECO on 08/04/2020 04:15 am
I'm actually more concerned about water between and under the tiles on Earth.

There will be small gaps between the tiles and a small space underneath the tiles.
These spaces may or may not have some form of padding or filling material....

The problem with small gaps and spaces are that they are great at drawing in water through capillary action. This water then is very hard to get out.

So....... The SS is sitting on the pad waiting for fueling and launch and it's raining.
Water is drawn between and below the tiles, largely filling the gaps.
You then add cryogenic fuel and oxidiser.
The water freezes, how much damage to the tiles does this cause?
How much additional weight is added to the vehicle from this trapped water? I would imagine it's non-trivial......

Do we know how the Space Shuttle was affected by this?

Perhaps the gaps between the tiles and mounting hardware and the gaps between the tiles themselves meant to accomodate reentry heat expansion are large enough to also accomodate expansion from frozen rainwater and humidity. It's not like both icy tile gaps and red hot expanded tiles are ever going to be a threat at the same time and compound each other or anything.
Title: Re: Starship heat shield
Post by: john smith 19 on 08/04/2020 05:46 am
Perhaps the gaps between the tiles and mounting hardware and the gaps between the tiles themselves meant to accomodate reentry heat expansion are large enough to also accomodate expansion from frozen rainwater and humidity. It's not like both icy tile gaps and red hot expanded tiles are ever going to be a threat at the same time and compound each other or anything.
Actually they might be.

Reentry during a rain storm?
Title: Re: Starship heat shield
Post by: john smith 19 on 08/04/2020 06:02 am
I'm actually more concerned about water between and under the tiles on Earth.

There will be small gaps between the tiles and a small space underneath the tiles.
These spaces may or may not have some form of padding or filling material....

The problem with small gaps and spaces are that they are great at drawing in water through capillary action. This water then is very hard to get out.

So....... The SS is sitting on the pad waiting for fueling and launch and it's raining.
Water is drawn between and below the tiles, largely filling the gaps.
You then add cryogenic fuel and oxidiser.
The water freezes, how much damage to the tiles does this cause?
How much additional weight is added to the vehicle from this trapped water? I would imagine it's non-trivial......
Depends on the porosity and surface tension of the tile material.
Quote from: Nevyn72
Do we know how the Space Shuttle was affected by this?
The short answer is badly  :(

All shuttle tiles were injected with a organic water repellent.  Pretty nasty stuff AIUI which burnt off on re-entry, multiplying the refurb work on the TPS.

Given the tiles were about 95% air and 5% tile they worked exactly like a sponge and IIRC could absorb several times their own weight in water.

In the later stages of the STS programme an applied physics team at Johnson (IIRC) developed a vacuum dewatering process that multiplied dry out rate several fold (ready in 1/3-1/4 the time of natural process).

Ames had developed a permanent solution using inorganic fluorides, which raised the surface tension and hence made the tiles repel water rather than suck it up. They never got permission to flight test it so we'll never know how permanent this solution was.  :(

Given we know ceramic tiles were not SX's first choice you can bet they have studied the pitfalls of this approach closely.  The benefit of being the second user of such material is that you can use the known issues list and avoid them in design (point mounting, not bonding. Allowing enough spacing that capillary action is not an issue etc) rather than having to live with them.   

The fact we've already been seeing sample tiles in place indicates this is technology SX are very keen to get right.

The area where shuttle can give no guidance is what happens when you put those tiles on mars for 26 months of thermal cycling, dust storms etc before taking off to come back to earth.

The answer is (hopefully) nothing very much, but there is a very good reason why those first flights won't have a crew on board.
Title: Re: Starship heat shield
Post by: rsdavis9 on 08/04/2020 12:04 pm
I'm actually more concerned about water between and under the tiles on Earth.

There will be small gaps between the tiles and a small space underneath the tiles.
These spaces may or may not have some form of padding or filling material....

The problem with small gaps and spaces are that they are great at drawing in water through capillary action. This water then is very hard to get out.

So....... The SS is sitting on the pad waiting for fueling and launch and it's raining.
Water is drawn between and below the tiles, largely filling the gaps.
You then add cryogenic fuel and oxidiser.
The water freezes, how much damage to the tiles does this cause?
How much additional weight is added to the vehicle from this trapped water? I would imagine it's non-trivial......
Depends on the porosity and surface tension of the tile material.
Quote from: Nevyn72
Do we know how the Space Shuttle was affected by this?
The short answer is badly  :(

All shuttle tiles were injected with a organic water repellent.  Pretty nasty stuff AIUI which burnt off on re-entry, multiplying the refurb work on the TPS.

Given the tiles were about 95% air and 5% tile they worked exactly like a sponge and IIRC could absorb several times their own weight in water.

In the later stages of the STS programme an applied physics team at Johnson (IIRC) developed a vacuum dewatering process that multiplied dry out rate several fold (ready in 1/3-1/4 the time of natural process).

Ames had developed a permanent solution using inorganic fluorides, which raised the surface tension and hence made the tiles repel water rather than suck it up. They never got permission to flight test it so we'll never know how permanent this solution was.  :(

Given we know ceramic tiles were not SX's first choice you can bet they have studied the pitfalls of this approach closely.  The benefit of being the second user of such material is that you can use the known issues list and avoid them in design (point mounting, not bonding. Allowing enough spacing that capillary action is not an issue etc) rather than having to live with them.   

The fact we've already been seeing sample tiles in place indicates this is technology SX are very keen to get right.

The area where shuttle can give no guidance is what happens when you put those tiles on mars for 26 months of thermal cycling, dust storms etc before taking off to come back to earth.

The answer is (hopefully) nothing very much, but there is a very good reason why those first flights won't have a crew on board.

The shuttle tiles never got cryogenic cold. I believe this will be the first vehicle with tiles to have cryogenic cold and 3000F reentry temp.(not at the same time)
Title: Re: Starship heat shield
Post by: livingjw on 08/04/2020 12:28 pm
For all of the above stated reasons, I believe the tiles will be mounted on something like Nomex felt between the tile and the tank. Instead of bonding like the Shuttle did, it appears they will be attached using studs. This allow each tile to deal with vehicle deformations due to stresses applied throughout the mission. Between some tiles we may see filler material similar to that used on the Shuttle, but we have not seen any sign of that so far.

John
That makes no sense.

Firstly steel is about 1/10 the thermal conductivity of aluminum and IIRC it's expansion coefficient is about 1/3 that of aluminum.  So the tanks contents are easier to keep cool and the tank stresses caused by expansion and contraction are much reduced.

The key reason for the pads was that the tiles were bonded to the aluminum skin originally so as the skin expanded the tiles either cracked (reducing most of them to about 6" wide as the safe size) or peeled. The pads isolated the tiles excellent thermal but poor mechanical properties from the skins excellent mechanical but poor thermal properties.

But SS tiles are point mounted, which should simplify mounting them, although the reduced expansion should also reduce stress on the tiles anyway.

- Mounting brittle tiles to stainless steel surfaces which are subjected to thermal, structural, vibration loads and localized buckling would benefit from some isolation. A felt insulating layer applied as a sheet before tile are applied would provide structural isolation, damping and gap insulation.

John
Title: Re: Starship heat shield
Post by: livingjw on 08/04/2020 12:32 pm
Another problem that needs to be solved is cryopumping while fueled on the pad.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20040001153.pdf

Water vapor will tend to condense inside the insulation. It will then rapidly expand upon during launch. TPS needs to minimize water and vapor entry but also allow for it to escape easily enough so as not to cause damage to the tile.

John
Title: Re: Starship heat shield
Post by: rsdavis9 on 08/04/2020 12:37 pm
I wonder whether they could just have the tile standoff from the hull. The 3 point studs could have a spacer or step to prevent the tile from contacting the hull. No porous material to soak up frozen water. Air is a good insulator as long as it's velocity is limited.

The X-33 was going to use high temp metal with standoffs from the composite hull. And it had metal tiles instead of ceramic tiles. Right?
Title: Re: Starship heat shield
Post by: livingjw on 08/04/2020 12:59 pm
I wonder whether they could just have the tile standoff from the hull. The 3 point studs could have a spacer or step to prevent the tile from contacting the hull. No porous material to soak up frozen water. Air is a good insulator as long as it's velocity is limited.

The X-33 was going to use high temp metal with standoffs from the composite hull. And it had metal tiles instead of ceramic tiles. Right?

You are correct, metal tiles were considered for improved ruggedness and reduced maintenance. They have some shortcomings:

- can't handle the higher heat loads caused by higher reentry speeds. Need either ceramics or cooling.
- metal tiles and support structure were heavier than directly bonded ceramic tile.

SpaceX appears to be searching for something better.

John
Title: Re: Starship heat shield
Post by: envy887 on 08/04/2020 03:00 pm
For all of the above stated reasons, I believe the tiles will be mounted on something like Nomex felt between the tile and the tank. Instead of bonding like the Shuttle did, it appears they will be attached using studs. This allow each tile to deal with vehicle deformations due to stresses applied throughout the mission. Between some tiles we may see filler material similar to that used on the Shuttle, but we have not seen any sign of that so far.

John
That makes no sense.

Firstly steel is about 1/10 the thermal conductivity of aluminum and IIRC it's expansion coefficient is about 1/3 that of aluminum.  So the tanks contents are easier to keep cool and the tank stresses caused by expansion and contraction are much reduced.

The key reason for the pads was that the tiles were bonded to the aluminum skin originally so as the skin expanded the tiles either cracked (reducing most of them to about 6" wide as the safe size) or peeled. The pads isolated the tiles excellent thermal but poor mechanical properties from the skins excellent mechanical but poor thermal properties.

But SS tiles are point mounted, which should simplify mounting them, although the reduced expansion should also reduce stress on the tiles anyway.

- Mounting brittle tiles to stainless steel surfaces which are subjected to thermal, structural, vibration loads and localized buckling would benefit from some isolation. A felt insulating layer applied as a sheet before tile are applied would provide structural isolation, damping and gap insulation.

John

The insulating layer would also flex if liquid water freezes under it, so there's little risk of ice expansion fracturing a tile.

Liquid water flashing to vapor during launch or reentry is a much bigger concern than anything to do with ice expansion.
Title: Re: Starship heat shield
Post by: _MECO on 08/04/2020 11:04 pm
Perhaps the gaps between the tiles and mounting hardware and the gaps between the tiles themselves meant to accomodate reentry heat expansion are large enough to also accomodate expansion from frozen rainwater and humidity. It's not like both icy tile gaps and red hot expanded tiles are ever going to be a threat at the same time and compound each other or anything.
Actually they might be.

Reentry during a rain storm?

Convective and radiative heat transfer from hypersonic air is a hell of a drug- even at stagnation points. If you can get water to survive through the shock front and work its way under the tiles and freeze against an empty steel tank hotter than a frying pan while sandwiched under tiles hot enough that expansion is an issue, I might just be a little surprised.
Title: Re: Starship heat shield
Post by: Keldor on 08/05/2020 01:22 am
Another problem that needs to be solved is cryopumping while fueled on the pad.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20040001153.pdf

Water vapor will tend to condense inside the insulation. It will then rapidly expand upon during launch. TPS needs to minimize water and vapor entry but also allow for it to escape easily enough so as not to cause damage to the tile.

John

One of the nice things about stainless steel is that the temperature it can withstand is close enough to reentry temperatures that it's acceptable to have decent sized cracks between the tiles - just the shade of the "canyon walls" and the flow stagnation are enough to keep the temperature at the bottom of the cracks cool enough.  This means there's ample room for water vapor to escape, so no chance for pressure buildup.

Tiles absorbing water is harder to deal with, though.  They'd need either some sort of high melting point coating compound, or maybe they could put the tiles through some sort of torch treatment to vitrify the surface and melt it into a thin solid layer?  Even then, you still have to worry about the area where the fasteners are embedded.

Water trapped inside the tiles vaporizing is bad, especially if the tiles are sealed.
Title: Re: Starship heat shield
Post by: john smith 19 on 08/05/2020 06:17 am
I wonder whether they could just have the tile standoff from the hull. The 3 point studs could have a spacer or step to prevent the tile from contacting the hull. No porous material to soak up frozen water. Air is a good insulator as long as it's velocity is limited.
Yes that's how I'm picturing this.
Quote from: rsdavis9
The X-33 was going to use high temp metal with standoffs from the composite hull. And it had metal tiles instead of ceramic tiles. Right?
"Metal" is a bit of an exaggeration.

Think "thick foil" food containers wrapping a high temperature felt. 
Title: Re: Starship heat shield
Post by: john smith 19 on 08/05/2020 06:18 am
The shuttle tiles never got cryogenic cold. I believe this will be the first vehicle with tiles to have cryogenic cold and 3000F reentry temp.(not at the same time)
Good point.

However it was pointed out that something as thin as a layer of paint stops ice formation the surface of the F9 tanks, and they are 10x the thermal conductivity of steel.  Bare steel may be enough.
Title: Re: Starship heat shield
Post by: john smith 19 on 08/05/2020 06:22 am
- Mounting brittle tiles to stainless steel surfaces which are subjected to thermal, structural, vibration loads and localized buckling would benefit from some isolation. A felt insulating layer applied as a sheet before tile are applied would provide structural isolation, damping and gap insulation.

John
Agreed, but AIUI that is what the studs provide.  :(

The only actual contact between the tiles and the skin is through those studs,  so the only way the skin can stress them is through loads through the studs.
Title: Re: Starship heat shield
Post by: livingjw on 08/05/2020 02:29 pm
- Mounting brittle tiles to stainless steel surfaces which are subjected to thermal, structural, vibration loads and localized buckling would benefit from some isolation. A felt insulating layer applied as a sheet before tile are applied would provide structural isolation, damping and gap insulation.

John
Agreed, but AIUI that is what the studs provide.  :(

The only actual contact between the tiles and the skin is through those studs,  so the only way the skin can stress them is through loads through the studs.

I don't think you want the tile floating on metal studs and not touching anywhere else. Probably don't want a gap allowing hot gases to circulate below the tile. Without something like a deformable felt underlayment, the edges of the tile will touch and deflect in unpredictable ways. Also, attachments to metal studs provide little or no damping.

John
Title: Re: Starship heat shield
Post by: john smith 19 on 08/05/2020 06:37 pm
Tiles absorbing water is harder to deal with, though.  They'd need either some sort of high melting point coating compound, or maybe they could put the tiles through some sort of torch treatment to vitrify the surface and melt it into a thin solid layer?  Even then, you still have to worry about the area where the fasteners are embedded.
Bad idea. This roughly describes the shuttle tile coating. That thin layer was very brittle and prone to impact damage. When a newer (but heavier) design was developed that created a graded protection running deeper into the tile that had 1/10 the number of damaged tiles.
Quote from: Keldor
Water trapped inside the tiles vaporizing is bad, especially if the tiles are sealed.
Quite true.

During the early shuttle studies Grumman suggested what were basically Autoclaved Aerated Concrete, made from power plant fly ash. This has roughly 1/3 the SG of water (It floats) made by adding aluminum powder which when mixed with water released H2 as a foaming agent. This is a closed cell foam to survive up to about 1700c.
Title: Re: Starship heat shield
Post by: enbandi on 08/05/2020 08:03 pm
One of the new robotic arms are already installed and labelled "heat shield". With that i think the questions about stud installation are settled. Seems like automated installation, to barrel segments, before stacking. (quite the opposite to what I guessed).

Will be interesting to see how they address the stud alignment through stacking. But maybe with the gaps beetween tiles (hence more tolerant tile positioning) that would not be a big problem at all.


See the last photo in this post by BCG.

5 ring high section.
Another section stacked in the mid bay.
Inside tent #1.
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 08/05/2020 08:10 pm
One of the new robotic arms are already installed and labelled "heat shield". With that i think the questions about stud installation are settled. Seems like automated installation, to barrel segments, before stacking. (quite the opposite to what I guessed).

Will be interesting to see how they address the stud alignment through stacking. But maybe with the gaps beetween tiles (hence more tolerant tile positioning) that would not be a big problem at all.


See the last photo in this post by BCG.

5 ring high section.
Another section stacked in the mid bay.
Inside tent #1.

I would think at least some area around the edge of each ring would need to be free of tiles during welding.

But if they're using robots to do the welding, I don't see why they couldn't also use robots to add the tiles on top of the welds after the welding for a ring is done.

So I would guess at a flow that sees a ring covered with tiles only after it has been welded to the ring above and then only partway down to leave room for the next weld.  No alignment of tiles needed because the lower ring wouldn't have any tiles attached before the weld.
Title: Re: Starship heat shield
Post by: Doesitfloat on 08/05/2020 08:50 pm
One of the new robotic arms are already installed and labelled "heat shield". With that i think the questions about stud installation are settled. Seems like automated installation, to barrel segments, before stacking. (quite the opposite to what I guessed).

Will be interesting to see how they address the stud alignment through stacking. But maybe with the gaps beetween tiles (hence more tolerant tile positioning) that would not be a big problem at all.


See the last photo in this post by BCG.

5 ring high section.
Another section stacked in the mid bay.
Inside tent #1.
They just got these welding bots last week.  I would expect them to try out the new process on some rings rather than a completed tank. 
Title: Re: Starship heat shield
Post by: samgineer on 08/05/2020 09:18 pm
One of the new robotic arms are already installed and labelled "heat shield". With that i think the questions about stud installation are settled. Seems like automated installation, to barrel segments, before stacking. (quite the opposite to what I guessed).

Will be interesting to see how they address the stud alignment through stacking. But maybe with the gaps between tiles (hence more tolerant tile positioning) that would not be a big problem at all.


See the last photo in this post by BCG.

5 ring high section.
Another section stacked in the mid bay.
Inside tent #1.

I think stacking itself is quite precise, they are using guides and tolerations might be pretty tight. Attachment mechanism on tiles itself may be able to compensate little imperfection of stacking.
Title: Re: Starship heat shield
Post by: Oersted on 08/06/2020 10:32 am
I am imagining tiles attached with three stand-off studs that are firmly fixed on the Starship hull but able to travel in small radial grooves on the tile, to allow for thermal expansion of the hull.

An alternative method for countering thermal expansion stress could be studs with some in-built flex, a bit like the stand-off skin fasteners used on the SR-71.

How does that sound?
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/06/2020 03:51 pm
One of the new robotic arms are already installed and labelled "heat shield". With that i think the questions about stud installation are settled. Seems like automated installation, to barrel segments, before stacking. (quite the opposite to what I guessed).

Will be interesting to see how they address the stud alignment through stacking. But maybe with the gaps beetween tiles (hence more tolerant tile positioning) that would not be a big problem at all.


See the last photo in this post by BCG.

5 ring high section.
Another section stacked in the mid bay.
Inside tent #1.
They just got these welding bots last week.  I would expect them to try out the new process on some rings rather than a completed tank.
They may have already done that.
Title: Re: Starship heat shield
Post by: xvel on 08/06/2020 07:21 pm
Tiles after the hop doesn't look great
Title: Re: Starship heat shield
Post by: TheUltimateConan on 08/06/2020 07:53 pm
it looks like the tiles with 3 holes visible from the outside broke. The tiles above do not have these holes and are looking quite good. I think they got the data they wanted.
Title: Re: Starship heat shield
Post by: wannamoonbase on 08/06/2020 08:51 pm
it looks like the tiles with 3 holes visible from the outside broke. The tiles above do not have these holes and are looking quite good. I think they got the data they wanted.

They don't look great.  But it's some data.  Even if it's a very short gentle flight.

Making orbit and back is a lot more aggressive.  But great to be start taking a shot and seeing what works.
Title: Re: Starship heat shield
Post by: SkyRate on 08/06/2020 09:26 pm
it looks like the tiles with 3 holes visible from the outside broke. The tiles above do not have these holes and are looking quite good. I think they got the data they wanted.
They don't look great.  But it's some data.  Even if it's a very short gentle flight.
Making orbit and back is a lot more aggressive.  But great to be start taking a shot and seeing what works.
OTOH, the landing, especially on short legs and at 1 atm, might involve some of the worst pressure and vibration loads on the skirt.
Title: Re: Starship heat shield
Post by: _MECO on 08/06/2020 09:36 pm
it looks like the tiles with 3 holes visible from the outside broke. The tiles above do not have these holes and are looking quite good. I think they got the data they wanted.

They don't look great.  But it's some data.  Even if it's a very short gentle flight.

Making orbit and back is a lot more aggressive.  But great to be start taking a shot and seeing what works.

I think seeing tiles pristine, nearly destroyed, and missing completely next to what is obviously more than one mounting system is a really good sign. It means the solution for mounting the tiles is rich with different options (if hopefully not profuse with them).

This "see what sticks" approach likely means they're not butting up against the limitations of their materials yet. In iterative development, the first iterations always see the largest differences between each other and it's usually easiest to see what to change at that stage. It would be much more worrying if we saw tiles like this destroyed on SN15 or something all with the same type of mounting hardware exposed.
Title: Re: Starship heat shield
Post by: eriblo on 08/06/2020 11:34 pm
it looks like the tiles with 3 holes visible from the outside broke. The tiles above do not have these holes and are looking quite good. I think they got the data they wanted.
They don't look great.  But it's some data.  Even if it's a very short gentle flight.
Making orbit and back is a lot more aggressive.  But great to be start taking a shot and seeing what works.
OTOH, the landing, especially on short legs and at 1 atm, might involve some of the worst pressure and vibration loads on the skirt.
The image on SN5 in flight tweeted by Elon is right at the limit with regard to resolution and angle but it looks like the three bottom/right "single spiral fitting" tiles are already gone while at least one of the "three rods" tiles is still there.
I totally agree that a tile and attachment combo that survives on the skirt during such a landing should have no problem with the mechanical loads encountered on an operational Starship (with heat and potential impacts being extra factors not tested in flight so far).
Title: Re: Starship heat shield
Post by: wes_wilson on 08/07/2020 12:26 am
it looks like the tiles with 3 holes visible from the outside broke. The tiles above do not have these holes and are looking quite good. I think they got the data they wanted.

They don't look great.  But it's some data.  Even if it's a very short gentle flight.

Making orbit and back is a lot more aggressive.  But great to be start taking a shot and seeing what works.

I think seeing tiles pristine, nearly destroyed, and missing completely next to what is obviously more than one mounting system is a really good sign. It means the solution for mounting the tiles is rich with different options (if hopefully not profuse with them).

This "see what sticks" approach likely means they're not butting up against the limitations of their materials yet. In iterative development, the first iterations always see the largest differences between each other and it's usually easiest to see what to change at that stage. It would be much more worrying if we saw tiles like this destroyed on SN15 or something all with the same type of mounting hardware exposed.

It's also possible that the missing tiles actually represent a successful test of certain aspects of the heat shield.  Orbital debris, landing debris, take off debris are all going to exist within the operating domain of this vessel.  Since the tiles are directly attached to the ship, it's important that when they are damaged or torn off that they detach in a manner that doesn't puncture or tear the hull.  So, it's possible that even the loss of the tiles represented a successful test of losing them without losing the hull.

Title: Re: Starship heat shield
Post by: livingjw on 08/07/2020 05:22 pm
Speculation:

- It appears to me that these tiles got hit hard, probably early in the flight.

- The white tubes attached to the studs appear to have been molded into a solid block of insulation.

- The spiral connectors don't appear to have any white insulation substrate on them. Makes me think they were not bonded or did not bond well to the insulation block.

- From the rub marks under the missing tiles, it appears that they had isolation padding around the perimeter and one in the center.

- It looks like there is some inter-tile filler between some of the tile.

Comments, other ideas?

John
Title: Re: Starship heat shield
Post by: Step55 on 08/07/2020 05:48 pm
Speculation:

- It appears to me that these tiles got hit hard, probably early in the flight.

- The white tubes attached to the studs appear to have been molded into a solid block of insulation.

- The spiral connectors don't appear to have any white insulation substrate on them. Makes me think they were not bonded or did not bond well to the insulation block.

- From the rub marks under the missing tiles, it appears that they had isolation padding around the perimeter and one in the center.

- It looks like there is some inter-tile filler between some of the tile.

Comments, other ideas?

John

Elon mentioned in one of his tweets that the white tubes/insulation is furnace rope.
Title: Re: Starship heat shield
Post by: Johnnyhinbos on 08/07/2020 05:52 pm
Speculation:

- It appears to me that these tiles got hit hard, probably early in the flight.

- The white tubes attached to the studs appear to have been molded into a solid block of insulation.

- The spiral connectors don't appear to have any white insulation substrate on them. Makes me think they were not bonded or did not bond well to the insulation block.

- From the rub marks under the missing tiles, it appears that they had isolation padding around the perimeter and one in the center.

- It looks like there is some inter-tile filler between some of the tile.

Comments, other ideas?

John
I was of the mindset that the majority of the damage was shock caused from the landing - it's must have been one heck of a jar to cause the collapsing of the large hole area of the bottom half of the legs. These tiles look hard, un-elastic and brittle. The ones with the cracks look like the cracks propagate from the three mounting studs in each time. Those tiles may not have had any of the adhesive bonding that the top row appears to have, so they were more prone to shock at the mounting points (as opposed to having bonding all around)
Title: Re: Starship heat shield
Post by: Keldor on 08/07/2020 06:27 pm
Speculation:

- It appears to me that these tiles got hit hard, probably early in the flight.

- The white tubes attached to the studs appear to have been molded into a solid block of insulation.

- The spiral connectors don't appear to have any white insulation substrate on them. Makes me think they were not bonded or did not bond well to the insulation block.

- From the rub marks under the missing tiles, it appears that they had isolation padding around the perimeter and one in the center.

- It looks like there is some inter-tile filler between some of the tile.

Comments, other ideas?

John
I was of the mindset that the majority of the damage was shock caused from the landing - it's must have been one heck of a jar to cause the collapsing of the large hole area of the bottom half of the legs. These tiles look hard, un-elastic and brittle. The ones with the cracks look like the cracks propagate from the three mounting studs in each time. Those tiles may not have had any of the adhesive bonding that the top row appears to have, so they were more prone to shock at the mounting points (as opposed to having bonding all around)

The 1.0 legs almost certainly use crush core as the sole form of shock absorption.  As such, partially collapsing like that is normal and expected even in a gentle landing.

They use it now because it's super easy to develop and manufacture.  Eventually, or even soon, they'll have a more sophisticated landing gear that doesn't need replacement of crush cores between flights, but this is a relatively low priority compared to flight tests.

My suspicion is that the acoustic environment that close to the engines is the cause of the tile failures.  It's hard to appreciate the power of sound waves at these intensities, put perhaps we can start by looking at the force of air pressure. 

A tile the size of the ones they're using will have on the order of tons of force worth of air pressure acting on it.  Normally, this is perfectly fine since it's in equilibrium with pressure from the other side.  However, a rocket engine like Raptor is so loud that the "dips" between the sound waves have a pressure drop a significant portion of the way to a vacuum.  And so the tiles will be experiencing pressure differentials in alternating directions exerting hundreds of kg of force to their surfaces, many times per second.

The most convincing demonstration of just how loud rockets are is a video of a Falcon 9 launch, taken from a small airplane.  Upon launch, the sound of the rocked *drowned out* the sound of the airplane's engine, despite the microphone being perhaps 1 meter away from the engine, and despite the rocket being perhaps 20 km away!  Now, a Falcon 9 is much louder than a single Raptor, but that's pretty academic at this scale.
Title: Re: Starship heat shield
Post by: DusanC on 08/07/2020 07:11 pm
Speculation:

- It appears to me that these tiles got hit hard, probably early in the flight.
IMHO Vibrations. Sound energy making the steel sheet oscillate hard.

Quote
- The white tubes attached to the studs appear to have been molded into a solid block of insulation.
Dunno, but to me it looks like that they were placed in a star pattern and the tile mounted over.
Quote

- The spiral connectors don't appear to have any white insulation substrate on them. Makes me think they were not bonded or did not bond well to the insulation block.
Maybe they were cast in the tile?

Quote
- From the rub marks under the missing tiles, it appears that they had isolation padding around the perimeter and one in the center.

- It looks like there is some inter-tile filler between some of the tile.

Comments, other ideas?

John

These last two create bending loads from undamped oscillations that broke the brittle tile that had cracks starting points at the mounting hiles.

These problems are usually solved by:
1. Use less brittle materials (low probability)
2. Use more damping (first thing they'll try)
3. Decrease bending of tile

Because 2 and 3 I thought that they'll use a insulating felt sheat so that when you tighten the flat tile over circular sheet metal most loads would be at the middle.

IMHO they just have to make the connection of tile to SS skin elastic and damped in every direction and around all axis if they want to keep using these brittle tiles.
Title: Re: Starship heat shield
Post by: livingjw on 08/07/2020 08:28 pm
- Very sceptical that such damage was done by vibration. The damaged tile look flattened.

- Also, why didn't any damage happen on earlier engine runs?

John
Title: Re: Starship heat shield
Post by: DusanC on 08/07/2020 08:37 pm
- Very sceptical that such damage was done by vibration. The damaged tile look flattened.

- Also, why didn't any damage happen on earlier engine runs?

John
IMHO on earlier runs the skirt was more rigid as it was fixed to launch mount so the amplitudes and accelerations were lower.
Title: Re: Starship heat shield
Post by: livingjw on 08/07/2020 08:45 pm
Speculation:

- It appears to me that these tiles got hit hard, probably early in the flight.

- The white tubes attached to the studs appear to have been molded into a solid block of insulation.

- The spiral connectors don't appear to have any white insulation substrate on them. Makes me think they were not bonded or did not bond well to the insulation block.

- From the rub marks under the missing tiles, it appears that they had isolation padding around the perimeter and one in the center.

- It looks like there is some inter-tile filler between some of the tile.

Comments, other ideas?

John
I was of the mindset that the majority of the damage was shock caused from the landing - it's must have been one heck of a jar to cause the collapsing of the large hole area of the bottom half of the legs. These tiles look hard, un-elastic and brittle. The ones with the cracks look like the cracks propagate from the three mounting studs in each time. Those tiles may not have had any of the adhesive bonding that the top row appears to have, so they were more prone to shock at the mounting points (as opposed to having bonding all around)

- I agree, these tile appear to be brittle, similar to ruggedised Shuttle tile, but designed with internal structure (the white tubes) to attach to the metal studs.

- I agree, the cracks look like the cracks propagate from the three mounting studs. The tubes house the mounting point for the studs. I believe the tubes are molded into the hexagonal insulation block. The insulation block is covered with a thin ruggedized outer coating. When the tiles were hit they were crushed inward causing the studs to punch and crack the outer surface.

- I do not believe there is any adhesive involved. I believe white material around the intact tile is isolation felt.

I have attached a sketch of a similar tile scheme that I drew a while back. Not exactly the same, but similar. I think the tubes we saw were co-cured into something like AETB.

John
Title: Re: Starship heat shield
Post by: Keldor on 08/08/2020 03:38 am
- Very sceptical that such damage was done by vibration. The damaged tile look flattened.

- Also, why didn't any damage happen on earlier engine runs?

John

It might have to do with the height of the skirt above the ground at landing.  The clearance is very low on SN5, so the entire engine chamber is going to have some interesting acoustic effects while the engine is firing straight into the landing pad at touchdown.  Notice how violently the camera shook during touchdown in the clip SpaceX released compared to the rest of the flight.

Simply adding longer legs could mitigate a lot of this, and it could be perfectly reasonable to add extra reinforcement just to the tiles on the skirt.
Title: Re: Starship heat shield
Post by: DusanC on 08/08/2020 02:25 pm
- Very sceptical that such damage was done by vibration. The damaged tile look flattened.

- Also, why didn't any damage happen on earlier engine runs?

John
One interesting thing is that tiles look like some of them were splashed with something, and more interestingly only those splashed are broken or missing.
Title: Re: Starship heat shield
Post by: Keldor on 08/08/2020 06:43 pm
- Very sceptical that such damage was done by vibration. The damaged tile look flattened.

- Also, why didn't any damage happen on earlier engine runs?

John
One interesting thing is that tiles look like some of them were splashed with something, and more interestingly only those splashed are broken or missing.

Water from the noise suppression system, followed by dust sticking to the wet parts during the flight?
Title: Re: Starship heat shield
Post by: OTV Booster on 08/09/2020 12:50 pm
- Very sceptical that such damage was done by vibration. The damaged tile look flattened.

- Also, why didn't any damage happen on earlier engine runs?

John
One interesting thing is that tiles look like some of them were splashed with something, and more interestingly only those splashed are broken or missing.

Water from the noise suppression system, followed by dust sticking to the wet parts during the flight?
Looking close, it looks like scouring. And it carries over into the undamaged tiles but much reduced. Maybe they're playing with different surface treatments?

Title: Re: Starship heat shield
Post by: nicp on 08/09/2020 05:35 pm
Do we have dimensions, especially thickness, for these tiles?
Title: Re: Starship heat shield
Post by: john smith 19 on 08/10/2020 06:15 am
I wonder what are those star shaped bars?

Some of them stay star shaped, others like they've been knocked around.

Tiles mounted to bars mounted to studs to allow the studs to slid out as they expand?

Bars molded into the tiles?

BTW I'm pretty sure SX won't want to go the isolation pad/bonding route. That was very fiddly and expensive.
Not impossible to automate but I can see it being very tricky. How do you define "Press it down just hard enough to stick to the pad, but not to glue the pad material to the skin" ? :(
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/10/2020 10:23 pm
Looks like they have attached a few more tiles to one of the prototypes. Seems to be a big gap down the middle and some of the tiles aren't lined up that well. I assume there're just testing out the attachment process. It also seems that there are multiple layers under the tile itself - presumably some form of insulation.

(https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=51332.0;attach=1962660;image)
Title: Re: Starship heat shield
Post by: 50_Caliber on 08/10/2020 10:32 pm
I wonder if they'll cover the entire side? It occurs to me, if they wanted a signature SpaceX symbol on their Star ships, they could just make different colored tile hexagons where it would show on the heat tiles.
Title: Re: Starship heat shield
Post by: Oersted on 08/10/2020 10:34 pm
Tiles applied in a big "X"..... - Hmmmm, what would be the symbology behind that?..  🤔😁
Title: Re: Starship heat shield
Post by: OTV Booster on 08/10/2020 10:34 pm
I wonder what are those star shaped bars?

Some of them stay star shaped, others like they've been knocked around.

Tiles mounted to bars mounted to studs to allow the studs to slid out as they expand?

Bars molded into the tiles?

BTW I'm pretty sure SX won't want to go the isolation pad/bonding route. That was very fiddly and expensive.
Not impossible to automate but I can see it being very tricky. How do you define "Press it down just hard enough to stick to the pad, but not to glue the pad material to the skin" ? :(
Here's a blowup of Mary's pic of the bars. Weird. They seem to have a woven surface and the ends appear tied off. Almost look like heavy tubes of sand used for vehicle traction in snow. They also appeared to either be fixed on the outer end of the mounting pins or are free to slide and just happen to be there. One set is in a 'Y' configuration, the others are random. Could it be that they are normally in a delta configuration? I almost feel like I'm talking about generator wiring.


It's really impossible to say what the material is. The only thing that comes to mind is woven fiberglass but it looks like Teflon. Teflon makes no sense from a heat perspective. I'm running mental models of what might be going on here but nothing is clear enough to even warrant a speculation.


The second pic from Mary shows tiles on the rings where the robot was working. The point of interest is a few tiles on the left side. There is something white along the edge. The camera angle is from the right so whatever we're seeing is not tile edge. Maybe those external clip arrangements or maybe part of a felt pad or extruded goop.


A side point. Not all the pins have tiles. Can't see it in this crop but the tiles are laid out in a big 'X'. How autonomous is that robot? Are we seeing emergent AH? Artificial Humor? ???


Phil

Title: Re: Starship heat shield
Post by: RoboGoofers on 08/10/2020 11:39 pm
I wonder what are those star shaped bars?

Some of them stay star shaped, others like they've been knocked around.

Tiles mounted to bars mounted to studs to allow the studs to slid out as they expand?

Bars molded into the tiles?

BTW I'm pretty sure SX won't want to go the isolation pad/bonding route. That was very fiddly and expensive.
Not impossible to automate but I can see it being very tricky. How do you define "Press it down just hard enough to stick to the pad, but not to glue the pad material to the skin" ? :(
Here's a blowup of Mary's pic of the bars. Weird. They seem to have a woven surface and the ends appear tied off. Almost look like heavy tubes of sand used for vehicle traction in snow. They also appeared to either be fixed on the outer end of the mounting pins or are free to slide and just happen to be there. One set is in a 'Y' configuration, the others are random. Could it be that they are normally in a delta configuration? I almost feel like I'm talking about generator wiring.


It's really impossible to say what the material is. The only thing that comes to mind is woven fiberglass but it looks like Teflon. Teflon makes no sense from a heat perspective. I'm running mental models of what might be going on here but nothing is clear enough to even warrant a speculation.


The second pic from Mary shows tiles on the rings where the robot was working. The point of interest is a few tiles on the left side. There is something white along the edge. The camera angle is from the right so whatever we're seeing is not tile edge. Maybe those external clip arrangements or maybe part of a felt pad or extruded goop.


A side point. Not all the pins have tiles. Can't see it in this crop but the tiles are laid out in a big 'X'. How autonomous is that robot? Are we seeing emergent AH? Artificial Humor? ???


Phil
maybe harder ceramic tubes to spread the load into the bulk of the tile. Bonding between the hard ceramic and the exterior tile ceramic might be weak, so maybe a fiberglass sock around the tube/rod to act as reinforcement, like wire mesh in concrete
Title: Re: Starship heat shield
Post by: Nevyn72 on 08/11/2020 12:00 am
I think they are trolling us! But that is very cool, but it looks like they have a spacing issue.

I think the spacing is quite deliberate.

All of these tiles appear to be the 'three pin through' type, all of which either fell off or were cracked on SN5.

The spacing appears greater than that on SN5, mostly a little bit, although you can see the metal skin in between, and quite a bit down the centre line. Perhaps they are trying to test if vibrations are causing the tiles to bump against each other and fail due to brittleness? How big a gap is required to aviod this?

I will be curious to see if other methods for affixing tiles are used on different parts of this barrel section.

I wonder if this is a pathfinder for tile fixing or if it will actually fly?

A cross post from the updates thread, probably better suited here.
Title: Re: Starship heat shield
Post by: TorenAltair on 08/11/2020 12:06 am
You have to "learn" a robot, so this very well might just be a first step to adjust it to the work needed. No need to panic or such things here because there are gaps between the tiles.
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/11/2020 10:58 am
You have to "learn" a robot, so this very well might just be a first step to adjust it to the work needed. No need to panic or such things here because there are gaps between the tiles.
Yes I suspect they are still trying out different tile arrangements and types so they have not focused on the spacing element yet. It seems that the white support elements have been arranged in such a way that there are diamond shaped spaces below the tiles that alternate between layers (upright "Y" upside down "Y" on each layer of tile supports.
Title: Re: Starship heat shield
Post by: Step55 on 08/11/2020 11:09 am
I wonder what are those star shaped bars?

Some of them stay star shaped, others like they've been knocked around.

Tiles mounted to bars mounted to studs to allow the studs to slid out as they expand?

Bars molded into the tiles?

BTW I'm pretty sure SX won't want to go the isolation pad/bonding route. That was very fiddly and expensive.
Not impossible to automate but I can see it being very tricky. How do you define "Press it down just hard enough to stick to the pad, but not to glue the pad material to the skin" ? :(
Here's a blowup of Mary's pic of the bars. Weird. They seem to have a woven surface and the ends appear tied off. Almost look like heavy tubes of sand used for vehicle traction in snow. They also appeared to either be fixed on the outer end of the mounting pins or are free to slide and just happen to be there. One set is in a 'Y' configuration, the others are random. Could it be that they are normally in a delta configuration? I almost feel like I'm talking about generator wiring.


It's really impossible to say what the material is. The only thing that comes to mind is woven fiberglass but it looks like Teflon. Teflon makes no sense from a heat perspective. I'm running mental models of what might be going on here but nothing is clear enough to even warrant a speculation.


The second pic from Mary shows tiles on the rings where the robot was working. The point of interest is a few tiles on the left side. There is something white along the edge. The camera angle is from the right so whatever we're seeing is not tile edge. Maybe those external clip arrangements or maybe part of a felt pad or extruded goop.


A side point. Not all the pins have tiles. Can't see it in this crop but the tiles are laid out in a big 'X'. How autonomous is that robot? Are we seeing emergent AH? Artificial Humor? ???


Phil

The white tubes are ceramic fire rope / furnace gasket.
Title: Re: Starship heat shield
Post by: DusanC on 08/11/2020 11:24 am
I wonder what are those star shaped bars?

Some of them stay star shaped, others like they've been knocked around.

Tiles mounted to bars mounted to studs to allow the studs to slid out as they expand?

Bars molded into the tiles?

BTW I'm pretty sure SX won't want to go the isolation pad/bonding route. That was very fiddly and expensive.
Not impossible to automate but I can see it being very tricky. How do you define "Press it down just hard enough to stick to the pad, but not to glue the pad material to the skin" ? :(
Here's a blowup of Mary's pic of the bars. Weird. They seem to have a woven surface and the ends appear tied off. Almost look like heavy tubes of sand used for vehicle traction in snow. They also appeared to either be fixed on the outer end of the mounting pins or are free to slide and just happen to be there. One set is in a 'Y' configuration, the others are random. Could it be that they are normally in a delta configuration? I almost feel like I'm talking about generator wiring.


It's really impossible to say what the material is. The only thing that comes to mind is woven fiberglass but it looks like Teflon. Teflon makes no sense from a heat perspective. I'm running mental models of what might be going on here but nothing is clear enough to even warrant a speculation.


The second pic from Mary shows tiles on the rings where the robot was working. The point of interest is a few tiles on the left side. There is something white along the edge. The camera angle is from the right so whatever we're seeing is not tile edge. Maybe those external clip arrangements or maybe part of a felt pad or extruded goop.


A side point. Not all the pins have tiles. Can't see it in this crop but the tiles are laid out in a big 'X'. How autonomous is that robot? Are we seeing emergent AH? Artificial Humor? ???


Phil

The white tubes are ceramic fire rope / furnace gasket.
Sequence of current heat shield mounting (IMHO):
1. Robot(s) welds the studs;
2. Human places the heat resistant rope (square crossection);
3. Human places the tiles.

Idea that robot places the tiles is premature.

I wouldn't use the rope but heat resistant cloth and if there should be holes in it (for slimming weight) I'd prefabricate the holes pattern on waterjet. Easier to mount and more robust in use.
Title: Re: Starship heat shield
Post by: HVM on 08/11/2020 11:42 am
Are the studs threaded or are there other fastening methods visible? Odd that they selected three pin arrangement (-Surprised Pikachu), all three pin tiles at SN5 were fractured, but still attached (You could say -Fractured but Whole.)
Title: Re: Starship heat shield
Post by: Kazioo on 08/11/2020 01:13 pm
I just noticed that the tiles have been applied in the shape of the SpaceX logo
(photo from bocachicagal)

My wishful thinking theory that I realize is most likely not true:
They developed a software that dynamically and procedurally spreads and arranges tiles in the most optimal way for a given surface. What we are seeing is a result of a test of that software after importing a bitmap with SpaceX's logo and clicking "print".

I suppose automatic tracking of position and orientation with sub mm precision relatively to this kind of article would be extremely difficult to implement. But it would be so awesome to have a "smart" adaptive heat shield printing robot...
Title: Re: Starship heat shield
Post by: livingjw on 08/11/2020 01:49 pm

The white tubes are ceramic fire rope / furnace gasket.

It is more likely that it is a rigid ceramic composite. My guess would be alumina fiber based.

John
Title: Re: Starship heat shield
Post by: OTV Booster on 08/11/2020 05:28 pm
I just noticed that the tiles have been applied in the shape of the SpaceX logo
(photo from bocachicagal)

My wishful thinking theory that I realize is most likely not true:
They developed a software that dynamically and procedurally spreads and arranges tiles in the most optimal way for a given surface. What we are seeing is a result of a test of that software after importing a bitmap with SpaceX's logo and clicking "print".

I suppose automatic tracking of position and orientation with sub mm precision relatively to this kind of article would be extremely difficult to implement. But it would be so awesome to have a "smart" adaptive heat shield printing robot...
Positioning accuracy is a solved problem. In the 1980's Intelledex arms had each joint premapped for mechanical irregularities and burned into a ROM on the controller. IIRC the accuracy was measured in thousandths of an inch. Don't remember the precision.


Surely 30+ years later this is common.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/11/2020 05:33 pm

The white tubes are ceramic fire rope / furnace gasket.

It is more likely that it is a rigid ceramic composite. My guess would be alumina fiber based.

John
What purpose?


I was thinking that if the tubes are soft they would allow some tile float while buffering between the tile and skin.


Phil
Title: Re: Starship heat shield
Post by: Step55 on 08/11/2020 06:01 pm

The white tubes are ceramic fire rope / furnace gasket.

It is more likely that it is a rigid ceramic composite. My guess would be alumina fiber based.

John
What purpose?


I was thinking that if the tubes are soft they would allow some tile float while buffering between the tile and skin.


Phil

https://twitter.com/elonmusk/status/1171308928476385281
Title: Re: Starship heat shield
Post by: ShaunML09 on 08/11/2020 06:51 pm
As speculated by many here, they are testing the tiles in larger sections to see how they perform under cryo, load and deformation

https://mobile.twitter.com/elonmusk/status/1293250823296884746
Title: Re: Starship heat shield
Post by: OTV Booster on 08/12/2020 03:57 am

The white tubes are ceramic fire rope / furnace gasket.

It is more likely that it is a rigid ceramic composite. My guess would be alumina fiber based.

John
What purpose?


I was thinking that if the tubes are soft they would allow some tile float while buffering between the tile and skin.


Phil

https://twitter.com/elonmusk/status/1171308928476385281 (https://twitter.com/elonmusk/status/1171308928476385281)
That tweet is 11 months stale. Mary's pic from this afternoon shows something that might be called marshmallowy sandwiched under some of the tiles. Elon was talking about furnace rope or something similar stuffed in the space between tiles.


Those tubes in my earlier posts are impaled on the studs. Can't see them sealing anything.


Phil
Title: Re: Starship heat shield
Post by: awests on 08/12/2020 05:12 am

The white tubes are ceramic fire rope / furnace gasket.

It is more likely that it is a rigid ceramic composite. My guess would be alumina fiber based.

John
What purpose?


I was thinking that if the tubes are soft they would allow some tile float while buffering between the tile and skin.


Phil

https://twitter.com/elonmusk/status/1171308928476385281 (https://twitter.com/elonmusk/status/1171308928476385281)
That tweet is 11 months stale. Mary's pic from this afternoon shows something that might be called marshmallowy sandwiched under some of the tiles. Elon was talking about furnace rope or something similar stuffed in the space between tiles.


Those tubes in my earlier posts are impaled on the studs. Can't see them sealing anything.


Phil
What’s to say that it’s not a more rigid material encased by the rope? Basically a composite of sorts. The tie offs and fraying at the end to me indicate the ceramic rope while the rigidity of the pieces points toward something rigid.

I agree with other posters, wouldn’t you want some sort of compliance between tiles, in addition to underneath with the felt like padding as described by Livingjw?
Title: Re: Starship heat shield
Post by: john smith 19 on 08/12/2020 05:53 am

https://twitter.com/elonmusk/status/1171308928476385281
This tweet may be 11 months old but Musks point still stands.

You're going to use SS because it's allowable operating temperature is much higher than aluminum.

Shuttle tiles were bonded with Room Temperature Vulcanizing adhesive, which AIUI is basically the stuff you stick bathroom tiles up with. 

I'm not sure how far above 183c (design limit for shuttle skin) it can go before it degrades and softens, but I'll bet it's a long way below what SS can handle.

So now you need a high temperature glue/adhesive/cement/whatever  and you're looking (probably) at the sort of stuff they use to hold furnace bricks together with. IE inorganic formulations.

So you're looking for a formulation that's a) Chemically compatible with steel b)Chemically compatible with some kind of knitted felt strain isolation pad material c) Capable of handling the backside temp of the tiles.

Such a formulation may be possible but I doubt it's OTS.  :(

BTW In 2020 "Industrial fasteners" includes nuts, bolts and washers in ceramics like zirconia and alumina.
A hex head bolt that can survive 1600 can a) Be recessed into the tile from the front b) Need no protection from re-entry heat. It needs a torque controlled wrench so it's not damaged when being driven home but that's not exactly cutting edge shop hardware these days.

Not saying they'll go that way, just pointing out that options exist now that did not exist in the 70's and which have sufficient usage (or big enough margin) that their use would not be that risky.
Title: Re: Starship heat shield
Post by: livingjw on 08/12/2020 01:32 pm

The white tubes are ceramic fire rope / furnace gasket.

It is more likely that it is a rigid ceramic composite. My guess would be alumina fiber based.

John

What purpose?

I was thinking that if the tubes are soft they would allow some tile float while buffering between the tile and skin.

Phil

- I think there are some misconceptions about the nature of rigid alumina insulation based tiles. They are very fragile. They have the consistency of foam insulation. They have very little strength. Without their protective outer covering, you can poke holes in it with your pinky. If you want to mechanically fasten one you need to embed something in the insulation block to anchor to. That is what you are seeing with the ceramic tubes dangling from the studs.  The little spiral fittings would do the same for the small hex tile.

- The ceramic rope Elon mentioned has a different purpose. It is use to insulate between tiles.

-  The ceramic rope material, or Nomex felt, could also be used to seal and isolate the underside of the brittle tile from the vehicle.

John
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/12/2020 03:16 pm
So how serious is the loss of a single tile to Starship? Presumably there are some areas where loss of a tile would be catastrophic, but what percentage? 10%, 50% 90%. How survivable is the loss of 1 tile and how likely is the loss of 1 tile going to lead to the loss of a lot more down wind? Or is this the $64,000 question?
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 08/12/2020 03:41 pm
So how serious is the loss of a single tile to Starship? Presumably there are some areas where loss of a tile would be catastrophic, but what percentage? 10%, 50% 90%. How survivable is the loss of 1 tile and how likely is the loss of 1 tile going to lead to the loss of a lot more down wind? Or is this the $64,000 question?

Nobody outside of SpaceX knows for sure, but I think there's a general sense among most observers that loss of any single tile will not lead to the loss of the vehicle.

This isn't like the shuttle where there was aluminum underneath with a low melting temperature.  This is stainless steel, with a very high melting temperature.  Heating absorbed through one missing tile will be transferred over a wide area of the steel skin.
Title: Re: Starship heat shield
Post by: envy887 on 08/12/2020 04:05 pm
So how serious is the loss of a single tile to Starship? Presumably there are some areas where loss of a tile would be catastrophic, but what percentage? 10%, 50% 90%. How survivable is the loss of 1 tile and how likely is the loss of 1 tile going to lead to the loss of a lot more down wind? Or is this the $64,000 question?

Nobody outside of SpaceX knows for sure, but I think there's a general sense among most observers that loss of any single tile will not lead to the loss of the vehicle.

This isn't like the shuttle where there was aluminum underneath with a low melting temperature.  This is stainless steel, with a very high melting temperature.  Heating absorbed through one missing tile will be transferred over a wide area of the steel skin.

Stainless is a lousy conductor and the conduction path in the lateral direction is very thin, so I wouldn't expect heat to go sideways far from the patch directly under a missing tile. What it will do is heat up and then radiatively transfer at t^4 to the rest of the tank interior. Since stainless can tolerate a considerably higher temp than aluminum, the t^4 heat transfer is much, much higher, and can easily reach equilibrium with ~100 kW/m^2 heat flux on the windward side.

Since the underside of 1 tile is ~0.1 square m, and the rest of the tank interior is around 100 to 1000 square m, the heat flux at the rest of the tank is very low. So losing 1 tile is probably not an issue at all. Losing 10 tiles might be a problem. Losing 1000 is probably a very serious issue, since that would be a large hot spot that can't shed enough heat to the inside of the vehicle to maintain equilibrium while still cool enough for stainless to maintain enough strength to hold tank pressure.
Title: Re: Starship heat shield
Post by: intelati on 08/12/2020 04:15 pm
So how serious is the loss of a single tile to Starship? Presumably there are some areas where loss of a tile would be catastrophic, but what percentage? 10%, 50% 90%. How survivable is the loss of 1 tile and how likely is the loss of 1 tile going to lead to the loss of a lot more down wind? Or is this the $64,000 question?

Nobody outside of SpaceX knows for sure, but I think there's a general sense among most observers that loss of any single tile will not lead to the loss of the vehicle.

This isn't like the shuttle where there was aluminum underneath with a low melting temperature.  This is stainless steel, with a very high melting temperature.  Heating absorbed through one missing tile will be transferred over a wide area of the steel skin.

Stainless is a lousy conductor and the conduction path in the lateral direction is very thin, so I wouldn't expect heat to go sideways far from the patch directly under a missing tile. What it will do is heat up and then radiatively transfer at t^4 to the rest of the tank interior. Since stainless can tolerate a considerably higher temp than aluminum, the t^4 heat transfer is much, much higher, and can easily reach equilibrium with ~100 kW/m^2 heat flux on the windward side.

Since the underside of 1 tile is ~0.1 square m, and the rest of the tank interior is around 100 to 1000 square m, the heat flux at the rest of the tank is very low. So losing 1 tile is probably not an issue at all. Losing 10 tiles might be a problem. Losing 1000 is probably a very serious issue, since that would be a large hot spot that can't shed enough heat to the inside of the vehicle to maintain equilibrium while still cool enough for stainless to maintain enough strength to hold tank pressure.

Bringing up a good point. It's not that Starship can lose 100 tiles. It's 100 tiles in a localized area. Just spitballing a figure here, it should be something like lose 'more than 5 tiles in one 10 sqm. area, and no more than 1000 overall'  or something like that.

With the limited conduction, failures away from one another should be mostly independent as long as they are isolated.
Title: Re: Starship heat shield
Post by: DistantTemple on 08/12/2020 04:16 pm

The white tubes are ceramic fire rope / furnace gasket.

It is more likely that it is a rigid ceramic composite. My guess would be alumina fiber based.

John

What purpose?

I was thinking that if the tubes are soft they would allow some tile float while buffering between the tile and skin.

Phil

- I think there are some misconceptions about the nature of rigid alumina insulation based tiles. They are very fragile. They have the consistency of foam insulation. They have very little strength. Without their protective outer covering, you can poke holes in it with your pinky. If you want to mechanically fasten one you need to embed something in the insulation block to anchor to. That is what you are seeing with the ceramic tubes dangling from the studs.  The little spiral fittings would do the same for the small hex tile.

- The ceramic rope Elon mentioned has a different purpose. It is use to insulate between tiles.

-  The ceramic rope material, or Nomex felt, could also be used to seal and isolate the underside of the brittle tile from the vehicle.

John
I thought SX was using much stronger tiles... not Alumina ones! The SX pictures of testing them last year.... left me with the impression of a glazed metallic tile. Elon does say that the backs will be hot and radiate a lot of heat! There were discussions about dispersing heat energy, and reflection, etc.
So I was very surprised to see the tiles apparently broken during the test on SN5 last week!
I expect the vibration is extreme, and maybe the extra stiffening on SN6's skirt will help a number of issues including reducing vibration.... although when the VacRaptors are fixed to the skirt..... !!!!! that will be another story!
Title: Re: Starship heat shield
Post by: DistantTemple on 08/12/2020 04:53 pm
The nature and form of the "rope" insulation:
Because a vast quantity of this type of product will be used, SX can design it in a form that best suits the SS. Its current cheapness, standard shape, size, quality and utility, are no longer important, if SX needs a quantity that will allow easy and cheap mass-production of their design.
The pieces we have seen on SN5 look as if (some of them) were anchored on the studs.... which is odd as the picture of the "X" of tiles on SN6 appears to show them trapped aligned under the tile edges.

Other options:
A large or continuous sheet covering all/most of the tiled surface. Cons: weight?  spread of tiles being ripped off! PROs: easy, anchored on all pins, protects hull evenly from radited heat as well as plasma, may cushion vibration, stops plasma path to hull however it gets behind a tile.

Formed into"Y" sections, for one vertex meeting point, (or several "Y"'s at once). In manufacture a thin sheet could be cut and folded so that "unwanted" material from the centre of each tile is used to thicken the area behind the tile joints. The arms of the "Y" are wide enough to impale (into pre-formed holes) onto the tile mounting pins. PRO's. Same "weight" (or thinner) material provides much better cushion and insulation at the tile gaps. Three fixed points for each "Y" provide reliable anchoring.

Moulded into "U" cross section. If the tile edges turn back towards the hull as if folded, then a "U" cross-sectioned fibre pad can "contain" two adjacent edges, and even have a tongue that separates them.... now it is an "E" with each gap (in the "E") containing one tile edge! PRO's This allows damping of vibration of tiles, removal of contact/impact between tiles, and a complex and so secure obstruction of all plasma paths.

I don't know how these could be made, whether layers of fabric would be built up, and sewn, or whether fibres could be blown and compressed into a mould....  Whether it needs any stainless wire stiffening etc. But although it has gone from "off the shelf" rope to a carefully designed manufactured product, it could be very cost effective if it  is:
1. very secure and naturally stable in its location,
2. saves tile damage through tile vibration, and contact with adjacent tiles.
3. provides an excellent secure barrier to any plasma or hot gas ingress between tile gaps - or even between adjacent tiles!
4. if it can additionally reduce the risk of single tile loss spreading by frustrating the airflow's path under the next tile then it could be an outstanding solution.
Edit: The "E" version may safely allow slightly wider tile gaps, and more tolerance for fitting the tiles because it so thoroughly protects the gaps.
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/12/2020 04:55 pm

The white tubes are ceramic fire rope / furnace gasket.

It is more likely that it is a rigid ceramic composite. My guess would be alumina fiber based.

John

What purpose?

I was thinking that if the tubes are soft they would allow some tile float while buffering between the tile and skin.

Phil

- I think there are some misconceptions about the nature of rigid alumina insulation based tiles. They are very fragile. They have the consistency of foam insulation. They have very little strength. Without their protective outer covering, you can poke holes in it with your pinky. If you want to mechanically fasten one you need to embed something in the insulation block to anchor to. That is what you are seeing with the ceramic tubes dangling from the studs.  The little spiral fittings would do the same for the small hex tile.

- The ceramic rope Elon mentioned has a different purpose. It is use to insulate between tiles.

-  The ceramic rope material, or Nomex felt, could also be used to seal and isolate the underside of the brittle tile from the vehicle.

John
I thought SX was using much stronger tiles... not Alumina ones! The SX pictures of testing them last year.... left me with the impression of a glazed metallic tile. Elon does say that the backs will be hot and radiate a lot of heat! There were discussions about dispersing heat energy, and reflection, etc.
So I was very surprised to see the tiles apparently broken during the test on SN5 last week!
I expect the vibration is extreme, and maybe the extra stiffening on SN6's skirt will help a number of issues including reducing vibration.... although when the VacRaptors are fixed to the skirt..... !!!!! that will be another story!
Well I know very little about alumina tiles, other than alumina is refractory and I would suspect breakable like china. However a quick internet search produced this:
https://www.morgantechnicalceramics.com/en-gb/materials/alumina/98-alumina/
I was a little surprised to say the least.

Another point of note alumina is white and I would expect alumina tiles to be white or shades of grey perhaps if something has been added. But SpaceX tiles are black, so either they're not alumina or they're mixed with a lot of secret sauce to make them black. But thinking back the shuttle tiles were black and made out of silica which is also white so what am I missing?
Title: Re: Starship heat shield
Post by: philw1776 on 08/12/2020 05:52 pm

The white tubes are ceramic fire rope / furnace gasket.

It is more likely that it is a rigid ceramic composite. My guess would be alumina fiber based.

John

What purpose?

I was thinking that if the tubes are soft they would allow some tile float while buffering between the tile and skin.

Phil

- I think there are some misconceptions about the nature of rigid alumina insulation based tiles. They are very fragile. They have the consistency of foam insulation. They have very little strength. Without their protective outer covering, you can poke holes in it with your pinky. If you want to mechanically fasten one you need to embed something in the insulation block to anchor to. That is what you are seeing with the ceramic tubes dangling from the studs.  The little spiral fittings would do the same for the small hex tile.

- The ceramic rope Elon mentioned has a different purpose. It is use to insulate between tiles.

-  The ceramic rope material, or Nomex felt, could also be used to seal and isolate the underside of the brittle tile from the vehicle.

John
I thought SX was using much stronger tiles... not Alumina ones! The SX pictures of testing them last year.... left me with the impression of a glazed metallic tile. Elon does say that the backs will be hot and radiate a lot of heat! There were discussions about dispersing heat energy, and reflection, etc.
So I was very surprised to see the tiles apparently broken during the test on SN5 last week!
I expect the vibration is extreme, and maybe the extra stiffening on SN6's skirt will help a number of issues including reducing vibration.... although when the VacRaptors are fixed to the skirt..... !!!!! that will be another story!

Has it been definitively ruled out that the missing tiles were not struck by debris from the test stand, etc?  If not, maybe another reason Musk wants to do more GSE testing hops.
Title: Re: Starship heat shield
Post by: midaswelby on 08/12/2020 05:56 pm
I'm an old worn out construction guy, not a rocket scientist.  But the very interesting discussion and speculation on this thread regarding heat tile application has gotten me thinking.  It seems clear that there is going to be an application of the heat resistant rope, per Elon tweets, but that may evolve in a number of ways.  My limited understanding of heat tile properties notwithstanding, it seems to me that they can be manufactured in a variety of shapes and sizes.  If the SX tiles are made to spec, then perhaps there could be a groove or recessed trough in the backside that would accept a specific dimension of the heat seal rope.  If there is a small amount of pressure induced on the fabric when tiles are attached and torqued, the incompatible expansion and contraction of the tile and tank skin might be mitigated to an acceptable value.  Likewise, if there is a "blanket" of a similar material covering the entire region that has had tile mount studs installed, this could possibly provide additional flexibility and insulative properties to help with absorption of vibration and thermal expansion/contraction, and allow for the slight offsets associated with placing flat tiles on convex surfaces.  I have to admit that the visual of installing fiberglass batt insulation in my past came to mind.  Insulative, lightweight, conforms to many different shapes, can be compressed or not.  But most of all, glass fibers, manufactured to various specs.  Just my two cents.  Now I'm back to reading what the smart folks write!   ;D
Title: Re: Starship heat shield
Post by: Kazioo on 08/12/2020 06:19 pm
So how serious is the loss of a single tile to Starship? Presumably there are some areas where loss of a tile would be catastrophic, but what percentage? 10%, 50% 90%. How survivable is the loss of 1 tile and how likely is the loss of 1 tile going to lead to the loss of a lot more down wind? Or is this the $64,000 question?

Nobody outside of SpaceX knows for sure, but I think there's a general sense among most observers that loss of any single tile will not lead to the loss of the vehicle.

This isn't like the shuttle where there was aluminum underneath with a low melting temperature.  This is stainless steel, with a very high melting temperature.  Heating absorbed through one missing tile will be transferred over a wide area of the steel skin.

Relevant video

https://youtu.be/BswkvaAaqSM?t=162

- 700 heat shield tiles damaged
- 1 tile lost
- survived thanks to a steel plate
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 08/12/2020 06:38 pm
Relevant video

- 700 heat shield tiles damaged
- 1 tile lost
- survived thanks to a steel plate

Scary!

It's good to know that Starship's tiles won't have a foam-and-ice-covered tank or SRBs nearby that might shed material that could impact the tiles, and that it will be steel under the entire tiled area.
Title: Re: Starship heat shield
Post by: r8ix on 08/12/2020 06:59 pm
The problem with the discussion above is that Starship has to be ready for immediate reuse >90% of the time. Loss of single tile is not acceptable in that scenario…
Title: Re: Starship heat shield
Post by: OTV Booster on 08/12/2020 07:11 pm

The white tubes are ceramic fire rope / furnace gasket.

It is more likely that it is a rigid ceramic composite. My guess would be alumina fiber based.

John
What purpose?


I was thinking that if the tubes are soft they would allow some tile float while buffering between the tile and skin.


Phil

https://twitter.com/elonmusk/status/1171308928476385281 (https://twitter.com/elonmusk/status/1171308928476385281)
That tweet is 11 months stale. Mary's pic from this afternoon shows something that might be called marshmallowy sandwiched under some of the tiles. Elon was talking about furnace rope or something similar stuffed in the space between tiles.


Those tubes in my earlier posts are impaled on the studs. Can't see them sealing anything.


Phil
What’s to say that it’s not a more rigid material encased by the rope? Basically a composite of sorts. The tie offs and fraying at the end to me indicate the ceramic rope while the rigidity of the pieces points toward something rigid.

I agree with other posters, wouldn’t you want some sort of compliance between tiles, in addition to underneath with the felt like padding as described by Livingjw?
An interesting link on thermal rope from old_geez on the discussion thread. It has a wire inside.
https://www.morganthermalceramics.com/media/2596/ropes_murugappa.pdf (https://www.morganthermalceramics.com/media/2596/ropes_murugappa.pdf)


I'm not sure what you mean by compliance. height?  It would do that. I was just talking about sealing.


Looking at the third tile down in the crotch of the X. Look at the reflection of the edge. It might be an undercut to help trap some rope. The tiles above it be the same thing but boogered in manufacturing.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/12/2020 07:11 pm

The white tubes are ceramic fire rope / furnace gasket.

It is more likely that it is a rigid ceramic composite. My guess would be alumina fiber based.

John
What purpose?


I was thinking that if the tubes are soft they would allow some tile float while buffering between the tile and skin.


Phil

https://twitter.com/elonmusk/status/1171308928476385281 (https://twitter.com/elonmusk/status/1171308928476385281)
That tweet is 11 months stale. Mary's pic from this afternoon shows something that might be called marshmallowy sandwiched under some of the tiles. Elon was talking about furnace rope or something similar stuffed in the space between tiles.


Those tubes in my earlier posts are impaled on the studs. Can't see them sealing anything.


Phil
What’s to say that it’s not a more rigid material encased by the rope? Basically a composite of sorts. The tie offs and fraying at the end to me indicate the ceramic rope while the rigidity of the pieces points toward something rigid.

I agree with other posters, wouldn’t you want some sort of compliance between tiles, in addition to underneath with the felt like padding as described by Livingjw?
Title: Re: Starship heat shield
Post by: Johnnyhinbos on 08/12/2020 07:12 pm
It makes me really happy to see the heat shield tile X... the tanks are probably some of the easiest parts of Starship to build, but it's the fine details that have had me a little worried, like the amount of tiles they're going to need to cover the ship, or the connections between the aero surfaces and the body. Seeing the initial results of their (officially labeled) heat shield robot is huge - a few of those robots in a tent could bang out an entire SS heat shield in no time.

tl;dr: The heat shield mounting robot to me is a sign of them entering the "next level" of testing, where (to use the parlance of our times) "**** gets real"

Agree, in fact the test that did placement in a logo, may have actually been a test to design and automate tile placement accurately. They may have just done the logo in CAD/robotic software and just said "go for it".... and this is initial results.
Replied to this over in the heat shield thread for consistency.

So you think the tile placement is automated eh? Personally, I highly doubt it at this stage. I think the bots are stud welding as the cylinder is rotated. Automated stud feed and welding is an established process that is easily off the shelf. Perhaps at this point the cylinder isn't even rotated. Picking and placing tiles, while fastening them to the three studs (and possibly placing a backfill behind the tile), I think, is too far along the automation path at this point.

https://www.youtube.com/watch?v=-gjj4SxYo4Q (https://www.youtube.com/watch?v=-gjj4SxYo4Q)


https://www.youtube.com/watch?v=b0rk6Eiv94I

Title: Re: Starship heat shield
Post by: ChrisWilson68 on 08/12/2020 07:16 pm
The problem with the discussion above is that Starship has to be ready for immediate reuse >90% of the time. Loss of single tile is not acceptable in that scenario…

Sure, I don't think anyone thinks losing tiles is meant to be a common occurrence.  I think it's more like having crumple zones in your car -- you try to avoid ever needing them, but if something bad happens, you don't want anyone to die.
Title: Re: Starship heat shield
Post by: DistantTemple on 08/12/2020 07:16 pm
The problem with the discussion above is that Starship has to be ready for immediate reuse >90% of the time. Loss of single tile is not acceptable in that scenario…
1. Still its not a loss of the ship.
2. We have a ways to go before immediate reuse.
3. Even accepting what you say, how much it violates your standard, is dependent on the frequency and area of tile loss, and severity of heating. If the frequency of such issues is <10% then it fits your target.

I take it for granted that they will strictly not just clip a new tile in place, but the loss will trigger a close inspection, including to somehow assess the level of heat damage to the hull/tank. I assume once any annealing has happened, a section would have to be cut out, as the cold-rolled properties would be lost, so that SS is out of action for a week(s?) or more. However if the properties of the steel are within tolerance (however that can be established?) then its a new tile and off you go.
Title: Re: Starship heat shield
Post by: r8ix on 08/12/2020 08:13 pm
The problem with the discussion above is that Starship has to be ready for immediate reuse >90% of the time. Loss of single tile is not acceptable in that scenario…
1. Still its not a loss of the ship.
2. We have a ways to go before immediate reuse.
3. Even accepting what you say, how much it violates your standard, is dependent on the frequency and area of tile loss, and severity of heating. If the frequency of such issues is <10% then it fits your target.

I take it for granted that they will strictly not just clip a new tile in place, but the loss will trigger a close inspection, including to somehow assess the level of heat damage to the hull/tank. I assume once any annealing has happened, a section would have to be cut out, as the cold-rolled properties would be lost, so that SS is out of action for a week(s?) or more. However if the properties of the steel are within tolerance (however that can be established?) then its a new tile and off you go.
1&2, Agreed. Point 3, however doesn’t work out statistically. With a fleet of 1000 Starships, and an expectation that they should achieve 10 flights without significant refurbishment, and 8000 tiles per Starship, you’d have to have fewer than 1% with any tile issues on any flight, which implies 6 nines average reliability per tile per flight. So the goal has to be essentially perfect tile performance, consistently, or fleet reusability degrades very quickly.
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/12/2020 08:55 pm
Why are the tiles black?
Title: Re: Starship heat shield
Post by: envy887 on 08/12/2020 10:55 pm
Why are the tiles black?

For high emissivity. They get rid of heat by radiation.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/12/2020 11:06 pm

The white tubes are ceramic fire rope / furnace gasket.

It is more likely that it is a rigid ceramic composite. My guess would be alumina fiber based.

John
What purpose?


I was thinking that if the tubes are soft they would allow some tile float while buffering between the tile and skin.


Phil

https://twitter.com/elonmusk/status/1171308928476385281 (https://twitter.com/elonmusk/status/1171308928476385281)
That tweet is 11 months stale. Mary's pic from this afternoon shows something that might be called marshmallowy sandwiched under some of the tiles. Elon was talking about furnace rope or something similar stuffed in the space between tiles.


Those tubes in my earlier posts are impaled on the studs. Can't see them sealing anything.


Phil
What’s to say that it’s not a more rigid material encased by the rope? Basically a composite of sorts. The tie offs and fraying at the end to me indicate the ceramic rope while the rigidity of the pieces points toward something rigid.

I agree with other posters, wouldn’t you want some sort of compliance between tiles, in addition to underneath with the felt like padding as described by Livingjw?
An interesting link from old_geez on the prototype discussion thread. That rope has a stainless wire core.
https://www.morganthermalceramics.com/media/2596/ropes_murugappa.pdf (https://www.morganthermalceramics.com/media/2596/ropes_murugappa.pdf)


I'm not sure what you mean by compliance. Height? A good thing but not the sealing I was getting at.


If you look at the reflection of the left bottom most tile in the crotch of the X, it looks like there may be a recess along the edge on the back of the tile. The ones above it look irregular. Maybe boogered during manufacture?


A rope that squishes enough to span between tiles? Pre applied or pounded in? Or maybe something with a T cross section with the stem up? I'm trying to picture something that stops flow intrusion and maybe water intrusion, while keeping a free floating tile from chafing the skin. If it applies a slight preload of the tile against the mechanical attachment on the pins that might help damp vibration but has the potential of increasing chafing at that point.


I'm guessing SS EDL will follow F9's landing attempts for awhile getting the tiles to work right. It does have the advantage of upping the ante on temps a bit at a time Instead of the all or nothing of landing.


It looks like the hardest piece of the puzzle.


Phil

Title: Re: Starship heat shield
Post by: Twark_Main on 08/12/2020 11:06 pm
Why are the tiles black?

For high emissivity. They get rid of heat by radiation.

At 2300 F, only 0.1% of the black body curve energy is emitted in the visible spectrum. Whether it's black in the IR matters, but its reflectivity in the visible spectrum is almost irrelevant (but it has the downside of absorbing more solar radiation).
Title: Re: Starship heat shield
Post by: CJ on 08/12/2020 11:16 pm
The problem with the discussion above is that Starship has to be ready for immediate reuse >90% of the time. Loss of single tile is not acceptable in that scenario…
1. Still its not a loss of the ship.

Per the video Kazioo posted (thanks!), on Atlantis the missing tile caused burn-though of the steel plate. Only the aluminum under it remained. I have no clue how thick that "steel plate" was, now what steeel it was made of, but unless Starship's hull is thicker (or more resistant) a similar burn-though could result in loss of vehicle; it'd lose all pressure-derived strength if this occurred on the skin of one of the prop tanks.

My hunch is that Space-X might size the tiles small enough that losing one will not result in LOV. (assuming going smaller is possible, and assuming that they have not already done this).
Title: Re: Starship heat shield
Post by: Oersted on 08/12/2020 11:20 pm
Odd that they selected three pin arrangement (-Surprised Pikachu), all three pin tiles at SN5 were fractured, but still attached

The three-pin arrangement assures three-sided symmetry of the tile which simplifies the production process a lot: the tiles basically have no fixed orientation but can be turned "any way you may wish".
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 08/12/2020 11:21 pm
The problem with the discussion above is that Starship has to be ready for immediate reuse >90% of the time. Loss of single tile is not acceptable in that scenario…
1. Still its not a loss of the ship.

Per the video Kazioo posted (thanks!), on Atlantis the missing tile caused burn-though of the steel plate. Only the aluminum under it remained. I have no clue how thick that "steel plate" was, now what steeel it was made of, but unless Starship's hull is thicker (or more resistant) a similar burn-though could result in loss of vehicle; it'd lose all pressure-derived strength if this occurred on the skin of one of the prop tanks.

My hunch is that Space-X might size the tiles small enough that losing one will not result in LOV. (assuming going smaller is possible, and assuming that they have not already done this).

The far different shape and density of a re-entering Starship make it hard to draw conclusions from a fact about the shuttle.
Title: Re: Starship heat shield
Post by: Oersted on 08/12/2020 11:24 pm
It's good to know that Starship's tiles won't have a foam-and-ice-covered tank or SRBs nearby that might shed material that could impact the tiles, and that it will be steel under the entire tiled area.

There may still be parts of the upper body flaps that could fall off and impact the fuselage. And all the tiles on those flaps and on the upper fuselage that could fall off and damage the lower flaps, leg covers and fuselage.

Unfortunately Starship won´t be completely impervious to self-inflicted damage during launch...
Title: Re: Starship heat shield
Post by: envy887 on 08/12/2020 11:37 pm
Why are the tiles black?

For high emissivity. They get rid of heat by radiation.

At 2300 F, only 0.1% of the black body curve energy is emitted in the visible spectrum. Whether it's black in the IR matters, but its reflectivity in the visible spectrum is almost irrelevant (but it has the downside of absorbing more solar radiation).
I've read some research into materials that are highly reflective in visible and also high-emissivity in IR, but as far as I can tell they aren't common.
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 08/12/2020 11:37 pm
It's good to know that Starship's tiles won't have a foam-and-ice-covered tank or SRBs nearby that might shed material that could impact the tiles, and that it will be steel under the entire tiled area.

There may still be parts of the upper body flaps that could fall off and impact the fuselage. And all the tiles on those flaps and on the upper fuselage that could fall off and damage the lower flaps, leg covers and fuselage.

Unfortunately Starship won´t be completely impervious to self-inflicted damage during launch...

I agree, not completely impervious, but I think far, far less vulnerable to it.  I don't remember anyone ever worrying that a shuttle tile would fall off and damage another shuttle tile.  If you have tiles falling off from above, I'd suggest you already have a serious problem with your tiles.

It seems a lot different to me than foam on the ET or ablative heat shield material on the tops of the SRBs.  Starship is meant to be rapidly reusable many times over, so it has to be designed to be much more sturdy, not something pieces will just fall off of.
Title: Re: Starship heat shield
Post by: envy887 on 08/12/2020 11:39 pm
It's good to know that Starship's tiles won't have a foam-and-ice-covered tank or SRBs nearby that might shed material that could impact the tiles, and that it will be steel under the entire tiled area.

There may still be parts of the upper body flaps that could fall off and impact the fuselage. And all the tiles on those flaps and on the upper fuselage that could fall off and damage the lower flaps, leg covers and fuselage.

Unfortunately Starship won´t be completely impervious to self-inflicted damage during launch...

If tiles are falling off, they have bigger issues than whether they hit something downstream.
Title: Re: Starship heat shield
Post by: DistantTemple on 08/12/2020 11:41 pm
The problem with the discussion above is that Starship has to be ready for immediate reuse >90% of the time. Loss of single tile is not acceptable in that scenario…
1. Still its not a loss of the ship.

Per the video Kazioo posted (thanks!), on Atlantis the missing tile caused burn-though of the steel plate. Only the aluminum under it remained. I have no clue how thick that "steel plate" was, now what steeel it was made of, but unless Starship's hull is thicker (or more resistant) a similar burn-though could result in loss of vehicle; it'd lose all pressure-derived strength if this occurred on the skin of one of the prop tanks.

My hunch is that Space-X might size the tiles small enough that losing one will not result in LOV. (assuming going smaller is possible, and assuming that they have not already done this).
In that video, it was the Alumimium that burned through(Edit you are correct) and it was lucky that there was a steel plate underneath that was in the process of burning through, but "luckily" had not succumbed by the time they got through reentry. It was the steel and the luck that the missing tile was just there that saved them.
However that only reduces but does not negate your argument.
The reentry profile of Shuttle and Starship are totally different. I don't think the shuttle "skydived" at about 90 degrees to the apparent airflow, like the Starship is planning to. If I remember rightly, argument on this site was the broard smooth cylinder of the Starship, will create a shock wave some metres off of the surface where much of the heating will take place. The smooth cylindrical shape will present less "hot spots" than the wings etc of the Shuttle. However comes the reply, the Starship has flippers/dragerons/whatever sticking out. I suggest these are less of a risk than the shuttle's wings etc, as if there is heat damage or burn through, that of itself will not cause an immediate breakup of the vehicle, as they are separate add-ons and not part of the main pressure vessel. They could cause a lack of controll or uncontrollable roll etc, but with their function as a big airbrake, I would guess they could be badly damaged befor the ship was doomed. A burn through on the shuttle wing risked fast colabse of the aluminium structure of the wing, asymmetric force on the two wins, uncontrollable spin and immediate breakup. (my interpretation) 
Edit: I watched it gain, yes you are right, it had got through the steel plate and was "working on the Aluminium underneath" So yes steel is vulnerable. However I won't change my whole comment, as the "re-entry profile" is all still relevant.
Title: Re: Starship heat shield
Post by: Twark_Main on 08/12/2020 11:42 pm
Why are the tiles black?

For high emissivity. They get rid of heat by radiation.

At 2300 F, only 0.1% of the black body curve energy is emitted in the visible spectrum. Whether it's black in the IR matters, but its reflectivity in the visible spectrum is almost irrelevant (but it has the downside of absorbing more solar radiation).
I've read some research into materials that are highly reflective in visible and also high-emissivity in IR, but as far as I can tell they aren't common.

Based on this NASA document, I don't see much correlation. High emissivity is the rule, even among white materials and coatings. Achieving low emissivity is the trick.

https://ntrs.nasa.gov/citations/19840015630
Title: Re: Starship heat shield
Post by: john smith 19 on 08/13/2020 05:38 am
Based on this NASA document, I don't see much correlation. High emissivity is the rule, even among white materials and coatings. Achieving low emissivity is the trick.

https://ntrs.nasa.gov/citations/19840015630
On orbit it's been the ratio of emissivity to absorbance that's been difficult.

Recent work (NASA sponsored IIRC under NAIC and there were posts on it on this site) suggested you could tailor both  the peak emission wavelength and this ratio. IE not a black body. Obviously if you can reduce the tiles absorbance at the wavelengths the shockwave is emitting at while enhancing their emission at their operating temperature that can lower heat getting into the vehicle quite a lot.
Title: Re: Starship heat shield
Post by: john smith 19 on 08/13/2020 05:50 am
Well I know very little about alumina tiles, other than alumina is refractory and I would suspect breakable like china. However a quick internet search produced this:
https://www.morgantechnicalceramics.com/en-gb/materials/alumina/98-alumina/
I was a little surprised to say the least.

Another point of note alumina is white and I would expect alumina tiles to be white or shades of grey perhaps if something has been added. But SpaceX tiles are black, so either they're not alumina or they're mixed with a lot of secret sauce to make them black. But thinking back the shuttle tiles were black and made out of silica which is also white so what am I missing?
Welcome to the world of technical ceramics.   :)

Here there are lots of different grades that have either different formulations or heat treatments that produce substantially different properties.

Black coatings on Shuttle tiles were IIRC a fine colored glass frit that was baked on IOW an enamel coating.

What was unusual about the shuttle tiles was they were made of fibers that were formed into a rigid foam
Title: Re: Starship heat shield
Post by: john smith 19 on 08/13/2020 06:00 am
If there is a small amount of pressure induced on the fabric when tiles are attached and torqued, the incompatible expansion and contraction of the tile and tank skin might be mitigated to an acceptable value.  Likewise, if there is a "blanket" of a similar material covering the entire region that has had tile mount studs installed, this could possibly provide additional flexibility and insulative properties to help with absorption of vibration and thermal expansion/contraction, and allow for the slight offsets associated with placing flat tiles on convex surfaces.  I have to admit that the visual of installing fiberglass batt insulation in my past came to mind. 
And you'd be right.

Shuttle blanket was about 1/4 the installation cost of tile. SoA blankets are refractory fiber (not glass, has a higher temp rating) in superalloy foil boxes to make them waterproof. They are used on the X37b. Not sure if they are bonded or bolted to the airframe.

What's different about starship tiles is that the goal is to make them all the same, whereas shuttle tiles were almost all unique in size, shape and thickness. Not interchangeable and a PITA for inventory management.

While blankets can cover large ares in a single piece they have 2 issues. 1) They are made to order b) If the blanket is blown off the whole area is exposed.

Oh, and who wants to fly into space wrapped in a quilt (albeit a very high tech quilt) ?  :)
Title: Re: Starship heat shield
Post by: Kazioo on 08/13/2020 10:43 am
The problem with the discussion above is that Starship has to be ready for immediate reuse >90% of the time. Loss of single tile is not acceptable in that scenario…
1. Still its not a loss of the ship.

Per the video Kazioo posted (thanks!), on Atlantis the missing tile caused burn-though of the steel plate. Only the aluminum under it remained. I have no clue how thick that "steel plate" was, now what steeel it was made of, but unless Starship's hull is thicker (or more resistant) a similar burn-though could result in loss of vehicle; it'd lose all pressure-derived strength if this occurred on the skin of one of the prop tanks.

My hunch is that Space-X might size the tiles small enough that losing one will not result in LOV. (assuming going smaller is possible, and assuming that they have not already done this).
In that video, it was the Alumimium that burned through(Edit you are correct) and it was lucky that there was a steel plate underneath that was in the process of burning through, but "luckily" had not succumbed by the time they got through reentry. It was the steel and the luck that the missing tile was just there that saved them.
However that only reduces but does not negate your argument.
The reentry profile of Shuttle and Starship are totally different. I don't think the shuttle "skydived" at about 90 degrees to the apparent airflow, like the Starship is planning to. If I remember rightly, argument on this site was the broard smooth cylinder of the Starship, will create a shock wave some metres off of the surface where much of the heating will take place. The smooth cylindrical shape will present less "hot spots" than the wings etc of the Shuttle. However comes the reply, the Starship has flippers/dragerons/whatever sticking out. I suggest these are less of a risk than the shuttle's wings etc, as if there is heat damage or burn through, that of itself will not cause an immediate breakup of the vehicle, as they are separate add-ons and not part of the main pressure vessel. They could cause a lack of controll or uncontrollable roll etc, but with their function as a big airbrake, I would guess they could be badly damaged befor the ship was doomed. A burn through on the shuttle wing risked fast colabse of the aluminium structure of the wing, asymmetric force on the two wins, uncontrollable spin and immediate breakup. (my interpretation) 
Edit: I watched it gain, yes you are right, it had got through the steel plate and was "working on the Aluminium underneath" So yes steel is vulnerable. However I won't change my whole comment, as the "re-entry profile" is all still relevant.


That's probably why as of February 2020 SpaceX still considered using transpiration cooling around flap joints:

https://twitter.com/elonmusk/status/1228396138870407169

https://twitter.com/elonmusk/status/1228400791880269824

After the switch to tiles there was the plan to add it to hot spots:

https://twitter.com/elonmusk/status/1107380559834046465

I suppose this common belief that SpaceX completely scrapped any plans for transpiration cooling is, I think, a misunderstanding.
Title: Re: Starship heat shield
Post by: kevinstout on 08/13/2020 11:06 am
What is the primary driver for the tile size?  I.e. why not bigger?


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Title: Re: Starship heat shield
Post by: olemars on 08/13/2020 11:14 am
What is the primary driver for the tile size?  I.e. why not bigger?


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Curvature is probably one reason. It'll be interesting to see how it looks when they start tiling the nosecone where you get curvature in two dimensions.
Title: Re: Starship heat shield
Post by: Frogstar_Robot on 08/13/2020 11:20 am
What is the primary driver for the tile size?  I.e. why not bigger?


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Curvature is probably one reason. It'll be interesting to see how it looks when they start tiling the nosecone where you get curvature in two dimensions.

Is not possible to create curved tiles?
Title: Re: Starship heat shield
Post by: KBK on 08/13/2020 12:42 pm
Odd that they selected three pin arrangement (-Surprised Pikachu), all three pin tiles at SN5 were fractured, but still attached

The three-pin arrangement assures three-sided symmetry of the tile which simplifies the production process a lot: the tiles basically have no fixed orientation but can be turned "any way you may wish".

Three points also disallows some forms of unwanted resonance vibration modes to arise. this, when considering potential resonance modes vs stability vs mounting vs ability to handle adverse issues (adjacent tile loss) vs ability to tweak position vs expansion/contraction (unequal or otherwise), etc.

As you go through the assessment of one, two, three, and four mount points, three is the only one that has the potential to tick all the boxes well enough to get the job properly done.

Six sides also reduces the issue of edge separation/contraction in unequal loading of expansion/contraction, and so on. As we go through the 3,4,5,6,7, etc number of sides, 6 is the sweet spot. When combined with the optimal 3 point mount. Both are in their 'sweet spot', so they make an almost natural pairing...
Title: Re: Starship heat shield
Post by: _MECO on 08/13/2020 04:09 pm
What is the primary driver for the tile size?  I.e. why not bigger?


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Curvature is probably one reason. It'll be interesting to see how it looks when they start tiling the nosecone where you get curvature in two dimensions.

Is not possible to create curved tiles?

Possible; but expensive. Why waste resources making many specialist tile types when you can get good at making a minimal number of tile types over and over again as cheaply as possible? Sticking to only two or three types expedites manufacturing and repair, not to mention reducing overhead costs. That's not to say there won't be any curved tiles. I personally just expect a minimum of different types where possible.

Anyway, the smaller the standard hex tile is, the tighter the curvature that can be conformed to without needing specialist curved tiles. There's probably some sort of efficiency maxima in there where the tiles are small enough that the most development and production resources are saved while also large enough as to be sturdy against vibration/expansion and not have too much weight in mounting brackets/take too long to install.
Title: Re: Starship heat shield
Post by: Johnnyhinbos on 08/13/2020 04:42 pm
Folks have talked about resonances and flight / temperature flexing, but I've not seen a single post about the obvious elephant in the room...

All one has to do is to simply look at one of these full up SN[x] tank section to see the issue - without internal pressure, the cylinder is loaded with deformations, and deformations that aren't steady state. How will the tiles, and associated inter-tile fillers, deal with all this natural deformation? I doubt the expectation will be that it will always be pressurized - from before tile installation on. But perhaps? A stiff five ring stack is one thing, but a full up tank section, let along the payload area, is a completely different issue...
Title: Re: Starship heat shield
Post by: Frogstar_Robot on 08/13/2020 04:55 pm
What is the primary driver for the tile size?  I.e. why not bigger?


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Curvature is probably one reason. It'll be interesting to see how it looks when they start tiling the nosecone where you get curvature in two dimensions.

Is not possible to create curved tiles?

Possible; but expensive. Why waste resources making many specialist tile types when you can get good at making a minimal number of tile types over and over again as cheaply as possible? Sticking to only two or three types expedites manufacturing and repair, not to mention reducing overhead costs. That's not to say there won't be any curved tiles. I personally just expect a minimum of different types where possible.

Anyway, the smaller the standard hex tile is, the tighter the curvature that can be conformed to without needing specialist curved tiles. There's probably some sort of efficiency maxima in there where the tiles are small enough that the most development and production resources are saved while also large enough as to be sturdy against vibration/expansion and not have too much weight in mounting brackets/take too long to install.

You only need one curved tile type for the main cylinder, and can still use a hex tile for nose. So that is two tile types. I don't think any of your reasoning applies here.
Title: Re: Starship heat shield
Post by: rakaydos on 08/13/2020 05:01 pm
What is the primary driver for the tile size?  I.e. why not bigger?


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Curvature is probably one reason. It'll be interesting to see how it looks when they start tiling the nosecone where you get curvature in two dimensions.

Is not possible to create curved tiles?

Possible; but expensive. Why waste resources making many specialist tile types when you can get good at making a minimal number of tile types over and over again as cheaply as possible? Sticking to only two or three types expedites manufacturing and repair, not to mention reducing overhead costs. That's not to say there won't be any curved tiles. I personally just expect a minimum of different types where possible.

Anyway, the smaller the standard hex tile is, the tighter the curvature that can be conformed to without needing specialist curved tiles. There's probably some sort of efficiency maxima in there where the tiles are small enough that the most development and production resources are saved while also large enough as to be sturdy against vibration/expansion and not have too much weight in mounting brackets/take too long to install.

You only need one curved tile type for the main cylinder, and can still use a hex tile for nose. So that is two tile types. I don't think any of your reasoning applies here.
That's got the reverse problem- the chance of instalation error because you didnt  notice which way the tile is curved.
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/13/2020 05:05 pm
What is the primary driver for the tile size?  I.e. why not bigger?


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Curvature is probably one reason. It'll be interesting to see how it looks when they start tiling the nosecone where you get curvature in two dimensions.

Is not possible to create curved tiles?

Possible; but expensive. Why waste resources making many specialist tile types when you can get good at making a minimal number of tile types over and over again as cheaply as possible? Sticking to only two or three types expedites manufacturing and repair, not to mention reducing overhead costs. That's not to say there won't be any curved tiles. I personally just expect a minimum of different types where possible.

Anyway, the smaller the standard hex tile is, the tighter the curvature that can be conformed to without needing specialist curved tiles. There's probably some sort of efficiency maxima in there where the tiles are small enough that the most development and production resources are saved while also large enough as to be sturdy against vibration/expansion and not have too much weight in mounting brackets/take too long to install.

You only need one curved tile type for the main cylinder, and can still use a hex tile for nose. So that is two tile types. I don't think any of your reasoning applies here.
I don't think that's correct - see the link at the top of the first page of this thread for a diagram. As the diameter of the ship narrows in the nose the hexagons will start to overlap. Each ring of tiles or at least every few rings will need to have a specific shape, you can't use the same tessellated hexagons all the way.
Title: Re: Starship heat shield
Post by: Frogstar_Robot on 08/13/2020 05:26 pm
That's got the reverse problem- the chance of instalation error because you didnt  notice which way the tile is curved.

It is less than a trivial exercise to design a tile that can only be fitted correctly.
Title: Re: Starship heat shield
Post by: Frogstar_Robot on 08/13/2020 05:32 pm
I don't think that's correct - see the link at the top of the first page of this thread for a diagram. As the diameter of the ship narrows in the nose the hexagons will start to overlap. Each ring of tiles or at least every few rings will need to have a specific shape, you can't use the same tessellated hexagons all the way.

I agree, it's not my idea to use a hex tile. I would have a range of curved tiles for the nose. But apparently SpaceX logistics can't handle more than one type of tile?!

I was expecting a technical reason, like the tiles are cast in large flat sheets and then machined into sections. But I think the Shuttle tiles were cast. If so, then it should be eminently feasible to cast curved tiles. Being a regular solid, the SS/SH can be tiled with a relatively small of tile shapes. Obviously, curved tiles fit a curved surface better.

And to head off another lame objection, no, I am not suggesting a huge range of unique tile shapes like the shuttle used.

Seeing as Elon thinks like an engineer, I would expect to see some curved tiles in future iterations.
Title: Re: Starship heat shield
Post by: DistantTemple on 08/13/2020 06:41 pm
The nature and form of the "rope" insulation:
Because a vast quantity of this type of product will be used, SX can design it in a form that best suits the SS. Its current cheapness, standard shape, size, quality and utility, are no longer important, if SX needs a quantity that will allow easy and cheap mass-production of their design.
The pieces we have seen on SN5 look as if (some of them) were anchored on the studs.... which is odd as the picture of the "X" of tiles on SN6 appears to show them trapped aligned under the tile edges.

Other options:
A large or continuous sheet covering all/most of the tiled surface. Cons: weight?  spread of tiles being ripped off! PROs: easy, anchored on all pins, protects hull evenly from radited heat as well as plasma, may cushion vibration, stops plasma path to hull however it gets behind a tile.

Formed into"Y" sections, for one vertex meeting point, (or several "Y"'s at once). In manufacture a thin sheet could be cut and folded so that "unwanted" material from the centre of each tile is used to thicken the area behind the tile joints. The arms of the "Y" are wide enough to impale (into pre-formed holes) onto the tile mounting pins. PRO's. Same "weight" (or thinner) material provides much better cushion and insulation at the tile gaps. Three fixed points for each "Y" provide reliable anchoring.

Moulded into "U" cross section. If the tile edges turn back towards the hull as if folded, then a "U" cross-sectioned fibre pad can "contain" two adjacent edges, and even have a tongue that separates them.... now it is an "E" with each gap (in the "E") containing one tile edge! PRO's This allows damping of vibration of tiles, removal of contact/impact between tiles, and a complex and so secure obstruction of all plasma paths.

I don't know how these could be made, whether layers of fabric would be built up, and sewn, or whether fibres could be blown and compressed into a mould....  Whether it needs any stainless wire stiffening etc. But although it has gone from "off the shelf" rope to a carefully designed manufactured product, it could be very cost effective if it  is:
1. very secure and naturally stable in its location,
2. saves tile damage through tile vibration, and contact with adjacent tiles.
3. provides an excellent secure barrier to any plasma or hot gas ingress between tile gaps - or even between adjacent tiles!
4. if it can additionally reduce the risk of single tile loss spreading by frustrating the airflow's path under the next tile then it could be an outstanding solution.
Edit: The "E" version may safely allow slightly wider tile gaps, and more tolerance for fitting the tiles because it so thoroughly protects the gaps.
Since this is still being discussed in detail, I am re-posting my suggestion, with an ADDED diagram.... The "E" is now only conceptual and not very obvious, but the principle is there still.
I have shown a version that only covers one "Y", but obviously a larger "gasket" covering several would mean less joins, faster installation, and anchoring on more pins.
Assuming there is some slack in the mounting on the pins, maybe a spring clip, my gasket could help keep adjoining surfaces flush,and the gaps even.

PS anyone recommend a free CAD program.... I have looked and tried, but never found!!!!
Title: Re: Starship heat shield
Post by: DistantTemple on 08/13/2020 06:49 pm
Folks have talked about resonances and flight / temperature flexing, but I've not seen a single post about the obvious elephant in the room...

All one has to do is to simply look at one of these full up SN[x] tank section to see the issue - without internal pressure, the cylinder is loaded with deformations, and deformations that aren't steady state. How will the tiles, and associated inter-tile fillers, deal with all this natural deformation? I doubt the expectation will be that it will always be pressurized - from before tile installation on. But perhaps? A stiff five ring stack is one thing, but a full up tank section, let along the payload area, is a completely different issue...
So some kind of spring grip/clip to attach the tile to each mounting pin, and a moulded ceramic fibre "gasket" as I describe in my post just above. There is room for more slack/tolerance if the gasket is engineered to fit the gap. It will have the necessary give.
Title: Re: Starship heat shield
Post by: HVM on 08/13/2020 07:35 pm
... but I've not seen a single post about the obvious elephant in the room...
What about ice? Not problem with Shuttle orbiter but with X-33 and SS.

Quick check out, non of the test tiles seems to be at the frosty part of the ship(let).
Title: Re: Starship heat shield
Post by: OTV Booster on 08/13/2020 08:15 pm
The nature and form of the "rope" insulation:
Because a vast quantity of this type of product will be used, SX can design it in a form that best suits the SS. Its current cheapness, standard shape, size, quality and utility, are no longer important, if SX needs a quantity that will allow easy and cheap mass-production of their design.
The pieces we have seen on SN5 look as if (some of them) were anchored on the studs.... which is odd as the picture of the "X" of tiles on SN6 appears to show them trapped aligned under the tile edges.

Other options:
A large or continuous sheet covering all/most of the tiled surface. Cons: weight?  spread of tiles being ripped off! PROs: easy, anchored on all pins, protects hull evenly from radited heat as well as plasma, may cushion vibration, stops plasma path to hull however it gets behind a tile.

Formed into"Y" sections, for one vertex meeting point, (or several "Y"'s at once). In manufacture a thin sheet could be cut and folded so that "unwanted" material from the centre of each tile is used to thicken the area behind the tile joints. The arms of the "Y" are wide enough to impale (into pre-formed holes) onto the tile mounting pins. PRO's. Same "weight" (or thinner) material provides much better cushion and insulation at the tile gaps. Three fixed points for each "Y" provide reliable anchoring.

Moulded into "U" cross section. If the tile edges turn back towards the hull as if folded, then a "U" cross-sectioned fibre pad can "contain" two adjacent edges, and even have a tongue that separates them.... now it is an "E" with each gap (in the "E") containing one tile edge! PRO's This allows damping of vibration of tiles, removal of contact/impact between tiles, and a complex and so secure obstruction of all plasma paths.

I don't know how these could be made, whether layers of fabric would be built up, and sewn, or whether fibres could be blown and compressed into a mould....  Whether it needs any stainless wire stiffening etc. But although it has gone from "off the shelf" rope to a carefully designed manufactured product, it could be very cost effective if it  is:
1. very secure and naturally stable in its location,
2. saves tile damage through tile vibration, and contact with adjacent tiles.
3. provides an excellent secure barrier to any plasma or hot gas ingress between tile gaps - or even between adjacent tiles!
4. if it can additionally reduce the risk of single tile loss spreading by frustrating the airflow's path under the next tile then it could be an outstanding solution.
Edit: The "E" version may safely allow slightly wider tile gaps, and more tolerance for fitting the tiles because it so thoroughly protects the gaps.
Since this is still being discussed in detail, I am re-posting my suggestion, with an ADDED diagram.... The "E" is now only conceptual and not very obvious, but the principle is there still.
I have shown a version that only covers one "Y", but obviously a larger "gasket" covering several would mean less joins, faster installation, and anchoring on more pins.
Assuming there is some slack in the mounting on the pins, maybe a spring clip, my gasket could help keep adjoining surfaces flush,and the gaps even.

PS anyone recommend a free CAD program.... I have looked and tried, but never found!!!!
Ahhh, now I see what you were getting at. Not so different than what I was getting at about a recess under the edge of the tiles.


free CAD? I'd be looking in the Linux world.


Phil
Title: Re: Starship heat shield
Post by: DistantTemple on 08/13/2020 08:29 pm
Quote from: OTV Booster
Ahhh, now I see what you were getting at. Not so different than what I was getting at about a recess under the edge of the tiles.
 
Crikey glancing back now my original writing is almost unintelligible .... almost like a patent specification!!!

The diagram I think is OK! So here it is. It (the gasket) can be fairly firm, and be fairly accurately shaped, but with some "spongyness" to allow the returned edges of the tiles to press(/bed) into it and make a "seal" - which will have enough give to cope with expansion and contraction due to pressure, cryo cooling, and popping out of "dents"during pressurisation. The somewhat wider tile gaps will have a tongue of the gasket to fll the space and cushion /stop contact between adjacent tiles due to vibration etc.

CAD - ideally on my windows laptop. I don't have linux - except on a raspberry pie, which I guess is under powered for even simple CAD... But thanks.
stud=pin
Title: Re: Starship heat shield
Post by: _MECO on 08/13/2020 08:32 pm
What is the primary driver for the tile size?  I.e. why not bigger?


Sent from my iPhone using Tapatalk

Curvature is probably one reason. It'll be interesting to see how it looks when they start tiling the nosecone where you get curvature in two dimensions.

Is not possible to create curved tiles?

Possible; but expensive. Why waste resources making many specialist tile types when you can get good at making a minimal number of tile types over and over again as cheaply as possible? Sticking to only two or three types expedites manufacturing and repair, not to mention reducing overhead costs. That's not to say there won't be any curved tiles. I personally just expect a minimum of different types where possible.

Anyway, the smaller the standard hex tile is, the tighter the curvature that can be conformed to without needing specialist curved tiles. There's probably some sort of efficiency maxima in there where the tiles are small enough that the most development and production resources are saved while also large enough as to be sturdy against vibration/expansion and not have too much weight in mounting brackets/take too long to install.

You only need one curved tile type for the main cylinder, and can still use a hex tile for nose. So that is two tile types. I don't think any of your reasoning applies here.

You don't think there's weird curvature where the tanks meet the chines, between the chines and the aero surfaces, the edges of the chines, edges of the aero surfaces, possibly inside the hinges of the aero surfaces, where the fairing reduces in diameter, surrounding RCS ports, and covering the nose? There's going to have to be some specialization in tile shape.
Title: Re: Starship heat shield
Post by: old_geez on 08/13/2020 08:39 pm
Cad program? Try Onshape. Free for hobbyists.
https://www.onshape.com/products/free?hsCtaTracking=12ef09fd-fa65-48a5-a496-d17c85a4662a%7C7bfa3811-7cbc-49db-9c26-50fb7bd007cd (https://www.onshape.com/products/free?hsCtaTracking=12ef09fd-fa65-48a5-a496-d17c85a4662a%7C7bfa3811-7cbc-49db-9c26-50fb7bd007cd)

My thoughts with the Ceramic rope were similar to how it’s used in reactor vessels. Simply packed in between the tiles. Usually three+ rows.
Given the hex tile layout, alternate rows could take different directions, ensuring no gaps at rope ends.
Title: Re: Starship heat shield
Post by: DanielW on 08/13/2020 08:51 pm
FreeCad works on windows as well. There is also OpenScad if you are more of a programmer.
Title: Re: Starship heat shield
Post by: john smith 19 on 08/13/2020 08:58 pm
What is the primary driver for the tile size?  I.e. why not bigger?


Sent from my iPhone using Tapatalk

Curvature is probably one reason. It'll be interesting to see how it looks when they start tiling the nosecone where you get curvature in two dimensions.

Is not possible to create curved tiles?

Possible; but expensive. Why waste resources making many specialist tile types when you can get good at making a minimal number of tile types over and over again as cheaply as possible? Sticking to only two or three types expedites manufacturing and repair, not to mention reducing overhead costs. That's not to say there won't be any curved tiles. I personally just expect a minimum of different types where possible.

Anyway, the smaller the standard hex tile is, the tighter the curvature that can be conformed to without needing specialist curved tiles. There's probably some sort of efficiency maxima in there where the tiles are small enough that the most development and production resources are saved while also large enough as to be sturdy against vibration/expansion and not have too much weight in mounting brackets/take too long to install.

You only need one curved tile type for the main cylinder, and can still use a hex tile for nose. So that is two tile types. I don't think any of your reasoning applies here.

You don't think there's weird curvature where the tanks meet the chines, between the chines and the aero surfaces, the edges of the chines, edges of the aero surfaces, possibly inside the hinges of the aero surfaces, where the fairing reduces in diameter, surrounding RCS ports, and covering the nose? There's going to have to be some specialization in tile shape.
It helps if you think of this like the techniques of computer graphics where the shapes are composed of polygons.

So you want a shape that can fit with copies of itself (IE a Platonic shape). You want a minimum number of different sizes and a minimum number of different mounting layouts for them to hang off.

Figuring out a good size for these tiles (big enough to cover maximum area, small enough to cover the common level of curvature of most of the hull) is the sort of task computer simulations were made for.
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/13/2020 09:05 pm
I don't think that's correct - see the link at the top of the first page of this thread for a diagram. As the diameter of the ship narrows in the nose the hexagons will start to overlap. Each ring of tiles or at least every few rings will need to have a specific shape, you can't use the same tessellated hexagons all the way.

I agree, it's not my idea to use a hex tile. I would have a range of curved tiles for the nose. But apparently SpaceX logistics can't handle more than one type of tile?!

I was expecting a technical reason, like the tiles are cast in large flat sheets and then machined into sections. But I think the Shuttle tiles were cast. If so, then it should be eminently feasible to cast curved tiles. Being a regular solid, the SS/SH can be tiled with a relatively small of tile shapes. Obviously, curved tiles fit a curved surface better.

And to head off another lame objection, no, I am not suggesting a huge range of unique tile shapes like the shuttle used.

Seeing as Elon thinks like an engineer, I would expect to see some curved tiles in future iterations.
There may or may not be curved tiles. My point is that a single tile however curved cannot cover the whole vehicle. I think we all agree that there will be special cases like the moving surfaces, I’m not considering those, I’m talking about the main body of Starship. The cylinder can be covered with a single type of tile, but the nose section can't. Each specific radii of the nose will require its own tile type regardless because the curvature is different and the radius is different as well. This doesn’t mean  thousands of tile types, but it probably does mean many dozens.

I’m fairly certain this is true for hexagonal tiles. What shape of curved tiles did you have in mind and how would they be fitted to the nose?
Title: Re: Starship heat shield
Post by: DistantTemple on 08/13/2020 09:08 pm
Cad program? Try Onshape. Free for hobbyists.
https://www.onshape.com/products/free?hsCtaTracking=12ef09fd-fa65-48a5-a496-d17c85a4662a%7C7bfa3811-7cbc-49db-9c26-50fb7bd007cd (https://www.onshape.com/products/free?hsCtaTracking=12ef09fd-fa65-48a5-a496-d17c85a4662a%7C7bfa3811-7cbc-49db-9c26-50fb7bd007cd)

My thoughts with the Ceramic rope were similar to how it’s used in reactor vessels. Simply packed in between the tiles. Usually three+ rows.
Given the hex tile layout, alternate rows could take different directions, ensuring no gaps at rope ends.
TY am following up OnShape.
The rope doesn't have to be off the shelf. I know sx likes OTS (we think), once they get a system worked out it will be mass produced. Slotting a precision gasket onto the pins/posts will be fast and foolproof, and possible to automate. Stuffing rope into the gap will not. Its almost certain to have to be a human task like caulking a ship! (way hay me herties) Also it will only achieve two goals. 1- stop hot gas/plasma ingress, and 2 - cushion between tiles.
The "gasket" I propose does far more, damping all movement, and help to level adjacent tiles. The cost of its complexity is eliminated  (I hope) by mass production and extremely simple and fast installation.
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/13/2020 09:13 pm
using the same size hexagons would cause overlap
Title: Re: Starship heat shield
Post by: xvel on 08/13/2020 09:23 pm
Just read the whole thread because you're arguing over and over about whether 2+2 is 4 or 5
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/13/2020 09:33 pm
Just read the whole thread because you're arguing over and over about whether 2+2 is 4 or 5
I have read the whole thread. I started it.
Title: Re: Starship heat shield
Post by: _MECO on 08/13/2020 09:36 pm
What is the primary driver for the tile size?  I.e. why not bigger?


Sent from my iPhone using Tapatalk

Curvature is probably one reason. It'll be interesting to see how it looks when they start tiling the nosecone where you get curvature in two dimensions.

Is not possible to create curved tiles?

Possible; but expensive. Why waste resources making many specialist tile types when you can get good at making a minimal number of tile types over and over again as cheaply as possible? Sticking to only two or three types expedites manufacturing and repair, not to mention reducing overhead costs. That's not to say there won't be any curved tiles. I personally just expect a minimum of different types where possible.

Anyway, the smaller the standard hex tile is, the tighter the curvature that can be conformed to without needing specialist curved tiles. There's probably some sort of efficiency maxima in there where the tiles are small enough that the most development and production resources are saved while also large enough as to be sturdy against vibration/expansion and not have too much weight in mounting brackets/take too long to install.

You only need one curved tile type for the main cylinder, and can still use a hex tile for nose. So that is two tile types. I don't think any of your reasoning applies here.

You don't think there's weird curvature where the tanks meet the chines, between the chines and the aero surfaces, the edges of the chines, edges of the aero surfaces, possibly inside the hinges of the aero surfaces, where the fairing reduces in diameter, surrounding RCS ports, and covering the nose? There's going to have to be some specialization in tile shape.
It helps if you think of this like the techniques of computer graphics where the shapes are composed of polygons.

So you want a shape that can fit with copies of itself (IE a Platonic shape). You want a minimum number of different sizes and a minimum number of different mounting layouts for them to hang off.

Figuring out a good size for these tiles (big enough to cover maximum area, small enough to cover the common level of curvature of most of the hull) is the sort of task computer simulations were made for.

Polygonal extruded prisms aren't the only shape that exist. However, I admittedly have no clue how these tiles are manufactured. Maybe it's extremely hard to do anything but a flat two-dimensional sandwich. But maybe it's case that they could be manufactured with compound curves, splines, smooth swept/lofted geometry etc. You are certainly right in that computational methods are a major driving force though.

Not only is the space of what is easy/hard/expensive/effective to manufacture with TUFROC-based TPS tiles a problem of far too many dimensions for me to understand, but also most of those dimensions are problems of design and manufacture in which I have no experience or knowledge. All I'm sure of is that adherence to the KISS principle is king here. Are there going to be a thousand unique types of differently shaped tile like with STS? Of course not. Are there only going to be two types of which both are two different sizes of flat hexagonal prism? My gut says no.
Title: Re: Starship heat shield
Post by: xvel on 08/13/2020 09:36 pm
Just read the whole thread because you're arguing over and over about whether 2+2 is 4 or 5
I have read the whole thread. I started it.
and you are the one that explains to everyone over and over that 2+2 is equal to 4 ;)
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/13/2020 10:05 pm
Just read the whole thread because you're arguing over and over about whether 2+2 is 4 or 5
I have read the whole thread. I started it.
and you are the one that explains to everyone over and over that 2+2 is equal to 4 ;)
Hurrah if everyone agrees than good, just seemed to me that someone was suggesting otherwise. I will let it drop.
Title: Re: Starship heat shield
Post by: DistantTemple on 08/13/2020 11:57 pm
2 pints of marbles, + 2 pints of sand anyone?
5 pints of the mixture is not correct.
Title: Re: Starship heat shield
Post by: livingjw on 08/14/2020 01:41 am

....
The reentry profile of Shuttle and Starship are totally different. I don't think the shuttle "skydived" at about 90 degrees to the apparent airflow, like the Starship is planning to....

During the hottest parts of the reentry, Starship will want to be producing lift and will probably be closer to 50 degrees AoA. This is not much higher than the Shuttle's maximum which I believe was about 45 degrees.

John
Title: Re: Starship heat shield
Post by: livingjw on 08/14/2020 01:49 am
What is the primary driver for the tile size?  I.e. why not bigger?


Sent from my iPhone using Tapatalk

Curvature is probably one reason. It'll be interesting to see how it looks when they start tiling the nosecone where you get curvature in two dimensions.

Is not possible to create curved tiles?

It is possible. After molding they can be machined very easily.

John
Title: Re: Starship heat shield
Post by: envy887 on 08/14/2020 01:54 am
...
Edit: I watched it gain, yes you are right, it had got through the steel plate and was "working on the Aluminium underneath" So yes steel is vulnerable. However I won't change my whole comment, as the "re-entry profile" is all still relevant.

Thin layers of steel will conduct plenty of heat right through, more than enough to weaken or melt aluminum on the back side. Depending on the steel, you can melt aluminum behind it while having little to no effect on the steel itself.

Surviving reentry is all about dissipating heat. Higher temperatures dissipate a LOT more heat, especially when you get to temps where radiation dominates, since radiative dissipation scales with the 4th power of temperature.
Title: Re: Starship heat shield
Post by: livingjw on 08/14/2020 01:59 am
Folks have talked about resonances and flight / temperature flexing, but I've not seen a single post about the obvious elephant in the room...

All one has to do is to simply look at one of these full up SN[x] tank section to see the issue - without internal pressure, the cylinder is loaded with deformations, and deformations that aren't steady state. How will the tiles, and associated inter-tile fillers, deal with all this natural deformation? I doubt the expectation will be that it will always be pressurized - from before tile installation on. But perhaps? A stiff five ring stack is one thing, but a full up tank section, let along the payload area, is a completely different issue...

- Completely agree. The shuttle airframe was required not to have any local skin buckling because they were bonding the tile through a thin felt layer.

- Starship will be using mechanical attachment which should make it able to handle some level of local skin deformation, but it will have to have the tiles' weak brittle bottoms protected from the hard deformable metal skin. This might even be a bigger problem for the flaps, if they continue to be constructed, as they are now, with skins that  buckle.

John
Title: Re: Starship heat shield
Post by: john smith 19 on 08/14/2020 05:56 am
Is not possible to create curved tiles?

It is possible. After molding they can be machined very easily.

John
True.

But unwise.  :(

NA Rockwell Manufacturing division were very proud that the had manage to make c24 000 nearly all unique in thickness and top surface profile.

It was a massive PITA because if a tile was damaged it had to be machined exactly to shape, and if black then have the surface coat added and baked on.

Later Boeing devised a near net shape process using slip casting onto a fairly easily made porous former which could (not sure if it was used) permit bigger blocks (less stress in firing) and lower machining.

Now, think about how much hardware you're going to need on mars  to do repairs this way.

This is where interchangability really pays off.
Title: Re: Starship heat shield
Post by: john smith 19 on 08/14/2020 06:07 am

Polygonal extruded prisms aren't the only shape that exist. However, I admittedly have no clue how these tiles are manufactured. Maybe it's extremely hard to do anything but a flat two-dimensional sandwich. But maybe it's case that they could be manufactured with compound curves, splines, smooth swept/lofted geometry etc. You are certainly right in that computational methods are a major driving force though.

Not only is the space of what is easy/hard/expensive/effective to manufacture with TUFROC-based TPS tiles a problem of far too many dimensions for me to understand, but also most of those dimensions are problems of design and manufacture in which I have no experience or knowledge. All I'm sure of is that adherence to the KISS principle is king here. Are there going to be a thousand unique types of differently shaped tile like with STS? Of course not. Are there only going to be two types of which both are two different sizes of flat hexagonal prism? My gut says no.
Your gut is probably right.

The ideal is one flat hexagon that can be wrapped adequately  around all their target shapes and can pack flat for transport to mars (without the risk of a stack of them cracking the ones at the bottom  :( )

IRL that is probably impossible. So practically a small number of designs will be used. Number and size TBD by testing and probably a lot of computer runs.

BTW it is an assumption that tiles need to be curve.

The key demonstration that this is not needed was the Brazil/Germany SHAFEX II (Sharp Edged Flight Experiment) that instead of using a smooth nose on a two stage sounding rocket built it out of flat RCC polygons (cut with a water jet IIRC).  Mostly IIRC pentagons and triangles.

The key development was the software to do this around an arbitrary shape and to confirm the aerodynamic properties were close enough to those of a smooth nose.

OTOH they didn't need to fit them round both +ve and -ve curvature shapes (like around the control surfaces).
Title: Re: Starship heat shield
Post by: KBK on 08/14/2020 02:24 pm
The suggestion, in the physicality of the thing, re the sharp edges, is that the thermal stressing on the sharper edges.. would likely have to fit within a stressing envelope of some kind, whereas there may be a few more degrees of wiggle room in a more rounded tile and shape application.

That the sharp edged thingamabob rocket shape and tile/etc application, has a subtle but potentially critical caveat in it's equation, when compared to the more rounded and/or aerodynamic shapes.

This, of course, indicates neither good nor bad in the weighting of either shape or application, as the overall scenario is more complex than that singular aspect.

Ie, that one can just hang that sharp edged tile out there to burn, while the underlying structure is more robust and less stressed mechanically and thermally due to construction and intent..and so on. All things in the comparison being unequal, etc.

I'm partially interested in the subject as one of my inventions was a new and untested form of highly manipulable low cost ceramic nanopowder composite oxide creation. I know the process works perfectly but it has yet to be applied to ceramic nanopowder compositions. Empirical and done/tested/produced, not theoretical.

Any morphology, any composite, any particle size. Just dial the process in...and away you go....no more complex than squeezing out pasta.

One could probably even make it out as a hard formed porous buckling isolator, which ultimately could act a bit like a thermal diode. Lots of free toys hiding inside...
Title: Re: Starship heat shield
Post by: equiserre on 08/14/2020 04:16 pm
The suggestion, in the physicality of the thing, re the sharp edges, is that the thermal stressing on the sharper edges.. would likely have to fit within a stressing envelope of some kind, whereas there may be a few more degrees of wiggle room in a more rounded tile and shape application.

That the sharp edged thingamabob rocket shape and tile/etc application, has a subtle but potentially critical caveat in it's equation, when compared to the more rounded and/or aerodynamic shapes.

This, of course, indicates neither good nor bad in the weighting of either shape or application, as the overall scenario is more complex than that singular aspect.

Ie, that one can just hang that sharp edged tile out there to burn, while the underlying structure is more robust and less stressed mechanically and thermally due to construction and intent..and so on. All things in the comparison being unequal, etc.

I'm partially interested in the subject as one of my inventions was a new and untested form of highly manipulable low cost ceramic nanopowder composite oxide creation. I know the process works perfectly but it has yet to be applied to ceramic nanopowder compositions. Empirical and done/tested/produced, not theoretical.

Any morphology, any composite, any particle size. Just dial the process in...and away you go....no more complex than squeezing out pasta.

One could probably even make it out as a hard formed porous buckling isolator, which ultimately could act a bit like a thermal diode. Lots of free toys hiding inside...

I´m going straight to my English language school to claim my money back
Title: Re: Starship heat shield
Post by: OTV Booster on 08/14/2020 05:32 pm

....
The reentry profile of Shuttle and Starship are totally different. I don't think the shuttle "skydived" at about 90 degrees to the apparent airflow, like the Starship is planning to....

During the hottest parts of the reentry, Starship will want to be producing lift and will probably be closer to 50 degrees AoA. This is not much higher than the Shuttle's maximum which I believe was about 45 degrees.

John
Hmmm. So stagnation won't be a line up the middle but a point a bit above where the nosecone starts curving.


Recalibrating! Recalibrating! Mental processes recalibrating.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/14/2020 06:09 pm
Is not possible to create curved tiles?

It is possible. After molding they can be machined very easily.

John
True.

But unwise.  :(

NA Rockwell Manufacturing division were very proud that the had manage to make c24 000 nearly all unique in thickness and top surface profile.

It was a massive PITA because if a tile was damaged it had to be machined exactly to shape, and if black then have the surface coat added and baked on.

Later Boeing devised a near net shape process using slip casting onto a fairly easily made porous former which could (not sure if it was used) permit bigger blocks (less stress in firing) and lower machining.

Now, think about how much hardware you're going to need on mars  to do repairs this way.

This is where interchangability really pays off.
OTOH, Rockwell didn't have additive manufacturing. If inspection on Mars shows a bad tile, a replacement need only be good enough for one EDL. In US army aviation parlance of back in the day, a red X (grounded) log entry becomes a circled red X (one time flight only). Conceivably a substitute tile might even be ablative.


Tiles are mission critical and unless Elon pulls another rabbit out of a hat, they will have a non-zero failure rate. The barrel and flap surfaces can all have the same tiles but the fin edges, raceways, fin hinge areas and nose cone will have adjustment of some kind.


3-D printing is maturing so fast and has so much promise I can't quite imagine even the first Mars base not having the capability.


Phil
Title: Re: Starship heat shield
Post by: OTV Booster on 08/14/2020 06:24 pm
The suggestion, in the physicality of the thing, re the sharp edges, is that the thermal stressing on the sharper edges.. would likely have to fit within a stressing envelope of some kind, whereas there may be a few more degrees of wiggle room in a more rounded tile and shape application.

That the sharp edged thingamabob rocket shape and tile/etc application, has a subtle but potentially critical caveat in it's equation, when compared to the more rounded and/or aerodynamic shapes.

This, of course, indicates neither good nor bad in the weighting of either shape or application, as the overall scenario is more complex than that singular aspect.

Ie, that one can just hang that sharp edged tile out there to burn, while the underlying structure is more robust and less stressed mechanically and thermally due to construction and intent..and so on. All things in the comparison being unequal, etc.

I'm partially interested in the subject as one of my inventions was a new and untested form of highly manipulable low cost ceramic nanopowder composite oxide creation. I know the process works perfectly but it has yet to be applied to ceramic nanopowder compositions. Empirical and done/tested/produced, not theoretical.

Any morphology, any composite, any particle size. Just dial the process in...and away you go....no more complex than squeezing out pasta.

One could probably even make it out as a hard formed porous buckling isolator, which ultimately could act a bit like a thermal diode. Lots of free toys hiding inside...
Hmmm. I read this after my post about additive manufacturing. You obviously have some trade secrets so just tell me to butt out and no hard feeling.


If I don't need to butt out, is your process traditionally fired, plasma sprayed or something else? If plasma sprayed its at least a close cousin to 3-D printing.


Phil
Title: Re: Starship heat shield
Post by: rsdavis9 on 08/14/2020 08:30 pm
The shuttle used carbon carbon on the leading edges. Maybe the flaps edges will be carbon carbon. I think they were close to one long piece on the shuttle.
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 08/14/2020 08:36 pm
The shuttle used carbon carbon on the leading edges. Maybe the flaps edges will be carbon carbon. I think they were close to one long piece on the shuttle.

And the failure of that leading-edge reinforced carbon carbon after a foam strike is what doomed Columbia.
Title: Re: Starship heat shield
Post by: HVM on 08/14/2020 10:02 pm
The shuttle used carbon carbon on the leading edges. Maybe the flaps edges will be carbon carbon. I think they were close to one long piece on the shuttle.

And the failure of that leading-edge reinforced carbon carbon after a foam strike is what doomed Columbia.
Are ice impacts possible at SS? Quick comparison for dimensions for STS says yes, but:

No solids -> Less Gs?
Fins are not wings, but air brakes -> No leading edges, just edges.
Also no insulation foam -> No foam impacts. (But loose tiles are worse than ice + foam...)

(Ok, already discussed at page 20, but any way, ice build up is needed to be taken into account with the fastening method design.)
Title: Re: Starship heat shield
Post by: livingjw on 08/14/2020 10:13 pm
The shuttle used carbon carbon on the leading edges. Maybe the flaps edges will be carbon carbon. I think they were close to one long piece on the shuttle.

No, many short pieces. Google: Shuttle leading edge and look at "images"

John
Title: Re: Starship heat shield
Post by: DistantTemple on 08/14/2020 11:46 pm
The suggestion, in the physicality of the thing, re the sharp edges, is that the thermal stressing on the sharper edges.. would likely have to fit within a stressing envelope of some kind, whereas there may be a few more degrees of wiggle room in a more rounded tile and shape application.

That the sharp edged thingamabob rocket shape and tile/etc application, has a subtle but potentially critical caveat in it's equation, when compared to the more rounded and/or aerodynamic shapes.

This, of course, indicates neither good nor bad in the weighting of either shape or application, as the overall scenario is more complex than that singular aspect.

Ie, that one can just hang that sharp edged tile out there to burn, while the underlying structure is more robust and less stressed mechanically and thermally due to construction and intent..and so on. All things in the comparison being unequal, etc.

I'm partially interested in the subject as one of my inventions was a new and untested form of highly manipulable low cost ceramic nanopowder composite oxide creation. I know the process works perfectly but it has yet to be applied to ceramic nanopowder compositions. Empirical and done/tested/produced, not theoretical.

Any morphology, any composite, any particle size. Just dial the process in...and away you go....no more complex than squeezing out pasta.

One could probably even make it out as a hard formed porous buckling isolator, which ultimately could act a bit like a thermal diode. Lots of free toys hiding inside...
Are you trolling us KBK?
Title: Re: Starship heat shield
Post by: sdsds on 08/15/2020 01:59 am
Sorry don't know if this is the best place for this question, but here goes:

Is there a generally accepted comparison between the heat shield requirements of re-entry from LEO and those of aero-capture from e.g. lunar or martian TEI?

Gut says aero-capture should be much less stressing (thermally, structurally, etc.) than full re-entry. But IANARS....
Title: Re: Starship heat shield
Post by: rakaydos on 08/15/2020 02:16 am
Sorry don't know if this is the best place for this question, but here goes:

Is there a generally accepted comparison between the heat shield requirements of re-entry from LEO and those of aero-capture from e.g. lunar or martian TEI?

Gut says aero-capture should be much less stressing (thermally, structurally, etc.) than full re-entry. But IANARS....

Aero BREAKING can be arbitrarally low stress, but aero CAPTURE from an interplanetary trajectory to eliptiical capture orbit, is usually more stressful than a LEO entry. You only have once chance to slow down, so you have to be aggressive, going deep while still fast enough to go flying out past the moon again.
Title: Re: Starship heat shield
Post by: cdebuhr on 08/15/2020 02:31 am
Sorry don't know if this is the best place for this question, but here goes:

Is there a generally accepted comparison between the heat shield requirements of re-entry from LEO and those of aero-capture from e.g. lunar or martian TEI?

Gut says aero-capture should be much less stressing (thermally, structurally, etc.) than full re-entry. But IANARS....

Aero BREAKING can be arbitrarally low stress, but aero CAPTURE from an interplanetary trajectory to eliptiical capture orbit, is usually more stressful than a LEO entry. You only have once chance to slow down, so you have to be aggressive, going deep while still fast enough to go flying out past the moon again.
Intersting - OK, here's a follow up question: Obviously (I think ...) aero-capture from an interplanetary trajectory to elliptical capture orbit, should be somewhat less demanding that direct EDL from the same interplanetary trajectory, but how much less?  I sometimes see discussion of perhaps using aero-capture followed by multiple aero-braking passes prior to EDL in cases where direct EDL would exceed the vehicle survival envelope, but unless aero-capture is substantially less demanding that direct EDL, there might not be much of a point.
Title: Re: Starship heat shield
Post by: rakaydos on 08/15/2020 02:39 am
Sorry don't know if this is the best place for this question, but here goes:

Is there a generally accepted comparison between the heat shield requirements of re-entry from LEO and those of aero-capture from e.g. lunar or martian TEI?

Gut says aero-capture should be much less stressing (thermally, structurally, etc.) than full re-entry. But IANARS....

Aero BREAKING can be arbitrarally low stress, but aero CAPTURE from an interplanetary trajectory to eliptiical capture orbit, is usually more stressful than a LEO entry. You only have once chance to slow down, so you have to be aggressive, going deep while still fast enough to go flying out past the moon again.
Intersting - OK, here's a follow up question: Obviously (I think ...) aero-capture from an interplanetary trajectory to elliptical capture orbit, should be somewhat less demanding that direct EDL from the same interplanetary trajectory, but how much less?  I sometimes see discussion of perhaps using aero-capture followed by multiple aero-braking passes prior to EDL in cases where direct EDL would exceed the vehicle survival envelope, but unless aero-capture is substantially less demanding that direct EDL, there might not be much of a point.
I know enough to know there is a mathematical answer to your question, but my credentials come from Kerbal Space Program, so even if I could come up with numbers, I wouldn't trust them with a real-world scenario.
Title: Re: Starship heat shield
Post by: john smith 19 on 08/15/2020 10:20 am
Gut says aero-capture should be much less stressing (thermally, structurally, etc.) than full re-entry. But IANARS....
As is the case a lot of the time "It depends."

In this case on a couple of things.

1) How big is the excess of entry speed over the orbital velocity at this orbital altitude. If it's a few 100 m/s then no, if it's 1000s of m/s then yes it will be.

2) How aerodynamic is the vehicle.  Aero braking has been used to raise the orbit on at least one of the Mars probes. Each pass shaved a little (1 m/s?) off the orbital velocity. All aerials and solar arrays fully deployed (I don't think they could be retracted anyway).

But capture is 1 pass. You loose all the excess velocity in 1 pass. coming into Mars orbit at 20kms and mars orbital velocity at that altitude is 4Kms that's 16kms you need to loose in 1 go.  There is no 2nd chance as you ar not in orbit to do so.

Aero capture is a potential game changer for fast travel between planets. Worst case it's worse than either say Mars entry or Earth re-entry from existing transfers.
Title: Re: Starship heat shield
Post by: RoboGoofers on 08/15/2020 11:37 am
Sorry don't know if this is the best place for this question, but here goes:

Is there a generally accepted comparison between the heat shield requirements of re-entry from LEO and those of aero-capture from e.g. lunar or martian TEI?

Gut says aero-capture should be much less stressing (thermally, structurally, etc.) than full re-entry. But IANARS....

Aero BREAKING can be arbitrarally low stress, but aero CAPTURE from an interplanetary trajectory to eliptiical capture orbit, is usually more stressful than a LEO entry. You only have once chance to slow down, so you have to be aggressive, going deep while still fast enough to go flying out past the moon again.
Intersting - OK, here's a follow up question: Obviously (I think ...) aero-capture from an interplanetary trajectory to elliptical capture orbit, should be somewhat less demanding that direct EDL from the same interplanetary trajectory, but how much less?  I sometimes see discussion of perhaps using aero-capture followed by multiple aero-braking passes prior to EDL in cases where direct EDL would exceed the vehicle survival envelope, but unless aero-capture is substantially less demanding that direct EDL, there might not be much of a point.
there's is a minimum force trajectory that will just capture, but at earth you'll have already transited the Van Allen belts by the time you hit the atmosphere. So I think mission planers will probably want to drop below the belts in the first pass, which is pretty aggressive. Might as well just go straight to EDL at that point.
Title: Re: Starship heat shield
Post by: SteveU on 08/15/2020 01:41 pm
Sorry if this has already been discussed and I missed it.  My biggest concern is loosing tiles - and while the attachment methods have been discusses I haven’t seen any discussion of what the mechanical forces are that the tiles will have to survive.

Obviously the thermal expansion and contraction of the tanks.

Sonic vibration generated by SH during initial stages of launch - but just how big are those forces?

Vibration from the SS Raptors transmitted through the hull?

My biggest unknown - how much turbulence is there at the surface of the tiles during EDL?  And when does the peak occur?
Title: Re: Starship heat shield
Post by: Keldor on 08/15/2020 01:51 pm
Sorry don't know if this is the best place for this question, but here goes:

Is there a generally accepted comparison between the heat shield requirements of re-entry from LEO and those of aero-capture from e.g. lunar or martian TEI?

Gut says aero-capture should be much less stressing (thermally, structurally, etc.) than full re-entry. But IANARS....

Aero BREAKING can be arbitrarally low stress, but aero CAPTURE from an interplanetary trajectory to eliptiical capture orbit, is usually more stressful than a LEO entry. You only have once chance to slow down, so you have to be aggressive, going deep while still fast enough to go flying out past the moon again.
Intersting - OK, here's a follow up question: Obviously (I think ...) aero-capture from an interplanetary trajectory to elliptical capture orbit, should be somewhat less demanding that direct EDL from the same interplanetary trajectory, but how much less?  I sometimes see discussion of perhaps using aero-capture followed by multiple aero-braking passes prior to EDL in cases where direct EDL would exceed the vehicle survival envelope, but unless aero-capture is substantially less demanding that direct EDL, there might not be much of a point.
there's is a minimum force trajectory that will just capture, but at earth you'll have already transited the Van Allen belts by the time you hit the atmosphere. So I think mission planers will probably want to drop below the belts in the first pass, which is pretty aggressive. Might as well just go straight to EDL at that point.

Remember that when coming from an interplanetary trajectory, they can choose any inclination they want essentially for free, with the restriction that perigee be roughly over the ecliptic.  (This has ramifications depending on what season it is when you're coming back)  So if you approach in a polar inclination, you may well be able to go around over the top of the belts and avoid most of the radiation.
Title: Re: Starship heat shield
Post by: RoboGoofers on 08/15/2020 02:09 pm
Sorry don't know if this is the best place for this question, but here goes:

Is there a generally accepted comparison between the heat shield requirements of re-entry from LEO and those of aero-capture from e.g. lunar or martian TEI?

Gut says aero-capture should be much less stressing (thermally, structurally, etc.) than full re-entry. But IANARS....

Aero BREAKING can be arbitrarally low stress, but aero CAPTURE from an interplanetary trajectory to eliptiical capture orbit, is usually more stressful than a LEO entry. You only have once chance to slow down, so you have to be aggressive, going deep while still fast enough to go flying out past the moon again.
Intersting - OK, here's a follow up question: Obviously (I think ...) aero-capture from an interplanetary trajectory to elliptical capture orbit, should be somewhat less demanding that direct EDL from the same interplanetary trajectory, but how much less?  I sometimes see discussion of perhaps using aero-capture followed by multiple aero-braking passes prior to EDL in cases where direct EDL would exceed the vehicle survival envelope, but unless aero-capture is substantially less demanding that direct EDL, there might not be much of a point.
there's is a minimum force trajectory that will just capture, but at earth you'll have already transited the Van Allen belts by the time you hit the atmosphere. So I think mission planers will probably want to drop below the belts in the first pass, which is pretty aggressive. Might as well just go straight to EDL at that point.

Remember that when coming from an interplanetary trajectory, they can choose any inclination they want essentially for free, with the restriction that perigee be roughly over the ecliptic.  (This has ramifications depending on what season it is when you're coming back)  So if you approach in a polar inclination, you may well be able to go around over the top of the belts and avoid most of the radiation.
granted, like Apollo. But that only helps with direct entry. if you're doing multiple passes sooner or later you end up in the belts.
Title: Re: Starship heat shield
Post by: eriblo on 08/15/2020 08:51 pm
Sorry don't know if this is the best place for this question, but here goes:

Is there a generally accepted comparison between the heat shield requirements of re-entry from LEO and those of aero-capture from e.g. lunar or martian TEI?

Gut says aero-capture should be much less stressing (thermally, structurally, etc.) than full re-entry. But IANARS....

Aero BREAKING can be arbitrarally low stress, but aero CAPTURE from an interplanetary trajectory to eliptiical capture orbit, is usually more stressful than a LEO entry. You only have once chance to slow down, so you have to be aggressive, going deep while still fast enough to go flying out past the moon again.
Intersting - OK, here's a follow up question: Obviously (I think ...) aero-capture from an interplanetary trajectory to elliptical capture orbit, should be somewhat less demanding that direct EDL from the same interplanetary trajectory, but how much less?  I sometimes see discussion of perhaps using aero-capture followed by multiple aero-braking passes prior to EDL in cases where direct EDL would exceed the vehicle survival envelope, but unless aero-capture is substantially less demanding that direct EDL, there might not be much of a point.
Some rough numbers: LEO reentry is ~7.8 km/s and lunar reentry ~11 km/s (just below escape velocity). Squaring these numbers you get 61 and 121 (representing kinetic energy per unit mass). So a good rule of thumb is that lunar reentry needs to get rid of twice the energy. Anything interplanetary is going to have even more energy.

So from a simplistic energy viewpoint a reusable TPS capable of LEO reentry can do a lunar reentry by getting rid of half the energy in a first pass, cooling of during an intermediate elliptical orbit and then doing a standard reentry. This approach could extend to interplanetary reentries up to ~13.5 km/s by splitting it in three.

This does of course not work in real life due to the maximum temperature limitations of the TPS and the fact that the plasma temperature increases rapidly with velocity. It is possible to decrease the temperature by staying at a higher altitude but the drag decreases rapidly and it is already hard to slow down enough during a single pass.

Starship should be able to reenter from the Moon but the question is how many passes will be required - if the TPS is just good enough for LEO (like the Space Shuttle) then it might take a relatively long time and, as mentioned previously, lead to excessive radiation exposure. The higher the maximum temperature of the TPS, the lower the ballistic coefficient and the higher the lift to drag ratio (to stay longer at the optimal altitude) the better.

For interplanetary trajectories the hard limit is indeed if you can get below escape velocity on the first pass. I am quite curios about the capabilities (on paper) of their current TPS designs, especially with regard to the faster return trajectories they would like to do.
Title: Re: Starship heat shield
Post by: midaswelby on 08/15/2020 10:42 pm
Sorry don't know if this is the best place for this question, but here goes:

Is there a generally accepted comparison between the heat shield requirements of re-entry from LEO and those of aero-capture from e.g. lunar or martian TEI?

Gut says aero-capture should be much less stressing (thermally, structurally, etc.) than full re-entry. But IANARS....

Aero BREAKING can be arbitrarally low stress, but aero CAPTURE from an interplanetary trajectory to eliptiical capture orbit, is usually more stressful than a LEO entry. You only have once chance to slow down, so you have to be aggressive, going deep while still fast enough to go flying out past the moon again.
Intersting - OK, here's a follow up question: Obviously (I think ...) aero-capture from an interplanetary trajectory to elliptical capture orbit, should be somewhat less demanding that direct EDL from the same interplanetary trajectory, but how much less?  I sometimes see discussion of perhaps using aero-capture followed by multiple aero-braking passes prior to EDL in cases where direct EDL would exceed the vehicle survival envelope, but unless aero-capture is substantially less demanding that direct EDL, there might not be much of a point.
Some rough numbers: LEO reentry is ~7.8 km/s and lunar reentry ~11 km/s (just below escape velocity). Squaring these numbers you get 61 and 121 (representing kinetic energy per unit mass). So a good rule of thumb is that lunar reentry needs to get rid of twice the energy. Anything interplanetary is going to have even more energy.

So from a simplistic energy viewpoint a reusable TPS capable of LEO reentry can do a lunar reentry by getting rid of half the energy in a first pass, cooling of during an intermediate elliptical orbit and then doing a standard reentry. This approach could extend to interplanetary reentries up to ~13.5 km/s by splitting it in three.

This does of course not work in real life due to the maximum temperature limitations of the TPS and the fact that the plasma temperature increases rapidly with velocity. It is possible to decrease the temperature by staying at a higher altitude but the drag decreases rapidly and it is already hard to slow down enough during a single pass.

Starship should be able to reenter from the Moon but the question is how many passes will be required - if the TPS is just good enough for LEO (like the Space Shuttle) then it might take a relatively long time and, as mentioned previously, lead to excessive radiation exposure. The higher the maximum temperature of the TPS, the lower the ballistic coefficient and the higher the lift to drag ratio (to stay longer at the optimal altitude) the better.

For interplanetary trajectories the hard limit is indeed if you can get below escape velocity on the first pass. I am quite curios about the capabilities (on paper) of their current TPS designs, especially with regard to the faster return trajectories they would like to do.

I'm curious to know if a fully-fueled  SS returning to Earth orbit would need aero braking maneuvers at all.  If there are in-orbit refueling capabilities at both Mars and Earth, then sufficient propellants for both acceleration and deceleration in both directions would set up the easiest possible re-entry conditions.  Am I being a dumbass here?   ;D
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 08/15/2020 11:14 pm
I'm curious to know if a fully-fueled  SS returning to Earth orbit would need aero braking maneuvers at all.  If there are in-orbit refueling capabilities at both Mars and Earth, then sufficient propellants for both acceleration and deceleration in both directions would set up the easiest possible re-entry conditions.  Am I being a dumbass here?   ;D

You're right that it would be the easiest possible re-entry conditions.  But it would also be expensive, because it would use up all that propellant that was sent to Mars orbit.  Better TPS would save a lot of Starship flights, allowing more of those flights to be devoted to cargo and passengers.

Also, if the TPS is better, even if you have all that propellant you can combine the additional propellant with the great TPS to get really short transit times.

So, while it's possible to do a Mars architecture with TPS that can only do LEO re-entry, you get a lot more throughput from a given number of Starships if you have better TPS.
Title: Re: Starship heat shield
Post by: Twark_Main on 08/16/2020 02:22 am
Sorry don't know if this is the best place for this question, but here goes:

Is there a generally accepted comparison between the heat shield requirements of re-entry from LEO and those of aero-capture from e.g. lunar or martian TEI?

Gut says aero-capture should be much less stressing (thermally, structurally, etc.) than full re-entry. But IANARS....

Aero BREAKING can be arbitrarally low stress, but aero CAPTURE from an interplanetary trajectory to eliptiical capture orbit, is usually more stressful than a LEO entry. You only have once chance to slow down, so you have to be aggressive, going deep while still fast enough to go flying out past the moon again.
Intersting - OK, here's a follow up question: Obviously (I think ...) aero-capture from an interplanetary trajectory to elliptical capture orbit, should be somewhat less demanding that direct EDL from the same interplanetary trajectory, but how much less?  I sometimes see discussion of perhaps using aero-capture followed by multiple aero-braking passes prior to EDL in cases where direct EDL would exceed the vehicle survival envelope, but unless aero-capture is substantially less demanding that direct EDL, there might not be much of a point.
there's is a minimum force trajectory that will just capture, but at earth you'll have already transited the Van Allen belts by the time you hit the atmosphere. So I think mission planers will probably want to drop below the belts in the first pass, which is pretty aggressive. Might as well just go straight to EDL at that point.

Remember that when coming from an interplanetary trajectory, they can choose any inclination they want essentially for free, with the restriction that perigee be roughly over the ecliptic.  (This has ramifications depending on what season it is when you're coming back)  So if you approach in a polar inclination, you may well be able to go around over the top of the belts and avoid most of the radiation.
granted, like Apollo. But that only helps with direct entry. if you're doing multiple passes sooner or later you end up in the belts.

Sorry, but clearly it doesn't only help with direct entry. Depends on how big each pass is, an aerobraking trajectory can bypass the belts almost entirely using this technique.
Title: Re: Starship heat shield
Post by: Keldor on 08/16/2020 04:06 am
Sorry don't know if this is the best place for this question, but here goes:

Is there a generally accepted comparison between the heat shield requirements of re-entry from LEO and those of aero-capture from e.g. lunar or martian TEI?

Gut says aero-capture should be much less stressing (thermally, structurally, etc.) than full re-entry. But IANARS....

Aero BREAKING can be arbitrarally low stress, but aero CAPTURE from an interplanetary trajectory to eliptiical capture orbit, is usually more stressful than a LEO entry. You only have once chance to slow down, so you have to be aggressive, going deep while still fast enough to go flying out past the moon again.
Intersting - OK, here's a follow up question: Obviously (I think ...) aero-capture from an interplanetary trajectory to elliptical capture orbit, should be somewhat less demanding that direct EDL from the same interplanetary trajectory, but how much less?  I sometimes see discussion of perhaps using aero-capture followed by multiple aero-braking passes prior to EDL in cases where direct EDL would exceed the vehicle survival envelope, but unless aero-capture is substantially less demanding that direct EDL, there might not be much of a point.
there's is a minimum force trajectory that will just capture, but at earth you'll have already transited the Van Allen belts by the time you hit the atmosphere. So I think mission planers will probably want to drop below the belts in the first pass, which is pretty aggressive. Might as well just go straight to EDL at that point.

Remember that when coming from an interplanetary trajectory, they can choose any inclination they want essentially for free, with the restriction that perigee be roughly over the ecliptic.  (This has ramifications depending on what season it is when you're coming back)  So if you approach in a polar inclination, you may well be able to go around over the top of the belts and avoid most of the radiation.
granted, like Apollo. But that only helps with direct entry. if you're doing multiple passes sooner or later you end up in the belts.

Sorry, but clearly it doesn't only help with direct entry. Depends on how big each pass is, an aerobraking trajectory can bypass the belts almost entirely using this technique.

The Van Allen Belts don't really extend all that high.  Bypassing them would just take an aerobraking pass from a mid-high orbit above them to a low orbit beneath, which seems more than possible for a vehicle designed to survive EDL.

What about if they did one pass to capture into a highly eccentric polar orbit from interplanetary, a second pass to drop to low orbit, and a final pass to land?  What sorts of peak heating would we be looking at during those braking passes, compared to the reentry from low orbit, and also compared to just doing everything in a direct reentry?
Title: Re: Starship heat shield
Post by: john smith 19 on 08/16/2020 07:23 am
I'm curious to know if a fully-fueled  SS returning to Earth orbit would need aero braking maneuvers at all. 
If there are in-orbit refueling capabilities at both Mars and Earth,
That's a big if for mars given it takes 4 additional flights to load an SS with prop.
Quote from: midaswelby
then sufficient propellants for both acceleration and deceleration in both directions would set up the easiest possible re-entry conditions.  Am I being a dumbass here?   ;D
No. the  KISS principle suggests early flights will keep the trajectory as simple as possible.

But note areocapture is very different from aerobraking

Aerobraking requires you are already in an orbit around your target planet. NASA has used it since the Magellan entry around Venus in the 90's. "Skip" entries can be viewed as a special case of aerobraking.

Aerocapture is a potential game changer for shortening travel times but has not been demonstrated, However NASA's last study on the matter concluded they could do it around Titan, Mars and maybe Venus right now, without flight demonstrators. Which is a very bold statement by NASA standards.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/16/2020 03:06 pm
Sorry if this has already been discussed and I missed it.  My biggest concern is loosing tiles - and while the attachment methods have been discusses I haven’t seen any discussion of what the mechanical forces are that the tiles will have to survive.

Obviously the thermal expansion and contraction of the tanks.

Sonic vibration generated by SH during initial stages of launch - but just how big are those forces?

Vibration from the SS Raptors transmitted through the hull?

My biggest unknown - how much turbulence is there at the surface of the tiles during EDL?  And when does the peak occur?
If you mean swirls and eddies, probably none while hypersonic. I speak from a great depth of not knowing much.


Using a sphere as a simplified model, the hypersonic air compresses and heats on the leading point, forms a shockwave, and has nowhere to go. This is the stagnation point. A tiny smidge to the side the compressed air is free to move radially and is free to expand slightly. This effect is greater the further from the stagnation point. Lateral movement is virtually impossible (I think). Looking from the side, this flow looks like a bow wave spreading further from the surface the further it is from the stagnation point. The outer edge of this flow is the shockwave. I'm not sure, but I think this flow is supersonic.


It is this flow that holds the plasma off the surface. As the flow passes beyond the 'equator', the stagnation point being the 'pole', there is the chance for turbulence, but this will be in the wake of the SS and is a step beyond my understanding so YMMV.


Applying this to SS is not simple. A post within the last couple of pages pointed out that the AoA will be ~50deg putting the stagnation point on the nosecone somewhere between the cylinder and the tip.  Use your imagination to visualize the radial flow from this point. I'm still working on it.


Each flap will also be facing this environment which leads me to believe they will never be face on square to the flow while hypersonic. The transition from raceways is critical. The MK1 raceways had the leading edge forming a rough tangent to the hull allowing a smooth flow transition. If the fins angle forward if this angle the shock could impinge on them which would rip them apart.


I'm trying to visualize the tiles at the stagnation point without much luck yet. If there is packing between them there shouldn't be much problem but without packing (I'm wandering into Wonderland here) there might be flow underneath the tiles. The flow is hot from compression which is not a good thing but at least the tiles would still protect from the plasma's radiative heating. If the flow is supersonic I'm not sure of its impact on the mounting pins and tile edges but I can't see anything good coming of it.


My conclusion is that turbulence, in the traditional sense, should not be a problem but without a robust packing scheme there could be other problems. My understanding really only approached amateur level on this so YMMV.


Phil
Title: Re: Starship heat shield
Post by: SteveU on 08/16/2020 06:22 pm
Sorry if this has already been discussed and I missed it.  My biggest concern is loosing tiles - and while the attachment methods have been discusses I haven’t seen any discussion of what the mechanical forces are that the tiles will have to survive.

Obviously the thermal expansion and contraction of the tanks.

Sonic vibration generated by SH during initial stages of launch - but just how big are those forces?

Vibration from the SS Raptors transmitted through the hull?

My biggest unknown - how much turbulence is there at the surface of the tiles during EDL?  And when does the peak occur?
If you mean swirls and eddies, probably none while hypersonic. I speak from a great depth of not knowing much.


Using a sphere as a simplified model, the hypersonic air compresses and heats on the leading point, forms a shockwave, and has nowhere to go. This is the stagnation point. A tiny smidge to the side the compressed air is free to move radially and is free to expand slightly. This effect is greater the further from the stagnation point. Lateral movement is virtually impossible (I think). Looking from the side, this flow looks like a bow wave spreading further from the surface the further it is from the stagnation point. The outer edge of this flow is the shockwave. I'm not sure, but I think this flow is supersonic.


It is this flow that holds the plasma off the surface. As the flow passes beyond the 'equator', the stagnation point being the 'pole', there is the chance for turbulence, but this will be in the wake of the SS and is a step beyond my understanding so YMMV.


Applying this to SS is not simple. A post within the last couple of pages pointed out that the AoA will be ~50deg putting the stagnation point on the nosecone somewhere between the cylinder and the tip.  Use your imagination to visualize the radial flow from this point. I'm still working on it.


Each flap will also be facing this environment which leads me to believe they will never be face on square to the flow while hypersonic. The transition from raceways is critical. The MK1 raceways had the leading edge forming a rough tangent to the hull allowing a smooth flow transition. If the fins angle forward if this angle the shock could impinge on them which would rip them apart.


I'm trying to visualize the tiles at the stagnation point without much luck yet. If there is packing between them there shouldn't be much problem but without packing (I'm wandering into Wonderland here) there might be flow underneath the tiles. The flow is hot from compression which is not a good thing but at least the tiles would still protect from the plasma's radiative heating. If the flow is supersonic I'm not sure of its impact on the mounting pins and tile edges but I can't see anything good coming of it.


My conclusion is that turbulence, in the traditional sense, should not be a problem but without a robust packing scheme there could be other problems. My understanding really only approached amateur level on this so YMMV.


Phil
Thanks Phil - your explanation helps.

Guess I should have explained my concern better - will there be enough turbulence during those periods of peak heating that would rip a tile off.  Based on your explanation, probably not.  Bigger issue with hot gases getting between and under the tiles causing thermal rather than pure mechanical damage. Right?
Title: Re: Starship heat shield
Post by: OTV Booster on 08/16/2020 09:56 pm
Sorry if this has already been discussed and I missed it.  My biggest concern is loosing tiles - and while the attachment methods have been discusses I haven’t seen any discussion of what the mechanical forces are that the tiles will have to survive.

Obviously the thermal expansion and contraction of the tanks.

Sonic vibration generated by SH during initial stages of launch - but just how big are those forces?

Vibration from the SS Raptors transmitted through the hull?

My biggest unknown - how much turbulence is there at the surface of the tiles during EDL?  And when does the peak occur?
If you mean swirls and eddies, probably none while hypersonic. I speak from a great depth of not knowing much.


Using a sphere as a simplified model, the hypersonic air compresses and heats on the leading point, forms a shockwave, and has nowhere to go. This is the stagnation point. A tiny smidge to the side the compressed air is free to move radially and is free to expand slightly. This effect is greater the further from the stagnation point. Lateral movement is virtually impossible (I think). Looking from the side, this flow looks like a bow wave spreading further from the surface the further it is from the stagnation point. The outer edge of this flow is the shockwave. I'm not sure, but I think this flow is supersonic.


It is this flow that holds the plasma off the surface. As the flow passes beyond the 'equator', the stagnation point being the 'pole', there is the chance for turbulence, but this will be in the wake of the SS and is a step beyond my understanding so YMMV.


Applying this to SS is not simple. A post within the last couple of pages pointed out that the AoA will be ~50deg putting the stagnation point on the nosecone somewhere between the cylinder and the tip.  Use your imagination to visualize the radial flow from this point. I'm still working on it.


Each flap will also be facing this environment which leads me to believe they will never be face on square to the flow while hypersonic. The transition from raceways is critical. The MK1 raceways had the leading edge forming a rough tangent to the hull allowing a smooth flow transition. If the fins angle forward if this angle the shock could impinge on them which would rip them apart.


I'm trying to visualize the tiles at the stagnation point without much luck yet. If there is packing between them there shouldn't be much problem but without packing (I'm wandering into Wonderland here) there might be flow underneath the tiles. The flow is hot from compression which is not a good thing but at least the tiles would still protect from the plasma's radiative heating. If the flow is supersonic I'm not sure of its impact on the mounting pins and tile edges but I can't see anything good coming of it.


My conclusion is that turbulence, in the traditional sense, should not be a problem but without a robust packing scheme there could be other problems. My understanding really only approached amateur level on this so YMMV.


Phil
Thanks Phil - your explanation helps.

Guess I should have explained my concern better - will there be enough turbulence during those periods of peak heating that would rip a tile off.  Based on your explanation, probably not.  Bigger issue with hot gases getting between and under the tiles causing thermal rather than pure mechanical damage. Right?
I'm really not qualified to have anything more than a guess. And a week one at that.


I'm not sure how gas getting under the tiles would behave. If it expands and drops subsonic it might even add a tad of cooling, or it might crack the tiles.


If it's supersonic and the flow hits a mounting pin it would likely cut through but this is extrapolated from the little I know of the destructiveness of shock impingement. Other bad things could happen too but that's way deeper into it than I understand. All in all, the edge packing seems important.


On rethought, the hypersonic flow might pressurize under the tile and hit an equilibrium stopping further flow. Wouldn't that be convenient?


More expertise needed to take this any further.


Phil
Title: Re: Starship heat shield
Post by: armchairfan on 08/16/2020 10:32 pm
Apropos multiple-pass reentry ... a year-old (i.e. ancient) tweet from Elon:

https://twitter.com/elonmusk/status/1176566245925085184

Quote
For sure more than one pass coming back to Earth. To Mars could maybe work single pass, but two passes probably wise.
Title: Re: Starship heat shield
Post by: john smith 19 on 08/17/2020 06:34 am
Hypersonic flow can be very destructive. Think of it like a cutting torch. Fast moving. Very hot.

What happens if it gets to the skin depends on what matters more. Thermal conductivity or melting point. Steel's thermal conductivity is about 1/10 that of aluminum but its BP is about 2.5x higher.

If mp trumps lambda the heat stays local but enough of it is conducted away to prevent failure. If lambda trumps mp it stays local and builds up to a point where the skin fails.

If the tiles are on stand offs from the skin a tile loss creates a duct for airflow to heat much more of the skin, with nothing to stop the flow

Earth base fire regulations require intumescent fire protection. This swells on heating to block smoke flow and protect things like light fittings. Something like that on back sides of the tile might be needed. The tiles stay mostly out of contact with the skin.

Tile fails -->Hot airflow triggers swelling around edges --> airflow localized at missing tile area --> backside cooling adequate to prevent structural failure

Well, it might work this way. But preventing a tile failure to begin with is still best. :(
Title: Re: Starship heat shield
Post by: HVM on 08/17/2020 08:53 pm
Odd that they selected three pin arrangement (-Surprised Pikachu), all three pin tiles at SN5 were fractured, but still attached

The three-pin arrangement assures three-sided symmetry of the tile which simplifies the production process a lot: the tiles basically have no fixed orientation but can be turned "any way you may wish".
But where are the tri-pins here, ha! Three plasma true bungs?
Title: Re: Starship heat shield
Post by: Twark_Main on 08/17/2020 08:56 pm
Three plasma true bungs?

I'll have the same, barkeep, and one Pan-Galactic Gargle Blaster to go!  :D
Title: Re: Starship heat shield
Post by: HVM on 08/24/2020 06:03 pm
The tile design is not there yet.
Title: Re: Starship heat shield
Post by: rsdavis9 on 08/24/2020 06:05 pm
The tile design is not there yet.

vibration from a single engine shattering tile?
Think of 6 at once.
Maybe when they attach the vacuum bells to the skirt it wont vibrate as much?
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 08/24/2020 07:21 pm
The tile design is not there yet.

vibration from a single engine shattering tile?
Think of 6 at once.
Maybe when they attach the vacuum bells to the skirt it wont vibrate as much?

I don't see evidence of shattering in that picture, just a missing tile.

They're trying things right now.  They're learning what doesn't work.  I don't see failures now as a sign that they aren't going to find a solution that does work.

Title: Re: Starship heat shield
Post by: enbandi on 08/24/2020 07:23 pm
The tile design is not there yet.

I think those tiles are not the latest design. Installed 2 months ago. Designed and manufactured probably before the first SN4 static fore results.

I think we seen a fully pinned barrel section, which I read as a sign of confidence of what they have now. (Can be a pin welding experiment also, WO finalized tile design)
Title: Re: Starship heat shield
Post by: Rocket Science on 08/24/2020 07:38 pm
Might be worth investigating a large heat shield glove formed in a mold as a possibility... Mass reproducible, simpler, repairable, replaceable, less fragile and labor intensive... IMHO
Title: Re: Starship heat shield
Post by: HVM on 08/24/2020 07:58 pm
I don't see evidence of shattering in that picture, just a missing tile.
We don't see skirt's metal wall, we see a white hexagon that can be felt pad, adhesive or the inner insulator of the tile.

Felt pads are gray, test adhesive is green, and insulator showing in the inner part of the tile's edge is white... Ergo.
Title: Re: Starship heat shield
Post by: envy887 on 08/24/2020 09:29 pm
Might be worth investigating a large heat shield glove formed in a mold as a possibility... Mass reproducible, simpler, repairable, replaceable, less fragile and labor intensive... IMHO

Larger sections would probably be more fragile, if anything.
Title: Re: Starship heat shield
Post by: Rocket Science on 08/24/2020 09:52 pm
Might be worth investigating a large heat shield glove formed in a mold as a possibility... Mass reproducible, simpler, repairable, replaceable, less fragile and labor intensive... IMHO

Larger sections would probably be more fragile, if anything.
Large section heat shield material was specified for the Boeing X-20 Dyna-Soar and we are now almost six decades advanced in material science since then... What I have in mind would add structural integrity for the vehicle as well...YMMV
Title: Re: Starship heat shield
Post by: EeeVee3 on 08/25/2020 09:13 am
It might be that the Hex tiles are required to allow the expansion and contraction of the steel tanks that will take place due to temperature and pressure fluctuations, which would crack a large molded piece.
Title: Re: Starship heat shield
Post by: enbandi on 08/25/2020 01:10 pm
Might be worth investigating a large heat shield glove formed in a mold as a possibility... Mass reproducible, simpler, repairable, replaceable, less fragile and labor intensive... IMHO

Larger sections would probably be more fragile, if anything.
Large section heat shield material was specified for the Boeing X-20 Dyna-Soar and we are now almost six decades advanced in material science since then... What I have in mind would add structural integrity for the vehicle as well...YMMV

Maybe not the best/most valid example, as it is predate all the experience with the shuttle....

Nice concept, but a concept only.....
Title: Re: Starship heat shield
Post by: livingjw on 08/25/2020 01:20 pm
Tile broke, adhesive held, felt isolation pad held. Tile insulation blocks have very little strength.
Title: Re: Starship heat shield
Post by: envy887 on 08/25/2020 01:24 pm
Tile broke, adhesive held, felt isolation pad held. Tile insulation blocks have very little strength.

Hmm. Why is the white hex so much smaller than the surrounding tiles?

It looks like the black exterior shell has some thickness, perhaps 0.5 to 0.75 inch, and is probably a more structural material then the white tile interior which is mainly insulation. So ISTM that the high-temp adhesive was primarily holding the black shell, and when the adhesive failed around the edges, the while interior material also fractured and most of the tile fell off.
Title: Re: Starship heat shield
Post by: Rocket Science on 08/25/2020 01:32 pm
Might be worth investigating a large heat shield glove formed in a mold as a possibility... Mass reproducible, simpler, repairable, replaceable, less fragile and labor intensive... IMHO

Larger sections would probably be more fragile, if anything.
Large section heat shield material was specified for the Boeing X-20 Dyna-Soar and we are now almost six decades advanced in material science since then... What I have in mind would add structural integrity for the vehicle as well...YMMV

Maybe not the best/most valid example, as it is predate all the experience with the shuttle....

Nice concept, but a concept only.....
StarShip is still only a concept...
Title: Re: Starship heat shield
Post by: envy887 on 08/25/2020 01:36 pm
Might be worth investigating a large heat shield glove formed in a mold as a possibility... Mass reproducible, simpler, repairable, replaceable, less fragile and labor intensive... IMHO

Larger sections would probably be more fragile, if anything.
Large section heat shield material was specified for the Boeing X-20 Dyna-Soar and we are now almost six decades advanced in material science since then... What I have in mind would add structural integrity for the vehicle as well...YMMV

Maybe not the best/most valid example, as it is predate all the experience with the shuttle....

Nice concept, but a concept only.....

It's similar to how the heat shields on Orion, Starliner, Dragon, etc work: the TPS tiles are attached to a substructure, and that subassembly is then attached to the vehicle primary structure / pressure vessel. Or the TPS is directly integrated into a composite secondary structure, like the avcoat injected cells on Apollo and the initial Orion shield.

Shuttle went the route of attaching the TPS directly to the vehicle primary structure, with the TPS assembly itself having little structural role. At the scale of Shuttle and Starship, the mass penalty for a second structure is probably a significant negative factor.
Title: Re: Starship heat shield
Post by: livingjw on 08/25/2020 01:40 pm
Tile broke, adhesive held, felt isolation pad held. Tile insulation blocks have very little strength.

Hmm. Why is the white hex so much smaller than the surrounding tiles?

It looks like the black exterior shell has some thickness, perhaps 0.5 to 0.75 inch, and is probably a more structural material then the white tile interior which is mainly insulation. So ISTM that the high-temp adhesive was primarily holding the black shell, and when the adhesive failed around the edges, the while interior material also fractured and most of the tile fell off.

- To me, this looks very similar to the Shuttle tiling technique. Bondline temperatures will be higher. I don't know how well this would work for flap surfaces unless their skins are designed to not buckle.

- Outer surface coating on Shuttle tile does not cover the bottom, though, the bottom is strengthened before bonding to the felt, but I forget exactly how.

- The outer surface coating is very thin. I suspect that there is an overhang around the perimeter of the tile base to anchor filler material which goes between the tile.

John
Title: Re: Starship heat shield
Post by: Rocket Science on 08/25/2020 01:46 pm
Might be worth investigating a large heat shield glove formed in a mold as a possibility... Mass reproducible, simpler, repairable, replaceable, less fragile and labor intensive... IMHO

Larger sections would probably be more fragile, if anything.
Large section heat shield material was specified for the Boeing X-20 Dyna-Soar and we are now almost six decades advanced in material science since then... What I have in mind would add structural integrity for the vehicle as well...YMMV

Maybe not the best/most valid example, as it is predate all the experience with the shuttle....

Nice concept, but a concept only.....

It's similar to how the heat shields on Orion, Starliner, Dragon, etc work: the TPS tiles are attached to a substructure, and that subassembly is then attached to the vehicle primary structure / pressure vessel. Or the TPS is directly integrated into a composite secondary structure like the avcoat injected cells on Apollo and the initial Orion shield.

Shuttle went the route of attaching the TPs directly to the vehicle primary structure. At the scale of Shuttle and Starship, the mass penalty for a second structure is probably a significant negative factor.
I stated is the other StarShip thread some time back that as currently envisioned the structure is not up to repeated cycling and reentry forces and "may" need additional stiffeners such as longerons IMHO. Thus the heat shield structure that I suggest is what will provide that just as I suggested the "Grid-Fins" 10 years back. They are learning as they go, time will tell what the vehicle evolves into... I continue to enjoy sitting back and observing the process... :)
Title: Re: Starship heat shield
Post by: livingjw on 08/25/2020 01:53 pm

I stated is the other StarShip thread some time back that as currently envisioned the structure is not up to repeated cycling and reentry forces and "may" need additional stiffeners such as longerons IMHO. Thus the heat shield structure that I suggest is what will provide that just as I suggested the "Grid-Fins" 10 years back. They are learning as they go, time will tell what the vehicle evolves into... I continue to enjoy sitting back and observing the process... :)

Are you saying that SpaceX has not analyzed and design their vehicle tank structure correctly? I don't understand why you think that their pressure stabilized tank structure is inadequate for reentry. Care to elaborate?

John
Title: Re: Starship heat shield
Post by: Rocket Science on 08/25/2020 02:02 pm

I stated is the other StarShip thread some time back that as currently envisioned the structure is not up to repeated cycling and reentry forces and "may" need additional stiffeners such as longerons IMHO. Thus the heat shield structure that I suggest is what will provide that just as I suggested the "Grid-Fins" 10 years back. They are learning as they go, time will tell what the vehicle evolves into... I continue to enjoy sitting back and observing the process... :)

Are you saying that SpaceX has not analyzed and design their vehicle tank structure correctly? I don't understand why you think that their pressure stabilized tank structure is inadequate for reentry. Care to elaborate?

John
It would not be the first structure or vehicle that did not perform as envisioned by designers. Engineering history texts are full of what to be wary of and I pass that on to my students. It will have to prove itself in test flights and operation as have other vehicles... The design has changed before by SpaceX and "may" change again as they are breaking new ground... IMHO

Edit:typo
Title: Re: Starship heat shield
Post by: livingjw on 08/25/2020 02:16 pm

I stated is the other StarShip thread some time back that as currently envisioned the structure is not up to repeated cycling and reentry forces and "may" need additional stiffeners such as longerons IMHO. Thus the heat shield structure that I suggest is what will provide that just as I suggested the "Grid-Fins" 10 years back. They are learning as they go, time will tell what the vehicle evolves into... I continue to enjoy sitting back and observing the process... :)

Are you saying that SpaceX has not analyzed and design their vehicle tank structure correctly? I don't understand why you think that their pressure stabilized tank structure is inadequate for reentry. Care to elaborate?

John
I would not be the first structure or vehicle that did not perform as envisioned by designers. Engineering history texts are full of what to be wary of and I pass that on to my students. It will have to prove itself in test flights and operation as have other vehicles... The design has changed before by SpaceX and "may" change again as they are breaking new ground... IMHO

- I agree, structure has to be tested in flight. I also agree that the design has changed and will continue to, but you made a very specific claim:
   ...." the structure is not up to repeated cycling and reentry forces and "may" need additional stiffeners such as longerons"....

Why do you think the current structure is inadequate for repeated cycling and reentry forces?

John
Title: Re: Starship heat shield
Post by: envy887 on 08/25/2020 02:23 pm
Might be worth investigating a large heat shield glove formed in a mold as a possibility... Mass reproducible, simpler, repairable, replaceable, less fragile and labor intensive... IMHO

Larger sections would probably be more fragile, if anything.
Large section heat shield material was specified for the Boeing X-20 Dyna-Soar and we are now almost six decades advanced in material science since then... What I have in mind would add structural integrity for the vehicle as well...YMMV

Maybe not the best/most valid example, as it is predate all the experience with the shuttle....

Nice concept, but a concept only.....

It's similar to how the heat shields on Orion, Starliner, Dragon, etc work: the TPS tiles are attached to a substructure, and that subassembly is then attached to the vehicle primary structure / pressure vessel. Or the TPS is directly integrated into a composite secondary structure like the avcoat injected cells on Apollo and the initial Orion shield.

Shuttle went the route of attaching the TPs directly to the vehicle primary structure. At the scale of Shuttle and Starship, the mass penalty for a second structure is probably a significant negative factor.
I stated is the other StarShip thread some time back that as currently envisioned the structure is not up to repeated cycling and reentry forces and "may" need additional stiffeners such as longerons IMHO. Thus the heat shield structure that I suggest is what will provide that just as I suggested the "Grid-Fins" 10 years back. They are learning as they go, time will tell what the vehicle evolves into... I continue to enjoy sitting back and observing the process... :)

I think a double structure is always heavier than just making the primary strong enough in the first place. On small vehicles the separate subassembly is used because it's easier to put together that way, not because it makes the final assembly stronger for a given mass. But handling a huge heatshield subassembly is just as unwieldy as handling a huge vehicle with an integrated heatshield, so that reason goes away with size.

If it not easier to handle/assemble, and it's not lighter, what's the point?
Title: Re: Starship heat shield
Post by: Rocket Science on 08/25/2020 02:59 pm

I stated is the other StarShip thread some time back that as currently envisioned the structure is not up to repeated cycling and reentry forces and "may" need additional stiffeners such as longerons IMHO. Thus the heat shield structure that I suggest is what will provide that just as I suggested the "Grid-Fins" 10 years back. They are learning as they go, time will tell what the vehicle evolves into... I continue to enjoy sitting back and observing the process... :)

Are you saying that SpaceX has not analyzed and design their vehicle tank structure correctly? I don't understand why you think that their pressure stabilized tank structure is inadequate for reentry. Care to elaborate?

John
I would not be the first structure or vehicle that did not perform as envisioned by designers. Engineering history texts are full of what to be wary of and I pass that on to my students. It will have to prove itself in test flights and operation as have other vehicles... The design has changed before by SpaceX and "may" change again as they are breaking new ground... IMHO

- I agree, structure has to be tested in flight. I also agree that the design has changed and will continue to, but you made a very specific claim:
   ...." the structure is not up to repeated cycling and reentry forces and "may" need additional stiffeners such as longerons"....

Why do you think the current structure is inadequate for repeated cycling and reentry forces?

John
John, without boring folks too much on the wrong thread I don't see the load paths though the structure stressed skin without a keel structure from the control fins on a reusable vehicle as envisioned by Elon... They are tackling the design by "first principles" so it is evolutionary process by nature... For example Columbia and Challenger were overbuilt and later vehicle were lighter as the database grew. I rather take weight out and simplify through flight test and production. It just a different approach... If the design succeeds as is I'm happy to have learned something new that has been added to the aerospace database... :)
Title: Re: Starship heat shield
Post by: volker2020 on 08/25/2020 03:24 pm
Tile broke, adhesive held, felt isolation pad held. Tile insulation blocks have very little strength.
None thing I don't understand about this picture. Where are the welded pins? Was this tile only glued to the surface?
Title: Re: Starship heat shield
Post by: rsdavis9 on 08/25/2020 03:32 pm
Tile broke, adhesive held, felt isolation pad held. Tile insulation blocks have very little strength.
None thing I don't understand about this picture. Where are the welded pins? Was this tile only glued to the surface?

It looks like this tile was a test of glued only. We have seen tiles that are stud pinned and seen a cracked remnant.
Title: Re: Starship heat shield
Post by: enbandi on 08/25/2020 04:21 pm
Tile broke, adhesive held, felt isolation pad held. Tile insulation blocks have very little strength.
None thing I don't understand about this picture. Where are the welded pins? Was this tile only glued to the surface?

It looks like this tile was a test of glued only. We have seen tiles that are stud pinned and seen a cracked remnant.

Remember the timeline which is a bit fuzzy here. What we see now is SN6 manufactured 2 months ago, but only recently tested/fired. Before that there was SN5 with different pin styles, and lately we seen some pin welding experiments also.

Timeline if I remember correctly:
 - SN5 built, pinned tiles, different styles (1 pin, 3 pin, holes, and continous surface)
 - SN6 built, glued tiles
 - Pin welding experiments, different pin types (rounded, double clip, etc...)
 - SN5 results (some tiles held, some of them broken: that is where we seen the ramains of the internal reinforcing studs)
 - Pin welding on full barrel section

If I read this correctly, one of the SN5 techniques have been found adequate, and they moved ahead with that. If that is true, this SN6 stlye, with adhesives could be a backup plan, now unnecessary.
Title: Re: Starship heat shield
Post by: livingjw on 08/26/2020 12:27 am

- I agree, structure has to be tested in flight. I also agree that the design has changed and will continue to, but you made a very specific claim:
   ...." the structure is not up to repeated cycling and reentry forces and "may" need additional stiffeners such as longerons"....

Why do you think the current structure is inadequate for repeated cycling and reentry forces?

John
John, without boring folks too much on the wrong thread I don't see the load paths though the structure stressed skin without a keel structure from the control fins on a reusable vehicle as envisioned by Elon... They are tackling the design by "first principles" so it is evolutionary process by nature... For example Columbia and Challenger were overbuilt and later vehicle were lighter as the database grew. I rather take weight out and simplify through flight test and production. It just a different approach... If the design succeeds as is I'm happy to have learned something new that has been added to the aerospace database... :)

- I agree, early development vehicles are designed with more robustness to cover uncertainty in the loads and stress models. As flight data is gathered the design is refined to better match reality. The point I want to make is that the loads and stress models exist before the vehicle is built, even development vehicles.  I am sure its not your intent, but you make it sound like SpaceX is winging it. I am positive they have full computer models of the loads and stresses for the entire vehicle throughout the flight envelope.

- Forward and aft flap actuators are the only points which apply a spanwise moment to the vehicle. We definitely have seen the forward internal structural ring which transmits flap torque through the nose cone. I am pretty sure we have seen the aft internal structural ring as well.

- What would the keel structure do?  The Flap torque goes across the vehicle. A keel would resist lengthwise moments and is not needed since the pressurized tanks provide all the lengthwise bending strength needed.

- I am still confused as to your concern. A diagram might help.

John

Title: Re: Starship heat shield
Post by: livingjw on 08/26/2020 01:30 am
Looks like SpaceX is getting serious about mechanically fastened TPS.
Title: Re: Starship heat shield
Post by: GWH on 08/26/2020 01:42 am
Thats a lot of weld on studs! Good task for a robot.
Title: Re: Starship heat shield
Post by: Dr.Unhold on 08/26/2020 09:45 am
So, most (or all?) of the tile fastening tests were performed at the skirt of SS.

Do you think this is because there the most stresses, e.g. from vibrations, are?

I ask with this question in mind: Is there the possibility that welding tiles affects the strength of the tank? (Thus they postpone testing there because it only makes sense for them to test it on their final alloy tanks)
Title: Re: Starship heat shield
Post by: HVM on 08/26/2020 12:01 pm
Thats a lot of weld on studs! Good task for a robot.
Stud weld point locations are marked with pen and ruler (or straightedge with slight curve ; ) so not a robot work, yet?
Title: Re: Starship heat shield
Post by: SkyRate on 08/26/2020 12:43 pm
So, most (or all?) of the tile fastening tests were performed at the skirt of SS.
Do you think this is because there the most stresses, e.g. from vibrations, are?
Vibration/acoustic stress should be the worst there, and the skirt might even experience large-scale flexing. Especially during landing, on short legs, the engine bay must have a lot of low-frequency resonances. I wish we could see high-speed footage.
On the other hand there will be very different thermal stresses on the outside of the tanks. They will shrink significantly when fueled, so the tile gaps will have to accommodate that. SN4 had a 7-tile test patch near the bottom of the CH4 tank.
Title: Re: Starship heat shield
Post by: Rocket Science on 08/26/2020 03:08 pm

- I agree, structure has to be tested in flight. I also agree that the design has changed and will continue to, but you made a very specific claim:
   ...." the structure is not up to repeated cycling and reentry forces and "may" need additional stiffeners such as longerons"....

Why do you think the current structure is inadequate for repeated cycling and reentry forces?

John
John, without boring folks too much on the wrong thread I don't see the load paths though the structure stressed skin without a keel structure from the control fins on a reusable vehicle as envisioned by Elon... They are tackling the design by "first principles" so it is evolutionary process by nature... For example Columbia and Challenger were overbuilt and later vehicle were lighter as the database grew. I rather take weight out and simplify through flight test and production. It just a different approach... If the design succeeds as is I'm happy to have learned something new that has been added to the aerospace database... :)

- I agree, early development vehicles are designed with more robustness to cover uncertainty in the loads and stress models. As flight data is gathered the design is refined to better match reality. The point I want to make is that the loads and stress models exist before the vehicle is built, even development vehicles.  I am sure its not your intent, but you make it sound like SpaceX is winging it. I am positive they have full computer models of the loads and stresses for the entire vehicle throughout the flight envelope.

- Forward and aft flap actuators are the only points which apply a spanwise moment to the vehicle. We definitely have seen the forward internal structural ring which transmits flap torque through the nose cone. I am pretty sure we have seen the aft internal structural ring as well.

- What would the keel structure do?  The Flap torque goes across the vehicle. A keel would resist lengthwise moments and is not needed since the pressurized tanks provide all the lengthwise bending strength needed.

- I am still confused as to your concern. A diagram might help.

John
John, I make no accusations of SpaceX "winging it". I'm only quoting Elon's design philosophy of working from "first principles of physics" thus writing their own textbook as they progress though development. Competitors will go through years of engineering analysis before ever considering bending metal to the point of paralysis.  Elon prefers to bend metal and engineer as you go...They continue to go where other aerospace giants fear to tread which I think is awesome... :)

~Rob
Title: Re: Starship heat shield
Post by: scdavis on 08/26/2020 04:32 pm
Thats a lot of weld on studs! Good task for a robot.
Stud weld point locations are marked with pen and ruler (or straightedge with slight curve ; ) so not a robot work, yet?

I couldn't guess from the image whether a robot was used or not - the pen marks might suggest it was manual, but not quite proof.

If I were them, I'd start with a 2-stud fixture and program the robot to weld the 3 studs with high precision. The position of the tile itself does not need to be nearly as precise since they design has a gap between tiles. I'd mark up the barrel from a template (as in the image), then test the robot's ability to affix the 3 studs accurately. Visual inspection after would show the robot placed each stud where it needs to go (matches pen marks). Then I'd update the robot programming to be able to weld a vertical section of tiles; then a patch of adjacent tiles.
Title: Re: Starship heat shield
Post by: Johnnyhinbos on 08/26/2020 06:32 pm
Thats a lot of weld on studs! Good task for a robot.
Stud weld point locations are marked with pen and ruler (or straightedge with slight curve ; ) so not a robot work, yet?
I'm fairly confident the pins were stud welded by one of the new robots. Right after the attached photo we started to see the bulk install of pins and heat shield patterns.


Image credit: BocaChicaGal
Title: Re: Starship heat shield
Post by: enbandi on 08/26/2020 08:12 pm
Thats a lot of weld on studs! Good task for a robot.
Stud weld point locations are marked with pen and ruler (or straightedge with slight curve ; ) so not a robot work, yet?

More like QA/test markings. After the robotic installation, they measured back the result, and marked directly on the surface (any other way are a bit hard to follow which stud is which).
Title: Re: Starship heat shield
Post by: HVM on 09/07/2020 03:51 pm
...Edit: All the TPS tiles fell off!
Not surprising because just a static fire fractured one of them.
Title: Re: Starship heat shield
Post by: CJ on 09/07/2020 08:45 pm
...Edit: All the TPS tiles fell off!
Not surprising because just a static fire fractured one of them.

Looks to me like they have some major problems regarding that method of tile mount. I hope the pinned tiles (which these are not) fare better.

I'm wondering if they are having a resonance problem; perhaps the shape, size, and composition of the tiles makes them prone to resonance issues in the acoustic environment they experience. 

I also wonder if the tile mounting compound (I think that's what it is) that we see in the pics (the white) could also have some ablative thermal properties of its own, or could be made to have, so that it could protect the steel below enough for one survivable reentry in case of the loss of a tile. Far better than LOV, if so.

Would anyone happen to know how critical a prop tank burn-through would be during reentry? I know Starship relies on tank pressure for some of its structural strength, but is that strength crucial for reentry and landing? The reason I ask is that if it is, a single burn-through on a tank skin is LOV. If not, the loss of a single may be survivable. 
Title: Re: Starship heat shield
Post by: InterestedEngineer on 09/07/2020 09:25 pm


I also wonder if the tile mounting compound (I think that's what it is) that we see in the pics (the white) could also have some ablative thermal properties of its own, or could be made to have, so that it could protect the steel below enough for one survivable reentry in case of the loss of a tile. Far better than LOV, if so.


If an ablative blanket works, I start to wonder whether coming up with a method to quickly wrap a light enough ablative blanket around a Starship after each re-entry might be fast and cheap enough to consider it a "refueling" step - i.e. do it every time.  Analogous to the discontinued idea of the battery swap "refuel" on a Tesla


Awaiting the throwing of rocks.
Title: Re: Starship heat shield
Post by: Slarty1080 on 09/07/2020 09:47 pm
...Edit: All the TPS tiles fell off!
Not surprising because just a static fire fractured one of them.

Looks to me like they have some major problems regarding that method of tile mount. I hope the pinned tiles (which these are not) fare better.

I'm wondering if they are having a resonance problem; perhaps the shape, size, and composition of the tiles makes them prone to resonance issues in the acoustic environment they experience. 

I also wonder if the tile mounting compound (I think that's what it is) that we see in the pics (the white) could also have some ablative thermal properties of its own, or could be made to have, so that it could protect the steel below enough for one survivable reentry in case of the loss of a tile. Far better than LOV, if so.

Would anyone happen to know how critical a prop tank burn-through would be during reentry? I know Starship relies on tank pressure for some of its structural strength, but is that strength crucial for reentry and landing? The reason I ask is that if it is, a single burn-through on a tank skin is LOV. If not, the loss of a single may be survivable.
I think any burn through = LOV. As soon as there is a hole pressurised gas or liquid will be ejected from the hole acting like an RCS. During re-entry forces on the skin near the hole and pressure from inside would also probably cause a major tear / rupture.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/07/2020 10:06 pm
...Edit: All the TPS tiles fell off!
Not surprising because just a static fire fractured one of them.

Looks to me like they have some major problems regarding that method of tile mount. I hope the pinned tiles (which these are not) fare better.

I'm wondering if they are having a resonance problem; perhaps the shape, size, and composition of the tiles makes them prone to resonance issues in the acoustic environment they experience. 

I also wonder if the tile mounting compound (I think that's what it is) that we see in the pics (the white) could also have some ablative thermal properties of its own, or could be made to have, so that it could protect the steel below enough for one survivable reentry in case of the loss of a tile. Far better than LOV, if so.

Would anyone happen to know how critical a prop tank burn-through would be during reentry? I know Starship relies on tank pressure for some of its structural strength, but is that strength crucial for reentry and landing? The reason I ask is that if it is, a single burn-through on a tank skin is LOV. If not, the loss of a single may be survivable.
I think there's a misconception here. Maybe mine, maybe yours. My take is that the white is not the bonding. The bonding goo was green. This looks like the tile delaminated and the white is the layer under the black face.


I'm waiting for a closeup to see if it delaminated immediately under the surface layer or across the bottom. I think I saw a closeup from after the static fire and that white layer looked real thin. If this is right the bonding worked like a champ and the tile couldn't take it. Maybe vibration, maybe differential thermal expansion.


And yeah, I have to go with the crowd. A burn through is LOM.
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 09/07/2020 10:11 pm
And yeah, I have to go with the crowd. A burn through is LOM.

Yes, burn through is likely LOM.  But loss of a tile does not necessarily equal burn through.
Title: Re: Starship heat shield
Post by: CJ on 09/07/2020 10:20 pm
Looks to me like they have some major problems regarding that method of tile mount. I hope the pinned tiles (which these are not) fare better.

I'm wondering if they are having a resonance problem; perhaps the shape, size, and composition of the tiles makes them prone to resonance issues in the acoustic environment they experience. 

I also wonder if the tile mounting compound (I think that's what it is) that we see in the pics (the white) could also have some ablative thermal properties of its own, or could be made to have, so that it could protect the steel below enough for one survivable reentry in case of the loss of a tile. Far better than LOV, if so.

Would anyone happen to know how critical a prop tank burn-through would be during reentry? I know Starship relies on tank pressure for some of its structural strength, but is that strength crucial for reentry and landing? The reason I ask is that if it is, a single burn-through on a tank skin is LOV. If not, the loss of a single may be survivable.
I think there's a misconception here. Maybe mine, maybe yours. My take is that the white is not the bonding. The bonding goo was green. This looks like the tile delaminated and the white is the layer under the black face.


I'm waiting for a closeup to see if it delaminated immediately under the surface layer or across the bottom. I think I saw a closeup from after the static fire and that white layer looked real thin. If this is right the bonding worked like a champ and the tile couldn't take it. Maybe vibration, maybe differential thermal expansion.


And yeah, I have to go with the crowd. A burn through is LOM.

If there is a misconception here, I suspect it is mine. I find your reasoning persuasive - the white is part of the tile. 

I found a closeup that may help regarding where the tiles came apart. (one of BocaChicaGals superb photos.). 4th pic down.
https://forum.nasaspaceflight.com/index.php?topic=51332.msg2129576#msg2129576
One thing I can see is that the misconception was indeed mine; the adhesive isn't the white, it's the green.
Title: Re: Starship heat shield
Post by: livingjw on 09/07/2020 10:34 pm
This looks very much similar to Shuttle tile. The white appears to be fractured insulation tile which is white. The black outer covering is paper thin glass like coating to toughen the outer layer of the fragile insulation block.

They look like they are even mounted on a felt pad, but maybe not.

John
Title: Re: Starship heat shield
Post by: RoboGoofers on 09/08/2020 01:20 am
When the attachment system fails, is half a tile (bonded) better than no tile(clips)?
Title: Re: Starship heat shield
Post by: _MECO on 09/08/2020 01:50 am
Another closeup of busted heat shield tiles from the photos and updates thread.
Title: Re: Starship heat shield
Post by: livingjw on 09/08/2020 03:07 am
When the attachment system fails, is half a tile (bonded) better than no tile(clips)?

The attachment did not fail, the tile did. It wasn't strong enough.

John
Title: Re: Starship heat shield
Post by: Redclaws on 09/08/2020 03:25 am
John,

I find that strength issue and your comment that it looks similar to the shuttle tile very concerning - If you don’t mind taking a shot at the question, what’s to avoid the brittleness and general extreme fussiness (stemming in significant part from the fragility, I think) that plagued the shuttle tiles?
Title: Re: Starship heat shield
Post by: Wolfram66 on 09/08/2020 03:28 am
John,

I find that strength issue and your comment that it looks similar to the shuttle tile very concerning - If you don’t mind taking a shot at the question, what’s to avoid the brittleness and general extreme fussiness (stemming in significant part from the fragility, I think) that plagued the shuttle tiles?

I am thinking these tiles are more in the lines of the X-37B tufroc tiles.
Title: Re: Starship heat shield
Post by: Redclaws on 09/08/2020 03:34 am
Wolfram,

Can you square that with John’s comments above about apparent tile design?  I don’t really know how TUFROC compares to the shuttle tile design.
Title: Re: Starship heat shield
Post by: warp99 on 09/08/2020 04:52 am
John,

I find that strength issue and your comment that it looks similar to the shuttle tile very concerning - If you don’t mind taking a shot at the question, what’s to avoid the brittleness and general extreme fussiness (stemming in significant part from the fragility, I think) that plagued the shuttle tiles?

The TUFROC system is supposed to provide greater tile strength by embedding the silica/alumina ceramic in a fiber matrix.

The fractured tiles show no sign of that in the fracture zone so either it is not TUFROC or the fibers are very short and only provide very localised support.  There could still be a long way to go on the tile development front but at least they are learning of the issues at an early stage. 

Personally I think they could adopt an ablative tile system like PICA-X for early flights until the ceramic tiles have reached sufficient maturity.  SpaceX have stated numerous times that the Dragon heatshield is barely damaged by re-entry and could be used many times.  It would be feasible to say replace heat affected tiles on the center line of the windward side of tankers after five flights and the complete set of tiles after ten flights and still perform the Artemis and Dear Moon missions for example.
Title: Re: Starship heat shield
Post by: Ocisly on 09/08/2020 05:49 am
Another closeup of busted heat shield tiles from the photos and updates thread.
Do we know for sure that the tiles fell off?

It's possible they were removed after flight for inspection.
Title: Re: Starship heat shield
Post by: _MECO on 09/08/2020 06:33 am
Another closeup of busted heat shield tiles from the photos and updates thread.
Do we know for sure that the tiles fell off?

It's possible they were removed after flight for inspection.

Good point. They're still clearly broken though
Title: Re: Starship heat shield
Post by: HVM on 09/08/2020 08:38 am
STS TPS: If you are not visited KSC as US high-schooler
https://youtu.be/CchPemGaEmw

And how tiles are bond, (didn't work for SpX)
https://youtu.be/qA4P6jqjQBg
I want to see The Hyper Sonic DC-3!
Title: Re: Starship heat shield
Post by: livingjw on 09/08/2020 01:50 pm
John,

I find that strength issue and your comment that it looks similar to the shuttle tile very concerning - If you don’t mind taking a shot at the question, what’s to avoid the brittleness and general extreme fussiness (stemming in significant part from the fragility, I think) that plagued the shuttle tiles?

The TUFROC system is supposed to provide greater tile strength by embedding the silica/alumina ceramic in a fiber matrix.


The fractured tiles show no sign of that in the fracture zone so either it is not TUFROC or the fibers are very short and only provide very localised support.  There could still be a long way to go on the tile development front but at least they are learning of the issues at an early stage. 

Personally I think they could adopt an ablative tile system like PICA-X for early flights until the ceramic tiles have reached sufficient maturity.  SpaceX have stated numerous times that the Dragon heatshield is barely damaged by re-entry and could be used many times.  It would be feasible to say replace heat affected tiles on the center line of the windward side of tankers after five flights and the complete set of tiles after ten flights and still perform the Artemis and Dear Moon missions for example.

- TUFROC is not one thing, but a set of improvements to various materials used to produce a Thermal Protection System, TPS.

- Fused silica/alumina ceramic has been strengthened by additions of different binders.

- More robust outer coverings have been developed since the original Shuttle tile.

- Imbedding structural elements for mechanical attachments we have already seen. These can be made from structural ceramic such as silicon carbide composite, co-cured into the tile.

- There are many options. They are sifting through them.

- Greate video of the high school tour demo. Shows pretty much the whole process except the machining to final size and the outer coating.

John
Title: Re: Starship heat shield
Post by: Redclaws on 09/08/2020 02:18 pm
Thanks very much for the interesting answers.

I agree they could clearly use an ablative/consumable heat shield for a while, but for true rapid reusability...  Hopefully they can sort something out.
Title: Re: Starship heat shield
Post by: Rocket Science on 09/08/2020 03:08 pm
I would do this demo with my Physics students years back with my Shuttle tile samples for the Thermodynamics unit... It always blew their minds... ;D
https://www.youtube.com/watch?v=Pp9Yax8UNoM
Title: Re: Starship heat shield
Post by: RoboGoofers on 09/08/2020 04:15 pm
When the attachment system fails, is half a tile (bonded) better than no tile(clips)?

The attachment did not fail, the tile did. It wasn't strong enough.

John
true. That I meant was more whether a half thick tile is better than no tile?
Title: Re: Starship heat shield
Post by: OTV Booster on 09/08/2020 05:21 pm
This looks very much similar to Shuttle tile. The white appears to be fractured insulation tile which is white. The black outer covering is paper thin glass like coating to toughen the outer layer of the fragile insulation block.

They look like they are even mounted on a felt pad, but maybe not.

John
I found the pic and had it queued up but MECO beat me to it. There is a tan layer under the white. This could be the felt layer and reinforces my earlier speculation that the problem might be vibration.


The felt (if that's what it is) should take care of differential thermal expansion. With the skin surface being curved and the tile being flat, the center of the tile would damp slightly different than the edges and the tile would be 'ringing' at different frequencies across its width. Normally I would expect this to break the edges off but I'm guessing the black covering is stiffer than the white, so it delaminated instead.


Whatever the mechanism, that green goo works really well.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/08/2020 05:25 pm
When the attachment system fails, is half a tile (bonded) better than no tile(clips)?
If they can get the problem down to a low roar, it might be ok for a 'one EDL only'. Maybe.
Title: Re: Starship heat shield
Post by: eriblo on 09/08/2020 05:27 pm
When the attachment system fails, is half a tile (bonded) better than no tile(clips)?

The attachment did not fail, the tile did. It wasn't strong enough.

John
true. That I meant was more whether a half thick tile is better than no tile?
It wont hurt and might be enough. Looking at the properties* of 304L it seems like it might start annealing and loosing the full-hard strength around 680-700K so the goal is likely to for the tiles to keep it below that. The steel should however be able to take maybe 300-400K more before rupturing (if the tanks are pressurized to a little over 1 atm, i.e. 1/8 of maximum pressure).

*It is a little harder do find data for high enough temperatures and short time scales.
Title: Re: Starship heat shield
Post by: enbandi on 09/14/2020 12:03 pm
Taking the number of tiles (studs for now) on SN8 and the announced 20km hop, the exclusion zone under the trajectory will be an interesting place.

Nomadd should be able to collect some tile samples from the beach after. :)

A bit more seriously: given the latest results (some tiles hold, but its not guaranteed) will they risk that hop with numerous tiles? Tile fragments landing in the ocean may not a problem, but they can end up with debris cleaning/pickup teams at the beach, if not for environmental than for ITAR.
Title: Re: Starship heat shield
Post by: rsdavis9 on 09/14/2020 04:42 pm
Taking the number of tiles (studs for now) on SN8 and the announced 20km hop, the exclusion zone under the trajectory will be an interesting place.

Nomadd should be able to collect some tile samples from the beach after. :)

A bit more seriously: given the latest results (some tiles hold, but its not guaranteed) will they risk that hop with numerous tiles? Tile fragments landing in the ocean may not a problem, but they can end up with debris cleaning/pickup teams at the beach, if not for environmental than for ITAR.

I would say SN8 will only have test tile locations. SN8 will be subsonic and not even close to requiring tiles.
Title: Re: Starship heat shield
Post by: wannamoonbase on 09/14/2020 06:11 pm
Taking the number of tiles (studs for now) on SN8 and the announced 20km hop, the exclusion zone under the trajectory will be an interesting place.

Nomadd should be able to collect some tile samples from the beach after. :)

A bit more seriously: given the latest results (some tiles hold, but its not guaranteed) will they risk that hop with numerous tiles? Tile fragments landing in the ocean may not a problem, but they can end up with debris cleaning/pickup teams at the beach, if not for environmental than for ITAR.

I would say SN8 will only have test tile locations. SN8 will be subsonic and not even close to requiring tiles.

I think you want to put on a good number of tiles.  Especially in areas of concern, such as those areas that bridge cryogenic to ambient temperature, control surface transitions etc. 

The leading edges of terminating tiles might be important too.
Title: Re: Starship heat shield
Post by: enbandi on 09/14/2020 06:22 pm
Taking the number of tiles (studs for now) on SN8 and the announced 20km hop, the exclusion zone under the trajectory will be an interesting place.

Nomadd should be able to collect some tile samples from the beach after. :)

A bit more seriously: given the latest results (some tiles hold, but its not guaranteed) will they risk that hop with numerous tiles? Tile fragments landing in the ocean may not a problem, but they can end up with debris cleaning/pickup teams at the beach, if not for environmental than for ITAR.

I would say SN8 will only have test tile locations. SN8 will be subsonic and not even close to requiring tiles.

I think you want to put on a good number of tiles.  Especially in areas of concern, such as those areas that bridge cryogenic to ambient temperature, control surface transitions etc. 

The leading edges of terminating tiles might be important too.

Checked the pics again, and they have 3 arreas with ~30 tile worth studs each (on the visible surface). So ~100 tiles as minimum, maybe more depending on how many on flaps and nose cone. (suspect where the studs are, there will be tiles. Partial stud covering does not make real sense otherways)

Not negligible from the debris perspective, but less than I remembered. There are fully stud covered sections on the photos, but maybe I mixed that up and those are SN 9-10 or whatever.
Title: Re: Starship heat shield
Post by: HVM on 09/14/2020 06:30 pm
Was that heavy pin pattern, on SN8 or 9, I try find it again at update thread but it is bit too dense.
[Edit] Ok, Mary's photo of SN8 have a tri-pin pattern but I don't see pins. Do they test stud welds effect to the skin of the ship? And the pin picture part is for SN9. (?)

https://forum.nasaspaceflight.com/index.php?topic=51332.1420
Title: Re: Starship heat shield
Post by: enbandi on 09/14/2020 09:20 pm
Was that heavy pin pattern, on SN8 or 9, I try find it again at update thread but it is bit too dense.
[Edit] Ok, Mary's photo of SN8 have a tri-pin pattern but I don't see pins. Do they test stud welds effect to the skin of the ship? And the pin picture part is for SN9. (?)

https://forum.nasaspaceflight.com/index.php?topic=51332.1420

Maybe the pins are there but not visible from this angle. Its a low res image on the specific area.

But if you are right, and its only the pattern, than I got my answer: the pins was there but removed, presumably to avoid risk/debris on the wider area (20km hop).

Edit: SN8 was also booked for a 150m hop If i remember correctly, but now it goes directly for the 20km. It makes sense: they can accept falling tiles on those 150m (affecting the pad area only), but cannot take the risk (or get approval) for the same on a 20km flight, with a much longer downrange.
Title: Re: Starship heat shield
Post by: Slarty1080 on 09/15/2020 09:59 am
Was that heavy pin pattern, on SN8 or 9, I try find it again at update thread but it is bit too dense.
[Edit] Ok, Mary's photo of SN8 have a tri-pin pattern but I don't see pins. Do they test stud welds effect to the skin of the ship? And the pin picture part is for SN9. (?)

https://forum.nasaspaceflight.com/index.php?topic=51332.1420

Maybe the pins are there but not visible from this angle. Its a low res image on the specific area.

But if you are right, and its only the pattern, than I got my answer: the pins was there but removed, presumably to avoid risk/debris on the wider area (20km hop).

Edit: SN8 was also booked for a 150m hop If i remember correctly, but now it goes directly for the 20km. It makes sense: they can accept falling tiles on those 150m (affecting the pad area only), but cannot take the risk (or get approval) for the same on a 20km flight, with a much longer downrange.
I can't see it would be that much of an issue. The launch area, beach and immediate sea lanes will be cleared before launch. So what if a few silica tiles fall off and flutter into the sea or onto the beach. I would have thought the worst restriction that might be imposed would be to ensure the beach was tidied up afterwards. 
Title: Re: Starship heat shield
Post by: enbandi on 09/15/2020 11:25 am
Was that heavy pin pattern, on SN8 or 9, I try find it again at update thread but it is bit too dense.
[Edit] Ok, Mary's photo of SN8 have a tri-pin pattern but I don't see pins. Do they test stud welds effect to the skin of the ship? And the pin picture part is for SN9. (?)

https://forum.nasaspaceflight.com/index.php?topic=51332.1420

Maybe the pins are there but not visible from this angle. Its a low res image on the specific area.

But if you are right, and its only the pattern, than I got my answer: the pins was there but removed, presumably to avoid risk/debris on the wider area (20km hop).

Edit: SN8 was also booked for a 150m hop If i remember correctly, but now it goes directly for the 20km. It makes sense: they can accept falling tiles on those 150m (affecting the pad area only), but cannot take the risk (or get approval) for the same on a 20km flight, with a much longer downrange.
I can't see it would be that much of an issue. The launch area, beach and immediate sea lanes will be cleared before launch. So what if a few silica tiles fall off and flutter into the sea or onto the beach. I would have thought the worst restriction that might be imposed would be to ensure the beach was tidied up afterwards.

Its silica (not only) tiles and insulation pads (what is the matetial for that?).  Issues can be personal safety, ITAR, environmental.

It could be a no go by either causing a real issue, or by simply lenghtening the approval process. For example insulation pad material needs additional paperwork for environmental assesment. But any combination of those factors could be enough to skip this test from the first flight.
Title: Re: Starship heat shield
Post by: Keldor on 09/15/2020 06:15 pm
Was that heavy pin pattern, on SN8 or 9, I try find it again at update thread but it is bit too dense.
[Edit] Ok, Mary's photo of SN8 have a tri-pin pattern but I don't see pins. Do they test stud welds effect to the skin of the ship? And the pin picture part is for SN9. (?)

https://forum.nasaspaceflight.com/index.php?topic=51332.1420

Maybe the pins are there but not visible from this angle. Its a low res image on the specific area.

But if you are right, and its only the pattern, than I got my answer: the pins was there but removed, presumably to avoid risk/debris on the wider area (20km hop).

Edit: SN8 was also booked for a 150m hop If i remember correctly, but now it goes directly for the 20km. It makes sense: they can accept falling tiles on those 150m (affecting the pad area only), but cannot take the risk (or get approval) for the same on a 20km flight, with a much longer downrange.
I can't see it would be that much of an issue. The launch area, beach and immediate sea lanes will be cleared before launch. So what if a few silica tiles fall off and flutter into the sea or onto the beach. I would have thought the worst restriction that might be imposed would be to ensure the beach was tidied up afterwards.

Its silica (not only) tiles and insulation pads (what is the matetial for that?).  Issues can be personal safety, ITAR, environmental.

It could be a no go by either causing a real issue, or by simply lenghtening the approval process. For example insulation pad material needs additional paperwork for environmental assesment. But any combination of those factors could be enough to skip this test from the first flight.

I suspect it's a simple matter of wanting to do the 20km hop test sooner rather than later.  It will likely take a week to attach the all tiles, and they won't be needed for 20km.  So SN8 flies without tiles, gets basic flight data, and some subsequent prototype will be the first to fly a higher altitude mission with a full heat shield.

It's also possible that all the broken tiles they've had on the recent static fires and hops have forced them to go back and experiment with their tile design.  This would represent a fairly significant delay as they do more testing and then have to restart their production line to make whatever improved tiles they need, perhaps something on the order of a month.  In this case, there's no sense in having the low altitude tests wait on tiles they don't actually need.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/15/2020 08:37 pm
Was that heavy pin pattern, on SN8 or 9, I try find it again at update thread but it is bit too dense.
[Edit] Ok, Mary's photo of SN8 have a tri-pin pattern but I don't see pins. Do they test stud welds effect to the skin of the ship? And the pin picture part is for SN9. (?)

https://forum.nasaspaceflight.com/index.php?topic=51332.1420 (https://forum.nasaspaceflight.com/index.php?topic=51332.1420)

Maybe the pins are there but not visible from this angle. Its a low res image on the specific area.

But if you are right, and its only the pattern, than I got my answer: the pins was there but removed, presumably to avoid risk/debris on the wider area (20km hop).

Edit: SN8 was also booked for a 150m hop If i remember correctly, but now it goes directly for the 20km. It makes sense: they can accept falling tiles on those 150m (affecting the pad area only), but cannot take the risk (or get approval) for the same on a 20km flight, with a much longer downrange.
I think we would see some shadows if the pins were there.
Title: Re: Starship heat shield
Post by: Oersted on 09/15/2020 09:13 pm
I am beginning to fear that the damn' tiles may be the long pole in Starship development.

Starship has such a nice, regular 50.-cal bullet shape that they could probably pull a huge heat-resistant textile sock over the whole thing and stitch all the tiles onto that (with some other method covering the body flaps).

Hmm, perhaps better leave the job to the experts...
Title: Re: Starship heat shield
Post by: Lars-J on 09/16/2020 01:09 am
Hmm, perhaps better leave the job to the experts...

Since when has that stopped anyone on this forum (myself included) sharing our "wisdom"? ;D
Title: Re: Starship heat shield
Post by: wannamoonbase on 09/16/2020 01:15 am
Hmm, perhaps better leave the job to the experts...

Since when has that stopped anyone on this forum (myself included) sharing our "wisdom"? ;D

Lars-J,

You know it.  The heat shield has always seemed like the single biggest challenge.  There are so many aspects that the heat sheild needs to encompass.

Cheap and quick to install and install
Coutour to the shape of the vehicle, like the aero-surfaces and the nose cone
Bridge cryogenic and non-cryo sections of the vehicle
Survive the contraction and expansion
Survive re-entry

It's going to be wild.
Title: Re: Starship heat shield
Post by: Hog on 09/16/2020 12:54 pm
I am beginning to fear that the damn' tiles may be the long pole in Starship development.

Starship has such a nice, regular 50.-cal bullet shape that they could probably pull a huge heat-resistant textile sock over the whole thing and stitch all the tiles onto that (with some other method covering the body flaps).

Hmm, perhaps better leave the job to the experts...
emphasis mine
We have seen this before, some 4 decades ago.  Be it "old" or "new", one constant is that "space is hard".
Title: Re: Starship heat shield
Post by: cuddihy on 09/17/2020 11:58 pm
It's interesting, it's been a while since we've seen more tiles getting placed as was done on SN-5 /SN-6. Would think they'd be placing them all over SN-8 now already otherwise.

Maybe they're back to the drawing board on tiles? Or at least waiting for a new batch with different mechanical properties to come in?

It seems like whatever combination of tile structural strength or lack of resilience, it kind of looked like a "start over" situation since none of the tiles survived even the single Raptor launch /return environment.
Title: Re: Starship heat shield
Post by: Mandella on 09/18/2020 01:27 am
I am beginning to fear that the damn' tiles may be the long pole in Starship development.

Starship has such a nice, regular 50.-cal bullet shape that they could probably pull a huge heat-resistant textile sock over the whole thing and stitch all the tiles onto that (with some other method covering the body flaps).

Hmm, perhaps better leave the job to the experts...
emphasis mine
We have seen this before, some 4 decades ago.  Be it "old" or "new", one constant is that "space is hard".

In this case, it's more like "getting back from space in one piece is hard."

The good thing is that their Artemis contribution doesn't require a heat shield, so if the tiles take longer it doesn't threaten that potential contract. Ditto for Dear Moon, if they are willing to bring down the passengers in a Dragon at the end of the journey.

Starlink launching not so much though, unless they go expendable for the Starship part, and I don't think they want to do that. Although it might be worth it to waste a stripped down cargo Starship second stage to yeet up 400 Starlinks at a time.

In any case, I wouldn't be surprised if the first full up tile tests for actual re-entry were Starships that were loaded with Starlinks upon launch.
Title: Re: Starship heat shield
Post by: Rocket Science on 09/18/2020 01:37 am
I am beginning to fear that the damn' tiles may be the long pole in Starship development.

Starship has such a nice, regular 50.-cal bullet shape that they could probably pull a huge heat-resistant textile sock over the whole thing and stitch all the tiles onto that (with some other method covering the body flaps).

Hmm, perhaps better leave the job to the experts...
emphasis mine
We have seen this before, some 4 decades ago.  Be it "old" or "new", one constant is that "space is hard".
I remember Columbia shedding her tiles from a simple ferry flight on the back of the SCA...
Title: Re: Starship heat shield
Post by: Thrustpuzzle on 09/18/2020 01:56 am
I remember Columbia shedding her tiles from a simple ferry flight on the back of the SCA...
Good memory. It was due to flying through a rainstorm, and the water forced over 250 tiles to be replaced. Not sure if any were actually shed.
Here's a detailed and readable document (https://spaceflight.nasa.gov/shuttle/archives/sts-107/investigation/tps_safety.pdf) about the shuttle TPS safety issues and maintenance. Of note, the biggest chronic problems kept being the RTV (silicon rubber adhesive), especially with regards to dealing with rain or other chemicals (like waterproofing, cleaners, or incidental chemical spills) I can imagine that Starship's mechanical pin fastener strategy would sidestep much of that chronic problem.
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 09/18/2020 02:20 am
Starlink launching not so much though, unless they go expendable for the Starship part, and I don't think they want to do that. Although it might be worth it to waste a stripped down cargo Starship second stage to yeet up 400 Starlinks at a time.

I would think that would definitely be worth it.  400 Starlinks is more than 6 times the 60 that fly on Falcon 9.  The estimates for a partially reusable F9 launch are around $15 million.  So Starship would have to cost $100 million to equal the price-per-Starlink of current F9 launches.  As long as the Super Heavy boosters are being recovered (no orbital heat shield needed, just F9-level protection) and as long as they have ramped up Raptor engine production enough, it seems quite likely expendable Starship would beat F9 for Starlink launches.

Plus, they get a free orbital re-entry test on every Starlink launch.
Title: Re: Starship heat shield
Post by: tbellman on 09/18/2020 08:53 am
The good thing is that their Artemis contribution doesn't require a heat shield, so if the tiles take longer it doesn't threaten that potential contract.

In principle, yes, they could fly both the HLS lander and CLPS deliveries without reentry and landing on Earth.  But it would require expending half a dozen or so tankers for each payload flight.

Quote from: Mandella
Ditto for Dear Moon, if they are willing to bring down the passengers in a Dragon at the end of the journey.

Also requires expending several tankers.  Even more tankers than for the HLS and CLPS missions, even; if you can't trust the heatshield, then you need to do propulsive braking into LEO when returning from the Moon, instead of aerobraking, which requires even more propellant (and likely doing a second refuelling while en route towards the Moon).

So, practically speaking, I find it unlikely.  It would increase their costs quite a lot.  But they may do it even if EDL hasn't been perfected.  Even if one out of three tanker landings fail, it would still bring down their costs quite a lot; but on the other hand, it requires them to have manufacturing up to speed, so they have enough new tankers available to replace those that are lost.
Title: Re: Starship heat shield
Post by: Terra Incognita on 09/18/2020 01:22 pm
If the tiles prove too troublesome might we see a return to transpirational cooling?

The advantages would be that the perforated transpirational layer should survive vibration, easy to conform to the curves, contract when cold closing the pores and opening them when warm when needed.
Title: Re: Starship heat shield
Post by: Robotbeat on 09/18/2020 01:40 pm
If the tiles prove too troublesome might we see a return to transpirational cooling?

The advantages would be that the perforated transpirational layer should survive vibration, easy to conform to the curves, contract when cold closing the pores and opening them when warm when needed.
Transpiration cooling is really massive and complicated.

It'll still be used, but probably only sparingly.
Title: Re: Starship heat shield
Post by: goretexguy on 09/18/2020 03:48 pm
The advantages would be that the perforated transpirational layer should survive vibration, easy to conform to the curves, contract when cold closing the pores and opening them when warm when needed.

I think transpiration pores will get wider upon cooling, and smaller with heating.
Title: Re: Starship heat shield
Post by: Rocket Science on 09/18/2020 03:56 pm
I remember Columbia shedding her tiles from a simple ferry flight on the back of the SCA...
Good memory. It was due to flying through a rainstorm, and the water forced over 250 tiles to be replaced. Not sure if any were actually shed.
Here's a detailed and readable document (https://spaceflight.nasa.gov/shuttle/archives/sts-107/investigation/tps_safety.pdf) about the shuttle TPS safety issues and maintenance. Of note, the biggest chronic problems kept being the RTV (silicon rubber adhesive), especially with regards to dealing with rain or other chemicals (like waterproofing, cleaners, or incidental chemical spills) I can imagine that Starship's mechanical pin fastener strategy would sidestep much of that chronic problem.
Here is the event I'm speaking of...

"Nearly four years later on March 8, 1979, Columbia rolled out of the Palmdale facility to begin its multi-day journey across the nation to its launch site, the Kennedy Space Center (KSC) in Florida. The first step was an overland haul to the NASA Dryden Flight Research Center at Edwards Air Force Base (AFB) 36 miles away. Two days later, workers there hoisted Columbia onto the Shuttle Carrier Aircraft (SCA), a Boeing 747 aircraft modified to transport Space Shuttle orbiters. During a test flight, thousands of the orbiter’s temporary thermal protection system tiles fell off. Columbia was returned to the hanger where over 100 men and women worked for nine days reapplying the tiles."

Always great to talk about the Shuttle experience... :)

https://www.nasa.gov/feature/40-years-ago-space-shuttle-columbia-arrives-at-kennedy-space-center
Title: Re: Starship heat shield
Post by: edzieba on 09/18/2020 04:31 pm
The advantages would be that the perforated transpirational layer should survive vibration, easy to conform to the curves, contract when cold closing the pores and opening them when warm when needed.

I think transpiration pores will get wider upon cooling, and smaller with heating.
Holes in a material expand when the material itself expands. This is how thermal shrink-fit collets work.
Title: Re: Starship heat shield
Post by: Mandella on 09/18/2020 04:58 pm
The good thing is that their Artemis contribution doesn't require a heat shield, so if the tiles take longer it doesn't threaten that potential contract.

In principle, yes, they could fly both the HLS lander and CLPS deliveries without reentry and landing on Earth.  But it would require expending half a dozen or so tankers for each payload flight.

Quote from: Mandella
Ditto for Dear Moon, if they are willing to bring down the passengers in a Dragon at the end of the journey.

Also requires expending several tankers.  Even more tankers than for the HLS and CLPS missions, even; if you can't trust the heatshield, then you need to do propulsive braking into LEO when returning from the Moon, instead of aerobraking, which requires even more propellant (and likely doing a second refuelling while en route towards the Moon).

So, practically speaking, I find it unlikely.  It would increase their costs quite a lot.  But they may do it even if EDL hasn't been perfected.  Even if one out of three tanker landings fail, it would still bring down their costs quite a lot; but on the other hand, it requires them to have manufacturing up to speed, so they have enough new tankers available to replace those that are lost.

I need to write that on my hand, since for some reason I keep forgetting that orbital refueling needs tankers.

 :-[

So yeah, possible if using expendable tankers, but it changes things.

Still, a stripped down "Starship" which is really hardly a Starship at all, lacking all body flaps and landing gear and running nothing but vacuum Raptors might not be much more costly than the existing Falcon 9 second stage, could get the job done. Be interesting to see a real cost breakdown of it, but we'd have to know internal financial figures that we don't have access to to be anywhere close to accurate.

In any case, getting far from the subject of heat shields. Theoretical expendable Starships probably needs its own thread.
Title: Re: Starship heat shield
Post by: Slarty1080 on 09/18/2020 05:15 pm
The good thing is that their Artemis contribution doesn't require a heat shield, so if the tiles take longer it doesn't threaten that potential contract.

In principle, yes, they could fly both the HLS lander and CLPS deliveries without reentry and landing on Earth.  But it would require expending half a dozen or so tankers for each payload flight.

Quote from: Mandella
Ditto for Dear Moon, if they are willing to bring down the passengers in a Dragon at the end of the journey.

Also requires expending several tankers.  Even more tankers than for the HLS and CLPS missions, even; if you can't trust the heatshield, then you need to do propulsive braking into LEO when returning from the Moon, instead of aerobraking, which requires even more propellant (and likely doing a second refuelling while en route towards the Moon).

So, practically speaking, I find it unlikely.  It would increase their costs quite a lot.  But they may do it even if EDL hasn't been perfected.  Even if one out of three tanker landings fail, it would still bring down their costs quite a lot; but on the other hand, it requires them to have manufacturing up to speed, so they have enough new tankers available to replace those that are lost.

I need to write that on my hand, since for some reason I keep forgetting that orbital refueling needs tankers.

 :-[

So yeah, possible if using expendable tankers, but it changes things.

Still, a stripped down "Starship" which is really hardly a Starship at all, lacking all body flaps and landing gear and running nothing but vacuum Raptors might not be much more costly than the existing Falcon 9 second stage, could get the job done. Be interesting to see a real cost breakdown of it, but we'd have to know internal financial figures that we don't have access to to be anywhere close to accurate.

In any case, getting far from the subject of heat shields. Theoretical expendable Starships probably needs its own thread.
I think they really need 6 raptors on Starship to get into orbit.
Title: Re: Starship heat shield
Post by: envy887 on 09/18/2020 05:23 pm
The good thing is that their Artemis contribution doesn't require a heat shield, so if the tiles take longer it doesn't threaten that potential contract.

In principle, yes, they could fly both the HLS lander and CLPS deliveries without reentry and landing on Earth.  But it would require expending half a dozen or so tankers for each payload flight.

Quote from: Mandella
Ditto for Dear Moon, if they are willing to bring down the passengers in a Dragon at the end of the journey.

Also requires expending several tankers.  Even more tankers than for the HLS and CLPS missions, even; if you can't trust the heatshield, then you need to do propulsive braking into LEO when returning from the Moon, instead of aerobraking, which requires even more propellant (and likely doing a second refuelling while en route towards the Moon).

So, practically speaking, I find it unlikely.  It would increase their costs quite a lot.  But they may do it even if EDL hasn't been perfected.  Even if one out of three tanker landings fail, it would still bring down their costs quite a lot; but on the other hand, it requires them to have manufacturing up to speed, so they have enough new tankers available to replace those that are lost.

I need to write that on my hand, since for some reason I keep forgetting that orbital refueling needs tankers.

 :-[

So yeah, possible if using expendable tankers, but it changes things.

Still, a stripped down "Starship" which is really hardly a Starship at all, lacking all body flaps and landing gear and running nothing but vacuum Raptors might not be much more costly than the existing Falcon 9 second stage, could get the job done. Be interesting to see a real cost breakdown of it, but we'd have to know internal financial figures that we don't have access to to be anywhere close to accurate.

In any case, getting far from the subject of heat shields. Theoretical expendable Starships probably needs its own thread.
I think they really need 6 raptors on Starship to get into orbit.

They could do orbital entry heat shield testing with only 3 Raptors on the Starship and about 12 on the booster, with both being full size other than the number of engines.

https://forum.nasaspaceflight.com/index.php?topic=47179.msg2125700#msg2125700

That would limit them to only a nominal payload, perhaps 20 Starlinks. But it might be a good way to get a lot of test flights in even if SL Raptors production-constrained and RVac isn't available.
Title: Re: Starship heat shield
Post by: Twark_Main on 09/18/2020 11:40 pm
But  it would require expending half a dozen or so tankers for each payload flight.

...

Also requires expending several tankers.

The things that are expended needn't be full "tankers" per-se. The heatshield, body flaps, payload interface, and payload fairing can be omitted. Maybe tack on a small nose cone. Some launches will no doubt double as test flights and therefore require a full vehicle, but this provides an option to augment that flight rate if needed.

Do I expect SpaceX to do this? No, not in the default case. Is it an option available to reduce the cost penalty in case they run into R&D delays? Sure.
Title: Re: Starship heat shield
Post by: Slarty1080 on 09/18/2020 11:44 pm
But  it would require expending half a dozen or so tankers for each payload flight.

...

Also requires expending several tankers.

The things that are expended needn't be full "tankers" per-se. The heatshield, body flaps, payload interface, and payload fairing can be omitted. Maybe tack on a small nose cone. Some launches will no doubt double as test flights and therefore require a full vehicle, but this provides an option to augment that flight rate if needed.

Do I expect SpaceX to do this? No, not in the default case. Is it an option available to reduce the cost penalty in case they run into R&D delays? Sure.
I know what you mean, but the heat shield can't be omitted - at least not on this thread  ;)
Title: Re: Starship heat shield
Post by: Twark_Main on 09/18/2020 11:52 pm
But  it would require expending half a dozen or so tankers for each payload flight.

...

Also requires expending several tankers.

The things that are expended needn't be full "tankers" per-se. The heatshield, body flaps, payload interface, and payload fairing can be omitted. Maybe tack on a small nose cone. Some launches will no doubt double as test flights and therefore require a full vehicle, but this provides an option to augment that flight rate if needed.

Do I expect SpaceX to do this? No, not in the default case. Is it an option available to reduce the cost penalty in case they run into R&D delays? Sure.
I know what you mean, but the heat shield can't be omitted - at least not on this thread  ;)

Not sure what you mean.

Just pointing out that it isn't required to expend tankers, as claimed. What you do with this information is up to you. :)
Title: Re: Starship heat shield
Post by: Slarty1080 on 09/19/2020 12:06 am
But  it would require expending half a dozen or so tankers for each payload flight.

...

Also requires expending several tankers.

The things that are expended needn't be full "tankers" per-se. The heatshield, body flaps, payload interface, and payload fairing can be omitted. Maybe tack on a small nose cone. Some launches will no doubt double as test flights and therefore require a full vehicle, but this provides an option to augment that flight rate if needed.

Do I expect SpaceX to do this? No, not in the default case. Is it an option available to reduce the cost penalty in case they run into R&D delays? Sure.
I know what you mean, but the heat shield can't be omitted - at least not on this thread  ;)

Not sure what you mean.

Just pointing out that it isn't required to expend tankers, as claimed. What you do with this information is up to you. :)
Sorry, an obscure joke of mine, I should know better - we are wandering slightly off topic - we cant omit the heat shield on a Starship heat shield thread (without going off topic).
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 09/19/2020 12:49 am
I think it's possible that they'll fly expendable Starships to launch Starlink.

But expendable tankers to support a Dear Moon or NASA lunar landings?  I find that much harder to believe.  Dear Moon isn't on any kind of deadline, so it can just wait until they've ironed out the problems.  And NASA lunar landings are planned for 2024 at the earliest.  It seems hard to believe that they couldn't come up with some kind of working TPS solution in the next four years.

Note also that by expendable Starships I mean expendable in the same sense that early Falcon 9 first stages were expendable -- with every flight being used as an experiment to work on getting recover to work, even if on a particular flight there was no realistic hope of actual recovery.
Title: Re: Starship heat shield
Post by: Twark_Main on 09/19/2020 12:58 am
I think it's possible that they'll fly expendable Starships to launch Starlink.

But expendable tankers to support a Dear Moon or NASA lunar landings?  I find that much harder to believe.  Dear Moon isn't on any kind of deadline, so it can just wait until they've ironed out the problems.  And NASA lunar landings are planned for 2024 at the earliest.  It seems hard to believe that they couldn't come up with some kind of working TPS solution in the next four years.

Note also that by expendable Starships I mean expendable in the same sense that early Falcon 9 first stages were expendable -- with every flight being used as an experiment to work on getting recover to work, even if on a particular flight there was no realistic hope of actual recovery.

I don't disagree actually. Like I said,

Some launches will no doubt double as test flights and therefore require a full vehicle, but this provides an option to augment that flight rate if needed. (Naturally if it's not needed, you don't do it. :) )

Do I expect SpaceX to do this? No, not in the default case. Is it an option available to reduce the cost penalty in case they run into R&D delays? Sure.
Title: Re: Starship heat shield
Post by: steveleach on 09/19/2020 12:34 pm
Note also that by expendable Starships I mean expendable in the same sense that early Falcon 9 first stages were expendable -- with every flight being used as an experiment to work on getting recover to work, even if on a particular flight there was no realistic hope of actual recovery.
I think that this is exactly what they'll do. The primary mission of a tanker is getting fuel into another Starship; the EDL side is an experimental bonus.

SpaceX can accomplish a lot of their early goals without (successful) EDL, but they need refuelling for almost everything.

So the tankers will have heatshields, but SpaceX won't be at all fussed if they don't work very well to start with - as long as they are learning from any failures, of course.
Title: Re: Starship heat shield
Post by: V96 on 09/19/2020 12:45 pm
Just found this new SpaceX Job  posting on linkedin (7 hours ago)

"
MATERIALS ENGINEER, STARSHIP (HEATSHIELD)

This role would be on the materials engineering team, supporting alloy and process design. The materials engineering team supports materials across SpaceX via identification, development and implementation of advanced materials and processes. This role will be part of a team of engineers and process specialists developing new materials and processing solutions for different projects, including an early stage project to develop a metallic heat shield for Starship.
"

Moving away from the ceramic heat tiles toward a metallic heat shield? I'm confused
not sure if posted here already, but if not
Title: Re: Starship heat shield
Post by: philw1776 on 09/19/2020 02:31 pm
Although it may seem like corporate heresy, the option to use a disposable/repairable heat shield EARLY ON in Starship flights exists.  SpaceX gets each Starship back for refurbishment for subsequent flight(s) and gets valuable flight data while gradual improvements are made to the heat shield design, OR that particular design approach is abandoned because it cannot lead to eventual re-usability.

Minimum viable product to achieve the Starlink Launcher or Tanker or whatever missions.
Just more expensive and resource intensive than the long term goal, but gets 'em flyin'.
Title: Re: Starship heat shield
Post by: Coastal Ron on 09/19/2020 02:40 pm
Although it may seem like corporate heresy, the option to use a disposable/repairable heat shield EARLY ON in Starship flights exists.  SpaceX gets each Starship back for refurbishment for subsequent flight(s) and gets valuable flight data while gradual improvements are made to the heat shield design, OR that particular design approach is abandoned because it cannot lead to eventual re-usability.

While it would be an intriguing idea, it may be impractical since it would likely result in a very heavy heat shield that would alter the characteristics of the Starship. As it is they are trying to directly mount heat shield tiles to the body of the tanks, which means the attachment system is three metal studs.

But if you are going to make a removable heat shield you need to create a new structure that the heat shields attach to, AND it has to attach to the body of the vehicle in a very secure way. That would likely weigh a lot, and all that weight goes on the side falling into the gravity well, and has to be counteracted by the flip maneuver - which makes that flip maneuver harder.

However, if they can't figure out the simple method of attaching the tiles directly to the body of the Starship, then maybe this would be their only option. We'll have to see what they end up with...
Title: Re: Starship heat shield
Post by: philw1776 on 09/19/2020 02:45 pm
Adding 10 tonnes or a couple 10 tonnes to an EARLY 100-150 tonne payload Starship still allows flights.
For example, if payload of Starship is "only" 100 tonnes, TEMPORARILY adding 20 tonnes extra of prototype heat-shield allows 80 tonnes to orbit with refurbishment re-use. Totally within the start off with a minimum viable product solution space.
Title: Re: Starship heat shield
Post by: Robotbeat on 09/19/2020 03:02 pm
Although it may seem like corporate heresy, the option to use a disposable/repairable heat shield EARLY ON in Starship flights exists.  SpaceX gets each Starship back for refurbishment for subsequent flight(s) and gets valuable flight data while gradual improvements are made to the heat shield design, OR that particular design approach is abandoned because it cannot lead to eventual re-usability.

Minimum viable product to achieve the Starlink Launcher or Tanker or whatever missions.
Just more expensive and resource intensive than the long term goal, but gets 'em flyin'.
Might as well make the whole ship (besides booster) disposable, then.

A disposable/replaceable heatshield is NOT a trivial thing to make, you can't be like "well, this is a crappier solution so it doesn't require expensive engineering." No. Doesn't work like that. You STILL have to do a ton of expensive engineering and tooling and design iteration even just for an ablative or replaceable heatshield. There's a large opportunity cost for picking that option, and fundamentally it doesn't save anything except a little weight.

What they'll most likely do is do their best with the heatshield tech they have, then fly hopefully-not-expendable-but-if-recovery-fails-that-is-okay upper stages, like they did with Falcon 9 booster stages.
Title: Re: Starship heat shield
Post by: Robotbeat on 09/19/2020 03:06 pm
Adding 10 tonnes or a couple 10 tonnes to an EARLY 100-150 tonne payload Starship still allows flights.
For example, if payload of Starship is "only" 100 tonnes, TEMPORARILY adding 20 tonnes extra of prototype heat-shield allows 80 tonnes to orbit with refurbishment re-use. Totally within the start off with a minimum viable product solution space.
Minimum viable product is expending the Starship upper stage.

All you're asking them to do is to develop their heatshield TWICE, which makes development twice as expensive.
Title: Re: Starship heat shield
Post by: Robotbeat on 09/19/2020 03:10 pm
They might have to go with some sort of secondary structure to attach the heatshield to, but I definitely don't see them going away from a reusable heatshield.

Because a Mars mission requires a reusable heatshield. Has to be used for both Mars entry and Mars return. Yeah, it's possible in principle to develop a dual-heat-pulse ablative shield, but that's actually a fairly low TRL solution, not standard proven technology. (And note this is partly why they went away from attempting to reuse PICA-X: it's actually very non-trivial to reuse an ablative heatshield because it becomes brittle after the first use.)
Title: Re: Starship heat shield
Post by: eriblo on 09/19/2020 03:47 pm
They might have to go with some sort of secondary structure to attach the heatshield to, but I definitely don't see them going away from a reusable heatshield.

Because a Mars mission requires a reusable heatshield. Has to be used for both Mars entry and Mars return. Yeah, it's possible in principle to develop a dual-heat-pulse ablative shield, but that's actually a fairly low TRL solution, not standard proven technology. (And note this is partly why they went away from attempting to reuse PICA-X: it's actually very non-trivial to reuse an ablative heatshield because it becomes brittle after the first use.)
I think the most up to date statements we have are still:

Quote from: SpaceX website
Starship will enter Mars’ atmosphere at 7.5 kilometers per second and decelerate aerodynamically. The vehicle’s heat shield is designed to withstand multiple entries, but given that the vehicle is coming into Mars' atmosphere so hot, we still expect to see some ablation of the heat shield (similar to wear and tear on a brake pad)...
There are two interesting points:

- "Some ablation" has to be a really minor amount to be compatible with the TUFROC-like look of the current tiles (i.e. a very thin tougher coating on a brittle ceramic foam core). As you state a different (much heavier) ablative TPS could do it but would not be as easy as it might first appear.

- 7.5 km/s is actually less than the easiest reentry from LEO for which they certainly would like a completely reusable TPS. Although the need to capture in the smaller gravity/radius might lead to a higher peak load (anybody got some good estimates?) it would still suggest that this is right at the limit. The question then is what they are thinking with regard to lunar and especially interplanetary returns. Doing fast transits back from Mars will quickly lead to velocities exceeding anything done to date...
Title: Re: Starship heat shield
Post by: Robotbeat on 09/19/2020 03:56 pm
They might have to go with some sort of secondary structure to attach the heatshield to, but I definitely don't see them going away from a reusable heatshield.

Because a Mars mission requires a reusable heatshield. Has to be used for both Mars entry and Mars return. Yeah, it's possible in principle to develop a dual-heat-pulse ablative shield, but that's actually a fairly low TRL solution, not standard proven technology. (And note this is partly why they went away from attempting to reuse PICA-X: it's actually very non-trivial to reuse an ablative heatshield because it becomes brittle after the first use.)
I think the most up to date statements we have are still:

Quote from: SpaceX website
Starship will enter Mars’ atmosphere at 7.5 kilometers per second and decelerate aerodynamically. The vehicle’s heat shield is designed to withstand multiple entries, but given that the vehicle is coming into Mars' atmosphere so hot, we still expect to see some ablation of the heat shield (similar to wear and tear on a brake pad)...
...
Nope, that's an old statement from when they were still using PICA-X. Look it up, they haven't changed that.
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 09/19/2020 04:24 pm
Adding 10 tonnes or a couple 10 tonnes to an EARLY 100-150 tonne payload Starship still allows flights.
For example, if payload of Starship is "only" 100 tonnes, TEMPORARILY adding 20 tonnes extra of prototype heat-shield allows 80 tonnes to orbit with refurbishment re-use. Totally within the start off with a minimum viable product solution space.

In addition to the fact that this would be a huge additional cost that is a technological dead-end, it would also mean that they aren't getting any testing data to help them make progress on their reusable heat shield on any flights that use an expendable heat shield.

I don't think Musk would see a Starship with an expendable heat shield as a minimal viable product version of Starship because it doesn't meet a key requirement of Starship: full, cheap reusability.
Title: Re: Starship heat shield
Post by: awests on 09/19/2020 04:25 pm
I find the “Responsibilities” section interesting:

Work closely with product design engineering teams to define requirements
Work with materials engineers to assess best in class approaches for powder metal processing consolidating and data analysis
Develop laboratory capabilities and analysis methods to implement such approaches and collaborate with vendors and external labs to augment internal capabilities
Specify, design, install, commission and/or validate metal processing equipment to support techniques such as melting, forging, rolling, and heat treating
Lead process development of developmental materials and processing techniques through parameter optimization, DOE experiments, and trials to support alloy design activities
Complete high heat flux experiments to evaluate material performance
Ensure developed materials meet all material design requirements


Sent from my iPhone using Tapatalk
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 09/19/2020 04:28 pm
SpaceX can accomplish a lot of their early goals without (successful) EDL, but they need refuelling for almost everything.

They don't need refueling for Starlink launches, and Starlink launches are almost everything in terms of early need for Starship.

They need refueling for lunar and martian missions, but those are longer term.
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 09/19/2020 04:34 pm
Just found this new SpaceX Job  posting on linkedin (7 hours ago)

"
MATERIALS ENGINEER, STARSHIP (HEATSHIELD)

This role would be on the materials engineering team, supporting alloy and process design. The materials engineering team supports materials across SpaceX via identification, development and implementation of advanced materials and processes. This role will be part of a team of engineers and process specialists developing new materials and processing solutions for different projects, including an early stage project to develop a metallic heat shield for Starship.
"

Moving away from the ceramic heat tiles toward a metallic heat shield? I'm confused
not sure if posted here already, but if not

Note that this doesn't say whether the "metallic heat shield for Starship" is meant for the main heat shield protecting the bulk of the fuselage or a more special-purpose heat shield for particular areas such as control surface joints and the engine bay.

It's also not clear whether this metallic heat shield is intended for the first generation of Starship heat shield or as a possible version 2.0 upgrade after Starship is already flying with a ceramic tile reusable heat shield.
Title: Re: Starship heat shield
Post by: JamesH65 on 09/19/2020 04:36 pm
Adding 10 tonnes or a couple 10 tonnes to an EARLY 100-150 tonne payload Starship still allows flights.
For example, if payload of Starship is "only" 100 tonnes, TEMPORARILY adding 20 tonnes extra of prototype heat-shield allows 80 tonnes to orbit with refurbishment re-use. Totally within the start off with a minimum viable product solution space.
Minimum viable product is expending the Starship upper stage.

All you're asking them to do is to develop their heatshield TWICE, which makes development twice as expensive.

Which could be OK, depending on timescales. If they really really need to get Starlink aloft ASAP it might be worth spending the money twice. Once on a known dead end, but quickly, then a more leisurely redesign of a much better version. That IS the agile way.

Title: Re: Starship heat shield
Post by: eriblo on 09/19/2020 04:52 pm
They might have to go with some sort of secondary structure to attach the heatshield to, but I definitely don't see them going away from a reusable heatshield.

Because a Mars mission requires a reusable heatshield. Has to be used for both Mars entry and Mars return. Yeah, it's possible in principle to develop a dual-heat-pulse ablative shield, but that's actually a fairly low TRL solution, not standard proven technology. (And note this is partly why they went away from attempting to reuse PICA-X: it's actually very non-trivial to reuse an ablative heatshield because it becomes brittle after the first use.)
I think the most up to date statements we have are still:

Quote from: SpaceX website
Starship will enter Mars’ atmosphere at 7.5 kilometers per second and decelerate aerodynamically. The vehicle’s heat shield is designed to withstand multiple entries, but given that the vehicle is coming into Mars' atmosphere so hot, we still expect to see some ablation of the heat shield (similar to wear and tear on a brake pad)...
...
Nope, that's an old statement from when they were still using PICA-X. Look it up, they haven't changed that.
Yeah, I'll concede that it is likely a lazy repeat of previous statements for the carbon fiber version (and the video is the old one). I think it might technically be correct ::) as the "latest" with regard to Mars entry (and Elon did talk about the tiles "acting as sensors" by ablating when too hot in the same time frame) but this is probably just indicative of the lack of Mars TPS specific updates...
Title: Re: Starship heat shield
Post by: steveleach on 09/19/2020 06:42 pm
SpaceX can accomplish a lot of their early goals without (successful) EDL, but they need refuelling for almost everything.

They don't need refueling for Starlink launches, and Starlink launches are almost everything in terms of early need for Starship.

They need refueling for lunar and martian missions, but those are longer term.
I don't think Starlink is really a "goal" for SpaceX, it is more a way of funding their goals.

Regardless, EDL isn't required for Starlink either, it just makes it cheaper by allowing for Starship reuse.

This is all wandering away from what I was trying to get at though, which was that (imho) SpaceX will want to launch tankers to practice refuelling even if they don't yet have the heatshields to return them.
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 09/19/2020 06:52 pm
SpaceX can accomplish a lot of their early goals without (successful) EDL, but they need refuelling for almost everything.

They don't need refueling for Starlink launches, and Starlink launches are almost everything in terms of early need for Starship.

They need refueling for lunar and martian missions, but those are longer term.
I don't think Starlink is really a "goal" for SpaceX, it is more a way of funding their goals.

Regardless, EDL isn't required for Starlink either, it just makes it cheaper by allowing for Starship reuse.

This is all wandering away from what I was trying to get at though, which was that (imho) SpaceX will want to launch tankers to practice refuelling even if they don't yet have the heatshields to return them.

I strongly disagree with that.

I believe that SpaceX will definitely make the heat shield work before even starting on tankers.

Once they have cheap reuse of Starship, they can launch lots of Starlink satellites cheaply.  As you say, that funds everything else.  Why would getting huge amounts of funding as soon as possible not be a priority?

Cheap reuse of Starship also allows them to shift everything else Falcon 9 launches to Starship as soon as possible.  Some customers will be conservative and have to see Starship in action for a while before they make the leap.  But whatever it takes to get a particular customer to switch to Starship, that path doesn't start until Starship is being successfully reused cheaply.

Cheap reuse also allows them to be much more effective much more quickly with their orbital refueling development.  It would be much, much more expensive for SpaceX to try to do orbital refueling development if they have to throw away the tanker on every test flight.
Title: Re: Starship heat shield
Post by: steveleach on 09/19/2020 07:06 pm
SpaceX can accomplish a lot of their early goals without (successful) EDL, but they need refuelling for almost everything.

They don't need refueling for Starlink launches, and Starlink launches are almost everything in terms of early need for Starship.

They need refueling for lunar and martian missions, but those are longer term.
I don't think Starlink is really a "goal" for SpaceX, it is more a way of funding their goals.

Regardless, EDL isn't required for Starlink either, it just makes it cheaper by allowing for Starship reuse.

This is all wandering away from what I was trying to get at though, which was that (imho) SpaceX will want to launch tankers to practice refuelling even if they don't yet have the heatshields to return them.

I strongly disagree with that.

I believe that SpaceX will definitely make the heat shield work before even starting on tankers.

Once they have cheap reuse of Starship, they can launch lots of Starlink satellites cheaply.  As you say, that funds everything else.  Why would getting huge amounts of funding as soon as possible not be a priority?

Cheap reuse of Starship also allows them to shift everything else Falcon 9 launches to Starship as soon as possible.  Some customers will be conservative and have to see Starship in action for a while before they make the leap.  But whatever it takes to get a particular customer to switch to Starship, that path doesn't start until Starship is being successfully reused cheaply.

Cheap reuse also allows them to be much more effective much more quickly with their orbital refueling development.  It would be much, much more expensive for SpaceX to try to do orbital refueling development if they have to throw away the tanker on every test flight.
Starlink is viable even when launched 60 at a time on an expendable Falcon second stage. It will be even more viable if launched 600 at a time on a potentially-expendable Starship. Reuse just makes it even cheaper still.

I'm obviously not arguing against reuse/EDL/heatshields; they are core to the Starship strategy and SpaceX will be working on them as fast as they can.

However, refuelling is also core to the strategy and (as I see it) becomes critical sooner because they need it for the Mars 2022 window.

EDL is also important for Mars 2022, though I think if SpaceX have refuelling and not EDL then they'd go anyway and just burn a Starship up in the Martian atmosphere. If they have EDL and not refuelling then nothing happens in 2022.

I believe SpaceX will work on both (as well as everything else) but they won't let a lack of progress on one hold back the other at all. Even if that mean practicing refuelling with tankers that fail to return successfully time after time because they haven't got a heat shield that works.
Title: Re: Starship heat shield
Post by: KBK on 09/19/2020 09:44 pm
I find the “Responsibilities” section interesting:

Work closely with product design engineering teams to define requirements
Work with materials engineers to assess best in class approaches for powder metal processing consolidating and data analysis
Develop laboratory capabilities and analysis methods to implement such approaches and collaborate with vendors and external labs to augment internal capabilities
Specify, design, install, commission and/or validate metal processing equipment to support techniques such as melting, forging, rolling, and heat treating
Lead process development of developmental materials and processing techniques through parameter optimization, DOE experiments, and trials to support alloy design activities
Complete high heat flux experiments to evaluate material performance
Ensure developed materials meet all material design requirements


Sent from my iPhone using Tapatalk

Sounds like it's right up my alley. Or at least I laid the foundation for it to have a chance to be a success...

I have turned down some of the bigger 'players', so far. I won't work for the weapons makers. China tried to lure me through Malaysian offices, and a few others...
Title: Re: Starship heat shield
Post by: Fizrock on 09/19/2020 09:56 pm
Here's an interesting comment on metallic heatshields from /u/flshr19 on reddit:
 
Quote
Reusable metallic heat shields have been a holy grail in TPS technology since I first started working in that area during the Space Shuttle conceptual design period (1969-late 1971). My lab developed prototype metallic heat shields fabricated from niobium (aka columbium) coated with various ceramic oxides for increased oxidation resistance. We tested them up to 3000F (1649C) in specialized furnaces at air pressures typical of entry into the Earth's atmosphere. Mechanical tension and flexing loads were applied during these tests to determine the adhesion characteristics of the coatings. These samples could do a hundred simulated Shuttle entries without losing the coating.

See https://ntrs.nasa.gov/citations/19730024093

Nearly 25 years later in 1995 I worked on a NASA Langley contract to develop metallic heat shields for the X-33.

https://ntrs.nasa.gov/citations/20040095922

Interest in metallic heat shields has run hot and cold for the past 50 years. Maybe SpaceX can find a use for some of the previous work and develop a metallic heat shield that actually flies on a real spacecraft.
 
 
Comment source: https://www.reddit.com/r/spacex/comments/inkzwp/starship_development_thread_14/g5v3786/
Title: Re: Starship heat shield
Post by: OTV Booster on 09/19/2020 11:12 pm
Does anybody have employee numbers for BC? I'm going to take a BOE stab at marginal costs for one SS with an eye to the economics of expendable on early launches. Or has this already been done somewhere?
Title: Re: Starship heat shield
Post by: Keldor on 09/19/2020 11:28 pm
Does anybody have employee numbers for BC? I'm going to take a BOE stab at marginal costs for one SS with an eye to the economics of expendable on early launches. Or has this already been done somewhere?

Hrmm - you could try counting cars in the aerial photos of the build site.  Should give you a decent estimate of the number of workers, assuming there's not a lot of carpooling going on.  I don't think we've seen any SpaceX busses.
Title: Re: Starship heat shield
Post by: brainbit on 09/19/2020 11:34 pm
Excuse my ignorance. Has any work been done on tungsten? I have a memory of using tungsten steel a long time ago. For a metal heat shield I imagine tungsten as being the best material, it is used to make light bulb filaments so can be made into wire. It has a melting point 3410 C. Is there a reason tungsten is not used?     
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 09/19/2020 11:51 pm
Excuse my ignorance. Has any work been done on tungsten? I have a memory of using tungsten steel a long time ago. For a metal heat shield I imagine tungsten as being the best material, it is used to make light bulb filaments so can be made into wire. It has a melting point 3410 C. Is there a reason tungsten is not used?   

Tungsten is dense, so it adds a lot of mass.  There are other metals that have a high enough melting point with less density.  For example, titanium has a lower melting point but still high enough for a lot of purposes and at less than a quarter the density.  The costs of tungsten and titanium are roughly comparable.

But pure elemental metals are far from the only choices.  There is a vast space of choices of alloys of multiple materials with varying properties and costs.  Among all those choices, Tungsten isn't a very useful choice for TPS.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/20/2020 04:11 am
Philw1776 raised the issue of ablative as a temporary expedient and didn't exactly get shot down but he did get some flak.


One counter was the cost of developing two systems. There is some R&D overlap and reusing a (WAG) $5m ship will pay for a fair chunk of R&D. I actually doubt if it would come in under $10m. An ablative will inform on heat patterns and intensity for a more sophisticated system and may end up as a field repair technique.


Rafael uses 10 tons as the current estimate and another 10-20 tons will not be a a good thing but it is less bad than not flying or flying disposable. I can see this offset mass putting limitations on a landing profile but not driving it into the impossible. There is a lot of control authority in those raptors. Just takes more propellant, and loss of payload capacity. ISTM that getting 50 tons to reusable LEO is better than getting 100 throwaway tons, or worse yet, not flying at all.


On the nuts and bolts end, the stainless substructure hints at a lighter ablative construction than a traditional capsule. The thick insulating honeycomb needed to protect an aluminum shell can be much thinner, and maybe could go away.


AIUI, the Mercury capsule used a resinous material. This suggests that a spray on might work. Removal and replacement after each flight violates the principal of fast turnaround. So what. It's an expedient. Fast turnaround isn't  going to show up all at once so any particular launch cadence will demand a fleet pipeline of some particular depth. If heat shield servicing lengthens the turnaround time that pipeline will have to get longer. It isn't as if SX won't have a long term use for a bunch of ships.


It may turn out that the long term fix is already in hand as a contingency plan and will show itself to be more than adequate and economical. If it's not, a less than ideal quick and dirty looks like a good way to get starlink up, nail refueling, gain flight experience, and show progress on HLS.



Title: Re: Starship heat shield
Post by: Lotick on 09/20/2020 07:23 am
Excuse my ignorance. Has any work been done on tungsten? I have a memory of using tungsten steel a long time ago. For a metal heat shield I imagine tungsten as being the best material, it is used to make light bulb filaments so can be made into wire. It has a melting point 3410 C. Is there a reason tungsten is not used?   

For TPS materials, not only melting point matters, but also weight and thermal conductivity. I think metal foam might be a good candidate. The foamy structure allows the thermal conductivity to be reduced tenfold. There are high melting point alloy / metal foams such as nickel-iron (1400-1450 ° C) or titanium (1668 ° C). In terms of weight, titanium foam is probably the best choice.

https://www.samaterials.com/465-foam-metal
Title: Re: Starship heat shield
Post by: mmeijeri on 09/20/2020 08:37 am
Maybe spray-on Teflon could work as a temporary expedient. It wouldn't be nearly enough by itself as it is too difficult to make it thick enough if you spray it on, but maybe it could be applied to hot spots as additional protection. Of course that wouldn't help if the problem was tiles crumbling or falling off because of vibration.
Title: Re: Starship heat shield
Post by: sebk on 09/20/2020 08:44 am
Excuse my ignorance. Has any work been done on tungsten? I have a memory of using tungsten steel a long time ago. For a metal heat shield I imagine tungsten as being the best material, it is used to make light bulb filaments so can be made into wire. It has a melting point 3410 C. Is there a reason tungsten is not used?   

What others have said, but also/primarily oxidation resistance at high temperatures is a requirement and tungsten is not the best there.
Title: Re: Starship heat shield
Post by: HVM on 09/20/2020 12:19 pm
Just found this new SpaceX Job  posting on linkedin (7 hours ago)

"
MATERIALS ENGINEER, STARSHIP (HEATSHIELD)

This role would be on the materials engineering team, supporting alloy and process design. The materials engineering team supports materials across SpaceX via identification, development and implementation of advanced materials and processes. This role will be part of a team of engineers and process specialists developing new materials and processing solutions for different projects, including an early stage project to develop a metallic heat shield for Starship.
"

Moving away from the ceramic heat tiles toward a metallic heat shield? I'm confused
MrWeezy's find, SpX is already searching different paths for TPS.
Title: Re: Starship heat shield
Post by: philw1776 on 09/20/2020 03:52 pm
Philw1776 raised the issue of ablative as a temporary expedient and didn't exactly get shot down but he did get some flak.


One counter was the cost of developing two systems. There is some R&D overlap and reusing a (WAG) $5m ship will pay for a fair chunk of R&D. I actually doubt if it would come in under $10m. An ablative will inform on heat patterns and intensity for a more sophisticated system and may end up as a field repair technique.


Rafael uses 10 tons as the current estimate and another 10-20 tons will not be a a good thing but it is less bad than not flying or flying disposable. I can see this offset mass putting limitations on a landing profile but not driving it into the impossible. There is a lot of control authority in those raptors. Just takes more propellant, and loss of payload capacity. ISTM that getting 50 tons to reusable LEO is better than getting 100 throwaway tons, or worse yet, not flying at all.


On the nuts and bolts end, the stainless substructure hints at a lighter ablative construction than a traditional capsule. The thick insulating honeycomb needed to protect an aluminum shell can be much thinner, and maybe could go away.


AIUI, the Mercury capsule used a resinous material. This suggests that a spray on might work. Removal and replacement after each flight violates the principal of fast turnaround. So what. It's an expedient. Fast turnaround isn't  going to show up all at once so any particular launch cadence will demand a fleet pipeline of some particular depth. If heat shield servicing lengthens the turnaround time that pipeline will have to get longer. It isn't as if SX won't have a long term use for a bunch of ships.


It may turn out that the long term fix is already in hand as a contingency plan and will show itself to be more than adequate and economical. If it's not, a less than ideal quick and dirty looks like a good way to get starlink up, nail refueling, gain flight experience, and show progress on HLS.

Here is what I said...
"the option to use a disposable/repairable heat shield EARLY ON in Starship flights exists.  SpaceX gets each Starship back for refurbishment for subsequent flight(s) and gets valuable flight data while gradual improvements are made to the heat shield design, OR that particular design approach is abandoned because it cannot lead to eventual re-usability."

Clarification.
I wasn't thinking about ablative, although that is a possibility. Simply suggested a "not ready for full repeated re-use without refurbishment" which some posters took to mean total TPS changeout, ablative, or whatever. 
To be more clear, I stand by my stated prediction that minimum viable product re-flights will start out with portions of the heat shield, whatever technology, being disposed/repaired/replaced.  And that initial design will evolve to a final design, just like recoverable boosters did, only more rapidly. We've already seen tile attachment designs fail with replacements undoubtedly in the works.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/20/2020 04:21 pm
Excuse my ignorance. Has any work been done on tungsten? I have a memory of using tungsten steel a long time ago. For a metal heat shield I imagine tungsten as being the best material, it is used to make light bulb filaments so can be made into wire. It has a melting point 3410 C. Is there a reason tungsten is not used?   

For TPS materials, not only melting point matters, but also weight and thermal conductivity. I think metal foam might be a good candidate. The foamy structure allows the thermal conductivity to be reduced tenfold. There are high melting point alloy / metal foams such as nickel-iron (1400-1450 ° C) or titanium (1668 ° C). In terms of weight, titanium foam is probably the best choice.

https://www.samaterials.com/465-foam-metal (https://www.samaterials.com/465-foam-metal)
I didn't know that foamed titanium was a thing and found this: [size=78%]https://en.m.wikipedia.org/wiki/Titanium_foam (https://en.m.wikipedia.org/wiki/Titanium_foam)[/size]


There's a lot of info there with discussion of the relationship between cell size, shape, open/closed, and the impact on strength, thermal and corrosive properties. Looks very promising except for titanium being really expensive.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/20/2020 04:31 pm
Maybe spray-on Teflon could work as a temporary expedient. It wouldn't be nearly enough by itself as it is too difficult to make it thick enough if you spray it on, but maybe it could be applied to hot spots as additional protection. Of course that wouldn't help if the problem was tiles crumbling or falling off because of vibration.
And tractor beams slide right off. Seriously, I don't know how they do it with frying pans but I once worked with a special glue for Teflon. It might have been a precursor to superglue. I was not impressed.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/20/2020 04:40 pm
Philw1776 raised the issue of ablative as a temporary expedient and didn't exactly get shot down but he did get some flak.


One counter was the cost of developing two systems. There is some R&D overlap and reusing a (WAG) $5m ship will pay for a fair chunk of R&D. I actually doubt if it would come in under $10m. An ablative will inform on heat patterns and intensity for a more sophisticated system and may end up as a field repair technique.


Rafael uses 10 tons as the current estimate and another 10-20 tons will not be a a good thing but it is less bad than not flying or flying disposable. I can see this offset mass putting limitations on a landing profile but not driving it into the impossible. There is a lot of control authority in those raptors. Just takes more propellant, and loss of payload capacity. ISTM that getting 50 tons to reusable LEO is better than getting 100 throwaway tons, or worse yet, not flying at all.


On the nuts and bolts end, the stainless substructure hints at a lighter ablative construction than a traditional capsule. The thick insulating honeycomb needed to protect an aluminum shell can be much thinner, and maybe could go away.


AIUI, the Mercury capsule used a resinous material. This suggests that a spray on might work. Removal and replacement after each flight violates the principal of fast turnaround. So what. It's an expedient. Fast turnaround isn't  going to show up all at once so any particular launch cadence will demand a fleet pipeline of some particular depth. If heat shield servicing lengthens the turnaround time that pipeline will have to get longer. It isn't as if SX won't have a long term use for a bunch of ships.


It may turn out that the long term fix is already in hand as a contingency plan and will show itself to be more than adequate and economical. If it's not, a less than ideal quick and dirty looks like a good way to get starlink up, nail refueling, gain flight experience, and show progress on HLS.

Here is what I said...
"the option to use a disposable/repairable heat shield EARLY ON in Starship flights exists.  SpaceX gets each Starship back for refurbishment for subsequent flight(s) and gets valuable flight data while gradual improvements are made to the heat shield design, OR that particular design approach is abandoned because it cannot lead to eventual re-usability."

Clarification.
I wasn't thinking about ablative, although that is a possibility. Simply suggested a "not ready for full repeated re-use without refurbishment" which some posters took to mean total TPS changeout, ablative, or whatever. 
To be more clear, I stand by my stated prediction that minimum viable product re-flights will start out with portions of the heat shield, whatever technology, being disposed/repaired/replaced.  And that initial design will evolve to a final design, just like recoverable boosters did, only more rapidly. We've already seen tile attachment designs fail with replacements undoubtedly in the works.
My bad on putting the word ablative in your mouth. It's more narrow than what you were saying.
Title: Re: Starship heat shield
Post by: Fizrock on 09/20/2020 05:03 pm
So I looked a bit more at those studies I references earlier on metallic heatshields.
 
For the people talking about materials, niobium (previously known as columbium) with a ceramic-oxide coating seems to be a great candidate. 
 
Quote
The R-512E (Si-20Cr-20Fe) fused slurry silicide coating process was optimized to coat full size (20" x 20") single face rib and corrugation stiffened panels fabricated from FS-85 columbium alloy for 100 mission Space Shuttle heat shield applications. Structural life under simulated Space Shuttle lift-off stresses and reentry conditions demonstrated reuse capability well beyond 100 flights for R-512E coated FS-85 columbium heat shield panels. 


Reading this, I'm now kind of curious why NASA went with the ceramic tiles for the Shuttle. The results from this testing sounds very promising.
 
https://ntrs.nasa.gov/citations/19730024093   
 
This study looked primarily at honeycomb structures, particularly titanium and Inconel. Someone mentioned metal foam earlier and I wonder if that would work in the same way.     
 
https://ntrs.nasa.gov/citations/20040095922 
 
Both studies also did lots of stress testing on the tiles outside of just simulated reentries. 
 
Title: Re: Starship heat shield
Post by: mmeijeri on 09/20/2020 05:09 pm
And tractor beams slide right off. Seriously, I don't know how they do it with frying pans but I once worked with a special glue for Teflon. It might have been a precursor to superglue. I was not impressed.

I misremembered reading that Teflon had been used on X-15, though not very successfully. In fact it was something called MA-25S. I do think Teflon has been used before, maybe on early warheads. One potential advantage would be that it ablates cleanly. Or maybe I'm misremembering again.

BTW: this is all theoretical, they probably won't be using spray-on materials even as a temporary expedient.
Title: Re: Starship heat shield
Post by: Oli on 09/20/2020 05:09 pm
Since they already have "wings", they can make them bigger to reduce that ballistic coefficient until a metallic heat shield becomes feasible. Furthermore, they don't necessarily need aerocapture once ISRU on the Moon and Mars becomes a reality.
Title: Re: Starship heat shield
Post by: Robotbeat on 09/20/2020 05:18 pm
So I looked a bit more at those studies I references earlier on metallic heatshields.
 
For the people talking about materials, niobium (previously known as columbium) with a ceramic-oxide coating seems to be a great candidate. 
 
Quote
The R-512E (Si-20Cr-20Fe) fused slurry silicide coating process was optimized to coat full size (20" x 20") single face rib and corrugation stiffened panels fabricated from FS-85 columbium alloy for 100 mission Space Shuttle heat shield applications. Structural life under simulated Space Shuttle lift-off stresses and reentry conditions demonstrated reuse capability well beyond 100 flights for R-512E coated FS-85 columbium heat shield panels. 


Reading this, I'm now kind of curious why NASA went with the ceramic tiles for the Shuttle. The results from this testing sounds very promising.
  ...
Ceramic is WAY lighter, and Shuttle had very little payload. It weighed 78 tons dry and originally could get almost no payload to higher orbits like ISS. It took a few upgrades like the MUCH lighter external tank (which eventually saved 8.5 tons over the original tank) to get payload to ISS up to 16 tons. So using metallic TPS could eliminated the entire payload to many orbits that Shuttle used.


Also, we hadn't had experiences with all the headaches the more brittle ceramic tiles caused.
Title: Re: Starship heat shield
Post by: Robotbeat on 09/20/2020 05:49 pm
Philw1776 raised the issue of ablative as a temporary expedient and didn't exactly get shot down but he did get some flak.


One counter was the cost of developing two systems. There is some R&D overlap and reusing a (WAG) $5m ship will pay for a fair chunk of R&D. I actually doubt if it would come in under $10m. An ablative will inform on heat patterns and intensity for a more sophisticated system and may end up as a field repair technique.


Rafael uses 10 tons as the current estimate and another 10-20 tons will not be a a good thing but it is less bad than not flying or flying disposable. I can see this offset mass putting limitations on a landing profile but not driving it into the impossible. There is a lot of control authority in those raptors. Just takes more propellant, and loss of payload capacity. ISTM that getting 50 tons to reusable LEO is better than getting 100 throwaway tons, or worse yet, not flying at all.


On the nuts and bolts end, the stainless substructure hints at a lighter ablative construction than a traditional capsule. The thick insulating honeycomb needed to protect an aluminum shell can be much thinner, and maybe could go away.


AIUI, the Mercury capsule used a resinous material. This suggests that a spray on might work. Removal and replacement after each flight violates the principal of fast turnaround. So what. It's an expedient. Fast turnaround isn't  going to show up all at once so any particular launch cadence will demand a fleet pipeline of some particular depth. If heat shield servicing lengthens the turnaround time that pipeline will have to get longer. It isn't as if SX won't have a long term use for a bunch of ships.


It may turn out that the long term fix is already in hand as a contingency plan and will show itself to be more than adequate and economical. If it's not, a less than ideal quick and dirty looks like a good way to get starlink up, nail refueling, gain flight experience, and show progress on HLS.

Here is what I said...
"the option to use a disposable/repairable heat shield EARLY ON in Starship flights exists.  SpaceX gets each Starship back for refurbishment for subsequent flight(s) and gets valuable flight data while gradual improvements are made to the heat shield design, OR that particular design approach is abandoned because it cannot lead to eventual re-usability."

Clarification.
I wasn't thinking about ablative, although that is a possibility. Simply suggested a "not ready for full repeated re-use without refurbishment" which some posters took to mean total TPS changeout, ablative, or whatever. 
To be more clear, I stand by my stated prediction that minimum viable product re-flights will start out with portions of the heat shield, whatever technology, being disposed/repaired/replaced.  And that initial design will evolve to a final design, just like recoverable boosters did, only more rapidly. We've already seen tile attachment designs fail with replacements undoubtedly in the works.
Based on your sort of vague description of your idea, either:
1) It's essentially what they're already doing
or
2) It'll require a bunch of extra engineering.

Just to get it to work a single time takes a LOT of engineering time. So either you're describing their current plan or you're describing almost a doubling of engineering work into their heatshield.
Title: Re: Starship heat shield
Post by: JamesH65 on 09/20/2020 06:27 pm
Philw1776 raised the issue of ablative as a temporary expedient and didn't exactly get shot down but he did get some flak.


One counter was the cost of developing two systems. There is some R&D overlap and reusing a (WAG) $5m ship will pay for a fair chunk of R&D. I actually doubt if it would come in under $10m. An ablative will inform on heat patterns and intensity for a more sophisticated system and may end up as a field repair technique.


Rafael uses 10 tons as the current estimate and another 10-20 tons will not be a a good thing but it is less bad than not flying or flying disposable. I can see this offset mass putting limitations on a landing profile but not driving it into the impossible. There is a lot of control authority in those raptors. Just takes more propellant, and loss of payload capacity. ISTM that getting 50 tons to reusable LEO is better than getting 100 throwaway tons, or worse yet, not flying at all.


On the nuts and bolts end, the stainless substructure hints at a lighter ablative construction than a traditional capsule. The thick insulating honeycomb needed to protect an aluminum shell can be much thinner, and maybe could go away.


AIUI, the Mercury capsule used a resinous material. This suggests that a spray on might work. Removal and replacement after each flight violates the principal of fast turnaround. So what. It's an expedient. Fast turnaround isn't  going to show up all at once so any particular launch cadence will demand a fleet pipeline of some particular depth. If heat shield servicing lengthens the turnaround time that pipeline will have to get longer. It isn't as if SX won't have a long term use for a bunch of ships.


It may turn out that the long term fix is already in hand as a contingency plan and will show itself to be more than adequate and economical. If it's not, a less than ideal quick and dirty looks like a good way to get starlink up, nail refueling, gain flight experience, and show progress on HLS.

Here is what I said...
"the option to use a disposable/repairable heat shield EARLY ON in Starship flights exists.  SpaceX gets each Starship back for refurbishment for subsequent flight(s) and gets valuable flight data while gradual improvements are made to the heat shield design, OR that particular design approach is abandoned because it cannot lead to eventual re-usability."

Clarification.
I wasn't thinking about ablative, although that is a possibility. Simply suggested a "not ready for full repeated re-use without refurbishment" which some posters took to mean total TPS changeout, ablative, or whatever. 
To be more clear, I stand by my stated prediction that minimum viable product re-flights will start out with portions of the heat shield, whatever technology, being disposed/repaired/replaced.  And that initial design will evolve to a final design, just like recoverable boosters did, only more rapidly. We've already seen tile attachment designs fail with replacements undoubtedly in the works.
Based on your sort of vague description of your idea, either:
1) It's essentially what they're already doing
or
2) It'll require a bunch of extra engineering.

Just to get it to work a single time takes a LOT of engineering time. So either you're describing their current plan or you're describing almost a doubling of engineering work into their heatshield.

Almost certainly not double. If it were double they would just go straight for the finished/final article. The point being made is that its possible that they will go for a quick and easy method to get to a MVP, then work on a better method long term. This might be cost effective because they need to get Starlink up and running quickly, and if they make more money back from an early use of SS with 'replaceable tiles' that its cost to develop it, it's the cheaper route.


Of course, we have no idea what they are doing.
Title: Re: Starship heat shield
Post by: Fizrock on 09/20/2020 06:39 pm
So I looked a bit more at those studies I references earlier on metallic heatshields.
 
For the people talking about materials, niobium (previously known as columbium) with a ceramic-oxide coating seems to be a great candidate. 
 
Quote
The R-512E (Si-20Cr-20Fe) fused slurry silicide coating process was optimized to coat full size (20" x 20") single face rib and corrugation stiffened panels fabricated from FS-85 columbium alloy for 100 mission Space Shuttle heat shield applications. Structural life under simulated Space Shuttle lift-off stresses and reentry conditions demonstrated reuse capability well beyond 100 flights for R-512E coated FS-85 columbium heat shield panels. 


Reading this, I'm now kind of curious why NASA went with the ceramic tiles for the Shuttle. The results from this testing sounds very promising.
  ...
Ceramic is WAY lighter, and Shuttle had very little payload. It weighed 78 tons dry and originally could get almost no payload to higher orbits like ISS. It took a few upgrades like the MUCH lighter external tank (which eventually saved 8.5 tons over the original tank) to get payload to ISS up to 16 tons. So using metallic TPS could eliminated the entire payload to many orbits that Shuttle used.


Also, we hadn't had experiences with all the headaches the more brittle ceramic tiles caused.
 
 
True, but that second study does say that the masses of the newer, honeycomb shields are comparable to regular TPS. Even beter, actually
 
Quote
The unit masses of the current SA/HC metallic TPS and the AETB-8 tiles are quite similar over the entire heating range.
Ceramic tiles, including AETB-8, were the only TPS that could withstand the highest heating, highest temperature
conditions studied. The advanced metallic TPS concept demonstrated the lowest mass over most of the heating
range, and the benefits of using efficient multilayer insulation are most evident at the higher heat loads. While
this advanced metallic TPS concept has not undergone rigorous design and testing, these results indicate that
metallic TPS have the potential to be mass competitive with blanket TPS concepts at moderate heating levels and
significantly lighter than ceramic tiles over their applicable temperature ranges.
 
So the super light stuff may not have been around for the Shuttle, but it would seem that there could actually be mass savings for Starship if this were employed.
Title: Re: Starship heat shield
Post by: Robotbeat on 09/20/2020 06:45 pm
Philw1776 raised the issue of ablative as a temporary expedient and didn't exactly get shot down but he did get some flak.


One counter was the cost of developing two systems. There is some R&D overlap and reusing a (WAG) $5m ship will pay for a fair chunk of R&D. I actually doubt if it would come in under $10m. An ablative will inform on heat patterns and intensity for a more sophisticated system and may end up as a field repair technique.


Rafael uses 10 tons as the current estimate and another 10-20 tons will not be a a good thing but it is less bad than not flying or flying disposable. I can see this offset mass putting limitations on a landing profile but not driving it into the impossible. There is a lot of control authority in those raptors. Just takes more propellant, and loss of payload capacity. ISTM that getting 50 tons to reusable LEO is better than getting 100 throwaway tons, or worse yet, not flying at all.


On the nuts and bolts end, the stainless substructure hints at a lighter ablative construction than a traditional capsule. The thick insulating honeycomb needed to protect an aluminum shell can be much thinner, and maybe could go away.


AIUI, the Mercury capsule used a resinous material. This suggests that a spray on might work. Removal and replacement after each flight violates the principal of fast turnaround. So what. It's an expedient. Fast turnaround isn't  going to show up all at once so any particular launch cadence will demand a fleet pipeline of some particular depth. If heat shield servicing lengthens the turnaround time that pipeline will have to get longer. It isn't as if SX won't have a long term use for a bunch of ships.


It may turn out that the long term fix is already in hand as a contingency plan and will show itself to be more than adequate and economical. If it's not, a less than ideal quick and dirty looks like a good way to get starlink up, nail refueling, gain flight experience, and show progress on HLS.

Here is what I said...
"the option to use a disposable/repairable heat shield EARLY ON in Starship flights exists.  SpaceX gets each Starship back for refurbishment for subsequent flight(s) and gets valuable flight data while gradual improvements are made to the heat shield design, OR that particular design approach is abandoned because it cannot lead to eventual re-usability."

Clarification.
I wasn't thinking about ablative, although that is a possibility. Simply suggested a "not ready for full repeated re-use without refurbishment" which some posters took to mean total TPS changeout, ablative, or whatever. 
To be more clear, I stand by my stated prediction that minimum viable product re-flights will start out with portions of the heat shield, whatever technology, being disposed/repaired/replaced.  And that initial design will evolve to a final design, just like recoverable boosters did, only more rapidly. We've already seen tile attachment designs fail with replacements undoubtedly in the works.
Based on your sort of vague description of your idea, either:
1) It's essentially what they're already doing
or
2) It'll require a bunch of extra engineering.

Just to get it to work a single time takes a LOT of engineering time. So either you're describing their current plan or you're describing almost a doubling of engineering work into their heatshield.

Almost certainly not double. If it were double they would just go straight for the finished/final article. The point being made is that its possible that they will go for a quick and easy method to get to a MVP...
There is no quick, easy fix for a large and lightweight thermal protection system, reparable or disposable or whathaveyou. It requires careful engineering. Just the way things are in aerospace.
Title: Re: Starship heat shield
Post by: Robotbeat on 09/20/2020 06:46 pm
So I looked a bit more at those studies I references earlier on metallic heatshields.
 
For the people talking about materials, niobium (previously known as columbium) with a ceramic-oxide coating seems to be a great candidate. 
 
Quote
The R-512E (Si-20Cr-20Fe) fused slurry silicide coating process was optimized to coat full size (20" x 20") single face rib and corrugation stiffened panels fabricated from FS-85 columbium alloy for 100 mission Space Shuttle heat shield applications. Structural life under simulated Space Shuttle lift-off stresses and reentry conditions demonstrated reuse capability well beyond 100 flights for R-512E coated FS-85 columbium heat shield panels. 


Reading this, I'm now kind of curious why NASA went with the ceramic tiles for the Shuttle. The results from this testing sounds very promising.
  ...
Ceramic is WAY lighter, and Shuttle had very little payload. It weighed 78 tons dry and originally could get almost no payload to higher orbits like ISS. It took a few upgrades like the MUCH lighter external tank (which eventually saved 8.5 tons over the original tank) to get payload to ISS up to 16 tons. So using metallic TPS could eliminated the entire payload to many orbits that Shuttle used.


Also, we hadn't had experiences with all the headaches the more brittle ceramic tiles caused.
 
 
True, but that second study does say that the masses of the newer, honeycomb shields are comparable to regular TPS. Even beter, actually
 
Quote
The unit masses of the current SA/HC metallic TPS and the AETB-8 tiles are quite similar over the entire heating range.
Ceramic tiles, including AETB-8, were the only TPS that could withstand the highest heating, highest temperature
conditions studied. The advanced metallic TPS concept demonstrated the lowest mass over most of the heating
range, and the benefits of using efficient multilayer insulation are most evident at the higher heat loads. While
this advanced metallic TPS concept has not undergone rigorous design and testing, these results indicate that
metallic TPS have the potential to be mass competitive with blanket TPS concepts at moderate heating levels and
significantly lighter than ceramic tiles over their applicable temperature ranges.
 
So the super light stuff may not have been around for the Shuttle, but it would seem that there could actually be mass savings for Starship if this were employed.
Yeah, agreed there have been advances. I was just answering the question of why they went with ceramic originally for Shuttle (which was developed in the 1970s).
Title: Re: Starship heat shield
Post by: Robotbeat on 09/20/2020 07:25 pm
One should point out that Shuttle lost a lot of tiles after the first few flights, too. NASA was *a lot* more careful with STS-1 and STS-2 than SpaceX has been with Starship hops, obviously, but also it was too late for them to switch. SpaceX has the luxury of being extremely aggressive with early fly-and-try-and-redesign-and-build-and-repeat, so they're able to learn their lesson with ceramic maybe being a bad choice earlier than Shuttle did.

As far as why they didn't just take Shuttle's lessons to heart, well, there's always a certain amount of hubris and naivete when doing a new, grand project like this on an aggressive timescale, and the key is always to be quick to correct mistakes. Sometimes the old wisdom is wrong or obsolete, so sometimes you should just try it (even if 9 times out of 10 the accepted wisdom is right).

Still, as Jeff Greason said, "It's always amazing how six months on the test stand can save you a few hours in the library."
Title: Re: Starship heat shield
Post by: steveleach on 09/20/2020 08:38 pm
There is no quick, easy fix for a large and lightweight thermal protection system, reparable or disposable or whathaveyou. It requires careful engineering. Just the way things are in aerospace.
The only thing I know about all this is that I'd struggle to imagine a better platform for experimenting with heatshield materials and designs than Starship.

SpaceX could put a completely different variant on every orbital SN they build and just see which ones make it to the ground in one piece. It isn't just designed to be reusable, it's also designed to be cheap to manufacture, and all its competitors burn up on entry anyway.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/20/2020 10:34 pm
And tractor beams slide right off. Seriously, I don't know how they do it with frying pans but I once worked with a special glue for Teflon. It might have been a precursor to superglue. I was not impressed.

I misremembered reading that Teflon had been used on X-15, though not very successfully. In fact it was something called MA-25S. I do think Teflon has been used before, maybe on early warheads. One potential advantage would be that it ablates cleanly. Or maybe I'm misremembering again.

BTW: this is all theoretical, they probably won't be using spray-on materials even as a temporary expedient.
Why not?
Title: Re: Starship heat shield
Post by: ChrisWilson68 on 09/20/2020 10:38 pm
One should point out that Shuttle lost a lot of tiles after the first few flights, too. NASA was *a lot* more careful with STS-1 and STS-2 than SpaceX has been with Starship hops, obviously, but also it was too late for them to switch. SpaceX has the luxury of being extremely aggressive with early fly-and-try-and-redesign-and-build-and-repeat, so they're able to learn their lesson with ceramic maybe being a bad choice earlier than Shuttle did.

As far as why they didn't just take Shuttle's lessons to heart, well, there's always a certain amount of hubris and naivete when doing a new, grand project like this on an aggressive timescale, and the key is always to be quick to correct mistakes. Sometimes the old wisdom is wrong or obsolete, so sometimes you should just try it (even if 9 times out of 10 the accepted wisdom is right).

Still, as Jeff Greason said, "It's always amazing how six months on the test stand can save you a few hours in the library."

I haven't seen any evidence that SpaceX has failed to take Shuttle's lessons to heart.  They've been testing a tile system that has some things in common with the shuttle TPS and some things that are different.  It doesn't seem to me you'd have to ignore the Shuttle experience to think that's a potentially reasonable idea.

I also think it's a bit premature to conclude that ceramic tiles are a bad choice.  Perhaps they just need to make some modifications and then they'll have a ceramic tile system that works really well for them.  Or maybe not.  We don't really know.  But even if it turns out ceramic isn't the way to go, I don't think that's necessarily ignoring the lessons from Shuttle, it could well be that they were fully aware of the Shuttle experience but wanted to explore more of the design space of ceramic tiles than Shuttle had.

We know that they have had a series of tests and missing tiles afterwards.  Not every tile was missing after every test.  We don't know all the factors that went into why the tiles ended up missing.  We don't know if there is some easy fix.  We also know that they're exploring metallic TPS.  That doesn't necessarily mean that they have given up on ceramics or that ceramics won't work.  Even if they're quite confident they can fix the problems with the ceramics and that they'll work really well, it's just prudent to explore the possibility that they could produce an even better TPS.

Not long ago, SpaceX had a series of tank failures.  There was a lot of worry here about whether welding stainless steel turned out just not to work.  But then suddenly they stopped losing tanks.  They figured out the issues and fixed them.  Looking back a year from now, it might be the same story with their ceramic tiles -- a series of failed tests, then an unbroken string of successes.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/20/2020 11:07 pm
Philw1776 raised the issue of ablative as a temporary expedient and didn't exactly get shot down but he did get some flak.


One counter was the cost of developing two systems. There is some R&D overlap and reusing a (WAG) $5m ship will pay for a fair chunk of R&D. I actually doubt if it would come in under $10m. An ablative will inform on heat patterns and intensity for a more sophisticated system and may end up as a field repair technique.


Rafael uses 10 tons as the current estimate and another 10-20 tons will not be a a good thing but it is less bad than not flying or flying disposable. I can see this offset mass putting limitations on a landing profile but not driving it into the impossible. There is a lot of control authority in those raptors. Just takes more propellant, and loss of payload capacity. ISTM that getting 50 tons to reusable LEO is better than getting 100 throwaway tons, or worse yet, not flying at all.


On the nuts and bolts end, the stainless substructure hints at a lighter ablative construction than a traditional capsule. The thick insulating honeycomb needed to protect an aluminum shell can be much thinner, and maybe could go away.


AIUI, the Mercury capsule used a resinous material. This suggests that a spray on might work. Removal and replacement after each flight violates the principal of fast turnaround. So what. It's an expedient. Fast turnaround isn't  going to show up all at once so any particular launch cadence will demand a fleet pipeline of some particular depth. If heat shield servicing lengthens the turnaround time that pipeline will have to get longer. It isn't as if SX won't have a long term use for a bunch of ships.


It may turn out that the long term fix is already in hand as a contingency plan and will show itself to be more than adequate and economical. If it's not, a less than ideal quick and dirty looks like a good way to get starlink up, nail refueling, gain flight experience, and show progress on HLS.

Here is what I said...
"the option to use a disposable/repairable heat shield EARLY ON in Starship flights exists.  SpaceX gets each Starship back for refurbishment for subsequent flight(s) and gets valuable flight data while gradual improvements are made to the heat shield design, OR that particular design approach is abandoned because it cannot lead to eventual re-usability."

Clarification.
I wasn't thinking about ablative, although that is a possibility. Simply suggested a "not ready for full repeated re-use without refurbishment" which some posters took to mean total TPS changeout, ablative, or whatever. 
To be more clear, I stand by my stated prediction that minimum viable product re-flights will start out with portions of the heat shield, whatever technology, being disposed/repaired/replaced.  And that initial design will evolve to a final design, just like recoverable boosters did, only more rapidly. We've already seen tile attachment designs fail with replacements undoubtedly in the works.
Based on your sort of vague description of your idea, either:
1) It's essentially what they're already doing
or
2) It'll require a bunch of extra engineering.

Just to get it to work a single time takes a LOT of engineering time. So either you're describing their current plan or you're describing almost a doubling of engineering work into their heatshield.

Almost certainly not double. If it were double they would just go straight for the finished/final article. The point being made is that its possible that they will go for a quick and easy method to get to a MVP...
There is no quick, easy fix for a large and lightweight thermal protection system, reparable or disposable or whathaveyou. It requires careful engineering. Just the way things are in aerospace.
Maybe I'm under thinking it. ISTM a lot of lessons (engineering effort) from an interim less than ideal design would cross over. There is the obvious thermal lessons but issues around the hinges will become much clearer. That's a BIG thing. If the early design is tiles or panels of some sort it teaches how to work with compound curves and attachment points.


I know this is not all there is to it but it is a not insignificant part of it. A lot of problems go away if you throw mass at them.


It will not kill the program if the first orbital ship has only a 50 ton payload capacity. That means they can launch ~150 starlinks in one wack and they have a shot at reuse. If it splashes it will be regrettable but informative. If it doesn't splash the next iteration will be lighter.



Title: Re: Starship heat shield
Post by: OTV Booster on 09/20/2020 11:17 pm
One should point out that Shuttle lost a lot of tiles after the first few flights, too. NASA was *a lot* more careful with STS-1 and STS-2 than SpaceX has been with Starship hops, obviously, but also it was too late for them to switch. SpaceX has the luxury of being extremely aggressive with early fly-and-try-and-redesign-and-build-and-repeat, so they're able to learn their lesson with ceramic maybe being a bad choice earlier than Shuttle did.

As far as why they didn't just take Shuttle's lessons to heart, well, there's always a certain amount of hubris and naivete when doing a new, grand project like this on an aggressive timescale, and the key is always to be quick to correct mistakes. Sometimes the old wisdom is wrong or obsolete, so sometimes you should just try it (even if 9 times out of 10 the accepted wisdom is right).

Still, as Jeff Greason said, "It's always amazing how six months on the test stand can save you a few hours in the library."
No hard evidence but the impression I've got is they couldn't get the numbers to work out on everything else and sort of backed into ceramic by default because in theory, the numbers worked. We all know about 'in theory.'


It's not looking so good so far but being a fly on a very distant wall, my view is superficial. No matter what they do, it will be entertaining and informative.
Title: Re: Starship heat shield
Post by: philw1776 on 09/21/2020 12:06 am
Philw1776 raised the issue of ablative as a temporary expedient and didn't exactly get shot down but he did get some flak.


One counter was the cost of developing two systems. There is some R&D overlap and reusing a (WAG) $5m ship will pay for a fair chunk of R&D. I actually doubt if it would come in under $10m. An ablative will inform on heat patterns and intensity for a more sophisticated system and may end up as a field repair technique.


Rafael uses 10 tons as the current estimate and another 10-20 tons will not be a a good thing but it is less bad than not flying or flying disposable. I can see this offset mass putting limitations on a landing profile but not driving it into the impossible. There is a lot of control authority in those raptors. Just takes more propellant, and loss of payload capacity. ISTM that getting 50 tons to reusable LEO is better than getting 100 throwaway tons, or worse yet, not flying at all.


On the nuts and bolts end, the stainless substructure hints at a lighter ablative construction than a traditional capsule. The thick insulating honeycomb needed to protect an aluminum shell can be much thinner, and maybe could go away.


AIUI, the Mercury capsule used a resinous material. This suggests that a spray on might work. Removal and replacement after each flight violates the principal of fast turnaround. So what. It's an expedient. Fast turnaround isn't  going to show up all at once so any particular launch cadence will demand a fleet pipeline of some particular depth. If heat shield servicing lengthens the turnaround time that pipeline will have to get longer. It isn't as if SX won't have a long term use for a bunch of ships.


It may turn out that the long term fix is already in hand as a contingency plan and will show itself to be more than adequate and economical. If it's not, a less than ideal quick and dirty looks like a good way to get starlink up, nail refueling, gain flight experience, and show progress on HLS.

Here is what I said...
"the option to use a disposable/repairable heat shield EARLY ON in Starship flights exists.  SpaceX gets each Starship back for refurbishment for subsequent flight(s) and gets valuable flight data while gradual improvements are made to the heat shield design, OR that particular design approach is abandoned because it cannot lead to eventual re-usability."

Clarification.
I wasn't thinking about ablative, although that is a possibility. Simply suggested a "not ready for full repeated re-use without refurbishment" which some posters took to mean total TPS changeout, ablative, or whatever. 
To be more clear, I stand by my stated prediction that minimum viable product re-flights will start out with portions of the heat shield, whatever technology, being disposed/repaired/replaced.  And that initial design will evolve to a final design, just like recoverable boosters did, only more rapidly. We've already seen tile attachment designs fail with replacements undoubtedly in the works.
Based on your sort of vague description of your idea, either:
1) It's essentially what they're already doing
or
2) It'll require a bunch of extra engineering.

Just to get it to work a single time takes a LOT of engineering time. So either you're describing their current plan or you're describing almost a doubling of engineering work into their heatshield.

I'd guess close to #1 which was my conjecture, although I have no insider info. 
As to 2 it's as before, in your imagination, and only if design approach completely fails, e.g. parachuting F9s into the ocean for re-use.
Title: Re: Starship heat shield
Post by: kkattula on 09/21/2020 03:24 am
Excuse my ignorance. Has any work been done on tungsten? I have a memory of using tungsten steel a long time ago. For a metal heat shield I imagine tungsten as being the best material, it is used to make light bulb filaments so can be made into wire. It has a melting point 3410 C. Is there a reason tungsten is not used?   

For TPS materials, not only melting point matters, but also weight and thermal conductivity. I think metal foam might be a good candidate. The foamy structure allows the thermal conductivity to be reduced tenfold. There are high melting point alloy / metal foams such as nickel-iron (1400-1450 ° C) or titanium (1668 ° C). In terms of weight, titanium foam is probably the best choice.

https://www.samaterials.com/465-foam-metal


I seem to remember (but can't find) someone on this forum once suggesting a platinum heat-shield could be very effective. If a little pricey.  Maybe if Psyche works out...
Title: Re: Starship heat shield
Post by: Framryk on 09/21/2020 11:07 am
Excuse my ignorance. Has any work been done on tungsten? I have a memory of using tungsten steel a long time ago. For a metal heat shield I imagine tungsten as being the best material, it is used to make light bulb filaments so can be made into wire. It has a melting point 3410 C. Is there a reason tungsten is not used?   

For TPS materials, not only melting point matters, but also weight and thermal conductivity. I think metal foam might be a good candidate. The foamy structure allows the thermal conductivity to be reduced tenfold. There are high melting point alloy / metal foams such as nickel-iron (1400-1450 ° C) or titanium (1668 ° C). In terms of weight, titanium foam is probably the best choice.

https://www.samaterials.com/465-foam-metal

I really like the idea of foamed titanium (https://www.samaterials.com/foam-metal/1816-titanium-foam.html) with a protective very thin titanium solid metal overlayer (kind of like a metal foam sandwich). Thermal resistance (melting point) of 1670 degC, against a full duration re-entry profile of Tmax of 1400 degC (?) (https://en.m.wikipedia.org/wiki/Titanium_foam)

We use mirror insulation on my site, a thin metal outer sheet (razor sharp edges!) and a concertina folded sheet metal interior or a foamed metal interior (kind of looks "scintered").

From https://forum.nasaspaceflight.com/index.php?topic=50049.msg2042556#msg2042556, total heat shield area should be around 774.72m2. The density quoted at ~0.3 g/cm3 (300 kg/m3) for a total TPS volume of 23.34 m3 (I think this assumed a 3 cm thick tile) leads to a TPS total weight of about 7 tonnes, excluding mounting pins and a very thin metal layer - should be possible for around the original 10 tonne TPS estimate?

Easy to calculate, difficult to test I guess!
Title: Re: Starship heat shield
Post by: rsdavis9 on 09/21/2020 01:07 pm
I find it interesting that the place we have seen tile loss is on the engine skirt. Have we seen tiles elsewhere and were they lost?

For the orbital starship they will never fire engines at sea level air pressure. The engines will start for the first time at stage separation. The much lower pressure air will transmit sound at a much lower level and cause much less vibration in the engine skirt. So possibly we are seeing tile loss in an area which wont be a problem with the orbital launches.

EDIT: of course this doesn't account for the vac raptors closer to the skirt.
Title: Re: Starship heat shield
Post by: Robotbeat on 09/21/2020 02:43 pm
It's good to put the tiles in kind of the worst-case spot for vibrations for these tests. You want a really robust solution.
Title: Re: Starship heat shield
Post by: sebk on 09/21/2020 03:55 pm
Excuse my ignorance. Has any work been done on tungsten? I have a memory of using tungsten steel a long time ago. For a metal heat shield I imagine tungsten as being the best material, it is used to make light bulb filaments so can be made into wire. It has a melting point 3410 C. Is there a reason tungsten is not used?   

For TPS materials, not only melting point matters, but also weight and thermal conductivity. I think metal foam might be a good candidate. The foamy structure allows the thermal conductivity to be reduced tenfold. There are high melting point alloy / metal foams such as nickel-iron (1400-1450 ° C) or titanium (1668 ° C). In terms of weight, titanium foam is probably the best choice.

https://www.samaterials.com/465-foam-metal

I really like the idea of foamed titanium (https://www.samaterials.com/foam-metal/1816-titanium-foam.html) with a protective very thin titanium solid metal overlayer (kind of like a metal foam sandwich). Thermal resistance (melting point) of 1670 degC, against a full duration re-entry profile of Tmax of 1400 degC (?) (https://en.m.wikipedia.org/wiki/Titanium_foam)

We use mirror insulation on my site, a thin metal outer sheet (razor sharp edges!) and a concertina folded sheet metal interior or a foamed metal interior (kind of looks "scintered").

From https://forum.nasaspaceflight.com/index.php?topic=50049.msg2042556#msg2042556, total heat shield area should be around 774.72m2. The density quoted at ~0.3 g/cm3 (300 kg/m3) for a total TPS volume of 23.34 m3 (I think this assumed a 3 cm thick tile) leads to a TPS total weight of about 7 tonnes, excluding mounting pins and a very thin metal layer - should be possible for around the original 10 tonne TPS estimate?

Easy to calculate, difficult to test I guess!

Titanium, even remotely close to its melting point is incompatible with oxygen containing air (it's also incompatible with LOX and with few bar oxygen even at room temperature). Data from Columbia disaster has shown higher than expected burn-up of titanium elements. Some titanium pieces almost completely vanished while directly attached aluminum parts remained.
Title: Re: Starship heat shield
Post by: rsdavis9 on 09/21/2020 04:27 pm

Titanium, even remotely close to its melting point is incompatible with oxygen containing air (it's also incompatible with LOX and with few bar oxygen even at room temperature). Data from Columbia disaster has shown higher than expected burn-up of titanium elements. Some titanium pieces almost completely vanished while directly attached aluminum parts remained.

And Ti and N2O4 under pressure isn't great with impact. :)
Title: Re: Starship heat shield
Post by: Slarty1080 on 09/21/2020 06:33 pm
I find it interesting that the place we have seen tile loss is on the engine skirt. Have we seen tiles elsewhere and were they lost?

For the orbital starship they will never fire engines at sea level air pressure. The engines will start for the first time at stage separation. The much lower pressure air will transmit sound at a much lower level and cause much less vibration in the engine skirt. So possibly we are seeing tile loss in an area which wont be a problem with the orbital launches.

EDIT: of course this doesn't account for the vac raptors closer to the skirt.
I believe they will fire the engines at sea level when Starship lands retropropulsively.
Title: Re: Starship heat shield
Post by: SkyRate on 09/21/2020 07:20 pm
I find it interesting that the place we have seen tile loss is on the engine skirt. Have we seen tiles elsewhere and were they lost?
SN4 had a 7-tile test patch near the bottom of the CH4 tank. It lasted as long as SN4 did...
Title: Re: Starship heat shield
Post by: Keldor on 09/21/2020 08:07 pm
I find it interesting that the place we have seen tile loss is on the engine skirt. Have we seen tiles elsewhere and were they lost?

For the orbital starship they will never fire engines at sea level air pressure. The engines will start for the first time at stage separation. The much lower pressure air will transmit sound at a much lower level and cause much less vibration in the engine skirt. So possibly we are seeing tile loss in an area which wont be a problem with the orbital launches.

EDIT: of course this doesn't account for the vac raptors closer to the skirt.

They'll fire those rockets at sea level when they land it, of course.

I think the big problem may be the cavity under the skirt where the engine nozzles are.  It has very little little clearance off the ground, and when you looked at the footage from the camera mounted in there that SpaceX released, you can see the camera start violently shaking during the final seconds before touchdown.

This might be solved just with longer landing legs.  If not, putting some vents on the leeward side as well as some baffles in there might help to disrupt resonance.  It might also work to just put stiffeners on the skirt, in the case the whole thing distorting from the huge acoustic forces was cracking the tiles, although this wouldn't bode well for thermal expansion during reentry.  One other possibility is embedding some sort of mesh inside the tiles.  A sort of ceramic rebar, if you will.  This will, of course, make the tiles heavier, but the trouble area is likely just the skirt, so this represents only a small portion of the total heat shield that needs the reinforcement.

Long term options might be to put a hole in the middle of the landing pad with a flame diverter under it.  I think their landing accuracy is good enough for this to not cause a problem, other than the extra time and effort needed to construct the pad.

Anyway, they also put some test heat shield tiles on hopper, which, IIRC, were just fine after the test.
Title: Re: Starship heat shield
Post by: rsdavis9 on 09/21/2020 08:16 pm
Anyway, they also put some test heat shield tiles on hopper, which, IIRC, were just fine after the test.

So that points to the skirt being too "flimsy". Hopper was what 10 mm? starship is 4 mm.
Also hopper had longer legs.
Title: Re: Starship heat shield
Post by: Pueo on 09/21/2020 08:38 pm

Titanium, even remotely close to its melting point is incompatible with oxygen containing air (it's also incompatible with LOX and with few bar oxygen even at room temperature). Data from Columbia disaster has shown higher than expected burn-up of titanium elements. Some titanium pieces almost completely vanished while directly attached aluminum parts remained.

Could you impregnate the titanium foam with TEOS and then heat it up to give the pores a nice silicon-dioxide coating as an oxidation barrier?
Title: Re: Starship heat shield
Post by: john smith 19 on 09/21/2020 08:47 pm
So I looked a bit more at those studies I references earlier on metallic heatshields.
 
For the people talking about materials, niobium (previously known as columbium) with a ceramic-oxide coating seems to be a great candidate. 


Reading this, I'm now kind of curious why NASA went with the ceramic tiles for the Shuttle. The results from this testing sounds very promising.
 
https://ntrs.nasa.gov/citations/19730024093   
 
This study looked primarily at honeycomb structures, particularly titanium and Inconel. Someone mentioned metal foam earlier and I wonder if that would work in the same way.     
 
https://ntrs.nasa.gov/citations/20040095922 
 
Both studies also did lots of stress testing on the tiles outside of just simulated reentries. 
So did I. Thanks for finding those.

Thermal protection system design involves balancing a whole bunch of variables to to deliver multiple constraints.

Now look at material densities in terms of specific gravity relative to water.

Silica at 100% of theoretical density 2.65
Niobium 8.5
Molybdenum 10.56
Tantalum 12
Tungsten 20

And the Silica tiles were 95% air.

To do as well you'd have to build those panels out of very thin material.  The ones that Rohr delivered to the X33 programme were foil thickness, rather than what most people think of as sheet.  :(

And this is just the TPS, not the actual airtight skin of the orbiter (which is aluminum, with IIRC a max use temperature of about 153c).

Of course 3 decades of tile maintenance and repair have made the limitations of ceramic tile technology very clear. But understand that the TUFROC tiles SX are using were never used on Shuttle, although they are being used on the X37b.
Title: Re: Starship heat shield
Post by: john smith 19 on 09/21/2020 08:51 pm
I misremembered reading that Teflon had been used on X-15, though not very successfully. In fact it was something called MA-25S. I do think Teflon has been used before, maybe on early warheads. One potential advantage would be that it ablates cleanly. Or maybe I'm misremembering again.

BTW: this is all theoretical, they probably won't be using spray-on materials even as a temporary expedient.
I can't recall the reference (may have been a early Apollo radome) but Teflon has been used as an ablator and on some reentry vehicles. It burns off clean but it's burn off temperature is quite low, about 400c IIRC>
Title: Re: Starship heat shield
Post by: enbandi on 09/24/2020 06:46 am
Was that heavy pin pattern, on SN8 or 9, I try find it again at update thread but it is bit too dense.
[Edit] Ok, Mary's photo of SN8 have a tri-pin pattern but I don't see pins. Do they test stud welds effect to the skin of the ship? And the pin picture part is for SN9. (?)

https://forum.nasaspaceflight.com/index.php?topic=51332.1420

Now, ot this picture the pins/studs seem to be there. Not only the pattern, but the pins also:
https://twitter.com/cnunezimages/status/1308948295465795587

So back to the original question again: will be test  tiles on the 20 km flight?
Title: Re: Starship heat shield
Post by: livingjw on 09/24/2020 01:57 pm
https://twitter.com/cnunezimages/status/1309125893097480197

Quote
SN8 Aft Flap / Up close Pano / Click to Expand -
@elonmusk #bocachicatomars #SN8 #SpaceX #iCANimagine LLC @SpaceIntellige3
  -  CNunezIMAGES.com

There is no way in hell that you can attach TPS to such a surface. Most probably another expedient stand in for testing.

John
Title: Re: Starship heat shield
Post by: livingjw on 09/24/2020 03:02 pm
The fins appear to be another expedient prototype for testing. No way you can attach TPS to those panels. They will have to either go to honeycomb or fluted/corrugated surface (ala SR-71) panels to keep them from oil canning. They could do the tops with wrinkles, but not the bottoms.

John
Title: Re: Starship heat shield
Post by: Nomadd on 09/24/2020 03:24 pm
There is no way in hell that you can attach TPS to such a surface. Most probably another expedient stand in for testing.
John
I'm half expecting another big surprise with the fins. Since they're not pressurized or protecting delicate stuff inside, it seems like you wouldn't want to use the same scheme the tanks will.
Title: Re: Starship heat shield
Post by: wannamoonbase on 09/24/2020 03:50 pm
There is no way in hell that you can attach TPS to such a surface. Most probably another expedient stand in for testing.
John
I'm half expecting another big surprise with the fins. Since they're not pressurized or protecting delicate stuff inside, it seems like you wouldn't want to use the same scheme the tanks will.

It looks like a thin crooked cookie sheet

The leading side could be much different than the trailing size.  It would seem that it could be thinner toward the outer edge as well, the fins look kind of fat.

Just gotta start flying and iterating.
Title: Re: Starship heat shield
Post by: r8ix on 09/24/2020 03:58 pm
There is no way in hell that you can attach TPS to such a surface. Most probably another expedient stand in for testing.
John
I'm half expecting another big surprise with the fins. Since they're not pressurized or protecting delicate stuff inside, it seems like you wouldn't want to use the same scheme the tanks will.

It looks like a thin crooked cookie sheet

The leading side could be much different than the trailing size.  It would seem that it could be thinner toward the outer edge as well, the fins look kind of fat.

Just gotta start flying and iterating.

Don't forget telephoto distortion. It's smoother than it looks...
Title: Re: Starship heat shield
Post by: vaporcobra on 09/24/2020 05:47 pm
https://twitter.com/cnunezimages/status/1309125893097480197

Quote
SN8 Aft Flap / Up close Pano / Click to Expand -
@elonmusk #bocachicatomars #SN8 #SpaceX #iCANimagine LLC @SpaceIntellige3
  -  CNunezIMAGES.com

There is no way in hell that you can attach TPS to such a surface. Most probably another expedient stand in for testing.

John

It likely looks worse than it is, concave mirrors LOVE to exaggerate differences. Mk1's fins were ironically much smoother (probably at the expense of weight).
Title: Re: Starship heat shield
Post by: Morgun on 09/24/2020 06:11 pm
The fins appear to be another expedient prototype for testing. No way you can attach TPS to those panels. They will have to either go to honeycomb or fluted/corrugated surface (ala SR-71) panels to keep them from oil canning. They could do the tops with wrinkles, but not the bottoms.

John

Since the fins are made off site wouldn't the TPS version come in on the truck with the TPS already fully assembled?
Title: Re: Starship heat shield
Post by: rsdavis9 on 09/24/2020 06:36 pm
https://twitter.com/cnunezimages/status/1309125893097480197

Quote
SN8 Aft Flap / Up close Pano / Click to Expand -
@elonmusk #bocachicatomars #SN8 #SpaceX #iCANimagine LLC @SpaceIntellige3
  -  CNunezIMAGES.com

There is no way in hell that you can attach TPS to such a surface. Most probably another expedient stand in for testing.

John

Maybe fluid cooling for the fins only. They are one of the hardest surfaces to tile over.
Gaseous cold O2.
Water mist.

Title: Re: Starship heat shield
Post by: enbandi on 09/24/2020 06:42 pm
The fins appear to be another expedient prototype for testing. No way you can attach TPS to those panels. They will have to either go to honeycomb or fluted/corrugated surface (ala SR-71) panels to keep them from oil canning. They could do the tops with wrinkles, but not the bottoms.

John

Thinking about that a bit deeper: an airtight skin under the TPS has no real purpose (other than providing a mounting surface for the TPS). So they might try to integrate those functions/eliminate the skin completely. A grid like support structure with a bit more sturdy tiles or whatever.

If they do so, what we see now is a coplete dead end/strictly temporary solution.
Title: Re: Starship heat shield
Post by: rsdavis9 on 09/24/2020 06:53 pm
The fins appear to be another expedient prototype for testing. No way you can attach TPS to those panels. They will have to either go to honeycomb or fluted/corrugated surface (ala SR-71) panels to keep them from oil canning. They could do the tops with wrinkles, but not the bottoms.

John

Thinking about that a bit deeper: an airtight skin under the TPS has no real purpose (other than providing a mounting surface for the TPS). So they might try to integrate those functions/eliminate the skin completely. A grid like support structure with a bit more sturdy tiles or whatever.

If they do so, what we see now is a coplete dead end/strictly temporary solution.

Make them out of the X-33 superalloy for the heat shield? You could make it very thin since there is no pressure to support.
Title: Re: Starship heat shield
Post by: Nomadd on 09/24/2020 07:08 pm
Anyway, they also put some test heat shield tiles on hopper, which, IIRC, were just fine after the test.

So that points to the skirt being too "flimsy". Hopper was what 10 mm? starship is 4 mm.
Also hopper had longer legs.

  Hopper was more like 14mm.
Title: Re: Starship heat shield
Post by: AstroWare on 09/24/2020 07:45 pm
The fins appear to be another expedient prototype for testing. No way you can attach TPS to those panels. They will have to either go to honeycomb or fluted/corrugated surface (ala SR-71) panels to keep them from oil canning. They could do the tops with wrinkles, but not the bottoms.

John
Is there a chance there won't be any TPS -tiles- on the fins? Just the starship body and wing root covers?

The starship body will provide the vast majority of the braking force on reentry. During peak heat load, The fins could be swept back extremely far to the point where the steel structure would be sufficient. We know the leeward side won't have tiles TPS after all. Even swept back to being nearly parallel to airstream should provide some control authority.

After peak heating they could be gradually extended into the airstream to provide greater deceleration and control.

Even if it is determined that the fins can not survive without -any- TPS, a different type of TPS could be used, such as an ablative coating designed to last dozens of flights.

Refurbishment of consumable TPS on flaps alone could be done off the vehicle. If a flap is getting towards the end of useful life, swap it out. Starships keep flying and send the old flap back for refurbishment.
Title: Re: Starship heat shield
Post by: Bananas_on_Mars on 09/24/2020 08:11 pm
Maybe they plan to make the flaps from inconel or similar?

The flaps for all suborbital testing might just need the right shape for now.

And the big differences between the main body and the flaps are that the surface doesnt need to bear all forces, and does not experience cryogenic temperatures.

Maybe just a thin layer of inconel on some kind of felt, on top of a stainless steel structure?
Title: Re: Starship heat shield
Post by: Slarty1080 on 09/24/2020 08:29 pm
Maybe they plan to make the flaps from inconel or similar?

The flaps for all suborbital testing might just need the right shape for now.

And the big differences between the main body and the flaps are that the surface doesnt need to bear all forces, and does not experience cryogenic temperatures.

Maybe just a thin layer of inconel on some kind of felt, on top of a stainless steel structure?
The main tank has to be there to contain the propellants, but does there need to be a continuous surface under the fins heat shield? Wouldn't an open framework of attachment points work?
Title: Re: Starship heat shield
Post by: Twark_Main on 09/24/2020 08:39 pm
Maybe they plan to make the flaps from inconel or similar?

The flaps for all suborbital testing might just need the right shape for now.

And the big differences between the main body and the flaps are that the surface doesnt need to bear all forces, and does not experience cryogenic temperatures.

Maybe just a thin layer of inconel on some kind of felt, on top of a stainless steel structure?
The main tank has to be there to contain the propellants, but does there need to be a continuous surface under the fins heat shield? Wouldn't an open framework of attachment points work?

It seems like an open grid would allow superheated air to enter and overheat the structure.
Title: Re: Starship heat shield
Post by: enbandi on 09/24/2020 08:53 pm
Maybe they plan to make the flaps from inconel or similar?

The flaps for all suborbital testing might just need the right shape for now.

And the big differences between the main body and the flaps are that the surface doesnt need to bear all forces, and does not experience cryogenic temperatures.

Maybe just a thin layer of inconel on some kind of felt, on top of a stainless steel structure?
The main tank has to be there to contain the propellants, but does there need to be a continuous surface under the fins heat shield? Wouldn't an open framework of attachment points work?

It seems like an open grid would allow superheated air to enter and overheat the structure.

A sructural grid, closed by the TPS/tiles itself (airtight to the required extent).

But AstroWare's sugestion with folded back fins and no TPS at all sounds much better (if possible).
Title: Re: Starship heat shield
Post by: mandrewa on 09/24/2020 11:27 pm
Here's an interesting comment on metallic heatshields from /u/flshr19 on reddit:
 
Quote
Reusable metallic heat shields have been a holy grail in TPS technology since I first started working in that area during the Space Shuttle conceptual design period (1969-late 1971). My lab developed prototype metallic heat shields fabricated from niobium (aka columbium) coated with various ceramic oxides for increased oxidation resistance. We tested them up to 3000F (1649C) in specialized furnaces at air pressures typical of entry into the Earth's atmosphere. Mechanical tension and flexing loads were applied during these tests to determine the adhesion characteristics of the coatings. These samples could do a hundred simulated Shuttle entries without losing the coating.

See https://ntrs.nasa.gov/citations/19730024093

Nearly 25 years later in 1995 I worked on a NASA Langley contract to develop metallic heat shields for the X-33.

https://ntrs.nasa.gov/citations/20040095922

Interest in metallic heat shields has run hot and cold for the past 50 years. Maybe SpaceX can find a use for some of the previous work and develop a metallic heat shield that actually flies on a real spacecraft.
 
 
Comment source: https://www.reddit.com/r/spacex/comments/inkzwp/starship_development_thread_14/g5v3786/

So I've read the Space Shuttle paper and it seems like a lot of work has already been done on metallic heat shields for the Space Shuttle.  In fact it sounds like the Space Shuttle had another realistic option than the ceramic tiles that were actually used.

The material evaluated in this study had two layers, and both were made from of a niobium alloy, with the inner layer being corrugated and the outer layer being flat.  The niobium alloy can be welded and that was how the two layers were fastened together.  And then the whole thing was dipped in a slurry made of a volatile binder (acrylic or nitrocellulose) carrying silicon, chromium, and iron atoms that would leave a thin coating over the alloy once the binder had evaporated.

This coating shields the niobium alloy from oxidation to which it would otherwise be vulnerable.

Many samples were repeatedly subjected to stresses simulating a shuttle flight including 90,000 psi of acoustic stress during the launch itself.  The coating would gradually lose thickness on every launch and landing simulation but on average these heat shield squares (20" x 20") were good for at least 200 launches.

Samples were prepared that were deliberately damaged and then tested repeatedly and the material failed gradually, not catastrophically.  Micrometeorite damage should not matter, except that each such damaged tile will eventually (within 20 launches) need to be replaced.

One of my questions reading the paper was how the weight of the niobium alloy panels compares to the weight of a ceramic tile. I'm still not sure of the answer, but it sounds like it might be lighter.
Title: Re: Starship heat shield
Post by: john smith 19 on 09/25/2020 05:59 am

One of my questions reading the paper was how the weight of the niobium alloy panels compares to the weight of a ceramic tile. I'm still not sure of the answer, but it sounds like it might be lighter.
Quote from: John Smith 19
Thermal protection system design involves balancing a whole bunch of variables to to deliver multiple constraints.

Now look at material densities in terms of specific gravity relative to water.

Silica at 100% of theoretical density 2.65
Niobium 8.5
Molybdenum 10.56
Tantalum 12
Tungsten 20

And the Silica tiles were 95% air.

To do as well you'd have to build those panels out of very thin material.  The ones that Rohr delivered to the X33 programme were foil thickness, rather than what most people think of as sheet.  :(
Title: Re: Starship heat shield
Post by: john smith 19 on 09/25/2020 06:35 am

The starship body will provide the vast majority of the braking force on reentry. During peak heat load, The fins could be swept back extremely far to the point where the steel structure would be sufficient. We know the leeward side won't have tiles TPS after all. Even swept back to being nearly parallel to airstream should provide some control authority.

After peak heating they could be gradually extended into the airstream to provide greater deceleration and control.
The problem with flaps is not heating so much but airflow leakage through the hinge from the lower to the upper surface. That needs AFAP an air tight seal.
Very large seal x very high temperature --> Massive PITA
At high altitudes air is so thin you can use Newton's model of air, which is like light beams. So imagine the airflow is a light source and see which parts of a model are (literally) in shadow.
The problems are at the leading edges of any structure in the airflow. That's where the air slows down and dumps its heat.
BTW the Shuttle rudder (at around a 45 deg entry angle to the flow) was mostly ineffective and the pilot had to rely on RCS authority until they were relatively low in the atmosphere. Projects had looked at a V tail to improve this. If SS is coming in steeper any surface in shadow will have less control authority.

Quote from: AstroWare
Even if it is determined that the fins can not survive without -any- TPS, a different type of TPS could be used, such as an ablative coating designed to last dozens of flights.

Refurbishment of consumable TPS on flaps alone could be done off the vehicle. If a flap is getting towards the end of useful life, swap it out. Starships keep flying and send the old flap back for refurbishment.
It's a reasonable idea.

As a general point I'll note the issues with coatings shown up by the gold coating of the SSME turbine blades.

The coating has to be perfect or the underlying material will start to be attacked immediately
The coating has to be inspected regularly to make sure it has not been damaged.
If damaged a process must exist for the coating to be either a)Stripped off or b) "Touched up" without damaging the part (or in the case of a touch up weakening the rest of the coating)

The ideal solution is find an underlying material that does not need a coating at all.  :)
Failing that the ideal coating is one that is impossible to damage under the exposure conditions throughout its life.
In principle that eliminate all the inspection, stripping, re-coating issues in one move. Lifetime protection.
Finding such a coating (depending on the process conditions involved) that meets all of the actual requirements, can be quite difficult.
Title: Re: Starship heat shield
Post by: AstroWare on 09/25/2020 06:32 pm

The starship body will provide the vast majority of the braking force on reentry. During peak heat load, The fins could be swept back extremely far to the point where the steel structure would be sufficient. We know the leeward side won't have tiles TPS after all. Even swept back to being nearly parallel to airstream should provide some control authority.

After peak heating they could be gradually extended into the airstream to provide greater deceleration and control.
The problem with flaps is not heating so much but airflow leakage through the hinge from the lower to the upper surface. That needs AFAP an air tight seal.
Very large seal x very high temperature --&gt; Massive PITA
At high altitudes air is so thin you can use Newton's model of air, which is like light beams. So imagine the airflow is a light source and see which parts of a model are (literally) in shadow.
The problems are at the leading edges of any structure in the airflow. That's where the air slows down and dumps its heat.
BTW the Shuttle rudder (at around a 45 deg entry angle to the flow) was mostly ineffective and the pilot had to rely on RCS authority until they were relatively low in the atmosphere. Projects had looked at a V tail to improve this. If SS is coming in steeper any surface in shadow will have less control authority.

Quote from: AstroWare
Even if it is determined that the fins can not survive without -any- TPS, a different type of TPS could be used, such as an ablative coating designed to last dozens of flights.

Refurbishment of consumable TPS on flaps alone could be done off the vehicle. If a flap is getting towards the end of useful life, swap it out. Starships keep flying and send the old flap back for refurbishment.
It's a reasonable idea.

As a general point I'll note the issues with coatings shown up by the gold coating of the SSME turbine blades.

The coating has to be perfect or the underlying material will start to be attacked immediately
The coating has to be inspected regularly to make sure it has not been damaged.
If damaged a process must exist for the coating to be either a)Stripped off or b) "Touched up" without damaging the part (or in the case of a touch up weakening the rest of the coating)

The ideal solution is find an underlying material that does not need a coating at all.  :)
Failing that the ideal coating is one that is impossible to damage under the exposure conditions throughout its life.
In principle that eliminate all the inspection, stripping, re-coating issues in one move. Lifetime protection.
Finding such a coating (depending on the process conditions involved) that meets all of the actual requirements, can be quite difficult.
All good points, thanks.

Wouldn't the starship flaps act more like a V-tail then the Shuttle vertical stabilizer? The shuttle stabilizer was far away from the airstream, whereas the starship body flaps are tangential. Using the shadow analogy, body flaps seem much more likely to have an effect earlier. Enough control? No idea. But starship will also have an RCS system. It would seem like a good trade study to look at reducing TPS on the fins by using RCS.

As for the hinge, the wing roots could be designed so that they extend beyond the hinge so the hinge is always in "shadow". May still have to deal against indirect airflow, but that should be easier then being in the main flow.

Then the "leading edge" of the body flaps is nearly parallel to the airstream, and somewhere along the flap surface instead of the hinge.

(Warning poor sketch ahead )
(https://uploads.tapatalk-cdn.com/20200925/84fa265b21d63ecc96e78a5a973017cd.jpg)
Title: Re: Starship heat shield
Post by: freddo411 on 09/25/2020 08:08 pm

As for the hinge, the wing roots could be designed so that they extend beyond the hinge so the hinge is always in "shadow". May still have to deal against indirect airflow, but that should be easier then being in the main flow.

Then the "leading edge" of the body flaps is nearly parallel to the airstream, and somewhere along the flap surface instead of the hinge.

(Warning poor sketch ahead )
(https://uploads.tapatalk-cdn.com/20200925/84fa265b21d63ecc96e78a5a973017cd.jpg)

That is a very fine sketch.
Title: Re: Starship heat shield
Post by: AstroWare on 09/25/2020 08:12 pm



As for the hinge, the wing roots could be designed so that they extend beyond the hinge so the hinge is always in "shadow". May still have to deal against indirect airflow, but that should be easier then being in the main flow.

Then the "leading edge" of the body flaps is nearly parallel to the airstream, and somewhere along the flap surface instead of the hinge.

(Warning poor sketch ahead )
(https://uploads.tapatalk-cdn.com/20200925/84fa265b21d63ecc96e78a5a973017cd.jpg)

That is a very fine sketch.

Well thanks. Someday maybe I'll learn how to use CAD...
Title: Re: Starship heat shield
Post by: rsdavis9 on 09/25/2020 08:19 pm
I think they will want the extra ballistic coefficient from the flaps fully extended to keep the heat down for reentry. The downside is the flaps need something. The upside is the rest of the vehicle will be cooler.
Title: Re: Starship heat shield
Post by: Ionmars on 09/25/2020 09:09 pm

Wouldn't the starship flaps act more like a V-tail then the Shuttle vertical stabilizer? The shuttle stabilizer was far away from the airstream, whereas the starship body flaps are tangential. Using the shadow analogy, body flaps seem much more likely to have an effect earlier. Enough control? No idea. But starship will also have an RCS system. It would seem like a good trade study to look at reducing TPS on the fins by using RCS.

As for the hinge, the wing roots could be designed so that they extend beyond the hinge so the hinge is always in "shadow". May still have to deal against indirect airflow, but that should be easier then being in the main flow.

Then the "leading edge" of the body flaps is nearly parallel to the airstream, and somewhere along the flap surface instead of the hinge.

(Warning poor sketch ahead )
(https://uploads.tapatalk-cdn.com/20200925/84fa265b21d63ecc96e78a5a973017cd.jpg)
I disagree. This is s good sketch.  :)

But I don't know if it's correct.
Added: Your concept is same as mine; just don't know if we are correct.
Title: Re: Starship heat shield
Post by: FutureSpaceTourist on 09/25/2020 10:16 pm
https://twitter.com/julia_bergeron/status/1309617081181233153

Quote
It appears that SpaceX has solidified some of the heat shield processes for Starship. New equipment has been added to the Cape Canaveral facility with evidence of more to come. Similar tanks were seen at Cidco Rd indicating some processes may occur there as well. #Starship
Title: Re: Starship heat shield
Post by: HVM on 09/26/2020 11:57 am
Quote
It appears that SpaceX has solidified some of the heat shield processes for Starship. New equipment has been added to the Cape Canaveral facility with evidence of more to come. Similar tanks were seen at Cidco Rd indicating some processes may occur there as well. #Starship
Coima builds dust-collectors and filtration systems, mainly for woodworking industry. Does mass-production of silica tiles emit dust? Or are they going back to the PICA-X (-3)?
Title: Re: Starship heat shield
Post by: john smith 19 on 09/26/2020 12:06 pm
Quote
It appears that SpaceX has solidified some of the heat shield processes for Starship. New equipment has been added to the Cape Canaveral facility with evidence of more to come. Similar tanks were seen at Cidco Rd indicating some processes may occur there as well. #Starship
Coima builds dust-collectors and filtration systems, mainly for woodworking industry. Does mass-production of silica tiles emit dust? Or are they going back to the PICA-X (-3)?
Depends if the tiles are baked to near net shape or if they are baked in bigger pieces and cut into sections, and of course how much final machining each section gets.

My instinct would be (if at all possible) to make the tiles in reverse, with the top hat of the ROCCI first, then cast the silica structure into and around it, again to near net shape.

It's likely all mfg processes will generate some dust if the TPS is rigid (there are conformable SICA and PICA grades that are flexible and make laying it down and attaching it much easier, but I think their performance is a bit lower. Very handy for working around doors and other openings however).

Silica dust is pretty nasty so dust control would be very important in a modern H&S context. 
Title: Re: Starship heat shield
Post by: john smith 19 on 09/26/2020 01:10 pm
All good points, thanks.

Wouldn't the starship flaps act more like a V-tail then the Shuttle vertical stabilizer? The shuttle stabilizer was far away from the airstream, whereas the starship body flaps are tangential. Using the shadow analogy, body flaps seem much more likely to have an effect earlier. Enough control? No idea. But starship will also have an RCS system. It would seem like a good trade study to look at reducing TPS on the fins by using RCS.
True. The classic trade is Bigger flaps --> more control authority --> less RCS propellant usage.
However that was for shuttle, where RCS was a separate fuel system. SS uses more of a unified system and yes smaller flaps --> smaller mass --> smaller TPS area.
I guarantee a team will be working this problem right now. Initially to just get something that works. Later to refine the options.
What makes all this really tricky is that it's not just the fractions saved (or increased) it's the actual numbers as well.

Say I cut the flap area by 50% and increase RCS propellant usage by 10%. The entry sim shows SS survives to landing (that is not guaranteed, and the differences between "Perfect landing. Well done" and "You pancaked" can by subtle ) Win!
Except the flap mass was 100Kg to begin with and the current RCS propellant mass usage is 3000Kg
I've saved 50Kg by spending 300Kg.
Since this is a 2nd stage the structural mass : payload trade is 1:1.
IOW I just cut payload to orbit by 250Kg as well. (other mass units are available)
That is not going to get me a performance bonus this month  :(

Obviously this is grossly exaggerated. The joker is the entry trajectory could make a big difference to all those numbers. You have to choose a parameter to work around, so you can decide directly if this result is better or worse. Unfortunately there are several that you could use for that decision and there are second order effect regarding maintenance and replacement costs. The obvious choice is of course no flaps. The fact they are there at all says that simply does not work.
Quote from: AstroWare
As for the hinge, the wing roots could be designed so that they extend beyond the hinge so the hinge is always in "shadow". May still have to deal against indirect airflow, but that should be easier then being in the main flow.

Then the "leading edge" of the body flaps is nearly parallel to the airstream, and somewhere along the flap surface instead of the hinge.
You draw a fair hand. CAD is great for changes to a design but somewhat excessive for early work, along with the discipline needed to translate into "CADese" 

It's good plan provided  the flaps only have to deflect backward (I think the body flap that protected the shuttle engines had this, but the wing control surfaces had to deflect both up and down).

As air pressure rises the Knunsden number falls and the Newtonian flow model breaks down (the falling Knusden number tells you roughly when the Newton flow model becomes unreliable). Some flow starts sliding down the flap around the pivot point (and it will be hot), lowering the pressure the flap is exerting on the flow.  That little triangular area between the near end of the flap by the hinge mounting area is going to form  some kind of vortex flow but I've no idea how big or serious it would be. 

It's not just a blow torch pointing directly at the flap, it's also a blow torch blowing across it with a scouring effect.

OTOH the backside temperature is much cooler. This is why people have looked at heat pipes to lower skin temp by spreading out (and dumping) the heat into the lee area. RCC with embedded Refractory metal pipes (Nb or Ta with Na, K or Li filling) were tested for leading edge cooling on Shuttle but never deployed. They found a D shape cross section was much more efficient at heat extraction than the normal circular tube.
Title: Re: Starship heat shield
Post by: HVM on 09/26/2020 01:19 pm
https://twitter.com/julia_bergeron/status/1309617081181233153

Quote
It appears that SpaceX has solidified some of the heat shield processes for Starship. New equipment has been added to the Cape Canaveral facility with evidence of more to come. Similar tanks were seen at Cidco Rd indicating some processes may occur there as well. #Starship
Maybe we can get *Julia to take photos of warning labels (or lack of them)?

[Edit]*Julia Bergeron ----------------^
Title: Re: Starship heat shield
Post by: Johnnyhinbos on 09/26/2020 01:54 pm
Maybe we can get Julia to take photos of warning labels (or lack of them)?
Wholia?
Title: Re: Starship heat shield
Post by: Eerie on 09/26/2020 02:54 pm
Was the possibility of Starship variants having different heat shield discussed? The tanker variant only needs to go to LEO, after all.
Title: Re: Starship heat shield
Post by: Twark_Main on 09/26/2020 11:31 pm

The starship body will provide the vast majority of the braking force on reentry. During peak heat load, The fins could be swept back extremely far to the point where the steel structure would be sufficient. We know the leeward side won't have tiles TPS after all. Even swept back to being nearly parallel to airstream should provide some control authority.

After peak heating they could be gradually extended into the airstream to provide greater deceleration and control.
The problem with flaps is not heating so much but airflow leakage through the hinge from the lower to the upper surface. That needs AFAP an air tight seal.
Very large seal x very high temperature --> Massive PITA
At high altitudes air is so thin you can use Newton's model of air, which is like light beams. So imagine the airflow is a light source and see which parts of a model are (literally) in shadow.
The problems are at the leading edges of any structure in the airflow. That's where the air slows down and dumps its heat.

Elon himself  proposed purging the hinge area with gas, to exclude hot gas from entering.

https://twitter.com/elonmusk/status/1228400791880269824

I believe this, combined with the geometry detailed in AstroWare's excellent diagram, will be the ultimate solution.
Title: Re: Starship heat shield
Post by: randomly on 09/26/2020 11:52 pm
I don't there is the option of counting on folding the fins back during re-entry. The fins may need to be extended out to compensate for where the Center of Mass ends up. The fins need to both give control and to compensate for adjusting center of drag to the center of mass, and the center of mass may end up in quite a large range depending on payload etc.
Title: Re: Starship heat shield
Post by: Overtone on 09/27/2020 12:08 am
The problem with flaps is not heating so much but airflow leakage through the hinge from the lower to the upper surface. That needs AFAP an air tight seal.

Thanks for the detailed explanation John.

I don't understand why airflow leakage to the upper surface is a problem.  If this aerosurface were a flap for a wing meant to generate lift, I get that you need a low pressure region behind the upper surface.  But the elonerons (flings?  call them what you will) are drag surfaces.

SS obviously can't have thermal heating in the hinge area or near it on the upper surface, so some amount of a seal combined with cold gas injection at high pressure will help.  But it's not clear to me why an air tight seal is important for SS. You could just extend the aerosurface out by a fraction of a degree more to compensate for any lost drag due to air leakage through the hinge.  If that simplifies the design of the seal, it seems it would be well worth it.

Can you explain for novices like me?   Thanks!

Title: Re: Starship heat shield
Post by: john smith 19 on 09/27/2020 02:14 pm
I don't understand why airflow leakage to the upper surface is a problem.  If this aerosurface were a flap for a wing meant to generate lift, I get that you need a low pressure region behind the upper surface.  But the elonerons (flings?  call them what you will) are drag surfaces.
Welcome to the site. Cal them what you like. I quite like Elorons. They are designed to exert a force on the vehicle. When high speed air flow is slowed down it gets hot. Under ordinary entry conditions that from 7800m/s  to zero. From mars it will be much higher.

The issues are pressure leaks mean a less effective surface. Bigger surface --> more mass to carry to mars and back. And remember Musk didn't want any surfaces like this to begin with.

Hot air flow also attacks the attachment points for those surfaces and the associated actuator hardware driving them, which will be working pretty hard.

So what's easier? Harden the area around the pivot and drive or stop the airflow from getting there int eh first place?
Quote from: Overtone
SS obviously can't have thermal heating in the hinge area or near it on the upper surface, so some amount of a seal combined with cold gas injection at high pressure will help.  But it's not clear to me why an air tight seal is important for SS. You could just extend the aerosurface out by a fraction of a degree more to compensate for any lost drag due to air leakage through the hinge.  If that simplifies the design of the seal, it seems it would be well worth it.

Can you explain for novices like me?   Thanks!
The honest answer is it may not be.
Like a lot of these design questions the devils in the details. :( Avoiding the problem (of hot airflow leakage) opens up your choice of materials for the pivot and actuator area and should cut your cooling requirements to those areas.
OTOH hardening those areas and swallowing the increased surface area may be the lighter option.

I think SX have run (and will continue to run) a lot of simulations in this area to balance surface mass, TPS mass, coolant mass and RCS propellant mass.

And some of those masses are "better" than others. Propellants and coolants could be made at mars and reloaded but hardware has to be carried all the way to mars and back.

Never forget SS is an upper stage.
Every unit of mass added to the structure (or propellant assigned to RCS, OMS or landing) means 1 unit off the payload.
On a booster 1 unit of additional booster mass cuts the payload (IE the US mass) by between 1/6 and 1/13 of that unit).
Title: Re: Starship heat shield
Post by: john smith 19 on 09/27/2020 02:28 pm
The problem with flaps is not heating so much but airflow leakage through the hinge from the lower to the
Elon himself  proposed purging the hinge area with gas, to exclude hot gas from entering.

https://twitter.com/elonmusk/status/1228400791880269824

I believe this, combined with the geometry detailed in AstroWare's excellent diagram, will be the ultimate solution.
We certainly will.

I think the key issue shown in Astorware's diagram is wheather they are limited to being no more than 90deg to the body. If so you can keep the actual hinges out of direct airflow.
Title: Re: Starship heat shield
Post by: livingjw on 09/27/2020 02:36 pm
....

I think the key issue shown in Astorware's diagram is wheather they are limited to being no more than 90deg to the body. If so you can keep the actual hinges out of direct airflow.

- Flaps will have to extend for control, so they will be protected by TPS.

- SpaceX can keep the hinges out of the direct flow as shown in Astorware's sketch of the fairing, but you cannot keep the hinge out of the indirect air that will expand (Prandtl Meyer expansion) into the hinge area.

John
Title: Re: Starship heat shield
Post by: Overtone on 09/27/2020 03:46 pm
I don't understand why airflow leakage to the upper surface is a problem.  If this aerosurface were a flap for a wing meant to generate lift, I get that you need a low pressure region behind the upper surface.  But the elonerons (flings?  call them what you will) are drag surfaces.
Welcome to the site. Cal them what you like. I quite like Elorons. They are designed to exert a force on the vehicle. When high speed air flow is slowed down it gets hot. Under ordinary entry conditions that from 7800m/s  to zero. From mars it will be much higher.

The issues are pressure leaks mean a less effective surface. Bigger surface --> more mass to carry to mars and back. And remember Musk didn't want any surfaces like this to begin with.

Hot air flow also attacks the attachment points for those surfaces and the associated actuator hardware driving them, which will be working pretty hard.

So what's easier? Harden the area around the pivot and drive or stop the airflow from getting there int eh first place?
Quote from: Overtone
SS obviously can't have thermal heating in the hinge area or near it on the upper surface, so some amount of a seal combined with cold gas injection at high pressure will help.  But it's not clear to me why an air tight seal is important for SS. You could just extend the aerosurface out by a fraction of a degree more to compensate for any lost drag due to air leakage through the hinge.  If that simplifies the design of the seal, it seems it would be well worth it.

Can you explain for novices like me?   Thanks!
The honest answer is it may not be.
Like a lot of these design questions the devils in the details. :( Avoiding the problem (of hot airflow leakage) opens up your choice of materials for the pivot and actuator area and should cut your cooling requirements to those areas.
OTOH hardening those areas and swallowing the increased surface area may be the lighter option.

I think SX have run (and will continue to run) a lot of simulations in this area to balance surface mass, TPS mass, coolant mass and RCS propellant mass.

And some of those masses are "better" than others. Propellants and coolants could be made at mars and reloaded but hardware has to be carried all the way to mars and back.

Never forget SS is an upper stage.
Every unit of mass added to the structure (or propellant assigned to RCS, OMS or landing) means 1 unit off the payload.
On a booster 1 unit of additional booster mass cuts the payload (IE the US mass) by between 1/6 and 1/13 of that unit).

Thanks, very educational!
Title: Re: Starship heat shield
Post by: Lars-J on 09/27/2020 05:58 pm
I don't there is the option of counting on folding the fins back during re-entry. The fins may need to be extended out to compensate for where the Center of Mass ends up. The fins need to both give control and to compensate for adjusting center of drag to the center of mass, and the center of mass may end up in quite a large range depending on payload etc.
Exactly. Depending on the center of mass, a re-entry could in theory happen with the fins fully extended or completely folded. (Or anywhere in between) Which does make the joints a very critical part of the TPS design.
Title: Re: Starship heat shield
Post by: john smith 19 on 09/27/2020 06:28 pm
- Flaps will have to extend for control, so they will be protected by TPS.

- SpaceX can keep the hinges out of the direct flow as shown in Astorware's sketch of the fairing, but you cannot keep the hinge out of the indirect air that will expand (Prandtl Meyer expansion) into the hinge area.

John
Exactly.

Avoiding direct exposure definitely helps, but that corner region is where the issues will be.

It'll be interesting to see what SX go with.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/28/2020 02:06 am
I'm a bit adrift here. Harking back to AstroWare's pic and with subsonic speeds, I would expect any local flow across the hinge gap to cause low pressure and suction at the gap, not flow into it.  At hypersonic speeds I'd expect the hot (but not killer hot) surface flow within the shock wave standoff to do something similar. Or is it killer hot and I'm also missing something? Wouldn't be the first time.


Perhaps this has been discussed and I didn't realize it as there has been terminology I'm not familiar with.
Title: Re: Starship heat shield
Post by: john smith 19 on 09/28/2020 06:50 am
I'm a bit adrift here. Harking back to AstroWare's pic and with subsonic speeds, I would expect any local flow across the hinge gap to cause low pressure and suction at the gap, not flow into it.  At hypersonic speeds I'd expect the hot (but not killer hot) surface flow within the shock wave standoff to do something similar. Or is it killer hot and I'm also missing something? Wouldn't be the first time.

Perhaps this has been discussed and I didn't realize it as there has been terminology I'm not familiar with.
A couple of things. The straight line Newton approximation is for very low pressure in the high atmosphere. As atmospheric density rises there is a huge increase in the interactions between air molecules and Prandtl–Meyer expansion (https://en.wikipedia.org/wiki/Prandtl%E2%80%93Meyer_expansion_fan) develops as the flows comes round that corner, filling up that triangular shaped space with hot air to push through the gap.

There are several different effects during entry. You have to consider how pressure, temperature and speed change during the decent. Coming from higher than orbital speed (EG the Moon) the air ionizes and dissociates. The concept of a single temperature breaks down (giving stunningly high values of skin temperature). This needs a real gas model with 11 species. OTOH air density is so low that the Newtonian straight line model works 

Deeper in and slower down you've gone through slip flow into continuum flow. You're still in the high Mach range but now air is only dissociating and not ionizing so a 9 species model is adequate. Conventional gas flow models apply but the flow is still supersonic so lots of continuing heat input.

Near ground. Sub mach. No heat build up as airflow not decelerating through mach limit. Conventional flow and single gas temperature adequate. 

Ideally you slowly lose most of your velocity in the high atmosphere then glide down to earth at sub mach speeds. This is unworkable because the wing area needed to keep a vehicle in orbit by winged lift alone at these altitudes would be huge.
It's only the orbital speed that's keeping you at orbital speed.
However every m/s you can lose in the high, thin atmosphere make the TPS task easier. At this altitude slowing down is literally a very large number of impacts with individual air molecules, allowing time for the heat to diffuse across the skin and reradiate out. Every second you can keep that airframe square on to the airstream is a win.
As the air density builds up the input becomes continuous and the air blanket now traps some of that reradiated heat, heating you even more.
The question is can the problem be solved with available TPS given all the constraints on the SS TPS due to its very complex operating environment. We'll be finding out over the next few years.  :(
Title: Re: Starship heat shield
Post by: Twark_Main on 09/28/2020 11:46 pm
[snip]

Ideally you slowly lose most of your velocity in the high atmosphere then glide down to earth at sub mach speeds. This is unworkable because the wing area needed to keep a vehicle in orbit by winged lift alone at these altitudes would be huge.

Not quite decelerating to subsonic speeds, but ISTM a mild version of this is what was meant by the Dragon wing idea Musk was toying with earlier. Large surface area hot metal TPS. Large single-layer stainless skin to minimizes mass-per-area and radiate heat from both sides (the dragon wing "membrane"), structurally supported by periodic ribs (the dragon wing "fingers").

High lift to drag and modest peak heating means it can bleed of speed high in Earth's atmosphere for a nice gentle reentry heating profile. On Mars it has plenty of lift so it can aerocapture at a reasonably high altitude and low heating rate, increasing landed mass and/or allowing for faster Mars transits.

Ultimately they went with the current ceramic tile TPS, but if that TPS solution becomes a delaying factor the hot metal Dragon wing TPS could swing back to 51% and suddenly become the new "plan of record."

https://twitter.com/elonmusk/status/1117563679099240449?lang=en
Title: Re: Starship heat shield
Post by: rakaydos on 09/29/2020 02:50 am
[snip]

Ideally you slowly lose most of your velocity in the high atmosphere then glide down to earth at sub mach speeds. This is unworkable because the wing area needed to keep a vehicle in orbit by winged lift alone at these altitudes would be huge.

Not quite decelerating to subsonic speeds, but ISTM a mild version of this is what was meant by the Dragon wing idea Musk was toying with earlier. Large surface area hot metal TPS. Large single-layer stainless skin to minimizes mass-per-area and radiate heat from both sides (the dragon wing "membrane"), structurally supported by periodic ribs (the dragon wing "fingers").

High lift to drag and modest peak heating means it can bleed of speed high in Earth's atmosphere for a nice gentle reentry heating profile. On Mars it has plenty of lift so it can aerocapture at a reasonably high altitude and low heating rate, increasing landed mass and/or allowing for faster Mars transits.

Ultimately they went with the current ceramic tile TPS, but if that TPS solution becomes a delaying factor the hot metal Dragon wing TPS could swing back to 51% and suddenly become the new "plan of record."

https://twitter.com/elonmusk/status/1117563679099240449?lang=en

This is one reason I personally prefer "Dragging Wings" to "Elonerons."
Title: Re: Starship heat shield
Post by: john smith 19 on 09/29/2020 06:25 am

Not quite decelerating to subsonic speeds, but ISTM a mild version of this is what was meant by the Dragon wing idea Musk was toying with earlier. Large surface area hot metal TPS. Large single-layer stainless skin to minimizes mass-per-area and radiate heat from both sides (the dragon wing "membrane"), structurally supported by periodic ribs (the dragon wing "fingers").

High lift to drag and modest peak heating means it can bleed of speed high in Earth's atmosphere for a nice gentle reentry heating profile. On Mars it has plenty of lift so it can aerocapture at a reasonably high altitude and low heating rate, increasing landed mass and/or allowing for faster Mars transits.
Using the numbers for SS304 (SG 7.805) and shim thickness of 0.1mm (4 mils) gives you about 128 m^2 for a 100Kg (not including the deployment mechanism or ribs). Let's say that adds 25Kg. Or 0.78125kg/m^2

The question is how much TPS does that save you? If more than 125Kg that might be a win if the cost of the whole structure is also cheaper than the TPS it saves that's a win as both are expendable.
A quick google says Dragon mass is 4.2t and its down mass 3 tonnes. So is a penalty of 1.73% of landing mass worth the decelleration it can give? The orbital Velocity Vs Altitude curve brackets how long you can stay on orbit quite tightly at the entry interface. High decelleration in the high atmosphere (1-2g if possible) --> Much easier time of the TPS.

But SS goal is full reusablility. No expendable parts. It's landing mass is (last time I checked) 85t +150t payload. How big will those wings be now?

I could see them being useful for aerocapture where you need all the surface area you can get. IMHO the ability to brake from much higher than minimum speed is the key technology to opening up mars (and other planets) without waiting more than 2 years for every trip to go out.
[EDIT. For me the most exciting recent result in TPS have been the safe returns of the X37b's after years on orbit.  This was not guaranteed as LEO has quite a lot of debris well below the detectable size range from earth (10cm) but well above the size needed to damage a satellite.  This has never been done before.

That leaves the effect of martian weather on the TPS as the big unknown.

IMHO Starship TPS development is the "Grand Challenge" of TPS this decade. It will (if it has not already done so) attract the most qualified TPS developers, and whoever leads it will be the goto person for TPS development for a decade afterward. ]
Title: Re: Starship heat shield
Post by: steveleach on 09/29/2020 04:46 pm
IMHO Starship TPS development is the "Grand Challenge" of TPS this decade. It will (if it has not already done so) attract the most qualified TPS developers, and whoever leads it will be the goto person for TPS development for a decade afterward.
What really intrigues me about this idea is that SpaceX have also already demonstrated two things about Starship development...

1. They are more than happy to have multiple Starship prototypes on the go at once
2. They are willing to have multiple teams competing towards the same goal

So not only would the SpaceX TPS division be the place to work for TPS developers, it could well be that the top two or three TPS development teams in the world are all working on Starship.
Title: Re: Starship heat shield
Post by: Twark_Main on 09/30/2020 04:22 am
[snip]

Ideally you slowly lose most of your velocity in the high atmosphere then glide down to earth at sub mach speeds. This is unworkable because the wing area needed to keep a vehicle in orbit by winged lift alone at these altitudes would be huge.

Not quite decelerating to subsonic speeds, but ISTM a mild version of this is what was meant by the Dragon wing idea Musk was toying with earlier. Large surface area hot metal TPS. Large single-layer stainless skin to minimizes mass-per-area and radiate heat from both sides (the dragon wing "membrane"), structurally supported by periodic ribs (the dragon wing "fingers").

High lift to drag and modest peak heating means it can bleed of speed high in Earth's atmosphere for a nice gentle reentry heating profile. On Mars it has plenty of lift so it can aerocapture at a reasonably high altitude and low heating rate, increasing landed mass and/or allowing for faster Mars transits.

Ultimately they went with the current ceramic tile TPS, but if that TPS solution becomes a delaying factor the hot metal Dragon wing TPS could swing back to 51% and suddenly become the new "plan of record."

https://twitter.com/elonmusk/status/1117563679099240449?lang=en

This is one reason I personally prefer "Dragging Wings" to "Elonerons."

I guess I'm the only one who prefers to call them what Elon Musk chooses to calls them: "body flaps."

They're flaps (deployable drag structures). They're on the body, not the wing. Body flaps.
Title: Re: Starship heat shield
Post by: meekGee on 09/30/2020 11:19 am
[snip]

Ideally you slowly lose most of your velocity in the high atmosphere then glide down to earth at sub mach speeds. This is unworkable because the wing area needed to keep a vehicle in orbit by winged lift alone at these altitudes would be huge.

Not quite decelerating to subsonic speeds, but ISTM a mild version of this is what was meant by the Dragon wing idea Musk was toying with earlier. Large surface area hot metal TPS. Large single-layer stainless skin to minimizes mass-per-area and radiate heat from both sides (the dragon wing "membrane"), structurally supported by periodic ribs (the dragon wing "fingers").

High lift to drag and modest peak heating means it can bleed of speed high in Earth's atmosphere for a nice gentle reentry heating profile. On Mars it has plenty of lift so it can aerocapture at a reasonably high altitude and low heating rate, increasing landed mass and/or allowing for faster Mars transits.

Ultimately they went with the current ceramic tile TPS, but if that TPS solution becomes a delaying factor the hot metal Dragon wing TPS could swing back to 51% and suddenly become the new "plan of record."

https://twitter.com/elonmusk/status/1117563679099240449?lang=en

This is one reason I personally prefer "Dragging Wings" to "Elonerons."

I guess I'm the only one who prefers to call them what Elon Musk chooses to calls them: "body flaps."

They're flaps (deployable drag structures). They're on the body, not the wing. Body flaps.
But traditional aviation flaps are exactly not drag surfaces.

Speed brakes are. Located in different places and operate very differently.

You can skip the aviation analogy all together and say they're flaps in the "uneducated" simple English literal sense of the word, as if you're naming them from scratch.  "Flaps" because they flap. No relation to airplane flaps.
Title: Re: Starship heat shield
Post by: Frogstar_Robot on 09/30/2020 02:18 pm
[snip]

Ideally you slowly lose most of your velocity in the high atmosphere then glide down to earth at sub mach speeds. This is unworkable because the wing area needed to keep a vehicle in orbit by winged lift alone at these altitudes would be huge.

Not quite decelerating to subsonic speeds, but ISTM a mild version of this is what was meant by the Dragon wing idea Musk was toying with earlier. Large surface area hot metal TPS. Large single-layer stainless skin to minimizes mass-per-area and radiate heat from both sides (the dragon wing "membrane"), structurally supported by periodic ribs (the dragon wing "fingers").

High lift to drag and modest peak heating means it can bleed of speed high in Earth's atmosphere for a nice gentle reentry heating profile. On Mars it has plenty of lift so it can aerocapture at a reasonably high altitude and low heating rate, increasing landed mass and/or allowing for faster Mars transits.

Ultimately they went with the current ceramic tile TPS, but if that TPS solution becomes a delaying factor the hot metal Dragon wing TPS could swing back to 51% and suddenly become the new "plan of record."

https://twitter.com/elonmusk/status/1117563679099240449?lang=en

This is one reason I personally prefer "Dragging Wings" to "Elonerons."

I guess I'm the only one who prefers to call them what Elon Musk chooses to calls them: "body flaps."

They're flaps (deployable drag structures). They're on the body, not the wing. Body flaps.
But traditional aviation flaps are exactly not drag surfaces.

Speed brakes are. Located in different places and operate very differently.

You can skip the aviation analogy all together and say they're flaps in the "uneducated" simple English literal sense of the word, as if you're naming them from scratch.  "Flaps" because they flap. No relation to airplane flaps.

Flaps on aircraft are intended to increase lift. They do also increase drag, but that it is not a problem at low speeds where they are used. A flap is basically the same as a retractable wing, but viewed from the opposite direction.

The body flaps on Starship would also increase lift, as well as drag, depending on angle of attack. AIUI at the angle of entry of Starship, it's a bit moot, lift and drag are acting in the same direction.
Title: Re: Starship heat shield
Post by: meekGee on 09/30/2020 02:26 pm

This is one reason I personally prefer "Dragging Wings" to "Elonerons."

I guess I'm the only one who prefers to call them what Elon Musk chooses to calls them: "body flaps."

They're flaps (deployable drag structures). They're on the body, not the wing. Body flaps.
But traditional aviation flaps are exactly not drag surfaces.

Speed brakes are. Located in different places and operate very differently.

You can skip the aviation analogy all together and say they're flaps in the "uneducated" simple English literal sense of the word, as if you're naming them from scratch.  "Flaps" because they flap. No relation to airplane flaps.

Flaps on aircraft are intended to increase lift. They do also increase drag, but that it is not a problem at low speeds where they are used. A flap is basically the same as a retractable wing, but viewed from the opposite direction.

The body flaps on Starship would also increase lift, as well as drag, depending on angle of attack. AIUI at the angle of entry of Starship, it's a bit moot, lift and drag are acting in the same direction.
Flaps extend the trailing edge, flow continues across them and remains attached, in fact the flaps allow the wing to increase the AoA without flow separation.  The added drag is "lift drag".

Here, just like with speed brakes, the surfaces extend across the airflow, generating barn door drag.  There is no attached flow, they are stalled by design.   If there's any lift generated, it's "kite lift".

So if you fall back to aviation analogs, flaps is the wrong term.

But I think the term rolls right off the tongue, and if you're going to disrupt aviation, you may as well be completely disrespectful and disrupt the nomenclature while you're at it.

"Hello, airplanes?  It's blimps.  You win.  Bye!"
Title: Re: Starship heat shield
Post by: livingjw on 09/30/2020 03:36 pm
....  AIUI at the angle of entry of Starship, it's a bit moot, lift and drag are acting in the same direction.

By definition, lift is always perpendicular to drag.

John
Title: Re: Starship heat shield
Post by: envy887 on 09/30/2020 03:45 pm
....  AIUI at the angle of entry of Starship, it's a bit moot, lift and drag are acting in the same direction.

By definition, lift is always perpendicular to drag.

John

Also, Starship spends the majority of hypersonic reentry into the atmosphere at ~60 degree AoA, where the body flaps are certainly producing both lift and drag.

It's only in the transonic/subsonic descent stage  where it's falling straight down at 90 degrees AoA (skydiver mode) that the flaps do not produce any net lift.
Title: Re: Starship heat shield
Post by: meekGee on 09/30/2020 06:21 pm
....  AIUI at the angle of entry of Starship, it's a bit moot, lift and drag are acting in the same direction.

By definition, lift is always perpendicular to drag.

John

Also, Starship spends the majority of hypersonic reentry into the atmosphere at ~60 degree AoA, where the body flaps are certainly producing both lift and drag.

It's only in the transonic/subsonic descent stage  where it's falling straight down at 90 degrees AoA (skydiver mode) that the flaps do not produce any net lift.
We're drifting, but even though "lift is lift", there's a fundamental difference between lift that's cause by differences in attached flow on either side of a surface (wing, flap) and lift that's generated by kinetic momentum change of the air (brakes, simple kites, barn doors)

Title: Re: Starship heat shield
Post by: Bananas_on_Mars on 09/30/2020 08:39 pm
We're drifting, but even though "lift is lift", there's a fundamental difference between lift that's cause by differences in attached flow on either side of a surface (wing, flap) and lift that's generated by kinetic momentum change of the air (brakes, simple kites, barn doors)

Nah, lift in both cases is generated by imparting momentum to the air in the opposite direction of your lift vector.
Title: Re: Starship heat shield
Post by: meekGee on 09/30/2020 08:43 pm
We're drifting, but even though "lift is lift", there's a fundamental difference between lift that's cause by differences in attached flow on either side of a surface (wing, flap) and lift that's generated by kinetic momentum change of the air (brakes, simple kites, barn doors)

Nah, lift in both cases is generated by imparting momentum to the air in the opposite direction of your lift vector.
The end result is similar, but the mechanism in which it is produced is fundamentally important.

The two cases are distinguishable, inherently - you can look at the airflow around a flap and a brake and tell which is which, even without checking the part number...
Title: Re: Starship heat shield
Post by: HVM on 09/30/2020 10:20 pm
Quote
It appears that SpaceX has solidified some of the heat shield processes for Starship. New equipment has been added to the Cape Canaveral facility with evidence of more to come. Similar tanks were seen at Cidco Rd indicating some processes may occur there as well. #Starship
Coima builds dust-collectors and filtration systems, mainly for woodworking industry. Does mass-production of silica tiles emit dust? Or are they going back to the PICA-X (-3)?
I think that collector is for PICA production but it's not for SS, It's speed-run iteration and re-qualification for Crew Dragon heat shield.
Title: Re: Starship heat shield
Post by: livingjw on 09/30/2020 11:52 pm
....
The two cases are distinguishable, inherently - you can look at the airflow around a flap and a brake and tell which is which, even without checking the part number...

A flap at high AoA, say greater than 45 degrees, is completely separated on the leeward side. It is producing both lift and drag. How is this fundamentally different than the SS body flap? 

John
Title: Re: Starship heat shield
Post by: meekGee on 10/01/2020 12:17 am
....
The two cases are distinguishable, inherently - you can look at the airflow around a flap and a brake and tell which is which, even without checking the part number...

A flap at high AoA, say greater than 45 degrees, is completely separated on the leeward side. It is producing both lift and drag. How is this fundamentally different than the SS body flap? 

John
Well at a high AoA the entire wing will stall too, right?

But the purpose of the flap is to allow the flow to remain attached at higher AoAs (and lower speeds) than would otherwise be possible.

The purpose of the SS control surfaces is to operate like brakes - stick out into the flow with no intention of having it attached.  If there's lift generated it is simply because they're not at 90 degrees, but absence of any type of lift was not the criteria.

The difference between flaps and brakes is not whether they generate any kind of lift, but how the air is supposed to behave around them.

In an airplane.  Which starship is not.

So why not stop trying to justfiy the name based on airplane analogies?  They don't work, and it doesn't matter, since this is not an airplane.

Title: Re: Starship heat shield
Post by: livingjw on 10/01/2020 12:31 am
....
The two cases are distinguishable, inherently - you can look at the airflow around a flap and a brake and tell which is which, even without checking the part number...

A flap at high AoA, say greater than 45 degrees, is completely separated on the leeward side. It is producing both lift and drag. How is this fundamentally different than the SS body flap? 

John
Well at a high AoA the entire wing will stall too, right?

But the purpose of the flap is to allow the flow to remain attached at higher AoAs (and lower speeds) than would otherwise be possible.

The purpose of the SS control surfaces is to operate like brakes - stick out into the flow with no intention of having it attached.  If there's lift generated it is simply because they're not at 90 degrees, but absence of any type of lift was not the criteria.

The difference between flaps and brakes is not whether they generate any kind of lift, but how the air is supposed to behave around them.

In an airplane.  Which starship is not.

So why not stop trying to justify the name based on airplane analogies?  They don't work, and it doesn't matter, since this is not an airplane.

- The purpose of most aircraft flaps is to increase CLmax and at high flap angles to increase CD for landing.
- Deflection of flaps decrease the maximum AoA of a wing.
- I am not trying to justify the name "body flap". I am using term because that is what Elon used.
- The name seems reasonable enough. If something else sticks, so be it.

John
Title: Re: Starship heat shield
Post by: Johnnyhinbos on 10/01/2020 03:24 am
Sigh. And there the thread goes, following in the path of last night’s debate...

Every once in a while just pause in your typing and glance at the thread title. It may provide guidance.
Title: Re: Starship heat shield
Post by: Slarty1080 on 10/01/2020 07:33 am
So which SN will be first to get the full complement of heat shield tiles?
Title: Re: Starship heat shield
Post by: sebk on 10/01/2020 09:05 am
....  AIUI at the angle of entry of Starship, it's a bit moot, lift and drag are acting in the same direction.

By definition, lift is always perpendicular to drag.

John

Also, Starship spends the majority of hypersonic reentry into the atmosphere at ~60 degree AoA, where the body flaps are certainly producing both lift and drag.

It's only in the transonic/subsonic descent stage  where it's falling straight down at 90 degrees AoA (skydiver mode) that the flaps do not produce any net lift.
We're drifting, but even though "lift is lift", there's a fundamental difference between lift that's cause by differences in attached flow on either side of a surface (wing, flap) and lift that's generated by kinetic momentum change of the air (brakes, simple kites, barn doors)

In hypersonic regime the "kite lift" is the primary lift as compression in front of the wing dominates any effects from underpressure behind it (this also indicates/explains why hypersonic L:D almost invariably sucks).
Title: Re: Starship heat shield
Post by: meekGee on 10/01/2020 12:12 pm
....  AIUI at the angle of entry of Starship, it's a bit moot, lift and drag are acting in the same direction.

By definition, lift is always perpendicular to drag.

John

Also, Starship spends the majority of hypersonic reentry into the atmosphere at ~60 degree AoA, where the body flaps are certainly producing both lift and drag.

It's only in the transonic/subsonic descent stage  where it's falling straight down at 90 degrees AoA (skydiver mode) that the flaps do not produce any net lift.
We're drifting, but even though "lift is lift", there's a fundamental difference between lift that's cause by differences in attached flow on either side of a surface (wing, flap) and lift that's generated by kinetic momentum change of the air (brakes, simple kites, barn doors)

In hypersonic regime the "kite lift" is the primary lift as compression in front of the wing dominates any effects from underpressure behind it (this also indicates/explains why hypersonic L:D almost invariably sucks).
Hey good point about his being the wrong thread..  quote this elsewhere (where?) To continue there...
Title: Re: Starship heat shield
Post by: OTV Booster on 10/01/2020 05:43 pm
[snip]

Ideally you slowly lose most of your velocity in the high atmosphere then glide down to earth at sub mach speeds. This is unworkable because the wing area needed to keep a vehicle in orbit by winged lift alone at these altitudes would be huge.

Not quite decelerating to subsonic speeds, but ISTM a mild version of this is what was meant by the Dragon wing idea Musk was toying with earlier. Large surface area hot metal TPS. Large single-layer stainless skin to minimizes mass-per-area and radiate heat from both sides (the dragon wing "membrane"), structurally supported by periodic ribs (the dragon wing "fingers").

High lift to drag and modest peak heating means it can bleed of speed high in Earth's atmosphere for a nice gentle reentry heating profile. On Mars it has plenty of lift so it can aerocapture at a reasonably high altitude and low heating rate, increasing landed mass and/or allowing for faster Mars transits.

Ultimately they went with the current ceramic tile TPS, but if that TPS solution becomes a delaying factor the hot metal Dragon wing TPS could swing back to 51% and suddenly become the new "plan of record."

https://twitter.com/elonmusk/status/1117563679099240449?lang=en (https://twitter.com/elonmusk/status/1117563679099240449?lang=en)

This is one reason I personally prefer "Dragging Wings" to "Elonerons."

I guess I'm the only one who prefers to call them what Elon Musk chooses to calls them: "body flaps."

They're flaps (deployable drag structures). They're on the body, not the wing. Body flaps.
It's Elon's game and he gets to call things whatever he wants but fins is only four characters. If anybody comes across me referring to SS fins, I'm using shorthand for body flaps.


Edit: if I'm in an expansive mood I may waste a character and call them flaps - even if they don't flap. They don't do that, do they? ::)
Title: Re: Starship heat shield
Post by: rsdavis9 on 10/01/2020 07:10 pm
Before launch I would expect some flapping... :)
Title: Re: Starship heat shield
Post by: pjm1 on 10/01/2020 08:35 pm
Before launch I would expect some flapping... :)

I dunno, I think Elon's winging it a bit.
Title: Re: Starship heat shield
Post by: steveleach on 10/01/2020 08:39 pm
Edit: if I'm in an expansive mood I may waste a character and call them flaps - even if they don't flap. They don't do that, do they? ::)
Isn't it generally considered a really bad sign (at least in aerospace) if your flaps are flapping?

In fact, in aviation the only things you want flapping are wings and event then, only in ornithopters and avian dinosaurs.

But they don't have heat shields.
Title: Re: Starship heat shield
Post by: beelsebob on 10/01/2020 11:17 pm
....  AIUI at the angle of entry of Starship, it's a bit moot, lift and drag are acting in the same direction.

By definition, lift is always perpendicular to drag.

John
No?  For example, when plummeting like a stone, lift and drag are collinear.  In fact, they're the same force.
Title: Re: Starship heat shield
Post by: beelsebob on 10/01/2020 11:20 pm
....
The two cases are distinguishable, inherently - you can look at the airflow around a flap and a brake and tell which is which, even without checking the part number...

A flap at high AoA, say greater than 45 degrees, is completely separated on the leeward side. It is producing both lift and drag. How is this fundamentally different than the SS body flap? 

John
It's not. The entire purpose of a flap is to keep airflow attached to the leeward side of the wing by allowing some of the high pressure air under the wing to energize the low pressure side.  That allows the wing to operate at a higher angle of attack, and produce more lift before stalling.  It also causes the wing to produce more drag.

Elenerons don't operate in any way similarly to flaps on aircraft.
Title: Re: Starship heat shield
Post by: Twark_Main on 10/02/2020 12:01 am
....  AIUI at the angle of entry of Starship, it's a bit moot, lift and drag are acting in the same direction.

By definition, lift is always perpendicular to drag.

John
No?  For example, when plummeting like a stone, lift and drag are collinear.  In fact, they're the same force.

Yes. https://en.wikipedia.org/wiki/Lift_(force) (https://en.wikipedia.org/wiki/Lift_(force))

"A fluid flowing around the surface of an object exerts a force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the force parallel to the flow direction."

In the plummeting stone example, lift is zero.
Title: Re: Starship heat shield
Post by: tyrred on 10/02/2020 01:03 am
How much drag can the heat shield produce without significantly affecting the lift of the rocket on the climb up?

 ;)
Title: Re: Starship heat shield
Post by: WormPicker959 on 10/02/2020 03:28 am
I think we need the lift a heatshield sighting would impart. The lack of it is really dragging this thread down.
Title: Re: Starship heat shield
Post by: OTV Booster on 10/03/2020 02:39 pm
I think we need the lift a heatshield sighting would impart. The lack of it is really dragging this thread down.
I think you're creating a flap.
Title: Re: Starship heat shield
Post by: livingjw on 10/10/2020 04:08 pm
A thin Carbon/SiC composite shell is good to ~1600 C. Metals cannot compete. Fill the shell with insulation and mechanically attach.

John
Title: Re: Starship heat shield
Post by: InterestedEngineer on 10/11/2020 05:48 am
A thin Carbon/SiC composite shell is good to ~1600 C. Metals cannot compete. Fill the shell with insulation and mechanically attach.

John

I tried Googling for Carbon/SiC composites and the closest I got was this:

https://www.sglcarbon.com/en/markets-solutions/material/sigrasic-carbon-fiber-reinforced-silicon-carbide/

Working temperature in vacuum/inert gas of 1200 degC, in oxygen 450 degC, which probably means it really doesn't like oxidation, and doesn't form a passivization layer.

Any example data sheets we could look at?
Title: Re: Starship heat shield
Post by: giulio on 10/11/2020 09:04 am

hi I'm new to the forum, I found this document on the subject space heat material:

https://www.researchgate.net/publication/227221472_Carbon_Fibre_Reinforced_Silicon_Carbide_Composites_CSiC_CC-SiC
Title: Re: Starship heat shield
Post by: john smith 19 on 10/11/2020 10:15 am

hi I'm new to the forum, I found this document on the subject space heat material:

https://www.researchgate.net/publication/227221472_Carbon_Fibre_Reinforced_Silicon_Carbide_Composites_CSiC_CC-SiC
Welcome to the site. 

This looks interesting. Good point about the 10x cost reduction over 1st gen systems.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/11/2020 10:22 am
A thin Carbon/SiC composite shell is good to ~1600 C. Metals cannot compete. Fill the shell with insulation and mechanically attach.

John
That sounds like a single use temperature rather than cyclic to me.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/11/2020 10:33 am
I tried Googling for Carbon/SiC composites and the closest I got was this:

https://www.sglcarbon.com/en/markets-solutions/material/sigrasic-carbon-fiber-reinforced-silicon-carbide/

Working temperature in vacuum/inert gas of 1200 degC, in oxygen 450 degC, which probably means it really doesn't like oxidation, and doesn't form a passivization layer.

Any example data sheets we could look at?
This stuff is for use in vacuum furnaces. I'm guessing the issue is miss match of TCE causes cracking of the skin and exposure of the graphite, at which point the graphite becomes "Designer coal."  :(

That performance is still pretty impressive and the company looks interesting. 

BTW just to put thermal conductivity figures in perspective the uranium dioxide fuel pellets in LWR's have a thermal conductivity < 2W/mk. That's why they can have a center line temperature of 1200c and peripheral temp several 100c lower. So it's in the ballpark in that respect.

Given that it can take years (decades) to qualify a new material in some applications it makes sense to avoid them and design the vehicle around the capabilities of existing materials.
"Design the vehicle and by the time it's ready for testing the materials to make it out of will be there" is IMHO a very bad strategy for getting an operational vehicle flying soon. It may be unavoidable if no candidates exist but after 7 decades of materials research for reentry survivable materials (and 7 decades of general progress in high temperature materials to support all sorts of applications) that is not the case.
Title: Re: Starship heat shield
Post by: livingjw on 10/11/2020 04:05 pm
A thin Carbon/SiC composite shell is good to ~1600 C. Metals cannot compete. Fill the shell with insulation and mechanically attach.

John
That sounds like a single use temperature rather than cyclic to me.

Certainly low cycles. Also coatings are available to help with oxidation. My point is this material is currently being produced commercially and can be fabricated in very thin sheets. Perfect for TPS tile shells.

John
Title: Re: Starship heat shield
Post by: InterestedEngineer on 10/11/2020 04:15 pm

hi I'm new to the forum, I found this document on the subject space heat material:

https://www.researchgate.net/publication/227221472_Carbon_Fibre_Reinforced_Silicon_Carbide_Composites_CSiC_CC-SiC

From the paper:

Quote
Due to the anisotropic coefficient of thermal expansion (CTE) of C/C, C/SiC and C/CSiC, the
oxidation protection of these composites is more difficult than it is for non-reinforced
carbon or graphite bulk materials. The mismatch of CTE between the CVD-SiC coating and
the carbon fibre reinforcement creates cracks in the SiC coating during the cooling-down
period after deposition. Crack formation starts at approximately 100 ◦C below the CVD
coating temperature. Therefore, CVD-SiC coated composites show the highest oxidation
rate at about 800 ◦C, the maximum between crack opening and oxidation kinetics. As a result,
sophisticated oxidation and corrosion coatings can only reduce the material degradation in
a certain temperature interval under static conditions, but all available protection coatings
are not able to prevent oxidation completely under dynamic conditions.
Title: Re: Starship heat shield
Post by: KBK on 10/12/2020 03:42 am
This, done as a transpiration modification, may help in the hotspots.

The basic premise can be investigated, and then possibly applied in a transpiration system.

It's about the vortex function, and there is some small expertise in vortex injectors at SpaceX. It is talking about a 25% reduction in drag, potentially, plus the added bonus, with transpiration as a driving force, to direct flow, via a hard structure install. This may also aid in the flap to body interface problem. Analysis is required.


Aerodynamicists reveal link between fish scales and aircraft drag (https://phys.org/news/2020-10-aerodynamicists-reveal-link-fish-scales.html)

Quote
Using the specially equipped laminar water tunnel at the University of Stuttgart in Germany, Professor Bruecker and Professor Rist (University of Stuttgart) have tested the hypothesis of a transition (drag) delay by experimenting with a smooth flat plate and a flat plate covered with biomimetic fish scale arrays.

Their surprising research outcome runs counter to the common belief that roughness promotes by-pass transition. Instead, the scales largely increase the stability of the base flow similar to an array of vortex generators.

A technical realization of such patterns on aerodynamic surfaces will pave the way towards the drastic reduction in fuel consumption and future zero-emission flight.

Possible to use the scale idea on it's own as a passive system, or to try to manipulate the effect with strategic vortex enhancement. Possibly even a two level system where one is almost a back up, or both are required for only one sort of flight profile.

It's final form might even be partially structural, thus alleviating some of the mass cost of the addition/solution.

I can't help but think of applying it even further back in the various systems of flow....

Additionally, if one knows a new outlier position, then it's potentially useful anti may reveal itself.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 10/12/2020 05:21 am

Possible to use the scale idea on it's own as a passive system, or to try to manipulate the effect with strategic vortex enhancement. Possibly even a two level system where one is almost a back up, or both are required for only one sort of flight profile.



I believe Starship will have an Angle of Attack of 60% when entering the atmosphere.

The problem with a fish scale solution is the scales will be 60% angled to the direction of airflow possibly ripping off when supersonic.  Or alternatively 60% angled to the direction of flow on entry of the atmosphere.

Still, interesting to think about.  Maybe the tiles shouldn't be just flat, but rather bumpy:

https://www.nasa.gov/connect/chat/laminar_flow_chat.html
Title: Re: Starship heat shield
Post by: KBK on 10/12/2020 05:46 am
I loosely used the words 'hard structure' to indicate that direction of method of potential application of the salient points.  ;)  Perhaps more precision was in order...
Title: Re: Starship heat shield
Post by: OTV Booster on 10/12/2020 11:53 am
Very interesting research. The work was inspired by flow in water. The testing was done in water. My gut says that optimization of the scales length/width ratio will be heavily dependent on fluid viscosity. As viscosity goes down the optimal length will increase. In a gas environment the optimum scales will resemble ...  feathers!
Title: Re: Starship heat shield
Post by: KBK on 10/12/2020 01:44 pm
Very interesting research. The work was inspired by flow in water. The testing was done in water. My gut says that optimization of the scales length/width ratio will be heavily dependent on fluid viscosity. As viscosity goes down the optimal length will increase. In a gas environment the optimum scales will resemble ...  feathers!

The pressures and temperatures involved in re-entry and in ascent, change/alter that formula quite a bit. A clue, provided with zero research at this time..is...how the researchers immediately tied it to aircraft..and that the work was done by or connected to aerodynamicists. It's right in the title..

Ie, that transpiration is not solely an act of dealing with temperature, it's also about aiding in getting off the zero mark with surface stiction issues.

One can design their vortex generators (if applied) to utilize ultrasonics, possibly. Whatever the result of that test, it will inform, and the knowledge base would be greater. That an HF stutter acceleration might be better than a static flow. The modifier in carrying the concept over...is that the pressures and flow on descent is unidirectional (well, conceptually, it is). Depends on the pressures and accelerations available in the act of transpiration itself, and if any additional acceleration would be of any benefit, or even necessary. Ie, if deemed effective... it might be turned on it's head to allow for transpiration fuel conservation, or over a more widespread area with the same original fuel use...

That thing where a perfectly wrong answer to a perfectly wrong question points the way to the right question and the right answer. That if the right direction is not clear in the given cloud of potential, then find it's antipode by finding the worst mistake and observing the results. From mental exercise all the way to a real world test, if necessary. Differential defines the nature of reality.

Of course, applying kiss principles in all of it, re necessity vs advantage vs failure potential.
Title: Re: Starship heat shield
Post by: mandrewa on 10/12/2020 07:33 pm
The issue with ceramic heat shield tiles is their fragility, rigidity, and the difficulty in attaching them to a substrate.  In particular, if they flex they will break.

Niobium alloys with a thin silica-rich coating (to protect it from oxidation) can bend and are even elastic.  But a niobium alloy with its coating weighs more than comparable ceramic heat shield tiles assuming a niobium alloy thickness greater than that of a foil.

Another advantage the niobium has is that micrometeorites that would shatter part of a ceramic heat shield tile will have a negligible impact on the heat shielding capacity of the niobium alloy.

In comparing the two, we also need to include the weight of the systems needed to attach the two materials to the stainless steel skin of the Starship.  Since niobium alloys can be welded to niobium alloys I wonder if it might also be possible to spot weld them to stainless steel.

Niobium alloys are light enough that they were seriously considered for the Space Shuttle.  Now as I understand it there was no insulation under that double niobium layer that was tested for the Space Shuttle.  Two thin layers of niobium sheet by themselves were enough to protect the aluminum structure underneath.

It could be that niobium alloy is the better solution on the parts of the Starship skin where bending and flexing can be anticipated, as for instance the skirt.

In addition I wonder about combining the niobium alloy with methane cooling since the niobium can so easily be given corrugations and other three dimensional structure.

Since the niobium alloy can be readily formed to make channels, the sheet could be used to simultaneously guide the methane gas to where it is needed and to serve as heat shielding at the same time.
Title: Re: Starship heat shield
Post by: livingjw on 10/13/2020 12:21 am
The issue with ceramic heat shield tiles is their fragility, rigidity, and the difficulty in attaching them to a substrate.  In particular, if they flex they will break.

Niobium alloys with a thin silica-rich coating (to protect it from oxidation) can bend and are even elastic.  But a niobium alloy with its coating weighs more than comparable ceramic heat shield tiles assuming a niobium alloy thickness greater than that of a foil.

Another advantage the niobium has is that micrometeorites that would shatter part of a ceramic heat shield tile will have a negligible impact on the heat shielding capacity of the niobium alloy.

In comparing the two, we also need to include the weight of the systems needed to attach the two materials to the stainless steel skin of the Starship.  Since niobium alloys can be welded to niobium alloys I wonder if it might also be possible to spot weld them to stainless steel.

Niobium alloys are light enough that they were seriously considered for the Space Shuttle.  Now as I understand it there was no insulation under that double niobium layer that was tested for the Space Shuttle.  Two thin layers of niobium sheet by themselves were enough to protect the aluminum structure underneath.

It could be that niobium alloy is the better solution on the parts of the Starship skin where bending and flexing can be anticipated, as for instance the skirt.

In addition I wonder about combining the niobium alloy with methane cooling since the niobium can so easily be given corrugations and other three dimensional structure.

Since the niobium alloy can be readily formed to make channels, the sheet could be used to simultaneously guide the methane gas to where it is needed and to serve as heat shielding at the same time.

- C/SiC composites are pretty tough. They are used in turbine engines. Mounting appears to use felt pad to isolate tile from structure.

- I don't believe two layers of metal are going to protect an aluminum structure from reentry heat. Do you have a reference document about the work? Probably used insulation as well.

John

Title: Re: Starship heat shield
Post by: mandrewa on 10/13/2020 03:08 am
The issue with ceramic heat shield tiles is their fragility, rigidity, and the difficulty in attaching them to a substrate.  In particular, if they flex they will break.

Niobium alloys with a thin silica-rich coating (to protect it from oxidation) can bend and are even elastic.  But a niobium alloy with its coating weighs more than comparable ceramic heat shield tiles assuming a niobium alloy thickness greater than that of a foil.

Another advantage the niobium has is that micrometeorites that would shatter part of a ceramic heat shield tile will have a negligible impact on the heat shielding capacity of the niobium alloy.

In comparing the two, we also need to include the weight of the systems needed to attach the two materials to the stainless steel skin of the Starship.  Since niobium alloys can be welded to niobium alloys I wonder if it might also be possible to spot weld them to stainless steel.

Niobium alloys are light enough that they were seriously considered for the Space Shuttle.  Now as I understand it there was no insulation under that double niobium layer that was tested for the Space Shuttle.  Two thin layers of niobium sheet by themselves were enough to protect the aluminum structure underneath.

It could be that niobium alloy is the better solution on the parts of the Starship skin where bending and flexing can be anticipated, as for instance the skirt.

In addition I wonder about combining the niobium alloy with methane cooling since the niobium can so easily be given corrugations and other three dimensional structure.

Since the niobium alloy can be readily formed to make channels, the sheet could be used to simultaneously guide the methane gas to where it is needed and to serve as heat shielding at the same time.

- C/SiC composites are pretty tough. They are used in turbine engines. Mounting appears to use felt pad to isolate tile from structure.

- I don't believe two layers of metal are going to protect an aluminum structure from reentry heat. Do you have a reference document about the work? Probably used insulation as well.

John


Rereading the paper again that inspired these thoughts, see https://ntrs.nasa.gov/citations/19730024093, I do wonder if I'm seeing the full context.  I find no mention of any insulation, other than than the two layers of niobium alloy, one flat and one corrugated, and coated with a thin fused silicon/chromium/iron coating.

But maybe there actually is such a thing and the authors simply assumed that the people reading it would know that from the context.
Title: Re: Starship heat shield
Post by: maquinsa on 10/13/2020 11:45 am
The issue with ceramic heat shield tiles is their fragility, rigidity, and the difficulty in attaching them to a substrate.  In particular, if they flex they will break.

Niobium alloys with a thin silica-rich coating (to protect it from oxidation) can bend and are even elastic.  But a niobium alloy with its coating weighs more than comparable ceramic heat shield tiles assuming a niobium alloy thickness greater than that of a foil.

Another advantage the niobium has is that micrometeorites that would shatter part of a ceramic heat shield tile will have a negligible impact on the heat shielding capacity of the niobium alloy.

In comparing the two, we also need to include the weight of the systems needed to attach the two materials to the stainless steel skin of the Starship.  Since niobium alloys can be welded to niobium alloys I wonder if it might also be possible to spot weld them to stainless steel.

Niobium alloys are light enough that they were seriously considered for the Space Shuttle.  Now as I understand it there was no insulation under that double niobium layer that was tested for the Space Shuttle.  Two thin layers of niobium sheet by themselves were enough to protect the aluminum structure underneath.

It could be that niobium alloy is the better solution on the parts of the Starship skin where bending and flexing can be anticipated, as for instance the skirt.

In addition I wonder about combining the niobium alloy with methane cooling since the niobium can so easily be given corrugations and other three dimensional structure.

Since the niobium alloy can be readily formed to make channels, the sheet could be used to simultaneously guide the methane gas to where it is needed and to serve as heat shielding at the same time.

- C/SiC composites are pretty tough. They are used in turbine engines. Mounting appears to use felt pad to isolate tile from structure.

- I don't believe two layers of metal are going to protect an aluminum structure from reentry heat. Do you have a reference document about the work? Probably used insulation as well.

John


Rereading the paper again that inspired these thoughts, see https://ntrs.nasa.gov/citations/19730024093, I do wonder if I'm seeing the full context.  I find no mention of any insulation, other than than the two layers of niobium alloy, one flat and one corrugated, and coated with a thin fused silicon/chromium/iron coating.

But maybe there actually is such a thing and the authors simply assumed that the people reading it would know that from the context.

Well they may not need an insulator if the gap between the two layers is large enough.
Title: Re: Starship heat shield
Post by: livingjw on 10/13/2020 01:45 pm
The issue with ceramic heat shield tiles is their fragility, rigidity, and the difficulty in attaching them to a substrate.  In particular, if they flex they will break.

Niobium alloys with a thin silica-rich coating (to protect it from oxidation) can bend and are even elastic.  But a niobium alloy with its coating weighs more than comparable ceramic heat shield tiles assuming a niobium alloy thickness greater than that of a foil.

Another advantage the niobium has is that micrometeorites that would shatter part of a ceramic heat shield tile will have a negligible impact on the heat shielding capacity of the niobium alloy.

In comparing the two, we also need to include the weight of the systems needed to attach the two materials to the stainless steel skin of the Starship.  Since niobium alloys can be welded to niobium alloys I wonder if it might also be possible to spot weld them to stainless steel.

Niobium alloys are light enough that they were seriously considered for the Space Shuttle.  Now as I understand it there was no insulation under that double niobium layer that was tested for the Space Shuttle.  Two thin layers of niobium sheet by themselves were enough to protect the aluminum structure underneath.

It could be that niobium alloy is the better solution on the parts of the Starship skin where bending and flexing can be anticipated, as for instance the skirt.

In addition I wonder about combining the niobium alloy with methane cooling since the niobium can so easily be given corrugations and other three dimensional structure.

Since the niobium alloy can be readily formed to make channels, the sheet could be used to simultaneously guide the methane gas to where it is needed and to serve as heat shielding at the same time.

- C/SiC composites are pretty tough. They are used in turbine engines. Mounting appears to use felt pad to isolate tile from structure.

- I don't believe two layers of metal are going to protect an aluminum structure from reentry heat. Do you have a reference document about the work? Probably used insulation as well.

John


Rereading the paper again that inspired these thoughts, see https://ntrs.nasa.gov/citations/19730024093, I do wonder if I'm seeing the full context.  I find no mention of any insulation, other than than the two layers of niobium alloy, one flat and one corrugated, and coated with a thin fused silicon/chromium/iron coating.

But maybe there actually is such a thing and the authors simply assumed that the people reading it would know that from the context.

This is hot structure, not TPS.

Edit: Appears to be for heat shield panels. These would be considered "secondary structure", not primary structure.

John
Title: Re: Starship heat shield
Post by: edzieba on 10/13/2020 02:15 pm
While likely not the optimum TPS, the current ceramic tiles have the notable advantages that a) they have been proven to work on large lifting-body vehicles performing angled entries with both direct impingement and spanwise flow and b) you can go out and hire a lot of the guys who designed and manufactured them if you want to get some manufactured that you can be reasonably confident will fulfil specification on the first production run.

High TRL, almost-off-the-shelf, and lets you spend your initial time and effort tweaking knobs in tile spec and attachment mechanism rather than worrying about if the tiles themselves can be made or that they will work. Use some of your monumental payload capacity to carry a suboptimal thermal protection system, and you can operate your vehicle while designing that future optimal system. It's a heck of a lot nicer than eschewing "it's not great, but it works!" for a future theoretically better system and either expending Starships or not launching them at all in the meantime.
Title: Re: Starship heat shield
Post by: KBK on 10/13/2020 02:49 pm
I'm sure that this is a path that is considered, among all the other potentials. An unspoken part of the package, I'm sure.

Sort of a 'page one, chapter one' part of the playbook. Status quo and state of mind, in  the Modus Operandi.

I'd even go so far as to wager that this was on the table as a possible forking in directions.... on the very first day that the idea of a larger rocket was considered.
Title: Re: Starship heat shield
Post by: mandrewa on 10/13/2020 03:12 pm
Here are the dimensions for the metallic thermal protection system proposed for the
VentureStar.

0.4 mm titanium outer facesheet
6.4 mm deep Inconel 617 and titanium honeycomb sandwich
0.4 mm titanium inner facesheet
50.6 mm Saffil insulation
0.4 mm titanium foil
9.5 mm air gap

And it's all mounted with four screws per panel on an aluminum substructure.

That's a total depth of 2.67 inches, including the air gap, or 2.29 inches excluding the air
gap.

In contrast the simple two layer niobium alloy foil sandwich proposed for the space shuttle
had a total depth of about 14.7 mm (0.58") which includes about 14 mm of enclosed air.

I had been picturing the niobium alloy as a metal sheet, but assuming I have the dimensions
correct now, it is really just a foil, some 0.3 mm thick plus the 3 mil depth (6 mil total) of
the fused silicon/chromium/iron coating.

This niobium alloy foil can be welded to itself, but the idea of spot welding this to
stainless steel probably doesn't make sense.

Unlike with the VentureStar paper, there is no discussion in the Space Shuttle paper of how
the niobium foil would be mounted on the aluminum substrate.

It is striking that the thickness of the niobium alloy foil is about the same thickness
as the titanium foil and that the depth of the Inconel 617 and titanium sandwich is a little less
than half the depth of the two layers of niobium alloy that were to be welded together for the
space shuttle.

We only need to add a 40 mm layer of insulation to the two layers of niobium alloy and the
two systems would have had the same overall dimensions (about 2.67" deep).

I feel like it was an oversight to not include the mounting system in the many tests of durability
of the niobium foil panels that were done for the space shuttle study as surely those mount points
would have had an impact on the durability.

Now the fact that the substructure is stainless steel on the Starship and not aluminum will surely
decrease the thickness of the needed insulation.  Or maybe it can be completely replaced with
an air gap, and this would surely be the case if it's being supplemented by methane cooling.

(The VentureStar metallic TPS dimensions came from "Reusable metallic thermal protection systems development"
by Max L. Blosser, Carl J. Martin, Kamran Daryabeigi, and Carl C. Poteet)

(Edited: Some corrections after re-reading.)
Title: Re: Starship heat shield
Post by: leovinus on 10/13/2020 03:39 pm
(The VentureStar metallic TPS dimensions came from "Reusable metallic thermal protection systems development"
by Max L. Blosser, Carl J. Martin, Kamran Daryabeigi, and Carl C. Poteet)

That would be this article for the details and graphics.
https://www.cs.odu.edu/~mln/ltrs-pdfs/NASA-98-3ewtps-mlb.pdf
Title: Re: Starship heat shield
Post by: livingjw on 10/13/2020 03:45 pm
- The cited paper was a study of niobium panels for "a" space shuttle. Not "the" space shuttle. The structural concept was probably different from "the" space shuttle.

- It was a heat shield panel coating study, not a complete TPS study. Probably need to trace back and find the vehicle studies that these panels were tied to.

John

Title: Re: Starship heat shield
Post by: eriblo on 10/13/2020 04:50 pm
Here are the dimensions for the metallic thermal protection system proposed for the
VentureStar.

0.4 mm titanium outer facesheet
6.4 mm deep Inconel 617 and titanium honeycomb sandwich
0.4 mm titanium inner facesheet
50.6 mm Saffil insulation
0.4 mm titanium foil
9.5 mm air gap

And it's all mounted with four screws per panel on an aluminum substructure.

That's a total depth of 2.67 inches, including the air gap, or 2.29 inches excluding the air
gap.

In contrast the simple two layer niobium alloy foil sandwich proposed for the space shuttle
had a total depth of about 14.7 mm (0.58") which includes about 14 mm of enclosed air.

I had been picturing the niobium alloy as a metal sheet, but assuming I have the dimensions
correct now, it is really just a foil, some 0.3 mm thick plus the 3 mil depth (6 mil total) of
the fused silicon/chromium/iron coating.

This niobium alloy foil can be welded to itself, but the idea of spot welding this to
stainless steel probably doesn't make sense.

Unlike with the VentureStar paper, there is no discussion in the Space Shuttle paper of how
the niobium foil would be mounted on the aluminum substrate.

It is striking that the thickness of the niobium alloy foil is about the same thickness
as the titanium foil and that the depth of the Inconel 617 and titanium sandwich is a little less
than half the depth of the two layers of niobium alloy that were to be welded together for the
space shuttle.

We only need to add a 40 mm layer of insulation to the two layers of niobium alloy and the
two systems would have had the same overall dimensions (about 2.67" deep).

I feel like it was an oversight to not include the mounting system in the many tests of durability
of the niobium foil panels that were done for the space shuttle study as surely those mount points
would have had an impact on the durability.

Now the fact that the substructure is stainless steel on the Starship and not aluminum will surely
decrease the thickness of the needed insulation.  Or maybe it can be completely replaced with
an air gap, and this would surely be the case if it's being supplemented by methane cooling.

(The VentureStar metallic TPS dimensions came from "Reusable metallic thermal protection systems development"
by Max L. Blosser, Carl J. Martin, Kamran Daryabeigi, and Carl C. Poteet)

(Edited: Some corrections after re-reading.)
The study you cited for the niobium heat shield is as John mentioned just for a single wind facing surface layer, not a complete heat shield. Other studies (like this one https://ntrs.nasa.gov/citations/19770015587) looked at the whole system.

Easy way to see that you would need insulation: The reentry temperature profile they used had ~1000 s above 1200 C. At this temperature the panel (emissivity 0.9) will radiate ~240 kW/m^2 on both sides. Even assuming a perfect vacuum behind the panel and a rather high reflectivity of 90% for a highly polished aluminium skin this will transfer ~27kW/m^2 of heat. This will raise the temperature of a 1 mm thick skin from room temperature to the maximum (175 C) allowed for structural reasons in ~15 s and to the melting point in ~90 s. Scale with your preferred equivalent thickness for the skin and thermally attached structure.
Title: Re: Starship heat shield
Post by: mandrewa on 10/13/2020 06:55 pm
Thanks for finding that paper, eriblo.  I read through it and here is a brief summary.

From "Summary report of evaluation of coated columbium alloy heat shields for Space Shuttle
thermal protection system application," by W.E. Black

"The final system design had a unit weight (including heat shield, retainers, insulation, and
supporting structure) of 23 kg/m^2 (4.7 lb/ft^2)..."

From Figure 1 we get the terminology for describing the different elements of the system.  There
is (a) the "heat shield," which is a sandwich of two layers of niobium alloy foil enclosing
17 mm of air.  There is (b) the "insulation," made from Fiberfrax H insulation (a ceramic fiber
blanket).  There is (c) the substructure or the frame of this version of the Space Shuttle, which
is made from titanium and not aluminum! And then there is the "support structure" or mounting
hardware which consists of six screws per panel and other hardware to push down on four "tee-beams"
that do not attach directly to the niobium foil heat shield but do press down on all four outer
edges of the heat shield (and its neighbors).

The heat shield was 17.8 mm deep.
The insulation was 86 mm deep.
And the TPS panels in total were were 103.8 mm deep or 4 inches.

In addition to tests in the laboratory the full system was tested on a "Rockwell International
high cross-range orbiter launched on a Convair recoverable booster."

From that testing: "The maximum panel temperature after 2500 seconds of reentry would be below
480 K (400 degree F)."

The goals were to have a thermal protection system that:
(1) minimized weight and volume;
(2) was reusable for 100 missions;
(3) was externally removable from the vehicle;
(4) permitted inspection and on orbit repair; and
(5) accommodated thermally and mechanically induced stresses, deflections, and rotations.

"Those components that are questionable for an additional mission must be easily removable
for repair or replacement."

"The ability to inspect the joints and coating is of sufficient importance as to impact
the panel design; therefore, each configuration was evaluated for its ability or complexity
to be inspected by visual means as well as by radiography, electron-emission, thermoelectric
emission, and ultrasonics."

"If a vehicle was bombarded by micrometeoroids and sustained detectable damage while on station,
the options are: (1) to replace the damaged heat shield (by ferrying a replacement part to the
vehicle or by an on-board store), (2) repair the damaged areas (this is feasible, especially
by using the plug repair method, ref. 8 ), or (3) reenter the atmosphere without repair."

"With the specimens employed it is apparent that good field repairs can be made and that heat
shield sustaining severe damage (such as through-penetrations) can be made serviceable for many
additional cycles. In observing the effects of the two repair processes there was no preference
of one over the other."

"To reproduce the various lightning strike effects on a columbium alloy heat shield three types
of tests were conducted."

"In summary, the panels could withstand the maximum current use rate (dI/dt) and a typical
cloud-to-cloud discharge (high Q) without perforation. Some coating damage is possible within
approximately a 1.27 cm (0.5 inch) radius. However, it is expected that at least one successful
reentry could be made."
Title: Re: Starship heat shield
Post by: livingjw on 10/21/2020 02:25 am
Interesting new twist on the tile attachment studs. The bottom center stud is definitely different. Some cute new fastening scheme?

John
Title: Re: Starship heat shield
Post by: KBK on 10/21/2020 05:22 am
[zubenelgenubi: Attach images. Do not embed them.]
Photo Credit: Nomadd

The mounts appear to set up to be oriented so their pull/stressing are even and across one another, to create a motional mode that limits their motion to within a set of limited modes, and physical distances in a given motion that a tile may undergo - that reflects upon the tile shape, with regard to the least physical interference with one another when under load conditions.

Very common in at least one field of design I know of (probably a good few hundred of iterations and attempts in design).  And there are quite a few others (fields of employ).

If they are not (set up that way), well, that is at least how one might think of trying to do it. They certainly bear the appearance of doing so. This is the mounting design I expected to see. There was no other real option for the optimal six sided tile.
Title: Re: Starship heat shield
Post by: HVM on 10/21/2020 08:08 am
Those caps are bigger and more uneven than in tent build Model 3. And one tile is already broken... You're instilling me with a lot of confidence, Doc.

Ok, it's not actual heat shield. It's a structural and bonding test of the tiles.
Title: Re: Starship heat shield
Post by: rsdavis9 on 10/21/2020 03:41 pm
So per tile is that 4 rather tapered pins and one kind of hollow center pin?

EDIT: Still 3 pins. The bottom pin is turned at a different angle so it looks different. Looks to be like a loop so something can latch on to it.
Title: Re: Starship heat shield
Post by: Nomadd on 10/21/2020 05:11 pm
 One pin seems to be missing, but there's a mark there. I wonder if they stress test them after welding.
Title: Re: Starship heat shield
Post by: envy887 on 10/21/2020 05:28 pm
Interesting new twist on the tile attachment studs. The bottom center stud is definitely different. Some cute new fastening scheme?

John

They all look the same to me... just rotated 60 degrees from each other. They look like 2-pronged forks, with something at the end of each tine. Maybe a snap feature that engages with something embedded in the tile, when the tile is pushed on?

That would make installation fast and simple. Not sure how well it will hold.
Title: Re: Starship heat shield
Post by: Nomadd on 10/21/2020 06:05 pm
 I never really looked that close. It looks like sprung retainer clips.
 If I only knew someone with a better lens and more skill who was crazy enough to slog through two miles of muck to get a better photo.
Title: Re: Starship heat shield
Post by: WormPicker959 on 10/22/2020 01:12 am
Interesting new twist on the tile attachment studs. The bottom center stud is definitely different. Some cute new fastening scheme?

John

So, zooming in on Mary's image (from here: https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=51332.0;attach=1982392;image), it looks to me like the three studs/prongs/attachments are simply angled differently, so they look different when viewed from afar. But my best guess is they are all two-prong thingies, oriented radially (see attached).

Edit: modified link to Mary's photo
Title: Re: Starship heat shield
Post by: WormPicker959 on 10/22/2020 01:25 am
One pin seems to be missing, but there's a mark there. I wonder if they stress test them after welding.

...and based on this image from Nomadd, it looks like the "prongs" are flat-ish triangles, with the flat sides oriented towards the center? Attached is a (bad) sketch of what I'm thinking.

Edit: to add that the "mark" there looks like a paper/plastic bag covering it in Mary's photo, linked to in my previous post.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/22/2020 05:57 am
Those caps are bigger and more uneven than in tent build Model 3. And one tile is already broken... You're instilling me with a lot of confidence, Doc.

Ok, it's not actual heat shield. It's a structural and bonding test of the tiles.
Could be. And at least one of those tiles is either seriously discolored, cracked or has a very uneven surface.

Plus do really know if these are proud of the surface and not holes in the skin with the mouting fittings concealed under the tiles themselves?

I had a thought that ceramics can be 10x stronger in compression than tension. If the whole tank were heated to say 200c and the tiles mounted to pins as it cooled back down they would be put under huge compression.

While this is theoretically possible it would also make individual tile repairs impossible and tile installation would become an all-or-nothing task. The holes in the tiles would sized for the pin spacing at +200c, not room temperature :(
Title: Re: Starship heat shield
Post by: Seamurda on 10/23/2020 09:39 pm
The issue with ceramic heat shield tiles is their fragility, rigidity, and the difficulty in attaching them to a substrate.  In particular, if they flex they will break.

Niobium alloys with a thin silica-rich coating (to protect it from oxidation) can bend and are even elastic.  But a niobium alloy with its coating weighs more than comparable ceramic heat shield tiles assuming a niobium alloy thickness greater than that of a foil.

Another advantage the niobium has is that micrometeorites that would shatter part of a ceramic heat shield tile will have a negligible impact on the heat shielding capacity of the niobium alloy.

In comparing the two, we also need to include the weight of the systems needed to attach the two materials to the stainless steel skin of the Starship.  Since niobium alloys can be welded to niobium alloys I wonder if it might also be possible to spot weld them to stainless steel.

Niobium alloys are light enough that they were seriously considered for the Space Shuttle.  Now as I understand it there was no insulation under that double niobium layer that was tested for the Space Shuttle.  Two thin layers of niobium sheet by themselves were enough to protect the aluminum structure underneath.

It could be that niobium alloy is the better solution on the parts of the Starship skin where bending and flexing can be anticipated, as for instance the skirt.

In addition I wonder about combining the niobium alloy with methane cooling since the niobium can so easily be given corrugations and other three dimensional structure.

Since the niobium alloy can be readily formed to make channels, the sheet could be used to simultaneously guide the methane gas to where it is needed and to serve as heat shielding at the same time.

- C/SiC composites are pretty tough. They are used in turbine engines. Mounting appears to use felt pad to isolate tile from structure.

- I don't believe two layers of metal are going to protect an aluminum structure from reentry heat. Do you have a reference document about the work? Probably used insulation as well.

John

The SIC/SIC components in gas turbines are actually quite chunky. One of the big issues is dealing with the difficulty of forming them into useful shapes and how to attach them to metallic components.

Most components in a gas turbine are also held in position very loosely by entrapment with other components that are assembled in afterwards until you get to a casing flange
Title: Re: Starship heat shield
Post by: livingjw on 10/24/2020 12:47 am
The issue with ceramic heat shield tiles is their fragility, rigidity, and the difficulty in attaching them to a substrate.  In particular, if they flex they will break.

Niobium alloys with a thin silica-rich coating (to protect it from oxidation) can bend and are even elastic.  But a niobium alloy with its coating weighs more than comparable ceramic heat shield tiles assuming a niobium alloy thickness greater than that of a foil.

Another advantage the niobium has is that micrometeorites that would shatter part of a ceramic heat shield tile will have a negligible impact on the heat shielding capacity of the niobium alloy.

In comparing the two, we also need to include the weight of the systems needed to attach the two materials to the stainless steel skin of the Starship.  Since niobium alloys can be welded to niobium alloys I wonder if it might also be possible to spot weld them to stainless steel.

Niobium alloys are light enough that they were seriously considered for the Space Shuttle.  Now as I understand it there was no insulation under that double niobium layer that was tested for the Space Shuttle.  Two thin layers of niobium sheet by themselves were enough to protect the aluminum structure underneath.

It could be that niobium alloy is the better solution on the parts of the Starship skin where bending and flexing can be anticipated, as for instance the skirt.

In addition I wonder about combining the niobium alloy with methane cooling since the niobium can so easily be given corrugations and other three dimensional structure.

Since the niobium alloy can be readily formed to make channels, the sheet could be used to simultaneously guide the methane gas to where it is needed and to serve as heat shielding at the same time.

- C/SiC composites are pretty tough. They are used in turbine engines. Mounting appears to use felt pad to isolate tile from structure.

- I don't believe two layers of metal are going to protect an aluminum structure from reentry heat. Do you have a reference document about the work? Probably used insulation as well.

John

The SIC/SIC components in gas turbines are actually quite chunky. One of the big issues is dealing with the difficulty of forming them into useful shapes and how to attach them to metallic components.

Most components in a gas turbine are also held in position very loosely by entrapment with other components that are assembled in afterwards until you get to a casing flange

Very thin C/SiC can be laid up, a few thousandths of of an inch.

John
Title: Re: Starship heat shield
Post by: john smith 19 on 10/27/2020 05:56 am
The SIC/SIC components in gas turbines are actually quite chunky. One of the big issues is dealing with the difficulty of forming them into useful shapes and how to attach them to metallic components.
Which suggest the big issue is not their fragility after firing but making sure they are fired all the way through properly to begin with. It also makes them sound heavy. Shuttle tiles won because they are actually about 95% pore and 5% tile, but were very fragile.

Very thin C/SiC can be laid up, a few thousandths of of an inch.

John
True, but that does not appear to be the case here, and very labor intensive. I think they are using some kind of casting approach.

I'm finding it difficult to judge size of these tiles. They have substantial thickness so I'd say at least 1cm but maybe closer to an inch? Shuttle standard (after the cracking issues) was about 6" wide, which IIRC gave them a tile job of about 24 000 tiles (which would be some bathroom  :) )
Title: Re: Starship heat shield
Post by: livingjw on 10/27/2020 02:24 pm
The SIC/SIC components in gas turbines are actually quite chunky. One of the big issues is dealing with the difficulty of forming them into useful shapes and how to attach them to metallic components.
Which suggest the big issue is not their fragility after firing but making sure they are fired all the way through properly to begin with. It also makes them sound heavy. Shuttle tiles won because they are actually about 95% pore and 5% tile, but were very fragile.

Very thin C/SiC can be laid up, a few thousandths of of an inch.

John
True, but that does not appear to be the case here, and very labor intensive. I think they are using some kind of casting approach.

I'm finding it difficult to judge size of these tiles. They have substantial thickness so I'd say at least 1cm but maybe closer to an inch? Shuttle standard (after the cracking issues) was about 6" wide, which IIRC gave them a tile job of about 24 000 tiles (which would be some bathroom  :) )

- Space X tiles are ~.31 m across and ~4 cm thick, based on photos relative to 9 m diameter tanks.

- They have been examining many alternatives.

- We have seen that the outer shell appears to be a thin coated material over insulation. Some of those shells appeared to be rather brittle, suggesting thin ceramic. Others appear to be more substantial, suggesting something with some strength.

- They have experimented with both mechanical and bonded attachment. Mechanical attachment seems to have worked out better. Mechanical attachment experimentation is apparent and appears to still be evolving.

- Mechanical attachment of outer shell through weaker insulation to studs has been seen.

- insulation maybe solid or batt, mounted on what appears to be a felt pad to spread localized stresses and for protection between tile.

- This leads me to speculate on some form of coated Carbon/SiC composite shell filled with insulation, backed with felt, mechanically attached. Automating the layup of a thin C/SiC shell should be possible.

John
Title: Re: Starship heat shield
Post by: john smith 19 on 10/28/2020 06:48 am
- Space X tiles are ~.31 m across and ~4 cm thick,
Like my old college landladies home-made pizza  :)
TBH that's only 2x wider and longer than the typical shuttle tile.  OTOH I guess it's a good size if you want minimal unique tiles
Quote from: livingjw
- They have been examining many alternatives.
Yes the design space (even for just ceramic based systems) is huge.
Quote from: livingjw
- We have seen that the outer shell appears to be a thin coated material over insulation. Some of those shells appeared to be rather brittle, suggesting thin ceramic. Others appear to be more substantial, suggesting something with some strength.
Pretty much the TUFROC patent. Not so much a patent for a set of materials to make a TPS but an architecture for a TPS, although (unlike the patent) I'm not sure the top surface skin goes down the sides in order to protect from plasma ingress (which otherwise needed all those fiddly little gap filling bits).
Quote from: livingjw
- They have experimented with both mechanical and bonded attachment. Mechanical attachment seems to have worked out better. Mechanical attachment experimentation is apparent and appears to still be evolving.
When you consider every scenario (and what you've got to do to support that scenario, like a repair paste that you can use in deep space or on the surface of mars etc) mechanical fastening (especially given that TCE for steel is 1/3 that of aluminum) seems the better way to go.
Quote from: livingjw
- Mechanical attachment of outer shell through weaker insulation to studs has been seen.
Pretty much the TUFROC patent
Quote from: livingjw
- insulation maybe solid or batt, mounted on what appears to be a felt pad to spread localized stresses and for protection between tile.
That's the attraction of this architecture. You can keep the insulation inside the "top hat" and it can be pretty fragile. That means low density --> lower conductivity.
Quote from: livingjw
- This leads me to speculate on some form of coated Carbon/SiC composite shell filled with insulation, backed with felt, mechanically attached. Automating the layup of a thin C/SiC shell should be possible.

John
Do you mean backed with felt to retain the insulation inside a rigid 5 sized box or as a mounting material of the tile to the skin? On Shuttle the felt isolation pads (I picture it as being like a thin layer of wadded up nylon stocking material) was necessary to cope with the high CTE of the aluminum skin and because of expected mass of a fastener based solution.

This just leaves tile vibration induced by air loads as a reason to include some kind of felt pad.

When you consider the scale SS is expected to operate on any solution will have to allow automation. Robots cope better with rigid materials and fixed locations to move a part to so I think they will try to avoid felt or batting. Ideally you'd like any material failure to be very obvious, like a color change or a highly visible crack once it's above it's safe stress level.  Worst case something you can see through the helmet of a space suit.  :(

A trickier question is wheather the shell should just be the top surface or have sides as well. The latter gives you a box you can put very fragile (loft or foamed zirconia type) insulation into.

On the downside mass production of a fiber reinforced ceramic hexagon box shape is likely to be quite tricky. This is also now a fixed component. You don't have a material you can cut to shape otherwise you lose the benefits of the side walls (insulation containment and protection from water ingress on the ground and plasma getting between the tiles during entry).
 
That's not important if the same design can cope with all parts of the vehicle but that's unlikely to be the case for leading edges of the control surfaces.  How many spares to carry to mars (and will they survive 26 months of martian weather)?

It's clear the design is evolving. I'm sure we'll see more changes once they start higher speed and altitude tests.
Title: Re: Starship heat shield
Post by: livingjw on 10/28/2020 02:46 pm
....
Do you mean backed with felt to retain the insulation inside a rigid 6 sized box or as a mounting material of the tile to the skin? On Shuttle the felt isolation pads (I picture it as being like a thin layer of wadded up nylon stocking material) was necessary to cope with the high CTE of the aluminum skin and because of expected mass of a fastener based solution.

This just leaves tile vibration induced by air loads as a reason to include some kind of felt pad.

When you consider the scale SS is expected to operate on any solution will have to allow automation. Robots cope better with rigid materials and fixed locations to move a part to so I think they will try to avoid felt or batting. Ideally you'd like any material failure to be very obvious, like a color change or a highly visible crack once it's above it's safe stress level.  Worst case something you can see through the helmet of a space suit.  :(

A trickier question is whether the shell should just be the top surface or have sides as well. The latter gives you a box you can put very fragile (loft or foamed zirconia type) insulation into.

On the downside mass production of a fiber reinforced ceramic hexagon box shape is likely to be quite tricky. This is also now a fixed component. You don't have a material you can cut to shape otherwise you lose the benefits of the side walls (insulation containment and protection from water ingress on the ground and plasma getting between the tiles during entry).
 
That's not important if the same design can cope with all parts of the vehicle but that's unlikely to be the case for leading edges of the control surfaces.  How many spares to carry to mars (and will they survive 26 months of martian weather)?


- Felt is composed of teased or needled together fibers.  I believe fibers used for shuttle were Nomex. Felt is made in a wide range of thicknesses. I would expect a thickness in the range of 5 - 10 mm. I believe its use would be for vibration damping and fitting against a structure which changes shape due to oil canning etc. The same felt could be molded to protect the space between the tile. The felt part is flexible, and precisely trimmable. Don't see why placement and attachment to the tile could not be automated. The tile could be manufactured with the felt already attached, ready for attachment to the Starship.

- The tile shell is going to need side walls and sealed in some sense against water vapor. I don't see this as  "tricky". Its basically a flat layup of a few layers, then blocked in a form ready for firing.

- The felt would not be used for attaching tile. Tile are mechanically attached.

- Felt could be used to retain batting inside the tile shell, but I suspect they might want something less permeable to water, though maybe hydrophobic felt.

- Certainly a significant design and development problem, but I don't see road blocks WRT to automation. Automating layup of the tile shell, coating tile shell, filling with insulation, sealing tiles against water vapor, or attaching felt to tile. These types of operations are automated now.

- Uniquely shaped replacement parts will need to be fabricated onboard for repairs, but these would be one use items.

John
Title: Re: Starship heat shield
Post by: john smith 19 on 11/01/2020 08:58 pm
- Felt is composed of teased or needled together fibers.  I believe fibers used for shuttle were Nomex. Felt is made in a wide range of thicknesses. I would expect a thickness in the range of 5 - 10 mm. I believe its use would be for vibration damping and fitting against a structure which changes shape due to oil canning etc. The same felt could be molded to protect the space between the tile. The felt part is flexible, and precisely trimmable. Don't see why placement and attachment to the tile could not be automated. The tile could be manufactured with the felt already attached, ready for attachment to the Starship.

- The tile shell is going to need side walls and sealed in some sense against water vapor. I don't see this as  "tricky". Its basically a flat layup of a few layers, then blocked in a form ready for firing.

- The felt would not be used for attaching tile. Tile are mechanically attached.

- Felt could be used to retain batting inside the tile shell, but I suspect they might want something less permeable to water, though maybe hydrophobic felt.

- Certainly a significant design and development problem, but I don't see road blocks WRT to automation. Automating layup of the tile shell, coating tile shell, filling with insulation, sealing tiles against water vapor, or attaching felt to tile. These types of operations are automated now.

- Uniquely shaped replacement parts will need to be fabricated onboard for repairs, but these would be one use items.

John
Felting looks to be a quite a useful way to make materials that are very difficult to weave into larger structures.  They can be used for vibration damping but I think the issue with shuttle TPS was because the tiles were bonded, creating an extended joint area between the tiles and the skin. Once you go to a point mounting (and a skin that expands and contracts 1/3 that of aluminum for the same change in temperature) things get much easier.
Title: Re: Starship heat shield
Post by: livingjw on 11/01/2020 09:35 pm

Felting looks to be a quite a useful way to make materials that are very difficult to weave into larger structures.  They can be used for vibration damping but I think the issue with shuttle TPS was because the tiles were bonded, creating an extended joint area between the tiles and the skin. Once you go to a point mounting (and a skin that expands and contracts 1/3 that of aluminum for the same change in temperature) things get much easier.

C/SiC has good strength but it is brittle. If it was just thermal expansion, I would agree with you, but in certain areas the Starship structure going to move and distort. I think SpaceX will want a compliance layer between them.

John
Title: Re: Starship heat shield
Post by: john smith 19 on 11/02/2020 05:59 am

Felting looks to be a quite a useful way to make materials that are very difficult to weave into larger structures.  They can be used for vibration damping but I think the issue with shuttle TPS was because the tiles were bonded, creating an extended joint area between the tiles and the skin. Once you go to a point mounting (and a skin that expands and contracts 1/3 that of aluminum for the same change in temperature) things get much easier.

C/SiC has good strength but it is brittle. If it was just thermal expansion, I would agree with you, but in certain areas the Starship structure going to move and distort. I think SpaceX will want a compliance layer between them.

John
I can see your point but I think moving from an area to a point attachment (and the move to SS) makes a lot of those issues much smaller.  OTOH I could see vibration of the tiles hitting the skin could be an issue. In that case having a cushion material seems like a pretty good idea.

It's pretty clear the TPS is still evolving. I don't think the detail design is anywhere close to finished and will change some more after altitude and speed testing.
Title: Re: Starship heat shield
Post by: Navier–Stokes on 11/09/2020 04:34 pm
Quote
Space Exploration Technologies Corp. (SpaceX) of Hawthorne, California
SpaceX will partner with Langley to capture imagery and thermal measurements of its Starship vehicle during orbital re-entry over the Pacific Ocean. With the data, the company plans to advance a reusable thermal protection system, which protects the vehicle from aerodynamic heating, for missions returning from low-Earth orbit, the Moon, and Mars.
https://www.nasa.gov/directorates/spacetech/2020_NASA_Announcement_of_Collaboration_Opportunity_ACO_Selections
Title: Re: Starship heat shield
Post by: WormPicker959 on 11/14/2020 09:33 pm
Alright, so nobody's posted on the new TPS photos, so I'll have a go.

Mary's most recent shot, post static fire:
https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=51332.0;attach=1988280;image

To me, it looks like we learn two things from this:
1. Haven't solved the issue with vibration damage to the tiles.
2. There's some additional Y-shaped structure that I don't think we've seen before. I don't know enough about this stuff to say anything smart about it.

The pessimist in me is thinking it's bad they can't figure out how to attach these things without them breaking/falling off. The optimist in me is thinking that the other ones aren't broken, and that's better than some previous static fires where they've all fallen off. Perhaps they are again testing different types of tiles/fasteners, and here we see 8/9 remaining attached? If the pessimist is right, an 8/9 pass rate is far too low (obviously). If the optimist is right, it's plausible they've solved the issue, or at least have come close to doing so.

What do you all think?

Edit: on a second note, maybe 8/9 is too generous. Looks like there might be chips/damage to some other tiles, not sure the degree to which this could/would be incapacitating.
Title: Re: Starship heat shield
Post by: HVM on 11/14/2020 10:17 pm
8/9 is better than 0/6 right?
Title: Re: Starship heat shield
Post by: Vonbraun on 11/14/2020 10:21 pm
To me the constant breaking of tiles on the fielded prototype means, that they do not currently understand the mechanism of this type of failure or there are multiple underlying issues (making it difficult to pinpoint).
For this type of component you would essentially simulate the required conditions in a laboratory, because its trivial and small in scale?

If i were testing these on the prototype, i would put a covering plate over the whole thing in order to shield them from debris. Probably create other sets too for different variable reductions (acoustic, air stream, etc.). Its easier to find issues when you can rule out invidual causes first.
Title: Re: Starship heat shield
Post by: Redclaws on 11/14/2020 10:24 pm
Why would you want to shield them from debris?  Debris impact was one of *the* problems for the shuttle heat shield and if you have expected debris, you’d better be able to handle them!
Title: Re: Starship heat shield
Post by: ioncloud9 on 11/14/2020 10:33 pm
Why would you want to shield them from debris?  Debris impact was one of *the* problems for the shuttle heat shield and if you have expected debris, you’d better be able to handle them!

This thing is supposed to be able to land on unimproved surfaces on Mars with its heatshield. I would bet its not debris. It probably isnt thermal expansion of the tank during cycling. The brackets look like they should prevent the tiles from being damaged by that. Its probably vibration issues during engine firing. They will have to figure out how to design a bracket that can hold the tiles, dampen the vibrations, be highly heat resistant, lightweight, and securely hold the tiles so they do not easily fall off or break.
Title: Re: Starship heat shield
Post by: Vonbraun on 11/14/2020 10:48 pm
Why would you want to shield them from debris?  Debris impact was one of *the* problems for the shuttle heat shield and if you have expected debris, you’d better be able to handle them!

Did this tile break from debris, acoustic, thermal, UV, cherry picker etc. damage or possible combination of these? How would Spacex tell the difference?
Title: Re: Starship heat shield
Post by: Redclaws on 11/14/2020 11:16 pm
Point sort of taken; I suspect they’ll be able to sort that out without changing the environment around the tiles.  They can add sensors and do post-mortems.
Title: Re: Starship heat shield
Post by: equiserre on 11/14/2020 11:29 pm
Alright, so nobody's posted on the new TPS photos, so I'll have a go.

Mary's most recent shot, post static fire:
https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=51332.0;attach=1988280;image

To me, it looks like we learn two things from this:
1. Haven't solved the issue with vibration damage to the tiles.
2. There's some additional Y-shaped structure that I don't think we've seen before. I don't know enough about this stuff to say anything smart about it.

The pessimist in me is thinking it's bad they can't figure out how to attach these things without them breaking/falling off. The optimist in me is thinking that the other ones aren't broken, and that's better than some previous static fires where they've all fallen off. Perhaps they are again testing different types of tiles/fasteners, and here we see 8/9 remaining attached? If the pessimist is right, an 8/9 pass rate is far too low (obviously). If the optimist is right, it's plausible they've solved the issue, or at least have come close to doing so.

What do you all think?

Edit: on a second note, maybe 8/9 is too generous. Looks like there might be chips/damage to some other tiles, not sure the degree to which this could/would be incapacitating.

Also, that was only 3 seconds and no supersonic airstream
Title: Re: Starship heat shield
Post by: RoboGoofers on 11/14/2020 11:36 pm
For all we know all of these tiles may be different compositions or anealing times or any multitude of variables.

In other words it may seem scary to us but it's just data to SpaceX.
Title: Re: Starship heat shield
Post by: AU1.52 on 11/15/2020 12:08 am
Could also be due to the edges having nothing to support them. In the final solution all the edge tiles will have some boundary material they are against.
Title: Re: Starship heat shield
Post by: oiorionsbelt on 11/15/2020 01:14 am
What if there are 9 slightly different variations of tile and attachment techniques and they just discovered the right one.
 :)
Title: Re: Starship heat shield
Post by: Wolfram66 on 11/15/2020 01:26 am
Neodymium extruded foam with SiC tufroc shell?
Title: Re: Starship heat shield
Post by: _MECO on 11/15/2020 03:10 am
Alright, so nobody's posted on the new TPS photos, so I'll have a go.

Mary's most recent shot, post static fire:
https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=51332.0;attach=1988280;image

To me, it looks like we learn two things from this:
1. Haven't solved the issue with vibration damage to the tiles.
2. There's some additional Y-shaped structure that I don't think we've seen before. I don't know enough about this stuff to say anything smart about it.

The pessimist in me is thinking it's bad they can't figure out how to attach these things without them breaking/falling off. The optimist in me is thinking that the other ones aren't broken, and that's better than some previous static fires where they've all fallen off. Perhaps they are again testing different types of tiles/fasteners, and here we see 8/9 remaining attached? If the pessimist is right, an 8/9 pass rate is far too low (obviously). If the optimist is right, it's plausible they've solved the issue, or at least have come close to doing so.

What do you all think?

Edit: on a second note, maybe 8/9 is too generous. Looks like there might be chips/damage to some other tiles, not sure the degree to which this could/would be incapacitating.

I don't know enough either but I'm not gonna let that stop me  ;D

I think that metal three-fold structure might be some kind of skeleton that the tiles are formed or set around that both serve as hardpoints to connect to the mounting hardware as well as to distribute loads transmitted to the ceramic through said hardware. It's like the flat part of the little plastic table thing that keeps your pizza box from collapsing. Without it the three plastic spikes could poke right through the top of the box.
Title: Re: Starship heat shield
Post by: cuddihy on 11/15/2020 03:43 am
Could be the tile breakage problem is all related to ground affected acoustics and once the SS is securely mounted on top of a Superheavy 50 m off the pad this will all be no problem.
Title: Re: Starship heat shield
Post by: john smith 19 on 11/15/2020 10:29 am
This thing is supposed to be able to land on unimproved surfaces on Mars with its heatshield. I would bet its not debris. It probably isnt thermal expansion of the tank during cycling. The brackets look like they should prevent the tiles from being damaged by that. Its probably vibration issues during engine firing. They will have to figure out how to design a bracket that can hold the tiles, dampen the vibrations, be highly heat resistant, lightweight, and securely hold the tiles so they do not easily fall off or break.
Exactly (and that's not a full list) . :(

This is the difference between having a high temperature material (which looks good in a lab test) and a Thermal Protection System that incorporates that material and handles all the other bits of the problem.

Wrapping the cylindrical part of SS is the easier part of the job. No one should have expected that would make it "easy" in an absolute sense. Pre SS most of SX's experience was with ablatives, which (I presume) have been ground-ruled out of the design

Note that NASA developed (and patented) a way to fasten materials with hugely different TCE's together (IE Shuttle tiles or RCC and orbiter skin) in the early 80's.  The patent expired loooong ago.



To me, it looks like we learn two things from this:
1. Haven't solved the issue with vibration damage to the tiles.
2. There's some additional Y-shaped structure that I don't think we've seen before. I don't know enough about this stuff to say anything smart about it.
Could be we've never seen it before. Could be because this is the first time it's been there to see.

And judging by its performance might also be the last time we will see it.  :(

IIRC 8/9 intact is a substantial improvement on previous flights.

Consider what the term "evolving" a design actually means.

1) Use CFD and FAE to develop an idea of what the environment will be
2) Develop multiple ways to cope with those conditions
3) set up (and instrument) the actual environment
4) Run the flight test
5) Check the instrumentation to see if the expected environment was close to the actual IE have you designed your TPS to the real conditions.
6) Examine the different variants
7) If the actual conditions didn't match the design conditions redesign all variants with actual, update the models and return to 3
8) If actual matches design conditions drop worst variants. If best meet all parameters then Job Done. Otherwise redesign top ones to improve on their weaknesses and return to 3.

The jokers in this game is that all design is a trade off.

So you get some designs that are close (but not quite over the line) to what you need. You change them slightly to fix that but in doing so a) Their performance drops on other parameters Back to 2) b) You hit a hard limit on the overall system. Refine the changes so you keep under the overall limit (but risk make all the tiles specific to their exact location on the hull. We all know what a PITA that turned out to be on Shuttle) otherwise back to 2).

The SS TPS development team know all this. It's just what happen IRL when the the plan meets the (complex) physics, chemistry and mfg (because they will be made on a huge scale) needs of the problem.

And it's what makes TPS development such great sport.  :)
Title: Re: Starship heat shield
Post by: eriblo on 11/15/2020 10:39 am
Could be the tile breakage problem is all related to ground affected acoustics and once the SS is securely mounted on top of a Superheavy 50 m off the pad this will all be no problem.
I think that tiles mounted on the skirt during the landing (especially with the current short legs) represent by far the worst case with regard to the mechanical stresses on the mounting system, perhaps followed by three engine static fire. The fact that many of the tiles survived on SN5 makes me think they might have been ok for flight (with the thermal environment during reentry adding a different dimension). It seems like it is the strength of the tile material that is the current weak point and that the pin mounting method isolates them to some degree as the ones that appeared glued in place all sheared of completely.

It is probably easy to make the tiles stronger by making them denser but the strength has to increase disproportionately since the forces scale as the mass and denser tiles need to be even thicker to provide the same insulation (further increasing the weight of the whole TPS). There is likely a lot of iteration with regard to material composition as well as micro and macro scale structure in tandem with the more obvious ones with different mounting methods.
Title: Re: Starship heat shield
Post by: john smith 19 on 11/15/2020 10:51 am
I think that tiles mounted on the skirt during the landing (especially with the current short legs) represent by far the worst case with regard to the mechanical stresses on the mounting system, perhaps followed by three engine static fire.
And hence the ideal location to test design quickly. Most early designs may fail, but the 2nd and 3rd generation designs should be good for the whole vehicle without further failure.
Quote from: eriblo
It is probably easy to make the tiles stronger by making them denser but the strength has to increase disproportionately since the forces scale as the mass and denser tiles need to be even thicker to provide the same insulation (further increasing the weight of the whole TPS). There is likely a lot of iteration with regard to material composition as well as micro and macro scale structure in tandem with the more obvious ones with different mounting methods.
Avoiding that mass increase (or minimizing it if that's not possible) is what makes this tricky.   :(

What options are available (and viable) depend on the exact details of what's being used.

It's important to keep an eye on the big picture here. These conditions are the foothills of the problem.  Whatever redesign is done has to ultimately survive the reentry heating from mars.
Title: Re: Starship heat shield
Post by: Cheapchips on 11/15/2020 10:53 am
Could be the tile breakage problem is all related to ground affected acoustics and once the SS is securely mounted on top of a Superheavy 50 m off the pad this will all be no problem.

The final design does need to work for P2P booster free launches too.
Title: Re: Starship heat shield
Post by: Oersted on 11/15/2020 04:57 pm
SpaceX does absolutely not want an over-engineered solution for the TPS. A main point of going for stainless was to enable a lighter TPS. Consequently it makes sense for them to "work their way up", i.e. see which easy, minimal solutions stick (literally) and which don't. They are going through those solutions at the moment and will "work their way up" to the minimal solution which is both reliable, cheap and easy to maintain. Conclusion: we are going to see a lot of tiles failing in different failure modes and, presumably, by the time they will be needed SpaceX will have a great solution.
Title: Re: Starship heat shield
Post by: Oersted on 11/16/2020 10:12 pm
Per Mary's newest pics of SN9 being lifted outside of the High Bay, it looks like it has quite a few heatshield tiles on it, and possibly thousands of the 3-pronged mounts on the methane tank section!
https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52205.0;attach=1989053;image

Title: Re: Starship heat shield
Post by: wannamoonbase on 11/16/2020 10:34 pm
SpaceX does absolutely not want an over-engineered solution for the TPS. A main point of going for stainless was to enable a lighter TPS. Consequently it makes sense for them to "work their way up", i.e. see which easy, minimal solutions stick (literally) and which don't. They are going through those solutions at the moment and will "work their way up" to the minimal solution which is both reliable, cheap and easy to maintain. Conclusion: we are going to see a lot of tiles failing in different failure modes and, presumably, by the time they will be needed SpaceX will have a great solution.

We'll lets see how they hold up on re-entry and reuse.  From what we've seen with the limited heat shield install so far, I'm almost expecting to see a ton of missing and broken tiles and a lot of rethinking. 

SpaceX is smart, I'm sure they are on top of it.
Title: Re: Starship heat shield
Post by: WormPicker959 on 11/17/2020 12:51 am
It looks my dumb sketches have been vindicated  8)

Also, that they've attached a whole bunch of tiles says to me that they're fairly confident about the attachment mechanism, or that they're now testing some larger-scale attachment efforts - perhaps the robotic prong-attacher thingy we've seen, or simply the higher-throughput attachment of lots of things (with or without robots).

This seems like a good sign! I think we'll be able to tell something from how many of these tiles survive, as it seems less likely, given the sheer number of them, that they're testing multiple types of attachment here. But what the hell do I know!

Title: Re: Starship heat shield
Post by: eriblo on 11/17/2020 12:55 am
Some close-up shots.
Certainly looks like they have a system they want to test on a larger scale. 73 tiles on the LOX tank with 10 truncated to form a straight line (but no beveling or other transition). Tile attachment pins on the forward and common dome sections with the later seeming to have better weld settings. It seems like compensating for the overlap when stacking the sections is still on the To-Do list.
Title: Re: Starship heat shield
Post by: Nevyn72 on 11/17/2020 02:51 am
Some close-up shots.
Certainly looks like they have a system they want to test on a larger scale. 73 tiles on the LOX tank with 10 truncated to form a straight line (but no beveling or other transition). Tile attachment pins on the forward and common dome sections with the later seeming to have better weld settings. It seems like compensating for the overlap when stacking the sections is still on the To-Do list.

Bolding mine for emphasis.

Almost sounds like a system for the join line in the heat shield of a detachable nose section! ;D
Title: Re: Starship heat shield
Post by: Spaceman_From_Italy on 11/17/2020 04:51 am
Some close-up shots.
Certainly looks like they have a system they want to test on a larger scale. 73 tiles on the LOX tank with 10 truncated to form a straight line (but no beveling or other transition). Tile attachment pins on the forward and common dome sections with the later seeming to have better weld settings. It seems like compensating for the overlap when stacking the sections is still on the To-Do list.

Bolding mine for emphasis.

Almost sounds like a system for the join line in the heat shield of a detachable nose section! ;D

I still don't believe that. There are plenty of other reasons to have truncated tiles (flaps, body-flap interfaces, bottom of the ship). It seems absurd to me that such a fundamental element of design has never once been mentioned unambiguously in the updates or by Elon on Twitter or shown in renders. It also seems unreasonably complex, heavy and risky for little benefit
Title: Re: Starship heat shield
Post by: HVM on 11/17/2020 10:49 am
Better, but still; if those were floor tiles I'll would fire the contractor and send tiles back to manufacturer...
Title: Re: Starship heat shield
Post by: tyrred on 11/17/2020 11:31 am
Better, but still; if those were floor tiles I'll would fire the contractor and send tiles back to manufacturer...

Floor tiles don't stretch around a 9 meter  diameter curvature, they tend to be a bit flatter  ;)

It also doesn't help to fire the pioneering engineers who are tasked with "this hasn't been done before, iterate a bunch of designs and let's test them out"
Title: Re: Starship heat shield
Post by: DusanC on 11/17/2020 12:33 pm
Better, but still; if those were floor tiles I'll would fire the contractor and send tiles back to manufacturer...
I believe "large" tile gaps are for thermal dilatation.
Title: Re: Starship heat shield
Post by: edzieba on 11/17/2020 12:48 pm
Even in terms of regular old not-smacking-into-the-Straosphere aerodynamic effects that amount of surface unevenness is not great.
Title: Re: Starship heat shield
Post by: eriblo on 11/17/2020 02:23 pm
Even in terms of regular old not-smacking-into-the-Straosphere aerodynamic effects that amount of surface unevenness is not great.
It will not be a problem with regard to aerodynamics - have you seen the rivets, bolts, corrugations and external fittings and pipes on other launch vehicles?

The question is how it will affect the boundary layer transition and the resulting increase in heating during reentry. Only SpaceX knows what their models say -  they might be right at the limit where even the 2.5 mm difference between flat and curved tiles matter. Or they could have plenty of margin even with the equivalent of missing tiles. And nobody will take the model output as more than a rough guide line untill they are validated with plenty of real data.
Title: Re: Starship heat shield
Post by: livingjw on 11/17/2020 02:46 pm
Even in terms of regular old not-smacking-into-the-Straosphere aerodynamic effects that amount of surface unevenness is not great.
It will not be a problem with regard to aerodynamics - have you seen the rivets, bolts, corrugations and external fittings and pipes on other launch vehicles?

The question is how it will affect the boundary layer transition and the resulting increase in heating during reentry. Only SpaceX knows what their models say -  they might be right at the limit where even the 2.5 mm difference between flat and curved tiles matter. Or they could have plenty of margin even with the equivalent of missing tiles. And nobody will take the model output as more than a rough guide line untill they are validated with plenty of real data.

Boundary layer will transition very quickly. I would assume nearly complete turbulent flow once you get into significant atmosphere.

John
Title: Re: Starship heat shield
Post by: OTV Booster on 11/17/2020 03:31 pm
Some close-up shots.
Certainly looks like they have a system they want to test on a larger scale. 73 tiles on the LOX tank with 10 truncated to form a straight line (but no beveling or other transition). Tile attachment pins on the forward and common dome sections with the later seeming to have better weld settings. It seems like compensating for the overlap when stacking the sections is still on the To-Do list.

Bolding mine for emphasis.

Almost sounds like a system for the join line in the heat shield of a detachable nose section! ;D

I still don't believe that. There are plenty of other reasons to have truncated tiles (flaps, body-flap interfaces, bottom of the ship). It seems absurd to me that such a fundamental element of design has never once been mentioned unambiguously in the updates or by Elon on Twitter or shown in renders. It also seems unreasonably complex, heavy and risky for little benefit
Hey, welcome to the forum. You jump in with both feet.
Title: Re: Starship heat shield
Post by: _MECO on 11/17/2020 03:35 pm
Better, but still; if those were floor tiles I'll would fire the contractor and send tiles back to manufacturer...

Holy cow! I guess they've settled on a scalable design then  :)
Title: Re: Starship heat shield
Post by: gaballard on 11/17/2020 07:51 pm
Everything about SS development has been focused on finding out what the bare minimum they can get away with is. If emergency tile repairs have to be made off-planet, it’s good to know how imperfect they can be and still work. Starting rough and moving towards fineness is the best way to find the “sweet spot”, if you will.
Title: Re: Starship heat shield
Post by: Robotbeat on 11/17/2020 08:05 pm
Yeah, whereas they've been doing fewer high altitude test flights than I thought they would at this time, they're also making greater progress towards a real tile-based heatshield and vacuum Raptor than I thought they would by this time. And with like nearly 50 Raptors having been produced, they seem to have a large enough engine production rate that they could reasonably have a 20-some-engine Super Heavy variant ready for some sort of hot fire test or even test launch sometime in the first half of next year (and could even have the body mostly finished this year).

Slips will keep happening. Undoubtedly. But Starship has a decent chance of beating SLS, Ariane 6, New Glenn, and even Vulcan to orbit. Pretty remarkable the chance is somewhat greater than 0%.

We'll see, of course.
Title: Re: Starship heat shield
Post by: john smith 19 on 11/17/2020 09:27 pm
It will not be a problem with regard to aerodynamics - have you seen the rivets, bolts, corrugations and external fittings and pipes on other launch vehicles?
Going up, no. It's the coming back down again that this is likely to cause trouble for.
Quote from: eriblo
The question is how it will affect the boundary layer transition and the resulting increase in heating during reentry. Only SpaceX knows what their models say -  they might be right at the limit where even the 2.5 mm difference between flat and curved tiles matter. Or they could have plenty of margin even with the equivalent of missing tiles. And nobody will take the model output as more than a rough guide line untill they are validated with plenty of real data.
True.

If you believe it is better to "fail early" then you shouldn't just hope for failures, you should provoke them.

A few sticking up tiles should get that started nicely.
Title: Re: Starship heat shield
Post by: john smith 19 on 11/17/2020 09:33 pm
Boundary layer will transition very quickly. I would assume nearly complete turbulent flow once you get into significant atmosphere.

John
Given that turbulent boundary layers transfer heat to the skin 4x or more faster than laminar I think they'd like to try to keep it laminar as AFAP. And then there are possible shock/shock interactions between the canards and the body and canards and other aerosurfaces.

The contents of those tanks are going to be churning enough already with a severe temperature gradient from front windward side of the vehicle to leeward.

One thing I hadn't noticed before.  There are 2 different kinds of tile mount. The fairly substantial "posts" at about the middle of the tile width (but too many of them to be just at the actual center) and the edge ones which look sort of like tuning forks.
Title: Re: Starship heat shield
Post by: Robotbeat on 11/17/2020 09:41 pm
Tuning forks on the outside make sense to deal with thermal expansion.
Title: Re: Starship heat shield
Post by: Pheogh on 11/17/2020 09:41 pm
I noticed in Mary's pictures of SN9 showing the new tiles that the aero covers appear to be curved into the re-entry airflow which seems counter intuitive to me. Can someone explain why you would want these surface pointed into the flow instead of away like an airplane wing or the delta surfaces on shuttle? I'm sure I am missing something.
Title: Re: Starship heat shield
Post by: Crispy on 11/17/2020 09:59 pm
One thing I hadn't noticed before.  There are 2 different kinds of tile mount. The fairly substantial "posts" at about the middle of the tile width (but too many of them to be just at the actual center) and the edge ones which look sort of like tuning forks.

I don't think so. There are three posts per tile, each of which is a pair of triangular spikes, each 120° from the other.

Title: Re: Starship heat shield
Post by: Sciencefan on 11/17/2020 10:49 pm
Was it discussed why the edges of the tiles look thick but only thin black layer inside its middle?

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=51332.0;attach=1988280;image
Title: Re: Starship heat shield
Post by: marsbase on 11/17/2020 11:30 pm

If you believe it is better to "fail early" then you shouldn't just hope for failures, you should provoke them.
I guess you want to "provoke" a response?   There are a couple of principles involved.  One of them is, if you must fail, it's better to fail early.  Doesn't mean you want to fail but in an enterprise like this, some failures are inevitable. Another principle is to start with what you think is the minimal successful design.  There will be many factors to minimize such as weight, cost, ease of manufacture, durability etc. You may not be minimizing all of them at once but rather systematically working through the possibilities.  And if there is a failure you may have to move to a less than optimal design.  You do as few trade-offs as possible to get something that works.
Title: Re: Starship heat shield
Post by: DreamyPickle on 11/17/2020 11:47 pm
Why are people expecting the heat shield to looks smooth as bathroom tile? If you look at photos of the heat shield on the space shuttle they also have considerable variation:
Title: Re: Starship heat shield
Post by: eriblo on 11/18/2020 12:26 am
Was it discussed why the edges of the tiles look thick but only thin black layer inside its middle?

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=51332.0;attach=1988280;image
They seem to follow the same concept as the Space Shuttle tiles: The body of the tile is a low density porous white ceramic with a tougher black glaze-like layer on the sides and top surface. We have not seen any sign that they black surface layer extends to the bottom and most of the failures seem to stem from the white bulk material not being strong enough to stay attached to the supports.
Title: Re: Starship heat shield
Post by: eriblo on 11/18/2020 12:35 am
Why are people expecting the heat shield to looks smooth as bathroom tile? If you look at photos of the heat shield on the space shuttle they also have considerable variation:
The Shuttle tiles were (nominally) smoother than most bathroom floors -  the top surfaces were just as flat and level and the gaps were relatively narrow (although generally not "grouted"). That not to say that it had to be perfect, they often had minor (or not so minor) surface damage and gap fillers stickling out a few mm. Some of the last flights even tested the effect of a deliberate protrusion up to 0.5 inch.
Title: Re: Starship heat shield
Post by: JaimeZX on 11/18/2020 02:55 am
If you believe it is better to "fail early" then you shouldn't just hope for failures, you should provoke them.
That's FINE, but you would no doubt want to have the system heavily instrumented in the areas where you want to "provoke" failures, and probably have the areas for provocation stacked towards the end of a test flight, so you can collect as much useful data as possible with each mission. 

Then, if possible, stack the possible/intended failures in "increasing likelihood of catastrophic failure" to test your various system hypotheses up to the departure of controlled flight (or telemetry downlink).
Title: Re: Starship heat shield
Post by: Nevyn72 on 11/18/2020 04:21 am
Unfortunately that didn't take much to cause damage to the tiles.....

Just moving the tank portion of SN9 around a bit and placing it on a couple of different surfaces caused one of the tiles to crack and lose a bit of the black coating.

Image below clipped from BocaChicGal's most recent uploads.
Title: Re: Starship heat shield
Post by: awests on 11/18/2020 05:12 am
Unfortunately that didn't take much to cause damage to the tiles.....

Just moving the tank portion of SN9 around a bit and placing it on a couple of different surfaces caused one of the tiles to crack and lose a bit of the black coating.

Image below clipped from BocaChicGal's most recent uploads.
The earliest photos of the this tile arrangement on SN9 show that tile to have some damage. At this time, I don’t think we can postulate that the movement around the worksite caused this damage.
Title: Re: Starship heat shield
Post by: john smith 19 on 11/18/2020 05:58 am
Tuning forks on the outside make sense to deal with thermal expansion.
In this context possibly more like toasting forks. :)
One thing I hadn't noticed before.  There are 2 different kinds of tile mount. The fairly substantial "posts" at about the middle of the tile width (but too many of them to be just at the actual center) and the edge ones which look sort of like tuning forks.

I don't think so. There are three posts per tile, each of which is a pair of triangular spikes, each 120° from the other.
Yes it's clearer that the are all the same.
Title: Re: Starship heat shield
Post by: john smith 19 on 11/18/2020 05:58 am
I guess you want to "provoke" a response?   There are a couple of principles involved.  One of them is, if you must fail, it's better to fail early.  Doesn't mean you want to fail but in an enterprise like this, some failures are inevitable. Another principle is to start with what you think is the minimal successful design.  There will be many factors to minimize such as weight, cost, ease of manufacture, durability etc. You may not be minimizing all of them at once but rather systematically working through the possibilities.  And if there is a failure you may have to move to a less than optimal design.  You do as few trade-offs as possible to get something that works.
Ideally yes, but given the potential number of parameters and the number variants that could be a very big list. Time to run a design-of-experiements matrix to identify the minimum number of samples you need to collect maximum data

That's FINE, but you would no doubt want to have the system heavily instrumented in the areas where you want to "provoke" failures, and probably have the areas for provocation stacked towards the end of a test flight, so you can collect as much useful data as possible with each mission. 
In an ideal world yes, and that patch might well be heavily instrumented.
However this is not an aircraft. You have limited control over when this aspect will be "tested."
Quote from: JaimeZX
Then, if possible, stack the possible/intended failures in "increasing likelihood of catastrophic failure" to test your various system hypotheses up to the departure of controlled flight (or telemetry downlink).
If possible, yes. If not you have a choice. a) Test it some other way. b) Ensure this situation never happens. Ever.

a) results in messier test results but keeps the programme rolling. b) can severely limit the operating envelope of the final vehicle.  Given Musk's goals for operations that is a much bigger issue.
Title: Re: Starship heat shield
Post by: john smith 19 on 11/18/2020 06:10 am
Just a reminder that there is the "conspiracy" theory of history and the "cock-up" theory of history.

We could just be looking at a bad Friday afternoon in the tiling shop.  :(

And the decision was made "We've got to fly something. Lets do it anyway and if (or more likely when) the tile comes off we'll have learned how far we can push the installation tolerances"

When you know nothing about a situation all data is good data

And another reminder.  On this design wrapping the body (constant single axis of curvature) is the easier bit of this design. The leading edges and root-to-body transition areas are going to be much trickier. They would probably scale down the individual tiles to wrap them better. Might be enough to do the job.

Otherwise more drastic steps will be needed. Standard size (and thickness tiles are a major enabler of relatively simple tile production and vehicle repair.  Those are virtues that shouldn't be sacrifices easily.
Title: Re: Starship heat shield
Post by: DreamyPickle on 11/18/2020 06:31 am
This is clearly not going to protect against heat, it was installed for prototyping reasons.

They want to find out how the shield will survive against vibration and light aerodynamic loads and if 10% of the tiles fall off then that's just more useful data.
Title: Re: Starship heat shield
Post by: HVM on 11/18/2020 08:19 am
Why are people expecting the heat shield to looks smooth as bathroom tile? If you look at photos of the heat shield on the space shuttle they also have considerable variation:
Maybe you should show image before the first flight to be fair. I think Endeavour's tiles would put any floor tile installer in shame. (Don' look forward RCS it's seems to be mock up but rest of the tiles...)
Title: Re: Starship heat shield
Post by: edzieba on 11/18/2020 09:36 am
Why are people expecting the heat shield to looks smooth as bathroom tile? If you look at photos of the heat shield on the space shuttle they also have considerable variation:
Maybe you should show image before the first flight to be fair. I think Endeavour's tiles would put any floor tile installer in shame. (Don' look forward RCS it's seems to be mock up but rest of the tiles...)
Even post-flight, the tiles may be discoloured but the surface roughness is extremely low.
(Warped view due to phone camera, not California local space-time distortion)
Title: Re: Starship heat shield
Post by: marsbase on 11/18/2020 12:00 pm
And another reminder.  On this design wrapping the body (constant single axis of curvature) is the easier bit of this design. The leading edges and root-to-body transition areas are going to be much trickier. They would probably scale down the individual tiles to wrap them better. Might be enough to do the job.
Not disagreeing with you on this, but recently Elon has mentioned that evaporative cooling is still a possibility in some locations. He said that ITAR prevented discussion of the details.
Title: Re: Starship heat shield
Post by: TorenAltair on 11/18/2020 12:37 pm
Do you really compare an operational craft to a development model, not even a real prototype as a lot is still missing, and then critisize the heat shield solution of SpaceX?
Title: Re: Starship heat shield
Post by: envy887 on 11/18/2020 03:58 pm
Unfortunately that didn't take much to cause damage to the tiles.....

Just moving the tank portion of SN9 around a bit and placing it on a couple of different surfaces caused one of the tiles to crack and lose a bit of the black coating.

Image below clipped from BocaChicGal's most recent uploads.

It might have chipped before or during installation. "Does a chipped tile fall off during static fire or hop" seems like a fairly important question to answer.
Title: Re: Starship heat shield
Post by: john smith 19 on 11/18/2020 08:17 pm
Not disagreeing with you on this, but recently Elon has mentioned that evaporative cooling is still a possibility in some locations. He said that ITAR prevented discussion of the details.
Reaction Engines have known for years that their canards will need active cooling due to shock interference between them and either the wings or the main body.  IRC they estimated it will take about 400Kg of LH2. In terms of re entry SS is not that different.

Obviously SS won't have that and of course I'm quite sure the design team are working furiously to avoid any liquid cooling. Might be possible. Might not. 

The appearance of the first SS after the first flight to 50 Kft will make very interesting viewing.
Title: Re: Starship heat shield
Post by: northstar on 11/27/2020 10:52 pm
Not disagreeing with you on this, but recently Elon has mentioned that evaporative cooling is still a possibility in some locations. He said that ITAR prevented discussion of the details.
Reaction Engines have known for years that their canards will need active cooling due to shock interference between them and either the wings or the main body.  IRC they estimated it will take about 400Kg of LH2. In terms of re entry SS is not that different.

Obviously SS won't have that and of course I'm quite sure the design team are working furiously to avoid any liquid cooling. Might be possible. Might not. 

The appearance of the first SS after the first flight to 50 Kft will make very interesting viewing.

I don't find crumpled tinfoil that interesting myself.... ;)
Title: Re: Starship heat shield
Post by: john smith 19 on 12/03/2020 06:10 am
I don't find crumpled tinfoil that interesting myself.... ;)
As John Carmack and Armadillo Aerospace showed the exact way they crumple can be very instructive about what loads they were under and what they can survive.

Some of the tiles should be in good enough shape to see how they handled high(ish) speed as well.
Title: Re: Starship heat shield
Post by: enbandi on 12/04/2020 11:50 pm
Seems like additional/alternative methods will be tested, involving sprayed/coated heat shield material. The attached document is an environmental permit (registration) for a coating process at SpaceX Boca Chica site. Among a ton of administrative details two materials to be used described:

Quote
SpaceX Toughened Unipiece Fibrous Insulation (TUFI) Slurry
MANUFACTURER: Space Exploration Technologies
8550 Astronaut Blvd.
Cape Canaveral, FL 32920
INTENDED USE: Thermal Protection Insulation

Quote
SpaceX Reaction Cured Glass (RCG)
MANUFACTURER: Space Exploration Technologies
8550 Astronaut Blvd.
Cape Canaveral, FL 32920
INTENDED USE: Thermal Protection Tile Coating

8550 Astronaut at Canaveral is their "Starship Tile Facility".
Title: Re: Starship heat shield
Post by: MD on 12/05/2020 02:39 am
Seems like additional/alternative methods will be tested, involving sprayed/coated heat shield material. The attached document is an environmental permit (registration) for a coating process at SpaceX Boca Chica site. Among a ton of administrative details two materials to be used described:

Quote
SpaceX Toughened Unipiece Fibrous Insulation (TUFI) Slurry
MANUFACTURER: Space Exploration Technologies
8550 Astronaut Blvd.
Cape Canaveral, FL 32920
INTENDED USE: Thermal Protection Insulation

Quote
SpaceX Reaction Cured Glass (RCG)
MANUFACTURER: Space Exploration Technologies
8550 Astronaut Blvd.
Cape Canaveral, FL 32920
INTENDED USE: Thermal Protection Tile Coating

8550 Astronaut at Canaveral is their "Starship Tile Facility".

Thanks, enbandi, for the .pdf attached to your post.
"AIR NSR_163215-321866_Permits_Public_20201201_Applications_5466877_.pdf"

My reading of this permit application does not indicate a use for starship, but rather GSE.
The two above quotes are from Safety Data Sheets that are included in the Supporting Information section of the application.
Here is the Process Description section of the same application.

Quote
SpaceX is proposing unenclosed surface coating operations at the site (EPN SURF-1). Carbon steel
(i.e., A36, A500, A572, etc.) materials will be coated within a painting tent with the option to vent
directly to the atmosphere or through a three-walled water wash filter. Coatings will be applied
using high-volume low-pressure (HVLP) spray guns (assuming a transfer efficiency of 65%) and
will be allowed to air dry once applied. Emissions calculations have conservatively been
estimated assuming no control from the water wash filter.

Emissions will include volatile organic compounds (VOCs), particulate matter (PM), and
hazardous air pollutants (HAPs).

So unless SpaceX will make tiles out of carbon steel, (which I guess they could), this application is not for the heat shield tiles of starship. Maybe for the OLP. Maybe this is part of SpaceX's attempt to avoid having a flame diverter.
Title: Re: Starship heat shield
Post by: enbandi on 12/05/2020 03:57 pm
Speaking about the tile facility, this is from a recent inspection report:

Quote
The facility employs approximately 20 people and has been operating at this location since 2019. Operating
hours are 24 hours a day, seven days a week working three shifts. Brevard County provides potable water and
sanitary sewer services. The property is owned by Cape Canaveral Joint Venture, 516 Delannoy Ave., Cocoa, Florida 32922.

INSPECTION HISTORY
The facility has never been inspected by the Department for compliance with state and federal hazardous waste
regulations.

Process Description:
An opening conference was held to discuss the purpose of the inspection, and processes performed and wastes
generated at the facility.
The facility operates in a 40,000 square-foot unit of the building to manufacture heat-shield tiles for Space
Exploration Technologies Corp's Starship vehicle. Current facility operations are performing process
improvements of the tiles. Production of the final tiles is slated for end of year 2020.

Processes at the facility include:
 - Slurry Mix-casting billets, one billet will make two tiles;
 - Cast-sintering billets;
 - Machining-create tiles from billet and shape tiles into desired form;
 - Coatings-apply two coatings to tiles;
 - Kiln-dry tiles;
 - Water proofing-drive out water from tiles and apply a coating; and
 - Hardware-final assembly of tile.

INSPECTION NARRATIVE
The inspection began in Casting. Purified silicon is added to a tank where a slurry is made. When the slurry is
at the proper consistency it is distributed to the casting molds to create the billet. A vacuum is applied to the
case to remove excess water. The water is reused to make slurry.

A kiln is used to dry the billet. After drying, the billet is split in two pieces thereby creating the rudimentary tiles.
The tiles are shaped to the desired form using a router. A shop vacuum is used to clean up silicone from the
router. In this area were satellite accumulation areas: one for a 30-gallon drum of hazardous waste isopropyl
alcohol (IPA) solids, one for a 55-gallon drum of hazardous waste aerosol cans, and one for a 55-gallon drum of
hazardous waste two-part epoxy. The drums were properly labeled "Hazardous Waste" and were closed. None
of the containers were marked with the hazards of the contents [40 CFR 262.15(a)(5)(ii)]. Also in the area was a
55-gallon drum of non-hazardous waste petroleum contact solids.

Emergency equipment noted in the area included a spill kit and eye wash station.

A coating is manufactured and applied to the tiles. An automated machine applies the coating. The final coating
that will be applied to the tiles is still undergoing development. In this area were satellite accumulation areas:
one for a 55-gallon drum of hazardous waste paint liquids and another for a 55-gallon drum of hazardous waste
paint solids. The drums were properly labeled "Hazardous Waste", marked with the hazards of the contents,
and were closed. The wastes are generated from maintenance of the coating equipment. Also in the area was
a 55-gallon drum of non-hazardous waste petroleum contact solids and a 30-gallon drum of non-hazardous
waste frit and water. The petroleum contact solids are an oily debris waste generated from equipment
maintenance. The frit and water are generated from drying slurry.

In the water proofing process, a mixture of methyl-trimethoxy silane (MTMS) and acetic acid is applied to seal
the tiles.

Florida Department of Environmental Protection
Pre-Arranged Inspection for LQG (>1000 kg/month) Facility
Space Exploration Technologies DBA Starship Tile Facility
09/23/2020
Title: Re: Starship heat shield
Post by: livingjw on 12/05/2020 05:33 pm
More evidence that SpaceX is planning on mechanically attached, shuttle and X-37 derived tile. They appear to be co-curing mechanical attachment fittings into the AETB blocks.

Attached a good summary of variations of tile and leading edge systems derived from shuttle and currently used on X-37.

John
Title: Re: Starship heat shield
Post by: oldAtlas_Eguy on 12/05/2020 10:53 pm
The other item from this report is the start of production scale operations: late 2020/beginning 2021. The then remaining question is how long it will take to produce a 50% of SS surface area set of tiles? If they plan on being able to do a complete set every month that will be quite a production line upgrade from the infrastructure/equipment described in the report.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 12/06/2020 03:55 am
More evidence that SpaceX is planning on mechanically attached, shuttle and X-37 derived tile. They appear to be co-curing mechanical attachment fittings into the AETB blocks.

Attached a good summary of variations of tile and leading edge systems derived from shuttle and currently used on X-37.

John

Notice the X-37 is encapsulated in a fairing at launch, somewhat isolated from the vibrations of the launch vehicle.

i wonder whether the X-37 heat shields can stand the full vibration of 6 raptors firing nearby (and 28-ish firing 70 meters back)
Title: Re: Starship heat shield
Post by: edzieba on 12/06/2020 02:09 pm
That really does sound very similar to the STS tiles: Sintered Silica fibre base, reaction-cured-glass coating, then Silane + Acetic acid waterproofing (methyl-trimethoxy silane rather than dimethylethoxy silane though).

Not really a surprise: start with a high TRL tile you know works to get a suboptimal but working solution, and use operationally that while you R&D a better solution.
Title: Re: Starship heat shield
Post by: Hog on 12/07/2020 01:42 pm
TRL=Technology Readiness Level

The higher the number, the more mature a technology is.

https://en.wikipedia.org/wiki/Technology_readiness_level
Title: Re: Starship heat shield
Post by: launchwatcher on 12/08/2020 01:13 pm
TRL=Technology Readiness Level

The higher the number, the more mature a technology is.

https://en.wikipedia.org/wiki/Technology_readiness_level
Alternatively (from https://www.granttremblay.com/blog/trls)..

Title: Re: Starship heat shield
Post by: Faerwald on 12/10/2020 04:02 am
I believe that on the belly flop video from spacex twitter the heat shield still looks intact just as the engines relight.
I just can't get a good screenshot at the moment.
Title: Re: Starship heat shield
Post by: AJW on 12/10/2020 08:55 am
I can't say this is definitive, but it appears that the tiles may have been intact after launch.  SpaceX may be able to tick off another success checkbox.

First photo is from Jack Beyer's mega-pixel photo. 
Second is SpaceX flight video during the descent.
Third is from the first-person descent cam, and the descent cam with color adjust.

Title: Re: Starship heat shield
Post by: HVM on 12/10/2020 12:19 pm
First I read "...but it appears that the tiles may have been intact after flight." pretty sure they are not...

But you're right, those tiles seem to stick. Next we need to know; do they work as a thermal protection system.
Title: Re: Starship heat shield
Post by: DreamyPickle on 12/10/2020 12:25 pm
At this point is it safe to say that the heat shield is the most difficult technical problem remaining on Starship?

The aerodynamics have been shown to work and the flight envelope can be expanded, but dealing with actual re-entry heating is still unproven.
Title: Re: Starship heat shield
Post by: AJW on 12/10/2020 02:06 pm
Another good image of the tiles during flight, this one from just before the shut down of the first engine.  Credit: NickyX15A on YouTube.

Title: Re: Starship heat shield
Post by: Nomadd on 12/10/2020 02:36 pm
At this point is it safe to say that the heat shield is the most difficult technical problem remaining on Starship?

The aerodynamics have been shown to work and the flight envelope can be expanded, but dealing with actual re-entry heating is still unproven.
  I'd say so. My biggest concern was engines restarting after all the acrobatics, but that seems to have gone pretty well.
 Other that the heat shield, just about everything else seems to be details.
Title: Re: Starship heat shield
Post by: guckyfan on 12/10/2020 02:47 pm
I have no doubt they can make heat shield tiles that are up to the task of thermal protection, at least for LEO reentry. What we need to see is a method of mounting them, simple and efficient. Not like the early ones we saw dropping off during static fires or short hops. Seems the few on SN8 did hold until the crash but do they hold repeated stresses?
Title: Re: Starship heat shield
Post by: wannamoonbase on 12/10/2020 02:58 pm
At this point is it safe to say that the heat shield is the most difficult technical problem remaining on Starship?

The aerodynamics have been shown to work and the flight envelope can be expanded, but dealing with actual re-entry heating is still unproven.
  I'd say so. My biggest concern was engines restarting after all the acrobatics, but that seems to have gone pretty well.
 Other that the heat shield, just about everything else seems to be details.

Really intense details, there is plenty of engineering left, but I agree, it doesn't seem impossible.

The heat shield, they'll figure out some way for one to work.  Whether their first trys work or not, it is the biggest remaining risk.

I love that Elon doesn't wait for perfect and keeps improving.  It took a decade or more to get Falcon 9 into the Block 5 configuration.  Starship can be flying, earning it's keep with Starlink and payload delivery all while being constantly improved. 

As the saying goes, you will over estimate what you can do in 1 year and under estimate what you can do in 10 years.  I think Elon's 2 year goals are unreasonable, but 10 years, yeah they could be doing all of them.

Fully reusable 2 stage, dam, it's actually going to happen.
Title: Re: Starship heat shield
Post by: AJW on 12/10/2020 04:59 pm
Someone had suggested that the flaps/elonerons might not need tiles if they were folded when reentering the atmosphere.  This photo taken during the flip gives a clear view of airflow crossing the supporting structures and the flaps at low speed.
Title: Re: Starship heat shield
Post by: Cheapchips on 12/10/2020 05:45 pm
Someone had suggested that the flaps/elonerons might not need tiles if they were folded when reentering the atmosphere.  This photo taken during the flip gives a clear view of airflow crossing the supporting structures and the flaps at low speed.

I thought the whole point was to wiggle them around in the airflow to control reentry?
Title: Re: Starship heat shield
Post by: Lars-J on 12/10/2020 06:38 pm
Someone had suggested that the flaps/elonerons might not need tiles if they were folded when reentering the atmosphere.  This photo taken during the flip gives a clear view of airflow crossing the supporting structures and the flaps at low speed.

That is missing the point, though.... they will not be folded all the way during re-entry. Depending on the payload and mass distribution during re-entry, and the phases of flight, the fins could be folded back all the way or extended all the way.
Title: Re: Starship heat shield
Post by: equiserre on 12/10/2020 06:54 pm
Someone had suggested that the flaps/elonerons might not need tiles if they were folded when reentering the atmosphere.  This photo taken during the flip gives a clear view of airflow crossing the supporting structures and the flaps at low speed.

That is missing the point, though.... they will not be folded all the way during re-entry. Depending on the payload and mass distribution during re-entry, and the phases of flight, the fins could be folded back all the way or extended all the way.

You are describing only one function of the fins: trim for CG location. But they are also needed to actively control the trajectory. The will be moving around all the time. See Spacex reentry simulations.

That is why it is also wrong to say the fins are there to provide more surface area. No, they are a minor fraction of the total surface area. The ballistic coefficient is provided by the whole bulk of the body sideways to the flow. The fins only for trim plus pitch, yaw, roll.
Title: Re: Starship heat shield
Post by: vaporcobra on 12/11/2020 06:36 pm
At this point is it safe to say that the heat shield is the most difficult technical problem remaining on Starship?

The aerodynamics have been shown to work and the flight envelope can be expanded, but dealing with actual re-entry heating is still unproven.
  I'd say so. My biggest concern was engines restarting after all the acrobatics, but that seems to have gone pretty well.
 Other that the heat shield, just about everything else seems to be details.

Plus Raptor seemingly performing great during an almost five-minute continuous burn! :D I'm definitely on the heat shield train after that success. But even then, Starship is or will be the first full-scale hot structure reentry vehicle ever built or tested, which could potentially make the heat shield problem much easier to solve. If that's the case, sealing the flap-hinge gap is probably the hardest remaining problem for Starship

Would be very interesting to get a general sense of how tolerant of limited tile failures, tile gaps, imperfect reentry AoA, etc Starship will be with a ~100% steel hull.
Title: Re: Starship heat shield
Post by: CJ on 12/12/2020 10:56 pm
Elon Musk just tweeted something about heat shields;

Quote
Replying to @PPathole @ErcXspace @SpaceX
I still have a soft spot in my heart for transpiration cooking. In theory, it would use more mass than a tile heatshield, but that remains to be seen.

 Replying to @PPathole @ErcXspace @SpaceX
*cooling haha
View conversation · Reply Retweet Like
Elon Musk    Elon Musk
@elonmusk
   7h

This seems to indicate (IMHO) that transpiration cooling is still under consideration, though perhaps as a backup method in case tiles don't work out.


 

Title: Re: Starship heat shield
Post by: freddo411 on 12/13/2020 03:43 am
The shuttle had a moving tail flap.   So there is already an existence proof of at least one way to solve moving reentry parts
Title: Re: Starship heat shield
Post by: GetCrispy on 12/13/2020 03:53 am
The shuttle had a moving tail flap.   So there is already an existence proof of at least one way to solve moving reentry parts

Wasn’t the tail of the shuttle almost completely occluded from the airstream due tue the entry angle? Whereas Starship will require the heat shield to be directly exposed to the airstream for the entire entry duration.
Title: Re: Starship heat shield
Post by: KelvinZero on 12/13/2020 04:40 am
If that's the case, sealing the flap-hinge gap is probably the hardest remaining problem for Starship

Would be very interesting to get a general sense of how tolerant of limited tile failures, tile gaps, imperfect reentry AoA, etc Starship will be with a ~100% steel hull.
Just a layman's idea: if there was a pressurised layer behind the tiles then instead of plasma pushing in you could get cold gas pushing out and thus get concentrated transpiration cooling on just that crack.. which presumably would only use a very small budget of gas if an entire-hull transpiration based system is even halfway plausible.
Title: Re: Starship heat shield
Post by: alastairmayer on 12/13/2020 06:29 am
The shuttle had a moving tail flap.   So there is already an existence proof of at least one way to solve moving reentry parts

Wasn’t the tail of the shuttle almost completely occluded from the airstream due tue the entry angle? Whereas Starship will require the heat shield to be directly exposed to the airstream for the entire entry duration.

Yeah, parent likely meant the Shuttle body flap at the aft end, which also served to protect the engine bells.
Title: Re: Starship heat shield
Post by: Terra Incognita on 12/13/2020 08:09 pm
If that's the case, sealing the flap-hinge gap is probably the hardest remaining problem for Starship

Would be very interesting to get a general sense of how tolerant of limited tile failures, tile gaps, imperfect reentry AoA, etc Starship will be with a ~100% steel hull.
Just a layman's idea: if there was a pressurised layer behind the tiles then instead of plasma pushing in you could get cold gas pushing out and thus get concentrated transpiration cooling on just that crack.. which presumably would only use a very small budget of gas if an entire-hull transpiration based system is even halfway plausible.

I'm not sure why the Raptors have to continuously vent cold gas during the flight but could this existing venting be used to provide some meaningful protection for the Flaperons?
Title: Re: Starship heat shield
Post by: docmordrid on 12/13/2020 09:39 pm
Another good image of the tiles during flight, this one from just before the shut down of the first engine.  Credit: NickyX15A on YouTube.

My small tweak

Title: Re: Starship heat shield
Post by: BigDustyman on 12/14/2020 03:53 pm
Could they use flexible blanket material like on upper surfaces of shuttle
Title: Re: Starship heat shield
Post by: Taxidermista on 12/15/2020 07:25 am
From the Steve Jurvetson twitter account, posted yesterday:

"New Starship Prototype with Heat Shield stud mounts for Orbital Reentry."

(https://previews.dropbox.com/p/thumb/ABDkszyz7eFWzueBNhewj4wmkgwK8Qy6Ug0ldEdcOYL_ALXrwLaMSs_t3gePqsP5SG8fmKyfEWeJ8wCGdoeZwxaMBw8689RhcU7IYDZPqD332YKNbaJuIE8lc12nztBPq6FMw1c-VqaeZL8Dz3-ACcTnouOjJmUiHLThJR1HNFgFvwcXDfhQbAWhpUGlYOdlOL9uF6NS7Q8udVlWjTNwSwB9TWvUcjfXtHfmktMihSNBtYFSySydl40zLZTpmkPl0gqSm7iEKthMW8wxXRgMeJrvZwMUwqvRtU7gqF4zbPTiezGQ78up4kRKZkz5Ozb7KP-kBztQe8QU9xyZPg-iSIRnuY5XEVURIYNKyf64YXzt_g/p.jpeg?fv_content=true&size_mode=5)
Title: Re: Starship heat shield
Post by: Crispy on 12/15/2020 07:41 am
https://twitter.com/FutureJurvetson/status/1337960795615850497

Photo in question:
Title: Re: Starship heat shield
Post by: Corvus Corax on 12/15/2020 02:11 pm
Slightly OT, but that ring weld looks absolutely perfect. Amazing.

I'm very curious how that heat tile attachment system works. It looks like each one is hinged at the attachment point to reduce vibration/flex stress.
Title: Re: Starship heat shield
Post by: DreamyPickle on 12/15/2020 02:31 pm
How does this compare to tile attachment systems on previous vehicles? My impression is that they were based on adhesives rather than mechanical fasteners.
Title: Re: Starship heat shield
Post by: Corvus Corax on 12/19/2020 02:22 pm
The brackets have an interesting asymmetrical structure to them. The plates/fins have inconsistent thickness along their length. It looks to me as though they are meant to bend toward each other to facilitate insertion and then spring back into a home position that captures a female receptacle.

Of particular interest, to me, is what the heck are those asymmetrically positioned posts that protrude into the space between the plates/fins?
Title: Re: Starship heat shield
Post by: Nomadd on 12/19/2020 03:23 pm
The brackets have an interesting asymmetrical structure to them. The plates/fins have inconsistent thickness along their length. It looks to me as though they are meant to bend toward each other to facilitate insertion and then spring back into a home position that captures a female receptacle.

Of particular interest, to me, is what the heck are those asymmetrically positioned posts that protrude into the space between the plates/fins?
I'd assumed the opposite, but the tips are ramped on the outside and the inside, so it's hard to tell. I'm trying to picture some sort of double capture mechanism.
 Something like a tapered cylinder with a pin across the opening, so the pin slides past the built up parts the same time the taper in the cylinder forces the end closed.
Title: Re: Starship heat shield
Post by: eriblo on 12/19/2020 04:11 pm
[...]
Of particular interest, to me, is what the heck are those asymmetrically positioned posts that protrude into the space between the plates/fins?
Where do you see those? The pins in Jurvetsons photo are all the symmetrical groupings of 3 spaced every 30 cm (long diameter).
Title: Re: Starship heat shield
Post by: Corvus Corax on 12/19/2020 04:47 pm
[...]
Of particular interest, to me, is what the heck are those asymmetrically positioned posts that protrude into the space between the plates/fins?
Where do you see those? The pins in Jurvetsons photo are all the symmetrical groupings of 3 spaced every 30 cm (long diameter).

I'm talking specifically on a single mounting pin, not the grouping of three. If you look at the zoomed in picture I posted, you'll see that it consists of two blades/fins parallel to one another. Each blade has several surface features of interest.

The first is that there are chamfered protrusions extending outwards from each blade/fin. To my eye, it looks as though they are intended to lock the tile in place by bending inwards until some female receptacle captures them and subsequently allow the blades to spring back to their parallel position.

The second is that there are small horizontally opposed pins/cylinders that extend toward the opposing blade from the inside. They are asymmetrically mounted. I'm curious about what their purpose is.

The third is that there are small cutaways in the bracket plane, near the top, when you look at them from the side.
Title: Re: Starship heat shield
Post by: eriblo on 12/19/2020 05:34 pm
[...]
Of particular interest, to me, is what the heck are those asymmetrically positioned posts that protrude into the space between the plates/fins?
Where do you see those? The pins in Jurvetsons photo are all the symmetrical groupings of 3 spaced every 30 cm (long diameter).

I'm talking specifically on a single mounting pin, not the grouping of three. If you look at the zoomed in picture I posted, you'll see that it consists of two blades/fins parallel to one another. Each blade has several surface features of interest.

The first is that there are chamfered protrusions extending outwards from each blade/fin. To my eye, it looks as though they are intended to lock the tile in place by bending inwards until some female receptacle captures them and subsequently allow the blades to spring back to their parallel position.

The second is that there are small horizontally opposed pins/cylinders that extend toward the opposing blade from the inside. They are asymmetrically mounted. I'm curious about what their purpose is.

The third is that there are small cutaways in the bracket plane, near the top, when you look at them from the side.
Ah, sorry - I read through that too quickly and thought you were talking about extra pins (posts) in between the tiles (plates).

Otherwise I mostly agree although I think that the two "blades/plates" of each pin are more or less symmetrical for the same reason that there are two: to ensure that any vibration or movement in one direction that might loosen the grip of a single one makes the second one hold more securely. My impression from the not quite resolved pictures we have is that the two blades end in opposing and overlapping hooks that can grip a single transverse bar in the middle like a mixed overhand/underhand barbell grip.
Title: Re: Starship heat shield
Post by: Jcc on 12/19/2020 06:43 pm
Hard to tell exactly how long these blades/pins are, but it seems about 5 centimeters or so. If they latch to an internal structure inside the tile and don't reach the surface of the tile, that implies the tiles are a bit thicker than the blades/pins are long, which is surprising, because early prototypes looked thinner than that. Or else, the tiles might not actually be in contact with the tank but that seems unlikely because they would vibrate.

Thoughts?
Title: Re: Starship heat shield
Post by: eriblo on 12/19/2020 06:48 pm
Hard to tell exactly how long these blades/pins are, but it seems about 5 centimeters or so. If they latch to an internal structure inside the tile and don't reach the surface of the tile, that implies the tiles are a bit thicker than the blades/pins are long, which is surprising, because early prototypes looked thinner than that. Or else, the tiles might not actually be in contact with the tank but that seems unlikely because they would vibrate.

Thoughts?
There is (or was at one point at least) a "marshmallows-looking" rope seal in between the bottom of the tiles and surface.
Title: Re: Starship heat shield
Post by: vulture4 on 12/19/2020 07:06 pm
It looks to me as though the outer sides of the pins engage the inside of a metal ring in the tile; some sets of pins seem at random orientations making it hard to see how a bar between the pins would be gripped. The tiles are fairly thick and there may be a gap between the tile inner surface and the steel hull.
Title: Re: Starship heat shield
Post by: livingjw on 12/19/2020 07:22 pm
It looks to me as though the outer sides of the pins engage the inside of a metal ring in the tile; some sets of pins seem at random orientations making it hard to see how a bar between the pins would be gripped. The tiles are fairly thick and there may be a gap between the tile inner surface and the steel hull.

Pretty sure they sit on a felt pad.

John
Title: Re: Starship heat shield
Post by: daavery on 12/19/2020 07:53 pm
it looks to me like each of the pins in a set of 3 pins are orientated 120 deg from each other
Title: Re: Starship heat shield
Post by: john smith 19 on 12/19/2020 07:54 pm
[...]
Of particular interest, to me, is what the heck are those asymmetrically positioned posts that protrude into the space between the plates/fins?
Where do you see those? The pins in Jurvetsons photo are all the symmetrical groupings of 3 spaced every 30 cm (long diameter).

I'm talking specifically on a single mounting pin, not the grouping of three. If you look at the zoomed in picture I posted, you'll see that it consists of two blades/fins parallel to one another. Each blade has several surface features of interest.

The first is that there are chamfered protrusions extending outwards from each blade/fin. To my eye, it looks as though they are intended to lock the tile in place by bending inwards until some female receptacle captures them and subsequently allow the blades to spring back to their parallel position.

The second is that there are small horizontally opposed pins/cylinders that extend toward the opposing blade from the inside. They are asymmetrically mounted. I'm curious about what their purpose is.

The third is that there are small cutaways in the bracket plane, near the top, when you look at them from the side.
I'm thinking snap fit arrangement of some kind. The two "spades" wrapping around a bar of ceramic. Since ceramics are very stiff pretty much any bending would have to be taken up by the metal parts.
Title: Re: Starship heat shield
Post by: john smith 19 on 12/19/2020 07:55 pm
it looks to me like each of the pins in a set of 3 pins are orientated 120 deg from each other
They are.
Title: Re: Starship heat shield
Post by: HVM on 12/19/2020 07:59 pm
Just for reminder, broken tile from SN8. We can see structure inside tile where tile-side weld stud lock sits:
(Did falling tile fractures take the felt pad with them, or is it missing at all)
Title: Re: Starship heat shield
Post by: Rekt1971 on 12/19/2020 08:13 pm
Not sure if it has been discussed here before but it looks like SN10 fin has some attachment points for heatshield tiles.

Credit: Nomadd
Title: Re: Starship heat shield
Post by: jthygesen on 12/19/2020 08:45 pm
Not sure if it has been discussed here before but it looks like SN10 fin has some attachment points for heatshield tiles.

Credit: Nomadd

Yes and if I’m decoding those triangle patterns correctly it looks as if it might get two different kinds of tile. At least I think I see two sizes of triangles.
Title: Re: Starship heat shield
Post by: xvel on 12/19/2020 08:58 pm
Not sure if it has been discussed here before but it looks like SN10 fin has some attachment points for heatshield tiles.

Credit: Nomadd

Yes and if I’m decoding those triangle patterns correctly it looks as if it might get two different kinds of tile. At least I think I see two sizes of triangles.

Correct, and this is not the first time
SN5
(https://pbs.twimg.com/media/EZxmcnVXsAAhqTO.jpg)
Title: Re: Starship heat shield
Post by: Jcc on 12/20/2020 03:16 pm
It looks to me as though the outer sides of the pins engage the inside of a metal ring in the tile; some sets of pins seem at random orientations making it hard to see how a bar between the pins would be gripped. The tiles are fairly thick and there may be a gap between the tile inner surface and the steel hull.

Pretty sure they sit on a felt pad.

John

A felt pad makes sense since the backing should be somewhat compressible. In order to latch, the hook needs to reach a bit beyond the bar it hooks onto, then settle back, and still be snug to not vibrate. Also this allows some variation in tolerances, including due to thermal expansion, and still latch reliably.
Title: Re: Starship heat shield
Post by: Wolfram66 on 12/20/2020 04:13 pm
Not sure if it has been discussed here before but it looks like SN10 fin has some attachment points for heatshield tiles.

Credit: Nomadd

Someone had mentioned why they were on the leeward side if fin and not the heating side.
This is a test of the mechanics of attachment to the Elonerons and not a test of protection.
Testing tile connections on leeward side is to test vibration intensity during launch and ascent.
Leeward side may also protects the tile vibration results from face on airflow during descent .
Incremental testing of each test case. When they’re happy with the vibration and durability test, they will put them on windward side.

My 2 cents
Title: Re: Starship heat shield
Post by: Corvus Corax on 12/20/2020 04:23 pm
Not sure if it has been discussed here before but it looks like SN10 fin has some attachment points for heatshield tiles.

Credit: Nomadd

Someone had mentioned why they were on the leeward side if fin and not the heating side.
This is a test of the mechanics of attachment to the Elonerons and not a test of protection.
Testing tile connections on leeward side is to test vibration intensity during launch and ascent.
Leeward side may also protects the tile vibration results from face on airflow during descent .
Incremental testing of each test case. When they’re happy with the vibration and durability test, they will put them on windward side.

My 2 cents

Either that, or some poor guy has just been fired...
Title: Re: Starship heat shield
Post by: Nomadd on 12/20/2020 04:45 pm
 There are probably fifty factors I'm not considering, but I can see where it could be harder keeping tiles on the leeward side of the flaps if turbulance is a major issue.
Title: Re: Starship heat shield
Post by: chopsticks on 12/20/2020 05:02 pm
Perhaps there would be less risk of damage to the leading edge (windward side) if a tile would fall off and impact the lower fin.

Sent from my Redmi Note 7 using Tapatalk

Title: Re: Starship heat shield
Post by: Slarty1080 on 12/21/2020 09:42 am
Perhaps there would be less risk of damage to the leading edge (windward side) if a tile would fall off and impact the lower fin.

Sent from my Redmi Note 7 using Tapatalk
Perhaps there's less effect on the airflow over the fin, so less turbulence. The whole of Starship is a bit of a balancing act so they might well want to avoid extra turbulence especially on the control surfaces.
Title: Re: Starship heat shield
Post by: john smith 19 on 12/21/2020 04:08 pm
Just for reminder, broken tile from SN8. We can see structure inside tile where tile-side weld stud lock sits:
(Did falling tile fractures take the felt pad with them, or is it missing at all)
So it looks like the "spades" grasp those short cross bars.

It's really quite a complex internal structure that needs to be baked in.
Title: Re: Starship heat shield
Post by: john smith 19 on 12/21/2020 04:11 pm
It looks to me as though the outer sides of the pins engage the inside of a metal ring in the tile; some sets of pins seem at random orientations making it hard to see how a bar between the pins would be gripped. The tiles are fairly thick and there may be a gap between the tile inner surface and the steel hull.

Pretty sure they sit on a felt pad.

John

A felt pad makes sense since the backing should be somewhat compressible. In order to latch, the hook needs to reach a bit beyond the bar it hooks onto, then settle back, and still be snug to not vibrate. Also this allows some variation in tolerances, including due to thermal expansion, and still latch reliably.
Felt pad inside the tile. OK that makes sens but these things are starting to get really complex.  :( :(
Title: Re: Starship heat shield
Post by: InterestedEngineer on 12/29/2020 04:43 pm
Felt pad inside the tile. OK that makes sens but these things are starting to get really complex.  :( :(

Tile has been layered over a surface that decouples movement of the underlying structure from the tiles for thousands of years.

Not that complicated

Edit/Lar: Fix quotes
Title: Re: Starship heat shield
Post by: wannamoonbase on 12/29/2020 04:53 pm
There are probably fifty factors I'm not considering, but I can see where it could be harder keeping tiles on the leeward side of the flaps if turbulance is a major issue.

Build, fly, discover.

Tiles around edges of control surfaces and the termination of the tile covering on the vehicle I think will be interesting.

In areas where tiles aren't the standard hexagon, do they make tiles as large as possible?
Title: Re: Starship heat shield
Post by: john smith 19 on 12/30/2020 06:07 am
Quote from: John Smith 19
Felt pad inside the tile. OK that makes sens but these things are starting to get really complex.  :( :(

Tile has been layered over a surface that decouples movement of the underlying structure from the tiles for thousands of years.

Not that complicated
As long as the structure a) Doesn't have serious weight limits b) Doesn't have to hold one (or more) l atmospheres of pressure,  c) Operate with an inside to outside delta T of up to 1200-1400c d) Has no exposure to high speed air flow that will cause buffeting and could cause resonance  then I'd agree with you.

AFAIK The structures that have had to face all of those conditions would be Buran and Shuttle (the X37b is in a shroud on ascent). I can't think of any others

And SS requires fast turnaround for frequent reuse. Buran was never launched again and shuttle turnaround was far from rapid.

When you factor those requirements in you end up with the tile designs we have been seeing. However I'm pretty sure the design is still evolving, although I've no idea what to.

So 2021 looks to be pretty exciting for the TPS design and mfg team.  :)
Title: Re: Starship heat shield
Post by: Nomadd on 12/30/2020 06:25 pm
 Trying for some detail, but I don't have the lens or the skill of what's her name.
 SN9
Title: Re: Starship heat shield
Post by: HVM on 12/30/2020 08:25 pm
I don't see felt pad here, only uncoated white part of the tile. It is possible that the y-shaped structure (seen inside of the broken tile) is designed to take strain of the silicon tile and no felt pad is needed?
Title: Re: Starship heat shield
Post by: livingjw on 12/31/2020 12:12 am
I don't see felt pad here, only uncoated white part of the tile. It is possible that the y-shaped structure (seen inside of the broken tile) is designed to take strain of the silicon tile and no felt pad is needed?

And other tiles look like there is felt (at least as gap filler) around the outside.

John
Title: Re: Starship heat shield
Post by: Robotbeat on 12/31/2020 12:17 am
I don't see felt pad here, only uncoated white part of the tile. It is possible that the y-shaped structure (seen inside of the broken tile) is designed to take strain of the silicon tile and no felt pad is needed?

And other tiles look like there is felt (at least as gap filler) around the outside.

John
The picture is saturated. What's the white material on the backside of the tiles?
Title: Re: Starship heat shield
Post by: livingjw on 12/31/2020 12:32 am
I don't see felt pad here, only uncoated white part of the tile. It is possible that the y-shaped structure (seen inside of the broken tile) is designed to take strain of the silicon tile and no felt pad is needed?

And other tiles look like there is felt (at least as gap filler) around the outside.

John
The picture is saturated. What's the white material on the backside of the tiles?

As HVM pointed out, the tile's glassy outer shell only extends part way down the hexagonal insulation block. It looks like at least some of the tile have an undercut around their edge where felt or gap fillers can be placed.

John
Title: Re: Starship heat shield
Post by: cdebuhr on 12/31/2020 12:32 am
I don't see felt pad here, only uncoated white part of the tile. It is possible that the y-shaped structure (seen inside of the broken tile) is designed to take strain of the silicon tile and no felt pad is needed?

And other tiles look like there is felt (at least as gap filler) around the outside.

John
The picture is saturated. What's the white material on the backside of the tiles?
The black tiles are quite regular, whereas the white layer is quite irregular and doesn't always match up well with the edges of the black part.  To my eye, it looks like these layers are in fact two separate items:  the outer layer consists of the black tiles that appear to be consistently identical to a reasonable tolerance, whereas the inner layer consists of separate white felt (?) pads that are quite roughly cut out and only approximately match the footprint of their corresponding tiles.

That's what it looks like to me anyway.  As to why one would do it this way, or if this even makes any sense, I leave to those who know what they're actually talking about.
Title: Re: Starship heat shield
Post by: Nevyn72 on 12/31/2020 06:04 am
I don't see felt pad here, only uncoated white part of the tile. It is possible that the y-shaped structure (seen inside of the broken tile) is designed to take strain of the silicon tile and no felt pad is needed?

And other tiles look like there is felt (at least as gap filler) around the outside.

John
The picture is saturated. What's the white material on the backside of the tiles?
The black tiles are quite regular, whereas the white layer is quite irregular and doesn't always match up well with the edges of the black part.  To my eye, it looks like these layers are in fact two separate items:  the outer layer consists of the black tiles that appear to be consistently identical to a reasonable tolerance, whereas the inner layer consists of separate white felt (?) pads that are quite roughly cut out and only approximately match the footprint of their corresponding tiles.

That's what it looks like to me anyway.  As to why one would do it this way, or if this even makes any sense, I leave to those who know what they're actually talking about.

This is pretty close however I would differ on the lower white level.

It almost appears the lower white level is a thick felt pad to cushion the black tile against the steel skin with the locking pins compressing the black section against the white. Each of these pads is matching in size but offset a little bit so it extends underneath the adjacent tile as it is installed.

Thus each tile overlaps the felt of the adjacent tile to one side and blocks the gap between tiles to the skin beneath.

The net effect is a little bit like fish scales or bird feathers and removes the need for a separate 'insulation rope' to fill the gap between tiles.
Title: Re: Starship heat shield
Post by: Robotbeat on 12/31/2020 03:32 pm
I agree it looks like a white felt pad on the back, but it could be just a trick of the light.
Title: Re: Starship heat shield
Post by: DBMandrake on 12/31/2020 03:44 pm
Wasn’t there a tweet or comment from Elon a while ago saying that there would be some kind of “caulk” behind the tiles to seal them against hot gas flow behind the tiles ? Also I imagine that a slightly compressible material (compared to steel anyway) behind the tiles acting as a sort of gasket would help keep the mechanical attachment of the tiles more secure against flexing of the tank wall and vibration due to keeping some tension on the attachment point.
Title: Re: Starship heat shield
Post by: Nomadd on 12/31/2020 03:59 pm
 I have to wonder about a tile test rig that could reproduce all flight conditions. It just doesn't seem reasonable that they should have to wait for test flights to discover the tiles aren't holding. Maybe figuring hull flex/vibration/temperature/whatever conditions isn't that easy.
 You'd think re-entry would be the hardest, but I still remember that the worst tile loss the Shuttle ever had was on a 747 transport flight.
Title: Re: Starship heat shield
Post by: TiagoLourenc0 on 12/31/2020 04:24 pm
I have to wonder about a tile test rig that could reproduce all flight conditions. It just doesn't seem reasonable that they should have to wait for test flights to discover the tiles aren't holding. Maybe figuring hull flex/vibration/temperature/whatever conditions isn't that easy.
 You'd think re-entry would be the hardest, but I still remember that the worst tile loss the Shuttle ever had was on a 747 transport flight.

Perhaps they can test the various conditions one at a time, then use the flights to do further testing.
Title: Re: Starship heat shield
Post by: HVM on 12/31/2020 04:52 pm
I have to wonder about a tile test rig that could reproduce all flight conditions. It just doesn't seem reasonable that they should have to wait for test flights to discover the tiles aren't holding. Maybe figuring hull flex/vibration/temperature/whatever conditions isn't that easy.
 You'd think re-entry would be the hardest, but I still remember that the worst tile loss the Shuttle ever had was on a 747 transport flight.
Backside of this steel plate is one intern splashing liquid nitrogen on it, and another one giving it good blows with the hammer. (Third intern takes notes, so it is Science)
Title: Re: Starship heat shield
Post by: Hog on 01/01/2021 01:16 am
I have to wonder about a tile test rig that could reproduce all flight conditions. It just doesn't seem reasonable that they should have to wait for test flights to discover the tiles aren't holding. Maybe figuring hull flex/vibration/temperature/whatever conditions isn't that easy.
 You'd think re-entry would be the hardest, but I still remember that the worst tile loss the Shuttle ever had was on a 747 transport flight.
Were they lost during that first delivery mission, or simply shipped without tiles so they would be installed for STS-1?  There's sources for either scenario. 
Title: Re: Starship heat shield
Post by: Cheapchips on 01/05/2021 06:55 pm
The robot in the windbreak is presumably for fixing tile studs to the cone?  Is the metal rig to provide a firm backing when they do that?

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2002958;image

Photo credit: Nomadd
Title: Re: Starship heat shield
Post by: Johnnyhinbos on 01/08/2021 03:36 am
Not a single peep on the wacky new tiles on SN15.

Image credit: BocaChicaGal
Title: Re: Starship heat shield
Post by: cwr on 01/08/2021 04:24 am
I have to wonder about a tile test rig that could reproduce all flight conditions. It just doesn't seem reasonable that they should have to wait for test flights to discover the tiles aren't holding. Maybe figuring hull flex/vibration/temperature/whatever conditions isn't that easy.
 You'd think re-entry would be the hardest, but I still remember that the worst tile loss the Shuttle ever had was on a 747 transport flight.
Were they lost during that first delivery mission, or simply shipped without tiles so they would be installed for STS-1?  There's sources for either scenario.

My recollection is that the initial delivery of Columbia to KSC was with the tiles
installed. There was horror at how many were lost on that delivery flight
and it took a long time to repair the damage.

Carl
Title: Re: Starship heat shield
Post by: HVM on 01/08/2021 08:17 am
SN9 tiles seems to be fine after static fire...
Title: Re: Starship heat shield
Post by: Anderqual on 01/08/2021 11:19 am
The robot in the windbreak is presumably for fixing tile studs to the cone?  Is the metal rig to provide a firm backing when they do that?

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2002958;image

Photo credit: Nomadd
I was thinking that the frame might be a jig for the new larger nosecone panels and the robot arm might be to weld them together. It might be for the pins or maybe both.
Title: Re: Starship heat shield
Post by: lstr on 01/09/2021 05:39 pm
From these photos

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=50748.0;attach=2002130;image
https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=50748.0;attach=1989664;image

it seems to me like some (or all) of the white material on the back of the tiles was probably viscous at the time of tile placement, because of:
1. Very irregular appearance around the edges
2. Somewhat irregular tile placement
3. White material here and there and inside some tile gaps (maybe alternate explanation of defective/cracked tiles?)
Title: Re: Starship heat shield
Post by: DreamyPickle on 01/10/2021 10:39 am
Latest video from Mary has a few shots that show heat shield tiles removed from SN5 or SN6.

There is white residue in perfectly hexagonal shapes, maybe some form of adhesive.
Title: Re: Starship heat shield
Post by: livingjw on 01/10/2021 02:25 pm
Latest video from Mary has a few shots that show heat shield tiles removed from SN5 or SN6.

There is white residue in perfectly hexagonal shapes, maybe some form of adhesive.

These were the glued on tile. I believe what you are seeing is the remains of fractured insulation block. The insulation is brittle and not very strong. The green is the adhesive.

John
Title: Re: Starship heat shield
Post by: livingjw on 01/10/2021 02:28 pm
From these photos

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=50748.0;attach=2002130;image
https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=50748.0;attach=1989664;image

it seems to me like some (or all) of the white material on the back of the tiles was probably viscous at the time of tile placement, because of:
1. Very irregular appearance around the edges
2. Somewhat irregular tile placement
3. White material here and there and inside some tile gaps (maybe alternate explanation of defective/cracked tiles?)

The white material is most likely a high temperature felt like material used for vibration isolation and gap filler.

John
Title: Re: Starship heat shield
Post by: Kazioo on 01/10/2021 03:53 pm
Maybe the white material is something like the "Superwool" this company makes:

https://morganthermalceramics.com/media/1141/english-superwool_brochure_single_pages.pdf

https://morganthermalceramics.com/media/5952/thermal-ceramics-product-overview_april2019_websize.pdf

(They mention heat shields for aerospace industry as one of the applications)
Title: Re: Starship heat shield
Post by: HVM on 01/10/2021 04:08 pm
...(They mention heat shields for aerospace industry as one of the applications)
I am pretty sure that means near hot engine parts, and not re-entry vehicles...
Title: Re: Starship heat shield
Post by: OTV Booster on 01/10/2021 07:29 pm
...(They mention heat shields for aerospace industry as one of the applications)
I am pretty sure that means near hot engine parts, and not re-entry vehicles...
Even if the the intended use is around engines there might be application for this or something similar, if protected from direct hypersonic flow. The black glassy surface layer does that. The tile gaps may be of too small a scale for local flow to enter. They will be buried in either the stagnation or the relatively slow surface flow. I think.
Title: Re: Starship heat shield
Post by: Kazioo on 01/10/2021 09:21 pm
They mention temperatures 1600°C and even higher for some of these product. Sounds really good, especially if it's primarily a vibration dampening solution.

Elon said that "Marshmellow-looking thing is a rope seal".
Title: Re: Starship heat shield
Post by: Hog on 01/15/2021 02:17 pm
I have to wonder about a tile test rig that could reproduce all flight conditions. It just doesn't seem reasonable that they should have to wait for test flights to discover the tiles aren't holding. Maybe figuring hull flex/vibration/temperature/whatever conditions isn't that easy.
 You'd think re-entry would be the hardest, but I still remember that the worst tile loss the Shuttle ever had was on a 747 transport flight.
Were they lost during that first delivery mission, or simply shipped without tiles so they would be installed for STS-1?  There's sources for either scenario.

My recollection is that the initial delivery of Columbia to KSC was with the tiles
installed. There was horror at how many were lost on that delivery flight
and it took a long time to repair the damage.

Carl
"Nearly four years later on March 8, 1979, Columbia rolled out of the Palmdale facility to begin its multi-day journey across the nation to its launch site, the Kennedy Space Center (KSC) in Florida. The first step was an overland haul to the NASA Dryden Flight Research Center at Edwards Air Force Base (AFB) 36 miles away. Two days later, workers there hoisted Columbia onto the Shuttle Carrier Aircraft (SCA), a Boeing 747 aircraft modified to transport Space Shuttle orbiters. During a test flight, thousands of the orbiter’s temporary thermal protection system tiles fell off. Columbia was returned to the hanger where over 100 men and women worked for nine days reapplying the tiles. Weather then delayed Columbia’s departure until March 20, when the SCA/Shuttle duo flew from Dryden to Biggs AFB in El Paso, Texas, since weather prevented them from reaching their planned refueling stop at Kelly AFB in San Antonio, Texas, until the next day. About 200,000 people went to view the shuttle during its overnight layover in San Antonio. Astronaut Donald K. “Deke” Slayton, program manager for Shuttle Flight Test Operations, was interviewed. After another overnight stop at Eglin AFB in Florida, Columbia atop the SCA touched down at KSC’s Shuttle Landing Facility on March 24."

https://www.nasa.gov/feature/40-years-ago-space-shuttle-columbia-arrives-at-kennedy-space-center

I didn't realize that temporary tiles were installed for the initial delivery flight of Columbia in 1979.  A single skilled installer could install 1.7 tiles per week. 


attachments
1) Columbia atop Shuttle Carrier Aircraft as they take off from Dryden which required a 36 mile overland jaunt to Dryden from the Palmdale plant
2) OV-102 Columbia and SCA landing at KSC
Title: Re: Starship heat shield
Post by: Stimbergi on 01/15/2021 03:56 pm
Tiles on aft flap
Credit: BocaChicaGal
Title: Re: Starship heat shield
Post by: Robotbeat on 01/23/2021 05:39 pm
Tiles on aft flap
Credit: BocaChicaGal
ooo! Very good!

Anyone see any large sections of heatshield on any of the Starships past SN9?
Title: Re: Starship heat shield
Post by: WormPicker959 on 01/26/2021 08:55 pm
Tiles on aft flap
Credit: BocaChicaGal
ooo! Very good!

Anyone see any large sections of heatshield on any of the Starships past SN9?

Only thing I see is here (from BocaChicaGal): https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2007474;image

from this update:
A few TPS tiles on the nosecone barrel section.
SN11 nosecone was hooked up to the crane for a while.

Some tiles attached to the barrel section of SN11 nosecone. Looks like they'll be testing some of the smaller tiles again.
Title: Re: Starship heat shield
Post by: Haur on 01/26/2021 09:47 pm
There was three lines of 7 tiles on SN15's common dome stack as well

SN15 common dome section stacked in the mid bay.
Title: Re: Starship heat shield
Post by: Robotbeat on 01/29/2021 05:08 pm
This appears to be the most tiles yet spotted on a Starship (and with patches of tiles distributed in at least 4 spots, I guess to get good test coverage of the different conditions on different parts of Starship). SN10:

https://twitter.com/nickyx15a/status/1355214865221246977

Quote
SN10 has begun rolling to the street!!!
@SpaceflightIns
Title: Re: Starship heat shield
Post by: leovinus on 01/29/2021 06:58 pm
More decorative than informative but Paul Wooster of SpaceX presented today at the Planetary Science Decadal Survey, Mars presentation M8. (https://forum.nasaspaceflight.com/index.php?topic=51500.40) Look at his background :) Image attached.
Title: Re: Starship heat shield
Post by: OTV Booster on 01/31/2021 05:24 pm
Some observations on SN10's tiles. The big block of tiles are set in the 'pin' field and mechanically attached. The lower block are not in a pin field. To my JRS (Junior Rocket Scientist - I hope to get my decoder ring any day now) eye, all that drippy and swirly stuff looks like they etched the surface with acid to put a tooth on it for better bonding.

Some of the lower tiles look like like they're bonded with the marshmallowy stuff that Elon mentioned. To my mind a good solution would be a high temp bonding that maintains a bit of marshmallowy flexibility at cryo and EDL temps. Is there anything like this on the horizon that doesn't use unobtanium?

A couple other observations. It looks like there were some efforts to etch the left side of the big patch. There is also some runny red.

Minimum conclusion: they're still exploring on attachment. Any other ideas out there?
Title: Re: Starship heat shield
Post by: livingjw on 02/01/2021 04:14 am
Interesting. Maybe some kind of high temperature foamed silicone based system? One problem with bonding is applying pressure consistently during cure.

John
Title: Re: Starship heat shield
Post by: DigitalMan on 02/01/2021 04:37 am
Interesting. Maybe some kind of high temperature foamed silicone based system? One problem with bonding is applying pressure consistently during cure.

John

If these tiles were also bolted on, it would provide a good environment for an adhesive to cure (I do this frequently with things I build).

We previously saw tiles that had been damaged (not in a crash), I would think an adhesive would provide a better mechanism for distributing energy across the tile to the attach points compared to only bolting it on.
Title: Re: Starship heat shield
Post by: Nomadd on 02/01/2021 05:14 am
 They're probably thinking about field repair. Hard to do with adhesive.
Title: Re: Starship heat shield
Post by: _MECO on 02/01/2021 06:46 am
They're probably thinking about field repair. Hard to do with adhesive.

With completely mechanical/fastener-based tile attachment, it might even be possible to do last minute on-orbit replacement. Something as simple as chiseling out the old tile while on EVA and snapping a new one in its place that you got from the pile of identical spares in the cargo hold could make the difference between a normal EDL and another Columbia. I could imagine Starships being accompanied by extendable boom cameras or even free-flying RCS drones that inspect their bellies for damage periodically.
Title: Re: Starship heat shield
Post by: Jimmy_C on 02/01/2021 03:38 pm
They're probably thinking about field repair. Hard to do with adhesive.

With completely mechanical/fastener-based tile attachment, it might even be possible to do last minute on-orbit replacement. Something as simple as chiseling out the old tile while on EVA and snapping a new one in its place that you got from the pile of identical spares in the cargo hold could make the difference between a normal EDL and another Columbia. I could imagine Starships being accompanied by extendable boom cameras or even free-flying RCS drones that inspect their bellies for damage periodically.

Columbia was due to damaged Reinforced Carbon-Carbon panels on the wing's leading edge.
Title: Re: Starship heat shield
Post by: Robotbeat on 02/01/2021 03:42 pm
They're probably thinking about field repair. Hard to do with adhesive.

With completely mechanical/fastener-based tile attachment, it might even be possible to do last minute on-orbit replacement. Something as simple as chiseling out the old tile while on EVA and snapping a new one in its place that you got from the pile of identical spares in the cargo hold could make the difference between a normal EDL and another Columbia. I could imagine Starships being accompanied by extendable boom cameras or even free-flying RCS drones that inspect their bellies for damage periodically.

Columbia was due to damaged Reinforced Carbon-Carbon panels on the wing's leading edge.
That doesn’t really change his point. A heatshield failure on another spot on the vehicle could’ve also caused the same result. Which is also why NASA developed a method for on-orbit repair of heatshield tiles after Columbia. Basically the same thing he’s talking about.
Title: Re: Starship heat shield
Post by: Jimmy_C on 02/01/2021 03:58 pm
They're probably thinking about field repair. Hard to do with adhesive.

With completely mechanical/fastener-based tile attachment, it might even be possible to do last minute on-orbit replacement. Something as simple as chiseling out the old tile while on EVA and snapping a new one in its place that you got from the pile of identical spares in the cargo hold could make the difference between a normal EDL and another Columbia. I could imagine Starships being accompanied by extendable boom cameras or even free-flying RCS drones that inspect their bellies for damage periodically.

Columbia was due to damaged Reinforced Carbon-Carbon panels on the wing's leading edge.
That doesn’t really change his point. A heatshield failure on another spot on the vehicle could’ve also caused the same result. Which is also why NASA developed a method for on-orbit repair of heatshield tiles after Columbia. Basically the same thing he’s talking about.

It's important to be accurate with history. In any case, I don't agree that an adhesive based repair method would be obsolete. When a fastener bolt breaks, replacing a tile without adhesive would be hard.
Title: Re: Starship heat shield
Post by: OTV Booster on 02/01/2021 06:12 pm
Interesting. Maybe some kind of high temperature foamed silicone based system? One problem with bonding is applying pressure consistently during cure.

John
Maybe a two part fast setup mix with a cooperative robot arm to apply pressure for a couple moments. Maybe UV curing like at the dentist? Maybe start the curing without the tile then add the tile with a thin coat of something that reactivates a thin layer of the marshmallow?


So many ideas. So few facts. What's the spot market doing on unobtanium?
Title: Re: Starship heat shield
Post by: OTV Booster on 02/01/2021 06:19 pm
They're probably thinking about field repair. Hard to do with adhesive.
You can fix just about anything with a P38, green 100mph tape and C-rat peanut butter. Two of the three are adhesive.
Title: Re: Starship heat shield
Post by: OTV Booster on 02/01/2021 06:22 pm
They're probably thinking about field repair. Hard to do with adhesive.

With completely mechanical/fastener-based tile attachment, it might even be possible to do last minute on-orbit replacement. Something as simple as chiseling out the old tile while on EVA and snapping a new one in its place that you got from the pile of identical spares in the cargo hold could make the difference between a normal EDL and another Columbia. I could imagine Starships being accompanied by extendable boom cameras or even free-flying RCS drones that inspect their bellies for damage periodically.

Columbia was due to damaged Reinforced Carbon-Carbon panels on the wing's leading edge.
That doesn’t really change his point. A heatshield failure on another spot on the vehicle could’ve also caused the same result. Which is also why NASA developed a method for on-orbit repair of heatshield tiles after Columbia. Basically the same thing he’s talking about.

It's important to be accurate with history. In any case, I don't agree that an adhesive based repair method would be obsolete. When a fastener bolt breaks, replacing a tile without adhesive would be hard.
And it only needs to work one time.
Title: Re: Starship heat shield
Post by: Fizrock on 02/03/2021 08:00 am
Of note: SN9 did not appear to lose any tiles on the test flight.   
 
At least not until the last moment...
Title: Re: Starship heat shield
Post by: Nevyn72 on 02/03/2021 10:00 pm
Of note: SN9 did not appear to lose any tiles on the test flight.   
 
At least not until the last moment...

Looking at the frost line on that picture you can see why they put the tiles where they did.
Title: Re: Starship heat shield
Post by: wannamoonbase on 02/03/2021 10:06 pm
Of note: SN9 did not appear to lose any tiles on the test flight.   
 
At least not until the last moment...

Looking at the frost line on that picture you can see why they put the tiles where they did.

I'm not that concerned with them shedding tiles on these flights.  They are really gentle.  Being launched on top of a SH and orbital re-entry, that could be the shocker. 

The typical hexagon tiles in a field layout seem straight forward enough to make and attach.  The specialty tiles around the edges, nose cone and control surfaces.  Those will be interesting.

This is going to be a fun year to watch.
Title: Re: Starship heat shield
Post by: Nevyn72 on 02/03/2021 10:28 pm
Of note: SN9 did not appear to lose any tiles on the test flight.   
 
At least not until the last moment...

Looking at the frost line on that picture you can see why they put the tiles where they did.

I'm not that concerned with them shedding tiles on these flights.  They are really gentle.  Being launched on top of a SH and orbital re-entry, that could be the shocker. 

The typical hexagon tiles in a field layout seem straight forward enough to make and attach.  The specialty tiles around the edges, nose cone and control surfaces.  Those will be interesting.

This is going to be a fun year to watch.

True, I was mainly commenting on the fact the tiles appeared to be located on a band of maximum frosting on the tank section.

Probably trying to assess how well they cope with temperature related expansion and contraction?
Title: Re: Starship heat shield
Post by: marsbase on 02/03/2021 10:38 pm
I'm not that concerned with them shedding tiles on these flights.  They are really gentle.  Being launched on top of a SH and orbital re-entry, that could be the shocker. 

These SS test flights are extremely low g with no concern for gravity losses. Of course there will be some hard to predict resonances in a SS/SH stack.  But in general, I think the more engines you have, the smoother the ride.  And the heavily loaded stack will have lots of damping.  It gets rough when there is only one engine and the mass has dropped to a minimum, as the astronauts on Crew-1 discovered as second stage fuel ran low.  Of course you are right about orbital re-entry.  That will be torturous.
Title: Re: Starship heat shield
Post by: WormPicker959 on 02/05/2021 11:06 pm
Having just seen Mary's great new closeups of the tiles (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2188891#msg2188891), has me thinking: is it possible that they are not testing different attachment mechanisms to see what works, but rather are optimizing different attachment mechanisms that will ultimately be used for different regions of the starship? As in, what's the possibility that the tiles will be attached differently on different parts of the vehicle? I could see some pros and cons, but perhaps all of you smarter than me could help me out:

Pros:
-Different conditions could get different treatments
-No need for one-size fits-all solution - can optimize for different things in different places
-If attachment is hard/expensive in some regions, no need to use that attachment mechanism everywhere

Cons:
-More complexity in manufacturing
-No one-size-fits-all means different failure modes for each region
-Different thermal characteristics (?) in different parts can cause problems (I have no idea about this one)

I think to some degree they will have to have some different/custom attachment regions, like surrounding the hinges and at leading edges, so perhaps this is more of a question of the degree to which they're expanding that notion. Basically: maybe these aren't trials of possible attachment methods, but rather tests of needed attachment methods.
Title: Re: Starship heat shield
Post by: edzieba on 02/05/2021 11:09 pm
The lowermost attachment variant ('full height' RCG coating, thin white felt, red RTV silicone) looks very STS. Would be amusing if that ended up being the most successful variant after all!
Title: Re: Starship heat shield
Post by: jthygesen on 02/06/2021 09:34 am
The lowermost attachment variant ('full height' RCG coating, thin white felt, red RTV silicone) looks very STS. Would be amusing if that ended up being the most successful variant after all!

To me the red stuff looks more like a board of some kind, perhaps some kind of cement board? Although I don’t see how that makes any sense, so you’re probably right.

Original Image credit: Bocachicagal.
Title: Re: Starship heat shield
Post by: edzieba on 02/06/2021 10:43 am
The lowermost attachment variant ('full height' RCG coating, thin white felt, red RTV silicone) looks very STS. Would be amusing if that ended up being the most successful variant after all!

To me the red stuff looks more like a board of some kind, perhaps some kind of cement board? Although I don’t see how that makes any sense, so you’re probably right.

Original Image credit: Bocachicagal.
Compare the 'rippled' red substance to the rippled red RTV silicone of the STS tile mounting system (images attached). With the structure of the tiles themselves being close to identical (other than being 6-sided rather than 4-sided), it it makes sense to test alternate attachment mechanisms vs. a 'known working' mechanism.

As a side note: reading through Orbiter Thermal Protection System Lessons Learned (attached) mentions the use of Dimethyl-Ethoxy Silane (DMES) as a rewaterproofing agent - to prevent moisture penetration into the structure of the tile - as avoiding the issues of underpenetration (Scotchguard) and RTV chemical degradation (Disilazane) with previous rewaterproofing agents, at the downside of producing toxic fumes during application. The FDEP report on the SpaceX tile production facility mentions the use of Methyl-Trimethoxy Silane (MTMS), likely as a replacement.
Any chemists familiar with either (or both) able to cast any light on their differences? If SpaceX select the mechanical (or a non-RTV-Silicone-based) attachment mechanism, I wonder if Disilazane might be reconsidered.
Title: Re: Starship heat shield
Post by: OTV Booster on 02/07/2021 11:28 pm
On Mary's pic, the top three sub sized tiles have an interesting structure. This is on SN10, the patch of tiles just below the big patch.

Zoom in on all three of these tiles and it looks like the glassy layer is made hollow with at least one corner missing on some of the side walls. On the right most tile the bottom right corner does not show this. On the next layer down, full sized tiles, the rightmost tile shares this feature on its upper right corner. Others don't where it should be usable if there.


In places the white stuff does look like felt, or more exactly, it looks like (but surely isn't) styrofoam hacked with a bread knife. In other places I swear it looks like French cream oozing out of a cheap pastry.

Don't know what to make of this except that they seem to be still noodling basic structure in addition to attachment. BTW, this is one of the areas that was showing all swirly and streaky. The must have had a job posting for Rocket Washer that I missed.


Edit: the pic came across too low res to show what I was talking about so I added a tighter crop and this link to the original post.
 [size=78%]https://forum.nasaspaceflight.com/index.php?topic=52398.msg2188891#msg2188891 (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2188891#msg2188891)[/size]
Title: Re: Starship heat shield
Post by: dwheeler on 02/08/2021 06:40 pm
February 7th 2021 Updates:  Starship priorities

https://twitter.com/elonmusk/status/1358594029101879298
Tweet Contents:  What’s your biggest priority with Starship right now? What currently feels like the most uphill battle or most urgent problem to solve?
1. Orbital launch tower that can stack
2. Enough Raptors for orbit booster
3. Improve ship & booster mass


Somewhat reassuring that Elon doesn't put the heat shield problem in his current top 3 urgent-problems-to-solve list. I think it's been the problem I've been most anxious about with Starship...
Title: Re: Starship heat shield
Post by: sevenperforce on 02/08/2021 06:45 pm
On Mary's pic, the top three sub sized tiles have an interesting structure. This is on SN10, the patch of tiles just below the big patch.
I wonder...with these sub-sized tiles, are they planning on using them in combination to create a tesselation up the ogive?

Title: Re: Starship heat shield
Post by: laszlo on 02/08/2021 08:07 pm
February 7th 2021 Updates:  Starship priorities

https://twitter.com/elonmusk/status/1358594029101879298
Tweet Contents:  What’s your biggest priority with Starship right now? What currently feels like the most uphill battle or most urgent problem to solve?
1. Orbital launch tower that can stack
2. Enough Raptors for orbit booster
3. Improve ship & booster mass


Somewhat reassuring that Elon doesn't put the heat shield problem in his current top 3 urgent-problems-to-solve list. I think it's been the problem I've be most anxious about with Starship...

Just means that he's willing to run them as expendables while putting up starlink.
Title: Re: Starship heat shield
Post by: xvel on 02/08/2021 08:10 pm
to even test a heat shield you need at least first two first
Title: Re: Starship heat shield
Post by: Crispy on 02/08/2021 08:58 pm
On Mary's pic, the top three sub sized tiles have an interesting structure. This is on SN10, the patch of tiles just below the big patch.
I wonder...with these sub-sized tiles, are they planning on using them in combination to create a tesselation up the ogive?


Most likely they're testing the adhesion and resilience of various size tiles. There are probably all sorts of cost/ease/sturdiness tradeoffs at every size and they need good data to make a good choice.
Title: Re: Starship heat shield
Post by: sevenperforce on 02/08/2021 10:10 pm
I wonder...with these sub-sized tiles, are they planning on using them in combination to create a tesselation up the ogive?
Most likely they're testing the adhesion and resilience of various size tiles. There are probably all sorts of cost/ease/sturdiness tradeoffs at every size and they need good data to make a good choice.
On the other hand, these tiles ARE the perfect ratio to produce an ogive....
Title: Re: Starship heat shield
Post by: _MECO on 02/08/2021 11:34 pm
I wonder...with these sub-sized tiles, are they planning on using them in combination to create a tesselation up the ogive?
Most likely they're testing the adhesion and resilience of various size tiles. There are probably all sorts of cost/ease/sturdiness tradeoffs at every size and they need good data to make a good choice.
On the other hand, these tiles ARE the perfect ratio to produce an ogive....

I'm not seeing it 100%. With perfectly hexagonal tiles like this, aren't there going to be a zillion tiny gaps everywhere? Even accounting for the fact that I edited that diagram on a flat surface in MS paint as opposed to mapped onto a curved surface in 3D space, it's very clear that there will be substantial gaps when you start trying to get the tiles to tessellate perfectly.
Title: Re: Starship heat shield
Post by: rakaydos on 02/08/2021 11:52 pm
I wonder...with these sub-sized tiles, are they planning on using them in combination to create a tesselation up the ogive?
Most likely they're testing the adhesion and resilience of various size tiles. There are probably all sorts of cost/ease/sturdiness tradeoffs at every size and they need good data to make a good choice.
On the other hand, these tiles ARE the perfect ratio to produce an ogive....

I'm not seeing it 100%. With perfectly hexagonal tiles like this, aren't there going to be a zillion tiny gaps everywhere? Even accounting for the fact that I edited that diagram on a flat surface in MS paint as opposed to mapped onto a curved surface in 3D space, it's very clear that there will be substantial gaps when you start trying to get the tiles to tessellate perfectly.
As long as those gaps are small enough that the stainless steel backing can redistribute the heat, that should be survivable.
Title: Re: Starship heat shield
Post by: _MECO on 02/09/2021 12:28 am
I wonder...with these sub-sized tiles, are they planning on using them in combination to create a tesselation up the ogive?
Most likely they're testing the adhesion and resilience of various size tiles. There are probably all sorts of cost/ease/sturdiness tradeoffs at every size and they need good data to make a good choice.
On the other hand, these tiles ARE the perfect ratio to produce an ogive....

I'm not seeing it 100%. With perfectly hexagonal tiles like this, aren't there going to be a zillion tiny gaps everywhere? Even accounting for the fact that I edited that diagram on a flat surface in MS paint as opposed to mapped onto a curved surface in 3D space, it's very clear that there will be substantial gaps when you start trying to get the tiles to tessellate perfectly.
As long as those gaps are small enough that the stainless steel backing can redistribute the heat, that should be survivable.

Survivable throughout the lifetime of a given Starship... citation needed?
Title: Re: Starship heat shield
Post by: rakaydos on 02/09/2021 12:37 am
I wonder...with these sub-sized tiles, are they planning on using them in combination to create a tesselation up the ogive?
Most likely they're testing the adhesion and resilience of various size tiles. There are probably all sorts of cost/ease/sturdiness tradeoffs at every size and they need good data to make a good choice.
On the other hand, these tiles ARE the perfect ratio to produce an ogive....

I'm not seeing it 100%. With perfectly hexagonal tiles like this, aren't there going to be a zillion tiny gaps everywhere? Even accounting for the fact that I edited that diagram on a flat surface in MS paint as opposed to mapped onto a curved surface in 3D space, it's very clear that there will be substantial gaps when you start trying to get the tiles to tessellate perfectly.
As long as those gaps are small enough that the stainless steel backing can redistribute the heat, that should be survivable.

Survivable throughout the lifetime of a given Starship... citation needed?
Insufficient data. I think the relevant numbers would be the steel's heat conductivity  and emission to the inside, over whatever the duration and temperature of reentry (given the gaps), and the temperature that removes the "cold rolled" effect that the tanks are taking advantage of. If the gaps are small enough that no part of the hull passes the threshold temperature, (which is an open question, but is what I assume with my post) then there shouldn't be a problem.
Title: Re: Starship heat shield
Post by: JamesH65 on 02/09/2021 10:19 am
Gaps are filled anyway between the current ones AIUI, this just means a slightly larger gap filler in a few places.
Title: Re: Starship heat shield
Post by: Slarty1080 on 02/09/2021 04:42 pm
I wonder...with these sub-sized tiles, are they planning on using them in combination to create a tesselation up the ogive?
Most likely they're testing the adhesion and resilience of various size tiles. There are probably all sorts of cost/ease/sturdiness tradeoffs at every size and they need good data to make a good choice.
On the other hand, these tiles ARE the perfect ratio to produce an ogive....

I'm not seeing it 100%. With perfectly hexagonal tiles like this, aren't there going to be a zillion tiny gaps everywhere? Even accounting for the fact that I edited that diagram on a flat surface in MS paint as opposed to mapped onto a curved surface in 3D space, it's very clear that there will be substantial gaps when you start trying to get the tiles to tessellate perfectly.
As long as those gaps are small enough that the stainless steel backing can redistribute the heat, that should be survivable.
Its simply not possible to tessellate a tapering curved surface with a single size of hexagonal tile. the gaps and mismatches will grow row upon row. This was discussed right at the start of this thread on page 1.
Title: Re: Starship heat shield
Post by: whitelancer64 on 02/09/2021 04:58 pm
February 7th 2021 Updates:  Starship priorities

*snip tweet*
Tweet Contents:  What’s your biggest priority with Starship right now? What currently feels like the most uphill battle or most urgent problem to solve?
1. Orbital launch tower that can stack
2. Enough Raptors for orbit booster
3. Improve ship & booster mass


Somewhat reassuring that Elon doesn't put the heat shield problem in his current top 3 urgent-problems-to-solve list. I think it's been the problem I've be most anxious about with Starship...

Just means that he's willing to run them as expendables while putting up starlink.

Or, perhaps more likely, that by the time an orbital test launch happens, he is confident they'll have worked out which combination of tile(s) and adhesion method(s) to use.
Title: Re: Starship heat shield
Post by: rakaydos on 02/09/2021 06:49 pm
I wonder...with these sub-sized tiles, are they planning on using them in combination to create a tesselation up the ogive?
Most likely they're testing the adhesion and resilience of various size tiles. There are probably all sorts of cost/ease/sturdiness tradeoffs at every size and they need good data to make a good choice.
On the other hand, these tiles ARE the perfect ratio to produce an ogive....

I'm not seeing it 100%. With perfectly hexagonal tiles like this, aren't there going to be a zillion tiny gaps everywhere? Even accounting for the fact that I edited that diagram on a flat surface in MS paint as opposed to mapped onto a curved surface in 3D space, it's very clear that there will be substantial gaps when you start trying to get the tiles to tessellate perfectly.
As long as those gaps are small enough that the stainless steel backing can redistribute the heat, that should be survivable.
Its simply not possible to tessellate a tapering curved surface with a single size of hexagonal tile. the gaps and mismatches will grow row upon row. This was discussed right at the start of this thread on page 1.
The bolded leads me to believe you have lost the current thread of discussion.
Title: Re: Starship heat shield
Post by: sevenperforce on 02/09/2021 11:26 pm
As long as those gaps are small enough that the stainless steel backing can redistribute the heat, that should be survivable.
Its simply not possible to tessellate a tapering curved surface with a single size of hexagonal tile. the gaps and mismatches will grow row upon row. This was discussed right at the start of this thread on page 1.
But with two sizes of hexagonal tile in the same ratio currently shown on SN10, you can tesselate an ogive quite efficiently.

I went ahead and wrapped the tile pattern around an ogive with the same proportions as Starship. The largest gaps are only a little larger than the existing gaps between the smaller tiles pictured on SN10 currently, and that's without any rotation of the tiles themselves. If you rotate the tiles then you can have substantially more coverage. You could also have a single uniquely-shaped "keystone" tile to fill the largest gap.

The point is that the exact same pattern can be repeated indefinitely. So you have two tile shapes (max of 3) rather than continuously-shrinking tiles.
Title: Re: Starship heat shield
Post by: rakaydos on 02/10/2021 12:04 am
As long as those gaps are small enough that the stainless steel backing can redistribute the heat, that should be survivable.
Its simply not possible to tessellate a tapering curved surface with a single size of hexagonal tile. the gaps and mismatches will grow row upon row. This was discussed right at the start of this thread on page 1.
But with two sizes of hexagonal tile in the same ratio currently shown on SN10, you can tesselate an ogive quite efficiently.

I went ahead and wrapped the tile pattern around an ogive with the same proportions as Starship. The largest gaps are only a little larger than the existing gaps between the smaller tiles pictured on SN10 currently, and that's without any rotation of the tiles themselves. If you rotate the tiles then you can have substantially more coverage. You could also have a single uniquely-shaped "keystone" tile to fill the largest gap.

The point is that the exact same pattern can be repeated indefinitely. So you have two tile shapes (max of 3) rather than continuously-shrinking tiles.
As effective as the pattern is, I suspect SpaceX will not be putting the weakest part of the pattern, right on the midline where the heating will be the greatest. Perhaps if you offset by half a pattern-width?
Title: Re: Starship heat shield
Post by: RoboGoofers on 02/10/2021 12:21 am
Maybe gaps just might be ok with a stainless steel backing, but gaps are not ok for high mach. The tiles will peal off like shingles in a hurricane.
Title: Re: Starship heat shield
Post by: Sciencefan on 02/10/2021 12:34 am
If the problem is that they need more shapes of tiles it will be solved eventually...
Title: Re: Starship heat shield
Post by: Slarty1080 on 02/10/2021 08:11 am
If the problem is that they need more shapes of tiles it will be solved eventually...
It has already been solved. One potential solution is shown on page 1 of this thread and there are plenty more using multiple tile types. The real questions are how few types you can get away with and how much gap is acceptable. I don't know the answers although I suspect they approximate "to quite a lot" and "not very much" respectively.

As well as the curve of the nose there are other areas that will need special treatment such as edges and flaps.
Title: Re: Starship heat shield
Post by: jak Kennedy on 02/10/2021 08:33 am
Maybe gaps just might be ok with a stainless steel backing, but gaps are not ok for high mach. The tiles will peal off like shingles in a hurricane.
It's probably been covered further back but at high mach numbers the air density will be very low and therefore much lower forces on anything even slightly streamlined.
Title: Re: Starship heat shield
Post by: sevenperforce on 02/10/2021 04:34 pm
After looking at this image repeatedly I realized there are actually three different sizes of tiles here.

(https://forum.nasaspaceflight.com/assets/50748.0/2010890.jpg)
Title: Re: Starship heat shield
Post by: Sciencefan on 02/10/2021 04:47 pm
After looking at this image repeatedly I realized there are actually three different sizes of tiles here.

Not only size, there was pentagonal tiles on SN9.
https://twitter.com/NASASpaceflight/status/1328514492414746630

The real problem imo is ice that tends to fill gaps and causes cracks in TPS. Maybe they need overlapped tiles.
Title: Re: Starship heat shield
Post by: edzieba on 02/11/2021 12:18 pm
Or just use the tried and tested method successful on other tiled TPS: fill the gaps with gap filler.
Title: Re: Starship heat shield
Post by: volker2020 on 02/12/2021 02:35 pm
In the Joe Rogan interview with Elon, he points out, that “get the gaps just right” is one of the major problems at this point. I wonder why they can not overlap. Nature came up with this solution a number of times.
Title: Re: Starship heat shield
Post by: edzieba on 02/12/2021 02:47 pm
Overlapping scales cause problems when not aligned to airflow, and Starship is exposed to airflow in 3 orientations (and 4 directions):
- Aligned along the long axis, nose forward (during launch)
- 70° angle of attack (during entry)
- 90° angle of attack (during skydive)
- Aligned along the long axis, tail first (during landing)

In nature, creatures with overlapping scales either have them aligned to a single axis of flow (swimming creatures), replace scaled areas with membrane areas (pterosaurs, gliding lizards, etc), or evolve those scales in very high aspect ratio feathers that can interlock rather than just layer and whose axis can be reoriented by muscles under the skin (birds).
On top of that, the tiles are 'thick' compared to their other two dimensions: they have a very low aspect ratio. They have a minimum thickness to make them effective as a TPS, and if you make them larger they are both harder to fabricate and more brittle.
Title: Re: Starship heat shield
Post by: sevenperforce on 02/12/2021 03:02 pm
In the Joe Rogan interview with Elon, he points out, that “get the gaps just right” is one of the major problems at this point. I wonder why they can not overlap. Nature came up with this solution a number of times.
I think attachment and replacement become problems with overlap. Especially with a dragonskin-style overlap -- you'd have to remove a thousand tiles just to replace one broken one.

Overlap also creates problems with thickness and edge exposure. Do you make the tiles half as thick as they need to be and do two layers? What happens to the ones with an edge exposed to the re-entry plasma?
Title: Re: Starship heat shield
Post by: _MECO on 02/12/2021 04:55 pm
Overlapping scales cause problems when not aligned to airflow, and Starship is exposed to airflow in 3 orientations (and 4 directions):
- Aligned along the long axis, nose forward (during launch)
- 70° angle of attack (during entry)
- 90° angle of attack (during skydive)
- Aligned along the long axis, tail first (during landing)

In nature, creatures with overlapping scales either have them aligned to a single axis of flow (swimming creatures), replace scaled areas with membrane areas (pterosaurs, gliding lizards, etc), or evolve those scales in very high aspect ratio feathers that can interlock rather than just layer and whose axis can be reoriented by muscles under the skin (birds).
On top of that, the tiles are 'thick' compared to their other two dimensions: they have a very low aspect ratio. They have a minimum thickness to make them effective as a TPS, and if you make them larger they are both harder to fabricate and more brittle.

Airflow in subsonic or even transonic flight has got to be completely irrelevant. Of the three stages of EDL you listed, only the reenty part will have concerning aero forces on the shell. What isn't trivial though, is winds experienced on ascent. Surface finish has a huge effect on drag, and overlapping scales would probably cut into payload capacity for that reason.

If you want my prediction, I think SpaceX will be filling those gaps with specialty tiles. This isn't the space shuttle. It won't be the end of the world if they end up needing to make two kinds of hinge tile, two kinds of flap edge tile, six or seven types of gap tile for the nose, and a nose tile. There's a big difference between producing that versus 24,000 unique individual tiles.
Title: Re: Starship heat shield
Post by: Redclaws on 02/12/2021 05:40 pm
Quote
Not only size, there was pentagonal tiles on SN9.

Those really look like they were cut down to fit the mounting area rather than a novel shape intended for use, since they’re all at that same spot...  but could be an indication of plans for edges of sections?  Implying sections...  Who knows, I suppose.
Title: Re: Starship heat shield
Post by: sebk on 02/12/2021 05:51 pm
Overlapping scales cause problems when not aligned to airflow, and Starship is exposed to airflow in 3 orientations (and 4 directions):
- Aligned along the long axis, nose forward (during launch)
- 70° angle of attack (during entry)
- 90° angle of attack (during skydive)
- Aligned along the long axis, tail first (during landing)

In nature, creatures with overlapping scales either have them aligned to a single axis of flow (swimming creatures), replace scaled areas with membrane areas (pterosaurs, gliding lizards, etc), or evolve those scales in very high aspect ratio feathers that can interlock rather than just layer and whose axis can be reoriented by muscles under the skin (birds).
On top of that, the tiles are 'thick' compared to their other two dimensions: they have a very low aspect ratio. They have a minimum thickness to make them effective as a TPS, and if you make them larger they are both harder to fabricate and more brittle.

Airflow in subsonic or even transonic flight has got to be completely irrelevant. Of the three stages of EDL ypu listed, only the reenty part will have concerning aero forces on the shell. What isn't trivial though, is winds experienced on ascent. Surface finish has a huge effect on drag, and overlapping scales would probably cut into payload capacity for that reason.

Actually aerodynamic forces are the greatest during Max-Q on ascent rather than reentry. It's bout 30-35kPa vs 10-20kPa of dynamic pressure.
Title: Re: Starship heat shield
Post by: Keldor on 02/12/2021 06:42 pm
Overlapping scales cause problems when not aligned to airflow, and Starship is exposed to airflow in 3 orientations (and 4 directions):
- Aligned along the long axis, nose forward (during launch)
- 70° angle of attack (during entry)
- 90° angle of attack (during skydive)
- Aligned along the long axis, tail first (during landing)

In nature, creatures with overlapping scales either have them aligned to a single axis of flow (swimming creatures), replace scaled areas with membrane areas (pterosaurs, gliding lizards, etc), or evolve those scales in very high aspect ratio feathers that can interlock rather than just layer and whose axis can be reoriented by muscles under the skin (birds).
On top of that, the tiles are 'thick' compared to their other two dimensions: they have a very low aspect ratio. They have a minimum thickness to make them effective as a TPS, and if you make them larger they are both harder to fabricate and more brittle.

Airflow in subsonic or even transonic flight has got to be completely irrelevant. Of the three stages of EDL ypu listed, only the reenty part will have concerning aero forces on the shell. What isn't trivial though, is winds experienced on ascent. Surface finish has a huge effect on drag, and overlapping scales would probably cut into payload capacity for that reason.

If you want my prediction, I think SpaceX will be filling those gaps with specialty tiles. This isn't the space shuttle. It won't be the end of the world if they end up needing to make two kinds of hinge tile, two kinds of flap edge tile, six or seven types of gap tile for the nose, and a nose tile. There's a big difference between producing that versus 24,000 unique individual tiles.

Have you seen what a tornado will do to shingles on the roof of a house?  Even the most powerful tornados are low speed subsonic, very comparable to the terminal velocity of Starship at the end of its belly flop maneuver when it flips to upright to land.  Don't underestimate aerodynamic forces.
Title: Re: Starship heat shield
Post by: _MECO on 02/13/2021 12:01 am
Overlapping scales cause problems when not aligned to airflow, and Starship is exposed to airflow in 3 orientations (and 4 directions):
- Aligned along the long axis, nose forward (during launch)
- 70° angle of attack (during entry)
- 90° angle of attack (during skydive)
- Aligned along the long axis, tail first (during landing)

In nature, creatures with overlapping scales either have them aligned to a single axis of flow (swimming creatures), replace scaled areas with membrane areas (pterosaurs, gliding lizards, etc), or evolve those scales in very high aspect ratio feathers that can interlock rather than just layer and whose axis can be reoriented by muscles under the skin (birds).
On top of that, the tiles are 'thick' compared to their other two dimensions: they have a very low aspect ratio. They have a minimum thickness to make them effective as a TPS, and if you make them larger they are both harder to fabricate and more brittle.

Airflow in subsonic or even transonic flight has got to be completely irrelevant. Of the three stages of EDL ypu listed, only the reenty part will have concerning aero forces on the shell. What isn't trivial though, is winds experienced on ascent. Surface finish has a huge effect on drag, and overlapping scales would probably cut into payload capacity for that reason.

If you want my prediction, I think SpaceX will be filling those gaps with specialty tiles. This isn't the space shuttle. It won't be the end of the world if they end up needing to make two kinds of hinge tile, two kinds of flap edge tile, six or seven types of gap tile for the nose, and a nose tile. There's a big difference between producing that versus 24,000 unique individual tiles.

Have you seen what a tornado will do to shingles on the roof of a house?  Even the most powerful tornados are low speed subsonic, very comparable to the terminal velocity of Starship at the end of its belly flop maneuver when it flips to upright to land.  Don't underestimate aerodynamic forces.

The angle of attack is only 70 degrees or better on Starship, and roofing tiles aren't equivalent to house tiles. Besides, I'm just saying that those stages of EDL aren't relevant. If the tiles can stand escape-velocity-plus-C3 speeds at 70 degrees, of course they can withstand 0.9 mach at 90 degrees or 30 meters per second during the landing flip.
Title: Re: Starship heat shield
Post by: Torbjorn Larsson, OM on 02/13/2021 01:11 am
In the Joe Rogan interview with Elon, he points out, that “get the gaps just right” is one of the major problems at this point. I wonder why they can not overlap. Nature came up with this solution a number of times.

In the Joe Rogan interview with Elon, he points out, that “get the gaps just right” is one of the major problems at this point. I wonder why they can not overlap. Nature came up with this solution a number of times.
I think attachment and replacement become problems with overlap. Especially with a dragonskin-style overlap -- you'd have to remove a thousand tiles just to replace one broken one.

Overlap also creates problems with thickness and edge exposure. Do you make the tiles half as thick as they need to be and do two layers? What happens to the ones with an edge exposed to the re-entry plasma?

Could you make loose finger joints in the tile materials?

If they are "just so" when ambient temperature  they may be pulled out and replaced, depending on mount.
Title: Re: Starship heat shield
Post by: edzieba on 02/15/2021 11:11 am
Overlapping scales cause problems when not aligned to airflow, and Starship is exposed to airflow in 3 orientations (and 4 directions):
- Aligned along the long axis, nose forward (during launch)
- 70° angle of attack (during entry)
- 90° angle of attack (during skydive)
- Aligned along the long axis, tail first (during landing)

In nature, creatures with overlapping scales either have them aligned to a single axis of flow (swimming creatures), replace scaled areas with membrane areas (pterosaurs, gliding lizards, etc), or evolve those scales in very high aspect ratio feathers that can interlock rather than just layer and whose axis can be reoriented by muscles under the skin (birds).
On top of that, the tiles are 'thick' compared to their other two dimensions: they have a very low aspect ratio. They have a minimum thickness to make them effective as a TPS, and if you make them larger they are both harder to fabricate and more brittle.

Airflow in subsonic or even transonic flight has got to be completely irrelevant. Of the three stages of EDL ypu listed, only the reenty part will have concerning aero forces on the shell. What isn't trivial though, is winds experienced on ascent. Surface finish has a huge effect on drag, and overlapping scales would probably cut into payload capacity for that reason.

If you want my prediction, I think SpaceX will be filling those gaps with specialty tiles. This isn't the space shuttle. It won't be the end of the world if they end up needing to make two kinds of hinge tile, two kinds of flap edge tile, six or seven types of gap tile for the nose, and a nose tile. There's a big difference between producing that versus 24,000 unique individual tiles.

Have you seen what a tornado will do to shingles on the roof of a house?  Even the most powerful tornados are low speed subsonic, very comparable to the terminal velocity of Starship at the end of its belly flop maneuver when it flips to upright to land.  Don't underestimate aerodynamic forces.

The angle of attack is only 70 degrees or better on Starship, and roofing tiles aren't equivalent to house tiles. Besides, I'm just saying that those stages of EDL aren't relevant. If the tiles can stand escape-velocity-plus-C3 speeds at 70 degrees, of course they can withstand 0.9 mach at 90 degrees or 30 meters per second during the landing flip.
But not orthogonal flow, as in ascent.
Lapped structures are flow optimal only in one axis, and get progressively worse as you deviate from that axis. Starship experiences dense flow at high velocities (high subsonic and above supersonic) on orthogonal axes.
No capes overlap!
Title: Re: Starship heat shield
Post by: _MECO on 02/15/2021 01:43 pm
Overlapping scales cause problems when not aligned to airflow, and Starship is exposed to airflow in 3 orientations (and 4 directions):
- Aligned along the long axis, nose forward (during launch)
- 70° angle of attack (during entry)
- 90° angle of attack (during skydive)
- Aligned along the long axis, tail first (during landing)

In nature, creatures with overlapping scales either have them aligned to a single axis of flow (swimming creatures), replace scaled areas with membrane areas (pterosaurs, gliding lizards, etc), or evolve those scales in very high aspect ratio feathers that can interlock rather than just layer and whose axis can be reoriented by muscles under the skin (birds).
On top of that, the tiles are 'thick' compared to their other two dimensions: they have a very low aspect ratio. They have a minimum thickness to make them effective as a TPS, and if you make them larger they are both harder to fabricate and more brittle.

Airflow in subsonic or even transonic flight has got to be completely irrelevant. Of the three stages of EDL ypu listed, only the reenty part will have concerning aero forces on the shell. What isn't trivial though, is winds experienced on ascent. Surface finish has a huge effect on drag, and overlapping scales would probably cut into payload capacity for that reason.

If you want my prediction, I think SpaceX will be filling those gaps with specialty tiles. This isn't the space shuttle. It won't be the end of the world if they end up needing to make two kinds of hinge tile, two kinds of flap edge tile, six or seven types of gap tile for the nose, and a nose tile. There's a big difference between producing that versus 24,000 unique individual tiles.

Have you seen what a tornado will do to shingles on the roof of a house?  Even the most powerful tornados are low speed subsonic, very comparable to the terminal velocity of Starship at the end of its belly flop maneuver when it flips to upright to land.  Don't underestimate aerodynamic forces.

The angle of attack is only 70 degrees or better on Starship, and roofing tiles aren't equivalent to house tiles. Besides, I'm just saying that those stages of EDL aren't relevant. If the tiles can stand escape-velocity-plus-C3 speeds at 70 degrees, of course they can withstand 0.9 mach at 90 degrees or 30 meters per second during the landing flip.
But not orthogonal flow, as in ascent.
Lapped structures are flow optimal only in one axis, and get progressively worse as you deviate from that axis. Starship experiences dense flow at high velocities (high subsonic and above supersonic) on orthogonal axes.
No capes overlap!

I mean, yeah. I'm just saying that overlapping tiles would suck because they would represent a horrible surface "finish" that would constantly rob delta-V from the vehicle all the way through ascent - regardless of how sturdy they are.
Title: Re: Starship heat shield
Post by: Blueshift on 02/20/2021 04:09 am
Covering this section with sheets of ?
(https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2013503;image)

Looks like liner for tiles to me. Could be the first SN in the works to get a full heat shield.
Title: Re: Starship heat shield
Post by: jthygesen on 02/20/2021 08:16 am
I'm not entirely certain, but I believe that the material on this starship section is Kaowool.  It's an amazingly insulative material that I have personal experience with using in metal foundries, and it can handle sustained temperatures in excess of 1,000° C.

If you would like to know more, here is a useful website that goes into greater detail about its properties:  https://www.foundryservice.com/product/kaowool-blanket-products-1800of-2600of-insulation-blankets/kaowool-blanket/ (https://www.foundryservice.com/product/kaowool-blanket-products-1800of-2600of-insulation-blankets/kaowool-blanket/)

Thought this would be useful here.
Title: Re: Starship heat shield
Post by: DreamyPickle on 02/21/2021 03:00 pm
Haven't seen this posted in this thread already but latest video from Mary clearly shows hexagonal tiles being laid around the bottom of the tank:

clip (https://www.youtube.com/watch?v=a2jPmB6iriU&t=565s)

It starts around 9:25, unfortunately I can't get linking to youtube timestamps to work in this forum.
Title: Re: Starship heat shield
Post by: Cheapchips on 02/21/2021 03:08 pm

Mary's video might give us a very rough 'go' to estimate the maximum time to tile a whole ship.

Also, you could see the barrel rotate after a couple of people left, presumably the pegging robot going back to work?
Title: Re: Starship heat shield
Post by: _MECO on 02/21/2021 05:07 pm
Covering this section with sheets of ?
(https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2013503;image)

Looks like liner for tiles to me. Could be the first SN in the works to get a full heat shield.

Which means they may intend for it to do high velocity EDL maneuvers or even to make orbit! We could be laying eyes on the Heart of Gold for the first time.
Title: Re: Starship heat shield
Post by: Lars-J on 02/21/2021 05:27 pm
I think the first “full heat shield” flight will just be a Starship (without SuperHeavy) flight to high altitude, almost as high/far it can go and still return.

But it all depends on how quickly the booster test articles qualify. But it might not be until BN5 (or later) that they launch a full stack.
Title: Re: Starship heat shield
Post by: Robotbeat on 02/21/2021 05:58 pm
The lowermost attachment variant ('full height' RCG coating, thin white felt, red RTV silicone) looks very STS. Would be amusing if that ended up being the most successful variant after all!

To me the red stuff looks more like a board of some kind, perhaps some kind of cement board? Although I don’t see how that makes any sense, so you’re probably right.

Original Image credit: Bocachicagal.
Red silicone.
Title: Re: Starship heat shield
Post by: chopsticks on 02/21/2021 07:32 pm
I find it curious that they might be doing a full heatshield (might being the key word here) yet we haven't seen any tiles on any nosecones yet (or have I missed it?). For that matter, we haven't spotted tiles either on aero covers or close to any hinge points. Who knows, they might just go for it assuming they are confident enough in the fastening mechanism to fix tiles everywhere by now. Perhaps getting tiles so stay on the tank section during multiple regimes is the hardest part.

Just thinking out loud here.
Title: Re: Starship heat shield
Post by: marsbase on 02/21/2021 07:46 pm
I find it curious that they might be doing a full heatshield (might being the key word here) yet we haven't seen any tiles on any nosecones yet (or have I missed it?). For that matter, we haven't spotted tiles either on aero covers or close to any hinge points. Who knows, they might just go for it assuming they are confident enough in the fastening mechanism to fix tiles everywhere by now. Perhaps getting tiles so stay on the tank section during multiple regimes is the hardest part.

Just thinking out loud here.
I know that Elon says he does the hard parts first.  But these body tiles may be "hard enough".  Once they can get the tiles to stay on the cylinder, they can try using a similar technique on flaps and conical sections.  Going the other way might not help since the specialty applications may be more difficult than necessary when applied to the cylinder.  Also just thinking out loud. :)
Title: Re: Starship heat shield
Post by: cuddihy on 02/23/2021 04:23 am
Hard for mass production is a bigger concern than hard for a few prototypes.

So if you make 20 starships this year it’s still a small batch of hinge surfaces and flaps you have to cover this year, but it’s 100s of thousands of body tiles. Production, emplacement, wear all have to be reliable, repeatable or body tiles becomes the simple thing that eats the rest of the program.

Title: Re: Starship heat shield
Post by: Dr.Unhold on 03/04/2021 11:06 am
They seem to have made great progress with the attachments of TPS tiles, judging by the SN10 flight.

- all tiles seem to be still attached after ascent (pic 1, source: Everyday Astronaut Youtube Video of SN10)
- at least the large batch of tiles still seems to be attached after, not so soft, landing (pic2, NSF Youtube Video of SN10)
- unfortunately, I did not find a better shot of the windward side of SN10 after landing, before RUD.
Title: Re: Starship heat shield
Post by: xvel on 03/04/2021 04:34 pm
there is better shot of tiles just before landing, all looks good
Title: Re: Starship heat shield
Post by: rsdavis9 on 03/05/2021 02:36 pm
So my eye balling guess is the that the fins are about 1/3 of the cross sectional area?
Anybody else actually calculated it from the dimensions?
So what is the formula for ballistic coefficient to peak heating? Total heat load? I thought there was a square term somewhere in there.

So I am trying to get an idea of how much the lower ballistic coefficient helps?
Title: Re: Starship heat shield
Post by: eriblo on 03/05/2021 07:06 pm
So my eye balling guess is the that the fins are about 1/3 of the cross sectional area?
Anybody else actually calculated it from the dimensions?
So what is the formula for ballistic coefficient to peak heating? Total heat load? I thought there was a square term somewhere in there.

So I am trying to get an idea of how much the lower ballistic coefficient helps?
Peak heat flux and total heat load both scale roughly as (ballistic coefficient)1/2 for convective heating. So peak temperature would go as (BC)1/8.

The flaps will increase the effective radius of the cylindrical body when deployed beyond the Mach angle so their contribution will be larger than just their projected area. My guess is that there has been "a few" simulation runs to figure out how far they can deploy them before impacting lift and stability.

An interesting consequence of having larger aft flaps is that the max payload reentries might have a slightly disproportionate increase in ballistic coefficient...
Title: Re: Starship heat shield
Post by: rsdavis9 on 03/05/2021 07:19 pm
So my eye balling guess is the that the fins are about 1/3 of the cross sectional area?
Anybody else actually calculated it from the dimensions?
So what is the formula for ballistic coefficient to peak heating? Total heat load? I thought there was a square term somewhere in there.

So I am trying to get an idea of how much the lower ballistic coefficient helps?
Peak heat flux and total heat load both scale roughly as (ballistic coefficient)1/2 for convective heating. So peak temperature would go as (BC)1/8.

The flaps will increase the effective radius of the cylindrical body when deployed beyond the Mach angle so their contribution will be larger than just their projected area. My guess is that there has been "a few" simulation runs to figure out how far they can deploy them before impacting lift and stability.

An interesting consequence of having larger aft flaps is that the max payload reentries might have a slightly disproportionate increase in ballistic coefficient...
thanks.

I found this formula for peak heat flux.
      qdot = 1.83E-4*v^3*sqrt(rho/radius)
      v=velocity
      rho=atmospheric density kg/m^3
      radius of nose
      qdot=watts/m^2

Title: Re: Starship heat shield
Post by: eriblo on 03/05/2021 07:37 pm
[...]
I found this formula for peak heat flux.
      qdot = 1.83E-4*v^3*sqrt(rho/radius)
      v=velocity
      rho=atmospheric density kg/m^3
      radius of nose
      qdot=watts/m^2
I have found this useful for back-of-the-envelope (or wolframalpha) calculations (PDF): https://tfaws.nasa.gov/TFAWS12/Proceedings/Aerothermodynamics%20Course.pdf
Title: Re: Starship heat shield
Post by: erv on 03/06/2021 02:13 pm
At the end of the video from the Mexican side shared in updates thread (https://forum.nasaspaceflight.com/index.php?topic=52924.msg2201015#msg2201015) we can see that after the landing the big patch of tiles is there as intact as can be seen and I think at least one of the smaller ones as well. Wondering what is its status after the RUD though ;)
Title: Re: Starship heat shield
Post by: equiserre on 03/06/2021 02:45 pm
So my eye balling guess is the that the fins are about 1/3 of the cross sectional area?
Anybody else actually calculated it from the dimensions?
So what is the formula for ballistic coefficient to peak heating? Total heat load? I thought there was a square term somewhere in there.

So I am trying to get an idea of how much the lower ballistic coefficient helps?
I calculated the projected areas from dimensions as best we know:
cylinder + nosecone= 412 m2
Forward fins +aft fins+ the root chines at 90 deg AoA=160m2
Title: Re: Starship heat shield
Post by: rsdavis9 on 03/06/2021 02:52 pm
So my eye balling guess is the that the fins are about 1/3 of the cross sectional area?
Anybody else actually calculated it from the dimensions?
So what is the formula for ballistic coefficient to peak heating? Total heat load? I thought there was a square term somewhere in there.

So I am trying to get an idea of how much the lower ballistic coefficient helps?
I calculated the projected areas from dimensions as best we know:
cylinder + nosecone= 412 m2
Forward fins +aft fins+ the root chines at 90 deg AoA=160m2

So 2.6 to 1
Title: Re: Starship heat shield
Post by: DreamyPickle on 03/08/2021 03:06 pm
SN10's landing was much harder than designed so if the heat shield can survive that it can survive any reasonable shock.

Looking at SN11 the shielded area is roughly double, at this rate we'll have to wait for SN20 or more to get a full heatshield that can face re-entry.
Title: Re: Starship heat shield
Post by: Cheapchips on 03/08/2021 03:17 pm
Looking at SN11 the shielded area is roughly double, at this rate we'll have to wait for SN20 or more to get a full heatshield that can face re-entry.

They need roughly 10,000 don't they?  Doubling each time would see that many by SN19.
Title: Re: Starship heat shield
Post by: IanThePineapple on 03/08/2021 03:36 pm
SN11 has 360 tiles on the body, unsure if any on the flaps. SN10 had 246. Interesting to watch it grow over time.
Title: Re: Starship heat shield
Post by: steveleach on 03/08/2021 03:40 pm
SN11 has 360 tiles on the body, unsure if any on the flaps. SN10 had 246. Interesting to watch it grow over time.
I'm confused - what advantage would there be in having the greater number of tiles?
Title: Re: Starship heat shield
Post by: zeekakboos on 03/08/2021 03:44 pm
SN11 has 360 tiles on the body, unsure if any on the flaps. SN10 had 246. Interesting to watch it grow over time.
I'm confused - what advantage would there be in having the greater number of tiles?


I think they mean more coverage of the prototypes, not a greater number of tiles for a full heatshield.
Title: Re: Starship heat shield
Post by: steveleach on 03/08/2021 03:50 pm
SN11 has 360 tiles on the body, unsure if any on the flaps. SN10 had 246. Interesting to watch it grow over time.
I'm confused - what advantage would there be in having the greater number of tiles?


I think they mean more coverage of the prototypes, not a greater number of tiles for a full heatshield.
Yes, that's what I assumed they meant.

But why have more tiles on the prototypes? What does the larger patch tell you that the smaller one doesn't?
Title: Re: Starship heat shield
Post by: eriblo on 03/08/2021 03:57 pm
SN11 has 360 tiles on the body, unsure if any on the flaps. SN10 had 246. Interesting to watch it grow over time.
I'm confused - what advantage would there be in having the greater number of tiles?


I think they mean more coverage of the prototypes, not a greater number of tiles for a full heatshield.
Yes, that's what I assumed they meant.

But why have more tiles on the prototypes? What does the larger patch tell you that the smaller one doesn't?
You get more practice installing them and better statistics on the installation processes and mechanical/thermal performance.
Title: Re: Starship heat shield
Post by: zeekakboos on 03/08/2021 04:01 pm
SN11 has 360 tiles on the body, unsure if any on the flaps. SN10 had 246. Interesting to watch it grow over time.
I'm confused - what advantage would there be in having the greater number of tiles?


I think they mean more coverage of the prototypes, not a greater number of tiles for a full heatshield.
Yes, that's what I assumed they meant.

But why have more tiles on the prototypes? What does the larger patch tell you that the smaller one doesn't?
You get more practice installing them and better statistics on the installation processes and mechanical/thermal performance.
And maybe as prototypes are built and SX sees the likelihood of each crashing shrink they're willing to install more tiles.
Title: Re: Starship heat shield
Post by: steveleach on 03/08/2021 04:35 pm
SN11 has 360 tiles on the body, unsure if any on the flaps. SN10 had 246. Interesting to watch it grow over time.
I'm confused - what advantage would there be in having the greater number of tiles?


I think they mean more coverage of the prototypes, not a greater number of tiles for a full heatshield.
Yes, that's what I assumed they meant.

But why have more tiles on the prototypes? What does the larger patch tell you that the smaller one doesn't?
You get more practice installing them and better statistics on the installation processes and mechanical/thermal performance.
And maybe as prototypes are built and SX sees the likelihood of each crashing shrink they're willing to install more tiles.
But if the justification is practice and data gathering, why not just put on the full set?
Title: Re: Starship heat shield
Post by: Stan-1967 on 03/08/2021 04:38 pm
I have also been wondering if they will get better or worse landing profiles with more of the heat shield installed as, the additional mass of the heatshield moves the center of mass of Starship ( in the Z-Y plane ) away from the geometric centerline of the vehicle.  I had a hard time finding reliable guestimates of the heatshield mass, but a 15t heatshield would make a 662kN*m moment arm. 

If the landing is to be on two engines, it seems like you want to prioritize moving the CoM towards the thrust vector of the primary landing engines.  That would minimize the off axis gimbal angle needed for the asymetric CoM.  Would it even be possible to move the centroid three center raptors slightly towards the asymetic CG to have better control in nominal & off nominal landings?

edited X-Y plane to Z-Y plane.  My understanding is that x-axis is along the length of the ship
Title: Re: Starship heat shield
Post by: zeekakboos on 03/08/2021 04:41 pm
SN11 has 360 tiles on the body, unsure if any on the flaps. SN10 had 246. Interesting to watch it grow over time.
I'm confused - what advantage would there be in having the greater number of tiles?


I think they mean more coverage of the prototypes, not a greater number of tiles for a full heatshield.
Yes, that's what I assumed they meant.

But why have more tiles on the prototypes? What does the larger patch tell you that the smaller one doesn't?
You get more practice installing them and better statistics on the installation processes and mechanical/thermal performance.
And maybe as prototypes are built and SX sees the likelihood of each crashing shrink they're willing to install more tiles.
But if the justification is practice and data gathering, why not just put on the full set?
Cost? and of course they don't really need the full heatshield for actually protecting the vehicle until probably >SN15 so might as well work your way up
Title: Re: Starship heat shield
Post by: steveleach on 03/08/2021 04:55 pm
Yes, that's what I assumed they meant.

But why have more tiles on the prototypes? What does the larger patch tell you that the smaller one doesn't?
You get more practice installing them and better statistics on the installation processes and mechanical/thermal performance.
And maybe as prototypes are built and SX sees the likelihood of each crashing shrink they're willing to install more tiles.
But if the justification is practice and data gathering, why not just put on the full set?
Cost? and of course they don't really need the full heatshield for actually protecting the vehicle until probably >SN15 so might as well work your way up
Yep, OK. So that means they need to use the smallest area they can.

There are drivers to have more, and drivers to have less.

I'm trying to figure out if anyone has a theory on why SN11 has more than SN10.

I'll throw in a theory of my own, just to move the discussion on: they have a fixed "budget" for tiles on each prototype, and they are getting better at installing them so the same budget lets them install more tiles.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 03/08/2021 05:01 pm
I have also been wondering if they will get better or worse landing profiles with more of the heat shield installed as, the additional mass of the heatshield moves the center of mass of Starship ( in the X-Y plane ) away from the geometric centerline of the vehicle.  I had a hard time finding reliable guestimates of the heatshield mass, but a 15t heatshield would make a 662kN*m moment arm. 

If the landing is to be on two engines, it seems like you want to prioritize moving the CoM towards the thrust vector of the primary landing engines.  That would minimize the off axis gimbal angle needed for the asymetric CoM.  Would it even be possible to move the centroid three center raptors slightly towards the asymetic CG to have better control in nominal & off nominal landings?

there's likely going to be a service tunnel on the leeward side where  you currently see exposed wires, which will counter balance some of the heatshield mass.

also the 15t isn't 4.5 meters out, it's a half circle so COM is  0.42 * 4.5 = 1.9 meters out.  so it's really 280kN*m.

The service tunnel needs to only mass  280kn*m/4.5 / 9.8 = 6.4 tons to counter this.  Probably won't weigh that much unless they put the battery on the lweward side.

COM for a half circle:  ( https://www.youtube.com/watch?v=Vf2bUXjUGJE )

Much discussion beyond this needs to go to the Engineering thread.  I"m pasting this thread there.
Title: Re: Starship heat shield
Post by: Cheapchips on 03/08/2021 06:26 pm
I'm trying to figure out if anyone has a theory on why SN11 has more than SN10.

I'll throw in a theory of my own, just to move the discussion on: they have a fixed "budget" for tiles on each prototype, and they are getting better at installing them so the same budget lets them install more tiles.

They might still be trying out slightly different tile manufacturing / ramping up manufacturing.  Wasn't there something about that  in a job ad?

Didn't SN10 also have a significant area of unused attachment studs? They might not have had enough tiles to populate it. Or it was just the stud robot going nuts.  :)
Title: Re: Starship heat shield
Post by: steveleach on 03/08/2021 06:33 pm
I'm trying to figure out if anyone has a theory on why SN11 has more than SN10.

I'll throw in a theory of my own, just to move the discussion on: they have a fixed "budget" for tiles on each prototype, and they are getting better at installing them so the same budget lets them install more tiles.

They might still be trying out slightly different tile manufacturing / ramping up manufacturing.  Wasn't there something about that  in a job ad?

Didn't SN10 also have a significant area of unused attachment studs? They might not have had enough tiles to populate it. Or it was just the stud robot going nuts.  :)
Yep, though you could argue that manufacturing capacity is just how they determine the "tile budget" for each SN, so it's basically a variant.

Any other ideas?
Title: Re: Starship heat shield
Post by: Genial Precis on 03/08/2021 07:26 pm
My completely uninformed guess is that the heat shield-attaching processes are being worked out, but it's not a high priority because you want to adjust things in response to high-fidelity real data about how it performs in use, which they only get so much of in these tests where there's no heat to shield. There's no incentive to spend a lot of time optimizing things for an objective you haven't tested yet.

I'm not at all sure either why the amount of heat shield would increase but not so quickly.
Title: Re: Starship heat shield
Post by: Jimmy_C on 03/08/2021 07:46 pm
I'm not at all sure either why the amount of heat shield would increase but not so quickly.

While a part waits for it's turn to be moved to the next stage of the assembly line, the heat shield fairy robot practices on it. The method for applying heat shields just gets quicker each time. At least that's my best guess. They might be trying to figure out the error rate.
Title: Re: Starship heat shield
Post by: awests on 03/08/2021 08:10 pm
Some crazy good close-ups of the tiles:

https://twitter.com/cooper_hime/status/1369029998934392833?s=21

Credit: Cooper Hime


Sent from my iPhone using Tapatalk
Title: Re: Starship heat shield
Post by: Lars-J on 03/08/2021 09:21 pm
Another good shot, with humans for scale:

https://twitter.com/Cooper_Hime/status/1368961299976192003
Title: Re: Starship heat shield
Post by: steveleach on 03/08/2021 09:33 pm
Why do they use half-tiles on the top and bottom, but not the left and right?
Title: Re: Starship heat shield
Post by: Slarty1080 on 03/08/2021 09:35 pm
Why do they use half-tiles on the top and bottom, but not the left and right?
They will have to use half tiles at the bottom at least, but need not used half tiles at the sides (although they might)
Title: Re: Starship heat shield
Post by: steveleach on 03/08/2021 09:48 pm
Why do they use half-tiles on the top and bottom, but not the left and right?
They will have to use half tiles at the bottom at least, but need not used half tiles at the sides (although they might)
Can you imagine Elon letting them build it (the "final" version) without straight sides? He wants his spaceships to look good.
Title: Re: Starship heat shield
Post by: spacenut on 03/08/2021 09:53 pm
I would think the solar panels that would be installed on the opposite side of the heat tiles would somewhat offset the c/g.  Also a rail that may run down the center of the leeward side for the elevator to glide down with the cargo and crew versions.  Maybe they should install some offset mass depending on the mass of the tiles when testing. 
Title: Re: Starship heat shield
Post by: mikegi on 03/08/2021 10:03 pm
SN11 has 360 tiles on the body, unsure if any on the flaps. SN10 had 246. Interesting to watch it grow over time.
I'm confused - what advantage would there be in having the greater number of tiles?


I think they mean more coverage of the prototypes, not a greater number of tiles for a full heatshield.
Yes, that's what I assumed they meant.

But why have more tiles on the prototypes? What does the larger patch tell you that the smaller one doesn't?
IIRC, SN10 had tiles on the body and flaps. My guess is that they're testing various points to see how they behave during ascent and landing (vibration, etc.). At some point I imagine the heat shield engineers will say, how about successfully landing one of these beasts so we can take a look at the results! :)
Title: Re: Starship heat shield
Post by: horninfbb on 03/08/2021 10:36 pm
Looking at Nomadd's photos (and others'), there are regularly spaced holes in the flap fairings - has this been seen on past SN's?  Is it possible they'll vent the engine chill gases through these holes behind tiles to cool the harder-to-shield complex moving flap interface?
Nomadd's photo here.
Title: Re: Starship heat shield
Post by: Haur on 03/08/2021 10:46 pm
Looking at Nomadd's photos (and others'), there are regularly spaced holes in the flap fairings - has this been seen on past SN's?  Is it possible they'll vent the engine chill gases through these holes behind tiles to cool the harder-to-shield complex moving flap interface?
Nomadd's photo here.

They allow access to the aerocover frame fixings. See this image from bocachicagal of some delivered last month.
Title: Re: Starship heat shield
Post by: OTV Booster on 03/09/2021 04:28 pm
I'm trying to figure out if anyone has a theory on why SN11 has more than SN10.

I'll throw in a theory of my own, just to move the discussion on: they have a fixed "budget" for tiles on each prototype, and they are getting better at installing them so the same budget lets them install more tiles.

They might still be trying out slightly different tile manufacturing / ramping up manufacturing.  Wasn't there something about that  in a job ad?

Didn't SN10 also have a significant area of unused attachment studs? They might not have had enough tiles to populate it. Or it was just the stud robot going nuts.  :)
What we haven't seen is tiles on the hard parts. My first take on images of 11 coming out of the high bay was that they had some patches on the nose. Closer examination showed it to be the lifting shackles.


A fully populated cylinder is necessary, but not sufficient. They know their business better than I do. Just sayin...
Title: Re: Starship heat shield
Post by: OTV Booster on 03/09/2021 04:31 pm
My completely uninformed guess is that the heat shield-attaching processes are being worked out, but it's not a high priority because you want to adjust things in response to high-fidelity real data about how it performs in use, which they only get so much of in these tests where there's no heat to shield. There's no incentive to spend a lot of time optimizing things for an objective you haven't tested yet.

I'm not at all sure either why the amount of heat shield would increase but not so quickly.
To ease into the changes more tiles make in handling?
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 03/09/2021 05:04 pm
Sn10,as the pictures that we saw, has many spots of tiles. There are two spots of tiles in the lower part, and one  is not as the bigger square spot. There are tiles with distorted shap, very similar to a draw by an user, that maybe are for the nose cone area.
Title: Re: Starship heat shield
Post by: JCopernicus on 03/09/2021 05:14 pm
Looking at Nomadd's photos (and others'), there are regularly spaced holes in the flap fairings - has this been seen on past SN's?  Is it possible they'll vent the engine chill gases through these holes behind tiles to cool the harder-to-shield complex moving flap interface?
Nomadd's photo here.

They allow access to the aerocover frame fixings. See this image from bocachicagal of some delivered last month.

Those those noodles hint at a possible water landing?
Title: Re: Starship heat shield
Post by: Oersted on 03/09/2021 07:16 pm
https://twitter.com/cooper_hime/status/1369016118459965443

That white layer looks like a felt pad to me. What do you guys think?
Title: Re: Starship heat shield
Post by: FutureSpaceTourist on 03/09/2021 07:53 pm
https://twitter.com/cnunezimages/status/1369389055826419716
Title: Re: Starship heat shield
Post by: awests on 03/09/2021 08:06 pm
https://twitter.com/cooper_hime/status/1369016118459965443

That white layer looks like a felt pad to me. What do you guys think?
Further up thread someone mentioned it looked similar to Kaowool
Title: Re: Starship heat shield
Post by: InterestedEngineer on 03/10/2021 02:20 am
Further up thread someone mentioned it looked similar to Kaowool

I'm starting to think of the tiles as a way to protect the Kaowool from wind and keep it in place mechanically.

i.e. the tile's function is mechanical, not really insulation.   Of course it has to survive insane amounts of heat to do its job, so some insulation properties are needed to protect the connection point to the hull.

Title: Re: Starship heat shield
Post by: Johnnyhinbos on 03/10/2021 02:55 am
https://twitter.com/cooper_hime/status/1369477304930467841
Title: Re: Starship heat shield
Post by: InterestedEngineer on 03/10/2021 04:24 am

I'm starting to think of the tiles as a way to protect the Kaowool from wind and keep it in place mechanically.

i.e. the tile's function is mechanical, not really insulation.   Of course it has to survive insane amounts of heat to do its job, so some insulation properties are needed to protect the connection point to the hull.

Even crazier idea:  If Kaowool is the main insulator and we just need a mechanical system to keep it in place and prevent it from blowing away in a Mach 2.5 wind (max Q), why not just keep it place with a high temperature wire mesh?

For example a Tungsten wire mesh.  https://metalcutting.com/knowledge-center/properties-applications-tungsten-wire/

I suspect there are weaving machines that could mass produce a wire mesh.

Question is whether a tungsten mesh could be made light enough is a good question.  Off to hit the calculator.

EDIT:  actual tungsten meshes (and inconel):  https://nickel-wiremesh.com/material/tungsten-mesh/
Title: Re: Starship heat shield
Post by: FutureSpaceTourist on 03/10/2021 05:57 am
https://twitter.com/tylerg1998/status/1369518843228545026

Quote
A quick edit I made showing the progression between the amounts of heat shield tiles on #Starship SNs 8-11. #SpaceX has definitely been piling them on as of late!

And to think, we could soon see one with a full TPS layout. 👀

📸: Me, @thejackbeyer
Title: Re: Starship heat shield
Post by: CruddyCuber on 03/10/2021 06:29 am

I'm starting to think of the tiles as a way to protect the Kaowool from wind and keep it in place mechanically.

i.e. the tile's function is mechanical, not really insulation.   Of course it has to survive insane amounts of heat to do its job, so some insulation properties are needed to protect the connection point to the hull.

Even crazier idea:  If Kaowool is the main insulator and we just need a mechanical system to keep it in place and prevent it from blowing away in a Mach 2.5 wind (max Q), why not just keep it place with a high temperature wire mesh?

For example a Tungsten wire mesh.  https://metalcutting.com/knowledge-center/properties-applications-tungsten-wire/

I suspect there are weaving machines that could mass produce a wire mesh.

Question is whether a tungsten mesh could be made light enough is a good question.  Off to hit the calculator.

EDIT:  actual tungsten meshes (and inconel):  https://nickel-wiremesh.com/material/tungsten-mesh/

  In my experience with kaowool in foundries, it needs to be coated in refractory cement to protect it.  Kaowool is an amazing insulator, but I highly doubt that it could withstand the dynamic environment of reentry on its own, given that it can't survive the conditions of a comparatively gentle metal foundry without protection.
Insulation is far from the only factor to consider when designing a heat shield, and while kaowool is an amazing insulator, I highly doubt it would ever survive reentry without heat shield tiles to protect it, regardless of how well you secure it with mesh.

That said, I find your tungsten mesh idea intriguing, not for securing kaowool as a standalone heat shield, but as a potential alternative or redundant method of securing TPS tiles.  However, I know next to nothing about tungsten, and would appreciate input from people more knowledgable of its properties than myself.
Title: Re: Starship heat shield
Post by: HVM on 03/10/2021 06:45 am
Better, but still; if those were floor tiles I'll would fire the contractor and send tiles back to manufacturer...

https://twitter.com/cnunezimages/status/1369389055826419716
Ha, that dude just took picture of his bathroom tiles... And you can't tell me otherwise
Title: Re: Starship heat shield
Post by: sebk on 03/10/2021 11:53 am
Tungsten is too easy to oxidize. If you want a metal able to survive in 2000K hot air you'd rather use niobium.
Title: Re: Starship heat shield
Post by: equiserre on 03/10/2021 12:18 pm
How does the heatshield handle water trapped and absorbed from rain? especially the felt or wool, but also the ceramic tiles? how did the shuttle handle this issue?
Title: Re: Starship heat shield
Post by: Rocket Surgeon on 03/10/2021 12:21 pm
How does the heatshield handle water trapped and absorbed from rain? especially the felt or wool, but also the ceramic tiles? how did the shuttle handle this issue?

Given its flying up to vaccum, any water would probably vaporise once in orbit and then escape if not completely sealed in.
Title: Re: Starship heat shield
Post by: sebk on 03/10/2021 12:27 pm
How does the heatshield handle water trapped and absorbed from rain? especially the felt or wool, but also the ceramic tiles? how did the shuttle handle this issue?


Shuttle tiles were impregnated. And had to be re-impregnated after every flight because re-entry evaporated the stuff.
According to environmental statement info for Starship tile production (the same facility where Shuttle tiles were made, in fact) the Starship tiles are impregnated too (using similar, but different substance).

I don't know what the do (if anything) for that insulating under-tile mat, though.
Title: Re: Starship heat shield
Post by: equiserre on 03/10/2021 12:45 pm
How does the heatshield handle water trapped and absorbed from rain? especially the felt or wool, but also the ceramic tiles? how did the shuttle handle this issue?

Given its flying up to vaccum, any water would probably vaporise once in orbit and then escape if not completely sealed in.

Yes, but I was asking about the problems in the atmosphere: 1st weight increase, a mat or felt can hold a lot of water; 2nd solid ice forming in the mat from cryo tank walls. Are those issues  significant or minor?
Title: Re: Starship heat shield
Post by: Robotbeat on 03/10/2021 12:46 pm
How does the heatshield handle water trapped and absorbed from rain? especially the felt or wool, but also the ceramic tiles? how did the shuttle handle this issue?


Shuttle tiles were impregnated. And had to be re-impregnated after every flight because re-entry evaporated the stuff.
According to environmental statement info for Starship tile production (the same facility where Shuttle tiles were made, in fact) the Starship tiles are impregnated too (using similar, but different substance).

I don't know what the do (if anything) for that insulating under-tile mat, though.
Impregnated with what? Shuttle and Starship.
Title: Re: Starship heat shield
Post by: equiserre on 03/10/2021 12:47 pm
How does the heatshield handle water trapped and absorbed from rain? especially the felt or wool, but also the ceramic tiles? how did the shuttle handle this issue?


Shuttle tiles were impregnated. And had to be re-impregnated after every flight because re-entry evaporated the stuff.
According to environmental statement info for Starship tile production (the same facility where Shuttle tiles were made, in fact) the Starship tiles are impregnated too (using similar, but different substance).

I don't know what the do (if anything) for that insulating under-tile mat, though.

I undestand the Shuttle had an under-tile mat or felt as well. Do you know if/how was that protected from rainwater?
Title: Re: Starship heat shield
Post by: samgineer on 03/10/2021 12:54 pm
How does the heatshield handle water trapped and absorbed from rain? especially the felt or wool, but also the ceramic tiles? how did the shuttle handle this issue?


Shuttle tiles were impregnated. And had to be re-impregnated after every flight because re-entry evaporated the stuff.
According to environmental statement info for Starship tile production (the same facility where Shuttle tiles were made, in fact) the Starship tiles are impregnated too (using similar, but different substance).

I don't know what the do (if anything) for that insulating under-tile mat, though.

I undestand the Shuttle had an under-tile mat or felt as well. Do you know if/how was that protected from rainwater?

Shuttle tiles was glued with red heat resistant silicone witch even SpaceX tested/ing on Starship to attach tiles to engine section. It make no sense to glue wool, it's suitable only for mechanical attachment.
Title: Re: Starship heat shield
Post by: spacenut on 03/10/2021 12:55 pm
The under tile mat could be treated to resist water and it is waterproof, like Goretex or using silicone spray on shoes or clothing to make it waterproof.  I have used the stuff called Camp Dry when I have been camping or hunting during damp or rainy weather.  Stuff works good.  Tight woven wool also resists water.  I know SpaceX doesn't want water behind the tiles for three reasons.  One is freezing against the cold walls when full of liquid methane or oxygen.  Two is extreme heating upon re-entry.  And three is the extra weight or mass during liftoff.  So I think it is some type of moisture resistant padding. 
Title: Re: Starship heat shield
Post by: RedLineTrain on 03/13/2021 10:00 pm
Wow, this is a super-simple tile application technique.  Is that all that is required, or does it need to be welded into place somehow?

https://twitter.com/thejackbeyer/status/1370853087410278407
Title: Re: Starship heat shield
Post by: eriblo on 03/13/2021 10:38 pm
Wow, this is a super-simple tile application technique.  Is that all that is required, or does it need to be welded into place somehow?
[Tweet]
From what we have seen so far it does look like it is that simple:

Robot welds studs onto the barrel. Studs have two tapered prongs with some kind of hooking/latching protrusion at the end. Three studs per tile.

High temperature mineral/refractory cheramic fiber mats are fitted to the barrel side and the studs are pressed through. No sign of further fastening but it is not ruled out.

Tiles are pressed fitted onto the studs, slightly compressing the mat until looked in place.


Cracked or faulty tiles can be removed by piercing the tile with a sharp metal object at the location of the three studs (likely just breaking the tile around the attachment points).
Title: Re: Starship heat shield
Post by: ThatOldJanxSpirit on 03/14/2021 08:05 am
Wow, this is a super-simple tile application technique.  Is that all that is required, or does it need to be welded into place somehow?
[Tweet]
From what we have seen so far it does look like it is that simple:

Robot welds studs onto the barrel. Studs have two tapered prongs with some kind of hooking/latching protrusion at the end. Three studs per tile.

High temperature mineral/refractory cheramic fiber mats are fitted to the barrel side and the studs are pressed through. No sign of further fastening but it is not ruled out.

Tiles are pressed fitted onto the studs, slightly compressing the mat until looked in place.


Cracked or faulty tiles can be removed by piercing the tile with a sharp metal object at the location of the three studs (likely just breaking the tile around the attachment points).

A quick trip down memory lane. In the early Shuttle program the average tile installation rate was 1.3 tiles per worker per week.

https://history.nasa.gov/sts1/pages/tps.html

No doubt it improved later, but it’s a great reminder of how transformational some of these simple manufacturing processes can be.
Title: Re: Starship heat shield
Post by: DreamyPickle on 03/14/2021 08:20 am
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.
Title: Re: Starship heat shield
Post by: BT52 on 03/14/2021 09:39 am
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.

Generally there is rule of thump for automation. If human cannot do task blindfolded you should not do robotization of that process.
Title: Re: Starship heat shield
Post by: steveleach on 03/14/2021 01:22 pm
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.

Generally there is rule of thump for automation. If human cannot do task blindfolded you should not do robotization of that process.
Better not let AI drive cars then  ;D

I suspect that once they've fully tiled a Starship and verified that the mounting process is robust they will invest in automation of it. For the moment they don't actually know whether they'll stick with this method, so any investment would be at risk.
Title: Re: Starship heat shield
Post by: Johnnyhinbos on 03/14/2021 01:41 pm
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.

Generally there is rule of thump for automation. If human cannot do task blindfolded you should not do robotization of that process.
Oh - I thought the rule of thump was if at first it doesn’t fit, thump it in...
Title: Re: Starship heat shield
Post by: Broccoli32 on 03/14/2021 02:13 pm
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.

Elon has already made the mistake of over-automating, it doesn’t work. People are far superior to machines when it comes to work like this. What may be simple to humans can be complex for machines vice versa. 
Title: Re: Starship heat shield
Post by: eriblo on 03/14/2021 02:27 pm
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.
Elon has already made the mistake of over-automating, it doesn’t work. People are far superior to machines when it comes to work like this. What may be simple to humans can be complex for machines vice versa. 
I would agree - The step requiring the most time and precision, welding the studs, is already automated (at least for the barrel sections).

From the videos it takes two SpaceXers 4 minutes to install ~4 m2 of insulation blanket/mat and ~10 s for one person to attach one tile. Rounding a bit that is ~5 person-minutes/m2 for blanket+tile installation which extrapolates to < 80 person-hours of slightly variable and delicate (but not especially physically demanding or difficult) work for the whole ~800 m2 heat shield. Hardly seems like a prime target for automation even if you add a magnitude for overhead and any finicky bits...
Title: Re: Starship heat shield
Post by: ZachF on 03/14/2021 02:34 pm
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.
Elon has already made the mistake of over-automating, it doesn’t work. People are far superior to machines when it comes to work like this. What may be simple to humans can be complex for machines vice versa. 
I would agree - The step requiring the most time and precision, welding the studs, is already automated (at least for the barrel sections).

From the videos it takes two SpaceXers 4 minutes to install ~4 m2 of insulation blanket/mat and ~10 s for one person to attach one tile. Rounding a bit that is ~5 person-minutes/m2 for blanket+tile installation which extrapolates to < 80 person-hours of slightly variable and delicate (but not especially physically demanding or difficult) work for the whole ~800 m2 heat shield. Hardly seems like a prime target for automation even if you add a magnitude for overhead and any finicky bits...

Less than $10,000 in labor per Starship if we assume even a $50/hr cost. Literally peanuts. Plus they can perform QA at the same time.
Title: Re: Starship heat shield
Post by: ZachF on 03/14/2021 02:36 pm
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.

Generally there is rule of thump for automation. If human cannot do task blindfolded you should not do robotization of that process.
Oh - I thought the rule of thump was if at first it doesn’t fit, thump it in...

...That didn't work out too well for Proton  :o ;D
Title: Re: Starship heat shield
Post by: steveleach on 03/14/2021 02:47 pm
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.
Elon has already made the mistake of over-automating, it doesn’t work. People are far superior to machines when it comes to work like this. What may be simple to humans can be complex for machines vice versa. 
I would agree - The step requiring the most time and precision, welding the studs, is already automated (at least for the barrel sections).

From the videos it takes two SpaceXers 4 minutes to install ~4 m2 of insulation blanket/mat and ~10 s for one person to attach one tile. Rounding a bit that is ~5 person-minutes/m2 for blanket+tile installation which extrapolates to < 80 person-hours of slightly variable and delicate (but not especially physically demanding or difficult) work for the whole ~800 m2 heat shield. Hardly seems like a prime target for automation even if you add a magnitude for overhead and any finicky bits...

Less than $10,000 in labor per Starship if we assume even a $50/hr cost. Literally peanuts. Plus they can perform QA at the same time.
But if you plan to build at least 100 Starships you can afford to invest $1m in automation for it.
Title: Re: Starship heat shield
Post by: HVM on 03/14/2021 02:51 pm
These are prototypes, if installer robot is needed, Tesla Grohmann Automation GmbH will design it for SpaceX.
Title: Re: Starship heat shield
Post by: ZachF on 03/14/2021 02:57 pm
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.
Elon has already made the mistake of over-automating, it doesn’t work. People are far superior to machines when it comes to work like this. What may be simple to humans can be complex for machines vice versa. 
I would agree - The step requiring the most time and precision, welding the studs, is already automated (at least for the barrel sections).

From the videos it takes two SpaceXers 4 minutes to install ~4 m2 of insulation blanket/mat and ~10 s for one person to attach one tile. Rounding a bit that is ~5 person-minutes/m2 for blanket+tile installation which extrapolates to < 80 person-hours of slightly variable and delicate (but not especially physically demanding or difficult) work for the whole ~800 m2 heat shield. Hardly seems like a prime target for automation even if you add a magnitude for overhead and any finicky bits...

Less than $10,000 in labor per Starship if we assume even a $50/hr cost. Literally peanuts. Plus they can perform QA at the same time.
But if you plan to build at least 100 Starships you can afford to invest $1m in automation for it.

Automation doesn't always work better than people.
Title: Re: Starship heat shield
Post by: Johnnyhinbos on 03/14/2021 03:06 pm
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.
Elon has already made the mistake of over-automating, it doesn’t work. People are far superior to machines when it comes to work like this. What may be simple to humans can be complex for machines vice versa. 
I would agree - The step requiring the most time and precision, welding the studs, is already automated (at least for the barrel sections).

From the videos it takes two SpaceXers 4 minutes to install ~4 m2 of insulation blanket/mat and ~10 s for one person to attach one tile. Rounding a bit that is ~5 person-minutes/m2 for blanket+tile installation which extrapolates to &lt; 80 person-hours of slightly variable and delicate (but not especially physically demanding or difficult) work for the whole ~800 m2 heat shield. Hardly seems like a prime target for automation even if you add a magnitude for overhead and any finicky bits...

Less than $10,000 in labor per Starship if we assume even a $50/hr cost. Literally peanuts. Plus they can perform QA at the same time.
But if you plan to build at least 100 Starships you can afford to invest $1m in automation for it.

Automation doesn't always work better than people.
True - though this task looks (ultimately) tailor  made for automation.
Title: Re: Starship heat shield
Post by: Malatrope on 03/14/2021 03:08 pm
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.
Elon has already made the mistake of over-automating, it doesn’t work. People are far superior to machines when it comes to work like this. What may be simple to humans can be complex for machines vice versa. 
I would agree - The step requiring the most time and precision, welding the studs, is already automated (at least for the barrel sections).

From the videos it takes two SpaceXers 4 minutes to install ~4 m2 of insulation blanket/mat and ~10 s for one person to attach one tile. Rounding a bit that is ~5 person-minutes/m2 for blanket+tile installation which extrapolates to < 80 person-hours of slightly variable and delicate (but not especially physically demanding or difficult) work for the whole ~800 m2 heat shield. Hardly seems like a prime target for automation even if you add a magnitude for overhead and any finicky bits...

Less than $10,000 in labor per Starship if we assume even a $50/hr cost. Literally peanuts. Plus they can perform QA at the same time.
But if you plan to build at least 100 Starships you can afford to invest $1m in automation for it.

I agree. Over a decade ago I developed vision systems/sensor suites for use with Kuka robots that did a very similar operation. The pick-and-place operation moved at a little bit faster than one second per installation. Not only was it more than ten times faster than a human could do it, the error rate was non-existent because the sensing systems did post-placement inspection, eliminating the need for separate QA. The cost of this system was significantly less than one million dollars.
Title: Re: Starship heat shield
Post by: OTV Booster on 03/14/2021 03:26 pm
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.

Generally there is rule of thump for automation. If human cannot do task blindfolded you should not do robotization of that process.
Better not let AI drive cars then  ;D

I suspect that once they've fully tiled a Starship and verified that the mounting process is robust they will invest in automation of it. For the moment they don't actually know whether they'll stick with this method, so any investment would be at risk.
A significant number of drivers would do no worse blindfolded. :'(
Title: Re: Starship heat shield
Post by: alastairmayer on 03/14/2021 05:03 pm
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.

Elon has already made the mistake of over-automating, it doesn’t work. People are far superior to machines when it comes to work like this. What may be simple to humans can be complex for machines vice versa.

This is true, but it doesn't necessarily mean the process can't be improved with some (relatively simple) tooling.  For example, ISTM that the application of the thermal underpads could be improved with some kind of hand roller to keep them smooth and avoid bending the pins.
Title: Re: Starship heat shield
Post by: alastairmayer on 03/14/2021 05:04 pm
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.

Generally there is rule of thump for automation. If human cannot do task blindfolded you should not do robotization of that process.
Better not let AI drive cars then  ;D

I suspect that once they've fully tiled a Starship and verified that the mounting process is robust they will invest in automation of it. For the moment they don't actually know whether they'll stick with this method, so any investment would be at risk.
A significant number of drivers would do no worse blindfolded. :'(
You have to wonder why drive-up ATMs have braille on the keypads.... ;)
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 03/14/2021 06:59 pm
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.
Elon has already made the mistake of over-automating, it doesn’t work. People are far superior to machines when it comes to work like this. What may be simple to humans can be complex for machines vice versa. 
I would agree - The step requiring the most time and precision, welding the studs, is already automated (at least for the barrel sections).

From the videos it takes two SpaceXers 4 minutes to install ~4 m2 of insulation blanket/mat and ~10 s for one person to attach one tile. Rounding a bit that is ~5 person-minutes/m2 for blanket+tile installation which extrapolates to < 80 person-hours of slightly variable and delicate (but not especially physically demanding or difficult) work for the whole ~800 m2 heat shield. Hardly seems like a prime target for automation even if you add a magnitude for overhead and any finicky bits...

Less than $10,000 in labor per Starship if we assume even a $50/hr cost. Literally peanuts. Plus they can perform QA at the same time.
But if you plan to build at least 100 Starships you can afford to invest $1m in automation for it.

I agree. Over a decade ago I developed vision systems/sensor suites for use with Kuka robots that did a very similar operation. The pick-and-place operation moved at a little bit faster than one second per installation. Not only was it more than ten times faster than a human could do it, the error rate was non-existent because the sensing systems did post-placement inspection, eliminating the need for separate QA. The cost of this system was significantly less than one million dollars.

I think that they will automate it later. Now it isn't the top priority. But if they want to build 100 or more Starships they need automation, like as being said. Maybe they need this work to be performed a couple of times by humanss to know how to do the automation, if there are problems, etc. But investing time and money (I think a robot wouldn't be super expensive, but it has to be nearly perfect, behind that heat shield there are people, hence IMO it will be more expensive than a tipical industrial application) on this is IMO premature.
Title: Re: Starship heat shield
Post by: BT52 on 03/14/2021 07:14 pm
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.

Generally there is rule of thump for automation. If human cannot do task blindfolded you should not do robotization of that process.
Better not let AI drive cars then  ;D

I suspect that once they've fully tiled a Starship and verified that the mounting process is robust they will invest in automation of it. For the moment they don't actually know whether they'll stick with this method, so any investment would be at risk.

Not even a risk. At current conceptual stage that would even be completely pointless and waste of resources. Sure they could throw ideas around and do mini test or two. So yeah

Later when u got everything set and proved trough orbital test, they will probably take o look into:
-assembly automation
-AI scanning after flight
-repair and its replacement
-reusability and take a look Mars robot version
Title: Re: Starship heat shield
Post by: Keldor on 03/14/2021 09:10 pm
I'm surprised to see workers mounting tiles manually. It looks simple to automate and that might happen later.

Generally there is rule of thump for automation. If human cannot do task blindfolded you should not do robotization of that process.
Better not let AI drive cars then  ;D

I suspect that once they've fully tiled a Starship and verified that the mounting process is robust they will invest in automation of it. For the moment they don't actually know whether they'll stick with this method, so any investment would be at risk.

Not even a risk. At current conceptual stage that would even be completely pointless and waste of resources. Sure they could throw ideas around and do mini test or two. So yeah

Later when u got everything set and proved trough orbital test, they will probably take o look into:
-assembly automation
-AI scanning after flight
-repair and its replacement
-reusability and take a look Mars robot version

It's not even just that their design might be adjusted.  Hardware and software to drive automation takes time to develop.  Realistically, that robot and associated control software to mount tiles will take months to develop, once they have the tile design finalized.  But there's no reason they can't put the tiles on by hand until the automated method is ready.
Title: Re: Starship heat shield
Post by: Faerwald on 03/15/2021 02:09 am
I am surprised that there is no overlap between blankets. Might be something we will see in future.

May also see longer blanket in the future. Might be awkward working with longer blankets in the horizontal direction but perhaps vertically starting from the top could be fairly easy.

Set up a scaffold while one worker is pushing the blanket over the studs a worker on the level above could be installing the tiles.
Title: Re: Starship heat shield
Post by: _MECO on 03/15/2021 05:11 am
Wow, this is a super-simple tile application technique.  Is that all that is required, or does it need to be welded into place somehow?
[Tweet]
From what we have seen so far it does look like it is that simple:

Robot welds studs onto the barrel. Studs have two tapered prongs with some kind of hooking/latching protrusion at the end. Three studs per tile.

High temperature mineral/refractory cheramic fiber mats are fitted to the barrel side and the studs are pressed through. No sign of further fastening but it is not ruled out.

Tiles are pressed fitted onto the studs, slightly compressing the mat until looked in place.


Cracked or faulty tiles can be removed by piercing the tile with a sharp metal object at the location of the three studs (likely just breaking the tile around the attachment points).

Isn't it true that each tile has an embedded, trilaterally-symmetric metal "Y" shaped skeleton to stiffen it? I swear I saw that sonewhere. Removing tiles might mean just whacking over the stud points with a hammer until enough of the ceramic is chipped away that you can directly get at the backside of the skeleton. Then the studs can be unclipped and the tile removed without having to be completely destroyed. You could even do this on-orbit, clicking spare tiles into place to save your skin.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 03/15/2021 05:31 am
I am surprised that there is no overlap between blankets. Might be something we will see in future.

May also see longer blanket in the future. Might be awkward working with longer blankets in the horizontal direction but perhaps vertically starting from the top could be fairly easy.

Set up a scaffold while one worker is pushing the blanket over the studs a worker on the level above could be installing the tiles.

I've installed more than the average vacation homeowner's share of siding.  Process Looks pretty similar.  I find it amusing that that SpaceX has figured out a system that hundreds of thousands in the light construction trade could install.

Having the fastener hidden and quick to install is brilliant, as with houses, the fastener is the weak point of any protective covering, especially if you have a house in an area that gets 50 inches of rain per year like I do.  (hint:  The rot nearly always starts at a fastener penetration).  Gluing on siding or window trim is not something I would care to try.  I don't even like waiting for caulk to set (if you do things right you don't need caulk, but that's too far off topic)

The blanket is analagous to building paper/tar paper or polypropylene rain screen. Taller doesn't get it installed much faster, it just increases the awkward time and error rate.   
Title: Re: Starship heat shield
Post by: InterestedEngineer on 03/15/2021 05:34 am
Isn't it true that each tile has an embedded, trilaterally-symmetric metal "Y" shaped skeleton to stiffen it? I swear I saw that sonewhere. Removing tiles might mean just whacking over the stud points with a hammer until enough of the ceramic is chipped away that you can directly get at the backside of the skeleton. Then the studs can be unclipped and the tile removed without having to be completely destroyed. You could even do this on-orbit, clicking spare tiles into place to save your skin.

So, like removing Hardi siding from a house.

I feel like some engineer at SpaceX had a Hardi siding project they did in the last 10 years.
Title: Re: Starship heat shield
Post by: enbandi on 03/15/2021 06:16 am

Isn't it true that each tile has an embedded, trilaterally-symmetric metal "Y" shaped skeleton to stiffen it? I swear I saw that sonewhere. Removing tiles might mean just whacking over the stud points with a hammer until enough of the ceramic is chipped away that you can directly get at the backside of the skeleton. Then the studs can be unclipped and the tile removed without having to be completely destroyed. You could even do this on-orbit, clicking spare tiles into place to save your skin.

The tiles has an embedded Y shape something.  Or 3 separate straight bones arranged in Y. That was seen on the pics of the failed tiles of SN 4-5-6 era.

As for removal, the video shows a cordless drill (or something like that) used by the worker, so drill it where required and unclip then.

Interesting part, that previously we seen tiles with 3 holes (where the clips are) in mixed use of tiles without them. We interpreted as the testing of different mounting methods/tile types. But I think the tiles with holes could be simply procedural test articles: tiles with permanent/premade holes to install and remove multiple times (for practice/fit checks).
Title: Re: Starship heat shield
Post by: Faerwald on 03/15/2021 06:22 am
I am surprised that there is no overlap between blankets. Might be something we will see in future.

May also see longer blanket in the future. Might be awkward working with longer blankets in the horizontal direction but perhaps vertically starting from the top could be fairly easy.

Set up a scaffold while one worker is pushing the blanket over the studs a worker on the level above could be installing the tiles.

I've installed more than the average vacation homeowner's share of siding.  Process Looks pretty similar.  I find it amusing that that SpaceX has figured out a system that hundreds of thousands in the light construction trade could install.

Having the fastener hidden and quick to install is brilliant, as with houses, the fastener is the weak point of any protective covering, especially if you have a house in an area that gets 50 inches of rain per year like I do.  (hint:  The rot nearly always starts at a fastener penetration).  Gluing on siding or window trim is not something I would care to try.  I don't even like waiting for caulk to set (if you do things right you don't need caulk, but that's too far off topic)

The blanket is analagous to building paper/tar paper or polypropylene rain screen. Taller doesn't get it installed much faster, it just increases the awkward time and error rate.

If you grab a roll of blanket and go to the top of the rocket. Holt the edge and just let it unroll downward you could then just start pushing it on from top to bottom. Nothing awkward in that. Also because the blanket is flexible and has some give it don't need to be aligned properly at the top. Just pull it into alignment as you work your way down.

I fully understand the fastener issue. The amount of issues we have at work with corrosion of tek screws holding down tank roof sheeting is large.

For the blanket I would be a little worried that gaps between the sheets may allow plasma to get to the steel underneath.

I wonder how different that blanket is to standard Superwool 607?

And yeah I agree that this method is amusingly straightforward. It looks like they found out what the right question was first instead of the right answer first. I hope it works as intended but it sure looks promising.

Finding the right question first is incredibly underrated. Me and my colleagues all had a laugh when saw the Sandy Munroe interview. That resonated so well with what we deal with.
Title: Re: Starship heat shield
Post by: edzieba on 03/15/2021 03:30 pm
I am surprised that there is no overlap between blankets.
Either an overlap, half-thickness pads with a full lap, or go along the seams with a block of felting needles to incorporate the two pieces.

It'll be interesting to see the order of operations:
- Apply TPS to a barrel section, then stack barrels. Near-ground-level work for TPS application, but risks damage to TPS from handling and welding process, and still requires some elevated work to apply the TPS over joins.
- Stack barrels (with studs in place) then apply TPS. Lower risk of damage (just bent studs) and TPS application can be continuous, but requires lots of working at high elevations - even without any safety issues, hauling tiles up batch by batch on cherrypickers is going to slow things down a lot, as is trying to handle moderately fragile tiles and floppy rockwool-like sheets while literally flapping in the breeze.
Title: Re: Starship heat shield
Post by: Rocket Science on 03/15/2021 03:35 pm
The smartest most skilled robot is still a human working robotically...
Title: Re: Starship heat shield
Post by: rsdavis9 on 03/15/2021 03:49 pm
I am surprised that there is no overlap between blankets.
Either an overlap, half-thickness pads with a full lap, or go along the seams with a block of felting needles to incorporate the two pieces.

It'll be interesting to see the order of operations:
- Apply TPS to a barrel section, then stack barrels. Near-ground-level work for TPS application, but risks damage to TPS from handling and welding process, and still requires some elevated work to apply the TPS over joins.
- Stack barrels (with studs in place) then apply TPS. Lower risk of damage (just bent studs) and TPS application can be continuous, but requires lots of working at high elevations - even without any safety issues, hauling tiles up batch by batch on cherrypickers is going to slow things down a lot, as is trying to handle moderately fragile tiles and floppy rockwool-like sheets while literally flapping in the breeze.

I always thought that application of tiles on rings and then stack was not going to be precise enough for the 1mm(?) gap between tiles after the stacks are connected. So tiling the whole vehicle after assembly was going to the only way.

How about a complete circular walkway around the whole circumference and lowered and raised by lift cables. Then once available tiles have been depleted from the platform bring it to the ground and re-raise. Could just be half a circle but might be less stable.

Probably wrong as usual.
Title: Re: Starship heat shield
Post by: Crispy on 03/15/2021 03:51 pm
I am surprised that there is no overlap between blankets.
Either an overlap, half-thickness pads with a full lap, or go along the seams with a block of felting needles to incorporate the two pieces.

It'll be interesting to see the order of operations:
- Apply TPS to a barrel section, then stack barrels. Near-ground-level work for TPS application, but risks damage to TPS from handling and welding process, and still requires some elevated work to apply the TPS over joins.
- Stack barrels (with studs in place) then apply TPS. Lower risk of damage (just bent studs) and TPS application can be continuous, but requires lots of working at high elevations - even without any safety issues, hauling tiles up batch by batch on cherrypickers is going to slow things down a lot, as is trying to handle moderately fragile tiles and floppy rockwool-like sheets while literally flapping in the breeze.
Didn't we see support rails for a vertical access platform in the high bay?
A semi-circular platform could provide continuous stable access to the whole of one side of the vehicle.
Title: Re: Starship heat shield
Post by: steveleach on 03/15/2021 05:11 pm
The smartest most skilled robot is still a human working robotically...
Sounds like you haven't met some of the humans I have :-)

Someone on the other side of the shop drops a crate of tools, the tile installer (bored out of his mind after installing 139 tiles so far today) glances over to see what happened, makes a witty remark to his mate, and fails to push one of the studs quite hard enough.

A bit later, the QA guy is checking the tiles but needs a bathroom break, bad. Just gotta finish checking this one section first though. He's trying not to rush it.

A few weeks later a tanker is lost on reentry.
Title: Re: Starship heat shield
Post by: DreamyPickle on 03/15/2021 05:25 pm
Do we have any idea about the SN of the section that we saw being covered in heat tiles?
Title: Re: Starship heat shield
Post by: alastairmayer on 03/15/2021 05:31 pm
The smartest most skilled robot is still a human working robotically...

Unfortunately, that's probably also the most error prone.
Title: Re: Starship heat shield
Post by: Rocket Science on 03/15/2021 05:35 pm
The smartest most skilled robot is still a human working robotically...

Unfortunately, that's probably also the most error prone.
Incomparable at this point for the level of technology and low production number...
Title: Re: Starship heat shield
Post by: testguy on 03/15/2021 05:48 pm
Can’t help thinking back to the early Shuttle days and tile installation.  OMG what a change for the better. Who should care about robots for now.  Think about the orders of magnitude reduction in touch labor!


Title: Re: Starship heat shield
Post by: enbandi on 03/15/2021 06:09 pm
....
I always thought that application of tiles on rings and then stack was not going to be precise enough for the 1mm(?) gap between tiles after the stacks are connected. So tiling the whole vehicle after assembly was going to the only way.
.....

Was my impression too, actually wrote several post arguing along the same lines. But based on what we see now the section (3-4 rings) based method is their way.
- stacking and barrel section buildup done that way, and production of rocket body seems kind a matured process
- they have a stud welder robot cell/station for such sections
- i think we seen pinned sections mated/stacked later on (not with tiles however)

So I guess they can stack with adequate precision, in which case tiles can be installed before stackink. Actually the tiles itself can be used as a stacking guide to provide alignment (or not, if too fraigle. But special ones made of metal to be used through the stacking and replaced later are still a possibility)
Title: Re: Starship heat shield
Post by: rsdavis9 on 03/15/2021 06:26 pm
....
I always thought that application of tiles on rings and then stack was not going to be precise enough for the 1mm(?) gap between tiles after the stacks are connected. So tiling the whole vehicle after assembly was going to the only way.
.....

Was my impression too, actually wrote several post arguing along the same lines. But based on what we see now the section (3-4 rings) based method is their way.
- stacking and barrel section buildup done that way, and production of rocket body seems kind a matured process
- they have a stud welder robot cell/station for such sections
- i think we seen pinned sections mated/stacked later on (not with tiles however)

So I guess they can stack with adequate precision, in which case tiles can be installed before stackink. Actually the tiles itself can be used as a stacking guide to provide alignment (or not, if too fraigle. But special ones made of metal to be used through the stacking and replaced later are still a possibility)

They still need to do the weld between barrel sections. So I would guess one row of custom fit tiles. You got to cover the weld! Not too bad. It also allows tiling to occur on many barrels at the same time.
Title: Re: Starship heat shield
Post by: wannamoonbase on 03/15/2021 06:29 pm
The smartest most skilled robot is still a human working robotically...

Until they get tired or take a lunch break.

Robotic application has to be near the top of Elon's want list.  Even the unusual one off tiles near the flaps, nose and at terminal edges.

The hexagon tiles that are all identical are not nearly as big of a concern as those special ones.  Those are the ones I really want to see.
Title: Re: Starship heat shield
Post by: rsdavis9 on 03/15/2021 06:42 pm
....
I always thought that application of tiles on rings and then stack was not going to be precise enough for the 1mm(?) gap between tiles after the stacks are connected. So tiling the whole vehicle after assembly was going to the only way.
.....

Was my impression too, actually wrote several post arguing along the same lines. But based on what we see now the section (3-4 rings) based method is their way.
- stacking and barrel section buildup done that way, and production of rocket body seems kind a matured process
- they have a stud welder robot cell/station for such sections
- i think we seen pinned sections mated/stacked later on (not with tiles however)

So I guess they can stack with adequate precision, in which case tiles can be installed before stackink. Actually the tiles itself can be used as a stacking guide to provide alignment (or not, if too fraigle. But special ones made of metal to be used through the stacking and replaced later are still a possibility)

So missed the temporary metal tile placeholder on first reading...
So maybe one row of temp metal tiles on each section that are to be mated.
So something like this maybe:
Do the mate and alignment.
Remove temp metal tiles to weld.
Put on final tiles.
Title: Re: Starship heat shield
Post by: enbandi on 03/15/2021 06:53 pm
....

So missed the temporary metal tile placeholder on first reading...
So maybe one row of temp metal tiles on each section that are to be mated.
So something like this maybe:
Do the mate and alignment.
Remove temp metal tiles to weld.
Put on final tiles.

Something like this. Tiles over the weld dont havs to be custom/special ones. But they installed later, thats the difference.
I am not sure if they still use overlapping welds for stacking, in which case there can be a 4mm diff under the tiles level wise (sounds like something to be compensated).
Title: Re: Starship heat shield
Post by: OTV Booster on 03/15/2021 07:22 pm
I am surprised that there is no overlap between blankets. Might be something we will see in future.

May also see longer blanket in the future. Might be awkward working with longer blankets in the horizontal direction but perhaps vertically starting from the top could be fairly easy.

Set up a scaffold while one worker is pushing the blanket over the studs a worker on the level above could be installing the tiles.

I've installed more than the average vacation homeowner's share of siding.  Process Looks pretty similar.  I find it amusing that that SpaceX has figured out a system that hundreds of thousands in the light construction trade could install.

Having the fastener hidden and quick to install is brilliant, as with houses, the fastener is the weak point of any protective covering, especially if you have a house in an area that gets 50 inches of rain per year like I do.  (hint:  The rot nearly always starts at a fastener penetration).  Gluing on siding or window trim is not something I would care to try.  I don't even like waiting for caulk to set (if you do things right you don't need caulk, but that's too far off topic)

The blanket is analagous to building paper/tar paper or polypropylene rain screen. Taller doesn't get it installed much faster, it just increases the awkward time and error rate.
What are the chances that one of those guys installing was an engineer? Maybe the one who will program the robot.
Title: Re: Starship heat shield
Post by: OTV Booster on 03/15/2021 07:39 pm
....
I always thought that application of tiles on rings and then stack was not going to be precise enough for the 1mm(?) gap between tiles after the stacks are connected. So tiling the whole vehicle after assembly was going to the only way.
.....

Was my impression too, actually wrote several post arguing along the same lines. But based on what we see now the section (3-4 rings) based method is their way.
- stacking and barrel section buildup done that way, and production of rocket body seems kind a matured process
- they have a stud welder robot cell/station for such sections
- i think we seen pinned sections mated/stacked later on (not with tiles however)

So I guess they can stack with adequate precision, in which case tiles can be installed before stackink. Actually the tiles itself can be used as a stacking guide to provide alignment (or not, if too fraigle. But special ones made of metal to be used through the stacking and replaced later are still a possibility)

They still need to do the weld between barrel sections. So I would guess one row of custom fit tiles. You got to cover the weld! Not too bad. It also allows tiling to occur on many barrels at the same time.
The barrels look better with each ship and over time the top/bottom variance on the rings has shrunk to near insignificance. (Haven't seen any of those labels in a while) I think they're confident enough in their assembly that the barrel join will be a non issue, or they expect it to be by the time the tiles actually have to do their job.
Title: Re: Starship heat shield
Post by: Rocket Science on 03/15/2021 07:51 pm
The smartest most skilled robot is still a human working robotically...

Until they get tired or take a lunch break.

Robotic application has to be near the top of Elon's want list.  Even the unusual one off tiles near the flaps, nose and at terminal edges.

The hexagon tiles that are all identical are not nearly as big of a concern as those special ones.  Those are the ones I really want to see.
Yes, but not at "this point in time"... Let's see if the current theoretical iteration makes it through the "proof of concept" EDL multiple times successfully before any thoughts of robotic installation...

Edit ti add:
Title: Re: Starship heat shield
Post by: JamesH65 on 03/16/2021 07:22 am
The smartest most skilled robot is still a human working robotically...

Until they get tired or take a lunch break.

Robotic application has to be near the top of Elon's want list.  Even the unusual one off tiles near the flaps, nose and at terminal edges.

The hexagon tiles that are all identical are not nearly as big of a concern as those special ones.  Those are the ones I really want to see.
Yes, but not at "this point in time"... Let's see if the current theoretical iteration makes it through the "proof of concept" EDL multiple times successfully before any thoughts of robotic installation...

Edit ti add:

AIUI, the pins are already welded on robotically, so its already partially automated.  Not a big stretch from there to applying the tiles in the same way.
Title: Re: Starship heat shield
Post by: Rocket Science on 03/16/2021 01:25 pm
The smartest most skilled robot is still a human working robotically...

Until they get tired or take a lunch break.

Robotic application has to be near the top of Elon's want list.  Even the unusual one off tiles near the flaps, nose and at terminal edges.

The hexagon tiles that are all identical are not nearly as big of a concern as those special ones.  Those are the ones I really want to see.
Yes, but not at "this point in time"... Let's see if the current theoretical iteration makes it through the "proof of concept" EDL multiple times successfully before any thoughts of robotic installation...

Edit ti add:

AIUI, the pins are already welded on robotically, so its already partially automated.  Not a big stretch from there to applying the tiles in the same way.
Yes once again that is based on that this will be a successful design as is... TBD...
Title: Re: Starship heat shield
Post by: Slarty1080 on 03/18/2021 10:06 am
The smartest most skilled robot is still a human working robotically...

Until they get tired or take a lunch break.

Robotic application has to be near the top of Elon's want list.  Even the unusual one off tiles near the flaps, nose and at terminal edges.

The hexagon tiles that are all identical are not nearly as big of a concern as those special ones.  Those are the ones I really want to see.
Yes, but not at "this point in time"... Let's see if the current theoretical iteration makes it through the "proof of concept" EDL multiple times successfully before any thoughts of robotic installation...

Edit ti add:
Yes, IIRC Tesla actually overdid the automation at one point hand reverted some of the tasks to people. Automation needs to go in at the right point. Not to early and not too late. 
Title: Re: Starship heat shield
Post by: Barnalby on 03/18/2021 12:58 pm
Yes, IIRC Tesla actually overdid the automation at one point hand reverted some of the tasks to people. Automation needs to go in at the right point. Not to early and not too late.

"Render unto [ROBOTS] those things which are [ROBOTS]'s, render unto [WORKERS] those things which are [WORKERS]'s"
Title: Re: Starship heat shield
Post by: steveleach on 03/18/2021 01:17 pm
Yes, IIRC Tesla actually overdid the automation at one point hand reverted some of the tasks to people. Automation needs to go in at the right point. Not to early and not too late.

"Render unto [ROBOTS] those things which are [ROBOTS]'s, render unto [WORKERS] those things which are [WORKERS]'s"
Absolutely, though with robots continually getting more sophisticated and works continually getting more expensive....

I should report myself to the mods for drifting off-topic though.
Title: Re: Starship heat shield
Post by: rsdavis9 on 03/18/2021 03:56 pm

Yes, IIRC Tesla actually overdid the automation at one point hand reverted some of the tasks to people. Automation needs to go in at the right point. Not to early and not too late.

And one of the things that was over automated was:
Placement of insulating mat over the battery pack.
It turned out that robots like rigid thins but have problems with floppy things.
Another example was cable routing.
So at tesla they developed some kind of semi rigid cable system so robots could deal with it. Not sure if they have put it into production yet.
Title: Re: Starship heat shield
Post by: DigitalMan on 03/18/2021 05:21 pm

Yes, IIRC Tesla actually overdid the automation at one point hand reverted some of the tasks to people. Automation needs to go in at the right point. Not to early and not too late.

And one of the things that was over automated was:
Placement of insulating mat over the battery pack.
It turned out that robots like rigid thins but have problems with floppy things.
Another example was cable routing.
So at tesla they developed some kind of semi rigid cable system so robots could deal with it. Not sure if they have put it into production yet.


Not yet. I haven't heard any details why not.

I think tile placement could be reasonable for a robot, as long as there is a camera/mechanism for it to verify the proper attachment/prep.
Title: Re: Starship heat shield
Post by: Asteroza on 03/18/2021 10:03 pm

Yes, IIRC Tesla actually overdid the automation at one point hand reverted some of the tasks to people. Automation needs to go in at the right point. Not to early and not too late.

And one of the things that was over automated was:
Placement of insulating mat over the battery pack.
It turned out that robots like rigid thins but have problems with floppy things.
Another example was cable routing.
So at tesla they developed some kind of semi rigid cable system so robots could deal with it. Not sure if they have put it into production yet.

The alien dreadnought fiasco was a combo of being a little too early for lights out manufacturing, and trying to go for a highly adaptive robot environment that is like software (where the physical manufacturing line is easily reconfigurable, which is very close to software methodologies for fast cycle time on revisions, but also dangerously close to a seed factory AKA the factory that can build anything if given the proper inputs/raw materials). There are factory automation industry pushes to move to a digital twin type simulation environment for manufacturing, linked to CADCAM systems, such that designers/developers of products can make changes in their CAD software and see how that propagates to the manufacturing line. If the line itself can self reconfigure based on the results of the line changes simulated in the digital twin, you end up with a very adaptive system. Tesla already is at a stage where they don't really have model years, as they are altering the designs in production at a fairly high rate and fiddling with the manufacturing line accordingly. There's a reason Musk likes his tent production lines (easily tweaked).

The cable thing was a combo of floppiness and connectors designed for humans. The rigid cable allows robot placement, but a secondary objective was reducing cable count so the number of connectors humans had to handle was reduced. Musk said the parts industry as whole (and to a lesser extent the maintenance side) is focused on human usable connectors, so nobody is yet making connectors in bulk more suited for robots. Even Tesla levels of purchasing hasn't moved the needle much on that.
Title: Re: Starship heat shield
Post by: BenzinGooz on 03/19/2021 09:52 pm
Hi everyone,

I have a question regarding the heat shield. How will windward thrusters integrate into the tile mesh? Will they cut holes on some of the tiles where they can poke out a thruster? I assume those thrusters would be made out of some very temp tolerant material.
Title: Re: Starship heat shield
Post by: Lars-J on 03/19/2021 10:27 pm
Hi everyone,

I have a question regarding the heat shield. How will windward thrusters integrate into the tile mesh? Will they cut holes on some of the tiles where they can poke out a thruster? I assume those thrusters would be made out of some very temp tolerant material.

Like on Shuttle, all thrusters will likely be on the leeward(?) side (or edge of it), but angled/canted so they can produce thrust in the desired direction.
Title: Re: Starship heat shield
Post by: HVM on 03/19/2021 10:38 pm
Lars is a Ninja...

Like with the Space Shuttle Orbiter, there will be no thrusters directly pointing or in windward side, instead there will be thrusters with ~45 dec of windward vector in both side and they are used simultaneously, or so I guess. Also you have already seen tiles with pentagon configuration, so there will be more in each special case...
Title: Re: Starship heat shield
Post by: OTV Booster on 03/19/2021 11:31 pm
Hi everyone,

I have a question regarding the heat shield. How will windward thrusters integrate into the tile mesh? Will they cut holes on some of the tiles where they can poke out a thruster? I assume those thrusters would be made out of some very temp tolerant material.
And welcome to the forum.
Title: Re: Starship heat shield
Post by: joek on 03/20/2021 03:08 am
They still need to do the weld between barrel sections. So I would guess one row of custom fit tiles. You got to cover the weld! Not too bad. It also allows tiling to occur on many barrels at the same time.

Based on photos, there is a fibrous mat below the tiles which appears to be semi-continuous (not per-tile).  May complicate matters as it is not simply attaching a tile to points on the SS skin.
Title: Re: Starship heat shield
Post by: HVM on 03/20/2021 09:28 pm
Tiles on the flap(s), is this discussed here? I didn't find it. Two sizes and same pattern as in SN10 body.
Title: Re: Starship heat shield
Post by: enbandi on 03/20/2021 09:42 pm
Tiles on the flap(s), is this discussed here? I didn't find it. Two sizes and same pattern as in SN10 body.

And they are on the wrong side (leeward nor windward). Was similar arrangement on SN10. Guess they want to test the tiles, but dont want to mess with aerodinamics of the flaps (yet).
Title: Re: Starship heat shield
Post by: Keldor on 03/20/2021 11:30 pm
Tiles on the flap(s), is this discussed here? I didn't find it. Two sizes and same pattern as in SN10 body.

And they are on the wrong side (leeward nor windward). Was similar arrangement on SN10. Guess they want to test the tiles, but dont want to mess with aerodinamics of the flaps (yet).

It might not be feasible to test the tiles on the windward side without making a full heatshield for at least the fin.  The problem is that without the proper pieces on the edges, the tiles are not very aerodynamic, and so subjecting them to the airflow could easily rip them all off like shingles in a tornado.

The tiles on the centerline don't face this problem, since they are, to some extent inside a cushion of relatively still air.  But the flaps will probably have the highest sideways airflow at the surface of anywhere on the vehicle.
Title: Re: Starship heat shield
Post by: Pete on 03/21/2021 07:55 am
Tiles on the flap(s), is this discussed here? I didn't find it. Two sizes and same pattern as in SN10 body.

And they are on the wrong side (leeward nor windward). Was similar arrangement on SN10. Guess they want to test the tiles, but dont want to mess with aerodinamics of the flaps (yet).

Maybe testing the vibration aspects of flap mounting, without the problems of airflow added to the picture?

The tiles on the flaps will be an interesting problem in any case, as there are all sorts of sharp edges, lateral airflow, different/higher mechanical stresses, completely different thermal environment (no backing cryo tank), etc.
I would actually be a bit surprised if the exact same solution can be used for tankbody and flap shielding.
Title: Re: Starship heat shield
Post by: enbandi on 03/21/2021 10:01 am
...
It might not be feasible to test the tiles on the windward side without making a full heatshield for at least the fin.  The problem is that without the proper pieces on the edges, the tiles are not very aerodynamic, and so subjecting them to the airflow could easily rip them all off like shingles in a tornado.
.....

If you are right, that defines a cascading error behaviour. If one tile fail, neighbours will be peeled off easily by airflow an so...
I think this is something, what they want to avoid by engineering out of the system (tolerant tiles or so). And if such behaviour exists they migh also want to test it against.
But its my opinion only, you can be as well as right.
Title: Re: Starship heat shield
Post by: Broccoli32 on 03/23/2021 01:16 am
Large chunks out of two tiles broke off during the static fire, the larger patch also had small chips in several tiles.

Photo credit: Nomadd
Title: Re: Starship heat shield
Post by: Vultur on 03/23/2021 04:38 am
That seems troubling, as I'd think the static fire would be less stress than actually flying. (Or am I wrong about that?)

The heat shield is my big concern for Starship meeting its goals (with Raptor reliability/maintenance being second). It will need to do vastly better than Shuttle level of maintenance "finicky-ness", and much better than the demonstrated safety/reliability (1 reentry-related fatal accident out of 135 flights) as well, to meet its goals.

Do we know why the transpiration cooling was abandoned?
Title: Re: Starship heat shield
Post by: ThatOldJanxSpirit on 03/23/2021 05:29 am
That seems troubling, as I'd think the static fire would be less stress than actually flying. (Or am I wrong about that?)

The heat shield is my big concern for Starship meeting its goals (with Raptor reliability/maintenance being second). It will need to do vastly better than Shuttle level of maintenance "finicky-ness", and much better than the demonstrated safety/reliability (1 reentry-related fatal accident out of 135 flights) as well, to meet its goals.

Do we know why the transpiration cooling was abandoned?

The static fire acoustic environment, with three engines at high thrust operating close to the ground for a few seconds, should be worse than Starship will see in orbital operations. At staging engines will be starting in near vacuum. For landing it should only have two engines operating at minimal thrust.
Title: Re: Starship heat shield
Post by: Slarty1080 on 03/23/2021 08:21 am
That seems troubling, as I'd think the static fire would be less stress than actually flying. (Or am I wrong about that?)

The heat shield is my big concern for Starship meeting its goals (with Raptor reliability/maintenance being second). It will need to do vastly better than Shuttle level of maintenance "finicky-ness", and much better than the demonstrated safety/reliability (1 reentry-related fatal accident out of 135 flights) as well, to meet its goals.

Do we know why the transpiration cooling was abandoned?
Remember that this is a prototype used for a variety of testing. The large central bank of tiles all appear to be attached via the push fit two prong system and I suspect will be used for most of the tiling. But the smaller patches seem to have a different attachment mechanism, perhaps something they were testing to see if it worked better (it doesn't) or might be suitable for certain areas (it isn't). So probably useful info for them.

Part of the problem is cost so they probably want to try the cheapest solutions first and only start experimenting with more costly or complex set ups if they have to. I would expect to see a range of different options being tested out as time goes on.

Transpiration cooling is still in the waiting in the wings if needed, but it is inherently inefficient as it will use consumables and its probably also involves more complexity and cost. I predict that either we won't see it or if we do it will be a lot later on the high energy areas after they have tried a lot of other options.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 03/23/2021 08:26 am
Large chunks out of two tiles broke off during the static fire, the larger patch also had small chips in several tiles.

Photo credit: Nomadd

Did we see similar things with other prototipes?

It is not a good sign IMO, because there will be tiles closer to the engines. Static fire environment is harsher than launch one, but this issue has to be solved.

Could they be testing another tile attachment system (that didn't work)?
Title: Re: Starship heat shield
Post by: guckyfan on 03/23/2021 08:28 am
Do we know why the transpiration cooling was abandoned?

If I remember correctly, Elon Musk said they have come up with a low cost heat shield tile production method, that beats the metal transpiration cooling design.

To me he still gives the impression he likes the transpiration design.
Title: Re: Starship heat shield
Post by: HVM on 03/23/2021 08:47 am
Both fractured tile(s) -batches are bond with red adhesive, and have felt pads. Interesting to see that Y-like structure inside the tile is not some space-age-spring-suspended-contraption but three metal fasteners from local hardware store...
Title: Re: Starship heat shield
Post by: _MECO on 03/23/2021 12:35 pm
Both fractured tile(s) -batches are bond with red adhesive, and have felt pads. Interesting to see that Y-like structure inside the tile is not some space-time-spring-suspended-contraption but three metal fasteners from local hardware store...

Aha! I knew it! A little ago I made a post where I assumed that Starship TPS tiles had a triangular metal skeleton in them. This particular example may have been adhered with glue of some kind, yes, but if the overall structure remains the same for the mechanically attached tiles, then it bodes well for in-the-field serviceability. Replacing broken tiles on orbit, or on the surface of Mars or wherever can be as simple as digging over the mounting spots with a screwdriver until the mounting points on the skeleton are exposed, prying the studs open with said tool, removing the tile, and then snapping a new one in place.
Title: Re: Starship heat shield
Post by: Nomadd on 03/23/2021 01:20 pm
Both fractured tile(s) -batches are bond with red adhesive, and have felt pads. Interesting to see that Y-like structure inside the tile is not some space-time-spring-suspended-contraption but three metal fasteners from local hardware store...
The mounting Y is just buried in that crumbly white part with holes to the attachment points. The white stuff is giving way when they break. It's almost chalk like, but much lighter.
 I don't know if the smaller tiles, or the ones with the red stuff which don't seem to be failing, are made the same way. But they're obviously testing variations and not just sticking the same thing up every time. Even if they get a batch with no failures, they'll probably keep trying new materials, construction and mountings, so assuming they can't figure it out is unwarranted.
 Finding new ways to break them is just more data.

 I can see where static fires with the ship being held down by those six mounting points might flex the hull more than flying.
Title: Re: Starship heat shield
Post by: _MECO on 03/23/2021 01:45 pm
Both fractured tile(s) -batches are bond with red adhesive, and have felt pads. Interesting to see that Y-like structure inside the tile is not some space-time-spring-suspended-contraption but three metal fasteners from local hardware store...
The mounting Y is just buried in that crumbly white part with holes to the attachment points. The white stuff is giving way when they break. It's almost chalk like, but much lighter.
 I don't know if the smaller tiles, or the ones with the red stuff which don't seem to be failing, are made the same way. But they're obviously testing variations and not just sticking the same thing up every time. Even if they get a batch with no failures, they'll probably keep trying new materials, construction and mountings, so assuming they can't figure it out is unwarranted.
 Finding new ways to break them is just more data.

 I can see where static fires with the ship being held down by those six mounting points might flex the hull more than flying.

Lighter than chalk? That's amazingly fragile.
Title: Re: Starship heat shield
Post by: AnalogMan on 03/23/2021 03:49 pm
Both fractured tile(s) -batches are bond with red adhesive, and have felt pads. Interesting to see that Y-like structure inside the tile is not some space-time-spring-suspended-contraption but three metal fasteners from local hardware store...
The mounting Y is just buried in that crumbly white part with holes to the attachment points. The white stuff is giving way when they break. It's almost chalk like, but much lighter.
 I don't know if the smaller tiles, or the ones with the red stuff which don't seem to be failing, are made the same way. But they're obviously testing variations and not just sticking the same thing up every time. Even if they get a batch with no failures, they'll probably keep trying new materials, construction and mountings, so assuming they can't figure it out is unwarranted.
 Finding new ways to break them is just more data.

 I can see where static fires with the ship being held down by those six mounting points might flex the hull more than flying.

Lighter than chalk? That's amazingly fragile.

A Density comparison between chalk and Shuttle Orbiter tiles.

Chalk 156 lb/ft3 typically (varies from ~ 112 to 168 lb/ft3)

Shuttle Orbiter tiles:

LI-900 (black tiles on underside) 9 lb/ft3
LI-2200 (black higher strength around windows & landing gear doors) 22 lb/ft3

FRCI-12 (improved tiles to replace some LI tiles) 12 lb/ft3

LRSI-9  (white tiles on upper surfaces) 9 lb/ft3
LRSI-12 (white tiles on upper surfaces) 12 lb/ft3

BRI-18 (strongest & toughest tile produced, replacement for critical areas)  18 lb/ft3

Water 62.4 lb/ft3
Styrofoam packaging and insulation typically 1 to 2 lb/ft3

Conversion to metric:

1 lb/ft3 is equivalent to 0.016 g/cm3 or 16.0 kg/m3
Title: Re: Starship heat shield
Post by: Lars-J on 03/23/2021 03:52 pm
Both fractured tile(s) -batches are bond with red adhesive, and have felt pads. Interesting to see that Y-like structure inside the tile is not some space-time-spring-suspended-contraption but three metal fasteners from local hardware store...

Am I blind? I only see one fractured tile...
Title: Re: Starship heat shield
Post by: DigitalMan on 03/23/2021 03:58 pm
It could be that the tile below that one has its upper-right corner torn off.
Title: Re: Starship heat shield
Post by: Lars-J on 03/23/2021 04:14 pm
It could be that the tile below that one has its upper-right corner torn off.

No, never mind, for some reason I assumed it was the same patch focused on in the photos here: https://forum.nasaspaceflight.com/index.php?topic=50748.msg2209249#msg2209249

But there are two different. Just the same relative tile in two groups that failed.
Title: Re: Starship heat shield
Post by: Nomadd on 03/23/2021 11:34 pm
 26oz. Sq.Ft.
Title: Re: Starship heat shield
Post by: su27k on 03/24/2021 02:50 am
8kg per m^2, that's the TPS density? If so, the whole heat shield is only 5t or so, pretty light...
Title: Re: Starship heat shield
Post by: OTV Booster on 03/24/2021 05:35 pm
Both fractured tile(s) -batches are bond with red adhesive, and have felt pads. Interesting to see that Y-like structure inside the tile is not some space-time-spring-suspended-contraption but three metal fasteners from local hardware store...
The mounting Y is just buried in that crumbly white part with holes to the attachment points. The white stuff is giving way when they break. It's almost chalk like, but much lighter.
 I don't know if the smaller tiles, or the ones with the red stuff which don't seem to be failing, are made the same way. But they're obviously testing variations and not just sticking the same thing up every time. Even if they get a batch with no failures, they'll probably keep trying new materials, construction and mountings, so assuming they can't figure it out is unwarranted.
 Finding new ways to break them is just more data.

 I can see where static fires with the ship being held down by those six mounting points might flex the hull more than flying.
On launch the ship needs to be held down ~1 sec as the engines build thrust. Don't most rockets hold down until the engines reach equilibrium?  That'd be ~3 sec, which is about the timing of a static fire.


On an SX video of SN10 that had a clear angle it was ~2.5-3 seconds from the first sign of ignition to movement. Conclusion: static fire loading is essentially the same as a launch, EXCEPT for everything following shutdown, including transients, honks and barks.


Other than this, all you say makes good sense.
Title: Re: Starship heat shield
Post by: OTV Booster on 03/24/2021 05:42 pm
8kg per m^2, that's the TPS density? If so, the whole heat shield is only 5t or so, pretty light...
That's only for the white stuff. The black glassy outer surface and the metal 'Y' hardware will bump this up. Guesstimates generally come in at 10t.
Title: Re: Starship heat shield
Post by: envy887 on 03/24/2021 05:45 pm
They still need to do the weld between barrel sections. So I would guess one row of custom fit tiles. You got to cover the weld! Not too bad. It also allows tiling to occur on many barrels at the same time.

Based on photos, there is a fibrous mat below the tiles which appears to be semi-continuous (not per-tile).  May complicate matters as it is not simply attaching a tile to points on the SS skin.

The mounting studs welded to the SS skin poke right through the fiber pad. There's a video in the Production Updates thread somewhere of the installation process. The workers just push the pads on over the studs.
Title: Re: Starship heat shield
Post by: rsdavis9 on 03/24/2021 06:39 pm
They still need to do the weld between barrel sections. So I would guess one row of custom fit tiles. You got to cover the weld! Not too bad. It also allows tiling to occur on many barrels at the same time.

Based on photos, there is a fibrous mat below the tiles which appears to be semi-continuous (not per-tile).  May complicate matters as it is not simply attaching a tile to points on the SS skin.

The mounting studs welded to the SS skin poke right through the fiber pad. There's a video in the Production Updates thread somewhere of the installation process. The workers just push the pads on over the studs.

The original question for this set of replies was.
1. pre tile barrels and then figure out how to join them barrels so that tiles line up with their 1-2mm gap.
2. Wait till whole ship is assembled and then tile the whole thing.

Leaning towards number 1. Should be interesting how they will line up tiles between barrels.
Title: Re: Starship heat shield
Post by: _MECO on 03/24/2021 07:37 pm
They still need to do the weld between barrel sections. So I would guess one row of custom fit tiles. You got to cover the weld! Not too bad. It also allows tiling to occur on many barrels at the same time.

Based on photos, there is a fibrous mat below the tiles which appears to be semi-continuous (not per-tile).  May complicate matters as it is not simply attaching a tile to points on the SS skin.

The mounting studs welded to the SS skin poke right through the fiber pad. There's a video in the Production Updates thread somewhere of the installation process. The workers just push the pads on over the studs.

The original question for this set of replies was.
1. pre tile barrels and then figure out how to join them barrels so that tiles line up with their 1-2mm gap.
2. Wait till whole ship is assembled and then tile the whole thing.

Leaning towards number 1. Should be interesting how they will line up tiles between barrels.

They would have to at least leave a single band of slots on the top and bottom of the circumference of each ring before stacking. What with the shims they use to line up the sections and all. And I haven't paid too much attention to how those things are welded together, but you can't tell me that they don't need access to that seam from the outside.
Title: Re: Starship heat shield
Post by: Nomadd on 03/24/2021 10:40 pm
8kg per m^2, that's the TPS density? If so, the whole heat shield is only 5t or so, pretty light...
That's only for the white stuff. The black glassy outer surface and the metal 'Y' hardware will bump this up.
It's for the complete tile, hardware, black stuff and all. No idea about underlayment or blue stuff.
Title: Re: Starship heat shield
Post by: sucramdi on 03/24/2021 11:09 pm
Here's an interesting clip, SpaceX workers working on the damaged tile. Nice sense of scale of the tile and detail of the back while they're holding it. Photo is a screen grab from the video.

https://www.youtube.com/watch?v=eny57M5sxHk
Title: Re: Starship heat shield
Post by: Vultur on 03/25/2021 06:00 am
Part of the problem is cost so they probably want to try the cheapest solutions first and only start experimenting with more costly or complex set ups if they have to. I would expect to see a range of different options being tested out as time goes on.

Transpiration cooling is still in the waiting in the wings if needed, but it is inherently inefficient as it will use consumables and its probably also involves more complexity and cost. I predict that either we won't see it or if we do it will be a lot later on the high energy areas after they have tried a lot of other options.

Good points. Maybe I am overly concerned about this -- it just looks a lot like the troublesome Shuttle heat shield.
Title: Re: Starship heat shield
Post by: HVM on 03/25/2021 09:49 am
Here's an interesting clip, SpaceX workers working on the damaged tile. Nice sense of scale of the tile and detail of the back while they're holding it. Photo is a screen grab from the video.
Tiles are hollow?
Title: Re: Starship heat shield
Post by: enbandi on 03/25/2021 11:42 am
Here's an interesting clip, SpaceX workers working on the damaged tile. Nice sense of scale of the tile and detail of the back while they're holding it. Photo is a screen grab from the video.
Tiles are hollow?

Nice catch. The Y structure is clearly visible on the back side, which is most probably means that a slight depression exists there.
Actually the broken tile, and the replacement are from a separate area/batch. This hollow out thing can be the specialty of that batch.

Pictures from  the video above.
Title: Re: Starship heat shield
Post by: HVM on 03/25/2021 11:55 am
Like A or B?
Title: Re: Starship heat shield
Post by: Nevyn72 on 03/25/2021 11:57 am
Like A or B?

Nice picture!

I think it's A.
Title: Re: Starship heat shield
Post by: edzieba on 03/25/2021 12:56 pm
I'd guess B, the tiles are insulators so you'd want to keep any conductive parts as far from the hot side as possible.

I'd be interested in what metal the insert is made of. The Silica fibre tiles are sintered at north of 1260°C, so dimensional stability and high temp oxidation (and consequent contamination of the tile) seem like they would be obstacles - along with most lightweight alloys just melting into a puddle.
Title: Re: Starship heat shield
Post by: Nomadd on 03/25/2021 01:41 pm
Like A or B?
A. At least for one out of several types they've tried.
 They're working on some structural testing rigs. Maybe they'll come up with a better tile tester while they're at it. Staying intact for a flight isn't good enough. They need to add some margin.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 03/27/2021 12:44 am
They still need to do the weld between barrel sections. So I would guess one row of custom fit tiles. You got to cover the weld! Not too bad. It also allows tiling to occur on many barrels at the same time.

Based on photos, there is a fibrous mat below the tiles which appears to be semi-continuous (not per-tile).  May complicate matters as it is not simply attaching a tile to points on the SS skin.

The mounting studs welded to the SS skin poke right through the fiber pad. There's a video in the Production Updates thread somewhere of the installation process. The workers just push the pads on over the studs.

The original question for this set of replies was.
1. pre tile barrels and then figure out how to join them barrels so that tiles line up with their 1-2mm gap.
2. Wait till whole ship is assembled and then tile the whole thing.

Leaning towards number 1. Should be interesting how they will line up tiles between barrels.

They would have to at least leave a single band of slots on the top and bottom of the circumference of each ring before stacking. What with the shims they use to line up the sections and all. And I haven't paid too much attention to how those things are welded together, but you can't tell me that they don't need access to that seam from the outside.

3:   Hybrid model.  Tile all but the ends of each section, then hand-tile one or two rows around where the sections join after assembly.  I think there's 6 section joins so that's not that many tiles, and when a section join occurs there's already scaffolding or other infrastructure to make working on the joint easy

Build small amounts of tiles in -2, -1, +1, +2 mm size increments to deal with the variance in the size of the gaps where the sections are joined.
Title: Re: Starship heat shield
Post by: OTV Booster on 03/27/2021 03:50 pm
They still need to do the weld between barrel sections. So I would guess one row of custom fit tiles. You got to cover the weld! Not too bad. It also allows tiling to occur on many barrels at the same time.

Based on photos, there is a fibrous mat below the tiles which appears to be semi-continuous (not per-tile).  May complicate matters as it is not simply attaching a tile to points on the SS skin.

The mounting studs welded to the SS skin poke right through the fiber pad. There's a video in the Production Updates thread somewhere of the installation process. The workers just push the pads on over the studs.

The original question for this set of replies was.
1. pre tile barrels and then figure out how to join them barrels so that tiles line up with their 1-2mm gap.
2. Wait till whole ship is assembled and then tile the whole thing.

Leaning towards number 1. Should be interesting how they will line up tiles between barrels.

They would have to at least leave a single band of slots on the top and bottom of the circumference of each ring before stacking. What with the shims they use to line up the sections and all. And I haven't paid too much attention to how those things are welded together, but you can't tell me that they don't need access to that seam from the outside.

3:   Hybrid model.  Tile all but the ends of each section, then hand-tile one or two rows around where the sections join after assembly.  I think there's 6 section joins so that's not that many tiles, and when a section join occurs there's already scaffolding or other infrastructure to make working on the joint easy

Build small amounts of tiles in -2, -1, +1, +2 mm size increments to deal with the variance in the size of the gaps where the sections are joined.
No direct evidence but ISTM they've got the tolerances down fine enough that any gap variance between sections would be within reach of the rope caulking that's been discussed. No need for fiddly sizing. Worst case, a little banging on the prongs could give 1-2mm without screwing things up. Not meant as a long term solution.


Edit: the vid showing the guys not getting a tile to fit? There was one there before. Maybe some variance on tile size?
Title: Re: Starship heat shield
Post by: HVM on 03/31/2021 10:27 pm
SN15 have bigger patch of tiles than ever, but hard shadows don't help at all...
Title: Re: Starship heat shield
Post by: chevvie on 04/01/2021 09:49 am
SN15 have bigger patch of tiles than ever, but hard shadows don't help at all...

My OCD can't handle that 1 crooked tile up above.

But on a serious note, these tiles don't really seem to make for a nice smooth surface with all the small height differences. I wonder if they won't be ripped off during supersonic speeds.
Title: Re: Starship heat shield
Post by: edzieba on 04/01/2021 12:49 pm
Since these test vehicles won't be hitting the atmosphere (yet) they could simply not be caring about levelling the tiles yet, and instead just focusing on the installation process and adhesion during ascent (and terminal descent). Until the tiles have full coverage and edging (eliminating the 'lip# between tiled and non-tiled areas) they won't be aerodynamically representative of the final configuration, but they don't need to be just yet. Assuming the "SN20 for orbit" timeline holds out, there are at least 5 more Starships which can refine tile placement for passing through Max Q before they need to stay in place during hypersonic flow. And technically, the heatshield could remain in place through peak entry heating and then rip off at supersonic speeds without necessarily losing the vehicle: not ideal for re-use cost, but not a barrier to operational use.
Post-application tile levelling tools exist for your garden variety ceramic or stone tiles, so I would expect SpaceX to use those before they investigate any more exotic solution. e.g. a dab of high-temp potting compound into the tile tab receptacles immediately before install with a few hours cure time, install the tiles, level them relative to each other, then wait a few hours for the compound to cure and lock them in place before poking them.
Title: Re: Starship heat shield
Post by: enbandi on 04/01/2021 07:36 pm
Since these test vehicles won't be hitting the atmosphere (yet) they could simply not be caring about levelling the tiles yet....

A bit crazy idea: what if this uneven surface somehow help in insulation (so intentional)?

At much smaller scale and speed small dents and hills on a surface can create local turbulence which in turn cushioning the surface from laminar flow. Or something similar.
Title: Re: Starship heat shield
Post by: maquinsa on 04/01/2021 07:43 pm
Since these test vehicles won't be hitting the atmosphere (yet) they could simply not be caring about levelling the tiles yet....

A bit crazy idea: what if this uneven surface somehow help in insulation (so intentional)?

At much smaller scale and speed small dents and hills on a surface can create local turbulence which in turn cushioning the surface from laminar flow. Or something similar.

I don’t think the uneven surface is intentional but your idea makes sense: increasing the distance to the shockwave by having turbulent flow on the surface of the spacecraft increasing the boundary layer.
Title: Re: Starship heat shield
Post by: Oersted on 04/01/2021 08:31 pm
So let's have sharkskin tiles!
Title: Re: Starship heat shield
Post by: eriblo on 04/01/2021 09:22 pm
Since these test vehicles won't be hitting the atmosphere (yet) they could simply not be caring about levelling the tiles yet....

A bit crazy idea: what if this uneven surface somehow help in insulation (so intentional)?

At much smaller scale and speed small dents and hills on a surface can create local turbulence which in turn cushioning the surface from laminar flow. Or something similar.

I don’t think the uneven surface is intentional but your idea makes sense: increasing the distance to the shockwave by having turbulent flow on the surface of the spacecraft increasing the boundary layer.
Turbulence massively increases teat transport across the flow (i.e. from the bow shock to the skin), se for example Wayne Hale's excellent blog posts.

https://blogs.nasa.gov/waynehalesblog/2009/01/22/post_1232662169255/

https://blogs.nasa.gov/waynehalesblog/2009/01/29/post_1233082616008/
Title: Re: Starship heat shield
Post by: cuddihy on 04/02/2021 03:57 pm
ISRU is OT for heat shield.

Back to it, why can’t the heat shield tiles be asymmetric thickness to allow overlapping/ sliding with thermal expansion?

Got the turbulence argument, how much variation produces significant turbulence? Is the tile thickness was such that the overlap portion was close in thickness to the thicker non-overlay portion, wouldn’t the turbulence not be any more of a factor than it is already with the variation between tile edges already?
Title: Re: Starship heat shield
Post by: Oersted on 04/02/2021 06:54 pm
Turbulence massively increases teat transport across the flow (i.e. from the bow shock to the skin), se for example Wayne Hale's excellent blog posts.

https://blogs.nasa.gov/waynehalesblog/2009/01/22/post_1232662169255/

https://blogs.nasa.gov/waynehalesblog/2009/01/29/post_1233082616008/

I checked out the links and was disappointed not to see anything about teat transport.
Title: Re: Starship heat shield
Post by: enbandi on 04/02/2021 11:55 pm
Minor detail on the tile manufacturing. This is from a permitting document for the Cidco site.

Quote
2.4 Silica Purification Process
The Cidco facility also includes a silica purification process. Bales of silica fibers are treated to be used in the manufacture of light-weight “bricks” used on the exterior of spacecraft. These bricks are manufactured at a separate SpaceX facility.   Bales of silica fiber are delivered to the Cidco facility for processing and purification before being used as raw material for brick production. Bales weigh approximately 25 kilograms and are stored in a covered storage pavilion. To begin processing, bales are loaded manually into an insulation blower which cuts the fibers into small pieces before blowing the silica into a series of heated tanks of nitric acid. SpaceX can process a single bale in 10-15 minutes.  The series of nitric acid tanks are fed by a 68% nitric acid solution delivered to the Cidco facility by truck. The solution is diluted to 15% nitric acid solution in the first tank with hot water produced by a series of four (4) natural gas-fired hot water heaters. Each natural gas heater has a maximum heat input capacity of  0.199 MMBtu/hr. Hot water generated using the hot water heaters is also circulated in coils around tanks to maintain the tanks at a target temperature. The nitric acid concentration is diluted in each progressive tank. After passing through the final tank, the silica-acid solution is discharged with a concentration of 1.5% nitric acid solution into a rotary drum which separates the silica slurry from the solution.   The silica slurry is shipped to another SpaceX facility located in Cape Canaveral and the acid solution is neutralized to a pH between 6 and 8 and sent to an evaporation tower. The evaporation tower has a maximum heat input capacity of 7.5 MMBtu/hr and combusts natural gas to heat and evaporate the wastewater generated in the silica preparation process.7 Emissions of PM resulting from dissolved solids in the wastewater are controlled by the tower’s packed bed mist eliminators.
Title: Re: Starship heat shield
Post by: livingjw on 04/08/2021 03:55 pm
It appears that there are at least two variations in TPS attachment on SN15. A portion seems to have the insulating felt blanket, but a portion does not.

John
Title: Re: Starship heat shield
Post by: rsdavis9 on 04/08/2021 04:18 pm
It appears that there are at least two variations in TPS attachment on SN15. A portion seems to have the insulating felt blanket, but a portion does not.

John

So is this on a 3 ring barrel section?
When I look at the pic there appears to be a short ring near the middle?
And clearly in the methane tank section.

So does everybody think this is how they will tile?
Tile barrel sections with straight edges.
Join barrels
Add in missing band between barrels.
?
Title: Re: Starship heat shield
Post by: WiresMN on 04/08/2021 04:30 pm
It appears that there are at least two variations in TPS attachment on SN15. A portion seems to have the insulating felt blanket, but a portion does not.

John
I think the whole thing has felt, but it is really hard to see in some areas. I circled where it can be seen poking out in the blown-up image that BocaChicaGal posted. I have included a cropped version of the original. The image source goes to BocaChicaGal.
Title: Re: Starship heat shield
Post by: IanThePineapple on 04/08/2021 04:36 pm
SN15 has 829 tiles installed on its belly. SN11 only had 384

https://twitter.com/IanPineapple/status/1380197565115858949
Title: Re: Starship heat shield
Post by: HVM on 04/08/2021 04:47 pm
It appears that there are at least two variations in TPS attachment on SN15. A portion seems to have the insulating felt blanket, but a portion does not.

John
I think the whole thing has felt, but it is really hard to see in some areas. I circled where it can be seen poking out in the blown-up image that BocaChicaGal posted. I have included a cropped version of the original. The image source goes to BocaChicaGal.
Here it is without the tiles: (Some reason I remembered it having a product name in big blue letters on...)
Also video:
https://youtu.be/i490-TIDHbM
Title: Re: Starship heat shield
Post by: Nomadd on 04/08/2021 05:10 pm
It appears that there are at least two variations in TPS attachment on SN15. A portion seems to have the insulating felt blanket, but a portion does not.

John
I think the whole thing has felt, but it is really hard to see in some areas. I circled where it can be seen poking out in the blown-up image that BocaChicaGal posted. I have included a cropped version of the original. The image source goes to BocaChicaGal.

Little different angle.
 The tiles don't seem to sit very flush.
Title: Re: Starship heat shield
Post by: joek on 04/08/2021 05:31 pm
Little different angle.
The tiles don't seem to sit very flush.
Maybe a test of "good enough (at least for now)"?
Title: Re: Starship heat shield
Post by: HVM on 04/08/2021 05:32 pm
Little different angle.
 The tiles don't seem to sit very flush.
Bit of forced perspective with false colors from 70s, it not look so bad.
Title: Re: Starship heat shield
Post by: Nomadd on 04/08/2021 05:36 pm
Little different angle.
The tiles don't seem to sit very flush.
Maybe a test of "good enough (at least for now)"?
Maybe. It just irks me because now my brain has to wonder if it's pin placement, brackets in the tiles, fuzzy backing getting caught in the clip or hull irregularities. Like it wasn't busy enough trying to figure out why people watch curling.
Title: Re: Starship heat shield
Post by: livingjw on 04/08/2021 06:05 pm
My bad. Nomad's picture shows that it appears attached all the same way.
Carry on.

John
Title: Re: Starship heat shield
Post by: Interro on 04/08/2021 07:21 pm
There appears to be a patch of 12 on each left flap (looking from the aft side)

https://twitter.com/BocaCharts/status/1380238229941673989?s=20 (https://twitter.com/BocaCharts/status/1380238229941673989?s=20)
Title: Re: Starship heat shield
Post by: enbandi on 04/08/2021 08:11 pm
Little different angle.
The tiles don't seem to sit very flush.
Maybe a test of "good enough (at least for now)"?
Maybe. It just irks me because now my brain has to wonder if it's pin placement, brackets in the tiles, fuzzy backing getting caught in the clip or hull irregularities. Like it wasn't busy enough trying to figure out why people watch curling.

Can you estimate if the tile attachments are solid/rigid or something with a small degree of freedom? If they created a flexible attachent system (make sense vs cryo and resonation), uneven surface can be the result of random last positions per tile.
Title: Re: Starship heat shield
Post by: Chris Bergin on 04/08/2021 10:41 pm
https://twitter.com/TylerG1998/status/1380288314876571648
Title: Re: Starship heat shield
Post by: Keldor on 04/08/2021 11:40 pm
It appears that there are at least two variations in TPS attachment on SN15. A portion seems to have the insulating felt blanket, but a portion does not.

John
I think the whole thing has felt, but it is really hard to see in some areas. I circled where it can be seen poking out in the blown-up image that BocaChicaGal posted. I have included a cropped version of the original. The image source goes to BocaChicaGal.
Here it is without the tiles: (Some reason I remembered it having a product name in big blue letters on...)
Also video:


Hmm.  Looking at the process, I'm betting it's the insulation layer they're putting on here that's causing all the unevenness in the tiles.  It's going on a bit wrinkly and uneven, if you will.

Thankfully, this is pretty clearly just a result of the way they're applying it by hand.  I don't believe it will be that hard to make a machine that can smoothly press pieces of insulation to the hull - I'm picturing some sort of thing vaguely like a big paint roller - but of course they're not going to make such a machine until they have the tile (and insulation) design close to finalized so that the machine's requirements are known.

Short term, I feel like if they punched the holes in the insulation for the pins before laying it on, it would go on a lot easier. There are many industries where cutting forms out of large sheets of various materials is needed, so a machine capable of doing this should be readily available.
Title: Re: Starship heat shield
Post by: alphacentauri on 04/09/2021 12:03 am
What is the significance of tile placement on the prototypes? Big rectangular area near the middle (with a corner missing on SN15) and the small clusters near the top and bottom that are located differently on each ship. I assume they're testing the adhesion method. Are there differences in tank temperature or some other properties of the tank at those specific locations?
Title: Re: Starship heat shield
Post by: oliver602 on 04/09/2021 12:10 am
It appears that there are at least two variations in TPS attachment on SN15. A portion seems to have the insulating felt blanket, but a portion does not.

John
I think the whole thing has felt, but it is really hard to see in some areas. I circled where it can be seen poking out in the blown-up image that BocaChicaGal posted. I have included a cropped version of the original. The image source goes to BocaChicaGal.
Here it is without the tiles: (Some reason I remembered it having a product name in big blue letters on...)
Also video:


Hmm.  Looking at the process, I'm betting it's the insulation layer they're putting on here that's causing all the unevenness in the tiles.  It's going on a bit wrinkly and uneven, if you will.

Thankfully, this is pretty clearly just a result of the way they're applying it by hand.  I don't believe it will be that hard to make a machine that can smoothly press pieces of insulation to the hull - I'm picturing some sort of thing vaguely like a big paint roller - but of course they're not going to make such a machine until they have the tile (and insulation) design close to finalized so that the machine's requirements are known.

Short term, I feel like if they punched the holes in the insulation for the pins before laying it on, it would go on a lot easier. There are many industries where cutting forms out of large sheets of various materials is needed, so a machine capable of doing this should be readily available.

I think the height of teach tile would be set by the depth of the hole in the back of the tile and the length of the pins. The insulation looks soft. Any unevenness could be tolerance in the pins/holes. They look like split peg shaped clips.
Title: Re: Starship heat shield
Post by: oiorionsbelt on 04/09/2021 01:38 am
Why do they cut that top & bottom row of tiles?
Title: Re: Starship heat shield
Post by: Nomadd on 04/09/2021 02:06 am
Why do they cut that top & bottom row of tiles?
Because when they do the real thing, some of them will need to be trimmed. They need to test those too since the mounting won't be the same.
 Maybe there are weird aerodynamic effects from zagged tile lines.
Title: Re: Starship heat shield
Post by: HVM on 04/09/2021 06:36 am
Those tile are not cut, five point tiles are build like that from the factory. Long side have same black glazed
borosilicate(?) coating over the white silicon fiber tile as other faces.
Title: Re: Starship heat shield
Post by: FutureSpaceTourist on 04/09/2021 07:31 am
https://twitter.com/cnunezimages/status/1380337952111403011
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 04/09/2021 09:10 am
What is the significance of tile placement on the prototypes? Big rectangular area near the middle (with a corner missing on SN15) and the small clusters near the top and bottom that are located differently on each ship. I assume they're testing the adhesion method. Are there differences in tank temperature or some other properties of the tank at those specific locations?

Obviusly there will be heat tiles in the nose section too, and there there aren't taks, so  during the launch will experienc different temperature. When in space and during reentry tanks(except headers, but these are inside) will be empt, so the temperature will be uniform (except for the differencies caused by different reentry heating).
Title: Re: Starship heat shield
Post by: Rocket Surgeon on 04/09/2021 10:48 am
https://twitter.com/cnunezimages/status/1380337952111403011

Hexagons are Bestagons!
Title: Re: Starship heat shield
Post by: Hog on 04/09/2021 03:17 pm


Hexagons are Bestagons!

I gotta say that seeing this TPS development going on right before our eyes is pretty exciting! 

Shields up!
Title: Re: Starship heat shield
Post by: oiorionsbelt on 04/09/2021 05:52 pm
Going back to those 5 sided tiles. It was mentioned that the hexagonal shape was to prevent a straight lines for the plasma to get into. It seems as though the 5 sided version will leave a continuous line with whatever they 'mate' with, thereby leaving a path for the plasma to follow. How would that be addressed?
Title: Re: Starship heat shield
Post by: Barnalby on 04/09/2021 06:02 pm
You need the straight edge tiles for stuff like the edge of the heat shield at the transition between the shielded half of Starship and the bare stainless half of Starship as well as the bottom edge of the skirt.
Title: Re: Starship heat shield
Post by: wannamoonbase on 04/09/2021 06:25 pm
You need the straight edge tiles for stuff like the edge of the heat shield at the transition between the shielded half of Starship and the bare stainless half of Starship as well as the bottom edge of the skirt.

Good point on the edge tiles. 

The transition tiles for the flaps and the nose cone are of the utmost interest.  I'm sure we'll see them soon.
Title: Re: Starship heat shield
Post by: Barnalby on 04/09/2021 06:36 pm
We're going to have to wait until we see the transonic/supersonic capable fins and fairings before we see how they tile them. 

IIRC SN15 might be the last of the subsonic only Starships so we might see them as early as SN16.
Title: Re: Starship heat shield
Post by: HVM on 04/09/2021 06:43 pm
You need the straight edge tiles for stuff like the edge of the heat shield at the transition between the shielded half of Starship and the bare stainless half of Starship as well as the bottom edge of the skirt.

Good point on the edge tiles. 

The transition tiles for the flaps and the nose cone are of the utmost interest.  I'm sure we'll see them soon.
Carbon-carbon?

Hexagons are Bestagons!
But can you trust a man who can't tell ICBM apart from SLBM?
Title: Re: Starship heat shield
Post by: enbandi on 04/09/2021 06:46 pm
Going back to those 5 sided tiles. It was mentioned that the hexagonal shape was to prevent a straight lines for the plasma to get into. It seems as though the 5 sided version will leave a continuous line with whatever they 'mate' with, thereby leaving a path for the plasma to follow. How would that be addressed?

I think there is no problem, if the straight lines are perpendicular to your motion/air flow. And that is how they want to use them where we seen them: at the ring/module connection cross sections. Also not a problem at the bottom of the skirt.
Title: Re: Starship heat shield
Post by: Interro on 04/09/2021 08:06 pm
Just a quick update on SN15's tile counting:

Just found Mars Embassy's rollout video, with some awesome closeup shots of the heat tiles on the back of the flaps. Below are screenshots of the two tile groups on the back of the flaps.

This confirms the count I published on twitter (@BocaCharts)

https://www.youtube.com/watch?v=WNLtkWpdTMo&ab_channel=MarsEmbassy (https://www.youtube.com/watch?v=WNLtkWpdTMo&ab_channel=MarsEmbassy)
Title: Re: Starship heat shield
Post by: FutureSpaceTourist on 04/09/2021 08:33 pm
https://twitter.com/bojay_stellar/status/1380189540653105153

Quote
Starship with full tile set! Augmented reality, by editing my render onto a pic by @BocaChicaGal . Looks so surreal.
Title: Re: Starship heat shield
Post by: turbopump2 on 04/09/2021 10:55 pm
I'm still confounded by an apparent incongruity between what's being done in terms of the single layer hexagonal tiles and the notion that:

- losing a _single tile would jeopardize the vehicle:
    - worst case burn through the metal hull, a better case being damage to the frame, precluding any reuse (Buran, apparently losing 3 adjacent tiles under the wing with a _titanium structure)
- losing a tile would lead to zipping off more
- that many tiles with a large gap without filler may compound the problem
- there is no materials science magic for tiles if lost even when made of TUFROC

then again the space shuttle probably survived many tile damages and ?  tile losses apart from STS-27 with an aluminium frame only.

Gut feeling is that a 2nd layer say of an ablative material wrapped over or better under the tiles may be a good idea
Title: Re: Starship heat shield
Post by: livingjw on 04/10/2021 12:09 am
I'm still confounded by an apparent incongruity between what's being done in terms of the single layer hexagonal tiles and the notion that:

- losing a single tile would jeopardize the vehicle:
    - worst case burn through the metal hull, a better case being damage to the frame, precluding any reuse (Buran, apparently losing 3 adjacent tiles under the wing with a _titanium structure)
- losing a tile would lead to zipping off more
- that many tiles with a large gap without filler may compound the problem
- there is no materials science magic for tiles if lost even when made of TUFROC

then again the space shuttle probably survived many tile damages and ?  tile losses apart from STS-27 with an aluminium frame only.

Gut feeling is that a 2nd layer say of an ablative material wrapped over or better under the tiles may be a good idea

- losing a single tile could jeopardize the vehicle, but maybe not, because you have a insulating blanket under the tile and a shear layer will form over the cavity formed by the missing tile. Only testing will tell.

- losing a tile could lead to zipping off more, but I'm sure they will analyze and test to make sure it doesn't.

- loss of many tiles with large gap without filler (are you referring to the insulating blanket?) will definitely compound the problem. They will do their darndest to make sure this does not happen.

John

Title: Re: Starship heat shield
Post by: KBK on 04/10/2021 04:28 am
Here's an interesting clip, SpaceX workers working on the damaged tile. Nice sense of scale of the tile and detail of the back while they're holding it. Photo is a screen grab from the video.

https://www.youtube.com/watch?v=eny57M5sxHk

Thanks for that.

It seems the force distribution through the possible flextural and resonance modes is not stable and low enough in levels, throughout the entire envelope of possible motion and stressing.

The suggestion is to have a small raised area on the back of the tile, furthest out at the three open corners. something that fits the stressing potentials. This, once the optimum pressing upon the thermal pad is figured out.

This would cancel one possible resonance mode and also drain those tips of unwanted collecting energies. Possibly enough to keep the tile out of fracture range, and shifting in it's position. Basically one is playing two modes, one against the other (in and out) and having motion potential, and with respect to mounting torsion being damped.

Again, reiterating... right now, undesirable mechanical energies would gather at those open unsupported tips.  And the slight redesign of the backing, adding protrusions of some minimal sort, would possibly alleviate some mounting and stressing problems.

It all depends on the fragility of the tile, design of the backing, and so on.....but the video seen, does hint strongly at a problem area re energetic damping, stressing, and drainage.

If that is not sufficient, then there are other KISS related possibilities.

Just an idea (lots of work with fairly finicky wideband vibration control and dealing with flextural modes, mounting systems, etc, in the past 30 years).
Title: Re: Starship heat shield
Post by: Nomadd on 04/10/2021 05:06 am
 I wonder why he wasn't using a jig, or just another tile with cork glued to the raised parts to push that replacement tile on. Maybe they're required to fix the issue if they don't snap on easily instead of forcing them. They're pretty fragile. Or the original tile popped off because it was wedged in too tight, so the same size replacement was also a bad fit.
 I'm picturing a bunch of those strips they test crank bearing clearances with shoved between tiles to see how cryo testing and engine firing messes with the gaps. Or really good camera pointed at them.
Title: Re: Starship heat shield
Post by: edzieba on 04/10/2021 10:08 am
I wonder why he wasn't using a jig, or just another tile with cork glued to the raised parts to push that replacement tile on. Maybe they're required to fix the issue if they don't snap on easily instead of forcing them. They're pretty fragile. Or the original tile popped off because it was wedged in too tight, so the same size replacement was also a bad fit.
 I'm picturing a bunch of those strips they test crank bearing clearances with shoved between tiles to see how cryo testing and engine firing messes with the gaps. Or really good camera pointed at them.
Photogrammetry would be ideal for measuring 3D motion and deformation (tiles are too homogenous, so they'd need to pain or stick on a 'speckle' pattern to track).
Title: Re: Starship heat shield
Post by: Blueshift on 04/10/2021 12:51 pm
I'm still confounded by an apparent incongruity between what's being done in terms of the single layer hexagonal tiles and the notion that:

- losing a single tile would jeopardize the vehicle:
    - worst case burn through the metal hull, a better case being damage to the frame, precluding any reuse (Buran, apparently losing 3 adjacent tiles under the wing with a _titanium structure)
- losing a tile would lead to zipping off more
- that many tiles with a large gap without filler may compound the problem
- there is no materials science magic for tiles if lost even when made of TUFROC

then again the space shuttle probably survived many tile damages and ?  tile losses apart from STS-27 with an aluminium frame only.

Gut feeling is that a 2nd layer say of an ablative material wrapped over or better under the tiles may be a good idea

- losing a single tile could jeopardize the vehicle, but maybe not, because you have a insulating blanket under the tile and a shear layer will form over the cavity formed by the missing tile. Only testing will tell.

- losing a tile could lead to zipping off more, but I'm sure they will analyze and test to make sure it doesn't.

- loss of many tiles with large gap without filler (are you referring to the insulating blanket?) will definitely compound the problem. They will do their darndest to make sure this does not happen.

John

Why not use a kind of "water cannon" inside the tanks which is guided by an infrared system? In case of a tile failure the camera would sense the temperature increase and spray fuel onto the affected surface.
Title: Re: Starship heat shield
Post by: AC in NC on 04/10/2021 01:16 pm
Why not use a kind of "water cannon" inside the tanks which is guided by an infrared system? In case of a tile failure the camera would sense the temperature increase and spray fuel onto the affected surface.
::)
Title: Re: Starship heat shield
Post by: OTV Booster on 04/10/2021 03:00 pm
Little different angle.
The tiles don't seem to sit very flush.
Maybe a test of "good enough (at least for now)"?
Maybe. It just irks me because now my brain has to wonder if it's pin placement, brackets in the tiles, fuzzy backing getting caught in the clip or hull irregularities. Like it wasn't busy enough trying to figure out why people watch curling.
Awe, give it a couple reentries and it'll all smooth out. And get back to working that broom.
Title: Re: Starship heat shield
Post by: OTV Booster on 04/10/2021 04:49 pm
https://twitter.com/bojay_stellar/status/1380189540653105153 (https://twitter.com/bojay_stellar/status/1380189540653105153)

Quote
Starship with full tile set! Augmented reality, by editing my render onto a pic by @BocaChicaGal . Looks so surreal.
That pic is worth passing along. Has a muscle car feel. Or steam punk. Or something. Credits as given.
Title: Re: Starship heat shield
Post by: OTV Booster on 04/10/2021 04:52 pm
I'm still confounded by an apparent incongruity between what's being done in terms of the single layer hexagonal tiles and the notion that:

- losing a _single tile would jeopardize the vehicle:
    - worst case burn through the metal hull, a better case being damage to the frame, precluding any reuse (Buran, apparently losing 3 adjacent tiles under the wing with a _titanium structure)
- losing a tile would lead to zipping off more
- that many tiles with a large gap without filler may compound the problem
- there is no materials science magic for tiles if lost even when made of TUFROC

then again the space shuttle probably survived many tile damages and ?  tile losses apart from STS-27 with an aluminium frame only.

Gut feeling is that a 2nd layer say of an ablative material wrapped over or better under the tiles may be a good idea
Gotta walk before you run. This is not the finished product.
Title: Re: Starship heat shield
Post by: OTV Booster on 04/10/2021 06:20 pm
Here's an interesting clip, SpaceX workers working on the damaged tile. Nice sense of scale of the tile and detail of the back while they're holding it. Photo is a screen grab from the video.

https://www.youtube.com/watch?v=eny57M5sxHk (https://www.youtube.com/watch?v=eny57M5sxHk)

Thanks for that.

It seems the force distribution through the possible flextural and resonance modes is not stable and low enough in levels, throughout the entire envelope of possible motion and stressing.

The suggestion is to have a small raised area on the back of the tile, furthest out at the three open corners. something that fits the stressing potentials. This, once the optimum pressing upon the thermal pad is figured out.

This would cancel one possible resonance mode and also drain those tips of unwanted collecting energies. Possibly enough to keep the tile out of fracture range, and shifting in it's position. Basically one is playing two modes, one against the other (in and out) and having motion potential, and with respect to mounting torsion being damped.

Again, reiterating... right now, undesirable mechanical energies would gather at those open unsupported tips.  And the slight redesign of the backing, adding protrusions of some minimal sort, would possibly alleviate some mounting and stressing problems.

It all depends on the fragility of the tile, design of the backing, and so on.....but the video seen, does hint strongly at a problem area re energetic damping, stressing, and drainage.

If that is not sufficient, then there are other KISS related possibilities.

Just an idea (lots of work with fairly finicky wideband vibration control and dealing with flextural modes, mounting systems, etc, in the past 30 years).
IIUC, what you're saying is the unsupported tile corners need to be pre loaded? Makes sense.


Beware of wear on the lip face. It might need a stainless insert. Which might rub through the batting and then the hull. Crap! No wonder they say space is hard.


A thought. We've taken the goal of an inexpensive heatshield, added rapid turnaround then collectively shuddered at all the tile problems the shuttle had. Maybe is just isn't possible to do a lifetime heatshield with current technology. We shouldn't let perfect be the enemy of good.


Would a periodic rebuild of the tile system be all that bad a thing? Testing will give us a number but might it be done every 5th reentry? Would it be a deal killer if it were every 3rd? The airframes are, as rockets go, not all that expensive. Needing even 20% extra doesn't cost too much. The engines swap out easy enough.


Ship goes into maintenance for its 5 flight service, the engines and heatshield get stripped off. Engines get any TLC needed and go onto a ship finishing up servicing. In the meantime the ship gets a good inspection and the heatshield gets a rebuild.

Title: Re: Starship heat shield
Post by: OTV Booster on 04/10/2021 06:33 pm
I wonder why he wasn't using a jig, or just another tile with cork glued to the raised parts to push that replacement tile on. Maybe they're required to fix the issue if they don't snap on easily instead of forcing them. They're pretty fragile. Or the original tile popped off because it was wedged in too tight, so the same size replacement was also a bad fit.
 I'm picturing a bunch of those strips they test crank bearing clearances with shoved between tiles to see how cryo testing and engine firing messes with the gaps. Or really good camera pointed at them.
That stuff is plastigauge. ISTM the gaps will be a lot larger. If big enough for rope caulking, maybe 3-4mm. Any chance you've been close enough to see?
Title: Re: Starship heat shield
Post by: Slarty1080 on 04/10/2021 08:09 pm
I'm still confounded by an apparent incongruity between what's being done in terms of the single layer hexagonal tiles and the notion that:

- losing a single tile would jeopardize the vehicle:
    - worst case burn through the metal hull, a better case being damage to the frame, precluding any reuse (Buran, apparently losing 3 adjacent tiles under the wing with a _titanium structure)
- losing a tile would lead to zipping off more
- that many tiles with a large gap without filler may compound the problem
- there is no materials science magic for tiles if lost even when made of TUFROC

then again the space shuttle probably survived many tile damages and ?  tile losses apart from STS-27 with an aluminium frame only.

Gut feeling is that a 2nd layer say of an ablative material wrapped over or better under the tiles may be a good idea

- losing a single tile could jeopardize the vehicle, but maybe not, because you have a insulating blanket under the tile and a shear layer will form over the cavity formed by the missing tile. Only testing will tell.

- losing a tile could lead to zipping off more, but I'm sure they will analyze and test to make sure it doesn't.

- loss of many tiles with large gap without filler (are you referring to the insulating blanket?) will definitely compound the problem. They will do their darndest to make sure this does not happen.

John

Why not use a kind of "water cannon" inside the tanks which is guided by an infrared system? In case of a tile failure the camera would sense the temperature increase and spray fuel onto the affected surface.
The problem is that when the tank warms up the gas pressure inside will rise until the tank ruptures. It is conceivable that this sort of arrangement might save the ship under a few very specific circumstances, but any extended heating would destroy the ship fairly rapidly. Adding a fair amount of mass and complexity to every flight in order to save the ship from a small subset of situations that occur very infrequently is not SpaceX style. They would rather spend the mass in making the tile system more robust so the problem doesn't occur in the first place.
Title: Re: Starship heat shield
Post by: envy887 on 04/11/2021 12:44 am
I'm still confounded by an apparent incongruity between what's being done in terms of the single layer hexagonal tiles and the notion that:

- losing a single tile would jeopardize the vehicle:
    - worst case burn through the metal hull, a better case being damage to the frame, precluding any reuse (Buran, apparently losing 3 adjacent tiles under the wing with a _titanium structure)
- losing a tile would lead to zipping off more
- that many tiles with a large gap without filler may compound the problem
- there is no materials science magic for tiles if lost even when made of TUFROC

then again the space shuttle probably survived many tile damages and ?  tile losses apart from STS-27 with an aluminium frame only.

Gut feeling is that a 2nd layer say of an ablative material wrapped over or better under the tiles may be a good idea

- losing a single tile could jeopardize the vehicle, but maybe not, because you have a insulating blanket under the tile and a shear layer will form over the cavity formed by the missing tile. Only testing will tell.

- losing a tile could lead to zipping off more, but I'm sure they will analyze and test to make sure it doesn't.

- loss of many tiles with large gap without filler (are you referring to the insulating blanket?) will definitely compound the problem. They will do their darndest to make sure this does not happen.

John

Why not use a kind of "water cannon" inside the tanks which is guided by an infrared system? In case of a tile failure the camera would sense the temperature increase and spray fuel onto the affected surface.

Probably not needed. The tank wall structure under the tile will heat up and radiate to the rest of the tank. BOTE calc suggests that it can easily dump over 100 kW/m2 without exceeding the working temp of stainless, which (except on a leading edge) should be plenty of flux.
Title: Re: Starship heat shield
Post by: Nomadd on 04/11/2021 12:50 am
 Fun fact...When they remove a tile on purpose, they bore 1/2" holes over the three attachment points so they can release the clips.
Title: Re: Starship heat shield
Post by: KBK on 04/11/2021 12:50 am
Here's an interesting clip, SpaceX workers working on the damaged tile. Nice sense of scale of the tile and detail of the back while they're holding it. Photo is a screen grab from the video.

https://www.youtube.com/watch?v=eny57M5sxHk (https://www.youtube.com/watch?v=eny57M5sxHk)

Thanks for that.

It seems the force distribution through the possible flextural and resonance modes is not stable and low enough in levels, throughout the entire envelope of possible motion and stressing.

The suggestion is to have a small raised area on the back of the tile, furthest out at the three open corners. something that fits the stressing potentials. This, once the optimum pressing upon the thermal pad is figured out.

This would cancel one possible resonance mode and also drain those tips of unwanted collecting energies. Possibly enough to keep the tile out of fracture range, and shifting in it's position. Basically one is playing two modes, one against the other (in and out) and having motion potential, and with respect to mounting torsion being damped.

Again, reiterating... right now, undesirable mechanical energies would gather at those open unsupported tips.  And the slight redesign of the backing, adding protrusions of some minimal sort, would possibly alleviate some mounting and stressing problems.

It all depends on the fragility of the tile, design of the backing, and so on.....but the video seen, does hint strongly at a problem area re energetic damping, stressing, and drainage.

If that is not sufficient, then there are other KISS related possibilities.

Just an idea (lots of work with fairly finicky wideband vibration control and dealing with flextural modes, mounting systems, etc, in the past 30 years).
IIUC, what you're saying is the unsupported tile corners need to be pre loaded? Makes sense.


Beware of wear on the lip face. It might need a stainless insert. Which might rub through the batting and then the hull. Crap! No wonder they say space is hard.


A thought. We've taken the goal of an inexpensive heatshield, added rapid turnaround then collectively shuddered at all the tile problems the shuttle had. Maybe is just isn't possible to do a lifetime heatshield with current technology. We shouldn't let perfect be the enemy of good.


Would a periodic rebuild of the tile system be all that bad a thing? Testing will give us a number but might it be done every 5th reentry? Would it be a deal killer if it were every 3rd? The airframes are, as rockets go, not all that expensive. Needing even 20% extra doesn't cost too much. The engines swap out easy enough.


Ship goes into maintenance for its 5 flight service, the engines and heatshield get stripped off. Engines get any TLC needed and go onto a ship finishing up servicing. In the meantime the ship gets a good inspection and the heatshield gets a rebuild.

It can look like a small flat bottomed rib that points toward the center of the tile, to keep the load on the thermal blanket out of trouble.

If one does the 4k still frame thing through every part of that video where the back of the tile is visible, it looks like they made the back concave and then the sharpest part of the concavity is right at the outer lip for edge support. (highest curvature at the outer lip, for being the strongest rib)

The potential problem comes when the load along those edges is continual, all the way out to those corner peaks. For those outer edges and their stressing, it's a lot like having a flat back. This full 'brim' (one could say) may be necessary for sealing it, and for stiffening. But the small inner pointing rib (at the outer corner) may add just enough uneven loading (or extra pressure - or different pressure might be more accurate) to stop the outer corners from having motion and travel problems. Even pressure like the brim as a full edge treatment probably does not do much to address this particular issue. Try the video at 4k and at 1:17, and then do some frame stop motion, in when it is handled.

It may be camera issues and shadows, but it looks like the concavity is there. If it is there...that is a fairly smart bit, I must say. It probably came into being along with the thermal pad being put into play. A long story about radical discontinuity being your friend comes into play here...

If adding a small rib in the orientation stated, then keeping the concavity with the extra rib will also help drainage. The radical discontinuity part means that no matter what the load and level of contact is, that there is always a zone of energy damping or exchange/flow that fits the given live load of the moment. The current tile backing design is close, real close....

It is difficult to say if this would be useful or not, but I feel that something along those lines as a slight change, may indeed help.

If it works, then improvement comes with no significant extra mass added. Bonus.
Title: Re: Starship heat shield
Post by: Blueshift on 04/11/2021 11:30 am
The problem is that when the tank warms up the gas pressure inside will rise until the tank ruptures. It is conceivable that this sort of arrangement might save the ship under a few very specific circumstances, but any extended heating would destroy the ship fairly rapidly. Adding a fair amount of mass and complexity to every flight in order to save the ship from a small subset of situations that occur very infrequently is not SpaceX style. They would rather spend the mass in making the tile system more robust so the problem doesn't occur in the first place.

I'm quite confident that there are pressure relief valves in the tanks which exclude this scenario.

In regards to tiles failing in "few very specific circumstances": currently tile failure rather looks like norm than exception. Even after improvements, it's quite possible that tile failure will remain a more or less frequent event.

In that case, as envy887 writes, either the intrinsic heat dissipation is enough to prevent a local wall failure - or you better have a backup system.
Title: Re: Starship heat shield
Post by: OTV Booster on 04/11/2021 05:29 pm
Fun fact...When they remove a tile on purpose, they bore 1/2" holes over the three attachment points so they can release the clips.
Straight drill or a cookie cutter?
Title: Re: Starship heat shield
Post by: cdebuhr on 04/11/2021 05:41 pm
Fun fact...When they remove a tile on purpose, they bore 1/2" holes over the three attachment points so they can release the clips.
Straight drill or a cookie cutter?
It'd have to be a core drill if they don't want to mangle the attachment clips.
Title: Re: Starship heat shield
Post by: _MECO on 04/11/2021 09:48 pm
Fun fact...When they remove a tile on purpose, they bore 1/2" holes over the three attachment points so they can release the clips.
I'd guessed earlier that's what you'd do instead of breaking the whole tile off. Do you think one day those holes will get drilled out on-orbit during an EVA for emergency tile replscement?
Title: Re: Starship heat shield
Post by: Nomadd on 04/11/2021 10:06 pm
Fun fact...When they remove a tile on purpose, they bore 1/2" holes over the three attachment points so they can release the clips.
I'd guessed earlier that's what you'd do instead of breaking the whole tile off. Do you think one day those holes will get drilled out on-orbit during an EVA for emergency tile replscement?
It seems easy enough. A jig you could set up in your garage. I imagine procedures will evolve with the tiles. Like, what to do if one of the clips pops off or gets mangled.
 I watched a long documentary on the development of an electric wrench for Hubble repair. I'm fairly sure SpaceX won't need to spend that much time and money on it.
 That video made me wonder if the underlayment puffed out when the tile disappeared, causing the difficulty in putting the new one on.
Title: Re: Starship heat shield
Post by: DigitalMan on 04/11/2021 11:59 pm
Fun fact...When they remove a tile on purpose, they bore 1/2" holes over the three attachment points so they can release the clips.
I'd guessed earlier that's what you'd do instead of breaking the whole tile off. Do you think one day those holes will get drilled out on-orbit during an EVA for emergency tile replscement?
It seems easy enough. A jig you could set up in your garage. I imagine procedures will evolve with the tiles. Like, what to do if one of the clips pops off or gets mangled.
 I watched a long documentary on the development of an electric wrench for Hubble repair. I'm fairly sure SpaceX won't need to spend that much time and money on it.
 That video made me wonder if the underlayment puffed out when the tile disappeared, causing the difficulty in putting the new one on.

I hope SpaceX would consider bringing along a variety of tools, just in case. Story talked about how much work it was to convince higher-ups to let him bring a come along for Hubble repair, which he wound up needing.
Title: Re: Starship heat shield
Post by: Keldor on 04/12/2021 01:13 am
Fun fact...When they remove a tile on purpose, they bore 1/2" holes over the three attachment points so they can release the clips.
Straight drill or a cookie cutter?
It'd have to be a core drill if they don't want to mangle the attachment clips.
Yeah, I have to imagine that the inserts for the clips have grooves for the clips to slide out of, so that when they're aligned properly as when a tile is installed, the clips snap in and are locked like normal, but if you rotate the insert (i.e. by removing the rest of the tile so that it can rotate freely), by about 60 or 90 degrees, then the, uh, springy part of the clips? will line up with the grooves and can just be slid off.
Title: Re: Starship heat shield
Post by: KBK on 04/12/2021 02:29 am
Fun fact...When they remove a tile on purpose, they bore 1/2" holes over the three attachment points so they can release the clips.
Straight drill or a cookie cutter?
It'd have to be a core drill if they don't want to mangle the attachment clips.

With an alignment jig, of course, that fits over the tile.
Title: Re: Starship heat shield
Post by: AU1.52 on 04/12/2021 03:25 am
In the latest photo of the large section of tiles by bocachicagal and RGV Aerial, there are a column of tiles with very noticeable gaps. Looking at some of these tiles even closer reveals that some of the tiles are not same the exact same size and thus the gaps.


Do we know why they are not all the same size or does that not really matter for these early prototypes? Is it hard to make them all the exact same size?


Also how will they size the tiles to fit the tapering nose?
Title: Re: Starship heat shield
Post by: FrankX on 04/12/2021 04:02 am
Fun fact...When they remove a tile on purpose, they bore 1/2" holes over the three attachment points so they can release the clips.
I'd guessed earlier that's what you'd do instead of breaking the whole tile off. Do you think one day those holes will get drilled out on-orbit during an EVA for emergency tile replscement?
It seems easy enough. A jig you could set up in your garage. I imagine procedures will evolve with the tiles. Like, what to do if one of the clips pops off or gets mangled.
 I watched a long documentary on the development of an electric wrench for Hubble repair. I'm fairly sure SpaceX won't need to spend that much time and money on it.
 That video made me wonder if the underlayment puffed out when the tile disappeared, causing the difficulty in putting the new one on.

I didn't realize they were making them easy to replace in space.  That sure makes mars takeoffs less of a concern.

Does anyone know if the is small, maybe handheld existing tech to quickly scan the tiles for hairline cracks or fractures while in space?   Be it xray, or infra red, or super high res photos.

I'm imagining them sending out a person, or small drone to do a spacewalk around the ship and inspect every tile before each landing.  What fun, I would do that job for free. lol
Title: Re: Starship heat shield
Post by: Thrustpuzzle on 04/12/2021 06:32 am
The tiles are likely so brittle and frangible that you don't need a drill to remove one, just a hand-pushed cookie cutter punch. The alignment jig is a good idea though, since bent mounting pins are a more labor intensive problem than replacing a tile.
Title: Re: Starship heat shield
Post by: enbandi on 04/12/2021 06:51 am
In the latest photo of the large section of tiles by bocachicagal and RGV Aerial, there are a column of tiles with very noticeable gaps. Looking at some of these tiles even closer reveals that some of the tiles are not same the exact same size and thus the gaps.


Do we know why they are not all the same size or does that not really matter for these early prototypes? Is it hard to make them all the exact same size?


Also how will they size the tiles to fit the tapering nose?

As we know, for tile manufacturing first some billets casted, than tiles machined to final shape from those billets. The precision of a machining operation should be in the sub mm range. So I would say the tiles are exactly the same size (or at least the white core of them).

What can vary is the final black coating (i dont think so). Or the inner position of the metal stiffeners/attachement points, which should be embedded at casting: a bit less accurate process.

Unevennes can be anything like intentional (gaps and or tiles with some free movement), procedural or from the pad or the stud/clips. But if its tile manufacturing related, my guess is the position of the Y bones.
Title: Re: Starship heat shield
Post by: Vonbraun on 04/12/2021 06:57 am
In the latest photo of the large section of tiles by bocachicagal and RGV Aerial, there are a column of tiles with very noticeable gaps. Looking at some of these tiles even closer reveals that some of the tiles are not same the exact same size and thus the gaps.


Do we know why they are not all the same size or does that not really matter for these early prototypes? Is it hard to make them all the exact same size?


Also how will they size the tiles to fit the tapering nose?

What you are seeing here is probably the required 2-dimensional tolerances of the tile to pin connections. Tile will lock up very tightly against the underlying soft insulation making it difficult to move after snapping it in place and there are no references either until you lay out the nearby tiles. So you could end up with adjances tiles being at opposite ends of their connection tolerances.

These kinds of things cause hard problems, you can see that right now the tiles do not match the dimensions of stacks either. Rows are freely running along the progression of segments, so some of them are bound to end up over horizontal weld, but this is easily solved by changing the dimensions slightly.

Also what they can eventually do is to have CNC arm factor in the stacks measured height. There are probably +-5mm accumulated error involved per each 4-stack and this can be nullified by scaling rows accordingly. Another reason to not have too tightly toleranced tile connections.
Title: Re: Starship heat shield
Post by: _MECO on 04/12/2021 06:58 am
The tiles are likely so brittle and frangible that you don't need a drill to remove one, just a hand-pushed cookie cutter punch. The alignment jig is a good idea though, since bent mounting pins are a more labor intensive problem than replacing a tile.
Only makes me wonder how an astronaut is going to be able to hold onto the belly of a SS when trying to remove or install a tile up there. You push into the tile, and start moving back... what arrests your motion? Not a whole lot out there to hang onto. Maybe some kind of MMU system is needed.
Title: Re: Starship heat shield
Post by: enbandi on 04/12/2021 07:03 am
Calling back this video from a few weeks ago: you can see the tile removal, involving a cordless drill.
From 16:40

https://youtu.be/6IbalvQWD34
Title: Re: Starship heat shield
Post by: Vonbraun on 04/12/2021 07:05 am
Only makes me wonder how an astronaut is going to be able to hold onto the belly of a SS when trying to remove or install a tile up there. You push into the tile, and start moving back... what arrests your motion? Not a whole lot out there to hang onto. Maybe some kind of MMU system is needed.

All of the starship-in-space problems are solved by having even more starships. So naturally in this case you have couple of orbiting starships as stations, which can pull up on the side when requested, so you can stand on it while doing the repairs.
Title: Re: Starship heat shield
Post by: Eerie on 04/12/2021 08:36 am
The tiles are likely so brittle and frangible that you don't need a drill to remove one, just a hand-pushed cookie cutter punch. The alignment jig is a good idea though, since bent mounting pins are a more labor intensive problem than replacing a tile.
Only makes me wonder how an astronaut is going to be able to hold onto the belly of a SS when trying to remove or install a tile up there. You push into the tile, and start moving back... what arrests your motion? Not a whole lot out there to hang onto. Maybe some kind of MMU system is needed.

A harness going all around the circumference of Starship should work. Just needs about 30 meters of rope.
Title: Re: Starship heat shield
Post by: Slarty1080 on 04/12/2021 08:57 am
In the latest photo of the large section of tiles by bocachicagal and RGV Aerial, there are a column of tiles with very noticeable gaps. Looking at some of these tiles even closer reveals that some of the tiles are not same the exact same size and thus the gaps.


Do we know why they are not all the same size or does that not really matter for these early prototypes? Is it hard to make them all the exact same size?


Also how will they size the tiles to fit the tapering nose?
All of the main body tiles should be the same (within certain tolerances and a few exceptions). But the nose cones will need numerous different shaped tiles unless they go for a different solution for the nose. But assuming they stay with the hex based tiles one solution is illustrated in the second post of this thread. It would require a different tile shape for each ring of tiles around the nose plus a nose cap.
Title: Re: Starship heat shield
Post by: edzieba on 04/12/2021 01:08 pm
In the latest photo of the large section of tiles by bocachicagal and RGV Aerial, there are a column of tiles with very noticeable gaps. Looking at some of these tiles even closer reveals that some of the tiles are not same the exact same size and thus the gaps.


Do we know why they are not all the same size or does that not really matter for these early prototypes? Is it hard to make them all the exact same size?


Also how will they size the tiles to fit the tapering nose?

As we know, for tile manufacturing first some billets casted, than tiles machined to final shape from those billets. The precision of a machining operation should be in the sub mm range. So I would say the tiles are exactly the same size (or at least the white core of them).
Sintering silica-fibre billets then milling the billets to size (before RCG coating) was how the STS tiles were made. If I were SpaceX and I wanted to mass produce effectively the same tiles but at a vastly lower cost, I would try and avoid that milling step entirely: achieve dimensional accuracy by correctly sizing the wet mould to account for shrinkage, and control shrinkage through controlling initial moisture content, bakeout time, and bakeout temperature (and temperature over time). Variance in those parameters risks an oversize or undersize tile, but avoiding post machining means you can come out ahead even if you occasionally need to toss out a bad patch.
We know from the Astronaut Blvd FDEP. report that "After drying, the billet is split in two pieces thereby creating the rudimentary tiles. The tiles are shaped to the desired form using a router". I expect the split is face-to-face, to allow the backside cavities to be formed as part of the mould and to allow a single cutting op to face two tiles (rather than one at a time). That router's days are numbered!
Title: Re: Starship heat shield
Post by: BT52 on 04/12/2021 04:18 pm
Yeah i agree. Like idea no sanding. I m  very close to ceramic "grindig" sintering processes. So you could even set tolerant field on upper level. Then u can quite easily sort out witch tiles u need sandown or machined a bit.  IDK about 10% for post process should be achievable. And other 5% is simply scrap. Quite nice way to optimise whole line for tiles. Technology is cheap and very well understood. From sintering, ovens, filtering tech and recycling. Tho recycling is pain in the ass. So there is even more reason to reduce machining at minimum.

Title: Re: Starship heat shield
Post by: livingjw on 04/12/2021 04:42 pm
Does anyone have information on the possibility of co-curing the mechanical attachment structure into the silica ceramic insulation block? I am assuming that is what they are doing, but have no evidence.

John
Title: Re: Starship heat shield
Post by: BT52 on 04/12/2021 04:52 pm
Does anyone have information on the possibility of co-curing the mechanical attachment structure into the silica ceramic insulation block? I am assuming that is what they are doing, but have no evidence.

John

Not feasible. At least from mine experience with ceramic grinding processes. But u can be very creative with tungsten or similar inserts afterwards.
Title: Re: Starship heat shield
Post by: livingjw on 04/12/2021 05:05 pm
Does anyone have information on the possibility of co-curing the mechanical attachment structure into the silica ceramic insulation block? I am assuming that is what they are doing, but have no evidence.

John

Not feasible. At least from mine experience with ceramic grinding processes. But u can be very creative with tungsten or similar inserts afterwards.

I was thinking of inserting something like C/Sic attachment skeleton into mold before sintering silica insulation block. Can you explain what the the problems are? Thanks.

John
Title: Re: Starship heat shield
Post by: KBK on 04/12/2021 05:14 pm
The tiles are likely so brittle and frangible that you don't need a drill to remove one, just a hand-pushed cookie cutter punch. The alignment jig is a good idea though, since bent mounting pins are a more labor intensive problem than replacing a tile.

yep. It would put the entire ship at risk for no definable reason. I tend to have a problem with doing it right on circuit boards. Like removing surface mount blown IC's by hand, by one leg or side at a time... and and leaving the entire chip intact.

It's a dead chip, idiot! (I try to remember to tell myself)...cut the legs off, remove their little corpsey bits... - and stop risking the traces and thus risk the entire board.....!

Point being, don't risk even one single bent or over-stressed tile mount. Not one. Ever.
Title: Re: Starship heat shield
Post by: BT52 on 04/12/2021 05:38 pm
Does anyone have information on the possibility of co-curing the mechanical attachment structure into the silica ceramic insulation block? I am assuming that is what they are doing, but have no evidence.

John

Not feasible. At least from mine experience with ceramic grinding processes. But u can be very creative with tungsten or similar inserts afterwards.

I was thinking of inserting something like C/Sic attachment skeleton into mold before sintering silica insulation block. Can you explain what the the problems are? Thanks.

Ahh i see. Yeah thats what they probably do. I was thinking if u have in mind any metal or "lower" melting materials. That said materials create voids and irregularities in ceramic matrixes during curing proceses. Still i any discussion how to made coupling area strong as possible and "cheap" to produce. Mine gut feeling is for nice lip inside rib of tile.
 
Title: Re: Starship heat shield
Post by: InterestedEngineer on 04/12/2021 06:18 pm
What kind of telemetry would SpaceX want for reentry?  With the addition of a Starlink antenna that can get real time data out from behind the plasma bow shock, it would be very useful to have telemetry on the tiles.

Since temperature sensors with bluetooth or wifi are cheap, why not embed one in each tile, and run a series of antennas under the white cladding?   

Any loss of communication means a tile loss.  The temperature sensor can sense how hot the tile is getting (might be good to have a sensor on all 6 corners)

It will be very difficult to debug a burned up Starship without real time telemetry.   What are some other ideas on how to get real time telemetry of the tile performance?
Title: Re: Starship heat shield
Post by: jthygesen on 04/12/2021 06:31 pm
What kind of telemetry would SpaceX want for reentry?  With the addition of a Starlink antenna that can get real time data out from behind the plasma bow shock, it would be very useful to have telemetry on the tiles.

Since temperature sensors with bluetooth or wifi are cheap, why not embed one in each tile, and run a series of antennas under the white cladding?   

Any loss of communication means a tile loss.  The temperature sensor can sense how hot the tile is getting (might be good to have a sensor on all 6 corners)

It will be very difficult to debug a burned up Starship without real time telemetry.   What are some other ideas on how to get real time telemetry of the tile performance?

I would suggest monitoring the tank wall from inside with one or more thermal cameras. IMHO they don’t really need to know how hot the tiles get, but I think they really need to know how hot the load bearing tank walls get.
Title: Re: Starship heat shield
Post by: enbandi on 04/12/2021 06:43 pm
Does anyone have information on the possibility of co-curing the mechanical attachment structure into the silica ceramic insulation block? I am assuming that is what they are doing, but have no evidence.

John

Not feasible. At least from mine experience with ceramic grinding processes. But u can be very creative with tungsten or similar inserts afterwards.

What we seen as remnants of the attach skeleton was an u shaped metallic thing, seemd like thin, long, bended sheet metal or alike. Hard to imagine how can they carve the required place to insert. Also do not remember any obvious extetnal features hinting such a process. Any idea?

(If not inserted at casting) The only way I can imagine of if they create a sandwich, with two tile faces and the skeleton between.... which does not sounds cheap, easy or fast.

Edit: lates pics of the attachments
..... Interesting to see that Y-like structure inside the tile is not some space-age-spring-suspended-contraption but three metal fasteners from local hardware store...
https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=50748.0;attach=2021315;sess=52467
Title: Re: Starship heat shield
Post by: jthygesen on 04/12/2021 06:48 pm
It appears that they have marked several tiles that are touching or very close to their neighbours. Perhaps these need to be refitted?

See attached zoom of photo from @bocachicagal.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 04/12/2021 07:04 pm
I appears that they have marked several tiles that are touching or very close to their neighbours. Perhaps these need to be refitted?

It's good at this stage to have tiles a mixed distance away from each other.  If they don't lose the tightly nested tiles, then they don't have to worry about that later.  If they do, then they know to enforce a minimum separation tolerance.
Title: Re: Starship heat shield
Post by: BT52 on 04/12/2021 07:55 pm
Heh fascinating KISS problem to have. I had too much free time. SO i made mock-up how they could approach that problem. From conceptual level ofc

EDIT deleted pic

Title: Re: Starship heat shield
Post by: xvel on 04/12/2021 08:10 pm
what problem
Title: Re: Starship heat shield
Post by: Pheogh on 04/12/2021 09:42 pm
I was recently able to see Endeavor at the California Science Center and got a really close look at the tile arrangement at the elevons. I was wondering if anyone knows how the heating regime of Starships flaps differ from the Shuttle. Is the heating completely different or are there any lessons learned from Shuttle (elevons) that are directly or indirectly applicable to Starship?
Title: Re: Starship heat shield
Post by: BT52 on 04/12/2021 09:53 pm
what problem

No problem. Just manner of speaking. Sorry. Heat shield is problem that needs to be solved. :D Atm we dont have empirical data that works in current form. So SpaceX is constantly working on solution.  :D
Title: Re: Starship heat shield
Post by: joek on 04/12/2021 09:56 pm
Heh fascinating KISS problem to have. I had too much free time. SO i made mock-up how they could approach that problem. From conceptual level ofc
Think your image is similar to what SpaceX is doing, only the pin is not directly into the tile base-edge material, but into an internal support structure (not at the edge).  Per previous discussion-images show that.
Title: Re: Starship heat shield
Post by: BT52 on 04/12/2021 09:58 pm
I was recently able to see Endeavor at the California Science Center and got a really close look at the tile arrangement at the elevons. I was wondering if anyone knows how the heating regime of Starships flaps differ from the Shuttle. Is the heating completely different or are there any lessons learned from Shuttle (elevons) that are directly or indirectly applicable to Starship?

Interesting question. Doesn't bluntness  (in case of SS aft flaps higher AoA) actually helps in lowering the overall heat flux  transfer due "bow shock wave"? Does anyone has more knowledge about it. Or at least educated guess.
Title: Re: Starship heat shield
Post by: joek on 04/12/2021 10:00 pm
I was recently able to see Endeavor at the California Science Center and got a really close look at the tile arrangement at the elevons. I was wondering if anyone knows how the heating regime of Starships flaps differ from the Shuttle. Is the heating completely different or are there any lessons learned from Shuttle (elevons) that are directly or indirectly applicable to Starship?

Likely Shuttle experience has heavily informed Starship solution. Details of course closely held by SpaceX.  What was it about the Shuttle elevon tile arrangement that struck you as particularly relevant?
Title: Re: Starship heat shield
Post by: joek on 04/12/2021 10:04 pm
Interesting question. Doesn't bluntness  (in case of SS aft flaps higher AoA) actually helps in lowering the overall heat flux  transfer due "bow shock wave"? Does anyone has more knowledge about it. Or at least educated guess.

Starship will be "fluffier" than Shuttle, thus reducing peak heat flux; SS flaps contribute to that.
Title: Re: Starship heat shield
Post by: BT52 on 04/12/2021 10:08 pm
Heh fascinating KISS problem to have. I had too much free time. SO i made mock-up how they could approach that problem. From conceptual level ofc
Think your image is similar to what SpaceX is doing, only the pin is not directly into the tile base-edge material, but into an internal support structure (not at the edge).  Per previous discussion-images show that.

That pic is mine crossection :D in model. I wanna to show how i m interpreting their "concept" idea.
Title: Re: Starship heat shield
Post by: alastairmayer on 04/12/2021 10:13 pm
In the latest photo of the large section of tiles by bocachicagal and RGV Aerial, there are a column of tiles with very noticeable gaps. Looking at some of these tiles even closer reveals that some of the tiles are not same the exact same size and thus the gaps.

Do we know why they are not all the same size or does that not really matter for these early prototypes? Is it hard to make them all the exact same size?

Maybe they just want to test the effects of different sized gaps in the tiles. It would be useful information.
Title: Re: Starship heat shield
Post by: joek on 04/12/2021 10:14 pm
Working once doesn't mean they don't have to worry about it. Working 20 times doesn't mean they don't have to worry about it. They need to know exactly what's going on because they can't test every possible combination of variables.

To that point, SpaceX is likely trying multiple variants and validating their models. As their typical MO, those are occurring in parallel. As you stated, they can't test every combination.  When they believe their models are accurate, will likely see refinement on final solution
Title: Re: Starship heat shield
Post by: Pheogh on 04/12/2021 10:16 pm
Well the first thing I was struck by was that I expected there to possibly be RCC panels along the edges. I think intuitively I knew this wouldn't be the case but still it appears that the tiles are very similar to the body tiles although they do look a bit different. Also the gap and the hardware that hold the actuating point appears to be a different material than the tiles. The other thing I found interesting was that the gap between the Elevon and Wing although small is not insignificant which made me wonder if there was heat bleed through at that seam. All in all I came away thinking that unless the entry regime and geometry is completely different then the flaps on Starship should be a similar configuration.

The point of the post was just to reach out to the forum and see if anyone had more information about how the shuttle elevons performed in the entry environment and what were the particular engineering challenges and solutions that allowed a hinged flap to operate effectively in the reentry regime. Wondering if there are particular lessons learned that are directly applicable to Starship Flaps?
Title: Re: Starship heat shield
Post by: rsdavis9 on 04/12/2021 11:40 pm
I remember elon saying that hot gas instrusion in the flap to flap fairing gap was a problem they were looking at.

I think the starship reentering at a higher angle of attack than the shuttle may force more hot gas into the gap. He mentioned possibly having cold gas injecting behind the gap.
Title: Re: Starship heat shield
Post by: Lars-J on 04/13/2021 02:03 am
But the flaps on Starship does have one benefit compared to Shuttle... They will never extend beyond level. So this means that the underside can extend out extra and give extra protection to the joint. (see quick and dirty sketch)
Title: Re: Starship heat shield
Post by: BT52 on 04/13/2021 05:34 am
Yeah exactly. SS could made protection overlap there, sure. Or do that at least in hinge area. Rest you could bleed off thought gap if u find aero or even weight benefit (doubt in last point because is not so intuitive).  So yeah semi easy fix
Title: Re: Starship heat shield
Post by: edzieba on 04/13/2021 11:51 am
Does anyone have information on the possibility of co-curing the mechanical attachment structure into the silica ceramic insulation block? I am assuming that is what they are doing, but have no evidence.

John
The STS tiles were sintered at 1260°C. Being a near identical tile, I would expect the Starship tile sintering to occur at a similar temperature. Titanium might be fine, but that's uncomfortably 'squishy' for Steel or Nickel alloys. The huge difference in CTE could be a big problem unless the tile cavity for the insert could be sized to allow the insert to slide within the cavity without cracking or falling out (at the expense of positioning accuracy). Inserting the internal frame afterwards seems like less hassle.
Title: Re: Starship heat shield
Post by: rsdavis9 on 04/13/2021 12:11 pm
But the flaps on Starship does have one benefit compared to Shuttle... They will never extend beyond level. So this means that the underside can extend out extra and give extra protection to the joint. (see quick and dirty sketch)

But it is still metal and metal in the gap. So either heat sink it with something(cold gas) or put a tile like material coating. Maybe a thin coat of some paint like high temp stuff. Thin enough that it doesn't need tiles but will still insulate and resist the hot gas.

Definitely helps to have a small gap though.

EDIT: or like the tiles on the main tank. Get the gap small enough to not matter.

Title: Re: Starship heat shield
Post by: edzieba on 04/13/2021 01:57 pm
The hinge joints are in the 'lee' of the fixed aerodynamic covering. Like on the upper side of the Shuttle (or any other entering vehicle for that matter), the leeward heat flux is a lot lower, almost all radiative heating from the plasma wake visible from behind the vehicle. Using a flexible TPS as a seal right in the crook of the hinge to prevent a flow path forming would likely be sufficient (e.g. the 'chain seal' of the STS body flap) to prevent hot gas being blown through.
Title: Re: Starship heat shield
Post by: xvel on 04/13/2021 03:31 pm
ehh, maybe a little physics recap so we don't end up in a fantasy world:

Thermal insulation only slows down heat transfer, you still need to take that heat somewhere from the other side, only slower if you have better insulation
Title: Re: Starship heat shield
Post by: livingjw on 04/13/2021 04:52 pm
Does anyone have information on the possibility of co-curing the mechanical attachment structure into the silica ceramic insulation block? I am assuming that is what they are doing, but have no evidence.

John
The STS tiles were sintered at 1260°C. Being a near identical tile, I would expect the Starship tile sintering to occur at a similar temperature. Titanium might be fine, but that's uncomfortably 'squishy' for Steel or Nickel alloys. The huge difference in CTE could be a big problem unless the tile cavity for the insert could be sized to allow the insert to slide within the cavity without cracking or falling out (at the expense of positioning accuracy). Inserting the internal frame afterwards seems like less hassle.

Thanks for the sinter temperature. C/SiC can handle that.

John
Title: Re: Starship heat shield
Post by: InterestedEngineer on 04/13/2021 05:44 pm
Does anyone have information on the possibility of co-curing the mechanical attachment structure into the silica ceramic insulation block? I am assuming that is what they are doing, but have no evidence.

John
The STS tiles were sintered at 1260°C. Being a near identical tile, I would expect the Starship tile sintering to occur at a similar temperature. Titanium might be fine, but that's uncomfortably 'squishy' for Steel or Nickel alloys. The huge difference in CTE could be a big problem unless the tile cavity for the insert could be sized to allow the insert to slide within the cavity without cracking or falling out (at the expense of positioning accuracy). Inserting the internal frame afterwards seems like less hassle.

Thanks for the sinter temperature. C/SiC can handle that.

John

How much will C/SiC shrink when it cools vs. the ceramic?
Title: Re: Starship heat shield
Post by: Robotbeat on 04/13/2021 06:03 pm
Interesting question. Doesn't bluntness  (in case of SS aft flaps higher AoA) actually helps in lowering the overall heat flux  transfer due "bow shock wave"? Does anyone has more knowledge about it. Or at least educated guess.

Starship will be "fluffier" than Shuttle, thus reducing peak heat flux; SS flaps contribute to that.
Will it? Seems to me to be about the same. But leading edges probably will have lower peak heating as they won't be angled directly into the airstream as on shuttle.
Title: Re: Starship heat shield
Post by: enbandi on 04/13/2021 06:06 pm
Does anyone have information on the possibility of co-curing the mechanical attachment structure into the silica ceramic insulation block? I am assuming that is what they are doing, but have no evidence.

John
The STS tiles were sintered at 1260°C. Being a near identical tile, I would expect the Starship tile sintering to occur at a similar temperature. Titanium might be fine, but that's uncomfortably 'squishy' for Steel or Nickel alloys. The huge difference in CTE could be a big problem unless the tile cavity for the insert could be sized to allow the insert to slide within the cavity without cracking or falling out (at the expense of positioning accuracy). Inserting the internal frame afterwards seems like less hassle.

Thanks for the sinter temperature. C/SiC can handle that.

John

I think, visuals don't really match that (see attached), but please correct me if I am wrong.
Also, we suspect that they experimenting with multiple types/methods: so your C/Sic solution can be the working one, where we cannot observe broken ones.

Photo credit for Nomadd, cropped by HVM, this post:
...
Title: Re: Starship heat shield
Post by: OTV Booster on 04/13/2021 08:22 pm
Fun fact...When they remove a tile on purpose, they bore 1/2" holes over the three attachment points so they can release the clips.
Straight drill or a cookie cutter?
It'd have to be a core drill if they don't want to mangle the attachment clips.
A lot of tiles show a color discontinuity where a clip is expected. I'm wondering if one line of testing is tiles with a through hole  with a step for the clips to grab and a relatively thin plug to cover the hole. This would facilitate repair by allowing a straight carbide or diamond drill like used for ceramic tiles, and leave an unambiguous mark where to drill. No measurement necessary. If it works out.
Title: Re: Starship heat shield
Post by: OTV Booster on 04/13/2021 08:37 pm
Fun fact...When they remove a tile on purpose, they bore 1/2" holes over the three attachment points so they can release the clips.
I'd guessed earlier that's what you'd do instead of breaking the whole tile off. Do you think one day those holes will get drilled out on-orbit during an EVA for emergency tile replscement?
It seems easy enough. A jig you could set up in your garage. I imagine procedures will evolve with the tiles. Like, what to do if one of the clips pops off or gets mangled.
 I watched a long documentary on the development of an electric wrench for Hubble repair. I'm fairly sure SpaceX won't need to spend that much time and money on it.
 That video made me wonder if the underlayment puffed out when the tile disappeared, causing the difficulty in putting the new one on.

I didn't realize they were making them easy to replace in space.  That sure makes mars takeoffs less of a concern.

Does anyone know if the is small, maybe handheld existing tech to quickly scan the tiles for hairline cracks or fractures while in space?   Be it xray, or infra red, or super high res photos.

I'm imagining them sending out a person, or small drone to do a spacewalk around the ship and inspect every tile before each landing.  What fun, I would do that job for free. lol
This has been discussed. My favorite is acoustic. Standard method of testing a grinding wheel for hairline cracks is to support it in the middle and give it a tap. A cracked wheel sounds very different. Hmm. A robot drone with a clip on pickup and a BB gun?


ISTM an array of internal pickups with output filtered through a spectrum analyzer would have a good chance of picking up the distinctive sound of a cracking tile even through the worst of EDL. Probably wouldn't point to the exact tile but would narrow the area of interest.
Title: Re: Starship heat shield
Post by: OTV Booster on 04/13/2021 08:42 pm
Only makes me wonder how an astronaut is going to be able to hold onto the belly of a SS when trying to remove or install a tile up there. You push into the tile, and start moving back... what arrests your motion? Not a whole lot out there to hang onto. Maybe some kind of MMU system is needed.

All of the starship-in-space problems are solved by having even more starships. So naturally in this case you have couple of orbiting starships as stations, which can pull up on the side when requested, so you can stand on it while doing the repairs.
Suction cups? :o
Title: Re: Starship heat shield
Post by: joek on 04/13/2021 08:59 pm
Only makes me wonder how an astronaut is going to be able to hold onto the belly of a SS when trying to remove or install a tile up there. You push into the tile, and start moving back... what arrests your motion? Not a whole lot out there to hang onto. Maybe some kind of MMU system is needed.
All of the starship-in-space problems are solved by having even more starships. So naturally in this case you have couple of orbiting starships as stations, which can pull up on the side when requested, so you can stand on it while doing the repairs.
Suction cups? :o

New thread: Starship in-space repairs (https://forum.nasaspaceflight.com/index.php?topic=53579.0) to keep this thread focused more on the heat shield.
Title: Re: Starship heat shield
Post by: OTV Booster on 04/13/2021 09:14 pm
In the latest photo of the large section of tiles by bocachicagal and RGV Aerial, there are a column of tiles with very noticeable gaps. Looking at some of these tiles even closer reveals that some of the tiles are not same the exact same size and thus the gaps.


Do we know why they are not all the same size or does that not really matter for these early prototypes? Is it hard to make them all the exact same size?


Also how will they size the tiles to fit the tapering nose?

As we know, for tile manufacturing first some billets casted, than tiles machined to final shape from those billets. The precision of a machining operation should be in the sub mm range. So I would say the tiles are exactly the same size (or at least the white core of them).
Sintering silica-fibre billets then milling the billets to size (before RCG coating) was how the STS tiles were made. If I were SpaceX and I wanted to mass produce effectively the same tiles but at a vastly lower cost, I would try and avoid that milling step entirely: achieve dimensional accuracy by correctly sizing the wet mould to account for shrinkage, and control shrinkage through controlling initial moisture content, bakeout time, and bakeout temperature (and temperature over time). Variance in those parameters risks an oversize or undersize tile, but avoiding post machining means you can come out ahead even if you occasionally need to toss out a bad patch.
We know from the Astronaut Blvd FDEP. report that "After drying, the billet is split in two pieces thereby creating the rudimentary tiles. The tiles are shaped to the desired form using a router". I expect the split is face-to-face, to allow the backside cavities to be formed as part of the mould and to allow a single cutting op to face two tiles (rather than one at a time). That router's days are numbered!
So far it seems impossible to avoid some unique shapes on the nose and around the fins. Bummer. For in flight repairs it's no big thing to have a supply of the widely used hex tiles, but what about the odd shapes?


Just for a working number let's say there are 30 different shapes. It could be much higher or a bit lower. The only options I can come up with are an onboard supply, onboard fabrication capability or a temporary one time use substitution.


A problem with an onboard inventory is how many of each shape. Some positions will have a higher wear rate, so more of them. But how many? It will take many reentries to develop a reliable statistical model with expected variance. The loss of a ship because of heatshield failure is lamentable but for a crewed mission it is unacceptable. Maybe a reliable model will be in hand before crew flights.


Onboard fabrication has its own difficulties. Unless the fab facility is large, production will be slow. If production is modeled on earth based production, 0G introduces a variable that needs to be explored before it can be considered reliable. Additive manufacturing shares this problem.


A temporary one use fix has promise. What comes to mind is a spray on or caulked ablative. It's not sexy but it promises to be quick, simple and reliable. If loss of one tile does not threaten LOM, orbital launches could substitute ablative material for one tile. It would still need on orbit installation testing and a tryout with direct entry velocities.
Title: Re: Starship heat shield
Post by: OTV Booster on 04/13/2021 09:34 pm
I appears that they have marked several tiles that are touching or very close to their neighbours. Perhaps these need to be refitted?

It's good at this stage to have tiles a mixed distance away from each other.  If they don't lose the tightly nested tiles, then they don't have to worry about that later.  If they do, then they know to enforce a minimum separation tolerance.
Elon tweeted something about rope filler between tiles. Besides blocking physical and thermal intrusion it would help damp out edge vibration. To allow this a minimum gap is needed. Allowing vibrating and buzzing tiles to touch seems to be inviting trouble. But yes, for now they need to play with it to find minimum and maximum allowable gap.


I can just picture the greenest intern hanging down the side of the SS with a mallet, rope and wooden drift, just like pounding oakum on a wooden ship. LOL  ;D
Title: Re: Starship heat shield
Post by: OTV Booster on 04/13/2021 09:44 pm
Does anyone have information on the possibility of co-curing the mechanical attachment structure into the silica ceramic insulation block? I am assuming that is what they are doing, but have no evidence.

John
The STS tiles were sintered at 1260°C. Being a near identical tile, I would expect the Starship tile sintering to occur at a similar temperature. Titanium might be fine, but that's uncomfortably 'squishy' for Steel or Nickel alloys. The huge difference in CTE could be a big problem unless the tile cavity for the insert could be sized to allow the insert to slide within the cavity without cracking or falling out (at the expense of positioning accuracy). Inserting the internal frame afterwards seems like less hassle.
How would differential expansion be dealt with, in any technique?
Title: Re: Starship heat shield
Post by: _MECO on 04/13/2021 11:42 pm
Only makes me wonder how an astronaut is going to be able to hold onto the belly of a SS when trying to remove or install a tile up there. You push into the tile, and start moving back... what arrests your motion? Not a whole lot out there to hang onto. Maybe some kind of MMU system is needed.

All of the starship-in-space problems are solved by having even more starships. So naturally in this case you have couple of orbiting starships as stations, which can pull up on the side when requested, so you can stand on it while doing the repairs.
Suction cups? :o
Haha kind of hard to get good suction with no external pressure

Okay I'll pack up and move to the EVA tile thread now :)
Title: Re: Starship heat shield
Post by: livingjw on 04/14/2021 12:38 am
Does anyone have information on the possibility of co-curing the mechanical attachment structure into the silica ceramic insulation block? I am assuming that is what they are doing, but have no evidence.

John
The STS tiles were sintered at 1260°C. Being a near identical tile, I would expect the Starship tile sintering to occur at a similar temperature. Titanium might be fine, but that's uncomfortably 'squishy' for Steel or Nickel alloys. The huge difference in CTE could be a big problem unless the tile cavity for the insert could be sized to allow the insert to slide within the cavity without cracking or falling out (at the expense of positioning accuracy). Inserting the internal frame afterwards seems like less hassle.

Thanks for the sinter temperature. C/SiC can handle that.

John

I think, visuals don't really match that (see attached), but please correct me if I am wrong.
Also, we suspect that they experimenting with multiple types/methods: so your C/Sic solution can be the working one, where we cannot observe broken ones.

Photo credit for Nomadd, cropped by HVM, this post:
...

I missed this picture. The last one I saw appeared to be round and ceramic. It is hard to tell, but that one looks metallic and could have been slid in from the corners. I would love to get more info on their production.

John
Title: Re: Starship heat shield
Post by: Pueo on 04/14/2021 12:40 am
I appears that they have marked several tiles that are touching or very close to their neighbours. Perhaps these need to be refitted?

It's good at this stage to have tiles a mixed distance away from each other.  If they don't lose the tightly nested tiles, then they don't have to worry about that later.  If they do, then they know to enforce a minimum separation tolerance.
Elon tweeted something about rope filler between tiles. Besides blocking physical and thermal intrusion it would help damp out edge vibration. To allow this a minimum gap is needed. Allowing vibrating and buzzing tiles to touch seems to be inviting trouble. But yes, for now they need to play with it to find minimum and maximum allowable gap.


I can just picture the greenest intern hanging down the side of the SS with a mallet, rope and wooden drift, just like pounding oakum on a wooden ship. LOL  ;D

The shuttle had at least two methods for gap filling between tiles, one was a ceramic cloth "pillow" stuffed with silica fibers for larger gaps, the other was a strip of multilayered ceramic cloth coated with silica and silicon boride/carbide for extra emissivity.  The strip method was generally for gaps of 3 mm or less.  One of the tricks with the strip method was to bond two layers with once slightly wider than the other so that it would bend and wedge itself in the gap better when being blasted.
Title: Re: Starship heat shield
Post by: enbandi on 04/14/2021 06:04 am
....

I think, visuals don't really match that (see attached), but please correct me if I am wrong.
Also, we suspect that they experimenting with multiple types/methods: so your C/Sic solution can be the working one, where we cannot observe broken ones.

Photo credit for Nomadd, cropped by HVM, this post:
...

I missed this picture. The last one I saw appeared to be round and ceramic. It is hard to tell, but that one looks metallic and could have been slid in from the corners. I would love to get more info on their production.

John

Seen those ceramic, rounded ones too around SN4 or SN5.

For this metallic one: to slid from the corners you have to create a void, relatively long and thin and I guess precise. That sounds like a real pain (form manufacturing standpoint), either as a casting or a later machining challenge.
Judged on this picture it almost seems like that the attachment rails are glued on from behind with some fiber mat stripes or material compatible equivalent. (Remnants of the stripes are visible, with straight edges).

 
Title: Re: Starship heat shield
Post by: edzieba on 04/14/2021 10:14 am
ehh, maybe a little physics recap so we don't end up in a fantasy world:

Thermal insulation only slows down heat transfer, you still need to take that heat somewhere from the other side, only slower if you have better insulation
That's not how insulative TPS works: the goal is not to delay soak-through (that just means your structure melts during descent and landing rather than entry) but to reject heat. Usually through re-radiation, but the time you reach tick enough atmosphere at a slow enough velocity for convection to be a factor your TPS will have mostly cooled off.
In the latest photo of the large section of tiles by bocachicagal and RGV Aerial, there are a column of tiles with very noticeable gaps. Looking at some of these tiles even closer reveals that some of the tiles are not same the exact same size and thus the gaps.


Do we know why they are not all the same size or does that not really matter for these early prototypes? Is it hard to make them all the exact same size?


Also how will they size the tiles to fit the tapering nose?

As we know, for tile manufacturing first some billets casted, than tiles machined to final shape from those billets. The precision of a machining operation should be in the sub mm range. So I would say the tiles are exactly the same size (or at least the white core of them).
Sintering silica-fibre billets then milling the billets to size (before RCG coating) was how the STS tiles were made. If I were SpaceX and I wanted to mass produce effectively the same tiles but at a vastly lower cost, I would try and avoid that milling step entirely: achieve dimensional accuracy by correctly sizing the wet mould to account for shrinkage, and control shrinkage through controlling initial moisture content, bakeout time, and bakeout temperature (and temperature over time). Variance in those parameters risks an oversize or undersize tile, but avoiding post machining means you can come out ahead even if you occasionally need to toss out a bad patch.
We know from the Astronaut Blvd FDEP. report that "After drying, the billet is split in two pieces thereby creating the rudimentary tiles. The tiles are shaped to the desired form using a router". I expect the split is face-to-face, to allow the backside cavities to be formed as part of the mould and to allow a single cutting op to face two tiles (rather than one at a time). That router's days are numbered!
So far it seems impossible to avoid some unique shapes on the nose and around the fins. Bummer. For in flight repairs it's no big thing to have a supply of the widely used hex tiles, but what about the odd shapes?


Just for a working number let's say there are 30 different shapes. It could be much higher or a bit lower. The only options I can come up with are an onboard supply, onboard fabrication capability or a temporary one time use substitution.


A problem with an onboard inventory is how many of each shape. Some positions will have a higher wear rate, so more of them. But how many? It will take many reentries to develop a reliable statistical model with expected variance. The loss of a ship because of heatshield failure is lamentable but for a crewed mission it is unacceptable. Maybe a reliable model will be in hand before crew flights.


Onboard fabrication has its own difficulties. Unless the fab facility is large, production will be slow. If production is modeled on earth based production, 0G introduces a variable that needs to be explored before it can be considered reliable. Additive manufacturing shares this problem.


A temporary one use fix has promise. What comes to mind is a spray on or caulked ablative. It's not sexy but it promises to be quick, simple and reliable. If loss of one tile does not threaten LOM, orbital launches could substitute ablative material for one tile. It would still need on orbit installation testing and a tryout with direct entry velocities.
Lots of repair concepts generated in the STS era. Replacement TPS has no requirement to resemble standard TPS: its only requirements are to adhere (not necessarily via original anchoring method) and work once. All other requirements (e.g. mass, reusability, unit cost) go out the window for an emergency patch.
Title: Re: Starship heat shield
Post by: Slarty1080 on 04/14/2021 11:02 am
In the latest photo of the large section of tiles by bocachicagal and RGV Aerial, there are a column of tiles with very noticeable gaps. Looking at some of these tiles even closer reveals that some of the tiles are not same the exact same size and thus the gaps.


Do we know why they are not all the same size or does that not really matter for these early prototypes? Is it hard to make them all the exact same size?


Also how will they size the tiles to fit the tapering nose?

As we know, for tile manufacturing first some billets casted, than tiles machined to final shape from those billets. The precision of a machining operation should be in the sub mm range. So I would say the tiles are exactly the same size (or at least the white core of them).
Sintering silica-fibre billets then milling the billets to size (before RCG coating) was how the STS tiles were made. If I were SpaceX and I wanted to mass produce effectively the same tiles but at a vastly lower cost, I would try and avoid that milling step entirely: achieve dimensional accuracy by correctly sizing the wet mould to account for shrinkage, and control shrinkage through controlling initial moisture content, bakeout time, and bakeout temperature (and temperature over time). Variance in those parameters risks an oversize or undersize tile, but avoiding post machining means you can come out ahead even if you occasionally need to toss out a bad patch.
We know from the Astronaut Blvd FDEP. report that "After drying, the billet is split in two pieces thereby creating the rudimentary tiles. The tiles are shaped to the desired form using a router". I expect the split is face-to-face, to allow the backside cavities to be formed as part of the mould and to allow a single cutting op to face two tiles (rather than one at a time). That router's days are numbered!
So far it seems impossible to avoid some unique shapes on the nose and around the fins. Bummer. For in flight repairs it's no big thing to have a supply of the widely used hex tiles, but what about the odd shapes?


Just for a working number let's say there are 30 different shapes. It could be much higher or a bit lower. The only options I can come up with are an onboard supply, onboard fabrication capability or a temporary one time use substitution.


A problem with an onboard inventory is how many of each shape. Some positions will have a higher wear rate, so more of them. But how many? It will take many reentries to develop a reliable statistical model with expected variance. The loss of a ship because of heatshield failure is lamentable but for a crewed mission it is unacceptable. Maybe a reliable model will be in hand before crew flights.


Onboard fabrication has its own difficulties. Unless the fab facility is large, production will be slow. If production is modeled on earth based production, 0G introduces a variable that needs to be explored before it can be considered reliable. Additive manufacturing shares this problem.


A temporary one use fix has promise. What comes to mind is a spray on or caulked ablative. It's not sexy but it promises to be quick, simple and reliable. If loss of one tile does not threaten LOM, orbital launches could substitute ablative material for one tile. It would still need on orbit installation testing and a tryout with direct entry velocities.
I would have thought taking a supply of regular tiles and modifying them in orbit would be possible as an emergency measure. If my proposed tile solution was used (see picture at the very top of page 1 of this thread) all tiles would be hexagonal but the nose tiles would need a single cut at an angle dependant on their placement. Perhaps a small rotary cutter in a jig sealed in a tile sized box would work? Cut edges could be coated with some ablative paint. At the end of the day it just needs to get back down once.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 04/14/2021 04:27 pm
Today we saw new tiles placed on sn15, now the patch is more sqare-ish.

Any idea of why to put tiles one after rollout? As we know this operation takes very little time.
Title: Re: Starship heat shield
Post by: OTV Booster on 04/14/2021 05:11 pm
Today we saw new tiles placed on sn15, now the patch is more sqare-ish.

Any idea of why to put tiles one after rollout? As we know this operation takes very little time.
Maybe that's how the scheduling/manpower/road closure/tile availability/rocket god puzzle shook out.
Title: Re: Starship heat shield
Post by: Nomadd on 04/14/2021 05:25 pm
Today we saw new tiles placed on sn15, now the patch is more sqare-ish.

Any idea of why to put tiles one after rollout? As we know this operation takes very little time.
There's no need to delay rollout if all the tiles aren't available right away. Maybe because some cracked on on install or they didn't have enough for any other reason. Or, they did it on purpose or just decided to add some. They usually have more clips welded on than tiles installed.
Title: Re: Starship heat shield
Post by: wannamoonbase on 04/14/2021 05:42 pm
Today we saw new tiles placed on sn15, now the patch is more sqare-ish.

Any idea of why to put tiles one after rollout? As we know this operation takes very little time.
There's no need to delay rollout if all the tiles aren't available right away. Maybe because some cracked on on install or they didn't have enough for any other reason. Or, they did it on purpose or just decided to add some. They usually have more clips welded on than tiles installed.

I read a recent article (Space News I think) about the tile manufacturing in FL.  It sounded like they were limited in the through put of the equipment.

Seems they are ramping up that capability now as well. 
Title: Re: Starship heat shield
Post by: cartman on 04/14/2021 08:16 pm
All this tile discussion made me dig at my old Endeavour pics and that's always a good thing :)
Here are a few closeups i think may be relevant here
Title: Re: Starship heat shield
Post by: InterestedEngineer on 04/14/2021 09:22 pm
Today we saw new tiles placed on sn15, now the patch is more sqare-ish.

Any idea of why to put tiles one after rollout? As we know this operation takes very little time.
Maybe that's how the scheduling/manpower/road closure/tile availability/rocket god puzzle shook out.

Testing field replacement of tiles (on scheduling accident or on purpose).

We'll see if it works after the static fire
Title: Re: Starship heat shield
Post by: KBK on 04/14/2021 10:19 pm
Re a spare and with possible mounting issues in play:

A geared mechanism which moves to being under the edges of the remaining tiles, and then a glued/adhesed/friction fit plug over the access port to the geared mechanism (for the temp single use tile)

think of it (mechanistically) like a safe door with a cover for the access to the door control.

One could have multiple geared backing shapes and then multiple spare tile shapes. and then mix the two into a functional pair when the given tile loss is confronted. this, as part f the repair package, as it is not always going to be a guarantee that the mounts are functional. Something that points in that direction, as a design goes, possibly.

To possibly even pierce the blanket and anchor/grip the base area of adjacent mounts.
Title: Re: Starship heat shield
Post by: Nomadd on 04/14/2021 11:00 pm
 I think I found the mythical heat tile graveyard near the SN11 landing site. All small pieces. I thought of gathering enough to make a smoker, but I suppose it would turn out they outgassed cyanide when they got hot or something.
 It looks like the tiles don't have a Y shaped metal bracket inside like I thought, but three individual brackets.
 I was going to post a picture, but a terrible apparition arose and said "I am the demon ITAR. Put down the camera or suffer the consequences"
Title: Re: Starship heat shield
Post by: AC in NC on 04/14/2021 11:24 pm
I think I found the mythical heat tile graveyard near the SN11 landing site. All small pieces.

Damn.  I hate that is completely out of line to even wish that some were big enough and you could run some brittleness experiments for us.
Title: Re: Starship heat shield
Post by: KBK on 04/15/2021 12:19 am
  I was going to post a picture, but a terrible apparition arose and said "I am the demon ITAR. Put down the camera or suffer the consequences"

I can't help but believe (before this post came along)  that some of the aspects of your ability to hold your position with respect to Boca Chica and publication involving it, is due to your discretion - and it's lack of wavering, knowing where the line is, etc.
Title: Re: Starship heat shield
Post by: BT52 on 04/15/2021 05:37 am
I think I found the mythical heat tile graveyard near the SN11 landing site. All small pieces. I thought of gathering enough to make a smoker, but I suppose it would turn out they outgassed cyanide when they got hot or something.
 It looks like the tiles don't have a Y shaped metal bracket inside like I thought, but three individual brackets.
 I was going to post a picture, but a terrible apparition arose and said "I am the demon ITAR. Put down the camera or suffer the consequences"

So is inserted into slit on each 120deg axis. Reasonable as we speculated when we saw the picture. Makes sense You increase pressure contact and spread load across bigger crossection of brittle tile material. quite good. Even better as i thought.
Title: Re: Starship heat shield
Post by: edzieba on 04/15/2021 10:40 am
I think I found the mythical heat tile graveyard near the SN11 landing site. All small pieces. I thought of gathering enough to make a smoker, but I suppose it would turn out they outgassed cyanide when they got hot or something.
 It looks like the tiles don't have a Y shaped metal bracket inside like I thought, but three individual brackets.
 I was going to post a picture, but a terrible apparition arose and said "I am the demon ITAR. Put down the camera or suffer the consequences"
Heat it above 103°C to flash off the Methyltrimethoxysilane waterproofing agent (fumes are flammable, and don't huff them), and you'll have an inert silica fibre brick with a borosilicate glass coating. A flat chunk would make for a nice trivet.
Title: Re: Starship heat shield
Post by: Oersted on 04/15/2021 09:03 pm
I could suggest a company with a lot of experience if they want some advice on how to just click tiles firmly into place....
Title: Re: Starship heat shield
Post by: ETurner on 04/15/2021 09:49 pm
A fun fact of geometry:
Y-shaped grooves (uniquely) accommodate arbitrary mounting-pin displacements: For any pin displacement, there is a tile position that fits and is fully constrained. With this constraint system, expansion and bending of mounting surfaces neither stress nor loosen tiles.
https://en.wikipedia.org/wiki/Kinematic_coupling (https://en.wikipedia.org/wiki/Kinematic_coupling)
Title: Re: Starship heat shield
Post by: enbandi on 04/16/2021 06:14 am
A fun fact of geometry:
Y-shaped grooves (uniquely) accommodate arbitrary mounting-pin displacements: For any pin displacement, there is a tile position that fits and is fully constrained. With this constraint system, expansion and bending of mounting surfaces neither stress nor loosen tiles.
https://en.wikipedia.org/wiki/Kinematic_coupling (https://en.wikipedia.org/wiki/Kinematic_coupling)

Good idea, but this require free movement of nuts along the length of the Y elements (legs?).

Something like elongated holes on the back of the tile, freely moving legs in their voids. The elongated holes should be observable.
Title: Re: Starship heat shield
Post by: ETurner on 04/16/2021 10:49 am
A fun fact of geometry:
Y-shaped grooves (uniquely) accommodate arbitrary mounting-pin displacements: For any pin displacement, there is a tile position that fits and is fully constrained. With this constraint system, expansion and bending of mounting surfaces neither stress nor loosen tiles.
https://en.wikipedia.org/wiki/Kinematic_coupling (https://en.wikipedia.org/wiki/Kinematic_coupling)

Good idea, but this require free movement of nuts along the length of the Y elements (legs?).

Something like elongated holes on the back of the tile, freely moving legs in their voids. The elongated holes should be observable.
Yes, there would be elongated holes and some mobility. Have we seen this, or ruled it out?
Title: Re: Starship heat shield
Post by: enbandi on 04/16/2021 10:57 am
A fun fact of geometry:
Y-shaped grooves (uniquely) accommodate arbitrary mounting-pin displacements: For any pin displacement, there is a tile position that fits and is fully constrained. With this constraint system, expansion and bending of mounting surfaces neither stress nor loosen tiles.
https://en.wikipedia.org/wiki/Kinematic_coupling (https://en.wikipedia.org/wiki/Kinematic_coupling)

Good idea, but this require free movement of nuts along the length of the Y elements (legs?).

Something like elongated holes on the back of the tile, freely moving legs in their voids. The elongated holes should be observable.
Yes, there would be elongated holes and some mobility. Have we seen this, or ruled it out?

Not enough data I think. I have these images, cropped from a video (several page upthread), but not the best resolution. The hole seems round (not elongated).

EDIT: source: https://youtu.be/eny57M5sxHk?t=76

Title: Re: Starship heat shield
Post by: ETurner on 04/16/2021 12:31 pm
A fun fact of geometry:
Y-shaped grooves (uniquely) accommodate arbitrary mounting-pin displacements: For any pin displacement, there is a tile position that fits and is fully constrained. With this constraint system, expansion and bending of mounting surfaces neither stress nor loosen tiles.
https://en.wikipedia.org/wiki/Kinematic_coupling (https://en.wikipedia.org/wiki/Kinematic_coupling)

Good idea, but this require free movement of nuts along the length of the Y elements (legs?).

Something like elongated holes on the back of the tile, freely moving legs in their voids. The elongated holes should be observable.
Yes, there would be elongated holes and some mobility. Have we seen this, or ruled it out?

Not enough data I think. I have these images, cropped from a video (several page upthread), but not the best resolution. The hole seems round (not elongated).

It looks like there might be some elongation, but if so, it’s very slight.
The pins are split perpendicular to the groove axes, and this may give them some elastic mobility in the right directions. (Pin shapes might also account for slightly elongated holes, if that’s what we’re seeing.)
Title: Re: Starship heat shield
Post by: edzieba on 04/16/2021 01:16 pm
A fun fact of geometry:
Y-shaped grooves (uniquely) accommodate arbitrary mounting-pin displacements: For any pin displacement, there is a tile position that fits and is fully constrained. With this constraint system, expansion and bending of mounting surfaces neither stress nor loosen tiles.
https://en.wikipedia.org/wiki/Kinematic_coupling (https://en.wikipedia.org/wiki/Kinematic_coupling)
While the tile position is fully constrained, it is not constant. In particular, orientation is not retained as pins move, which means tiles can attempt to self-intersect (read: crush each other into bits) for offset pin geometries. Anisotropic expansion could also result in lateral tile displacement (e.g. a surface constrained axially by stringers but free to expand radially would cause tiles to shift up or down depending on pin triangle orientation).
Title: Re: Starship heat shield
Post by: rsdavis9 on 04/16/2021 01:42 pm
A fun fact of geometry:
Y-shaped grooves (uniquely) accommodate arbitrary mounting-pin displacements: For any pin displacement, there is a tile position that fits and is fully constrained. With this constraint system, expansion and bending of mounting surfaces neither stress nor loosen tiles.
https://en.wikipedia.org/wiki/Kinematic_coupling (https://en.wikipedia.org/wiki/Kinematic_coupling)
While the tile position is fully constrained, it is not constant. In particular, orientation is not retained as pins move, which means tiles can attempt to self-intersect (read: crush each other into bits) for offset pin geometries. Anisotropic expansion could also result in lateral tile displacement (e.g. a surface constrained axially by stringers but free to expand radially would cause tiles to shift up or down depending on pin triangle orientation).

How long are the pins?
I assume they will bend somewhat with tile expansion and contraction. This will provide some relief of the tile to tile interation.
Title: Re: Starship heat shield
Post by: Nomadd on 04/16/2021 02:00 pm
A fun fact of geometry:
Y-shaped grooves (uniquely) accommodate arbitrary mounting-pin displacements: For any pin displacement, there is a tile position that fits and is fully constrained. With this constraint system, expansion and bending of mounting surfaces neither stress nor loosen tiles.
https://en.wikipedia.org/wiki/Kinematic_coupling (https://en.wikipedia.org/wiki/Kinematic_coupling)
Good idea, but this require free movement of nuts along the length of the Y elements (legs?).
Something like elongated holes on the back of the tile, freely moving legs in their voids. The elongated holes should be observable.
Yes, there would be elongated holes and some mobility. Have we seen this, or ruled it out?
Not enough data I think. I have these images, cropped from a video (several page upthread), but not the best resolution.
The hole seems round (not elongated).

That's the hole in the tile material. It's hard to drill an oblong hole, and machining or punching might not work that well. The hole in the bracket is about 5x3.
Title: Re: Starship heat shield
Post by: ETurner on 04/16/2021 02:03 pm
A fun fact of geometry:
Y-shaped grooves (uniquely) accommodate arbitrary mounting-pin displacements: For any pin displacement, there is a tile position that fits and is fully constrained. With this constraint system, expansion and bending of mounting surfaces neither stress nor loosen tiles.
https://en.wikipedia.org/wiki/Kinematic_coupling (https://en.wikipedia.org/wiki/Kinematic_coupling)
While the tile position is fully constrained, it is not constant. In particular, orientation is not retained as pins move, which means tiles can attempt to self-intersect (read: crush each other into bits) for offset pin geometries. Anisotropic expansion could also result in lateral tile displacement [...]
Yes. My assumption, based on what we see, is that inter-tile spacing can be large enough to accommodate manufacturing tolerances,  in-flight deformation, etc., while avoiding inter-tile collisions, but that the pin-tile contacts need to be tight (no rattling!) and are by nature potentially more sensitive to misalignments that would apply stress to tiles. What the Y-constraint kinematics say is that allowing Y-arm-aligned pin compliance (or pin/tile displacement) is enough to accommodate substantial tolerances, deformation, etc., while both retaining tight coupling and avoiding tile stress. Which is kind of cool as an engineering principle, and maybe as a SpaceX design feature.
Title: Re: Starship heat shield
Post by: ETurner on 04/16/2021 02:05 pm
The hole in the bracket is about 5x3.
Picture, or ITAR?
Title: Re: Starship heat shield
Post by: Nomadd on 04/16/2021 02:10 pm
The hole in the bracket is about 5x3.
Picture, or ITAR?
I'm starting to warm up to ITAR. You can use that as an excuse for anything.
 
 "Where's that circular saw you borrowed six months ago?"

  "Sorry, ITAR prevents me from talking about that."
Title: Re: Starship heat shield
Post by: ETurner on 04/16/2021 02:29 pm
The hole in the bracket is about 5x3.
Picture, or ITAR?
I'm starting to warm up to ITAR. You can use that as an excuse for anything.
 
 "Where's that circular saw you borrowed six months ago?"

  "Sorry, ITAR prevents me from talking about that."
Mmmph. Barn doors, horses. (Still confusing, maybe obsolete.)
Just for reminder, broken tile from SN8. We can see structure inside tile where tile-side weld stud lock sits:
Title: Re: Starship heat shield
Post by: Nomadd on 04/17/2021 04:16 pm
 The white sheet underlayment comes to 3kg Sq. meter.
 Once again, it could be one of 50 types they're trying for all I know, or only in certain areas. You don't even see it in some photos.
Title: Re: Starship heat shield
Post by: Oersted on 04/22/2021 09:18 am
That's much heavier than I thought it would be. Hefty stuff. I'd like to hear more about it. Does it fray/rip easily? How compressible is it? What does it smell like?  :-)
Title: Re: Starship heat shield
Post by: BT52 on 04/22/2021 10:35 am
Glass fiber I assume. So it's not quite sniffing friendly. :)
Title: Re: Starship heat shield
Post by: Kazioo on 04/22/2021 10:56 am
Not sure how thick this layer is, but 25mm Superwool HT 128 and 20mm Superwool HT 160 both would be 3.2 kg/m2, so it could be that or a similar material.
Title: Re: Starship heat shield
Post by: Nomadd on 04/22/2021 03:29 pm
 
That's much heavier than I thought it would be. Hefty stuff. I'd like to hear more about it. Does it fray/rip easily? How compressible is it? What does it smell like?  :-)
Title: Re: Starship heat shield
Post by: livingjw on 04/22/2021 03:35 pm
Glass fiber I assume. So it's not quite sniffing friendly. :)

I believe the Shuttle used Nomex felt pads.

John
Title: Re: Starship heat shield
Post by: Hog on 04/22/2021 10:39 pm
Glass fiber I assume. So it's not quite sniffing friendly. :)

I believe the Shuttle used Nomex felt pads.

John
Yes, the Strain Isolation Pads (SIP) were made of Nomex-felt.  The orbiter skin-to-SIP and SIP-TPS tile interfaces used an adhesive which I believe to be an RTV silicone, no mounting pins.
Title: Re: Starship heat shield
Post by: livingjw on 04/22/2021 11:19 pm
Glass fiber I assume. So it's not quite sniffing friendly. :)

I believe the Shuttle used Nomex felt pads.

John
Yes, the Strain Isolation Pads (SIP) were made of Nomex-felt.  The orbiter skin-to-SIP and SIP-TPS tile interfaces used an adhesive which I believe to be an RTV silicone, no mounting pins.

Correct.
Title: Re: Starship heat shield
Post by: AU1.52 on 04/23/2021 12:09 am
SN15 now has a complete section of TPS tiles. It is good they are able to quickly add new tile sections and do not appear to have issue fitting tiles between existing tile sections or fitting at height.
Title: Re: Starship heat shield
Post by: _MECO on 04/23/2021 01:01 am
A fun fact of geometry:
Y-shaped grooves (uniquely) accommodate arbitrary mounting-pin displacements: For any pin displacement, there is a tile position that fits and is fully constrained. With this constraint system, expansion and bending of mounting surfaces neither stress nor loosen tiles.
https://en.wikipedia.org/wiki/Kinematic_coupling (https://en.wikipedia.org/wiki/Kinematic_coupling)
Oh my god! Kinematic coupling! I read a Hackaday article on the concept ages ago and was trying to remember the name of the it so I could find the article again and keep learning more. Thank you so much. Sorry if this comment is technically OT. Yes it makes tons of sense for those tiles.

https://hackaday.com/2019/09/11/books-you-should-read-exact-constraint-machine-design-using-kinematic-principles/
Title: Re: Starship heat shield
Post by: Nomadd on 04/23/2021 03:17 am
 A section with well over ten heat tiles hiding in the corner of Tent 3, and what looks like the underlayment.
Title: Re: Starship heat shield
Post by: _MECO on 04/23/2021 05:49 am
A section with well over ten heat tiles hiding in the corner of Tent 3, and what looks like the underlayment.
Ten? What are you talking about? I count at least fourteen.
Title: Re: Starship heat shield
Post by: edzieba on 04/23/2021 10:43 am
A section with well over ten heat tiles hiding in the corner of Tent 3, and what looks like the underlayment.
I don't think that second photo is the underlayment. There's a pair of flanges sticking out, so probably some variety of flippy-flappy-aerosurface.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 04/24/2021 06:37 am

https://twitter.com/MarcusHouse/status/1385776584645177344


Seems like sn17 will have a big heat shield. Could we see a complete one before sn20? IMO it is reasonable, because they will habe to know how  a complete heat shield performs (since we saw broken tiles)
Title: Re: Starship heat shield
Post by: Daan on 04/24/2021 12:01 pm

https://twitter.com/MarcusHouse/status/1385776584645177344


Seems like sn17 will have a big heat shield. Could we see a complete one before sn20? IMO it is reasonable, because they will habe to know how  a complete heat shield performs (since we saw broken tiles)

They could send SN17 as high as they can and check how the heatshield does, instead of skipping to orbit on SN20 and risking having no heatshield to inspect if the reentry fails.
Title: Re: Starship heat shield
Post by: grndkntrl on 04/24/2021 07:58 pm
A section with well over ten heat tiles hiding in the corner of Tent 3, and what looks like the underlayment.
I don't think that second photo is the underlayment. There's a pair of flanges sticking out, so probably some variety of flippy-flappy-aerosurface.

Yeah, Looking at the full size photo, that's clearly one of the flaps, probably the aft ones. There was another delivery of these in the last few days.
Title: Re: Starship heat shield
Post by: TOG on 04/27/2021 05:12 pm
Team - General Heat Shield question regarding SN15:
Was there any obvious damage from the static fire?
(Thank you in advance!)
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 04/27/2021 08:15 pm
Team - General Heat Shield question regarding SN15:
Was there any obvious damage from the static fire?
(Thank you in advance!)

SN15 suffered a few broken tiles during the static fire test.

As Mary reported, yes. Like with sn11 it happened in the lower patches.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 04/27/2021 09:05 pm
Team - General Heat Shield question regarding SN15:
Was there any obvious damage from the static fire?
(Thank you in advance!)

link to Mary's post regarding tiles.  Looks like main field was fine, bottom lost some:

https://forum.nasaspaceflight.com/index.php?topic=53509.msg2228413#msg2228413
Title: Re: Starship heat shield
Post by: OTV Booster on 04/27/2021 11:13 pm
What are the chances it's as much the size of the patch as the location? Topmost small patch had no dings but it's a good ways from the energy source. The big main patch seemed to have no problems. Only the two lower small patches lost tiles.


Speculations from a slightly more than nodding familiarity with acoustics. Adding a tile should drop the local resonant frequency. The padding acts as a high frequency damper between the skin and the tile and soak up some of the acoustic energy. The pins are a fairly straight acoustic conduit but the padding should drop delivered amplitude a bit. The mass and stiffness of the tile should force a local drop in harmonic frequency at the risk of cracking the tile around the pin.


A large array of tiles might have a this problem around the edge but it should be more acoustically benign inward from the edge. Or, and here is where I am adrift, the large patch might establish a large low frequency resonance area that encompasses the edge and protects it from high frequency vibrations.


Keep in mind that there is no math behind what I'm speculating but overall, ISTM the more tiles, the more acoustically benign the environment. The nosecone, raceways and flaps will not be easy. Nor will the edge condition of the engine bay bottom or the abrupt change at the top and bottom dome weld lines.
Title: Re: Starship heat shield
Post by: Kazioo on 04/28/2021 10:10 am
Good thing Starship is not a SSTO and Super Heavy doesn't have tiles, so in the actual launch there shouldn't be this kind of kick of static fire so close to the ground.

But they sill need those static fires to test new Starships, so how about adding tiles to the lower parts only after they are done with static fires?

However, this may still be a problem on Mars. Imagine launching to Earth and losing tiles before you even leave the Martian atmosphere...
Title: Re: Starship heat shield
Post by: ETurner on 04/28/2021 01:08 pm
Making some of the lower tiles more robust (reinforced? densified? cushioned?) wouldn’t be the end of the world in terms of vehicle mass or complexity (same shape, some delta in production, one more type).
Title: Re: Starship heat shield
Post by: DreamyPickle on 04/28/2021 01:26 pm
A simple but worrying explanation is that the small tile patches lower down the vehicle experience more vibration due to being closer to the engine.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 04/28/2021 04:23 pm
What are the chances it's as much the size of the patch as the location? Topmost small patch had no dings but it's a good ways from the energy source. The big main patch seemed to have no problems. Only the two lower small patches lost tiles.


Speculations from a slightly more than nodding familiarity with acoustics. Adding a tile should drop the local resonant frequency. The padding acts as a high frequency damper between the skin and the tile and soak up some of the acoustic energy. The pins are a fairly straight acoustic conduit but the padding should drop delivered amplitude a bit. The mass and stiffness of the tile should force a local drop in harmonic frequency at the risk of cracking the tile around the pin.


A large array of tiles might have a this problem around the edge but it should be more acoustically benign inward from the edge. Or, and here is where I am adrift, the large patch might establish a large low frequency resonance area that encompasses the edge and protects it from high frequency vibrations.


Keep in mind that there is no math behind what I'm speculating but overall, ISTM the more tiles, the more acoustically benign the environment. The nosecone, raceways and flaps will not be easy. Nor will the edge condition of the engine bay bottom or the abrupt change at the top and bottom dome weld lines.

Great point. This would explain very weel why they are going to have a full heat shield(as it seems) for sn17. Landing sn15 will be crucial to understand how tiles perfom,  and would be very intersting to know if:

1) damages occur  during the flight
2) if they happen on the liftoff or during ascent or skydiver (but in this latest case eventual damage could be caused by not having all the surface covered, )
3)if there are problems with the flip.

What could we say about the suborbital test stand? Could it being too low the cause of tile braking, assuming the cause is acustic?
Title: Re: Starship heat shield
Post by: Slarty1080 on 04/28/2021 04:49 pm
What are the chances it's as much the size of the patch as the location? Topmost small patch had no dings but it's a good ways from the energy source. The big main patch seemed to have no problems. Only the two lower small patches lost tiles.


Speculations from a slightly more than nodding familiarity with acoustics. Adding a tile should drop the local resonant frequency. The padding acts as a high frequency damper between the skin and the tile and soak up some of the acoustic energy. The pins are a fairly straight acoustic conduit but the padding should drop delivered amplitude a bit. The mass and stiffness of the tile should force a local drop in harmonic frequency at the risk of cracking the tile around the pin.


A large array of tiles might have a this problem around the edge but it should be more acoustically benign inward from the edge. Or, and here is where I am adrift, the large patch might establish a large low frequency resonance area that encompasses the edge and protects it from high frequency vibrations.


Keep in mind that there is no math behind what I'm speculating but overall, ISTM the more tiles, the more acoustically benign the environment. The nosecone, raceways and flaps will not be easy. Nor will the edge condition of the engine bay bottom or the abrupt change at the top and bottom dome weld lines.
It seems both tiles lost from both sections were on the lower row adjacent to smaller tiles directly below them. Not sur eif this is relevant?
Title: Re: Starship heat shield
Post by: InterestedEngineer on 04/28/2021 10:54 pm
Making some of the lower tiles more robust (reinforced? densified? cushioned?) wouldn’t be the end of the world in terms of vehicle mass or complexity (same shape, some delta in production, one more type).

From the look of  the tiles removed, I don't see the white blanket under the lower two section of tiles that experienced tile fractures.  There is a blanket on the large section:

https://forum.nasaspaceflight.com/index.php?topic=53509.msg2229139#msg2229139

Not sure what that means, except maybe the blanket helps.
Title: Re: Starship heat shield
Post by: Oersted on 04/29/2021 02:02 pm
Good thing Starship is not a SSTO and Super Heavy doesn't have tiles, so in the actual launch there shouldn't be this kind of kick of static fire so close to the ground.

But they sill need those static fires to test new Starships, so how about adding tiles to the lower parts only after they are done with static fires?

However, this may still be a problem on Mars. Imagine launching to Earth and losing tiles before you even leave the Martian atmosphere...

On Mars lift-off will take place in near-vacuum conditions, so there will be smaller pressure-related stress on the tiles. It will look more like Earthly staging conditions than lift-off conditions.

Also, there will be a few months of interplanetary coast during which tile issues can be remedied before they are needed for re-entry.
Title: Re: Starship heat shield
Post by: wannamoonbase on 04/29/2021 09:24 pm
If SN15 lands intact tomorrow the heat shield is going to be in the hot seat.

Can they make enough tiles.
Are they durable enough.
Will the ones on the nose survive launch and Max-Q
Can they produce and attach tiles to the non-uniform areas on the surfaces and nose?
How many test flights is this going to take to get right?

Fun times.
Title: Re: Starship heat shield
Post by: OTV Booster on 04/30/2021 12:14 am
Making some of the lower tiles more robust (reinforced? densified? cushioned?) wouldn’t be the end of the world in terms of vehicle mass or complexity (same shape, some delta in production, one more type).

From the look of  the tiles removed, I don't see the white blanket under the lower two section of tiles that experienced tile fractures.  There is a blanket on the large section:

https://forum.nasaspaceflight.com/index.php?topic=53509.msg2229139#msg2229139 (https://forum.nasaspaceflight.com/index.php?topic=53509.msg2229139#msg2229139)

Not sure what that means, except maybe the blanket helps.
Those tiles look like they might have individual pieces of blanket. But then again it really looks more like their mounted on a pad of French cream filling, so what do I know.
Title: Re: Starship heat shield
Post by: rsdavis9 on 04/30/2021 05:12 pm
I can just imagine this conversation inside spacex.

Heat shield engineer: Can't you make the skirt sturdier so it doesn't vibrate so much. I have a car with steel panels that doesn't vibrate.

Skirt engineer: Can't you make those ceramic pottery things stronger so they don't break. I have dishes at home I can drop on the floor and they don't break.(corelle)
Title: Re: Starship heat shield
Post by: OTV Booster on 04/30/2021 05:25 pm
I can just imagine this conversation inside spacex.

Heat shield engineer: Can't you make the skirt sturdier so it doesn't vibrate so much. I have a car with steel panels that doesn't vibrate.

Skirt engineer: Can't you make those ceramic pottery things stronger so they don't break. I have dishes at home I can drop on the floor and they don't break.(corelle)
Obviously they need to mount the dishes on the car. Never know what you'll learn until you try.  8)
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 04/30/2021 07:49 pm
Making some of the lower tiles more robust (reinforced? densified? cushioned?) wouldn’t be the end of the world in terms of vehicle mass or complexity (same shape, some delta in production, one more type).

From the look of  the tiles removed, I don't see the white blanket under the lower two section of tiles that experienced tile fractures.  There is a blanket on the large section:

https://forum.nasaspaceflight.com/index.php?topic=53509.msg2229139#msg2229139 (https://forum.nasaspaceflight.com/index.php?topic=53509.msg2229139#msg2229139)

Not sure what that means, except maybe the blanket helps.
Those tiles look like they might have individual pieces of blanket. But then again it really looks more like their mounted on a pad of French cream filling, so what do I know.

What do we know about this blanket? Is its pourpouse termal insulation only? Could it help to spread loads?
Title: Re: Starship heat shield
Post by: matthewkantar on 04/30/2021 08:24 pm
If there is going to be a problem with the heat shield, best place for it would be on the skirt, right?
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 04/30/2021 08:50 pm
If there is going to be a problem with the heat shield, best place for it would be on the skirt, right?

Possible, but IMO the worst places are the leading edges of the elonerons and the nose cone tip. Skirt could be a problem if tiles keep breaking.
Title: Re: Starship heat shield
Post by: Slarty1080 on 04/30/2021 09:12 pm
If there is going to be a problem with the heat shield, best place for it would be on the skirt, right?

Possible, but IMO the worst places are the leading edges of the elonerons and the nose cone tip. Skirt could be a problem if tiles keep breaking.
We haven't seen those yet. And they will both need to be specialized parts, so might use different technology and perhaps have a little more lea way on cost.
Title: Re: Starship heat shield
Post by: KBK on 04/30/2021 09:44 pm
IIRC, from looking at the various images..the attachment method for the lower tiles on SN15 appears to be different than that attachment method of the main mass of them.

Again, those currently un-anchored tips  (of the six sided ceramic panel) need to be damped, at the tips, furthest from the center points. three mount points, and then the opposite unsupported tips anchored via a more full backing piece, possibly a 6 legged one. and the outer tip is shaped .. maybe a lot like the stylized T on the Tesla logo, but 3-d, with depth. and that tip presses lightly into the thermal blanket..

That slight bit of loading will lock the tip into position which cuts the vibration and motion in 3 axis, by approximately a full magnitude. The next question to be asked, is what sort of affect does this stability attempt have on the thermal blanket. and what is the mass penalty. Done right, it's probably not all that significant. SpaceX has done all the heavy lifting already, re the thermal blanket specs. If they thought it would disintegrate from too much vibration, that blanket would not be there at all right now. Which means it likely has the overhead for this mount modification..

something akin to the supplied image. in it, this is the general shape of the tile support with the open corners and the regular three mount arms. the bumped corners are the 'unsupported' corners. they press into the thermal blanket.

One modifies the general concept until it works. It ain't done until the spaghetti sticks to the fridge. building a vibration test mount to get this done is not the biggest deal either. one could probably get to where they need to be in a week or two. I know I could. At least an answer would pop out of it. regardless of the veracity of the answer.. an end point would definitely appear.
Title: Re: Starship heat shield
Post by: HVM on 05/05/2021 10:59 pm
No missing tiles? Perfect flight.
Title: Re: Starship heat shield
Post by: Lars-J on 05/06/2021 02:56 am
No missing tiles? Perfect flight.

There might be some missing ones around the skirt at the bottom, hard to tell with these two images.
Title: Re: Starship heat shield
Post by: cuddihy on 05/06/2021 03:26 am
Either way it seems the static fires are rougher on the tiles than actual flight as some have speculated due to acoustic reflections from the ground.
Title: Re: Starship heat shield
Post by: hallmh on 05/06/2021 11:10 am

I think some tiles were lost from the bottom row of the small patch below the main one - a handful, really.
Title: Re: Starship heat shield
Post by: tyrred on 05/06/2021 03:08 pm
Any post-landing photos of the leeward side of the port flaps? Curious if all the tiles attached on those flaps are still intact.
Title: Re: Starship heat shield
Post by: HVM on 05/06/2021 07:20 pm
No missing tiles? Perfect flight.
https://twitter.com/RGVaerialphotos/status/1390382784720605185
Title: Re: Starship heat shield
Post by: AU1.52 on 05/06/2021 08:15 pm
No missing tiles? Perfect flight.
https://twitter.com/RGVaerialphotos/status/1390382784720605185 (https://twitter.com/RGVaerialphotos/status/1390382784720605185)


One is not bad at all! and at an edge!
Title: Re: Starship heat shield
Post by: WormPicker959 on 05/06/2021 08:44 pm
No missing tiles? Perfect flight.
https://twitter.com/RGVaerialphotos/status/1390382784720605185 (https://twitter.com/RGVaerialphotos/status/1390382784720605185)


One is not bad at all! and at an edge!

Looks like the upper patch of the two lower patches lost a lot of tiles too:
https://twitter.com/RGVaerialphotos/status/1390385056670179329?s=20
Title: Re: Starship heat shield
Post by: AU1.52 on 05/06/2021 11:24 pm
Posting to correct topic:


The shiny side of the Starship who lived.
Looks like only one damaged tile on the back of SN15's aft flap. Harder to tell with the tiles on the forward flap being in deep shadow but I would expect that damage would be visible if there was any.
Title: Re: Starship heat shield
Post by: docmordrid on 05/07/2021 05:01 am
No missing tiles? Perfect flight.
https://twitter.com/RGVaerialphotos/status/1390382784720605185 (https://twitter.com/RGVaerialphotos/status/1390382784720605185)

One is not bad at all! and at an edge!

Zoom-crop of missing tile for documentary purposes...
Title: Re: Starship heat shield
Post by: schuttle89 on 05/07/2021 03:53 pm
So it seems that edge tiles have an issue whereas big blocks have been ok thus far. Obviously need to see orbital launch but if this holds then a Mars-bound or return starship could just need repair to some edge tiles before entry. Also would be interesting to see if a starship could survive entry missing a couple edge tiles.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 05/07/2021 04:00 pm
Is there any way we can know if the tiles broke during launch or during skydive or at landing? Is the quality of the video sufficient to see the falling tile?
Title: Re: Starship heat shield
Post by: CMac on 05/07/2021 04:39 pm
There were pics of just after launch and tiles were missing on skirt at that point
Title: Re: Starship heat shield
Post by: RedLineTrain on 05/07/2021 05:34 pm
Behind that missing tile, I expected to see an insulation blanket.

Edit:  Or perhaps the blanket is there and we are just seeing the mounting material that is part of the missing tile?
Title: Re: Starship heat shield
Post by: Lars-J on 05/07/2021 05:50 pm
Behind that missing tile, I expected to see an insulation blanket.

Edit:  Or perhaps the blanket is there and we are just seeing the mounting material that is part of the missing tile?

Yes the blanket is still there... Note that the blanket section extends beyond the entire tiled area.
Title: Re: Starship heat shield
Post by: envy887 on 05/07/2021 06:36 pm
I can just imagine this conversation inside spacex.

Heat shield engineer: Can't you make the skirt sturdier so it doesn't vibrate so much. I have a car with steel panels that doesn't vibrate.

Skirt engineer: Can't you make those ceramic pottery things stronger so they don't break. I have dishes at home I can drop on the floor and they don't break.(corelle)

"Your car doesn't have three 10 million horsepower engines on the other side of the panel."
Title: Re: Starship heat shield
Post by: inonepiece on 05/07/2021 07:02 pm
However, this may still be a problem on Mars. Imagine launching to Earth and losing tiles before you even leave the Martian atmosphere...
Stick them back on in Earth orbit?
Title: Re: Starship heat shield
Post by: CJ on 05/07/2021 10:27 pm

IMHO, the heat shield may well be the most difficult remaining technical issue, and the skirt (due to vibration/acoustics) may well be the hardest location to deal with.

At this juncture, given that they seem to be having a lot of problems with tiles on the skirt, I'm wondering if they'll end up having to go with a different formulation of tile (tougher, and alas heavier) for the skirt. On the other hand, it might turn out that the problem is primarily acoustics, in which case the problem may not occur in operational use (vastly different acoustic environment at stage separation, due to no ground reflection, near vacuum, etc).

I'm also wondering if the underlayment we see might be made of material capable of preventing (via ablation) reentry burn-through of the underlying stainless steel in the case of the loss of a single tile in an area. If so, that would be a massive increase in safety factor.

 
Title: Re: Starship heat shield
Post by: tyrred on 05/07/2021 10:37 pm
All but a corner of the tiles on the port aft flap survived.
Harder to tell on the port fore flap as it's stowed away and more in shadow.
Credit: Nomadd images
Title: Re: Starship heat shield
Post by: InterestedEngineer on 05/08/2021 03:50 am
Behind that missing tile, I expected to see an insulation blanket.

Edit:  Or perhaps the blanket is there and we are just seeing the mounting material that is part of the missing tile?

Yes the blanket is still there... Note that the blanket section extends beyond the entire tiled area.

Here's a hypothesis on tile failures allowing one safe re-entry:

1.  All the failures so far have shown the bracket in place, still holding down the blanket
2.  The blanket by itself is enough to protect the stainless steel from excessive heat
3.  a prime purpose of the tile is to protect the bracket that holds down the blankets

Therefore losing a tile as we see in the pictures will cause the bracket to melt, but stay intact long enough to keep the blanket intact thus preventing damage to the stainless steel sheet that is the structure of the Starship body.

Wouldn't want to go through re-entry more than once on a damaged tile, but once seems to have some redundancy.  Removing a slagged bracket will require someone with a welder to remove the melted bracket and clip and put in a new clip (followed by a tile), so would require a lift to get the person up there, but can be done in hours.

Thus tile loss becomes more of a maintenance time issue, not a safety issue.
Title: Re: Starship heat shield
Post by: Pueo on 05/08/2021 11:07 pm
I wonder if we'll see a high emissivity applied to the inside of the propellant tanks to increase radiative heat transfer from the windward tank side to the leeward side.  It would be like how the Space Shuttle leading edges used cross-radiation within the U-shaped RRC panels.  I suppose the trick would be finding a lox and hot oxygen compatible high emissivity coating that's also simple to apply to the large steel plates before they are welded into rings, or even better after stacking.  That or you could just let a relatively high emissivity oxide film develop as the lox tank walls heat up during the first re-entry.

I definitely expect to see some high emissivity inner coating applied to the flaps.
Title: Re: Starship heat shield
Post by: BT52 on 05/09/2021 05:31 pm
I wonder if we'll see a high emissivity applied to the inside of the propellant tanks to increase radiative heat transfer from the windward tank side to the leeward side.  It would be like how the Space Shuttle leading edges used cross-radiation within the U-shaped RRC panels.  I suppose the trick would be finding a lox and hot oxygen compatible high emissivity coating that's also simple to apply to the large steel plates before they are welded into rings, or even better after stacking.  That or you could just let a relatively high emissivity oxide film develop as the lox tank walls heat up during the first re-entry.

I definitely expect to see some high emissivity inner coating applied to the flaps.

Very interesting. Nice idea i like it. I could see for now they will wait till orbital test and see if they got some hotspots on windward side of hull. In that case i case see they will do special treatments as u motioned on those areas.
Title: Re: Starship heat shield
Post by: WormPicker959 on 05/10/2021 10:39 pm
With the most recent photos from the SpaceX Flickr, we can conclude that the post-landing damage on the upper-of-the-lower tile sections (don't know how to refer to it, see attached image) happened sometime post-launch. There was damage in these sections following static fire, so we know that's a harsh environment for the tiles. Launch itself doesn't appear to have damaged the tiles, so it must be something in the ascent, belly-flop, flip, or landing phases that resulted in damage. My bet would be on landing.

However, I'd expect that if they were damaged upon landing, we'd be able to see some debris on/near the pad. I've looked at several of RGV's aerial shots directly after landing, and I can't find any solid evidence of that. Not exactly dispositive, but there's that. I don't know if there are sufficiently high resolution shots available of the landing burn to determine if the tiles were already damaged by the time SN15 got below the clouds again.

Edit: noob image posting question: I made the attached image in Preview, saved as png. The forum preview is quite blurry, but clicking through it seems fine. Is there a better format/encoding to post in so that the image is small/compressed yet not blurry in the forum preview, so that casual readers don't have to click through to get the gist of the post?
Title: Re: Starship heat shield
Post by: Crispy on 05/11/2021 09:03 am
Edit: noob image posting question: I made the attached image in Preview, saved as png. The forum preview is quite blurry, but clicking through it seems fine. Is there a better format/encoding to post in so that the image is small/compressed yet not blurry in the forum preview, so that casual readers don't have to click through to get the gist of the post?
There's nothing you can do. The preview is always blurry.
Title: Re: Starship heat shield
Post by: Thrustpuzzle on 05/11/2021 10:25 am
I wonder if we'll see a high emissivity applied to the inside of the propellant tanks to increase radiative heat transfer from the windward tank side to the leeward side.  It would be like how the Space Shuttle leading edges used cross-radiation within the U-shaped RRC panels.  I suppose the trick would be finding a lox and hot oxygen compatible high emissivity coating that's also simple to apply to the large steel plates before they are welded into rings, or even better after stacking.
A sodium dichromate wash applied to one side of the steel before coiling produces a robust black burnished surface and doesn't affect welding. The surface burnish doesn't flake and it's compatable with pure oxygen.  It's actually even used to passify stainless steel to make it more corrosion and chemical resistant.  I do not know if it has any problem with methane, but as far as I can tell it'd be OK.

Sodum dichromate is really nasty stuff to handle but it's also something that would be applied offsite by the stainless steel mill during production. It would likely need a custom treatment method to treat one side of the sheet but not the other (so it's not quite as simple as running the steel through a chemical bath like most passivization methods).

It is not at all practical to apply to the inside of the rings after manufacture; sodium dichromate is just too nasty to spray or wipe in place.
Title: Re: Starship heat shield
Post by: rakaydos on 05/11/2021 10:41 am
I wonder if we'll see a high emissivity applied to the inside of the propellant tanks to increase radiative heat transfer from the windward tank side to the leeward side.  It would be like how the Space Shuttle leading edges used cross-radiation within the U-shaped RRC panels.  I suppose the trick would be finding a lox and hot oxygen compatible high emissivity coating that's also simple to apply to the large steel plates before they are welded into rings, or even better after stacking.
A sodium dichromate wash applied to one side of the steel before coiling produces a robust black burnished surface and doesn't affect welding. The surface burnish doesn't flake and it's compatable with pure oxygen.  It's actually even used to passify stainless steel to make it more corrosion and chemical resistant.  I do not know if it has any problem with methane, but as far as I can tell it'd be OK.

Sodum dichromate is really nasty stuff to handle but it's also something that would be applied offsite by the stainless steel mill during production. It would likely need a custom treatment method to treat one side of the sheet but not the other (so it's not quite as simple as running the steel through a chemical bath like most passivization methods).

It is not at all practical to apply to the inside of the rings after manufacture; sodium dichromate is just too nasty to spray or wipe in place.

All the bolded sounds like it would drive up the cost of materials, so I dont think SpaceX will pursue this approach until and unless they feel the reward will match the cost.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 05/11/2021 06:59 pm
I wonder if we'll see a high emissivity applied to the inside of the propellant tanks to increase radiative heat transfer from the windward tank side to the leeward side.  It would be like how the Space Shuttle leading edges used cross-radiation within the U-shaped RRC panels.  I suppose the trick would be finding a lox and hot oxygen compatible high emissivity coating that's also simple to apply to the large steel plates before they are welded into rings, or even better after stacking.
A sodium dichromate wash applied to one side of the steel before coiling produces a robust black burnished surface and doesn't affect welding. The surface burnish doesn't flake and it's compatable with pure oxygen.  It's actually even used to passify stainless steel to make it more corrosion and chemical resistant.  I do not know if it has any problem with methane, but as far as I can tell it'd be OK.

Sodum dichromate is really nasty stuff to handle but it's also something that would be applied offsite by the stainless steel mill during production. It would likely need a custom treatment method to treat one side of the sheet but not the other (so it's not quite as simple as running the steel through a chemical bath like most passivization methods).

It is not at all practical to apply to the inside of the rings after manufacture; sodium dichromate is just too nasty to spray or wipe in place.

All the bolded sounds like it would drive up the cost of materials, so I dont think SpaceX will pursue this approach until and unless they feel the reward will match the cost.

Sodium Dichromate would also drive up the cost of insurance.  Read the MSDS

http://browardcentralscience.org/msds/s/sodium%20dichromate.pdf
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 05/11/2021 07:31 pm
With the most recent photos from the SpaceX Flickr, we can conclude that the post-landing damage on the upper-of-the-lower tile sections (don't know how to refer to it, see attached image) happened sometime post-launch. There was damage in these sections following static fire, so we know that's a harsh environment for the tiles. Launch itself doesn't appear to have damaged the tiles, so it must be something in the ascent, belly-flop, flip, or landing phases that resulted in damage. My bet would be on landing.

However, I'd expect that if they were damaged upon landing, we'd be able to see some debris on/near the pad. I've looked at several of RGV's aerial shots directly after landing, and I can't find any solid evidence of that. Not exactly dispositive, but there's that. I don't know if there are sufficiently high resolution shots available of the landing burn to determine if the tiles were already damaged by the time SN15 got below the clouds again.

Edit: noob image posting question: I made the attached image in Preview, saved as png. The forum preview is quite blurry, but clicking through it seems fine. Is there a better format/encoding to post in so that the image is small/compressed yet not blurry in the forum preview, so that casual readers don't have to click through to get the gist of the post?

Has the RGV's flyover happened befrore crews approached sn15? In the other someone may have picked up the tiles.

But I would think the damage didn't happen at the landing, since it was pretty gentle and the force on the tile is only the deceleration due to its (small) weight. I'd rather think that the damage happened during raptos re-light, the most shockfull (does this word exist? It means full of shocks ) part of the flight, maybe after the launch. The the tile part fell from over 500 m and nearly polverized.
Title: Re: Starship heat shield
Post by: WormPicker959 on 05/11/2021 08:05 pm
With the most recent photos from the SpaceX Flickr, we can conclude that the post-landing damage on the upper-of-the-lower tile sections (don't know how to refer to it, see attached image) happened sometime post-launch. There was damage in these sections following static fire, so we know that's a harsh environment for the tiles. Launch itself doesn't appear to have damaged the tiles, so it must be something in the ascent, belly-flop, flip, or landing phases that resulted in damage. My bet would be on landing.

However, I'd expect that if they were damaged upon landing, we'd be able to see some debris on/near the pad. I've looked at several of RGV's aerial shots directly after landing, and I can't find any solid evidence of that. Not exactly dispositive, but there's that. I don't know if there are sufficiently high resolution shots available of the landing burn to determine if the tiles were already damaged by the time SN15 got below the clouds again.

Edit: noob image posting question: I made the attached image in Preview, saved as png. The forum preview is quite blurry, but clicking through it seems fine. Is there a better format/encoding to post in so that the image is small/compressed yet not blurry in the forum preview, so that casual readers don't have to click through to get the gist of the post?

Has the RGV's flyover happened befrore crews approached sn15? In the other someone may have picked up the tiles.

But I would think the damage didn't happen at the landing, since it was pretty gentle and the force on the tile is only the deceleration due to its (small) weight. I'd rather think that the damage happened during raptos re-light, the most shockfull (does this word exist? It means full of shocks ) part of the flight, maybe after the launch. The the tile part fell from over 500 m and nearly polverized.

I couldn't see any tile debris from the spacex livestream shots right after landing either, so I agree that the damage-on-landing hypothesis is not supported. I suppose I'd guess the raptor relight would be my second guess, and the tile debris would have fallen quite far if that's the case. I wonder if Nomadd or BocaChicaGal have come across any tile debris in their various wanderings. I doubt they'd be utterly destroyed falling from that height, they should be fairly light with a lot of drag, so more like a block of foam than a pane of glass while falling.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 05/11/2021 08:11 pm
With the most recent photos from the SpaceX Flickr, we can conclude that the post-landing damage on the upper-of-the-lower tile sections (don't know how to refer to it, see attached image) happened sometime post-launch. There was damage in these sections following static fire, so we know that's a harsh environment for the tiles. Launch itself doesn't appear to have damaged the tiles, so it must be something in the ascent, belly-flop, flip, or landing phases that resulted in damage. My bet would be on landing.

However, I'd expect that if they were damaged upon landing, we'd be able to see some debris on/near the pad. I've looked at several of RGV's aerial shots directly after landing, and I can't find any solid evidence of that. Not exactly dispositive, but there's that. I don't know if there are sufficiently high resolution shots available of the landing burn to determine if the tiles were already damaged by the time SN15 got below the clouds again.

Edit: noob image posting question: I made the attached image in Preview, saved as png. The forum preview is quite blurry, but clicking through it seems fine. Is there a better format/encoding to post in so that the image is small/compressed yet not blurry in the forum preview, so that casual readers don't have to click through to get the gist of the post?

Has the RGV's flyover happened befrore crews approached sn15? In the other someone may have picked up the tiles.

But I would think the damage didn't happen at the landing, since it was pretty gentle and the force on the tile is only the deceleration due to its (small) weight. I'd rather think that the damage happened during raptos re-light, the most shockfull (does this word exist? It means full of shocks ) part of the flight, maybe after the launch. The the tile part fell from over 500 m and nearly polverized.

I couldn't see any tile debris from the spacex livestream shots right after landing either, so I agree that the damage-on-landing hypothesis is not supported. I suppose I'd guess the raptor relight would be my second guess, and the tile debris would have fallen quite far if that's the case. I wonder if Nomadd or BocaChicaGal have come across any tile debris in their various wanderings. I doubt they'd be utterly destroyed falling from that height, they should be fairly light with a lot of drag, so more like a block of foam than a pane of glass while falling.

Judging from the pictures, none of the brackets failed.

What's left would probably turn to dust after falling 500m
Title: Re: Starship heat shield
Post by: Kazioo on 05/11/2021 09:20 pm
Any ideas what could be the next step to solve the cracking problem?
Better vibration isolation (maybe something in the brackets)?
Different materials for the actual tiles?
We know they were testing some metallic tiles before they switched to ceramics.
Title: Re: Starship heat shield
Post by: Keldor on 05/11/2021 09:53 pm
I wonder if we'll see a high emissivity applied to the inside of the propellant tanks to increase radiative heat transfer from the windward tank side to the leeward side.  It would be like how the Space Shuttle leading edges used cross-radiation within the U-shaped RRC panels.  I suppose the trick would be finding a lox and hot oxygen compatible high emissivity coating that's also simple to apply to the large steel plates before they are welded into rings, or even better after stacking.  That or you could just let a relatively high emissivity oxide film develop as the lox tank walls heat up during the first re-entry.

I definitely expect to see some high emissivity inner coating applied to the flaps.

You don't want heat transfer between the propellant and the rest of the vehicle.  That stuff is cryogenic, and has to stay very cold at all times.  If anything, you might consider adding insulation to further reduce heat transfer.
Title: Re: Starship heat shield
Post by: Pueo on 05/11/2021 11:56 pm
I wonder if we'll see a high emissivity applied to the inside of the propellant tanks to increase radiative heat transfer from the windward tank side to the leeward side.  It would be like how the Space Shuttle leading edges used cross-radiation within the U-shaped RRC panels.  I suppose the trick would be finding a lox and hot oxygen compatible high emissivity coating that's also simple to apply to the large steel plates before they are welded into rings, or even better after stacking.  That or you could just let a relatively high emissivity oxide film develop as the lox tank walls heat up during the first re-entry.

I definitely expect to see some high emissivity inner coating applied to the flaps.

You don't want heat transfer between the propellant and the rest of the vehicle.  That stuff is cryogenic, and has to stay very cold at all times.  If anything, you might consider adding insulation to further reduce heat transfer.

During launch and cruise heat transfer between the tank walls and propellant by conduction and convection will far out strip the heat transfer by radiation from a high emissivity inner surface.  During re-entry the needed propellant will be in the header tanks, which can be wrapped with high reflectivity metal foil to significantly reduce radiative heat transfer from the primary tank walls.
Title: Re: Starship heat shield
Post by: subsolanus on 05/13/2021 04:22 pm
Here is what a gap can do:

https://space.stackexchange.com/questions/18932/any-imagery-from-shuttle-columbias-silts-pod-on-the-internet

This is from the infrared camera mounted in Columbia.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 05/13/2021 05:17 pm
Any ideas what could be the next step to solve the cracking problem?
Better vibration isolation (maybe something in the brackets)?
Different materials for the actual tiles?
We know they were testing some metallic tiles before they switched to ceramics.

I think that better brakets is the way to go. But I would be carefull speaking of the braking problem until we see a full TPS. Nearly all tile broken are in the edges.
Title: Re: Starship heat shield
Post by: thechungster on 05/13/2021 08:19 pm
Just a small and quick observation

Per the latest SN15 video by SpaceX, the missing heat shield tile on the big patch around the methane tank only came off on touchdown! Unclear about the other broken tiles down near the skirt however...
Title: Re: Starship heat shield
Post by: Slarty1080 on 05/13/2021 08:47 pm
Any ideas what could be the next step to solve the cracking problem?
Better vibration isolation (maybe something in the brackets)?
Different materials for the actual tiles?
We know they were testing some metallic tiles before they switched to ceramics.

I think that better brakets is the way to go. But I would be carefull speaking of the braking problem until we see a full TPS. Nearly all tile broken are in the edges.
Given that the tiles on the orbital prototype will be in a different vibrational environment from those on the prototypes seen to date. I wouldn't be surprised to see them try exactly the same unmodified tiles across the entire windward surface on SN20 just to see if it works.
Title: Re: Starship heat shield
Post by: Reynold on 05/14/2021 01:07 pm
I'm curious whether there is a way to get data while the Starship prototype is reentering?  I know normally there is the plasma generated that makes communication hard, if not impossible, which could make it hard to tell if a failure on reentry is the heat shield, or control system, or what. 

Do we know if they can communicate with Cargo or Crew dragon during reentry now? 
Title: Re: Starship heat shield
Post by: Alvian@IDN on 05/14/2021 01:14 pm
I'm curious whether there is a way to get data while the Starship prototype is reentering?  I know normally there is the plasma generated that makes communication hard, if not impossible, which could make it hard to tell if a failure on reentry is the heat shield, or control system, or what. 

Do we know if they can communicate with Cargo or Crew dragon during reentry now?
They're gonna using the NASA plane chartered fr Vandenberg to collect the reentry data over the Pacific
Title: Re: Starship heat shield
Post by: steveleach on 05/14/2021 01:15 pm
I'm curious whether there is a way to get data while the Starship prototype is reentering?  I know normally there is the plasma generated that makes communication hard, if not impossible, which could make it hard to tell if a failure on reentry is the heat shield, or control system, or what. 

Do we know if they can communicate with Cargo or Crew dragon during reentry now?
I thought that was the point of using a Starlink terminal for comms on Starship; it is on the "back" of the vehicle, pointing upwards through the gap in the plasma behind the vehicle.

Dragon doesn't have Starlink on it as far as I'm aware.
Title: Re: Starship heat shield
Post by: maquinsa on 05/14/2021 01:15 pm
I'm curious whether there is a way to get data while the Starship prototype is reentering?  I know normally there is the plasma generated that makes communication hard, if not impossible, which could make it hard to tell if a failure on reentry is the heat shield, or control system, or what. 

Do we know if they can communicate with Cargo or Crew dragon during reentry now?

Don’t know about cargo dragon but crew 1 had a blackout during entry
Title: Re: Starship heat shield
Post by: cscott on 05/14/2021 03:54 pm
They can use NASA TDRS as an orbital relay to transmit through the plasma hole behind the vehicle.
Title: Re: Starship heat shield
Post by: Redclaws on 05/14/2021 04:08 pm
They can use NASA TDRS as an orbital relay to transmit through the plasma hole behind the vehicle.

If so, why didn’t they last time?
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 05/14/2021 04:29 pm
I never understood how (please explain me if you know), but the shuttle had nearly continuose telemetry during reentry.
Title: Re: Starship heat shield
Post by: cscott on 05/14/2021 04:49 pm
The shape of the capsule limits the size of the plasma "hole" on the lee side.  It's still possible that no TDRS satellite is viewable through the hole.  Shuttle was big and broad giving much better viewing angles behind the plasma sheath.

Starship is expected to reenter broad side down, so it should have decent viewing angles. The flaps may be tucked in, though, so that it will probably have much better viewing lengthwise than widthwise.  A lot depends on exactly where the TDRS (and starlink) birds are.  Starlink should actually be "better" since they are moving so there should be at least snatches of time they are visible through the plasma hole.

More details: https://urgentcomm.com/2003/03/01/shuttle-blackout-myth-persists/
Title: Re: Starship heat shield
Post by: OTV Booster on 05/14/2021 05:03 pm
I'm curious whether there is a way to get data while the Starship prototype is reentering?  I know normally there is the plasma generated that makes communication hard, if not impossible, which could make it hard to tell if a failure on reentry is the heat shield, or control system, or what. 

Do we know if they can communicate with Cargo or Crew dragon during reentry now?
They're gonna using the NASA plane chartered fr Vandenberg to collect the reentry data over the Pacific
Is this fact or surmise?
Title: Re: Starship heat shield
Post by: eriblo on 05/14/2021 05:20 pm
I'm curious whether there is a way to get data while the Starship prototype is reentering?  I know normally there is the plasma generated that makes communication hard, if not impossible, which could make it hard to tell if a failure on reentry is the heat shield, or control system, or what. 

Do we know if they can communicate with Cargo or Crew dragon during reentry now?
They're gonna using the NASA plane chartered fr Vandenberg to collect the reentry data over the Pacific
Is this fact or surmise?
My guess is slight extrapolation from the 2020 ACO selections: (https://www.nasa.gov/directorates/spacetech/2020_NASA_Announcement_of_Collaboration_Opportunity_ACO_Selections)
Quote
Space Exploration Technologies Corp. (SpaceX) of Hawthorne, California
SpaceX will partner with Langley to capture imagery and thermal measurements of its Starship vehicle during orbital re-entry over the Pacific Ocean. With the data, the company plans to advance a reusable thermal protection system, which protects the vehicle from aerodynamic heating, for missions returning from low-Earth orbit, the Moon, and Mars.
Title: Re: Starship heat shield
Post by: Greg Hullender on 05/18/2021 02:30 pm
It's actually mathematically impossible to tile a rounded cone with any sort of uniform warped hexagon.  If you try it, you'll find that it works alright at the beginning, but as the surface continues curving, your hexagons will become more and more distorted until you're forced to add pentagons to the mix.  This is a direct consequence of the Euler Identity.

There's just no way to avoid requiring a large number of different tile shapes when trying to tile a surface with non-zero curvature.  (A cylinder has, mathematically speaking, zero curvature, just to be clear on this.  Not so for a rounded cone)
This is true if the tiles must abut each other with no gaps, but if small gaps are allowed between the tiles, that's the same as inserting arbitrary small polygons. This is a bit like a "Missing-Square Puzzle (https://en.wikipedia.org/wiki/Missing_square_puzzle)." The question is how large the gaps can be and still have a workable heat shield.
Title: Re: Starship heat shield
Post by: BT52 on 05/18/2021 02:39 pm
Good point about missing triangles. But it's quite mood point. Just made unique cone and wing edges and call it a day. Especially if they will keep snap on attachment method. That's is most intriguing for me. To save couple of tiles just to play with gaps doesn't seems good for me. Especially when we know unique tiles will have massive heat peaks. Elerons leading and failing edge. Also hinge cover and nose tip will be heat zones of interest.
Title: Re: Starship heat shield
Post by: ETurner on 05/18/2021 03:18 pm
This is true if the tiles must abut each other with no gaps, but if small gaps are allowed between the tiles, that's the same as inserting arbitrary small polygons.
I don’t see how this can work on a nosecone with substantial curvature.

If gaps are small compared to tiles, then each hexagon will be at the intersection of three rows of hexagons aligned with and extending more-or-less perpendicularly from its sides. The same is true for the hexagons in those rows, and the result is a grid. If we allow small gaps, the grid can stretch and curve to some extent, but it has to stretch a lot unless the shape is nearly flat (cones and cylinders are flat in this sense -- they have zero Gaussian curvature (https://en.wikipedia.org/wiki/Gaussian_curvature)). To see how there might be an inescapable problem, imagine trying to paste a grid to a hemisphere without cutting or folding it at the edges, or stretching the middle by a large factor.

Trapezoidal tiles can avoid this problem because they don’t have to align in all directions. Think of the nosecone as a distorted globe with its pole at the tip and the transition to a cylinder at the equator. Trapezoidal tiles of fixed height and base-width can fill bands of latitude without gaps lining up to form lines of longitude (therefore, there are no lines that must converge toward the pole). Tiling a cone does require a range of shapes with different convergence angles, but if we allow small gaps, each shape can be used in rows that cover a moderate range of latitudes.

Hexagons can’t do this because they must align side-to-side with neighbors in all directions: “lines of latitude” are jagged and force alignments that stretch from equator to pole -- in effect, lines of longitude.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 05/18/2021 04:15 pm
I tried to understand this more mathematical discussion, but it was a bit too complicate for me, but it is actually very intersting.

My questions are:

1)does this need for many different tiles in the nosecone kill the principia of having everywere the same tiles onto SS, to simplify installation and eventual repairs (so not having to carry one exact copy of every tile, like if evry tille was different)?
2)How could having a lot of different tiles impact their manufacturing?
Title: Re: Starship heat shield
Post by: Slarty1080 on 05/18/2021 08:08 pm
I tried to understand this more mathematical discussion, but it was a bit too complicate for me, but it is actually very intersting.

My questions are:

1)does this need for many different tiles in the nosecone kill the principia of having everywere the same tiles onto SS, to simplify installation and eventual repairs (so not having to carry one exact copy of every tile, like if evry tille was different)?
2)How could having a lot of different tiles impact their manufacturing?
I think these issues have already been discussed several times on this thread. It is sometimes difficult to visualize what is being discussed, but I suggest my original (simplified) tile picture in post 1 of this thread is probably still a reasonable guess as to a likely configuration for the nose cone (I would be interested if anyone thinks it wouldn't work and why). If this pattern is chosen then the manufacturing of each latitude type of tile is just a matter of milling / cutting two opposite edges at an angle suitable for that latitude. If needed it would also be possible to reduce the length of the tiles as well but this would require more cuts.
Title: Re: Starship heat shield
Post by: ETurner on 05/18/2021 09:18 pm
I tried to understand this more mathematical discussion, but it was a bit too complicate for me, but it is actually very intersting.

My questions are:

1)does this need for many different tiles in the nosecone kill the principia of having everywere the same tiles onto SS, to simplify installation and eventual repairs (so not having to carry one exact copy of every tile, like if evry tille was different)?
2)How could having a lot of different tiles impact their manufacturing?
I think these issues have already been discussed several times on this thread. It is sometimes difficult to visualize what is being discussed, but I suggest my original (simplified) tile picture in post 1 of this thread is probably still a reasonable guess as to a likely configuration for the nose cone (I would be interested if anyone thinks it wouldn't work and why). If this pattern is chosen then the manufacturing of each latitude type of tile is just a matter of milling / cutting two opposite edges at an angle suitable for that latitude. If needed it would also be possible to reduce the length of the tiles as well but this would require more cuts.
The scheme you show is geometrically sound, but the proportions don’t reflect the large ratio between a (reasonable) nose-cap circumference and the (actual) bottom-of-cone circumference. A large ratio would force the tiles near the top to be much slimmer than those near the bottom. Any of several schemes could remedy this, but would require breaking the alignment of hexagons at various latitude lines. The trapezoid scheme drops alignment completely at all latitudes.

In any of these schemes, the number of distinct tile shapes on the nosecone can be substantially less the number of rows, which is a far cry from the thousands upon thousands of unique tiles on Shuttle.

The ugly sketch below illustrates features of a trapezoid scheme showing 4 rows with 2 tile shapes. Actual fits could be better -- perfect if N(tile-shapes) = N(rows).
Title: Re: Starship heat shield
Post by: Slarty1080 on 05/18/2021 09:49 pm
I tried to understand this more mathematical discussion, but it was a bit too complicate for me, but it is actually very intersting.

My questions are:

1)does this need for many different tiles in the nosecone kill the principia of having everywere the same tiles onto SS, to simplify installation and eventual repairs (so not having to carry one exact copy of every tile, like if evry tille was different)?
2)How could having a lot of different tiles impact their manufacturing?
I think these issues have already been discussed several times on this thread. It is sometimes difficult to visualize what is being discussed, but I suggest my original (simplified) tile picture in post 1 of this thread is probably still a reasonable guess as to a likely configuration for the nose cone (I would be interested if anyone thinks it wouldn't work and why). If this pattern is chosen then the manufacturing of each latitude type of tile is just a matter of milling / cutting two opposite edges at an angle suitable for that latitude. If needed it would also be possible to reduce the length of the tiles as well but this would require more cuts.
The scheme you show is geometrically sound, but the proportions don’t reflect the large ratio between a (reasonable) nose-cap circumference and the (actual) bottom-of-cone circumference. A large ratio would force the tiles near the top to be much slimmer than those near the bottom. Any of several schemes could remedy this, but would require breaking the alignment of hexagons at various latitude lines. The trapezoid scheme drops alignment completely at all latitudes.

In any of these schemes, the number of distinct tile shapes on the nosecone can be substantially less the number of rows, which is a far cry from the thousands upon thousands of unique tiles on Shuttle.

The ugly sketch below illustrates features of a trapezoid scheme showing 4 rows with 2 tile shapes. Actual fits could be better -- perfect if N(tile-shapes) = N(rows).
Yes correct my scheme only shows a small fragment of the required circumference to save space. And also true that the tiles near the top would be a lot narrower all other things being equal. But this arrangement allows a uniform gap between tiles to be maintained under all circumstances.

Your pattern does allow some flexibility in how the tiles may be used but at the cost of variable tile gaps and the potential risk of vertical gap alignments between latitude rings.
Title: Re: Starship heat shield
Post by: ETurner on 05/18/2021 09:59 pm

Yes correct my scheme only shows a small fragment of the required circumference to save space. And also true that the tiles near the top would be a lot narrower all other things being equal. But this arrangement allows a uniform gap between tiles to be maintained under all circumstances.

Your pattern does allow some flexibility in how the tiles may be used but at the cost of variable tile gaps and the potential risk of vertical gap alignments between latitude rings.
If we allow one shape per row (as in your hex-tile illustration), the trapezoidal scheme likewise allows uniform gaps.

Hot gas flow into grooves formed by aligned gaps seems like the key question. Avoiding this has been a stated advantage of hexagonal tile schemes (no long straight grooves); how important this is now that the tiles will be backed by a ceramic blanket seems unclear without better computational fluid dynamics and heat transfer calculations than I can do in my head (which clearly needs a major upgrade).
Title: Re: Starship heat shield
Post by: Greg Hullender on 05/18/2021 10:31 pm
This is true if the tiles must abut each other with no gaps, but if small gaps are allowed between the tiles, that's the same as inserting arbitrary small polygons.
I don’t see how this can work on a nosecone with substantial curvature.

.
.
.

Trapezoidal tiles can avoid this problem because they don’t have to align in all directions. . . . Tiling a cone does require a range of shapes with different convergence angles, but if we allow small gaps, each shape can be used in rows that cover a moderate range of latitudes.

Hexagons can’t do this because they must align side-to-side with neighbors in all directions: “lines of latitude” are jagged and force alignments that stretch from equator to pole -- in effect, lines of longitude.
Oh I'm not saying all the tiles have to be the same or even that they all have to be hexagons. I'm just saying that if there is at least some allowable amount of gap then you can reduce the number of unique tiles simply by tolerating some amount of gap. You appear to be saying much the same thing in a different way.

Your picture with the trapezoids is a nice illustration of one way to do it with, as you say, N unique shapes for the nose (hopefully N < 10 or so) plus (presumably) one shape (a square?) for the body and a unique tile for the nose.

To avoid the problem of long channels, I wonder if someone can accomplish much the same thing your trapezoids do with a limited set of (say) hexagons and pentagons? Again, a key question is how much gap can be tolerated.

Title: Re: Starship heat shield
Post by: ETurner on 05/18/2021 10:48 pm

To avoid the problem of long channels, I wonder if someone can accomplish much the same thing your trapezoids do with a limited set of (say) hexagons and pentagons? Again, a key question is how much gap can be tolerated.
Hexagons + pentagons + heptagons can do the job, covering curved surfaces with some trade-off of number of shapes vs. uniformity of gaps. If straight channels are out, then this kind of scheme might be attractive.

The pentagons and heptagons go together as follows:
Title: Re: Starship heat shield
Post by: Redclaws on 05/18/2021 11:06 pm

To avoid the problem of long channels, I wonder if someone can accomplish much the same thing your trapezoids do with a limited set of (say) hexagons and pentagons? Again, a key question is how much gap can be tolerated.
Hexagons + pentagons + heptagons can do the job, covering curved surfaces with some trade-off of number of shapes vs. uniformity of gaps. If straight channels are out, then this kind of scheme might be attractive.

The pentagons and heptagons go together as follows:

It seems fairly clear that SpaceX is OK with some amount of gap + liner in the gaps.  How much do they actually need to "stretch" that to make the tiles fit?  Especially if they're willing to do things like trim off part of (half of?) one of their existing tiles.

That seems more likely than making multiple shapes?
Title: Re: Starship heat shield
Post by: leovinus on 05/18/2021 11:11 pm
This is true if the tiles must abut each other with no gaps, but if small gaps are allowed between the tiles, that's the same as inserting arbitrary small polygons.
I don’t see how this can work on a nosecone with substantial curvature.

.
.
.

Trapezoidal tiles can avoid this problem because they don’t have to align in all directions. . . . Tiling a cone does require a range of shapes with different convergence angles, but if we allow small gaps, each shape can be used in rows that cover a moderate range of latitudes.

Hexagons can’t do this because they must align side-to-side with neighbors in all directions: “lines of latitude” are jagged and force alignments that stretch from equator to pole -- in effect, lines of longitude.
Oh I'm not saying all the tiles have to be the same or even that they all have to be hexagons. I'm just saying that if there is at least some allowable amount of gap then you can reduce the number of unique tiles simply by tolerating some amount of gap. You appear to be saying much the same thing in a different way.

Your picture with the trapezoids is a nice illustration of one way to do it with, as you say, N unique shapes for the nose (hopefully N < 10 or so) plus (presumably) one shape (a square?) for the body and a unique tile for the nose.

To avoid the problem of long channels, I wonder if someone can accomplish much the same thing your trapezoids do with a limited set of (say) hexagons and pentagons? Again, a key question is how much gap can be tolerated.

At the risk of being trampled on (again) but if you are concerned about long channels et al then have you considered aperiodic Penrose tiling (https://en.m.wikipedia.org/wiki/Penrose_tiling)? Visit the Alhambra castle in Granada in Spain and your tiling will never be the same.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 05/19/2021 01:32 am
It's actually mathematically impossible to tile a rounded cone with any sort of uniform warped hexagon.  If you try it, you'll find that it works alright at the beginning, but as the surface continues curving, your hexagons will become more and more distorted until you're forced to add pentagons to the mix.  This is a direct consequence of the Euler Identity.

There's just no way to avoid requiring a large number of different tile shapes when trying to tile a surface with non-zero curvature.  (A cylinder has, mathematically speaking, zero curvature, just to be clear on this.  Not so for a rounded cone)
This is true if the tiles must abut each other with no gaps, but if small gaps are allowed between the tiles, that's the same as inserting arbitrary small polygons. This is a bit like a "Missing-Square Puzzle (https://en.wikipedia.org/wiki/Missing_square_puzzle)." The question is how large the gaps can be and still have a workable heat shield.

In terms of tiles, it might be helpful to define "large" number, "large" being agonizing for the manufacturing or maintenance process 45 meters up in the air.

One type of tile is ideal.  2 or 3 types is okay.  Any more than that a human can't easily reach he other stack of tiles and slows down, though (on the ground at least) a rotating mechanism and movable racks can make than number larger.

So anything more than 3-5 types of tiles will make manufacturing and maintenance painful.   A good goal would be no more than 3 types of tiles.

Another constraint is being able to fit a triangle bracket inside the tile (the tile's real job is to protect the bracket and the bracket keeps the blanket in place).

another constraint is no continuous lines that allow plasma to build up.

So, what 3 shapes of tiles will satisfy these three constraints?
Title: Re: Starship heat shield
Post by: InterestedEngineer on 05/19/2021 01:35 am

To avoid the problem of long channels, I wonder if someone can accomplish much the same thing your trapezoids do with a limited set of (say) hexagons and pentagons? Again, a key question is how much gap can be tolerated.
Hexagons + pentagons + heptagons can do the job, covering curved surfaces with some trade-off of number of shapes vs. uniformity of gaps. If straight channels are out, then this kind of scheme might be attractive.

The pentagons and heptagons go together as follows:

3 types of tiles + 1 for the ends.

no continuous lines prevents plasma build up

tri-bracket fits inside of tile.

looks like a winner to me.

Title: Re: Starship heat shield
Post by: Nascent Ascent on 05/19/2021 01:38 am
Are they limited to only making planar tiles of a certain size?  Could they make large multi-curved surfaces?

Are these tiles sintered or processed in a chamber that would limit the size?
Title: Re: Starship heat shield
Post by: xvel on 05/19/2021 01:55 am
they can't be big because of different thermal expansion coefficient of steel and tile material.
Title: Re: Starship heat shield
Post by: livingjw on 05/19/2021 03:46 am
they can't be big because of different thermal expansion coefficient of steel and tile material.

Their brittleness and low strength also limits their size.

John
Title: Re: Starship heat shield
Post by: KBK on 05/19/2021 12:51 pm
they can't be big because of different thermal expansion coefficient of steel and tile material.

Their brittleness and low strength also limits their size.

John

Which indicates a need for vibrational stability, load evenness, and structured support backing of some sort...

...where the structured support backing has issues with the thermal expansion. Which means the coupling cannot be as (mechanically) tight/intimate as one desires. Known or expected solutions tend to be invalidated by the more fully realized set of variables in this equation.

Overall, a pile of bits of data which don't jibe with one another in the real world of implementation in said real world. Nothing new in the real world (implementation part of) of engineering, it seems. There's always a head scratcher available for those who want to take on the horror of the given difficult job.

Functional end points in such rumination tends to amuse me, as many times answers found take on the form of the old saw: "intelligence is applied laziness".
Title: Re: Starship heat shield
Post by: ETurner on 05/19/2021 01:05 pm
[tiles] can't be big because of different thermal expansion coefficient of steel and tile material.

• Yes, where metal is embedded in tiles, differential expansion is a problem.

But, rigid kinematic constraints on tile positions are fully compatible with any amount of differential expansion between the tiles and the surface:

A fun fact of geometry:
Y-shaped grooves (uniquely) accommodate arbitrary mounting-pin displacements: For any pin displacement, there is a tile position that fits and is fully constrained. With this constraint system, expansion and bending of mounting surfaces neither stress nor loosen tiles.
https://en.wikipedia.org/wiki/Kinematic_coupling (https://en.wikipedia.org/wiki/Kinematic_coupling)
Title: Re: Starship heat shield
Post by: edzieba on 05/19/2021 01:10 pm
Note that that kinematic relationship only holds for planar expansion. Sadly, Starship is a combination of singly-curved and doubly-curved surfaces, so the infinite-flat-plane Starship can comfortably re-enter above the planet of spherical cows, but the real-world Starship isn't so lucky and has to deal with the pin Z displacement strain even if the internal clips are free to slide independently in X and Y.
Title: Re: Starship heat shield
Post by: tenkendojo on 05/19/2021 01:57 pm
they can't be big because of different thermal expansion coefficient of steel and tile material.

Their brittleness and low strength also limits their size.

John

Would it be possible to reinforce the tiles with some sort of embedded glass fibre mesh to reduce it's brittleness? IIRC glass fibre could withstand up to 1,200 C temperature, not sure if that's sufficient for reinforcing heat tiles.
Title: Re: Starship heat shield
Post by: ETurner on 05/19/2021 02:51 pm
Note that that kinematic relationship only holds for planar expansion.
Why?
As an analogy, consider that three points define a plane, but will also define the position (aside from a mirror reflection) of any sphere large enough for one hemisphere to touch all of them.
Title: Re: Starship heat shield
Post by: Tangilinear Interjar on 05/19/2021 03:30 pm
It seems to me that whatever the complex tiling scheme they choose to use it will consist of hexagrams only as that's the only shape they have tested. (Of course aside from the edge pieces.)

If they were considering some other shapes I expect they would have tested them. Just the structure of the Y with relation to a quadrilateral could be an issue.
Title: Re: Starship heat shield
Post by: Slarty1080 on 05/19/2021 03:46 pm

To avoid the problem of long channels, I wonder if someone can accomplish much the same thing your trapezoids do with a limited set of (say) hexagons and pentagons? Again, a key question is how much gap can be tolerated.
Hexagons + pentagons + heptagons can do the job, covering curved surfaces with some trade-off of number of shapes vs. uniformity of gaps. If straight channels are out, then this kind of scheme might be attractive.

The pentagons and heptagons go together as follows:
I don't think it would work as drawn because the areas of hexagons to either side of centre line T won't tessellate on a curved surface. One way round that would be to have additional non hexagonal tiles at intervals around the circumference (possibly what you intended?) but regular pentagons and heptagons won't fit. Irregular pentagons and heptagons could fit, but as the curvature of the nose changes and becomes steeper the pentagons and heptagons will need to change in shape to accommodate the change in geometry.
Title: Re: Starship heat shield
Post by: ETurner on 05/19/2021 05:38 pm

To avoid the problem of long channels, I wonder if someone can accomplish much the same thing your trapezoids do with a limited set of (say) hexagons and pentagons? Again, a key question is how much gap can be tolerated.
Hexagons + pentagons + heptagons can do the job, covering curved surfaces with some trade-off of number of shapes vs. uniformity of gaps. If straight channels are out, then this kind of scheme might be attractive.

The pentagons and heptagons go together as follows:
I don't think it would work as drawn because the areas of hexagons to either side of centre line T won't tessellate on a curved surface. One way round that would be to have additional non hexagonal tiles at intervals around the circumference (possibly what you intended?) but regular pentagons and heptagons won't fit. Irregular pentagons and heptagons could fit, but as the curvature of the nose changes and becomes steeper the pentagons and heptagons will need to change in shape to accommodate the change in geometry.
Yes, with the scheme above there is still a trade-off between reducing the number of tile shapes and reducing the variation in gap widths. Three shapes is probably not enough to provide a good fit, and as you suggest, the optimal pentagons and heptagons would in any case be asymmetric to fit their asymmetric contexts. To improve the fit, the next tiles to distort would probably be hexagons that touch both a pentagon and heptagon.
--------------------------
There is, however, a different heptagon/pentagon tweak that fits well with your initial all-hex diagram and allows uniform gaps -- no trade-off -- with about the same number of tile shapes. If aligned gaps (forming long, straight grooves) must be avoided, this hybrid scheme would be my current favorite. It is almost as tidy as a one-shape-per-row trapezoid scheme, but all the grooves zig-zag.The very ugly diagram below shows the geometric principle: Rows of hexagons continue from north to south, growing wider until a tile-width reset, which requires one row of heptagons and one row of alternating hexagons and pentagons before hexagons resume.

(The 5-6-7 width-reset bands would be high up the side where the circumference starts to shrink rapidly.)
Title: Re: Starship heat shield
Post by: Slarty1080 on 05/19/2021 06:09 pm

To avoid the problem of long channels, I wonder if someone can accomplish much the same thing your trapezoids do with a limited set of (say) hexagons and pentagons? Again, a key question is how much gap can be tolerated.
Hexagons + pentagons + heptagons can do the job, covering curved surfaces with some trade-off of number of shapes vs. uniformity of gaps. If straight channels are out, then this kind of scheme might be attractive.

The pentagons and heptagons go together as follows:
I don't think it would work as drawn because the areas of hexagons to either side of centre line T won't tessellate on a curved surface. One way round that would be to have additional non hexagonal tiles at intervals around the circumference (possibly what you intended?) but regular pentagons and heptagons won't fit. Irregular pentagons and heptagons could fit, but as the curvature of the nose changes and becomes steeper the pentagons and heptagons will need to change in shape to accommodate the change in geometry.
Yes, with the scheme above there is still a trade-off between reducing the number of tile shapes and reducing the variation in gap widths. Three shapes is probably not enough to provide a good fit, and as you suggest, the optimal pentagons and heptagons would in any case be asymmetric to fit their asymmetric contexts. To improve the fit, the next tiles to distort would probably be hexagons that touch both a pentagon and heptagon.
--------------------------
There is, however, a different heptagon/pentagon tweak that fits well with your initial all-hex diagram and allows uniform gaps -- no trade-off -- with about the same number of tile shapes. If aligned gaps (forming long, straight grooves) must be avoided, this hybrid scheme would be my current favorite. It is almost as tidy as a one-shape-per-row trapezoid scheme, but all the grooves zig-zag.The very ugly diagram below shows the geometric principle: Rows of hexagons continue from north to south, growing wider until a tile-width reset, which requires one row of heptagons and one row of alternating hexagons and pentagons before hexagons resume.

(The 5-6-7 width-reset bands would be high up the side where the circumference starts to shrink rapidly.)
I must say I am intrigued by your diagram, but I can’t visualize it in its finished form. The trouble is that 3 dimensional tiling geometry is not easy (at least not for me).

If you can describe it very clearly in words I will try to build a paper model. Note there should be gaps in between some of the tiles in a 2D projection as the circumference decreases towards the top of the nose so each “latitude” of tiles will need fewer tiles or smaller tiles.
 
Title: Re: Starship heat shield
Post by: ETurner on 05/19/2021 06:54 pm
I must say I am intrigued by your diagram, but I can’t visualize it in its finished form. The trouble is that 3 dimensional tiling geometry is not easy (at least not for me).

If you can describe it very clearly in words I will try to build a paper model. Note there should be gaps in between some of the tiles in a 2D projection as the circumference decreases towards the top of the nose so each “latitude” of tiles will need fewer tiles or smaller tiles.
Here’s an attempt at a description:

Imagine that all the polygons are neatened up to be identical along latitude-rows (which form circular arcs in the diagram). Extend the pattern to add more meridians (the radial lines in the diagram) and latitude rows (where there is a choice of 6, 7, and (5,6) rows).   Imagine that the pattern is printed on a rubber sheet. Stretch the sheet around the nosecone, revising it to place the 7+(5,6) bands at latitudes where the hexagons would become too crowded toward the nose or to stretched toward the bottom. (Note that the hexagons toward the center of the diagram span twice as many lines of longitude as the hexagons further out.)

Does that make a useful mental image?

To make a non-stretchable paper model would of course require translating this geometry into polygon dimensions that fit the varying circumference and convergence-angles of longitude-lines as they run up the side.
Title: Re: Starship heat shield
Post by: livingjw on 05/19/2021 08:01 pm
they can't be big because of different thermal expansion coefficient of steel and tile material.

Their brittleness and low strength also limits their size.

John

Would it be possible to reinforce the tiles with some sort of embedded glass fibre mesh to reduce it's brittleness? IIRC glass fibre could withstand up to 1,200 C temperature, not sure if that's sufficient for reinforcing heat tiles.

They are made up of silica fibers (and small amounts of other elements) sparsely bonded together so that their volume is ~90% void. They are weak and light because they are mostly made up of nothing.

John
Title: Re: Starship heat shield
Post by: Robotbeat on 05/19/2021 08:17 pm
they can't be big because of different thermal expansion coefficient of steel and tile material.

Their brittleness and low strength also limits their size.

John

Would it be possible to reinforce the tiles with some sort of embedded glass fibre mesh to reduce it's brittleness? IIRC glass fibre could withstand up to 1,200 C temperature, not sure if that's sufficient for reinforcing heat tiles.

They are made up of silica fibers (and small amounts of other elements) sparsely bonded together so that their volume is ~90% void. They are weak and light because they are mostly made up of nothing.

John
The Shuttle tiles are like that, but I thought these tiles were much denser and thinner.

Still brittle, but not styrofoam.
Title: Re: Starship heat shield
Post by: pjm1 on 05/19/2021 08:23 pm
Apologies if this has already been suggested and discounted - I've lost track in this and possibly other threads...

What is the problem with simply using equilateral and slightly narrower isosceles triangles on the ogive?  If the equilaterals are "A" or "V" and the narrower isosc triangles are v then at the bottom (near cylinder) you could us a tessellation like:

AVAVAVAVAVAvAVAVAVAVAVAVAVAVAVAVAVAvAVAVAVAVAVA (for example)

whereas next to the nose you might use:

AvAvAvAvAvAvAv (again, as an example).

You'd pick the width of the isosc triangle such that it perfectly fits alongside the circumference of the nose protector.  You then use fewer isosc triangles as you progress down towards the cylinder part of the ogive as the angle of curvature loosens off.

Sorry for poor terminology but hopefully you get what I mean.  You might be able to get the packing close enough such that there aren't circumferential gap lines??

edited for some missing "V"s in my first illustration!
Title: Re: Starship heat shield
Post by: livingjw on 05/19/2021 08:27 pm
they can't be big because of different thermal expansion coefficient of steel and tile material.

Their brittleness and low strength also limits their size.

John

Would it be possible to reinforce the tiles with some sort of embedded glass fibre mesh to reduce it's brittleness? IIRC glass fibre could withstand up to 1,200 C temperature, not sure if that's sufficient for reinforcing heat tiles.

They are made up of silica fibers (and small amounts of other elements) sparsely bonded together so that their volume is ~90% void. They are weak and light because they are mostly made up of nothing.

John
The Shuttle tiles are like that, but I thought these tiles were much denser and thinner.

Still brittle, but not styrofoam.

- Shuttle silica tile were made in a range densities from ~8 to ~22 lbs/ft^3

John
Title: Re: Starship heat shield
Post by: Slarty1080 on 05/19/2021 08:40 pm
I must say I am intrigued by your diagram, but I can’t visualize it in its finished form. The trouble is that 3 dimensional tiling geometry is not easy (at least not for me).

If you can describe it very clearly in words I will try to build a paper model. Note there should be gaps in between some of the tiles in a 2D projection as the circumference decreases towards the top of the nose so each “latitude” of tiles will need fewer tiles or smaller tiles.
Here’s an attempt at a description:

Imagine that all the polygons are neatened up to be identical along latitude-rows (which form circular arcs in the diagram). Extend the pattern to add more meridians (the radial lines in the diagram) and latitude rows (where there is a choice of 6, 7, and (5,6) rows).   Imagine that the pattern is printed on a rubber sheet. Stretch the sheet around the nosecone, revising it to place the 7+(5,6) bands at latitudes where the hexagons would become too crowded toward the nose or to stretched toward the bottom. (Note that the hexagons toward the center of the diagram span twice as many lines of longitude as the hexagons further out.)

Does that make a useful mental image?

To make a non-stretchable paper model would of course require translating this geometry into polygon dimensions that fit the varying circumference and convergence-angles of longitude-lines as they run up the side.
I think I can visualize what you are trying to do now but I suspect there will be many more tile sizes than you think. Won’t the hexagons in the lowest layer be slightly larger than those in the next layer up? And won’t the hexagons in that layer be slightly larger than those in the next layer above that (the hexagon / pentagon layer)?

The hexagons in the top layer could match the size of hexagons from other layers as they cover more meridian lines, but it is unlikely to be nearby layers as they will be much larger covering twice the radius.

In planning how I might model my own tile plan I discovered that the slope is actually fairly gentle. If the tiles are roughly 25cm in diameter and the curved part of the nose cone is roughly 12m tall there are roughly 48 latitude rows of tiles. This means that the meridian lines will be much closer to parallel and the deviation between each layer will be slight.
Title: Re: Starship heat shield
Post by: Slarty1080 on 05/19/2021 08:45 pm
In trying to model some different tile plans I have identified two related aspects that I had not considered before:

What is a reasonable limit on the ratio of length to width for a tile* and what is a reasonable minimum number of tiles to use in a layer around the 180 degrees of heat shield to properly approximate a circular cross section**?

*I’m proposing that the number of tiles in a layer remains constant in every layer of the nose cone. The consequence of this is that the tiles will become narrower and narrower towards the pinnacle/nose tip piece. This might be a problem.
 
** The fewer tiles used in a layer around the circumference layer the wider they can be, but the poorer the fit will be to a circle. For example if only 3 tiles were chosen to stretch around the half circle of the heat shield that the overall cross sectional shape at that point would be more like a hexagon than a circle (Assuming flat tiles are used in all cases note).

I also need to estimate the size of the standard tiles: From the videos a while back very roughly I would say 25cm across? And the height of the curved Nose cone section ~ 12m high (variable curvature)?
Title: Re: Starship heat shield
Post by: ETurner on 05/19/2021 09:00 pm
I think I can visualize what you are trying to do now but I suspect there will be many more tile sizes than you think. Won’t the hexagons in the lowest layer be slightly larger than those in the next layer up? And won’t the hexagons in that layer be slightly larger than those in the next layer above that (the hexagon / pentagon layer)?
Yes. The taper of the nosecone requires different tile widths at different heights. Almost the same number of tile-types would be required by this scheme and the all-hex scheme that you presented at the top of the thread: One type per row (aside from using two types in a few (5,6) rows).
Title: Re: Starship heat shield
Post by: Slarty1080 on 05/19/2021 11:07 pm
Apologies if this has already been suggested and discounted - I've lost track in this and possibly other threads...

What is the problem with simply using equilateral and slightly narrower isosceles triangles on the ogive?  If the equilaterals are "A" or "V" and the narrower isosc triangles are v then at the bottom (near cylinder) you could us a tessellation like:

AVAVAVAVAVAvAVAVAVAVAVAVAVAVAVAVAVAvAVAVAVAVAVA (for example)

whereas next to the nose you might use:

AvAvAvAvAvAvAv (again, as an example).

You'd pick the width of the isosc triangle such that it perfectly fits alongside the circumference of the nose protector.  You then use fewer isosc triangles as you progress down towards the cylinder part of the ogive as the angle of curvature loosens off.

Sorry for poor terminology but hopefully you get what I mean.  You might be able to get the packing close enough such that there aren't circumferential gap lines??

edited for some missing "V"s in my first illustration!
Well yes I think it works from a tile tessellation perspective. Equilateral triangles on their own would also work on the main cylindrical body of starship, but they have decided to use hexagons instead. I wonder if triangles pose breakage problems with their acute angles?
Title: Re: Starship heat shield
Post by: Reynold on 05/20/2021 03:38 am
I got to see a demo of a Shuttle tile once, the person doing the demo could put a blow torch on the front of the tile until it glowed while holding the tile in his hand, set down the torch, and put his free hand on the front of the tile which had already cooled enough to allow it.  Then it was passed around, and it did actually feel a lot like styrofoam weight-wise.  Amazing material, pity it was so fragile. 

I also read that the weight of the paperwork that documented a Shuttle's tiles (manufacturing history, placement, etc.) weighed more than the Shuttle.  For the Starship, I just suspect the length of the thread discussing the heat shield will be longer than the Starship ends up being high. . . :)
Title: Re: Starship heat shield
Post by: cscott on 05/20/2021 03:39 am
You can fuse Av and AV together to make trapezoids, so you don't need to have the tiles be pointy.
Title: Re: Starship heat shield
Post by: JaimeZX on 05/20/2021 04:59 am
How do you keep your triangle tiles from having long, unbroken seam lines? Unfortunately the ASCII art isn't sufficiently stimulating my brain on this point.
Title: Re: Starship heat shield
Post by: alang on 05/20/2021 06:53 am
Apologies if this has already been suggested and discounted - I've lost track in this and possibly other threads...
.
.
.

Musk is quoted as wanting to avoid straight paths where gas could accelerate:
https://www.digitaltrends.com/cool-tech/spacex-hexagon-heat-shield-tiles/

Edit: and I'm sure his team is mathematically inclined and there has been work work on  the mathematics of tiling:
https://en.m.wikipedia.org/wiki/Penrose_tiling
Try that in your bathroom first :-)


Title: Re: Starship heat shield
Post by: Slarty1080 on 05/20/2021 08:24 am
Apologies if this has already been suggested and discounted - I've lost track in this and possibly other threads...
.
.
.

Musk is quoted as wanting to avoid straight paths where gas could accelerate:
https://www.digitaltrends.com/cool-tech/spacex-hexagon-heat-shield-tiles/

Edit: and I'm sure his team is mathematically inclined and there has been work work on  the mathematics of tiling:
https://en.m.wikipedia.org/wiki/Penrose_tiling
Try that in your bathroom first :-)
Yes good point its not just straight lines down the vehicle, straight lines around the vehicle might also pose a problem.

As for Penrose tiles they are fine for 2D planes but IFAIK less so for 3D curved surfaces and 3D curved surfaces with variable curvature. That's the interesting part of trying to second guess what is likely.
Title: Re: Starship heat shield
Post by: CruddyCuber on 05/24/2021 01:36 am
What are your guys' thoughts regarding the way this section is tiled?  It appears that a large straight gap was left between the tiles of the two barrel sections, rather than it being covered with standard hexagonal tiles. 

Image credit: Bocachicagal
Title: Re: Starship heat shield
Post by: cdebuhr on 05/24/2021 01:53 am
What are your guys' thoughts regarding the way this section is tiled?  It appears that a large straight gap was left between the tiles of the two barrel sections, rather than it being covered with standard hexagonal tiles. 

Image credit: Bocachicagal
Interesting.  It looks to me like the straight line is on a circumferential weld, and you can see one of the tie-down fittings for the recovery transporter (do we have a name for that thing yet? Megagrabber?), so I think this is the boundary between the leg skirt and the aft dome section.  At the wide gap you can see a reinforcing band which I presume is the band reinforcement for the area where the aft dome joins the barrel section.  It seems to me that they're all in of tiling these things section-by-section prior to joining, and now they're working out how to the bridge the gaps in the TPS once the section are joined together.

They do have the white thermal blanket covering the weld, so maybe they figure the gap between tiles is small enough to get away with?  As long as it survives re-entry at all, perhaps that's good enough for now, this likely being a single use vehicle and all?  Maybe they'll stuff ablative thermal goo into the gap?  As for the bigger gap, presumably they'll weld on some studs and tile that area.

I guess what I'm saying is it you want answers, ask someone who has a clue ... right now, that's not me!
Title: Re: Starship heat shield
Post by: Nevyn72 on 05/24/2021 02:22 am
That's the seam line where the detachable nose section separates.....

*runs away and hides*
Title: Re: Starship heat shield
Post by: Alvian@IDN on 05/24/2021 02:39 am
What are your guys' thoughts regarding the way this section is tiled?  It appears that a large straight gap was left between the tiles of the two barrel sections, rather than it being covered with standard hexagonal tiles. 

Image credit: Bocachicagal
It could also be a SN17 thrust section, since the SN20 actual aft dome section is spotted
https://twitter.com/StarshipGazer/status/1396631745466970114?s=19
Title: Re: Starship heat shield
Post by: jthygesen on 05/24/2021 08:56 am
What are your guys' thoughts regarding the way this section is tiled?  It appears that a large straight gap was left between the tiles of the two barrel sections, rather than it being covered with standard hexagonal tiles. 

Image credit: Bocachicagal

I think the "large" gap was not tiled because they needed to add the reinforcement band there. I was wondering how well this "large" gap could be filled with tiles later so I did a (quick and very bad) edit of the picture (from BocaChicaGal) to try it and it looks like three rows of tiles would fit perfectly. So presumably they will add studs to the reinforced section and tile it later. Although it seems more cumbersome.

Edit: For clarity.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 05/24/2021 05:16 pm
What are your guys' thoughts regarding the way this section is tiled?  It appears that a large straight gap was left between the tiles of the two barrel sections, rather than it being covered with standard hexagonal tiles. 

Image credit: Bocachicagal

Looks like to me there's an integer rounding whoopsie going on with the straight line around the circumference thing.

The larger gap, as another poster pointed out, has an integer number of tiles in the gap.

So the idea of putting on the tiles before joining sections and then filling in the gap after assembly has an integer rounding problem in a few spots.

Can one address the rounding issue at the same time as addressing the nosecone, with only 3 types of tiles total to keep manufacturing and maintenance inventories and travel iterations manageable?

What a fun geometry problem!
Title: Re: Starship heat shield
Post by: HVM on 05/24/2021 05:40 pm
Cap with pentagon tiles is clearly designed feature, why it's there I have no clue. And the larger cap: SpaceX seems to test adhesive bond tiles many times, so maybe there is some point of the ship skin where studs can't be welded on.
Title: Re: Starship heat shield
Post by: OTV Booster on 05/24/2021 08:49 pm
What are your guys' thoughts regarding the way this section is tiled?  It appears that a large straight gap was left between the tiles of the two barrel sections, rather than it being covered with standard hexagonal tiles. 

Image credit: Bocachicagal
Interesting.  It looks to me like the straight line is on a circumferential weld, and you can see one of the tie-down fittings for the recovery transporter (do we have a name for that thing yet? Megagrabber?), so I think this is the boundary between the leg skirt and the aft dome section.  At the wide gap you can see a reinforcing band which I presume is the band reinforcement for the area where the aft dome joins the barrel section.  It seems to me that they're all in of tiling these things section-by-section prior to joining, and now they're working out how to the bridge the gaps in the TPS once the section are joined together.

They do have the white thermal blanket covering the weld, so maybe they figure the gap between tiles is small enough to get away with?  As long as it survives re-entry at all, perhaps that's good enough for now, this likely being a single use vehicle and all?  Maybe they'll stuff ablative thermal goo into the gap?  As for the bigger gap, presumably they'll weld on some studs and tile that area.

I guess what I'm saying is it you want answers, ask someone who has a clue ... right now, that's not me!
One thing noticeable is the partial tiles abutting the gap are large enough to all have three studs.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 05/26/2021 07:23 pm
So why is there a circular area of damaged tiles in this picture by bocachicagal?

Seems like a weird bit of damage.  The blanket is intact.

Title: Re: Starship heat shield
Post by: Slarty1080 on 05/26/2021 07:37 pm
So why is there a circular area of damaged tiles in this picture by bocachicagal?

Seems like a weird bit of damage.  The blanket is intact.
That is a hole cut right through the metal skin. The black area is not tiles its inside the tank
Title: Re: Starship heat shield
Post by: InterestedEngineer on 05/26/2021 09:19 pm
So why is there a circular area of damaged tiles in this picture by bocachicagal?

Seems like a weird bit of damage.  The blanket is intact.
That is a hole cut right through the metal skin. The black area is not tiles its inside the tank

your eyes, better than mine.

I have to think that's a test article then, that's one ugly shaped hole.
Title: Re: Starship heat shield
Post by: chopsticks on 05/27/2021 03:42 am
Well no tiles on the back side of the flaps, eh? I wonder if that means no TPS at all. The SpaceX renders all have shown the top flaps black (presumably tiled) in the past. It will also be interesting to see the heat shield design on the body of the rocket since it won't be a straight seam dividing it in half.
Title: Re: Starship heat shield
Post by: Kiwi53 on 05/27/2021 05:42 am
So why is there a circular area of damaged tiles in this picture by bocachicagal?

Seems like a weird bit of damage.  The blanket is intact.
That is a hole cut right through the metal skin. The black area is not tiles its inside the tank

your eyes, better than mine.

I have to think that's a test article then, that's one ugly shaped hole.

IIRC, this was labelled as being part of SN17, and is now scrapped.
It will be interesting to see if SN16 ever flies, or goes straight from the High Bay to the scrap area
Title: Re: Starship heat shield
Post by: Slarty1080 on 05/27/2021 06:10 am
So why is there a circular area of damaged tiles in this picture by bocachicagal?

Seems like a weird bit of damage.  The blanket is intact.
That is a hole cut right through the metal skin. The black area is not tiles its inside the tank

your eyes, better than mine.

I have to think that's a test article then, that's one ugly shaped hole.
Yes its scrap. they must have wanted a particular skin section for test purposes. I think there was even a high contrast picture on one of the threads showing the inside although I can't find it now. As someone said on another thread - just cut a hole in it... how big and what shape hole? Yes and do it quickly.
Title: Re: Starship heat shield
Post by: Poseidon on 05/27/2021 09:29 am
Hello

How complex is it to manufacture such heat tiles???
I mean, how many different materials are needed?
How many production steps and how long do they take?
Highly automatable or not?
Do they need intensive testing after production or is the production reliable (high yield)?
...

Thanks
Title: Re: Starship heat shield
Post by: edzieba on 06/05/2021 07:20 pm
Nosecone barrel section moved in front of the windbreak.
Working on the TPS.
A layer of some sort of mesh scrim is being added to a section of SN16, between the tiles and the mineral wool underlay.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 06/05/2021 07:25 pm
Hello

How complex is it to manufacture such heat tiles???
I mean, how many different materials are needed?
How many production steps and how long do they take?
Highly automatable or not?
Do they need intensive testing after production or is the production reliable (high yield)?
...

Thanks



Those are all difficult questions to answer.

In this article there is a lot of information.

https://www.nasaspaceflight.com/2021/04/new-permits-spacex-cidco-roberts/
Title: Re: Starship heat shield
Post by: ETurner on 06/05/2021 08:43 pm
Have we seen tiles for anything but flap and tank surfaces yet?
I’d expect to see a more complete set of heat shield components fly before SpaceX tests atmospheric entry.
Title: Re: Starship heat shield
Post by: su27k on 06/07/2021 11:38 am
This video/slideshow has some close up of the clips used to attach the tiles, including some markers that may indicate errors made by robotic welder when welding the clips.

Starting from 23:48

https://www.youtube.com/watch?v=mACCIg5uHGU
Title: Re: Starship heat shield
Post by: rakaydos on 06/07/2021 04:43 pm
Have we seen tiles for anything but flap and tank surfaces yet?
I’d expect to see a more complete set of heat shield components fly before SpaceX tests atmospheric entry.
We've seen the complete set- Hexes, half hexes, and two different sizes of smaller hexes. With the smaller hexes, they can tile the nose cone in a way that leaves only small gaps, and with the half hexes they can  be flush with the wing roots and other moving parts.
Title: Re: Starship heat shield
Post by: Okie_Steve on 06/07/2021 04:59 pm
https://twitter.com/starshipgazer/status/1401708724100730882

Quote
SpaceX got a special delivery while I was there today. Looks like pallets of equipment to build a "Mini-Bakery" at Starbase. "The Bakery" is what they call the heat shield manufacturing facility in Cape Canaveral Florida. Now they can make heat shield tiles at Starbase also. 😃

From the production update thread. Depending on how "mini" it is I wonder if they will just be producing custom shapes and/or replacements for inevitable breakage during volume construction.
Title: Re: Starship heat shield
Post by: livingjw on 06/07/2021 05:00 pm
Have we seen tiles for anything but flap and tank surfaces yet?
I’d expect to see a more complete set of heat shield components fly before SpaceX tests atmospheric entry.
We've seen the complete set- Hexes, half hexes, and two different sizes of smaller hexes. With the smaller hexes, they can tile the nose cone in a way that leaves only small gaps, and with the half hexes they can  be flush with the wing roots and other moving parts.

I expect many more distinct shapes to appear.

John
Title: Re: Starship heat shield
Post by: ETurner on 06/07/2021 05:07 pm
Have we seen tiles for anything but flap and tank surfaces yet?
I’d expect to see a more complete set of heat shield components fly before SpaceX tests atmospheric entry.
We've seen the complete set- Hexes, half hexes, and two different sizes of smaller hexes. With the smaller hexes, they can tile the nose cone in a way that leaves only small gaps, and with the half hexes they can  be flush with the wing roots and other moving parts.
The half-hexes definitely help. Is there a diagram (better: photo!) showing how large + small hexes can cover a double-curved nosecone? The geometry isn’t obvious to me unless there are many sizes, and maybe additional shapes. Half-hexes could help cover a double-curved surface by providing straight(-ish) lines along which tiles can be out of register -- this can relax the nasty global distortions that result from wrapping a two-dimensional grid of aligned tiles over a curved surface.
Title: Re: Starship heat shield
Post by: rakaydos on 06/07/2021 05:14 pm
Have we seen tiles for anything but flap and tank surfaces yet?
I’d expect to see a more complete set of heat shield components fly before SpaceX tests atmospheric entry.
We've seen the complete set- Hexes, half hexes, and two different sizes of smaller hexes. With the smaller hexes, they can tile the nose cone in a way that leaves only small gaps, and with the half hexes they can  be flush with the wing roots and other moving parts.
The half-hexes definitely help. Is there a diagram (better: photo!) showing how large + small hexes can cover a double-curved nosecone? The geometry isn’t obvious to me unless there are many sizes, and maybe additional shapes. Half-hexes could help cover a double-curved surface by providing straight(-ish) lines along which tiles can be out of register -- this can relax the nasty global distortions that result from wrapping a two-dimensional grid of aligned tiles over a curved surface.
Several examples across the posts on this page: https://forum.nasaspaceflight.com/index.php?topic=50748.900

(it was further back than I thought!)
Title: Re: Starship heat shield
Post by: ETurner on 06/07/2021 06:41 pm
Have we seen tiles for anything but flap and tank surfaces yet?
I’d expect to see a more complete set of heat shield components fly before SpaceX tests atmospheric entry.
We've seen the complete set- Hexes, half hexes, and two different sizes of smaller hexes. With the smaller hexes, they can tile the nose cone in a way that leaves only small gaps, and with the half hexes they can  be flush with the wing roots and other moving parts.
The half-hexes definitely help. Is there a diagram (better: photo!) showing how large + small hexes can cover a double-curved nosecone? The geometry isn’t obvious to me unless there are many sizes, and maybe additional shapes. Half-hexes could help cover a double-curved surface by providing straight(-ish) lines along which tiles can be out of register -- this can relax the nasty global distortions that result from wrapping a two-dimensional grid of aligned tiles over a curved surface.
Several examples across the posts on this page: https://forum.nasaspaceflight.com/index.php?topic=50748.900 (https://forum.nasaspaceflight.com/index.php?topic=50748.900)

(it was further back than I thought!)
All of these examples look pretty bad to me. There are large gaps that won’t go away.
The pattern illustrated in this post (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2190404#msg2190404) is close to one that would work, but fixing it would require back-to-back half-hex tiles to relieve the alignment problem that I mentioned. (Look at the jagged gaps between row 5 and row 6, then imagine a straight line-of-latitude, half-hex interface instead.)
Title: Re: Starship heat shield
Post by: rakaydos on 06/07/2021 08:09 pm
Have we seen tiles for anything but flap and tank surfaces yet?
I’d expect to see a more complete set of heat shield components fly before SpaceX tests atmospheric entry.
We've seen the complete set- Hexes, half hexes, and two different sizes of smaller hexes. With the smaller hexes, they can tile the nose cone in a way that leaves only small gaps, and with the half hexes they can  be flush with the wing roots and other moving parts.
The half-hexes definitely help. Is there a diagram (better: photo!) showing how large + small hexes can cover a double-curved nosecone? The geometry isn’t obvious to me unless there are many sizes, and maybe additional shapes. Half-hexes could help cover a double-curved surface by providing straight(-ish) lines along which tiles can be out of register -- this can relax the nasty global distortions that result from wrapping a two-dimensional grid of aligned tiles over a curved surface.
Several examples across the posts on this page: https://forum.nasaspaceflight.com/index.php?topic=50748.900 (https://forum.nasaspaceflight.com/index.php?topic=50748.900)

(it was further back than I thought!)
All of these examples look pretty bad to me. There are large gaps that won’t go away.
The pattern illustrated in this post (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2190404#msg2190404) is close to one that would work, but fixing it would require back-to-back half-hex tiles to relieve the alignment problem that I mentioned. (Look at the jagged gaps between row 5 and row 6, then imagine a straight line-of-latitude, half-hex interface instead.)
It may look bad, but the question is, is it enough? The hot structure concept means that you dont need 100% coverage, so some large games may be fine if they are otherwise supported.
Title: Re: Starship heat shield
Post by: ETurner on 06/07/2021 09:02 pm
It may look bad, but the question is, is it enough? The hot structure concept means that you dont need 100% coverage, so some large games may be fine if they are otherwise supported.
Yes, but it’s not difficult to get much better packing with a hex + half-hex pattern, schematically something like this:

⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫

 ...but shifted to fit bumps into hollows, and allowing sheer/misalignment across the ⌫⌦ lines.
Things still get funny near the tip of the cone (see Slarty’s first post in this thread).
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/07/2021 09:35 pm
Have we seen tiles for anything but flap and tank surfaces yet?
I’d expect to see a more complete set of heat shield components fly before SpaceX tests atmospheric entry.
We've seen the complete set- Hexes, half hexes, and two different sizes of smaller hexes. With the smaller hexes, they can tile the nose cone in a way that leaves only small gaps, and with the half hexes they can  be flush with the wing roots and other moving parts.
The half-hexes definitely help. Is there a diagram (better: photo!) showing how large + small hexes can cover a double-curved nosecone? The geometry isn’t obvious to me unless there are many sizes, and maybe additional shapes. Half-hexes could help cover a double-curved surface by providing straight(-ish) lines along which tiles can be out of register -- this can relax the nasty global distortions that result from wrapping a two-dimensional grid of aligned tiles over a curved surface.
Several examples across the posts on this page: https://forum.nasaspaceflight.com/index.php?topic=50748.900 (https://forum.nasaspaceflight.com/index.php?topic=50748.900)

(it was further back than I thought!)
All of these examples look pretty bad to me. There are large gaps that won’t go away.
The pattern illustrated in this post (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2190404#msg2190404) is close to one that would work, but fixing it would require back-to-back half-hex tiles to relieve the alignment problem that I mentioned. (Look at the jagged gaps between row 5 and row 6, then imagine a straight line-of-latitude, half-hex interface instead.)
As you correctly identify there would be alignment problems. Having just a few tile shapes would lead to many gaps and using back to back half tiles would cause straight lines of sizable length that we know need to be avoided as they act as plasma channels.

The only way that I am aware of to get a really good fit is to have one tile size per latitude of the nose cone (see example on the first page of this thread). The real trade off is how important is it to have a closely fitting tiles on the heat shield v how important is it to minimise the number of tiles. My money is on closely fitting tiles being more important.

But we will see. It is perhaps possible they will have some other solution for the nose that does only include a few tile sizes and perhaps some filler or other clever device or perhaps bigger gaps don't matter, but IMO more tile sizes are more likely.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/07/2021 09:38 pm
It may look bad, but the question is, is it enough? The hot structure concept means that you dont need 100% coverage, so some large games may be fine if they are otherwise supported.
Yes, but it’s not difficult to get much better packing with a hex + half-hex pattern, schematically something like this:

⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫

 ...but shifted to fit bumps into hollows, and allowing sheer/misalignment across the ⌫⌦ lines.
Things still get funny near the tip of the cone (see Slarty’s first post in this thread).
One other issue as I mentioned above, is the straight line issue between the x's in your diagram.
Title: Re: Starship heat shield
Post by: rsdavis9 on 06/07/2021 10:05 pm
It may look bad, but the question is, is it enough? The hot structure concept means that you dont need 100% coverage, so some large games may be fine if they are otherwise supported.
Yes, but it’s not difficult to get much better packing with a hex + half-hex pattern, schematically something like this:

⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫

 ...but shifted to fit bumps into hollows, and allowing sheer/misalignment across the ⌫⌦ lines.
Things still get funny near the tip of the cone (see Slarty’s first post in this thread).
One other issue as I mentioned above, is the straight line issue between the x's in your diagram.

Stagger them?
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/07/2021 10:08 pm
It may look bad, but the question is, is it enough? The hot structure concept means that you dont need 100% coverage, so some large games may be fine if they are otherwise supported.
Yes, but it’s not difficult to get much better packing with a hex + half-hex pattern, schematically something like this:

⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫

 ...but shifted to fit bumps into hollows, and allowing sheer/misalignment across the ⌫⌦ lines.
Things still get funny near the tip of the cone (see Slarty’s first post in this thread).
One other issue as I mentioned above, is the straight line issue between the x's in your diagram.

Stagger them?
I fear not. Try it with pencil and paper...
Title: Re: Starship heat shield
Post by: ETurner on 06/07/2021 10:22 pm
It may look bad, but the question is, is it enough? The hot structure concept means that you dont need 100% coverage, so some large games may be fine if they are otherwise supported.
Yes, but it’s not difficult to get much better packing with a hex + half-hex pattern, schematically something like this:

⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫

 ...but shifted to fit bumps into hollows, and allowing sheer/misalignment across the ⌫⌦ lines.
Things still get funny near the tip of the cone (see Slarty’s first post in this thread).
One other issue as I mentioned above, is the straight line issue between the x's in your diagram.
Compared to some of the big-gap designs posted earlier, this seems not so bad!
But trying to make sense of the engineering constraints, what about the straight line (=circumferential) grooves between back-to-back rows of half-hex tiles elsewhere on the vehicle? Unless I’m mistaken, these are part of the current design.

I also expect to see more tile sizes and shapes.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/07/2021 10:43 pm
It may look bad, but the question is, is it enough? The hot structure concept means that you dont need 100% coverage, so some large games may be fine if they are otherwise supported.
Yes, but it’s not difficult to get much better packing with a hex + half-hex pattern, schematically something like this:

⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫

 ...but shifted to fit bumps into hollows, and allowing sheer/misalignment across the ⌫⌦ lines.
Things still get funny near the tip of the cone (see Slarty’s first post in this thread).
One other issue as I mentioned above, is the straight line issue between the x's in your diagram.
Compared to some of the big-gap designs posted earlier, this seems not so bad!
But trying to make sense of the engineering constraints, what about the straight line (=circumferential) grooves between back-to-back rows of half-hex tiles elsewhere on the vehicle? Unless I’m mistaken, these are part of the current design.

I also expect to see more tile sizes and shapes.
I believe the only reason for the half tiles is for areas like the bottom of the skirt. Its a "straight line" (alright its a circle but...) and it doesn't matter about plasma here as its the edge of the ship. I would be very suprised to see these half tiles used anywhere other than this sort of edge situation.
Title: Re: Starship heat shield
Post by: ETurner on 06/07/2021 11:13 pm
So the choices seem to be:
a) big gaps, or
b) straight channels, or
c) several (many?) more tile shapes, or
d) ??
Title: Re: Starship heat shield
Post by: xvel on 06/07/2021 11:16 pm
conical fairing
Title: Re: Starship heat shield
Post by: ETurner on 06/07/2021 11:24 pm
conical fairing
Where?
Title: Re: Starship heat shield
Post by: joek on 06/07/2021 11:42 pm
...
But we will see. It is perhaps possible they will have some other solution for the nose that does only include a few tile sizes and perhaps some filler or other clever device or perhaps bigger gaps don't matter, but IMO more tile sizes are more likely.

Agree nose section will likely be different. Is that an issue? Doubtful given intended scale. While a common solution is ideal, a "special case" solution for the nose (and other parts) is less onerous ((less "special") if you are building hundreds of them.
Title: Re: Starship heat shield
Post by: Keldor on 06/08/2021 03:45 am
It's actually pretty important that the heatshield have a smooth surface.  You need laminar airflow beneath it, and if it becomes turbulent, the surface temperature will rise drastically.

Here we can see an image of the heat shield of STS 128, in which they intentionally raised one of the tiles about a quarter inch above the surrounding tiles as part of an experiment concerning heat shield peak heating.  Notice how turbulence from that single slightly raised tile caused a large area around it to experience significantly greater heating.

Concerning airflow channels in the heat shield, here's an image from a simulation of surface air speeds against the heatshield of Columbia during its ill fated reentry after the leading edge was damaged.  We can see that the resulting surface air speed in the area behind the damaged spot increased by an order of magnitude.  This ultimately resulted in erosion and burn through and loss of vehicle and crew.

It should be clear that the small scale aerodynamics around the heat shield are very sensitive, and the gaps between tiles have to be carefully dealt with.  The "rough fit" suggestions I see are honestly probably worse than no head shield at all, since at least if you don't have a heat shield, you have a nice smooth body with laminar flow, and the peak heating will drop by a good 500C degrees from turbulent flow that a rough heat shield would cause.  Or possible the heat difference could be much more.  The laminar flow region is providing a protective shield against the air in the shockwave, which will be in the 5000C degrees range, hot enough to vaporize every material known to mankind.  Disturb the flow separation at your own risk!

[zubenelgenubi: Attach image files. Do not embed them.]
Title: Re: Starship heat shield
Post by: eriblo on 06/08/2021 10:23 am
.
[...]
Concerning airflow channels in the heat shield, here's an image from a simulation of surface air speeds against the heatshield of Columbia during its ill fated reentry after the leading edge was damaged.  We can see that the resulting surface air speed in the area behind the damaged spot increased by an order of magnitude.  This ultimately resulted in erosion and burn through and loss of vehicle and crew.
[...]
Not that it changes your argument much but I believe that the second image is s simulation of the gas flow inside the wing resulting from the breached RCC panel.
Title: Re: Starship heat shield
Post by: Mike_1179 on 06/08/2021 11:15 am
So the choices seem to be:
a) big gaps, or
b) straight channels, or
c) several (many?) more tile shapes, or
d) ??

Would RCC panels like were used on the curved nose and wing leading edges work for the curved nose? You can form complicates curved shapes and they’re reusable
Title: Re: Starship heat shield
Post by: Rocket Surgeon on 06/08/2021 11:22 am
So the choices seem to be:
a) big gaps, or
b) straight channels, or
c) several (many?) more tile shapes, or
d) ??

Would RCC panels like were used on the curved nose and wing leading edges work for the curved nose? You can form complicates curved shapes and they’re reusable

Technically yes, but they would need to be replaced after each flight, or if not every flight, at regular intervals.
They disspate heat through ablation
Title: Re: Starship heat shield
Post by: Mike_1179 on 06/08/2021 11:35 am

Would RCC panels like were used on the curved nose and wing leading edges work for the curved nose? You can form complicates curved shapes and they’re reusable

Technically yes, but they would need to be replaced after each flight, or if not every flight, at regular intervals.
They disspate heat through ablation

I thought the RCC panels were coated with silicon carbide to reduce oxidation and allow them to be reusable. They weren’t ablative.

I know they were incredible expensive, but my comment was more around non-tile TPS for complicated surfaces
Title: Re: Starship heat shield
Post by: eriblo on 06/08/2021 12:51 pm
I strongly believe that Starship will have "perfect tiling", i.e. there will be no intentional gaps beyond those required by thermal contraction/expansion, vibrations and placement tolerances. It is going to need more types of tiles but it should be on the order of a few hundred with a decent number of tiles for most of them. For the nose cone I am personally a fan of the tapered hexagons suggested on the first page of this thread, with each row being identical. My addition would be a doubling once the tiles get wide enough which would require a handful of rows to use two mirrored pentagonal tile types instead. 

Paraphrasing Elon in the Joe Rogan podcast:
You have to get the gaps just right, if it gets too big you get plasma in the crack (and that's bad) and if it's too small they are going to bang together.

If cm scale gaps were ok they would hardly be concerned about differential thermal expansion and vibrations. Sure, Starship would likely survive with big gaps or even missing tiles. The blankets are made from similar materials and could survive similar temperatures as the tiles (if not higher depending on composition) but turbulence, shock impingement and lower emissivity would lead to higher temperatures. The steel can get quite hot before failing but will start to anneal and lose the hardening at a significantly lower temperature - fine for survivability but likely instant scrapping if it happens in the tanks.

Also remember that re-entries from LEO, while being by far the most common case, represent the lower end of the performance envelope. I am really curious as to how far they can take the reusable tiles or whether they will need ablative solutions for high energy tankers or lunar/Mars returns.
Title: Re: Starship heat shield
Post by: eriblo on 06/08/2021 01:07 pm

Would RCC panels like were used on the curved nose and wing leading edges work for the curved nose? You can form complicates curved shapes and they’re reusable

Technically yes, but they would need to be replaced after each flight, or if not every flight, at regular intervals.
They disspate heat through ablation

I thought the RCC panels were coated with silicon carbide to reduce oxidation and allow them to be reusable. They weren’t ablative.

I know they were incredible expensive, but my comment was more around non-tile TPS for complicated surfaces
While they were indeed limited by oxidation they were rated for something like 50-100 flights depending on location according to the CAIB report.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/08/2021 01:21 pm
I strongly believe that Starship will have "perfect tiling", i.e. there will be no intentional gaps beyond those required by thermal contraction/expansion, vibrations and placement tolerances. It is going to need more types of tiles but it should be on the order of a few hundred with a decent number of tiles for most of them. For the nose cone I am personally a fan of the tapered hexagons suggested on the first page of this thread, with each row being identical. My addition would be a doubling once the tiles get wide enough which would require a handful of rows to use two mirrored pentagonal tile types instead. 

Paraphrasing Elon in the Joe Rogan podcast:
You have to get the gaps just right, if it gets too big you get plasma in the crack (and that's bad) and if it's too small they are going to bang together.

If cm scale gaps were ok they would hardly be concerned about differential thermal expansion and vibrations. Sure, Starship would likely survive with big gaps or even missing tiles. The blankets are made from similar materials and could survive similar temperatures as the tiles (if not higher depending on composition) but turbulence, shock impingement and lower emissivity would lead to higher temperatures. The steel can get quite hot before failing but will start to anneal and lose the hardening at a significantly lower temperature - fine for survivability but likely instant scrapping if it happens in the tanks.

Also remember that re-entries from LEO, while being by far the most common case, represent the lower end of the performance envelope. I am really curious as to how far they can take the reusable tiles or whether they will need ablative solutions for high energy tankers or lunar/Mars returns.
The narrowing hexagon approach on page 1 shows promise but will potentially suffer from narrow tiles towards the nose tip. So I'm interested in your double pentagon tile idea but I can't quite imagine them. Would these tiles have a some concave edges? And how would they link up with the hexagonal tiles? I note that the hex "grain" on starship runs around the circumference rather than vertically up the side. Any chance of a diagram?
Title: Re: Starship heat shield
Post by: edzieba on 06/08/2021 01:33 pm
Does anyone know (or have an estimate of) the curve function of the current nose? If the rate of change of tangent angle is relatively constant (Sphere, cone, or Ogive should satisfy that) you can use a single tapered tile design to tile the entire nose. If it changes (e.g. curvature increases with height, e.g. a Parabolic curve) then several 'steps' would be needed with increasing tapers, depending on the allowable tolerance.
This also may be the reason the nose is 'pointier than necessary': By reducing the curvature, you reduce the number of tile variants needed for a given tolerance.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/08/2021 05:19 pm
Does anyone know (or have an estimate of) the curve function of the current nose? If the rate of change of tangent angle is relatively constant (Sphere, cone, or Ogive should satisfy that) you can use a single tapered tile design to tile the entire nose. If it changes (e.g. curvature increases with height, e.g. a Parabolic curve) then several 'steps' would be needed with increasing tapers, depending on the allowable tolerance.
This also may be the reason the nose is 'pointier than necessary': By reducing the curvature, you reduce the number of tile variants needed for a given tolerance.
I believe it is an ogive curve with a variable rate of curvature. A separate tile shape will be needed for each line of latitude of the nose if the intention is to make it a snug fit (which seems to be very likely).

It would be handy if there was just one tile for the entire ship, but there won't be. Its no big deal its not the shuttle. There seems to be a fixation on the idea that there has to be just a handful of tile types. There doesn't.
Title: Re: Starship heat shield
Post by: OTV Booster on 06/08/2021 07:26 pm
Have we seen tiles for anything but flap and tank surfaces yet?
I’d expect to see a more complete set of heat shield components fly before SpaceX tests atmospheric entry.
We've seen the complete set- Hexes, half hexes, and two different sizes of smaller hexes. With the smaller hexes, they can tile the nose cone in a way that leaves only small gaps, and with the half hexes they can  be flush with the wing roots and other moving parts.
The half-hexes definitely help. Is there a diagram (better: photo!) showing how large + small hexes can cover a double-curved nosecone? The geometry isn’t obvious to me unless there are many sizes, and maybe additional shapes. Half-hexes could help cover a double-curved surface by providing straight(-ish) lines along which tiles can be out of register -- this can relax the nasty global distortions that result from wrapping a two-dimensional grid of aligned tiles over a curved surface.
Several examples across the posts on this page: https://forum.nasaspaceflight.com/index.php?topic=50748.900 (https://forum.nasaspaceflight.com/index.php?topic=50748.900)

(it was further back than I thought!)
All of these examples look pretty bad to me. There are large gaps that won’t go away.
The pattern illustrated in this post (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2190404#msg2190404) is close to one that would work, but fixing it would require back-to-back half-hex tiles to relieve the alignment problem that I mentioned. (Look at the jagged gaps between row 5 and row 6, then imagine a straight line-of-latitude, half-hex interface instead.)
It may look bad, but the question is, is it enough? The hot structure concept means that you dont need 100% coverage, so some large games may be fine if they are otherwise supported.
"... is it enough?"  is probably a question SX has too. For SX, good enough next week is better than perfect in three years.
Title: Re: Starship heat shield
Post by: OTV Booster on 06/08/2021 07:52 pm
It may look bad, but the question is, is it enough? The hot structure concept means that you dont need 100% coverage, so some large games may be fine if they are otherwise supported.
Yes, but it’s not difficult to get much better packing with a hex + half-hex pattern, schematically something like this:

⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫

 ...but shifted to fit bumps into hollows, and allowing sheer/misalignment across the ⌫⌦ lines.
Things still get funny near the tip of the cone (see Slarty’s first post in this thread).
One other issue as I mentioned above, is the straight line issue between the x's in your diagram.
Compared to some of the big-gap designs posted earlier, this seems not so bad!
But trying to make sense of the engineering constraints, what about the straight line (=circumferential) grooves between back-to-back rows of half-hex tiles elsewhere on the vehicle? Unless I’m mistaken, these are part of the current design.

I also expect to see more tile sizes and shapes.
I believe the only reason for the half tiles is for areas like the bottom of the skirt. Its a "straight line" (alright its a circle but...) and it doesn't matter about plasma here as its the edge of the ship. I would be very suprised to see these half tiles used anywhere other than this sort of edge situation.
The half tiles are really larger than half. They are big enough to cover three pins. To butt flat to flat either the apex to flat dimension is the same as a normal tiles apex to apex, or the pin pattern would have to change. If used only as edging, this problem goes away.


I think apex to flat is a smaller than apex to apex. Sigh, time to use a real computer and do some pixel counting.

Title: Re: Starship heat shield
Post by: Pueo on 06/08/2021 07:57 pm
So the choices seem to be:
a) big gaps, or
b) straight channels, or
c) several (many?) more tile shapes, or
d) ??

Hemispherical nose cone could allow for tiling via a Goldberg polyhedron, which would have relatively few tile shapes.  Would probably require the use of an extensible drag-reducing aerospike for launch, and retesting the control system for the belly flop.
Title: Re: Starship heat shield
Post by: OTV Booster on 06/08/2021 08:11 pm
It's actually pretty important that the heatshield have a smooth surface.  You need laminar airflow beneath it, and if it becomes turbulent, the surface temperature will rise drastically.

Here we can see an image of the heat shield of STS 128, in which they intentionally raised one of the tiles about a quarter inch above the surrounding tiles as part of an experiment concerning heat shield peak heating.  Notice how turbulence from that single slightly raised tile caused a large area around it to experience significantly greater heating.

Concerning airflow channels in the heat shield, here's an image from a simulation of surface air speeds against the heatshield of Columbia during its ill fated reentry after the leading edge was damaged.  We can see that the resulting surface air speed in the area behind the damaged spot increased by an order of magnitude.  This ultimately resulted in erosion and burn through and loss of vehicle and crew.

It should be clear that the small scale aerodynamics around the heat shield are very sensitive, and the gaps between tiles have to be carefully dealt with.  The "rough fit" suggestions I see are honestly probably worse than no head shield at all, since at least if you don't have a heat shield, you have a nice smooth body with laminar flow, and the peak heating will drop by a good 500C degrees from turbulent flow that a rough heat shield would cause.  Or possible the heat difference could be much more.  The laminar flow region is providing a protective shield against the air in the shockwave, which will be in the 5000C degrees range, hot enough to vaporize every material known to mankind.  Disturb the flow separation at your own risk!

[zubenelgenubi: Attach image files. Do not embed them.]
The dramatic heating was downstream of the protuberance. The heating around the elavon gap was less pronounce but it may have been more dramatic if it hadn't run out of airframe. Still, the impact of a channel isn't quite the same as something sticking up into the laminar flow. Surely there is some relationship between the laminar flow mach number and the gap dimensions. If there isn't, no gap is acceptable, including that formed by the slightly rounded edges of the tiles even if butted tight together.
Title: Re: Starship heat shield
Post by: rsdavis9 on 06/08/2021 09:03 pm
So the choices seem to be:
a) big gaps, or
b) straight channels, or
c) several (many?) more tile shapes, or
d) ??

Hemispherical nose cone could allow for tiling via a Goldberg polyhedron, which would have relatively few tile shapes.  Would probably require the use of an extensible drag-reducing aerospike for launch, and retesting the control system for the belly flop.

So if I read that correctly then a there are 3 tile shapes and sizes? gp(3,0)
https://en.wikipedia.org/wiki/Goldberg_polyhedron
Title: Re: Starship heat shield
Post by: ETurner on 06/08/2021 09:58 pm
So the choices seem to be:
a) big gaps, or
b) straight channels, or
c) several (many?) more tile shapes, or
d) ??

Hemispherical nose cone could allow for tiling via a Goldberg polyhedron, which would have relatively few tile shapes.  Would probably require the use of an extensible drag-reducing aerospike for launch, and retesting the control system for the belly flop.

So if I read that correctly then a there are 3 tile shapes and sizes? gp(3,0)
https://en.wikipedia.org/wiki/Goldberg_polyhedron (https://en.wikipedia.org/wiki/Goldberg_polyhedron)
If there are many tiles between the pentagons, then there must be hexagons of many different sizes and shapes: Regular grid, meet spherical distortion.
Title: Re: Starship heat shield
Post by: OTV Booster on 06/09/2021 03:20 pm
It may look bad, but the question is, is it enough? The hot structure concept means that you dont need 100% coverage, so some large games may be fine if they are otherwise supported.
Yes, but it’s not difficult to get much better packing with a hex + half-hex pattern, schematically something like this:

⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫
⌦⎔⎔⎔⌫⌦⎔⎔⌫

 ...but shifted to fit bumps into hollows, and allowing sheer/misalignment across the ⌫⌦ lines.
Things still get funny near the tip of the cone (see Slarty’s first post in this thread).
One other issue as I mentioned above, is the straight line issue between the x's in your diagram.
Compared to some of the big-gap designs posted earlier, this seems not so bad!
But trying to make sense of the engineering constraints, what about the straight line (=circumferential) grooves between back-to-back rows of half-hex tiles elsewhere on the vehicle? Unless I’m mistaken, these are part of the current design.

I also expect to see more tile sizes and shapes.
I believe the only reason for the half tiles is for areas like the bottom of the skirt. Its a "straight line" (alright its a circle but...) and it doesn't matter about plasma here as its the edge of the ship. I would be very suprised to see these half tiles used anywhere other than this sort of edge situation.
The half tiles are really larger than half. They are big enough to cover three pins. To butt flat to flat either the apex to flat dimension is the same as a normal tiles apex to apex, or the pin pattern would have to change. If used only as edging, this problem goes away.

I think apex to flat is a smaller than apex to apex. Sigh, time to use a real computer and do some pixel counting.
The apex to flat is 133 pixels. Apex to apex is 169. In both cases the vertical side is 83 pixels. These flats are the same as the full hex except they're cut off from the 10 o'clock to the 2 o'clock apexes. They are for edges. If used anywhere else the pin pattern would have to change. Not impossible.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/09/2021 06:18 pm
So the choices seem to be:
a) big gaps, or
b) straight channels, or
c) several (many?) more tile shapes, or
d) ??

Hemispherical nose cone could allow for tiling via a Goldberg polyhedron, which would have relatively few tile shapes.  Would probably require the use of an extensible drag-reducing aerospike for launch, and retesting the control system for the belly flop.

So if I read that correctly then a there are 3 tile shapes and sizes? gp(3,0)
https://en.wikipedia.org/wiki/Goldberg_polyhedron
Very interesting, although unfortunately the nose of Starship has a variable curvature so this would not work as described. That said there might be some scope especially as the tiles only cover half the ship, but I doubt it. We shall see.
Title: Re: Starship heat shield
Post by: eriblo on 06/09/2021 08:30 pm
I strongly believe that Starship will have "perfect tiling", i.e. there will be no intentional gaps beyond those required by thermal contraction/expansion, vibrations and placement tolerances. It is going to need more types of tiles but it should be on the order of a few hundred with a decent number of tiles for most of them. For the nose cone I am personally a fan of the tapered hexagons suggested on the first page of this thread, with each row being identical. My addition would be a doubling once the tiles get wide enough which would require a handful of rows to use two mirrored pentagonal tile types instead. 

Paraphrasing Elon in the Joe Rogan podcast:
You have to get the gaps just right, if it gets too big you get plasma in the crack (and that's bad) and if it's too small they are going to bang together.

If cm scale gaps were ok they would hardly be concerned about differential thermal expansion and vibrations. Sure, Starship would likely survive with big gaps or even missing tiles. The blankets are made from similar materials and could survive similar temperatures as the tiles (if not higher depending on composition) but turbulence, shock impingement and lower emissivity would lead to higher temperatures. The steel can get quite hot before failing but will start to anneal and lose the hardening at a significantly lower temperature - fine for survivability but likely instant scrapping if it happens in the tanks.

Also remember that re-entries from LEO, while being by far the most common case, represent the lower end of the performance envelope. I am really curious as to how far they can take the reusable tiles or whether they will need ablative solutions for high energy tankers or lunar/Mars returns.
The narrowing hexagon approach on page 1 shows promise but will potentially suffer from narrow tiles towards the nose tip. So I'm interested in your double pentagon tile idea but I can't quite imagine them. Would these tiles have a some concave edges? And how would they link up with the hexagonal tiles? I note that the hex "grain" on starship runs around the circumference rather than vertically up the side. Any chance of a diagram?
Behold the Diagrams! Quick and dirty with greatly exaggerated differences between rows - if one limits tiles to the same maximum dimensions then a doubling is only needed for every factor of 2 change in nose radius. The one I meant was the first one but the others are options if one wants to avoid the two tile long straight gap at the cost of a notched tile or a smaller insert diamond tile (which can be bigger at the cost of three instead of two types of tiles).
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/09/2021 10:02 pm

It would be handy if there was just one tile for the entire ship, but there won't be. Its no big deal its not the shuttle. There seems to be a fixation on the idea that there has to be just a handful of tile types. There doesn't.

There is a not a fixation, there are those of us with manufacturing engineering experience that know that "less parts is better".   We "fixated" on having at most one type of fastener for an oscilloscope assembly (a specific example in my past).

The reasons are not just inventory management, though that is important, it's the ability of an operator to easily deal with more than one handful of parts at a time.  It is difficult to have more than 5-10 types of parts on hand at a manufacturing station in a building while sitting and reaching for the parts, and even more difficult while 40 meters in the air on a lift.  The more similar looking the parts, the lower the practical number, due to human cognition limitations.

Go ahead and work out the number of up/down lift movements, operator reaches, choice mistakes, at 40 meters in the air while dealing with 3 parts.  Now do that for 30 parts.   It'll be an order of magnitude more difficult for the 30 parts version.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/09/2021 10:09 pm
Behold the Diagrams! Quick and dirty with greatly exaggerated differences between rows - if one limits tiles to the same maximum dimensions then a doubling is only needed for every factor of 2 change in nose radius. The one I meant was the first one but the others are options if one wants to avoid the two tile long straight gap at the cost of a notched tile or a smaller insert diamond tile (which can be bigger at the cost of three instead of two types of tiles).

The third diagram has an issue with too small of tiles to fit a proper tri-bracket into.

The second has the least number of shapes.  My favorite.

thanks!
Title: Re: Starship heat shield
Post by: ETurner on 06/09/2021 10:41 pm
Go ahead and work out the number of up/down lift movements, operator reaches, choice mistakes, at 40 meters in the air while dealing with 3 parts.  Now do that for 30 parts.   It'll be an order of magnitude more difficult for the 30 parts version.
But what if there is just one kind of tile per row, or two at most? The complexity seems pretty low (very repetitive work), and tiles can be stenciled with row numbers and this-side-up arrows.

One or two shapes per row is enough to enable a perfect fit over the whole structure, but using fewer and fewer tile-shapes leads to worse and worse gaps. I’ve seen no good solution with regular hexagons regardless of shape. The reasons seem inherent in the geometry of the surface.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/09/2021 11:18 pm
Go ahead and work out the number of up/down lift movements, operator reaches, choice mistakes, at 40 meters in the air while dealing with 3 parts.  Now do that for 30 parts.   It'll be an order of magnitude more difficult for the 30 parts version.
But what if there is just one kind of tile per row, or two at most? The complexity seems pretty low (very repetitive work), and tiles can be stenciled with row numbers and this-side-up arrows.

One or two shapes per row is enough to enable a perfect fit over the whole structure, but using fewer and fewer tile-shapes leads to worse and worse gaps. I’ve seen no good solution with regular hexagons regardless of shape. The reasons seem inherent in the geometry of the surface.

There is a good solution involving non-hexagons in the thread just above.  Picture #1 and Picture #2 look workable, and there's 4 different tiles total.

with unique tiles per row, after every row, the picker machine (or human) must unload and reload their feeder.   Furthermore you can only work on about 2-3 rows at at a time (depending on how many rows per type), which requires horizontal movements.  doable on a scaffolding or rotating stand but possibly inefficient if the robot or human's reach is more than 3 rows , but vertical movements are far easier on a lift than horizontal movements around a circle.

The nosecone from a drawing I found is 14 meters, so that's 20-40 tile types you are talking about.   Inventory management is going to be so fun.  The "ooops we dropped one and ran out" problem means an extra two tiles, x 30, versus a handful of extras if there's a handful of tile types.   Not to mention storage area, the tiles will look pretty similar between rows leading to confusion.

I'm sure I'm forgetting about another half dozen reasons why "no part is the best part" and "the fewer parts the better"

The arguments are asymmetrical, it's much more difficult to talk someone out of extra parts than to talk someone into an extra part.  So "no part is the best part" was the mantra we used in manufacturing, just like Elon, and any vaguely looking tie in a design argument automatically went to the solution with less parts, without further discussion.   Engineering managers ruthlessly enforced this discipline.

In other words the burden of proof is on the engineer asking for the extra part (that'd be you).  Maybe you should point out why the 3-5 part solutions in this thread are lacking.  Some of them do not involve extra gaps.
Title: Re: Starship heat shield
Post by: ETurner on 06/10/2021 12:31 am
Go ahead and work out the number of up/down lift movements, operator reaches, choice mistakes, at 40 meters in the air while dealing with 3 parts.  Now do that for 30 parts.   It'll be an order of magnitude more difficult for the 30 parts version.
But what if there is just one kind of tile per row, or two at most? The complexity seems pretty low (very repetitive work), and tiles can be stenciled with row numbers and this-side-up arrows.

One or two shapes per row is enough to enable a perfect fit over the whole structure, but using fewer and fewer tile-shapes leads to worse and worse gaps. I’ve seen no good solution with regular hexagons regardless of shape. The reasons seem inherent in the geometry of the surface.

There is a good solution involving non-hexagons in the thread just above.  Picture #1 and Picture #2 look workable, and there's 4 different tiles total.

with unique tiles per row, after every row, the picker machine (or human) must unload and reload their feeder.   Furthermore you can only work on about 2-3 rows at at a time (depending on how many rows per type), which requires horizontal movements.  doable on a scaffolding or rotating stand but possibly inefficient if the robot or human's reach is more than 3 rows , but vertical movements are far easier on a lift than horizontal movements around a circle.

The nosecone from a drawing I found is 14 meters, so that's 20-40 tile types you are talking about.   Inventory management is going to be so fun.  The "ooops we dropped one and ran out" problem means an extra two tiles, x 30, versus a handful of extras if there's a handful of tile types.   Not to mention storage area, the tiles will look pretty similar between rows leading to confusion.

I'm sure I'm forgetting about another half dozen reasons why "no part is the best part" and "the fewer parts the better"

The arguments are asymmetrical, it's much more difficult to talk someone out of extra parts than to talk someone into an extra part.  So "no part is the best part" was the mantra we used in manufacturing, just like Elon, and any vaguely looking tie in a design argument automatically went to the solution with less parts, without further discussion.   Engineering managers ruthlessly enforced this discipline.

In other words the burden of proof is on the engineer asking for the extra part (that'd be you).  Maybe you should point out why the 3-5 part solutions in this thread are lacking.  Some of them do not involve extra gaps.
Cover a sphere with lines of latitude and longitude, and note that the rectangle-like grid will have different shapes at every latitude (and triangles around the poles). Show me how a few tile shapes can cover a sphere, and I’ll be happy and amazed. Show me how two sizes of hexagons can do the job, and I’ll be astounded.

The problem of covering a double-curved nosecone is not fundamentally different from covering a sphere. No uniform grid can do it, which means that uniform tilings can’t do it. Diagrams that suggest otherwise are misleading.

I kind of like the hexagon-pentagon-heptagon pattern that I sketched earlier in this thread, but eriblo’s diagrams a few posts back have nice features, too. All these schemes solve the same variable-circumference problems.

That said, I’d prefer simpler solutions, and some variation in gaps is acceptable. There are trade-offs. Maybe the right solution is soft, wide gap-fillers to accommodate badly fitting tiles.
Title: Re: Starship heat shield
Post by: Hyperborealis on 06/10/2021 01:17 am
Is there a limit on the size and shape of the tile? Is there a reason they can't make a single piece, to cover the entire nose cone?
Title: Re: Starship heat shield
Post by: BT52 on 06/10/2021 06:09 am
In theory not. But in practice is controllable curing of big and especially ceramic ok Ike materials pain in ass. It's similar ok problem like carbon fiber autoclaves. So size is quite limitation. Sure mashing would be necessary to as void huge volumetric extensions or contractions. Don't mention porosity and worse towns of said approach. Truly fascinating problem
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 06/10/2021 07:15 am
Is there a limit on the size and shape of the tile? Is there a reason they can't make a single piece, to cover the entire nose cone?

tiles are quite fragile, so big size are worse for vibration, and in case of damage you can't repair only one tile.
Title: Re: Starship heat shield
Post by: edzieba on 06/10/2021 10:42 am
Cover a sphere with lines of latitude and longitude, and note that the rectangle-like grid will have different shapes at every latitude (and triangles around the poles). Show me how a few tile shapes can cover a sphere, and I’ll be happy and amazed. Show me how two sizes of hexagons can do the job, and I’ll be astounded.
Goldberg Polyhedra (https://en.wikipedia.org/wiki/Goldberg_polyhedron) were referenced jsut a few posts back. One tiling uses two sizes of hex and one size of pentagon to seamlessly tile a sphere. The Starship case is easier than a sphere: because only tiling a partial surface is required and the edge conditions are undefined (i.e. you don't need to match up to an exact line) there may be even more efficient tiling's available. For example, one that uses two hex sizes plus a dedicated TPS application for the tip of the nose.
Title: Re: Starship heat shield
Post by: HVM on 06/10/2021 11:31 am
Is there a limit on the size and shape of the tile? Is there a reason they can't make a single piece, to cover the entire nose cone?

tiles are quite fragile, so big size are worse for vibration, and in case of damage you can't repair only one tile.
Shuttle used carbon-carbon at leading edges and nose, and X-37B uses TUFROC is same purpose. Maybe we see long rumored TUFROCX at SS nose and bodyflaps...
Title: Re: Starship heat shield
Post by: ETurner on 06/10/2021 11:45 am
Cover a sphere with lines of latitude and longitude, and note that the rectangle-like grid will have different shapes at every latitude (and triangles around the poles). Show me how a few tile shapes can cover a sphere, and I’ll be happy and amazed. Show me how two sizes of hexagons can do the job, and I’ll be astounded.
Goldberg Polyhedra (https://en.wikipedia.org/wiki/Goldberg_polyhedron) were referenced jsut a few posts back. One tiling uses two sizes of hex and one size of pentagon to seamlessly tile a sphere. The Starship case is easier than a sphere: because only tiling a partial surface is required and the edge conditions are undefined (i.e. you don't need to match up to an exact line) there may be even more efficient tiling's available. For example, one that uses two hex sizes plus a dedicated TPS application for the tip of the nose.
A large (many-tile) triangular facet (the corners are in the pentagons) cannot be accurately tiled with regular hexagons, much less by hexagons of a single size. Think of a sheet of paper with a regular hexagonal grid printed on it. Paste it on a sphere, get creases. Precise tiling can’t work because geometry. Full stop.

Same story with the nosecone: Paste the pattern on the surface. Creases = nonuniform tile spacing.

Tiling with uniform tiles and variable but not-too-large gaps may be OK, but this gets back to the question of tolerable gap sizes. If these are large, everything becomes easier.

Fun fact: No more than 60 points can be placed on a sphere such that each point has an identical environment (for example, identical angles and distances to neighbors). These points correspond to the carbon atoms of the C60 fullerene:
Title: Re: Starship heat shield
Post by: hallmh on 06/10/2021 12:11 pm

A large (many-tile) triangular facet (the corners are in the pentagons) cannot be accurately tiled with regular hexagons, much less by hexagons of a single size.

I don't think there's any suggestion that the hexagons on the surface of a Goldberg polyhedron are the same size, or even regular. GPs have three rules: faces must be pentagonal or hexagonal, they must meet at 3-cornered vertices, and they have icosahedral symmetry. Nothing in there about regular polygons - although I expect the pentagons are regular, and the hexagons are sometimes regular.

So the previous post, which said that one arrangement had pentagons and two sizes of hexagon, seems perfectly reasonable to me.
Title: Re: Starship heat shield
Post by: ETurner on 06/10/2021 01:12 pm

A large (many-tile) triangular facet (the corners are in the pentagons) cannot be accurately tiled with regular hexagons, much less by hexagons of a single size.

I don't think there's any suggestion that the hexagons on the surface of a Goldberg polyhedron are the same size, or even regular. GPs have three rules: faces must be pentagonal or hexagonal, they must meet at 3-cornered vertices, and they have icosahedral symmetry. Nothing in there about regular polygons - although I expect the pentagons are regular, and the hexagons are sometimes regular.

So the previous post, which said that one arrangement had pentagons and two sizes of hexagon, seems perfectly reasonable to me.
Why two sizes, not one or twenty? In harsh, immutable, geometric reality, a set of polygons with only two or three shapes can form only curved polyhedral surfaces with very few facets compared to the number of tiles on the SS nosecone. I invite anyone to try to find an actual example of a few shapes tiling a sphere with an unbounded number of facets. The claims that posters have made regarding Goldberg polyhedra are mistaken.

Many people apparently have strong but misleading intuitions about this kind of question. (Intuition test:
Why are there no more than 5 Platonic solids and 13 Archimedean solids (https://en.wikipedia.org/wiki/Archimedean_solid )?

Title: Re: Starship heat shield
Post by: Redclaws on 06/10/2021 01:34 pm

A large (many-tile) triangular facet (the corners are in the pentagons) cannot be accurately tiled with regular hexagons, much less by hexagons of a single size.

I don't think there's any suggestion that the hexagons on the surface of a Goldberg polyhedron are the same size, or even regular. GPs have three rules: faces must be pentagonal or hexagonal, they must meet at 3-cornered vertices, and they have icosahedral symmetry. Nothing in there about regular polygons - although I expect the pentagons are regular, and the hexagons are sometimes regular.

So the previous post, which said that one arrangement had pentagons and two sizes of hexagon, seems perfectly reasonable to me.
Why two sizes, not one or twenty? In harsh, immutable, geometric reality, a set of polygons with only two or three shapes can form only curved polyhedral surfaces with very few facets compared to the number of tiles on the SS nosecone. I invite anyone to try to find an actual example of a few shapes tiling a sphere with an unbounded number of facets. The claims that posters have made regarding Goldberg polyhedra are mistaken.

Many people apparently have strong but misleading intuitions about this kind of question. (Intuition test:
Why are there no more than 5 Platonic solids and 13 Archimedean solids (https://en.wikipedia.org/wiki/Archimedean_solid)?

You’ll want to add a space before the closing parenthesis or it becomes part of the link.

Can you explain the use/meaning of the “facets” in the sentence above?  Does it refer to the tiles? It sounds like it refers to facets of the sphere, which doesn’t make sense (at least to me).
Title: Re: Starship heat shield
Post by: edzieba on 06/10/2021 01:36 pm
In harsh, immutable, geometric reality, a set of polygons with only two or three shapes can form only curved polyhedral surfaces with very few facets compared to the number of tiles on the SS nosecone.
Luckily Starship only needs to fly in the upper atmosphere rather than in a world of perfect polyhedra, so it is acceptable to have varying gaps between tiles, varying tile tangents, and incomplete tilings (stick all your singularities on the back where you aren't applying any tiles) as long as they are within acceptable tolerances.
Title: Re: Starship heat shield
Post by: Redclaws on 06/10/2021 01:48 pm

A large (many-tile) triangular facet (the corners are in the pentagons) cannot be accurately tiled with regular hexagons, much less by hexagons of a single size.

I don't think there's any suggestion that the hexagons on the surface of a Goldberg polyhedron are the same size, or even regular. GPs have three rules: faces must be pentagonal or hexagonal, they must meet at 3-cornered vertices, and they have icosahedral symmetry. Nothing in there about regular polygons - although I expect the pentagons are regular, and the hexagons are sometimes regular.

So the previous post, which said that one arrangement had pentagons and two sizes of hexagon, seems perfectly reasonable to me.
Why two sizes, not one or twenty? In harsh, immutable, geometric reality, a set of polygons with only two or three shapes can form only curved polyhedral surfaces with very few facets compared to the number of tiles on the SS nosecone. I invite anyone to try to find an actual example of a few shapes tiling a sphere with an unbounded number of facets. The claims that posters have made regarding Goldberg polyhedra are mistaken.

Many people apparently have strong but misleading intuitions about this kind of question. (Intuition test:
Why are there no more than 5 Platonic solids and 13 Archimedean solids (https://en.wikipedia.org/wiki/Archimedean_solid)?

The 5 Platonic solids are about angles and angle defects.  When you stick shapes with more than N sides together in the manner of a Platonic solid, you need some leftover angle to make the tiling non-flat (and at least 3 sides meeting).  The corner angle of a 6 sided polygon is 132 degrees, so you can’t put 3 of them in to 360 degrees.

I would be curious to hear an intuitive explanation of the Archimedean solids, I can’t see one, but I never studied topology either.
Title: Re: Starship heat shield
Post by: Redclaws on 06/10/2021 01:53 pm
In harsh, immutable, geometric reality, a set of polygons with only two or three shapes can form only curved polyhedral surfaces with very few facets compared to the number of tiles on the SS nosecone.
Luckily Starship only needs to fly in the upper atmosphere rather than in a world of perfect polyhedra, so it is acceptable to have varying gaps between tiles, varying tile tangents, and incomplete tilings (stick all your singularities on the back where you aren't applying any tiles) as long as they are within acceptable tolerances.

This times 1000.  They’ll get most of the way there and then fudge as needed.

I still think it’s interesting to ask what basic approach they’ll take before they fudge their way to the finish line (that’s not intended as a criticism) - tiling a cone with curved sides is not easily done without a lot of tile variation or comparatively complex (and irregular, with regard to the tiles appearing along a slice in the direction of airflow) tilings.
Title: Re: Starship heat shield
Post by: Redclaws on 06/10/2021 01:55 pm
In harsh, immutable, geometric reality, a set of polygons with only two or three shapes can form only curved polyhedral surfaces with very few facets compared to the number of tiles on the SS nosecone.
Luckily Starship only needs to fly in the upper atmosphere rather than in a world of perfect polyhedra, so it is acceptable to have varying gaps between tiles, varying tile tangents, and incomplete tilings (stick all your singularities on the back where you aren't applying any tiles) as long as they are within acceptable tolerances.

This times 1000.  They’ll get most of the way there and then fudge as needed.

I still think it’s interesting to ask what basic approach they’ll take before they fudge their way to the finish line (that’s not intended as a criticism) - tiling a cone with curved sides is not easily done without a lot of tile variation or comparatively complex (and irregular, with regard to the tiles appearing along a slice in the direction of airflow) tilings.

I imagine this has been covered in this thread (there’s a lot here...), but the basic approach the shuttle took to its curved surfaces is just tons and tons of tiles of differing sizes, right?
Title: Re: Starship heat shield
Post by: Reynold on 06/10/2021 02:34 pm
I imagine this has been covered in this thread (there’s a lot here...), but the basic approach the shuttle took to its curved surfaces is just tons and tons of tiles of differing sizes, right?

Yes, and that took an estimated 300 man-years to install on Columbia (see earlier post), so I think the people in this thread are hoping there is a better solution.  There are a lot of smart people in NSF, so it is possible they will even come up with an idea that SpaceX has not thought of.  Until they read this thread.  :)
Title: Re: Starship heat shield
Post by: ETurner on 06/10/2021 02:36 pm

A large (many-tile) triangular facet (the corners are in the pentagons) cannot be accurately tiled with regular hexagons, much less by hexagons of a single size.

I don't think there's any suggestion that the hexagons on the surface of a Goldberg polyhedron are the same size, or even regular. GPs have three rules: faces must be pentagonal or hexagonal, they must meet at 3-cornered vertices, and they have icosahedral symmetry. Nothing in there about regular polygons - although I expect the pentagons are regular, and the hexagons are sometimes regular.

So the previous post, which said that one arrangement had pentagons and two sizes of hexagon, seems perfectly reasonable to me.
Why two sizes, not one or twenty? In harsh, immutable, geometric reality, a set of polygons with only two or three shapes can form only curved polyhedral surfaces with very few facets compared to the number of tiles on the SS nosecone. I invite anyone to try to find an actual example of a few shapes tiling a sphere with an unbounded number of facets. The claims that posters have made regarding Goldberg polyhedra are mistaken.

Many people apparently have strong but misleading intuitions about this kind of question. (Intuition test:
Why are there no more than 5 Platonic solids and 13 Archimedean solids (https://en.wikipedia.org/wiki/Archimedean_solid)? (https://en.wikipedia.org/wiki/Archimedean_solid)?)

You’ll want to add a space before the closing parenthesis or it becomes part of the link.

Can you explain the use/meaning of the “facets” in the sentence above?  Does it refer to the tiles? It sounds like it refers to facets of the sphere, which doesn’t make sense (at least to me).
I’m not sure what word to use, but I mean something like “geometric features that would correspond to closely-fit tiles that cover a sphere”. (Thanks, I’ve fixed the link.)
Title: Re: Starship heat shield
Post by: Redclaws on 06/10/2021 02:52 pm

A large (many-tile) triangular facet (the corners are in the pentagons) cannot be accurately tiled with regular hexagons, much less by hexagons of a single size.

I don't think there's any suggestion that the hexagons on the surface of a Goldberg polyhedron are the same size, or even regular. GPs have three rules: faces must be pentagonal or hexagonal, they must meet at 3-cornered vertices, and they have icosahedral symmetry. Nothing in there about regular polygons - although I expect the pentagons are regular, and the hexagons are sometimes regular.

So the previous post, which said that one arrangement had pentagons and two sizes of hexagon, seems perfectly reasonable to me.
Why two sizes, not one or twenty? In harsh, immutable, geometric reality, a set of polygons with only two or three shapes can form only curved polyhedral surfaces with very few facets compared to the number of tiles on the SS nosecone. I invite anyone to try to find an actual example of a few shapes tiling a sphere with an unbounded number of facets. The claims that posters have made regarding Goldberg polyhedra are mistaken.

Many people apparently have strong but misleading intuitions about this kind of question. (Intuition test:
Why are there no more than 5 Platonic solids and 13 Archimedean solids (https://en.wikipedia.org/wiki/Archimedean_solid)? (https://en.wikipedia.org/wiki/Archimedean_solid)?)

You’ll want to add a space before the closing parenthesis or it becomes part of the link.

Can you explain the use/meaning of the “facets” in the sentence above?  Does it refer to the tiles? It sounds like it refers to facets of the sphere, which doesn’t make sense (at least to me).
I’m not sure what word to use, but I mean something like “geometric features that would correspond to closely-fit tiles that cover a sphere”. (Thanks, I’ve fixed the link.)

Thanks, that makes sense.  I think saying “of the sphere” is a little puzzling there.  Maybe break out that facets refers to tiles in a tiling of the sphere (which makes it faceted, which a bare sphere is of course not).
Title: Re: Starship heat shield
Post by: eriblo on 06/10/2021 03:01 pm
I imagine this has been covered in this thread (there’s a lot here...), but the basic approach the shuttle took to its curved surfaces is just tons and tons of tiles of differing sizes, right?
Yes, and that took an estimated 300 man-years to install on Columbia (see earlier post), so I think the people in this thread are hoping there is a better solution.  There are a lot of smart people in NSF, so it is possible they will even come up with an idea that SpaceX has not thought of.  Until they read this thread.  :)
Yes, there are some strong opinions about the allowable size of the set of tile types - 1 being a common suggestion ::) 
While the cylindrical portion of Starship can be perfectly tiled with regular hexagons this is sadly not the case for compound curves like the nose cone or flap fairings. There are various possible approaches:

Somewhat similar to the shuttle would be to do perfect tiling by fitting polyhedra constructed from regular polygons around the shape and then projecting the vertices onto the curved surface. This is the principle of the Goldberg polyhedra mentioned above (and geodesic domes which are their mathematical duals). The result will be very nice looking surfaces covered with almost regular polygons of similar sizes (can be chosen to be mostly hexagons with some pentagons and/or diamonds) - but each tile will more or less be unique.

The number of tile types can be reduced, for example by adjusting tiles which are close to the same shape at the cost of the rest being slightly less symmetric and/or bigger gaps. Some think that relatively large gaps are permissible resulting in a much smaller number of types needed (just the standard hexagons if taken to the extreme...)

The other major suggestion is to continue the hexagon pattern from the cylinder upwards by tapering the hexagons as the radius decreases. This will reduce it to one or two unique types for each row (if one wants to avoid large numbers of excessively narrow tiles) while allowing perfect tiling of the nose cone.
Title: Re: Starship heat shield
Post by: Greg Hullender on 06/10/2021 03:12 pm
The 5 Platonic solids are about angles and angle defects.  When you stick shapes with more than N sides together in the manner of a Platonic solid, you need some leftover angle to make the tiling non-flat (and at least 3 sides meeting).  The corner angle of a 6 sided polygon is 132 degrees, so you can’t put 3 of them in to 360 degrees.

I would be curious to hear an intuitive explanation of the Archimedean solids, I can’t see one, but I never studied topology either.
The extension of this to the 13 Archimedean Solids is pretty straightforward. Does this answer your question: https://ywhmaths.webs.com/Geometry/ArchimedeanSolids.pdf
Title: Re: Starship heat shield
Post by: cscott on 06/10/2021 03:19 pm
You only need two tile types: a hexagon and a diamond.  You intersperse a diamond to "drop a tile".  The nose cone ogive has a specific radius at every height.  If on row N it has a radius of (making up numbers) 540 hexagons, and on row N+2 it has a radius of 520 hexagons, then row N+1 includes 20 diamond tiles replacing hexes, appropriately spaced out.

This also works in the other orientation (hexagon flats facing up), where you end up with pentagons instead of diamonds, but all the photos I've seen so far of cylinder sections have the hexagon points facing up, so let's assume that's how the nosecone will be oriented as well.

This solution is somewhat "lumpy" in that the curvature change happens at the points where the diamonds are interspersed, but a little bit of lumpiness could be acceptable given the ratio of nosecone to tile size.

I'm assuming the nosecone starting radius is 9m.  What's the height of the nosecone from start of taper to tip, and what's the tile size?  Assuming a Von Kármán ogive (https://en.wikipedia.org/wiki/Nose_cone_design#Haack_series) it would be straightforward to estimate how many diamonds are needed in each row.
Title: Re: Starship heat shield
Post by: edzieba on 06/10/2021 03:34 pm
This is the principle of the Goldberg polyhedra mentioned above (and geodesic domes which are their mathematical duals). The result will be very nice looking surfaces covered with almost regular polygons of similar sizes (can be chosen to be mostly hexagons with some pentagons and/or diamonds) - but each tile will more or less be unique.
It can be quite a lot less than unique, e.g. 5 hexagon variants and one pentagon variant (http://dmccooey.com/polyhedra/DualGeodesicIcosahedron13.html). Even better, many of those variants have edge lengths within 1% of each other, so those 5 variants could be covered by 3 or maybe 2 variants depending on acceptable gap variance. But on top of that, you do not need to perfectly tile Starship, you only need a partial tiling, which means many of the problems encountered in perfect sphere tilings simply are not problems in the first place.
Title: Re: Starship heat shield
Post by: rakaydos on 06/10/2021 03:41 pm
Given that we've observed SpaceX use 3 sizes of regular hexagon, plus a slightly-more-than half-tile pentagon...

How many solutions to tiling the nose fit with just those tile sizes and no more?
Title: Re: Starship heat shield
Post by: cscott on 06/10/2021 03:49 pm
The issue with the half tile pentagon is that it leaves "channels" running circumferentially around the starship.  Folks have *claimed* that such unimpeded plasma paths would be Very Bad and so I think we've mostly avoided using them.

The "easiest" tile pattern is just to tile the nose in horizontal strips, with pentagons on the bottom and top.  This can accommodate any misalignment in the radius (number of hexagons) in each strip as the nose tapers.  The only reason that hasn't been seriously proposed is the plasma channel 'problem'.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/10/2021 04:05 pm
The issue with the half tile pentagon is that it leaves "channels" running circumferentially around the starship.  Folks have *claimed* that such unimpeded plasma paths would be Very Bad and so I think we've mostly avoided using them.

One of those "folks" is Elon himself.

Given that SpaceX are undisputed experts at Computational Fluid Dynamics (CFD) simulations, I'm inclined to believe him.

Title: Re: Starship heat shield
Post by: cscott on 06/10/2021 04:07 pm
Just to add some ballpark numbers:

From https://forum.nasaspaceflight.com/index.php?topic=51474.msg2111091#msg2111091 we have an estimate of tile being 35cm-40cm, presumably across the flats (not point to point).  I'm going to use 38.5cm as the flat-to-flat distance, because it makes 6 rows fit exactly in 2m, which is convenient for this estimate. (Two rows fit in 1.5 x the point-to-point height because of the way the hexagons tile.)

The Starship payload users guide gives radii vs height.  This is for the *inside* of the payload fairing, not the outside, but since we're just getting a ballpark estimate we'll use this.

Number of tiles will be pi*radius/.385, rounded up, because we're only tiling the windward half.

So we've got something like:

Height:  Radius:  # of tiles
 8m  4.00m  33
 9m  3.85m  31
10m 3.68m  30
11m 3.49m  28
12m 3.27m  27
13m 3.04m  25
14m 2.78m  23
15m 2.51m  20
16m 2.20m  18
17.24m 1.80m 15

So we'd only need 3 diamond tiles in the 6 rows between 8m and 10m, about 1 in every other row.
In the sharper section between 15m and 17m, we'd need 5 diamond tiles in 6 rows, so about 1/row.

On the other hand, the relatively small number of "curvature adjustment points" might make the tiled curvature somewhat lumpy.  But you would only need about 15 diamond tiles compared to 250 hexagon tiles to make this work.
Title: Re: Starship heat shield
Post by: OTV Booster on 06/10/2021 04:21 pm
The issue with the half tile pentagon is that it leaves "channels" running circumferentially around the starship.  Folks have *claimed* that such unimpeded plasma paths would be Very Bad and so I think we've mostly avoided using them.

One of those "folks" is Elon himself.

Given that SpaceX are undisputed experts at Computational Fluid Dynamics (CFD) simulations, I'm inclined to believe him.
I asked a question earlier about laminar flow velocity in relation to groove dimension and got no reply. There must be some spherical cow relationship for a starting point in figuring out what depth, width and angle relationships might introduce turbulence. I can't even figure out search terms to look this up without the search itself becoming a research project.
Title: Re: Starship heat shield
Post by: eriblo on 06/10/2021 04:42 pm
This is the principle of the Goldberg polyhedra mentioned above (and geodesic domes which are their mathematical duals). The result will be very nice looking surfaces covered with almost regular polygons of similar sizes (can be chosen to be mostly hexagons with some pentagons and/or diamonds) - but each tile will more or less be unique.
It can be quite a lot less than unique, e.g. 5 hexagon variants and one pentagon variant (http://dmccooey.com/polyhedra/DualGeodesicIcosahedron13.html). Even better, many of those variants have edge lengths within 1% of each other, so those 5 variants could be covered by 3 or maybe 2 variants depending on acceptable gap variance. But on top of that, you do not need to perfectly tile Starship, you only need a partial tiling, which means many of the problems encountered in perfect sphere tilings simply are not problems in the first place.
Yes, for a sphere you have the inherent symmetry of the base polyhedron around each of the original vertices. The problem is when you deform it into a ogive surface so that the symmetry is only preserved perpendicular to the rotational axis...
Title: Re: Starship heat shield
Post by: OTV Booster on 06/10/2021 04:48 pm
Something I don't remember seeing any discussion on is tile size and decreasing radius creating conformity problems. On a 9m tank the edges of the tiles stand off further than the center. As the radius decreases, if the tile stays the same size, the edge standoff would be greater.


Doing small tweaks to the tile size so other shapes can be inserted to improve surface mapping doesn't make this go away. This disparity between a flat tile and a curved surface has been suggested as a way of adding tension to dampen vibration. If the disparity grows too great, this technique stops working. Worse, a single tile failure exposes a sizable pocket under the next tile just waiting for some flow to rip it off. This could easily cascade into a catastrophic failure.


My conclusion is that once tiling reaches the nose cone the tiles have to start getting smaller. On the nose itself, tufroc or carbon-carbon might be acceptable. If that increases maintenance, well, it is what it is.

Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/10/2021 04:53 pm
Just to add some ballpark numbers:
Height:  Radius:  # of tiles
 8m  4.00m  33
 9m  3.85m  31
10m 3.68m  30
11m 3.49m  28
12m 3.27m  27
13m 3.04m  25
14m 2.78m  23
15m 2.51m  20
16m 2.20m  18
17.24m 1.80m 15


Great analysis but the payload numbers are 1 meter shorter (diameter) than the actual steel likely due to a half meter keep out on each side.
Title: Re: Starship heat shield
Post by: ETurner on 06/10/2021 05:35 pm
Here’s a re-drawn illustration that shows the geometric principle of a scheme that can double/halve the number of tiles in a circumferential band (imagine this on paper wrapped around a cone). This is directly comparable to schemes illustrated by other posters above, but the tile shapes are closer to hexagonal. Also, it’s cool and looks like 5-7 defects in graphene.

[Edit: See this post (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2253561#msg2253561) for a more finished version.]
Title: Re: Starship heat shield
Post by: SteveU on 06/10/2021 05:38 pm
Here’s a re-drawn illustration that shows the geometric principle of a scheme that can double/halve the number of tiles in a circumferential band (imagine this on paper wrapped around a cone). This is directly comparable to schemes illustrated by other posters above, but the tile shapes are closer to hexagonal. Also, it’s cool and looks like 5-7 defects in graphene.
It would help if you labeled each tile size/shape - think I count 7?
Title: Re: Starship heat shield
Post by: eriblo on 06/10/2021 05:52 pm
Just to add some ballpark numbers:

From https://forum.nasaspaceflight.com/index.php?topic=51474.msg2111091#msg2111091 we have an estimate of tile being 35cm-40cm, presumably across the flats (not point to point).  I'm going to use 38.5cm as the flat-to-flat distance, because it makes 6 rows fit exactly in 2m, which is convenient for this estimate. (Two rows fit in 1.5 x the point-to-point height because of the way the hexagons tile.)

[...]
SpaceX have very nicely simplified our pixel counting by providing a ruler - many of the barrel sections have the circumference labeled in increments of 20 cm, see for example this post from SN10 (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2185904#msg2185904).

Lining these up with the studs gives very close to 11 marks / 9 stud patterns, i.e. ~24.4 cm small diameter (28.2 cm large diameter) for the "standard" tiles. Looking quickly at the small sub-patch there is some dirt but it looks like 3 of the large tiles are close to 5 marks wide, i.e. 33 cm small diameter, 38.5 cm large diameter.
Title: Re: Starship heat shield
Post by: Redclaws on 06/10/2021 06:02 pm
The 5 Platonic solids are about angles and angle defects.  When you stick shapes with more than N sides together in the manner of a Platonic solid, you need some leftover angle to make the tiling non-flat (and at least 3 sides meeting).  The corner angle of a 6 sided polygon is 132 degrees, so you can’t put 3 of them in to 360 degrees.

I would be curious to hear an intuitive explanation of the Archimedean solids, I can’t see one, but I never studied topology either.
The extension of this to the 13 Archimedean Solids is pretty straightforward. Does this answer your question: https://ywhmaths.webs.com/Geometry/ArchimedeanSolids.pdf

Ah, yes, thank you!  That is pretty straightforward.  The missing part for me was a correct understanding of the definition of Archimedean solid.  (or at least an understanding in those terms).
Title: Re: Starship heat shield
Post by: Redclaws on 06/10/2021 06:08 pm
The issue with the half tile pentagon is that it leaves "channels" running circumferentially around the starship.  Folks have *claimed* that such unimpeded plasma paths would be Very Bad and so I think we've mostly avoided using them.

One of those "folks" is Elon himself.

Given that SpaceX are undisputed experts at Computational Fluid Dynamics (CFD) simulations, I'm inclined to believe him.
I asked a question earlier about laminar flow velocity in relation to groove dimension and got no reply. There must be some spherical cow relationship for a starting point in figuring out what depth, width and angle relationships might introduce turbulence. I can't even figure out search terms to look this up without the search itself becoming a research project.

There should be some empirical rules of thumb, but understanding the transition between laminar and turbulent flow in general is literally one of the most important open problems in mechanics.
Title: Re: Starship heat shield
Post by: ETurner on 06/10/2021 06:14 pm
Here’s a re-drawn illustration that shows the geometric principle of a scheme that can double/halve the number of tiles in a circumferential band (imagine this on paper wrapped around a cone). This is directly comparable to schemes illustrated by other posters above, but the tile shapes are closer to hexagonal. Also, it’s cool and looks like 5-7 defects in graphene.
It would help if you labeled each tile size/shape - think I count 7?
There are 5 shapes shown -- each all-hexagon band has a single, bilaterally symmetric tile shape.

BTW, the role of the illustrated pattern is the same as the role of the patterns in eriblo’s diagrams here (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2250067#msg2250067). The number of shapes required for a whole nosecone depends less on the doubling/halving bands than it does on the tolerance for gap variations in the more numerous bands of tapered hexagons. Hexagon shapes can be reused if gaps are allowed to vary a bit, but perfect tiling requires one shape per row.
Title: Re: Starship heat shield
Post by: cscott on 06/10/2021 06:16 pm
So here's what the 'diamond defect' pattern would look like.  This is using the same 'ballpark' dimensions in my previous post, and follows the inside rather than the outside of the fairing.  Still, you can print this out and cut it out and tape it together and see how smooth/lumpy it ends up.
Title: Re: Starship heat shield
Post by: eriblo on 06/10/2021 06:18 pm
Here’s a re-drawn illustration that shows the geometric principle of a scheme that can double/halve the number of tiles in a circumferential band (imagine this on paper wrapped around a cone). This is directly comparable to schemes illustrated by other posters above, but the tile shapes are closer to hexagonal. Also, it’s cool and looks like 5-7 defects in graphene.
It would help if you labeled each tile size/shape - think I count 7?
There are 5 shapes shown -- each all-hexagon band has a single, bilaterally symmetric tile shape.

BTW, the role of the illustrated pattern is the same as the role of the patterns in eriblo’s diagrams here (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2250067#msg2250067). The number of shapes required for a whole nosecone depends less on the doubling/halving bands than it does on the tolerance for gap variations in the more numerous bands of tapered hexagons. Hexagon shapes can be reused if gaps are allowed to vary a bit, but perfect tiling requires one shape per row.
Indeed, for a flat cone you can re-use the same tapered hexagons whenever the radius doubles but for a ogive each row is unique as the surface angle changes as well. It should however be possible to use the same hexagon (upside down) for the bottom row and the first transition row by tweaking the pentagons and heptagons.
Title: Re: Starship heat shield
Post by: ETurner on 06/10/2021 06:20 pm
Still, you can print this out and cut it out and tape it together and see how smooth/lumpy it ends up.
These will not be nice:
Title: Re: Starship heat shield
Post by: ETurner on 06/10/2021 06:43 pm
More 5-6-7 geometric motifs. Three (5?) tile shapes + some gap variability can do a lot.
Source here: https://science.sciencemag.org/content/330/6006/946 (https://science.sciencemag.org/content/330/6006/946)
[Edit: At least 2 hexagons adjacent to the 5-7 pairs should probably be special, asymmetric shapes hence maybe 5 rather than 3 shapes.]

[Edit: See this post (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2253561#msg2253561) for a more finished version]
Title: Re: Starship heat shield
Post by: r8ix on 06/10/2021 06:54 pm
It's important to remember that they have more flexibility than some of the purely geometric speculation allows for, because they're only goin half-way around. That gives them a lot of wiggle room at the (literal) edges, which can simplify things on the "belly".
Title: Re: Starship heat shield
Post by: cscott on 06/10/2021 07:20 pm
Still, you can print this out and cut it out and tape it together and see how smooth/lumpy it ends up.
These will not be nice:
Yes, but your 5-6-7 pattern will be almost the same.  The vertex angle is related to how much you are reducing the circumference.  I'm doing "1 hex flat-to-flat width in one row", your 5-6-7 pattern reduces the circumference 2 hex widths in 3(ish) rows.  So the polyhedron vertex angle is much the same.

You can snub the vertex to smooth it out by using a larger composite tile at the vertex.  In the diamond defect case you can do this just by fusing the diamond to one or all of the adjacent hexagons -- and you'd still only have two tile shapes.

Your version effectively uses five tile shapes to snub the vertex in a slightly different way.

But the real improvement would be a scheme to reduce the circumference by a small fraction of a full flat-to-flat width.  The would increase the number of vertices in the polyhedral approximation.
Title: Re: Starship heat shield
Post by: ETurner on 06/10/2021 07:46 pm
Still, you can print this out and cut it out and tape it together and see how smooth/lumpy it ends up.
These will not be nice:
Yes, but your 5-6-7 pattern will be almost the same.  The vertex angle is related to how much you are reducing the circumference.  I'm doing "1 hex flat-to-flat width in one row", your 5-6-7 pattern reduces the circumference 2 hex widths in 3(ish) rows.  So the polyhedron vertex angle is much the same.

You can snub the vertex to smooth it out by using a larger composite tile at the vertex.  In the diamond defect case you can do this just by fusing the diamond to one or all of the adjacent hexagons -- and you'd still only have two tile shapes.

Your version effectively uses five tile shapes to snub the vertex in a slightly different way.

But the real improvement would be a scheme to reduce the circumference by a small fraction of a full flat-to-flat width.  The would increase the number of vertices in the polyhedral approximation.
Try what you suggested above, starting with just a small, single-diamond region if you want: Cut it out, tape it together, and post a photo.

Also, in the 5-7 tilt.jpg image above, there are no vertices in the sense that I think you mean. The defects tilt the adjacent regions rather than forcing conical protrusions (5 + 7 = 6 + 6).
Title: Re: Starship heat shield
Post by: Oersted on 06/10/2021 08:02 pm
The inescapable conclusion from the last couple of pages is that they'll just have to ditch the sexy 50-cal bullet shape of Starship and transmogrify it into a tubby cylinder with a half-sphere on top. A heavy but necessary sacrifice on the altar of geometry...
Title: Re: Starship heat shield
Post by: ETurner on 06/10/2021 08:17 pm
The inescapable conclusion from the last couple of pages is that they'll just have to ditch the sexy 50-cal bullet shape of Starship and transmogrify it into a tubby cylinder with a half-sphere on top. A heavy but necessary sacrifice on the altar of geometry...
Or maybe use 1/100 as many distinct tile shapes as there are distinct components in a Raptor (to pick a ratio out of Mars-thin air). Horrors!

We’ll see soon enough.
Title: Re: Starship heat shield
Post by: cscott on 06/10/2021 08:28 pm
Try what you suggested above, starting with just a small, single-diamond region if you want: Cut it out, tape it together, and post a photo.
I'd like to encourage you to do the same: expand your 5-6-7 into a full nose cone.  You'll see that each 5-6-7 places a vertex in a polyhedron approximation of the nose cone, and you'll have plenty of 6-6-6 "normal hexes" in between (because the nose cone does not taper all that quickly).
Quote
Also, in the 5-7 tilt.jpg image above, there are no vertices in the sense that I think you mean. The defects tilt the adjacent regions rather than forcing conical protrusions (5 + 7 = 6 + 6).
Tilting adjacent faces makes a vertex.
Title: Re: Starship heat shield
Post by: ETurner on 06/10/2021 08:53 pm
Try what you suggested above, starting with just a small, single-diamond region if you want: Cut it out, tape it together, and post a photo.
I'd like to encourage you to do the same: expand your 5-6-7 into a full nose cone.
I’ve suggested that you make a physical model of a small patch, not “a full nose cone”. You will find that it is a hopeless non-starter. I have nothing more to say. Here is the pattern again, a detail pulled from your large diagram:

Title: Re: Starship heat shield
Post by: Slarty1080 on 06/10/2021 09:35 pm
I strongly believe that Starship will have "perfect tiling", i.e. there will be no intentional gaps beyond those required by thermal contraction/expansion, vibrations and placement tolerances. It is going to need more types of tiles but it should be on the order of a few hundred with a decent number of tiles for most of them. For the nose cone I am personally a fan of the tapered hexagons suggested on the first page of this thread, with each row being identical. My addition would be a doubling once the tiles get wide enough which would require a handful of rows to use two mirrored pentagonal tile types instead. 

Paraphrasing Elon in the Joe Rogan podcast:
You have to get the gaps just right, if it gets too big you get plasma in the crack (and that's bad) and if it's too small they are going to bang together.

If cm scale gaps were ok they would hardly be concerned about differential thermal expansion and vibrations. Sure, Starship would likely survive with big gaps or even missing tiles. The blankets are made from similar materials and could survive similar temperatures as the tiles (if not higher depending on composition) but turbulence, shock impingement and lower emissivity would lead to higher temperatures. The steel can get quite hot before failing but will start to anneal and lose the hardening at a significantly lower temperature - fine for survivability but likely instant scrapping if it happens in the tanks.

Also remember that re-entries from LEO, while being by far the most common case, represent the lower end of the performance envelope. I am really curious as to how far they can take the reusable tiles or whether they will need ablative solutions for high energy tankers or lunar/Mars returns.
The narrowing hexagon approach on page 1 shows promise but will potentially suffer from narrow tiles towards the nose tip. So I'm interested in your double pentagon tile idea but I can't quite imagine them. Would these tiles have a some concave edges? And how would they link up with the hexagonal tiles? I note that the hex "grain" on starship runs around the circumference rather than vertically up the side. Any chance of a diagram?
Behold the Diagrams! Quick and dirty with greatly exaggerated differences between rows - if one limits tiles to the same maximum dimensions then a doubling is only needed for every factor of 2 change in nose radius. The one I meant was the first one but the others are options if one wants to avoid the two tile long straight gap at the cost of a notched tile or a smaller insert diamond tile (which can be bigger at the cost of three instead of two types of tiles).
The problem with these designs (and with the original on page 1) is that each row of tiles requires a different shape. In these examples there are 4 rows and 4 or more tile types. The top row is not compatible with the bottom row as the hexagon side lengths are different.
Title: Re: Starship heat shield
Post by: cscott on 06/10/2021 09:37 pm
The angle is indeed too sharp when you remove an entire hex-width from a row at one point.  (And I drafted my diamond shapes too squat.)  But my point is that your design also decreases the radius by the same amount in roughly the same vertical distance, and so will have exactly the same problems.

By the ballpark figures, you need to remove about 2 hex widths over 6 rows, and doing that at one or two locations is going to yield suboptimal results.  Let's say half a decagon is 'smooth enough' -- that implies that you need at least 5 "defect sites" to remove those 2 hex widths, so each defect site can only remove .4 (or less, if you have more defect sites) of a hex width.  Your 5-6-7 needs to be 6.6-x-7 -- and my "diamond defect" would be better if it removed 1/3 of a hex width per row instead of a full hex width.

(I'm assuming your top row of 5 is intended to be the same size/shape as your first row of 7.  If you are continuously scaling the hexagons as well then we should just return to the design of the very first post in this thread, which uses a different shape per row.  That's not a bad design, honestly.)

Replacing my diamond shape with a equal-sided pentagon (not the home-plate shape we've seen) would remove ~.37 of a hex width.  That's promising, but it leaves a persistent defect: that position in the row will have to be a "points sidewise" hexagon instead of a "points up" hexagon in all subsequent rows.  It could work, though...
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/10/2021 09:52 pm

It would be handy if there was just one tile for the entire ship, but there won't be. Its no big deal its not the shuttle. There seems to be a fixation on the idea that there has to be just a handful of tile types. There doesn't.

There is a not a fixation, there are those of us with manufacturing engineering experience that know that "less parts is better".   We "fixated" on having at most one type of fastener for an oscilloscope assembly (a specific example in my past).

The reasons are not just inventory management, though that is important, it's the ability of an operator to easily deal with more than one handful of parts at a time.  It is difficult to have more than 5-10 types of parts on hand at a manufacturing station in a building while sitting and reaching for the parts, and even more difficult while 40 meters in the air on a lift.  The more similar looking the parts, the lower the practical number, due to human cognition limitations.

Go ahead and work out the number of up/down lift movements, operator reaches, choice mistakes, at 40 meters in the air while dealing with 3 parts.  Now do that for 30 parts.   It'll be an order of magnitude more difficult for the 30 parts version.
Well perhaps fixation was the wrong word - I'm sorry. And I suspect that we don't even disagree. In fact I think everyone is in agreement that:
Using 40 odd different tile types is a pain in the neck and if at all possible it should be avoided.

But the real question is can it be avoided? If it can't be avoided then they will just have to use 40 types of tile inconvenient as it may be.

If it can be avoided then that would be fantastic and would be the way to go. I would dearly love to see the tile plan, but so far I am not convinced that it is possible. I have seen a lot of attempts shown that won't work.

That said I remain open minded to some solution being found. The most interesting so far is the Goldberg polyhedra concept. It works on a sphere with constant change in radius, but I don't think it works on a variable radius nose cone like Starship. Then again only half the ship needs tiling... Still trying to visualize this one. 
Title: Re: Starship heat shield
Post by: eriblo on 06/10/2021 10:37 pm
I strongly believe that Starship will have "perfect tiling", i.e. there will be no intentional gaps beyond those required by thermal contraction/expansion, vibrations and placement tolerances. It is going to need more types of tiles but it should be on the order of a few hundred with a decent number of tiles for most of them. For the nose cone I am personally a fan of the tapered hexagons suggested on the first page of this thread, with each row being identical. My addition would be a doubling once the tiles get wide enough which would require a handful of rows to use two mirrored pentagonal tile types instead. 

Paraphrasing Elon in the Joe Rogan podcast:
You have to get the gaps just right, if it gets too big you get plasma in the crack (and that's bad) and if it's too small they are going to bang together.

If cm scale gaps were ok they would hardly be concerned about differential thermal expansion and vibrations. Sure, Starship would likely survive with big gaps or even missing tiles. The blankets are made from similar materials and could survive similar temperatures as the tiles (if not higher depending on composition) but turbulence, shock impingement and lower emissivity would lead to higher temperatures. The steel can get quite hot before failing but will start to anneal and lose the hardening at a significantly lower temperature - fine for survivability but likely instant scrapping if it happens in the tanks.

Also remember that re-entries from LEO, while being by far the most common case, represent the lower end of the performance envelope. I am really curious as to how far they can take the reusable tiles or whether they will need ablative solutions for high energy tankers or lunar/Mars returns.
The narrowing hexagon approach on page 1 shows promise but will potentially suffer from narrow tiles towards the nose tip. So I'm interested in your double pentagon tile idea but I can't quite imagine them. Would these tiles have a some concave edges? And how would they link up with the hexagonal tiles? I note that the hex "grain" on starship runs around the circumference rather than vertically up the side. Any chance of a diagram?
Behold the Diagrams! Quick and dirty with greatly exaggerated differences between rows - if one limits tiles to the same maximum dimensions then a doubling is only needed for every factor of 2 change in nose radius. The one I meant was the first one but the others are options if one wants to avoid the two tile long straight gap at the cost of a notched tile or a smaller insert diamond tile (which can be bigger at the cost of three instead of two types of tiles).
The problem with these designs (and with the original on page 1) is that each row of tiles requires a different shape. In these examples there are 4 rows and 4 or more tile types. The top row is not compatible with the bottom row as the hexagon side lengths are different.
Yes, I believe this is the best you can do without gaps on a compound curve.
Title: Re: Starship heat shield
Post by: DistantTemple on 06/10/2021 11:18 pm
Here’s a re-drawn illustration that shows the geometric principle of a scheme that can double/halve the number of tiles in a circumferential band (imagine this on paper wrapped around a cone). This is directly comparable to schemes illustrated by other posters above, but the tile shapes are closer to hexagonal. Also, it’s cool and looks like 5-7 defects in graphene.
I like this a lot. It is clearly repeatable; the "top" row becoming the bottom row of the next repeat of the same pattern.

It appears to narrow much too quickly, but I'm certain that that can be adjusted accurately by lengthening all these tile designs vertically.

However, over the vertical repeat of the pattern, the number of horizontal hexagons halves! This seems far to fast, and would lead to extremely "tall" shapes, (and therefore vulnerable to snapping in half!), so despite its virtues, I think it needs further development to become "the answer".

Image credit: ETurner from his post linked and quoted here.
Title: Re: Starship heat shield
Post by: DistantTemple on 06/11/2021 12:00 am
Sorry I have not read all posts above.... but....
Everyone seems to be trying to cover the conical-ish nose as we see it, that is with horizontal (perpendicular to the long axis of the SS), meaning each band has a squeezed top in comparison to its bottom, and assuming one long horizontal seam is not allowed, gives rise to these beautiful, complex geometric designs.

However a cone is not a complex curve, and can be bent out of flat sheet! Therefore if it is tiled in rows of standard hexagons AS IF IT WERE STILL A FLAT SHEET then there should be no difficult gaps!

Unfortunately the nose is not a perfect cone, and much worse there is the transition from the cylinder, to the cone-ish, and the transition to the nose.

Leaving aside these issues, such a pattern would create a beautiful "bow up" on the belly of the nose, sweeping in a (seeming) smooth curve to the Elonerons!

EDIT: Added rough paper cone. No one else seems to have approached the issue from this pov.
Title: Re: Starship heat shield
Post by: Scintillant on 06/11/2021 01:22 am
Sorry I have not read all posts above.... but....
Everyone seems to be trying to cover the conical-ish nose as we see it, that is with horizontal (perpendicular to the long axis of the SS), meaning each band has a squeezed top in comparison to its bottom, and assuming one long horizontal seam is not allowed, gives rise to these beautiful, complex geometric designs.

However a cone is not a complex curve, and can be bent out of flat sheet! Therefore if it is tiled in rows of standard hexagons AS IF IT WERE STILL A FLAT SHEET then there should be no difficult gaps!

Unfortunately the nose is not a perfect cone, and much worse there is the transition from the cylinder, to the cone-ish, and the transition to the nose.

Leaving aside these issues, such a pattern would create a beautiful "bow up" on the belly of the nose, sweeping in a (seeming) smooth curve to the Elonerons!

A cone can be made from a sheet, yes, but the nose is far from a perfect cone. It's got variable curvature, whereas a cone has no curvature in the vertical direction. That's why you can't just tile the nose with hexagons - "leaving aside those issues" means solving an entirely different problem.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/11/2021 05:05 am
That said I remain open minded to some solution being found. The most interesting so far is the Goldberg polyhedra concept. It works on a sphere with constant change in radius, but I don't think it works on a variable radius nose cone like Starship. Then again only half the ship needs tiling... Still trying to visualize this one.

Perhaps there is a "fixation" on avoiding short but wide gaps.   I've seen posted shuttle data that shows that when items stick out it causes a lot of extra heating when it breaks up the laminar flow.

What about small gaps?  They aren't the same thing as items sticking out.  I don't know much about hypersonic air flow but I do know a bit about surfboard hydrodynamics, and items sticking out act on the water flow much differently than voids and indentations (voids are generally bad, things sticking out not so bad).   My point in bringing this up is that innies may not be the same thing as outies when it comes to heating.

A specific example is that when the Shuttle lost a tile over a steel bracing it wasn't fatal.  So a rather wide gap could be tolerated.

Wide gaps means less tile types, which is clear from all the excellent examples being posted here.

The gaps by themselves, as long as they don't involve disrupting the flow, are protected from radiant heating by the mineral wool (or whatever the blanket is), which at my guess is as good as the tiles at insulation, just not able to stay in place without the majority of its surface being covered with tiles.
Title: Re: Starship heat shield
Post by: Keldor on 06/11/2021 07:31 am
It's important to remember that they have more flexibility than some of the purely geometric speculation allows for, because they're only goin half-way around. That gives them a lot of wiggle room at the (literal) edges, which can simplify things on the "belly".

This doesn't make a difference here.  Any area of non-zero curvature will not be tilable by constant shapes.  All only having to deal with a portion of the curved area does is allow us to distort a flat tiling and not end up with singularities due to different topology.  However, a distorted tiling means different types of tiles, so it's not going to solve our problem.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 06/11/2021 08:26 am
How did they design the tiles for the Shuttle?Did they use some kind of algorithm?

Could be possible for SpaceX to code a program exploring a lot of possible tiling schems to find the best? Or is this a non automatable problem, that needs the human mind?
Title: Re: Starship heat shield
Post by: Horasio on 06/11/2021 09:01 am
How did they design the tiles for the Shuttle?Did they use some kind of algorithm?

Could be possible for SpaceX to code a program exploring a lot of possible tiling schems to find the best? Or is this a non automatable problem, that needs the human mind?

This is a very much automatable problem. We're looking at the field of "geometry processing" and "geometric design". I have seen several papers in this field that look at the problem of covering a freeform shape (the nosecone here, but these works have architecture in mind) with flat panel of as few as possible different types. If time permits, I'll try to dig these papers and put links here. (maybe google for 'computational architecture').

Also, this hexagonal tiling reminds me of "centroidal voronoi tesselation". A simple procedure would be to place (virtual) seeds on the surface of the nosecone, andd optimize them (by moving them around on the surface) so that each seed coincide with the centroid of its voronoi cell (in the Voronoi diagram of the seeds restricted to the surface, or the intrinsic Voronoi diagram).
Then, you will have a nice hexagonal tiling provided that there are justt the right number of seeds (otherwise, just add more, or remove some until happy). Problem will be that there will be many types of tiles, at least one per "horizontal row" of tiles, even if the optimization is done well. So then you should use that as input to the computation architecture stuff just mentioned.
(Just wrote this is a hurry, I'm sorry if it doesn't make sense  :))
Title: Re: Starship heat shield
Post by: cscott on 06/11/2021 01:07 pm
I'd really appreciate the links if you can dig them up.  I found this yesterday:
https://www.researchgate.net/publication/227280537_A_Note_on_Planar_Hexagonal_Meshes
Which goes over several ways to create hex tilings. It boils down to an optimization problem, and the optimizer could be given "identical tile shapes" as a goal.

Personally I'm optimistic that a mixture of hexes and regular pentagons with the same edge length *could* do the job.

But the neglected issue here is automation and that robot stud welder.  So far we've seen regular grids.  It may be that SpaceX "optimizes for manufacturability" here by using one tile shape per "latitude" (cf the first post in this thread) because it allows the stud attachment points to be on a regular grid, even if the tile shapes are different. The metal attachment brackets could also be substantially the same for every tile. OTOH that makes tile manufacturing more involved, with about 30 different tile shapes to juggle.  And as folks have noted, the tile sizes probably need to shrink at the tip of the nose, so you're going to have variations in your attachment grid in any case.

On the gripping hand: why build a fancy multiaxis robot if you didn't intent to take advantage of it by welding studs at essentially arbitrary points on a complex surface?  You probably have the same registration and reach problems whether you are trying to do a regular orthogonal grid or something free form.
Title: Re: Starship heat shield
Post by: rsdavis9 on 06/11/2021 02:15 pm
Okay I get .2435m for flat to flat size for the tiles.

Here is what I did:
1. Notice red line is the barrel size of 1.829m from various labels on rolls
2. Notice the blue is what a single tile "rises".
3. I count 8.66 tiles for the # of tiles per this barrel. 9 tiles but the last one is missing the slant part of the rise.
4. calcs
D= point to point
d= flat to flat
R= edge and radius
r=d/2
rise=1.5*R
R=rise/1.5
r=R*sqrt(3)/2

1.829m/8.66 =.211m rise
R=.211m/1.5 =  .1406m
r=.1406m*sqrt(3)/2 = .1217m
d=.1217m*2 = .2435m

I think I did the calc correctly.
https://en.wikipedia.org/wiki/Hexagon

Credit jack beyer from production update thread for the image.

Title: Re: Starship heat shield
Post by: rakaydos on 06/11/2021 03:38 pm
It's important to remember that they have more flexibility than some of the purely geometric speculation allows for, because they're only goin half-way around. That gives them a lot of wiggle room at the (literal) edges, which can simplify things on the "belly".

This doesn't make a difference here.  Any area of non-zero curvature will not be tilable by constant shapes.  All only having to deal with a portion of the curved area does is allow us to distort a flat tiling and not end up with singularities due to different topology.  However, a distorted tiling means different types of tiles, so it's not going to solve our problem.

I'm seeing a lot of "reduce the number of tiles in a band around starship's circomberence" approaches.

Has anyone tried "single unbroken line of hexagons from the edge of the cylinder to the nose, then tile in both directions for a quarter of a cone each, optimizing for minimize gaps"?

It's probably a more complicated problem, but as Keldor points out, it hides most of the worst distortions off the pattern.
Title: Re: Starship heat shield
Post by: Pueo on 06/11/2021 05:58 pm
This is the principle of the Goldberg polyhedra mentioned above (and geodesic domes which are their mathematical duals). The result will be very nice looking surfaces covered with almost regular polygons of similar sizes (can be chosen to be mostly hexagons with some pentagons and/or diamonds) - but each tile will more or less be unique.
It can be quite a lot less than unique, e.g. 5 hexagon variants and one pentagon variant (http://dmccooey.com/polyhedra/DualGeodesicIcosahedron13.html). Even better, many of those variants have edge lengths within 1% of each other, so those 5 variants could be covered by 3 or maybe 2 variants depending on acceptable gap variance. But on top of that, you do not need to perfectly tile Starship, you only need a partial tiling, which means many of the problems encountered in perfect sphere tilings simply are not problems in the first place.
Yes, for a sphere you have the inherent symmetry of the base polyhedron around each of the original vertices. The problem is when you deform it into a ogive surface so that the symmetry is only preserved perpendicular to the rotational axis...

This is why when I first suggested Goldberg polyhedra it was in the context of changing the nosecone geometry from an ogive to a hemisphere with an extensible drag reducing aerospike.  Such a drastic change to the vehicle geometry at this point makes it significantly less likely to be the approach taken by SpaceX.  Perhaps a sphere-capped bicone, tricone, or even quintcone that approximates the ogive more closely could be pursued, but I still find it unlikely.
Title: Re: Starship heat shield
Post by: OTV Booster on 06/11/2021 06:54 pm
The issue with the half tile pentagon is that it leaves "channels" running circumferentially around the starship.  Folks have *claimed* that such unimpeded plasma paths would be Very Bad and so I think we've mostly avoided using them.

One of those "folks" is Elon himself.

Given that SpaceX are undisputed experts at Computational Fluid Dynamics (CFD) simulations, I'm inclined to believe him.
I asked a question earlier about laminar flow velocity in relation to groove dimension and got no reply. There must be some spherical cow relationship for a starting point in figuring out what depth, width and angle relationships might introduce turbulence. I can't even figure out search terms to look this up without the search itself becoming a research project.

There should be some empirical rules of thumb, but understanding the transition between laminar and turbulent flow in general is literally one of the most important open problems in mechanics.
Seems like SX will be interested in flight data on this. What would the instrumentation look like? What I come up with is infrared imaging from inside the tank or maybe acoustic. Maybe both to check against each other. Anything else besides a ridiculously big array of thermocouples? 
Title: Re: Starship heat shield
Post by: OTV Booster on 06/11/2021 06:56 pm
Here’s a re-drawn illustration that shows the geometric principle of a scheme that can double/halve the number of tiles in a circumferential band (imagine this on paper wrapped around a cone). This is directly comparable to schemes illustrated by other posters above, but the tile shapes are closer to hexagonal. Also, it’s cool and looks like 5-7 defects in graphene.
It would help if you labeled each tile size/shape - think I count 7?
There are 5 shapes shown -- each all-hexagon band has a single, bilaterally symmetric tile shape.

BTW, the role of the illustrated pattern is the same as the role of the patterns in eriblo’s diagrams here (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2250067#msg2250067). The number of shapes required for a whole nosecone depends less on the doubling/halving bands than it does on the tolerance for gap variations in the more numerous bands of tapered hexagons. Hexagon shapes can be reused if gaps are allowed to vary a bit, but perfect tiling requires one shape per row.
Maybe variable gaps would be a good thing for a first flight. Get some data on limits.
Title: Re: Starship heat shield
Post by: maquinsa on 06/11/2021 07:10 pm
Why not use a rotational hexagonal pattern for the nose heatshield? I’ve seen somewhere a render that used this pattern
Edit: added render
Edit 2: credit alex svan
Title: Re: Starship heat shield
Post by: maquinsa on 06/11/2021 07:13 pm
Why not use a rotational hexagonal pattern for the nose heatshield? I’ve seen somewhere a render that used this pattern
Edit: added render

It leaves no space between tiles but leaves rough edges that would need a different type of tiles
Title: Re: Starship heat shield
Post by: JCopernicus on 06/11/2021 07:22 pm
Why not use a rotational hexagonal pattern for the nose heatshield? I’ve seen somewhere a render that used this pattern
Edit: added render

It leaves no space between tiles but leaves rough edges that would need a different type of tiles

Better to have small different trim and the infill the same, than a varied infill.
Title: Re: Starship heat shield
Post by: cscott on 06/11/2021 07:48 pm
More to the point, that is just a CGI texture map; it ignores physical constraints.  See this section here for example, where you can see a number of implausible tile boundaries.
Title: Re: Starship heat shield
Post by: Horasio on 06/11/2021 08:32 pm
How did they design the tiles for the Shuttle?Did they use some kind of algorithm?

Could be possible for SpaceX to code a program exploring a lot of possible tiling schems to find the best? Or is this a non automatable problem, that needs the human mind?

This is a very much automatable problem. We're looking at the field of "geometry processing" and "geometric design". I have seen several papers in this field that look at the problem of covering a freeform shape (the nosecone here, but these works have architecture in mind) with flat panel of as few as possible different types. If time permits, I'll try to dig these papers and put links here. (maybe google for 'computational architecture').
[...]

I'd really appreciate the links if you can dig them up.  I found this yesterday:
https://www.researchgate.net/publication/227280537_A_Note_on_Planar_Hexagonal_Meshes
Which goes over several ways to create hex tilings. It boils down to an optimization problem, and the optimizer could be given "identical tile shapes" as a goal.
[...]

So, the paper that I had in mind is here : http://graphics.stanford.edu/~niloy/research/paneling/paneling_sig_10.html (http://graphics.stanford.edu/~niloy/research/paneling/paneling_sig_10.html)
and more generally, the work of Helmut Pottmann and his colleagues during the last decade, say.
The referenced paper is more general than required with SS nosecone, but it does address the question of minimizing the number of panel types.
Hope this satisfies your curiosity  ;D
Title: Re: Starship heat shield
Post by: OTV Booster on 06/11/2021 09:01 pm
Manufacturability and repairability are more important than solving interesting but complex topo problems.


The nose will be one of the most difficult thermal problems. The small radius means that the shock standoff will be thinnest here and in all probability the heatshield will have to cover the entire circumference in this area. I would guess that the laminar flow velocity will be atypically high over the nose right at the point where a flat tile on a highly curved surface will offer an intrusion at each vertex. IMO it will need atypically small tiles, a monolithic curved custom piece or a curved custom multi piece assembly.


On the Ogive, ISTM that each row could be a unique hex and keep manufacturing overall simpler than a complex array of hexes, penta's and triangles. The right and left sides of each tile would taper just enough to compensate for the change in circumference. The top vertex might need adjusting, as would the bottom vertex on the next row up. As it's already a custom shape there is no added discomfort once the tile moulds are built.  As the vertical radius decreases the top to bottom apex dimension would have to diminish else the vertexes themselves would become an intrusion into the laminar flow.


This moves away from one tile shape and a basic dimension which, IMO, is unrealistic. I haven't run the numbers but this would add what, 40-60 unique tiles shapes? In the context of the shuttle, this is nothing. In the context of total SS part count, this is nothing. The pin pattern would change in a predictable pattern. Tile manufacturing of multiple shapes isn't going to be a serious burden. Manufacturing to this design would be simpler than a complex interaction of shapes who's only somewhat dubious virtue is allowing the tank hex tiles to be inserted periodically.


The most important goal is a heatshield that works. Once that happens optimizations can be looked at. It's the SpaceX way.


The side fairings are a whole other conversation.



Title: Re: Starship heat shield
Post by: maquinsa on 06/11/2021 09:12 pm
More to the point, that is just a CGI texture map; it ignores physical constraints.  See this section here for example, where you can see a number of implausible tile boundaries.

I’m only addressing the tiling of a double curvature surface, the flap-body interface is another problem.

Also, I haven’t said it before but this pattern is asymmetric. I don’t know if that messes up the aerodynamics
Title: Re: Starship heat shield
Post by: eriblo on 06/11/2021 09:29 pm
More to the point, that is just a CGI texture map; it ignores physical constraints.  See this section here for example, where you can see a number of implausible tile boundaries.

I’m only addressing the tiling of a double curvature surface, the flap-body interface is another problem.

Also, I haven’t said it before but this pattern is asymmetric. I don’t know if that messes up the aerodynamics
The more detailed renders are mostly examples of the approach mentioned earlier - wrap the nose cone in a shape with simple curvature (in this case likely a cone) and adjust each point to the correct surface. This is a standard graphics texture approach and produces very nice looking tiling - but each of those tiles are likely unique. No problem for computers but complicated in real life...
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 06/11/2021 09:30 pm
I'd really appreciate the links if you can dig them up.  I found this yesterday:
https://www.researchgate.net/publication/227280537_A_Note_on_Planar_Hexagonal_Meshes
Which goes over several ways to create hex tilings. It boils down to an optimization problem, and the optimizer could be given "identical tile shapes" as a goal.

Personally I'm optimistic that a mixture of hexes and regular pentagons with the same edge length *could* do the job.

But the neglected issue here is automation and that robot stud welder.  So far we've seen regular grids.  It may be that SpaceX "optimizes for manufacturability" here by using one tile shape per "latitude" (cf the first post in this thread) because it allows the stud attachment points to be on a regular grid, even if the tile shapes are different. The metal attachment brackets could also be substantially the same for every tile. OTOH that makes tile manufacturing more involved, with about 30 different tile shapes to juggle.  And as folks have noted, the tile sizes probably need to shrink at the tip of the nose, so you're going to have variations in your attachment grid in any case.


I think that for the first flights they will go with the "same latitude same tile " approach, because there won't be crewed flights for a while. They will gain experience and I'm confidente they will be able to point out if it is better to change approach and how much spare tiles to bring in orbit.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/11/2021 09:48 pm
Seems we have only seen 4 tile types so far. The cut end hexagons (assumed to be for the base of Starship) and three sizes of hexagon. I was wondering why they need three sizes of hexagons and how these could be incorporated into the page one scheme.

Perhaps they are necessary to reduce the length of the tiles to help prevent them getting excessively narrow towards the nose tip. This could also make successive tile layers smaller to help cope with increased curvature.

There still needs to be one type of tile per nose layer, but the 3 hexagonal ones we have seen may be the 3 basic sizes they use. All the others are simply cut down on two sides.
Title: Re: Starship heat shield
Post by: Keldor on 06/11/2021 10:00 pm
Seems we have only seen 4 tile types so far. The cut end hexagons (assumed to be for the base of Starship) and three sizes of hexagon. I was wondering why they need three sizes of hexagons and how these could be incorporated into the page one scheme.

Perhaps they are necessary to reduce the length of the tiles to help prevent them getting excessively narrow towards the nose tip. This could also make successive tile layers smaller to help cope with increased curvature.

There still needs to be one type of tile per nose layer, but the 3 hexagonal ones we have seen may be the 3 basic sizes they use. All the others are simply cut down on two sides.

Most likely the ones we've seen are still prototype tiles, testing the general properties of the tile design itself.  They're not going to waste money tooling up for all the shapes they'll eventually need until they have a tile design and manufacturing method that they know works.  So they're just making representative samples.
Title: Re: Starship heat shield
Post by: cscott on 06/11/2021 10:31 pm


There still needs to be one type of tile per nose layer, but the 3 hexagonal ones we have seen may be the 3 basic sizes they use. All the others are simply cut down on two sides.

I like this approach.  Effectively there would be only three "attachment Y" types, and you'd keep using (cut down versions of) a single hex until it got too narrow for the attachment Y, and then you'd drop down to the next smaller size.  It would also be "field repairable" given a set of the three tile sizes and a saw (are these tiles machinable?).

If you want to be a bit more elegant your side cuts can be tapered so each hex is larger width-wise on the bottom than on the top.  This angle will be really small though and you can probably just tolerate a slightly wider gap at the bottom of the tile.
Title: Re: Starship heat shield
Post by: eriblo on 06/12/2021 01:07 am
Just to get some numbers on the scale of the problem to compare with the Shuttles >21000 tiles, each unique.

Based on Fael's estimates (https://forum.nasaspaceflight.com/index.php?topic=50049.msg2042096#msg2042096):

Cylindrical fuselage half area: 513 m2
Total fin area (single side): 120 m2
Nose cone half area: 143 m2

Area of standard 24.4 cm minor diameter tile: 515 cm2

Assuming that the average tile surface is the same this would give just over 15000 tiles, ~12000 of which are the standard regular hexagon (fins+cylinder). If every tile on the nose cone is unique that would be ~3000 tile types although the smaller radius areas of the nose cone and fin fairings might need smaller tiles increasing it a bit.

--------------------------------------------

Eyeball guesstimates for a somewhat improved number (assuming perfect tiling with all tiles sized similarly to the current ones):

NOSE CONE: The length along the curve of the nose cone is about 15 meters which corresponds to ~70 vertical rows if one uses the "unique rows of identical tapered hexagons" approach and keeps the average tile height the same the standard hexagons (where each row is ~21.1 cm tall). 5 doubling rows should be enough to keep the tile width reasonable (as discussed previously) which would add at most 5 types. ETurner's heptagon/pentagon pattern might not add any as it is roughly the same height as two rows.

FINS: The fins are flat but will need special tiles along the edges. ~2 types should be enough for each of the "straight" edges (3 on the aft, 1 on the forward fins - should be symmetric) for a total of ~10. The number needed for "slanted" edges depend on the exact angle with the best case being 2 each for 30° or 60° relative to the pattern and the worst being a unique tile for each row. This would be ~50 for each of the forward and ~40 for each of the aft fins (mirror symmetric).

Note that this assumes that a single line of edge tiles are needed, either by curved tiles wrapping around or by interfacing to some other type of TPS. If multiple tile types are needed to wrap around the edges as well these numbers could easily be doubled or tripled.

FIN FAIRINGS: These also look flat enough for hexagons but are going to need special tiles at the edges as well. For the aft fairings I roughly guesstimate it to 50-75 each (most are mirror symmetric). The forward fairings intersect the nose cone along a curve ~12 m long which might need on the order of 2 x 60 types for the fairing/nosecone junction on each side. Add 40-60 each for the froward part and other edges.

COMMENTS: The nose cone tiling seems to relatively easily be made a minor contributor to the total number of tile types needed. The find edges and fairings are a much larger source of tile variation, especially the forward ones and the estimate is very sensitive to the exact design of the fin edges (angle and wrap around approach). There would likely be a requirement for some tiles to be curved in one direction at the tighter radii - a larger number of smaller tiles could be used instead.

SUMMARY: For this approach I get 600-700 tile types if no special attention is paid to the fin angles. Using only fin edge angles along the hexagon symmetry lines would reduce the number of tile types by close to 200 with other intermediate angles having smaller reductions. However, if the fins need multiple rows of special tiles around the edge this could increase the number by a corresponding ~200 per extra row.

Most reduction can likely be found in the tightly curved upper part of each faring and the forward fairing/nose cone junction. Replacing each two facing flat tiles at the fairing/nose cone junction with a compound tile would for example be a ~150 tile type reduction.

TL;DR: I can see a reduction to say 400-500 tile types if they want to but it could also increase to be on the order of 800-1000 if other design considerations dominate.
Title: Re: Starship heat shield
Post by: Keldor on 06/12/2021 02:00 am
I guess a really important question about different tile shapes is what's involved in manufacturing the varients.  It they each need seperate molds, etc, then managing a large number of tile types will not be fun.  On the other hand, if they can start with a handful of different types of blanks (needed for large/small tiles where you might have to have the attachment points closer or further apart), and then for a specific tile, just put the correct size blank in the CNC and set it to grind the blank into the specific shape you need, things will be far easier.

Presumably would be a couple steps post CNC involving coating layers, but you're still looking at cutting the "Bad news:  Bill accidentally dropped the entire palette of pattern 72 tiles while lifting them, and, needless to say, we don't have enough spares to cover that.  We need replacments ASAP" delay to a very quick program change on the CNC and some amount of post processing, followed by overnight shipping, as opposed to a lengthy lay-up starting from scratch.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/12/2021 03:12 am
I guess a really important question about different tile shapes is what's involved in manufacturing the varients.  It they each need seperate molds, etc, then managing a large number of tile types will not be fun.  On the other hand, if they can start with a handful of different types of blanks (needed for large/small tiles where you might have to have the attachment points closer or further apart), and then for a specific tile, just put the correct size blank in the CNC and set it to grind the blank into the specific shape you need, things will be far easier.

Presumably would be a couple steps post CNC involving coating layers, but you're still looking at cutting the "Bad news:  Bill accidentally dropped the entire palette of pattern 72 tiles while lifting them, and, needless to say, we don't have enough spares to cover that.  We need replacments ASAP" delay to a very quick program change on the CNC and some amount of post processing, followed by overnight shipping, as opposed to a lengthy lay-up starting from scratch.

Seems to me the most likely place to drop a tile would be at placement.

the CNC machine better be on the same site as placement.
Title: Re: Starship heat shield
Post by: ETurner on 06/12/2021 12:10 pm
Some observations and a first-flight speculation:

1) General objective: Test atmospheric entry.

2) Specific objective: Test tile attachment, robustness, aerodynamics, effectiveness.

3) Problem: Tiling the nose looks like a pain, and prototype attachment (etc.) systems may be replaced.

4) Solution: For initial flights, slap a layer of ablative TPS material on the nose (could be a spray-on, heavy is OK), test tiles on cylindrical surfaces, later adapt a successful design to the nose geometry.
Title: Re: Starship heat shield
Post by: ETurner on 06/12/2021 03:00 pm
Here are some previous 5-6-7 patterns stitched together to clarify the concept. The number of tile shapes needed for a good fit may not be very large -- 1 pentagon + 1 heptagon + 2 flanking hexagons + 1 to 3 large-area-fill hexagons might do the job.

[Edit: Sharply converging surfaces toward the tip would require several more tapered hexagon shapes, with the number depending on the radius of the nose cap. To choose a round number, the overall scheme might require ~10 tile shapes, not counting those directly adjacent to the flaps and nose cap.]

[Edit #2: The 5-7 patterns in the peeled surface below are aligned along meridians, but this is neither necessary nor optimal for smooth gradation of curvature.]
[Edit #3: See this post (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2253561#msg2253561) for a more finished version.]
Title: Re: Starship heat shield
Post by: Sciencefan on 06/12/2021 03:23 pm
The discussion here is too focused on hexagonality, when probably straight gaps between rows of the tiles is not the issue anymore as we saw them on SN15-16.
Title: Re: Starship heat shield
Post by: ETurner on 06/12/2021 03:41 pm
The discussion here is too focused on hexagonality, when probably straight gaps between rows of the tiles is not the issue anymore as we saw them on SN15-16.
Spoilsport. Allowing rows of trapezoids makes it too easy.
(But you may well be right.)
Title: Re: Starship heat shield
Post by: r8ix on 06/12/2021 03:44 pm
The discussion here is too focused on hexagonality, when probably straight gaps between rows of the tiles is not the issue anymore as we saw them on SN15-16.

I don’t think you can make that inference, given the difference in velocities between SN15 and SN20 (and the fact that we think they were still testing attachment methods on 15…).
Title: Re: Starship heat shield
Post by: soyuzu on 06/12/2021 03:50 pm
Some observations and a first-flight speculation:

1) General objective: Test atmospheric entry.

2) Specific objective: Test tile attachment, robustness, aerodynamics, effectiveness.

3) Problem: Tiling the nose looks like a pain, and prototype attachment (etc.) systems may be replaced.

4) Solution: For initial flights, slap a layer of ablative TPS material on the nose (could be a spray-on, heavy is OK), test tiles on cylindrical surfaces, later adapt a successful design to the nose geometry.

SpaceX can use XIRCA (an in-house version of SIRCA) for this.

1) It can be machined to custom shapes and then applied directly to the spacecraft without post treatment.
2) SpaceX is currently used it on Block 5 base heat shield
3) Kistler K-1 used it for leading-edge heat shield, which suggests it should be able to handle the heat load on front cone as well as leading edge and flap hinge that will occur on Starship LEO reentry.
4) The “R” suggests it should be somewhat reusable.

Problem is we have not seen even some sort of test installation on any prototypes.
Title: Re: Starship heat shield
Post by: cscott on 06/12/2021 06:17 pm
Occam's razor really suggests the straight line latitude strips.  That matches the "home plate" pentagons we've already seen mounted, requires no changes to mounting stud pattern, etc.  A custom gap filler of some sort at intervals is probably sufficient to break up the flow along the latitude lines, if that is indeed a problem.

But it's much much more fun to consider the soccer-ball or crystallographic tilings. :)

Really, we should be worried about tiling the flap-to-body interface and the flap leading edges.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/12/2021 07:46 pm
Occam's razor really suggests the straight line latitude strips.  That matches the "home plate" pentagons we've already seen mounted, requires no changes to mounting stud pattern, etc.  A custom gap filler of some sort at intervals is probably sufficient to break up the flow along the latitude lines, if that is indeed a problem.

But it's much much more fun to consider the soccer-ball or crystallographic tilings. :)

Really, we should be worried about tiling the flap-to-body interface and the flap leading edges.
Have we seen any pentagonal tiles on any SN?
Title: Re: Starship heat shield
Post by: ETurner on 06/12/2021 09:21 pm
Occam's razor really suggests the straight line latitude strips.  That matches the "home plate" pentagons we've already seen mounted, requires no changes to mounting stud pattern, etc.  A custom gap filler of some sort at intervals is probably sufficient to break up the flow along the latitude lines, if that is indeed a problem.

But it's much much more fun to consider the soccer-ball or crystallographic tilings. :)

Really, we should be worried about tiling the flap-to-body interface and the flap leading edges.
Have we seen any pentagonal tiles on any SN?
There are “half hexagons” that look like standard tiles truncated to line up with the edge of a skirt: Technically pentagons, but not useful for a 5-6-7 scheme. I’ve seen no tiles that seem suitable for fitting double-curved surfaces. This makes me think that the initial orbital flights might use a quick-and-dirty ablative material on the nose while validating tile attachment (etc.) on the body where they’re easier to apply.

[Edit: We also haven’t seen a spray-on ablative coating, but if the material bonds well, there may be little to be learned from flying it on a suborbital vehicle.]
Title: Re: Starship heat shield
Post by: Nevyn72 on 06/12/2021 11:58 pm
Might it not be easier to consider the way to vary the shape of the tiles is that they are curved rather than many different size/number of sides?

Would this reduce the number of variants required?
That is a standardised 'curved' tile for the nose section?
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/13/2021 08:49 am
Might it not be easier to consider the way to vary the shape of the tiles is that they are curved rather than many different size/number of sides?

Would this reduce the number of variants required?
That is a standardised 'curved' tile for the nose section?
Making the tiles curved (curved to more accurately fit the nosecone) might help make the structure smoother which might help with reentry but at the cost of making the tile manufacture more complex and expensive. However it would not really effect the number of tiles required or the number of sides they would have as the tiles would still need to tesselate across the surface of the nosecone. 
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 06/13/2021 12:00 pm

It doesn’t look like NC18 has studs for the heat shield tiles, so maybe it’s just another orphan destined for the scrap yard?
🤔
Or early expendable and single-use orbital prototypes may use an ablative TPS material on the nose. This would allow testing of tile systems where the geometry is easy (cylindrical surfaces) and postpone the difficulties of tiling double-curved geometries (which require multiple tile shapes) until risks associated with attachment, robustness, aerodynamics, and effectiveness have been retired.

It's probably a bad assumption to say they can just slap on a proven heatshield tecnology to Starship's nose without much effort.  First, there's still quite a bit of developing and tooling involved in making the material into the new shape, but, more importantly, there are various reasons that such a heatshield could fail.  Adhesives could burn under the hot body/ thin heat shield design of Starship.  If they make the shield thicker to compensate, it won't match the tiled section, and the discontinuity will cause all sorts of exciting shockwave impringement problems, making very hot spots.  Indeed, just the nature of a ablative heatshield compared to the tiles could easily result in such a discontinuity all on its own.
IMO they will try to build a complete heat shield for the entire vehicle. They will then iteratively refine that heat shield until they can get Starship down into the ocean in one piece. After that when they can get it back to Boca Chica or a platform further refinements should be easier as they will be able to examine it.

There is a separate thread for the heatshield
https://forum.nasaspaceflight.com/index.php?topic=50748.1520
 (https://forum.nasaspaceflight.com/index.php?topic=50748.1520)

(as suggested bringing the discussion to the correct thread)

I agree. I think that if SpaceX ever places an ablative TPS on the nosecone (but I think it won't happen) for testing the other tiles they will do that only after a(or more)orbital flight with reentry failed. Why to use a lot of money building a nosecone ablative tps, to test if the other tiles in the cilindrical section work if you can test the normal heat shield first, and in case of mulfunction determinate if the issue was due to nosecone tiles, and eventually proceed with a ablative nose co'ne TPS for a test flight?
Title: Re: Starship heat shield
Post by: Nevyn72 on 06/13/2021 11:07 pm
Might it not be easier to consider the way to vary the shape of the tiles is that they are curved rather than many different size/number of sides?

Would this reduce the number of variants required?
That is a standardised 'curved' tile for the nose section?
Making the tiles curved (curved to more accurately fit the nosecone) might help make the structure smoother which might help with reentry but at the cost of making the tile manufacture more complex and expensive. However it would not really effect the number of tiles required or the number of sides they would have as the tiles would still need to tesselate across the surface of the nosecone.

I wasn't really expecting it would reduce either then number of tiles or the number of sides the tiles would have.
I was thinking it could possibly reduce the number of different tile shapes required...
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/14/2021 04:52 pm
Might it not be easier to consider the way to vary the shape of the tiles is that they are curved rather than many different size/number of sides?

Would this reduce the number of variants required?
That is a standardised 'curved' tile for the nose section?
Making the tiles curved (curved to more accurately fit the nosecone) might help make the structure smoother which might help with reentry but at the cost of making the tile manufacture more complex and expensive. However it would not really effect the number of tiles required or the number of sides they would have as the tiles would still need to tesselate across the surface of the nosecone.

I wasn't really expecting it would reduce either then number of tiles or the number of sides the tiles would have.
I was thinking it could possibly reduce the number of different tile shapes required...
I do not think it will.
Title: Re: Starship heat shield
Post by: KelvinZero on 06/16/2021 08:57 am
Just throwing it out there.. if you really want to cover a doubly curved surface with just one tile shape.. you could go with scale mail 8)
https://en.wikipedia.org/wiki/Scale_armour

Or..
https://discourse.mcneel.com/t/paneling-double-curved-surface-roof-tiles/82634

I will let myself out..
Title: Re: Starship heat shield
Post by: edzieba on 06/16/2021 10:04 am
Overlapping tiles have been discussed. They do not tolerate supersonic/hypersonic flows in multiple directions, which Starship will experience. Supersonic nose-to-tail during ascent, hypersonic and supersonic ventral-to-dorsal during EDL.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/16/2021 06:18 pm
Just throwing it out there.. if you really want to cover a doubly curved surface with just one tile shape.. you could go with scale mail 8)
https://en.wikipedia.org/wiki/Scale_armour

Or..
https://discourse.mcneel.com/t/paneling-double-curved-surface-roof-tiles/82634

I will let myself out..
The comment of your second link seems to assume that the tiles would be different... as in the dome at the end
Title: Re: Starship heat shield
Post by: FutureSpaceTourist on 06/17/2021 10:55 am
https://twitter.com/bocacharts/status/1405478878089465860

Quote
Heat Tiles: SN8-SN16
Title: Re: Starship heat shield
Post by: ETurner on 06/17/2021 05:10 pm
Continuing to refine an idea that may or may not have net merit compared to other options:

Covering a double-curved surface with well-fitted arrays of tiles is non-trivial, and the main systematic approaches discussed here have either varied tile shapes for each “latitude band” (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2251117#msg2251117) or (less explored to above) found a way to taper “longitude gores” (bands and gores are illustrated below).

If hexagon-like patterns are worth pursuing (avoiding aligned grooves, looking pretty, etc.), and the number of tile-shapes should be sharply limited, then the longitude-gore scheme below looks pretty good. In particular, there is no problem with tiles tending to narrow towards the tip and requiring doubling-bands to compensate. This scheme does require special design methods to do well (see below), and requires flexible programming of mounting-pin placement.

I present this scheme and diagram for consideration by people who can make sense of 2D --> 3D diagrams, and can imagine the effect of playing with the distribution of curvature-enabling 5-7 tile pairs.

Note that the nosecone taper can vary arbitrarily, and small variations in the spacing of identical hexagons can accommodate residual curvature between clusters containing 5-7 tile pairs and a few distorted near-neighbor hexagons. Shapes adjacent to the tip-cap and flaps are special cases in any scheme.

Design method:

• Parametric definition of 5, 7, and a few kinds of 6 sided tile shapes.
• Distance and orientation of tiles constrained to the nosecone surface.
• Use elastic restraints between adjacent tile edges to distribute gaps.
• Fiddle 5-7 positions and tile shapes to fit the surface nicely.

(No, we probably won’t see this, but it’s cool.)

[Edit: Unless the gap-to-tile ratio is increased (same gap, smaller tiles) the conditions for small numbers of tiles seem too stringent for this scheme. I’d vote to deal with aligned grooves and use trapezoids, which can fit better than these (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2240019#msg2240019).]
Title: Re: Starship heat shield
Post by: Reynold on 06/17/2021 05:52 pm
It is also possible they will rethink the exact curvature of their nose cone to minimize tiling complexity.  There may be a tradeoff between easy nose cone shape in stainless steel versus minimum number of tile shapes to cover the nose cone. 
Title: Re: Starship heat shield
Post by: ETurner on 06/17/2021 08:16 pm
It is also possible they will rethink the exact curvature of their nose cone to minimize tiling complexity.  There may be a tradeoff between easy nose cone shape in stainless steel versus minimum number of tile shapes to cover the nose cone.
I’m pretty sure that all ogives are about the same w.r.t. the curvature problem, in other words, that there’s little to be gained by fine-tuning the shape.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/17/2021 09:18 pm
Continuing to refine an idea that may or may not have net merit compared to other options:

Covering a double-curved surface with well-fitted arrays of tiles is non-trivial, and the main systematic approaches discussed here have either varied tile shapes for each “latitude band” (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2251117#msg2251117) or (less explored to above) found a way to taper “longitude gores” (bands and gores are illustrated below).

If hexagon-like patterns are worth pursuing (avoiding aligned grooves, looking pretty, etc.), and the number of tile-shapes should be sharply limited, then the longitude-gore scheme below looks pretty good. In particular, there is no problem with tiles tending to narrow towards the tip and requiring doubling-bands to compensate. This scheme does require special design methods to do well (see below), and requires flexible programming of mounting-pin placement.

I present this scheme and diagram for consideration by people who can make sense of 2D --> 3D diagrams, and can imagine the effect of playing with the distribution of curvature-enabling 5-7 tile pairs.

Note that the nosecone taper can vary arbitrarily, and small variations in the spacing of identical hexagons can accommodate residual curvature between clusters containing 5-7 tile pairs and a few distorted near-neighbor hexagons. Shapes adjacent to the tip-cap and flaps are special cases in any scheme.

Design method:

• Parametric definition of 5, 7, and a few kinds of 6 sided tile shapes.
• Distance and orientation of tiles constrained to the nosecone surface.
• Use elastic restraints between adjacent tile edges to distribute gaps.
• Fiddle 5-7 positions and tile shapes to fit the surface nicely.

(No, we probably won’t see this, but it’s cool.)

[Edit: Unless the gap-to-tile ratio is increased (same gap, smaller tiles) the conditions for small numbers of tiles seem too stringent for this scheme. I’d vote to deal with aligned grooves and use trapezoids, which can fit better than these (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2240019#msg2240019).]
The trouble is the sequences of multiple hexagons will not match the 3D surface. Also we have only seen hexagonal tiles of various sizes being tested.
Title: Re: Starship heat shield
Post by: ETurner on 06/17/2021 09:47 pm
The trouble is the sequences of multiple hexagons will not match the 3D surface. Also we have only seen hexagonal tiles of various sizes being tested.
Think of areas of regular hexagons as flexible sheets that can be stretched only slightly (like paper). Stretching = varying gap sizes. Split the nosecone into gores and cover it like a globe (often made by wrapping paper gores around a sphere). The problems are at the seams where the regular hexagonal grids collide. At those seams, colliding grids can be trimmed to leave gaps that can be filled with tastefully arranged 5-7 pairs and distorted hexagons. This actually works, with enough tiles, and maybe not too many.

Confusingly, in the illustration above, the “seams” (5-7 pairs, etc.) are in the middle of the gores, while the seams as drawn are in the middle of the hexagonal regions.

But as you say we’ve seen only hexagons, which we know can’t do the job alone. A bit of a mystery for the moment.
Title: Re: Starship heat shield
Post by: KelvinZero on 06/18/2021 03:54 am
It is also possible they will rethink the exact curvature of their nose cone to minimize tiling complexity.  There may be a tradeoff between easy nose cone shape in stainless steel versus minimum number of tile shapes to cover the nose cone.
I’m pretty sure that all ogives are about the same w.r.t. the curvature problem, in other words, that there’s little to be gained by fine-tuning the shape.
How about a cylinder where the nose is a diagonal slice.  :)

I can think of some variations not quite that bad, but also keeping the windward side a cylindrical section.

I still wonder (as a layman, and ignoring the fact they have no doubt simulated this over and over) if this is really the final hull shape. Even a small lip, I would have thought, would push the plasma stream away from the sides. Every other reentry shape I am aware of has gone with a flatter bottom.
Title: Re: Starship heat shield
Post by: eriblo on 06/18/2021 08:58 am
It is also possible they will rethink the exact curvature of their nose cone to minimize tiling complexity.  There may be a tradeoff between easy nose cone shape in stainless steel versus minimum number of tile shapes to cover the nose cone.
I’m pretty sure that all ogives are about the same w.r.t. the curvature problem, in other words, that there’s little to be gained by fine-tuning the shape.
How about a cylinder where the nose is a diagonal slice.  :)

I can think of some variations not quite that bad, but also keeping the windward side a cylindrical section.

I still wonder (as a layman, and ignoring the fact they have no doubt simulated this over and over) if this is really the final hull shape. Even a small lip, I would have thought, would push the plasma stream away from the sides. Every other reentry shape I am aware of has gone with a flatter bottom.
Vostok would like to have a word...
Title: Re: Starship heat shield
Post by: KelvinZero on 06/18/2021 09:03 am
Vostok would like to have a word...
Interesting! (but the exception proves the rule)
https://en.wikipedia.org/wiki/Vostok_(spacecraft)#Reentry
Title: Re: Starship heat shield
Post by: rsdavis9 on 06/18/2021 11:25 am
It is also possible they will rethink the exact curvature of their nose cone to minimize tiling complexity.  There may be a tradeoff between easy nose cone shape in stainless steel versus minimum number of tile shapes to cover the nose cone.
I’m pretty sure that all ogives are about the same w.r.t. the curvature problem, in other words, that there’s little to be gained by fine-tuning the shape.
How about a cylinder where the nose is a diagonal slice.  :)

I can think of some variations not quite that bad, but also keeping the windward side a cylindrical section.

I still wonder (as a layman, and ignoring the fact they have no doubt simulated this over and over) if this is really the final hull shape. Even a small lip, I would have thought, would push the plasma stream away from the sides. Every other reentry shape I am aware of has gone with a flatter bottom.

or how about a cone for the nose cone and then a diagonal slice of the cone.
Title: Re: Starship heat shield
Post by: ETurner on 06/18/2021 12:19 pm
or how about a cone for the nose cone and then a diagonal slice of the cone.
Cones are more easily tiled, but a full cone would sacrifice volume. I’m not picturing the diagonal slice, but a flat surface would sacrifice structural efficiency. SpaceX seems committed to ogives.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/18/2021 12:28 pm
or how about a cone for the nose cone and then a diagonal slice of the cone.
Cones are more easily tiled, but a full cone would sacrifice volume. I’m not picturing the diagonal slice, but a flat surface would sacrifice structural efficiency. SpaceX seems committed to ogives.
Yes minimising the number of tiles is useful but secondary to other issues of finding the best geometry to cope with reentry and hypersonic flight.
Title: Re: Starship heat shield
Post by: eriblo on 06/18/2021 03:40 pm
or how about a cone for the nose cone and then a diagonal slice of the cone.
Cones are more easily tiled, but a full cone would sacrifice volume. I’m not picturing the diagonal slice, but a flat surface would sacrifice structural efficiency. SpaceX seems committed to ogives.
Yes minimising the number of tiles is useful but secondary to other issues of finding the best geometry to cope with reentry and hypersonic flight.
Exactly - and an arbitrary ogive is only ~10% of the total number of tile types unless they really optimize the fin fairings (especially the forward ones). Even the simple flat fins might add a similar or larger number of tile types unless they are optimized (which should be much more forgiving aerodynamically). Added a standard tile tiling to Rafael's SN8 fin estimates - as can be seen an optimal combination of orientation and edge angles might have ~15 tile types per fin while an arbitrary choice can easily double or triple the number.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 06/18/2021 03:58 pm
or how about a cone for the nose cone and then a diagonal slice of the cone.
Cones are more easily tiled, but a full cone would sacrifice volume. I’m not picturing the diagonal slice, but a flat surface would sacrifice structural efficiency. SpaceX seems committed to ogives.
Yes minimising the number of tiles is useful but secondary to other issues of finding the best geometry to cope with reentry and hypersonic flight.

Are we sure that this possible new nose cone design won't affect payload mass distribution and aerodinamics during launch?
Title: Re: Starship heat shield
Post by: OTV Booster on 06/18/2021 04:06 pm
or how about a cone for the nose cone and then a diagonal slice of the cone.
Cones are more easily tiled, but a full cone would sacrifice volume. I’m not picturing the diagonal slice, but a flat surface would sacrifice structural efficiency. SpaceX seems committed to ogives.
Yes minimising the number of tiles is useful but secondary to other issues of finding the best geometry to cope with reentry and hypersonic flight.
You have your priorities right.
Title: Re: Starship heat shield
Post by: oiorionsbelt on 06/18/2021 08:40 pm
Speaking of nose cone shape priorities.

Quote
"You literally told them to make the Starship more pointy because of the movie 'The Dictator?'" a chuckling Rogan asked.

"Yep. And they know it, too," Musk replied with a laugh. "It's not like they're unaware of it. I thought it would be funny to make it more pointy, so we did.
 "Rogan then asked if pointiness gives Starship an aerodynamic edge. "It's arguably slightly worse," Musk said, spurring laughter from both men. But, he added, "it looks cooler."

Title: Re: Starship heat shield
Post by: Nevyn72 on 06/18/2021 11:40 pm
Just stepping back a bit....

Why are we convinced they are going to be using tiles on the nose?
Title: Re: Starship heat shield
Post by: KelvinZero on 06/19/2021 03:43 am
Quote from: Alberto-Girardi link=topic=50748.msg2253955#msg2253955
Are we sure that this possible new nose cone design won't affect payload mass distribution and aerodinamics during launch?
That is possible..  ;)
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/19/2021 07:58 am
Just stepping back a bit....

Why are we convinced they are going to be using tiles on the nose?
I think its an assumption. But if they don't use tiles what else is there that meets their requirements? And if they did have a material X that meets those requirements and is good for the nose, then why not use that across the whole ship instead of tiles?
Title: Re: Starship heat shield
Post by: livingjw on 06/19/2021 02:54 pm
Just stepping back a bit....

Why are we convinced they are going to be using tiles on the nose?

Advanced Carbon Carbon or Carbon/SIC mechanically attached panels (with insulation underneath) are alternative materials that have higher temperature capabilities than aluminide tiles. Downside, they are heavier. ESA has research rather large (~1m) mechanically attached panels.

John
Title: Re: Starship heat shield
Post by: cscott on 06/19/2021 02:57 pm
Here's a wild idea: what if SpaceX returns to transpiration cooling?  Perhaps we haven't seen the unusual tile types on the fins or nosecones because they will be transpiration cooled, and the hex tiles saves for the flatter more regular surfaces?

Elon recently mentioned using SN16 for a "hypersonic test" -- testing a transpiration cooling concept might be exactly the sort of "off the critical path" test which Elon might have in mind for it...
Title: Re: Starship heat shield
Post by: HVM on 06/19/2021 04:50 pm
Just stepping back a bit....

Why are we convinced they are going to be using tiles on the nose?
I think its an assumption. But if they don't use tiles what else is there that meets their requirements? And if they did have a material X that meets those requirements and is good for the nose, then why not use that across the whole ship instead of tiles?

Is there a limit on the size and shape of the tile? Is there a reason they can't make a single piece, to cover the entire nose cone?

tiles are quite fragile, so big size are worse for vibration, and in case of damage you can't repair only one tile.
Shuttle used carbon-carbon at leading edges and nose, and X-37B uses TUFROC is same purpose. Maybe we see long rumored TUFROCX at SS nose and bodyflaps...
Because both TUFROC and carbon-carbon are much heavier than Silicon tiles.
Title: Re: Starship heat shield
Post by: BT52 on 06/19/2021 10:55 pm
Still are we sure that transpiration cooling is really more efficient per W/m^2 of kg of taken payload pen? I m not so sure the transpiration cooling per unit of removed watt is really lighter, because of fuel weight and nozzle plating and piping u need attach on skin. Not i m mention all pumping loses and its ctrl complexity. Robustness and passiveness of tufrock or any other material isolation system is apparent.

In mine humble opinion the thing that makes transpiration cooling nice is seemingly easier fluid-like plate design - more organic structure like in nature ofc. So at end of day at early stages weight could easily be the same for whole thing.

So i would avoid transpiration as much as possible. With math and computation available engineers have all toys to crack that challenge.  Shape compromises and with smart optimisations we could reduce number of tile types and standardise the whole process from lunch to landing. And furthermore ease up post check-up and finally enable cheap, dirty reflight. 
Title: Re: Starship heat shield
Post by: KelvinZero on 06/20/2021 01:27 am
Still are we sure that transpiration cooling is really more efficient per W/m^2 of kg of taken payload pen?
I don't think that is being debated. SpaceX has explicitly said that it turned out heavier, when they changed their decision away from transpiration to tiles. (sorry could not find reference)

Elon Musk said they could use it in spots where heating was a problem. It seems unlikely that they would use it on a wide area just to avoid different tile shapes.. but who knows. What if the work of maintaining tiles in tricky spots was just such a bother that they did put up with a more massive solution for a smallish fraction of the hull. I keep hearing it is more about price than weight.

https://twitter.com/elonmusk/status/1107380559834046465?lang=en
Title: Re: Starship heat shield
Post by: Keldor on 06/20/2021 04:19 pm
Still are we sure that transpiration cooling is really more efficient per W/m^2 of kg of taken payload pen?
I don't think that is being debated. SpaceX has explicitly said that it turned out heavier, when they changed their decision away from transpiration to tiles. (sorry could not find reference)

Elon Musk said they could use it in spots where heating was a problem. It seems unlikely that they would use it on a wide area just to avoid different tile shapes.. but who knows. What if the work of maintaining tiles in tricky spots was just such a bother that they did put up with a more massive solution for a smallish fraction of the hull. I keep hearing it is more about price than weight.

https://twitter.com/elonmusk/status/1107380559834046465?lang=en

To be honest, I have a hard time imagining how a few dozen extra tile shapes could be more difficult to deal with than a complicated cooling manifold supplying methane over a large curved surface.  We're talking about different shaped tiles for each row up the nose, not every single tile custom like in the Shuttle.  Also, the Shuttle had the additional rather big problem of having to carefully chisel out the old tile, since they couldn't be detached otherwise, with enough precision to fit the replacement tile with hair's breadth gaps.
Title: Re: Starship heat shield
Post by: Jcc on 06/20/2021 08:15 pm
or how about a cone for the nose cone and then a diagonal slice of the cone.
Cones are more easily tiled, but a full cone would sacrifice volume. I’m not picturing the diagonal slice, but a flat surface would sacrifice structural efficiency. SpaceX seems committed to ogives.
Yes minimising the number of tiles is useful but secondary to other issues of finding the best geometry to cope with reentry and hypersonic flight.
Exactly - and an arbitrary ogive is only ~10% of the total number of tile types unless they really optimize the fin fairings (especially the forward ones). Even the simple flat fins might add a similar or larger number of tile types unless they are optimized (which should be much more forgiving aerodynamically). Added a standard tile tiling to Rafael's SN8 fin estimates - as can be seen an optimal combination of orientation and edge angles might have ~15 tile types per fin while an arbitrary choice can easily double or triple the number.

If a standard tile is cut to fit, does that represent a distinct tile type? In a way , yes, but as long as cutting them doesn't harm their performance, you can bulk manufacture the standard type. The the problem would be  how they are attached, as you may not have 3 attach points. They have experimented with different sizes of hexagons, they may come into play.

It's also unclear what you do with the thin sides of the flaps, and the edge between the thin and the wide sides of the flaps. They may need a special tile type for those areas.
Title: Re: Starship heat shield
Post by: su27k on 06/21/2021 05:31 am
https://youtu.be/FlYKVpOVrcM

Quote
Scheduled for 19 Jun 2021
NSF Live is NASASpaceflight.com's weekly show covering the latest in spaceflight. It is broadcast live on Saturdays at 3 pm Eastern (19:00 UTC). On each show, we rotate through various hosts and special guests.

In this week's episode, NASASpaceflight's John "Das" Galloway and Chris Gebhardt will speak with Jean Wright, a worker on the Space Shuttle's Thermal Protection Systems (TPS).

Additional coverage: https://www.nasaspaceflight.com/

Discussion about TPS on Starship starting from 1:23:23:

1. 2 lead engineers from NASA Thermal Protection System Facility (TPSF) started working for SpaceX 3 years ago on Starship TPS: Jeff Andrus (spelling?), Martin Wilson (Principal Thermal Engineer - SpaceX (https://www.linkedin.com/in/martin-wilson-bb615b18))

2. The clip used to attach the hex tile is called "bayonet clip"

3. Don't think gap filler is needed. Worst case they need the filler bar.

4. Will use robotics to paint the tile

5. Temperature similar to Shuttle tiles, 2,200 to 2,300F

6. Has thermal couples installed to read the temperature

Title: Re: Starship heat shield
Post by: edzieba on 06/21/2021 08:36 am
but as long as cutting them doesn't harm their performance, you can bulk manufacture the standard type.
Aby cutting must occur before the RCG stage, or the sides will be left uncoated.

The problem is not so much manufacture of the tiles themselves (that's an almost arbitrary choice of shape). It's the logistics of handling thousands of unique tiles rather than thousands of identical tiles. You can't just manufacture 10k 'Starship tiles', ship them by the pallet, and install them in the order you pick them up out of the crate. At the extreme, each is a unique shape and you must ensure that unique tile makes its way from manufacture to installation without being damaged, misplaced, installed one stud over, etc. If that happens, you then need to manufacture another unique tile (or manufacture at least two of every unique tile to start with, and have near 50% overhead).
Title: Re: Starship heat shield
Post by: ThatOldJanxSpirit on 06/21/2021 11:44 am
but as long as cutting them doesn't harm their performance, you can bulk manufacture the standard type.
Aby cutting must occur before the RCG stage, or the sides will be left uncoated.

The problem is not so much manufacture of the tiles themselves (that's an almost arbitrary choice of shape). It's the logistics of handling thousands of unique tiles rather than thousands of identical tiles. You can't just manufacture 10k 'Starship tiles', ship them by the pallet, and install them in the order you pick them up out of the crate. At the extreme, each is a unique shape and you must ensure that unique tile makes its way from manufacture to installation without being damaged, misplaced, installed one stud over, etc. If that happens, you then need to manufacture another unique tile (or manufacture at least two of every unique tile to start with, and have near 50% overhead).

There is no overhead here. Unused ‘spare’ tiles are simply part of the stock for future builds.
Title: Re: Starship heat shield
Post by: edzieba on 06/21/2021 12:29 pm
but as long as cutting them doesn't harm their performance, you can bulk manufacture the standard type.
Aby cutting must occur before the RCG stage, or the sides will be left uncoated.

The problem is not so much manufacture of the tiles themselves (that's an almost arbitrary choice of shape). It's the logistics of handling thousands of unique tiles rather than thousands of identical tiles. You can't just manufacture 10k 'Starship tiles', ship them by the pallet, and install them in the order you pick them up out of the crate. At the extreme, each is a unique shape and you must ensure that unique tile makes its way from manufacture to installation without being damaged, misplaced, installed one stud over, etc. If that happens, you then need to manufacture another unique tile (or manufacture at least two of every unique tile to start with, and have near 50% overhead).

There is no overhead here. Unused ‘spare’ tiles are simply part of the stock for future builds.
Until someone drops/chips/etc that second unique tile, and now an entire vehicle is waiting on the total lead time for a new tile to be manufactured and shipped, rather than on the lead-time for someone to grab the next tile in the pile.
Title: Re: Starship heat shield
Post by: rakaydos on 06/21/2021 01:04 pm
but as long as cutting them doesn't harm their performance, you can bulk manufacture the standard type.
Aby cutting must occur before the RCG stage, or the sides will be left uncoated.

The problem is not so much manufacture of the tiles themselves (that's an almost arbitrary choice of shape). It's the logistics of handling thousands of unique tiles rather than thousands of identical tiles. You can't just manufacture 10k 'Starship tiles', ship them by the pallet, and install them in the order you pick them up out of the crate. At the extreme, each is a unique shape and you must ensure that unique tile makes its way from manufacture to installation without being damaged, misplaced, installed one stud over, etc. If that happens, you then need to manufacture another unique tile (or manufacture at least two of every unique tile to start with, and have near 50% overhead).

There is no overhead here. Unused ‘spare’ tiles are simply part of the stock for future builds.
Until someone drops/chips/etc that second unique tile, and now an entire vehicle is waiting on the total lead time for a new tile to be manufactured and shipped, rather than on the lead-time for someone to grab the next tile in the pile.
I'm reminded of a segment of Eric Berger's book, Liftoff, where Falcon 1 testing is cut short by LOX shortage often enough that Elon throws out dire threats if there is ever a shortage again.

It seems like the solution here is to create a batch of, say, 50 of each "unique" tile, and after 30-40 are used, review the stock and decide if you need to run up another batch.
Title: Re: Starship heat shield
Post by: KelvinZero on 06/21/2021 02:14 pm
To be honest, I have a hard time imagining how a few dozen extra tile shapes could be more difficult to deal with than a complicated cooling manifold supplying methane over a large curved surface.  We're talking about different shaped tiles for each row up the nose, not every single tile custom like in the Shuttle.  Also, the Shuttle had the additional rather big problem of having to carefully chisel out the old tile, since they couldn't be detached otherwise, with enough precision to fit the replacement tile with hair's breadth gaps.
It was just an offhand thought that perhaps these tiles might prove similarly time consuming to the shuttle.. or only 10x easier instead of the 100x or 1000x we need.. but the problem gets solved by some brilliant, practically AI refurbishment tool that slides up the cylindrical portion of the starship in an hour or so, intensely inspecting each tile and replacing if necessary.

Also, they are already claiming to be thinking about directing transpiration cooling to trouble spots so the complexity is already assumed. Covering one broad area would be less fiddly than that.

Im not going to spend much effort to defend the idea though. I certainly have no quantitative argument that it is likely.
Title: Re: Starship heat shield
Post by: OTV Booster on 06/21/2021 08:52 pm
but as long as cutting them doesn't harm their performance, you can bulk manufacture the standard type.
Aby cutting must occur before the RCG stage, or the sides will be left uncoated.

The problem is not so much manufacture of the tiles themselves (that's an almost arbitrary choice of shape). It's the logistics of handling thousands of unique tiles rather than thousands of identical tiles. You can't just manufacture 10k 'Starship tiles', ship them by the pallet, and install them in the order you pick them up out of the crate. At the extreme, each is a unique shape and you must ensure that unique tile makes its way from manufacture to installation without being damaged, misplaced, installed one stud over, etc. If that happens, you then need to manufacture another unique tile (or manufacture at least two of every unique tile to start with, and have near 50% overhead).
Keeping the unique tile count down is a good thing. One shape would be great but reality intrudes. What number are we looking at? Twenty? 50? 150? My uninformed guess is somewhere between 100 and 150, plus some monolithic pieces around the nose and fin edges. Keeping track of it all, from manufacture to installation, is an issue, but this is a known and well exercised process.


Early installation will be a lot of hand work but will morph into a more automated process as each areas layout becomes more settled. The tanks followed this pattern.


Top priority is successful EDL. Second priority is making it inexpensive. 
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/21/2021 10:12 pm
but as long as cutting them doesn't harm their performance, you can bulk manufacture the standard type.
Aby cutting must occur before the RCG stage, or the sides will be left uncoated.

The problem is not so much manufacture of the tiles themselves (that's an almost arbitrary choice of shape). It's the logistics of handling thousands of unique tiles rather than thousands of identical tiles. You can't just manufacture 10k 'Starship tiles', ship them by the pallet, and install them in the order you pick them up out of the crate. At the extreme, each is a unique shape and you must ensure that unique tile makes its way from manufacture to installation without being damaged, misplaced, installed one stud over, etc. If that happens, you then need to manufacture another unique tile (or manufacture at least two of every unique tile to start with, and have near 50% overhead).

There is no overhead here. Unused ‘spare’ tiles are simply part of the stock for future builds.
Until someone drops/chips/etc that second unique tile, and now an entire vehicle is waiting on the total lead time for a new tile to be manufactured and shipped, rather than on the lead-time for someone to grab the next tile in the pile.
I'm reminded of a segment of Eric Berger's book, Liftoff, where Falcon 1 testing is cut short by LOX shortage often enough that Elon throws out dire threats if there is ever a shortage again.

It seems like the solution here is to create a batch of, say, 50 of each "unique" tile, and after 30-40 are used, review the stock and decide if you need to run up another batch.
With clear labeling on the back of the tiles even a few hundred tile type should not really be much of an issue. It might even be possible to create a jig to allow standard tiles to be very precisely cut to create some of the specialist shapes in a hurry. They would need to be able to coat the cut edge, not sure how hard that would be?
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/22/2021 02:00 am
Top priority is successful EDL. Second priority is making it inexpensive.

Top priority is designing the machine that designs the machine.  That is ten times harder than the actual item that is being built.

It would be helpful to do some reading on Design For Manufacturability.  Those proposing 10s or 100s of types of tiles are violating the first principle of DFM:

Quote
1 | Minimize Part Count
Reducing the number of parts in a product is the quickest way to reduce cost because you are reducing the amount of material required, the amount of engineering, production, labor, all the way down to shipping costs.

As well as the second:

Quote
2 | Standaradize Parts and Materials
Personalization and customization are expensive and time-consuming. Using quality standardized parts can shorten time to production as such parts are typically available and you can be more certain of their consistency.




https://news.ewmfg.com/blog/manufacturing/dfm-design-for-manufacturing
Title: Re: Starship heat shield
Post by: cdebuhr on 06/22/2021 02:09 am
Top priority is successful EDL. Second priority is making it inexpensive.

Top priority is designing the machine that designs the machine.  That is ten times harder than the actual item that is being built.

It would be helpful to do some reading on Design For Manufacturability.  Those proposing 10s or 100s of types of tiles are violating the first principle of DFM:

Quote
1 | Minimize Part Count
Reducing the number of parts in a product is the quickest way to reduce cost because you are reducing the amount of material required, the amount of engineering, production, labor, all the way down to shipping costs.

As well as the second:

Quote
2 | Standaradize Parts and Materials
Personalization and customization are expensive and time-consuming. Using quality standardized parts can shorten time to production as such parts are typically available and you can be more certain of their consistency.




https://news.ewmfg.com/blog/manufacturing/dfm-design-for-manufacturing
That's all well and good, but the unequivocal top priority for the heat shield is still to make EDL survivable.  Without a functional heat shield, it really doesn't matter how manufacturable the whole spacecraft it is.  If this ends up needing 150 unique tile shapes, so be it.
 While some may argue that SS could be a commercially successful super heavy lift LV even flying expendable, that misses the point.  "Colonize Mars" is the reason SpaceX exists, and for that EDL is non-negotiable.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/22/2021 03:38 am

That's all well and good, but the unequivocal top priority for the heat shield is still to make EDL survivable.  Without a functional heat shield, it really doesn't matter how manufacturable the whole spacecraft it is.  If this ends up needing 150 unique tile shapes, so be it.
 While some may argue that SS could be a commercially successful super heavy lift LV even flying expendable, that misses the point.  "Colonize Mars" is the reason SpaceX exists, and for that EDL is non-negotiable.

Confusing with 'it must survive EDL the first time" with "it must survive EDL after 10-15 iterations" leads to neglect of manufacturability.  In software engineering we call this "premature optimization of a non-primary metric".

SpaceX, if they follow prior work, will make it "probably good enough on the CFD simulation" and as simple as possible, and iterate from there.  My guess is 10 Starships burn up before success.  (i.e. twice as many prototypes as the flip n burn)

"we can't manufacture it" is worse than "it doesn't survive EDL", because the first problem prevents you from iterating to fix the second problem.

Title: Re: Starship heat shield
Post by: cdebuhr on 06/22/2021 04:47 am

That's all well and good, but the unequivocal top priority for the heat shield is still to make EDL survivable.  Without a functional heat shield, it really doesn't matter how manufacturable the whole spacecraft it is.  If this ends up needing 150 unique tile shapes, so be it.
 While some may argue that SS could be a commercially successful super heavy lift LV even flying expendable, that misses the point.  "Colonize Mars" is the reason SpaceX exists, and for that EDL is non-negotiable.

Confusing with 'it must survive EDL the first time" with "it must survive EDL after 10-15 iterations" leads to neglect of manufacturability.  In software engineering we call this "premature optimization of a non-primary metric".

SpaceX, if they follow prior work, will make it "probably good enough on the CFD simulation" and as simple as possible, and iterate from there.  My guess is 10 Starships burn up before success.  (i.e. twice as many prototypes as the flip n burn)

"we can't manufacture it" is worse than "it doesn't survive EDL", because the first problem prevents you from iterating to fix the second problem.
Obviously it must be manufacturable and it must survive EDL.  I don't think anyone is saying it must survive on the first try, nor did I mean to imply anything about what gets optimized when.   While I think I see the points your making, there can be a big difference between "manufacturable" and "optimally manufacturable".  They could tile the thing with 5,000 unique shapes and it wouldn't be un-buildable, it would just be an expensive pain in the backside.  I suspect both parameters here will have room for further optimization after the first craft survives.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/22/2021 09:44 am
Top priority is successful EDL. Second priority is making it inexpensive.

Top priority is designing the machine that designs the machine.  That is ten times harder than the actual item that is being built.

It would be helpful to do some reading on Design For Manufacturability.  Those proposing 10s or 100s of types of tiles are violating the first principle of DFM:

Quote
1 | Minimize Part Count
Reducing the number of parts in a product is the quickest way to reduce cost because you are reducing the amount of material required, the amount of engineering, production, labor, all the way down to shipping costs.

As well as the second:

Quote
2 | Standaradize Parts and Materials
Personalization and customization are expensive and time-consuming. Using quality standardized parts can shorten time to production as such parts are typically available and you can be more certain of their consistency.




https://news.ewmfg.com/blog/manufacturing/dfm-design-for-manufacturing
The problem faced is the nature of geometry itself not a desire to violate the first principles of DFM. I don't think anyone is in any doubt that ideally there would be just one type of tile. Yet we have already seen SpaceX  deviate from the first principles of DFM by using multiple tile sizes. I would be interested to know how you think the tiles should be arranged on Starship?
Title: Re: Starship heat shield
Post by: rakaydos on 06/22/2021 10:30 am
Top priority is successful EDL. Second priority is making it inexpensive.

Top priority is designing the machine that designs the machine.  That is ten times harder than the actual item that is being built.

It would be helpful to do some reading on Design For Manufacturability.  Those proposing 10s or 100s of types of tiles are violating the first principle of DFM:

Quote
1 | Minimize Part Count
Reducing the number of parts in a product is the quickest way to reduce cost because you are reducing the amount of material required, the amount of engineering, production, labor, all the way down to shipping costs.

As well as the second:

Quote
2 | Standaradize Parts and Materials
Personalization and customization are expensive and time-consuming. Using quality standardized parts can shorten time to production as such parts are typically available and you can be more certain of their consistency.




https://news.ewmfg.com/blog/manufacturing/dfm-design-for-manufacturing
The problem faced is the nature of geometry itself not a desire to violate the first principles of DFM. I don't think anyone is in any doubt that ideally there would be just one type of tile. Yet we have already seen SpaceX  deviate from the first principles of DFM by using multiple tile sizes. I would be interested to know how you think the tiles should be arranged on Starship?
Someone already demonstrated how SpaceX's 3 tile sizes could be used to tile a nosecone. y'all complained about gaps, without ever proving that the gaps in question were showstoppers. Y'all have since used gap-gate to justify throwing out all evidence of SpaceX's solution in favor of geometicly perfect shields with hundreds of specialized tiles.

At this point, we pretty much know what SN20's shield will look like. (unless SN20 goes shieldless, just to see how far it gets...). It might or might not work, not even spaceX knows. And SpaceX will iterate from there... probably with a 4th tile shape specifically for the single biggest repeating gap in the existing pattern, keyhole shaped.

(https://forum.nasaspaceflight.com/assets/50748.0/2011621.jpg)
Title: Re: Starship heat shield
Post by: ETurner on 06/22/2021 10:57 am
With clear labeling on the back of the tiles even a few hundred tile type should not really be much of an issue. It might even be possible to create a jig to allow standard tiles to be very precisely cut to create some of the specialist shapes in a hurry. They would need to be able to coat the cut edge, not sure how hard that would be?
Clearly labeling the tiles at manufacturing time (maybe stenciling on the front surface with ablatable white ink) and writing numbers on the skin and double-checking before adding the tile should be enough to allow reliable placement even by tired workers.

I would expect that a modest number of preformed tile shapes would do the job, with special shapes made by using CNC milling to whittle away some material, followed by coating. Assumption: making the tiles may require fancy molding and processing that might best be done away from a build site, but milling and coating could be done at a build site. The on-site requirements would seem to be:

1) A CNC machining setup with tiles held by jigs that attach where the tiles would clip to the vehicle.
2) Spray coating capacity (maybe with CNC nozzle control).
3) An oven to sinter the coating.
Checking the above, I found a source (https://depts.washington.edu/matseed/mse_resources/Webpage/Space%20Shuttle%20Tiles/Space%20Shuttle%20Tiles.htm) for all these steps in Shuttle tile manufacture:

(1) “After being sintered the block is ready to be cut and machined into the required dimensions.”
(2, 3) “The HRSI tiles are coated on the top and sides with a glassy material with a liquid carrier. This glass is sprayed on the tile to a coating thickness of .016 to .018 in. Once the tiles are coated they are baked in an oven at about 2,300°”

Handling, milling, spraying baking sounds like a small setup with quality control requiring only surface inspection, a good job for machine vision. Replacement of special tiles could be done locally and quickly, as needed.
Title: Re: Starship heat shield
Post by: edzieba on 06/22/2021 12:33 pm
With clear labeling on the back of the tiles even a few hundred tile type should not really be much of an issue. It might even be possible to create a jig to allow standard tiles to be very precisely cut to create some of the specialist shapes in a hurry. They would need to be able to coat the cut edge, not sure how hard that would be?
Clearly labeling the tiles at manufacturing time (maybe stenciling on the front surface with ablatable white ink) and writing numbers on the skin and double-checking before adding the tile should be enough to allow reliable placement even by tired workers.
You can uniquely label, use keyed fittings, and implement double- or triple-checking all you want. It will not stop someone hammering your IMU in upside-down, or connecting your TVC backwards.
An assembly where you have 10 unique but visually near-identical part variants, where all variants will physically fit in the location of any other variant, where variant-to-variant dimension deltas are of similar scale to within-variant tolerance, and removing a misplaced part (if discovered) is destructive to the part and potentially to the fixture? You're not manufacturing a product, you're manufacturing a headache.

Again, the actual manufacture of large number of unique fit-to-size tiles is not at issue. We know it can be done, STS did it decades ago. Figuring out ways to do it is attaching the wrong problem: the issue is whether you need to jump through that enormous number of dancing flying hoops in the first place.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/22/2021 02:35 pm
Top priority is successful EDL. Second priority is making it inexpensive.

Top priority is designing the machine that designs the machine.  That is ten times harder than the actual item that is being built.

It would be helpful to do some reading on Design For Manufacturability.  Those proposing 10s or 100s of types of tiles are violating the first principle of DFM:

Quote
1 | Minimize Part Count
Reducing the number of parts in a product is the quickest way to reduce cost because you are reducing the amount of material required, the amount of engineering, production, labor, all the way down to shipping costs.

As well as the second:

Quote
2 | Standaradize Parts and Materials
Personalization and customization are expensive and time-consuming. Using quality standardized parts can shorten time to production as such parts are typically available and you can be more certain of their consistency.




https://news.ewmfg.com/blog/manufacturing/dfm-design-for-manufacturing
The problem faced is the nature of geometry itself not a desire to violate the first principles of DFM. I don't think anyone is in any doubt that ideally there would be just one type of tile. Yet we have already seen SpaceX  deviate from the first principles of DFM by using multiple tile sizes. I would be interested to know how you think the tiles should be arranged on Starship?
Someone already demonstrated how SpaceX's 3 tile sizes could be used to tile a nosecone. y'all complained about gaps, without ever proving that the gaps in question were showstoppers. Y'all have since used gap-gate to justify throwing out all evidence of SpaceX's solution in favor of geometicly perfect shields with hundreds of specialized tiles.

At this point, we pretty much know what SN20's shield will look like. (unless SN20 goes shieldless, just to see how far it gets...). It might or might not work, not even spaceX knows. And SpaceX will iterate from there... probably with a 4th tile shape specifically for the single biggest repeating gap in the existing pattern, keyhole shaped.

(https://forum.nasaspaceflight.com/assets/50748.0/2011621.jpg)
Well that is a fair point. If they can accept gaps then they must have considered just using one type of tile... but presumably that was a step too far (gaps too big) and SpaceX have settled on 3 types of tile for the majority of the surfaces in order to optimise the number of tiles v size of the gaps trade. We should see with SN20 if they have settled for a neat many tiled approach or a slightly disordered 3 tile approach.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/22/2021 04:35 pm
They could tile the thing with 5,000 unique shapes and it wouldn't be un-buildable, it would just be an expensive pain in the backside.  I suspect both parameters here will have room for further optimization after the first craft survives.

No, they could not be successful with 5,000 unique shapes because it would take far too long to place them, and they would then not be able to iterate quickly enough.

Iteration speed is proportional to manufacturing speed and iteration speed is everything in a program like this.
Title: Re: Starship heat shield
Post by: RoboGoofers on 06/22/2021 04:42 pm
They could tile the thing with 5,000 unique shapes and it wouldn't be un-buildable, it would just be an expensive pain in the backside.  I suspect both parameters here will have room for further optimization after the first craft survives.

No, they could not be successful with 5,000 unique shapes because it would take far too long to place them, and they would then not be able to iterate quickly enough.

Iteration speed is proportional to manufacturing speed and iteration speed is everything in a program like this.
they don't need to be attached by hand. Just look to electronics manufacturing. A scaled up pick and place machine could attach tiles very quickly.
Title: Re: Starship heat shield
Post by: RoboGoofers on 06/22/2021 04:55 pm
Long straight seams need to be avoided to keep the plasma from accelerating in the gaps, but what about long curved seams?
particularly this makes me think of Dragon 2's heat shield.
image from this thread: https://forum.nasaspaceflight.com/index.php?topic=41016.0 (https://forum.nasaspaceflight.com/index.php?topic=41016.0)
Title: Re: Starship heat shield
Post by: AC in NC on 06/22/2021 05:31 pm
They could tile the thing with 5,000 unique shapes and it wouldn't be un-buildable, it would just be an expensive pain in the backside.  I suspect both parameters here will have room for further optimization after the first craft survives.

No, they could not be successful with 5,000 unique shapes because it would take far too long to place them, and they would then not be able to iterate quickly enough.

Iteration speed is proportional to manufacturing speed and iteration speed is everything in a program like this.
they don't need to be attached by hand. Just look to electronics manufacturing. A scaled up pick and place machine could attach tiles very quickly.

Watch Elon's last Battery Day presentation and video about the speed of the Battery production line.  Obviously the speeds would be far different in this case but the principle remains the same.  To get the throughput you want, you must eliminate the things that slow down the line running at a breakneck pace.

The "battery tabs" was what was slowing down battery production.  5000 unique tile shapes would slow down the pick and place.
Title: Re: Starship heat shield
Post by: cdebuhr on 06/22/2021 05:39 pm
They could tile the thing with 5,000 unique shapes and it wouldn't be un-buildable, it would just be an expensive pain in the backside.  I suspect both parameters here will have room for further optimization after the first craft survives.

No, they could not be successful with 5,000 unique shapes because it would take far too long to place them, and they would then not be able to iterate quickly enough.

Iteration speed is proportional to manufacturing speed and iteration speed is everything in a program like this.
OK, 5000 was perhaps slightly exaggerated, but I stand by my point.  I also think I hear what you're saying, and don't necessarily disagree, but I think we're talking about somewhat different stages in the whole process, and I think we're also somewhat out of sync semantically speaking.  I'm pretty sure if we were discussing this over a beer, we'd agree on a lot more than not.  In any case, I believe they will start with the simplest, most manufacturable design they think they can get away with that also has at least a chance of surviving EDL.  Even though the first few tries will almost certainly crash and burn (or more correctly, burn then crash), they will not go launching a bunch of prototypes that they know are doomed to certain failure just because they are easier to build.
Title: Re: Starship heat shield
Post by: OTV Booster on 06/22/2021 06:22 pm
They could tile the thing with 5,000 unique shapes and it wouldn't be un-buildable, it would just be an expensive pain in the backside.  I suspect both parameters here will have room for further optimization after the first craft survives.

No, they could not be successful with 5,000 unique shapes because it would take far too long to place them, and they would then not be able to iterate quickly enough.

Iteration speed is proportional to manufacturing speed and iteration speed is everything in a program like this.
Cdebuhr was just grabbing a number at he extreme to make a point. The engineering works but the economics suck.


The point was made that until we know what gaps are acceptable, we don't have a clue about tile layout. My methane producing gut says that Rakaydos's pattern is too open but what do I know.


A dozen different patters would be great but if the count goes up to 150, comparison to the shuttle is still all in SS's favor.


Side note: If each different tile shape has its own mold with no trim to fit, each tile can have a part number embossed 3D on the back. If there is danger of workers going brain dead and putting a round peg in a square hole, limit the amount of consecutive time on a brain numbing repetitive task like installing tiles, and totally isolate the working guy from launch fever.

Title: Re: Starship heat shield
Post by: rakaydos on 06/22/2021 06:36 pm

The point was made that until we know what gaps are acceptable, we don't have a clue about tile layout. My methane producing gut says that Rakaydos's pattern is too open but what do I know.
I dont know either, but recall that they seriously looked at deleting the heat shield entirely and rely just on the thermal mass of the steel. They dont need a whole lot of thermal protection, IIRC just enough to drop the peak heating by a sixth or so, below a thousand degrees.

They also have a history of starting with less than the accepted minimum, just to see what the real minimum is. Given the tiles seen, I wouldnt be suprised if SN24 had keyhole specialty tiles, but if SN 20 enters without them, dont expect SpaceX to pony up for an extra  tile manufacturing line.
Title: Re: Starship heat shield
Post by: wannamoonbase on 06/22/2021 06:50 pm

The point was made that until we know what gaps are acceptable, we don't have a clue about tile layout. My methane producing gut says that Rakaydos's pattern is too open but what do I know.
I dont know either, but recall that they seriously looked at deleting the heat shield entirely and rely just on the thermal mass of the steel. They dont need a whole lot of thermal protection, IIRC just enough to drop the peak heating by a sixth or so, below a thousand degrees.

They also have a history of starting with less than the accepted minimum, just to see what the real minimum is. Given the tiles seem, I wouldnt be suprised if SN24 had keyhole specialty tiles, but if SN 20 enters without them, dont expect SpaceX to pony up for an extra  tile manufacturing line.

I do love how SpaceX finds the minimum.  However, with a heatshield there is a prerequisite that they survive re-entry.

No doubt they've modeled this 1000's of times and have a good idea of the minimum requirement.  For most of the heat shield it's probably a debate over small thicknesses and gaps.

Specialty areas and transitions should be the areas of biggest concern.  The nose, transitions to the uncovered areas, areas by the flaps, even the edge along the engine bay.

Throw on a ton of instrumentation and start flying!

I can't wait to see what they do to SN20.
Title: Re: Starship heat shield
Post by: rsdavis9 on 06/22/2021 06:55 pm

The point was made that until we know what gaps are acceptable, we don't have a clue about tile layout. My methane producing gut says that Rakaydos's pattern is too open but what do I know.
I dont know either, but recall that they seriously looked at deleting the heat shield entirely and rely just on the thermal mass of the steel. They dont need a whole lot of thermal protection, IIRC just enough to drop the peak heating by a sixth or so, below a thousand degrees.

They also have a history of starting with less than the accepted minimum, just to see what the real minimum is. Given the tiles seem, I wouldnt be suprised if SN24 had keyhole specialty tiles, but if SN 20 enters without them, dont expect SpaceX to pony up for an extra  tile manufacturing line.

I do love how SpaceX finds the minimum.  However, with a heatshield there is a prerequisite that they survive re-entry.

No doubt they've modeled this 1000's of times and have a good idea of the minimum requirement.  For most of the heat shield it's probably a debate over small thicknesses and gaps.

Specialty areas and transitions should be the areas of biggest concern.  The nose, transitions to the uncovered areas, areas by the flaps, even the edge along the engine bay.

Throw on a ton of instrumentation and start flying!

I can't wait to see what they do to SN20.

From my notes stainless steel loses it's temper at 800C and melts at 1500C so that is a big enough gap that we should be getting SS back with steel that has lost its temper but is still intact enough to land.
So the ship won't refly but it will inform to where the heat shield needs to do better.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/22/2021 07:18 pm
Long straight seams need to be avoided to keep the plasma from accelerating in the gaps, but what about long curved seams?
particularly this makes me think of Dragon 2's heat shield.
image from this thread: https://forum.nasaspaceflight.com/index.php?topic=41016.0 (https://forum.nasaspaceflight.com/index.php?topic=41016.0)
Long curved seams might help with plasma at the margins but unfortunately won't help with the tessellation fit / number of tiles problem. And we have only seen 4 tile types from SpaceX so far. Three sizes of regular hexagon and a truncated hexagon (presumably for around the bottom of the skirt).
Title: Re: Starship heat shield
Post by: RoboGoofers on 06/22/2021 07:33 pm
Long straight seams need to be avoided to keep the plasma from accelerating in the gaps, but what about long curved seams?
particularly this makes me think of Dragon 2's heat shield.
image from this thread: https://forum.nasaspaceflight.com/index.php?topic=41016.0 (https://forum.nasaspaceflight.com/index.php?topic=41016.0)
Long curved seams might help with plasma at the margins but unfortunately won't help with the tessellation fit / number of tiles problem. And we have only seen 4 tile types from SpaceX so far. Three sizes of regular hexagon and a truncated hexagon (presumably for around the bottom of the skirt).
The tiling pattern discussion is beyond me but as to your second point, to me, that doesn't signify much. After all, we haven't seen any of the leading edge tiles or wing root tiles (or whatever they'll use in those places). We've also never seen any of the current tiles to date on the nose, so we can't be sure they'll use the same tiles there.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/22/2021 07:38 pm

The point was made that until we know what gaps are acceptable, we don't have a clue about tile layout. My methane producing gut says that Rakaydos's pattern is too open but what do I know.
I dont know either, but recall that they seriously looked at deleting the heat shield entirely and rely just on the thermal mass of the steel. They dont need a whole lot of thermal protection, IIRC just enough to drop the peak heating by a sixth or so, below a thousand degrees.

They also have a history of starting with less than the accepted minimum, just to see what the real minimum is. Given the tiles seen, I wouldnt be suprised if SN24 had keyhole specialty tiles, but if SN 20 enters without them, dont expect SpaceX to pony up for an extra  tile manufacturing line.

With the raw stainless steel exposed, hot spots are a huge problem because SS doesn't distribute heat well.

As I'm reminded every time I throw frozen peas into a stainless steel pan of barely boiling water, which burns my hand after the water furiously boils from being raised 1/2" by the peas and the waves from dropping the peas..   The sides of the pan 1/2" up from the water are at higher temperature than boiling water, because SS doesn't conduct heat very well.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/22/2021 08:19 pm
It will be interesting to see what SN20 looks like. There have been many suggestions here in the “minimize the gaps” v “minimize the tile types” debate. I have previously focused on minimize the gaps, but as rakaydos and others have pointed out, we don’t know what is an acceptable gap and SpaceX have only tested three different sizes of hexagonal tile. With that in mind I will suggest another nosecone tile arrangement with gaps that uses tiles touching side by side around the circumference but leaves variable gaps between the rows.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/22/2021 08:24 pm
Long straight seams need to be avoided to keep the plasma from accelerating in the gaps, but what about long curved seams?
particularly this makes me think of Dragon 2's heat shield.
image from this thread: https://forum.nasaspaceflight.com/index.php?topic=41016.0 (https://forum.nasaspaceflight.com/index.php?topic=41016.0)
Long curved seams might help with plasma at the margins but unfortunately won't help with the tessellation fit / number of tiles problem. And we have only seen 4 tile types from SpaceX so far. Three sizes of regular hexagon and a truncated hexagon (presumably for around the bottom of the skirt).
The tiling pattern discussion is beyond me but as to your second point, to me, that doesn't signify much. After all, we haven't seen any of the leading edge tiles or wing root tiles (or whatever they'll use in those places). We've also never seen any of the current tiles to date on the nose, so we can't be sure they'll use the same tiles there.
All true so the design from page 1 is still a contender as are many of the others that have been posted.
Title: Re: Starship heat shield
Post by: Vultur on 06/22/2021 08:34 pm
While the heat shield needs to survive EDL, there may be some number of different tile types above which other types of heat shield (like a transpiration cooled one) win out economically/manufacturing wise.

Since SpaceX considered transpiration cooling before going to the tile heat shield, presumably they think it will be easier to make work with tiles.

But if they end up needing some very large number of unique tiles, that decision might be reversed.
Title: Re: Starship heat shield
Post by: ETurner on 06/22/2021 10:02 pm
It will be interesting to see what SN20 looks like. There have been many suggestions here in the “minimize the gaps” v “minimize the tile types” debate. I have previously focused on minimize the gaps, but as rakaydos and others have pointed out, we don’t know what is an acceptable gap and SpaceX have only tested three different sizes of hexagonal tile. With that in mind I will suggest another nosecone tile arrangement with gaps that uses tiles touching side by side around the circumference but leaves variable gaps between the rows.
If large gaps are OK, then wouldn’t smaller tiles and larger gaps reduce the total mass of tiles by reducing the area covered? This isn’t what we see. Or maybe large gaps are OK in places, if offset by a thicker blanket, but accepting a mass penalty in those areas.
Title: Re: Starship heat shield
Post by: rakaydos on 06/22/2021 10:07 pm

The point was made that until we know what gaps are acceptable, we don't have a clue about tile layout. My methane producing gut says that Rakaydos's pattern is too open but what do I know.
I dont know either, but recall that they seriously looked at deleting the heat shield entirely and rely just on the thermal mass of the steel. They dont need a whole lot of thermal protection, IIRC just enough to drop the peak heating by a sixth or so, below a thousand degrees.

They also have a history of starting with less than the accepted minimum, just to see what the real minimum is. Given the tiles seen, I wouldnt be suprised if SN24 had keyhole specialty tiles, but if SN 20 enters without them, dont expect SpaceX to pony up for an extra  tile manufacturing line.

With the raw stainless steel exposed, hot spots are a huge problem because SS doesn't distribute heat well.

As I'm reminded every time I throw frozen peas into a stainless steel pan of barely boiling water, which burns my hand after the water furiously boils from being raised 1/2" by the peas and the waves from dropping the peas..   The sides of the pan 1/2" up from the water are at higher temperature than boiling water, because SS doesn't conduct heat very well.
I'm not sure that's entirely fair, unless you turn the burner off before throwing the peas in. Clearly, heat is going to transfer to the water faster than it's going to transfer along the surface of the steel, but there's still a decent heat transfer that way.

Also, it's not going to be "raw stainless steel exposed" to reentry- there's a thermal blanket between the tiles and the hull.
Title: Re: Starship heat shield
Post by: ETurner on 06/22/2021 10:11 pm
With clear labeling on the back of the tiles even a few hundred tile type should not really be much of an issue. It might even be possible to create a jig to allow standard tiles to be very precisely cut to create some of the specialist shapes in a hurry. They would need to be able to coat the cut edge, not sure how hard that would be?
Clearly labeling the tiles at manufacturing time (maybe stenciling on the front surface with ablatable white ink) and writing numbers on the skin and double-checking before adding the tile should be enough to allow reliable placement even by tired workers.
You can uniquely label, use keyed fittings, and implement double- or triple-checking all you want. It will not stop someone hammering your IMU in upside-down, or connecting your TVC backwards.
An assembly where you have 10 unique but visually near-identical part variants, where all variants will physically fit in the location of any other variant, where variant-to-variant dimension deltas are of similar scale to within-variant tolerance, and removing a misplaced part (if discovered) is destructive to the part and potentially to the fixture? You're not manufacturing a product, you're manufacturing a headache.

Again, the actual manufacture of large number of unique fit-to-size tiles is not at issue. We know it can be done, STS did it decades ago. Figuring out ways to do it is attaching the wrong problem: the issue is whether you need to jump through that enormous number of dancing flying hoops in the first place.
Jam a tile into a too-small space and it will break. Clip a tile into a too-large space and it leaves wide gaps. Check for broken tiles or wide gaps, and remove and replace as needed. Tell Joe to drink more coffee.

I don’t see a big problem here. Use as many tile shapes are are needed to fit the shape of the vehicle.
Title: Re: Starship heat shield
Post by: JamesH65 on 06/23/2021 09:50 am
With clear labeling on the back of the tiles even a few hundred tile type should not really be much of an issue. It might even be possible to create a jig to allow standard tiles to be very precisely cut to create some of the specialist shapes in a hurry. They would need to be able to coat the cut edge, not sure how hard that would be?
Clearly labeling the tiles at manufacturing time (maybe stenciling on the front surface with ablatable white ink) and writing numbers on the skin and double-checking before adding the tile should be enough to allow reliable placement even by tired workers.
You can uniquely label, use keyed fittings, and implement double- or triple-checking all you want. It will not stop someone hammering your IMU in upside-down, or connecting your TVC backwards.
An assembly where you have 10 unique but visually near-identical part variants, where all variants will physically fit in the location of any other variant, where variant-to-variant dimension deltas are of similar scale to within-variant tolerance, and removing a misplaced part (if discovered) is destructive to the part and potentially to the fixture? You're not manufacturing a product, you're manufacturing a headache.

Again, the actual manufacture of large number of unique fit-to-size tiles is not at issue. We know it can be done, STS did it decades ago. Figuring out ways to do it is attaching the wrong problem: the issue is whether you need to jump through that enormous number of dancing flying hoops in the first place.
Jam a tile into a too-small space and it will break. Clip a tile into a too-large space and it leaves wide gaps. Check for broken tiles or wide gaps, and remove and replace as needed. Tell Joe to drink more coffee.

I don’t see a big problem here. Use as many tile shapes are are needed to fit the shape of the vehicle.

The Space shuttle used as many tiles as were needed, and look how long it took to maintain those...

Title: Re: Starship heat shield
Post by: ETurner on 06/23/2021 10:58 am
With clear labeling on the back of the tiles even a few hundred tile type should not really be much of an issue. It might even be possible to create a jig to allow standard tiles to be very precisely cut to create some of the specialist shapes in a hurry. They would need to be able to coat the cut edge, not sure how hard that would be?
Clearly labeling the tiles at manufacturing time (maybe stenciling on the front surface with ablatable white ink) and writing numbers on the skin and double-checking before adding the tile should be enough to allow reliable placement even by tired workers.
You can uniquely label, use keyed fittings, and implement double- or triple-checking all you want. It will not stop someone hammering your IMU in upside-down, or connecting your TVC backwards.
An assembly where you have 10 unique but visually near-identical part variants, where all variants will physically fit in the location of any other variant, where variant-to-variant dimension deltas are of similar scale to within-variant tolerance, and removing a misplaced part (if discovered) is destructive to the part and potentially to the fixture? You're not manufacturing a product, you're manufacturing a headache.

Again, the actual manufacture of large number of unique fit-to-size tiles is not at issue. We know it can be done, STS did it decades ago. Figuring out ways to do it is attaching the wrong problem: the issue is whether you need to jump through that enormous number of dancing flying hoops in the first place.
Jam a tile into a too-small space and it will break. Clip a tile into a too-large space and it leaves wide gaps. Check for broken tiles or wide gaps, and remove and replace as needed. Tell Joe to drink more coffee.

I don’t see a big problem here. Use as many tile shapes are are needed to fit the shape of the vehicle.

The Space shuttle used as many tiles as were needed, and look how long it took to maintain those...

1) Shuttle needed them, so they had to use them. Not a good design, but the were stuck with it. Starship needs far fewer tile types (a much better design), but whatever it needs, it needs. Yes?

2) The felt-and-adhesive attachment method used for Shuttle tiles was a maintenance nightmare. Starship uses clips. Big difference. Shuttletilephobia has done its work, with good results.

3) If the machine to make the machine includes on-site, on-demand tile cutting and coating (as argued here (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2255359#msg2255359), this isn’t very difficult) then system costs of adding tile types is less than we’ve been assuming.

4) Claims that installation errors will be a tremendous problem are overblown (as argued here (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2255592#msg2255592)). They can be both rare and readily fixed.

Does anyone see a good argument against any of these points?
Title: Re: Starship heat shield
Post by: edzieba on 06/23/2021 11:35 am
With clear labeling on the back of the tiles even a few hundred tile type should not really be much of an issue. It might even be possible to create a jig to allow standard tiles to be very precisely cut to create some of the specialist shapes in a hurry. They would need to be able to coat the cut edge, not sure how hard that would be?
Clearly labeling the tiles at manufacturing time (maybe stenciling on the front surface with ablatable white ink) and writing numbers on the skin and double-checking before adding the tile should be enough to allow reliable placement even by tired workers.
You can uniquely label, use keyed fittings, and implement double- or triple-checking all you want. It will not stop someone hammering your IMU in upside-down, or connecting your TVC backwards.
An assembly where you have 10 unique but visually near-identical part variants, where all variants will physically fit in the location of any other variant, where variant-to-variant dimension deltas are of similar scale to within-variant tolerance, and removing a misplaced part (if discovered) is destructive to the part and potentially to the fixture? You're not manufacturing a product, you're manufacturing a headache.

Again, the actual manufacture of large number of unique fit-to-size tiles is not at issue. We know it can be done, STS did it decades ago. Figuring out ways to do it is attaching the wrong problem: the issue is whether you need to jump through that enormous number of dancing flying hoops in the first place.
Jam a tile into a too-small space and it will break. Clip a tile into a too-large space and it leaves wide gaps. Check for broken tiles or wide gaps, and remove and replace as needed. Tell Joe to drink more coffee.

I don’t see a big problem here. Use as many tile shapes are are needed to fit the shape of the vehicle.
In the 'unique tile' edge case, "all tiles installed one position to the left, because one tile was installed incorectly and then used as datum for the rest" = "entire heat shield scrapped and a new one manufactured" due to the destructive nature of tile removal.

Quick temporary bodges are anathema to Starship thus far. The goal of the development program has been developing the systems and techniques to efficiently and economically manufacture Starship. Designing 'one off' temporary heatshields or heat-shield designs that require two-man-rule or robots to install correctly are not manufacturable solutions. If there is a manufacturable solution to the TPS, then skip the time and money wasted on a temporary version and go for the one you actually want to use. This is why SpaceX have been happy to roll Starships off of the assembly line and straight into a back lot or scrap pile: the Starship itself isn't the goal, manufacturing one is. There is no value in constructing a TPS that you know is going to be replaced by a more manufacturable design.
Title: Re: Starship heat shield
Post by: ETurner on 06/23/2021 12:21 pm
With clear labeling on the back of the tiles even a few hundred tile type should not really be much of an issue. It might even be possible to create a jig to allow standard tiles to be very precisely cut to create some of the specialist shapes in a hurry. They would need to be able to coat the cut edge, not sure how hard that would be?
Clearly labeling the tiles at manufacturing time (maybe stenciling on the front surface with ablatable white ink) and writing numbers on the skin and double-checking before adding the tile should be enough to allow reliable placement even by tired workers.
You can uniquely label, use keyed fittings, and implement double- or triple-checking all you want. It will not stop someone hammering your IMU in upside-down, or connecting your TVC backwards.
An assembly where you have 10 unique but visually near-identical part variants, where all variants will physically fit in the location of any other variant, where variant-to-variant dimension deltas are of similar scale to within-variant tolerance, and removing a misplaced part (if discovered) is destructive to the part and potentially to the fixture? You're not manufacturing a product, you're manufacturing a headache.

Again, the actual manufacture of large number of unique fit-to-size tiles is not at issue. We know it can be done, STS did it decades ago. Figuring out ways to do it is attaching the wrong problem: the issue is whether you need to jump through that enormous number of dancing flying hoops in the first place.
Jam a tile into a too-small space and it will break. Clip a tile into a too-large space and it leaves wide gaps. Check for broken tiles or wide gaps, and remove and replace as needed. Tell Joe to drink more coffee.

I don’t see a big problem here. Use as many tile shapes are are needed to fit the shape of the vehicle.
In the 'unique tile' edge case, "all tiles installed one position to the left, because one tile was installed incorectly and then used as datum for the rest" = "entire heat shield scrapped and a new one manufactured" due to the destructive nature of tile removal.

Quick temporary bodges are anathema to Starship thus far. The goal of the development program has been developing the systems and techniques to efficiently and economically manufacture Starship. Designing 'one off' temporary heatshields or heat-shield designs that require two-man-rule or robots to install correctly are not manufacturable solutions. If there is a manufacturable solution to the TPS, then skip the time and money wasted on a temporary version and go for the one you actually want to use. This is why SpaceX have been happy to roll Starships off of the assembly line and straight into a back lot or scrap pile: the Starship itself isn't the goal, manufacturing one is. There is no value in constructing a TPS that you know is going to be replaced by a more manufacturable design.
In the 'unique tile' edge case, "all tiles installed one position to the left, because one tile was installed incorrectly and then used as datum for the rest" = "entire heat shield scrapped and a new one manufactured" due to the destructive nature of tile removal. --

How does this happen if tiles are labelled and positions are numbered (scribbled on steel with a Sharpy) and double-checked? A worker puts labelled-tile 1233 in numbered-position 1232, then puts labelled-tile 1234 in numbered-position 1233, etc., etc.? How often would this happen? (Maybe a robot would do it, but only once.)

Like this:
Clearly labeling the tiles at manufacturing time (maybe stenciling on the front surface with ablatable white ink) and writing numbers on the skin and double-checking before adding the tile should be enough to allow reliable placement even by tired workers.


Designing 'one off' temporary heatshields or heat-shield designs that require two-man-rule or robots to install correctly are not manufacturable solutions. --


OK, but ISTM that checking the numbering beforehand and checking for broken tiles and gaps afterward -- not even needed in areas where there are 10,000 identical tiles -- isn’t asking too much. I bet that lots of the work at SpaceX gets inspected after it’s done, and that someone checks the parts beforehand.

Again, the question is how many tile the design actually needs. This is more than 5, but a small fraction of the total number of tiles. And whatever it is, that’s what it is. The question is how to (1) minimize requirements, then (2) meet those requirements. Yes?

Not a temporary bodge, just doing the actual job.

Title: Re: Starship heat shield
Post by: rakaydos on 06/23/2021 12:31 pm
With clear labeling on the back of the tiles even a few hundred tile type should not really be much of an issue. It might even be possible to create a jig to allow standard tiles to be very precisely cut to create some of the specialist shapes in a hurry. They would need to be able to coat the cut edge, not sure how hard that would be?
Clearly labeling the tiles at manufacturing time (maybe stenciling on the front surface with ablatable white ink) and writing numbers on the skin and double-checking before adding the tile should be enough to allow reliable placement even by tired workers.
You can uniquely label, use keyed fittings, and implement double- or triple-checking all you want. It will not stop someone hammering your IMU in upside-down, or connecting your TVC backwards.
An assembly where you have 10 unique but visually near-identical part variants, where all variants will physically fit in the location of any other variant, where variant-to-variant dimension deltas are of similar scale to within-variant tolerance, and removing a misplaced part (if discovered) is destructive to the part and potentially to the fixture? You're not manufacturing a product, you're manufacturing a headache.

Again, the actual manufacture of large number of unique fit-to-size tiles is not at issue. We know it can be done, STS did it decades ago. Figuring out ways to do it is attaching the wrong problem: the issue is whether you need to jump through that enormous number of dancing flying hoops in the first place.
Jam a tile into a too-small space and it will break. Clip a tile into a too-large space and it leaves wide gaps. Check for broken tiles or wide gaps, and remove and replace as needed. Tell Joe to drink more coffee.

I don’t see a big problem here. Use as many tile shapes are are needed to fit the shape of the vehicle.
In the 'unique tile' edge case, "all tiles installed one position to the left, because one tile was installed incorectly and then used as datum for the rest" = "entire heat shield scrapped and a new one manufactured" due to the destructive nature of tile removal.

Quick temporary bodges are anathema to Starship thus far. The goal of the development program has been developing the systems and techniques to efficiently and economically manufacture Starship. Designing 'one off' temporary heatshields or heat-shield designs that require two-man-rule or robots to install correctly are not manufacturable solutions. If there is a manufacturable solution to the TPS, then skip the time and money wasted on a temporary version and go for the one you actually want to use. This is why SpaceX have been happy to roll Starships off of the assembly line and straight into a back lot or scrap pile: the Starship itself isn't the goal, manufacturing one is. There is no value in constructing a TPS that you know is going to be replaced by a more manufacturable design.
In the 'unique tile' edge case, "all tiles installed one position to the left, because one tile was installed incorrectly and then used as datum for the rest" = "entire heat shield scrapped and a new one manufactured" due to the destructive nature of tile removal. --

How does this happen if tiles are labelled and positions are numbered (scribbled on steel with a Sharpy) and double-checked? A worker puts labelled-tile 1233 in numbered-position 1232, then puts labelled-tile 1234 in numbered-position 1233, etc., etc.? How often would this happen? (Maybe a robot would do it, but only once.)
And if sharpie- guy fucked it up?
Title: Re: Starship heat shield
Post by: edzieba on 06/23/2021 01:07 pm
How often would this happen?
All the time.
Sharpie number is wrong. Sharpie number is ambiguous because of handwriting. Sharpie was cleaned off or obscured. Tile number is wrong. Tile number is ambiguous (e.g. off-by-one or transposable or invertible). Installer is tired. Installer is distracted. Installer shift changes. Install is two-handing to speed up operation, grabs tile N and N+1, reads number on N+1 and installs N in that position (and/or vice versa). Installer installs first tile wrong (for whatever reason), and installs all subsequent tiles wrong based on that tile location (because tiles were stacked in order of install, and install pattern is known) and this behaviour is rewarded due to increased productivity when installing before an error occurs. Checker makes any of the same mistakes as installer. Checker is looking for tiles to match, not looking for tiles to not match. Checker cannot see sharpie number (obscured by tile) so goes by relative tile position, or by map referencing (prone to error).
And those are just failure modes though of off the top of my head during the writing of that paragraph. When your protection against human error is "well, don't make an error then!" you have no error protection.

As for robots, those can be just as prone to human error due to humans needing to program and direct the robot. e.g. if the work coordinate system is based on the barrel being clocked in the fixture correctly, the barrel may be clocked in the fixture incorrectly. If it's based on using a specific stud as a datum, the wrong stud could be used. Stick a barcode under every stud pattern rather than sharpie? Whoops, wrong barcode was applied. Or the barcode printer has a bug and applies the same barcode to all spots. Or the barcode printer is iterating correctly, but one barcode got stuck in the applicator so every barcode is off by one. Etc.
Title: Re: Starship heat shield
Post by: ETurner on 06/23/2021 02:29 pm
With clear labeling on the back of the tiles even a few hundred tile type should not really be much of an issue. It might even be possible to create a jig to allow standard tiles to be very precisely cut to create some of the specialist shapes in a hurry. They would need to be able to coat the cut edge, not sure how hard that would be?
Clearly labeling the tiles at manufacturing time (maybe stenciling on the front surface with ablatable white ink) and writing numbers on the skin and double-checking before adding the tile should be enough to allow reliable placement even by tired workers.
You can uniquely label, use keyed fittings, and implement double- or triple-checking all you want. It will not stop someone hammering your IMU in upside-down, or connecting your TVC backwards.
An assembly where you have 10 unique but visually near-identical part variants, where all variants will physically fit in the location of any other variant, where variant-to-variant dimension deltas are of similar scale to within-variant tolerance, and removing a misplaced part (if discovered) is destructive to the part and potentially to the fixture? You're not manufacturing a product, you're manufacturing a headache.

Again, the actual manufacture of large number of unique fit-to-size tiles is not at issue. We know it can be done, STS did it decades ago. Figuring out ways to do it is attaching the wrong problem: the issue is whether you need to jump through that enormous number of dancing flying hoops in the first place.
Jam a tile into a too-small space and it will break. Clip a tile into a too-large space and it leaves wide gaps. Check for broken tiles or wide gaps, and remove and replace as needed. Tell Joe to drink more coffee.

I don’t see a big problem here. Use as many tile shapes are are needed to fit the shape of the vehicle.
In the 'unique tile' edge case, "all tiles installed one position to the left, because one tile was installed incorectly and then used as datum for the rest" = "entire heat shield scrapped and a new one manufactured" due to the destructive nature of tile removal.

Quick temporary bodges are anathema to Starship thus far. The goal of the development program has been developing the systems and techniques to efficiently and economically manufacture Starship. Designing 'one off' temporary heatshields or heat-shield designs that require two-man-rule or robots to install correctly are not manufacturable solutions. If there is a manufacturable solution to the TPS, then skip the time and money wasted on a temporary version and go for the one you actually want to use. This is why SpaceX have been happy to roll Starships off of the assembly line and straight into a back lot or scrap pile: the Starship itself isn't the goal, manufacturing one is. There is no value in constructing a TPS that you know is going to be replaced by a more manufacturable design.
In the 'unique tile' edge case, "all tiles installed one position to the left, because one tile was installed incorrectly and then used as datum for the rest" = "entire heat shield scrapped and a new one manufactured" due to the destructive nature of tile removal. --

How does this happen if tiles are labelled and positions are numbered (scribbled on steel with a Sharpy) and double-checked? A worker puts labelled-tile 1233 in numbered-position 1232, then puts labelled-tile 1234 in numbered-position 1233, etc., etc.? How often would this happen? (Maybe a robot would do it, but only once.)
And if sharpie- guy fucked it up?
“How does this happen if tiles are labelled and positions are numbered (scribbled on steel with a Sharpy) and double-checked?”
Also, occasional problems can be fixed.
Title: Re: Starship heat shield
Post by: ETurner on 06/23/2021 02:48 pm
How often would this happen?
All the time.
Sharpie number is wrong. Sharpie number is ambiguous because of handwriting. Sharpie was cleaned off or obscured. Tile number is wrong. Tile number is ambiguous (e.g. off-by-one or transposable or invertible). Installer is tired. Installer is distracted. Installer shift changes. Install is two-handing to speed up operation, grabs tile N and N+1, reads number on N+1 and installs N in that position (and/or vice versa). Installer installs first tile wrong (for whatever reason), and installs all subsequent tiles wrong based on that tile location (because tiles were stacked in order of install, and install pattern is known) and this behaviour is rewarded due to increased productivity when installing before an error occurs. Checker makes any of the same mistakes as installer. Checker is looking for tiles to match, not looking for tiles to not match. Checker cannot see sharpie number (obscured by tile) so goes by relative tile position, or by map referencing (prone to error).
And those are just failure modes though of off the top of my head during the writing of that paragraph. When your protection against human error is "well, don't make an error then!" you have no error protection.

As for robots, those can be just as prone to human error due to humans needing to program and direct the robot. e.g. if the work coordinate system is based on the barrel being clocked in the fixture correctly, the barrel may be clocked in the fixture incorrectly. If it's based on using a specific stud as a datum, the wrong stud could be used. Stick a barcode under every stud pattern rather than sharpie? Whoops, wrong barcode was applied. Or the barcode printer has a bug and applies the same barcode to all spots. Or the barcode printer is iterating correctly, but one barcode got stuck in the applicator so every barcode is off by one. Etc.
All the time. --
Every tile wrong? That’s what I’d call perfection!
Oh, you must mean “Occasional screwups on almost every vehicle”.

Checker is looking for tiles to match, not looking for tiles to not match. --

And tiles that are jammed and break, or are in a large hole and leave gaps, aren’t noticed and fixed. If they fit, they fit. If they don’t, it’s visible.

Etc.

When your protection against human error is "well, don't make an error then!" you have no error protection.
--
But occasional errors can be fixed.
Perfect installation is a straw man. C’mon, get serious: consider the whole process.
Title: Re: Starship heat shield
Post by: eriblo on 06/23/2021 03:04 pm
Errors can happen but it should be possible to reduce the rate quite a bit.

Possible example: Technician with AR glasses picks up tile to be installed and check for damage while the glasses scan a unique QR code printed on the tile and gives audio-visual confirmation. The glasses highlight correct placement using computer vision and external metrology. The technician then lines up unique marks printed on the tile edges with the corresponding marks on surrounding tiles while the glasses confirm orientation and scans the surrounding tiles QR codes for confirmation. Could be backed up with variations in mounting point placements (i.e. tile can not physically* be mounted in the wrong orientation or a close by location) at the cost of less commonality in tile manufacture and perhaps a slightly higher chance of errors by the stud welding robot.

*Barring sufficient insistence with a hammer...
Title: Re: Starship heat shield
Post by: OTV Booster on 06/23/2021 04:16 pm

The point was made that until we know what gaps are acceptable, we don't have a clue about tile layout. My methane producing gut says that Rakaydos's pattern is too open but what do I know.
I dont know either, but recall that they seriously looked at deleting the heat shield entirely and rely just on the thermal mass of the steel. They dont need a whole lot of thermal protection, IIRC just enough to drop the peak heating by a sixth or so, below a thousand degrees.

They also have a history of starting with less than the accepted minimum, just to see what the real minimum is. Given the tiles seem, I wouldnt be suprised if SN24 had keyhole specialty tiles, but if SN 20 enters without them, dont expect SpaceX to pony up for an extra  tile manufacturing line.

I do love how SpaceX finds the minimum.  However, with a heatshield there is a prerequisite that they survive re-entry.

No doubt they've modeled this 1000's of times and have a good idea of the minimum requirement.  For most of the heat shield it's probably a debate over small thicknesses and gaps.

Specialty areas and transitions should be the areas of biggest concern.  The nose, transitions to the uncovered areas, areas by the flaps, even the edge along the engine bay.

Throw on a ton of instrumentation and start flying!

I can't wait to see what they do to SN20.

From my notes stainless steel loses it's temper at 800C and melts at 1500C so that is a big enough gap that we should be getting SS back with steel that has lost its temper but is still intact enough to land.
So the ship won't refly but it will inform to where the heat shield needs to do better.
The tempering. We've not heard, or maybe more accurately, we haven't discussed this in quite a while. There's so much incidental welding, is this still a thing? Probably is but I wonder. Would SS work if unhardened?
Title: Re: Starship heat shield
Post by: OTV Booster on 06/23/2021 04:39 pm
With clear labeling on the back of the tiles even a few hundred tile type should not really be much of an issue. It might even be possible to create a jig to allow standard tiles to be very precisely cut to create some of the specialist shapes in a hurry. They would need to be able to coat the cut edge, not sure how hard that would be?
Clearly labeling the tiles at manufacturing time (maybe stenciling on the front surface with ablatable white ink) and writing numbers on the skin and double-checking before adding the tile should be enough to allow reliable placement even by tired workers.
You can uniquely label, use keyed fittings, and implement double- or triple-checking all you want. It will not stop someone hammering your IMU in upside-down, or connecting your TVC backwards.
An assembly where you have 10 unique but visually near-identical part variants, where all variants will physically fit in the location of any other variant, where variant-to-variant dimension deltas are of similar scale to within-variant tolerance, and removing a misplaced part (if discovered) is destructive to the part and potentially to the fixture? You're not manufacturing a product, you're manufacturing a headache.

Again, the actual manufacture of large number of unique fit-to-size tiles is not at issue. We know it can be done, STS did it decades ago. Figuring out ways to do it is attaching the wrong problem: the issue is whether you need to jump through that enormous number of dancing flying hoops in the first place.
Jam a tile into a too-small space and it will break. Clip a tile into a too-large space and it leaves wide gaps. Check for broken tiles or wide gaps, and remove and replace as needed. Tell Joe to drink more coffee.

I don’t see a big problem here. Use as many tile shapes are are needed to fit the shape of the vehicle.

The Space shuttle used as many tiles as were needed, and look how long it took to maintain those...
The shuttle... Let's think of the shuttle as a heatshield pathfinder. It taught us what not to do. It didn't teach us to not use tiles. It taught us keep the airframe shape as simple as possible. It taught us to pay attention to fastening. It taught us to really pay attention to reusability - not lip service.

According to Wikipedia, the shuttle had 24,300 unique tile shapes. This may be half the actual number if mirrored shapes (bilateral symmetry) were not counted.


I hit the wrong button. Continued:


If SX goes hog wild on SS and slaps tiles everywhere the can it will, at most, be 10% of this. Getting more realistic, not over 5%. They'll burn up a few finding a minimum workable solution and drop it further. Everything is up for redesign. Shape, materials, bayoneted, underlayment and transpiration. They might even do something wacky like field renewable ablative on critical areas if it makes turnaround faster.

They'll do whatever it takes and never look back at shuttle tile count.
Title: Re: Starship heat shield
Post by: OTV Booster on 06/23/2021 05:18 pm
With clear labeling on the back of the tiles even a few hundred tile type should not really be much of an issue. It might even be possible to create a jig to allow standard tiles to be very precisely cut to create some of the specialist shapes in a hurry. They would need to be able to coat the cut edge, not sure how hard that would be?
Clearly labeling the tiles at manufacturing time (maybe stenciling on the front surface with ablatable white ink) and writing numbers on the skin and double-checking before adding the tile should be enough to allow reliable placement even by tired workers.
You can uniquely label, use keyed fittings, and implement double- or triple-checking all you want. It will not stop someone hammering your IMU in upside-down, or connecting your TVC backwards.
An assembly where you have 10 unique but visually near-identical part variants, where all variants will physically fit in the location of any other variant, where variant-to-variant dimension deltas are of similar scale to within-variant tolerance, and removing a misplaced part (if discovered) is destructive to the part and potentially to the fixture? You're not manufacturing a product, you're manufacturing a headache.

Again, the actual manufacture of large number of unique fit-to-size tiles is not at issue. We know it can be done, STS did it decades ago. Figuring out ways to do it is attaching the wrong problem: the issue is whether you need to jump through that enormous number of dancing flying hoops in the first place.
Jam a tile into a too-small space and it will break. Clip a tile into a too-large space and it leaves wide gaps. Check for broken tiles or wide gaps, and remove and replace as needed. Tell Joe to drink more coffee.

I don’t see a big problem here. Use as many tile shapes are are needed to fit the shape of the vehicle.
In the 'unique tile' edge case, "all tiles installed one position to the left, because one tile was installed incorectly and then used as datum for the rest" = "entire heat shield scrapped and a new one manufactured" due to the destructive nature of tile removal.

Quick temporary bodges are anathema to Starship thus far. The goal of the development program has been developing the systems and techniques to efficiently and economically manufacture Starship. Designing 'one off' temporary heatshields or heat-shield designs that require two-man-rule or robots to install correctly are not manufacturable solutions. If there is a manufacturable solution to the TPS, then skip the time and money wasted on a temporary version and go for the one you actually want to use. This is why SpaceX have been happy to roll Starships off of the assembly line and straight into a back lot or scrap pile: the Starship itself isn't the goal, manufacturing one is. There is no value in constructing a TPS that you know is going to be replaced by a more manufacturable design.
Um, well yeah. The only problem is they don't really quite know what they need. Slap it together. See what didn't work. Fix. Repeat.


With each repetition that part that previously worked becomes more refined along with its manufacturing process. I keep harkening back to the tanks. They followed this process quite visibly. Think back to all the shucked pucks, burst seams and all that wacky early stuff that we raved and anguished over. It all morphed into "Those welds are looking better".


As for the inevitable screwups, I think you overstate the case. The early tanks had all sorts of weld deficiencies marked up. They either got fixed or scrapped. It got so routine we no longer pay much attention to the inspection markups. As the manufacturing process evolved the number of markups diminished (I think. I haven't been paying attention :D ).



Title: Re: Starship heat shield
Post by: Slarty1080 on 06/23/2021 05:39 pm
How often would this happen?
All the time.
Sharpie number is wrong. Sharpie number is ambiguous because of handwriting. Sharpie was cleaned off or obscured. Tile number is wrong. Tile number is ambiguous (e.g. off-by-one or transposable or invertible). Installer is tired. Installer is distracted. Installer shift changes. Install is two-handing to speed up operation, grabs tile N and N+1, reads number on N+1 and installs N in that position (and/or vice versa). Installer installs first tile wrong (for whatever reason), and installs all subsequent tiles wrong based on that tile location (because tiles were stacked in order of install, and install pattern is known) and this behaviour is rewarded due to increased productivity when installing before an error occurs. Checker makes any of the same mistakes as installer. Checker is looking for tiles to match, not looking for tiles to not match. Checker cannot see sharpie number (obscured by tile) so goes by relative tile position, or by map referencing (prone to error).
And those are just failure modes though of off the top of my head during the writing of that paragraph. When your protection against human error is "well, don't make an error then!" you have no error protection.

As for robots, those can be just as prone to human error due to humans needing to program and direct the robot. e.g. if the work coordinate system is based on the barrel being clocked in the fixture correctly, the barrel may be clocked in the fixture incorrectly. If it's based on using a specific stud as a datum, the wrong stud could be used. Stick a barcode under every stud pattern rather than sharpie? Whoops, wrong barcode was applied. Or the barcode printer has a bug and applies the same barcode to all spots. Or the barcode printer is iterating correctly, but one barcode got stuck in the applicator so every barcode is off by one. Etc.
Edzieba, I am curious, how do you think the tiles should be applied to Starship and how many types do you think there should be?
Title: Re: Starship heat shield
Post by: Ionmars on 06/23/2021 07:51 pm
We are still mulling over the tiling of the SS nosecone, so I might suggest another variation of Slarty1080's initial design. One option could be a tile pattern whereby  hexagonal tiles are stretched to become “six-sided polygons,” to better fit the surface of the nose cone.

Six-sided polygon means each side of a tile doesn’t have to be exactly parallel to its opposite side, or even equal in length. If we allow this variation, then we could employ rows of tiles on the nose of SS where  the width of each tile is more narrow at the top than across its bottom. Tiles along the top row of the nose could be much more narrow than the bottom row to adapt to the  much reduced circumference of the SS nose tip. In this approach, tiles could continue to be made flat and still approximate the curvature of the nose on different rows.

From what we know so far, nothing in the present manufacturing of tiles would preclude this variation in tile design.

Objectives of the this approach would be:
(1) Limit the number of tile shapes to one per row.
(2) Better approximate nose curvature using flat tiles.
(3) Better maintain consistent expansion gaps between tiles.

To exemplify how this might work, the sketch below shows a sample section of a nose  cone subdivided into areas wherein tiles would be installed. As suggested by tile sample A, each area along the bottom of the nose cone is 30cm wide at the bottom and tiles inside these areas would intersect with the top edges of 30cm hexagon tiles running across the barrel section. The top edges of these nose tiles are slightly more narrow at the top and would intersect with the bottom edges of tiles in the next row above. Tiles in each row would be identical with each other, but slightly different from the tiles in the row above it. [Note that the slope of the example nose cone is not the same as actual SS nose cone.]

The whole sample section of areas would accommodate 20 tiles in each row. From the bottom of the nose section to the top, the sample section would contain twenty rows with a constant height of 20cm 30cm for each row. However, each row would be less wide as the nose narrows toward the top, from 30 cm to 15cm, and the ratio of widths from bottom to top would be  2:1. Therefore a sample tile from the middle row would have an average width of 22.5cm and tile shape B would fit within it. A sample area  from the top row would have a width of 15cm along the top edge and tile shape C would fit within it.

Correction: The sketch suggests that the regular hexagons in the barrel section fit within a row of squares, but trigonometry shows they are actually rectangles of width = 30cm (between parallel sides) and height = 40.950 cm. Each row of tile areas would be 41cm +/- with varying widths.

Notes:
(1)There are inaccuracies in the example. An area should not lie directly above another area, but each row should be staggered to allows tiles in each row to intersect with tiles above and below. (My laziness in drawing)
(2) Areas are not projected to be viewed  in direct overhead perspective.


Title: Re: Starship heat shield
Post by: Vultur on 06/23/2021 08:05 pm
Again, the question is how many tile the design actually needs. This is more than 5, but a small fraction of the total number of tiles. And whatever it is, that’s what it is. The question is how to (1) minimize requirements, then (2) meet those requirements. Yes?

Not a temporary bodge, just doing the actual job.

That's a question but not necessarily the question.

If SpaceX thought it would need say 1,000 different tile types, would they have gone to tiles rather than sticking with the transpiration cooling idea?

Or could the shape of the nose be changed to require fewer tiles? Or the insulation blanket be changed to tolerate larger gaps?

The rest of the vehicle isn't necessarily a fixed "set-in-stone" design that needs however many tile types it needs.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/23/2021 09:43 pm
We are still mulling over the tiling of the SS nosecone, so I might suggest another variation of Slarty1080's initial design. One option could be a tile pattern whereby  hexagonal tiles are stretched to become “six-sided polygons,” to better fit the surface of the nose cone.

Six-sided polygon means each side of a tile doesn’t have to be exactly parallel to its opposite side, or even equal in length. If we allow this variation, then we could employ rows of tiles on the nose of SS where  the width of each tile is more narrow at the top than across its bottom. Tiles along the top row of the nose could be much more narrow than the bottom row to adapt to the  much reduced circumference of the SS nose tip. In this approach, tiles could continue to be made flat and still approximate the curvature of the nose on different rows.

From what we know so far, nothing in the present manufacturing of tiles would preclude this variation in tile design.

Objectives of the this approach would be:
(1) Limit the number of tile shapes to one per row.
(2) Better approximate nose curvature using flat tiles.
(3) Better maintain consistent expansion gaps between tiles.

To exemplify how this might work, the sketch below shows a sample section of a nose  cone subdivided into areas wherein tiles would be installed. As suggested by tile sample A, each area along the bottom of the nose cone is 30cm wide at the bottom and tiles inside these areas would intersect with the top edges of 30cm hexagon tiles running across the barrel section. The top edges of these nose tiles are slightly more narrow at the top and would intersect with the bottom edges of tiles in the next row above. Tiles in each row would be identical with each other, but slightly different from the tiles in the row above it. [Note that the slope of the example nose cone is not the same as actual SS nose cone.]

The whole sample section of areas would accommodate 20 tiles in each row. From the bottom of the nose section to the top, the sample section would contain twenty rows with a constant height of 20cm 30cm for each row. However, each row would be less wide as the nose narrows toward the top, from 30 cm to 15cm, and the ratio of widths from bottom to top would be  2:1. Therefore a sample tile from the middle row would have an average width of 22.5cm and tile shape B would fit within it. A sample area  from the top row would have a width of 15cm along the top edge and tile shape C would fit within it.
Correction: wrong number

Notes:
(1)There are inaccuracies in the example. An area should not lie directly above another area, but each row should be staggered to allows tiles in each row to intersect with tiles above and below. (My laziness in drawing)
(2) Areas are not projected to be viewed  in direct overhead perspective.
I'm not sure how this is different from the scheme on page one. Those tiles are irregular hexagonal polygons with non parallel sides and are not equal in length and there is one tile type per row.

This was updated in post #1541 to show how three basic tile types might be used to stop the tile becoming too long and thin.
Title: Re: Starship heat shield
Post by: Ionmars on 06/23/2021 11:10 pm

I'm not sure how this is different from the scheme on page one. Those tiles are irregular hexagonal polygons with non parallel sides and are not equal in length and there is one tile type per row.

This was updated in post #1541 to show how three basic tile types might be used to stop the tile becoming too long and thin.
Yes, you had the idea first. This variation just emphasizes one type of tile per row on the nose..
Title: Re: Starship heat shield
Post by: edzieba on 06/24/2021 09:25 am
How often would this happen?
All the time.
Sharpie number is wrong. Sharpie number is ambiguous because of handwriting. Sharpie was cleaned off or obscured. Tile number is wrong. Tile number is ambiguous (e.g. off-by-one or transposable or invertible). Installer is tired. Installer is distracted. Installer shift changes. Install is two-handing to speed up operation, grabs tile N and N+1, reads number on N+1 and installs N in that position (and/or vice versa). Installer installs first tile wrong (for whatever reason), and installs all subsequent tiles wrong based on that tile location (because tiles were stacked in order of install, and install pattern is known) and this behaviour is rewarded due to increased productivity when installing before an error occurs. Checker makes any of the same mistakes as installer. Checker is looking for tiles to match, not looking for tiles to not match. Checker cannot see sharpie number (obscured by tile) so goes by relative tile position, or by map referencing (prone to error).
And those are just failure modes though of off the top of my head during the writing of that paragraph. When your protection against human error is "well, don't make an error then!" you have no error protection.

As for robots, those can be just as prone to human error due to humans needing to program and direct the robot. e.g. if the work coordinate system is based on the barrel being clocked in the fixture correctly, the barrel may be clocked in the fixture incorrectly. If it's based on using a specific stud as a datum, the wrong stud could be used. Stick a barcode under every stud pattern rather than sharpie? Whoops, wrong barcode was applied. Or the barcode printer has a bug and applies the same barcode to all spots. Or the barcode printer is iterating correctly, but one barcode got stuck in the applicator so every barcode is off by one. Etc.
Edzieba, I am curious, how do you think the tiles should be applied to Starship and how many types do you think there should be?
Unless the current application method (pushpin) turns out to have issues, it is a reasonable attachment method for repeatable and reliable installation. Chemical adhesives have known issues with adhesion and application time, application is vulnerable to small chemistry variants (e.g. the issues STS had with spitting in the silicone mix to retard curing, or waterproofing sprays degrading the silicone) and require technical skill for successful application.
Tile variants should be a few as possible, with variants being as physically dissimilar as possible - such that tile variants can be distinguished without consulting serial numbers or tile maps (e.g. hexagons and kite shapes) - over as much area coverage as possible, and ideally using mutually incompatible pin arrangements - i.e. if you try and install the wrong tile, it will immediately fall off even if you hammered the pins into the frangible ceramic. Unique TPS variants (such as around the fin joints and aerocovers) should be as localised as possible.
Title: Re: Starship heat shield
Post by: rakaydos on 06/24/2021 11:33 am
“Everything should be made as simple as possible, but no simpler.” -Albert Einstein
Title: Re: Starship heat shield
Post by: cscott on 06/24/2021 11:55 am
The photos of the hot gas thrusters, presumably for fit checks, seem to show them in pods on the *outside* of the ring.  That's one more weird shape to accommodate with a heat shield.

How many tile shapes does dragon use?  It has a shield around its thrusters as well...
Title: Re: Starship heat shield
Post by: JamesH65 on 06/24/2021 12:11 pm

I'm not sure how this is different from the scheme on page one. Those tiles are irregular hexagonal polygons with non parallel sides and are not equal in length and there is one tile type per row.

This was updated in post #1541 to show how three basic tile types might be used to stop the tile becoming too long and thin.
Yes, you had the idea first. This variation just emphasizes one type of tile per row on the nose..

Depending on how big the gaps could be, you might get away with a shape spanning multiple rows rather than one shape per row.
Title: Re: Starship heat shield
Post by: Ionmars on 06/24/2021 12:44 pm

I'm not sure how this is different from the scheme on page one. Those tiles are irregular hexagonal polygons with non parallel sides and are not equal in length and there is one tile type per row.

This was updated in post #1541 to show how three basic tile types might be used to stop the tile becoming too long and thin.
Yes, you had the idea first. This variation just emphasizes one type of tile per row on the nose..

Depending on how big the gaps could be, you might get away with a shape spanning multiple rows rather than one shape per row.
Yes, this might work for the first few rows on the nose. But the curvature of the nose becomes more severe as you go up the rows and the fit between wide flat tiles and the nose surface becomes worse.

Eventually we will probably see tiles with curvature to match curved surfaces.
Title: Re: Starship heat shield
Post by: Crispy on 06/24/2021 12:53 pm
The photos of the hot gas thrusters, presumably for fit checks, seem to show them in pods on the *outside* of the ring.  That's one more weird shape to accommodate with a heat shield.

How many tile shapes does dragon use?  It has a shield around its thrusters as well...

They are mounted on Super Heavy, not Starship, so no heat shield concerns.
Title: Re: Starship heat shield
Post by: Ionmars on 06/24/2021 06:40 pm
SpX is addressing the issue of varying expansion gaps between tiles.

Considering how the robotic arm welds the tile attachment pins to the SS surface, ISTM the arm would require frequent adjustments to maintain equal distance between each group of three pins. For one thing, the circumferential surface receiving the pins is based on a (presumed) SS  radius of 450.0cm, whereas the underside of each tile is separated from that surface by an additional insulating blanket of 2 to 3 cm. This tiny increase in  effective radius might cause differences in location to accumulate across rows. There could also be small irregularities, such as warping of the surface or small differences in tile dimensions, that could accumulate across rows.

It is likely they are incorporating methods to accurately measure and adjust the location of each group of three pins before they are welded in place.
Title: Re: Starship heat shield
Post by: Ionmars on 06/24/2021 07:01 pm
In addition to adjusting location between groups of pins on the same row, it would also be necessary to check location with respect to pins in an adjacent row. If tiles are emplaced by row from the bottom up, then this would be the row just below the current row being worked.
Title: Re: Starship heat shield
Post by: Ionmars on 06/24/2021 07:41 pm
There could be a case where all the measurements between adjacent groups of pins are run through the tile placement program and no solution is found. That is, no tile could be placed onto the three pins and still have acceptable expansion gaps to adjacent tiles. In this case, a special tile would have to be produced to fulfill this requirement. Furthermore, if a special tile were required in one location on a row, it is probable that another special tile would be required on the next row above, and so on.

One way to minimize this problem could be to be begin pinning from each end of a row. The idea would be that small errors would accumulate as pinning proceeded towards the center of a row. Hopefully there would be a place in the middle where just one special tile could be created to accommodate the errors accumulated from each end.

Another way to minimize the problem could be to take advantage of the current SpX procedure of tiling each barrel section so that bare metal is left uncovered above and below the junction of two sections. The two sections are welded together and the bare area is then tiled over. So if we tile the upper section by row from the top down and tile the bottom section from the bottom up, then any column of special tiles will terminate at the bare metal section. Special tiles in this area would accommodate errors accumulated in both the horizontal and vertical directions, rather than continuing into another section.
Title: Re: Starship heat shield
Post by: Keldor on 06/25/2021 03:19 am
SpX is addressing the issue of varying expansion gaps between tiles.

Considering how the robotic arm welds the tile attachment pins to the SS surface, ISTM the arm would require frequent adjustments to maintain equal distance between each group of three pins. For one thing, the circumferential surface receiving the pins is based on a (presumed) SS  radius of 450.0cm, whereas the underside of each tile is separated from that surface by an additional insulating blanket of 2 to 3 cm. This tiny increase in  effective radius might cause differences in location to accumulate across rows. There could also be small irregularities, such as warping of the surface or small differences in tile dimensions, that could accumulate across rows.

It is likely they are incorporating methods to accurately measure and adjust the location of each group of three pins before they are welded in place.

I expect they're using some sort of fixed reference point(s) to let the arm calibrate itself.  It wouldn't be *that* hard to use a computer vision system to measure position to a sub-millimeter level based on triangulating from some reference marks, and they might not even need that (i.e., calibrate to the mm level for tile placement, and only have sub-mm for the three pins for a tile relative to each other).
Title: Re: Starship heat shield
Post by: OTV Booster on 06/25/2021 08:56 pm
SpX is addressing the issue of varying expansion gaps between tiles.

Considering how the robotic arm welds the tile attachment pins to the SS surface, ISTM the arm would require frequent adjustments to maintain equal distance between each group of three pins. For one thing, the circumferential surface receiving the pins is based on a (presumed) SS  radius of 450.0cm, whereas the underside of each tile is separated from that surface by an additional insulating blanket of 2 to 3 cm. This tiny increase in  effective radius might cause differences in location to accumulate across rows. There could also be small irregularities, such as warping of the surface or small differences in tile dimensions, that could accumulate across rows.

It is likely they are incorporating methods to accurately measure and adjust the location of each group of three pins before they are welded in place.

I expect they're using some sort of fixed reference point(s) to let the arm calibrate itself.  It wouldn't be *that* hard to use a computer vision system to measure position to a sub-millimeter level based on triangulating from some reference marks, and they might not even need that (i.e., calibrate to the mm level for tile placement, and only have sub-mm for the three pins for a tile relative to each other).
I've worked with robots with a matched and dedicated controller for each motor. The factory burns a controller ROM that maps periodic errors. Once that sucker knows where it is it's dead on for a goodly excursion.


Still, It's a lot of territory to cover. The entire arm needs to traverse or the tank needs to rotate. Both are potential sources of error. Maybe something like the alignment lasers for jigging assemblies with the arm as one of the targets so everything is set to the same coordinate system.
Title: Re: Starship heat shield
Post by: jthygesen on 07/01/2021 05:40 am
Perhaps this has been spotted before but I hadn’t seen before:
A mesh in between the insulative pads and the tiles.

Attached zoomed image of the first photo (by Mary) from this post:
Nosecone and barrel section in front of windbreak.
B3 in high bay.
GSE 5 mid #2 outside the tents.
Stargate sign.
Title: Re: Starship heat shield
Post by: edzieba on 07/01/2021 10:13 am
It was first spotted at the start of June (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2248077#msg2248077), doesn't appear to have been touched since.
Title: Re: Starship heat shield
Post by: dwheeler on 07/02/2021 06:01 pm
Is there any likelihood that ice/frost accumulates under the tiles when fueling on the pad? I don't have a good sense of how well air can permeate the matting under the tiles. If ice/frost does form, what eventually happens to it?
Title: Re: Starship heat shield
Post by: xvel on 07/02/2021 07:46 pm
Is there any likelihood that ice/frost accumulates under the tiles when fueling on the pad? I don't have a good sense of how well air can permeate the matting under the tiles. If ice/frost does form, what eventually happens to it?

(https://www.spaceflightinsider.com/wp-content/uploads/2021/04/image0.jpg)

SN15
nothing happens
Title: Re: Starship heat shield
Post by: Jcc on 07/02/2021 09:36 pm
Is there any likelihood that ice/frost accumulates under the tiles when fueling on the pad? I don't have a good sense of how well air can permeate the matting under the tiles. If ice/frost does form, what eventually happens to it?

The amount of frost should be limited to the moisture in the air contained within the padding, since the tiles provide insulation. On the bare metal surfaces, it collects moisture from a large volume of air that flows over it, and it accumulates, so the amount of potential frost on the tiled side should be small.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 07/06/2021 03:24 pm
It was first spotted at the start of June (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2248077#msg2248077), doesn't appear to have been touched since.

The mesh appears to be a thing that is staying, as the SN20 barrel has mesh on top of the (presumably mineral) felt pad:

https://forum.nasaspaceflight.com/index.php?topic=52398.msg2259488#msg2259488

My guess is the mesh is yet another mechanism to prevent the (presumably mineral) felt pad from peeling away if a tile is lost.  We discussed the possibility of a high temperature metal mesh in the thread above in lieu of the tiles.  Looks like they are going with 'all the above'.
Title: Re: Starship heat shield
Post by: CruddyCuber on 07/08/2021 11:16 pm
Reposting this here for you folks to mull over.

In one of Mary's latest shots you can see some heat shield tiles on the flap aero covers.
 
image credit: bocachicagal
Title: Re: Starship heat shield
Post by: RoboGoofers on 07/08/2021 11:29 pm
There's no felt under these new tiles. Presuming this isn't just a pathfinder test that'll be scrapped, any guesses?

Maybe the felt is needed because the tiles mounted on cryo tanks have frost or expansion complications?

Also these are each custom tiles, to my eyes.
Title: Re: Starship heat shield
Post by: cscott on 07/09/2021 12:02 am
Seems like they are going to hold tile size more or less constant (I think these are the smaller of the three standard sizes?) and vary the curvature as needed.  The result will probably look like the "simple CGI" renders where the hex grid is just distorted as needed to fit the ship.
Title: Re: Starship heat shield
Post by: dgkimpton on 07/09/2021 08:35 pm
If they can curve the surface of the tiles... I wonder why they didn't go for low-poly style flap covers and tiles with flat backs and then just curve the tile surface to achieve the outer shape?
Title: Re: Starship heat shield
Post by: Oersted on 07/09/2021 10:41 pm
Steel plate is easy to bend and curve and keeps its strength better that way rather than being assembled as flat plates. Cans are cylindrical for a reason.
Title: Re: Starship heat shield
Post by: OTV Booster on 07/09/2021 11:16 pm
Well, this answers one question. SX seems willing to do customized tile to some extent. What that extent is, is at yet unknown.


The curve is definitely a customization. What about the vitrified black? It normally covers the edge and only part way down the side. Here we see it covering the entire side. A customization or a change of plan?

There are what look like pins along the aft edge. A few off to the right of the top tile. Maybe not pins?

What is the black strip curling back over from the windward side? The edge will be one of the hot spots. Some special treatment or just the way the light is hitting the stainless?

Ohhh! So many questions.


Edit: went back and looked again. That black doesn't look like a lighting artifact.
Title: Re: Starship heat shield
Post by: midaswelby on 07/10/2021 12:03 am
Well, this answers one question. SX seems willing to do customized tile to some extent. What that extent is, is at yet unknown.


The curve is definitely a customization. What about the vitrified black? It normally covers the edge and only part way down the side. Here we see it covering the entire side. A customization or a change of plan?

There are what look like pins along the aft edge. A few off to the right of the top tile. Maybe not pins?

What is the black strip curling back over from the windward side? The edge will be one of the hot spots. Some special treatment or just the way the light is hitting the stainless?

Ohhh! So many questions.


Edit: went back and looked again. That black doesn't look like a lighting artifact.

OTV, I'm curious to know your take on something I "think" I see on the close up of the image that Mary took.  Bear with me here as I try to articulate this.
If you consider the apex of each point of the hex shape of the tiles as 2, 4, 6, 8, 10, and 12 o'clock, then the 8 o'c/10 o'c edge of the lower of the two full tiles shown seems to match up with the 2 o'c/4 o'c edge of a tile further away on the windward face of the cowling.  In other words, it (barely) looks to me like a pattern of tiles.  The view angle doesn't allow gaps or spacing to be determined, but it just seems to me that there is the possibility of several tiles of similar shape being attached in that area.  Absence of the felt and netting is obvious, maybe because it isn't necessary, as others have noted above.  I am intrigued by this new design step, to say the least.
Title: Re: Starship heat shield
Post by: OTV Booster on 07/10/2021 03:16 pm
Well, this answers one question. SX seems willing to do customized tile to some extent. What that extent is, is at yet unknown.


The curve is definitely a customization. What about the vitrified black? It normally covers the edge and only part way down the side. Here we see it covering the entire side. A customization or a change of plan?

There are what look like pins along the aft edge. A few off to the right of the top tile. Maybe not pins?

What is the black strip curling back over from the windward side? The edge will be one of the hot spots. Some special treatment or just the way the light is hitting the stainless?

Ohhh! So many questions.


Edit: went back and looked again. That black doesn't look like a lighting artifact.

OTV, I'm curious to know your take on something I "think" I see on the close up of the image that Mary took.  Bear with me here as I try to articulate this.
If you consider the apex of each point of the hex shape of the tiles as 2, 4, 6, 8, 10, and 12 o'clock, then the 8 o'c/10 o'c edge of the lower of the two full tiles shown seems to match up with the 2 o'c/4 o'c edge of a tile further away on the windward face of the cowling.  In other words, it (barely) looks to me like a pattern of tiles.  The view angle doesn't allow gaps or spacing to be determined, but it just seems to me that there is the possibility of several tiles of similar shape being attached in that area.  Absence of the felt and netting is obvious, maybe because it isn't necessary, as others have noted above.  I am intrigued by this new design step, to say the least.
I followed up through the O'c layout but I'm not sure about the other tile your matching against. Could you post a pic with both sets of tiles and highlight the one you're pointing out?


Something to keep in mind is the curve gives different foreshortening on the two haves of the tile. It tricks the eye into seeing a distorted rather than a regular hex. Ok. With that said, soon we'll see a different angle and see it really is a distorted hex.  :D
Title: Re: Starship heat shield
Post by: OTV Booster on 07/10/2021 03:24 pm
Got a question for anybody that has a clue.


Looking at the black thingie curling around the edge, it almost looks like roofing felt. I know it's not. Would it be possible to take that refractory felt underlayment and impregnate it with a glaze like is on the tiles? Could something like this give a higher level of protection and still have some limited flexibility?
Title: Re: Starship heat shield
Post by: livingjw on 07/10/2021 03:56 pm
I am pretty sure there are some lower temperature areas on the leeward side of the shuttle that are protected by teased Nomex felt bonded and coated with high temperature silicone adhesive. Only good to about 1100 F, if I remember right. If not, I'm sure someone will correct me. ;^)

Edit: Used in areas not to exceed 700 F. Called FRSI.

John
Title: Re: Starship heat shield
Post by: OTV Booster on 07/10/2021 07:47 pm
I am pretty sure there are some lower temperature areas on the leeward side of the shuttle that are protected by teased Nomex felt bonded and coated with high temperature silicone adhesive. Only good to about 1100 F, if I remember right. If not, I'm sure someone will correct me. ;^)

John
John, could you straighten me out on a point? AIUI the large circular cross section puts the shortest distance between the hull and shock front at the stagnation line, the windward center line. This is unlike a capsule where the tightest point is around the periphery. AIUI, the closest point is where compressive heating is greatest. I know radiative heating is there too, but I'm only asking about compressive.


Do I have this right?

Title: Re: Starship heat shield
Post by: livingjw on 07/11/2021 04:11 pm
I am pretty sure there are some lower temperature areas on the leeward side of the shuttle that are protected by teased Nomex felt bonded and coated with high temperature silicone adhesive. Only good to about 1100 F, if I remember right. If not, I'm sure someone will correct me. ;^)

John
John, could you straighten me out on a point? AIUI the large circular cross section puts the shortest distance between the hull and shock front at the stagnation line, the windward center line. This is unlike a capsule where the tightest point is around the periphery. AIUI, the closest point is where compressive heating is greatest. I know radiative heating is there too, but I'm only asking about compressive.


Do I have this right?

Yes, but also the shock will be pretty close at the edges of the control surface edges. This would be similar to the edges of a capsule where heating is also high.

John
Title: Re: Starship heat shield
Post by: OTV Booster on 07/11/2021 07:04 pm
I am pretty sure there are some lower temperature areas on the leeward side of the shuttle that are protected by teased Nomex felt bonded and coated with high temperature silicone adhesive. Only good to about 1100 F, if I remember right. If not, I'm sure someone will correct me. ;^)

John
John, could you straighten me out on a point? AIUI the large circular cross section puts the shortest distance between the hull and shock front at the stagnation line, the windward center line. This is unlike a capsule where the tightest point is around the periphery. AIUI, the closest point is where compressive heating is greatest. I know radiative heating is there too, but I'm only asking about compressive.


Do I have this right?

Yes, but also the shock will be pretty close at the edges of the control surface edges. This would be similar to the edges of a capsule where heating is also high.

John
That's actually what was in mind behind the question. Looks like there might be some positioning limits on the fins during that part of EDL, which leads to another question.


Again AIUI, the stagnation flow moves from the centerline out, and I assume it is continually replenished by gasses that make it through the shock wave. What velocities relative to the skin might we be looking at? Or does no gas ingress?


I'm trying to build a mental model and trying to understand where the fins get their control authority inside the stagnation flow (correct terminology?). If the area behind shock is not replenished there is nothing for the fins to act on. If it is replenished would it  be supersonic relative to the skin? That too would put limits on fin angle.


I kinda sorta have a picture of what happens outside the shock, but from the shock in, its murky.
Title: Re: Starship heat shield
Post by: RoboGoofers on 07/12/2021 12:08 am
Control comes from shifting center of pressure around relative to center of gravity. It's exactly the same as skydiving (except...)
Title: Re: Starship heat shield
Post by: OTV Booster on 07/12/2021 06:16 pm
Control comes from shifting center of pressure around relative to center of gravity. It's exactly the same as skydiving (except...)
Yeah, but if the flow behind the shock is nil what are the fins acting on? Part of the question was about gas transfer through the shock. No flow=nothing for the fins to act against. At the other extreme is the gas flow behind the shock going supersonic. This has its own problems. I'm trying to mental model the stagnation region in greater granularity than what we've seen yet.
Title: Re: Starship heat shield
Post by: groknull on 07/13/2021 01:31 am
Control comes from shifting center of pressure around relative to center of gravity. It's exactly the same as skydiving (except...)
Yeah, but if the flow behind the shock is nil what are the fins acting on? Part of the question was about gas transfer through the shock. No flow=nothing for the fins to act against. At the other extreme is the gas flow behind the shock going supersonic. This has its own problems. I'm trying to mental model the stagnation region in greater granularity than what we've seen yet.

Air behind the shock is subsonic*, but not stagnant**.  Very roughly speaking, moving the fin changes the volume and thus pressure of the subsonic air behind the shock, which alters the location of the shock wave.  That in turn changes the center of pressure that RoboGoofers described.

Shock waves are not brick walls.  They are regions that have been given a name because interesting stuff happens there.  The air is still moving in roughly the same direction just before, inside, and just after the shock, but properties like density, pressure and temperature can vary drastically.

A way of thinking about shock waves is to visualize driving on a freeway interrupted by an interchange, town, or construction.  You can be cruising along rapidly (supersonic) when the obstruction causes everybody to slow down (to subsonic) and pack more closely together (density increase).  The region of rapid transition from freeway speeds to crawling is the shock wave.  When you get through the slow section, you gradually speed back up to freeway speeds.  What happens at the interchange or town can have huge repercussions.  Opening up another lane or off ramp, or closing one due to an accident can drastically move the point of freeway slowdown (shock wave).

* Subsonic behind, but still near the shock wave.  If the flow becomes supersonic again, additional shock waves are possible behind the first.

** Inlet ramps and inlet cones of supersonic aircraft cause shock waves to form where the designers want them, with clean subsonic flow inside the inlet and into the engine.  The airflow is often substantial.  e.g. 77kg/s for the J79 per Wikipedia.  The J79 engine is less than a meter in diameter.  That doesn't directly answer your earlier question about actual flow behind the shock wave on a Starship, but might be food for thought.
Title: Re: Starship heat shield
Post by: livingjw on 07/13/2021 04:28 am
Hypersonic Newtonian flow model is a quick and simple model of hypersonic flow that is pretty accurate, given it simplicity. It's also easy to grasp. Give it a look see.

Note: This has nothing to do with Newtonian or non-Newtonian fluids.

John.
Title: Re: Starship heat shield
Post by: edzieba on 07/13/2021 11:20 am
Last night the nosecone sections were stacked.
Nose to the right of shot has studs and tiles applied.
Title: Re: Starship heat shield
Post by: RoboGoofers on 07/13/2021 02:02 pm
Control comes from shifting center of pressure around relative to center of gravity. It's exactly the same as skydiving (except...)
Yeah, but if the flow behind the shock is nil what are the fins acting on? Part of the question was about gas transfer through the shock. No flow=nothing for the fins to act against. At the other extreme is the gas flow behind the shock going supersonic. This has its own problems. I'm trying to mental model the stagnation region in greater granularity than what we've seen yet.
I was typing, trying to explain how I understand it, but I don't have training in hypersonic aerodynamics so don't want misinform. However I think there's a simplification that answers your question:
Consider that the ship is coming in from space and hitting the atmosphere. it's slamming into gas atoms and pushing them out of the way. Now, whatever happens upstream(shock fronts, boundary layers, etc) doesn't really change the fact that the ship is still moving through the atmosphere hitting gas atoms and pushing them out of the way. So that's what the fins are acting against.
Title: Re: Starship heat shield
Post by: Cheapchips on 07/13/2021 03:28 pm
Last night the nosecone sections were stacked.
Nose to the right of shot has studs and tiles applied.

Here's zoom in on bocachicagal's photo.

Title: Re: Starship heat shield
Post by: Nevyn72 on 07/14/2021 05:17 am
I noticed something interesting in this picture of S20's leg skirt.  If you look closely, 1/3 of the TPS tile attachment studs are a lighter color than the rest.  I've attached a picture highlighting some of the differently colored studs.

Each 'stud' is made up of two prongs aligned parallel to each other.

Each pair of prongs is orientated 120 degrees rotated relative to each of the other pairs of prongs in each set of 3 pairs.

The lighter ones you are seeing are just the flat surface of one set of prongs reflecting more light than the others.
Title: Re: Starship heat shield
Post by: eriblo on 07/14/2021 07:41 am
A slightly more substantial stud related observation: The studs seen on this nose cone appears to follow the standard pattern but upside down for all but one row visible. This suggests either "unique rows" or "regular with some gaps" tiling with some type dependent variation in stud orientation (to fit a different shape or to avoid installation mixup?).
https://twitter.com/JohnRand0061/status/1415150140814471170
Title: Re: Starship heat shield
Post by: cscott on 07/14/2021 12:45 pm
The studs are affixed right on top of the weld line, too.  On the barrel sections, isn't there usually a gap around the seam?  Here it's obvious the studs were added after the nose cone gores were welded together.

I wouldn't completely rule out operator error.  This could have been a trial run of the stud welding robot, not a "serious" attempt to affix tiles to a flight article.  But I agree that it is interesting that the stud welder even *has* an "upside down" mode that it could use.

Wild speculation, based on playing around with regular tilings: the radius shrinks slowly enough that you can go for a decent number of rows before you need to "drop a tile" to reach the next smaller radius. The opposite-direction studs might be a row of custom tiles that do the radius-shrink, and then we go back to the fixed hexes for awhile.

It is significant that the rows are all still parallel to the ground.  That rules out some of the more "creative" tiling possibilities.  Seems like we've narrowed the options to either "all custom" or "tile shapes vary per row", although some of the tile row shapes could still be "standard" hexagons.
Title: Re: Starship heat shield
Post by: sevenperforce on 07/14/2021 05:31 pm
A slightly more substantial stud related observation: The studs seen on this nose cone appears to follow the standard pattern but upside down for all but one row visible. This suggests either "unique rows" or "regular with some gaps" tiling with some type dependent variation in stud orientation (to fit a different shape or to avoid installation mixup?).
<snip>
Here's what I'm seeing.

The inverted row of studs lines up with the lower hex pattern, but not the upper hex pattern. This suggests that the upper hex pattern is using the same size tiles as the lower hex pattern, just with different placement to accommodate the ogive, and there's some sort of "transition" row for bridging the inevitable gap.

It could be something as simple as this....
Title: Re: Starship heat shield
Post by: eriblo on 07/14/2021 09:45 pm
A slightly more substantial stud related observation: The studs seen on this nose cone appears to follow the standard pattern but upside down for all but one row visible. This suggests either "unique rows" or "regular with some gaps" tiling with some type dependent variation in stud orientation (to fit a different shape or to avoid installation mixup?).
<snip>
Here's what I'm seeing.

The inverted row of studs lines up with the lower hex pattern, but not the upper hex pattern. This suggests that the upper hex pattern is using the same size tiles as the lower hex pattern, just with different placement to accommodate the ogive, and there's some sort of "transition" row for bridging the inevitable gap.

It could be something as simple as this....
Good observation. If a straight seam is ok they could just use two rows of the truncated "pentagonal" tiles with one of them upside down. That would be two tile types for part of the nose at the cost of larger vertical gaps: Starting at 4.5 m radius one missing tile on half the circumference would be ~4 mm of extra gap. It increases ~linearly with decreasing radius but most of the nose cone area has relatively large radius.
Title: Re: Starship heat shield
Post by: ETurner on 07/14/2021 11:20 pm
If a straight seam is ok
If straight seams can work, this greatly simplifies the design problem and reduces requirements for peculiar tiles. It would be worth some seam-engineering effort to make this true.
Title: Re: Starship heat shield
Post by: sevenperforce on 07/14/2021 11:44 pm
If a straight seam is ok
If straight seams can work, this greatly simplifies the design problem and reduces requirements for peculiar tiles. It would be worth some seam-engineering effort to make this true.
Elon has mentioned that the reason they don’t want straight seams generally is that hot plasma can accelerate up the seam. But if there are only a few places with a straight seam, then perhaps they can put additional thermal cloth underneath those particular areas.

If a straight seam is ok they could just use two rows of the truncated "pentagonal" tiles with one of them upside down. That would be two tile types for part of the nose at the cost of larger vertical gaps: Starting at 4.5 m radius one missing tile on half the circumference would be ~4 mm of extra gap. It increases ~linearly with decreasing radius but most of the nose cone area has relatively large radius.
Without any clever pixel counting, just eyeballing it, we seem to have about 19 tiles on the lower layer for every 18 tiles on the upper layer. So that should give us an idea of how large of a vertical gap they’ll be dealing with.
Title: Re: Starship heat shield
Post by: rakaydos on 07/15/2021 12:17 am
A slightly more substantial stud related observation: The studs seen on this nose cone appears to follow the standard pattern but upside down for all but one row visible. This suggests either "unique rows" or "regular with some gaps" tiling with some type dependent variation in stud orientation (to fit a different shape or to avoid installation mixup?).
<snip>
Here's what I'm seeing.

The inverted row of studs lines up with the lower hex pattern, but not the upper hex pattern. This suggests that the upper hex pattern is using the same size tiles as the lower hex pattern, just with different placement to accommodate the ogive, and there's some sort of "transition" row for bridging the inevitable gap.

It could be something as simple as this....
I wonder, it looks like you could alternate the pentagon on the top or bottom of the seam, and so interupt the seam with (unmatching) hexagons on both sides.
Title: Re: Starship heat shield
Post by: cscott on 07/15/2021 02:05 am


I wonder, it looks like you could alternate the pentagon on the top or bottom of the seam, and so interupt the seam with (unmatching) hexagons on both sides.

The problem is that the hexagons on top and bottom don't (in general) line up.  So you'd need to have custom tile shapes to account for the local "slip" between top and bottom.  But (a) you can fix the slip at 0 on the centerline, so a standard center pair can be used, and (b) the bottom pentagon can always have a zig in a fixed spot, so you only need a "full custom" tile above that, and (c) if you're patient and tolerances are loose enough, you could just wait until the slip gets to a known amount and put in the tile zigs at that point.  Depending on how flexible you are about how long the straight line seams can get and how closely the zigs must match.
Title: Re: Starship heat shield
Post by: OTV Booster on 07/15/2021 03:39 am
Control comes from shifting center of pressure around relative to center of gravity. It's exactly the same as skydiving (except...)
Yeah, but if the flow behind the shock is nil what are the fins acting on? Part of the question was about gas transfer through the shock. No flow=nothing for the fins to act against. At the other extreme is the gas flow behind the shock going supersonic. This has its own problems. I'm trying to mental model the stagnation region in greater granularity than what we've seen yet.
I was typing, trying to explain how I understand it, but I don't have training in hypersonic aerodynamics so don't want misinform. However I think there's a simplification that answers your question:
Consider that the ship is coming in from space and hitting the atmosphere. it's slamming into gas atoms and pushing them out of the way. Now, whatever happens upstream(shock fronts, boundary layers, etc) doesn't really change the fact that the ship is still moving through the atmosphere hitting gas atoms and pushing them out of the way. So that's what the fins are acting against.
Like you, I've no training in hypersonics. A shockwave is an interesting thing. Confusing, but interesting. The ship is moving faster than the air can get out of the way. It piles up. I wonder what an ambient pressure reading would be behind the shock front. I'm guessing high.


I did a google on hypersonic Newtonian flow yesterday. Time to start reading it.
Title: Re: Starship heat shield
Post by: OTV Booster on 07/15/2021 04:31 am


I wonder, it looks like you could alternate the pentagon on the top or bottom of the seam, and so interupt the seam with (unmatching) hexagons on both sides.

The problem is that the hexagons on top and bottom don't (in general) line up.  So you'd need to have custom tile shapes to account for the local "slip" between top and bottom.  But (a) you can fix the slip at 0 on the centerline, so a standard center pair can be used, and (b) the bottom pentagon can always have a zig in a fixed spot, so you only need a "full custom" tile above that, and (c) if you're patient and tolerances are loose enough, you could just wait until the slip gets to a known amount and put in the tile zigs at that point.  Depending on how flexible you are about how long the straight line seams can get and how closely the zigs must match.
That would work but ISTM to be too complicated for production.  IIUC, every few rows there is one row where all but one tile is custom to match the progressively out of phase zig zag. No two in the row duplicate. When the working guy gathers materials there might be coding of some sort but no easy eyeball verification. Multiple checks needed to make sure tile xyz isn't going into the slot for xyq.


There obviously (a dangerous word) will be some different sizes and shapes. We've seen three different sized hexes, bent hexes on the aero cover and truncated hexes. ISTM the least confusing way to do the ogive is to give each row its own unique custom hex with the bottom matching the previous row, and the sides tapered in enough that adjacent tiles edges are parallel.


It's still a fair number of custom shapes but at least all tiles in a row are interchangeable. Eventually installation will be robotic but until then, some working stiff has to keep it all sorted out. Even with robots, somebody has to make sure the feed hoppers are filled with the right shape. Get too many irregular shapes and you might as well hand feed the tiles to the bot.

Edit: On reread, I realized you were using spacing to avoid the phasing problem. That might work low on the ogive but up higher the rate of change of the slope increases and that technique will become problematic. With flat tiles and a decreasing radius the corners will be poking out further on each row. Tapered tiles get narrower on each row and stay more conformal. They might have to make each row progressively shorter up high to keep them even more conformal.
Title: Re: Starship heat shield
Post by: cscott on 07/15/2021 07:28 am
To be clear, based on those photos, my strong lean is that "long straight channels don't matter (much)" aka that they will find a different way to break up the flow (if flow in the circumferential direction even "matters").  Each row will be a regular hex, of one of the three-ish sizes we've seen, presumably smaller as you approach the nose, and when the radius has decreased "enough" there will be a pair of half-hex/pentagon rows to allow the rows to slip along the channel and the radius to decrease.  Hexes won't be appreciably rounded until you switch to full-custom at the tip of the nose/on the flap fairings/etc.
Title: Re: Starship heat shield
Post by: edzieba on 07/15/2021 10:33 am
Once they have a good idea of all their straight seam lengths (or more specifically, the difference in tile size between either side of a seam), they can find a range of common factors between those tile offsets. With that the straight seams can be replaced with serrated seams that minimise the continuous flow path length available. Depending on the range of common factors available this would determine how large the 'teeth' of the serrations could be without preventing good mating.
Title: Re: Starship heat shield
Post by: ETurner on 07/15/2021 11:01 am
To be clear, based on those photos, my strong lean is that "long straight channels don't matter (much)" aka that they will find a different way to break up the flow (if flow in the circumferential direction even "matters").  Each row will be a regular hex, of one of the three-ish sizes we've seen, presumably smaller as you approach the nose, and when the radius has decreased "enough" there will be a pair of half-hex/pentagon rows to allow the rows to slip along the channel and the radius to decrease.  Hexes won't be appreciably rounded until you switch to full-custom at the tip of the nose/on the flap fairings/etc.
My prediction: Rows of back-to-back truncated hexes where needed to solve phase problems, a straight-channel gap-filler/insulator between them if needed. All tiles in a row identical, several increments of increasingly tapered tiles moving up toward the strongly tapered part of the ogive. More distinct tapered shapes if fit is important, fewer shapes if fit is less important. Bar codes optional.
Title: Re: Starship heat shield
Post by: rakaydos on 07/15/2021 11:03 am


I wonder, it looks like you could alternate the pentagon on the top or bottom of the seam, and so interupt the seam with (unmatching) hexagons on both sides.

The problem is that the hexagons on top and bottom don't (in general) line up.  So you'd need to have custom tile shapes to account for the local "slip" between top and bottom.  But (a) you can fix the slip at 0 on the centerline, so a standard center pair can be used, and (b) the bottom pentagon can always have a zig in a fixed spot, so you only need a "full custom" tile above that, and (c) if you're patient and tolerances are loose enough, you could just wait until the slip gets to a known amount and put in the tile zigs at that point.  Depending on how flexible you are about how long the straight line seams can get and how closely the zigs must match.
If each hexagon is matched to a flat-topped pentagon, they dont have to match up. The point on the hexagon just has to be somewhere along the edge of the pentagonal tile.

--v-v-v--
^-^^-^

Edit: an MS paint edit of the original proposal.
Title: Re: Starship heat shield
Post by: sevenperforce on 07/15/2021 02:01 pm
If each hexagon is matched to a flat-topped pentagon, they dont have to match up. The point on the hexagon just has to be somewhere along the edge of the pentagonal tile.

--v-v-v--
^-^^-^

Edit: an MS paint edit of the original proposal.
Oh, yes, I like this. Very simple, very clean, and very difficult to mess up.

The only question, I suppose, is whether this amount of gapping is better or worse than a single long straight seam with no gaps. Either way you’d have additional insulation underneath, I imagine.
Title: Re: Starship heat shield
Post by: OTV Booster on 07/15/2021 02:23 pm


I wonder, it looks like you could alternate the pentagon on the top or bottom of the seam, and so interupt the seam with (unmatching) hexagons on both sides.

The problem is that the hexagons on top and bottom don't (in general) line up.  So you'd need to have custom tile shapes to account for the local "slip" between top and bottom.  But (a) you can fix the slip at 0 on the centerline, so a standard center pair can be used, and (b) the bottom pentagon can always have a zig in a fixed spot, so you only need a "full custom" tile above that, and (c) if you're patient and tolerances are loose enough, you could just wait until the slip gets to a known amount and put in the tile zigs at that point.  Depending on how flexible you are about how long the straight line seams can get and how closely the zigs must match.
If each hexagon is matched to a flat-topped pentagon, they dont have to match up. The point on the hexagon just has to be somewhere along the edge of the pentagonal tile.

--v-v-v--
 ^-^ ^-^

Edit: an MS paint edit of the original proposal.
I'm boning up on non Newtonian flow. It's gonna be slow.


Here's my fairly uninformed take on gap size. Staying with subsonic flow inside the shock front, depending on AoA, it'll be mostly circumferential, but not completely. Most of the flow will be circumferential directly into the diamond shaped voids you show. ISTM a critical measurement will be a ratio of tile height to gap width. If the gap is much more than the tile height, flow can get under the next tile and rip it off. As the gap narrows the flow only hits the side of the next tile. How dangerous this is depends on robustness of attachment. With the minimal gap seen on most of the tiles, the flow will, at worst, hit the corner of the tile but mostly flow over it. The exact angle of flow expansion coming off the leeward edge of a tile will be sensitive to flow velocity.


All this is subsonic and looks at flow, not thermal.
Title: Re: Starship heat shield
Post by: sevenperforce on 07/15/2021 06:48 pm
All right, I think I might be onto something here.

I did a little rudimentary pixel counting and tried to line up the one decent nosecone stud image we've got. Here's what I came up with.

(https://forum.nasaspaceflight.com/assets/50748.0/2046253.jpg)

There's a single inverted row in the middle, spaced to match the low rows, and a series of upper rows that are all spaced to match each other but are more widely spaced than the lower rows. I extrapolated that pattern out and filled in all the studs with regular hexagon tiles in the places where they would fit without colliding:

(https://forum.nasaspaceflight.com/assets/50748.0/2046255.jpg)

That's where I started thinking a little. We know these stud patterns are asymmetric; there is only one possible way to attach each tile to each stud pattern. You can't rotate a tile 120 degrees and just stick it on. Why do an inverted row? Is it just to remind the workers attaching the tiles that this is the "special" row? Maybe. But when I see asymmetric stud patterns laid out in an axisymmetric arrangement, I think about chirality and congruency.

I played around with it a little bit, and here's what I came up with:

(https://forum.nasaspaceflight.com/assets/50748.0/2046257.jpg)

I came up with two possibilities. On the left, you have just three unique tile types: the mirror pentagon, the right-handed pentagon, and the left-handed pentagon. The tiles on the upper layer are congruent with the tiles on the lower layer. There is no straight seam and the gaps are quite small.

On the right, you have more tile types: a mirror pentagon, four right-handed irregular hexagons, and four left-handed irregular hexagons. However, the right-handed and left-handed irregular hexagons are mirrored, and once again each tile on the upper layer is congruent with the tile directly below it, so you can simply rotate either matching tile 180 degrees to attach. This also has no straight seam, but it also has virtually no gaps at all.

I've also attached an image showing what both configurations would look like in the end.
Title: Re: Starship heat shield
Post by: cscott on 07/15/2021 08:14 pm
I still think there's just a straight line.  As you pointed out, it can be broken up with a "real" hexagon periodically when the rows line up. I bet that's enough, combined with a bit of filler in the straight channel.
Title: Re: Starship heat shield
Post by: sevenperforce on 07/15/2021 09:01 pm
I still think there's just a straight line.  As you pointed out, it can be broken up with a "real" hexagon periodically when the rows line up. I bet that's enough, combined with a bit of filler in the straight channel.
Like this?

This uses the truncated pentagon tiles we've already seen, plus an elongated pentagon and two mirrored irregular hexagons. Three new tile types, no gaps, only a very short straight channel.
Title: Re: Starship heat shield
Post by: cscott on 07/16/2021 01:57 am
Yup, that's more or less what I was thinking of.

 You could play with the shapes of the irregular end tiles a bit, but the basic idea is that you get a straight channel of about that length.  If that's acceptable, then the tiling gets simpler.
Title: Re: Starship heat shield
Post by: dgkimpton on 07/16/2021 05:56 am
Borrowing sevenperforce's template you can get to the attached layout without making any new tile shapes - just cutting the corners off a few standard tiles. Might be just good enough?
Title: Re: Starship heat shield
Post by: Ionmars on 07/16/2021 06:00 pm
ISTM the width of gaps between tiles must lie within a certain range (tolerance). If gaps were too narrow tiles could rub together and crack. If the gap were too wide, supersonic flow across tile surfaces during atmospheric entry could dip into the crack and create a super-hot spot. To avoid this, a standard gap tolerance range should be established.

Despite the need for a standard gap tolerance, it seems unlikely that pins could be placed on a row so perfectly that one standard tile could fit perfectly across the entire row. Each tile would have to maintain the standard gap tolerance on all six sides of itself, despite variations in the surface of SS, variations in the insulation layer, and variable adjustments made in the locations of the other tiles. As tiles were emplaced across a row of pins it seems likely that small errors would accumulate so there would be a space somewhere that was sufficiently irregular so that a standard tile would not fit. A method of accommodating  this situation would be needed.

To help illustrate one approach, I copied the excellent rendering of tiles (double row E) posted above by sevenperforce. I copied the bottom rows, inverted them, and placed them above the bottom rows, so that almost all tiles would have the same close-fitted tile gaps.

I expect that the first tile on each row (from left or from right) would be easier to fit perfectly because only two of its edges have to match the edges of two tiles on the row below (if working bottom up). If pinning each row from the left or right tile and working toward the middle, each tile has to match three sides with adjacent tiles and maintain the standard tile gap. If the pinning procedure begins from both ends, then there would be a place in the middle where one tile must match four edges (two from the same row and two from the row below). ISTM unlikely that a standard tile would fit exactly in this space, so a nonstandard (special) tile would usually be produced to fit this space. Each row on the barrel section of SS would utilize 18 standard-shaped tiles and one special tile.

Once a special tile was produced for any row, it seems probable that another special tile would be required in the next row above to match one side of the first special tile.

In the image below, the row of tiles lying over a weld line may require more special tiles. This is because the pinning of tiles on the upper and lower ring segments stops short of the two metal edges of the segments. Bare metal edges along the join line are welded together, followed by pinning one or two rows of tiles that cover the weld line. This procedure introduces the likelihood of additional mismatches between tiles in the top segment and tiles in the bottom segment and adjustments made by producing more special tiles. Ideally, one special tile could accommodate location errors in both X and Y directions, as indicated.   

Title: Re: Starship heat shield
Post by: elongated muskrat on 07/16/2021 06:54 pm
Image credit to Ocean Cam

Has the debate over whether SpaceX is willing to produce a more diverse array of heat shield sizes and shapes been solved yet? I think this image of the heat shielding for the forward flaps really adds to the argument that they are willing to sacrifice greater simplicity in manufacturing and tile placement for simpler patterns. Note how these tiles appear to be far smaller than ones we've seen before and how they they abruptly cut off the tile on the far left.
Title: Re: Starship heat shield
Post by: rsdavis9 on 07/16/2021 07:04 pm
ISTM the width of gaps between tiles must lie within a certain range (tolerance). If gaps were too narrow tiles could rub together and crack. If the gap were too wide, supersonic flow across tile surfaces during atmospheric entry could dip into the crack and create a super-hot spot. To avoid this, a standard gap tolerance range should be established.

Despite the need for a standard gap tolerance, it seems unlikely that pins could be placed on a row so perfectly that one standard tile could fit perfectly across the entire row. Each tile would have to maintain the standard gap tolerance on all six sides of itself, despite variations in the surface of SS, variations in the insulation layer, and variable adjustments made in the locations of the other tiles. As tiles were emplaced across a row of pins it seems likely that small errors would accumulate so there would be a space somewhere that was sufficiently irregular so that a standard tile would not fit. A method of accommodating  this situation would be needed.

To help illustrate one approach, I copied the excellent rendering of tiles (double row E) posted above by sevenperforce. I copied the bottom rows, inverted them, and placed them above the bottom rows, so that almost all tiles would have the same close-fitted tile gaps.

I expect that the first tile on each row (from left or from right) would be easier to fit perfectly because only two of its edges have to match the edges of two tiles on the row below (if working bottom up). If pinning each row from the left or right tile and working toward the middle, each tile has to match three sides with adjacent tiles and maintain the standard tile gap. If the pinning procedure begins from both ends, then there would be a place in the middle where one tile must match four edges (two from the same row and two from the row below). ISTM unlikely that a standard tile would fit exactly in this space, so a nonstandard (special) tile would usually be produced to fit this space. Each row on the barrel section of SS would utilize 18 standard-shaped tiles and one special tile.

Once a special tile was produced for any row, it seems probable that another special tile would be required in the next row above to match one side of the first special tile.

In the image below, the row of tiles lying over a weld line may require more special tiles. This is because the pinning of tiles on the upper and lower ring segments stops short of the two metal edges of the segments. Bare metal edges along the join line are welded together, followed by pinning one or two rows of tiles that cover the weld line. This procedure introduces the likelihood of additional mismatches between tiles in the top segment and tiles in the bottom segment and adjustments made by producing more special tiles. Ideally, one special tile could accommodate location errors in both X and Y directions, as indicated.

Starting from the center line should eliminate the special tile.

But I believe we are going to see truncated hexes(pentagons) between the barrel sections giving a straight line gap between barrel sections. Probably also a special size to them to match the barrels slight misplacement between barrels.

Zig Zag is a better tile gap but if the gap is small enough and deep enough straight line gaps should be acceptable. I think straight line gaps every so often for the nose cone will be the way they solve curvature problem of the nose.
Title: Re: Starship heat shield
Post by: ETurner on 07/16/2021 07:06 pm
Image credit to Ocean Cam

Has the debate over whether SpaceX is willing to produce a more diverse array of heat shield sizes and shapes been solved yet? I think this image of the heat shielding for the forward flaps really adds to the argument that they are willing to sacrifice greater simplicity in manufacturing and tile placement for simpler patterns. Note how these tiles appear to be far smaller than ones we've seen before and how they they abruptly cut off the tile on the far left.
Yes, and the main argument against using enough different tile shapes to actually fit the shape of the vehicle seems to be “Sleepy workers will mislabel the tiles or switch them around, and then -- Oh noes! Doom or cost explosion! It’s better to have gaps.”
Or am I missing something?
Title: Re: Starship heat shield
Post by: Cheapchips on 07/16/2021 07:20 pm
These photo show pins along the bottom of the fin for more tiles.

Looks like they're using they're using the backing insulation as filler on the hinge tiles?

https://twitter.com/StarshipGazer/status/1416111047015116806?
Title: Re: Starship heat shield
Post by: Kazioo on 07/16/2021 07:53 pm
I'm guessing that flaps not having a cryogenic propellant inside them will have a smaller range of thermal expansion, so tiles there probably don't need empty gaps between them and using filler might be okay.

The tank will have larger temperature range and therefore also larger thermal expansion range, so instead of using filler they went with the blanket underneath - something that maybe isn't needed on those parts of the ship where the filler can be used.
Title: Re: Starship heat shield
Post by: rsdavis9 on 07/16/2021 07:57 pm
I'm guessing that flaps not having a cryogenic propellant inside them will have a smaller range of thermal expansion, so tiles there probably don't need empty gaps between them and using filler might be okay.

The tank will have larger temperature range and therefore also larger thermal expansion range, so instead of using filler they went with the blanket underneath - something that maybe isn't needed on those parts of the ship where the filler can be used.

I believe the estimated temp on reentry is 3500C in the hot spots. Compare that to -182C(90K) boiling for LOX.
Not much difference in temp range.
Title: Re: Starship heat shield
Post by: rakaydos on 07/16/2021 07:58 pm
Image credit to Ocean Cam

Has the debate over whether SpaceX is willing to produce a more diverse array of heat shield sizes and shapes been solved yet? I think this image of the heat shielding for the forward flaps really adds to the argument that they are willing to sacrifice greater simplicity in manufacturing and tile placement for simpler patterns. Note how these tiles appear to be far smaller than ones we've seen before and how they they abruptly cut off the tile on the far left.
Yes, and the main argument against using enough different tile shapes to actually fit the shape of the vehicle seems to be “Sleepy workers will mislabel the tiles or switch them around, and then -- Oh noes! Doom or cost explosion! It’s better to have gaps.”
Or am I missing something?
I mean, it IS better to have gaps, if you CAN have gaps. That is the question that only SpaceX can answer.
Title: Re: Starship heat shield
Post by: OV103Fan on 07/16/2021 08:00 pm
I'm seeing red RTV adhesive on some of those tiles and gap fillers mounted to the flap.  I wonder if some are bonded to the surface rather than using the mounting studs?
Title: Re: Starship heat shield
Post by: livingjw on 07/16/2021 08:12 pm
- Theses tile near the hinge line on the hot side appear to be bonded on in a manner similar to the space shuttle. This may be due to tighter tolerances needed near the hinge for small and more consistent gap for sealing.

- The red is most probably high temperature RTV adhesive. In the shuttle it was used to bond the tiles to the sip and the sip to the airframe. I think they might have used it to also bond the gap fillers.

- Outboard of the hinge it looks like they revert back to mechanically attached tile over insulation blanket as we have seen on the main body.

Edit: I see OV103Fan beat me to it.

John
Title: Re: Starship heat shield
Post by: billh on 07/16/2021 08:16 pm
The leading edge tiles are thicker, too.
Title: Re: Starship heat shield
Post by: envy887 on 07/16/2021 08:19 pm
I'm guessing that flaps not having a cryogenic propellant inside them will have a smaller range of thermal expansion, so tiles there probably don't need empty gaps between them and using filler might be okay.

The tank will have larger temperature range and therefore also larger thermal expansion range, so instead of using filler they went with the blanket underneath - something that maybe isn't needed on those parts of the ship where the filler can be used.

I believe the estimated temp on reentry is 3500C in the hot spots. Compare that to -182C(90K) boiling for LOX.
Not much difference in temp range.

Looks like the Shuttle TPS peaked at around 1500 C.

Thermal expansion is about 1 part per million per Kelvin. For a 1500 K temp rise, that's one part in 667, or a 0.33 meter tile would need a 0.5 mm gap. Those seem like more than that, by a lot.
Title: Re: Starship heat shield
Post by: Redclaws on 07/16/2021 08:24 pm
Image credit to Ocean Cam

Has the debate over whether SpaceX is willing to produce a more diverse array of heat shield sizes and shapes been solved yet? I think this image of the heat shielding for the forward flaps really adds to the argument that they are willing to sacrifice greater simplicity in manufacturing and tile placement for simpler patterns. Note how these tiles appear to be far smaller than ones we've seen before and how they they abruptly cut off the tile on the far left.
Yes, and the main argument against using enough different tile shapes to actually fit the shape of the vehicle seems to be “Sleepy workers will mislabel the tiles or switch them around, and then -- Oh noes! Doom or cost explosion! It’s better to have gaps.”
Or am I missing something?

The actual argument is it significantly increases cost and complexity to have lots of kinds of tiles, for pretty obvious reasons already discussed in this thread.  It’s not impossible or undoable, but damn it sure would be nice to avoid.
Title: Re: Starship heat shield
Post by: livingjw on 07/16/2021 08:28 pm
The leading edge tiles are thicker, too.

- This is not a leading edge. It is a hinge line. It is cylindrical to maintain a small gap as the flap moves to help in sealing air from flowing through the hinge.

John
Title: Re: Starship heat shield
Post by: russianhalo117 on 07/16/2021 08:29 pm
ISTM the width of gaps between tiles must lie within a certain range (tolerance). If gaps were too narrow tiles could rub together and crack. If the gap were too wide, supersonic flow across tile surfaces during atmospheric entry could dip into the crack and create a super-hot spot. To avoid this, a standard gap tolerance range should be established.

Despite the need for a standard gap tolerance, it seems unlikely that pins could be placed on a row so perfectly that one standard tile could fit perfectly across the entire row. Each tile would have to maintain the standard gap tolerance on all six sides of itself, despite variations in the surface of SS, variations in the insulation layer, and variable adjustments made in the locations of the other tiles. As tiles were emplaced across a row of pins it seems likely that small errors would accumulate so there would be a space somewhere that was sufficiently irregular so that a standard tile would not fit. A method of accommodating  this situation would be needed.

To help illustrate one approach, I copied the excellent rendering of tiles (double row E) posted above by sevenperforce. I copied the bottom rows, inverted them, and placed them above the bottom rows, so that almost all tiles would have the same close-fitted tile gaps.

I expect that the first tile on each row (from left or from right) would be easier to fit perfectly because only two of its edges have to match the edges of two tiles on the row below (if working bottom up). If pinning each row from the left or right tile and working toward the middle, each tile has to match three sides with adjacent tiles and maintain the standard tile gap. If the pinning procedure begins from both ends, then there would be a place in the middle where one tile must match four edges (two from the same row and two from the row below). ISTM unlikely that a standard tile would fit exactly in this space, so a nonstandard (special) tile would usually be produced to fit this space. Each row on the barrel section of SS would utilize 18 standard-shaped tiles and one special tile.

Once a special tile was produced for any row, it seems probable that another special tile would be required in the next row above to match one side of the first special tile.

In the image below, the row of tiles lying over a weld line may require more special tiles. This is because the pinning of tiles on the upper and lower ring segments stops short of the two metal edges of the segments. Bare metal edges along the join line are welded together, followed by pinning one or two rows of tiles that cover the weld line. This procedure introduces the likelihood of additional mismatches between tiles in the top segment and tiles in the bottom segment and adjustments made by producing more special tiles. Ideally, one special tile could accommodate location errors in both X and Y directions, as indicated.

Starting from the center line should eliminate the special tile.

But I believe we are going to see truncated hexes(pentagons) between the barrel sections giving a straight line gap between barrel sections. Probably also a special size to them to match the barrels slight misplacement between barrels.

Zig Zag is a better tile gap but if the gap is small enough and deep enough straight line gaps should be acceptable. I think straight line gaps every so often for the nose cone will be the way they solve curvature problem of the nose.

An arrangement of pentagonal and hexagonal tiles has been mentioned on this forum this year along with other options. We will have to see. Avoiding a single piece RCC section on the nosecone is what they will try avoid.
Title: Re: Starship heat shield
Post by: billh on 07/16/2021 08:30 pm
The leading edge tiles are thicker, too.

- This is not a leading edge. It is a hinge line. It is cylindrical to maintain a small gap to help in sealing air from flowing through the hinge.

John
Thanks. I stand corrected!
Title: Re: Starship heat shield
Post by: Oersted on 07/16/2021 09:59 pm
Image credit to Ocean Cam

Has the debate over whether SpaceX is willing to produce a more diverse array of heat shield sizes and shapes been solved yet? I think this image of the heat shielding for the forward flaps really adds to the argument that they are willing to sacrifice greater simplicity in manufacturing and tile placement for simpler patterns. Note how these tiles appear to be far smaller than ones we've seen before and how they they abruptly cut off the tile on the far left.
Yes, and the main argument against using enough different tile shapes to actually fit the shape of the vehicle seems to be “Sleepy workers will mislabel the tiles or switch them around, and then -- Oh noes! Doom or cost explosion! It’s better to have gaps.”
Or am I missing something?

The actual argument is it significantly increases cost and complexity to have lots of kinds of tiles, for pretty obvious reasons already discussed in this thread.  It’s not impossible or undoable, but damn it sure would be nice to avoid.

Nice to avoid, well.... SpaceX is eminently capable of producing different-shaped tiles and keeping track of them during production and spacecraft assembly. Those challenges are rather small compared to all the other challenges they are dealing with. I think the pragmatic thing is just to produce the tiles needed instead of jumping through hoops and leaving gaps in order to increase production uniformity. Yeah, there might be 50 different tiles instead of five. No big deal.
Title: Re: Starship heat shield
Post by: Okie_Steve on 07/16/2021 10:14 pm
Starship is a significantly simpler and more uniform shape than Shuttle so do not worry about the massive numbers of unique tile shapes it required, which I suspect is the nightmare lurking in the back of people's minds, possibly subconsiously.
Title: Re: Starship heat shield
Post by: AstroDave on 07/16/2021 10:48 pm
Starship is a significantly simpler and more uniform shape than Shuttle so do not worry about the massive numbers of unique tile shapes it required, which I suspect is the nightmare lurking in the back of people's minds, possibly subconsiously.

  Being a child of the '70s means I missed the Apollo flights, was aware of Skylab, but really anticipated the next iteration of NASA flights that were the Shuttle Program. The tiles were such a disappointment in the delays they caused, so 'lurking nightmare in the subconscious' is an on point description.
  As you said, the more uniform shapes will cut down on the number of unique tiles. Very impressive that SpaceX is taking this challenge on, and hope that success is met sooner rather than later.
Title: Re: Starship heat shield
Post by: AU1.52 on 07/16/2021 11:00 pm
Image credit to Ocean Cam

Has the debate over whether SpaceX is willing to produce a more diverse array of heat shield sizes and shapes been solved yet? I think this image of the heat shielding for the forward flaps really adds to the argument that they are willing to sacrifice greater simplicity in manufacturing and tile placement for simpler patterns. Note how these tiles appear to be far smaller than ones we've seen before and how they they abruptly cut off the tile on the far left.
Yes, and the main argument against using enough different tile shapes to actually fit the shape of the vehicle seems to be “Sleepy workers will mislabel the tiles or switch them around, and then -- Oh noes! Doom or cost explosion! It’s better to have gaps.”
Or am I missing something?

The actual argument is it significantly increases cost and complexity to have lots of kinds of tiles, for pretty obvious reasons already discussed in this thread.  It’s not impossible or undoable, but damn it sure would be nice to avoid.

Nice to avoid, well.... SpaceX is eminently capable of producing different-shaped tiles and keeping track of them during production and spacecraft assembly. Those challenges are rather small compared to all the other challenges they are dealing with. I think the pragmatic thing is just to produce the tiles needed instead of jumping through hoops and leaving gaps in order to increase production uniformity. Yeah, there might be 50 different tiles instead of five. No big deal.


Also it appears that some of the tiles got damaged during the transport to Starbase. I see one chipped tile and missing tiles to the left (back of the end of the flap) where the white insulation is. It does seem the tiles are somewhat fragile.
Title: Re: Starship heat shield
Post by: vaporcobra on 07/17/2021 12:06 am
Image credit to Ocean Cam

Has the debate over whether SpaceX is willing to produce a more diverse array of heat shield sizes and shapes been solved yet? I think this image of the heat shielding for the forward flaps really adds to the argument that they are willing to sacrifice greater simplicity in manufacturing and tile placement for simpler patterns. Note how these tiles appear to be far smaller than ones we've seen before and how they they abruptly cut off the tile on the far left.

With Mary's photos, that's even clearer. In particular, check out these cap-like tiles forming a full ring around one of the flap's cylindrical endpoints. Not only are they nothing like any other tile visible, they're also different than the tiles on the other end. SpaceX clearly has no qualms with - or bottlenecks preventing - the creation of a diverse range of tile shapes.
Title: Re: Starship heat shield
Post by: ETurner on 07/17/2021 12:06 am
Image credit to Ocean Cam

Has the debate over whether SpaceX is willing to produce a more diverse array of heat shield sizes and shapes been solved yet? I think this image of the heat shielding for the forward flaps really adds to the argument that they are willing to sacrifice greater simplicity in manufacturing and tile placement for simpler patterns. Note how these tiles appear to be far smaller than ones we've seen before and how they they abruptly cut off the tile on the far left.
Yes, and the main argument against using enough different tile shapes to actually fit the shape of the vehicle seems to be “Sleepy workers will mislabel the tiles or switch them around, and then -- Oh noes! Doom or cost explosion! It’s better to have gaps.”
Or am I missing something?
I mean, it IS better to have gaps, if you CAN have gaps. That is the question that only SpaceX can answer.
More wide gaps, less mass. Wide gaps everywhere?
Title: Re: Starship heat shield
Post by: CyclicVoltmanatee on 07/17/2021 12:22 am
It looks like all the edge tiles are bonded to a thin metal underlayment that is also separate from the main flap structure. I think they can potentially install/remove large sections of these more intricate tile arrangements in a single go.

See attached image crop, originally posted by Dave G in the prototype thread … which I couldn’t figure out how to quote directly so I hope this satisfies citation responsibilities.

Edit: moved from prototype thread to here. :)
Title: Re: Starship heat shield
Post by: Ionmars on 07/17/2021 12:22 am
...
...
In the image below, the row of tiles lying over a weld line may require more special tiles. This is because the pinning of tiles on the upper and lower ring segments stops short of the two metal edges of the segments. Bare metal edges along the join line are welded together, followed by pinning one or two rows of tiles that cover the weld line. This procedure introduces the likelihood of additional mismatches between tiles in the top segment and tiles in the bottom segment and adjustments made by producing more special tiles. Ideally, one special tile could accommodate location errors in both X and Y directions, as indicated.

Starting from the center line should eliminate the special tile.
...
...
:)  Very good idea I didn't think of.
Title: Re: Starship heat shield
Post by: sevenperforce on 07/17/2021 01:12 am
Image credit to Ocean Cam

Has the debate over whether SpaceX is willing to produce a more diverse array of heat shield sizes and shapes been solved yet? I think this image of the heat shielding for the forward flaps really adds to the argument that they are willing to sacrifice greater simplicity in manufacturing and tile placement for simpler patterns. Note how these tiles appear to be far smaller than ones we've seen before and how they they abruptly cut off the tile on the far left.

With Mary's photos, that's even clearer. In particular, check out these cap-like tiles forming a full ring around one of the flap's cylindrical endpoints. Not only are they nothing like any other tile visible, they're also different than the tiles on the other end. SpaceX clearly has no qualms with - or bottlenecks preventing - the creation of a diverse range of tile shapes.
It is hard to tell with perspective, etc...do the curved pentagonal edge tiles get larger and larger as you move down the flap root? Or are they all the same size? If they are getting larger and larger then we are getting tiles which are completely non-interchangeable.
Title: Re: Starship heat shield
Post by: Bob Niland on 07/17/2021 01:44 am
vaporcobra: SpaceX clearly has no qualms with - or bottlenecks preventing - the creation of a diverse range of tile shapes

The variations in coloration are intriguing too, as is the flap edge view showing only plain-text ID info. (Update: I couldn't make it out, but it's not ID info)

I might be getting ahead of the timeline here, but I'd expect a possible goal-set to be:
1. Laser scan the larger as-built bare structures for precise 3D geometry.
2. Tesselate a tile layout based on projected mission profiles.
3. 3D manufacture tiles to that, each unique if necessary.
4. Print or engrave them with orienting QR codes + human-readable IDs.
5. Robo-emplace them.
6. Laser scan pre-mission (perhaps post static fire) for QA.
7. Laser scan post-mission. Robo-repair as needed.
Title: Re: Starship heat shield
Post by: sevenperforce on 07/17/2021 01:51 am
It looks like all the edge tiles are bonded to a thin metal underlayment that is also separate from the main flap structure. I think they can potentially install/remove large sections of these more intricate tile arrangements in a single go.

See attached image crop, originally posted by Dave G in the prototype thread … which I couldn’t figure out how to quote directly so I hope this satisfies citation responsibilities.

Edit: moved from prototype thread to here. :)
The tile thickness transition is cool. It really looks like they used computer modeling to say “here is where we need special tiles, and here is how they are shaped, and here is how they fit into the ordinary tiles we use everywhere else.”
Title: Re: Starship heat shield
Post by: chief on 07/17/2021 02:21 am
Also it appears that some of the tiles got damaged during the transport to Starbase. I see one chipped tile and missing tiles to the left (back of the end of the flap) where the white insulation is. It does seem the tiles are somewhat fragile.

I don't infer that from the absence of tiles in this area. If you look closely, you'll see KEEP OUT zones marked around the hoisting points - I think they've deliberately left some sections clear of tiles so that the hoisting straps do not foul on tiles. They can fill in the missing tiles once the flap is mounted to the nosecone.
Title: Re: Starship heat shield
Post by: cscott on 07/17/2021 02:27 am
I'm seeing a pragmatic compromise between "every tile is unique" and "there is only one tile shape".  For example, the "rim" tiles are full custom, but they did arrange it so there are an integral number of identical rim tiles.  Similarly, the cylindrical hinge tiles appear to be uniquely curved in each row -- but then the same four or so tile shapes repeat all down the hinge and transition to what looks like the standard hex grid on the flat surface.  So "as few as possible" tile shapes, but they haven't compromised in tile thickness or gap width just to have fewer shapes, and they are definitely not afraid of throwing in a custom shape where the geometry requires.  But once they have a custom shape, they try to reuse it as many times as they can.

LATER: On the end of the fin (not yet covered) I'd bet dollars to donuts they reuse the flat-sided pentagon tiles for the majority of that top edge, with just one or two custom tiles at the hinge end to follow the circular profile.
Title: Re: Starship heat shield
Post by: chief on 07/17/2021 02:27 am
...the flap edge view showing only plain-text ID info.

If you're referring to the text in the image crop in CyclicVoltmanatee's post, the text just says "NO FELT THIS SIDE". If not, do you have an image you could point to please?
Title: Re: Starship heat shield
Post by: OTV Booster on 07/17/2021 02:48 am
These photo show pins along the bottom of the fin for more tiles.

Looks like they're using they're using the backing insulation as filler on the hinge tiles?

https://twitter.com/StarshipGazer/status/1416111047015116806? (https://twitter.com/StarshipGazer/status/1416111047015116806?)
But wait, wait! There's more. A lot of interesting things in that pic. Not only does SX show us that they're not shy about curving tiles to match the surface they're working with, they show us that they are not shy about shaping the tile to match the edge limits of the underlying geometry. More interesting is that the are willing to modify the Z axis to keep the gap constant on a radius position. It's starting to look a bit shuttle like (do I have to start dodging thrown fruit?) but with a simpler geometry that will result in MUCH fewer tiles.

An interesting side note is the pins for curved tiles can not follow the radius. They must remain parallel to each other or the tile will not slip over them.

One thing they don't do on this example is vary the gap width within the limited area we can see.

Yet another interesting, but not earth shattering point is surface tiles lap past the end of the fin to protect the (most probably) end covering tiles.

Yet again interesting is the blanket looks to only underlay the the tiles on the flat. There is a black something covering the radius area but it is unclear if it runs under the radius tiles. There was something like it on the earlier pic showing a couple tiles on the forward lee of a fin root cover raceway. It looked flexible in that pic. A solid but flexible thermal treatment? What type material could this be?

Edit: added earlier pic (credit Mary).
Title: Re: Starship heat shield
Post by: Bob Niland on 07/17/2021 02:55 am
Chief: If you're referring to the text in the image crop in CyclicVoltmanatee's post, the text just says "NO FELT THIS SIDE". If not, do you have an image you could point to please?

Those are the ones. Thanks for clarifying what they say.
Title: Re: Starship heat shield
Post by: OTV Booster on 07/17/2021 03:16 am
Image credit to Ocean Cam

Has the debate over whether SpaceX is willing to produce a more diverse array of heat shield sizes and shapes been solved yet? I think this image of the heat shielding for the forward flaps really adds to the argument that they are willing to sacrifice greater simplicity in manufacturing and tile placement for simpler patterns. Note how these tiles appear to be far smaller than ones we've seen before and how they they abruptly cut off the tile on the far left.
Yes, and the main argument against using enough different tile shapes to actually fit the shape of the vehicle seems to be “Sleepy workers will mislabel the tiles or switch them around, and then -- Oh noes! Doom or cost explosion! It’s better to have gaps.”
Or am I missing something?
I said something in that direction but not as extreme as you put it. The point I was making was that having a series of tiles, each progressively slightly different than the previous is not a good thing. Better to have each row on the ogive (for example) have all the same tile and each row differ as necessary. There are places where different tile shapes are needed because the underlying shape changes abruptly. Hard to miss a cue like that even 11 hours into the shift with sweat running into your eyes. Been there. Done that.

Oversized gap=bad. Unnecessary fiddly work=bad. Matching the tiles to the underlying geometry=good.
Title: Re: Starship heat shield
Post by: rakaydos on 07/17/2021 09:33 am
I'm seeing a pragmatic compromise between "every tile is unique" and "there is only one tile shape".  For example, the "rim" tiles are full custom, but they did arrange it so there are an integral number of identical rim tiles.  Similarly, the cylindrical hinge tiles appear to be uniquely curved in each row -- but then the same four or so tile shapes repeat all down the hinge and transition to what looks like the standard hex grid on the flat surface.  So "as few as possible" tile shapes, but they haven't compromised in tile thickness or gap width just to have fewer shapes, and they are definitely not afraid of throwing in a custom shape where the geometry requires.  But once they have a custom shape, they try to reuse it as many times as they can.

LATER: On the end of the fin (not yet covered) I'd bet dollars to donuts they reuse the flat-sided pentagon tiles for the majority of that top edge, with just one or two custom tiles at the hinge end to follow the circular profile.
"As few (tile shapes) as possible, and no fewer."
Title: Re: Starship heat shield
Post by: mikegi on 07/17/2021 02:09 pm
The increasing number of unique tiles got me thinking about operations:

1. Anyone heard of an inspection protocol for the SS tiles in orbit? I guess it mostly matters for manned missions and since those will be a small fraction of total SS missions, it could be minimized.

2. Would they keep an inventory of tiles for repair on each manned SS and train at least one of the crewmembers in repair? Or would it be simpler to send up another SS with "mechanics" to rescue the crew and repair the damaged SS?

3. Would it be worthwhile to even try to repair a damaged but unmanned SS in orbit?
Title: Re: Starship heat shield
Post by: sevenperforce on 07/17/2021 02:20 pm
Because starship is steel, they could very readily design numerous small inspection robots with magnetic feet to crawl the exterior and photograph tiles.
Title: Re: Starship heat shield
Post by: Bob Niland on 07/17/2021 02:31 pm
sevenperforce: Because starship is steel, they could very readily design numerous small inspection robots with magnetic feet to crawl the exterior and photograph tiles.

The skin is 304L stainless, which at a glance, is considered to be either non-magnetic, or only weakly magnetic. So a mag crawler wouldn't be my top guess for an on-orbit inspection method.
Title: Re: Starship heat shield
Post by: sevenperforce on 07/17/2021 02:55 pm
sevenperforce: Because starship is steel, they could very readily design numerous small inspection robots with magnetic feet to crawl the exterior and photograph tiles.

The skin is 304L stainless, which at a glance, is considered to be either non-magnetic, or only weakly magnetic. So a mag crawler wouldn't be my top guess for an on-orbit inspection method.
Ah, too bad.
Title: Re: Starship heat shield
Post by: Oersted on 07/17/2021 10:59 pm
I'm seeing a pragmatic compromise between "every tile is unique" and "there is only one tile shape".  For example, the "rim" tiles are full custom, but they did arrange it so there are an integral number of identical rim tiles.  Similarly, the cylindrical hinge tiles appear to be uniquely curved in each row -- but then the same four or so tile shapes repeat all down the hinge and transition to what looks like the standard hex grid on the flat surface.  So "as few as possible" tile shapes, but they haven't compromised in tile thickness or gap width just to have fewer shapes, and they are definitely not afraid of throwing in a custom shape where the geometry requires.  But once they have a custom shape, they try to reuse it as many times as they can.

Can't help but noticing that it literally sounds as if you are talking about the LEGO Company here. They prefer to re-use blocks from former sets but don't shy away from making new blocks if necessary.
Title: Re: Starship heat shield
Post by: _MECO on 07/18/2021 07:55 am
sevenperforce: Because starship is steel, they could very readily design numerous small inspection robots with magnetic feet to crawl the exterior and photograph tiles.

The skin is 304L stainless, which at a glance, is considered to be either non-magnetic, or only weakly magnetic. So a mag crawler wouldn't be my top guess for an on-orbit inspection method.
I think the obvious long term answer to inspecting atmosphere-borne spacecraft bellies is using highly nimble and compact RCS drones, and autonomous ones at that. In the near term, unmanned missions could be uninspected and manned missions could involve EVA of some kind. There's also the possibility of cameras on booms (spinoff technology to deployable solar arrays?) but I don't see that as thorough enough.
Title: Re: Starship heat shield
Post by: Slarty1080 on 07/18/2021 10:27 am
Image credit to Ocean Cam

Has the debate over whether SpaceX is willing to produce a more diverse array of heat shield sizes and shapes been solved yet? I think this image of the heat shielding for the forward flaps really adds to the argument that they are willing to sacrifice greater simplicity in manufacturing and tile placement for simpler patterns. Note how these tiles appear to be far smaller than ones we've seen before and how they they abruptly cut off the tile on the far left.
Yes, and the main argument against using enough different tile shapes to actually fit the shape of the vehicle seems to be “Sleepy workers will mislabel the tiles or switch them around, and then -- Oh noes! Doom or cost explosion! It’s better to have gaps.”
Or am I missing something?

The actual argument is it significantly increases cost and complexity to have lots of kinds of tiles, for pretty obvious reasons already discussed in this thread.  It’s not impossible or undoable, but damn it sure would be nice to avoid.

Yes, there will be as few tile types as possible (and no fewer) what that number is nobody knows yet. SpaceX will hopefully have made a good guestimate of what it should be and we should get some confirmation after the re-entry of SN20.
Title: Re: Starship heat shield
Post by: geza on 07/18/2021 04:51 pm
The increasing number of unique tiles got me thinking about operations:

1. Anyone heard of an inspection protocol for the SS tiles in orbit? I guess it mostly matters for manned missions and since those will be a small fraction of total SS missions, it could be minimized.

2. Would they keep an inventory of tiles for repair on each manned SS and train at least one of the crewmembers in repair? Or would it be simpler to send up another SS with "mechanics" to rescue the crew and repair the damaged SS?

3. Would it be worthwhile to even try to repair a damaged but unmanned SS in orbit?

Don't forget that they wish send a huge number of people to Mars and an even larger number for P2P. Projects of such scale are infeasible with an unreliable heat shield, which has to be checked and, maybe, repair.
Title: Re: Starship heat shield
Post by: _MECO on 07/19/2021 04:45 am
The increasing number of unique tiles got me thinking about operations:

1. Anyone heard of an inspection protocol for the SS tiles in orbit? I guess it mostly matters for manned missions and since those will be a small fraction of total SS missions, it could be minimized.

2. Would they keep an inventory of tiles for repair on each manned SS and train at least one of the crewmembers in repair? Or would it be simpler to send up another SS with "mechanics" to rescue the crew and repair the damaged SS?

3. Would it be worthwhile to even try to repair a damaged but unmanned SS in orbit?

Don't forget that they wish send a huge number of people to Mars and an even larger number for P2P. Projects of such scale are infeasible with an unreliable heat shield, which has to be checked and, maybe, repair.

In the event that it's not possible to carry plentiful spares of every single tile type, it would probably be prudent to keep just the ones corresponding to parts of the vehicle where sensitive parts are or where peak heating occurs. It could be the difference between a vehicle becoming scrap after a successful EDL and having a fatal loss of vehicle.
Title: Re: Starship heat shield
Post by: geza on 07/19/2021 08:28 am
Note also that tile inspection & repair became a topic for the Shuttle because of the unsolvable foam shredding problem of the External Tank. Fortunately, there is no ET for Starship.
Title: Re: Starship heat shield
Post by: cscott on 07/19/2021 12:55 pm
I think you run the severity x frequency numbers for the spares and stock judiciously.  If 99% of the heat tile surface is Plain Old Hexagon, Standard Size, you definitely stock some of those.  If there is only one of a specific tile shape on the craft, but it's an immediate LOM if damage occurs, then you stock one of those too.  Probability of damage (given exposure, likely damage mechanisms, and the number of tiles of that shape) x severity to mission if damage occurs, weighed by some factor.
Title: Re: Starship heat shield
Post by: Jim on 07/19/2021 01:05 pm
The increasing number of unique tiles got me thinking about operations:

1. Anyone heard of an inspection protocol for the SS tiles in orbit? I guess it mostly matters for manned missions and since those will be a small fraction of total SS missions, it could be minimized.


Why is there a need to inspect on orbit?
Title: Re: Starship heat shield
Post by: Mike_1179 on 07/19/2021 01:38 pm
The increasing number of unique tiles got me thinking about operations:

1. Anyone heard of an inspection protocol for the SS tiles in orbit? I guess it mostly matters for manned missions and since those will be a small fraction of total SS missions, it could be minimized.


Why is there a need to inspect on orbit?

So if you can demonstrate that they don't fail, there is no need for inspections to verify they haven't failed? That seems like a reasonable way to look at most things; are there general rules that you still inspect things which, if they fail it's a loss of vehicle?
Title: Re: Starship heat shield
Post by: Star-Drive on 07/19/2021 01:44 pm
The increasing number of unique tiles got me thinking about operations:

1. Anyone heard of an inspection protocol for the SS tiles in orbit? I guess it mostly matters for manned missions and since those will be a small fraction of total SS missions, it could be minimized.


Why is there a need to inspect on orbit?
 

Lets try the 2003 NASA Space Shuttle Columbia leading edge failure that killed seven Astronauts for starters...
Title: Re: Starship heat shield
Post by: Jim on 07/19/2021 01:51 pm
The increasing number of unique tiles got me thinking about operations:

1. Anyone heard of an inspection protocol for the SS tiles in orbit? I guess it mostly matters for manned missions and since those will be a small fraction of total SS missions, it could be minimized.


Why is there a need to inspect on orbit?
 

Lets try the 2003 NASA Space Shuttle Columbia leading edge failure that killed seven Astronauts for starters...

Not a relevant to Starship
Title: Re: Starship heat shield
Post by: Jim on 07/19/2021 01:53 pm
The increasing number of unique tiles got me thinking about operations:

1. Anyone heard of an inspection protocol for the SS tiles in orbit? I guess it mostly matters for manned missions and since those will be a small fraction of total SS missions, it could be minimized.


Why is there a need to inspect on orbit?

So if you can demonstrate that they don't fail, there is no need for inspections to verify they haven't failed? That seems like a reasonable way to look at most things; are there general rules that you still inspect things which, if they fail it's a loss of vehicle?

Not a general rule
Title: Re: Starship heat shield
Post by: capoman on 07/19/2021 01:55 pm
Being a much more resistant vehicle to heat, a tile loss is much less likely to be catastrophic.

That being said, I do think SpaceX will be watching closely at tiles on their initial flights likely after landing, but if they can't determine when the tile failed, may do some inspection on orbit somehow.

I'm guessing that most of this will be a resolved and known issue by the time they start flying people. They intend to make many uncrewed flights first, which will help them resolve any potential heat tile issues. The goal of course is rapidly reusable, which would not require wasteful tile inspections in space.
Title: Re: Starship heat shield
Post by: edzieba on 07/19/2021 01:58 pm
The increasing number of unique tiles got me thinking about operations:

1. Anyone heard of an inspection protocol for the SS tiles in orbit? I guess it mostly matters for manned missions and since those will be a small fraction of total SS missions, it could be minimized.


Why is there a need to inspect on orbit?
Skittishness over past experience with HRSI tiles.

On the one hand, all current human rated spacecraft do not require a pre-entry TPS inspection. On the other hand, all current human rated spacecraft do not have their heatshield exposed until immediately prior to entry. Even for the majority of autonomous spacecraft that re-enter (e.g. X-37) or have re-entering elements (e.g. sample return probes), the TPS is not exposed until either in orbit, or until immediately before entry.

Starship will expose the entire TPS both while sitting on the pad (though presumably a shortly-before-launch optical inspection can be conducted without much issue) and during launch and while in orbit. The only other vehicles that exposed their TPS in this way were STS (vulnerable to foam shedding) and Buran (no foam strikes, but only one test flight with unknown post-flight tile condition other than "did not catastrophically fail"). MMOD to the TPS was one area of notable concern for CRS even with covered TPS, so it would be expected to be of concern for Starship, having a much larger cross-section.
Title: Re: Starship heat shield
Post by: Jim on 07/19/2021 02:09 pm
The increasing number of unique tiles got me thinking about operations:

1. Anyone heard of an inspection protocol for the SS tiles in orbit? I guess it mostly matters for manned missions and since those will be a small fraction of total SS missions, it could be minimized.


Why is there a need to inspect on orbit?
Skittishness over past experience with HRSI tiles.


These aren't HRSI and are not in a debris shedding environment.
Title: Re: Starship heat shield
Post by: edzieba on 07/19/2021 02:24 pm
The increasing number of unique tiles got me thinking about operations:

1. Anyone heard of an inspection protocol for the SS tiles in orbit? I guess it mostly matters for manned missions and since those will be a small fraction of total SS missions, it could be minimized.


Why is there a need to inspect on orbit?
Skittishness over past experience with HRSI tiles.


These aren't HRSI and are not in a debris shedding environment.
No debris shedding on launch, but the structure and method for manufacture (described in one of the environmental docs for the Astronaut Blvd. site) are almost identical to HRSI: sintered pure silica fibres, reaction-cured Borosilicate glass coating, then impregnated with acetic acid & a waterproofing agent. The only change is the waterproofing agent (methyl-trimethoxy silane rather than dimethylethoxy silane) and the shape.
Title: Re: Starship heat shield
Post by: Robotbeat on 07/19/2021 02:26 pm
The increasing number of unique tiles got me thinking about operations:

1. Anyone heard of an inspection protocol for the SS tiles in orbit? I guess it mostly matters for manned missions and since those will be a small fraction of total SS missions, it could be minimized.


Why is there a need to inspect on orbit?
Skittishness over past experience with HRSI tiles.


These aren't HRSI and are not in a debris shedding environment.
No debris shedding on launch, but the structure and method for manufacture (described in one of the environmental docs for the Astronaut Blvd. site) are almost identical to HRSI: sintered pure silica fibres, reaction-cured Borosilicate glass coating, then impregnated with acetic acid & a waterproofing agent. The only change is the waterproofing agent (methyl-trimethoxy silane rather than dimethylethoxy silane) and the shape.
The moral arc of the universe is long, but it bends toward "Starship is Shuttle reincarnated." ;)
Title: Re: Starship heat shield
Post by: Jim on 07/19/2021 02:27 pm
No debris shedding on launch, but the structure and method for manufacture (described in one of the environmental docs for the Astronaut Blvd. site) are almost identical to HRSI: sintered pure silica fibres, reaction-cured Borosilicate glass coating, then impregnated with acetic acid & a waterproofing agent. The only change is the waterproofing agent (methyl-trimethoxy silane rather than dimethylethoxy silane) and the shape.

Not PICAX?
Title: Re: Starship heat shield
Post by: Robotbeat on 07/19/2021 02:29 pm
No debris shedding on launch, but the structure and method for manufacture (described in one of the environmental docs for the Astronaut Blvd. site) are almost identical to HRSI: sintered pure silica fibres, reaction-cured Borosilicate glass coating, then impregnated with acetic acid & a waterproofing agent. The only change is the waterproofing agent (methyl-trimethoxy silane rather than dimethylethoxy silane) and the shape.

Not PICAX?
I don't believe SpaceX is using PICA-X anywhere on Starship.
Title: Re: Starship heat shield
Post by: edzieba on 07/19/2021 02:55 pm
No debris shedding on launch, but the structure and method for manufacture (described in one of the environmental docs for the Astronaut Blvd. site) are almost identical to HRSI: sintered pure silica fibres, reaction-cured Borosilicate glass coating, then impregnated with acetic acid & a waterproofing agent. The only change is the waterproofing agent (methyl-trimethoxy silane rather than dimethylethoxy silane) and the shape.

Not PICAX?
No sign of it so far (or SPAM). Using an ablator wouldn't match with their desire for rapid reuse with minimal refurbishment.
I'd be willing to bet that HRSI was picked almost purely because it is a flight-tested system with an existing trained talent pool that could be hired to manufacture, test, and apply it. That gets you to orbit a lot faster than any new TPS regardless of how much better the numbers look on paper. SpaceX have no qualms about dramatic mid-life vehicle upgrades and watching sunk costs bubble away as they are enthusiastically tossed overboard, so its not impossible Starship will see some other TPS eventually (e.g. metallic, transpiration, etc). Or maybe without the hazard of foam impacts HRSI will turn out to be 'good enough'.
Title: Re: Starship heat shield
Post by: Poseidon on 07/19/2021 03:03 pm
Note also that tile inspection & repair became a topic for the Shuttle because of the unsolvable foam shredding problem of the External Tank. Fortunately, there is no ET for Starship.

No external tank, but a collision with a bird is still possible, it happens everyday around the world with airplanes.
Title: Re: Starship heat shield
Post by: RoboGoofers on 07/19/2021 03:07 pm
Tiles can potentially break or come off on ascent so debris could be an issue. Obviously SpaceX doesn't want them to but we'll have to see what happens when they launch a fully tiled Starship. The tiles and attachments haven't really been tested very hard yet, at least as far as we have seen with the test flights.
Title: Re: Starship heat shield
Post by: Jim on 07/19/2021 03:27 pm
Note also that tile inspection & repair became a topic for the Shuttle because of the unsolvable foam shredding problem of the External Tank. Fortunately, there is no ET for Starship.

No external tank, but a collision with a bird is still possible, it happens everyday around the world with airplanes.

Not at speeds that matter for a launch vehicle.
Title: Re: Starship heat shield
Post by: sevenperforce on 07/19/2021 04:15 pm
MMOD damage would seem to be the most serious potential issue that would require inspection on orbit.

Did the Shuttle heat shield ever sustain MMOD damage on orbit? Obviously the Shuttle took a LOT of damage from MMODs generally but I don't recall any damage to the heat shield that was concerning. Or maybe the foam strike damage was simply so much more concerning that MMOD damage was comparatively negligible.

I suppose that SpaceX can quite readily mount a bunch of their tiles on steel with the thermal cloth backing and fire hypervelocity particles at them to see what happens. Possible that tiles would even act somewhat as a de facto Whipple shield. If hypervelocity impacts don't shatter the tiles completely it should be fine.

The worst-case scenario would be a low-angle hypervelocity impact that shreds several tiles in a row and sends shrapnel from those tiles into adjacent tiles.
Title: Re: Starship heat shield
Post by: rakaydos on 07/19/2021 04:31 pm
I think the biggest cause for an orbital shield inspection is reactionary- that is, if the crew reports  a sharp impact and slew, (a debris strike), there should be onboard means to see if they should come home, or wait for rescue.
Title: Re: Starship heat shield
Post by: envy887 on 07/19/2021 04:39 pm
Note also that tile inspection & repair became a topic for the Shuttle because of the unsolvable foam shredding problem of the External Tank. Fortunately, there is no ET for Starship.

No external tank, but a collision with a bird is still possible, it happens everyday around the world with airplanes.

Rather unlikely. The bird-containing air volume that a rocket sweeps through is several orders of magnitude smaller than a typical aircraft flight, and aircraft flights that hit birds are several orders of magnitude smaller than the total number of aircraft flights. So we're probably talking about a 10^-5 to 10^-7 type of probability here.
Title: Re: Starship heat shield
Post by: envy887 on 07/19/2021 04:42 pm
I think the biggest cause for an orbital shield inspection is reactionary- that is, if the crew reports  a sharp impact and slew, (a debris strike), there should be onboard means to see if they should come home, or wait for rescue.

A 1 kg bit of debris is not going to slew a 5,000,000 kg rocket. And crew won't hear much of anything over the 33 Raptors burning 100 m away.
Title: Re: Starship heat shield
Post by: eriblo on 07/19/2021 04:52 pm
I think the biggest cause for an orbital shield inspection is reactionary- that is, if the crew reports  a sharp impact and slew, (a debris strike), there should be onboard means to see if they should come home, or wait for rescue.

A 1 kg bit of debris is not going to slew a 5,000,000 kg rocket. And crew won't hear much of anything over the 33 Raptors burning 100 m away.
I think that might have been regarding MMOD once in orbit. Accelerometers/microphones attached to the structure would likely pick up any significant impact and for birds during launch you would also have ground imagery.
Title: Re: Starship heat shield
Post by: sevenperforce on 07/19/2021 05:09 pm
I think the biggest cause for an orbital shield inspection is reactionary- that is, if the crew reports  a sharp impact and slew, (a debris strike), there should be onboard means to see if they should come home, or wait for rescue.

A 1 kg bit of debris is not going to slew a 5,000,000 kg rocket. And crew won't hear much of anything over the 33 Raptors burning 100 m away.
I think that might have been regarding MMOD once in orbit. Accelerometers/microphones attached to the structure would likely pick up any significant impact and for birds during launch you would also have ground imagery.
Well, MMOD on orbit isn’t going to produce any noticeable signal or sensation to the crew. They won’t hear, see, or feel anything. But cryo-proofed microphones inside the tanks and attached to the steel inner skin would definitely be able to pick up the “ping” from an MMOD strike to the heat shield. They would probably be able to triangulate it as well.

Another issue would be an MMOD strike to the bare side of Starship. Piercing the outer skin could be bad. But they’d immediately pick that up due to the resulting leak. And Starship can probably de-orbit and land entirely on its header tanks, which are protected from MMOD.
Title: Re: Starship heat shield
Post by: Jim on 07/19/2021 05:12 pm
Tiles can potentially break or come off on ascent so debris could be an issue.

No, debris isn't the issue, tiles coming off is.  One doesn't worrying about secondary effects. 
Title: Re: Starship heat shield
Post by: Jim on 07/19/2021 05:16 pm
MMOD damage would seem to be the most serious potential issue that would require inspection on orbit.


No, it isn't an issue. 



The worst-case scenario would be a low-angle hypervelocity impact that shreds several tiles in a row and sends shrapnel from those tiles into adjacent tiles.

That is not the way it happens.  The micrometeoroid wouldn't last going through the top fused layer of the first tile.

You know what is used to collect micrometeoroids?  Aerogel.  Silica.
Title: Re: Starship heat shield
Post by: Okie_Steve on 07/19/2021 05:33 pm
MMOD damage would seem to be the most serious potential issue that would require inspection on orbit.


No, it isn't an issue.


Interesting. Is this because it is deemed statistically unlike to happen in the time frame of a flight, likely to be survivable, or something else? It certainly came to my (layman) mind.
Title: Re: Starship heat shield
Post by: Jim on 07/19/2021 05:41 pm

Interesting. Is this because it is deemed statistically unlike to happen in the time frame of a flight, likely to be survivable, or something else? It certainly came to my (layman) mind.

Did you know of any issues from it for the shuttle program?
Title: Re: Starship heat shield
Post by: rakaydos on 07/19/2021 05:58 pm

Interesting. Is this because it is deemed statistically unlike to happen in the time frame of a flight, likely to be survivable, or something else? It certainly came to my (layman) mind.

Did you know of any issues from it for the shuttle program?
There were notably less ASWS debris in orbit when shuttle was flying.
Title: Re: Starship heat shield
Post by: Okie_Steve on 07/19/2021 06:21 pm

Interesting. Is this because it is deemed statistically unlike to happen in the time frame of a flight, likely to be survivable, or something else? It certainly came to my (layman) mind.

Did you know of any issues from it for the shuttle program?

My only clear memory about a MMOD strike to a shuttle on orbit was a paint chip doing significant damage to a window. Which, as a non spaceflight professional, was enough to make me wonder about the possibility. From your statements I gather that the risk for loss of vehicle due to MMOD is low based on modeling and prior experience, at least compared to others issues. But that is just an assumption, hence the question.
Title: Re: Starship heat shield
Post by: Slarty1080 on 07/19/2021 06:24 pm

Interesting. Is this because it is deemed statistically unlike to happen in the time frame of a flight, likely to be survivable, or something else? It certainly came to my (layman) mind.

Did you know of any issues from it for the shuttle program?
From memory I believe that one of the orbiters windows was hit by something - probably a fleck of paint. It didn't penetrate but I think the window had to be replaced.
Title: Re: Starship heat shield
Post by: Jim on 07/19/2021 06:26 pm

From memory I believe that one of the orbiters windows was hit by something - probably a fleck of paint. It didn't penetrate but I think the window had to be replaced.


I was referring to tiles.  The radiators took damage too.
Title: Re: Starship heat shield
Post by: Slarty1080 on 07/19/2021 06:45 pm

From memory I believe that one of the orbiters windows was hit by something - probably a fleck of paint. It didn't penetrate but I think the window had to be replaced.
I was referring to tiles.  The radiators took damage too.
Fair enough.
I don't know how easily the tiles would be damaged by impacts, but I would have thought that up to a certain size impacts would just poke a smallish circular hole straight through the tile.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 07/19/2021 07:32 pm
Tiles can potentially break or come off on ascent so debris could be an issue.

No, debris isn't the issue, tiles coming off is.  One doesn't worrying about secondary effects.

Tiles coming off isn't an issue unless the mineral wool layer also peels back exposing the stainless steel to plasma or intense IR.

Looking back through SNx tile damage pics, almost all the damaged tiles show the bracket is still intact.

The tile material is there to protect the bracket that holds down the mineral wool which protects the stainless steel.

Multiple layers have to fail in one spot in order to risk vehicle loss.  As it should be for any well engineered vehicle.

Not sure what the multiple layers are at the flap edges, unless as someone mentioned above there's a metal layer below the tile.  presumably a high temp metal.
Title: Re: Starship heat shield
Post by: mikegi on 07/19/2021 07:37 pm
The increasing number of unique tiles got me thinking about operations:

1. Anyone heard of an inspection protocol for the SS tiles in orbit? I guess it mostly matters for manned missions and since those will be a small fraction of total SS missions, it could be minimized.


Why is there a need to inspect on orbit?
Because:

1. The tiles critical to survival of the ship/astronauts
2. There are thousands of tiles and any one of them could fail on launch
3. We can actually do things now if one or more fail (this isn't the Shuttle)

Item 3 is the most important one. Starships will be relatively "plentiful" compared to the Shuttle. Instead of telling the crew on an injured ship "you're screwed" because there are so few shuttles and it takes a long time to get one ready to launch, SpaceX could fire up another SS for a rescue/repair in days.

Anyway, in thinking about this some more, the only time you'd need a dedicated inspection device that floats around the ship would be for joyrides, where the SS simply goes into orbit and returns to Earth. Every other SS mission will docking in LEO with another SS (tankers, etc.). So, you could simply have a couple of ultra high res cameras on an SS looking outwards, have the ascending SS approach and roll to expose the tiles to the cameras.
Title: Re: Starship heat shield
Post by: envy887 on 07/19/2021 08:11 pm
The increasing number of unique tiles got me thinking about operations:

1. Anyone heard of an inspection protocol for the SS tiles in orbit? I guess it mostly matters for manned missions and since those will be a small fraction of total SS missions, it could be minimized.


Why is there a need to inspect on orbit?
Because:

1. The tiles critical to survival of the ship/astronauts
2. There are thousands of tiles and any one of them could fail on launch
3. We can actually do things now if one or more fail (this isn't the Shuttle)

Item 3 is the most important one. Starships will be relatively "plentiful" compared to the Shuttle. Instead of telling the crew on an injured ship "you're screwed" because there are so few shuttles and it takes a long time to get one ready to launch, SpaceX could fire up another SS for a rescue/repair in days.

Anyway, in thinking about this some more, the only time you'd need a dedicated inspection device that floats around the ship would be for joyrides, where the SS simply goes into orbit and returns to Earth. Every other SS mission will docking in LEO with another SS (tankers, etc.). So, you could simply have a couple of ultra high res cameras on an SS looking outwards, have the ascending SS approach and roll to expose the tiles to the cameras.

Repairing an uncrewed tanker probably won't worthwhile for some time. Even if the TPS is damaged it's probably cheaper to attempt a reentry and recovery offshore than to send a mission to repair it, and simply write off any failed reentries. It would be useful to know what damage is too much.
Title: Re: Starship heat shield
Post by: edzieba on 07/19/2021 08:37 pm
Tiles can potentially break or come off on ascent so debris could be an issue.

No, debris isn't the issue, tiles coming off is.  One doesn't worrying about secondary effects.

Tiles coming off isn't an issue unless the mineral wool layer also peels back exposing the stainless steel to plasma or intense IR.

Looking back through SNx tile damage pics, almost all the damaged tiles show the bracket is still intact.

The tile material is there to protect the bracket that holds down the mineral wool which protects the stainless steel.

Multiple layers have to fail in one spot in order to risk vehicle loss.  As it should be for any well engineered vehicle.

Not sure what the multiple layers are at the flap edges, unless as someone mentioned above there's a metal layer below the tile.  presumably a high temp metal.
No, the tiles are critical to survival. The mineral wool alone is not a sufficient TPS, even if it were to be arbitrarily anchored above the tank skin without any penetrations. The RCG layer on the outside of the tiles does a lot of work reradiating the energy dumped into the tiles by the plasma, and the low density tile body avoids conducting heat to the backer. Without those, you have a moderate-at-best insulator and little re-radiation.
Title: Re: Starship heat shield
Post by: Jim on 07/19/2021 08:43 pm
ause:

1. The tiles critical to survival of the ship/astronauts
2. There are thousands of tiles and any one of them could fail on launch
3. We can actually do things now if one or more fail (this isn't the Shuttle)


1.  That applies to many other systems
2.  No, you make them robust like on the Dragon so they don't and the debris shedding environment is gone.
3.  No, just as screwed if it is a lunar or mars mission.


either trust the TPS or find something else that works and doesn't post launch inspection.
Inflight inspections are not airline type operations and that is what SpaceX is trying to achieve.


Can't denigrate the shuttle and then make excuses when using shuttle type processes.
Title: Re: Starship heat shield
Post by: Oersted on 07/19/2021 10:17 pm
The front flaperons (or whatever they´re called this week) could be a source of high-speed turbulent airflow or debris which could damage the Starship TPS downstream.
Title: Re: Starship heat shield
Post by: envy887 on 07/19/2021 11:04 pm
Tiles can potentially break or come off on ascent so debris could be an issue.

No, debris isn't the issue, tiles coming off is.  One doesn't worrying about secondary effects.

Tiles coming off isn't an issue unless the mineral wool layer also peels back exposing the stainless steel to plasma or intense IR.

Looking back through SNx tile damage pics, almost all the damaged tiles show the bracket is still intact.

The tile material is there to protect the bracket that holds down the mineral wool which protects the stainless steel.

Multiple layers have to fail in one spot in order to risk vehicle loss.  As it should be for any well engineered vehicle.

Not sure what the multiple layers are at the flap edges, unless as someone mentioned above there's a metal layer below the tile.  presumably a high temp metal.
No, the tiles are critical to survival. The mineral wool alone is not a sufficient TPS, even if it were to be arbitrarily anchored above the tank skin without any penetrations. The RCG layer on the outside of the tiles does a lot of work reradiating the energy dumped into the tiles by the plasma, and the low density tile body avoids conducting heat to the backer. Without those, you have a moderate-at-best insulator and little re-radiation.

The tiles collectively are probably critical, but that criticality probably does not extend to every tile individually. Starship could probably lose a few square meters of contiguous tiles on each of the tank or engine bay sections (or cargo section, but maybe not if it contains a crew cabin) and maintain structural integrity by reradiating that heat flux through the tanks to the lee side walls. The white blanket would probably help too, since it would take some time to ablate away and act as insulation during that process.
Title: Re: Starship heat shield
Post by: sevenperforce on 07/20/2021 12:43 am

That is not the way it happens.  The micrometeoroid wouldn't last going through the top fused layer of the first tile.

You know what is used to collect micrometeoroids?  Aerogel.  Silica.
I’m happy to take your word for it, but it still prompts the further question: how large would a piece of debris need to be, traveling at a relative speed of eight or 9 km/s, to penetrate an entire tile?

Are we talking about a paint fleck? A fingernail clipping? A lugnut?
Title: Re: Starship heat shield
Post by: _MECO on 07/20/2021 05:38 am

From memory I believe that one of the orbiters windows was hit by something - probably a fleck of paint. It didn't penetrate but I think the window had to be replaced.


I was referring to tiles.  The radiators took damage too.
Wow, I hope those things are in a museum or at least in good care right now. If that's the first ever example of spacecraft radiators being holed by a high velocity impact it could be of historical importance, considering the eventuality of powering spacecraft with closed cycle heat engines and the tactical importance of radiators being a large target. I digress from the discussion by several decades though...

There are two ways Starship can mitigate heat shield damage. Assuming that no briefcase-sized chunks of orange insulation foam are going to dislodge and damage the TPS every fiftieth ascent, a Starship with sturdily attached tiles will need to do two things for long-term safety: inspect its own belly to enable EVA repairs at regular intervals, and take operational measures to minimize impacts on the heat shield.

Through either cameras on a boom, RCS drones, secondary vehicle/station inspections, or even manned EVA checkups, Starship (and really any large vehicle meant to perform EDL) should be able to identify when tiles critical to landing safely are damaged or gone. When they are identified there should be actual procedures in place to repair the heatshield. Shuttle would present her belly to the ISS so that missing tiles could be identified. I don't need to point out that if any actually had been, a lot of people would have been running around with their hair on fire. Not only should Starship be equipped with the means to fix mild/moderate TPS damage when they do happen, but the TPS should be robust enough in the first place that inspections aren't needed every single time a vehicle makes orbit.

The second measure I'm talking about is more long term. As the years go by and TSTO fully reusable launch systems become commonplace, LEO is going to become a more dangerous place to reside in. This may be a practice more informed by general trends in maintenance fees or public sentiment, but eventually Starship and similar systems will need to start parking higher and higher or else extremely low if they want to decrease their chances of having a collision. A Mars-bound Starship may want to refuel in highly elliptical orbit or even just in a 600x600. Or, if it has the operational agility and frequency of launches, to refuel inside of a 200x200 orbit and then inject before the orbit decays. Loitering between those two altitudes could be pretty dangerous in the future.
Title: Re: Starship heat shield
Post by: cscott on 07/20/2021 06:11 am
Re shuttle and iss micrometeorite damage:
https://www.nasa.gov/mission_pages/shuttle/multimedia/sts115/MMOD_impact.html

https://www.nasaspaceflight.com/2014/07/iss-managers-evaluating-mmod-radiator/
Title: Re: Starship heat shield
Post by: rakaydos on 07/20/2021 10:17 am
3.  No, just as screwed if it is a lunar or mars mission.

Is it? The tile system on Starship seems much more practical to carry a few spares in case an inspection discovers a problem returning home. And if more than one starship is returning from mars during a synod, it's plausable to dock and abandon an unsalvagable ship, spreading the payload and fuel among the other ships of the return fleet.
Title: Re: Starship heat shield
Post by: Slarty1080 on 07/20/2021 11:41 am
3.  No, just as screwed if it is a lunar or mars mission.

Is it? The tile system on Starship seems much more practical to carry a few spares in case an inspection discovers a problem returning home. And if more than one starship is returning from mars during a synod, it's plausable to dock and abandon an unsalvagable ship, spreading the payload and fuel among the other ships of the return fleet.
The big question is how likely is it that a tile will be broken v just have a small hole drilled through it? A 0.1 inch hole is one thing, a missing tile is something else entirely. Bigger debris that might supply enough energy to break a tile are less likely and might also puncture the surface of the tank below. So the inspect every tile and carry spares back up plan falls somewhere between "it doesn't matter" and "it won't work". Not sure how big this eventuality space is but it might be very small indeed.
Title: Re: Starship heat shield
Post by: AC in NC on 07/20/2021 02:59 pm
The big question is how likely is it that a tile will be broken v just have a small hole drilled through it? A 0.1 inch hole is one thing, a missing tile is something else entirely. Bigger debris that might supply enough energy to break a tile are less likely and might also puncture the surface of the tank below. So the inspect every tile and carry spares back up plan falls somewhere between "it doesn't matter" and "it won't work". Not sure how big this eventuality space is but it might be very small indeed.
Not sure if it's a real problem but I'm less worried about debris than simply fatigue or other stresses causing tile(s) to crack.  I'm not sure Shuttle didn't have some of that.  I'm of the opinion inspection/repair will be very necessary.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 07/20/2021 06:18 pm
[No, the tiles are critical to survival. The mineral wool alone is not a sufficient TPS,

Data?

Mineral wool, while very fragile, has a melting point of 1250-1450 degC depending on which kind.

All sorts here:   https://www.amazon.com/Forge-Insulation/s?k=Forge+Insulation
Title: Re: Starship heat shield
Post by: OTV Booster on 07/20/2021 06:23 pm
[No, the tiles are critical to survival. The mineral wool alone is not a sufficient TPS,

Data?

Mineral wool, while very fragile, has a melting point of 1250-1450 degC depending on which kind.

All sorts here:   https://www.amazon.com/Forge-Insulation/s?k=Forge+Insulation (https://www.amazon.com/Forge-Insulation/s?k=Forge+Insulation)
True for thermal. What about mechanical? It's not a kind environment.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 07/20/2021 06:48 pm
The front flaperons (or whatever they´re called this week) could be a source of high-speed turbulent airflow or debris which could damage the Starship TPS downstream.
ISTM that if there is such a problem they would have discovered that withsimulations months ago.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 07/20/2021 08:49 pm
[No, the tiles are critical to survival. The mineral wool alone is not a sufficient TPS,

Data?

Mineral wool, while very fragile, has a melting point of 1250-1450 degC depending on which kind.

All sorts here:   https://www.amazon.com/Forge-Insulation/s?k=Forge+Insulation (https://www.amazon.com/Forge-Insulation/s?k=Forge+Insulation)
True for thermal. What about mechanical? It's not a kind environment.

Mineral wool is very fragile, mechanical is a huge concern.

Every picture I've seen of damaged tiles, the metal bracket and part of the tile is still intact.   Hopefully enough to hold the wool down long enough to withstand hypersonic flow going by for a few minutes.

With hypersonic flow it's my understanding that a few gaps here and there don't disrupt the flow.   (contrast to something sticking out which does disrupt the flow and causes a lot of heating).   So a missing tile or two shouldn't cause impingment of the flow on the mineral wool.

Testing missing tiles at high speed conditions is something that can be simulated and done in a wind tunnel, though I doubt wind tunnels really enjoy flying debris that would happen if the hypothesis was wrong or a test to failure was done.
Title: Re: Starship heat shield
Post by: Oersted on 07/20/2021 09:33 pm
The front flaperons (or whatever they´re called this week) could be a source of high-speed turbulent airflow or debris which could damage the Starship TPS downstream.
ISTM that if there is such a problem they would have discovered that withsimulations months ago.

They surely did, but there is no way they could go without the front flaperons, so if there is a risk they must be prepared to accept it and/or have mitigating measures in place..
Title: Re: Starship heat shield
Post by: cscott on 07/20/2021 09:51 pm
Which way do you think that airflow goes after hitting the flaps?  There's not really any TPS to damage on the lee side of the ship.
Title: Re: Starship heat shield
Post by: Oersted on 07/20/2021 10:02 pm
Which way do you think that airflow goes after hitting the flaps?  There's not really any TPS to damage on the lee side of the ship.

During ascent it would primarily go straight down below the flaperons, along the edge of the TPS. There would also be shockwave effects travelling across the skin of the ship. SpaceX indubitably had their super-computers simulate the effects, but they will only get real data in flight, obviously.
Title: Re: Starship heat shield
Post by: cscott on 07/20/2021 10:37 pm
Which way do you think that airflow goes after hitting the flaps?  There's not really any TPS to damage on the lee side of the ship.

During ascent it would primarily go straight down below the flaperons, along the edge of the TPS. There would also be shockwave effects travelling across the skin of the ship. SpaceX indubitably had their super-computers simulate the effects, but they will only get real data in flight, obviously.
Ascent environment should be much gentler: the goal is to get out of the atmosphere as soon as possible and before significant acceleration.
Title: Re: Starship heat shield
Post by: sevenperforce on 07/20/2021 11:23 pm
During ascent it would primarily go straight down below the flaperons, along the edge of the TPS. There would also be shockwave effects travelling across the skin of the ship. SpaceX indubitably had their super-computers simulate the effects, but they will only get real data in flight, obviously.
Ascent environment should be much gentler: the goal is to get out of the atmosphere as soon as possible and before significant acceleration.
Agreed. Max-Q is going to happen at either subsonic or low-supersonic speeds; not anywhere near enough to damage these tiles.

I would wager that the kick-flip-land already demonstrated by SN15 put more stress on the tile connections than supersonic airflow at or near Max-Q.
Title: Re: Starship heat shield
Post by: sebk on 07/21/2021 10:27 am
Actually max-q pressures tend to be higher than reentry pressures of non-capsules.

It's usually ~0.35 bar vs ~0.2 bar
Title: Re: Starship heat shield
Post by: edzieba on 07/21/2021 12:22 pm
[No, the tiles are critical to survival. The mineral wool alone is not a sufficient TPS,

Data?

Mineral wool, while very fragile, has a melting point of 1250-1450 degC depending on which kind.

All sorts here:   https://www.amazon.com/Forge-Insulation/s?k=Forge+Insulation
Irrelevant. It does you no good whatsoever as a TPS if the mineral wool survives to >1000°C if it also does not act as an effective insulator and allows the steel behind it to also heat to >1000°C. That melting point is also for nice sedate conditions inside a furnace, not subjected to hypersonic plasma flow.
If the wool alone were sufficient, then it would be far simpler to use just the wool, and sew it down to the surface with mineral fibre thread (such that no steel component protrudes above the wool) rather than bothering with tiles in the first place.
Title: Re: Starship heat shield
Post by: envy887 on 07/21/2021 12:35 pm
[No, the tiles are critical to survival. The mineral wool alone is not a sufficient TPS,

Data?

Mineral wool, while very fragile, has a melting point of 1250-1450 degC depending on which kind.

All sorts here:   https://www.amazon.com/Forge-Insulation/s?k=Forge+Insulation
Irrelevant. It does you no good whatsoever as a TPS if the mineral wool survives to >1000°C if it also does not act as an effective insulator and allows the steel behind it to also heat to >1000°C. That melting point is also for nice sedate conditions inside a furnace, not subjected to hypersonic plasma flow.
If the wool alone were sufficient, then it would be far simpler to use just the wool, and sew it down to the surface with mineral fibre thread (such that no steel component protrudes above the wool) rather than bothering with tiles in the first place.

Are you talking about losing a tile or a few tiles, or losing hundreds? Those are quite different cases. The flowstream will be different, as will the heat sinks.
Title: Re: Starship heat shield
Post by: edzieba on 07/21/2021 12:43 pm
Even one tile is a large hole in the TPS that will result in local heating. Stainless Steel has a higher melting point than Aluminium alloys, but still not high enough to survive a large patch exposed with minimal protection (and the wool offers minimal protection without the tiles over the top). Remember that Starship is a monocoque design, the tank walls are the superstructure, and the vehicle is pressure stabilised. A hole compromises both of those, which is not good news for the dynamic high-load flip manoeuvre performed before landing.

Remember, it's no good just having the wool happily survive >1000°C glowing red hot while also allowing the steel behind it to heat up. It has one job as a TPS: to prevent the steel heating up. If it does not accomplish that, it is worthless as a TPS even if the wool itself survives (in nice sheets gently floating down above the debris cloud). Even the 'low' temperature ceramic fibre mats of STS had a metallic coating rather than just being bare wool to deal with radiant heating and convection. Contact conduction is not the primary heating method during entry, and conduction is where these types of ceramic fibre mats work as insulators.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 07/21/2021 01:22 pm
[No, the tiles are critical to survival. The mineral wool alone is not a sufficient TPS,

Data?

Mineral wool, while very fragile, has a melting point of 1250-1450 degC depending on which kind.

All sorts here:   https://www.amazon.com/Forge-Insulation/s?k=Forge+Insulation
Irrelevant. It does you no good whatsoever as a TPS if the mineral wool survives to >1000°C if it also does not act as an effective insulator and allows the steel behind it to also heat to >1000°C. That melting point is also for nice sedate conditions inside a furnace, not subjected to hypersonic plasma flow.
If the wool alone were sufficient, then it would be far simpler to use just the wool, and sew it down to the surface with mineral fibre thread (such that no steel component protrudes above the wool) rather than bothering with tiles in the first place.

Are you talking about losing a tile or a few tiles, or losing hundreds? Those are quite different cases. The flowstream will be different, as will the heat sinks.

A few tiles, no flow disruption.   Nobody is making claims about ceramic fiber insulation aka rock wool withstanding any sort of plasma flow directly.  Well at least not me.

To give you an idea of the insulation factor of rock wool, look at these ovens and the internal vs. external temperature on page 7 of this heater specification with the use of Watlow ceramic fiber.  at 3 inches thick a 1200 degC chamber is about 190degC on the outside.   BTU K factor of about 1.5.

https://thermalsolutionsoftexas.com/pdfs/heaters/specifications/heater-ceramic-high-temp.pdf
Title: Re: Starship heat shield
Post by: edzieba on 07/21/2021 01:33 pm
To give you an idea of the insulation factor of rock wool, look at these ovens and the internal vs. external temperature on page 7 of this heater specification with the use of Watlow ceramic fiber.  at 3 inches thick a 1200 degC chamber is about 190degC on the outside.   BTU K factor of about 1.5.

https://thermalsolutionsoftexas.com/pdfs/heaters/specifications/heater-ceramic-high-temp.pdf
Insualtion vs. direct conduction (heater bonded to pad) and very low intensity radiation vs. via hypersonic plasma flow are two VERY different regimes. If you want to claim that mineral wool is suitable for TPS, then I would suggest finding some evidence for it, such as hypersonic wind-tunnel tests like those undergone for all existing and proposed TPS types.

For example, that chart in that linked PDF shows performance for heating in the watts/square inch vs. peak temperature. The Watts/square inch range goes up to ~ 40, and shows the material is beyond safe operating limits at 1200°C above 12W/square inch. If it were to represent radiative heating for re-entry regimes, the chart would need to go to above 400 watts/square inch.

Merely having a melting point above 1200°C tells you nothing about its performance as a TPS for re-entry.
Title: Re: Starship heat shield
Post by: eriblo on 07/21/2021 03:40 pm
To give you an idea of the insulation factor of rock wool, look at these ovens and the internal vs. external temperature on page 7 of this heater specification with the use of Watlow ceramic fiber.  at 3 inches thick a 1200 degC chamber is about 190degC on the outside.   BTU K factor of about 1.5.

https://thermalsolutionsoftexas.com/pdfs/heaters/specifications/heater-ceramic-high-temp.pdf
Insualtion vs. direct conduction (heater bonded to pad) and very low intensity radiation vs. via hypersonic plasma flow are two VERY different regimes. If you want to claim that mineral wool is suitable for TPS, then I would suggest finding some evidence for it, such as hypersonic wind-tunnel tests like those undergone for all existing and proposed TPS types.

For example, that chart in that linked PDF shows performance for heating in the watts/square inch vs. peak temperature. The Watts/square inch range goes up to ~ 40, and shows the material is beyond safe operating limits at 1200°C above 12W/square inch. If it were to represent radiative heating for re-entry regimes, the chart would need to go to above 400 watts/square inch.

Merely having a melting point above 1200°C tells you nothing about its performance as a TPS for re-entry.
Since you are arguing against the very thing that InterestedEngineer said he was not suggesting in the part of the post you omitted to quote I will take your post to mean that high-temperature mineral wool can not be used as insulation in any high temperature applications and that its use on Starship is purely aesthetic in nature ;)
Title: Re: Starship heat shield
Post by: edzieba on 07/21/2021 04:23 pm
To give you an idea of the insulation factor of rock wool, look at these ovens and the internal vs. external temperature on page 7 of this heater specification with the use of Watlow ceramic fiber.  at 3 inches thick a 1200 degC chamber is about 190degC on the outside.   BTU K factor of about 1.5.

https://thermalsolutionsoftexas.com/pdfs/heaters/specifications/heater-ceramic-high-temp.pdf
Insualtion vs. direct conduction (heater bonded to pad) and very low intensity radiation vs. via hypersonic plasma flow are two VERY different regimes. If you want to claim that mineral wool is suitable for TPS, then I would suggest finding some evidence for it, such as hypersonic wind-tunnel tests like those undergone for all existing and proposed TPS types.

For example, that chart in that linked PDF shows performance for heating in the watts/square inch vs. peak temperature. The Watts/square inch range goes up to ~ 40, and shows the material is beyond safe operating limits at 1200°C above 12W/square inch. If it were to represent radiative heating for re-entry regimes, the chart would need to go to above 400 watts/square inch.

Merely having a melting point above 1200°C tells you nothing about its performance as a TPS for re-entry.
Since you are arguing against the very thing that InterestedEngineer said he was not suggesting in the part of the post you omitted to quote I will take your post to mean that high-temperature mineral wool can not be used as insulation in any high temperature applications and that its use on Starship is purely aesthetic in nature ;)
Only if you like making up imaginary strawmen to defeat rather than actual discourse.

The presence of a mineral wool backer is to reduce conduction of heat from the backside of the tiles, and allow for variance between the tile back surface and the tank outer wall (and to provide some 'preload' when latching the tiles internal metal frame the the stud-clips, so the tiles can be pressed 'in' ~a mm past the clip latch fingers, then released to seat the latches).

"A few tiles, no flow disruption" are two mutually exclusive statements. If a whole tile is gone and the underlaying mineral wool exposed, that's a major disruption to the TPS, not a small ignorable hole.
Title: Re: Starship heat shield
Post by: envy887 on 07/21/2021 04:27 pm
Even one tile is a large hole in the TPS that will result in local heating. Stainless Steel has a higher melting point than Aluminium alloys, but still not high enough to survive a large patch exposed with minimal protection (and the wool offers minimal protection without the tiles over the top). Remember that Starship is a monocoque design, the tank walls are the superstructure, and the vehicle is pressure stabilised. A hole compromises both of those, which is not good news for the dynamic high-load flip manoeuvre performed before landing.

Remember, it's no good just having the wool happily survive >1000°C glowing red hot while also allowing the steel behind it to heat up. It has one job as a TPS: to prevent the steel heating up. If it does not accomplish that, it is worthless as a TPS even if the wool itself survives (in nice sheets gently floating down above the debris cloud). Even the 'low' temperature ceramic fibre mats of STS had a metallic coating rather than just being bare wool to deal with radiant heating and convection. Contact conduction is not the primary heating method during entry, and conduction is where these types of ceramic fibre mats work as insulators.

The blankets are decent insulators. Shuttle could only use them in low heat flux areas because it was very limited in the total heat pulse it could dump into the vehicle. Starship is much less limited that way, at least in the tanks and engine bay. As the steel heats up it will dump lots of heat to the inside of the tank. At 1000 C it's losing about 100 kW/m^2, which was about the peak heat flux along the Shuttle centerline.

With the tiles, Starship wants to keep the skin temps to about 500C. With a small amount of tile loss, they can probably allow that skin temp to go up by another 400 C in that local area without a catastrophic failure. If the typical surface temps are 1200C, then the blanket only needs to provide a 300 C temperature drop across its thickness, where before the tile+blanket combination were providing at least a 700 C drop. This isn't entirely unreasonable.

In non-pressurized areas, it can probably survive both tile loss and blanket loss, since the structure is redundant and the skin will tend to yield locally and pass that load to the surrounding structure. It won't burn through as long as the skin can pass that heat flux to the interior.
Title: Re: Starship heat shield
Post by: HVM on 07/21/2021 06:53 pm
https://twitter.com/RGVaerialphotos/status/1417655353752399874
More from RGV
Title: Re: Starship heat shield
Post by: eriblo on 07/21/2021 07:19 pm
[...]
The presence of a mineral wool backer is to reduce conduction of heat from the backside of the tiles, and allow for variance between the tile back surface and the tank outer wall (and to provide some 'preload' when latching the tiles internal metal frame the the stud-clips, so the tiles can be pressed 'in' ~a mm past the clip latch fingers, then released to seat the latches).

"A few tiles, no flow disruption" are two mutually exclusive statements. If a whole tile is gone and the underlaying mineral wool exposed, that's a major disruption to the TPS, not a small ignorable hole.
I agree that the mineral wool looks like it is a nice solution to multiple problems: It provides part of the thermal insulation, it is part of the mechanical attachment system for the tiles and it forms a barrier preventing hot gas from getting beneath the tiles.

I also agree that it can not do the whole job by itself even if it is made from similar (or even identical) materials as the bulk of the tiles: It can not support the glass coating which provides the emissivity, chemical resistance/passivity and surface finish needed.

However, I do believe that the margin between "zero refurbishment" and catastrophic failure is large enough (literally many hundreds of degrees as envy887 points out) that it should be possible to fit the loss of a single (or possibly a few) tile(s) in there.

SpaceX has designed the system from the ground up and that they decide the size and thickness of the tiles and the underlying felt. If Starship can not survive a tile loss with the current tile size - but could do it with tiles of say half the size - then they would have to be awfully confident in the probability of tile loss not to sacrifice a few days of installation time and one or two percent of payload mass just to be sure. It is worth noting that they have tried out even larger tiles than the current standard ones...
Title: Re: Starship heat shield
Post by: InterestedEngineer on 07/21/2021 08:10 pm
"A few tiles, no flow disruption" are two mutually exclusive statements. If a whole tile is gone and the underlaying mineral wool exposed, that's a major disruption to the TPS, not a small ignorable hole.

You seem to make quite a lot of assertions without backing them up with any references or calculations.

I'm not an expert in hypersonic flow, but I do understand a bit about water flow across e.g. boat or surfboard surfaces, and small holes do not disrupt the flow in areas where flow doesn't directly impinge the surface.   

And since this very nice overview of reentry mechanics from the FAA compares water flows to hypersonic flows, I feel comfortable in doing so as well.   If you can find a real hypersonic flow reference that discusses gaps in the surface that says otherwise, please post it.  Note that this not the same thing as something sticking out into the flow, which does generate huge amounts of heat.  We're talking about gaps.

https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/cami/library/online_libraries/aerospace_medicine/tutorial/media/III.4.1.7_Returning_from_Space.pdf
Title: Re: Starship heat shield
Post by: InterestedEngineer on 07/21/2021 08:27 pm
For example, that chart in that linked PDF shows performance for heating in the watts/square inch vs. peak temperature. The Watts/square inch range goes up to ~ 40, and shows the material is beyond safe operating limits at 1200°C above 12W/square inch. If it were to represent radiative heating for re-entry regimes, the chart would need to go to above 400 watts/square inch.

Merely having a melting point above 1200°C tells you nothing about its performance as a TPS for re-entry.

A furnace insulator that is emitting heat back into the furnace and not the atmosphere is apples and oranges.

Mr Boltzmann to the rescue.  I have a feeling that T to the fourth power is going to be a major factor in the wool's favor. (and a major factor in the efficiency of furnaces).

Let's compare the emissions of Space Shuttle tiles to that of mineral wool.  Slightly not fair to Starship, as I believe Starship will take a shallower reentry angle than the Shuttle, but let's run with it.

Specifically, I'll pick Superwool Xtra, which is probably the wool SpaceX is using since it is biology friendly and has a reasonably high working temperature of 1450 degC.

Superwool Xtra has a working temperature of 1723 Kelvin, and an estimated emissivity of 0.5 (it's somewhere between 0.4 and 0.6, can't find a definitive number).

E = σεT^4

Which gives an emission at max working temperature of 250KW per square meter.

The Space shuttle tiles are used in areas where the temperature "does not exceed 1260 degC".   So that gives a working max temperature of 1533 Kelvin, with a really nice emissivity of 0.9.

That gives an emission at max working temperature of 282KW per square meter.

So you can see that the Superwool Xtra can shed heat just about as well as Space Shuttle Tiles.  And thus while its mechanical characteristics are terrible compared to Shuttle Tiles, its thermal capabilities are similar.

References:

https://www.nasa.gov/centers/johnson/pdf/584728main_Wings-ch4b-pgs182-199.pdf

https://www.process-heating.com/articles/93193-replacing-refractory-ceramic-fiber-linings

https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/cami/library/online_libraries/aerospace_medicine/tutorial/media/III.4.1.7_Returning_from_Space.pdf
Title: Re: Starship heat shield
Post by: InterestedEngineer on 07/21/2021 08:46 pm
I also agree that it can not do the whole job by itself even if it is made from similar (or even identical) materials as the bulk of the tiles: It can not support the glass coating which provides the emissivity, chemical resistance/passivity and surface finish needed.

emissivity is a bit overrated.  In the Boltzmann equation, T is to the fourth power and emissivity is linear.   I small increase in working temperature of the insulator will cover a lower emissivity quite easily.

SuperWool Xtra also has really good chemical resistance (possibly better than the tiles, for example with water).  I'm pretty sure they have to use some nasty chemicals to make the tiles not absorb stuff like water from the surrounding environment.

But yeah, surface finish and robustness facing Max-Q, SuperWool Xtra isn't going to cut it at all.   The "wool is a backup plan" only works on the way down *once*, you would not want to re-launch with missing tiles.   I'd also be a bit worried about what happens when they drop from hypersonic to supersonic or barely subsonic on the way down with missing tiles, missing tiles might cause the surface to unravel like a zipper when the airflow starts impinging directly on the surface.  Refurbishment would be more expensive than planned.  That's what test flights are for.

Fixing missing tiles at the launchpad is easy, fortunately.
Title: Re: Starship heat shield
Post by: eriblo on 07/21/2021 11:10 pm
I also agree that it can not do the whole job by itself even if it is made from similar (or even identical) materials as the bulk of the tiles: It can not support the glass coating which provides the emissivity, chemical resistance/passivity and surface finish needed.

emissivity is a bit overrated.  In the Boltzmann equation, T is to the fourth power and emissivity is linear.   I small increase in working temperature of the insulator will cover a lower emissivity quite easily.

SuperWool Xtra also has really good chemical resistance (possibly better than the tiles, for example with water).  I'm pretty sure they have to use some nasty chemicals to make the tiles not absorb stuff like water from the surrounding environment.

But yeah, surface finish and robustness facing Max-Q, SuperWool Xtra isn't going to cut it at all.   The "wool is a backup plan" only works on the way down *once*, you would not want to re-launch with missing tiles.   I'd also be a bit worried about what happens when they drop from hypersonic to supersonic or barely subsonic on the way down with missing tiles, missing tiles might cause the surface to unravel like a zipper when the airflow starts impinging directly on the surface.  Refurbishment would be more expensive than planned.  That's what test flights are for.

Fixing missing tiles at the launchpad is easy, fortunately.
Indeed, going hotter will usually beat emissivity but it does become relevant when you want to operate as close to the material limits as possible. The chemical reactivity/passivity is regarding the resistance to attack by dissociated nitrogen and oxygen as well as the catalytic heat transfer (reactive species recombining on the surface). If you can handle the heat the other properties are more of a reuse 100+ times issue and unlikely to be that important in an emergency.

The tiles are just made from insulation fibers that have been chopped up and sintered together - Shuttle tiles were made from pure silica or silica with some aluminoborosilicate and you might be able to do it with a similar composition to SuperWool (silica, alumina and potassium oxide with a bit of other oxides) although I would not be surprised if that mix is designed to prevent the fibers from sticking together at high temperatures.

The problem with water is not chemical, the large surface area just means that significant amount of water can be adsorbed from perspiration or atmospheric moisture. This increases the TPS mass and risks fracturing tiles during cold/hot cycles. How they have (or intend to) solve this problem is actually one of the things I am most curious about!
Title: Re: Starship heat shield
Post by: OTV Booster on 07/22/2021 12:06 am
Even one tile is a large hole in the TPS that will result in local heating. Stainless Steel has a higher melting point than Aluminium alloys, but still not high enough to survive a large patch exposed with minimal protection (and the wool offers minimal protection without the tiles over the top). Remember that Starship is a monocoque design, the tank walls are the superstructure, and the vehicle is pressure stabilised. A hole compromises both of those, which is not good news for the dynamic high-load flip manoeuvre performed before landing.

Remember, it's no good just having the wool happily survive >1000°C glowing red hot while also allowing the steel behind it to heat up. It has one job as a TPS: to prevent the steel heating up. If it does not accomplish that, it is worthless as a TPS even if the wool itself survives (in nice sheets gently floating down above the debris cloud). Even the 'low' temperature ceramic fibre mats of STS had a metallic coating rather than just being bare wool to deal with radiant heating and convection. Contact conduction is not the primary heating method during entry, and conduction is where these types of ceramic fibre mats work as insulators.
Your comment about STS mats having a metallic coating was a memory tickler for the grid overlay we've seen a couple of times on the SS matting. No impact on thermal properties but it might be a hint about mechanical properties.

If the SS mats only give conduction protection (this makes sense) they would have no value as a backup for a lost tile but would give an added measure for conduction through the tiles themselves. Perhaps the mat adds a bit of loading to dampen vibration (discussed earlier). This helps to not loose a tile in the first place, and their thermal property allows the tile thickness to be shaved a bit as a bonus.

There are other ways to loose a tile but every bit helps.


Edit: Edzeiba, ya Ninja'd me
Title: Re: Starship heat shield
Post by: OTV Booster on 07/22/2021 12:25 am
To give you an idea of the insulation factor of rock wool, look at these ovens and the internal vs. external temperature on page 7 of this heater specification with the use of Watlow ceramic fiber.  at 3 inches thick a 1200 degC chamber is about 190degC on the outside.   BTU K factor of about 1.5.

https://thermalsolutionsoftexas.com/pdfs/heaters/specifications/heater-ceramic-high-temp.pdf (https://thermalsolutionsoftexas.com/pdfs/heaters/specifications/heater-ceramic-high-temp.pdf)
Insualtion vs. direct conduction (heater bonded to pad) and very low intensity radiation vs. via hypersonic plasma flow are two VERY different regimes. If you want to claim that mineral wool is suitable for TPS, then I would suggest finding some evidence for it, such as hypersonic wind-tunnel tests like those undergone for all existing and proposed TPS types.

For example, that chart in that linked PDF shows performance for heating in the watts/square inch vs. peak temperature. The Watts/square inch range goes up to ~ 40, and shows the material is beyond safe operating limits at 1200°C above 12W/square inch. If it were to represent radiative heating for re-entry regimes, the chart would need to go to above 400 watts/square inch.

Merely having a melting point above 1200°C tells you nothing about its performance as a TPS for re-entry.
Since you are arguing against the very thing that InterestedEngineer said he was not suggesting in the part of the post you omitted to quote I will take your post to mean that high-temperature mineral wool can not be used as insulation in any high temperature applications and that its use on Starship is purely aesthetic in nature ;)
Only if you like making up imaginary strawmen to defeat rather than actual discourse.

The presence of a mineral wool backer is to reduce conduction of heat from the backside of the tiles, and allow for variance between the tile back surface and the tank outer wall (and to provide some 'preload' when latching the tiles internal metal frame the the stud-clips, so the tiles can be pressed 'in' ~a mm past the clip latch fingers, then released to seat the latches).

"A few tiles, no flow disruption" are two mutually exclusive statements. If a whole tile is gone and the underlaying mineral wool exposed, that's a major disruption to the TPS, not a small ignorable hole.
Loosing a tile is definitely not a good thing and it's reasonable that the wool matting will  give no thermal protection. BUT...  How much impact the loss of one tile will have during the worst of EDL is an open question.


It's been pointed out that as the skin heats the heat will both conduct out radially through the skin (stainless is a crappy conductor, so only a little) and radiatively into the tank. The hotter it gets the more efficient it radiates - that 4th power thing.


I don't think any of us have enough info to say anything about how this will play out other than to say loosing one tile is not as bad as loosing two, especially if they align with the local flow. I'd like to think loosing one tile is not LOM, but I really don't know.
Title: Re: Starship heat shield
Post by: OTV Booster on 07/22/2021 12:37 am
[...]
The presence of a mineral wool backer is to reduce conduction of heat from the backside of the tiles, and allow for variance between the tile back surface and the tank outer wall (and to provide some 'preload' when latching the tiles internal metal frame the the stud-clips, so the tiles can be pressed 'in' ~a mm past the clip latch fingers, then released to seat the latches).

"A few tiles, no flow disruption" are two mutually exclusive statements. If a whole tile is gone and the underlaying mineral wool exposed, that's a major disruption to the TPS, not a small ignorable hole.
I agree that the mineral wool looks like it is a nice solution to multiple problems: It provides part of the thermal insulation, it is part of the mechanical attachment system for the tiles and it forms a barrier preventing hot gas from getting beneath the tiles.

I also agree that it can not do the whole job by itself even if it is made from similar (or even identical) materials as the bulk of the tiles: It can not support the glass coating which provides the emissivity, chemical resistance/passivity and surface finish needed.

However, I do believe that the margin between "zero refurbishment" and catastrophic failure is large enough (literally many hundreds of degrees as envy887 points out) that it should be possible to fit the loss of a single (or possibly a few) tile(s) in there.

SpaceX has designed the system from the ground up and that they decide the size and thickness of the tiles and the underlying felt. If Starship can not survive a tile loss with the current tile size - but could do it with tiles of say half the size - then they would have to be awfully confident in the probability of tile loss not to sacrifice a few days of installation time and one or two percent of payload mass just to be sure. It is worth noting that they have tried out even larger tiles than the current standard ones...
There is a reasonable chance that SX engineers are scratching their heads over just these points. They've got their models, now they need some real world data to see how good the models are. With how fast they move it's even money they have 2-3 alternatives in the bag.


Guess we'll have to wait 'til they light that puppy off to find out.
Title: Re: Starship heat shield
Post by: Sciencefan on 07/24/2021 01:32 pm
Any thought about TPS alignment on the nose cone inside the tent?

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2048017;image
Title: Re: Starship heat shield
Post by: sevenperforce on 07/24/2021 02:16 pm
Any thought about TPS alignment on the nose cone inside the tent?

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2048017;image
Moving from top to bottom, the rows of tile studs are as follows:

Down
Up x2
Down
Up x2
Down
Up x4
Down
Up x3
Down
Up x4
Down
Up x5
Down
Up x11

There is an alignment discontinuity between each downward-pointing tile stud row and the upward-pointing tile stud row directly above it.

It feels like the most straightforward approach will be to simply use pentagons with a flat side for each of those misaligned rows, but we will see. The vertical spacing would seem to suggest it.

Assuming that this is the nosecone for SN20, I wonder if we will see glue-on tiles for the very tip or if we will see a thicker single-piece nosecone.
Title: Re: Starship heat shield
Post by: eriblo on 07/24/2021 02:56 pm
Any thought about TPS alignment on the nose cone inside the tent?

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2048017;image
I was just looking at the same thing but got ninja'd by sevenperforce ;) It looks like it follows on what we have seen before with studs in an inverted standard triangle pattern with most rows pointing "up" (red) and a few pointing "down" (green). We can see 38 rows with rows 1, 4, 7, 12, 16, 21 and 27 from the top being "down" with the pattern suggesting a seam with changing spacing above each "down" row. There is also a few missing studs along the center line of the image which might be the mid line of the nose cone: 2 triangles on row 8 and 1 triangle on rows 16 and 33. This might not be related to the heat shield directly but to allow for mounting/welding something on the inside at a later stage.

It is hard to tell if all the standard rows are the same tiles (with varying gaps) or not - the horizontal spacing changes but it is hard to tell if the triangles are the same size. The tiles might as suggested earlier not be sensitive to the exact radial position of the studs due to having slots in the brackets (rather than holes).
Title: Re: Starship heat shield
Post by: cscott on 07/24/2021 04:34 pm
The spacing of the "down" rows is about what I would expect for intervals where "dropping a tile" is necessary as the radius shrinks.  Less frequently at the bottom, more frequently near the nose.

I agree with previous posters that the down rows are.probably where we get pentagons flat-to-flat to let the tiling pattern slip to adjust to the new radius.

I also find the missing studs on the centerline interesting.  My first thought was that we'd get custom tiles there to break up the horizontal channels, but the missing studs don't seem to match up with the "down" rows in the way I'd expect.  I'll go with the "internal features on the centerline which require special support" suggestion for now.
Title: Re: Starship heat shield
Post by: sevenperforce on 07/24/2021 05:39 pm
The spacing of the "down" rows is about what I would expect for intervals where "dropping a tile" is necessary as the radius shrinks.  Less frequently at the bottom, more frequently near the nose.

I agree with previous posters that the down rows are.probably where we get pentagons flat-to-flat to let the tiling pattern slip to adjust to the new radius.
It is interesting that there is a four-row followed by a three-row followed by a four-row. I wonder if that three-row and everything beneath is standard-hex and the ones above it are all tapered tiles or something. Or perhaps it is just how the math worked out.

Quote
I also find the missing studs on the centerline interesting.  My first thought was that we'd get custom tiles there to break up the horizontal channels, but the missing studs don't seem to match up with the "down" rows in the way I'd expect.  I'll go with the "internal features on the centerline which require special support" suggestion for now.
Are they approximately at the lift points? Because that’s a good reason to have a gap. Ultimately they will have to come up with a different way to lift for rapid reusability, but for now it seems that they are going to stick with the same internal-member lift point approach.
Title: Re: Starship heat shield
Post by: jthygesen on 07/29/2021 08:44 am
https://twitter.com/StarshipGazer/status/1420464483366051848

A lot going on these days. In the photos from StarShip Gazer we can see the nose cone starting to be covered in heat shielding material. But what exactly are they doing? The nose appears black (perhaps just paint or a whole new type of shielding?) and they are attaching felt on top of this black part of the nose cone. Are we seeing new materials or just the part before they attach tiles?
Title: Re: Starship heat shield
Post by: simon82 on 07/29/2021 08:55 am
https://twitter.com/StarshipGazer/status/1420464483366051848

A lot going on these days. In the photos from StarShip Gazer we can see the nose cone starting to be covered in heat shielding material. But what exactly are they doing? The nose appears black (perhaps just paint or a whole new type of shielding?) and they are attaching felt on top of this black part of the nose cone. Are we seeing new materials or just the part before they attach tiles?

I think it's a part of another nosecone that just happens to be placed in a way that it seems part of the SN20 one.
Title: Re: Starship heat shield
Post by: Slarty1080 on 07/29/2021 08:58 am
https://twitter.com/StarshipGazer/status/1420464483366051848

A lot going on these days. In the photos from StarShip Gazer we can see the nose cone starting to be covered in heat shielding material. But what exactly are they doing? The nose appears black (perhaps just paint or a whole new type of shielding?) and they are attaching felt on top of this black part of the nose cone. Are we seeing new materials or just the part before they attach tiles?
What appears to be paint might actually just be shadow due to the curvature. As for the felt it looks like its some sort of test and rather haphazard. Irregular patches almost as if they were going to use a giant form of paper mache in felt!
Title: Re: Starship heat shield
Post by: ETurner on 07/29/2021 10:53 am
https://twitter.com/StarshipGazer/status/1420464483366051848 (https://twitter.com/StarshipGazer/status/1420464483366051848)

A lot going on these days. In the photos from StarShip Gazer we can see the nose cone starting to be covered in heat shielding material. But what exactly are they doing? The nose appears black (perhaps just paint or a whole new type of shielding?) and they are attaching felt on top of this black part of the nose cone. Are we seeing new materials or just the part before they attach tiles?
What appears to be paint might actually just be shadow due to the curvature. As for the felt it looks like its some sort of test and rather haphazard. Irregular patches almost as if they were going to use a giant form of paper mache in felt!
The reflection of the door looks pretty faint, as if from a dark, non-metallic surface.
Title: Re: Starship heat shield
Post by: RoboGoofers on 07/29/2021 01:58 pm
So there's definitely a straight horizontal seam. there also appears to be some diamond shaped tiles, though  it also kinda looks like hex tiles that are just broken where there's a dimple in the skin.
There's also that black liner inside the hinge, which is interesting.
The felt insulation looks very haphazard? they seem to be using some particularly small offcuts in places. waste not, want not?

Pics from Mary: https://forum.nasaspaceflight.com/index.php?topic=52398.msg2269074#msg2269074
Title: Re: Starship heat shield
Post by: eriblo on 07/29/2021 02:29 pm
So there's definitely a straight horizontal seam. there also appears to be some diamond shaped tiles, though  it also kinda looks like hex tiles that are just broken where there's a dimple in the skin.
There's also that black liner inside the hinge, which is interesting.
The felt insulation looks very haphazard? they seem to be using some particularly small offcuts in places. waste not, want not?

Pics from Mary: https://forum.nasaspaceflight.com/index.php?topic=52398.msg2269074#msg2269074
It sure looks like they have implemented several of our suggestions ;) Now we just have to wait for a better angle to settle the question about multiple tile types or just a few with gaps...

The black surface coating matches the one on the corresponding surfaces on the aft fins. Makes sense as sealing the hinged is a known major challenge. The exact shapes of the insulation is probably irrelevant - looks like they just do what is needed to cover the curved surface and trim the the excess later.

I wonder if there will be a separate panel or just the thicker adhesively attached tiles around the uncovered RCS nozzles and especially the lifting point ahead of the fin. Will some kind of hatch be needed or is it enough to have a deep recession?
Title: Re: Starship heat shield
Post by: Adriano on 07/29/2021 02:32 pm
Wild guess. They have a computer generated design of nose tiling. they divided the design in areas and cut the white felt in the shape of the areas. Perhaps the cutting was done by computer and included the holes of the attachment pins. Now they are applying the felt to the nose to test the fit. The patches are small because the felt is flat and needs to be stretched to match the curvature of the nose. Next step, they will have computer generated tiles for each felt area and they will test the fit of the tiles. As the entire process (cutting felt and cutting tiles) is computer generated, we may see a great variety of shapes. Possibly the tiles from each area are individually cut from material blanks matching the curvature of the nose (we saw precisely fitting tiles on the flaps) and they will prefer random shapes instead of trying to limit the variety of shapes of individual tiles on the nose. As I said, wild guess! But Taylor’s use a similar process when designing clothing…
Title: Re: Starship heat shield
Post by: Slarty1080 on 07/29/2021 03:54 pm
Wild guess. They have a computer generated design of nose tiling. they divided the design in areas and cut the white felt in the shape of the areas. Perhaps the cutting was done by computer and included the holes of the attachment pins. Now they are applying the felt to the nose to test the fit. The patches are small because the felt is flat and needs to be stretched to match the curvature of the nose. Next step, they will have computer generated tiles for each felt area and they will test the fit of the tiles. As the entire process (cutting felt and cutting tiles) is computer generated, we may see a great variety of shapes. Possibly the tiles from each area are individually cut from material blanks matching the curvature of the nose (we saw precisely fitting tiles on the flaps) and they will prefer random shapes instead of trying to limit the variety of shapes of individual tiles on the nose. As I said, wild guess! But Taylor’s use a similar process when designing clothing…
I was going to say "it all looks very haphazard" but I think there is method in the madness there. Looking at the photo above again in close up the felt areas mostly cover up to the edge and just beyond the studded areas. The odd shaped lines are probably due to the boundary line on the edge of the heat shield combined with other obstructions like the RCS vents. I assume they will just trim the excess felt after the tiles have been applied. It doesn't look as through the boundary line is going to be a neat "half way" demarcation line.
Title: Re: Starship heat shield
Post by: tenkendojo on 07/29/2021 03:55 pm
Wild guess. They have a computer generated design of nose tiling. they divided the design in areas and cut the white felt in the shape of the areas. Perhaps the cutting was done by computer and included the holes of the attachment pins. Now they are applying the felt to the nose to test the fit. The patches are small because the felt is flat and needs to be stretched to match the curvature of the nose. Next step, they will have computer generated tiles for each felt area and they will test the fit of the tiles. As the entire process (cutting felt and cutting tiles) is computer generated, we may see a great variety of shapes. Possibly the tiles from each area are individually cut from material blanks matching the curvature of the nose (we saw precisely fitting tiles on the flaps) and they will prefer random shapes instead of trying to limit the variety of shapes of individual tiles on the nose. As I said, wild guess! But Taylor’s use a similar process when designing clothing…

If you zoom in on the precious nosecone pic you will notice there's a great range of insulation blanket sizes and shapes. Many of the nosecone insulation blanket pieces are quite large and seem to have covered curved surfaces just fine. Those smaller pieces are likely used as gap fillers and cropping around RCS nozzles and other spots shouldn't be covered.
Title: Re: Starship heat shield
Post by: sevenperforce on 07/29/2021 04:25 pm
So there's definitely a straight horizontal seam. there also appears to be some diamond shaped tiles, though  it also kinda looks like hex tiles that are just broken where there's a dimple in the skin.
Closeups attached.

There's definitely a straight seam, which settles that question definitively.

I'm not sure if those are diamond-shaped gap fillers or not. It really does look like fractured hex tiles to me.
Title: Re: Starship heat shield
Post by: RoboGoofers on 07/29/2021 08:27 pm
Yep lots of broken tiles. maybe this is just a practice nosecone?

Photo from Mary
https://forum.nasaspaceflight.com/index.php?topic=52398.msg2269397#msg2269397
Title: Re: Starship heat shield
Post by: xvel on 07/29/2021 08:36 pm
I bet it will go to the scrapyard

(51% sure)
Title: Re: Starship heat shield
Post by: cscott on 07/30/2021 01:18 am
Seems to be further between straight line seams than I'd expect based on my rough experiments with nose cone curvature.  So maybe a combination of tapered hexes and pentagons.  Each tapered hex shape would give you a conical section, and you approximate the nose cone shape with a series of conical sections, joined by straight line seams bordered by the pentagons.

That yields 2 tile shapes per conical section, more or less.  Which isn't quite as few as "2 tile shapes total, with a seam every row or two or three" but isn't as many as "a unique tapered tile shape per row".

2 tile shapes * number of conical sections, tune the latter # until the CFD is just barely happy with the smoothness.
Title: Re: Starship heat shield
Post by: Hog on 07/30/2021 02:12 am
I also agree that it can not do the whole job by itself even if it is made from similar (or even identical) materials as the bulk of the tiles: It can not support the glass coating which provides the emissivity, chemical resistance/passivity and surface finish needed.

emissivity is a bit overrated.  In the Boltzmann equation, T is to the fourth power and emissivity is linear.   I small increase in working temperature of the insulator will cover a lower emissivity quite easily.

SuperWool Xtra also has really good chemical resistance (possibly better than the tiles, for example with water).  I'm pretty sure they have to use some nasty chemicals to make the tiles not absorb stuff like water from the surrounding environment.

But yeah, surface finish and robustness facing Max-Q, SuperWool Xtra isn't going to cut it at all.   The "wool is a backup plan" only works on the way down *once*, you would not want to re-launch with missing tiles.   I'd also be a bit worried about what happens when they drop from hypersonic to supersonic or barely subsonic on the way down with missing tiles, missing tiles might cause the surface to unravel like a zipper when the airflow starts impinging directly on the surface.  Refurbishment would be more expensive than planned.  That's what test flights are for.

Fixing missing tiles at the launchpad is easy, fortunately.
Indeed, going hotter will usually beat emissivity but it does become relevant when you want to operate as close to the material limits as possible. The chemical reactivity/passivity is regarding the resistance to attack by dissociated nitrogen and oxygen as well as the catalytic heat transfer (reactive species recombining on the surface). If you can handle the heat the other properties are more of a reuse 100+ times issue and unlikely to be that important in an emergency.

The tiles are just made from insulation fibers that have been chopped up and sintered together - Shuttle tiles were made from pure silica or silica with some aluminoborosilicate and you might be able to do it with a similar composition to SuperWool (silica, alumina and potassium oxide with a bit of other oxides) although I would not be surprised if that mix is designed to prevent the fibers from sticking together at high temperatures.

The problem with water is not chemical, the large surface area just means that significant amount of water can be adsorbed from perspiration or atmospheric moisture. This increases the TPS mass and risks fracturing tiles during cold/hot cycles. How they have (or intend to) solve this problem is actually one of the things I am most curious about!

Similar waterproofing as Shuttle used.
Title: Re: Starship heat shield
Post by: RoboGoofers on 07/30/2021 02:37 am
Yep lots of broken tiles. maybe this is just a practice nosecone?

Photo from Mary
https://forum.nasaspaceflight.com/index.php?topic=52398.msg2269397#msg2269397
also, note the studs on the windward side of the fin fairing. No studs at the transition, though.

I'm also very curious what the black mesh is composed of and its purpose. I assumed it was for restraint but the felt seems to stay on just fine in the places without it.
Title: Re: Starship heat shield
Post by: cscott on 07/30/2021 02:54 am
(probably 3 shapes per conical section: if the hexes are tapered the "up pentagon" won't be identical to the "down pentagon".)
Title: Re: Starship heat shield
Post by: Nevyn72 on 07/30/2021 03:49 am
While having a closer look at all the broken tiles on the nosecone picture taken by Mary (BocaChicaGal), linked below, I saw what I though was a small sized tile in freefall roughly below the work platform beside the nosecone.

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2049191;image

What do you think?
Am I seeing things?

Title: Re: Starship heat shield
Post by: Nostromo93 on 07/30/2021 04:22 am
While having a closer look at all the broken tiles on the nosecone picture taken by Mary (BocaChicaGal), linked below, I saw what I though was a small sized tile in freefall roughly below the work platform beside the nosecone.

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2049191;image

What do you think?
Am I seeing things?

I think it's a regular tile (blue outline) that has cracked, giving off different shades
Title: Re: Starship heat shield
Post by: eriblo on 07/30/2021 07:42 am
[...]
The problem with water is not chemical, the large surface area just means that significant amount of water can be adsorbed from perspiration or atmospheric moisture. This increases the TPS mass and risks fracturing tiles during cold/hot cycles. How they have (or intend to) solve this problem is actually one of the things I am most curious about!

Similar waterproofing as Shuttle used.
That would be the worst case scenario as the waterproofing on the Shuttle burnt off during reentry and required each individual tile to be injected with 2ml of dimethylethoxysilane by hand after each flight. That would probably take about as long as installing the tiles in the first place...
Title: Re: Starship heat shield
Post by: edzieba on 07/30/2021 09:59 am
Or take a page out of the early days of Shuttle: use off-the-shelf Scotchguard. It was an effective spray-on waterproofing agent, but degraded the RTV silicone adhesive. Starship is using clips for almost all its tile coverage, so that's a nonissue there. DMES or other waterproofing agent injection can be reserved for the few areas with bonded tiles (so far, seen on the flap leading edges and pivot roots).
Title: Re: Starship heat shield
Post by: JCopernicus on 07/30/2021 12:58 pm
The felt doesn't look haphazard it looks like a AI derived mesh.
Title: Re: Starship heat shield
Post by: xvel on 07/30/2021 02:34 pm
And those broken tiles aren't broken, but have AI derived shape which improves the flow of midichlorians.
Title: Re: Starship heat shield
Post by: dwheeler on 07/30/2021 03:22 pm
[...]
The problem with water is not chemical, the large surface area just means that significant amount of water can be adsorbed from perspiration or atmospheric moisture. This increases the TPS mass and risks fracturing tiles during cold/hot cycles. How they have (or intend to) solve this problem is actually one of the things I am most curious about!

Similar waterproofing as Shuttle used.
That would be the worst case scenario as the waterproofing on the Shuttle burnt off during reentry and required each individual tile to be injected with 2ml of dimethylethoxysilane by hand after each flight. That would probably take about as long as installing the tiles in the first place...

And I think in general the difference between tiling over cryogenic tanks vs the Shuttle orbiter needs to be appreciated. 
Title: Re: Starship heat shield
Post by: Hog on 07/30/2021 04:08 pm
[...]
The problem with water is not chemical, the large surface area just means that significant amount of water can be adsorbed from perspiration or atmospheric moisture. This increases the TPS mass and risks fracturing tiles during cold/hot cycles. How they have (or intend to) solve this problem is actually one of the things I am most curious about!

Similar waterproofing as Shuttle used.
That would be the worst case scenario as the waterproofing on the Shuttle burnt off during reentry and required each individual tile to be injected with 2ml of dimethylethoxysilane by hand after each flight. That would probably take about as long as installing the tiles in the first place...
Agreed, esp. about the labour intensive syringe injection of waterproofing.  Shuttle tiles in the early days could be installed by an experienced installer at the rate of 1.8 tiles per person per week. Takes a while as there were between 28,000-32,000 tiles per orbiter vehicle in the early days.  OV-102 Columbia was delivered to KSC with tile simulators installed in place of real tiles for the delivery/ferry flight atop a Shuttle Carrier Aircraft.  The "zipper-effect" of tile loss was feared during delivery.  But it works and works now-as that technology has been quite well developed by NASA.  The goal is quick turnaround, but a more immediate goal is to get Starship/Starbooster off the ground  I'm sure Elon and his posse' have quite a list of Starship "Block-II" ideas and I'd bet the farm that the Starship TPS is on that list.

Waterproofing that NASA used during STS(Space Transportation System=space shuttle)was dimethyldiethoxysilane, Space-X will be using methyltrimethoxysilane to waterproof their tiles. As discussed and providing great illumination on the exact composition of said tiles.  thank you edzieba!
Reply #1719 on: 07/19/2021 10:24 am
https://forum.nasaspaceflight.com/index.php?topic=50748.1700

No debris shedding on launch, but the structure and method for manufacture (described in one of the environmental docs for the Astronaut Blvd. site) are almost identical to HRSI: sintered pure silica fibres, reaction-cured Borosilicate glass coating, then impregnated with acetic acid & a waterproofing agent. The only change is the waterproofing agent (methyl-trimethoxy silane rather than dimethylethoxy silane) and the shape.
Title: Re: Starship heat shield
Post by: StormtrooperJoe on 07/30/2021 07:34 pm
The felt doesn't look haphazard it looks like a AI derived mesh.
I can't find it, but I saw on twitter a day or two ago that someone (supposedly) used CFD to create a render of what the heatshield might look like, and it matched SpaceX's current design perfectly.
Title: Re: Starship heat shield
Post by: Slarty1080 on 07/30/2021 08:15 pm
The felt doesn't look haphazard it looks like a AI derived mesh.
I can't find it, but I saw on twitter a day or two ago that someone (supposedly) used CFD to create a render of what the heatshield might look like, and it matched SpaceX's current design perfectly.
And what does the full heat shield look like?
Title: Re: Starship heat shield
Post by: livingjw on 07/30/2021 08:19 pm
[...]
The problem with water is not chemical, the large surface area just means that significant amount of water can be adsorbed from perspiration or atmospheric moisture. This increases the TPS mass and risks fracturing tiles during cold/hot cycles. How they have (or intend to) solve this problem is actually one of the things I am most curious about!

Similar waterproofing as Shuttle used.
That would be the worst case scenario as the waterproofing on the Shuttle burnt off during reentry and required each individual tile to be injected with 2ml of dimethylethoxysilane by hand after each flight. That would probably take about as long as installing the tiles in the first place...

And I think in general the difference between tiling over cryogenic tanks vs the Shuttle orbiter needs to be appreciated.

Cryo-pumping comes to mind. Cryo-tanks cause condensation and freezing of water next to the tank in the blanket.

John
Title: Re: Starship heat shield
Post by: StormtrooperJoe on 07/30/2021 09:09 pm
The felt doesn't look haphazard it looks like a AI derived mesh.
I can't find it, but I saw on twitter a day or two ago that someone (supposedly) used CFD to create a render of what the heatshield might look like, and it matched SpaceX's current design perfectly.
And what does the full heat shield look like?

https://twitter.com/AlexSvanArt/status/1420773434305437698?s=20

Only shows the nose regretably
Title: Re: Starship heat shield
Post by: Slarty1080 on 07/30/2021 09:21 pm
The felt doesn't look haphazard it looks like a AI derived mesh.
I can't find it, but I saw on twitter a day or two ago that someone (supposedly) used CFD to create a render of what the heatshield might look like, and it matched SpaceX's current design perfectly.
And what does the full heat shield look like?

https://twitter.com/AlexSvanArt/status/1420773434305437698?s=20

Only shows the nose regretably
And with most of the tiles missing
Title: Re: Starship heat shield
Post by: cscott on 07/30/2021 11:29 pm
I think the CFD was supposed to show the *extent* (ie perimeter) of the heat shield, based on computed heating.  Results seem pretty good in that light.
Title: Re: Starship heat shield
Post by: OTV Booster on 07/31/2021 01:06 am
Or take a page out of the early days of Shuttle: use off-the-shelf Scotchguard. It was an effective spray-on waterproofing agent, but degraded the RTV silicone adhesive. Starship is using clips for almost all its tile coverage, so that's a nonissue there. DMES or other waterproofing agent injection can be reserved for the few areas with bonded tiles (so far, seen on the flap leading edges and pivot roots).
Maybe the scotch guard can use a different vehicle? Surely the scotch guard itself isn't a solvent. It would be a great coup if it works.
Title: Re: Starship heat shield
Post by: pjm1 on 07/31/2021 07:21 am
Maybe just pop some plastic wrap around the whole startship once the tiles are fitted… stuff is so annoying in sticking to itself when you don’t want it to, it might even survive max-q until it’s burnt off on reentry

/s
Title: Re: Starship heat shield
Post by: Cheapchips on 07/31/2021 08:22 am
Everyday Astronaut's cone pic show's two 'horizonal line breaks' so far.  The aerocover has squarish tiles along the cone edge. Presumably more than one square tiletype, as the curve increases as you go higher?

https://twitter.com/Erdayastronaut/status/1421374728581832710?


Title: Re: Starship heat shield
Post by: cscott on 07/31/2021 11:43 am
The "squarish" tiles are what we call "pentagons" here.  They are a "home plate" shape.
Title: Re: Starship heat shield
Post by: Cheapchips on 07/31/2021 12:12 pm
The "squarish" tiles are what we call "pentagons" here.  They are a "home plate" shape.

 :) Wasn't refering to pentagons at the horizontal lines. The 'squarish' tiles I was referring to were the mild trapesoids along the edge of the fin aero covers, where it joins the cone.  Pretty sure they don't qualify as pentagons due to a side shortage.
Title: Re: Starship heat shield
Post by: JCopernicus on 07/31/2021 02:50 pm
The felt doesn't look haphazard it looks like a AI derived mesh.
I can't find it, but I saw on twitter a day or two ago that someone (supposedly) used CFD to create a render of what the heatshield might look like, and it matched SpaceX's current design perfectly.


Alot of people probably laughed at my post. I can't wait until the final production of the towers/catchers/etc are AI/generative driven for structure and manufacturing.
Title: Re: Starship heat shield
Post by: Blueshift on 07/31/2021 04:28 pm
https://twitter.com/ErcXspace/status/1421455365867294722

Seems they need to take a slower ascent profile with the grid fins out. Has the side effect to reduce aero loads on the tiles in denser parts of the atmosphere.

To be honest I was worried they would stay in place at max Q. Still think they have some iterations with the TPS tiles ahead.
Title: Re: Starship heat shield
Post by: xvel on 08/01/2021 01:16 am
Alot of people probably laughed at my post. I can't wait until the final production of the towers/catchers/etc are AI/generative driven for structure and manufacturing.

Buzzword driven? I don't think so...
Back to the topic, on the curved part of the nose the felt under the lowest row of tiles is cut to size and there are no clips welded under, even if the clips will be welded later, the felt probably would not be cut to size if the tiles were to be installed, what is supposed to go there?
Title: Re: Starship heat shield
Post by: Keldor on 08/01/2021 02:32 am
https://twitter.com/ErcXspace/status/1421455365867294722

Seems they need to take a slower ascent profile with the grid fins out. Has the side effect to reduce aero loads on the tiles in denser parts of the atmosphere.

To be honest I was worried they would stay in place at max Q. Still think they have some iterations with the TPS tiles ahead.

Or maybe it's easier to install the fins in the deployed position?  You know, so they can reach the points they need to weld?   :P

Also, can we avoid mixing photos and artist concept renders?  They can be hard to tell apart to the casual viewer.  I know this is a twitter post from someone who may never read this, but still.
Title: Re: Starship heat shield
Post by: xvel on 08/01/2021 02:37 am
Also Elon confirmed that they are not foldable
Also gridfin discussion is offtopic
Title: Re: Starship heat shield
Post by: guckyfan on 08/01/2021 10:24 am
Also Elon confirmed that they are not foldable
Also gridfin discussion is offtopic

But they can be put vertical, which should minimize drag.
Title: Re: Starship heat shield
Post by: rakaydos on 08/01/2021 11:13 am
Also Elon confirmed that they are not foldable
Also gridfin discussion is offtopic

But they can be put vertical, which should minimize drag.
should it? The fins are pretty broad, and the face of the fins is mostly holes. Which face produces less drag is not immediately obvous.
Title: Re: Starship heat shield
Post by: FutureSpaceTourist on 08/01/2021 12:41 pm
twitter.com/ringwatchers/status/1421674302173294594

Quote
Two things...

1. They seem to be increasing the tile size depending on how high a tile is on the nosecone.

2. Square tiles. That's all.

Image credit to @BocaChicaGal  with @NASASpaceflight

https://twitter.com/madeinmurlough/status/1421750411921346564

Quote
They probably start with the same size tile at the bottom of each section, and get *smaller* going up each section to fit the curvature. Then when they reset at the straight edges, the larger tiles starting again makes you think they're getting bigger going up.

twitter.com/mr__pine/status/1421759231640879110

Quote
They do! I have measured three different tile sizes in images, getting smaller towards the top and resetting at the edges

https://twitter.com/mr__pine/status/1421774506742386690

Quote
This is what I measured. Looks like three different sizes to me. There are six more tiles below to the next edge so three tiles per section fit
Title: Re: Starship heat shield
Post by: ETurner on 08/01/2021 01:47 pm
twitter.com/ringwatchers/status/1421674302173294594

Quote
Two things...

1. They seem to be increasing the tile size depending on how high a tile is on the nosecone.

2. Square tiles. That's all.

Image credit to @BocaChicaGal  with @NASASpaceflight

https://twitter.com/madeinmurlough/status/1421750411921346564 (https://twitter.com/madeinmurlough/status/1421750411921346564)

Quote
They probably start with the same size tile at the bottom of each section, and get *smaller* going up each section to fit the curvature. Then when they reset at the straight edges, the larger tiles starting again makes you think they're getting bigger going up.

twitter.com/mr__pine/status/1421759231640879110

Quote
They do! I have measured three different tile sizes in images, getting smaller towards the top and resetting at the edges

https://twitter.com/mr__pine/status/1421774506742386690 (https://twitter.com/mr__pine/status/1421774506742386690)

Quote
This is what I measured. Looks like three different sizes to me. There are six more tiles below to the next edge so three tiles per section fit
If you allow straight line seams and a few more tile types, this is the clean solution. Very nice.
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/01/2021 01:54 pm
If you allow straight line seams and a few more tile types, this is the clean solution. Very nice.
Yes it did appear at first that straight lines were not allowed, but they are so yes 3 tile types and a few straight line runs seems to do the trick. Lets hope it works!
Title: Re: Starship heat shield
Post by: xvel on 08/01/2021 02:19 pm
should it? The fins are pretty broad, and the face of the fins is mostly holes. Which face produces less drag is not immediately obvous.

This is offtopic but should be clarified, drag in rockets matters most at max-Q which happens to be at transsonic speeds, grid fins at transsonic speeds behaves more like flat plates than a bunch of holes. What they are doing is most likely very far from optimal, but maybe it's good enough for no payload "barely orbital" test.
Title: Re: Starship heat shield
Post by: sevenperforce on 08/01/2021 05:28 pm
I think I figured out how they did it, and it's ingenious, and I can't believe I didn't think of it.

No tapered tiles, just narrower tiles.

I went through and did a pixel count on the average width of each tile in each row, and this is how the math seems to work out.

Just two extra tile types, plus the pentagonal truncations.
Title: Re: Starship heat shield
Post by: hallmh on 08/01/2021 08:01 pm
If you allow straight line seams and a few more tile types, this is the clean solution. Very nice.
Yes it did appear at first that straight lines were not allowed, but they are so yes 3 tile types and a few straight line runs seems to do the trick. Lets hope it works!

We were told that straight lines were to be avoided, to prevent hot gases gaining velocity in a long seam. That makes sense, but it now appears that latitudinal straight lines are fine.

I'm surprised, as I'd expect a Starship doing a belly-flop reentry would have streamlines going that way; but I'm happy to be wrong.
Title: Re: Starship heat shield
Post by: HVM on 08/01/2021 08:52 pm
https://www.youtube.com/watch?v=tnBG-E8TpEQ
Masking tape or duct?
Title: Re: Starship heat shield
Post by: xvel on 08/01/2021 09:22 pm
The tiles were falling off, so they taped them.
I know a guy who knows a guy and he told me.
Title: Re: Starship heat shield
Post by: sevenperforce on 08/01/2021 09:51 pm
If you allow straight line seams and a few more tile types, this is the clean solution. Very nice.
Yes it did appear at first that straight lines were not allowed, but they are so yes 3 tile types and a few straight line runs seems to do the trick. Lets hope it works!

We were told that straight lines were to be avoided, to prevent hot gases gaining velocity in a long seam. That makes sense, but it now appears that latitudinal straight lines are fine.

I'm surprised, as I'd expect a Starship doing a belly-flop reentry would have streamlines going that way; but I'm happy to be wrong.
My best guess is that during peak re-entry, Starship won't be doing a pure belly-flop so much as a lifting-body re-entry, so there will be a significant angle of attack which will mean the plasma flow path is downward relative to latitudinal straight lines.

Very crude drawing of said re-entry and flow paths attached. You can see that longitudinal straight lines would be in the flow path but latitudinal ones are not.

Once Starship is through re-entry, it pitches farther forward to nearly a full belly-flop to achieve the highest possible drag and thus get the lowest terminal velocity before the kick-flip.
Title: Re: Starship heat shield
Post by: Redclaws on 08/01/2021 10:03 pm
If you allow straight line seams and a few more tile types, this is the clean solution. Very nice.
Yes it did appear at first that straight lines were not allowed, but they are so yes 3 tile types and a few straight line runs seems to do the trick. Lets hope it works!

We were told that straight lines were to be avoided, to prevent hot gases gaining velocity in a long seam. That makes sense, but it now appears that latitudinal straight lines are fine.

I'm surprised, as I'd expect a Starship doing a belly-flop reentry would have streamlines going that way; but I'm happy to be wrong.
My best guess is that during peak re-entry, Starship won't be doing a pure belly-flop so much as a lifting-body re-entry, so there will be a significant angle of attack which will mean the plasma flow path is downward relative to latitudinal straight lines.

Very crude drawing of said re-entry and flow paths attached. You can see that longitudinal straight lines would be in the flow path but latitudinal ones are not.

Once Starship is through re-entry, it pitches farther forward to nearly a full belly-flop to achieve the highest possible drag and thus get the lowest terminal velocity before the kick-flip.

Why wouldn’t the plasma flow around the sides?  Why would the flow be only vertical?
Title: Re: Starship heat shield
Post by: sevenperforce on 08/01/2021 10:50 pm
My best guess is that during peak re-entry, Starship won't be doing a pure belly-flop so much as a lifting-body re-entry, so there will be a significant angle of attack which will mean the plasma flow path is downward relative to latitudinal straight lines.

Very crude drawing of said re-entry and flow paths attached. You can see that longitudinal straight lines would be in the flow path but latitudinal ones are not.

Once Starship is through re-entry, it pitches farther forward to nearly a full belly-flop to achieve the highest possible drag and thus get the lowest terminal velocity before the kick-flip.

Why wouldn’t the plasma flow around the sides?  Why would the flow be only vertical?
Oh, plasma will absolutely flow around the sides during re-entry. I mean that the flow path around the sides will be at an angle. If you look at the pattern of heat shield tiles "spilling" around the flaps, you'll see that it forms an oblique angle to the flap root axis.

But this flow path will be at an angle to any latitudinal seams, which would seem to explain why they will be okay.
Title: Re: Starship heat shield
Post by: Redclaws on 08/02/2021 02:03 am
My best guess is that during peak re-entry, Starship won't be doing a pure belly-flop so much as a lifting-body re-entry, so there will be a significant angle of attack which will mean the plasma flow path is downward relative to latitudinal straight lines.

Very crude drawing of said re-entry and flow paths attached. You can see that longitudinal straight lines would be in the flow path but latitudinal ones are not.

Once Starship is through re-entry, it pitches farther forward to nearly a full belly-flop to achieve the highest possible drag and thus get the lowest terminal velocity before the kick-flip.

Why wouldn’t the plasma flow around the sides?  Why would the flow be only vertical?
Oh, plasma will absolutely flow around the sides during re-entry. I mean that the flow path around the sides will be at an angle. If you look at the pattern of heat shield tiles "spilling" around the flaps, you'll see that it forms an oblique angle to the flap root axis.

But this flow path will be at an angle to any latitudinal seams, which would seem to explain why they will be okay.

Interesting!  Ok, I can see it.  Huh.  That’s … huh.  Weird to think of that angle to the velocity vector, but of course that’s how angling during reentry works.
Title: Re: Starship heat shield
Post by: StormtrooperJoe on 08/02/2021 05:47 am
Could it be possible that they are using reinforced carbon-carbon for the tip of the nose? It would make some sense given that that's where peak heating is likely to be. That's where was used on the space shuttle afterall.
Title: Re: Starship heat shield
Post by: HVM on 08/02/2021 06:59 am
The tiles were falling off, so they taped them.
I know a guy who knows a guy and he told me.
You know perfectly well that those tapes are there before adhesive cures.
Title: Re: Starship heat shield
Post by: sevenperforce on 08/02/2021 06:49 pm
Just below the very tip of the nosecone, the taper is so short that they are only doing three layers of tiles between each consecutive latitudinal seam.

A glued-on large nosecone (or perhaps a 2-3 piece construct) seems likely.
Title: Re: Starship heat shield
Post by: Keldor on 08/02/2021 06:56 pm
Elon mentioned some time back that they were still considering doing transpirational cooling for specific high heat load locations.  If this is still the case, the tip of the nose, and indeed specific areas on the leading edges of fins where we haven't seen studs, are likely spots.

This could mean they're intending to put a distribution manifold layer over the existing cone, and then attach the tiles to the outside of this, possibly still using studs.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 08/02/2021 07:10 pm
Elon mentioned some time back that they were still considering doing transpirational cooling for specific high heat load locations.  If this is still the case, the tip of the nose, and indeed specific areas on the leading edges of fins where we haven't seen studs, are likely spots.

This could mean they're intending to put a distribution manifold layer over the existing cone, and then attach the tiles to the outside of this, possibly still using studs.
Interesting, but that would add a lot of complexity. As many said, probably SpaceX will add complexity only if the current design fails. But maybe the current design implies traspirational cooling.
Title: Re: Starship heat shield
Post by: sevenperforce on 08/02/2021 07:15 pm
Elon mentioned some time back that they were still considering doing transpirational cooling for specific high heat load locations.  If this is still the case, the tip of the nose, and indeed specific areas on the leading edges of fins where we haven't seen studs, are likely spots.

This could mean they're intending to put a distribution manifold layer over the existing cone, and then attach the tiles to the outside of this, possibly still using studs.
Interesting, but that would add a lot of complexity. As many said, probably SpaceX will add complexity only if the current design fails. But maybe the current design implies traspirational cooling.
A single-piece RCC nosecone seems more likely to me.
Title: Re: Starship heat shield
Post by: HVM on 08/02/2021 07:37 pm
"RCC" blah, I want TUFROCX and i want it NOW!
Title: Re: Starship heat shield
Post by: HVM on 08/02/2021 08:22 pm
Ok, joking aside. Bodyflaps are nearly as "hot" as the ship nose, and we have only see silica tiles in them-> Both shuttle's RCC and X-37's TUFROC are clearly distinct from both ships' silica tiles.

So more custom silica tiles for the SN20 nose, is my actual guess.
Title: Re: Starship heat shield
Post by: FutureSpaceTourist on 08/02/2021 11:35 pm
twitter.com/considercosmos/status/1422272308870205475

Quote
Ship 20 emerges from the midbay! #starship

https://twitter.com/spacepadreisle/status/1422273211606179842

Quote
How many tiles are there ;)

https://twitter.com/bocacharts/status/1422304837086154759

Quote
We've just counted a flap - we get 778 or 777 depending on whether there's a little triangular tile up on the edge of the flap where it meets the hinge.

https://twitter.com/bocacharts/status/1422320039244537857

Quote
Or maybe 779... Just seen @AustinDeSisto's photo of the other flap...

https://twitter.com/bocacharts/status/1422321288169893889

Quote
Or more! Just spotted that the edges might be two tiles deep. More to come then!

twitter.com/furqan263/status/1422306559070191617

Quote
I counted about 5,000 for the rest of the tank section of S20 plus or minus 200 tiles.

https://twitter.com/bocacharts/status/1422306989737140227

Quote
One thing about the flap-count is that we've counted the blank spots as well as the actual tiles.

5000 seems low to me... We'll have to count when there are some more photos of it...
Title: Re: Starship heat shield
Post by: AstroDave on 08/03/2021 04:57 am
   Some tiles are getting placed on studs that have been welded to the steel skin. Other tiles are being placed on smooth steel with some kind of adhesive. With adhesive, it would seem that replacing a broken tile would be difficult because of adhesive build up. Is anyone familiar with the kind of adhesive that might be used in this situation, and whether it could be removed easily with a solvent?

  Also, tiles on the root section of the body flaps seem to have a filler between them while tiles on the face of the flap do not. Any reasons for this? Will a filler come later?

  On a lighter note- Folks are free to do what they want with their free time, but could someone please give me a valid reason why knowing the number of tiles on starship is of importance. How much time does it take to count tiles into the thousands?
Title: Re: Starship heat shield
Post by: cuddihy on 08/03/2021 05:01 am

  On a lighter note- Folks are free to do what they want with their free time, but could someone please give me a valid reason why knowing the number of tiles on starship is of importance. How much time does it take to count tiles into the thousands?

I’ll be the MOTO and point out # of tiles is a (pretty) unambiguous metric with which to calculate complexity/labor/cost of the heat shield.
Title: Re: Starship heat shield
Post by: russianhalo117 on 08/03/2021 05:05 am
   Some tiles are getting placed on studs that have been welded to the steel skin. Other tiles are being placed on smooth steel with some kind of adhesive. With adhesive, it would seem that replacing a broken tile would be difficult because of adhesive build up. Is anyone familiar with the kind of adhesive that might be used in this situation, and whether it could be removed easily with a solvent?

  Also, tiles on the root section of the body flaps seem to have a filler between them while tiles on the face of the flap do not. Any reasons for this? Will a filler come later?

  On a lighter note- Folks are free to do what they want with their free time, but could someone please give me a valid reason why knowing the number of tiles on starship is of importance. How much time does it take to count tiles into the thousands?
Shuttle had RTV and what became branded Gorrilla Glue (I know Scot Manley recently referenced the latter in a recent video). I might be forgetting others.
Title: Re: Starship heat shield
Post by: RoadWithoutEnd on 08/03/2021 06:11 am

  On a lighter note- Folks are free to do what they want with their free time, but could someone please give me a valid reason why knowing the number of tiles on starship is of importance. How much time does it take to count tiles into the thousands?

I’ll be the MOTO and point out # of tiles is a (pretty) unambiguous metric with which to calculate complexity/labor/cost of the heat shield.

Number of tiles is far from unambiguous in guessing complexity, labor, or cost here.  First, we don't know what would constitute "a lot" vs. "a little," because this is breaking new industrial ground.  The closest analogy, Shuttle, was a rare and rarely-launched machine (average cadence about 1 per quarter) built under political frameworks where being labor-intensive was treated as a benefit, so we find no clues there.

Second, the tiles aren't all of the same design, so number is not even simple to define.

The number of different tile types would be more useful to know, and what it does to the cost of production and the pace of installation / refurbishment to have that complexity.
Title: Re: Starship heat shield
Post by: HVM on 08/03/2021 07:06 am
   Some tiles are getting placed on studs that have been welded to the steel skin. Other tiles are being placed on smooth steel with some kind of adhesive. With adhesive, it would seem that replacing a broken tile would be difficult because of adhesive build up. Is anyone familiar with the kind of adhesive that might be used in this situation, and whether it could be removed easily with a solvent?

  Also, tiles on the root section of the body flaps seem to have a filler between them while tiles on the face of the flap do not. Any reasons for this? Will a filler come later?

  On a lighter note- Folks are free to do what they want with their free time, but could someone please give me a valid reason why knowing the number of tiles on starship is of importance. How much time does it take to count tiles into the thousands?
Shuttle had RTV and what became branded Gorrilla Glue (I know Scot Manley recently referenced the latter in a recent video). I might be forgetting others.

All sources (and you) say that Shuttle TPS used room-temperature-vulcanizing silicone. But Gorilla Glue is polyurethane glue, so no.
Title: Re: Starship heat shield
Post by: AstroDave on 08/03/2021 03:15 pm

I’ll be the MOTO and point out # of tiles is a (pretty) unambiguous metric with which to calculate complexity/labor/cost of the heat shield.

Number of tiles is far from unambiguous in guessing complexity, labor, or cost here.
...

  Save yourselves the time and ask Elon.
Title: Re: Starship heat shield
Post by: cdebuhr on 08/03/2021 05:52 pm
I'm trying to figure out how they get each of all of those tiles in the right place.

I've tried something like this,
and a small error in final tile position here and a small error in final tile position there,
and soon the rows do not go straight around, but rather start to curve up,
and then down when a correction is attempted with the placement of later tiles.

For example, try to install roofing shingles (or floor tiles) just by laying them next to
each other, without any overall alignment guides and they will probably not go straight.
Experienced roofers can tell just by eyeballing the shingles, but that only comes with the experience.

There seems to be no pattern or markings on the starship they use for alignment purposes.

And then Spacex will place tiles that seem to wander up a diagonal on the side of the starship,
and later fill in on both sides, and they seem to all fit.

I've not seen any type of, for example, laser alignment tool or survey equipment.
I'm not seeing any kind of spacers being used to get uniform separation between tiles.

I'm not seeing any cutting or trimming of tiles.

Edited.
The vast majority of tiles are installed onto machine welded mounting posts.  It's a relatively small number that are glued on by hand.  Alignment is taken care of before the first tiles is even taken out of the box.
Title: Re: Starship heat shield
Post by: Modiseus on 08/03/2021 06:14 pm
I'm trying to figure out how they get each of all of those tiles in the right place.

I've tried something like this,
and a small error in final tile position here and a small error in final tile position there,
and soon the rows do not go straight around, but rather start to curve up,
and then down when a correction is attempted with the placement of later tiles.

For example, try to install roofing shingles (or floor tiles) just by laying them next to
each other, without any overall alignment guides and they will probably not go straight.
Experienced roofers can tell just by eyeballing the shingles, but that only comes with the experience.

There seems to be no pattern or markings on the starship they use for alignment purposes.

And then Spacex will place tiles that seem to wander up a diagonal on the side of the starship,
and later fill in on both sides, and they seem to all fit.

I've not seen any type of, for example, laser alignment tool or survey equipment.
I'm not seeing any kind of spacers being used to get uniform separation between tiles.

I'm not seeing any cutting or trimming of tiles.

Edited.

Starship Gazer has a nice closeup of workers installing the TPS tiles at the tip of the nosecone. There you can see that they use spacers between the tiles to get uniform separation.
https://www.youtube.com/watch?v=OlYbTp_4o0Q
Title: Re: Starship heat shield
Post by: envy887 on 08/03/2021 06:38 pm
I'm trying to figure out how they get each of all of those tiles in the right place.

I've tried something like this,
and a small error in final tile position here and a small error in final tile position there,
and soon the rows do not go straight around, but rather start to curve up,
and then down when a correction is attempted with the placement of later tiles.

For example, try to install roofing shingles (or floor tiles) just by laying them next to
each other, without any overall alignment guides and they will probably not go straight.
Experienced roofers can tell just by eyeballing the shingles, but that only comes with the experience.

There seems to be no pattern or markings on the starship they use for alignment purposes.

And then Spacex will place tiles that seem to wander up a diagonal on the side of the starship,
and later fill in on both sides, and they seem to all fit.

I've not seen any type of, for example, laser alignment tool or survey equipment.
I'm not seeing any kind of spacers being used to get uniform separation between tiles.

I'm not seeing any cutting or trimming of tiles.

Edited.

The tiles go on studs. The studs are welded on by robotic arms which, when set up properly, will be locate them properly to a fraction of a millimeter.
Title: Re: Starship heat shield
Post by: Davidthefat on 08/03/2021 06:44 pm
I'm trying to figure out how they get each of all of those tiles in the right place.

I've tried something like this,
and a small error in final tile position here and a small error in final tile position there,
and soon the rows do not go straight around, but rather start to curve up,
and then down when a correction is attempted with the placement of later tiles.

For example, try to install roofing shingles (or floor tiles) just by laying them next to
each other, without any overall alignment guides and they will probably not go straight.
Experienced roofers can tell just by eyeballing the shingles, but that only comes with the experience.

There seems to be no pattern or markings on the starship they use for alignment purposes.

And then Spacex will place tiles that seem to wander up a diagonal on the side of the starship,
and later fill in on both sides, and they seem to all fit.

I've not seen any type of, for example, laser alignment tool or survey equipment.
I'm not seeing any kind of spacers being used to get uniform separation between tiles.

I'm not seeing any cutting or trimming of tiles.

Edited.

The tiles go on studs. The studs are welded on by robotic arms which, when set up properly, will be locate them properly to a fraction of a millimeter.

How do they control the contour of the tanks themselves? You can locate where the tiles ought to be in space, but what you are attaching them to are off tolerance.
Title: Re: Starship heat shield
Post by: envy887 on 08/03/2021 07:22 pm
I'm trying to figure out how they get each of all of those tiles in the right place.

I've tried something like this,
and a small error in final tile position here and a small error in final tile position there,
and soon the rows do not go straight around, but rather start to curve up,
and then down when a correction is attempted with the placement of later tiles.

For example, try to install roofing shingles (or floor tiles) just by laying them next to
each other, without any overall alignment guides and they will probably not go straight.
Experienced roofers can tell just by eyeballing the shingles, but that only comes with the experience.

There seems to be no pattern or markings on the starship they use for alignment purposes.

And then Spacex will place tiles that seem to wander up a diagonal on the side of the starship,
and later fill in on both sides, and they seem to all fit.

I've not seen any type of, for example, laser alignment tool or survey equipment.
I'm not seeing any kind of spacers being used to get uniform separation between tiles.

I'm not seeing any cutting or trimming of tiles.

Edited.

The tiles go on studs. The studs are welded on by robotic arms which, when set up properly, will be locate them properly to a fraction of a millimeter.

How do they control the contour of the tanks themselves? You can locate where the tiles ought to be in space, but what you are attaching them to are off tolerance.

I think the tank sections set on a jig that holds them in shape during stud welding.
Title: Re: Starship heat shield
Post by: Keldor on 08/03/2021 07:23 pm
I'm trying to figure out how they get each of all of those tiles in the right place.

I've tried something like this,
and a small error in final tile position here and a small error in final tile position there,
and soon the rows do not go straight around, but rather start to curve up,
and then down when a correction is attempted with the placement of later tiles.

For example, try to install roofing shingles (or floor tiles) just by laying them next to
each other, without any overall alignment guides and they will probably not go straight.
Experienced roofers can tell just by eyeballing the shingles, but that only comes with the experience.

There seems to be no pattern or markings on the starship they use for alignment purposes.

And then Spacex will place tiles that seem to wander up a diagonal on the side of the starship,
and later fill in on both sides, and they seem to all fit.

I've not seen any type of, for example, laser alignment tool or survey equipment.
I'm not seeing any kind of spacers being used to get uniform separation between tiles.

I'm not seeing any cutting or trimming of tiles.

Edited.

The tiles go on studs. The studs are welded on by robotic arms which, when set up properly, will be locate them properly to a fraction of a millimeter.

How do they control the contour of the tanks themselves? You can locate where the tiles ought to be in space, but what you are attaching them to are off tolerance.

One thing to consider is that even if the body is slightly off shape, all the error in a local area will be in the same direction, and that globally, the amount of absolute error will change very slowly (since rapidly changing error is easily visible as bumps and dents). This means that although the tile mest may slide across the surface where it's slightly out of position, globally, the error gets absorbed through slight variations in tile spacing.  You can think of it as projecting an ideal perfect mesh onto a slightly imperfect surface.  So long as that surface is still "close enough" to the ideal surface, the projected mesh will still be close to perfect.  When placing the pins, you conceptually (the actual algoritm the machine uses might be slightly different, but it's the same idea) start a bit outside the absolute mesh position, then move inward until you reach the surface, which might be a few milimeters in front of or behind where it was supposed to be, but is still good enough.

Special care still has to be taken in certain locations, such as around the areas where the flaps interface with the body.  These cannot tolerate error relative to the actual shape.  The simplest solution here is to measure the absolute location of these places as the rocket sits on the assembly stand, then feed this information into a computer solver, which figures out how to distort the target mesh a little bit to get a best fit where the critical points to line up with the measured physical error.  The tweaked absolute mesh positions are then fed into the stud welding machine, which welds the studs accordingly.
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/03/2021 07:36 pm
I'm trying to figure out how they get each of all of those tiles in the right place.

I've tried something like this,
and a small error in final tile position here and a small error in final tile position there,
and soon the rows do not go straight around, but rather start to curve up,
and then down when a correction is attempted with the placement of later tiles.

For example, try to install roofing shingles (or floor tiles) just by laying them next to
each other, without any overall alignment guides and they will probably not go straight.
Experienced roofers can tell just by eyeballing the shingles, but that only comes with the experience.

There seems to be no pattern or markings on the starship they use for alignment purposes.

And then Spacex will place tiles that seem to wander up a diagonal on the side of the starship,
and later fill in on both sides, and they seem to all fit.

I've not seen any type of, for example, laser alignment tool or survey equipment.
I'm not seeing any kind of spacers being used to get uniform separation between tiles.

I'm not seeing any cutting or trimming of tiles.

Edited.

The tiles go on studs. The studs are welded on by robotic arms which, when set up properly, will be locate them properly to a fraction of a millimeter.

How do they control the contour of the tanks themselves? You can locate where the tiles ought to be in space, but what you are attaching them to are off tolerance.

One thing to consider is that even if the body is slightly off shape, all the error in a local area will be in the same direction, and that globally, the amount of absolute error will change very slowly (since rapidly changing error is easily visible as bumps and dents). This means that although the tile mest may slide across the surface where it's slightly out of position, globally, the error gets absorbed through slight variations in tile spacing.  You can think of it as projecting an ideal perfect mesh onto a slightly imperfect surface.  So long as that surface is still "close enough" to the ideal surface, the projected mesh will still be close to perfect.  When placing the pins, you conceptually (the actual algoritm the machine uses might be slightly different, but it's the same idea) start a bit outside the absolute mesh position, then move inward until you reach the surface, which might be a few milimeters in front of or behind where it was supposed to be, but is still good enough.

Special care still has to be taken in certain locations, such as around the areas where the flaps interface with the body.  These cannot tolerate error relative to the actual shape.  The simplest solution here is to measure the absolute location of these places as the rocket sits on the assembly stand, then feed this information into a computer solver, which figures out how to distort the target mesh a little bit to get a best fit where the critical points to line up with the measured physical error.  The tweaked absolute mesh positions are then fed into the stud welding machine, which welds the studs accordingly.
So very little room for error, but hopefully very little room is still enough room.
Title: Re: Starship heat shield
Post by: FutureSpaceTourist on 08/03/2021 07:53 pm
https://twitter.com/fael097/status/1422611449977970694

Quote
Not exactly 100% accurate, but a quick artistic representation of Starship 20's nosecone heatshield, based on the latest pics we've seen. will update as soon as they're done with it and we have better pictures.
Title: Re: Starship heat shield
Post by: Keldor on 08/03/2021 08:19 pm
I'm trying to figure out how they get each of all of those tiles in the right place.

I've tried something like this,
and a small error in final tile position here and a small error in final tile position there,
and soon the rows do not go straight around, but rather start to curve up,
and then down when a correction is attempted with the placement of later tiles.

For example, try to install roofing shingles (or floor tiles) just by laying them next to
each other, without any overall alignment guides and they will probably not go straight.
Experienced roofers can tell just by eyeballing the shingles, but that only comes with the experience.

There seems to be no pattern or markings on the starship they use for alignment purposes.

And then Spacex will place tiles that seem to wander up a diagonal on the side of the starship,
and later fill in on both sides, and they seem to all fit.

I've not seen any type of, for example, laser alignment tool or survey equipment.
I'm not seeing any kind of spacers being used to get uniform separation between tiles.

I'm not seeing any cutting or trimming of tiles.

Edited.

The tiles go on studs. The studs are welded on by robotic arms which, when set up properly, will be locate them properly to a fraction of a millimeter.

How do they control the contour of the tanks themselves? You can locate where the tiles ought to be in space, but what you are attaching them to are off tolerance.

One thing to consider is that even if the body is slightly off shape, all the error in a local area will be in the same direction, and that globally, the amount of absolute error will change very slowly (since rapidly changing error is easily visible as bumps and dents). This means that although the tile mest may slide across the surface where it's slightly out of position, globally, the error gets absorbed through slight variations in tile spacing.  You can think of it as projecting an ideal perfect mesh onto a slightly imperfect surface.  So long as that surface is still "close enough" to the ideal surface, the projected mesh will still be close to perfect.  When placing the pins, you conceptually (the actual algoritm the machine uses might be slightly different, but it's the same idea) start a bit outside the absolute mesh position, then move inward until you reach the surface, which might be a few milimeters in front of or behind where it was supposed to be, but is still good enough.

Special care still has to be taken in certain locations, such as around the areas where the flaps interface with the body.  These cannot tolerate error relative to the actual shape.  The simplest solution here is to measure the absolute location of these places as the rocket sits on the assembly stand, then feed this information into a computer solver, which figures out how to distort the target mesh a little bit to get a best fit where the critical points to line up with the measured physical error.  The tweaked absolute mesh positions are then fed into the stud welding machine, which welds the studs accordingly.
So very little room for error, but hopefully very little room is still enough room.
There's actually probably more room for error than it would seem.  In the same way as a number of small errors can accumulate to a large error, a large error can be removed though a number of small local errors.  The key is that they can position tiles in absolute space, rather than relative to nearby tiles, which removes the cumulative term.

Another seemingly harmful thing that's actually in their favor is that to a large extent we're dealing with cosine error when we talk about slightly out of shape tanks.  If the tiles had to fit snugly together, then a tiny difference in width would result in a large "bump" sticking up, but since the tiles have some clearance, a large bump can be corrected absorbed into a tiny change in spacing.
Title: Re: Starship heat shield
Post by: uhuznaa on 08/03/2021 08:35 pm
Elon mentioned some time back that they were still considering doing transpirational cooling for specific high heat load locations.  If this is still the case, the tip of the nose, and indeed specific areas on the leading edges of fins where we haven't seen studs, are likely spots.

This could mean they're intending to put a distribution manifold layer over the existing cone, and then attach the tiles to the outside of this, possibly still using studs.
Interesting, but that would add a lot of complexity. As many said, probably SpaceX will add complexity only if the current design fails. But maybe the current design implies traspirational cooling.

Just looking at all the people attaching tiles, and the fact that there seem to be several damaged tiles already, this just doesn't look very conductive to rapid and cheap reuse... Especially for a craft that has to fly to Mars and enter there and fly back years later and reenter on Earth.

I still think that this is good enough for now but in the long run thin overlapping scales of stainless steel on stand-offs with transpiration cooling under them and through the gaps between them would be more durable and less damage-prone, even if harder to engineer and to install in the first place. But there must be room for optimization later anyway...
Title: Re: Starship heat shield
Post by: xvel on 08/03/2021 08:36 pm
https://en.wikipedia.org/wiki/Prototype
Title: Re: Starship heat shield
Post by: Hog on 08/03/2021 08:59 pm
Could it be possible that they are using reinforced carbon-carbon for the tip of the nose? It would make some sense given that that's where peak heating is likely to be. That's where was used on the space shuttle afterall.
STS also had it all along the leading edges of the wings comprised of 22 panels per wing, in addition to the nose cap for temps exceeding 1,260°C(2,300 °F). .
Title: Re: Starship heat shield
Post by: Noto on 08/04/2021 08:03 am
In the latest picture by Jack Beyer in the Master Update Thread (Reply #2861 (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2272189#msg2272189)) we see the very tip of the nosecone being covered with individual heat tiles as opposed to a single cap, often suggested to be a Carbon-Carbon cap like the shuttle. It sparked a few questions:


We know SpaceX at one point intended to use TUFROC, but we never got any confirmation in what extend it would be used on Starship. As far as I understand heat shield tech, TUFROC has the potential to replace the need for separate carbon-carbon pieces and have 1 type of tile for the whole ship (with variations in shape & thickness). Is this an indication they are using something like TUFROC for all tiles on Starship, including the leading edges?

 
Title: Re: Starship heat shield
Post by: Douglas59 on 08/04/2021 08:37 am
https://twitter.com/fael097/status/1422611449977970694

Quote
Not exactly 100% accurate, but a quick artistic representation of Starship 20's nosecone heatshield, based on the latest pics we've seen. will update as soon as they're done with it and we have better pictures.

Looking at this and one of Jack Beyer's latest photos for more detail: https://twitter.com/thejackbeyer/status/1422730126123544577/photo/1. 

It is interesting that the sectioned tile scheme on this first ship is breaking one of the design rules we thought were set by Elon (no straight channels in the direction of expected reentry plasma flow).

What are the chances this was an early prototype decision to simplify the tiling and not a permanent choice? Maybe the gap is small enough or the entry attack angle is enough to avoid the plasma channeling. If angle of attack is a factor, how critical might this attack angle margin be?

Interesting also that the straight edge section borders align perfectly with underlying welding joints in several cases. This can't be accidental. Why would this be a good choice? Could it be to allow easier fabrication and fitting of custom tiles due to section assembly dimensional errors?

The full assembly of this is going to be rather epic. Somebody is going to come up with a great 1/30 scale x-thousand piece puzzle using additive printing to allow us all to "follow along at home" and appreciate the task: "How fast can you assemble and tile a Starship" competitions and youtube videos..... It would only be 1.7 meters tall. Great Christmas present for a budding aerospace engineer.
Title: Re: Starship heat shield
Post by: cscott on 08/04/2021 12:27 pm
"No straight lines" was a made-up rule, or rather a rule we erroneously interpreted as having no possible exceptions instead of a mere guideline. Listen to Elon's interview with Tim Dodd and take step 1 of his 5-step process to heart.

The tile horizontal lines follow the weld horizontal lines for the simple reason that both are constructed as conical segment approximations to the complex ideal surface.  It's not surprising that the number of conical segments requires for the tiles to adequately approximate the surface is exactly the same as the number of conical segments required for the steel to adequately approximate the surface.

And of course there are practical benefits to aligning the conical segments. Conical-segment tiles will naturally lay better if they are being placed on a matching cone, and otherwise the weld lines would be particularly tricky spots, etc.
Title: Re: Starship heat shield
Post by: Twark_Main on 08/04/2021 02:21 pm
We know SpaceX at one point intended to use TUFROC

Do we though? As I've pointed out before (https://forum.nasaspaceflight.com/index.php?topic=47305.msg1936751#msg1936751), the only known connection is a single Space Act Agreement (https://web.archive.org/web/20201112021526/https://www.nasa.gov/saa/domestic/28344_Fully_Executed_Annex_One_SAA2-403419-1.pdf) for, essentially, "every document on every TPS tech NASA has ever worked on, plus oh yeah throw in a TUFROC brochure. Signed, NASA's TUFROC guy." Everything past that, AFAIK, has been pure outside conjecture that ultimately traces back to that one document.

It's not terribly illuminating of SpaceX's future plans (and presumably SpaceX circa June 2018 would have considered that a feature not a bug), but it's been tremendous free advertising for TUFROC.

Or did some other SpaceX-TUFROC connection appear somewhere and I missed it?
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/04/2021 02:53 pm
"No straight lines" was a made-up rule, or rather a rule we erroneously interpreted as having no possible exceptions instead of a mere guideline. Listen to Elon's interview with Tim Dodd and take step 1 of his 5-step process to heart.

The tile horizontal lines follow the weld horizontal lines for the simple reason that both are constructed as conical segment approximations to the complex ideal surface.  It's not surprising that the number of conical segments requires for the tiles to adequately approximate the surface is exactly the same as the number of conical segments required for the steel to adequately approximate the surface.

And of course there are practical benefits to aligning the conical segments. Conical-segment tiles will naturally lay better if they are being placed on a matching cone, and otherwise the weld lines would be particularly tricky spots, etc.
If I remember correctly there was an Elon Musk quote to the effect that they did not want straight lines for the plasma to be channeled through.
Title: Re: Starship heat shield
Post by: sevenperforce on 08/04/2021 03:18 pm
It is interesting that the sectioned tile scheme on this first ship is breaking one of the design rules we thought were set by Elon (no straight channels in the direction of expected reentry plasma flow).

What are the chances this was an early prototype decision to simplify the tiling and not a permanent choice? Maybe the gap is small enough or the entry attack angle is enough to avoid the plasma channeling. If angle of attack is a factor, how critical might this attack angle margin be?
I think any entry angle significantly off 90 degrees will prevent plasma channeling through circumferential seams. There are no longitudinal seams.
Title: Re: Starship heat shield
Post by: edzieba on 08/04/2021 03:31 pm
We know SpaceX at one point intended to use TUFROC
No. There was a single connection between SpaceX and TUFROC: a Space Act Agreement for knowledge transfer of TPS technology, mentioned as one among many technologies that NASA were providing SpaceX information on. In addition, TUFROC is not some magical super-material as people seem to think it is: it's a sintered silica tile (as SpaceX are currently using, LI-900 in all but branding) with an RCC cap on top.

Starship has a continued and recurring absence of RCC. Even high thermal load areas like the nose and flap edges have been tiled with the same totally-not-HRSI sintered silica tiles as the rest of the body.
Title: Re: Starship heat shield
Post by: rakaydos on 08/04/2021 03:51 pm
"No straight lines" was a made-up rule, or rather a rule we erroneously interpreted as having no possible exceptions instead of a mere guideline. Listen to Elon's interview with Tim Dodd and take step 1 of his 5-step process to heart.

The tile horizontal lines follow the weld horizontal lines for the simple reason that both are constructed as conical segment approximations to the complex ideal surface.  It's not surprising that the number of conical segments requires for the tiles to adequately approximate the surface is exactly the same as the number of conical segments required for the steel to adequately approximate the surface.

And of course there are practical benefits to aligning the conical segments. Conical-segment tiles will naturally lay better if they are being placed on a matching cone, and otherwise the weld lines would be particularly tricky spots, etc.
If I remember correctly there was an Elon Musk quote to the effect that they did not want straight lines for the plasma to be channeled through.
"Step 1: make your requirements less dumb."
Title: Re: Starship heat shield
Post by: Cheapchips on 08/04/2021 04:19 pm
"No straight lines" was a made-up rule, or rather a rule we erroneously interpreted as having no possible exceptions instead of a mere guideline. Listen to Elon's interview with Tim Dodd and take step 1 of his 5-step process to heart.

The tile horizontal lines follow the weld horizontal lines for the simple reason that both are constructed as conical segment approximations to the complex ideal surface.  It's not surprising that the number of conical segments requires for the tiles to adequately approximate the surface is exactly the same as the number of conical segments required for the steel to adequately approximate the surface.

And of course there are practical benefits to aligning the conical segments. Conical-segment tiles will naturally lay better if they are being placed on a matching cone, and otherwise the weld lines would be particularly tricky spots, etc.
If I remember correctly there was an Elon Musk quote to the effect that they did not want straight lines for the plasma to be channeled through.

It was this tweet, in response to "why hexagons". 

Quote
No straight path for hot gas to accelerate through the gaps

https://twitter.com/elonmusk/status/1107379727302451200?
Title: Re: Starship heat shield
Post by: WormPicker959 on 08/04/2021 04:29 pm
"No straight lines" was a made-up rule, or rather a rule we erroneously interpreted as having no possible exceptions instead of a mere guideline. Listen to Elon's interview with Tim Dodd and take step 1 of his 5-step process to heart.

The tile horizontal lines follow the weld horizontal lines for the simple reason that both are constructed as conical segment approximations to the complex ideal surface.  It's not surprising that the number of conical segments requires for the tiles to adequately approximate the surface is exactly the same as the number of conical segments required for the steel to adequately approximate the surface.

And of course there are practical benefits to aligning the conical segments. Conical-segment tiles will naturally lay better if they are being placed on a matching cone, and otherwise the weld lines would be particularly tricky spots, etc.
If I remember correctly there was an Elon Musk quote to the effect that they did not want straight lines for the plasma to be channeled through.

It was this tweet, in response to "why hexagons". 

Quote
No straight path for hot gas to accelerate through the gaps

https://twitter.com/elonmusk/status/1107379727302451200?

To my mind, there are two possibilities:
1) The SN20 layout is inconsistent with this tweet. This implies the rational/design changed, which is not crazy to imagine.
2) The SN20 layout is consistent with this tweet. Perhaps only vertical straight gaps matter? There are still non of those.
Title: Re: Starship heat shield
Post by: envy887 on 08/04/2021 04:54 pm
"No straight lines" was a made-up rule, or rather a rule we erroneously interpreted as having no possible exceptions instead of a mere guideline. Listen to Elon's interview with Tim Dodd and take step 1 of his 5-step process to heart.

The tile horizontal lines follow the weld horizontal lines for the simple reason that both are constructed as conical segment approximations to the complex ideal surface.  It's not surprising that the number of conical segments requires for the tiles to adequately approximate the surface is exactly the same as the number of conical segments required for the steel to adequately approximate the surface.

And of course there are practical benefits to aligning the conical segments. Conical-segment tiles will naturally lay better if they are being placed on a matching cone, and otherwise the weld lines would be particularly tricky spots, etc.
If I remember correctly there was an Elon Musk quote to the effect that they did not want straight lines for the plasma to be channeled through.

It was this tweet, in response to "why hexagons". 

Quote
No straight path for hot gas to accelerate through the gaps

https://twitter.com/elonmusk/status/1107379727302451200?

Square tiles like Shuttle's have straight lines on every single row.
Title: Re: Starship heat shield
Post by: xvel on 08/04/2021 05:09 pm
but there isn't really much of a gap between tiles on space shuttle
Title: Re: Starship heat shield
Post by: cscott on 08/04/2021 05:55 pm
Elon's step 1 is "question the requirements, *especially* if they come from someone smart".  Elon mentioned straight lines and we took (our interpretation of) what he said as gospel.  His step 1 is to ignore that and get back to the fundamental physical requirements (or lack thereof). 

My own opinion is that he was stating a general principle -- *in general* hex tiles are superior to square because the gaps don't line up -- and we in the forum took it as some inviolate law of plasma aerodynamics.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/04/2021 08:22 pm
This is dead on topic but from a very different direction.
https://arstechnica.com/science/2021/07/mergers-twists-and-pentagons-the-architecture-of-honeycombs/ (https://arstechnica.com/science/2021/07/mergers-twists-and-pentagons-the-architecture-of-honeycombs/)
Title: Re: Starship heat shield
Post by: Oersted on 08/04/2021 10:24 pm
"No straight lines" was a made-up rule, or rather a rule we erroneously interpreted as having no possible exceptions instead of a mere guideline. Listen to Elon's interview with Tim Dodd and take step 1 of his 5-step process to heart.

The tile horizontal lines follow the weld horizontal lines for the simple reason that both are constructed as conical segment approximations to the complex ideal surface.  It's not surprising that the number of conical segments requires for the tiles to adequately approximate the surface is exactly the same as the number of conical segments required for the steel to adequately approximate the surface.

And of course there are practical benefits to aligning the conical segments. Conical-segment tiles will naturally lay better if they are being placed on a matching cone, and otherwise the weld lines would be particularly tricky spots, etc.
If I remember correctly there was an Elon Musk quote to the effect that they did not want straight lines for the plasma to be channeled through.

Interestingly (to me at least) the same rationale was behind the zig-zagging trenches of World war One. No straight lines for shrapnel to fly through...
Title: Re: Starship heat shield
Post by: OTV Booster on 08/04/2021 11:14 pm
"No straight lines" was a made-up rule, or rather a rule we erroneously interpreted as having no possible exceptions instead of a mere guideline. Listen to Elon's interview with Tim Dodd and take step 1 of his 5-step process to heart.

The tile horizontal lines follow the weld horizontal lines for the simple reason that both are constructed as conical segment approximations to the complex ideal surface.  It's not surprising that the number of conical segments requires for the tiles to adequately approximate the surface is exactly the same as the number of conical segments required for the steel to adequately approximate the surface.

And of course there are practical benefits to aligning the conical segments. Conical-segment tiles will naturally lay better if they are being placed on a matching cone, and otherwise the weld lines would be particularly tricky spots, etc.
If I remember correctly there was an Elon Musk quote to the effect that they did not want straight lines for the plasma to be channeled through.

It was this tweet, in response to "why hexagons". 

Quote
No straight path for hot gas to accelerate through the gaps

https://twitter.com/elonmusk/status/1107379727302451200? (https://twitter.com/elonmusk/status/1107379727302451200?)

To my mind, there are two possibilities:
1) The SN20 layout is inconsistent with this tweet. This implies the rational/design changed, which is not crazy to imagine.
2) The SN20 layout is consistent with this tweet. Perhaps only vertical straight gaps matter? There are still non of those.
A third possibility. When Elon said no straight lines... he thought his would include circumferential and the ongoing R&D showed it weren't so. His statement of design goal still stands but the specific solution being noodled at the time proved to be overkill. He made the requirements less dumb.
Title: Re: Starship heat shield
Post by: WormPicker959 on 08/05/2021 03:21 am
"No straight lines" was a made-up rule, or rather a rule we erroneously interpreted as having no possible exceptions instead of a mere guideline. Listen to Elon's interview with Tim Dodd and take step 1 of his 5-step process to heart.

The tile horizontal lines follow the weld horizontal lines for the simple reason that both are constructed as conical segment approximations to the complex ideal surface.  It's not surprising that the number of conical segments requires for the tiles to adequately approximate the surface is exactly the same as the number of conical segments required for the steel to adequately approximate the surface.

And of course there are practical benefits to aligning the conical segments. Conical-segment tiles will naturally lay better if they are being placed on a matching cone, and otherwise the weld lines would be particularly tricky spots, etc.
If I remember correctly there was an Elon Musk quote to the effect that they did not want straight lines for the plasma to be channeled through.

It was this tweet, in response to "why hexagons". 

Quote
No straight path for hot gas to accelerate through the gaps

https://twitter.com/elonmusk/status/1107379727302451200? (https://twitter.com/elonmusk/status/1107379727302451200?)

To my mind, there are two possibilities:
1) The SN20 layout is inconsistent with this tweet. This implies the rational/design changed, which is not crazy to imagine.
2) The SN20 layout is consistent with this tweet. Perhaps only vertical straight gaps matter? There are still non of those.
A third possibility. When Elon said no straight lines... he thought his would include circumferential and the ongoing R&D showed it weren't so. His statement of design goal still stands but the specific solution being noodled at the time proved to be overkill. He made the requirements less dumb.
Agreed, this is what I mean by the first possibility - design changed, was less dumb. We see this all the time with Starship, so it's not that surprising.
Title: Re: Starship heat shield
Post by: Noto on 08/05/2021 08:30 am
Or did some other SpaceX-TUFROC connection appear somewhere and I missed it?
No. There was a single connection between SpaceX and TUFROC: a Space Act Agreement for knowledge transfer of TPS technology, mentioned as one among many technologies that NASA were providing SpaceX information on.

My apologies, I didn't try to claim SpaceX is using TUFROC. I was referring to that single Space Act agreement. I specifically used the wording 'at one point intended' to clarify we only have a single source, which doesn't tell us anything except SpaceX was interested in the tech. Apparently I failed to convey that.


In addition, TUFROC is not some magical super-material as people seem to think it is: it's a sintered silica tile (as SpaceX are currently using, LI-900 in all but branding) with an RCC cap on top.

Starship has a continued and recurring absence of RCC. Even high thermal load areas like the nose and flap edges have been tiled with the same totally-not-HRSI sintered silica tiles as the rest of the body.

How do we know SpaceX is using LI-900 sintered silica tiles, and more specifically 'totally-not-HRSI'. Are there visual clues?

Maybe my question should've been: Do the heat tiles we see now tell us anything about what material SpaceX is using? I was expecting different looking tiles on the nose and the leading edges.






Title: Re: Starship heat shield
Post by: edzieba on 08/05/2021 02:01 pm
How do we know SpaceX is using LI-900 sintered silica tiles, and more specifically 'totally-not-HRSI'. Are there visual clues?
An environmental protection report (https://prodenv.dep.state.fl.us/DepNexus/public/electronic-documents/FLR000231449/facility!search) on the Astronaut Blvd. site (tile production site) described the raw materials and manufacturing process, matching the description for HRSI:
Sintered Silica fibre base, reaction-cured-glass coating, then Silane + Acetic acid waterproofing (methyl-trimethoxy silane rather than dimethylethoxy silane though).
Title: Re: Starship heat shield
Post by: Kazioo on 08/05/2021 02:02 pm
New info from Jean Wright on the NSF livestream:

She claims that the white blanket is apparently SIP (Stress/Strain Isolation Pad) made of Nomex felt.
However, according to Wikipedia: This white, flexible fabric offered protection at up to 371 °C (700 °F).

This is a temperature much closer to what aluminium can sustain than stainless steel, so it's a quite confusing choice of material in the context of this Elon's tweet:

https://twitter.com/elonmusk/status/1154194820929212419

Or she just misunderstood the question and thought that NSF guys were asking about the white blankets on the Shuttle?
Title: Re: Starship heat shield
Post by: Robotbeat on 08/05/2021 02:22 pm
New info from Jean Wright on the NSF livestream:

She claims that the white blanket is apparently SIP (Stress/Strain Isolation Pad) made of Nomex felt.
However, according to Wikipedia: This white, flexible fabric offered protection at up to 371 °C (700 °F).

This is a temperature much closer to what aluminium can sustain than stainless steel, so it's a quite confusing choice of material in the context of this Elon's tweet:

https://twitter.com/elonmusk/status/1154194820929212419

Or she just misunderstood the question and thought that NSF guys were asking about the white blankets on the Shuttle?
I was thinking the same thing. Also, it looked like they were using red RTV adhesive for the nose cone, which can go up to 343C, or roughly aluminum. (Although the tiles being attached look thick and therefore insulating, like Shuttle tiles and not like the thinner tiles on most of the rest of the body, so the heat on thick-tile backside may not be a problem.)

But I think a lot of these decisions are made for sake of expediency. Also, it might be okay if the Nomex felt degrades on reentry.

(IF it's actually Nomex.)

Also, 370C is pretty high for aluminum. You lose the vast majority of aluminum's strength at 370C or even 343C whereas stainless retains most of its strength, so even still at the fabric or adhesive maximum temperatures, stainless is much stronger than aluminum.

Oh, also, in areas of the underside of the tank, you might have cryo propellant that could help keep the stainless cold. And the ullage gas will be transporting the very high heat away via convection in other areas, as well as the radiation others have mentioned (which becomes quite significant at ~800-1000C or so due to the fourth power of radiation). So that gives you a bit of resiliency to lost tiles.
Title: Re: Starship heat shield
Post by: RoboGoofers on 08/05/2021 03:32 pm
As we've seen, as thick as the tiles are they are easy to crack, so thinner tiles just might not be strong enough. There are also elements inside the tile that attach to the prongs on the tanks, so maybe those elements dictate the tile thickness.
Title: Re: Starship heat shield
Post by: Robotbeat on 08/05/2021 03:44 pm
I still think refractory metal tiles are a good way to go. Niobium based alloys can go to same temperature as shuttle heatshield tiles, or 1260C or so.
Title: Re: Starship heat shield
Post by: Kazioo on 08/05/2021 03:54 pm
New info from Jean Wright on the NSF livestream:

She claims that the white blanket is apparently SIP (Stress/Strain Isolation Pad) made of Nomex felt.
However, according to Wikipedia: This white, flexible fabric offered protection at up to 371 °C (700 °F).

This is a temperature much closer to what aluminium can sustain than stainless steel, so it's a quite confusing choice of material in the context of this Elon's tweet:

https://twitter.com/elonmusk/status/1154194820929212419

Or she just misunderstood the question and thought that NSF guys were asking about the white blankets on the Shuttle?
I was thinking the same thing. Also, it looked like they were using red RTV adhesive for the nose cone, which can go up to 343C, or roughly aluminum. (Although the tiles being attached look thick and therefore insulating, like Shuttle tiles and not like the thinner tiles on most of the rest of the body, so the heat on thick-tile backside may not be a problem.)

But I think a lot of these decisions are made for sake of expediency. Also, it might be okay if the Nomex felt degrades on reentry.

(IF it's actually Nomex.)

Also, 370C is pretty high for aluminum. You lose the vast majority of aluminum's strength at 370C or even 343C whereas stainless retains most of its strength, so even still at the fabric or adhesive maximum temperatures, stainless is much stronger than aluminum.

Oh, also, in areas of the underside of the tank, you might have cryo propellant that could help keep the stainless cold. And the ullage gas will be transporting the very high heat away via convection in other areas, as well as the radiation others have mentioned (which becomes quite significant at ~800-1000C or so due to the fourth power of radiation). So that gives you a bit of resiliency to lost tiles.


The graph you posted is especially interesting when compared to Elon's claim that Stainless Steel can sustain 1 177 °C (1450 K / 2 150 °F).

https://twitter.com/elonmusk/status/1088091464909766656
Title: Re: Starship heat shield
Post by: JCopernicus on 08/05/2021 04:19 pm
I like how there's a bunch of random black bandaids all over the heat tiles.
Title: Re: Starship heat shield
Post by: ETurner on 08/05/2021 04:47 pm
The graph you posted is especially interesting when compared to Elon's claim that Stainless Steel can sustain 1 177 °C (1450 K / 2 150 °F).
Another consideration, aside from loss of strength at temperature, is loss of strength after cooling as a result of changes in the metal due to annealing:
Quote
A 304L-type austenitic stainless steel was subjected to plate rolling at ambient temperature and at 573 K to total strains of 3 and then annealed at temperatures of 873, 973 and 1073 K. The structural changes during annealing were associated with the austenite reversal (for the cold rolled samples), recrystallization and grain growth, which depended significantly on the annealing temperature. The grain growth exponent of 4 and 5 was obtained after annealing at 973 K/1073 K for the cold and warm rolled samples, whereas very sluggish grain coarsening took place at 873 K....The grain coarsening during annealing was accompanied by gradual softening.

(Annealing behavior of a 304L stainless steel processed by large strain cold and warm rolling (https://www.sciencedirect.com/science/article/abs/pii/S0921509317302344))
Title: Re: Starship heat shield
Post by: Tangilinear Interjar on 08/05/2021 05:07 pm
People have wondered how these guys could have enough experience to do such a good job placing the tiles. It seems to me that there's been plenty of opportunity to practice this glue and fit process on the very complex shapes on the flaps.

Someone had to do those and I bet they have just spent the last few days in man-baskets placing tiles.

Another thought I had was does SpaceX have some limited ability to produce tiles in Boca Chica? And if so, how long is the production process? A few hours? They could be placing tiles and when they get to something that doesn't fit right a quick couple of pictures sent to Lisa the CAD girl, followed by a quick call and she has the water jet cutting a new shape 10 minutes later. Squirt it with some stuff, bake it and give it to Albert to run out to the rocket.
Title: Re: Starship heat shield
Post by: matthewkantar on 08/05/2021 05:09 pm
People have wondered how these guys could have enough experience to do such a good job placing the tiles. It seems to me that there's been plenty of opportunity to practice this glue and fit process on the very complex shapes on the flaps.

Someone had to do those and I bet they have just spent the last few days in man-baskets placing tiles.

Another thought I had was does SpaceX have some limited ability to produce tiles in Boca Chica? And if so, how long is the production process? A few hours? They could be placing tiles and when they get to something that doesn't fit right a quick couple of pictures sent to Lisa the CAD girl, followed by a quick call and she has the water jet cutting a new shape 10 minutes later. Squirt it with some stuff, bake it and give it to Albert to run out to the rocket.

I believe they have a portable "bakery" for making tiles onsite.
Title: Re: Starship heat shield
Post by: cscott on 08/05/2021 05:25 pm
The odd missing tiles indicated to me that it wasn't quite a same day turnaround, though.  By the time they had a replacement for the broken tile they'd moved the scaffolding to another area or whatever, since there are lots of little one-off gaps.  I'm sure they'll get filled at some point, but that suggested to me that there was a lead time to getting a replacement.
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/05/2021 05:34 pm
The odd missing tiles indicated to me that it wasn't quite a same day turnaround, though.  By the time they had a replacement for the broken tile they'd moved the scaffolding to another area or whatever, since there are lots of little one-off gaps.  I'm sure they'll get filled at some point, but that suggested to me that there was a lead time to getting a replacement.
I doubt the missing tiles are missing due to not having enough tiles. More likely the pins were damaged or needed some sort of cleaning before the new tile was applied and they didn't have time. Also it looks like they just didn't have enough time as there are some largish areas with no tiles. Also some sort of special alignment procedure might be required for some of the edge cases - again out of time.
Title: Re: Starship heat shield
Post by: Rocket Surgeon on 08/05/2021 05:37 pm
Honestly, I think they just ran out of time to do the stack today, and they'll have time during the rest of the test campaign.
They gotta at least do a pressure test and they've shown they can mount them out at the pad with SN15...

Why hold things up?
Title: Re: Starship heat shield
Post by: StarshipTrooper on 08/05/2021 05:44 pm
It's interesting that there are large swaths missing from the heat shield during stacking. If the stacking were a PR stunt, as others have implied in the forum, wouldn't it be better to wait until they were more evenly covered? If they stack it with missing tiles it must mean that it is a functional check-off item more than any PR stunt.
Title: Re: Starship heat shield
Post by: edzieba on 08/05/2021 05:44 pm
I still think refractory metal tiles are a good way to go. Niobium based alloys can go to same temperature as shuttle heatshield tiles, or 1260C or so.
Remember that the temperature the tile surface can tolerate is fairly far down the list of important properties to act as a TPS (as long as it doesn't ablate before you complete entry). It's not much good having a TPS that can tolerate 1500K if it allows the structure behind it to also heat up to 1500K. In that regard, Niobium is annoyingly conductive. Workable if you have a 'hot-structure' vehicle, not so great if your structure is also a cryogenic tank wall or right next to squishy flammable meat-bags.
People have wondered how these guys could have enough experience to do such a good job placing the tiles. It seems to me that there's been plenty of opportunity to practice this glue and fit process on the very complex shapes on the flaps.
There's also an army of veteran STS tile installers that could be hired to train current installers, at least for the RTV + felt technique.
Title: Re: Starship heat shield
Post by: mmeijeri on 08/05/2021 06:39 pm
Remember that the temperature the tile surface can tolerate is fairly far down the list of important properties to act as a TPS (as long as it doesn't ablate before you complete entry). It's not much good having a TPS that can tolerate 1500K if it allows the structure behind it to also heat up to 1500K. In that regard, Niobium is annoyingly conductive. Workable if you have a 'hot-structure' vehicle, not so great if your structure is also a cryogenic tank wall or right next to squishy flammable meat-bags.

Metallic tiles can be combined with insulating fibres as described in this NTRS paper:

Development of Metallic Thermal Protection Systems for the Reusable Launch Vehicle (https://ntrs.nasa.gov/api/citations/19970005361/downloads/19970005361.pdf)

Title: Re: Starship heat shield
Post by: Alberto-Girardi on 08/05/2021 06:59 pm
Since it seems that they are going to stack everything I see as a possibility that this first staking is only a fit check and more importantly to gain experience. Then they will de-stack everything and complete the TPS, and eventually test S20 with the thrust ram (but they would need to remove the engines.). May they hae decided instead to not complete the TPS, maybe because they now shifted the goal of the orbital first test only to the ascent part. They could add the remaining TPS later without de-stacking, but they would need to make workers work at high distance from the ground, which I think they want to avoid.
Title: Re: Starship heat shield
Post by: xvel on 08/05/2021 07:11 pm
maybe calm down and not overinterpret things
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/05/2021 09:00 pm
maybe calm down and not overinterpret things
Yeah lets just chill, nobody really knows. But that doesn't stop people from inventing theories (ha!). My theory is the fit check is needed and they can't continue with other things like testing the booster and ship until its done.
Title: Re: Starship heat shield
Post by: cscott on 08/05/2021 09:48 pm
The odd missing tiles indicated to me that it wasn't quite a same day turnaround, though.  By the time they had a replacement for the broken tile they'd moved the scaffolding to another area or whatever, since there are lots of little one-off gaps.  I'm sure they'll get filled at some point, but that suggested to me that there was a lead time to getting a replacement.
Elon provides some evidence that the issue is lead time:

twitter.com/nicansuini/status/1423296366273462286

Quote
Anyone have some spare tiles that SN20 can borrow? She’s a few short…

#Spacexnews #spacex #starbase #starship

https://twitter.com/elonmusk/status/1423387961362501634

Quote
Remaining tiles are on their way!

Title: Re: Starship heat shield
Post by: Robotbeat on 08/05/2021 10:04 pm
People have wondered how these guys could have enough experience to do such a good job placing the tiles. It seems to me that there's been plenty of opportunity to practice this glue and fit process on the very complex shapes on the flaps.

Someone had to do those and I bet they have just spent the last few days in man-baskets placing tiles.

Another thought I had was does SpaceX have some limited ability to produce tiles in Boca Chica? And if so, how long is the production process? A few hours? They could be placing tiles and when they get to something that doesn't fit right a quick couple of pictures sent to Lisa the CAD girl, followed by a quick call and she has the water jet cutting a new shape 10 minutes later. Squirt it with some stuff, bake it and give it to Albert to run out to the rocket.
Brownsville, Texas by jet (Elon and SpaceX have a few) is only about 3 hours away from their Florida site and 4 hours away from their California site. Probably not worth trying to get another facility up and running unless they were already planning on it.

The total weight of Shuttle’s tiles and TPS was about 8.5 tons. Assuming Starship is similar, and the SpaceX private jet has a payload capacity of about 2.8 tons, it takes just 3 flights to send all the tiles by jet. Or, about a third or a fourth of a Starship worth of tiles can be sent via SpaceX’s Gulfstream G550.
Title: Re: Starship heat shield
Post by: Keldor on 08/05/2021 10:34 pm
People have wondered how these guys could have enough experience to do such a good job placing the tiles. It seems to me that there's been plenty of opportunity to practice this glue and fit process on the very complex shapes on the flaps.

Someone had to do those and I bet they have just spent the last few days in man-baskets placing tiles.

Another thought I had was does SpaceX have some limited ability to produce tiles in Boca Chica? And if so, how long is the production process? A few hours? They could be placing tiles and when they get to something that doesn't fit right a quick couple of pictures sent to Lisa the CAD girl, followed by a quick call and she has the water jet cutting a new shape 10 minutes later. Squirt it with some stuff, bake it and give it to Albert to run out to the rocket.
Brownsville, Texas by jet (Elon and SpaceX have a few) is only about 3 hours away from their Florida site and 4 hours away from their California site. Probably not worth trying to get another facility up and running unless they were already planning on it.

The total weight of Shuttle’s tiles and TPS was about 8.5 tons. Assuming Starship is similar, and the SpaceX private jet has a payload capacity of about 2.8 tons, it takes just 3 flights to send all the tiles by jet. Or, about a third or a fourth of a Starship worth of tiles can be sent via SpaceX’s Gulfstream G550.

Yeah, overnight shipping isn't that big a cost in the large scheme of things, and in any case, I expect them to simply keep a nice stockpile of spare tiles on hand once things settle into rythm.  This is a one time cost, since unusued spares can sit around essentially for free until you need them.
Title: Re: Starship heat shield
Post by: StarshipTrooper on 08/06/2021 12:16 am
The odd missing tiles indicated to me that it wasn't quite a same day turnaround, though.  By the time they had a replacement for the broken tile they'd moved the scaffolding to another area or whatever, since there are lots of little one-off gaps.  I'm sure they'll get filled at some point, but that suggested to me that there was a lead time to getting a replacement.
Elon provides some evidence that the issue is lead time:

twitter.com/nicansuini/status/1423296366273462286

Quote
Anyone have some spare tiles that SN20 can borrow? She’s a few short…

#Spacexnews #spacex #starbase #starship

https://twitter.com/elonmusk/status/1423387961362501634

Quote
Remaining tiles are on their way!

Looks like someone got a box of tiles cause they're busy pushing them on!
Title: Re: Starship heat shield
Post by: Slothman on 08/06/2021 07:07 pm
So, how confident you think spacex are in the tps tiles if they pop off during transport back to the construction site?
Title: Re: Starship heat shield
Post by: xvel on 08/06/2021 07:17 pm
Probably already broken tile fell off

They were testing tiles on flights of SN 5, 6, 8, 9, 10, 11, 15 and looks like only problem is on the skirt, they fell off from vibration, tiles on the tank were fine.
Title: Re: Starship heat shield
Post by: StormtrooperJoe on 08/06/2021 07:21 pm
So, how confident you think spacex are in the tps tiles if they pop off during transport back to the construction site?
To me this does not bode very well, at least for early flights. If they are having tiles pop off moving a mile or 2 per hour on flat ground then I don't want too see how the perform during max q and reentry. Hopefully they can solve this issue in future iterations otherwise it calls into question the viability of Starship as a reusable vehicle
Title: Re: Starship heat shield
Post by: Lars-J on 08/06/2021 07:47 pm
So, how confident you think spacex are in the tps tiles if they pop off during transport back to the construction site?
To me this does not bode very well, at least for early flights. If they are having tiles pop off moving a mile or 2 per hour on flat ground then I don't want too see how the perform during max q and reentry. Hopefully they can solve this issue in future iterations otherwise it calls into question the viability of Starship as a reusable vehicle

I don't consider any of the tiles currently on SN20 as being final. For all we know they will now take off all tiles and redo them. So don't jump to conclusions yet.

If they were stacking for a real launch and a bunch of tiles fell off when moving at 2mph, then there might be cause for concern. But any of the tiles could be replaced or reapplied before that.
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/06/2021 11:46 pm
So it does seem that there will be perhaps a hundred or more special tiles required (2% of 5000):
https://twitter.com/elonmusk/status/1423674865626730500
 (https://twitter.com/elonmusk/status/1423674865626730500)
Title: Re: Starship heat shield
Post by: peregrine30 on 08/07/2021 12:02 am
Since what they have underneath the tiles is stainless steel now (vs. aluminum or composite), would the consequence or criticality of a missing tile during reentry be somewhat different? 
Title: Re: Starship heat shield
Post by: Nonproliferator on 08/07/2021 12:40 am
I notice that on the untiled band between the nosecone and the cylindrical section there are mounting pins from the edges to the centre, but then a large space where there are no pins at all on the midpoint of that circumference.

Its a curious arrangement, especially with the odd bracket smack in the middle. Anyone knowledgeable with thoughts? Is there any clear reason to not
a) stud this section?
b) glue on tiles instead of clipping on?

Clearly there was no problem applying studs this far down the cone.

Picture captured from NSF livestream
Title: Re: Starship heat shield
Post by: cscott on 08/07/2021 05:02 am
My first thought was that they must be able to pretty flexibly shift between the "pin mount" tiles and the "glued down with RTV" tiles, and they just chose to shift to glued application for some region around the bracket.  Maybe there's something on the other side of the wall which interfered with stud welding there, maybe there are some custom tiles needed, or maybe there's no particular reason, it's just that gluing some tiles is not a big deal so they played it safe and had the robot stud welder leave plenty of margin around the bracket.
Title: Re: Starship heat shield
Post by: Cheapchips on 08/07/2021 08:13 am
What does Musk mean by machining?  I thought the tiles were cast?
Title: Re: Starship heat shield
Post by: svlu on 08/07/2021 08:27 am
What does Musk mean by machining?  I thought the tiles were cast?
I would guess that it means that one take a standard tile and machine/grind it until it fits?
Title: Re: Starship heat shield
Post by: Cheapchips on 08/07/2021 08:38 am
What does Musk mean by machining?  I thought the tiles were cast?
I would guess that it means that one take a standard tile and machine/grind it until it fits?

I didn't think the the hex tiles were a single layer, which would preclude that. Could have got that wrong though.

Maybe slightly different make up for shaped tiles? Probably all glued as well so they don't have to machine around a mounting bracket?
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/07/2021 09:00 am
What does Musk mean by machining?  I thought the tiles were cast?
I would guess that it means that one take a standard tile and machine/grind it until it fits?

I didn't think the the hex tiles were a single layer, which would preclude that. Could have got that wrong though.

Maybe slightly different make up for shaped tiles? Probably all glued as well so they don't have to machine around a mounting bracket?
They might just cut them with a band saw or similar and then give them their top black coating. Although there are a hundred or so special tiles there are probably only a few dozen special tile types.
Title: Re: Starship heat shield
Post by: joek on 08/07/2021 09:07 am
What does Musk mean by machining?  I thought the tiles were cast?
I would guess that it means that one take a standard tile and machine/grind it until it fits?
I didn't think the the hex tiles were a single layer, which would preclude that. Could have got that wrong though.

Maybe slightly different make up for shaped tiles? Probably all glued as well so they don't have to machine around a mounting bracket?

Might be overthinking this. Consider "machining" to be "cut to fit"; any number of ways to do that which work for multi-layer constructs. Agree that if there are large(ish) embedded structures such as a mounting bracket, it is more complex. So they may take a different path for those; e.g., non-standard tile shapes, elide mounting bracket; cut to size; glue (or something like that).
Title: Re: Starship heat shield
Post by: RoboGoofers on 08/07/2021 11:24 am
I notice that on the untiled band between the nosecone and the cylindrical section there are mounting pins from the edges to the centre, but then a large space where there are no pins at all on the midpoint of that circumference.

Its a curious arrangement, especially with the odd bracket smack in the middle. Anyone knowledgeable with thoughts? Is there any clear reason to not
a) stud this section?
b) glue on tiles instead of clipping on?

Clearly there was no problem applying studs this far down the cone.

Picture captured from NSF livestream
not sure if they still do this but they used to attach a counterweight to the cone when stacking to balance the weight of the folded fins. Those tabs might be where it's mounted and they just didn't have time to cut them off an install the tile pins.
Title: Re: Starship heat shield
Post by: edzieba on 08/07/2021 12:09 pm
What does Musk mean by machining?  I thought the tiles were cast?
From the EPA report on the tile production site: the sintered silica blanks are cast and fired, then a router used to mill them to the desired profile, then sliced in half thickness-wise to form two tiles. The RCG coating is then applied, followed by waterproofing.
Title: Re: Starship heat shield
Post by: JCopernicus on 08/07/2021 01:44 pm
It could also mean they are machining the casts for specific shapes.
Title: Re: Starship heat shield
Post by: FutureSpaceTourist on 08/07/2021 02:44 pm
Nice tile shots

https://twitter.com/bottinphilip/status/1424012609800519698
Title: Re: Starship heat shield
Post by: MTom on 08/07/2021 05:59 pm
Part 2:

https://youtu.be/SA8ZBJWo73E

Quote
Join me as I take a tour of SpaceX's Starbase facility with Elon Musk as our tour guide! This is part 2 of 3, so stay tuned, there's another one coming!

If you need some notes on this video with key points, check out our article - https://everydayastronaut.com/starbase-tour-and-interview-with-elon-musk/

Need a rundown on Starship? I've got you covered with our "Complete Guide to Starship"
//youtu.be/-8p2JDTd13k

00:00 - Intro
00:45 - Tent 1 // Raptors
05:00 - Failure and the Space Shuttle
08:35 - Launch Escape Systems
10:50 - Tent 2
13:00 - Heat Shield Talk
16:20 - 1st Orbital Test
26:26 - Tent 3 // Nose Cones
37:40 - S20 Nose Cone // Reentry
51:00 - 69.420

Interesting part of Tim Dodd's interview about heat shield from 13:00.
Title: Re: Starship heat shield
Post by: HVM on 08/07/2021 08:13 pm
From updates
https://twitter.com/BottinPhilip/status/1424098154497064960
Title: Re: Starship heat shield
Post by: jpo234 on 08/07/2021 11:32 pm
Have we seen "The Bakery" yet? The one in Florida besides the Ron Jon distribution center?
Title: Re: Starship heat shield
Post by: cscott on 08/07/2021 11:38 pm
Yes, there's a whole thread here on the forums. Look for "Cidco Rd".

https://forum.nasaspaceflight.com/index.php?topic=48158.0

EDIT: I had the wrong facility, see below.
Title: Re: Starship heat shield
Post by: Aaron_Space on 08/07/2021 11:52 pm
The bakery facility thread: https://forum.nasaspaceflight.com/index.php?topic=48412.0
Title: Re: Starship heat shield
Post by: RoadWithoutEnd on 08/08/2021 08:24 am
From updates
https://twitter.com/BottinPhilip/status/1424098154497064960

Would love some details on this process.  Is it just visual inspection they're judging the install by, or are they subjecting installed tiles to some instruments?
Title: Re: Starship heat shield
Post by: FutureSpaceTourist on 08/08/2021 07:51 pm
https://youtu.be/-Lsbi-bVfk0

Edit to add:

twitter.com/djsnm/status/1424406321521065988

Quote
While everyone is making videos about how big the fully stacked Starship/Superheavy is I wanted to go into the design of the heat shield. I recorded this on Friday night and by Saturday morning It was already somewhat out of date.

https://twitter.com/djsnm/status/1424406778398220289

Quote
It's not too bad, but @elonmusk revealed a few things I wish I'd known when he talked to @Erdayastronaut
Title: Re: Starship heat shield
Post by: KBK on 08/09/2021 12:38 pm
With the new sectioned method of making the nose cone, accuracy and rigidity goes up substantially, re micro vibrational modes and levels. this may allow for a tile that is twice as big, in one dimension, at the least.

This may create an avenue for a better, more accurate tile mounting sytem, and with fewer gaps to fail via. After all, it's potentials in overall complex reliability per singular complex application action... multiplied by the number of applications. Buy fewer lottery tickets, is the game here.

(there are other complex factors in play here, obviously, but it is something to look at)
Title: Re: Starship heat shield
Post by: edzieba on 08/09/2021 01:16 pm
Larger tiles are much more fragile: while individual tile cost may decrease*, the odds are high that cost per unit area will increase once wastage and more complex handling procedures are taken into account.

* Unless a larger tile means you need to construct a brand new sintering oven.
Title: Re: Starship heat shield
Post by: sanman on 08/09/2021 01:21 pm
Just recalling Tim's comment to Elon about "dragon scales" -- I wonder, is hexagonal the optimal default shape for most tiles? If they were naturally evolved dragon scales or pterodactyl scales, they wouldn't be hexagonal. I'm imagining they'd be elongated to match the direction of airflow, in a way that prevents them from being dislodged. Bird feathers tend to overlap each other. Should the tile area only included its attachment area, or could it extend somewhat beyond that?
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 08/09/2021 01:23 pm
Larger tiles are much more fragile: while individual tile cost may decrease*, the odds are high that cost per unit area will increase once wastage and more complex handling procedures are taken into account.

* Unless a larger tile means you need to construct a brand new sintering oven.
Agree. Months ago I saw being mentioned that too large tiles may have the right oscillation frequency, that one that matches the vibrations of the vehicle.
Title: Re: Starship heat shield
Post by: JH on 08/09/2021 01:29 pm
Musk was talking about the mounting system having to accommodate thermal expansion and contraction, both for the steel and the tile. A larger tile would make this harder because mount points would move more relative to each other.
Title: Re: Starship heat shield
Post by: Redclaws on 08/09/2021 01:30 pm
Just recalling Tim's comment to Elon about "dragon scales" -- I wonder, is hexagonal the optimal default shape for most tiles? If they were naturally evolved dragon scales or pterodactyl scales, they wouldn't be hexagonal. I'm imagining they'd be elongated to match the direction of airflow, in a way that prevents them from being dislodged. Bird feathers tend to overlap each other. Should the tile area only included its attachment area, or could it extend somewhat beyond that?

Remember that the naturally evolved sort have a major, major constraint/ability that doesn’t apply here:
They grow outward from the thing they cover, and the only option for replacement is basically extrusion.  I think a lot of their shape is defined by that need.  (They also have a different purpose than this kind of heat shielding.)
Title: Re: Starship heat shield
Post by: edzieba on 08/09/2021 01:40 pm
Just recalling Tim's comment to Elon about "dragon scales" -- I wonder, is hexagonal the optimal default shape for most tiles? If they were naturally evolved dragon scales or pterodactyl scales, they wouldn't be hexagonal. I'm imagining they'd be elongated to match the direction of airflow, in a way that prevents them from being dislodged. Bird feathers tend to overlap each other. Should the tile area only included its attachment area, or could it extend somewhat beyond that?
Overlapping tiles don't work for Starship, as it encounters flow in multiple directions: hypersonic to supersonic to subsonic belly-first during entry, and subsonic to supersonic to hypersonic nose-first during launch. Unless you add hinge points and actuators to every tile to allow the lapping orientation to change between launch and landing, one or the other of those flight regimes will be attempting to rip the tiles off sideways.
Title: Re: Starship heat shield
Post by: RoboGoofers on 08/09/2021 01:47 pm
Just recalling Tim's comment to Elon about "dragon scales" -- I wonder, is hexagonal the optimal default shape for most tiles? If they were naturally evolved dragon scales or pterodactyl scales, they wouldn't be hexagonal. I'm imagining they'd be elongated to match the direction of airflow, in a way that prevents them from being dislodged. Bird feathers tend to overlap each other. Should the tile area only included its attachment area, or could it extend somewhat beyond that?
Overlapping tiles don't work for Starship, as it encounters flow in multiple directions: hypersonic to supersonic to subsonic belly-first during entry, and subsonic to supersonic to hypersonic nose-first during launch. Unless you add hinge points and actuators to every tile to allow the lapping orientation to change between launch and landing, one or the other of those flight regimes will be attempting to rip the tiles off sideways.
I wonder if they could be lapped (as in lap joint) so that there isn't a direct path between tiles while still having a flat outer profile. However I don't think that 2 half thickness layers behave the same as 1 full thickness layer.
Also, pterosaurs didn't have scales.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 08/09/2021 01:50 pm
Just recalling Tim's comment to Elon about "dragon scales" -- I wonder, is hexagonal the optimal default shape for most tiles? If they were naturally evolved dragon scales or pterodactyl scales, they wouldn't be hexagonal. I'm imagining they'd be elongated to match the direction of airflow, in a way that prevents them from being dislodged. Bird feathers tend to overlap each other. Should the tile area only included its attachment area, or could it extend somewhat beyond that?
Overlapping tiles don't work for Starship, as it encounters flow in multiple directions: hypersonic to supersonic to subsonic belly-first during entry, and subsonic to supersonic to hypersonic nose-first during launch. Unless you add hinge points and actuators to every tile to allow the lapping orientation to change between launch and landing, one or the other of those flight regimes will be attempting to rip the tiles off sideways.

This is enough to kill the concept. Put morover probably there will be problem due to drag.
Title: Re: Starship heat shield
Post by: KBK on 08/09/2021 02:31 pm
Larger tiles are much more fragile: while individual tile cost may decrease*, the odds are high that cost per unit area will increase once wastage and more complex handling procedures are taken into account.

* Unless a larger tile means you need to construct a brand new sintering oven.

the eventuality is one of automation, to some extent or another. This may be factored in to the complex equation for analysis. Obviously it's speculation based on speculation. weighting can be critical. Regardless, the placement by hand -with what is on hand/current- is also the same, to some degree.

Then the idea of playing with worst case scenarios as a starting point (hand applied, all hexagonal, etc), and then try to move upward from there. To make all the mistakes at the front end and have them solid and calculable, within the book of lore, from that point forward..
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/09/2021 02:46 pm
So what are the tags they are using to mark all the tiles for and are they colour coded?

https://twitter.com/BottinPhilip/status/1424363836971360258/photo/1
 (https://twitter.com/BottinPhilip/status/1424363836971360258/photo/1)

My thoughts:
a) tiles cracked
b) tiles not attached properly / uneven
c) gap tolerance is too great or too small
d) tile out of alignment with supporting attachment pins

a) requires investigation as to why the tile was cracked.
Could have been damaged during manufacture, in handling or during installation or cracked because there was insufficient space for it to fit properly.
b) might be rectified by manipulation (gentle hammering) or just cracks and needs replacement
c) unless the tile in question or one very close to it was mis formed in someway (in which case that one needs replacing) it is probably an alignment problem see below
d) either replace the underlying studs or make a custom tile to fit. either way is a lesson learned for the future.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 08/09/2021 06:32 pm
Close up pick of tiles being marked as either 'ok' or flagged with colored tape.

https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2051770;image

The yield isn't looking too good right now, assuming any flagged tile is a failure.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 08/09/2021 06:34 pm
Anyone figured out what the mesh is for?

Here's a crazy idea:  The mesh transports any heat that gets through a tile (cracked or missing) horizontally, distributing the heat over a wider area.   Would have to be a material that is highly conductive to heat.  (e.g. not stainless steel)
Title: Re: Starship heat shield
Post by: xvel on 08/09/2021 06:49 pm
Are you an engineer?
Title: Re: Starship heat shield
Post by: sevenperforce on 08/09/2021 07:09 pm
Anyone figured out what the mesh is for?

Here's a crazy idea:  The mesh transports any heat that gets through a tile (cracked or missing) horizontally, distributing the heat over a wider area.   Would have to be a material that is highly conductive to heat.  (e.g. not stainless steel)
I don't want to be too quick to crap on anyone's idea, but...your use of "crazy" here might be an understatement.

A wire mesh is just about the worst possible material for transferring heat conductively. You need surface area to do that. There's a reason wire filaments are used in incandescent bulbs.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/09/2021 07:44 pm
Here's a later pic of the tile marking from Mary. The red and green show a rough clustering.


Here's some total speculation. If the red is outside of positional tolerance and the green is good positioning this could be showing the robot arms variance at different reaches during pin install.


Or maybe red is off in the up and green in the down or something like that. Unmarked would be something the haven't got to yet or is good.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 08/09/2021 08:01 pm
Anyone figured out what the mesh is for?

Here's a crazy idea:  The mesh transports any heat that gets through a tile (cracked or missing) horizontally, distributing the heat over a wider area.   Would have to be a material that is highly conductive to heat.  (e.g. not stainless steel)
I don't want to be too quick to crap on anyone's idea, but...your use of "crazy" here might be an understatement.

A wire mesh is just about the worst possible material for transferring heat conductively. You need surface area to do that. There's a reason wire filaments are used in incandescent bulbs.

What's worse than crazy?

You ever participated in a creativity session?  The point isn't to go directly to a solution to a problem, it's to go indirectly.  And not veto someone's crazy idea, but think of it as a riff on the problem and like music creation, figure out what's behind the riff, or let it inspire your own riff.

The problem is heat getting through broken tiles impinges on a small surface area and there's no way to conduct the heat away, because the mineral wool and stainless steel are terrible at heat conduction.  The hot spot ultimately damages the stainless steel tank to the point of failure. So how would one conduct the heat away from the hot spot?

The conductivity of tungsten is about 10x that of stainless steel, so the mesh area would have to be > 1/10th that of the stainless steel, and the pictures show the mesh is probably 1/100 area or less, so yeah, it's not the mesh.   There's a tiny amount of heat conduction away, which is why I thought of the problem "what is a way to conduct heat away from a hot spot".

Having the entire bottom of the tile be a high temperature conductive metal (instead of just the 'Y' that we can see) might be a possible way to conduct the heat away from the hot spot, assuming the metal can slide over a nearby tiles' metal to create a point of contact for the conduction.  (e.g. the dragon scales idea, but the scales are hidden behind the ceramic part of the tile).

Or maybe not possible.  But worth thinking about, because parallel-to-the-surface heat conduction might mitigate hot spots enough that a few lost tiles don't matter.
Title: Re: Starship heat shield
Post by: Hyperborealis on 08/09/2021 08:03 pm
Nb. A close-up on the upper left hand picture of post #1945 shows a number of uncolored tiles marked "ok," and a number left blank. OTV Booster, your second speculation, or a version of it, seems more likely.
Title: Re: Starship heat shield
Post by: _MECO on 08/09/2021 08:27 pm
Here's a later pic of the tile marking from Mary. The red and green show a rough clustering.


Here's some total speculation. If the red is outside of positional tolerance and the green is good positioning this could be showing the robot arms variance at different reaches during pin install.


Or maybe red is off in the up and green in the down or something like that. Unmarked would be something the haven't got to yet or is good.
That's at least what I'm inclined to think. Just on elementary school logic red = bad, green = good, and no tape is an uninspected tile. If the thing in question they're testing is positioning, I wonder by what datum they're measuring said tile positions. You certainly can't just do each tile's location relative to the tiles next to it. Perhaps there are markings between the mounting pins.
Title: Re: Starship heat shield
Post by: Ludus on 08/09/2021 08:39 pm
This is the Erc X rendering of parallel Starship prop transfer Elon retweeted with flame emojis.
There seems to be a lot of tile cracking depicted on both ships as if that’s expected and normal. Is that expected?
 https://twitter.com/ercxspace/status/1424473919508131840?s=21 (https://twitter.com/ercxspace/status/1424473919508131840?s=21)
Title: Re: Starship heat shield
Post by: cscott on 08/09/2021 09:17 pm
Fwiw, my guess is:
1. Ok = inspected, no problems found
2. Green tape = no cracks on tile, but bad/loose fit (maybe needs stud adjustment, or adjusting mounting holes; I'm guessing "fixable without a new tile")
3. Red tape = tile cracked, needs replacement.
4. No marking = not yet inspected.
Title: Re: Starship heat shield
Post by: alphacentauri on 08/09/2021 09:55 pm
This is the Erc X rendering of parallel Starship prop transfer Elon retweeted with flame emojis.
There seems to be a lot of tile cracking depicted on both ships as if that’s expected and normal. Is that expected?
It looks to me like those tiles in the image were created by a lot of Photoshop transform/stretch/warp/clone operations on just a few tile patterns, to make straight tile images fit the curved nose cone. I see lots of warped repetitions of various "cracked" tile patterns. I would read nothing into this image about how tiles are expected to appear, it's just a poor job of cloning when you pixel peep it.
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/09/2021 10:27 pm
Fwiw, my guess is:
1. Ok = inspected, no problems found
2. Green tape = no cracks on tile, but bad/loose fit (maybe needs stud adjustment, or adjusting mounting holes; I'm guessing fixable without a new tile)
3. Red tape = tile cracked, needs replacement.
4. No marking = not yet inspected.
What about no cracks, good fit?
Title: Re: Starship heat shield
Post by: nacnud on 08/09/2021 10:33 pm
that's what ok means
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/09/2021 10:37 pm
that's what ok means
No tape = not inspected,
Red tape = replacement required
Green tape = adjustment required

how is "ok" indicated on the tiles?
Title: Re: Starship heat shield
Post by: AC in NC on 08/09/2021 10:40 pm
that's what ok means
No tape = not inspected,
Red tape = replacement required
Green tape = adjustment required

how is "ok" indicated on the tiles?

Writing
Title: Re: Starship heat shield
Post by: sevenperforce on 08/09/2021 11:39 pm
Looking closely at this image, I can see many red-marked tiles with visible cracks. None of the green-marked tiles have visible cracks or damage, but many of them do look misaligned.

(https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2051778;image)

My guess is that green means “loose” and red means “broken” and the rest are fine.

It does seem like a lot of inspection work. But when you consider that it took sixteen hours to replace a single Shuttle tile....
Title: Re: Starship heat shield
Post by: DanielW on 08/10/2021 12:10 am
I wonder why there don't seem to be two types of studs. One that is fixed in place and two that allow expansion/contraction. It seems like that would allow better placement / alignment and a stronger hold. Just make the top center stud of every tile fixed.
Title: Re: Starship heat shield
Post by: Nevyn72 on 08/10/2021 12:15 am
Given the heated/tiled side is on the bottom during re-entry wouldn't that have it's own self cooling system?

Basically any remaining cryo-temp fuel and oxidiser would be sloshing around inside the tank on the tiled side.

Basically the skin is stainless steel so is good at distributing (conducting) any hot point sources of heat leakage passing through the tiled surface. Then the inner surface of the skin is further cooled by sloshing remaining propellant.

How much would these two factors mitigate issues in the TPS?
Title: Re: Starship heat shield
Post by: _MECO on 08/10/2021 12:15 am
that's what ok means
No tape = not inspected,
Red tape = replacement required
Green tape = adjustment required

how is "ok" indicated on the tiles?

Writing
I love this place so much.
Title: Re: Starship heat shield
Post by: ETurner on 08/10/2021 12:22 am
Looking closely at this image, I can see many red-marked tiles with visible cracks. None of the green-marked tiles have visible cracks or damage, but many of them do look misaligned.

My guess is that green means “loose” and red means “broken” and the rest are fine.

It does seem like a lot of inspection work. But when you consider that it took sixteen hours to replace a single Shuttle tile....
That’s amazingly ugly, and difficult to understand:
Proper pin position + proper tile shape + kinematic coupling* = proper tile position + robustly-minimal stress.
But tlles are misaligned and broken, therefore... ???

-- Mispositioned pins or malformed tiles, hence misalignment?
-- Underconstrained kinematics, hence loose fits?
-- Overconstrained kinematics, hence stress and breakage?
-- Something else?

* A design with 3 pins in 3 grooves could work like a Maxwell coupling (https://en.wikipedia.org/wiki/Kinematic_coupling#Maxwell_coupling), tolerating misalignment (and differential thermal expansion) while providing rigid positioning without internal stress. (Bunch of pictures, lots of variants (https://www.google.com/search?q=maxwell+kinematic+coupling&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiSmIfimKXyAhWGahUIHQnVBzsQ_AUoAXoECAEQAw&biw=1378&bih=689))
Title: Re: Starship heat shield
Post by: InterestedEngineer on 08/10/2021 02:36 am

Basically the skin is stainless steel so is good at distributing (conducting) any hot point sources of heat leakage passing through the tiled surface. Then the inner surface of the skin is further cooled by sloshing remaining propellant.


Stainless steel is terrible at conducting heat, go look it up in any of the widely available charts online.

Or you can run an experiment.  Take a stainless steel pot, fill it 1/4 with water, and set it on top of a gas stove.   Just as the water is boiling, very carefully tilt the water (or throw in some frozen peas) and hear the water sizzle as it hits the area above the water which is well above boiling point.  I suggest you wear heat proof gloves to do this, I've burned myself throwing peas into a stainless steel pot.

(don't use a pot that's lined on the inside with aluminum or copper...  those distribute heat very well and it's why they make pots with aluminum or copper inside them)
Title: Re: Starship heat shield
Post by: cscott on 08/10/2021 02:47 am
Proper pin position + proper tile shape + kinematic coupling* = proper tile position + robustly-minimal stress.
But tlles are misaligned and broken, therefore... ???

-- Mispositioned pins or malformed tiles, hence misalignment?
-- Underconstrained kinematics, hence loose fits?
-- Overconstrained kinematics, hence stress and breakage?
-- Something else?

* A design with 3 pins in 3 grooves could work like a Maxwell coupling (https://en.wikipedia.org/wiki/Kinematic_coupling#Maxwell_coupling), tolerating misalignment (and differential thermal expansion) while providing rigid positioning without internal stress. (Bunch of pictures, lots of variants (https://www.google.com/search?q=maxwell+kinematic+coupling&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiSmIfimKXyAhWGahUIHQnVBzsQ_AUoAXoECAEQAw&biw=1378&bih=689))

I believe that we do "know" that this is a kinematic coupling that constrains the tile in a way which is tolerant of differential expansion of the tile and the steel.  And in *theory* this should precisely constrain the tile and there should never be a "loose" fit.

In practice I'm afraid "tolerance stacking" has struck again, and they've found that the pins are sometimes slightly too big or the grooves are slightly too narrow or the grooves/pins are too far from their ideal positions -- resulting in tile cracking.  Or else that the pins are sometimes too small or the grooves are too wide, resulting in an underconstrained tile aka "loose fit".

So it's another iterative round of design (and possibly expedient field repairs) to bring the tolerances back to what they should be.

If I had to guess, I'd expect (a) some slight pin errors on the stud welder, but that these are probably well understood, but (b) much more significant dimensional variance on the tiles, caused by relative humidity, temperature, variance in the kiln drying process, variance in the coating processes, etc.  They'll have to figure out what is causing the dimensions to drift after machining and constrain it.  Normal "manufacturing precise parts repeatably is hard" stuff.

(And, after hearing Elon Philosophy Of Manufacturing first-hand in the Everyday Astronaut interview, I'd suggest that Elon would say that if you're not throwing away a good # of tiles at this point, you're not trying hard enough to simplify tile manufacturing. No doubt they'll judiciously add back "just enough" complications to the tile bakery process to get the tolerances correct, without adding unnecessary complexity to control for factors that turn out not to matter enough.  And Elon's tweet did mention "final tiles" in his things-left-to-do list. I'd interpreted that as "the remaining tiles", but it's also possible that many/some of these are "draft" tiles, and that there are further process improvements that will be made to yield the "final" (version of the) tiles.)
Title: Re: Starship heat shield
Post by: Llian Rhydderch on 08/10/2021 04:20 am
Bottom line, SpaceX is iterating on this first ship to go high and hot, Ship 20.  They will not recover it.  Sounds that they will have several forms of data collection inside the tanks (per Musk with Tim Dodd interview, part 2 of 3).

They don't need the ship to survive the full reentry.

It would be a super nice-to-have to get some initial data from the first 20 to 60 seconds of the hot plasma encounter, so they can determine, after the fact, which issues of design, or tile placement, or groove size, or linear plasma channels between tiles, or heat at the body flaps--or with build process--will be the area they need to beef up.  Maybe learn some about ship strength failure modes as parts of the stainless steel heats excessively.

That's all.

They don't need tile perfection on the first test of the first hot tiled test article!
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/10/2021 07:43 am
Proper pin position + proper tile shape + kinematic coupling* = proper tile position + robustly-minimal stress.
But tlles are misaligned and broken, therefore... ???

-- Mispositioned pins or malformed tiles, hence misalignment?
-- Underconstrained kinematics, hence loose fits?
-- Overconstrained kinematics, hence stress and breakage?
-- Something else?

* A design with 3 pins in 3 grooves could work like a Maxwell coupling (https://en.wikipedia.org/wiki/Kinematic_coupling#Maxwell_coupling), tolerating misalignment (and differential thermal expansion) while providing rigid positioning without internal stress. (Bunch of pictures, lots of variants (https://www.google.com/search?q=maxwell+kinematic+coupling&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiSmIfimKXyAhWGahUIHQnVBzsQ_AUoAXoECAEQAw&biw=1378&bih=689))

I believe that we do "know" that this is a kinematic coupling that constrains the tile in a way which is tolerant of differential expansion of the tile and the steel.  And in *theory* this should precisely constrain the tile and there should never be a "loose" fit.

In practice I'm afraid "tolerance stacking" has struck again, and they've found that the pins are sometimes slightly too big or the grooves are slightly too narrow or the grooves/pins are too far from their ideal positions -- resulting in tile cracking.  Or else that the pins are sometimes too small or the grooves are too wide, resulting in an underconstrained tile aka "loose fit".

So it's another iterative round of design (and possibly expedient field repairs) to bring the tolerances back to what they should be.

If I had to guess, I'd expect (a) some slight pin errors on the stud welder, but that these are probably well understood, but (b) much more significant dimensional variance on the tiles, caused by relative humidity, temperature, variance in the kiln drying process, variance in the coating processes, etc.  They'll have to figure out what is causing the dimensions to drift after machining and constrain it.  Normal "manufacturing precise parts repeatably is hard" stuff.

(And, after hearing Elon Philosophy Of Manufacturing first-hand in the Everyday Astronaut interview, I'd suggest that Elon would say that if you're not throwing away a good # of tiles at this point, you're not trying hard enough to simplify tile manufacturing. No doubt they'll judiciously add back "just enough" complications to the tile bakery process to get the tolerances correct, without adding unnecessary complexity to control for factors that turn out not to matter enough.  And Elon's tweet did mention "final tiles" in his things-left-to-do list. I'd interpreted that as "the remaining tiles", but it's also possible that many/some of these are "draft" tiles, and that there are further process improvements that will be made to yield the "final" (version of the) tiles.)
Or maybe the rush to fit tiles meant they had to employ more tile fitters and some of them weren't as good as the others?
Title: Re: Starship heat shield
Post by: edzieba on 08/10/2021 08:23 am
Anyone figured out what the mesh is for?

Here's a crazy idea:  The mesh transports any heat that gets through a tile (cracked or missing) horizontally, distributing the heat over a wider area.   Would have to be a material that is highly conductive to heat.  (e.g. not stainless steel)
I don't want to be too quick to crap on anyone's idea, but...your use of "crazy" here might be an understatement.

A wire mesh is just about the worst possible material for transferring heat conductively. You need surface area to do that. There's a reason wire filaments are used in incandescent bulbs.

What's worse than crazy?

You ever participated in a creativity session?  The point isn't to go directly to a solution to a problem, it's to go indirectly.  And not veto someone's crazy idea, but think of it as a riff on the problem and like music creation, figure out what's behind the riff, or let it inspire your own riff.

The problem is heat getting through broken tiles impinges on a small surface area and there's no way to conduct the heat away, because the mineral wool and stainless steel are terrible at heat conduction.  The hot spot ultimately damages the stainless steel tank to the point of failure. So how would one conduct the heat away from the hot spot?

The conductivity of tungsten is about 10x that of stainless steel, so the mesh area would have to be > 1/10th that of the stainless steel, and the pictures show the mesh is probably 1/100 area or less, so yeah, it's not the mesh.   There's a tiny amount of heat conduction away, which is why I thought of the problem "what is a way to conduct heat away from a hot spot".

Having the entire bottom of the tile be a high temperature conductive metal (instead of just the 'Y' that we can see) might be a possible way to conduct the heat away from the hot spot, assuming the metal can slide over a nearby tiles' metal to create a point of contact for the conduction.  (e.g. the dragon scales idea, but the scales are hidden behind the ceramic part of the tile).

Or maybe not possible.  But worth thinking about, because parallel-to-the-surface heat conduction might mitigate hot spots enough that a few lost tiles don't matter.
No. /Jim

Long answer: if your goal is to 'conduct heat away' from an exposed area, the absolute worst place to route your heat conduction path to is under some insulating tiles.
Title: Re: Starship heat shield
Post by: ETurner on 08/10/2021 10:29 am
Proper pin position + proper tile shape + kinematic coupling* = proper tile position + robustly-minimal stress.
But tlles are misaligned and broken, therefore... ???

-- Mispositioned pins or malformed tiles, hence misalignment?
-- Underconstrained kinematics, hence loose fits?
-- Overconstrained kinematics, hence stress and breakage?
-- Something else?

* A design with 3 pins in 3 grooves could work like a Maxwell coupling (https://en.wikipedia.org/wiki/Kinematic_coupling#Maxwell_coupling), tolerating misalignment (and differential thermal expansion) while providing rigid positioning without internal stress. (Bunch of pictures, lots of variants (https://www.google.com/search?q=maxwell+kinematic+coupling&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiSmIfimKXyAhWGahUIHQnVBzsQ_AUoAXoECAEQAw&biw=1378&bih=689))

I believe that we do "know" that this is a kinematic coupling that constrains the tile in a way which is tolerant of differential expansion of the tile and the steel.  And in *theory* this should precisely constrain the tile and there should never be a "loose" fit.

In practice I'm afraid "tolerance stacking" has struck again, and they've found that the pins are sometimes slightly too big or the grooves are slightly too narrow or the grooves/pins are too far from their ideal positions -- resulting in tile cracking.  Or else that the pins are sometimes too small or the grooves are too wide, resulting in an underconstrained tile aka "loose fit".

So it's another iterative round of design (and possibly expedient field repairs) to bring the tolerances back to what they should be.

If I had to guess, I'd expect (a) some slight pin errors on the stud welder, but that these are probably well understood, but (b) much more significant dimensional variance on the tiles, caused by relative humidity, temperature, variance in the kiln drying process, variance in the coating processes, etc.  They'll have to figure out what is causing the dimensions to drift after machining and constrain it.  Normal "manufacturing precise parts repeatably is hard" stuff.

(And, after hearing Elon Philosophy Of Manufacturing first-hand in the Everyday Astronaut interview, I'd suggest that Elon would say that if you're not throwing away a good # of tiles at this point, you're not trying hard enough to simplify tile manufacturing. No doubt they'll judiciously add back "just enough" complications to the tile bakery process to get the tolerances correct, without adding unnecessary complexity to control for factors that turn out not to matter enough.  And Elon's tweet did mention "final tiles" in his things-left-to-do list. I'd interpreted that as "the remaining tiles", but it's also possible that many/some of these are "draft" tiles, and that there are further process improvements that will be made to yield the "final" (version of the) tiles.)
Seems about right, but the variation in tile height (making steps on the surface) looks pretty large, which seems like it might be a symptom of a pin/tile interface design problem (unless the pin-length control is garbage). My guess is that they need to iterate the snap-on interface between the pins and the holes/grooves on the tiles.

 Maybe add a part (no!) between the tiles and pins? -- But if so, then a very small, light, and simple part. Maybe something like a gadget made of springy steel sheet that is preinstalled and slides in a groove on the tile-side with a hole in it for a pin to snap into? Maybe put the snap-on interaction in the springy gadget and simplify the pins to something symmetric with a knob at the end? This would separate the pin snap-on requirement from tile-side mechanical contact and sliding mobility. Annealing in use and loss of springiness would be OK. Probably lots of options, and easy to prototype the geometries and motions. (Thinking while typing here.)
Title: Re: Starship heat shield
Post by: nacnud on 08/10/2021 11:14 am
Having adjusted cupboard/wardrobe doors to make them flush too many times, ok twice. I wonder if there is a similar mechanism inside the tile between the metal support bracket and the ceramic.
Title: Re: Starship heat shield
Post by: nacnud on 08/10/2021 11:29 am
Following on… your probably want to start adjusting the tiles from the centre out towards the sides as there is wiggle room at the edges of the TPS. Similar from top to bottom, but the rings of pentagonal tiles might change this… I don’t know about man lifts but working with ropes is always easier to work top down. You would also need to have all the tiles in place before fetteling with them so all the misalignments are obvious.



Title: Re: Starship heat shield
Post by: posigrade on 08/10/2021 02:09 pm
When I watched a worker hammer a tile in repeatly using a mallet during the Dodd/Musk #2 interview, it struck me that they're not handling tolerances as well as they could.
Title: Re: Starship heat shield
Post by: envy887 on 08/10/2021 02:31 pm
When I watched a worker hammer a tile in repeatly using a mallet during the Dodd/Musk #2 interview, it struck me that they're not handling tolerances as well as they could.

That was the back of his fist, not a mallet. There was a lot of pushing, tapping, and slapping on the tiles in the video, but no hammers that I could find.

Elon: "but as you can see, we're figuring it out"...

https://youtu.be/SA8ZBJWo73E?t=2779
Title: Re: Starship heat shield
Post by: envy887 on 08/10/2021 02:37 pm
Seems about right, but the variation in tile height (making steps on the surface) looks pretty large, which seems like it might be a symptom of a pin/tile interface design problem (unless the pin-length control is garbage). My guess is that they need to iterate the snap-on interface between the pins and the holes/grooves on the tiles.

 Maybe add a part (no!) between the tiles and pins? -- But if so, then a very small, light, and simple part. Maybe something like a gadget made of springy steel sheet that is preinstalled and slides in a groove on the tile-side with a hole in it for a pin to snap into? Maybe put the snap-on interaction in the springy gadget and simplify the pins to something symmetric with a knob at the end? This would separate the pin snap-on requirement from tile-side mechanical contact and sliding mobility. Annealing in use and loss of springiness would be OK. Probably lots of options, and easy to prototype the geometries and motions. (Thinking while typing here.)

There are pictures of uninstalled and broken tiles upthread showing a metallic-looking part embedded in the tile. That part most likely interfaces to the studs on the hull and spreads out the point contact loads into the brittle tile material. If they haven't eliminated it, that is...
Title: Re: Starship heat shield
Post by: Rossco on 08/10/2021 04:19 pm
Sorry if this has been covered but I notice up the belly of SS the tiles seem to be broken into sections with two rows of half tiles giving a distinctive line throughout the heatshield.
Initially I thought this might be due to the tiles being fitted prior to stacking, however they don't seem to match the build process - so are this expansion joints?
Title: Re: Starship heat shield
Post by: OTV Booster on 08/10/2021 04:28 pm
Fwiw, my guess is:
1. Ok = inspected, no problems found
2. Green tape = no cracks on tile, but bad/loose fit (maybe needs stud adjustment, or adjusting mounting holes; I'm guessing "fixable without a new tile")
3. Red tape = tile cracked, needs replacement.
4. No marking = not yet inspected.
A tile can have a bad fit and be cracked. The two might be connected and this would be good to know. None of the tiles have double marking so I'm guessing the two colors are marking variations of one problem.


Whatever the problem is, there is that clustering. The only thing I've come up with is arm variance over its reach. It could be something else. Somebody mentioned interior structure. Maybe affecting welding. Maybe causing minor variations in the outer mould line, hence pin placement. Any other ideas?


If I weren't so lazy I'd go back to earlier pics and use specular reflection to map surface variations and rack them up against the markings. Not having any software tools for this it would be a massive manual job. Maybe I'm not lazy, just smart.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/10/2021 05:01 pm
Looking closely at this image, I can see many red-marked tiles with visible cracks. None of the green-marked tiles have visible cracks or damage, but many of them do look misaligned.

(https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2051778;image)

My guess is that green means “loose” and red means “broken” and the rest are fine.

It does seem like a lot of inspection work. But when you consider that it took sixteen hours to replace a single Shuttle tile....
On close inspection, it's more complicated. Three down and one to the right of the circled tile there is black tape. There's black tape all over the place. Some red tape is short and at a diagonal but only on the periphery. Only a few of the red taped are cracked. I've attached another pic at higher resolution. It was cropped by Philip Bottin on Twitter without attribute.

On the extreme left is blue tape. I think I remember them using tan masking tape type stuff for holding them in place, but it might have been blue. Some of the black tape is covering glitches but not all, or at not visibly.

WHAT is going on here?
Title: Re: Starship heat shield
Post by: OTV Booster on 08/10/2021 05:07 pm
I wonder why there don't seem to be two types of studs. One that is fixed in place and two that allow expansion/contraction. It seems like that would allow better placement / alignment and a stronger hold. Just make the top center stud of every tile fixed.
The pins are fixed but the "Y" thingie on the back of the tile is where the pins seat into slots. Same effect.
Title: Re: Starship heat shield
Post by: Keldor on 08/10/2021 05:23 pm
Looking closely at this image, I can see many red-marked tiles with visible cracks. None of the green-marked tiles have visible cracks or damage, but many of them do look misaligned.

(https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2051778;image)

My guess is that green means “loose” and red means “broken” and the rest are fine.

It does seem like a lot of inspection work. But when you consider that it took sixteen hours to replace a single Shuttle tile....
On close inspection, it's more complicated. Three down and one to the right of the circled tile there is black tape. There's black tape all over the place. Some red tape is short and at a diagonal but only on the periphery. Only a few of the red taped are cracked. I've attached another pic at higher resolution. It was cropped by Philip Bottin on Twitter without attribute.

On the extreme left is blue tape. I think I remember them using tan masking tape type stuff for holding them in place, but it might have been blue. Some of the black tape is covering glitches but not all, or at not visibly.

WHAT is going on here?

It looks to me like at first they were just marking bad tiles by slapping on a bit of red tape, but at some point they decided they had a problem and decided to "map" an area with the red and green tape to look for trends.  It's also possible that it was just a different worker.

The blue tape is over the gaps between tiles (you can see this much more clearly in some of the other photos). Presumably they're using it to mark places where they're not happy with the tile spacing.

I'm not sure what the black tape is about either.  Covering the most blatently obvious broken tiles for the photo op when they stacked it?
Title: Re: Starship heat shield
Post by: OTV Booster on 08/10/2021 05:37 pm
Proper pin position + proper tile shape + kinematic coupling* = proper tile position + robustly-minimal stress.
But tlles are misaligned and broken, therefore... ???

-- Mispositioned pins or malformed tiles, hence misalignment?
-- Underconstrained kinematics, hence loose fits?
-- Overconstrained kinematics, hence stress and breakage?
-- Something else?

* A design with 3 pins in 3 grooves could work like a Maxwell coupling (https://en.wikipedia.org/wiki/Kinematic_coupling#Maxwell_coupling), tolerating misalignment (and differential thermal expansion) while providing rigid positioning without internal stress. (Bunch of pictures, lots of variants (https://www.google.com/search?q=maxwell+kinematic+coupling&source=lnms&tbm=isch&sa=X&ved=2ahUKEwiSmIfimKXyAhWGahUIHQnVBzsQ_AUoAXoECAEQAw&biw=1378&bih=689))

I believe that we do "know" that this is a kinematic coupling that constrains the tile in a way which is tolerant of differential expansion of the tile and the steel.  And in *theory* this should precisely constrain the tile and there should never be a "loose" fit.

In practice I'm afraid "tolerance stacking" has struck again, and they've found that the pins are sometimes slightly too big or the grooves are slightly too narrow or the grooves/pins are too far from their ideal positions -- resulting in tile cracking.  Or else that the pins are sometimes too small or the grooves are too wide, resulting in an underconstrained tile aka "loose fit".

So it's another iterative round of design (and possibly expedient field repairs) to bring the tolerances back to what they should be.

If I had to guess, I'd expect (a) some slight pin errors on the stud welder, but that these are probably well understood, but (b) much more significant dimensional variance on the tiles, caused by relative humidity, temperature, variance in the kiln drying process, variance in the coating processes, etc.  They'll have to figure out what is causing the dimensions to drift after machining and constrain it.  Normal "manufacturing precise parts repeatably is hard" stuff.

(And, after hearing Elon Philosophy Of Manufacturing first-hand in the Everyday Astronaut interview, I'd suggest that Elon would say that if you're not throwing away a good # of tiles at this point, you're not trying hard enough to simplify tile manufacturing. No doubt they'll judiciously add back "just enough" complications to the tile bakery process to get the tolerances correct, without adding unnecessary complexity to control for factors that turn out not to matter enough.  And Elon's tweet did mention "final tiles" in his things-left-to-do list. I'd interpreted that as "the remaining tiles", but it's also possible that many/some of these are "draft" tiles, and that there are further process improvements that will be made to yield the "final" (version of the) tiles.)
IIRC the plan is to add caulking between tiles. Probably the same stuff as the underlayment. In theory this should allow looser dimensional tolerance. If two tiles are expanding towards each other through a spot where manufacturing tolerances are stacking bad, the caulking would keep them from contacting and allow the thermal creep to push off in the opposite direction where hopefully the tolerances are stacking good. Unless the stacking gets stacked and there isn't enough room in any direction.


If this is as bad as it looks (not a done deal) does 20 become a pathfinder? This would delay launch for sure but maybe that is not all bad. It would give the FAA a chance to give a ruling and do the 30 day comment period. Sun Tzu recommended leaving a foe an escape route that they not fight with desperation.  ;)
Title: Re: Starship heat shield
Post by: volker2020 on 08/10/2021 05:40 pm
I was surprised to see, that they had no special tool to apply the tiles. I would have assumed that they would have some vacuum holder, allowing them to place the tile, while making sure no bending during application could break the tile. I might have assumed that would have a tool, to make sure that the placement of the pins is optimal.

Since both would have been rather low tech, it came as a surprise seeing one man hammer with his hand on a tile, known to break easily.
Title: Re: Starship heat shield
Post by: cscott on 08/10/2021 05:43 pm
Fwiw I thought the black "tape" might be an RTV-like tile-repair substance. Small fractures might be repaired in place.  Red would then be "big cracks", too big to patch.  I've been thinking that green might be "tile gaps too small", that is they don't leave enough room for expansion on one of the five or six sides---aka the tile might be "fine" (undamaged) but still something about the totality of the installation is unacceptable.

Wrt to "clustering" -- most likely IMO it reflects work patterns.  One particular worker who tended to bang on the tiles a little too hard, or one day's worth of robot stud welding where the machine wasn't calibrated quite right, something like that.
Title: Re: Starship heat shield
Post by: cscott on 08/10/2021 05:46 pm
Sorry if this has been covered but I notice up the belly of SS the tiles seem to be broken into sections with two rows of half tiles giving a distinctive line throughout the heatshield.
Initially I thought this might be due to the tiles being fitted prior to stacking, however they don't seem to match the build process - so are this expansion joints?
Lots of previous discussion on this, scroll up (way up).

Short story is that the radius of a cone shrinks as you approach the tip.  The horizonal gaps seem to be whether the hex tiles are allowed to "slip" past each other in order to accommodate the shrinking nose radius. (Or equivalently, where a smaller/larger/differently tapered set of tiles begins.). You'll notice that the vertical sides of the hexes shift their alignment above and below the horizontal gap.
Title: Re: Starship heat shield
Post by: nacnud on 08/10/2021 05:49 pm
I don’t they they are worried about 20 making it all the way back down again. Just the learning experience of getting it all the pieces together, stacked, filled with prop and launched off the pad is enough. 

Everything they are learning from this version of the TPS can be applied to the next vehicle. They must want to do the best job they can with what they have but I think they aren’t going to worry too much about applying changes to this vehicle.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/10/2021 05:57 pm
I was surprised to see, that they had no special tool to apply the tiles. I would have assumed that they would have some vacuum holder, allowing them to place the tile, while making sure no bending during application could break the tile. I might have assumed that would have a tool, to make sure that the placement of the pins is optimal.

Since both would have been rather low tech, it came as a surprise seeing one man hammer with his hand on a tile, known to break easily.
The Musk process informed by an earlier over automation debacle: Smack en till it hurts. Then tell me what tool you need for the next one.
Title: Re: Starship heat shield
Post by: edzieba on 08/11/2021 09:07 am
Alternate take on tile labelling: they started with "green = OK, red = not OK", then ran low on or out of tape and decided "writing 'OK' in silver sharpie" is fine too, and faster than adding and later removing tape.
Title: Re: Starship heat shield
Post by: exilon on 08/11/2021 09:36 am
They had red, green, and "ok" being put up simultaneously.
Title: Re: Starship heat shield
Post by: cscott on 08/11/2021 01:39 pm
They had red, green, and "ok" being put up simultaneously.
And once you know that "white smudge at apex of hexagon" means "ok" in the longer-distance shots, you can see tiles marked "ok" pretty early on.  Before the stacking, I think, though someone should dig through the archives to check.

I think before the final push (last few days before stacking) they were actually inspecting and fixing them in place as they went -- you can see a number of tiles with the black tape/rtv stuff, presumably over hairline cracks.  It was only the tiles added in the final push that got "rushed" and which now seem to be sprouting tape.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/11/2021 02:04 pm
Ok, the tape is definitely some sort of pattern. Curtesy of /r/SpaceX Masterrace on Twitter.

Title: Re: Starship heat shield
Post by: Alvian@IDN on 08/12/2021 05:25 am
I'm assuming heat shield tiles are on the critical path.
Only things on the critical path are being worked.
Heat shield tiles are being worked.

I'm wondering, why not eliminate the part? That is, heat shield tiles.
Instead, for the first earth-inbound starships, have a tanker meet and refuel the inbound starship,
before the inbound starship reaches earth and use the inbound starship engines to slow the ship down,
eliminating the need for heat shield tiles.
Use early tankers that will be thrown away anyway.
Fuel and tankers will be plentiful.
This even seems less risky.

Continue developing the tiles.
But off the critical path.
Deploy them when they are ready.

And get to mars faster.
Or am I missing something?

This thread is probably only suitable for introducing this idea.
Any suggestion where it should go?
(I know, that's two risky risky questions in a row! :-))
Mass to orbit will become small & even more complicated architecture. Reentering without encountering a plasma is almost a sci-fi territory
Title: Re: Starship heat shield
Post by: MTom on 08/12/2021 06:33 am
I'm assuming heat shield tiles are on the critical path.
Only things on the critical path are being worked.
Heat shield tiles are being worked.

I'm wondering, why not eliminate the part? That is, heat shield tiles.
Instead, for the first earth-inbound starships, have a tanker meet and refuel the inbound starship,
before the inbound starship reaches earth and use the inbound starship engines to slow the ship down,
eliminating the need for heat shield tiles.
Use early tankers that will be thrown away anyway.
Fuel and tankers will be plentiful.
This even seems less risky.

Continue developing the tiles.
But off the critical path.
Deploy them when they are ready.

And get to mars faster.
Or am I missing something?

This thread is probably only suitable for introducing this idea.
Any suggestion where it should go?
(I know, that's two risky risky questions in a row! :-))

IMHO if heat shield would be off the critical path, they would test it too.
In Agile methodology the critical functions have to be prioritised because they can lead to architectural changes. The necessary delaying of heat shield testing because of the lack of orbital flight tests is an actual development risk.
I'm confident spacex ranked the heat shield orbital testing high on their priority list.
Title: Re: Starship heat shield
Post by: dfp21 on 08/12/2021 07:04 am
After observing tiles falling off the ship, I think color-coding the tiles that didn't fall off is superfluous. I don't understand it at all. Are they planning on "fixing" the tiles that didn't fall off? Aren't they ignoring the elephant in the room?
Title: Re: Starship heat shield
Post by: _----_- on 08/12/2021 07:26 am
After observing tiles falling off the ship, I think color-coding the tiles that didn't fall off is superfluous. I don't understand it at all. Are they planning on "fixing" the tiles that didn't fall off? Aren't they ignoring the elephant in the room?

They may just be characterizing how the tiles failed before deciding what to do. My bet is on launching with only a partially fixed heatshield and letting it burn on re-entry. Make fixes on the next one.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 08/12/2021 08:29 am
Ok, the tape is definitely some sort of pattern. Curtesy of /r/SpaceX Masterrace on Twitter.

 ;D ;D ;D

I like this "Gioconda" SS version. They could use that system to draw ads on the rocket, but I think they will never do that.
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/12/2021 08:58 am
Seems that a lot of the tiles especially around the fin have been marked with numbers like -803, -05H, -05W, 720 etc
Perhaps these are the identifiers for the tile type?
https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2052313;image (https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2052313;image)
Title: Re: Starship heat shield
Post by: AC in NC on 08/12/2021 01:56 pm
Or am I missing something?
You are missing that a full SS doesn't have 9km/s of deltaV.  You've thrown away 8 tankers and burned up anyway.

The notion is ludicrous.  The fastest way to get to Mars [in a meaningful way which is the only interpretation that is correct here] is via a fully reusable system.
Title: Re: Starship heat shield
Post by: Rossco on 08/12/2021 02:48 pm
Sorry if this has been covered but I notice up the belly of SS the tiles seem to be broken into sections with two rows of half tiles giving a distinctive line throughout the heatshield.
Initially I thought this might be due to the tiles being fitted prior to stacking, however they don't seem to match the build process - so are this expansion joints?
Lots of previous discussion on this, scroll up (way up).

Short story is that the radius of a cone shrinks as you approach the tip.  The horizonal gaps seem to be whether the hex tiles are allowed to "slip" past each other in order to accommodate the shrinking nose radius. (Or equivalently, where a smaller/larger/differently tapered set of tiles begins.). You'll notice that the vertical sides of the hexes shift their alignment above and below the horizontal gap.

Oks that bit I get but its in the main barrel of SS, or is that very slightly tapered as well?
Title: Re: Starship heat shield
Post by: cscott on 08/12/2021 02:51 pm
I haven't noticed these on the main barrel, but if present the horizontal gaps almost certainly line up with the weld bead on barrel sections.
Title: Re: Starship heat shield
Post by: edzieba on 08/12/2021 02:54 pm
Part 2:

https://youtu.be/SA8ZBJWo73E

Quote
Join me as I take a tour of SpaceX's Starbase facility with Elon Musk as our tour guide! This is part 2 of 3, so stay tuned, there's another one coming!

If you need some notes on this video with key points, check out our article - https://everydayastronaut.com/starbase-tour-and-interview-with-elon-musk/

Need a rundown on Starship? I've got you covered with our "Complete Guide to Starship"
//youtu.be/-8p2JDTd13k

00:00 - Intro
00:45 - Tent 1 // Raptors
05:00 - Failure and the Space Shuttle
08:35 - Launch Escape Systems
10:50 - Tent 2
13:00 - Heat Shield Talk
16:20 - 1st Orbital Test
26:26 - Tent 3 // Nose Cones
37:40 - S20 Nose Cone // Reentry
51:00 - 69.420
At 36:20 you can see stacks upon stacks of crates. At 36:50 you can see a crate open with tiles inside, and from 37:00 you can see empty crates next to the tile installers (which appear to be flat-packed or nested, so the full crates seen earlier must have been full of tiles) and crates up on the cherrypickers with the tile installer.

The open crate is the first view of the backside of an intact tile, and it looks like the embedded metal rails that the attachment clips insert into are 'buried' under the silica tile surface. They may have been cast right into the billet, and they just let the attachment pins push straight through the friable sintered silica to reach the rails during installation rather than perform a dedicated milling step to expose them.
Title: Re: Starship heat shield
Post by: cscott on 08/12/2021 04:31 pm
That's interesting.  The closeups of the pins seem to show that they have circle shaped tops, which isn't exactly the shape I'd expect for something sharp enough to poke through the backside of the tile.

But it makes me wonder if the "mill out the back" step was one of those "let's see if we can remove this step" experiments.  It might have worked ok in the lab, but in the field misalignment when originally pushing in the pins might have caused enough stress when wiggling thing over to expose the actual metal rail to cause the tiles to crack.

This might be wide of the mark. But if my wild guess is correct, fixing the tile cracking might be as "simple" as restoring that tile machining step so that the tiles are aligned correctly on the pins at the start of the "push" and so damage doesn't occur.

OTOH, given that the tiles are intended to be infinitely reusable, it may be that some percentage of failure-on-installation is worth it in exchange for skipping an expensive machining step on a couple of thousand tiles.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/12/2021 08:37 pm
That's interesting.  The closeups of the pins seem to show that they have circle shaped tops, which isn't exactly the shape I'd expect for something sharp enough to poke through the backside of the tile.

But it makes me wonder if the "mill out the back" step was one of those "let's see if we can remove this step" experiments.  It might have worked ok in the lab, but in the field misalignment when originally pushing in the pins might have caused enough stress when wiggling thing over to expose the actual metal rail to cause the tiles to crack.

This might be wide of the mark. But if my wild guess is correct, fixing the tile cracking might be as "simple" as restoring that tile machining step so that the tiles are aligned correctly on the pins at the start of the "push" and so damage doesn't occur.

OTOH, given that the tiles are intended to be infinitely reusable, it may be that some percentage of failure-on-installation is worth it in exchange for skipping an expensive machining step on a couple of thousand tiles.
Yeah, not much point in getting too bent out of shape over tiles popping off. Yet.


It's a known long pole. It might be as minor as rotating the pins 90deg or as devastating as (shudder) a complete rethink on thermal protection.


Let's hope it's something minor. Maybe a pin redesign and tightening up tolerances on the weld bot. If they're still planning on inter-tile packing, that and better pin positioning might be enough.
Title: Re: Starship heat shield
Post by: edzieba on 08/13/2021 08:03 am
That's interesting.  The closeups of the pins seem to show that they have circle shaped tops, which isn't exactly the shape I'd expect for something sharp enough to poke through the backside of the tile.
The sintered silica tiles are pretty friable, kind of like a fine XPS foam. You could poke into the uncoated portion of one with a determined finger.
Title: Re: Starship heat shield
Post by: cscott on 08/13/2021 12:32 pm
Right. I'm just saying that a blunt pin is going to have more insertion force and potentially cause more damage if inserted at the wrong site and "wiggled around" to fit.  I understand why they'd want to skip an additional machining step on 5,000 tiles, but maybe this is the tension in their process they're working out.
Title: Re: Starship heat shield
Post by: ETurner on 08/13/2021 02:25 pm
Does anyone have a plausible explanation for why tiles end up at different distances from the skin?
In other words, why do we see steps on the surface?!?!
I would have expected that this tolerance would be important and easy to keep pretty tight, but I would have been wrong.
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/13/2021 02:51 pm
Does anyone have a plausible explanation for why tiles end up at different distances from the skin?
In other words, why do we see steps on the surface?!?!
I would have expected that this tolerance would be important and easy to keep pretty tight, but I would have been wrong.
Probably lots of reasons some cumulative on some occasions. I would put my money on the three biggest ones being:
minor variation in the pin orientation, they may not all be exactly perpendicular to the surface at all times and may not be exactly positioned with sufficient precision.
Slight distortion in the nose shape from the ideal conic form due to cumulative minor welding discrepancies.
Slight variation tile to tile in the depth and orientation of the fixing points

Title: Re: Starship heat shield
Post by: envy887 on 08/13/2021 03:00 pm
Does anyone have a plausible explanation for why tiles end up at different distances from the skin?
In other words, why do we see steps on the surface?!?!
I would have expected that this tolerance would be important and easy to keep pretty tight, but I would have been wrong.
Probably lots of reasons some cumulative on some occasions. I would put my money on the three biggest ones being:
minor variation in the pin orientation, they may not all be exactly perpendicular to the surface at all times and may not be exactly positioned with sufficient precision.
Slight distortion in the nose shape from the ideal conic form due to cumulative minor welding discrepancies.
Slight variation tile to tile in the depth and orientation of the fixing points

Some of the tiles seem to be off from the proper seated height by 5 or 10 mm. The tolerances on each component at much tighter than that, but if the pin and hole locations are out of tolerance by only a fraction of 1 mm they might bind up as they try to insert the tile over the pins and it wouldn't seat down all the way.

The solution is probably either to improve the manufacturing tolerances or change the tile/pin design to tolerate a less precise fit without binding.
Title: Re: Starship heat shield
Post by: ETurner on 08/13/2021 03:17 pm
Does anyone have a plausible explanation for why tiles end up at different distances from the skin?
In other words, why do we see steps on the surface?!?!
I would have expected that this tolerance would be important and easy to keep pretty tight, but I would have been wrong.
Probably lots of reasons some cumulative on some occasions. I would put my money on the three biggest ones being:
minor variation in the pin orientation, they may not all be exactly perpendicular to the surface at all times and may not be exactly positioned with sufficient precision.
Slight distortion in the nose shape from the ideal conic form due to cumulative minor welding discrepancies.
Slight variation tile to tile in the depth and orientation of the fixing points

Some of the tiles seem to be off from the proper seated height by 5 or 10 mm. The tolerances on each component at much tighter than that, but if the pin and hole locations are out of tolerance by only a fraction of 1 mm they might bind up as they try to insert the tile over the pins and it wouldn't seat down all the way.

The solution is probably either to improve the manufacturing tolerances or change the tile/pin design to tolerate a less precise fit without binding.
If pins fit in Y-oriented grooves (or short radially-aligned slots) then the mechanical constraints are such that lateral variations in position (of pins or slots) cannot cause binding. This narrows the possibilities for binding to either
1) What would seem to be an unnecessarily-constrained geometry (like pins in small holes rather than slots) or
2) A pin/tile incompatibility (crushed fiber-stuff?) that has nothing to do with pin placement or tile geometry.
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/13/2021 03:47 pm
Could they put the pins into the tile and cover the back with a slightly oversized hexagon of matting and then align and weld attach that as a unit to the ship and surrounding tiles?

Alternatively wait for the new longer form segments (more accurate alignment perhaps?) to be built into a nose cone and try again using refined attachment methods.
Title: Re: Starship heat shield
Post by: rsdavis9 on 08/13/2021 04:32 pm
The higher and lower tiles may simply be too much or too little fabric underneath. They just have to be more carefull when putting on the insulating blanket.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/13/2021 06:08 pm
Does anyone have a plausible explanation for why tiles end up at different distances from the skin?
In other words, why do we see steps on the surface?!?!
I would have expected that this tolerance would be important and easy to keep pretty tight, but I would have been wrong.
Speculation: Blanket layers overlapping. Mesh creep. Damaged/misplaced pin. Misaligned 'Y' thingie on the tile. Bad Karma.


It'd be good to have real info.
Title: Re: Starship heat shield
Post by: ETurner on 08/13/2021 07:32 pm
The higher and lower tiles may simply be too much or too little fabric underneath. They just have to be more carefull when putting on the insulating blanket.
Speculation: Blanket layers overlapping. Mesh creep. Damaged/misplaced pin. Misaligned 'Y' thingie on the tile. Bad Karma.

It'd be good to have real info.
If the blankets are uniform (they must be, or SpaceX wouldn’t use them), then they can’t be a cm or so too thick or thin (and lumpy -- thick under one tile but not its neighbor).

But then the problem would have to be gaps or overlaps -- but that seems too obviously a mistake. I mean, actual tile-scale gaps? Or any kind of double-thickness, look-at-that-edge-sticking-out overlap?

Rubbish pins, maybe, but with results that irregular -- in length? -- and not fixed? Still puzzled.

Y grooves by nature can’t be misaligned, which is their superpower. A pin missing the groove maybe, but ??

“Bad karma”: definite possibility.

“Real info”: probably the only hope, but I’d expect that we could put together a more consistent set of guesses.
Title: Re: Starship heat shield
Post by: RoboGoofers on 08/13/2021 07:57 pm
Maybe the temp fluctuations from an uneven tile surface won't matter as much when the tiles are mechanically attached? Are the fluctuations hot enough to weaken stainless?
Title: Re: Starship heat shield
Post by: Cheapchips on 08/13/2021 09:50 pm

I can't help but feel that 'tapeageddon' is a consequence of rushing the nosecone for the surge. The tank barrel sections have escaped such embellishment.  Maybe they've just not inspected that far yet or inspection was done out of sight, before the tank was stacked.
Title: Re: Starship heat shield
Post by: cscott on 08/13/2021 11:22 pm


If the blankets are uniform (they must be, or SpaceX wouldn’t use them), then they can’t be a cm or so too thick or thin (and lumpy -- thick under one tile but not its neighbor).

No, but they can easily bunch up, especially since you are putting flat rectangular fabric over a comic section, and apparently pushing it manually over the pin array.  So if you don't pull "tight enough" when you push the fabric over the pin you get a little wrinkle which eventually causes the tile to sit proud.
Title: Re: Starship heat shield
Post by: cscott on 08/13/2021 11:23 pm

I can't help but feel that 'tapeageddon' is a consequence of rushing the nosecone for the surge. The tank barrel sections have escaped such embellishment.  Maybe they've just not inspected that far yet or inspection was done out of sight, before the tank was stacked.
I think cylindrical sections are just fundamentally easier (regular, etc) than conic sections.

Also they've been doing larger and larger cylindrical sections on every starship.  This is the first time they are doing a nose cone.
Title: Re: Starship heat shield
Post by: Gunner on 08/14/2021 12:04 am
Today there was a close-up in the NSF video of the untiled section on the nosecone of S20.  It was quite uneven with bumps and dents and ridges.  Anyone who has laid ceramic tile over an uneven floor or wall soon realizes the final surface can look quite uneven if the underlayment is bumpy.  Since the barrel section looks much better than the nosecone, maybe the underlying surface is the culprit on the nosecone.  Do they grind down the weld ridge much?  That could cause quite a few issues laying tiles over it.

Also wondering how much the skin's expansion/contraction due to pressure and temperature changes will affect the tiles.  The Shuttle tiles had problems and did not need to deal with expansion and contraction!  I have this vision of tiles popping off S20 when it's fully pressurized and cold.

Sorry if this has been noted previously.  I just joined and only read back about 20 pages.  I have been concerned  for a couple years the heat shield will be the most difficult part of Starship.  I was blasted a couple times when I voiced by concerns on the Reddit forum.  I hope this forum is more favorable to concerns I have.
Title: Re: Starship heat shield
Post by: cscott on 08/14/2021 12:32 am
Well, I don't think this forum is any more friendly to concern trolling.  But sure, the heat shield is super hard.  Everything about starship/super heavy is super hard.  I don't know that the heat shield is "harder" than getting 29 full flow staged combustion engines to perform the mission, or harder than the catch tower, or harder than the clamshell payload deploy, or harder to cryogenic propellant transfer or...  The point is, it's all pretty hard and ambitious and we all enjoy watching SpaceX fail, fail again, fail some more, and finally succeed.
Title: Re: Starship heat shield
Post by: cuddihy on 08/14/2021 12:46 am
Even if the upcoming cryo test results in a shower of tiles falling off(which I don’t expect), it would still be a heck of a show.
Title: Re: Starship heat shield
Post by: RobLynn on 08/14/2021 04:38 am
They will have internal cameras in the interior volumes of starship to look for hot spots.  If they added a payload tank with a few tonnes of water and a distributed array of solenoid controlled spray nozzles at some stand off distance from inner surface of Starship (like center pivot irrigators use) then they could reactively cool any hot spots caused by tile failures etc.  That would give them a greater chance of exploring the entire re-entry profile and possibly allow the recovery of hardware to figure out what went wrong (or right).  Wouldn't be too hard or time consuming to do, and might speed up Starship development process significantly.
Title: Re: Starship heat shield
Post by: cscott on 08/14/2021 08:23 am
They wouldn't use water, they'd use methane.  And Elon has been wanting to do almost exactly this for some time; it's called "transpiration cooling".  But the complexity and weight have been prohibitive so far.
Title: Re: Starship heat shield
Post by: BT52 on 08/14/2021 09:13 am
They wouldn't use water, they'd use methane.  And Elon has been wanting to do almost exactly this for some time; it's called "transpiration cooling".  But the complexity and weight have been prohibitive so far.

I would say passive system wins on all fronts in matter of weight and complexity. They could use trans cooling for critical areas as was pointed in that interview.

Furthermore. All that alignment problems could get almost alleviated with new more unified nosecone with less parts.

OFC all that is try and error quick testing on full display. So many variables too consider. Is just better to put assembly, cryo-refill and at final end full reentry to the test.
Title: Re: Starship heat shield
Post by: ETurner on 08/14/2021 09:34 am


If the blankets are uniform (they must be, or SpaceX wouldn’t use them), then they can’t be a cm or so too thick or thin (and lumpy -- thick under one tile but not its neighbor).

No, but they can easily bunch up, especially since you are putting flat rectangular fabric over a comic section, and apparently pushing it manually over the pin array.  So if you don't pull "tight enough" when you push the fabric over the pin you get a little wrinkle which eventually causes the tile to sit proud.
This makes sense, especially with a very soft, low-density blanket. It could bunch up (compress from side to side) without getting much thicker, but then the compressed patch would be harder to push down against the surface. Even easier to overlook than an outright wrinkle.

I think you’ve got part of the puzzle, or the best explanation to date.
Title: Re: Starship heat shield
Post by: Rossco on 08/14/2021 10:44 am
I wonder if a solution would be to mount a piece the blanket to the back of each tile rather than to the body of SS itself?
Title: Re: Starship heat shield
Post by: DistantTemple on 08/14/2021 11:03 am
It looks like the sheet has been laid in an approximate way with overlaps in places. Usually that sort of ceramic blanket has flexibility to be squashed.
For complex curves eventually moulded sections could be manufactured to fit, including thicker sections etc if needed. This only makes sense as part of finalising those shapes, like the fairing to the top hinge of the flaps, etc. However curved sections for the nose make sense. Just slicing a bit off the roll will always be a compromise!
Title: Re: Starship heat shield
Post by: RobLynn on 08/14/2021 11:29 am
They wouldn't use water, they'd use methane.  And Elon has been wanting to do almost exactly this for some time; it's called "transpiration cooling".  But the complexity and weight have been prohibitive so far.

Water can provide about 3x as much cooling as methane per kg in this application, and hot spots are likely to occur far from where methane or LOX pools in tanks, including on fins, cargo volume, flanks and skirt.  Internal radiation may be sufficient to dissipate heat from hot spots in large volumes, but supplementary switchable water cooling is a safer bet.
Title: Re: Starship heat shield
Post by: joek on 08/14/2021 11:59 am
Water can provide about 3x as much cooling as methane per kg in this application, and hot spots are likely to occur far from where methane or LOX pools in tanks, including on fins, cargo volume, flanks and skirt.  Internal radiation may be sufficient to dissipate heat from hot spots in large volumes, but supplementary switchable water cooling is a safer bet.

Don't necessarily need liquid methane; venting gaseous methane may be sufficient. If liquid methane is desirable, use header tanks or similar. Water would require additional plumbing-mass, and from a systems perspective may not be safer given the increase in complexity. As always with SpaceX, it simply needs to be good enough, not the best.
Title: Re: Starship heat shield
Post by: cscott on 08/14/2021 12:00 pm
The water is dead mass.  The methane is already present and has done work as hydraulic fluid and pressurant and doesn't require additional weight for tankage.

This trade has been studied.  The result (at this point) is heat tiles.
Title: Re: Starship heat shield
Post by: joek on 08/14/2021 01:10 pm
The water is dead mass.  The methane is already present and has done work as hydraulic fluid and pressurant and doesn't require addition weight for tankage.

This trade has been studied.  The result (at this point) is heat tiles.

Two discussions: (1) Primary thermal protection. As you stated, the trades have been done and result is heat tiles. (2) Secondary thermal protection for hot spots (e.g., flap hinge areas). Per Musk's comments during Tim Dodd's videos, Musk indicated transpiration-secondary cooling for those areas may be required and is still on the table. And per Musk's comments, if that is needed, it will be methane (although he was not specific as to liquid or gaseous).
Title: Re: Starship heat shield
Post by: Crispy on 08/14/2021 01:37 pm
WRT the difficult of tiling the nosecone, I had a brainwave but I'm not sure if it's ever been seriously considered in the aerospace world. Instead of a surface with varying curvature, could you use two sections of a torus back to back? Then you'd be dealing with a more uniform curvature, where each strip of tiles could be identical to the last.

Is there some aerodynamic/buildability/other disadvantage to such a shape?

Title: Re: Starship heat shield
Post by: Slarty1080 on 08/14/2021 01:39 pm
It looks like the sheet has been laid in an approximate way with overlaps in places. Usually that sort of ceramic blanket has flexibility to be squashed.
For complex curves eventually moulded sections could be manufactured to fit, including thicker sections etc if needed. This only makes sense as part of finalising those shapes, like the fairing to the top hinge of the flaps, etc. However curved sections for the nose make sense. Just slicing a bit off the roll will always be a compromise!
I think the answer to the problem of the ill fitting, overlapping matting might be to cut the matting in the same shapes as the new nosecone gores.
Title: Re: Starship heat shield
Post by: xvel on 08/14/2021 02:29 pm
WRT the difficult of tiling the nosecone, I had a brainwave but I'm not sure if it's ever been seriously considered in the aerospace world. Instead of a surface with varying curvature, could you use two sections of a torus back to back? Then you'd be dealing with a more uniform curvature, where each strip of tiles could be identical to the last.

Is there some aerodynamic/buildability/other disadvantage to such a shape?

1. Nosecone is a pressure vessel for human starship and in the tip is lox header tank which is another pressure vessel, this shape is just bad for pressure vessels.
2. They just tiled a starship nosecone with no more problems than the rest of ship, where is this difficulty? Aren't you solving a problem that doesn't exist?
Title: Re: Starship heat shield
Post by: Slarty1080 on 08/14/2021 02:45 pm
WRT the difficult of tiling the nosecone, I had a brainwave but I'm not sure if it's ever been seriously considered in the aerospace world. Instead of a surface with varying curvature, could you use two sections of a torus back to back? Then you'd be dealing with a more uniform curvature, where each strip of tiles could be identical to the last.

Is there some aerodynamic/buildability/other disadvantage to such a shape?

1. Nosecone is a pressure vessel for human starship and in the tip is lox header tank which is another pressure vessel, this shape is just bad for pressure vessels.
2. They just tiled a starship nosecone with no more problems than the rest of ship, where is this difficulty? Aren't you solving a problem that doesn't exist?

I think we need to wait to see how ship 20 goes to see if there is a problem, and if there is we probably need to wait until after ship 21 to see how much of an issue it is.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/14/2021 03:01 pm
Does anyone have a plausible explanation for why tiles end up at different distances from the skin?
In other words, why do we see steps on the surface?!?!
I would have expected that this tolerance would be important and easy to keep pretty tight, but I would have been wrong.
Probably lots of reasons some cumulative on some occasions. I would put my money on the three biggest ones being:
minor variation in the pin orientation, they may not all be exactly perpendicular to the surface at all times and may not be exactly positioned with sufficient precision.
Slight distortion in the nose shape from the ideal conic form due to cumulative minor welding discrepancies.
Slight variation tile to tile in the depth and orientation of the fixing points

Some of the tiles seem to be off from the proper seated height by 5 or 10 mm. The tolerances on each component at much tighter than that, but if the pin and hole locations are out of tolerance by only a fraction of 1 mm they might bind up as they try to insert the tile over the pins and it wouldn't seat down all the way.

The solution is probably either to improve the manufacturing tolerances or change the tile/pin design to tolerate a less precise fit without binding.
If pins fit in Y-oriented grooves (or short radially-aligned slots) then the mechanical constraints are such that lateral variations in position (of pins or slots) cannot cause binding. This narrows the possibilities for binding to either
1) What would seem to be an unnecessarily-constrained geometry (like pins in small holes rather than slots) or
2) A pin/tile incompatibility (crushed fiber-stuff?) that has nothing to do with pin placement or tile geometry.
The size of the bayonet tip must be small enough to compress smaller than the slot. Once the slot is past the tip the bayonet clip is free to expand to capture the slot. To do this without play calls for close tolerances and replicability. Not that exotic a problem but this install calls for thousands of iterations on a surface with both variable shape and random variations from the ideal. It's not too surprising to see lateral movement, especially in a 'learn as you go' installation process.


It'll get better. I hope it gets good enough.
Title: Re: Starship heat shield
Post by: Ionmars on 08/14/2021 03:31 pm
Does anyone have a plausible explanation for why tiles end up at different distances from the skin?
In other words, why do we see steps on the surface?!?!
I would have expected that this tolerance would be important and easy to keep pretty tight, but I would have been wrong.
Probably lots of reasons some cumulative on some occasions. I would put my money on the three biggest ones being:
minor variation in the pin orientation, they may not all be exactly perpendicular to the surface at all times and may not be exactly positioned with sufficient precision.
Slight distortion in the nose shape from the ideal conic form due to cumulative minor welding discrepancies.
Slight variation tile to tile in the depth and orientation of the fixing points
cylindrical mesh brace

Spx might be considering ways to support the rings as they are pinned and tiled. One approach could be a “cylindrical mesh brace” as suggested in the sketch below. The purpose of the mesh brace would be to flatten dents and reduce misalignments while tiling.

When SpX stacked rings to form a cylinder, this cylinder would be placed onto a 9m cylinder composed of precisely-constructed rigid steel rings. Spacing between rings would be maintained by rigid inter-ring braces, thereby forming a mesh of rigid squares.

Mesh squares would be sized such that one hex tile laid onto the SS surface would be supported by one mesh square under the SS surface. The “Y” rails inside  the tile would lie inside the mesh square and not above any of the four mesh braces. This spacing would allow pins to be welded in place without interference from the mesh, or vice versa. During tiling the surface under each tile would be supported to resist any makeshift “applications of force” without misalignment.

Notes:
(1) The cylindrical mesh brace could be mounted in horizontal or vertical position.
(2) Expansion joints would allow the mesh cylinder to be temporarily reduced in size while an SS ring stack was mounted or dismounted from it.
(3) SpX would rather do without specialized equipment, so a mesh cylinder would be used only if other approaches were not sufficient.
Title: Re: Starship heat shield
Post by: cdebuhr on 08/14/2021 03:38 pm
They will have internal cameras in the interior volumes of starship to look for hot spots.  If they added a payload tank with a few tonnes of water and a distributed array of solenoid controlled spray nozzles at some stand off distance from inner surface of Starship (like center pivot irrigators use) then they could reactively cool any hot spots caused by tile failures etc.  That would give them a greater chance of exploring the entire re-entry profile and possibly allow the recovery of hardware to figure out what went wrong (or right).  Wouldn't be too hard or time consuming to do, and might speed up Starship development process significantly.
You realize what you're talking about is putting water lines, and even water spay nozzles inside a cryogenic storage tank, right?  In the unlikely event that the system worked as intended and didn't suffer from a bunch of frozen and/or ruptured water lines, valves, etc., then you'd have a bunch of water droplets in your cryogenic propellant.  Water ice is an interesting material in that its hardness is unusually sensitive to temperature.  By the time you get into the cryogenic regime, its effectively just another mineral.  You'd basically be dumping tons of sand into your propellant supply.

On top of that, this would add a massive amount of complexity for little long term benefit (I would argue no benefit, as I think the idea is sufficiently flawed as to be ... less than useful).  They'll just keep trying until they get it right.  It's the SpaceX way.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/14/2021 03:46 pm
I wonder if a solution would be to mount a piece the blanket to the back of each tile rather than to the body of SS itself?
Nifty idea. The backing pad could not extend beyond the tile itself or a slight misalignment would extend the pad into the space for the next pad install. Same problem, different root cause. The rope caulking we haven't heard much about lately would definitely be needed.


Alternatively, the pad could extend beyond three sides of the hex with the naked side oriented where the next tiles will go. The excess pad on three sides would be the caulking material. Edges and weirdy shapes would need special consideration.


Speaking of special consideration. One of Mary's update pics shows that they're measuring pin spacing. At a fast glance I'm seeing ~1mm variance over 45mm.


More interesting, looking at the shadow under the bottom edge of the pad at top, left of center, the shadow is scalloped. The pad itself looks to show very minor variance where tiles were previously installed and it lines up with the scallop. It is unclear if this is enough to account for the shadow or if there is an underlying variance in the steel.


And what is that double damned mesh? It looks like plastic. That doesn't make sense.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/14/2021 03:57 pm
WRT the difficult of tiling the nosecone, I had a brainwave but I'm not sure if it's ever been seriously considered in the aerospace world. Instead of a surface with varying curvature, could you use two sections of a torus back to back? Then you'd be dealing with a more uniform curvature, where each strip of tiles could be identical to the last.

Is there some aerodynamic/buildability/other disadvantage to such a shape?
The edge would allow the plasma an extreme close approach and act as a heat collection point even without the plasma issue.


But, maybe the seed of an idea. The topology is beyond be but could the tip of the nose morph into a sphere without reintroducing the problem it's designed to avoid?
Title: Re: Starship heat shield
Post by: cuddihy on 08/14/2021 04:14 pm
They will have internal cameras in the interior volumes of starship to look for hot spots.  If they added a payload tank with a few tonnes of water and a distributed array of solenoid controlled spray nozzles at some stand off distance from inner surface of Starship (like center pivot irrigators use) then they could reactively cool any hot spots caused by tile failures etc.  That would give them a greater chance of exploring the entire re-entry profile and possibly allow the recovery of hardware to figure out what went wrong (or right).  Wouldn't be too hard or time consuming to do, and might speed up Starship development process significantly.
You realize what you're talking about is putting water lines, and even water spay nozzles inside a cryogenic storage tank, right?  In the unlikely event that the system worked as intended and didn't suffer from a bunch of frozen and/or ruptured water lines, valves, etc., then you'd have a bunch of water droplets in your cryogenic propellant.  Water ice is an interesting material in that its hardness is unusually sensitive to temperature.  By the time you get into the cryogenic regime, its effectively just another mineral.  You'd basically be dumping tons of sand into your propellant supply.

On top of that, this would add a massive amount of complexity for little long term benefit (I would argue no benefit, as I think the idea is sufficiently flawed as to be ... less than useful).  They'll just keep trying until they get it right.  It's the SpaceX way.

Even if it were cryogenic propellant, it’d be a terrible idea. Talk about pressure regulation issues! You have hot ullage gas you’d be spraying cold propellant into, having it splash off a wall where it was gaining heat /vaporizing on one side and simultaneously collapsing ullage pressure on parts of the spray that bounced off with little or no heating. Result would be rapid ullage pressure collapse at the beginning followed by rapid over pressurization…or possibly rapid cycling between the two. Recipe for rapid breakup on return.
Title: Re: Starship heat shield
Post by: Adriano on 08/14/2021 04:18 pm
WRT the difficult of tiling the nosecone, I had a brainwave but I'm not sure if it's ever been seriously considered in the aerospace world. Instead of a surface with varying curvature, could you use two sections of a torus back to back? Then you'd be dealing with a more uniform curvature, where each strip of tiles could be identical to the last.

Is there some aerodynamic/buildability/other disadvantage to such a shape?

Aerodynamic: adding a chin to the nose will add a clear line of flow separation resulting in: simpler and lighter typing, as a single tile shape can be used for all the sirface, except the edges of course, and we now have a clear line of flow separation eliminating the additional tiling required by the current uncertainty and variability during reentry of the area needing tiling at the edges.
Simpler build: single tile shape for most of the nose.
Structural: need to add a flat structure working in compression stabilizing the plane joining the two torus parts. For the rest, the structure is stable. Note that a structure is anyway required to distribute the loads of the forward fins.
Space usage: the flat structure will complicate the usage of space for large payloads. A possibile solution is to use the nose as a reservoir and move the payload bay to the cylindrical part of the starship.
Title: Re: Starship heat shield
Post by: cdebuhr on 08/14/2021 04:22 pm
They will have internal cameras in the interior volumes of starship to look for hot spots.  If they added a payload tank with a few tonnes of water and a distributed array of solenoid controlled spray nozzles at some stand off distance from inner surface of Starship (like center pivot irrigators use) then they could reactively cool any hot spots caused by tile failures etc.  That would give them a greater chance of exploring the entire re-entry profile and possibly allow the recovery of hardware to figure out what went wrong (or right).  Wouldn't be too hard or time consuming to do, and might speed up Starship development process significantly.
You realize what you're talking about is putting water lines, and even water spay nozzles inside a cryogenic storage tank, right?  In the unlikely event that the system worked as intended and didn't suffer from a bunch of frozen and/or ruptured water lines, valves, etc., then you'd have a bunch of water droplets in your cryogenic propellant.  Water ice is an interesting material in that its hardness is unusually sensitive to temperature.  By the time you get into the cryogenic regime, its effectively just another mineral.  You'd basically be dumping tons of sand into your propellant supply.

On top of that, this would add a massive amount of complexity for little long term benefit (I would argue no benefit, as I think the idea is sufficiently flawed as to be ... less than useful).  They'll just keep trying until they get it right.  It's the SpaceX way.

Even if it were cryogenic propellant, it’d be a terrible idea. Talk about pressure regulation issues! You have hot ullage gas you’d be spraying cold propellant into, having it splash off a wall where it was gaining heat /vaporizing on one side and simultaneously collapsing ullage pressure on parts of the spray that bounced off with little or no heating. Result would be rapid ullage pressure collapse at the beginning followed by rapid over pressurization…or possibly rapid cycling between the two. Recipe for rapid breakup on return.
Yeah - I thought about that too.  And anyway you cut it the additional complexity would be ludicrous for what in essence is just early engineering tests anyway.  As long as they get some good pre-breakup telemetry, that should be good enough to help them move things along.  The idea as presented had enough wrong with it, I figured I'd just hit the highlights and go home.
Title: Re: Starship heat shield
Post by: OV103Fan on 08/14/2021 06:11 pm
They will have internal cameras in the interior volumes of starship to look for hot spots.  If they added a payload tank with a few tonnes of water and a distributed array of solenoid controlled spray nozzles at some stand off distance from inner surface of Starship (like center pivot irrigators use) then they could reactively cool any hot spots caused by tile failures etc.  That would give them a greater chance of exploring the entire re-entry profile and possibly allow the recovery of hardware to figure out what went wrong (or right).  Wouldn't be too hard or time consuming to do, and might speed up Starship development process significantly.
You realize what you're talking about is putting water lines, and even water spay nozzles inside a cryogenic storage tank, right?  In the unlikely event that the system worked as intended and didn't suffer from a bunch of frozen and/or ruptured water lines, valves, etc., then you'd have a bunch of water droplets in your cryogenic propellant.  Water ice is an interesting material in that its hardness is unusually sensitive to temperature.  By the time you get into the cryogenic regime, its effectively just another mineral.  You'd basically be dumping tons of sand into your propellant supply.

On top of that, this would add a massive amount of complexity for little long term benefit (I would argue no benefit, as I think the idea is sufficiently flawed as to be ... less than useful).  They'll just keep trying until they get it right.  It's the SpaceX way.

Even if it were cryogenic propellant, it’d be a terrible idea. Talk about pressure regulation issues! You have hot ullage gas you’d be spraying cold propellant into, having it splash off a wall where it was gaining heat /vaporizing on one side and simultaneously collapsing ullage pressure on parts of the spray that bounced off with little or no heating. Result would be rapid ullage pressure collapse at the beginning followed by rapid over pressurization…or possibly rapid cycling between the two. Recipe for rapid breakup on return.
Yeah - I thought about that too.  And anyway you cut it the additional complexity would be ludicrous for what in essence is just early engineering tests anyway.  As long as they get some good pre-breakup telemetry, that should be good enough to help them move things along.  The idea as presented had enough wrong with it, I figured I'd just hit the highlights and go home.

The way I read this, I suspect he was proposing the idea for just the payload area, not inside the cryo tanks and only as a temporary measure to help get a prototype back to aid future development.  I agree there would be no need to develop such a gizmo unless they are running into problems that cannot be solved by looking at the telemetry.
Title: Re: Starship heat shield
Post by: PaulinDevonUK on 08/17/2021 10:27 am
How about Ceramic Foam https://www.technicalfoamservices.co.uk/product/ceramic-filter-foam/ (https://www.technicalfoamservices.co.uk/product/ceramic-filter-foam/) for a more even liquid/gas disbursion? Light weight and heat resistant.

I have not designed a complete set up in my mind but thing a thin Stainless Steal backing sheet with appropriate holes behind this (something like a kitchen calendar design) is a start. I am not sure how ullage gas or liquid would be fed but I am sure some bright Spacex engineer will work out a simple solution.

Are the current heat shield tiles porous?
Title: Re: Starship heat shield
Post by: eriblo on 08/17/2021 11:37 am
How about Ceramic Foam https://www.technicalfoamservices.co.uk/product/ceramic-filter-foam/ (https://www.technicalfoamservices.co.uk/product/ceramic-filter-foam/) for a more even liquid/gas disbursion? Light weight and heat resistant.

I have not designed a complete set up in my mind but thing a thin Stainless Steal backing sheet with appropriate holes behind this (something like a kitchen calendar design) is a start. I am not sure how ullage gas or liquid would be fed but I am sure some bright Spacex engineer will work out a simple solution.

Are the current heat shield tiles porous?
The current tile base material is to the best of our knowledge a porous ceramic foam very similar to that used on the Space Shuttle. It is made from a jumble of cheramic fibers rather than by replicating the more homogeneous pore structure of a "standard" foam in order to minimize heat transfer by thermal radiation through the material.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 08/17/2021 08:45 pm
IDk if this has been noteb before, but since the tiles on the nose cone tip are glued there isn't any blanket. So, do you think that the tiles in the tip are different (maybe thicker??) to account the lack of the blancket?

BTW now we know that the assumption that the tiles existed only to protect the blancket is false.
Title: Re: Starship heat shield
Post by: eriblo on 08/17/2021 09:48 pm
IDk if this has been noteb before, but since the tiles on the nose cone tip are glued there isn't any blanket. So, do you think that the tiles in the tip are different (maybe thicker??) to account the lack of the blancket?

BTW now we know that the assumption that the tiles existed only to protect the blancket is false.
At the nose interface the glued tiles are about the same thickness as clip-on tiles + blanket while there might be some tapering on the fins (which could just be due to higher heat loading at the hinge). We do not know if the glued tiles are the same composition as the clip-on ones but I do not expect two parallel processes unless it is absolutely necessary.

I do not think we can tell if one system is better at insulating than the other - The glued tiles are only used on areas with small curvature/difficult geometry (which generally correspond to higher heating) but the clip-on tiles + blanket are used at the dorsal stagnation point/line.

One interesting point is that if the red glue is a RTV silicone adhesive like that used on the Shuttle then that will be the limiting part of the TPS and the hull temperature can then reach at most 300-320 °C in those areas. While still significantly more than the 175 °C limit for the Shuttle this is quite a bit lower than what the steel can take without any risk annealing and even further from the structural limits.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 08/18/2021 06:17 am
IDk if this has been noteb before, but since the tiles on the nose cone tip are glued there isn't any blanket. So, do you think that the tiles in the tip are different (maybe thicker??) to account the lack of the blancket?

BTW now we know that the assumption that the tiles existed only to protect the blancket is false.
At the nose interface the glued tiles are about the same thickness as clip-on tiles + blanket while there might be some tapering on the fins (which could just be due to higher heat loading at the hinge). We do not know if the glued tiles are the same composition as the clip-on ones but I do not expect two parallel processes unless it is absolutely necessary.

I do not think we can tell if one system is better at insulating than the other - The glued tiles are only used on areas with small curvature/difficult geometry (which generally correspond to higher heating) but the clip-on tiles + blanket are used at the dorsal stagnation point/line.

One interesting point is that if the red glue is a RTV silicone adhesive like that used on the Shuttle then that will be the limiting part of the TPS and the hull temperature can then reach at most 300-320 °C in those areas. While still significantly more than the 175 °C limit for the Shuttle this is quite a bit lower than what the steel can take without any risk annealing and even further from the structural limits.
Do other adhesive with higher max temperature exist and are usable, or probably the will stick with thecurrent one?
with a quick search the ,ain categories of high temp adhesive that I found were the silicone one and epoxy.
Title: Re: Starship heat shield
Post by: rsdavis9 on 08/18/2021 03:00 pm
There is wood stove cement. I have used to glue gasket material to my wood stove. Not sure how adhesive it is. It is a silica based water glass material.

I think they may go to more of the tiles being pinned. They probably didn't this time because of special cases and time needed. The curved surfaces should only need one pin.
Title: Re: Starship heat shield
Post by: dwheeler on 08/18/2021 04:32 pm
IDk if this has been noteb before, but since the tiles on the nose cone tip are glued there isn't any blanket. So, do you think that the tiles in the tip are different (maybe thicker??) to account the lack of the blancket?

BTW now we know that the assumption that the tiles existed only to protect the blancket is false.
<snip/>
One interesting point is that if the red glue is a RTV silicone adhesive like that used on the Shuttle then that will be the limiting part of the TPS and the hull temperature can then reach at most 300-320 °C in those areas.
<snip/>
It's also interesting that the off-the-shelf RTV silicone adhesives that a quick google turned up also have a lower temperature limit of around -55 °C which would seem to preclude it being used on the outsides of the cryo tanks.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/18/2021 04:40 pm
IDk if this has been noteb before, but since the tiles on the nose cone tip are glued there isn't any blanket. So, do you think that the tiles in the tip are different (maybe thicker??) to account the lack of the blancket?

BTW now we know that the assumption that the tiles existed only to protect the blancket is false.
At the nose interface the glued tiles are about the same thickness as clip-on tiles + blanket while there might be some tapering on the fins (which could just be due to higher heat loading at the hinge). We do not know if the glued tiles are the same composition as the clip-on ones but I do not expect two parallel processes unless it is absolutely necessary.

I do not think we can tell if one system is better at insulating than the other - The glued tiles are only used on areas with small curvature/difficult geometry (which generally correspond to higher heating) but the clip-on tiles + blanket are used at the dorsal stagnation point/line.

One interesting point is that if the red glue is a RTV silicone adhesive like that used on the Shuttle then that will be the limiting part of the TPS and the hull temperature can then reach at most 300-320 °C in those areas. While still significantly more than the 175 °C limit for the Shuttle this is quite a bit lower than what the steel can take without any risk annealing and even further from the structural limits.
The nose, where tiles are glued, is a sharp radius and one of the hottest point on EDL. With the header tank immediately behind them my thoughts turn to the temperature gradient they will face. The header should (WAG) be enough to keep the glue temps good, but that gradient. Wow.


Edit: dwheeler raises a good point on minimum temps.
Title: Re: Starship heat shield
Post by: edzieba on 08/18/2021 05:07 pm
IIRC the RTV silicone used on Shuttle (RTV560, an off-the-shelf product) is specced down to -115°C. Addition-cure Silicones alone have a enormous range of properties that be achieved by varying the specific composition, and then you have condensation-cure Silicones and other curing methods (though HTV would not be directly applicable) so you have a lot of latitude to design a silicone mix with the properties you need.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 08/19/2021 03:21 am
IIRC the RTV silicone used on Shuttle (RTV560, an off-the-shelf product) is specced down to -115°C. Addition-cure Silicones alone have a enormous range of properties that be achieved by varying the specific composition, and then you have condensation-cure Silicones and other curing methods (though HTV would not be directly applicable) so you have a lot of latitude to design a silicone mix with the properties you need.

Here are some interesting results courtesy of Bing.  Perhaps someone should try Google:

https://www.amazon.com/Technicqll-Temperature-Adhesive-Fireplace-Collectors/dp/B006U5K9EQ

https://www.sauereisen.com/ceramic-assembly/
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 08/19/2021 07:32 am
IDk if this has been noteb before, but since the tiles on the nose cone tip are glued there isn't any blanket. So, do you think that the tiles in the tip are different (maybe thicker??) to account the lack of the blancket?

BTW now we know that the assumption that the tiles existed only to protect the blancket is false.
<snip/>
One interesting point is that if the red glue is a RTV silicone adhesive like that used on the Shuttle then that will be the limiting part of the TPS and the hull temperature can then reach at most 300-320 °C in those areas.
<snip/>
It's also interesting that the off-the-shelf RTV silicone adhesives that a quick google turned up also have a lower temperature limit of around -55 °C which would seem to preclude it being used on the outsides of the cryo tanks.
That's interesting.

BTW, why a product that could be bought by everyone, and not customized is called "off the shelf"? It should be called "on[/iz] the shelf" IMO.
Title: Re: Starship heat shield
Post by: Vettedrmr on 08/19/2021 09:15 am
BTW, why a product that could be bought by everyone, and not customized is called "off the shelf"? It should be called "on[/iz] the shelf" IMO.

Because when you see someone using it, and ask them where they got it, the reply is "Oh, I just got it off the shelf at xxx store."
Title: Re: Starship heat shield
Post by: ETurner on 08/19/2021 10:41 am
Here are some interesting results courtesy of Bing.  Perhaps someone should try Google:

https://www.amazon.com/Technicqll-Temperature-Adhesive-Fireplace-Collectors/dp/B006U5K9EQ (https://www.amazon.com/Technicqll-Temperature-Adhesive-Fireplace-Collectors/dp/B006U5K9EQ)

https://www.sauereisen.com/ceramic-assembly/ (https://www.sauereisen.com/ceramic-assembly/)

All these are brittle ceramics.
Title: Re: Starship heat shield
Post by: cambrianera on 08/19/2021 10:50 am
https://www.galindberg.se/blogg/cryogenic-low-temperature-adhesives/
True low limit is only related to brittleness.
Title: Re: Starship heat shield
Post by: ETurner on 08/19/2021 11:15 am
Here are some interesting results courtesy of Bing.  Perhaps someone should try Google:

https://www.amazon.com/Technicqll-Temperature-Adhesive-Fireplace-Collectors/dp/B006U5K9EQ (https://www.amazon.com/Technicqll-Temperature-Adhesive-Fireplace-Collectors/dp/B006U5K9EQ)

https://www.sauereisen.com/ceramic-assembly/ (https://www.sauereisen.com/ceramic-assembly/)

All these are brittle ceramics.
Further...
A problem with brittle materials here is differential thermal expansion; another (these are ceramics) is adhesion to steel.
Here’s a material system I’ve never heard of that seems plausible, would provide for thermal expansion, and might satisfy adhesive material constraints:

1) Felt-equivalent (Shuttle-like, but higher temperature): Use a metal fiber layer (think of steel wool, then think of something better.) Also provides some thermal insulation.

2) Bonding to steel: Metal-metal bonds between metal fiber and steel by brazing; pick a brazing material/temperature that does not quickly anneal cold-rolled steel. Query: What surface prep would be needed?

3) Bonding to tile: Use a brittle (ceramic?) high temperature adhesive (see quoted post). Expect good adhesion to the porous ceramic tiles, rely on embedding of metal fibers to mechanically interlock the fiber layer with the ceramic layer. Maybe put some ceramic fiber in the adhesive. Maybe treat surfaces in the metal-fiber layer in some clever way before applying adhesive and tiles.

4) Find that breaking and removing tiles, then re-prepping the surface, is a pain. Maybe use a heaver system for replacement tiles: Leave a some brazed fiber on the surface (pull off most of the the old fiber first), slap on another metal-fiber layer (more brazing), glue on a somewhat thicker, denser tile.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/19/2021 05:35 pm
IDk if this has been noteb before, but since the tiles on the nose cone tip are glued there isn't any blanket. So, do you think that the tiles in the tip are different (maybe thicker??) to account the lack of the blancket?

BTW now we know that the assumption that the tiles existed only to protect the blancket is false.
<snip/>
One interesting point is that if the red glue is a RTV silicone adhesive like that used on the Shuttle then that will be the limiting part of the TPS and the hull temperature can then reach at most 300-320 °C in those areas.
<snip/>
It's also interesting that the off-the-shelf RTV silicone adhesives that a quick google turned up also have a lower temperature limit of around -55 °C which would seem to preclude it being used on the outsides of the cryo tanks.
That's interesting.

BTW, why a product that could be bought by everyone, and not customized is called "off the shelf"? It should be called "on[/iz] the shelf" IMO.
Are you trying to make sense of the English language? Stick with rocket science - it's easier.  ::)
Title: Re: Starship heat shield
Post by: rakaydos on 08/19/2021 05:42 pm
Those contact points with missing tiles are probably electromagnetic contact points for the arms to grab the starship.

Please dont change the title field.
Title: Re: Starship heat shield
Post by: ETurner on 08/20/2021 11:29 am

3) Bonding to tile: Use a brittle (ceramic?) high temperature adhesive (see quoted post). Expect good adhesion to the porous ceramic tiles, rely on embedding of metal fibers to mechanically interlock the fiber layer with the ceramic layer. Maybe put some ceramic fiber in the adhesive. Maybe treat surfaces in the metal-fiber layer in some clever way before applying adhesive and tiles.
Or better, use a silicone adhesive that turns into a ceramic at high temperatures, for example:

“Ceramizable composite is a kind of polymer matrix composite that can turn into ceramic material at a high temperature....”
https://www.mdpi.com/1996-1944/13/17/3708/pdf (https://www.mdpi.com/1996-1944/13/17/3708/pdf)

Using this kind of elastomer --> ceramic material should result in metal fibers embedded in a polymer when made, and embedded in a ceramic after high-temperature exposure. Should be good enough to hold a tile on.

On the fiber-sheet/stainless-steel side, the idea would be to paint the steel with a carrier loaded with medium-melting-point particles of a brazing-type alloy -- not “brazing” (wrong geometry, but using the kind of alloys that are used in brazing).
----------------------
All this is probably unnecessary, but could probably be made to work.
Title: Re: Starship heat shield
Post by: _MECO on 08/20/2021 12:02 pm
IDk if this has been noteb before, but since the tiles on the nose cone tip are glued there isn't any blanket. So, do you think that the tiles in the tip are different (maybe thicker??) to account the lack of the blancket?

BTW now we know that the assumption that the tiles existed only to protect the blancket is false.
<snip/>
One interesting point is that if the red glue is a RTV silicone adhesive like that used on the Shuttle then that will be the limiting part of the TPS and the hull temperature can then reach at most 300-320 °C in those areas.
<snip/>
It's also interesting that the off-the-shelf RTV silicone adhesives that a quick google turned up also have a lower temperature limit of around -55 °C which would seem to preclude it being used on the outsides of the cryo tanks.
That's interesting.

BTW, why a product that could be bought by everyone, and not customized is called "off the shelf"? It should be called "on[/iz] the shelf" IMO.
It's because you can literally take it off of a shelf from a store. If it were still there, you never decided to buy it. Kind of like saying how you got this sick roll of 301 stainless steel for free off the back of an unsupervised delivery truck in south Texas. Like taking 10 tons of candy from a baby!

IDk if this has been noteb before, but since the tiles on the nose cone tip are glued there isn't any blanket. So, do you think that the tiles in the tip are different (maybe thicker??) to account the lack of the blancket?

BTW now we know that the assumption that the tiles existed only to protect the blancket is false.
At the nose interface the glued tiles are about the same thickness as clip-on tiles + blanket while there might be some tapering on the fins (which could just be due to higher heat loading at the hinge). We do not know if the glued tiles are the same composition as the clip-on ones but I do not expect two parallel processes unless it is absolutely necessary.

I do not think we can tell if one system is better at insulating than the other - The glued tiles are only used on areas with small curvature/difficult geometry (which generally correspond to higher heating) but the clip-on tiles + blanket are used at the dorsal stagnation point/line.

One interesting point is that if the red glue is a RTV silicone adhesive like that used on the Shuttle then that will be the limiting part of the TPS and the hull temperature can then reach at most 300-320 °C in those areas. While still significantly more than the 175 °C limit for the Shuttle this is quite a bit lower than what the steel can take without any risk annealing and even further from the structural limits.
The nose, where tiles are glued, is a sharp radius and one of the hottest point on EDL. With the header tank immediately behind them my thoughts turn to the temperature gradient they will face. The header should (WAG) be enough to keep the glue temps good, but that gradient. Wow.


Edit: dwheeler raises a good point on minimum temps.

I don't understand why something like a single, giant kinematic coupling couldn't work to hold a large nose tile on. Maybe the metal skeleton in the tile might hsve to look different, but I think it could work.
Title: Re: Starship heat shield
Post by: Tangilinear Interjar on 08/25/2021 12:55 am
Are you talking about a big single cap tile or just a number of smaller tiles like we see? By a single kinematic attachment how are you suggesting to constrain the multiple other axies? Perhaps show a diagram of what you are thinking?
Title: Re: Starship heat shield
Post by: TomH on 08/25/2021 03:38 am
...why a product that could be bought by everyone, and not customized is called "off the shelf"? It should be called "on[/iz] the shelf" IMO.

It is called off the shelf, because you can pick it up, take it off the shelf and to the cashier, and pay for it. That being said, this is off-topic. I intend no offense by this, however NSF is not a class for English language learners. I encourage you to search elsewhere for English figurative language expressions.
Title: Re: Starship heat shield
Post by: john_aldrin on 08/25/2021 04:32 am
Every time I visit this thread I wonder why an overlapping tile isn't used. Think half-lap or tongue-and-groove, like one might find in flooring. This would solve the groove issues and allow for both thermal expansion and more relaxed location tolerance.

The idea is so obvious that I am sure it was considered and dismissed. Tell me what obvious flaw I am missing?

John
Title: Re: Starship heat shield
Post by: cscott on 08/25/2021 08:20 am
The flow goes in two orthogonal directions, so that overlapping during ascent will be exactly wrong during descent. (Or vice versa.)

This question actually comes up fairly regularly.
Title: Re: Starship heat shield
Post by: michcies on 08/25/2021 09:00 am
Every time I visit this thread I wonder why an overlapping tile isn't used. Think half-lap or tongue-and-groove, like one might find in flooring. This would solve the groove issues and allow for both thermal expansion and more relaxed location tolerance.

The idea is so obvious that I am sure it was considered and dismissed. Tell me what obvious flaw I am missing?

John

I think that having the tiles with tongue-and-groove will make the exchange of a tile practically impossible.
What also could be problematic is the brittleness of the tiles. They must not touch each other.
Title: Re: Starship heat shield
Post by: RoboGoofers on 08/25/2021 10:44 am
The flow goes in two orthogonal directions, so that overlapping during ascent will be exactly wrong during descent. (Or vice versa.)

This question actually comes up fairly regularly.
That's fish- or dragon-scale. Half lapped would present a smooth surface.
Title: Re: Starship heat shield
Post by: Crispy on 08/25/2021 11:21 am
Half lapped would still make removing a bad tile impossible. It would also make the custom tiles at aero covers etc. even more complicated in shape.
Title: Re: Starship heat shield
Post by: edzieba on 08/25/2021 11:24 am
It also results in tile rubbing, which is not good. The tiles are coated in a very thin layer of glass, and are not enormously strong themselves.
Title: Re: Starship heat shield
Post by: john_aldrin on 08/26/2021 04:20 am
While tongue-and-groove does require a special "tongueless" row every so often to allow tile replacement, half-lap does not - assuming we aren't talking about a contact/interference fit (which I assume we are not for any of these schemes, including the current one, due to expansion issues).

These same gaps that prevent contact (where both half laps are something less than the nominal height) also provide an even more effective labyrinthine flow path than the current tile gaps.

BTW, I am assuming rectangular tiles (top laps on two adjacent sides, bottoms on other two) when considering the above issues. Other shapes get more complicated.
Title: Re: Starship heat shield
Post by: TOG on 08/26/2021 04:53 pm
While tongue-and-groove does require a special "tongueless" row every so often to allow tile replacement, half-lap does not - assuming we aren't talking about a contact/interference fit (which I assume we are not for any of these schemes, including the current one, due to expansion issues).

These same gaps that prevent contact (where both half laps are something less than the nominal height) also provide an even more effective labyrinthine flow path than the current tile gaps.

BTW, I am assuming rectangular tiles (top laps on two adjacent sides, bottoms on other two) when considering the above issues. Other shapes get more complicated.

If you are going with the 1/2 laps and a 6 sided tile, then you would have every other straight edge an over or under.  So Starting at the top:

               OVER
  UNDER.              UNDER

   OVER.                OVER
              UNDER

When you get to the odd shapes that don't have six sides it gets “dicey”.
 
Title: Re: Starship heat shield
Post by: john_aldrin on 08/26/2021 07:29 pm
That configuration require a _lot_ more clearance to swap tiles in place. I think you generally want all the up laps to be adjacent, so you can lift/slide a tile out. With rectangular tiles it is definitely doable, and has been done in other applications. With hex it would take a bit more thought about the geometry to get the clearances right.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 08/27/2021 07:45 pm
Every time I visit this thread I wonder why an overlapping tile isn't used. Think half-lap or tongue-and-groove, like one might find in flooring. This would solve the groove issues and allow for both thermal expansion and more relaxed location tolerance.

The idea is so obvious that I am sure it was considered and dismissed. Tell me what obvious flaw I am missing?

John

I think the reason lapping/overlapping isn't used is vibration happens on all three axis, and there would be very little damping or distance between the laps and the tiles would collide, destroying each other (e.g. during a test fire, launch, etc)
Title: Re: Starship heat shield
Post by: BT52 on 08/28/2021 04:51 am
I think overlapping is also KISS problem for installation. Flooring is very sturdy. Unlike some foam and delicate ceramic coatings. Plus manufacturing becomes ass. Essentially you increase tolerancing in 3d space signifcantly. Hence higher cost, harder automation, more ppl training. All unwandet for mass produced reusable rocket sys.

Title: Re: Starship heat shield
Post by: Sciencefan on 08/28/2021 10:08 pm
Does anybody know are TPS tiles derived as modified NASA TUFROC, independently developed made of similar material and structure, or are they completely different?
Title: Re: Starship heat shield
Post by: edzieba on 08/28/2021 11:27 pm
Not TUFROC.

TUFROC is HRSI tiles covered with an RCC cap. No SpaceX tile (either those on Starship now nor those seen previously) have had RCC caps. TUFROC was mentioned among a whole bunch of other TPS technologies as part of a Space Act Agreement, and for some bizarre reason it's been latched onto as some sort of perceived super-TPS for no apparent reason.

From the tile manufacture process description from the FDEP inspection document, SpaceX's tiles are almost identical to shuttle-era HRSI tiles, with the main compositional difference being a slightly different waterproofing agent, and the physical difference being the internal attachment frame.
Title: Re: Starship heat shield
Post by: Redclaws on 08/28/2021 11:48 pm
Not TUFROC.

TUFROC is HRSI tiles covered with an RCC cap. No SpaceX tile (either those on Starship now nor those seen previously) have had RCC caps. TUFROC was mentioned among a whole bunch of other TPS technologies as part of a Space Act Agreement, and for some bizarre reason it's been latched onto as some sort of perceived super-TPS for no apparent reason.

From the tile manufacture process description from the FDEP inspection document, SpaceX's tiles are almost identical to shuttle-era HRSI tiles, with the main compositional difference being a slightly different waterproofing agent, and the physical difference being the internal attachment frame.

Ed,

Can you give a bit more background on the FDEP doc?  Maybe a link?  I’m just so surprised because I feel like it’s the first I’m hearing of this.  It feels like it really went semi-unnoticed here (at least in this thread?).
Title: Re: Starship heat shield
Post by: Sciencefan on 08/29/2021 12:19 am
If it is helpful here short overview of TUFROC

https://technology.nasa.gov/patent/TOP2-241

and related material HETC and ROCCI

https://www.nasa.gov/pdf/589887main_High%20Efficiency%20Tantalum-based%20Ceramic%20Structures.pdf

Refractory oxidative-resistant ceramic carbon insulation
High-temperature, lightweight, ceramic carbon insulation is prepared by coating or impregnating a porous carbon substrate with a siloxane gel derived from the reaction of an organodialkoxy silane and an organotrialkoxy silane in an acid or base medium in the presence of the carbon substrate. The siloxane gel is subsequently dried on the carbon substrate to form a ceramic carbon precursor. The carbon precursor is pyrolyzed, in an inert atmosphere, to form the ceramic insulation containing carbon, silicon, and oxygen. The carbon insulation is characterized as a porous, fibrous, carbon ceramic tile which is particularly useful as lightweight tiles for spacecraft.
Title: Re: Starship heat shield
Post by: edzieba on 08/29/2021 01:00 am
Not TUFROC.

TUFROC is HRSI tiles covered with an RCC cap. No SpaceX tile (either those on Starship now nor those seen previously) have had RCC caps. TUFROC was mentioned among a whole bunch of other TPS technologies as part of a Space Act Agreement, and for some bizarre reason it's been latched onto as some sort of perceived super-TPS for no apparent reason.

From the tile manufacture process description from the FDEP inspection document, SpaceX's tiles are almost identical to shuttle-era HRSI tiles, with the main compositional difference being a slightly different waterproofing agent, and the physical difference being the internal attachment frame.

Ed,

Can you give a bit more background on the FDEP doc?  Maybe a link?  I’m just so surprised because I feel like it’s the first I’m hearing of this.  It feels like it really went semi-unnoticed here (at least in this thread?).
FDEP Documents are here (https://prodenv.dep.state.fl.us/DepNexus/public/electronic-documents/FLR000231449/facility!search), go back in this thread ~ a year and a half (end of 2020) for discussion around them.
Title: Re: Starship heat shield
Post by: Redclaws on 08/29/2021 01:15 am
Not TUFROC.

TUFROC is HRSI tiles covered with an RCC cap. No SpaceX tile (either those on Starship now nor those seen previously) have had RCC caps. TUFROC was mentioned among a whole bunch of other TPS technologies as part of a Space Act Agreement, and for some bizarre reason it's been latched onto as some sort of perceived super-TPS for no apparent reason.

From the tile manufacture process description from the FDEP inspection document, SpaceX's tiles are almost identical to shuttle-era HRSI tiles, with the main compositional difference being a slightly different waterproofing agent, and the physical difference being the internal attachment frame.

Ed,

Can you give a bit more background on the FDEP doc?  Maybe a link?  I’m just so surprised because I feel like it’s the first I’m hearing of this.  It feels like it really went semi-unnoticed here (at least in this thread?).
FDEP Documents are here (https://prodenv.dep.state.fl.us/DepNexus/public/electronic-documents/FLR000231449/facility!search), go back in this thread ~ a year and a half (end of 2020) for discussion around them.

Thanks much, Ed.
Title: Re: Starship heat shield
Post by: Redclaws on 08/29/2021 01:17 am
Not TUFROC.

TUFROC is HRSI tiles covered with an RCC cap. No SpaceX tile (either those on Starship now nor those seen previously) have had RCC caps. TUFROC was mentioned among a whole bunch of other TPS technologies as part of a Space Act Agreement, and for some bizarre reason it's been latched onto as some sort of perceived super-TPS for no apparent reason.

From the tile manufacture process description from the FDEP inspection document, SpaceX's tiles are almost identical to shuttle-era HRSI tiles, with the main compositional difference being a slightly different waterproofing agent, and the physical difference being the internal attachment frame.

Ed,

Can you give a bit more background on the FDEP doc?  Maybe a link?  I’m just so surprised because I feel like it’s the first I’m hearing of this.  It feels like it really went semi-unnoticed here (at least in this thread?).
FDEP Documents are here (https://prodenv.dep.state.fl.us/DepNexus/public/electronic-documents/FLR000231449/facility!search), go back in this thread ~ a year and a half (end of 2020) for discussion around them.

Hmm, site is acting up - does anyone perhaps have a copy?  Or I’ll just try again later…
Title: Re: Starship heat shield
Post by: Sciencefan on 08/29/2021 02:22 am
Not TUFROC.
SpaceX's tiles are almost identical to shuttle-era HRSI tiles, with the main compositional difference being a slightly different waterproofing agent, and the physical difference being the internal attachment frame.

It is correct to refer to HRSI tiles as ceramic as they are mostly silica fibers?
Title: Re: Starship heat shield
Post by: RoadWithoutEnd on 08/29/2021 02:33 am
Do these details imply anything about the ship in general, or are they limited to trades within TPS internally?
Title: Re: Starship heat shield
Post by: northstar on 08/29/2021 04:05 am
Wondering what is the current estimate for the mass of the SN20 TPS.  A year ago discussions were guessing a density for the TPS system of about 13 kg/m^3, with a total system mass of 8,500 to 10,000 kg.

Has any more definitive information or speculation about the mass of the TPS system come out?
Title: Re: Starship heat shield
Post by: john_aldrin on 08/29/2021 06:29 am
Are they really primarily fiber? I'll also ask why they are referred to as ceramic.

And since their toughness is really such a factor in this new fast-paced installation environment (as well as in the Shuttle's service history), I'd be very interested in any video showing someone doing a little destructive testing (dropping, cutting, smashing) of one of these.

I see plenty of footage of heating them up and handling them, but I can't find anything demonstrating their physical resilience. Surely someone has experimented with a surplus or retired or rejected tile.
Title: Re: Starship heat shield
Post by: AnalogMan on 08/29/2021 10:41 am
Not TUFROC.

TUFROC is HRSI tiles covered with an RCC cap. No SpaceX tile (either those on Starship now nor those seen previously) have had RCC caps. TUFROC was mentioned among a whole bunch of other TPS technologies as part of a Space Act Agreement, and for some bizarre reason it's been latched onto as some sort of perceived super-TPS for no apparent reason.

From the tile manufacture process description from the FDEP inspection document, SpaceX's tiles are almost identical to shuttle-era HRSI tiles, with the main compositional difference being a slightly different waterproofing agent, and the physical difference being the internal attachment frame.

Ed,

Can you give a bit more background on the FDEP doc?  Maybe a link?  I’m just so surprised because I feel like it’s the first I’m hearing of this.  It feels like it really went semi-unnoticed here (at least in this thread?).
FDEP Documents are here (https://prodenv.dep.state.fl.us/DepNexus/public/electronic-documents/FLR000231449/facility!search), go back in this thread ~ a year and a half (end of 2020) for discussion around them.

Hmm, site is acting up - does anyone perhaps have a copy?  Or I’ll just try again later…

Attaching my copy of the Florida EPA Inspection report.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 08/29/2021 01:24 pm
...
A year ago discussions were guessing a density for the TPS system of about 13 kg/m^3, with a total system mass of 8,500 to 10,000 kg.
...
I knew they were light, but I didn't think so much! It is very impressive.
Title: Re: Starship heat shield
Post by: woods170 on 08/29/2021 07:37 pm
Not TUFROC.

TUFROC is HRSI tiles covered with an RCC cap.

Minor nits:

TUFROC has a ROCCI cap. Not RCC. Quite different from each other.
What you refer to as a HRSI tile is actually a TUFI AETB. More like FRCI, which was the much reinforced cousin of the HRSI tile.

https://technology.nasa.gov/patent/TOP2-241
https://core.ac.uk/download/pdf/42700645.pdf
Title: Re: Starship heat shield
Post by: livingjw on 08/29/2021 07:38 pm
...
A year ago discussions were guessing a density for the TPS system of about 13 kg/m^3, with a total system mass of 8,500 to 10,000 kg.
...
I knew they were light, but I didn't think so much! It is very impressive.

- I think he was off by a decimal point.  Tile insulation is similar to AETB. AETB has density in the 7-12 lb/ft^3 range  (112-192 kg/m^3)

- This is just the insulation block. You then need to add the toughened outer thin shell and the mechanical attachment embedded inside the tile. These are small but significant mass additions.

John
Title: Re: Starship heat shield
Post by: Jimmy_C on 08/31/2021 02:00 am
Do you think SpaceX might eventually deploy cameras like the Chinese and Japanese did to inspect the spacecraft in orbit? I can see value in learning how well the TPS survived liftoff.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 08/31/2021 12:57 pm
...
A year ago discussions were guessing a density for the TPS system of about 13 kg/m^3, with a total system mass of 8,500 to 10,000 kg.
...
I knew they were light, but I didn't think so much! It is very impressive.

- I think he was off by a decimal point.  Tile insulation is similar to AETB. AETB has density in the 7-12 lb/ft^3 range  (112-192 kg/m^3)

- This is just the insulation block. You then need to add the toughened outer thin shell and the mechanical attachment embedded inside the tile. These are small but significant mass additions.

John
Thanks. Now the numbers seem more reasonable.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 08/31/2021 04:21 pm
...
A year ago discussions were guessing a density for the TPS system of about 13 kg/m^3, with a total system mass of 8,500 to 10,000 kg.
...
I knew they were light, but I didn't think so much! It is very impressive.

- I think he was off by a decimal point.  Tile insulation is similar to AETB. AETB has density in the 7-12 lb/ft^3 range  (112-192 kg/m^3)

- This is just the insulation block. You then need to add the toughened outer thin shell and the mechanical attachment embedded inside the tile. These are small but significant mass additions.

John

Surface area of a cylinder:  diameter * pi * height.

*tiled* Surface area of Starship = 1/2 * 9m * 3.14 * 50 = ~700 m^2

depth of tile ~= 0.1m

Volume of tiles = 0.1 * 700 = 70m^3

70m^3 * 150 kg/m^3 ~= 10,000kg

How did others arrive at estimates of 10 tons of tiles?
Title: Re: Starship heat shield
Post by: livingjw on 08/31/2021 04:33 pm
...
A year ago discussions were guessing a density for the TPS system of about 13 kg/m^3, with a total system mass of 8,500 to 10,000 kg.
...
I knew they were light, but I didn't think so much! It is very impressive.

- I think he was off by a decimal point.  Tile insulation is similar to AETB. AETB has density in the 7-12 lb/ft^3 range  (112-192 kg/m^3)

- This is just the insulation block. You then need to add the toughened outer thin shell and the mechanical attachment embedded inside the tile. These are small but significant mass additions.

John

Surface area of a cylinder:  diameter * pi * height.

Surface area of Starship = 1/2 * 9m * 3.14 * 50 = ~700 m^2

depth of tile ~= 0.1m

Volume of tiles = 0.1 * 700 = 70m^3

70m^3 * 150 kg/m^3 ~= 10,000kg

How did others arrive at estimates of 10 tons of tiles?

Yes, there abouts.

John
Title: Re: Starship heat shield
Post by: aries1b on 09/01/2021 01:49 am
Not TUFROC.

TUFROC is HRSI tiles covered with an RCC cap. No SpaceX tile (either those on Starship now nor those seen previously) have had RCC caps. TUFROC was mentioned among a whole bunch of other TPS technologies as part of a Space Act Agreement, and for some bizarre reason it's been latched onto as some sort of perceived super-TPS for no apparent reason.

From the tile manufacture process description from the FDEP inspection document, SpaceX's tiles are almost identical to shuttle-era HRSI tiles, with the main compositional difference being a slightly different waterproofing agent, and the physical difference being the internal attachment frame.

Not particularly my area of expertise, but according to this article:

https://www.techbriefs.com/component/content/article/tb/pub/techbriefs/materials/2292

The shuttle tiles used RCC caps, whereas TUFROC uses a ROCCI cap.
Title: Re: Starship heat shield
Post by: AdrianK on 09/01/2021 01:47 pm
What happens if it rains on the Starship? Won't the white thermal insulator (under the tiles) be soaked in water, adding extra mass to the ship? When filled with cryogenic propellants, won't the soaked insulator expand and push the tiles out?
Title: Re: Starship heat shield
Post by: Vettedrmr on 09/01/2021 01:57 pm
You're making the assumption that the under-layer is water absorbent.  But, it's a good question, one of many that will need answers for before SS becomes operational.  Right now I don't *think* they load propellants into F9 if it's raining, since that's a violation of their weather constraints.

Have a good one,
Mike
Title: Re: Starship heat shield
Post by: xvel on 09/01/2021 02:48 pm
What happens if it rains on the Starship? Won't the white thermal insulator (under the tiles) be soaked in water, adding extra mass to the ship? When filled with cryogenic propellants, won't the soaked insulator expand and push the tiles out?

Water condense and freeze anyway

SN15

and nothing was broken after this.

But added mass...[they probably accounted for that.]

[zubenelgenubi: embedded image and snark removed]
Title: Re: Starship heat shield
Post by: envy887 on 09/01/2021 04:42 pm
What happens if it rains on the Starship? Won't the white thermal insulator (under the tiles) be soaked in water, adding extra mass to the ship? When filled with cryogenic propellants, won't the soaked insulator expand and push the tiles out?

Not if it's hydrophobic like the TPS on Falcon.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 09/01/2021 07:52 pm
You're making the assumption that the under-layer is water absorbent.  But, it's a good question, one of many that will need answers for before SS becomes operational.  Right now I don't *think* they load propellants into F9 if it's raining, since that's a violation of their weather constraints.

Have a good one,
Mike
I agree. But even if they didn't load props when rainin they would need to wait after the thing dries. But this is all useless discussion since we know that the blancket is hydrophobic.
Title: Re: Starship heat shield
Post by: liaoparda on 09/03/2021 05:44 pm
You're making the assumption that the under-layer is water absorbent.  But, it's a good question, one of many that will need answers for before SS becomes operational.  Right now I don't *think* they load propellants into F9 if it's raining, since that's a violation of their weather constraints.

Have a good one,
Mike
I agree. But even if they didn't load props when rainin they would need to wait after the thing dries. But this is all useless discussion since we know that the blancket is hydrophobic.

The blanket being waterproof has been confirmed? Usually waterproof insulation blankets have lower temperature rating than normal ones.

But even if the blanket is waterproofed in any form, water can still accumulate between tiles, between the blanket and the steel, find its way into the glue, etc. Even a small amount of water in the correct spot can exert enough force to easily flex a blanket and move tiles in top if it becomes ice when fuelling the ship.
I would say that for testing if it rains they will wait a few days to be sure any pockets of water are gone. When starship becomes commercial I will not find it strange if they keep them under a roof. Freezing water in cracks will never stop being a risk.
Title: Re: Starship heat shield
Post by: xvel on 09/03/2021 06:21 pm
Just stop it, Spacex flies people to the ISS, lands boosters one after another and forgets that sometimes it rains...
Title: Re: Starship heat shield
Post by: liaoparda on 09/05/2021 05:27 pm
Just stop it, Spacex flies people to the ISS, lands boosters one after another and forgets that sometimes it rains...

SpaceX booster landings are not at orbital speeds, and Dragon has an ablative heat shield that SpaceX refers to as "refurbishable". SpaceX or NASA have never made a heat shield for a quick reusable vehicle like SpaceX is trying to do with starship. To imply that this is not big deal because "SpaceX is already operating in space" is BS. Dragon shield doesn't have gaps and it is not in contact with cryogenic fuel, it is ablative and it doesn´t has to deal with rain; falcon 9 booster doesn't even have a heat shield to begin with, it re-enters at non orbital speeds.
Starship's heat shield is an incredible engineering challenge and SpaceX team is putting effort into it. It is normal to discuss it in this forum, and rain and ice are valid concerns to think about.
Title: Re: Starship heat shield
Post by: edzieba on 09/05/2021 07:53 pm
falcon 9 booster doesn't even have a heat shield to begin with
Falcon 9 has had multiple iteration of base heatshield (the 'dancefloor') from cork and SPAM coated aluminium to a titanium sandwich with water impingement cooling.
Title: Re: Starship heat shield
Post by: liaoparda on 09/05/2021 08:50 pm
falcon 9 booster doesn't even have a heat shield to begin with
Falcon 9 has had multiple iteration of base heatshield (the 'dancefloor') from cork and SPAM coated aluminium to a titanium sandwich with water impingement cooling.

Yes you are right, it has heat protection, but not a remotely equivalent one, that was the point. Last iteration was mostly inconel protection, making it reusable. In any case, it relies almost completely on engines creating a plasma barrier, that is the real heat shield falcon 9 has. The inconel is there to resist 300ºC aprox. Protecting against 1500ºC for orbital reentry is orders of magnitude more complex though, and Inconel is useless for it. So to imply that current inconel heat protection is even remotely related to starship's tile technology, that it is remotely conceived for the same situation, and that current experience on inconel 300ºC reusable heat protection and ablative non-reusable heat protection from dragon automatically renders any concerns on shartship's new tile technology meaningless have no sense to me. It's a totally new situation.
Title: Re: Starship heat shield
Post by: livingjw on 09/05/2021 10:41 pm
falcon 9 booster doesn't even have a heat shield to begin with
Falcon 9 has had multiple iteration of base heatshield (the 'dancefloor') from cork and SPAM coated aluminium to a titanium sandwich with water impingement cooling.

Yes you are right, it has heat protection, but not a remotely equivalent one, that was the point. Last iteration was mostly inconel protection, making it reusable. In any case, it relies almost completely on engines creating a plasma barrier, that is the real heat shield falcon 9 has. The inconel is there to resist 300ºC aprox. Protecting against 1500ºC for orbital reentry is orders of magnitude more complex though, and Inconel is useless for it. So to imply that current inconel heat protection is even remotely related to starship's tile technology, that it is remotely conceived for the same situation, and that current experience on inconel 300ºC reusable heat protection and ablative non-reusable heat protection from dragon automatically renders any concerns on shartship's new tile technology meaningless have no sense to me. It's a totally new situation.

- Falcon 9 booster engines are run to slow the booster in order to avoid high heating of the aluminum structure which cannot tolerate temperatures much above 350 F, 180C.

- Inconel should be good to ~1800F, 980C in a low stress heat shield application.

- Inconel should be fine for protecting SH engine fiddly bits during return to launch site. Nozzles may have to be cooled slightly with a slow flow of CH4.

-Water retention by the tile and the blanket are a real concern. I'm sure they have plans and options to deal with it. Wouldn't say its solved.

John
Title: Re: Starship heat shield
Post by: oiorionsbelt on 09/05/2021 11:16 pm
SpaceX did have water issues with the primary Dragon heat shield early on. They use the 'silvery' coating to help with water intrusion.



spelling
Title: Re: Starship heat shield
Post by: FutureSpaceTourist on 09/07/2021 06:42 am
Current status of S20

https://youtu.be/D1WgEY64QGw
Title: Re: Starship heat shield
Post by: brettly2021 on 09/08/2021 03:17 pm
previous post video shows upper part of sn20 heat shield tiles which were cracked been marked for replacement.
Question to ask is ( if not already discussed) why did these tiles crack so badly?
I believe it was soon after the sn20 was lifted onto the bn4 booster and taken off that the cracking was marked and repaired. Why did all those tiles crack?
My theory is that as the sn20 was lifted by the straps at nosecone, the top portion of the craft underwent a certain amount of bending or distortion during the lift, this distortion was enough to crack many many tiles, they are probably quite easily cracked I suspect.
The lower half of the ship was unaffected and not enough distortion of the stainless shell to effect the bottom half tiles.
But this leads me to wonder at lift off, the vibrational forces will be huge, I suspect the tiles will be cracking and falling off all over the place!! during liftoff phase.  There would need to be significant testing of how the tiles mounted as they are will respond to liftoff. I would think that the spaces inbetween the tiles need to be filled with a heat resistant flexible silicone or similar which reduce damage to tiles during liftoff. Even static test fires will give an indication how well the tiles will hold up.
If simply lifting the sn20 very slowly and calmly breaks so many tiles, vibration at takeoff will be many times worse outcome.
Title: Re: Starship heat shield
Post by: cscott on 09/08/2021 04:35 pm
You seem to start from a tenuous theory of your own and extrapolate that confidently to conclude the sky is falling.
Title: Re: Starship heat shield
Post by: equiserre on 09/08/2021 04:43 pm
previous post video shows upper part of sn20 heat shield tiles which were cracked been marked for replacement.
Question to ask is ( if not already discussed) why did these tiles crack so badly?
I believe it was soon after the sn20 was lifted onto the bn4 booster and taken off that the cracking was marked and repaired. Why did all those tiles crack?
My theory is that as the sn20 was lifted by the straps at nosecone, the top portion of the craft underwent a certain amount of bending or distortion during the lift, this distortion was enough to crack many many tiles, they are probably quite easily cracked I suspect.
The lower half of the ship was unaffected and not enough distortion of the stainless shell to effect the bottom half tiles.
But this leads me to wonder at lift off, the vibrational forces will be huge, I suspect the tiles will be cracking and falling off all over the place!! during liftoff phase.  There would need to be significant testing of how the tiles mounted as they are will respond to liftoff. I would think that the spaces inbetween the tiles need to be filled with a heat resistant flexible silicone or similar which reduce damage to tiles during liftoff. Even static test fires will give an indication how well the tiles will hold up.
If simply lifting the sn20 very slowly and calmly breaks so many tiles, vibration at takeoff will be many times worse outcome.
Tiles move independently. The max elongation between pins is in the order of 1-2 tenths of a mm. Plus, the pins design aparently lets the tiles move. It doesnt seem ro be a problem.
Title: Re: Starship heat shield
Post by: Sciencefan on 09/08/2021 04:47 pm
previous post video shows upper part of sn20 heat shield tiles which were cracked been marked for replacement.
Question to ask is ( if not already discussed) why did these tiles crack so badly?
I believe it was soon after the sn20 was lifted onto the bn4 booster and taken off that the cracking was marked and repaired. Why did all those tiles crack?
My theory is that as the sn20 was lifted by the straps at nosecone, the top portion of the craft underwent a certain amount of bending or distortion during the lift, this distortion was enough to crack many many tiles, they are probably quite easily cracked I suspect.
The lower half of the ship was unaffected and not enough distortion of the stainless shell to effect the bottom half tiles.
But this leads me to wonder at lift off, the vibrational forces will be huge, I suspect the tiles will be cracking and falling off all over the place!! during liftoff phase.  There would need to be significant testing of how the tiles mounted as they are will respond to liftoff. I would think that the spaces inbetween the tiles need to be filled with a heat resistant flexible silicone or similar which reduce damage to tiles during liftoff. Even static test fires will give an indication how well the tiles will hold up.
If simply lifting the sn20 very slowly and calmly breaks so many tiles, vibration at takeoff will be many times worse outcome.

The reasons are haste and shortage of the tiles. The worst affected areas were tiled last and it looks the tiles were damaged during installation.
Title: Re: Starship heat shield
Post by: rsdavis9 on 09/08/2021 08:10 pm
previous post video shows upper part of sn20 heat shield tiles which were cracked been marked for replacement.
Question to ask is ( if not already discussed) why did these tiles crack so badly?
I believe it was soon after the sn20 was lifted onto the bn4 booster and taken off that the cracking was marked and repaired. Why did all those tiles crack?
My theory is that as the sn20 was lifted by the straps at nosecone, the top portion of the craft underwent a certain amount of bending or distortion during the lift, this distortion was enough to crack many many tiles, they are probably quite easily cracked I suspect.
The lower half of the ship was unaffected and not enough distortion of the stainless shell to effect the bottom half tiles.
But this leads me to wonder at lift off, the vibrational forces will be huge, I suspect the tiles will be cracking and falling off all over the place!! during liftoff phase. There would need to be significant testing of how the tiles mounted as they are will respond to liftoff. I would think that the spaces inbetween the tiles need to be filled with a heat resistant flexible silicone or similar which reduce damage to tiles during liftoff. Even static test fires will give an indication how well the tiles will hold up.
If simply lifting the sn20 very slowly and calmly breaks so many tiles, vibration at takeoff will be many times worse outcome.

The reasons are haste and shortage of the tiles. The worst affected areas were tiled last and it looks the tiles were damaged during installation.

Also this has been tested many times. They have been putting tiles on SS's for a while now in many different places.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 09/10/2021 05:29 pm
previous post video shows upper part of sn20 heat shield tiles which were cracked been marked for replacement.
Question to ask is ( if not already discussed) why did these tiles crack so badly?
I believe it was soon after the sn20 was lifted onto the bn4 booster and taken off that the cracking was marked and repaired. Why did all those tiles crack?
My theory is that as the sn20 was lifted by the straps at nosecone, the top portion of the craft underwent a certain amount of bending or distortion during the lift, this distortion was enough to crack many many tiles, they are probably quite easily cracked I suspect.
The lower half of the ship was unaffected and not enough distortion of the stainless shell to effect the bottom half tiles.
But this leads me to wonder at lift off, the vibrational forces will be huge, I suspect the tiles will be cracking and falling off all over the place!! during liftoff phase. There would need to be significant testing of how the tiles mounted as they are will respond to liftoff. I would think that the spaces inbetween the tiles need to be filled with a heat resistant flexible silicone or similar which reduce damage to tiles during liftoff. Even static test fires will give an indication how well the tiles will hold up.
If simply lifting the sn20 very slowly and calmly breaks so many tiles, vibration at takeoff will be many times worse outcome.

The reasons are haste and shortage of the tiles. The worst affected areas were tiled last and it looks the tiles were damaged during installation.

Also this has been tested many times. They have been putting tiles on SS's for a while now in many different places.

Since this is the nose cone, where hex tiles don't exactly line up line they do on a cylinder, my guess is that they have tolerance issues on the nose cone with the tile sizes, pin placement, and movement of the underlying surface all contributing.

Hammering in tiles that wouldn't quite fit probably damaged them.  As would lifting causing movement of the underlying surface.

Fix:  make some slightly smaller tiles or shape custom ones for the locations that normal tiles won't fit.
Title: Re: Starship heat shield
Post by: punder on 09/10/2021 05:36 pm
Probably dumb question, but what about making the ogive steel a little thicker than on the cylinder pieces, and increase the tile gaps slightly?

Fire away. Like I said…  :D
Title: Re: Starship heat shield
Post by: c4fusion on 09/10/2021 05:38 pm
Since this is the nose cone, where hex tiles don't exactly line up line they do on a cylinder, my guess is that they have tolerance issues on the nose cone with the tile sizes, pin placement, and movement of the underlying surface all contributing.

Hammering in tiles that wouldn't quite fit probably damaged them.  As would lifting causing movement of the underlying surface.

Fix:  make some slightly smaller tiles or shape custom ones for the locations that normal tiles won't fit.

Or increase the tolerance on the pins on the new nose cone design.  Currently the new nose cone is fairly lumpy making it hard to have spacing like on the barrel.

Additionally, due to the nose cone being lumpy, I can imagine when they lift by the nose, the straighten of the nose cone sheet metal is causing additional damage.
Title: Re: Starship heat shield
Post by: Kazioo on 09/10/2021 07:46 pm
You're making the assumption that the under-layer is water absorbent.  But, it's a good question, one of many that will need answers for before SS becomes operational.  Right now I don't *think* they load propellants into F9 if it's raining, since that's a violation of their weather constraints.

Have a good one,
Mike
I agree. But even if they didn't load props when rainin they would need to wait after the thing dries. But this is all useless discussion since we know that the blancket is hydrophobic.

The blanket being waterproof has been confirmed? Usually waterproof insulation blankets have lower temperature rating than normal ones.

But even if the blanket is waterproofed in any form, water can still accumulate between tiles, between the blanket and the steel, find its way into the glue, etc. Even a small amount of water in the correct spot can exert enough force to easily flex a blanket and move tiles in top if it becomes ice when fuelling the ship.
I would say that for testing if it rains they will wait a few days to be sure any pockets of water are gone. When starship becomes commercial I will not find it strange if they keep them under a roof. Freezing water in cracks will never stop being a risk.

The info we got from Jean Wright on the NSF livestream was that the white blanket was SIP, made of Nomex felt. If that's true, this might be the same thing that Shuttle had.

And this is what NASA says about its waterproofing of FRSI blankets (FELT REUSABLE SURFACE INSULATION) that used the same Nomex material:

Quote
A white-pigmented silicon elastomer coating is used to waterproof the felt and provide required thermal and optical properties.
Title: Re: Starship heat shield
Post by: cscott on 09/10/2021 08:15 pm
The tiles are held with a split pin mechanism. "Hammering in" is the intended design.  It doesn't indicate that anything is out of tolerance.  The pins elastically deform to accept the tile then snap back to hold the tile once the tile has been hammered into place.

As OTV Booster says:

He's using a big soft mushy fist mallet that distributes stress. Stress would collect where the tile touches the pins, and this would be limited by the compressibility of the bayonet. Any force beyond that needed to compress the bayonet (plus a smidge of sliding friction) is too much. It's literally a matter of 'feel'.


The vitrified coating should help distribute impact stress and it will have a limit but higher than the fluffy white. Rock hammers not recommended.
Title: Re: Starship heat shield
Post by: flexbuffchest on 09/11/2021 03:19 pm
I haven't seen this info anywhere, so I apologize if it has been posted, but has anyone taken the time to see just how many unique tiles are currently being used? That'd be a daunting task but I'm curious as to what the minimum amount of unique tiles are needed for SN20 and then tracking it over time.
Title: Re: Starship heat shield
Post by: livingjw on 09/11/2021 04:06 pm
You're making the assumption that the under-layer is water absorbent.  But, it's a good question, one of many that will need answers for before SS becomes operational.  Right now I don't *think* they load propellants into F9 if it's raining, since that's a violation of their weather constraints.

Have a good one,
Mike
I agree. But even if they didn't load props when rainin they would need to wait after the thing dries. But this is all useless discussion since we know that the blancket is hydrophobic.

The blanket being waterproof has been confirmed? Usually waterproof insulation blankets have lower temperature rating than normal ones.

But even if the blanket is waterproofed in any form, water can still accumulate between tiles, between the blanket and the steel, find its way into the glue, etc. Even a small amount of water in the correct spot can exert enough force to easily flex a blanket and move tiles in top if it becomes ice when fuelling the ship.
I would say that for testing if it rains they will wait a few days to be sure any pockets of water are gone. When starship becomes commercial I will not find it strange if they keep them under a roof. Freezing water in cracks will never stop being a risk.

The info we got from Jean Wright on the NSF livestream was that the white blanket was SIP, made of Nomex felt. If that's true, this might be the same thing that Shuttle had.

And this is what NASA says about its waterproofing of FRSI blankets (FELT REUSABLE SURFACE INSULATION) that used the same Nomex material:

Quote
A white-pigmented silicon elastomer coating is used to waterproof the felt and provide required thermal and optical properties.

I don't think Star Ship is using FRSI Blankets. The white underlayment we see on Star Ship appears to be a looser batting material. Could be NOMEX or Silica based fiber.

John
Title: Re: Starship heat shield
Post by: Slarty1080 on 09/11/2021 10:45 pm
I haven't seen this info anywhere, so I apologize if it has been posted, but has anyone taken the time to see just how many unique tiles are currently being used? That'd be a daunting task but I'm curious as to what the minimum amount of unique tiles are needed for SN20 and then tracking it over time.
Somewhere here there is a very good high res photo that shows dozens of tile types around the nose and flaperon. Some of the tiles were written on and if I could find that photo and another of the lower flap area it might be possible to come up with a rough estimate. My google foo is not good enough and there's just too many threads with too much content...
Title: Re: Starship heat shield
Post by: Slarty1080 on 09/12/2021 02:10 pm
Rough estimate of the total number of tiles: 170
Based on these two images from Bocachicagirl:
(https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2056230;image)
(https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=52398.0;attach=2056228;image)

The main problem areas being around the flaps especially the top edge root and the curved root boundary and the trailing edges. There could be fewer types but when you know there are a few hundred awkward corner cases it might be easier just to number them and cut them to fit at this point in development. No need to worry if # 73 is almost exactly the same as #124 or if #36 is only 1mm bigger etc.

The main cylinder has 3 types of hexagon each with 3 variant lengths of being "cut in half" at 90 degrees. The nose has two specials one a quadrilateral and one pentagonal. There are also special shaped tiles on the hinge and edges. 
Title: Re: Starship heat shield
Post by: Wakecrash on 09/12/2021 02:27 pm
Just for fun, someone should start poll or a contest to guess number of tiles that will fall off from before its next lift to the time it is stacked.
Title: Re: Starship heat shield
Post by: Kazioo on 09/13/2021 02:05 pm
You're making the assumption that the under-layer is water absorbent.  But, it's a good question, one of many that will need answers for before SS becomes operational.  Right now I don't *think* they load propellants into F9 if it's raining, since that's a violation of their weather constraints.

Have a good one,
Mike
I agree. But even if they didn't load props when rainin they would need to wait after the thing dries. But this is all useless discussion since we know that the blancket is hydrophobic.

The blanket being waterproof has been confirmed? Usually waterproof insulation blankets have lower temperature rating than normal ones.

But even if the blanket is waterproofed in any form, water can still accumulate between tiles, between the blanket and the steel, find its way into the glue, etc. Even a small amount of water in the correct spot can exert enough force to easily flex a blanket and move tiles in top if it becomes ice when fuelling the ship.
I would say that for testing if it rains they will wait a few days to be sure any pockets of water are gone. When starship becomes commercial I will not find it strange if they keep them under a roof. Freezing water in cracks will never stop being a risk.

The info we got from Jean Wright on the NSF livestream was that the white blanket was SIP, made of Nomex felt. If that's true, this might be the same thing that Shuttle had.

And this is what NASA says about its waterproofing of FRSI blankets (FELT REUSABLE SURFACE INSULATION) that used the same Nomex material:

Quote
A white-pigmented silicon elastomer coating is used to waterproof the felt and provide required thermal and optical properties.

I don't think Star Ship is using FRSI Blankets. The white underlayment we see on Star Ship appears to be a looser batting material. Could be NOMEX or Silica based fiber.

John

The point is FSRI is also based on NOMEX, so if they reuse the materials from Shuttle then maybe they also reuse waterproofing methods.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 09/13/2021 08:32 pm
You're making the assumption that the under-layer is water absorbent.  But, it's a good question, one of many that will need answers for before SS becomes operational.  Right now I don't *think* they load propellants into F9 if it's raining, since that's a violation of their weather constraints.

Have a good one,
Mike
I agree. But even if they didn't load props when rainin they would need to wait after the thing dries. But this is all useless discussion since we know that the blancket is hydrophobic.

The blanket being waterproof has been confirmed? Usually waterproof insulation blankets have lower temperature rating than normal ones.

But even if the blanket is waterproofed in any form, water can still accumulate between tiles, between the blanket and the steel, find its way into the glue, etc. Even a small amount of water in the correct spot can exert enough force to easily flex a blanket and move tiles in top if it becomes ice when fuelling the ship.
I would say that for testing if it rains they will wait a few days to be sure any pockets of water are gone. When starship becomes commercial I will not find it strange if they keep them under a roof. Freezing water in cracks will never stop being a risk.

The info we got from Jean Wright on the NSF livestream was that the white blanket was SIP, made of Nomex felt. If that's true, this might be the same thing that Shuttle had.

And this is what NASA says about its waterproofing of FRSI blankets (FELT REUSABLE SURFACE INSULATION) that used the same Nomex material:

Quote
A white-pigmented silicon elastomer coating is used to waterproof the felt and provide required thermal and optical properties.

I doubt it's Nomex.  Why would you put something that has *lower* temperature capability over something with higher temperature capability?

Nomex:  About 200degC  (much above 250degC it just burns)
Stainless Steel:   about 600 degC  (can go almost double this but loses strength).


My bet is mineral wool.  The close up pictures look like mineral wool, and mineral wool has operating temperatures in the 1450degC area.   The newer kind is bio-compatable and used over the place in the oil industry.  Was discussed somewhere above in this thread.
Title: Re: Starship heat shield
Post by: Bananas_on_Mars on 09/13/2021 09:00 pm
Nomex:  About 200degC  (much above 250degC it just burns)
Stainless Steel:   about 600 degC  (can go almost double this but loses strength).

Do you have a source for that statement? AFAIK Aramide fibers have temperature ranges up to ~370 degrees C without degradation, beyond that you get a carbonization layer but no active burning.
Title: Re: Starship heat shield
Post by: rsdavis9 on 09/13/2021 09:04 pm
Nomex:  About 200degC  (much above 250degC it just burns)
Stainless Steel:   about 600 degC  (can go almost double this but loses strength).

Do you have a source for that statement? AFAIK Aramide fibers have temperature ranges up to ~370 degrees C without degradation, beyond that you get a carbonization layer but no active burning.

https://en.wikipedia.org/wiki/Nomex#Properties

370C it is.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 09/13/2021 09:18 pm
Nomex:  About 200degC  (much above 250degC it just burns)
Stainless Steel:   about 600 degC  (can go almost double this but loses strength).

Do you have a source for that statement? AFAIK Aramide fibers have temperature ranges up to ~370 degrees C without degradation, beyond that you get a carbonization layer but no active burning.

I'll note 370degC is still about half of what Stainless steel can handle.  So my point still stands.

That being said, here's my source:

https://www.dupont.com/content/dam/dupont/amer/us/en/personal-protection/public/documents/en/Nomex(R)%20Fiber%20Technical%20Guide.pdf

See figure 2.5.   I note a contradiction between the text of that figure and the graph of that figure.

It makes sense to put Nomex over Aluminum, but not over stainless steel.
Title: Re: Starship heat shield
Post by: c4fusion on 09/14/2021 05:44 am
If we want water resistance and a layer between the tile and the skin of the ship, can't they change to something like the attached image but made of metal wire (it's called HyperVent)?  From what I can tell the biggest reason they want something between the tiles and the skin of the ship is for vibration purposes and help dissipate some of the heat before it reaches the skin and this will do both.  While will still retain some water it should be much smaller amount and should be tolerable.
Title: Re: Starship heat shield
Post by: Bananas_on_Mars on 09/14/2021 09:43 am
Nomex:  About 200degC  (much above 250degC it just burns)
Stainless Steel:   about 600 degC  (can go almost double this but loses strength).

Do you have a source for that statement? AFAIK Aramide fibers have temperature ranges up to ~370 degrees C without degradation, beyond that you get a carbonization layer but no active burning.

I'll note 370degC is still about half of what Stainless steel can handle.  So my point still stands.

That being said, here's my source:

https://www.dupont.com/content/dam/dupont/amer/us/en/personal-protection/public/documents/en/Nomex(R)%20Fiber%20Technical%20Guide.pdf

See figure 2.5.   I note a contradiction between the text of that figure and the graph of that figure.

It makes sense to put Nomex over Aluminum, but not over stainless steel.
The graph looks like it‘s either for very long exposure (months/years) in an oxidising environment, or it‘s a degree Celsius/Fahrenheit mixup, both would somehow fit.

From my experience with aramide gloves/wicks, it behaves similar to what i would expect from an ablative heatshield. Maybe among other criteria they chose it for low heat conductivity, and possibly a backstop before the stainless steel in case they loose a tile?

My guess is ceramic/glass felt would have lower vibration tolerance and add inhalation exposure risk for workers, metallic fleece would have higher heat conductivity, thus possible ice-buildup problems on the pad.
Title: Re: Starship heat shield
Post by: JamesH65 on 09/14/2021 12:38 pm
They use Nomex in race car suits and firefighter suits for a reason....
Title: Re: Starship heat shield
Post by: favo on 09/14/2021 05:53 pm
Somewhere here there is a very good high res photo that shows dozens of tile types around the nose and flaperon. Some of the tiles were written on and if I could find that photo and another of the lower flap area it might be possible to come up with a rough estimate. My google foo is not good enough and there's just too many threads with too much content...

These from @StarshipGazer might be what you're thinking of.
https://twitter.com/StarshipGazer/status/1437118548619501568 (https://twitter.com/StarshipGazer/status/1437118548619501568)

(https://pbs.twimg.com/media/E_Grnu5XoAIU-WZ?format=jpg&name=4096x4096)
(https://pbs.twimg.com/media/E_GrrUbWEAU6Je3?format=jpg&name=4096x4096)
Title: Re: Starship heat shield
Post by: edzieba on 09/14/2021 06:06 pm
They use Nomex in race car suits and firefighter suits for a reason....
Racecar drivers may like to go fast, but they do not re-enter at hypervelocity (I suspect some would have been willing to give MOOSE a try, though).

Remember that between the tiles on STS were gapfill material made of silica and alumina fibres. These prevented hot gas ingress behind the tiles, where they were bonded to Nomex felt pads. This is because the tiles are the primary thermal protection, and their backside does not heat sufficiently for melting of the Nomex backer (SIPs- Strain Isolation Pads) to be a concern.
Starship appears to - thus far! - lack gapfillers. This means that hot gas ingress between tiles is a possibility. Ceramic fibre matting makes more sense here for its higher temperature tolerance, as it no longer needs to serve as the mechanical attachment mechanism as the Nomex SIPs did on STS.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 09/14/2021 08:52 pm

My guess is ceramic/glass felt would have lower vibration tolerance and add inhalation exposure risk for workers, metallic fleece would have higher heat conductivity, thus possible ice-buildup problems on the pad.

Modern wool such as Superwool is much more bio-safe, is used for sound insulation, and has a melting point of 1650 degC, and is used for insulation so its heat conductivity is low.  It is water resistant and retains all properties after water is gone.

What is still not good is its emmissivity, it doesn't shed heat like black tiles can.   But as a back up plan and for surface decoupling, it looks good.

https://www.morganthermalceramics.com/en-gb/engineered-solutions/superwool-xtra/?gclid=Cj0KCQjwkIGKBhCxARIsAINMioLmvPemKObPMNmg-wbv_G3ykAeSgaQD7YZVOhQ2wObW6al7sNQ-eRQaAvlNEALw_wcB

https://www.amazon.com/Superwool-Ceramic-Alternative-Kaowool-Insulation/dp/B07SQF7KYS
Title: Re: Starship heat shield
Post by: WormPicker959 on 09/14/2021 09:15 pm
Nomex:  About 200degC  (much above 250degC it just burns)
Stainless Steel:   about 600 degC  (can go almost double this but loses strength).

Do you have a source for that statement? AFAIK Aramide fibers have temperature ranges up to ~370 degrees C without degradation, beyond that you get a carbonization layer but no active burning.

I'll note 370degC is still about half of what Stainless steel can handle.  So my point still stands.

That being said, here's my source:

https://www.dupont.com/content/dam/dupont/amer/us/en/personal-protection/public/documents/en/Nomex(R)%20Fiber%20Technical%20Guide.pdf

See figure 2.5.   I note a contradiction between the text of that figure and the graph of that figure.

It makes sense to put Nomex over Aluminum, but not over stainless steel.

Based on this document, it appears it might be that Nomex is a bad choice for this application. It seems to me that (based on Fig. 2.5, page ) at around ~200C significant charring forms on the aramide fibers. The charring process is thought to be responsible for some of the heat-protective capabilities (page 24). Given the fact that the charring is (presumably) irreversible, it's not a reusable means by which to protect against temperatures >200C.

I think I must be reading some of this data wrong. The figure also contradicts the text directly above it. What am I missing?
Title: Re: Starship heat shield
Post by: InterestedEngineer on 09/14/2021 10:07 pm
I think I must be reading some of this data wrong. The figure also contradicts the text directly above it. What am I missing?

Looks to me like a double degC/degF conversion problem.

200degC accidentally converted again (times 9/5 plus 32) gives 400degC, which more accurately the char point of Nomex.

They probably started with degC, thought it was degF, and converted it by formula to a degC.    Not the first time, won't be the last.   The ghost of Mars Climate Orbiter is laughing
Title: Re: Starship heat shield
Post by: eriblo on 09/15/2021 02:23 pm
https://twitter.com/StarshipGazer/status/1437979086077534212
Looking at the final product (?) in Starship Grazers tweet I think that at least the circled tiles could be instrumented. They are placed at the likely stagnation point and to either side/below, never had the three mounting studs installed but instead have a central knob/possible hull penetration (see for example this post (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2285011#msg2285011) by Mary) and had their tiles glued into place (as seen in this post (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2286160#msg2286160) by Stephen).
Title: Re: Starship heat shield
Post by: Citabria on 09/16/2021 01:29 pm
I thought we learned from Shuttle days that smoothness is important to prevent shock waves. Remember the gap filler drama? Is SpaceX about to prove us all wrong, again?

Edit: photo credit: bocachicagal
Title: Re: Starship heat shield
Post by: frith01 on 09/16/2021 03:30 pm
Somewhat surprised they didn't use the symmetry of the tiles to allow for self-centering of the air flow since they knew they would have protruding tiles.    Instead of level surface of the tile,  have flat tile graded 1cm higher towards one edge as their "standard"  size hex tile,  and have it facing North  one one side, and  face south on the other side. 
Title: Re: Starship heat shield
Post by: xvel on 09/16/2021 03:36 pm
Or just go straight to solving this problem next time and not waste any time on temporary solutions? This is the first orbital prototype, it doesn't matter really, maybe it won't even fly.
Title: Re: Starship heat shield
Post by: woods170 on 09/16/2021 06:27 pm
Or just go straight to solving this problem next time and not waste any time on temporary solutions? This is the first orbital prototype, it doesn't matter really, maybe it won't even fly.

Emphasis mine.

Good insight.

But I said too much already.
Title: Re: Starship heat shield
Post by: woods170 on 09/16/2021 06:30 pm
I thought we learned from Shuttle days that smoothness is important to prevent shock waves. Remember the gap filler drama? Is SpaceX about to prove us all wrong, again?

Edit: photo credit: bocachicagal

Gap fillers were critical for Shuttle because the underlying structure was aluminium. The only reason shuttle Atlantis existed beyond STS-27 is because the one tile that sheared off completely happened to be sitting on top of a solid steel equipment mounting plate.

Guess what's sitting underneath Starship's tiles? It ain't easy melty stuff like aluminium for a reason.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 09/16/2021 07:38 pm
I thought we learned from Shuttle days that smoothness is important to prevent shock waves. Remember the gap filler drama? Is SpaceX about to prove us all wrong, again?

Edit: photo credit: bocachicagal

Gap fillers were critical for Shuttle because the underlying structure was aluminium. The only reason shuttle Atlantis existed beyond STS-27 is because the one tile that sheared off completely happened to be sitting on top of a solid steel equipment mounting plate.

Guess what's sitting underneath Starship's tiles? It ain't easy melty stuff like aluminium for a reason.

Yes. I'm mind boggled every time I remember of that mission. But the steel mounting was probably thicker than SS steel, and steel isn' used only for its termal proprieties. Still the ship should probably survive a few tile lost, due to the steel and the blancket.
Title: Re: Starship heat shield
Post by: cscott on 09/16/2021 09:25 pm

Cross-post, of relevance to the perennial "# of unique tiles" discussion:
Aerocovers are for the booster which has no heat shield tiles.  Probably just easier to make this way.

These ones are for a Starship though. Note the rounded part which covers the top of the flap hinge.
Yep, it is the forward -Y (starboard) fin tip fairing, this post (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2270083#msg2270083) shows the same delivery for S20 and this one (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2271518#msg2271518) shows the installation of the +Y one for S20.

So they did update the design from smooth to angular. Must help with tiles, I'd think...

Title: Re: Starship heat shield
Post by: Slarty1080 on 09/17/2021 08:25 am

Cross-post, of relevance to the perennial "# of unique tiles" discussion:
Aerocovers are for the booster which has no heat shield tiles.  Probably just easier to make this way.

These ones are for a Starship though. Note the rounded part which covers the top of the flap hinge.
Yep, it is the forward -Y (starboard) fin tip fairing, this post (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2270083#msg2270083) shows the same delivery for S20 and this one (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2271518#msg2271518) shows the installation of the +Y one for S20.

So they did update the design from smooth to angular. Must help with tiles, I'd think...
I wonder how much of the problem is down to minor irregularities in the underlying steel and pins? Minor warping and buckling due to welding might cause all manner of misalignments. But that should improve as they refine the process of manufacture especially when they use the new gores to make the nosecone. If they can get ship 20 down in one piece (and that's a big if), these improvements would just add to the safety margin. We shall see.
Title: Re: Starship heat shield
Post by: RoboGoofers on 09/17/2021 11:27 am
The header tank will be pressurized during reentry, and so should have been pressed during tile install. If it's depressurized now it could cause the surface irregularities we're seeing.
Title: Re: Starship heat shield
Post by: ETurner on 09/17/2021 12:33 pm
I wonder how much of the problem is down to minor irregularities in the underlying steel and pins? Minor warping and buckling due to welding might cause all manner of misalignments. But that should improve as they refine the process of manufacture especially when they use the new gores to make the nosecone. If they can get ship 20 down in one piece (and that's a big if), these improvements would just add to the safety margin. We shall see.
But we see irregular heights (tile-skin separations), which suggests that either (1) the pins have irregular lengths or (2) the pin lengths don’t determine the heights. Option (2) makes little sense -- what else would determine the heights? But option (1) makes no sense at all.  ???
Title: Re: Starship heat shield
Post by: JamesH65 on 09/17/2021 12:50 pm
Nothing that a really large orbital sander won't cure...;-)
Title: Re: Starship heat shield
Post by: cscott on 09/17/2021 01:19 pm
Nothing that a really large orbital sander won't cure...;-)
I bet even a suborbital sander would work!
Title: Re: Starship heat shield
Post by: Sohl on 09/17/2021 02:41 pm
But we see irregular heights (tile-skin separations), which suggests that either (1) the pins have irregular lengths or (2) the pin lengths don’t determine the heights. Option (2) makes little sense -- what else would determine the heights? But option (1) makes no sense at all.  ???
I'd guess it's basically (2), in that there is variation in how far into each tile the pin "grabs" the tile, and that it is not limited by a hard-stopped socket on the tile side.  For example, it could be a slot with some head space above the pin so the vertical position is not locked to just one point.  The installer pushes the tile onto the pins.  At some point they start engaging with slots in the tiles, maybe like a zip tie that goes one way but not the other without damage.  Some tiles go down a bit further on the pins than others, so the tile surfaces don't match.  Maybe some tile edges hit each other at points that don't fit as well so some tile cannot be pushed down as far as others.
Title: Re: Starship heat shield
Post by: RoboGoofers on 09/17/2021 04:05 pm
But we see irregular heights (tile-skin separations), which suggests that either (1) the pins have irregular lengths or (2) the pin lengths don’t determine the heights. Option (2) makes little sense -- what else would determine the heights? But option (1) makes no sense at all.  ???
I'd guess it's basically (2), in that there is variation in how far into each tile the pin "grabs" the tile, and that it is not limited by a hard-stopped socket on the tile side.  For example, it could be a slot with some head space above the pin so the vertical position is not locked to just one point.  The installer pushes the tile onto the pins.  At some point they start engaging with slots in the tiles, maybe like a zip tie that goes one way but not the other without damage.  Some tiles go down a bit further on the pins than others, so the tile surfaces don't match.  Maybe some tile edges hit each other at points that don't fit as well so some tile cannot be pushed down as far as others.
The tiles on the tip are glued on and don't use the attachment pins that are used elsewhere.
Title: Re: Starship heat shield
Post by: Sohl on 09/17/2021 06:58 pm
But we see irregular heights (tile-skin separations), which suggests that either (1) the pins have irregular lengths or (2) the pin lengths don’t determine the heights. Option (2) makes little sense -- what else would determine the heights? But option (1) makes no sense at all.  ???
I'd guess it's basically (2), in that there is variation in how far into each tile the pin "grabs" the tile, and that it is not limited by a hard-stopped socket on the tile side.  For example, it could be a slot with some head space above the pin so the vertical position is not locked to just one point.  The installer pushes the tile onto the pins.  At some point they start engaging with slots in the tiles, maybe like a zip tie that goes one way but not the other without damage.  Some tiles go down a bit further on the pins than others, so the tile surfaces don't match.  Maybe some tile edges hit each other at points that don't fit as well so some tile cannot be pushed down as far as others.
The tiles on the tip are glued on and don't use the attachment pins that are used elsewhere.

Good point, RoboGoofers!  That process may be a bit uneven now too if it is manual and they don't have jigs and such to help make it consistent.
Title: Re: Starship heat shield
Post by: AU1.52 on 09/17/2021 08:13 pm
But we see irregular heights (tile-skin separations), which suggests that either (1) the pins have irregular lengths or (2) the pin lengths don’t determine the heights. Option (2) makes little sense -- what else would determine the heights? But option (1) makes no sense at all.  ???
I'd guess it's basically (2), in that there is variation in how far into each tile the pin "grabs" the tile, and that it is not limited by a hard-stopped socket on the tile side.  For example, it could be a slot with some head space above the pin so the vertical position is not locked to just one point.  The installer pushes the tile onto the pins.  At some point they start engaging with slots in the tiles, maybe like a zip tie that goes one way but not the other without damage.  Some tiles go down a bit further on the pins than others, so the tile surfaces don't match.  Maybe some tile edges hit each other at points that don't fit as well so some tile cannot be pushed down as far as others.
The tiles on the tip are glued on and don't use the attachment pins that are used elsewhere.

Good point, RoboGoofers!  That process may be a bit uneven now too if it is manual and they don't have jigs and such to help make it consistent.


And from Tim Dodd's interview with Elon, we can assume most of the nose / tile infrastructure and installation will become automated as some point - once they have determined the best path forward. As said before all this is still experimental and subject to rud and change.
Title: Re: Starship heat shield
Post by: ETurner on 09/17/2021 09:59 pm
But we see irregular heights (tile-skin separations), which suggests that either (1) the pins have irregular lengths or (2) the pin lengths don’t determine the heights. Option (2) makes little sense -- what else would determine the heights? But option (1) makes no sense at all.  ???
I'd guess it's basically (2), in that there is variation in how far into each tile the pin "grabs" the tile, and that it is not limited by a hard-stopped socket on the tile side.[...]
That makes sense, but what bugs me is: Why?

A design choice like that seems kinda crazy, yet there is almost certainly some reason for it. My imagination fails me.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/17/2021 10:04 pm
Gotta throw $.02 into the bayonet clip discussion. There are two different types. Wikipedia only list the type that calls for a slight rotation after inserting, as in many automotive light bulbs. There is a second type that is commonly used in automotive door panels and is very much like the ones used for the tiles.


This second type is like in Mary's pic, below. The barbed head is slightly compressible and slightly larger than what it is intended to latch to. In this case it latches into the slot in the "Y" bracket on the back of the tile. So far, so good. Without something to load the bracket away from the skin such that the bracket engages and loads against the back side of the barb, the tile will be loose and rattle around.


The blanket is presumably intended to push the tile out and tighten things up a bit. I seriously doubt the QC on the pins and welding allows much variance. The tiles or the blanket seem more reasonable culprits. I've no background in ceramic structures and am not competent to judge this end of things. No experience with thermal blankets either, but I have owned and used textiles all my life.


All the recent discussion on the blanket has centered on thermal issues with no attention (I might have missed something) to its mechanical role.


Conjecture: maybe the blankets are lumpy or get over compressed during tile install. Or the brackets are unevenly mounted in the tiles. Or pins have been damaged during tile install.


One thing in the pin design does concern me. The head looks less barbed and more round. This is convenient for fabrication and tile removal but makes install less sturdy. If the blanket were bunched up around the pin it would maybe apply enough force to make the Y bracket ride further up the pin and even compress the latch action a bit. IIUC the blanket is forced down over the pins. If it punches a clean slit all is good. If it tears a hole some of the material could be doubled up, forcing the tile too high.


SX knows their business so it's a bit presumptuous for me to say they've got a bad pin design but this whole tile approach is something they're feeling their way through. They may already recognize the problem without any conjectures to cloud things up and have a redesign already in the works. 
Title: Re: Starship heat shield
Post by: docmordrid on 09/17/2021 10:31 pm
Reminds me of a Chrysler interior panel clip
Title: Re: Starship heat shield
Post by: OTV Booster on 09/17/2021 11:41 pm
I'm looking close at that pin pic and realized everything above is BS. All of a sudden I don't know how those pins work.


AFAIK we don't have good dimensions on the pins, the "Y" plate or the slots in it. Look at the first two rows or the second and third. The way the Y orients the round thingie I was calling a barb, will not engage the walls of the slot.


The structure below the round thingie looks to be wider than the slot. I think. If so, it would act as a stop. But not a latch. So what's this sucker doing?
Title: Re: Starship heat shield
Post by: docmordrid on 09/17/2021 11:55 pm
Functionally, as the point presses into a hole or slot, it compresses to fit through then expands to act like a molly. Removal is the reverse.
Title: Re: Starship heat shield
Post by: ETurner on 09/18/2021 09:56 am
I'm looking close at that pin pic and realized everything above is BS. All of a sudden I don't know how those pins work.


AFAIK we don't have good dimensions on the pins, the "Y" plate or the slots in it. Look at the first two rows or the second and third. The way the Y orients the round thingie I was calling a barb, will not engage the walls of the slot.


The structure below the round thingie looks to be wider than the slot. I think. If so, it would act as a stop. But not a latch. So what's this sucker doing?
Yeah. If the Y-bracket-thing had Y-oriented slots (which it seems that it should, if the thing works as a kinematic constraint system), then pins we see would be wide in the wrong (radial) direction to engage with the walls of the slots.

Also, not stopped and latched.

It’s a good rule of thumb to assume that SpaceX designs are good, and that anything that seems wrong is actually very clever. In this case, the huge number of crooked, protruding, and broken tiles suggests a real design problem. /sacrilege
Title: Re: Starship heat shield
Post by: rsdavis9 on 09/18/2021 12:05 pm
If blanket installation is a problem because of bunching, uneveness, etc.

How about a robot controlled cotton candy machine to form the blankets right on the skin directly. Fiberglass is made this way. Hot molten glass sprayed out and solidifies. 

https://en.wikipedia.org/wiki/Glass_fiber#Staple_fiber_process
Title: Re: Starship heat shield
Post by: enbandi on 09/18/2021 01:10 pm
I'm looking close at that pin pic and realized everything above is BS. All of a sudden I don't know how those pins work.


AFAIK we don't have good dimensions on the pins, the "Y" plate or the slots in it. Look at the first two rows or the second and third. The way the Y orients the round thingie I was calling a barb, will not engage the walls of the slot.


The structure below the round thingie looks to be wider than the slot. I think. If so, it would act as a stop. But not a latch. So what's this sucker doing?

The head of the pin is a ring/hole itself, so there can be a hidden latching mechanism behind/inside the slot, securing that ring in place.

Also the pins seems like cut and bended from a single sheet. Forming a ring perpendicular to the existing ones would be difficult with that technique.
Title: Re: Starship heat shield
Post by: enbandi on 09/18/2021 01:31 pm
....
It’s a good rule of thumb to assume that SpaceX designs are good, and that anything that seems wrong is actually very clever. In this case, the huge number of crooked, protruding, and broken tiles suggests a real design problem. /sacrilege

This is their Nth iteration of the pin system: we seen 3 different types tested simultaneously, smaller ones, single pin designs, and also different solutions at the y-socket side. What we see now is most likely a downselected/improved method based on all those. A major design flaw at this point would be really suprising.


On the other hand SpaceX doesn seem to bother much about protursions, same as they dont bother on gaps. Many of the uneven tiles are actually marked OK. So maybe the know something that we dont. Or they intend to start experimenting from really bottom up (improve only if necessary)
Title: Re: Starship heat shield
Post by: Vonbraun on 09/18/2021 02:02 pm
If blanket installation is a problem because of bunching, uneveness, etc.

How about a robot controlled cotton candy machine to form the blankets right on the skin directly. Fiberglass is made this way. Hot molten glass sprayed out and solidifies. 

https://en.wikipedia.org/wiki/Glass_fiber#Staple_fiber_process

From robotic assembly standpoint i bet the end product is going to be something, which is already attached on the underside of the tile. Easiest method is to die cut accurate parts and glue them on the tile (glue is only for assembly, can melt). Because die cutting is such a simple and inexpensive process, i wonder why they did not initially experiment with that. You can easily get raw felt size dies overnighted to your site if you are iterating and the stamping machines cost next to nothing.
Title: Re: Starship heat shield
Post by: BT52 on 09/18/2021 02:24 pm
Yeah even some robotic sewing machine could work to prevent problems in felt assembly. But i m sure even SpaceX doesn't want over commit towards solution too much. Maybe they will at orbital testing figure it out that they don't need underside felt material. Its just testing. And anything is possible.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/18/2021 02:29 pm
I'm looking close at that pin pic and realized everything above is BS. All of a sudden I don't know how those pins work.


AFAIK we don't have good dimensions on the pins, the "Y" plate or the slots in it. Look at the first two rows or the second and third. The way the Y orients the round thingie I was calling a barb, will not engage the walls of the slot.


The structure below the round thingie looks to be wider than the slot. I think. If so, it would act as a stop. But not a latch. So what's this sucker doing?

The head of the pin is a ring/hole itself, so there can be a hidden latching mechanism behind/inside the slot, securing that ring in place.

Also the pins seems like cut and bended from a single sheet. Forming a ring perpendicular to the existing ones would be difficult with that technique.
You might be on to something with a latch mechanism on the tile end. Maybe. Here's Mary's pick cropped down to one pin with a little image voodoo.


After looking at several pin pics I'm convinced the diagonal shiny bit reaching lower right to upper left and between the standoffs is a spring. As best I can tell it's a part of the lower standoff and bent in. It appears to be acting to force the upper standoff to the out position. Tentatively, there is a gap between the upper standoff and the PBRT (point, barb, round thingie).


In the second pic is a hook latch that is kind of analogous to the pin. If there is something in the tile that acts like the loop the hook latch is engaging, it might work. It would be a bear to get one pin to engage the tile properly. Three is mind boggling. This doesn't feel right so it's probably exactly what they're doing.
Title: Re: Starship heat shield
Post by: ETurner on 09/18/2021 06:12 pm
....
It’s a good rule of thumb to assume that SpaceX designs are good, and that anything that seems wrong is actually very clever. In this case, the huge number of crooked, protruding, and broken tiles suggests a real design problem. /sacrilege

This is their Nth iteration of the pin system: we seen 3 different types tested simultaneously, smaller ones, single pin designs, and also different solutions at the y-socket side. What we see now is most likely a downselected/improved method based on all those. A major design flaw at this point would be really suprising.
[...]
Yes, a major design flaw at this point would be really surprising, but I’m already surprised by the flaws in the product, and it’s hard not to blame the design. Surprise is already baked into the cake. I’m betting that we’ll see another iteration of the fasteners.
Title: Re: Starship heat shield
Post by: Adriano on 09/18/2021 06:39 pm
Or they will stop using the current attachment points on the nose and/ or strengthen the nose structure to avoid material deformation during lift.
Title: Re: Starship heat shield
Post by: Tangilinear Interjar on 09/18/2021 06:43 pm
How is it that after all this time we still don't have a GOOD picture of these clips?

I decided to try to model one up and in the process realized my Sketchup skills are really rusty but here is how I think the clip looks.  To me it looks like the loop part is something special, maybe not exactly like my model but in some pictures it does look like the loop is in fact two overlapping loop parts that slide across each other.  This design makes sense because it is a simple few steps to punch and press/bend into shape.

However after I put it all together and was going to post I realized that the pin is oriented to the Y chanel part in the tile rotated 90 degrees to what I have here (D'oh)!  So now I am confused again.
Title: Re: Starship heat shield
Post by: ETurner on 09/18/2021 08:28 pm
Or they will stop using the current attachment points on the nose and/ or strengthen the nose structure to avoid material deformation during lift.
The steel can’t deform enough to cause this kind of problem.
Title: Re: Starship heat shield
Post by: ETurner on 09/18/2021 08:30 pm
How is it that after all this time we still don't have a GOOD picture of these clips?

I decided to try to model one up and in the process realized my Sketchup skills are really rusty but here is how I think the clip looks.  To me it looks like the loop part is something special, maybe not exactly like my model but in some pictures it does look like the loop is in fact two overlapping loop parts that slide across each other.  This design makes sense because it is a simple few steps to punch and press/bend into shape.

However after I put it all together and was going to post I realized that the pin is oriented to the Y chanel part in the tile rotated 90 degrees to what I have here (D'oh)!  So now I am confused again.
Do we have a good picture of the Y channel, or whatever it is?
Title: Re: Starship heat shield
Post by: grndkntrl on 09/18/2021 09:37 pm
How is it that after all this time we still don't have a GOOD picture of these clips?

I decided to try to model one up and in the process realized my Sketchup skills are really rusty but here is how I think the clip looks.  To me it looks like the loop part is something special, maybe not exactly like my model but in some pictures it does look like the loop is in fact two overlapping loop parts that slide across each other.  This design makes sense because it is a simple few steps to punch and press/bend into shape.

However after I put it all together and was going to post I realized that the pin is oriented to the Y chanel part in the tile rotated 90 degrees to what I have here (D'oh)!  So now I am confused again.
Do we have a good picture of the Y channel, or whatever it is?

Yes, sort of:
Title: Re: Starship heat shield
Post by: eriblo on 09/18/2021 09:50 pm
How is it that after all this time we still don't have a GOOD picture of these clips?

I decided to try to model one up and in the process realized my Sketchup skills are really rusty but here is how I think the clip looks.  To me it looks like the loop part is something special, maybe not exactly like my model but in some pictures it does look like the loop is in fact two overlapping loop parts that slide across each other.  This design makes sense because it is a simple few steps to punch and press/bend into shape.

However after I put it all together and was going to post I realized that the pin is oriented to the Y chanel part in the tile rotated 90 degrees to what I have here (D'oh)!  So now I am confused again.
Do we have a good picture of the Y channel, or whatever it is?
Yes, sort of: [Attach images so they don't beak all the posts ;)]
Yeah, considering the distances involved I am impressed by what we actually get!

Tangilinear Interjar's model above is as good a guess for the studs as we have, although they are more drawn out/slender and the "head" is not circular but more mushroom-shaped (as can be seen in profile in the left insert below from this post (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2289896#msg2289896)). This means that the attachment is (at least in practice) irreversible and the tiles have to be drilled out to be removed (as seen in the second insert). The main image (from today's batch (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2291474#msg2291474) by Mary) once again show that the tiles have a tendency to fracture along their plane exposing the brackets and sometimes disintegrating completely leaving just the brackets behind before actually detaching.

It is worth noting the single bracket-lengths used to hold the insulation in place in the second insert (circled in red) have similar holes as those seen in grndkntrl's image, i.e. just big enough to accommodate the studs with no extra play in either dimension.
Title: Re: Starship heat shield
Post by: ETurner on 09/19/2021 12:13 am
How is it that after all this time we still don't have a GOOD picture of these clips?

I decided to try to model one up and in the process realized my Sketchup skills are really rusty but here is how I think the clip looks.  To me it looks like the loop part is something special, maybe not exactly like my model but in some pictures it does look like the loop is in fact two overlapping loop parts that slide across each other.  This design makes sense because it is a simple few steps to punch and press/bend into shape.

However after I put it all together and was going to post I realized that the pin is oriented to the Y chanel part in the tile rotated 90 degrees to what I have here (D'oh)!  So now I am confused again.
Do we have a good picture of the Y channel, or whatever it is?

Yes, sort of:
I’d like to see the side that faces the clip. Seeing the top side with material broken away only gives hints about the mechanical interface underneath.
Title: Re: Starship heat shield
Post by: enbandi on 09/19/2021 07:45 am
So based on the latest images (thanks guys) no magic on the socket side. The elongated hole in the brackets simply long as the tile head circle diameter (slightly below). And the studs firmly latch in as decribed above. And thus not provide/enable the suspected kinematic coupling.

But the Y brackets seems shorter than the half tile axis and the 3 of them seems also independent (not joined), so the kinematic coupling may provided by the metal brackets sliding inside the tile (or not exists at all).
Title: Re: Starship heat shield
Post by: meekGee on 09/19/2021 12:11 pm
I'm looking close at that pin pic and realized everything above is BS. All of a sudden I don't know how those pins work.


AFAIK we don't have good dimensions on the pins, the "Y" plate or the slots in it. Look at the first two rows or the second and third. The way the Y orients the round thingie I was calling a barb, will not engage the walls of the slot.


The structure below the round thingie looks to be wider than the slot. I think. If so, it would act as a stop. But not a latch. So what's this sucker doing?
Yeah. If the Y-bracket-thing had Y-oriented slots (which it seems that it should, if the thing works as a kinematic constraint system), then pins we see would be wide in the wrong (radial) direction to engage with the walls of the slots.

Also, not stopped and latched.

It’s a good rule of thumb to assume that SpaceX designs are good, and that anything that seems wrong is actually very clever. In this case, the huge number of crooked, protruding, and broken tiles suggests a real design problem. /sacrilege
It has to be kinematic, because of CTE mismatch.

I expect the elastic snap action is occurring at the bracket, not the pin.  Not sure why, but maybe something to do with the stud welding process.

Beyond that I'm all guessed out also.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/19/2021 04:56 pm
How is it that after all this time we still don't have a GOOD picture of these clips?

I decided to try to model one up and in the process realized my Sketchup skills are really rusty but here is how I think the clip looks.  To me it looks like the loop part is something special, maybe not exactly like my model but in some pictures it does look like the loop is in fact two overlapping loop parts that slide across each other.  This design makes sense because it is a simple few steps to punch and press/bend into shape.

However after I put it all together and was going to post I realized that the pin is oriented to the Y chanel part in the tile rotated 90 degrees to what I have here (D'oh)!  So now I am confused again.
Ahhhha, you see ze problem! Join the confusion. We probably haven't seen a really good pin pic because they are small and being backed by stainless, have a confusing welter of light and shadow. Throw in the welding scar and it only gets worse.

You're layout looks good. One change I'm fairly certain will hold up is only one spring. It longer and reaches across from one side to the other, which not being a mirror image, has a pad where the free end of the spring bears.

Edit: looks like two different pins.
Edit2: Maybe.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/19/2021 05:15 pm
So based on the latest images (thanks guys) no magic on the socket side. The elongated hole in the brackets simply long as the tile head circle diameter (slightly below). And the studs firmly latch in as decribed above. And thus not provide/enable the suspected kinematic coupling.

But the Y brackets seems shorter than the half tile axis and the 3 of them seems also independent (not joined), so the kinematic coupling may provided by the metal brackets sliding inside the tile (or not exists at all).
Where are you seeing the arms not joined?
Title: Re: Starship heat shield
Post by: enbandi on 09/19/2021 06:21 pm
.....
Where are you seeing the arms not joined?

I remember some pics of broken tiles, where the remaining arms were rotated. But i cannot find a decisive one. Maybe I am wrong.

On the first, the arms are clearly rotating, but that is an older/now outdated attachment version.
On the second, the arms are in place, but there is a white gap below the uppermost one.
The third is SN17 at the scrapyard, there are many misaligned lines, but can be anything due to low resolution.

All three is from the forum. 1, 2 from BocaChicaGal, the third is Nomadd.

Edit: maybe the SN17 pic give us a hint. Some of the arms are simply missing, while the rest of the tile are in place. That suggest that the arms are independent.
Title: Re: Starship heat shield
Post by: brettly2021 on 09/20/2021 01:23 pm
pic posted on previous page showing two broken tiles, not sure if anyone noticed on left side of that pic is nice pic of the clips, you can make out how that version works, very simple clip....pic attached, about as simple as you could possibly make it.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/20/2021 06:27 pm
pic posted on previous page showing two broken tiles, not sure if anyone noticed on left side of that pic is nice pic of the clips, you can make out how that version works, very simple clip....pic attached, about as simple as you could possibly make it.
I was seeing that too. The leaf spring bears on the top of the leg you mark as 'free', at least on this version.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/20/2021 06:31 pm
.....
Where are you seeing the arms not joined?

I remember some pics of broken tiles, where the remaining arms were rotated. But i cannot find a decisive one. Maybe I am wrong.

On the first, the arms are clearly rotating, but that is an older/now outdated attachment version.
On the second, the arms are in place, but there is a white gap below the uppermost one.
The third is SN17 at the scrapyard, there are many misaligned lines, but can be anything due to low resolution.

All three is from the forum. 1, 2 from BocaChicaGal, the third is Nomadd.

Edit: maybe the SN17 pic give us a hint. Some of the arms are simply missing, while the rest of the tile are in place. That suggest that the arms are independent.
Thanks for digging out those pics. I was picturing a slot running down each arm, not a hole. Did an early version have a slot? With a hole, the barb orientation makes perfect sense.
Title: Re: Starship heat shield
Post by: enbandi on 09/20/2021 11:36 pm
From the latest batch. Note the collars above the pinheads.
Title: Re: Starship heat shield
Post by: brettly2021 on 09/21/2021 08:05 am
my pic wrong, from todays pic above, you can zoom in a get alot of detail, here is one pin zoomed.
Title: Re: Starship heat shield
Post by: brettly2021 on 09/21/2021 08:32 am
a couple more close ups to help work out the details
Title: Re: Starship heat shield
Post by: cscott on 09/21/2021 01:58 pm
The collar looks like a feature meant to ensure tiles are at a uniform height.  I wonder if some of the "older" pins on starship are pre-collar, which would explain some of the unevenness.
Title: Re: Starship heat shield
Post by: ETurner on 09/21/2021 02:59 pm
The collar looks like a feature meant to ensure tiles are at a uniform height.  I wonder if some of the "older" pins on starship are pre-collar, which would explain some of the unevenness.
Pre-collar like the image linked in this post, presumably:
pic posted on previous page showing two broken tiles, not sure if anyone noticed on left side of that pic is nice pic of the clips, you can make out how that version works, very simple clip....pic attached, about as simple as you could possibly make it.
Those look like a surprisingly bad idea, and I guess they were.
Now turn the clips sideways and allow some radial motion in a slot to form a kinematic coupling and avoid stress.
Title: Re: Starship heat shield
Post by: xvel on 09/21/2021 03:14 pm
"old" and "new" are the same except for this "collar" thing, also I have no idea what those two spring thingies in the middle are for and how it is even possible that tiles can clip on lower or higher on this.
Title: Re: Starship heat shield
Post by: enbandi on 09/21/2021 06:00 pm
The collar looks like a feature meant to ensure tiles are at a uniform height.  I wonder if some of the "older" pins on starship are pre-collar, which would explain some of the unevenness.

There are already a sholuder not far below that collar, acting presumably as a stopper. The colar would be a redundant piece in that function. Seems illogical, why not raise shoulder height, if necessary?

Instead I have two, completely speculative idea.
The collar may act as a release on push mechanism, holding the clip tight for easier tile installation, released by the slot pushing it down. That would enable the springs to push the pin wider, to latch more firmly. Less likely as the collar seems unremovable.

Another function may be to hold the clip tight/straight, to prevent outward deformation. That is a possible failure mode in the prev version.  If too much force applied during install, clip legs may bend out (O shape), as they only connected at the top and bottom holding in that direction (springs prevent only invard bending). The collar can be a third, cross bar/reinforcement,  against that.

Edit: clarification.
Ps. O style bending can be an explanation for unevennes. If pin legs bend out, that would reduce the pin height. And that is also an installation process related issue.
Title: Re: Starship heat shield
Post by: envy887 on 09/21/2021 06:54 pm
The collar looks like a feature meant to ensure tiles are at a uniform height.  I wonder if some of the "older" pins on starship are pre-collar, which would explain some of the unevenness.

There are already a sholuder not far below that collar, acting presumably as a stopper. The colar would be a redundant piece in that function. Seems illogical, why not raise shoulder height, if necessary?

Instead I have two, completely speculative idea.
The collar may act as a release on push mechanism, holding the clip tight for easier tile installation, released by the slot pushing it down. That would enable the springs to push the pin wider, to latch more firmly. Less likely as the collar seems unremovable.

Another function may be to hold the clip tight/straight, to prevent outward deformation. That is a possible failure mode in the prev version.  If too much force applied during install, clip legs may bend out (O shape), as they only connected at the top and bottom holding in that direction (springs prevent only invard bending). The collar can be a third, cross bar/reinforcement,  against that.

Edit: clarification.
Ps. O style bending can be an explanation for unevennes. If pin legs bend out, that would reduce the pin height. And that is also an installation process related issue.

I don't think they want the tiles to release, ever. They are not serviceable, and a release mechanism is just a potential mode they don't want happening in flight.
Title: Re: Starship heat shield
Post by: JamesH65 on 09/21/2021 07:34 pm
The collar looks like a feature meant to ensure tiles are at a uniform height.  I wonder if some of the "older" pins on starship are pre-collar, which would explain some of the unevenness.

There are already a sholuder not far below that collar, acting presumably as a stopper. The colar would be a redundant piece in that function. Seems illogical, why not raise shoulder height, if necessary?

Instead I have two, completely speculative idea.
The collar may act as a release on push mechanism, holding the clip tight for easier tile installation, released by the slot pushing it down. That would enable the springs to push the pin wider, to latch more firmly. Less likely as the collar seems unremovable.

Another function may be to hold the clip tight/straight, to prevent outward deformation. That is a possible failure mode in the prev version.  If too much force applied during install, clip legs may bend out (O shape), as they only connected at the top and bottom holding in that direction (springs prevent only invard bending). The collar can be a third, cross bar/reinforcement,  against that.

Edit: clarification.
Ps. O style bending can be an explanation for unevennes. If pin legs bend out, that would reduce the pin height. And that is also an installation process related issue.

I don't think they want the tiles to release, ever. They are not serviceable, and a release mechanism is just a potential mode they don't want happening in flight.

Agreed, if they want to get a tile off, smash it and cut the Y.
Title: Re: Starship heat shield
Post by: ETurner on 09/21/2021 08:28 pm
No radial slots therefore no kinematic coupling therefore radial stresses.
Radial metal Y-arms can take radial loads therefore radial stresses need not be applied to fragile glass.
Seems pretty good, actually.
Title: Re: Starship heat shield
Post by: enbandi on 09/21/2021 08:33 pm
....
Instead I have two, completely speculative idea.
The collar may act as a release on push mechanism, holding the clip tight for easier tile installation, released by the slot pushing it down. That would enable the springs to push the pin wider, to latch more firmly. Less likely as the collar seems unremovable.
....

I don't think they want the tiles to release, ever. They are not serviceable, and a release mechanism is just a potential mode they don't want happening in flight.

Sorry if I wasnt clear, I dont meant a tile release system, but something to make installation easier. So try again: the collar may hold the pin tight (tension the springs) before tile installation. Then the tile (socket) push/release/remove the collar, so the springs push the pin back to original (wider) form, thus fastening the tile firm.
Title: Re: Starship heat shield
Post by: Sciencefan on 09/22/2021 01:59 pm
Interesting spot. Just happened that one of the tiles got stuck upside down.
Title: Re: Starship heat shield
Post by: cscott on 09/22/2021 02:30 pm
Interesting spot. Just happened that one of the tiles got stuck upside down.
I see radial slots here.  Maybe not as long as folks were expecting -- but what's the expected magnitude of thermal expansion, anyway? A couple of centimeters should do it.


No radial slots therefore no kinematic coupling therefore radial stresses.
Radial metal Y-arms can take radial loads therefore radial stresses need not be applied to fragile glass.
Seems pretty good, actually.

Title: Re: Starship heat shield
Post by: Sciencefan on 09/22/2021 03:25 pm
I see radial slots here.  Maybe not as long as folks were expecting -- but what's the expected magnitude of thermal expansion, anyway? A couple of centimeters should do it.

I think the reason is not that the pins can move in the slots but rather the pins themselves are less stiff in that direction.
Title: Re: Starship heat shield
Post by: ETurner on 09/22/2021 07:04 pm
Interesting spot. Just happened that one of the tiles got stuck upside down.
Looking at the deep hollows across the back surface of that tile, ISTM that much of the insulating capacity has been shifted from the tiles to the blanket. A further evolution in this direction would make the tiles essentially caps that hold the blanket in place and protect it from air flow. In this scenario, tile materials could be optimized for strength and toughness with little concern for thermal conductance. They would likely be thinner and denser -- and what we see may be already, relative to earlier versions.
Title: Re: Starship heat shield
Post by: Oersted on 09/22/2021 07:32 pm
Interesting spot. Just happened that one of the tiles got stuck upside down.
Looking at the deep hollows across the back surface of that tile, ISTM that much of the insulating capacity has been shifted from the tiles to the blanket. A further evolution in this direction would make the tiles essentially caps that hold the blanket in place and protect it from air flow. In this scenario, tile materials could be optimized for strength and toughness with little concern for thermal conductance. They would likely be thinner and denser -- and what we see may be already, relative to earlier versions.

That sounds totally wrong to me. If it was just about holding the blanket in place, then that could be done in a much easier way than with tiles. My guess is that the tiles deal with 95+ percent of the heat load.

Remember that hollow space in a vacuum is a great insulator (think your own double-glazing windows). Combined with the tile in front that hollow would mean that not much heat reaches the blanket.
Title: Re: Starship heat shield
Post by: CMac on 09/22/2021 08:03 pm
A major function of the tile surface is to be extremely hot and radiate energy away. The insulation plays the part of preventing heat transfer inward to the steel, allowing most energy to go to radiation.
Title: Re: Starship heat shield
Post by: ETurner on 09/22/2021 10:07 pm
Interesting spot. Just happened that one of the tiles got stuck upside down.
Looking at the deep hollows across the back surface of that tile, ISTM that much of the insulating capacity has been shifted from the tiles to the blanket. A further evolution in this direction would make the tiles essentially caps that hold the blanket in place and protect it from air flow. In this scenario, tile materials could be optimized for strength and toughness with little concern for thermal conductance. They would likely be thinner and denser -- and what we see may be already, relative to earlier versions.
That sounds totally wrong to me. If it was just about holding the blanket in place, then that could be done in a much easier way than with tiles. My guess is that the tiles deal with 95+ percent of the heat load.
There may be other ways to hold the blanket in place, but there’s a need for a surface that supports aerodynamic forces at high temperatures with joints to accommodate thermal expansion. Ceramic tiles do this, and can provide black, high-emissivity surfaces too. Metal might work, but metal-surfaced TPS options have been been considered and rejected by multiple development teams addressing the same problem. What are the other options, and how are they simpler?

Remember that hollow space in a vacuum is a great insulator (think your own double-glazing windows). Combined with the tile in front that hollow would mean that not much heat reaches the blanket.
There’s a reason why insulating structures (TPS tiles, house walls) so often fill spaces with fine fibers, not large voids, presumably to suppress convection and impede radiative transfer (keep in mind that hollow spaces fill with gas during entry). Double-glazed windows don’t contain fiber insulation because they must be transparent.
Title: Re: Starship heat shield
Post by: Alastor on 09/22/2021 10:16 pm
A major function of the tile surface is to be extremely hot and radiate energy away. The insulation plays the part of preventing heat transfer inward to the steel, allowing most energy to go to radiation.

In fact, if you want to keep something thermally insulated in a cryogenic vacuum environment, the strategy is to have a reduced surface of contact with the cryo surfaces with a very low conductivity material.
If you tiles heat up but can stand the heat and radiate it back to the outside, you want as little material as possible in direct contact between the hot parts and the cold ones. Insulation blanket only takes care of the residual heat.
Title: Re: Starship heat shield
Post by: Sciencefan on 09/22/2021 10:51 pm
In fact, if you want to keep something thermally insulated in a cryogenic vacuum environment, the strategy is to have a reduced surface of contact with the cryo surfaces with a very low conductivity material.

Too bad that the reentry plasma in front of a blunt body has nothing in common with vacuum.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/23/2021 07:51 am
Isn't the semi-hollow tile pic from SN17? Have we seen enough of the SN20 tiles to know if they're the same design?


If the blanket is the primary insulation isn't the edge the tile in contact going to compress it and negate its insulating properties exactly at the point where it's needed most? Perhaps the pin shoulders & yoke hold the tile off so it's touching but not compressing. But then the secondary blanket purpose we've been speculating about; mechanical loading to dampen vibration, doesn't work.


As usual, SX leaves me scratching my head.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/23/2021 08:16 am
Those pins are really bugging me. The way the spring thingies work, they load into the base. That makes no sense if the purpose is to keep an expansion tension at the top - unless only one leg is welded. Looking at the pick it looks like at least some of the welding marks do bias to one side.


If only one leg is welded then the collar becomes a pre installation expansion limiter for the barb. It also seems to act as a load spreader, keeping the Y from scuffing directly on the raw edges of the shoulder during high vibration.


Counter to this: if one leg is free why is it designed the same the welded leg? An SX quick & dirty?
Title: Re: Starship heat shield
Post by: Sciencefan on 09/23/2021 01:45 pm
Those pins are really bugging me. The way the spring thingies work, they load into the base. That makes no sense if the purpose is to keep an expansion tension at the top - unless only one leg is welded. Looking at the pick it looks like at least some of the welding marks do bias to one side.

Probably those tongues are not springs but electricity pins.
Title: Re: Starship heat shield
Post by: edzieba on 09/23/2021 01:49 pm
The blanket is definitely not the main insulator, it's only intended to insulate between the tile backside temperature and the tank wall, and provide some mechanical 'springiness' to back the tiles rather than placing them directly on metal. Unsintered silica fibre is not as insulating as kiln-fired sintered tile, lacks a lightweight waterproofing method, lacks a tightly bonded radiative cap, and is completely mechanically unsuitable to act as the main flow-contacting TPS surface.
Vacuum voids within the tile will be similarly insulating to the bulk sintered silica (greatly reduced conductivity, but adding some radiative transfer). However they have two extra benefits over bulk silica fibre:
1) Reduced mass ('adds lightness')
2) Reduced thermal mass. Meaning a hot tile retains less energy that it can later soak through to the tank wall. Less of a problem with a radiative TPS like Starships than with an ablative TPS like Dragon's, but still a consideration.
The reason STS dud not use hollow tiles was mechanical: the tiles were bonded, so any internal inhomogeneity would concentrate forces and aid in peeling them off. Starship already has a radically inhomogenous attachment system, so the voids would be somewhat moot. Adding voids does complicate fabrication though, however this makes the description of tile manufacture from the EPA document (tiles manufactured facing then split in two) make more sense: the voids can be manufactured on the 'outside' and the flat face formed in the cutting operation before RCG application.
Title: Re: Starship heat shield
Post by: ETurner on 09/23/2021 07:37 pm
The blanket is definitely not the main insulator, it's only intended to insulate between the tile backside temperature and the tank wall, and provide some mechanical 'springiness' to back the tiles rather than placing them directly on metal. Unsintered silica fibre is not as insulating as kiln-fired sintered tile, lacks a lightweight waterproofing method, lacks a tightly bonded radiative cap, and is completely mechanically unsuitable to act as the main flow-contacting TPS surface. [...]
What counts as the “main insulator” is unclear. The outer surface must deal with the highest temperatures and actual flow contact (which requires a hard surface), but most of the thermal resistance could be in the blanket. I’d call thermal resistance (reducing W/m2K) to be the main insulating function. The tiles being hotter is beside the point -- tile backside temperatures could  be quite high and most of the ΔT could be in the somewhat cooler blanket. I don’t think we know.

All else being equal, unsintered fibre should be more insulating. Sintering increases strength and rigidity but also creates paths for thermal conduction. In addition, the mechanical function of sintered tiles calls for substantial density, where blankets can be basically fluff.
Title: Re: Starship heat shield
Post by: Keldor on 09/23/2021 08:34 pm
The blanket is definitely not the main insulator, it's only intended to insulate between the tile backside temperature and the tank wall, and provide some mechanical 'springiness' to back the tiles rather than placing them directly on metal. Unsintered silica fibre is not as insulating as kiln-fired sintered tile, lacks a lightweight waterproofing method, lacks a tightly bonded radiative cap, and is completely mechanically unsuitable to act as the main flow-contacting TPS surface. [...]
What counts as the “main insulator” is unclear. The outer surface must deal with the highest temperatures and actual flow contact (which requires a hard surface), but most of the thermal resistance could be in the blanket. I’d call thermal resistance (reducing W/m2K) to be the main insulating function. The tiles being hotter is beside the point -- tile backside temperatures could  be quite high and most of the ΔT could be in the somewhat cooler blanket. I don’t think we know.

All else being equal, unsintered fibre should be more insulating. Sintering increases strength and rigidity but also creates paths for thermal conduction. In addition, the mechanical function of sintered tiles calls for substantial density, where blankets can be basically fluff.

What about the heat tolerance of the clips themselves?  They stick up beyond the blanket.  Is there any high temperature metal that can be welded to stainless steel?  What happens if they're heated to the annealing point?  They might have to stay as cool as the body of the vehicle.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 09/23/2021 08:44 pm
What about the heat tolerance of the clips themselves?  They stick up beyond the blanket.  Is there any high temperature metal that can be welded to stainless steel?  What happens if they're heated to the annealing point?  They might have to stay as cool as the body of the vehicle.

Great question.

You may have answered your own question.  The clips probably can be heated to the annealing point, all the way to almost melting (say 1300 degC).   The clips once engaged do not need to hold a lot of force, the full strength of stainless steel isn't required.

If I understand the great discussion above on springs in the clips correctly, the springs only compress on installation, so heat effects on spring characteristics don't matter either (though R&R of tiles may require R&R of the clips?)

Title: Re: Starship heat shield
Post by: InterestedEngineer on 09/23/2021 08:59 pm
The blanket is definitely not the main insulator, it's only intended to insulate between the tile backside temperature and the tank wall, and provide some mechanical 'springiness' to back the tiles rather than placing them directly on metal. Unsintered silica fibre is not as insulating as kiln-fired sintered tile, lacks a lightweight waterproofing method, lacks a tightly bonded radiative cap, and is completely mechanically unsuitable to act as the main flow-contacting TPS surface. [...]
What counts as the “main insulator” is unclear. The outer surface must deal with the highest temperatures and actual flow contact (which requires a hard surface), but most of the thermal resistance could be in the blanket. I’d call thermal resistance (reducing W/m2K) to be the main insulating function. The tiles being hotter is beside the point -- tile backside temperatures could  be quite high and most of the ΔT could be in the somewhat cooler blanket. I don’t think we know.

All else being equal, unsintered fibre should be more insulating. Sintering increases strength and rigidity but also creates paths for thermal conduction. In addition, the mechanical function of sintered tiles calls for substantial density, where blankets can be basically fluff.

I propose what we have here is a layered design, each layer protecting the inner layer and providing import functions for the whole, including backup  insulation for missing tiles.

The very outer layer (the black coating) can probably withstand 1500degC or so (WAG), and is designed for max emissivity.  The outer layer insulates/emits enough to keep the next layer below 1300degC.

The next layer is the white part of the tile, the clips, and the Y bracket.  This layer layer can withstand temperatures of 1300degC, and while mostly structural, and doesn't have enough stress on it to disallow annealing of the metal.  It holds enough heat to allow the outer layer the emit as much IR as it can to cool the entire structure.

The next layer is Superwool, which can withstand 1300degC and provide enough insulation to keep the next layer below 600 degC.  The Superwool provides enough insulation that it can withstand single missing tiles in the outer layer for at least LEO re-entry (not sure about return from Mars or Luna)

The final layer is the stainless tank, which can withstand temperatures of 600degC.  It sheds heat internally to the propellant.  Some math needs to be done to find the maximum heat capacity of the propellant and the related average temperature of the tank, but hot spots on the tank can hit 600degC with no harmful effects.

An interesting item that traverses layers are the clips that are welded to the tanks.   They can heat up to 1300degC (close to melting temperature), but if they are stainless they don't conduct heat well enough to heat the tank itself above 600degC.  I think.  I didn't actually run the math on that.   "Stainless steel as an insulator".  heh.
Title: Re: Starship heat shield
Post by: ETurner on 09/23/2021 09:09 pm
An interesting item that traverses layers are the clips that are welded to the tanks.   They can heat up to 1300degC (close to melting temperature), but if they are stainless they don't conduct heat well enough to heat the tank itself above 600degC.  I think.  I didn't actually run the math on that.   "Stainless steel as an insulator".  heh.
Yes, they’re thin enough that the quantity of heat transferred ( cross sectional area * conductivity * time * ΔT / length) will be small. Thermal energy will rapidly spread away from the skinny clip with the tank acting as a massive heat sink. So not a problem.
Title: Re: Starship heat shield
Post by: Oersted on 09/23/2021 10:18 pm
It would be so interesting to see the heat-gradient map supercomputer simulations SpaceX have been doing on their TPS.
Title: Re: Starship heat shield
Post by: midaswelby on 09/23/2021 10:24 pm
It would be so interesting to see the heat-gradient map supercomputer simulations SpaceX have been doing on their TPS.

I recall being quite surprised the first time I came across a video of the creation of the ceramic tile material.  The technician or researcher or whoever had on thick heat resistant gloves and removed a tile from a very hot furnace with a long handled tongs.  He set it on a table, took off the gloves, and picked up the tile bare handed, while it was still glowing red hot.  How are these tiles transmitting enough heat to the backside to create significant heat related problems to the TPS substrates and to the ship's skin itself?  I ask this with all sincerity, I can't see the problem from my uneducated perspective.
Title: Re: Starship heat shield
Post by: ETurner on 09/24/2021 12:06 am
It would be so interesting to see the heat-gradient map supercomputer simulations SpaceX have been doing on their TPS.

I recall being quite surprised the first time I came across a video of the creation of the ceramic tile material.  The technician or researcher or whoever had on thick heat resistant gloves and removed a tile from a very hot furnace with a long handled tongs.  He set it on a table, took off the gloves, and picked up the tile bare handed, while it was still glowing red hot.  How are these tiles transmitting enough heat to the backside to create significant heat related problems to the TPS substrates and to the ship's skin itself?  I ask this with all sincerity, I can't see the problem from my uneducated perspective.
Here’s a way to think about why touching a very hot, low-density, low-conductivity material is surprisingly safe. Consider two imaginary cases, then a real one:

-- If an imaginary material had zero thermal conductivity it would transfer no heat, no matter how hot it was.
-- If an imaginary material had zero heat capacity it would have no heat to transfer, no matter how hot it was.
-- If a real material has very low thermal conductivity and very low heat capacity (both associated with low density), these properties in combination limit transfer to very, very little heat, despite high initial temperatures.

In other words, only heat near the surface matters (low conductivity), and there just isn’t much heat there (low capacity). The surface cools very fast. Fingers are safe because they have relatively high heat capacity and conductivity, and can therefore take up small amounts of heat without getting very hot. What makes the demos even more striking is that silica tiles, being somewhat transparent, can glow red even after the surface has cooled.
Note that the only the low thermal conductivity helps with insulation. Where there’s an effectively unlimited source of external heat (the TPS situation), low heat capacity in the material itself doesn’t help.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 09/24/2021 05:03 am
It would be so interesting to see the heat-gradient map supercomputer simulations SpaceX have been doing on their TPS.

I recall being quite surprised the first time I came across a video of the creation of the ceramic tile material.  The technician or researcher or whoever had on thick heat resistant gloves and removed a tile from a very hot furnace with a long handled tongs.  He set it on a table, took off the gloves, and picked up the tile bare handed, while it was still glowing red hot.  How are these tiles transmitting enough heat to the backside to create significant heat related problems to the TPS substrates and to the ship's skin itself?  I ask this with all sincerity, I can't see the problem from my uneducated perspective.

That video, I believe, was for Space Shuttle tiles, and things have moved on quite a lot since the Space Shuttle.

1.  An airframe made of stainless can handle > 2x the temperature of Aluminum in the Space Shuttle
2.  Superwool wasn't around in the 1970s.
3.  Bracket attachment mechanism instead of glue means there's metal in the tile that will conduct and hold heat.

In short, different design characteristics means different requirements.
Title: Re: Starship heat shield
Post by: Slarty1080 on 09/24/2021 07:18 am
It would be so interesting to see the heat-gradient map supercomputer simulations SpaceX have been doing on their TPS.

I recall being quite surprised the first time I came across a video of the creation of the ceramic tile material.  The technician or researcher or whoever had on thick heat resistant gloves and removed a tile from a very hot furnace with a long handled tongs.  He set it on a table, took off the gloves, and picked up the tile bare handed, while it was still glowing red hot.  How are these tiles transmitting enough heat to the backside to create significant heat related problems to the TPS substrates and to the ship's skin itself?  I ask this with all sincerity, I can't see the problem from my uneducated perspective.

That video, I believe, was for Space Shuttle tiles, and things have moved on quite a lot since the Space Shuttle.

1.  An airframe made of stainless can handle > 2x the temperature of Aluminum in the Space Shuttle
2.  Superwool wasn't around in the 1970s.
3.  Bracket attachment mechanism instead of glue means there's metal in the tile that will conduct and hold heat.

In short, different design characteristics means different requirements.
True, and we don't know what the pins are made from. Probably steel but it might be a different grade from that used on the skin.
Title: Re: Starship heat shield
Post by: brettly2021 on 09/24/2021 08:46 am
I suspect somewhere near the top of the clip the metal slides past each side, its really hard to see exactly how the top of the clip is arranged, really need a super hi res photo of heaps of clips from different angles.
Picture attached black lines indicate very top section might not be one piece but the left and right sides slide over each other, or past each other when spring is compressed. The lower spring section ( green arrow) forces clip apart once in  position in tile, the collar simply stops it from expanding too far.

Thought of a reason why they are going to all this trouble: space shuttle issues with broken tiles, I dont think it was possible for the astronauts to replace broken tiles while in space, quite hard to
replace a tile when your in space if need to use glue etc, if it just clips in place, you can fix it before re-entry very simply.
Title: Re: Starship heat shield
Post by: JamesH65 on 09/24/2021 10:26 am
I suspect somewhere near the top of the clip the metal slides past each side, its really hard to see exactly how the top of the clip is arranged, really need a super hi res photo of heaps of clips from different angles.
Picture attached black lines indicate very top section might not be one piece but the left and right sides slide over each other, or past each other when spring is compressed. The lower spring section ( green arrow) forces clip apart once in  position in tile, the collar simply stops it from expanding too far.

Thought of a reason why they are going to all this trouble: space shuttle issues with broken tiles, I dont think it was possible for the astronauts to replace broken tiles while in space, quite hard to
replace a tile when your in space if need to use glue etc, if it just clips in place, you can fix it before re-entry very simply.

This is exactly how I had assumed it was working. Nice simple design, easy to manufacture, easy to use.
Title: Re: Starship heat shield
Post by: ETurner on 09/24/2021 10:35 am
Digging around a bit, it looks like Superwool (various grades) is inferior to LI-900 (Shuttle) tiles by a mass-efficiency figure of merit (conductivity-1 * density-1, data sources below). On the other hand, the Superwool data is for a material with typical applications in “Chimney insulation, Process heater linings, Pipe wrap, Annealing furnace linings...” none of which call strong efforts to minimize mass.

• Are there higher conductivity-1 * density-1 grades of Superwool or equivalent?

• Do we know what the actual blanket material is on SS?

Using an interim blanket material with an anticipated bespoke upgrade would be plausible. Producing a low-density felt based on a fancier ceramic-fiber feedstock shouldn’t be too capital intensive.

Data sources
Superwool: https://www.morganthermalceramics.com/media/1814/sw_blanket_data_sheet_english_1.pdf
LI-900 Tiles: http://mae-nas.eng.usu.edu/MAE_5420_Web/section3/appendix3.pdf
Title: Re: Starship heat shield
Post by: BT52 on 09/24/2021 12:09 pm
I suspect somewhere near the top of the clip the metal slides past each side, its really hard to see exactly how the top of the clip is arranged, really need a super hi res photo of heaps of clips from different angles.
Picture attached black lines indicate very top section might not be one piece but the left and right sides slide over each other, or past each other when spring is compressed. The lower spring section ( green arrow) forces clip apart once in  position in tile, the collar simply stops it from expanding too far.

Thought of a reason why they are going to all this trouble: space shuttle issues with broken tiles, I dont think it was possible for the astronauts to replace broken tiles while in space, quite hard to
replace a tile when your in space if need to use glue etc, if it just clips in place, you can fix it before re-entry very simply.

This is exactly how I had assumed it was working. Nice simple design, easy to manufacture, easy to use.

Yeah conceptually it remembers me on this kinda clips. IMO WE need more hq photos to really confirm how exact is that shape.

(https://www.czyh.com/uploadfiles/103.224.250.31/webid233/source/201604/146018683631.jpg)
Title: Re: Starship heat shield
Post by: InterestedEngineer on 09/24/2021 04:44 pm
Digging around a bit, it looks like Superwool (various grades) is inferior to LI-900 (Shuttle) tiles by a mass-efficiency figure of merit (conductivity-1 * density-1, data sources below). On the other hand, the Superwool data is for a material with typical applications in “Chimney insulation, Process heater linings, Pipe wrap, Annealing furnace linings...” none of which call strong efforts to minimize mass.

• Are there higher conductivity-1 * density-1 grades of Superwool or equivalent?

• Do we know what the actual blanket material is on SS?

Using an interim blanket material with an anticipated bespoke upgrade would be plausible. Producing a low-density felt based on a fancier ceramic-fiber feedstock shouldn’t be too capital intensive.

Data sources
Superwool: https://www.morganthermalceramics.com/media/1814/sw_blanket_data_sheet_english_1.pdf
LI-900 Tiles: http://mae-nas.eng.usu.edu/MAE_5420_Web/section3/appendix3.pdf

I didn't run the numbers but you are likely correct.

However, "good enough" is far better than "fragile but much better" when the temperature gradient is only 1300degC -> 600degC (versus 1300degC -> 250degC for Aluminum)

Never let perfect be the enemy of the good.
Title: Re: Starship heat shield
Post by: Keldor on 09/24/2021 06:21 pm
What about the heat tolerance of the clips themselves?  They stick up beyond the blanket.  Is there any high temperature metal that can be welded to stainless steel?  What happens if they're heated to the annealing point?  They might have to stay as cool as the body of the vehicle.

Great question.

You may have answered your own question.  The clips probably can be heated to the annealing point, all the way to almost melting (say 1300 degC).   The clips once engaged do not need to hold a lot of force, the full strength of stainless steel isn't required.

If I understand the great discussion above on springs in the clips correctly, the springs only compress on installation, so heat effects on spring characteristics don't matter either (though R&R of tiles may require R&R of the clips?)

Replacement of clips sounds like a really ugly problem, though.  You're talking about precision surface welding while up on a lift 100 feet in the air.  There's a reason they do all this stuff before stacking the rings.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/24/2021 09:31 pm
It would be so interesting to see the heat-gradient map supercomputer simulations SpaceX have been doing on their TPS.

I recall being quite surprised the first time I came across a video of the creation of the ceramic tile material.  The technician or researcher or whoever had on thick heat resistant gloves and removed a tile from a very hot furnace with a long handled tongs.  He set it on a table, took off the gloves, and picked up the tile bare handed, while it was still glowing red hot.  How are these tiles transmitting enough heat to the backside to create significant heat related problems to the TPS substrates and to the ship's skin itself?  I ask this with all sincerity, I can't see the problem from my uneducated perspective.
Here’s a way to think about why touching a very hot, low-density, low-conductivity material is surprisingly safe. Consider two imaginary cases, then a real one:

-- If an imaginary material had zero thermal conductivity it would transfer no heat, no matter how hot it was.
-- If an imaginary material had zero heat capacity it would have no heat to transfer, no matter how hot it was.
-- If a real material has very low thermal conductivity and very low heat capacity (both associated with low density), these properties in combination limit transfer to very, very little heat, despite high initial temperatures.

In other words, only heat near the surface matters (low conductivity), and there just isn’t much heat there (low capacity). The surface cools very fast. Fingers are safe because they have relatively high heat capacity and conductivity, and can therefore take up small amounts of heat without getting very hot. What makes the demos even more striking is that silica tiles, being somewhat transparent, can glow red even after the surface has cooled.
Note that the only the low thermal conductivity helps with insulation. Where there’s an effectively unlimited source of external heat (the TPS situation), low heat capacity in the material itself doesn’t help.
If that's the same clip I've seen, the tech was very careful to touch only the corners where cooling, even on the short trip from oven to table, would be maximized.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/24/2021 09:38 pm
I suspect somewhere near the top of the clip the metal slides past each side, its really hard to see exactly how the top of the clip is arranged, really need a super hi res photo of heaps of clips from different angles.
Picture attached black lines indicate very top section might not be one piece but the left and right sides slide over each other, or past each other when spring is compressed. The lower spring section ( green arrow) forces clip apart once in  position in tile, the collar simply stops it from expanding too far.

Thought of a reason why they are going to all this trouble: space shuttle issues with broken tiles, I dont think it was possible for the astronauts to replace broken tiles while in space, quite hard to
replace a tile when your in space if need to use glue etc, if it just clips in place, you can fix it before re-entry very simply.

This is exactly how I had assumed it was working. Nice simple design, easy to manufacture, easy to use.

Yeah conceptually it remembers me on this kinda clips. IMO WE need more hq photos to really confirm how exact is that shape.

(https://www.czyh.com/uploadfiles/103.224.250.31/webid233/source/201604/146018683631.jpg)
Actually, I'm impressed by the quality of some of the shots. Some of those photographers are using some fine (and heavy) glass.
Title: Re: Starship heat shield
Post by: Sciencefan on 09/24/2021 09:52 pm
No need to imagine things. Just the rounded head with a collar below, just tongues to connect to a welding machine are here.

(https://forum.nasaspaceflight.com/assets/50748.0/2061168.jpg)
Title: Re: Starship heat shield
Post by: Bob Niland on 09/24/2021 11:37 pm
It would be so interesting to see the heat-gradient map supercomputer simulations SpaceX have been doing on their TPS.
We may not find out, this decade, how Sx does overall TPS design & testing in detail, due to the apparent general Sx principle that taking the time to explain things, beyond acute necessity or management mood, puts the schedule in peril.

But I have to conclude that they are very comfortable with their models and ground-based TPS testing, just due to something, that as far as I know, we have not seen:
Sx has access to ride-share billets & arguable surplus Dragon trunk space, on any of many frequent Falcon9 orbital launches, but I don't recall seeing reports of reentry shapes or sub-scale vehicle test articles going along for the ride.

Update: Subsequent to posting this, I learned that CRS-18 did test some Starship prototype materials on the Dragon heat shield.
Title: Re: Starship heat shield
Post by: Alastor on 09/25/2021 12:03 am
In fact, if you want to keep something thermally insulated in a cryogenic vacuum environment, the strategy is to have a reduced surface of contact with the cryo surfaces with a very low conductivity material.
Too bad that the reentry plasma in front of a blunt body has nothing in common with vacuum.

Ok, let me break down that analogy further, since apparently it needs to be explained.

Externally, you have a very hot environment (reentry plasma). You want to insulate it from the inside, where you have a very cold environment (cryogenic propellant).
Your first barrier is the ceramic tiles. Their 3 main features are : they have a low conductivity. They are dark outside and clear inside.
Dark on the outside and light coloured inside means they will radiate more on the outside. Low heat conductivity means the temperature gradient will be higher across the tile, so they'll radiate even less inside.

After that, you have 1 thing for sure : steel pins that hold down the tiles. You don't have much choice for those, they are very heat conductive.

Then you have 2 options. Either you have direct contact between the blanket and the tile, or you have space that's air. Low density air in this case, since you're behind the shockwave, which is a discontinuity in pressure. So low thermal conductivity air too.
Air is transparent, the blanket is not.
So your 2 options are basically an optimization between :
 - The back of the tile radiates heat through a low conductivity transparent medium that also conducts some heat. Then you have a purely conductive layer. (hey, EXACTLY the situation in my vacuum chamber analogy, for those that stop thinking at "not a vacuum")
 - Everything is pretty much conductive, with 1 ceramic tile layer and 1 heat blanket layer. (so same again, but without the radiative term).

Whichever way you choose, you still have those pesky pins that will conduct a lot of heat since they are the most conductive stuff of the lot. So you better have them be as small cross section as you can to reduce that conductivity (and ideally, less conductive than steel would be better, but they obviously think they can get away with it, and it's easier to build).

All of this to say the ceramic tiles play indeed an essential role in all of this, since they radiate back and handle the plasma environment (which is mostly radiative heating, from what I remember, you hope to not have plasma impingement). Behind them, I believe it's likely there is a layer of low heat conductivity high altitude air before the thermal blanket. From a quick search, for example, above about 15km, air will be lower thermal conductivity than aerogel for example. So at high altitude, during reentry, I believe air will be the main insulator, while the thermal blanket will take care of the residual heat coming through when the air will densify lower in the atmosphere and become more conductive.
Title: Re: Starship heat shield
Post by: cscott on 09/25/2021 04:19 am
Stainless steel is one of the least heat-conductive metals.  It is typically used as a thermal break, for example on 3d printers or the handle of your frying pan.  There are certain grades of stainless which conduct even less heat than others.

Eg thermal conductivity of copper at room temperature is about 400 W/m K.  Aluminum is 240 W/m K. Stainless steel is 14 W/m K.  Hastelloy C steel gets down to 8.7 W/m K.

Manganese at 7 W/m K and inconel at 15 W/m K are the only real competition among metals.

(To compare: a ceramic coffee mug is about 3.8 W/m K; a glass is 1.1 W/m K.  Among ceramics, zirconia is 3  W/m K and Aluminum Nitride is 150 W/m K.)
Title: Re: Starship heat shield
Post by: dgkimpton on 09/25/2021 12:28 pm
Stainless steel is one of the least heat-conductive metals.  It is typically used as a thermal break, for example on 3d printers or the handle of your frying pan.  There are certain grades of stainless which conduct even less heat than others.

Eg thermal conductivity of copper at room temperature is about 400 W/m K.  Aluminum is 240 W/m K. Stainless steel is 14 W/m K.  Hastelloy C steel gets down to 8.7 W/m K.

Manganese at 7 W/m K and inconel at 15 W/m K are the only real competition among metals.

(To compare: a ceramic coffee mug is about 3.8 W/m K; a glass is 1.1 W/m K.  Among ceramics, zirconia is 3  W/m K and Aluminum Nitride is 150 W/m K.)
Whilst true... compared to thermal protection systems 14W /mK is comparatively very heat conductive, insulators are orders of magnitude less conductive.  E.g. standard building PIR insulation is down at 0.02 W/mK
Title: Re: Starship heat shield
Post by: ETurner on 09/25/2021 01:06 pm
Ratio of heat flows, pins/tile, approximating pin length = tile thickness (etc.):
A = cross sectional area of component
C = thermal conductivity of component material
(A_pins * C_pins) / ( A_tile * C_tile) ≈ actual importance of heat flow through pins.
Title: Re: Starship heat shield
Post by: Alastor on 09/25/2021 10:32 pm
Comparing the thermal conductivity of the tile and the pin is irrelevant, since they are not in parallel.
If the pins were in parallel of a perfect insulant, the total heat flow going through the tile would go through them, no matter the conductivity.

If you have to compare the conductivity of the stainless steel pins to anything, it's either the conductivity of the double layer air+insulant or the insulating blanket.

Whatever the case, they are both at least 2 orders of magnitude less conductive than the pins. So they can afford at least 100 times more surface before they become the main thermal path.
Which they hopefully are. Otherwise the pins would be badly designed.

Another thing that could be a concern with the pins would be the heat flow density. They will cause spot heating on the tanks. Which is fine, as long as the heat flow stays low enough.
Title: Re: Starship heat shield
Post by: ETurner on 09/25/2021 11:05 pm
Comparing the thermal conductivity of the tile and the pin is irrelevant, since they are not in parallel.
If the pins were in parallel of a perfect insulant, the total heat flow going through the tile would go through them, no matter the conductivity.

If you have to compare the conductivity of the stainless steel pins to anything, it's either the conductivity of the double layer air+insulant or the insulating blanket.

Whatever the case, they are both at least 2 orders of magnitude less conductive than the pins. So they can afford at least 100 times more surface before they become the main thermal path.
Which they hopefully are. Otherwise the pins would be badly designed.

Another thing that could be a concern with the pins would be the heat flow density. They will cause spot heating on the tanks. Which is fine, as long as the heat flow stays low enough.
Yes, where I say “tile”, please read “tile+insulation stack”.

Modeling the pins as thermally “in parallel” with the insulation stack -- which is to say, as crossing the full thickness -- gives an upper bound on the heat leak they can cause. In other words, if this upper bound is small, then a more detailed analysis will find a real value that is even smaller. I expect that plugging the A and C parameters into this super-simple would show that the fraction of heat transferred through the pins can’t be significant. No thermal FEA needed.

If I understand what you’re saying, we have the same view of the basic situation.
Title: Re: Starship heat shield
Post by: Alastor on 09/25/2021 11:09 pm
Yes, if that's what you mean, we are indeed in agreement.
Title: Re: Starship heat shield
Post by: cscott on 09/26/2021 12:00 am
My objection was only to this part of the original writeup:

"After that, you have 1 thing for sure : steel pins that hold down the tiles. You don't have much choice for those, they are very heat conductive. "

"Very" is only in comparison to the tiles; compared to most metals they are "not very conductive" and compared to ceramics and even glass they are "about the same".  There are indeed many options for what the pins could be made of, but other than inconel and magnesium perhaps, stainless is near optimal for the task.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 09/26/2021 02:44 am
Ratio of heat flows, pins/tile, approximating pin length = tile thickness (etc.):
A = cross sectional area of component
C = thermal conductivity of component material
(A_pins * C_pins) / ( A_tile * C_tile) ≈ actual importance of heat flow through pins.

area of pins looks to be about 16mm^2 times 3 pins ~= 50mm^2
area of tilees looks to be about 500mm*500mm = 250,000mm^2

Ratio of 5000:1

C_pins = 21 W/m-k
C_Superwool = .08 W/m-k

Ratio of 263.

proportion of heat flow through pins = 50*21 / (250000 * .08) = .05, or 5%.
Title: Re: Starship heat shield
Post by: Twark_Main on 09/26/2021 08:44 am
It would be so interesting to see the heat-gradient map supercomputer simulations SpaceX have been doing on their TPS.

I recall being quite surprised the first time I came across a video of the creation of the ceramic tile material.  The technician or researcher or whoever had on thick heat resistant gloves and removed a tile from a very hot furnace with a long handled tongs.  He set it on a table, took off the gloves, and picked up the tile bare handed, while it was still glowing red hot.  How are these tiles transmitting enough heat to the backside to create significant heat related problems to the TPS substrates and to the ship's skin itself?  I ask this with all sincerity, I can't see the problem from my uneducated perspective.
Here’s a way to think about why touching a very hot, low-density, low-conductivity material is surprisingly safe. Consider two imaginary cases, then a real one:

-- If an imaginary material had zero thermal conductivity it would transfer no heat, no matter how hot it was.
-- If an imaginary material had zero heat capacity it would have no heat to transfer, no matter how hot it was.
-- If a real material has very low thermal conductivity and very low heat capacity (both associated with low density), these properties in combination limit transfer to very, very little heat, despite high initial temperatures.

In other words, only heat near the surface matters (low conductivity), and there just isn’t much heat there (low capacity). The surface cools very fast. Fingers are safe because they have relatively high heat capacity and conductivity, and can therefore take up small amounts of heat without getting very hot. What makes the demos even more striking is that silica tiles, being somewhat transparent, can glow red even after the surface has cooled.

Note that the only the low thermal conductivity helps with insulation. Where there’s an effectively unlimited source of external heat (the TPS situation), low heat capacity in the material itself doesn’t help.

I don't know that that's entirely accurate. In a simplified steady-state situation it's true, except in the real world

A) low heat capacity means that the outside of the tile heats up "to temperature" faster, radiating away heat earlier in the reentry sequence, and

B) low heat capacity means the "heat soak" within the tiles is less, reducing the total magnitude of the heat pulse reaching the spacecraft later in the reentry sequence.


Of course this isn't strictly an "insulation" effect (which I think is what you meant), but saying that the low heat capacity "doesn't help" during reentry could potentially cause confusion.
Title: Re: Starship heat shield
Post by: Twark_Main on 09/26/2021 09:01 am
It would be so interesting to see the heat-gradient map supercomputer simulations SpaceX have been doing on their TPS.

I recall being quite surprised the first time I came across a video of the creation of the ceramic tile material.  The technician or researcher or whoever had on thick heat resistant gloves and removed a tile from a very hot furnace with a long handled tongs.  He set it on a table, took off the gloves, and picked up the tile bare handed, while it was still glowing red hot.  How are these tiles transmitting enough heat to the backside to create significant heat related problems to the TPS substrates and to the ship's skin itself?  I ask this with all sincerity, I can't see the problem from my uneducated perspective.

That video, I believe, was for Space Shuttle tiles, and things have moved on quite a lot since the Space Shuttle.

1.  An airframe made of stainless can handle > 2x the temperature of Aluminum in the Space Shuttle
2.  Superwool wasn't around in the 1970s.
3.  Bracket attachment mechanism instead of glue means there's metal in the tile that will conduct and hold heat.

In short, different design characteristics means different requirements.

1 makes it less likely for heat to cause damage, so that would only seem to reinforce midaswelby's point. 2 was covered by ETurner above. As for 3, the tiny amount of metal only makes for a small heat transfer / heat soak.

Do we have any indication that the Starship TPS tile technology has "moved on" beyond high-temperature, low-conductivity, low-specific heat ceramic foams (a la Shuttle)? Because on the contrary, everything I've seen indicates that the Starship tiles are a continuation of this type of TPS design, not an interruption.


I think midaswelby's point is entirely valid and correct. Post-Shuttle TPS ceramics should have similar-or-better thermal performance to the famous "hold the glowing tile" demo, so where exactly is the backside heat problem?  ???

https://www.youtube.com/watch?v=f46BJa4oYss

(peak 90s NASA video right there! :D )

EDIT https://www.youtube.com/watch?v=vt7yixO1j4o

(peak 70s version)
Title: Re: Starship heat shield
Post by: eriblo on 09/26/2021 02:18 pm
[...]
[...]
How are these tiles transmitting enough heat to the backside to create significant heat related problems to the TPS substrates and to the ship's skin itself?  I ask this with all sincerity, I can't see the problem from my uneducated perspective.
[...]
I think midaswelby's point is entirely valid and correct. Post-Shuttle TPS ceramics should have similar-or-better thermal performance to the famous "hold the glowing tile" demo, so where exactly is the backside heat problem?  ???
[...]
I thought ETurner explained it quite clearly...? The demo does not show some magic material that can never burn anything no matter what - it shows hot samples being carefully removed from a furnace and allowed to cool down before being touched. The time needed is just a few seconds due to the combination of low thermal capacity and conductivity but it is not like you could just stick your hand into the furnace and grab it at 2200°F directly.

This is a demo designed to demonstrate material properties, not how it handles reentry. That demo would be holding it in one hand and heating the other side to the same temperature as the furnace with a torch for 10+ minutes.

BTW, the "backside temperature/heat problem" will most likely never be completely "solved" since it is one of the primary TPS design factors. If the temperature behind the TPS (or one of its layers) is guaranteed to stay far below the limit no matter what it means that your can either expand the envelope or make the TPS lighter.
Title: Re: Starship heat shield
Post by: brettly2021 on 09/27/2021 07:11 am
that shuttle tile video posted by twark main was very interesting.
Seems silicone fibres and water ( probably other binding agents I would think), then a thin layer of ceramic material spray painted on top. I wonder what that ceramic coating was made of? thanks for posting that terrific stuff.
Title: Re: Starship heat shield
Post by: edzieba on 09/27/2021 12:48 pm
that shuttle tile video posted by twark main was very interesting.
Seems silicone fibres and water ( probably other binding agents I would think), then a thin layer of ceramic material spray painted on top. I wonder what that ceramic coating was made of? thanks for posting that terrific stuff.
Silica (not Silicone), no binder (the fibres are sintered together by heat), and the coating is Reaction Cured Glass (Borosilicate). STS tile composition manufacture is pretty extensively documented publicly, and the documents we have on the tiles SpaceX are using (Florida EPA report) indicate their tiles are nearly identical apart from dimensions and a slightly different waterproofing agent.
Title: Re: Starship heat shield
Post by: Twark_Main on 09/28/2021 04:47 pm
[...]
[...]
How are these tiles transmitting enough heat to the backside to create significant heat related problems to the TPS substrates and to the ship's skin itself?  I ask this with all sincerity, I can't see the problem from my uneducated perspective.
[...]
I think midaswelby's point is entirely valid and correct. Post-Shuttle TPS ceramics should have similar-or-better thermal performance to the famous "hold the glowing tile" demo, so where exactly is the backside heat problem?  ???
[...]
I thought ETurner explained it quite clearly...? The demo does not show some magic material that can never burn anything no matter what - it shows hot samples being carefully removed from a furnace and allowed to cool down before being touched. The time needed is just a few seconds due to the combination of low thermal capacity and conductivity but it is not like you could just stick your hand into the furnace and grab it at 2200°F directly.

This is a demo designed to demonstrate material properties, not how it handles reentry.

I should probably have clarified that I'm assuming a sophisticated understanding of what that demo "really shows," instead of assuming a naive and incorrect understanding.

So again, (other than the folks assuming someone else misunderstands the demo) where exactly is the problem? Per the impressive material properties shown in the Shuttle tile demo, any backside thermal problem should be easy to prevent/solve.

That demo would be holding it in one hand and heating the other side to the same temperature as the furnace with a torch for 10+ minutes.

Funny enough, that's also in the video. :)

BTW, the "backside temperature/heat problem" will most likely never be completely "solved" since it is one of the primary TPS design factors. If the temperature behind the TPS (or one of its layers) is guaranteed to stay far below the limit no matter what it means that your can either expand the envelope or make the TPS lighter.

If you have defined "no matter what" in terms of the nominal flight envelope (as opposed to unrealistic scenarios like putting Starship in a giant kiln for days on end), and "the [temperature] limit" is defined correctly, then surely there's no need to change anything ("either expand the envelope or make the TPS lighter"). It just means... the design closed.
Title: Re: Starship heat shield
Post by: Sciencefan on 09/28/2021 06:07 pm
Quote
Everyday Astronaut
How’re the titles gonna stay on during ascent? I’m still a little surprised nature didn’t have the right idea and do the tiles more like scales. On ascent there’d be less room for aerodynamic forces to rip them off and it’d allow for expansion and contraction of the steel


Quote
Elon Musk
That said, I’m not entirely convinced that this couldn’t be done with several overlapping scales of metal sheet with an insulator between scale armor & primary structure.



https://twitter.com/elonmusk/status/1442636642985160708
Title: Re: Starship heat shield
Post by: AU1.52 on 09/28/2021 07:00 pm
Why is the header tank vent positioned near tiles? Would it not be better to have the vent in the middle of the 'cool' side of the ship?
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 09/28/2021 07:12 pm
Elon says tile failure was caused by header tank vent:

https://twitter.com/elonmusk/status/1442630681360752640

Also, per LabPadre Rover Cam, pad is mostly clear, with just final few vehicles doing closeouts.

Interesting reason for the tiles blown off.

It seems to me that placing the vent on the wrong side, or not making the tiles attachments such that they can withstand a vent is such a stupid design error that it isn't an error. I throw at you this idea, could be possible that there was an error in the vent controll code configuration, someone forgotten to turn down the mass flow of the vent (below a value they know that does not cause damages, at the expens of a longer vent time), causing the damage?
Title: Re: Starship heat shield
Post by: eriblo on 09/28/2021 09:21 pm
Elon says tile failure was caused by header tank vent:

[tweet]

Also, per LabPadre Rover Cam, pad is mostly clear, with just final few vehicles doing closeouts.

Interesting reason for the tiles blown off.

It seems to me that placing the vent on the wrong side, or not making the tiles attachments such that they can withstand a vent is such a stupid design error that it isn't an error. I throw at you this idea, could be possible that there was an error in the vent controll code configuration, someone forgotten to turn down the mass flow of the vent (below a value they know that does not cause damages, at the expens of a longer vent time), causing the damage?
Most vents we have seen seem to be bang-bang controlled (i.e. go over pressure 1 - fully open until below pressure 2) so there might not be any way to decrease the flow.

If my speculative labeling of Nic's picture is correct the the vents would be the ~ 2cm diameter holes in each side of the two round posts ~1m from the edge of the TPS. If that is the case it would seem that the jets, helped by the Coandă effect, managed to get under the blanket and produce pressure differential large enough to dislodge some of the tiles (would only require a fraction of an atmosphere).

Maybe it should have been caught before it happened but it would at least be easy to remedy by welding a small ramp next to the vents and perhaps rotating and/or moving them slightly for later prototypes. The only relevance I can see for this failure mode for the rest of the TPS would be the forward facing edges behind the forward fins/ahead of the aft fins on ascent. We will see if they do anything there before launch...
Title: Re: Starship heat shield
Post by: daveglo on 09/29/2021 01:26 am
Quote
Elon Musk
That said, I’m not entirely convinced that this couldn’t be done with several overlapping scales of metal sheet with an insulator between scale armor & primary structure.


I have to admit, been pondering this design choice for a while, and wondering why this approach hasn't been pursued, using tungsten as the surface material.  Great thermal characteristics, although I don't know how bad the high-temperature oxidation would be.  Weight is an obvious issue too, but the toughness problem would be solved.

Need a high-tech metallurgist to come up with foamed tungsten plate as a primary heat shield surface.  Bulletproof!
Title: Re: Starship heat shield
Post by: Coastal Ron on 09/29/2021 01:53 am
Quote
Elon Musk
That said, I’m not entirely convinced that this couldn’t be done with several overlapping scales of metal sheet with an insulator between scale armor & primary structure.


I have to admit, been pondering this design choice for a while, and wondering why this approach hasn't been pursued, using tungsten as the surface material.  Great thermal characteristics, although I don't know how bad the high-temperature oxidation would be.  Weight is an obvious issue too, but the toughness problem would be solved.

Tungsten? That is one of the heaviest metals, and I would doubt that it would be a good heat shield.

The X-33 program was investigating metallic thermal panels, including one that used an Inconel honeycomb sandwich with a titanium inner panel, on top of a pad of fibrous insulation. Those panels might still be kind of heavy though.

It sounds like Musk might be thinking about much larger sheets laid over some sort of insulation. Maybe that could be true sheets and not panels? Not sure how that would work with the flip maneuver, where the sheets could be exposed to substantial wind effects and engine exhaust, but the current tiles certainly seem to have potential issues with that too.

Not sure if tiles popping off during pressurization tests is a good sign they have a durable design...
Title: Re: Starship heat shield
Post by: Robotbeat on 09/29/2021 02:08 am
Inconel isn't really any better than 310 Stainless (not pictured here, but Inconel and SS 310 have basically the same use temperature).  Tungsten is a bit more than twice as dense as both, but it is FAR higher temperature. So you may be able to use just a thin section of tungsten, maybe multiple layers with spacers, then an insulator and stainless or whatever beneath that.

The toughness of metal, even refractory metals like tungsten (element W), significant exceed the toughness of even the best ceramics, as you can see in the attached graph.

This is a hard problem. And I think the big reason to be hesitant of these refractory metals isn't that they're heavy but that working with them, and making them into the right shape, is pretty expensive and hard.
Title: Re: Starship heat shield
Post by: daveglo on 09/29/2021 02:37 am
This is a hard problem. And I think the big reason to be hesitant of these refractory metals isn't that they're heavy but that working with them, and making them into the right shape, is pretty expensive and hard.

100% agree with you.  But we all know that ceramics, while good at thermal and weight, suck at toughness.  Shuttle tiles showed us that was a bad choice for reusability.

What's needed is a metal "scale" that has the thermal tolerance and physical toughness, and then work the engineering and processing to get the weight down.
Title: Re: Starship heat shield
Post by: Redclaws on 09/29/2021 03:11 am
What metal could it be made from?  How would it insulate?  Etc, etc.
Title: Re: Starship heat shield
Post by: Gunner on 09/29/2021 04:45 am
I looked at this a few months ago....thought it was interesting.
https://ultramet.com/refractory-open-cell-foams/ceramic-and-metal-foams/
Title: Re: Starship heat shield
Post by: su27k on 09/29/2021 04:54 am
Quote
Elon Musk
That said, I’m not entirely convinced that this couldn’t be done with several overlapping scales of metal sheet with an insulator between scale armor & primary structure.


I have to admit, been pondering this design choice for a while, and wondering why this approach hasn't been pursued, using tungsten as the surface material.  Great thermal characteristics, although I don't know how bad the high-temperature oxidation would be.  Weight is an obvious issue too, but the toughness problem would be solved.

Need a high-tech metallurgist to come up with foamed tungsten plate as a primary heat shield surface.  Bulletproof!

They probably are pursuing it, they had a job posting for Starship Heatshield Materials Engineer (https://forum.nasaspaceflight.com/index.php?topic=51736.msg2134023#msg2134023) a year ago, specifically mentioned "an early stage project to develop a metallic heat shield for Starship"

But this is cutting edge R&D work, so probably takes a while before they can get something useful out of it.
Title: Re: Starship heat shield
Post by: edzieba on 09/29/2021 10:55 am
I have to admit, been pondering this design choice for a while, and wondering why this approach hasn't been pursued
TRL.
Sintered ceramic tiles with RCG coatings are flight-tested and flight-proven, with an existing base of industry that knows how to make them. Not quite COTS, but reasonably close.
Metallic TPS means developing a new system that has only seen some sub-scale testing, and no operational use. That's a lot of development cycle your vehicle now needs to wait on while you develop your TPS.
Title: Re: Starship heat shield
Post by: Pitpen on 09/29/2021 11:53 am
This is a hard problem. And I think the big reason to be hesitant of these refractory metals isn't that they're heavy but that working with them, and making them into the right shape, is pretty expensive and hard.

100% agree with you.  But we all know that ceramics, while good at thermal and weight, suck at toughness.  Shuttle tiles showed us that was a bad choice for reusability.

What's needed is a metal "scale" that has the thermal tolerance and physical toughness, and then work the engineering and processing to get the weight down.
I tend to disagree with this sentence. As a matter of fact, during shuttle era, ceramic tiles worked really well for their purposes that were "heat shielding". The Columbia disaster was due to an underestimation of tiles damages by the foam impacting during ascent. And regarding the humongous maintenance necessary to replace them we really hope that SpaceX have found a viable solution. Tiles are not designed to sustain mechanical stresses due to impact with solid objects nor to sustain any pressure gas realeased on them, so to me they are still the best compromise to succeed. I would wait for the first starship to test it before throwing ceramics under the bus. 
Title: Re: Starship heat shield
Post by: livingjw on 09/29/2021 01:46 pm
C/C, C/Sic or Sic/Sic panels with fiber insulation batts underneath is another possibility.

John
Title: Re: Starship heat shield
Post by: InterestedEngineer on 09/29/2021 03:43 pm
Inconel isn't really any better than 310 Stainless (not pictured here, but Inconel and SS 310 have basically the same use temperature).  Tungsten is a bit more than twice as dense as both, but it is FAR higher temperature. So you may be able to use just a thin section of tungsten, maybe multiple layers with spacers, then an insulator and stainless or whatever beneath that.

I think you are using the wrong chart for temperature.  That chart is for metals that one intends to use under stress - i.e. they keep their physical properties intact.

304 Stainless can go to 1300degC *if* you don't care very much about the strength or corrosion resistance of it.  It is likely in the current design that the pins will see close to this, but compared the ceramics, the pins are tough even after annealing.

So what one wants is the metal that has the a sufficiently high melting point with the lowest density while not losing all its corrosion resistance.  I don't know what that would be, but I'd bet someone at SpaceX is looking at it. 

Physical strength of the metal would be pretty far down the list of requirements for a metal tile.

Title: Re: Starship heat shield
Post by: InterestedEngineer on 09/29/2021 03:54 pm
Inconel isn't really any better than 310 Stainless (not pictured here, but Inconel and SS 310 have basically the same use temperature).  Tungsten is a bit more than twice as dense as both, but it is FAR higher temperature. So you may be able to use just a thin section of tungsten, maybe multiple layers with spacers, then an insulator and stainless or whatever beneath that.

I think you are using the wrong chart for temperature.  That chart is for metals that one intends to use under stress - i.e. they keep their physical properties intact.

304 Stainless can go to 1300degC *if* you don't care very much about the strength or corrosion resistance of it.  It is likely in the current design that the pins will see close to this, but compared the ceramics, the pins are tough even after annealing.

So what one wants is the metal that has the a sufficiently high melting point with the lowest density while not losing all its corrosion resistance.  I don't know what that would be, but I'd bet someone at SpaceX is looking at it. 

Physical strength of the metal would be pretty far down the list of requirements for a metal tile.

Found this great write up of using stainless steels at high temperatures:

https://nickelinstitute.org/media/1699/high_temperaturecharacteristicsofstainlesssteel_9004_.pdf

Alas only goes to 900degC. One has to really not care about strength at all (< 1/10th of rated strength at very high temps).  But compared to ceramic, still tougher.
Title: Re: Starship heat shield
Post by: daveglo on 09/29/2021 03:58 pm

I tend to disagree with this sentence. [snip]

I appreciate the perspective, but my point on ceramics was based on the fact that after every shuttle mission, there were significant efforts needed to restore the tiles that were damaged during the mission.  Keeping in mind SpaceX's stated goal of high-frequency reusability, a ceramic tile TPS that requires refurbishment flight after flight runs counter to that goal.

Yes, the early TPS is tiles.  It's a relatively-cheap, known quantity.  But to get the ultimate goal, I think fragile ceramics is a poor choice, and I'd be looking for something more robust.  And I'd gently point out that Elon has voiced skepticism on the ceramic tiles, too.

Personally, I think the whole system as it stands is too sketchy to survive re-entry, especially the clip-to-tile interface (works good in compression, not so much with lateral loads).  But it's certainly going to be a good show, and I hope SpaceX proves me wrong.
Title: Re: Starship heat shield
Post by: born01930 on 09/29/2021 04:00 pm
I wonder why they don't use ablative bolt on plates for the first few flights. SS isn't going to have a rapid turnaround for a while. Maybe they are heavier than ceramics? Seems like the weight penalty for the first few flights with no payload should be acceptable if it allows them to get up to orbit and back. Then figure out what is best for heat shield.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 09/29/2021 04:11 pm
I wonder why they don't use ablative bolt on plates for the first few flights. SS isn't going to have a rapid turnaround for a while. Maybe they are heavier than ceramics? Seems like the weight penalty for the first few flights with no payload should be acceptable if it allows them to get up to orbit and back. Then figure out what is best for heat shield.

the main problem is the added r&d
Title: Re: Starship heat shield
Post by: edzieba on 09/29/2021 04:37 pm
but my point on ceramics was based on the fact that after every shuttle mission, there were significant efforts needed to restore the tiles that were damaged during the mission.
STS tile damage was down to two factors:
Mostly: impact of foam and ice during ascent.
Occasionally: loss of tiles due to adhesion failure on ascent or descent.
Starship has no foam or ice shedding bodies next to or above it, so there is nothing to fall and impact the tiles.
Starship mainly uses mechanical attachment rather than chemical for the supermajority of its TPS, though there are small areas of chemically bonded tiles. However, the adhesion issues were on early STS missions where chemical compatibility issues were still being hammered out (mostly down to the initial rewaterproofing agent attacking the silicone, and tile installers spitting in the silicone to retard curing during application), both unlikely to be an issue with Starship now those lessons have been learned.
Title: Re: Starship heat shield
Post by: KilroySmith on 09/29/2021 05:59 pm
and tile installers spitting in the silicone to retard curing during application
You have got to be kidding me.  But a little research shows that, no, you're not. https://www.washingtonpost.com/wp-srv/articles/A38144-2003Feb6.html (https://www.washingtonpost.com/wp-srv/articles/A38144-2003Feb6.html).
   :-\
Title: Re: Starship heat shield
Post by: TomH on 09/29/2021 07:46 pm
I wonder why they don't use ablative bolt on plates for the first few flights. SS isn't going to have a rapid turnaround for a while. Maybe they are heavier than ceramics? Seems like the weight penalty for the first few flights with no payload should be acceptable if it allows them to get up to orbit and back. Then figure out what is best for heat shield.

the main problem is the added r&d

The main problem is that they learn nothing by chasing a tangent that is not going to be used. Better to learn by trying the approach they actually intend to use, then trouble shooting any problems that arise by analyzing the data.
Title: Re: Starship heat shield
Post by: AU1.52 on 09/29/2021 08:39 pm
I wonder why they don't use ablative bolt on plates for the first few flights. SS isn't going to have a rapid turnaround for a while. Maybe they are heavier than ceramics? Seems like the weight penalty for the first few flights with no payload should be acceptable if it allows them to get up to orbit and back. Then figure out what is best for heat shield.

the main problem is the added r&d

The main problem is that they learn nothing by chasing a tangent that is not going to be used. Better to learn by trying the approach they actually intend to use, then trouble shooting any problems that arise by analyzing the data.


And if necessary pivot and change direction if needed, like what they did with Composites to Stainless.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/29/2021 09:00 pm
Inconel isn't really any better than 310 Stainless (not pictured here, but Inconel and SS 310 have basically the same use temperature).  Tungsten is a bit more than twice as dense as both, but it is FAR higher temperature. So you may be able to use just a thin section of tungsten, maybe multiple layers with spacers, then an insulator and stainless or whatever beneath that.

I think you are using the wrong chart for temperature.  That chart is for metals that one intends to use under stress - i.e. they keep their physical properties intact.

304 Stainless can go to 1300degC *if* you don't care very much about the strength or corrosion resistance of it.  It is likely in the current design that the pins will see close to this, but compared the ceramics, the pins are tough even after annealing.

So what one wants is the metal that has the a sufficiently high melting point with the lowest density while not losing all its corrosion resistance.  I don't know what that would be, but I'd bet someone at SpaceX is looking at it. 

Physical strength of the metal would be pretty far down the list of requirements for a metal tile.
Does corrosion resistance carry over to chemical resistance to all the species that will be created? The plasma itself won't touch metal but there will be some fierce compression heating and gas migration through the shock wave.


Somehow I find the rust bucket image appealing for a ship with a few landings under its belt. Sort of like soot on on F9 but probably not as benign. Oh well.


Kids hanging around the space port: Hey mister, want your spaceship polished?

Title: Re: Starship heat shield
Post by: abaddon on 09/29/2021 09:08 pm
I know Shuttle was the first reentry vehicle to use reusable tiles instead of an ablative shield, but there's another more recent example we could look to as well.  Sure, it's much smaller, but the tiles seem much more successful to date.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/29/2021 09:25 pm

I tend to disagree with this sentence. [snip]

I appreciate the perspective, but my point on ceramics was based on the fact that after every shuttle mission, there were significant efforts needed to restore the tiles that were damaged during the mission.  Keeping in mind SpaceX's stated goal of high-frequency reusability, a ceramic tile TPS that requires refurbishment flight after flight runs counter to that goal.

Yes, the early TPS is tiles.  It's a relatively-cheap, known quantity.  But to get the ultimate goal, I think fragile ceramics is a poor choice, and I'd be looking for something more robust.  And I'd gently point out that Elon has voiced skepticism on the ceramic tiles, too.

Personally, I think the whole system as it stands is too sketchy to survive re-entry, especially the clip-to-tile interface (works good in compression, not so much with lateral loads).  But it's certainly going to be a good show, and I hope SpaceX proves me wrong.
A while back didn't Elon tweet something about rope like caulking between tiles? The closest we've seen is the blanket. It's the type of thing they might have in the toolbox but don't want to use if they don't have to. It would do a lot for vibration and lateral loads. Mental image: pounding oakum on wooden ships. 


As for tiles being an expedient, you might be right but if the expedient is good enough...  Turnaround time might be a place where reality and intentions have to find a compromise.


We saw the first go at mass tile inspection and servicing just a few weeks ago. It was slow but it was only a first try on an early design. If turnaround is 48 hours on a reasonably mature system I'd count that as a win. Aircraft like turnaround sounds great but we are talking rocket ships here.
Title: Re: Starship heat shield
Post by: matthewkantar on 09/29/2021 10:17 pm
I know Shuttle was the first reentry vehicle to use reusable tiles instead of an ablative shield, but there's another more recent example we could look to as well.  Sure, it's much smaller, but the tiles seem much more successful to date.

It probably helps that the newer vehicle goes up completely encapsulated in a fairing, so it never sits in the wether, doesn't experience any buffeting on the way up.
Title: Re: Starship heat shield
Post by: lstr on 09/29/2021 10:59 pm
Stupid tiles >:(
Heat shield will be the main challenge of spaceship reusability because tiles were, are, and guaranteed to remain a pain in the ass for some time, imo. But there are no other tested and working reusable alternatives for that size of ships. Anyway the ss 20 test will be crucial . In case of serious issues with the tiles in the re-entry, probably a scheme of a rapid-replaceable ablative will be good to get started prototyping asap. If either tiles or ablative can work, it gives time for R&D on alternatives, that must be aggressive ($$), unless tiles prove to be good (and safe) enough also for the rapid reusable scenario. The biggest issue with the tiles i see even if they work, is fast and reliable inspection and replacement after re-entry and I am not talking just about surface inspection. If you want to relax/remove this step, the only way to be sure is to determine the number of re-entries before inspection and/or replacement. But for this you need statistical analysis and enough consistent real data (including failures), so you can set safe limits. I guess at least 10 ships destructive testing is needed, with the posibility of getting you nowhere, if 1 ship/heatshield of 10 fails on 2nd reentry, you are back on inspections after each reentry if you are not going to risk a 10% probability of failure.
Title: Re: Starship heat shield
Post by: DanClemmensen on 09/30/2021 02:18 am
Stupid tiles >:(
Heat shield will be the main challenge of spaceship reusability because tiles were, are, and guaranteed to remain a pain in the ass for some time, imo. But there are no other tested and working reusable alternatives for that size of ships. Anyway the ss 20 test will be crucial . In case of serious issues with the tiles in the re-entry, probably a scheme of a rapid-replaceable ablative will be good to get started prototyping asap. If either tiles or ablative can work, it gives time for R&D on alternatives, that must be aggressive ($$), unless tiles prove to be good (and safe) enough also for the rapid reusable scenario. The biggest issue with the tiles i see even if they work, is fast and reliable inspection and replacement after re-entry and I am not talking just about surface inspection. If you want to relax/remove this step, the only way to be sure is to determine the number of re-entries before inspection and/or replacement. But for this you need statistical analysis and enough consistent real data (including failures), so you can set safe limits. I guess at least 10 ships destructive testing is needed, with the posibility of getting you nowhere, if 1 ship/heatshield of 10 fails on 2nd reentry, you are back on inspections after each reentry if you are not going to risk a 10% probability of failure.
If this analysis is correct (and it looks correct) then
 --we want quick inexpensive turnaround
 --we have no good alternative to tiles
 --we will probably need inspection of every tile before every launch
The only way I see to resolve this is to develop an effective completely automated inspection technique. This would likely require some redesign of the TPS, co-designed with the automated inspection system, to minimize cost and maximize inspection confidence at the system level.  I truly hope that the need for tile replacement will be so low that automated tile replacement is not economical.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 09/30/2021 03:02 am
Quote
Everyday Astronaut
How’re the titles gonna stay on during ascent? I’m still a little surprised nature didn’t have the right idea and do the tiles more like scales. On ascent there’d be less room for aerodynamic forces to rip them off and it’d allow for expansion and contraction of the steel


Quote
Elon Musk
That said, I’m not entirely convinced that this couldn’t be done with several overlapping scales of metal sheet with an insulator between scale armor & primary structure.



https://twitter.com/elonmusk/status/1442636642985160708

Here's a possible metal candidate for scales:

https://www.neonickel.com/generate-alloy-pdf/?id=42

"maintains strength and oxidation resistance up to 1232°C."

Not quite the 1477 degC needed, but close.

(1477 degC was the requirement for the space shuttle, not sure if SS is less or more for LEO)

BTW "maintain strength" means it was measured.  It's likely still well above the 0.4 MPa for ceramic tiles almost all the way to melting.
Title: Re: Starship heat shield
Post by: BT52 on 09/30/2021 03:54 am
Scales don't solve ur problems really.
-rubbing
-attachment method

Tiles seems much more efficient use of total surface area. And its effects on payload vs reliability. I think this is solvable engineering problem. I would argue that materials and tech are there. SO Main points of design are:

- AI automatic error detection
- robust attaching system=kinematic joint is still on table
-effective stable manufacturing inside tolerances.
Title: Re: Starship heat shield
Post by: TomH on 09/30/2021 04:47 am
Elon:
Quote
If tiles are not super thin, you get hot plasma “waterfalling” off edges of tiles, creating hotspots.

Eddy currents, standing waves, and other phenomena of fluid dynamics of plasma at hypersonic velocity is something very complex, and not nearly well enough understood. Coming off the trailing edges of those tiny shingles, it could be quite a challenge to cope with. Elon is right.
Title: Re: Starship heat shield
Post by: Lars-J on 09/30/2021 05:24 am
Layering tiles like scales is also complicated by the fact that the tiles won’t just experience airflow in one direction. During the ascent the flow is pretty much perpendicular to the flow during reentry, and you want to avoid tiles being ripped off at Max-Q.
Title: Re: Starship heat shield
Post by: Pitpen on 09/30/2021 06:23 am

I tend to disagree with this sentence. [snip]

I appreciate the perspective, but my point on ceramics was based on the fact that after every shuttle mission, there were significant efforts needed to restore the tiles that were damaged during the mission.  Keeping in mind SpaceX's stated goal of high-frequency reusability, a ceramic tile TPS that requires refurbishment flight after flight runs counter to that goal.

Yes, the early TPS is tiles.  It's a relatively-cheap, known quantity.  But to get the ultimate goal, I think fragile ceramics is a poor choice, and I'd be looking for something more robust.  And I'd gently point out that Elon has voiced skepticism on the ceramic tiles, too.

Personally, I think the whole system as it stands is too sketchy to survive re-entry, especially the clip-to-tile interface (works good in compression, not so much with lateral loads).  But it's certainly going to be a good show, and I hope SpaceX proves me wrong.
A while back didn't Elon tweet something about rope like caulking between tiles? The closest we've seen is the blanket. It's the type of thing they might have in the toolbox but don't want to use if they don't have to. It would do a lot for vibration and lateral loads. Mental image: pounding oakum on wooden ships. 


As for tiles being an expedient, you might be right but if the expedient is good enough...  Turnaround time might be a place where reality and intentions have to find a compromise.


We saw the first go at mass tile inspection and servicing just a few weeks ago. It was slow but it was only a first try on an early design. If turnaround is 48 hours on a reasonably mature system I'd count that as a win. Aircraft like turnaround sounds great but we are talking rocket ships here.
We should also take Elon ambitious plan of "rapid turnaround" with a grain of salt. Look at the F9 that has a record turnaround of dozens of days being suborbital. I would myself take a month as a success for orbital purposes. Surely this would impact an earth to earth use of Starship but frankly speaking I suspect that earth-earth SS is way down below in SpaceX priority list.
Title: Re: Starship heat shield
Post by: RobLynn on 09/30/2021 09:38 am
Quote
Everyday Astronaut
How’re the titles gonna stay on during ascent? I’m still a little surprised nature didn’t have the right idea and do the tiles more like scales. On ascent there’d be less room for aerodynamic forces to rip them off and it’d allow for expansion and contraction of the steel


Quote
Elon Musk
That said, I’m not entirely convinced that this couldn’t be done with several overlapping scales of metal sheet with an insulator between scale armor & primary structure.



https://twitter.com/elonmusk/status/1442636642985160708

Here's a possible metal candidate for scales:

https://www.neonickel.com/generate-alloy-pdf/?id=42

"maintains strength and oxidation resistance up to 1232°C."

Not quite the 1477 degC needed, but close.

(1477 degC was the requirement for the space shuttle, not sure if SS is less or more for LEO)

BTW "maintain strength" means it was measured.  It's likely still well above the 0.4 MPa for ceramic tiles almost all the way to melting.

Ductility at temperature is the key, something ceramics really don't do, while refractory metals are all hideously dense and badly susceptible to oxidation.  silicon+boron based coating systems for Molybdenum looks quite promising for ~100hour lives that heat shields need: https://d-nb.info/1226222633/34

Kanthal-A1 is a relatively cheap Iron Chromium Aluminum alloy used for heating elements in air up to about 1400°C (at which is is very weak), but could at least be formed as a somewhat ductile foil shell over a fibrous ceramic insulating core.

I agree that automated tile maintenance robots should largely fix this as a cost issue and are most likely being worked on by spacex.  The number of tile shapes in their inventory is a bit of a problem for the complexity of the tile manufacturing and mounting systems, and I suspect they will end up making a number of design compromises to reduce tiling complexity (would a spherical nose on starship help?)
Title: Re: Starship heat shield
Post by: JamesH65 on 09/30/2021 10:37 am

I tend to disagree with this sentence. [snip]

I appreciate the perspective, but my point on ceramics was based on the fact that after every shuttle mission, there were significant efforts needed to restore the tiles that were damaged during the mission.  Keeping in mind SpaceX's stated goal of high-frequency reusability, a ceramic tile TPS that requires refurbishment flight after flight runs counter to that goal.

Yes, the early TPS is tiles.  It's a relatively-cheap, known quantity.  But to get the ultimate goal, I think fragile ceramics is a poor choice, and I'd be looking for something more robust.  And I'd gently point out that Elon has voiced skepticism on the ceramic tiles, too.

Personally, I think the whole system as it stands is too sketchy to survive re-entry, especially the clip-to-tile interface (works good in compression, not so much with lateral loads).  But it's certainly going to be a good show, and I hope SpaceX proves me wrong.
A while back didn't Elon tweet something about rope like caulking between tiles? The closest we've seen is the blanket. It's the type of thing they might have in the toolbox but don't want to use if they don't have to. It would do a lot for vibration and lateral loads. Mental image: pounding oakum on wooden ships. 


As for tiles being an expedient, you might be right but if the expedient is good enough...  Turnaround time might be a place where reality and intentions have to find a compromise.


We saw the first go at mass tile inspection and servicing just a few weeks ago. It was slow but it was only a first try on an early design. If turnaround is 48 hours on a reasonably mature system I'd count that as a win. Aircraft like turnaround sounds great but we are talking rocket ships here.
We should also take Elon ambitious plan of "rapid turnaround" with a grain of salt. Look at the F9 that has a record turnaround of dozens of days being suborbital. I would myself take a month as a success for orbital purposes. Surely this would impact an earth to earth use of Starship but frankly speaking I suspect that earth-earth SS is way down below in SpaceX priority list.

Whilst I guess it is ambitious, its also, in Musk's own words, absolutely necessary to <24hr turnaround. So they will work and work at it until it works.
Title: Re: Starship heat shield
Post by: Slarty1080 on 09/30/2021 11:14 am

I tend to disagree with this sentence. [snip]

I appreciate the perspective, but my point on ceramics was based on the fact that after every shuttle mission, there were significant efforts needed to restore the tiles that were damaged during the mission.  Keeping in mind SpaceX's stated goal of high-frequency reusability, a ceramic tile TPS that requires refurbishment flight after flight runs counter to that goal.

Yes, the early TPS is tiles.  It's a relatively-cheap, known quantity.  But to get the ultimate goal, I think fragile ceramics is a poor choice, and I'd be looking for something more robust.  And I'd gently point out that Elon has voiced skepticism on the ceramic tiles, too.

Personally, I think the whole system as it stands is too sketchy to survive re-entry, especially the clip-to-tile interface (works good in compression, not so much with lateral loads).  But it's certainly going to be a good show, and I hope SpaceX proves me wrong.
A while back didn't Elon tweet something about rope like caulking between tiles? The closest we've seen is the blanket. It's the type of thing they might have in the toolbox but don't want to use if they don't have to. It would do a lot for vibration and lateral loads. Mental image: pounding oakum on wooden ships. 


As for tiles being an expedient, you might be right but if the expedient is good enough...  Turnaround time might be a place where reality and intentions have to find a compromise.


We saw the first go at mass tile inspection and servicing just a few weeks ago. It was slow but it was only a first try on an early design. If turnaround is 48 hours on a reasonably mature system I'd count that as a win. Aircraft like turnaround sounds great but we are talking rocket ships here.
We should also take Elon ambitious plan of "rapid turnaround" with a grain of salt. Look at the F9 that has a record turnaround of dozens of days being suborbital. I would myself take a month as a success for orbital purposes. Surely this would impact an earth to earth use of Starship but frankly speaking I suspect that earth-earth SS is way down below in SpaceX priority list.

Whilst I guess it is ambitious, its also, in Musk's own words, absolutely necessary to <24hr turnaround. So they will work and work at it until it works.
Never been done before and never will be done, until it is done and then its obviously just routine
Title: Re: Starship heat shield
Post by: brettly2021 on 09/30/2021 03:22 pm
Lars-J mentioned a few posts back the tiles have to stay intact during maxQ, well I think a couple of days ago we saw what happens when fast travelling gas hits the tiles, they fly off rather spectacularly. Did spacex purposely direct the gas at the tiles to see what would happen? or was it just an accident which shows what might be a worrying unplanned tile test. I guess the angle of that gas venting plays a role, but as the tiles are at the moment I'm expecting as mass shedding during launch and ascent.
Title: Re: Starship heat shield
Post by: gideonlow on 09/30/2021 04:18 pm
Lars-J mentioned a few posts back the tiles have to stay intact during maxQ, well I think a couple of days ago we saw what happens when fast travelling gas hits the tiles, they fly off rather spectacularly. Did spacex purposely direct the gas at the tiles to see what would happen? or was it just an accident which shows what might be a worrying unplanned tile test. I guess the angle of that gas venting plays a role, but as the tiles are at the moment I'm expecting as mass shedding during launch and ascent.

IMO borderline concern tr*lling.  If you watch the development of the Starship/Superheavy program over the last few years, you can see that their first try at nearly everything can be slathered with similar concerns.  You can also see how SpaceX dramatically improves with each iteration of a Starship component/sub-system.  This is Orbital Starship Heat Shield iteration 1, with no serious expectation that it will survive re-entry.  Glimpses of OSHS iteration 2 provided by Bocachicagal already show dramatic improvements.
Title: Re: Starship heat shield
Post by: rsdavis9 on 09/30/2021 04:21 pm
Also they have made a number of flights to 10km subsonic with minimal tile shedding. Probably tile numbers close to ~1000? Anybody know with the current flight profile when the full stack will pass subsonic to supersonic?
Basically when maxQ is?

Title: Re: Starship heat shield
Post by: OTV Booster on 09/30/2021 05:30 pm
Stupid tiles >:(
Heat shield will be the main challenge of spaceship reusability because tiles were, are, and guaranteed to remain a pain in the ass for some time, imo. But there are no other tested and working reusable alternatives for that size of ships. Anyway the ss 20 test will be crucial . In case of serious issues with the tiles in the re-entry, probably a scheme of a rapid-replaceable ablative will be good to get started prototyping asap. If either tiles or ablative can work, it gives time for R&D on alternatives, that must be aggressive ($$), unless tiles prove to be good (and safe) enough also for the rapid reusable scenario. The biggest issue with the tiles i see even if they work, is fast and reliable inspection and replacement after re-entry and I am not talking just about surface inspection. If you want to relax/remove this step, the only way to be sure is to determine the number of re-entries before inspection and/or replacement. But for this you need statistical analysis and enough consistent real data (including failures), so you can set safe limits. I guess at least 10 ships destructive testing is needed, with the posibility of getting you nowhere, if 1 ship/heatshield of 10 fails on 2nd reentry, you are back on inspections after each reentry if you are not going to risk a 10% probability of failure.
It's routine to tap a grinder wheel before install to see if it has a hidden crack. It's a very different sound. ISTM this might be adaptable to the already installed tiles and could be robotized. One arm on a lift with a tapper and contact sound transducer could conceivably do an 8x8 section of tiles at a second each. The another 30-45 seconds to reposition for the next section. Call it an overall average of 2 seconds per tile per arm.


Don't know if it would really work but it seems to be worth looking at. If it works at all it should also work in vacuum.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/30/2021 05:35 pm
Layering tiles like scales is also complicated by the fact that the tiles won’t just experience airflow in one direction. During the ascent the flow is pretty much perpendicular to the flow during reentry, and you want to avoid tiles being ripped off at Max-Q.
And replacement becomes difficult.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/30/2021 07:19 pm

I tend to disagree with this sentence. [snip]

I appreciate the perspective, but my point on ceramics was based on the fact that after every shuttle mission, there were significant efforts needed to restore the tiles that were damaged during the mission.  Keeping in mind SpaceX's stated goal of high-frequency reusability, a ceramic tile TPS that requires refurbishment flight after flight runs counter to that goal.

Yes, the early TPS is tiles.  It's a relatively-cheap, known quantity.  But to get the ultimate goal, I think fragile ceramics is a poor choice, and I'd be looking for something more robust.  And I'd gently point out that Elon has voiced skepticism on the ceramic tiles, too.

Personally, I think the whole system as it stands is too sketchy to survive re-entry, especially the clip-to-tile interface (works good in compression, not so much with lateral loads).  But it's certainly going to be a good show, and I hope SpaceX proves me wrong.
A while back didn't Elon tweet something about rope like caulking between tiles? The closest we've seen is the blanket. It's the type of thing they might have in the toolbox but don't want to use if they don't have to. It would do a lot for vibration and lateral loads. Mental image: pounding oakum on wooden ships. 


As for tiles being an expedient, you might be right but if the expedient is good enough...  Turnaround time might be a place where reality and intentions have to find a compromise.


We saw the first go at mass tile inspection and servicing just a few weeks ago. It was slow but it was only a first try on an early design. If turnaround is 48 hours on a reasonably mature system I'd count that as a win. Aircraft like turnaround sounds great but we are talking rocket ships here.
We should also take Elon ambitious plan of "rapid turnaround" with a grain of salt. Look at the F9 that has a record turnaround of dozens of days being suborbital. I would myself take a month as a success for orbital purposes. Surely this would impact an earth to earth use of Starship but frankly speaking I suspect that earth-earth SS is way down below in SpaceX priority list.

Whilst I guess it is ambitious, its also, in Musk's own words, absolutely necessary to <24hr turnaround. So they will work and work at it until it works.
I've been struggling with the reason for this turnaround time and what I come up with is the launch surge necessary to refuel an accumulation tanker. I don't have Elon's tweets at hand but could he mean SH and the pad and not SS?


Recycling SH should be much easier than SS. IMO the pad would be harder than SH. what is the fastest a heavy launch pad has ever been turned around? What's the fastest for an F9 pad? We might end up seeing the launch table clad in tiles.


If it takes seven tankers (rounded up) to fill one accumulation tanker and the pad can take it, one SH and seven tankers can do one refueling campaign leaving a week for recycling each tanker. By that time the pad probably needs attention and the tanker turnaround can extend. Modify appropriately for higher capacity stretch tankers.


IMO a 24hr turnaround for SS is nutso. Nutso does not equal impossible. Impossible is a dangerous word in anything involving Musk.
Title: Re: Starship heat shield
Post by: Apollo-phill on 09/30/2021 08:06 pm
I was more than surprised when SpaceX said they were going use tiles for thermal protection - especially after the trials and tribulations that were observed during the Space Shuttle program..And the labour intensity following each flight and preparation for the following flight of same vehicle.

So, here is a " concept thought" that would need some development but might - only might - have some merit and application ? 

In early days of developing its recoverable spacecraft, China used ablative Cork heatshields . ( ( Thickness unknown ).Images exist showing several recovered spacecraft with these heatshields with craft intact.

Cork is a " sustainable commodity" on Earth

Now, there exists for the construction industry , spray on cork products that use like a spray gun applicator with a hand held hopper. It currently applies thin layers to walls and other surfaces. DIY products exist too as they can be used for thermal insulation, sound suppression and the like.

Now, could this technique be scaled up to provide several centimetre thicknesses onto Starship metallic hulls ? Applicator to be computer controlled and automated to traverse up/down and around hull to be covered ?

Each Starship atmospheric entry back to Earth sees part of Cork ablated away .

On launch pad , the" Cork Robot" travels up/down and around hull spraying on the required layer/s of" new cork" at a rate far faster than tile replacement. Odd tricky parts could be one operator applied if required ?

Perhaps some other Shuttle like large thermal blanket layers under cork layer permanently attached to hull as added precaution ?

Anyway, you can hopefully see the idea concept  - its wants developing further

Could it be exploited ?

Rather than Chinese " copying USA/Russia" let's " copy China" !


Phill

Title: Re: Starship heat shield
Post by: dgkimpton on 09/30/2021 08:43 pm
cork...
Sounds like a really expensive way to go - baking in extra launch costs for every launch. Not to mention with the planned flight rate there'd be no cork left in the world in very short order (remember, the goal is thousands of launches, not a few).

I'm not sure why everyone is already so keen to throw out the current TPS idea... at least give them a chance to launch one and see if it stands a chance or not.
Title: Re: Starship heat shield
Post by: jstrotha0975 on 09/30/2021 08:58 pm
Spray cork actually sounds like a good idea. Is there a synthetic cork?
Title: Re: Starship heat shield
Post by: Oersted on 09/30/2021 09:05 pm
Lots of people dissing tiles... But, if the Shuttle and Starship use tiles... - you know, there may be very good reasons for that. Weight to efficiency ratio is unbeatable (until the day where kryptonite and unobtainium and superconducting force fields come around...).
Title: Re: Starship heat shield
Post by: Lars-J on 09/30/2021 10:30 pm
Ablative spray on cork is a terrible idea... for a reusable gas-n-go system. Which is the plan with Starship.

Tiles make a lot more sense. Easy to inspect, easy to replace. (which should be infrequent) Are the tiles fully finished? Of course not, but there is no reason to panic.
Title: Re: Starship heat shield
Post by: marsbase on 09/30/2021 10:54 pm
Ablative spray on cork is a terrible idea... for a reusable gas-n-go system. Which is the plan with Starship.

Tiles make a lot more sense. Easy to inspect, easy to replace. (which should be infrequent) Are the tiles fully finished? Of course not, but there is no reason to panic.
The TPS is a solution under investigation.  There are many possible outcomes. It may be that the cylindrical portion of the rocket will have no problems with the tiles as they are.  Other parts may need another solution or special application techniques. And Elon has been clear that cooling with liquid propellant is still on the table. As Lars-J says, "no reason to panic".  I do think TPS is one of the most difficult remaining problems, but not the only one.
Title: Re: Starship heat shield
Post by: CruddyCuber on 09/30/2021 11:28 pm
Re:  cork heat shield.

Why would SpaceX pursue a disposable heat shield that requires extensive repair and replacement every flight when the entire point of the starship program is developing a rapidly and fully reusable launch system?

Also, a single use cork heat shield likely wouldn't work on Mars-bound starships because they have to withstand atmospheric entry twice.  You could make the heat shield thick enough to withstand both entries, or repair it on Mars, but that seems absolutely ridiculous from a mass and complexity standpoint.
Title: Re: Starship heat shield
Post by: dglow on 10/01/2021 01:24 am
Until we discover the native Martian cork, so it's all ISRU.
Title: Re: Starship heat shield
Post by: daveglo on 10/01/2021 01:45 am
Lots of people dissing tiles... But, if the Shuttle and Starship use tiles... - you know, there may be very good reasons for that. Weight to efficiency ratio is unbeatable (until the day where kryptonite and unobtainium and superconducting force fields come around...).

Not necessarily "dissing" tiles, but observing that ceramic tiles have a history of fragility, whether by ice impacts or launch vibrations.  By their nature, they break easily.

Shuttle used tiles because that was the best that 1970's technology had to offer.   I have no inside knowledge of an obvious better solution, but I can certainly make the case that SpaceX would WANT a better solution.  Sure, not today.  But a year, or five, down the road?  Absolutely.

And it won't have to be exceptionally exotic, but it may require some crafty technology to implement.  And really, isn't that kind of what SpaceX is pretty good at doing?

Maybe they find a way to make the ceramic much tougher.  Or maybe they find a way to make a metal tile.  Doesn't have to be a "scale".  But it ought to be stout, and highly reusable.  And light.

I just think the current tile solution is relatively cheap and fast.  And will probably work about as well as anything cheap and fast works.
Title: Re: Starship heat shield
Post by: Asteroza on 10/01/2021 03:32 am
Lots of people dissing tiles... But, if the Shuttle and Starship use tiles... - you know, there may be very good reasons for that. Weight to efficiency ratio is unbeatable (until the day where kryptonite and unobtainium and superconducting force fields come around...).

Not necessarily "dissing" tiles, but observing that ceramic tiles have a history of fragility, whether by ice impacts or launch vibrations.  By their nature, they break easily.

Shuttle used tiles because that was the best that 1970's technology had to offer.   I have no inside knowledge of an obvious better solution, but I can certainly make the case that SpaceX would WANT a better solution.  Sure, not today.  But a year, or five, down the road?  Absolutely.

And it won't have to be exceptionally exotic, but it may require some crafty technology to implement.  And really, isn't that kind of what SpaceX is pretty good at doing?

Maybe they find a way to make the ceramic much tougher.  Or maybe they find a way to make a metal tile.  Doesn't have to be a "scale".  But it ought to be stout, and highly reusable.  And light.

I just think the current tile solution is relatively cheap and fast.  And will probably work about as well as anything cheap and fast works.

Shuttle era would have had some access to hot structure and metallic TPS work from X-20, and some other semi-military stuff (what was it called? HAVE REGION or something similar?)
Title: Re: Starship heat shield
Post by: dglow on 10/01/2021 04:19 am
Shuttle era would have had some access to hot structure and metallic TPS work from X-20, and some other semi-military stuff (what was it called? HAVE REGION or something similar?)

I suspect it is already posted upthread, but take a look at this X-33 era research. (https://ntrs.nasa.gov/api/citations/20040095922/downloads/20040095922.pdf)
Title: Re: Starship heat shield
Post by: Slarty1080 on 10/01/2021 08:04 am
Lots of people dissing tiles... But, if the Shuttle and Starship use tiles... - you know, there may be very good reasons for that. Weight to efficiency ratio is unbeatable (until the day where kryptonite and unobtainium and superconducting force fields come around...).

Not necessarily "dissing" tiles, but observing that ceramic tiles have a history of fragility, whether by ice impacts or launch vibrations.  By their nature, they break easily.

Shuttle used tiles because that was the best that 1970's technology had to offer.   I have no inside knowledge of an obvious better solution, but I can certainly make the case that SpaceX would WANT a better solution.  Sure, not today.  But a year, or five, down the road?  Absolutely.

And it won't have to be exceptionally exotic, but it may require some crafty technology to implement.  And really, isn't that kind of what SpaceX is pretty good at doing?

Maybe they find a way to make the ceramic much tougher.  Or maybe they find a way to make a metal tile.  Doesn't have to be a "scale".  But it ought to be stout, and highly reusable.  And light.

I just think the current tile solution is relatively cheap and fast.  And will probably work about as well as anything cheap and fast works.
Cheap and fast is the way to go . If the current set up is a bit to cheap and fast then it will need to be less so. Such is life.
Title: Re: Starship heat shield
Post by: KelvinZero on 10/01/2021 12:27 pm
Rather than throwing out tiles, how about some wacky ideas to make a few broken/missing tiles more survivable. I guess that has already been covered somewhere in this huge thread?

Perhaps the tanks could be designed to survive having some holes since the landing fuel is in the header tanks?

How about a honeycomb of holes drilled partially through from the inside so that if the steel starts ablating away, instead of rupturing it begins sweating gas in that portion.

(edit: that may sound like it greatly weakens the tank but not necessarily. You are shaving off weight which could go elsewhere. I have seen several advanced topics where materials with cleverly constructed hollows can have bizarre strength for their weight)
Title: Re: Starship heat shield
Post by: ETurner on 10/01/2021 12:28 pm
How about a honeycomb of holes drilled partially through from the inside so that if the steel starts ablating away, instead of rupturing it begins sweating gas in that portion.
Steel would soften and melt before ablating.
Title: Re: Starship heat shield
Post by: eriblo on 10/01/2021 02:00 pm
How about a honeycomb of holes drilled partially through from the inside so that if the steel starts ablating away, instead of rupturing it begins sweating gas in that portion.
Steel would soften and melt before ablating.
Well, you would certainly get some if you start venting oxygen through holes in hot metal....
Title: Re: Starship heat shield
Post by: gpm on 10/01/2021 02:05 pm
Perhaps the tanks could be designed to survive having some holes since the landing fuel is in the header tanks?

This sounds the opposite of reusable... perhaps worth thinking about to increase the odds of humans surviving a heat shield failure, but very far down the road after they have unmanned flight working reliably enough.
Title: Re: Starship heat shield
Post by: tenkendojo on 10/01/2021 02:48 pm
https://mobile.twitter.com/elonmusk/status/1314741760568954880 (https://mobile.twitter.com/elonmusk/status/1314741760568954880)
I remember Elon mentioned awhile ago that they're considering using transpiration cooling on some areas. In light of recent tile blowaway event, I wonder if they have completely moved away from that or still have transpiration cooling as an option, at least in areas difficult to cover with heat tiles.
Title: Re: Starship heat shield
Post by: Redclaws on 10/01/2021 03:09 pm
https://mobile.twitter.com/elonmusk/status/1314741760568954880 (https://mobile.twitter.com/elonmusk/status/1314741760568954880)
I remember Elon mentioned awhile ago that they're considering using transpiration cooling on some areas. In light of recent tile blowaway event, I wonder if they have completely moved away from that or still have transpiration cooling as an option, at least in areas difficult to cover with heat tiles.

I think until we see it, it seems like we have to consider it aspirational.  Elon achieves amazing stuff but he also throws some ideas at the wall which are actually dramatically harder/lower TRL than they first appear or perhaps he immediately realizes.  I suspect transpiration cooling is one such.  I don’t think we’ll see it.

Some ideas sound hard but can be done fairly quickly with care and effort.  Others are more like research projects and can’t really be rushed much.  (I guess I’m kind of just saying “are much lower TRL”.)
Title: Re: Starship heat shield
Post by: DanClemmensen on 10/01/2021 03:12 pm
https://mobile.twitter.com/elonmusk/status/1314741760568954880 (https://mobile.twitter.com/elonmusk/status/1314741760568954880)
I remember Elon mentioned awhile ago that they're considering using transpiration cooling on some areas. In light of recent tile blowaway event, I wonder if they have completely moved away from that or still have transpiration cooling as an option, at least in areas difficult to cover with heat tiles.
Yep, more than half of the hull area is also the walls of the cryogenic LOX and LCH4. Those 3 mm thick walls are basically being actively cooled from the inside. Therefore, the "only" areas that need extra attention are the nose and the windward forward hull areas covered by the tiles. I suppose a conformal LCH4 "tank"  just inside the hull (i.e., double hull, cooling pipes, whatever) and connected to the main tank would do it. The question is how much heat can you store in the LOX and LCH4? there is only enough of the stuff left to land the Starship, and the Raptors need for it to still be liquid.
Title: Re: Starship heat shield
Post by: Oersted on 10/01/2021 03:33 pm
Lots of people dissing tiles... But, if the Shuttle and Starship use tiles... - you know, there may be very good reasons for that. Weight to efficiency ratio is unbeatable (until the day where kryptonite and unobtainium and superconducting force fields come around...).

Not necessarily "dissing" tiles, but observing that ceramic tiles have a history of fragility, whether by ice impacts or launch vibrations.  By their nature, they break easily.

Shuttle used tiles because that was the best that 1970's technology had to offer.   I have no inside knowledge of an obvious better solution, but I can certainly make the case that SpaceX would WANT a better solution.  Sure, not today.  But a year, or five, down the road?  Absolutely.

And it won't have to be exceptionally exotic, but it may require some crafty technology to implement.  And really, isn't that kind of what SpaceX is pretty good at doing?

Maybe they find a way to make the ceramic much tougher.  Or maybe they find a way to make a metal tile.  Doesn't have to be a "scale".  But it ought to be stout, and highly reusable.  And light.

I just think the current tile solution is relatively cheap and fast.  And will probably work about as well as anything cheap and fast works.

I am dead certain that SpaceX explored all possible and impossible solutions for the TPS before settling on tiles. That they ended up going for tiles, despite their complexity and relative fragility, I think speaks volumes about the benefits of tiles.
Title: Re: Starship heat shield
Post by: Slarty1080 on 10/01/2021 04:04 pm
https://mobile.twitter.com/elonmusk/status/1314741760568954880 (https://mobile.twitter.com/elonmusk/status/1314741760568954880)
I remember Elon mentioned awhile ago that they're considering using transpiration cooling on some areas. In light of recent tile blowaway event, I wonder if they have completely moved away from that or still have transpiration cooling as an option, at least in areas difficult to cover with heat tiles.
Yep, more than half of the hull area is also the walls of the cryogenic LOX and LCH4. Those 3 mm thick walls are basically being actively cooled from the inside. Therefore, the "only" areas that need extra attention are the nose and the windward forward hull areas covered by the tiles. I suppose a conformal LCH4 "tank"  just inside the hull (i.e., double hull, cooling pipes, whatever) and connected to the main tank would do it. The question is how much heat can you store in the LOX and LCH4? there is only enough of the stuff left to land the Starship, and the Raptors need for it to still be liquid.
We don't know if there are going to be problems with the existing tile arrangement or where those issues might be. But if there are, one area of concern was the flaps/hinges. I imagine that venting some methane there could be used to keep them cool. The problem with "storing heat in the LOX and CH4" is pressure increase. If they need extra methane they can easily adapt things so the header tank is a little larger.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 10/01/2021 04:27 pm
...

Perhaps the tanks could be designed to survive having some holes since the landing fuel is in the header tanks?


Im am not an engineer. But we know that the tanks are pressurized otherwise the ship would crumple because of the excess weight (and the crew cabin will add weight, to the "blank" ss  that iirc would sustain itself without pressurrization). If the tanks have holes, they can't be pressurized. I could be wrong though.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 10/01/2021 04:34 pm
I am dead certain that SpaceX explored all possible and impossible solutions for the TPS before settling on tiles. That they ended up going for tiles, despite their complexity and relative fragility, I think speaks volumes about the benefits of tiles.

I think the problem is very hard, and tiles are the least-worst solution.
Title: Re: Starship heat shield
Post by: tenkendojo on 10/01/2021 05:27 pm
...

Perhaps the tanks could be designed to survive having some holes since the landing fuel is in the header tanks?


Im am not an engineer. But we know that the tanks are pressurized otherwise the ship would crumple because of the excess weight (and the crew cabin will add weight, to the "blank" ss  that iirc would sustain itself without pressurrization). If the tanks have holes, they can't be pressurized. I could be wrong though.

For transpiration cooling you don't directly apply "holes" to the tank wall. Instead you direct small amount of CH4 to manifolds with transpiration "pores" alongsides the ship hull to achieve cooling.
Title: Re: Starship heat shield
Post by: rsdavis9 on 10/01/2021 05:32 pm
So the tiles blew off from the venting during the cryo test.
Do we know if the tiles that blew off were glued or pinned on?
Title: Re: Starship heat shield
Post by: eriblo on 10/01/2021 05:48 pm
So the tiles blew off from the venting during the cryo test.
Do we know if the tiles that blew off were glued or pinned on?
Pinned on - it looks like the jet from the vents got under the edge of the blanket and created a pressure differential high enough to break and/or detach the tiles on top. This failure mode is much less likely for glued tiles
Title: Re: Starship heat shield
Post by: DanClemmensen on 10/01/2021 06:30 pm
https://mobile.twitter.com/elonmusk/status/1314741760568954880 (https://mobile.twitter.com/elonmusk/status/1314741760568954880)
I remember Elon mentioned awhile ago that they're considering using transpiration cooling on some areas. In light of recent tile blowaway event, I wonder if they have completely moved away from that or still have transpiration cooling as an option, at least in areas difficult to cover with heat tiles.
Yep, more than half of the hull area is also the walls of the cryogenic LOX and LCH4. Those 3 mm thick walls are basically being actively cooled from the inside. Therefore, the "only" areas that need extra attention are the nose and the windward forward hull areas covered by the tiles. I suppose a conformal LCH4 "tank"  just inside the hull (i.e., double hull, cooling pipes, whatever) and connected to the main tank would do it. The question is how much heat can you store in the LOX and LCH4? there is only enough of the stuff left to land the Starship, and the Raptors need for it to still be liquid.
We don't know if there are going to be problems with the existing tile arrangement or where those issues might be. But if there are, one area of concern was the flaps/hinges. I imagine that venting some methane there could be used to keep them cool. The problem with "storing heat in the LOX and CH4" is pressure increase. If they need extra methane they can easily adapt things so the header tank is a little larger.
They don't have a choice. The heat that penetrates the TPS in the after half of the hull will enter the LOX or LCH4 through the single-wall stainless steel. The question is what happens next. Sure, boil-off and and transpiration will carry heat away, and that gas can be used in clever ways to carry off even more heat, but the Raptors will still need enough liquid propellant to land safely.
Title: Re: Starship heat shield
Post by: ETurner on 10/01/2021 06:53 pm
How about a honeycomb of holes drilled partially through from the inside so that if the steel starts ablating away, instead of rupturing it begins sweating gas in that portion.
Steel would soften and melt before ablating.
Well, you would certainly get some if you start venting oxygen through holes in hot metal....
But first you need small holes that go all the way through. I think what you get is either no holes or a big blowout. Not good for transpiration.
Title: Re: Starship heat shield
Post by: KelvinZero on 10/02/2021 04:06 pm
Perhaps the tanks could be designed to survive having some holes since the landing fuel is in the header tanks?

This sounds the opposite of reusable... perhaps worth thinking about to increase the odds of humans surviving a heat shield failure, but very far down the road after they have unmanned flight working reliably enough.
To clarify, yes, I was only talking about making a few broken tiles survivable for the crew.. and was assuming some sort of moderately expensive refurbishment of the vehicle eg cutting out an entire segment of the hull/tank and replacing it.

I had forgotten that the oxygen would have to get very hot while passing through the holes so that particular scheme is probably a non-starter apart from other issues.

I still think the general question is interesting though: can we make the loss of a few tiles survivable? Bonus points if your scheme requires minimal refurbishment as well.
Title: Re: Starship heat shield
Post by: abaddon on 10/02/2021 04:49 pm
STS-1 lost 16 tiles and survived (as well as suffering extensive damage on many others). It’s not impossible Starship could lose some tiles and survive.  I expect the first few orbital flights will have something to say on that front one way or another….
Title: Re: Starship heat shield
Post by: woods170 on 10/02/2021 05:23 pm
STS-1 lost 16 tiles and survived (as well as suffering extensive damage on many others). It’s not impossible Starship could lose some tiles and survive.  I expect the first few orbital flights will have something to say on that front one way or another….

Minor nit: STS-1 lost NO tiles on the hot (black) side. Only on the "cool" side, which is equivelant to the bare metal side of Starship.
Title: Starship heat shield
Post by: Bananas_on_Mars on 10/02/2021 07:58 pm
https://mobile.twitter.com/elonmusk/status/1314741760568954880 (https://mobile.twitter.com/elonmusk/status/1314741760568954880)
I remember Elon mentioned awhile ago that they're considering using transpiration cooling on some areas. In light of recent tile blowaway event, I wonder if they have completely moved away from that or still have transpiration cooling as an option, at least in areas difficult to cover with heat tiles.

I think until we see it, it seems like we have to consider it aspirational.  Elon achieves amazing stuff but he also throws some ideas at the wall which are actually dramatically harder/lower TRL than they first appear or perhaps he immediately realizes.  I suspect transpiration cooling is one such.  I don’t think we’ll see it.

Some ideas sound hard but can be done fairly quickly with care and effort.  Others are more like research projects and can’t really be rushed much.  (I guess I’m kind of just saying “are much lower TRL”.)
IIRC they‘re using transpiration cooling with water on the Falcon 9 first stage heatshield around the engines for reentry.

BTW i found a german PhD Thesis regarding transpiration cooling for CMC (Ceramic Matrix Composites) and C/C (Carbon/Carbon) structures. Haven‘t read it besides the abstract, but here‘s the link:

https://elib.uni-stuttgart.de/bitstream/11682/10685/1/Dissertation.pdf
Title: Re: Starship heat shield
Post by: AC in NC on 10/02/2021 08:24 pm
IIRC they‘re using transpiration cooling with water on the Falcon 9 first stage heatshield around the engines for reentry.
I don't believe that is correct.  I don't ever recall hearing anything like that and I think it would get enough airtime to be common knowledge if something like that existed.
Title: Re: Starship heat shield
Post by: Bananas_on_Mars on 10/02/2021 08:44 pm
IIRC they‘re using transpiration cooling with water on the Falcon 9 first stage heatshield around the engines for reentry.
I don't believe that is correct.  I don't ever recall hearing anything like that and I think it would get enough airtime to be common knowledge if something like that existed.
Ok, might be evaporation cooling (on the backside of the heatshield) instead of transpiration cooling, but here it is directly from the horses mouth:

“We replaced the old composite structure with a high-temperature titanium structure to support rapid reuse,” Musk said. “The base heat shield will also be, in some parts, actively cooled with water.”

https://spaceflightnow.com/2018/05/11/spacex-debuts-an-improved-human-rated-model-of-the-falcon-9-rocket/
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 10/02/2021 09:06 pm
...

Perhaps the tanks could be designed to survive having some holes since the landing fuel is in the header tanks?


Im am not an engineer. But we know that the tanks are pressurized otherwise the ship would crumple because of the excess weight (and the crew cabin will add weight, to the "blank" ss  that iirc would sustain itself without pressurrization). If the tanks have holes, they can't be pressurized. I could be wrong though.

For transpiration cooling you don't directly apply "holes" to the tank wall. Instead you direct small amount of CH4 to manifolds with transpiration "pores" alongsides the ship hull to achieve cooling.
I know that. If i understood correctly the original  post I quoted he meant that the main tanks could be made such that they can survive small holes caused by the local TPS failure.
Title: Re: Starship heat shield
Post by: golosio on 10/02/2021 10:13 pm
According to BradyKenniston, in the latest test on S20, in addition to the cryo test, hydraulic rams were used to simulate Raptor thrust.
Ship 20 completed its first major test before the Orbital Test Flight. It was loaded with liquid nitrogen, pressurized, and hydraulic rams were used to simulate Raptor engine thrust.
...
This sounds interesting because it means that apart from the tiles that have detached due to tank vent, the others have withstood the vibrations of this test well. Considering that it is the first time that a test of this kind has been done with the windward side entirely covered by tiles, IMO it is an excellent result, and I think there is ample margin for further improvement after the effect of the first reentries from orbital launches on tiles are known and data will be available.
Title: Re: Starship heat shield
Post by: wannamoonbase on 10/03/2021 12:03 am
According to BradyKenniston, in the latest test on S20, in addition to the cryo test, hydraulic rams were used to simulate Raptor thrust.
Ship 20 completed its first major test before the Orbital Test Flight. It was loaded with liquid nitrogen, pressurized, and hydraulic rams were used to simulate Raptor engine thrust.
...
This sounds interesting because it means that apart from the tiles that have detached due to tank vent, the others have withstood the vibrations of this test well. Considering that it is the first time that a test of this kind has been done with the windward side entirely covered by tiles, IMO it is an excellent result, and I think there is ample margin for further improvement after the effect of the first reentries from orbital launches on tiles are known and data will be available.

I agree that this is a good step forward.  However, the violent vibrations of the full stack, especially at Max Q will be the ultimate test.  If the heat shield gets through Max Q then we have something. 

Seems will be finding that out soon.  Can’t wait!
Title: Re: Starship heat shield
Post by: BT52 on 10/03/2021 08:28 am
IIRC they‘re using transpiration cooling with water on the Falcon 9 first stage heatshield around the engines for reentry.
I don't believe that is correct.  I don't ever recall hearing anything like that and I think it would get enough airtime to be common knowledge if something like that existed.
Ok, might be evaporation cooling (on the backside of the heatshield) instead of transpiration cooling, but here it is directly from the horses mouth:

“We replaced the old composite structure with a high-temperature titanium structure to support rapid reuse,” Musk said. “The base heat shield will also be, in some parts, actively cooled with water.”

https://spaceflightnow.com/2018/05/11/spacex-debuts-an-improved-human-rated-model-of-the-falcon-9-rocket/
Well many of us in this topic said. if needed, SpaceX could mount articulated sprinkler system inside tank.

Ofc could or would help in case if some tiles flew away during re-entry. Obviously if somehow whole skin doesn't do full "banana peel harakiri". As we saw this recent blowout failure that could happen quite easily. Efficacy's of said sys is in big hands of magnitude of heat transfer and where on hull would that happened. Also  depends how good wool insulation and sustained heating of steel is. Also i  must add, that i m quite (naively) confident and hopeful that Ship could survive it anyway. Just wool blanket and SS steel with active sprinkling could be one way ticket down towards emergency landing. And that is based solely on STS - 27  thermal mass luck.
Title: Re: Starship heat shield
Post by: KelvinZero on 10/04/2021 12:15 am
I know that. If i understood correctly the original  post I quoted he meant that the main tanks could be made such that they can survive small holes caused by the local TPS failure.
Yes that is what I meant. I remember hearing that the Starship tanks were not balloon tanks like the Centaur upper stage.. but I guess that does not mean they can land without pressure or support a 100 ton payload.
Title: Re: Starship heat shield
Post by: Twark_Main on 10/04/2021 11:53 am
IIRC they‘re using transpiration cooling with water on the Falcon 9 first stage heatshield around the engines for reentry.
I don't believe that is correct.  I don't ever recall hearing anything like that and I think it would get enough airtime to be common knowledge if something like that existed.
Ok, might be evaporation cooling (on the backside of the heatshield) instead of transpiration cooling, but here it is directly from the horses mouth:

“We replaced the old composite structure with a high-temperature titanium structure to support rapid reuse,” Musk said. “The base heat shield will also be, in some parts, actively cooled with water.”

https://spaceflightnow.com/2018/05/11/spacex-debuts-an-improved-human-rated-model-of-the-falcon-9-rocket/

Might just be integrated liquid cooling channels for hotspots (that's the way I originally read that quote). Circulating cold water also falls under the umbrella of "active cooling."
Title: Re: Starship heat shield
Post by: sebk on 10/04/2021 03:02 pm
...

Perhaps the tanks could be designed to survive having some holes since the landing fuel is in the header tanks?


Im am not an engineer. But we know that the tanks are pressurized otherwise the ship would crumple because of the excess weight (and the crew cabin will add weight, to the "blank" ss  that iirc would sustain itself without pressurrization). If the tanks have holes, they can't be pressurized. I could be wrong though.

Depending on hole size they could hold pressure for quite some time. For example 25cm^2 (for example 5x5cm i.e. 2"x2" for those more used to imperial) hole would lose ~1m^3/s. But this is gas, so losing entire volume of gas would reduce the pressure to 37% not to 0 (because as the gas decompresses unit volume is less of the gas). The smallest tank (Methane) is ~614m^3. It would take over 11 minutes  to get it from 3 bar to below sea level (getting below sea level would implode the tank by the end of bellyflop). If the initial pressure would be 6 bar, then it would take >18minutes to get it below sea level.

It his is methane tank, then this of course requires tank pressure control system to concurrently vent oxygen tank to prevent bulkhead inversion.
Title: Re: Starship heat shield
Post by: Echo_Jex on 10/04/2021 04:22 pm
...

Perhaps the tanks could be designed to survive having some holes since the landing fuel is in the header tanks?


Im am not an engineer. But we know that the tanks are pressurized otherwise the ship would crumple because of the excess weight (and the crew cabin will add weight, to the "blank" ss  that iirc would sustain itself without pressurrization). If the tanks have holes, they can't be pressurized. I could be wrong though.

Depending on hole size they could hold pressure for quite some time. For example 25cm^2 (for example 5x5cm i.e. 2"x2" for those more used to imperial) hole would lose ~1m^3/s. But this is gas, so losing entire volume of gas would reduce the pressure to 37% not to 0 (because as the gas decompresses unit volume is less of the gas). The smallest tank (Methane) is ~614m^3. It would take over 11 minutes  to get it from 3 bar to below sea level (getting below sea level would implode the tank by the end of bellyflop). If the initial pressure would be 6 bar, then it would take >18minutes to get it below sea level.

It his is methane tank, then this of course requires tank pressure control system to concurrently vent oxygen tank to prevent bulkhead inversion.
This is an interesting concept. This is my first post ever so don't expect this to be a great shower thought but here goes:
Assuming they have terminal velocity in belly flop when the pinhole leak is formed, and it's only releasing ullage gas, would the leak pressure would be greater than the windward pressure front, and essentially protect that spot from any further plasma/heat damage, until internal pressure starts to drop (which would take a while since the cryo would boil off internally and cool the leak/pressurize itself) and atmospheric density goes up until some zero psi Delta pressure value is reached? The instant after this moment would be just as catastrophic as the list of problems Sebk mentioned.
Title: Re: Starship heat shield
Post by: Slarty1080 on 10/04/2021 05:17 pm
...

Perhaps the tanks could be designed to survive having some holes since the landing fuel is in the header tanks?


Im am not an engineer. But we know that the tanks are pressurized otherwise the ship would crumple because of the excess weight (and the crew cabin will add weight, to the "blank" ss  that iirc would sustain itself without pressurrization). If the tanks have holes, they can't be pressurized. I could be wrong though.

Depending on hole size they could hold pressure for quite some time. For example 25cm^2 (for example 5x5cm i.e. 2"x2" for those more used to imperial) hole would lose ~1m^3/s. But this is gas, so losing entire volume of gas would reduce the pressure to 37% not to 0 (because as the gas decompresses unit volume is less of the gas). The smallest tank (Methane) is ~614m^3. It would take over 11 minutes  to get it from 3 bar to below sea level (getting below sea level would implode the tank by the end of bellyflop). If the initial pressure would be 6 bar, then it would take >18minutes to get it below sea level.

It his is methane tank, then this of course requires tank pressure control system to concurrently vent oxygen tank to prevent bulkhead inversion.
This is an interesting concept. This is my first post ever so don't expect this to be a good shower thought but here goes: Assuming they have terminal velocity in belly flop when the pinhole leak is formed, would the leak pressure PSI start higher than the perceived pressure of the windward pressure front, and essentially protect that spot from any further plasma/heat damage, until internal pressure starts to drop and atmospheric density goes up and some Delta pressure value is reached? The instant after this moment would be just as catastrophic as the list of problems Sebk mentioned.
Welcome to the forum! I would have thought that any hole in the oxygen tank causes by melting would generate a rapid disintegration as large quantities of oxygen gas came in contact with red hot steel leading to a bigger hole...
Title: Re: Starship heat shield
Post by: Twark_Main on 10/04/2021 10:14 pm
Rather than having the steel melt, it seems more feasible to have the small hole plugged by a metal that melts at a lower temperature. A thermal "fuse," essentially.
Title: Re: Starship heat shield
Post by: PraetorArcher on 10/04/2021 10:56 pm
Rather than having the steel melt, it seems more feasible to have the small hole plugged by a metal that melts at a lower temperature. A thermal "fuse," essentially.

How would you get the metal to stop melting? Are there metal pairings where the alloy has a lower melting point than either component?
Title: Re: Starship heat shield
Post by: Twark_Main on 10/04/2021 10:59 pm
In early days of developing its recoverable spacecraft, China used ablative Cork heatshields . ( ( Thickness unknown ).Images exist showing several recovered spacecraft with these heatshields with craft intact.

...

Could it be exploited ?

Rather than Chinese " copying USA/Russia" let's " copy China" !


Phill

Falcon 9 used a cork heat shield in the early days (https://spaceflightnow.com/falcon9/001/100416wdrobama/index.html), so they're familiar with the material. It's just not a good fit for this (fully and rapidly reusable) application.

Can anyone dig up any pictures of these Chinese cork heat shields? I'm not finding anything. :(
Title: Re: Starship heat shield
Post by: Twark_Main on 10/04/2021 11:18 pm
Rather than having the steel melt, it seems more feasible to have the small hole plugged by a metal that melts at a lower temperature. A thermal "fuse," essentially.

How would you get the metal to stop melting? Are there metal pairings where the alloy has a lower melting point than either component?

For the "fusible plug" (picture a rivet except it doesn't hold two things together) you'd simply choose an alloy with a melting point that's just below the Do Not Exceed temperature of the hull, but higher than the hull temperature with nominal tile coverage.

If tiles are shed in-flight and the hull becomes in danger of overheating, then the fusible plug melts releasing transpiration gas from the tank. But if the tiles are intact then the fusible plug doesn't get hot enough to melt.

Naturally the chosen alloy would need to be compatible with 304 stainless in terms of galvanic corrosion, CTE, etc.

The surrounding steel never gets hot enough to melt, so it doesn't alloy with the plug.
Title: Re: Starship heat shield
Post by: Eric Hedman on 10/04/2021 11:24 pm
Rather than having the steel melt, it seems more feasible to have the small hole plugged by a metal that melts at a lower temperature. A thermal "fuse," essentially.

How would you get the metal to stop melting? Are there metal pairings where the alloy has a lower melting point than either component?
Eutectoid Alloys:

https://qph.fs.quoracdn.net/main-qimg-588a27248dcd65f82663b42c1e4a71f9 (https://qph.fs.quoracdn.net/main-qimg-588a27248dcd65f82663b42c1e4a71f9)

This is a generic graph phase diagram of Eutectoid pairs.  Carbon steel is a eutectoid pair.

Edit - added a better description:

https://metallurgyfordummies.com/eutectoid-alloys.html (https://metallurgyfordummies.com/eutectoid-alloys.html)
Title: Re: Starship heat shield
Post by: envy887 on 10/05/2021 01:38 am
...

Perhaps the tanks could be designed to survive having some holes since the landing fuel is in the header tanks?


Im am not an engineer. But we know that the tanks are pressurized otherwise the ship would crumple because of the excess weight (and the crew cabin will add weight, to the "blank" ss  that iirc would sustain itself without pressurrization). If the tanks have holes, they can't be pressurized. I could be wrong though.

Depending on hole size they could hold pressure for quite some time. For example 25cm^2 (for example 5x5cm i.e. 2"x2" for those more used to imperial) hole would lose ~1m^3/s. But this is gas, so losing entire volume of gas would reduce the pressure to 37% not to 0 (because as the gas decompresses unit volume is less of the gas). The smallest tank (Methane) is ~614m^3. It would take over 11 minutes  to get it from 3 bar to below sea level (getting below sea level would implode the tank by the end of bellyflop). If the initial pressure would be 6 bar, then it would take >18minutes to get it below sea level.

It his is methane tank, then this of course requires tank pressure control system to concurrently vent oxygen tank to prevent bulkhead inversion.
This is an interesting concept. This is my first post ever so don't expect this to be a good shower thought but here goes: Assuming they have terminal velocity in belly flop when the pinhole leak is formed, would the leak pressure PSI start higher than the perceived pressure of the windward pressure front, and essentially protect that spot from any further plasma/heat damage, until internal pressure starts to drop and atmospheric density goes up and some Delta pressure value is reached? The instant after this moment would be just as catastrophic as the list of problems Sebk mentioned.
Welcome to the forum! I would have thought that any hole in the oxygen tank causes by melting would generate a rapid disintegration as large quantities of oxygen gas came in contact with red hot steel leading to a bigger hole...

That doesn't happen with stainless steels, for the same reasons that they don't really rust. The chemistry dynamics don't favor forming iron oxides. You can't cut stainless with a oxygen torch, either.

Also, it won't be hot for long, because the escaping oxygen gas is about 1,000 C colder than the steel and will cool it down if there's any significant flow. The only energy source is the reentry plasma, and if the escaping gas is pushing the plasma away, it will go cold.
Title: Re: Starship heat shield
Post by: TomH on 10/05/2021 03:47 am
...the escaping oxygen gas is about 1,000 C colder than the steel and will cool it down if there's any significant flow. The only energy source is the reentry plasma, and if the escaping gas is pushing the plasma away, it will go cold.

Also, expanding gas gets colder as the finite amount of heat within it is spread throughout a larger volume. Not sure how much of the heat might be carried away by convection. If the prop is liquid, a significant amount of heat might possibly be absorbed by enthalpy of evaporative state change.
Title: Re: Starship heat shield
Post by: DanClemmensen on 10/05/2021 03:56 am
I'm a bit concerned about releasing oxygen to cool the steel. Steel can burn. The ignition temperature of steel is maybe 1350 F, well below its melting point. If you supply oxygen, it will ignite and any hole will expand catastrophically.
Title: Re: Starship heat shield
Post by: Twark_Main on 10/05/2021 04:04 am
I'm a bit concerned about releasing oxygen to cool the steel. Steel can burn. The ignition temperature of steel is maybe 1350 F, well below its melting point. If you supply oxygen, it will ignite and any hole will expand catastrophically.

Therein lies the beauty of using a fusible plug. You can choose a low enough melting point to avoid any issues, since you're not depending on the actual steel itself melting.
Title: Re: Starship heat shield
Post by: edzieba on 10/05/2021 12:37 pm
The tanks are pressure stabilised for all operations other than standing still while empty, or floating in microgravity. During EDL, they must remain pressurised to flight pressure or the vehicle buckles and fails. Worse, while the tanks have nominal stringers to allow self-supporting when empty and unpressurised, in flight the tanks act as balloon tanks. Holes are contraindicated.

Rather than hoping a failed tile somehow results in merely a pinhole leak (rather than a weakened area the size of a failed tile ready to blow out once weak enough), better to avoid exposing the tank skin to reentry plasma in the first place.
Title: Re: Starship heat shield
Post by: AC in NC on 10/05/2021 03:26 pm
The tanks are pressure stabilised for all operations other than standing still while empty, or floating in microgravity. During EDL, they must remain pressurised to flight pressure or the vehicle buckles and fails. Worse, while the tanks have nominal stringers to allow self-supporting when empty and unpressurised, in flight the tanks act as balloon tanks. Holes are contraindicated.

Rather than hoping a failed tile somehow results in merely a pinhole leak (rather than a weakened area the size of a failed tile ready to blow out once weak enough), better to avoid exposing the tank skin to reentry plasma in the first place.

Precisely.

We seem to regularly get discussions crop up that are intellectually interesting but seem (to my eye at least) so far removed from anything that would ever be considered that I can't believe we're actually discussing them.  I suppose you have to in order to avoid shutting down the creative process, but OMG they are not going to do this.

Transpiration cooling is one thing.  This engineered failure-mode based cooling is off the charts.
Title: Re: Starship heat shield
Post by: envy887 on 10/05/2021 03:29 pm
The tanks are pressure stabilised for all operations other than standing still while empty, or floating in microgravity. During EDL, they must remain pressurised to flight pressure or the vehicle buckles and fails. Worse, while the tanks have nominal stringers to allow self-supporting when empty and unpressurised, in flight the tanks act as balloon tanks. Holes are contraindicated.

Rather than hoping a failed tile somehow results in merely a pinhole leak (rather than a weakened area the size of a failed tile ready to blow out once weak enough), better to avoid exposing the tank skin to reentry plasma in the first place.

The internal pressure needed to keep the main tanks from buckling during the landing burn is probably quite low compared to the pressure needed to resist ascent loads and feed the Raptors.

If the landing acceleration is 2 gees and the payload and other associated mass are 150 t, than only about 0.5 bar (gauge) pressure is needed to keep the structure in tension so it cannot buckle. That's only about 8% of the roughly 6 bar needed during ascent, and because at landing it's filled with gas rather than liquid the head pressure is trivial.

ISTM this means the necessary local steel strength behind a failed tile can be reduced by over 90% (compared to its condition during ascent) without being any more likely to burst a hole than it is during ascent.

As it turns out, this is the approximate reduction in the strength of stainless steel 304 as it increases from LOX temps (-180C) to reentry surface equilibrium temps (around 1000 to 1200 C). So even if the fiber pad is useless (it isn't), the temperature of the tank wall on reentry in even of a tile loss may not be an issue at all.
Title: Re: Starship heat shield
Post by: DanClemmensen on 10/05/2021 03:55 pm
I'm a bit concerned about releasing oxygen to cool the steel. Steel can burn. The ignition temperature of steel is maybe 1350 F, well below its melting point. If you supply oxygen, it will ignite and any hole will expand catastrophically.

Therein lies the beauty of using a fusible plug. You can choose a low enough melting point to avoid any issues, since you're not depending on the actual steel itself melting.

That's not the point. It does not matter how the oxygen gets to the surface of the steel: melt plugs, transpiration, whatever. If that surface is above the ignition temperature of steel, it will burn in that oxygen.  IMO they will just let the LOX and LCH4 cool the steel from the inside, and then find the best way to move the heat out of the liquid.
Title: Re: Starship heat shield
Post by: Twark_Main on 10/05/2021 05:43 pm
The tanks are pressure stabilised for all operations other than standing still while empty, or floating in microgravity. During EDL, they must remain pressurised to flight pressure or the vehicle buckles and fails. Worse, while the tanks have nominal stringers to allow self-supporting when empty and unpressurised, in flight the tanks act as balloon tanks. Holes are contraindicated.

Rather than hoping a failed tile somehow results in merely a pinhole leak (rather than a weakened area the size of a failed tile ready to blow out once weak enough), better to avoid exposing the tank skin to reentry plasma in the first place.

See Sebk's post upthread:

...

Perhaps the tanks could be designed to survive having some holes since the landing fuel is in the header tanks?


Im am not an engineer. But we know that the tanks are pressurized otherwise the ship would crumple because of the excess weight (and the crew cabin will add weight, to the "blank" ss  that iirc would sustain itself without pressurrization). If the tanks have holes, they can't be pressurized. I could be wrong though.

Depending on hole size they could hold pressure for quite some time. For example 25cm^2 (for example 5x5cm i.e. 2"x2" for those more used to imperial) hole would lose ~1m^3/s. But this is gas, so losing entire volume of gas would reduce the pressure to 37% not to 0 (because as the gas decompresses unit volume is less of the gas). The smallest tank (Methane) is ~614m^3. It would take over 11 minutes  to get it from 3 bar to below sea level (getting below sea level would implode the tank by the end of bellyflop). If the initial pressure would be 6 bar, then it would take >18minutes to get it below sea level.

It his is methane tank, then this of course requires tank pressure control system to concurrently vent oxygen tank to prevent bulkhead inversion.

Obviously having a hole in the tank is bad, but it's certainly less "contraindicated" than the hull actually melting due to tile loss.
Title: Re: Starship heat shield
Post by: Twark_Main on 10/05/2021 05:43 pm
I'm a bit concerned about releasing oxygen to cool the steel. Steel can burn. The ignition temperature of steel is maybe 1350 F, well below its melting point. If you supply oxygen, it will ignite and any hole will expand catastrophically.

Therein lies the beauty of using a fusible plug. You can choose a low enough melting point to avoid any issues, since you're not depending on the actual steel itself melting.

That's not the point. It does not matter how the oxygen gets to the surface of the steel: melt plugs, transpiration, whatever. If that surface is above the ignition temperature of steel, it will burn in that oxygen.  IMO they will just let the LOX and LCH4 cool the steel from the inside, and then find the best way to move the heat out of the liquid.

Obviously, the entire point would be to use a fusible plug that melts below said "ignition temperature of steel."
Title: Re: Starship heat shield
Post by: Twark_Main on 10/05/2021 05:46 pm
The tanks are pressure stabilised for all operations other than standing still while empty, or floating in microgravity. During EDL, they must remain pressurised to flight pressure or the vehicle buckles and fails. Worse, while the tanks have nominal stringers to allow self-supporting when empty and unpressurised, in flight the tanks act as balloon tanks. Holes are contraindicated.

Rather than hoping a failed tile somehow results in merely a pinhole leak (rather than a weakened area the size of a failed tile ready to blow out once weak enough), better to avoid exposing the tank skin to reentry plasma in the first place.

Precisely.

We seem to regularly get discussions crop up that are intellectually interesting but seem (to my eye at least) so far removed from anything that would ever be considered that I can't believe we're actually discussing them.  I suppose you have to in order to avoid shutting down the creative process, but OMG they are not going to do this.

Transpiration cooling is one thing.  This engineered failure-mode based cooling is off the charts.

Just like catching Super Heavy with a giant tower, right?  ::)
Title: Re: Starship heat shield
Post by: matthewkantar on 10/05/2021 05:47 pm
Just like catching Super Heavy with a giant tower, right?  ::)

No, not really. SpaceX has been public about aspirations to land stages on or near the launch mount for 5 years or so. They have never mentioned Swiss cheesing the propellant tanks.
Title: Re: Starship heat shield
Post by: Twark_Main on 10/05/2021 05:54 pm
Just like catching Super Heavy with a giant tower, right?  ::)

No, not really. SpaceX has been public about aspirations to land stages on or near the launch mount for 5 years or so.

You're missing the point. People still argued that 'common sense' says not to do that, just like you're arguing above.

Also, the "catching it with arms" concept isn't that old. You're conflating it with "landing on or near the launch mount," which is not the same thing.

They have never mentioned Swiss cheesing the propellant tanks.

I'm not arguing that SpaceX is doing this. I'm arguing that SpaceX should do this.

What I'm failing to see are any actual technical arguments as to why this concept wouldn't work. Specifically, how is complete hull failure leading to LOV / LOC preferable to replacing a few rivets before re-tiling? ???

Title: Re: Starship heat shield
Post by: ETurner on 10/05/2021 06:15 pm
What I'm failing to see are any actual technical arguments as to why this concept wouldn't work. Specifically, how is complete hull failure leading to LOV / LOC preferable to replacing a few rivets before re-tiling? ???
A key point is that having arrays of small holes for your fusible-rivets wouldn’t “swiss-cheese” anything. The amount of metal removed could be very small, and the strength reduction seems negligible. Whether this scheme is, in the end, an actual good idea is of course questionable, but it is at least surprisingly plausible. My vote: Cool!
Title: Re: Starship heat shield
Post by: AC in NC on 10/05/2021 06:23 pm
Just like catching Super Heavy with a giant tower, right?  ::)

No, not really. SpaceX has been public about aspirations to land stages on or near the launch mount for 5 years or so.

You're missing the point. People still argued that 'common sense' says not to do that, just like you're arguing above.

Also, the "catching it with arms" concept isn't that old. You're conflating it with "landing on or near the launch mount," which is not the same thing.

They have never mentioned Swiss cheesing the propellant tanks.

I'm not arguing that SpaceX is doing this. I'm arguing that SpaceX should do this.

What I'm failing to see are any actual technical arguments as to why this concept wouldn't work. Specifically, how is complete hull failure leading to LOV / LOC preferable to replacing a few rivets before re-tiling? ???

You are missing the point.  Wild ideas lie on a spectrum.  It's not a binary where "Oh, some other idea argued as 'not common sense' was adopted so anyone that argues 'not common sense' is, by default, automatically on shaky ground.

Catching on arms and catching on mount are closely related enough that they might as well be the same concept on the wild ideas spectrum.  There's not much qualitatively different about them as relates to the trades.

Of course it could probably be made to work, but LOV/LOC vs. Few Rivets is a false dichotomy.

The question is whether pursuing an incrementally better TPS is far more sensible than chasing an enormously complicated pipe dream for a case that should never be allowed to happen anyway.
Title: Re: Starship heat shield
Post by: androvsky on 10/05/2021 07:10 pm

You're missing the point. People still argued that 'common sense' says not to do that, just like you're arguing above.

Also, the "catching it with arms" concept isn't that old. You're conflating it with "landing on or near the launch mount," which is not the same thing.

They have never mentioned Swiss cheesing the propellant tanks.

I'm not arguing that SpaceX is doing this. I'm arguing that SpaceX should do this.

What I'm failing to see are any actual technical arguments as to why this concept wouldn't work. Specifically, how is complete hull failure leading to LOV / LOC preferable to replacing a few rivets before re-tiling? ???
It doesn't help with the cargo, fin, or skirt sections of the hull, so it's a problem that has to be solved a different way anyway. Might as well solve it for the whole vehicle.

They'd also be adding (tens of?) thousands of potential leak points to make normal vehicle use more difficult. Now you have thousands of seals that have to hold up in cryo temperatures, high (but deliberately not reentry) temps, and in space, and be reusable over many normal flights. If you use a metal alloy plug or stud that melts at the desired temperature, it won't keep up with tank stretching and contracting in different temperatures well. If you use something flexible, it's going to have a hard time with the cryo and/or high temperatures.

I think it's an interesting idea that might make the tank sections safer, but those are the potential problems I came up with.

If it were me, I'd go with the hint someone mentioned earlier in the thread about steel cookware needing an aluminum or copper coating to actually spread heat around. I can't help but wonder how thick (and heavy, and expensive) a copper coating on the inside of the tanks, skirt, and nosecone would have be to effectively spread heat to cooler parts of the ship if a few tiles were lost.
Title: Re: Starship heat shield
Post by: edzieba on 10/05/2021 07:17 pm
The tanks are pressure stabilised for all operations other than standing still while empty, or floating in microgravity. During EDL, they must remain pressurised to flight pressure or the vehicle buckles and fails. Worse, while the tanks have nominal stringers to allow self-supporting when empty and unpressurised, in flight the tanks act as balloon tanks. Holes are contraindicated.

Rather than hoping a failed tile somehow results in merely a pinhole leak (rather than a weakened area the size of a failed tile ready to blow out once weak enough), better to avoid exposing the tank skin to reentry plasma in the first place.

The internal pressure needed to keep the main tanks from buckling during the landing burn is probably quite low compared to the pressure needed to resist ascent loads and feed the Raptors.
The dynamic off-axis loading of the landing manoeuvre are more strenuous than the loads of launch.
Take a coke/beer can: to scale it is far thicker than the tank walls of Starship but it'll do for now. Empty it, then try and crush it vertically (along the long axis) without any angled force (put a book on top and press in the centre of that to minimise off-axis force). How take another can and try grabbing the ends of bending it. Far less force is needed before buckling occurs when torsion is involved than with purely axial loading, and the landing manoeuvre torsions the hell out of Starship.
For bonus points, poke a hole with a fine needle and perform the two tests again, and see how that influences the origin of the first buckling failure.
Obviously having a hole in the tank is bad, but it's certainly less "contraindicated" than the hull actually melting due to tile loss.
A hold is not like the vents in the tanks that nicely allow a controlled pressure release. Note how all the valves and vents on Starship are heavily gusseted: that's not mass added for fun, it's to avoid the tank wall ripping apart.
Title: Re: Starship heat shield
Post by: Slothman on 10/05/2021 08:02 pm
I'm a bit concerned about releasing oxygen to cool the steel. Steel can burn. The ignition temperature of steel is maybe 1350 F, well below its melting point. If you supply oxygen, it will ignite and any hole will expand catastrophically.

Therein lies the beauty of using a fusible plug. You can choose a low enough melting point to avoid any issues, since you're not depending on the actual steel itself melting.

That's not the point. It does not matter how the oxygen gets to the surface of the steel: melt plugs, transpiration, whatever. If that surface is above the ignition temperature of steel, it will burn in that oxygen.  IMO they will just let the LOX and LCH4 cool the steel from the inside, and then find the best way to move the heat out of the liquid.

How about a grid of small diameter pipes outside of the tank under the tiles, think under-floor heating. This can have fusible plugs like a fire suppression system without making a hole in the tank. It's just a bunch of added weight.
Title: Re: Starship heat shield
Post by: ETurner on 10/05/2021 08:09 pm

You're missing the point. People still argued that 'common sense' says not to do that, just like you're arguing above.

Also, the "catching it with arms" concept isn't that old. You're conflating it with "landing on or near the launch mount," which is not the same thing.

They have never mentioned Swiss cheesing the propellant tanks.

I'm not arguing that SpaceX is doing this. I'm arguing that SpaceX should do this.

What I'm failing to see are any actual technical arguments as to why this concept wouldn't work. Specifically, how is complete hull failure leading to LOV / LOC preferable to replacing a few rivets before re-tiling? ???
It doesn't help with the cargo, fin, or skirt sections of the hull, so it's a problem that has to be solved a different way anyway. Might as well solve it for the whole vehicle.

They'd also be adding (tens of?) thousands of potential leak points to make normal vehicle use more difficult. Now you have thousands of seals that have to hold up in cryo temperatures, high (but deliberately not reentry) temps, and in space, and be reusable over many normal flights. If you use a metal alloy plug or stud that melts at the desired temperature, it won't keep up with tank stretching and contracting in different temperatures well. If you use something flexible, it's going to have a hard time with the cryo and/or high temperatures.

I think it's an interesting idea that might make the tank sections safer, but those are the potential problems I came up with.
These are strong points. To keep the idea in the maybe-possibly-viable range would require candidate “rivet” materials that simultaneously meet several maybe-incompatible criteria: low(ish) melting point, compatible-enough thermal expansion coefficient, and OK w.r.t. galvanic corrosion problems. Turning the critic’s hat backward, could small holes (mm-scale) be drilled then filled with a brazing material?

If it were me, I'd go with the hint someone mentioned earlier in the thread about steel cookware needing an aluminum or copper coating to actually spread heat around. I can't help but wonder how thick (and heavy, and expensive) a copper coating on the inside of the tanks, skirt, and nosecone would have be to effectively spread heat to cooler parts of the ship if a few tiles were lost.
To provide a useful increment in thermal conduction, the aluminum or copper layer would have to be quite thick and heavy.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 10/05/2021 08:19 pm

You're missing the point. People still argued that 'common sense' says not to do that, just like you're arguing above.

Also, the "catching it with arms" concept isn't that old. You're conflating it with "landing on or near the launch mount," which is not the same thing.

They have never mentioned Swiss cheesing the propellant tanks.

I'm not arguing that SpaceX is doing this. I'm arguing that SpaceX should do this.

What I'm failing to see are any actual technical arguments as to why this concept wouldn't work. Specifically, how is complete hull failure leading to LOV / LOC preferable to replacing a few rivets before re-tiling? ???
It doesn't help with the cargo, fin, or skirt sections of the hull, so it's a problem that has to be solved a different way anyway. Might as well solve it for the whole vehicle.

They'd also be adding (tens of?) thousands of potential leak points to make normal vehicle use more difficult. Now you have thousands of seals that have to hold up in cryo temperatures, high (but deliberately not reentry) temps, and in space, and be reusable over many normal flights. If you use a metal alloy plug or stud that melts at the desired temperature, it won't keep up with tank stretching and contracting in different temperatures well. If you use something flexible, it's going to have a hard time with the cryo and/or high temperatures.

I think it's an interesting idea that might make the tank sections safer, but those are the potential problems I came up with.

If it were me, I'd go with the hint someone mentioned earlier in the thread about steel cookware needing an aluminum or copper coating to actually spread heat around. I can't help but wonder how thick (and heavy, and expensive) a copper coating on the inside of the tanks, skirt, and nosecone would have be to effectively spread heat to cooler parts of the ship if a few tiles were lost.

Thank you for making a technical argument against a fun creative idea, instead of just throwing rhetoric like "Rube Goldberg" around.

(Note, Rube Goldberg in the age of robotics is not a useful argument in many cases.  30 years ago placing thousands of pins accurately on a cylinder would have been Rube Goldberg, it no longer is.)
Title: Re: Starship heat shield
Post by: InterestedEngineer on 10/05/2021 08:25 pm
I'm a bit concerned about releasing oxygen to cool the steel. Steel can burn. The ignition temperature of steel is maybe 1350 F, well below its melting point. If you supply oxygen, it will ignite and any hole will expand catastrophically.

Therein lies the beauty of using a fusible plug. You can choose a low enough melting point to avoid any issues, since you're not depending on the actual steel itself melting.

That's not the point. It does not matter how the oxygen gets to the surface of the steel: melt plugs, transpiration, whatever. If that surface is above the ignition temperature of steel, it will burn in that oxygen.  IMO they will just let the LOX and LCH4 cool the steel from the inside, and then find the best way to move the heat out of the liquid.

How about a grid of small diameter pipes outside of the tank under the tiles, think under-floor heating. This can have fusible plugs like a fire suppression system without making a hole in the tank. It's just a bunch of added weight.

I can't imagine the leaks on thousands of meters of small pipes from the vibrations of engines.  There's thousands of joints that can vibrate apart.   I've had a copper pipe leak on an inside wall of my house from the use of nailguns on an outside wall.

Probably the same reason SpaceX abandoned transpiration cooling.

*if*  one can automate the placement of microholes by robots with appropriate thermal 'fuseable plug', that would still be less of a maintenance headache.   But alas only works on the LCH4 section.
Title: Re: Starship heat shield
Post by: AC in NC on 10/05/2021 08:58 pm
Thank you for making a technical argument against a fun creative idea, instead of just throwing rhetoric like "Rube Goldberg" around.

(Note, Rube Goldberg in the age of robotics is not a useful argument in many cases.  30 years ago placing thousands of pins accurately on a cylinder would have been Rube Goldberg, it no longer is.)

And yet it's perfectly apropos here precisely because it's not 30 years from now.  If in 30 years it's no longer a Rube Goldberg idea, then it won't be labelled such just as Robotic Pinning isn't labelled that now.

I just fail to see how anyone with a modicum of engineering background thinks that intentionally designing a pressure vessel to be perforated for an edge case is reasonable and something that the astronauts will find to be a fun creative idea.  It's taking a fairly straightforward concern and responding in a ridiculously complicated manner introducing all kinds of complexity and altering the integrity of the tank over its entire lifetime for that edge case that may never happen, may not be an issue if it does, and could be addressed in far simpler ways.  That's RGB.  Rube Goldberg Baby.
Title: Re: Starship heat shield
Post by: androvsky on 10/05/2021 09:04 pm

You're missing the point. People still argued that 'common sense' says not to do that, just like you're arguing above.

Also, the "catching it with arms" concept isn't that old. You're conflating it with "landing on or near the launch mount," which is not the same thing.

They have never mentioned Swiss cheesing the propellant tanks.

I'm not arguing that SpaceX is doing this. I'm arguing that SpaceX should do this.

What I'm failing to see are any actual technical arguments as to why this concept wouldn't work. Specifically, how is complete hull failure leading to LOV / LOC preferable to replacing a few rivets before re-tiling? ???
It doesn't help with the cargo, fin, or skirt sections of the hull, so it's a problem that has to be solved a different way anyway. Might as well solve it for the whole vehicle.

They'd also be adding (tens of?) thousands of potential leak points to make normal vehicle use more difficult. Now you have thousands of seals that have to hold up in cryo temperatures, high (but deliberately not reentry) temps, and in space, and be reusable over many normal flights. If you use a metal alloy plug or stud that melts at the desired temperature, it won't keep up with tank stretching and contracting in different temperatures well. If you use something flexible, it's going to have a hard time with the cryo and/or high temperatures.

I think it's an interesting idea that might make the tank sections safer, but those are the potential problems I came up with.
These are strong points. To keep the idea in the maybe-possibly-viable range would require candidate “rivet” materials that simultaneously meet several maybe-incompatible criteria: low(ish) melting point, compatible-enough thermal expansion coefficient, and OK w.r.t. galvanic corrosion problems. Turning the critic’s hat backward, could small holes (mm-scale) be drilled then filled with a brazing material?
If the diameter of the hole is smaller than the thickness of the steel, maybe that does help? It feels like the expansion ratio would still be an issue, but I'm not a materials engineer. But then there's a question of how big the holes have to be in order to be effective. It did cause me to start imagining the Raptors ingesting bits of formally molten plug material, which could cause issues upon landing if they did need to melt due to a lost tile.

Quote
If it were me, I'd go with the hint someone mentioned earlier in the thread about steel cookware needing an aluminum or copper coating to actually spread heat around. I can't help but wonder how thick (and heavy, and expensive) a copper coating on the inside of the tanks, skirt, and nosecone would have be to effectively spread heat to cooler parts of the ship if a few tiles were lost.
To provide a useful increment in thermal conduction, the aluminum or copper layer would have to be quite thick and heavy.
That's too bad, but kinda what I figured. Might be interesting to run the numbers at some point if I ever had some spare time.
Title: Re: Starship heat shield
Post by: marsbase on 10/05/2021 09:45 pm
It's taking a fairly straightforward concern and responding in a ridiculously complicated manner introducing all kinds of complexity and altering the integrity of the tank over its entire lifetime for that edge case that may never happen, may not be an issue if it does, and could be addressed in far simpler ways.
I tend to agree with you that risking the integrity of the entire tank is doubtful.  And yet..... something is going on with transpirational cooling.  So there must be hot spots that require some non-conventional solution.  And Elon's mention of ITAR suggests that this solution is sophisticated and non-obvious to the point of being a national security issue. So the fusible plug idea, perhaps coupled with an upstream valve, might offer failsafe protection against disaster.  It might be done only with methane and it might be intermittent.  Something is going on beyond tiles so I don't want to assume that even crazy ideas are impossible.  :)
Title: Re: Starship heat shield
Post by: Redclaws on 10/05/2021 09:58 pm
I will be very excited to be wrong about this, but I will lay a bet here:
I do not think any significant use of transpirational cooling will fly on a SpaceX vehicle in the next 5 years.  I feel like we are letting our optimism get away from us and drawing inspiration from extremely thin evidence.

Of course, I’d be very happy to be wrong!
Title: Re: Starship heat shield
Post by: DanClemmensen on 10/05/2021 10:01 pm
If it were me, I'd go with the hint someone mentioned earlier in the thread about steel cookware needing an aluminum or copper coating to actually spread heat around. I can't help but wonder how thick (and heavy, and expensive) a copper coating on the inside of the tanks, skirt, and nosecone would have be to effectively spread heat to cooler parts of the ship if a few tiles were lost.
Quality stainless steel cookware does not have a "copper coating". Cheap cookware has a coating to make it look like older expensive copper-bottomed cookware. Quality stainless steel cookware has an embedded fairly thick copper plate.  For the tank skins, the LOX and LCH4 will move heat far more efficiently by convection than any conceivable solid heat spreader. For the rest of the under-TPS hull, you need convection of some sort, possibly heat pipes.
Title: Re: Starship heat shield
Post by: ETurner on 10/05/2021 10:25 pm
Why cooling “only with methane”?
Is there any evidence that combustion is a risk for stainless?

Experimental evidence says otherwise:
Quote
From COMBUSTION OF METALS IN OXYGEN PHASE II: BULK BURNING EXPERIMENTS (https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nbsir73-345.pdf),  NBSIR 73-345:

“…we found that 304L stainless steel, if brought to its melting point and allowed to spread out in a layer not more than 1 /4 inch thick on a poorly conducting surface, would burn to completion if the oxygen pressure was over 50 psig.” (emphasis in the original text, pg 2)

“In no case did we seem to get ignition before melting....Sustained burning [of already-molten 304L] will not occur generally below 50 psig of oxygen.” (pg 19)
So, combustion conditions = melting point & high oxygen pressure, not merely hot at lower pressure.

I think we’ve seen some exaggeration of the combustibility of stainless steel in several discussions in this forum.
Maybe people are confusing 304L (Starship Stainless®) with other steel alloys (or with aluminum or something)?

Net assessment so far: Small fusible plugs in tank walls might possibly be good for something, somewhere, sometime -- or not.
Title: Re: Starship heat shield
Post by: Twark_Main on 10/05/2021 11:18 pm
What I'm failing to see are any actual technical arguments as to why this concept wouldn't work. Specifically, how is complete hull failure leading to LOV / LOC preferable to replacing a few rivets before re-tiling? ???

You are missing the point.  Wild ideas lie on a spectrum.  It's not a binary where "Oh, some other idea argued as 'not common sense' was adopted so anyone that argues 'not common sense' is, by default, automatically on shaky ground.

Catching on arms and catching on mount are closely related enough that they might as well be the same concept on the wild ideas spectrum.  There's not much qualitatively different about them as relates to the trades.

Similarly with this concept and "transpiration cooling."

The advantage of this over transpiration cooling is that it eliminates all the plumbing.

Of course it could probably be made to work, but LOV/LOC vs. Few Rivets is a false dichotomy.

The question is whether pursuing an incrementally better TPS is far more sensible than chasing an enormously complicated pipe dream for a case that should never be allowed to happen anyway.

"To design a spacecraft right takes an infinite amount of effort. This is why it's a good idea to design them to operate when some things are wrong."  -- Akin's Second Law of Spacecraft Design (https://spacecraft.ssl.umd.edu/akins_laws.html)
Title: Re: Starship heat shield
Post by: Twark_Main on 10/05/2021 11:22 pm
These are strong points. To keep the idea in the maybe-possibly-viable range would require candidate “rivet” materials that simultaneously meet several maybe-incompatible criteria: low(ish) melting point, compatible-enough thermal expansion coefficient, and OK w.r.t. galvanic corrosion problems.

Indeed. As I wrote,

Naturally the chosen alloy would need to be compatible with 304 stainless in terms of galvanic corrosion, CTE, etc.

Turning the critic’s hat backward, could small holes (mm-scale) be drilled then filled with a brazing material?

I'm curious if the holes could be machined to be larger diameter on the interior than on either end. This way the brazed "plug" would automatically be captive within the hole.

The material is only 3-4 mm thick, so  :-\
Title: Re: Starship heat shield
Post by: Twark_Main on 10/05/2021 11:29 pm
Thank you for making a technical argument against a fun creative idea, instead of just throwing rhetoric like "Rube Goldberg" around.

(Note, Rube Goldberg in the age of robotics is not a useful argument in many cases.  30 years ago placing thousands of pins accurately on a cylinder would have been Rube Goldberg, it no longer is.)

And yet it's perfectly apropos here precisely because it's not 30 years from now.  If in 30 years it's no longer a Rube Goldberg idea, then it won't be labelled such just as Robotic Pinning isn't labelled that now.

Or 1 year, given SpaceX timelines.  ;D

I just fail to see how anyone with a modicum of engineering background thinks that intentionally designing a pressure vessel to be perforated for an edge case is reasonable and something that the astronauts will find to be a fun creative idea.  It's taking a fairly straightforward concern and responding in a ridiculously complicated manner introducing all kinds of complexity and altering the integrity of the tank over its entire lifetime for that edge case that may never happen, may not be an issue if it does, and could be addressed in far simpler ways.  That's RGB.  Rube Goldberg Baby.

I think this is one of those "obvious in hindsight" issues where the safety backup will only be added in the wake of a very public failure. That's part of the SpaceX iterative design philosophy -- don't add it until you know you need it.

It will be very interesting to see the results of the first Starship reentry test.


AFAICT this "belt and suspenders" approach combines the best of both worlds: tiles as the fully-reusable primary heat shield, with a super-lightweight and ultra-simplified contingency transpiration system covering the primary failure mode of the tiles.
Title: Re: Starship heat shield
Post by: AC in NC on 10/05/2021 11:50 pm
Similarly with this concept and "transpiration cooling."

The advantage of this over transpiration cooling is that it eliminates all the plumbing.

"To design a spacecraft right takes an infinite amount of effort. This is why it's a good idea to design them to operate when some things are wrong."  -- Akin's Second Law of Spacecraft Design (https://spacecraft.ssl.umd.edu/akins_laws.html)

Not similar at all.  Mount Catching and Arm catching are alternatives ... you don't need both.  Planned-Perforation can't address all Primary and Backup Cooling needs.

I think this is one of those "obvious in hindsight" issues where the safety backup will only be added in the wake of a very public failure. That's part of the SpaceX iterative design philosophy -- don't add it until you know you need it.

It will be very interesting to see the results of the first Starship reentry test.

AFAICT this "belt and suspenders" approach combines the best of both worlds: tiles as the fully-reusable primary heat shield, with a super-lightweight and ultra-simplified contingency transpiration system covering the primary failure mode of the tiles.

Perhaps.  I agree the safety backup needs to be addressed early before any high-profile failure.  I don't think Planned-Perforation is very good for anything other than a last line of defense and it's too complex to be worth investing in as a last line of defense given that you'd still need other lines.  Better to beef up the other elements of the system.

This is one of those things that's speciously compelling, becoming a hobby-horse once it gets it worms it past your initial incredulity.  Be stronger.
Title: Re: Starship heat shield
Post by: chopsticks on 10/06/2021 12:57 am
I think we're putting the cart before the horse with this perforated hull thing. Clearly SpaceX is going to try tiles first - why not let them? From Tim Dodd's interview with Elon, it was clear that they don't overthink things; it's a waste of time. Some decision was made to try the tiles and see what happens. I have no doubt that if it doesn't end up being a good solution they will move on to something else but until then they're probably not all stressed about finding all sorts of backup methods until they first see how the cards fall.
Title: Re: Starship heat shield
Post by: marsbase on 10/06/2021 12:59 am
1)  Similar is a meaningless word.  Perforation cooling and Transpiration Cooling are similar in that the concepts do similar things (namely:  "cool" ... duh) but are completely different in that they cannot address the same scenarios.  Quit trying to play semantic games.
This is getting strange.  Exactly what do you think transpiration is anyway?  It means the movement of water from the stomata of a leaf.  In the most general sense, it is the movement of a fluid (or gas) through a perforation.  There is the related concept of the evaporation of the fluid causing a "transpiration pressure" which pulls more fluid behind it.  Do you think anyone has offered a definition of transpiration cooling that differentiates it from the movement of fluid under pressure through a small perforation?  These ideas are not only similar but as used so far seem to be identical.
Title: Re: Starship heat shield
Post by: Doc C on 10/06/2021 02:35 am
Similarly with this concept and "transpiration cooling."

The advantage of this over transpiration cooling is that it eliminates all the plumbing.

"To design a spacecraft right takes an infinite amount of effort. This is why it's a good idea to design them to operate when some things are wrong."  -- Akin's Second Law of Spacecraft Design (https://spacecraft.ssl.umd.edu/akins_laws.html)

Not similar at all.  Mount Catching and Arm catching are alternatives ... you don't need both.  Planned-Perforation can't address all Primary and Backup Cooling needs.

I think this is one of those "obvious in hindsight" issues where the safety backup will only be added in the wake of a very public failure. That's part of the SpaceX iterative design philosophy -- don't add it until you know you need it.

It will be very interesting to see the results of the first Starship reentry test.

AFAICT this "belt and suspenders" approach combines the best of both worlds: tiles as the fully-reusable primary heat shield, with a super-lightweight and ultra-simplified contingency transpiration system covering the primary failure mode of the tiles.

Perhaps.  I agree the safety backup needs to be addressed early before any high-profile failure.  I don't think Planned-Perforation is very good for anything other than a last line of defense and it's too complex to be worth investing in as a last line of defense given that you'd still need other lines.  Better to beef up the other elements of the system.

This is one of those things that's speciously compelling, becoming a hobby-horse once it gets it worms it past your initial incredulity.  Be stronger.

Be less obnoxious.   You're using a lot of vivid, emotive phrases like "hobby horse," and "worms past" and "be stronger" without actually making a better case.

Stop abusing people for simply disagreeing with you.  They roll their eyes at you because you're being self-important, condescending, bombastic... and unconvincing.
Title: Re: Starship heat shield
Post by: oiorionsbelt on 10/06/2021 02:50 am
I preferred when the heat shield currently being put on Starship 20 was discussed.
Title: Re: Starship heat shield
Post by: Twark_Main on 10/06/2021 03:11 am
I preferred when the heat shield currently being put on Starship 20 was discussed.

Me three. The thread was pretty much dead when (after having one of those "light-bulb" moments) I made a suggestion for how KelvinZero's idea (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2295905#msg2295905) could be modified to be workable, plus clear up a few misconceptions. I believe the technical part of that discussion has (mercifully) run its course. I'll be dropping the subject now.

Soooo.....  how 'bout that local sports team SN20? :D
Title: Re: Starship heat shield
Post by: TomH on 10/06/2021 04:02 am
...................

Hi, Welcome to the forum. That was some good advice.
Title: Re: Starship heat shield
Post by: edzieba on 10/06/2021 07:54 am
Why cooling “only with methane”?
Is there any evidence that combustion is a risk for stainless?

Experimental evidence says otherwise:
Quote
From COMBUSTION OF METALS IN OXYGEN PHASE II: BULK BURNING EXPERIMENTS (https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nbsir73-345.pdf),  NBSIR 73-345:

“…we found that 304L stainless steel, if brought to its melting point and allowed to spread out in a layer not more than 1 /4 inch thick on a poorly conducting surface, would burn to completion if the oxygen pressure was over 50 psig.” (emphasis in the original text, pg 2)

“In no case did we seem to get ignition before melting....Sustained burning [of already-molten 304L] will not occur generally below 50 psig of oxygen.” (pg 19)
So, combustion conditions = melting point & high oxygen pressure, not merely hot at lower pressure.

I think we’ve seen some exaggeration of the combustibility of stainless steel in several discussions in this forum.
Maybe people are confusing 304L (Starship Stainless®) with other steel alloys (or with aluminum or something)?

Net assessment so far: Small fusible plugs in tank walls might possibly be good for something, somewhere, sometime -- or not.
The tanks are are well above 50 PSIG (64 PSIA, or 4.4 Bar, vs. 6 Bar tank pressure). In addition, putting a thin sheet with molten edges in a hypersonic gas flow is going to mean you;re dealing with combustion of a spray of aerosolised molten metal, not a contiguous lump.

Hot stainless will burn in the conditions inside the tank. The optimum option remain to not allow presence of hot stainless in the first place.
Title: Re: Starship heat shield
Post by: ETurner on 10/06/2021 11:33 am
Why cooling “only with methane”?
Is there any evidence that combustion is a risk for stainless?

Experimental evidence says otherwise:
Quote
From COMBUSTION OF METALS IN OXYGEN PHASE II: BULK BURNING EXPERIMENTS (https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nbsir73-345.pdf),  NBSIR 73-345:

“…we found that 304L stainless steel, if brought to its melting point and allowed to spread out in a layer not more than 1 /4 inch thick on a poorly conducting surface, would burn to completion if the oxygen pressure was over 50 psig.” (emphasis in the original text, pg 2)

“In no case did we seem to get ignition before melting....Sustained burning [of already-molten 304L] will not occur generally below 50 psig of oxygen.” (pg 19)
So, combustion conditions = melting point & high oxygen pressure, not merely hot at lower pressure.

I think we’ve seen some exaggeration of the combustibility of stainless steel in several discussions in this forum.
Maybe people are confusing 304L (Starship Stainless®) with other steel alloys (or with aluminum or something)?

Net assessment so far: Small fusible plugs in tank walls might possibly be good for something, somewhere, sometime -- or not.
The tanks are are well above 50 PSIG (64 PSIA, or 4.4 Bar, vs. 6 Bar tank pressure). In addition, putting a thin sheet with molten edges in a hypersonic gas flow is going to mean you;re dealing with combustion of a spray of aerosolised molten metal, not a contiguous lump.

Hot stainless will burn in the conditions inside the tank. The optimum option remain to not allow presence of hot stainless in the first place.
The data seems to say that combusion requires melting, and if the structure is melting, then you’ve already lost the ship. Combustion might be a consequence of failure, but not a cause.

A plausible scenario for Twark’s scheme would be:

1) Tile fails
2) Heat leaks through blanket
3) Steel overheats
4) Fusible plugs melt, opening small holes that allow gas flow
5) Gas flows out through blanket, convecting heat away, steel cools
6) Vehicle returns safely
7) Local repairs before re-flight.

Weight added: Negligible.
Structural effects: Seem negligible (unless filling holes with fusible alloy causes loss of temper)
Mechanical complexity: No moving parts, no protruding parts, no joints.
Fusible metal and processing: ??Development and fabrication complexity: ??

The hobby horse still seems pretty lively, considering.

Title: Re: Starship heat shield
Post by: envy887 on 10/06/2021 12:10 pm
Why cooling “only with methane”?
Is there any evidence that combustion is a risk for stainless?

Experimental evidence says otherwise:
Quote
From COMBUSTION OF METALS IN OXYGEN PHASE II: BULK BURNING EXPERIMENTS (https://nvlpubs.nist.gov/nistpubs/Legacy/IR/nbsir73-345.pdf),  NBSIR 73-345:

“…we found that 304L stainless steel, if brought to its melting point and allowed to spread out in a layer not more than 1 /4 inch thick on a poorly conducting surface, would burn to completion if the oxygen pressure was over 50 psig.” (emphasis in the original text, pg 2)

“In no case did we seem to get ignition before melting....Sustained burning [of already-molten 304L] will not occur generally below 50 psig of oxygen.” (pg 19)
So, combustion conditions = melting point & high oxygen pressure, not merely hot at lower pressure.

I think we’ve seen some exaggeration of the combustibility of stainless steel in several discussions in this forum.
Maybe people are confusing 304L (Starship Stainless®) with other steel alloys (or with aluminum or something)?

Net assessment so far: Small fusible plugs in tank walls might possibly be good for something, somewhere, sometime -- or not.
The tanks are are well above 50 PSIG (64 PSIA, or 4.4 Bar, vs. 6 Bar tank pressure). In addition, putting a thin sheet with molten edges in a hypersonic gas flow is going to mean you;re dealing with combustion of a spray of aerosolised molten metal, not a contiguous lump.

Hot stainless will burn in the conditions inside the tank. The optimum option remain to not allow presence of hot stainless in the first place.
Any molten spray won't be in the tank, though. The stagnation pressure of the incoming plasma is only a fraction of a psi, so any flow through a hypothetical hole is going to go out of the tank, not into it. Outside it could vaporize, ionize, burn, or something, but who cares?

Also, I'm dubious that stainless 304 will melt at all in these conditions. At the melting point of stainless 304, the radiative flux into the cold tank sink (~275 kW/m2) would be about triple the flux coming in from the plasma stream along the vehicle centerline (~100 kW/m2 based on Shuttle data). If flux out is more than flux in, then it is above equilibrium temperature, i.e. unreachable in this scenario. The equilibrium temperature is about 1000 to 1100 C, which is quite far below the melting point of stainless 304. And that's before accounting for the isolator pad insulation, which will add thermal resistance and reduce flux.

I think the overwhelmingly most likely outcome of losing a tile, or a few tiles, is that the steel heats to around 700-900 C, above the annealing temperature, but does not burst, leak, or melt in any significant fashion. It certainly doesn't burn. The vehicle lands, and then is repaired by reinforcing or replacing that patch of steel and replacing the tile, or is scrapped.
Title: Re: Starship heat shield
Post by: rsdavis9 on 10/06/2021 12:34 pm
Ok
Instead of fusible plugs discussion (well mostly).

I asked before if the tiles blown off of S20 by the header tank vents had pins.
Every picture I have found of the tileless area has not shown any pins.
Anybody have evidence to the contrary? And yes this relates to the need of fusible plugs...

Also on fusible plugs, I think single tile loss would probably be survivable.  Just a guess from comments about reduced stress during reentry and lower ullage pressure and a single tile being a small enough spot to stay cooler. So best part is no part.
Title: Re: Starship heat shield
Post by: eriblo on 10/06/2021 01:16 pm
Ok
Instead of fusible plugs discussion (well mostly).

I asked before if the tiles blown off of S20 by the header tank vents had pins.
Every picture I have found of the tileless area has not shown any pins.
Anybody have evidence to the contrary? And yes this relates to the need of fusible plugs...

Also on fusible plugs, I think single tile loss would probably be survivable.  Just a guess from comments about reduced stress during reentry and lower ullage pressure and a single tile being a small enough spot to stay cooler. So best part is no part.
Which pictures have you been looking at? From Mary: (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2295258#msg2295258)
Title: Re: Starship heat shield
Post by: AC in NC on 10/06/2021 01:25 pm
1)  Similar is a meaningless word.  Perforation cooling and Transpiration Cooling are similar in that the concepts do similar things (namely:  "cool" ... duh) but are completely different in that they cannot address the same scenarios.  Quit trying to play semantic games.
This is getting strange.  Exactly what do you think transpiration is anyway?  It means the movement of water from the stomata of a leaf.  In the most general sense, it is the movement of a fluid (or gas) through a perforation.  There is the related concept of the evaporation of the fluid causing a "transpiration pressure" which pulls more fluid behind it.  Do you think anyone has offered a definition of transpiration cooling that differentiates it from the movement of fluid under pressure through a small perforation?  These ideas are not only similar but as used so far seem to be identical.
What exactly do you think I'm saying?  It seems clear enough to me.

There is the physical process and the engineering system that implements the physical process.  The terms Perforation Cooling or Transpiration Cooling can refer to either.  The physical processes are similar enough but the engineering systems and what can be accomplished with them are miles apart.  Because the physical process cannot exist without the engineering system, it's mendacious to suggest they are identical.
Title: Re: Starship heat shield
Post by: marsbase on 10/06/2021 01:48 pm
1)  Similar is a meaningless word.  Perforation cooling and Transpiration Cooling are similar in that the concepts do similar things (namely:  "cool" ... duh) but are completely different in that they cannot address the same scenarios.  Quit trying to play semantic games.
This is getting strange.  Exactly what do you think transpiration is anyway?  It means the movement of water from the stomata of a leaf.  In the most general sense, it is the movement of a fluid (or gas) through a perforation.  There is the related concept of the evaporation of the fluid causing a "transpiration pressure" which pulls more fluid behind it.  Do you think anyone has offered a definition of transpiration cooling that differentiates it from the movement of fluid under pressure through a small perforation?  These ideas are not only similar but as used so far seem to be identical.
What exactly do you think I'm saying?  It seems clear enough to me.

There is the physical process and the engineering system that implements the physical process.  The terms Perforation Cooling or Transpiration Cooling can refer to either.  The physical processes are similar enough but the engineering systems and what can be accomplished with them are miles apart.  Because the physical process cannot exist without the engineering system, it's mendacious to suggest they are identical.
Ok, so what engineering system has been defined for transpiration cooling?  Elon refuses to be specific, offering ITAR as a reason.   How do we know that Elon's plan for transpiration cooling does not involve "perforation cooling" or fusable plugs?  That's why I say that, so far, they appear to be identical.  Until such time as SpaceX actually explains its plans, we don't know.  Yes, fusable plugs seems like a far out idea, but so does any form of cooling that involves loss of propellant. And yet, Elon says that is still on the table.
Title: Re: Starship heat shield
Post by: rsdavis9 on 10/06/2021 01:58 pm
Ok
Instead of fusible plugs discussion (well mostly).

I asked before if the tiles blown off of S20 by the header tank vents had pins.
Every picture I have found of the tileless area has not shown any pins.
Anybody have evidence to the contrary? And yes this relates to the need of fusible plugs...

Also on fusible plugs, I think single tile loss would probably be survivable.  Just a guess from comments about reduced stress during reentry and lower ullage pressure and a single tile being a small enough spot to stay cooler. So best part is no part.
Which pictures have you been looking at? From Mary: (https://forum.nasaspaceflight.com/index.php?topic=52398.msg2295258#msg2295258)

I was looking at the blue circled areas and couldn't see the pins. My wife complains about how blind I am sometime.  :)

Didn't even see the area to the right there. I thought since there wasn't any blanket it didn't have tiles on it.

Thanks BTW.
Title: Re: Starship heat shield
Post by: AC in NC on 10/06/2021 02:41 pm
What exactly do you think I'm saying?  It seems clear enough to me.

There is the physical process and the engineering system that implements the physical process.  The terms Perforation Cooling or Transpiration Cooling can refer to either.  The physical processes are similar enough but the engineering systems and what can be accomplished with them are miles apart.  Because the physical process cannot exist without the engineering system, it's mendacious to suggest they are identical.
Ok, so what engineering system has been defined for transpiration cooling?  Elon refuses to be specific, offering ITAR as a reason.   How do we know that Elon's plan for transpiration cooling does not involve "perforation cooling" or fusable plugs?  That's why I say that, so far, they appear to be identical.  Until such time as SpaceX actually explains its plans, we don't know.  Yes, fusable plugs seems like a far out idea, but so does any form of cooling that involves loss of propellant. And yet, Elon says that is still on the table.
SpaceX hasn't shared a transpiration design but the topic has been well covered on this forum and it's reasonable to assume a system like those.  We don't know but I would lay good odds that Elon isn't going to use fusible plugs because they seem to me completely inconsistent with everything we know about his approach.  I can't imagine what such a system would do to the manufacturing, validation, and inspection processes.  Just doesn't seem what is aimed for.
Title: Re: Starship heat shield
Post by: OTV Booster on 10/06/2021 07:34 pm

You're missing the point. People still argued that 'common sense' says not to do that, just like you're arguing above.

Also, the "catching it with arms" concept isn't that old. You're conflating it with "landing on or near the launch mount," which is not the same thing.

They have never mentioned Swiss cheesing the propellant tanks.

I'm not arguing that SpaceX is doing this. I'm arguing that SpaceX should do this.

What I'm failing to see are any actual technical arguments as to why this concept wouldn't work. Specifically, how is complete hull failure leading to LOV / LOC preferable to replacing a few rivets before re-tiling? ???
It doesn't help with the cargo, fin, or skirt sections of the hull, so it's a problem that has to be solved a different way anyway. Might as well solve it for the whole vehicle.

They'd also be adding (tens of?) thousands of potential leak points to make normal vehicle use more difficult. Now you have thousands of seals that have to hold up in cryo temperatures, high (but deliberately not reentry) temps, and in space, and be reusable over many normal flights. If you use a metal alloy plug or stud that melts at the desired temperature, it won't keep up with tank stretching and contracting in different temperatures well. If you use something flexible, it's going to have a hard time with the cryo and/or high temperatures.

I think it's an interesting idea that might make the tank sections safer, but those are the potential problems I came up with.
These are strong points. To keep the idea in the maybe-possibly-viable range would require candidate “rivet” materials that simultaneously meet several maybe-incompatible criteria: low(ish) melting point, compatible-enough thermal expansion coefficient, and OK w.r.t. galvanic corrosion problems. Turning the critic’s hat backward, could small holes (mm-scale) be drilled then filled with a brazing material?

If it were me, I'd go with the hint someone mentioned earlier in the thread about steel cookware needing an aluminum or copper coating to actually spread heat around. I can't help but wonder how thick (and heavy, and expensive) a copper coating on the inside of the tanks, skirt, and nosecone would have be to effectively spread heat to cooler parts of the ship if a few tiles were lost.
To provide a useful increment in thermal conduction, the aluminum or copper layer would have to be quite thick and heavy.
Not so thick and heavy if it's on the outside of the skin. That would start spreading the heat before it even gets to the stainless. This avoids a problem. Put it on the inside and it conducts heat away from an already hot skin. This mitigates an existing problem.


Cookware uses a thick plate to deliver even heating over a large area. For SS the area and evenness if heating is irrelevant. Reducing max temp is the goal.
Title: Re: Starship heat shield
Post by: Vultur on 10/06/2021 07:39 pm
Also, I'm dubious that stainless 304 will melt at all in these conditions. At the melting point of stainless 304, the radiative flux into the cold tank sink (~275 kW/m2) would be about triple the flux coming in from the plasma stream along the vehicle centerline (~100 kW/m2 based on Shuttle data). If flux out is more than flux in, then it is above equilibrium temperature, i.e. unreachable in this scenario. The equilibrium temperature is about 1000 to 1100 C, which is quite far below the melting point of stainless 304. And that's before accounting for the isolator pad insulation, which will add thermal resistance and reduce flux.

I think the overwhelmingly most likely outcome of losing a tile, or a few tiles, is that the steel heats to around 700-900 C, above the annealing temperature, but does not burst, leak, or melt in any significant fashion. It certainly doesn't burn. The vehicle lands, and then is repaired by reinforcing or replacing that patch of steel and replacing the tile, or is scrapped.

Well, that's comforting.

So maybe nothing special is needed at all?

The nominal case (of course) is that the tiles protect the structure. But the fallback can be that the steel (+ insulation) handles it well enough to land safely, though not well enough to handle another launch (loses strength due to above annealing temperature)?

Am I understanding that correctly?
Title: Re: Starship heat shield
Post by: envy887 on 10/06/2021 07:43 pm

You're missing the point. People still argued that 'common sense' says not to do that, just like you're arguing above.

Also, the "catching it with arms" concept isn't that old. You're conflating it with "landing on or near the launch mount," which is not the same thing.

They have never mentioned Swiss cheesing the propellant tanks.

I'm not arguing that SpaceX is doing this. I'm arguing that SpaceX should do this.

What I'm failing to see are any actual technical arguments as to why this concept wouldn't work. Specifically, how is complete hull failure leading to LOV / LOC preferable to replacing a few rivets before re-tiling? ???
It doesn't help with the cargo, fin, or skirt sections of the hull, so it's a problem that has to be solved a different way anyway. Might as well solve it for the whole vehicle.

They'd also be adding (tens of?) thousands of potential leak points to make normal vehicle use more difficult. Now you have thousands of seals that have to hold up in cryo temperatures, high (but deliberately not reentry) temps, and in space, and be reusable over many normal flights. If you use a metal alloy plug or stud that melts at the desired temperature, it won't keep up with tank stretching and contracting in different temperatures well. If you use something flexible, it's going to have a hard time with the cryo and/or high temperatures.

I think it's an interesting idea that might make the tank sections safer, but those are the potential problems I came up with.
These are strong points. To keep the idea in the maybe-possibly-viable range would require candidate “rivet” materials that simultaneously meet several maybe-incompatible criteria: low(ish) melting point, compatible-enough thermal expansion coefficient, and OK w.r.t. galvanic corrosion problems. Turning the critic’s hat backward, could small holes (mm-scale) be drilled then filled with a brazing material?

If it were me, I'd go with the hint someone mentioned earlier in the thread about steel cookware needing an aluminum or copper coating to actually spread heat around. I can't help but wonder how thick (and heavy, and expensive) a copper coating on the inside of the tanks, skirt, and nosecone would have be to effectively spread heat to cooler parts of the ship if a few tiles were lost.
To provide a useful increment in thermal conduction, the aluminum or copper layer would have to be quite thick and heavy.
Not so thick and heavy if it's on the outside of the skin. That would start spreading the heat before it even gets to the stainless. This avoids a problem. Put it on the inside and it conducts heat away from an already hot skin. This mitigates an existing problem.


Cookware uses a thick plate to deliver even heating over a large area. For SS the area and evenness if heating is irrelevant. Reducing max temp is the goal.

To reduce max temp with a conductor the heat has to go somewhere to be rejected. Where is it going, how is it being rejected, and how much does a thin layer help it get there? Thin sheets are lousy for lateral heat transport.
Title: Re: Starship heat shield
Post by: envy887 on 10/06/2021 07:49 pm
Also, I'm dubious that stainless 304 will melt at all in these conditions. At the melting point of stainless 304, the radiative flux into the cold tank sink (~275 kW/m2) would be about triple the flux coming in from the plasma stream along the vehicle centerline (~100 kW/m2 based on Shuttle data). If flux out is more than flux in, then it is above equilibrium temperature, i.e. unreachable in this scenario. The equilibrium temperature is about 1000 to 1100 C, which is quite far below the melting point of stainless 304. And that's before accounting for the isolator pad insulation, which will add thermal resistance and reduce flux.

I think the overwhelmingly most likely outcome of losing a tile, or a few tiles, is that the steel heats to around 700-900 C, above the annealing temperature, but does not burst, leak, or melt in any significant fashion. It certainly doesn't burn. The vehicle lands, and then is repaired by reinforcing or replacing that patch of steel and replacing the tile, or is scrapped.

Well, that's comforting.

So maybe nothing special is needed at all?

The nominal case (of course) is that the tiles protect the structure. But the fallback can be that the steel (+ insulation) handles it well enough to land safely, though not well enough to handle another launch (loses strength due to above annealing temperature)?

Am I understanding that correctly?

That's about what I expect for the general tank acreage tiles, yes. Those are the vast majority of the TPS.

Hot spots, leading edges, and the crew compartment may have additional issues in the event of a tile loss. But those aren't balloon structures, so the effects of a burn-through on tank pressure and on the overall structural integrity of the vehicle is probably minimal. Potential effects on the functions of those structures will be addressed on an location-specific basis, in most cases with extra insulation IMO.
Title: Re: Starship heat shield
Post by: OTV Booster on 10/06/2021 08:11 pm

You're missing the point. People still argued that 'common sense' says not to do that, just like you're arguing above.

Also, the "catching it with arms" concept isn't that old. You're conflating it with "landing on or near the launch mount," which is not the same thing.

They have never mentioned Swiss cheesing the propellant tanks.

I'm not arguing that SpaceX is doing this. I'm arguing that SpaceX should do this.

What I'm failing to see are any actual technical arguments as to why this concept wouldn't work. Specifically, how is complete hull failure leading to LOV / LOC preferable to replacing a few rivets before re-tiling? ???
It doesn't help with the cargo, fin, or skirt sections of the hull, so it's a problem that has to be solved a different way anyway. Might as well solve it for the whole vehicle.

They'd also be adding (tens of?) thousands of potential leak points to make normal vehicle use more difficult. Now you have thousands of seals that have to hold up in cryo temperatures, high (but deliberately not reentry) temps, and in space, and be reusable over many normal flights. If you use a metal alloy plug or stud that melts at the desired temperature, it won't keep up with tank stretching and contracting in different temperatures well. If you use something flexible, it's going to have a hard time with the cryo and/or high temperatures.

I think it's an interesting idea that might make the tank sections safer, but those are the potential problems I came up with.
These are strong points. To keep the idea in the maybe-possibly-viable range would require candidate “rivet” materials that simultaneously meet several maybe-incompatible criteria: low(ish) melting point, compatible-enough thermal expansion coefficient, and OK w.r.t. galvanic corrosion problems. Turning the critic’s hat backward, could small holes (mm-scale) be drilled then filled with a brazing material?

If it were me, I'd go with the hint someone mentioned earlier in the thread about steel cookware needing an aluminum or copper coating to actually spread heat around. I can't help but wonder how thick (and heavy, and expensive) a copper coating on the inside of the tanks, skirt, and nosecone would have be to effectively spread heat to cooler parts of the ship if a few tiles were lost.
To provide a useful increment in thermal conduction, the aluminum or copper layer would have to be quite thick and heavy.
Not so thick and heavy if it's on the outside of the skin. That would start spreading the heat before it even gets to the stainless. This avoids a problem. Put it on the inside and it conducts heat away from an already hot skin. This mitigates an existing problem.


Cookware uses a thick plate to deliver even heating over a large area. For SS the area and evenness if heating is irrelevant. Reducing max temp is the goal.

To reduce max temp with a conductor the heat has to go somewhere to be rejected. Where is it going, how is it being rejected, and how much does a thin layer help it get there? Thin sheets are lousy for lateral heat transport.
Thin sheets, thick plates. No numbers. Conceptual. As thick as necessary, no more. More than electroplating and (WAG) less than 1mm.


Lateral conductivity for a high temp gradient, AFAIK, works better than a low temp gradient. What we're talking about is a hot spot which implies a high gradient. If the entire layer becomes the sink for a missing tile who cares. While the 'heat front' is spreading laterally it will do some admittedly crappy conduction to the cooler stainless.
Title: Re: Starship heat shield
Post by: OTV Booster on 10/06/2021 08:14 pm
Has anybody come up with an idea of what the mesh is made of? I swear it drapes like plastic. That makes no sense.
Title: Re: Starship heat shield
Post by: Rocket Science on 10/06/2021 08:19 pm
Has anybody come up with an idea of what the mesh is made of? I swear it drapes like plastic. That makes no sense.
It almost looks like Nomex Aramid...
Title: Re: Starship heat shield
Post by: Keldor on 10/06/2021 11:09 pm

You're missing the point. People still argued that 'common sense' says not to do that, just like you're arguing above.

Also, the "catching it with arms" concept isn't that old. You're conflating it with "landing on or near the launch mount," which is not the same thing.

They have never mentioned Swiss cheesing the propellant tanks.

I'm not arguing that SpaceX is doing this. I'm arguing that SpaceX should do this.

What I'm failing to see are any actual technical arguments as to why this concept wouldn't work. Specifically, how is complete hull failure leading to LOV / LOC preferable to replacing a few rivets before re-tiling? ???
It doesn't help with the cargo, fin, or skirt sections of the hull, so it's a problem that has to be solved a different way anyway. Might as well solve it for the whole vehicle.

They'd also be adding (tens of?) thousands of potential leak points to make normal vehicle use more difficult. Now you have thousands of seals that have to hold up in cryo temperatures, high (but deliberately not reentry) temps, and in space, and be reusable over many normal flights. If you use a metal alloy plug or stud that melts at the desired temperature, it won't keep up with tank stretching and contracting in different temperatures well. If you use something flexible, it's going to have a hard time with the cryo and/or high temperatures.

I think it's an interesting idea that might make the tank sections safer, but those are the potential problems I came up with.
These are strong points. To keep the idea in the maybe-possibly-viable range would require candidate “rivet” materials that simultaneously meet several maybe-incompatible criteria: low(ish) melting point, compatible-enough thermal expansion coefficient, and OK w.r.t. galvanic corrosion problems. Turning the critic’s hat backward, could small holes (mm-scale) be drilled then filled with a brazing material?

If it were me, I'd go with the hint someone mentioned earlier in the thread about steel cookware needing an aluminum or copper coating to actually spread heat around. I can't help but wonder how thick (and heavy, and expensive) a copper coating on the inside of the tanks, skirt, and nosecone would have be to effectively spread heat to cooler parts of the ship if a few tiles were lost.
To provide a useful increment in thermal conduction, the aluminum or copper layer would have to be quite thick and heavy.
Not so thick and heavy if it's on the outside of the skin. That would start spreading the heat before it even gets to the stainless. This avoids a problem. Put it on the inside and it conducts heat away from an already hot skin. This mitigates an existing problem.


Cookware uses a thick plate to deliver even heating over a large area. For SS the area and evenness if heating is irrelevant. Reducing max temp is the goal.

To reduce max temp with a conductor the heat has to go somewhere to be rejected. Where is it going, how is it being rejected, and how much does a thin layer help it get there? Thin sheets are lousy for lateral heat transport.
Thin sheets, thick plates. No numbers. Conceptual. As thick as necessary, no more. More than electroplating and (WAG) less than 1mm.


Lateral conductivity for a high temp gradient, AFAIK, works better than a low temp gradient. What we're talking about is a hot spot which implies a high gradient. If the entire layer becomes the sink for a missing tile who cares. While the 'heat front' is spreading laterally it will do some admittedly crappy conduction to the cooler stainless.

Even a 1mm thick layer of copper over something the size of the windward half of Starship would weigh around 4 tons.  And I doubt it would be anywhere near enough to do the job even for a single missing tile.  If we guestimate that the steel body can stand being heated 250C from normal reentry peak to the point where it's melting and falling apart like wet tissue paper, and we assume the tile is around half a meter across, we get around 500kW/m^2 of heat flux.  But the cross section of our 1 mm layer around the edge of the tile is only about 0.001m^2v  This means that it's only dissipating around 500W of energy through the copper layer, which is only enough to make a few little lightbulb filiments glow white hot, nowhere near the amount of energy involved in reentry across a whole tile!
Title: Re: Starship heat shield
Post by: KelvinZero on 10/07/2021 03:22 am
Hi.. I find this perforation topic (and any other ideas to make loss of tiles survivable) interesting, but it has clearly moved a fair way from the very concrete discussion of the tiles and upcoming tests etc.

Should we move it to a new thread? Someone could just start one and put a link here. I have a few more hairbrained schemes to add :-)
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 10/07/2021 04:16 am
Does anybody have a decent guess for the Mars altitude that will be considered "entry interface?"  Similarly, what speed do you think Starship will be able to handle at that interface?

I have pretty much the same questions for Earth.

I've been fooling with some delta-v and prop budgeting for martian Starship missions.  I've been assuming that Mars entry interface is about 70km altitude, and that max speed is about 12km/s.  That yields an arrival v∞ of 10.92km/s.

Do those sound in the right ballpark?  Anybody have better numbers?
Title: Re: Starship heat shield
Post by: tenkendojo on 10/07/2021 03:27 pm
Does anybody have a decent guess for the Mars altitude that will be considered "entry interface?"  Similarly, what speed do you think Starship will be able to handle at that interface?

I have pretty much the same questions for Earth.

I've been fooling with some delta-v and prop budgeting for martian Starship missions.  I've been assuming that Mars entry interface is about 70km altitude, and that max speed is about 12km/s.  That yields an arrival v∞ of 10.92km/s.

Do those sound in the right ballpark?  Anybody have better numbers?

Here's some reentry data from historical Mars landing missions, courtesy of NASA:
(https://upload.wikimedia.org/wikipedia/commons/thumb/d/d8/Mars-Science-Laboratory-Mars-Entry-Trajectory.png/1280px-Mars-Science-Laboratory-Mars-Entry-Trajectory.png)

See also here, on "Mars Pathfinder Atmospheric Entry Strategy" : https://nssdc.gsfc.nasa.gov/planetary/marsentry.html

Peak heating for Pathfinder entry at about 40km altitude, at speed roughly 6km/s.

One unique dynamic about Martian reentry is the presence of dust particles  pretty high up in the atmosphere, which may create problems for reusing heatshield.

Title: Re: Starship heat shield
Post by: ETurner on 10/07/2021 03:52 pm
One unique dynamic about Martian reentry is the presence of dust particles  pretty high up in the atmosphere, which may create problems for reusing heatshield.
I think we can make a pretty good estimate of the problem (or non-problem) based on two facts:

1) We can see though the upper atmosphere (at least under ordinary conditions), which means that the mass of dust per unit area must be much less than the mass of a continuous film of dust.

2) If the dust remains suspended in the atmosphere for a long time, the particles must be very small.

It’s hard to see how a low density of small particles could do much to the heat shield.

Dust storms may be another situation entirely: a lot more dust, and at least some of it goes quite high. On the ground, dust can accumulate into layers thick enough to impair photovoltaics. For a heat shield, aero forces on the way up should give it a good dusting-off!
Title: Re: Starship heat shield
Post by: OTV Booster on 10/07/2021 05:53 pm
Does anybody have a decent guess for the Mars altitude that will be considered "entry interface?"  Similarly, what speed do you think Starship will be able to handle at that interface?

I have pretty much the same questions for Earth.

I've been fooling with some delta-v and prop budgeting for martian Starship missions.  I've been assuming that Mars entry interface is about 70km altitude, and that max speed is about 12km/s.  That yields an arrival v∞ of 10.92km/s.

Do those sound in the right ballpark?  Anybody have better numbers?
Something that might feed into the problem is that martian and earth atmospheric density are roughly the same from ~120km to ~85km. This is from a NASA paper that I can't put my finger on.


Here's something I came across while looking for it. More than I can adsorb quickly. It covers reentry issues. Looks like your type of meat.
https://ntrs.nasa.gov/api/citations/20110003632/downloads/20110003632.pdf (https://ntrs.nasa.gov/api/citations/20110003632/downloads/20110003632.pdf)
Title: Re: Starship heat shield
Post by: grndkntrl on 10/07/2021 06:56 pm
Does anybody have a decent guess for the Mars altitude that will be considered "entry interface?"  Similarly, what speed do you think Starship will be able to handle at that interface?

I have pretty much the same questions for Earth.

I've been fooling with some delta-v and prop budgeting for martian Starship missions.  I've been assuming that Mars entry interface is about 70km altitude, and that max speed is about 12km/s.  That yields an arrival v∞ of 10.92km/s.

Do those sound in the right ballpark?  Anybody have better numbers?
Something that might feed into the problem is that martian and earth atmospheric density are roughly the same from ~120km to ~85km. This is from a NASA paper that I can't put my finger on.


Here's something I came across while looking for it. More than I can adsorb quickly. It covers reentry issues. Looks like your type of meat.
https://ntrs.nasa.gov/api/citations/20110003632/downloads/20110003632.pdf (https://ntrs.nasa.gov/api/citations/20110003632/downloads/20110003632.pdf)

There's also the attached graphic cropped from page 2 of "Mars pathfinder atmospheric entry reconstruction" (https://trs.jpl.nasa.gov/bitstream/handle/2014/20159/98-1027.pdf) paper by David A. Spencer et al, from 1998, showing entry at 130 km.

This Mars Insight lander page (https://mars.nasa.gov/insight/entry-descent-landing/) has its entry at 128 km:
Quote
"Entry, Descent, and Landing (EDL) begins when the spacecraft reaches the top of the Martian atmosphere, about 80 miles (about 128 kilometers) above the surface, and ends with the lander safe and sound on the surface of Mars six minutes later."

... Curiousity MSL (https://mars.nasa.gov/msl/timeline/edl/) has a similar statement putting its entry at 125 km:
Quote
"The entry, descent, and landing (EDL) phase began when the spacecraft reached the Martian atmosphere, about 125 kilometers (about 78 miles) above the surface..."


Title: Re: Starship heat shield
Post by: TheRadicalModerate on 10/07/2021 10:12 pm
Does anybody have a decent guess for the Mars altitude that will be considered "entry interface?"  Similarly, what speed do you think Starship will be able to handle at that interface?

I have pretty much the same questions for Earth.

I've been fooling with some delta-v and prop budgeting for martian Starship missions.  I've been assuming that Mars entry interface is about 70km altitude, and that max speed is about 12km/s.  That yields an arrival v∞ of 10.92km/s.

Do those sound in the right ballpark?  Anybody have better numbers?

Here's some reentry data from historical Mars landing missions, courtesy of NASA:
(https://upload.wikimedia.org/wikipedia/commons/thumb/d/d8/Mars-Science-Laboratory-Mars-Entry-Trajectory.png/1280px-Mars-Science-Laboratory-Mars-Entry-Trajectory.png)

See also here, on "Mars Pathfinder Atmospheric Entry Strategy" : https://nssdc.gsfc.nasa.gov/planetary/marsentry.html

Peak heating for Pathfinder entry at about 40km altitude, at speed roughly 6km/s.

One unique dynamic about Martian reentry is the presence of dust particles  pretty high up in the atmosphere, which may create problems for reusing heatshield.

Your chart shows considerably lower speeds than Apollo-era entry interface speeds, which were about 11km/s.  Is that because of some inherent property of the Mars atmosphere and scale height, or is it a function of the kinds of blunt-body L/D that your garden-variety martian probe can muster?  If so, is it possible that Starship's entry speed could be considerably higher?

At some point, I'd heard somebody suggesting that Starship would do Mars entry with negative lift, so that it could have a flight path angle that would otherwise cause it to skip out of the atmosphere but still stayed at a very high altitude for a long time.  However, I'm unclear on how such a trajectory would eventually wind up with the nose point forward and the Starship rightside-up.

If the charted numbers (125km entry interface @ 7500m/s) are close to the maximum, that implies an arrival v∞ = 5650m/s.  Here are some windows for both minimum energy and minimum time-of-flight, given that restriction.
Title: Re: Starship heat shield
Post by: tenkendojo on 10/07/2021 11:11 pm
Does anybody have a decent guess for the Mars altitude that will be considered "entry interface?"  Similarly, what speed do you think Starship will be able to handle at that interface?

I have pretty much the same questions for Earth.

I've been fooling with some delta-v and prop budgeting for martian Starship missions.  I've been assuming that Mars entry interface is about 70km altitude, and that max speed is about 12km/s.  That yields an arrival v∞ of 10.92km/s.

Do those sound in the right ballpark?  Anybody have better numbers?

Here's some reentry data from historical Mars landing missions, courtesy of NASA:
(https://upload.wikimedia.org/wikipedia/commons/thumb/d/d8/Mars-Science-Laboratory-Mars-Entry-Trajectory.png/1280px-Mars-Science-Laboratory-Mars-Entry-Trajectory.png)

See also here, on "Mars Pathfinder Atmospheric Entry Strategy" : https://nssdc.gsfc.nasa.gov/planetary/marsentry.html

Peak heating for Pathfinder entry at about 40km altitude, at speed roughly 6km/s.

One unique dynamic about Martian reentry is the presence of dust particles  pretty high up in the atmosphere, which may create problems for reusing heatshield.

Your chart shows considerably lower speeds than Apollo-era entry interface speeds, which were about 11km/s.  Is that because of some inherent property of the Mars atmosphere and scale height, or is it a function of the kinds of blunt-body L/D that your garden-variety martian probe can muster?  If so, is it possible that Starship's entry speed could be considerably higher?

At some point, I'd heard somebody suggesting that Starship would do Mars entry with negative lift, so that it could have a flight path angle that would otherwise cause it to skip out of the atmosphere but still stayed at a very high altitude for a long time.  However, I'm unclear on how such a trajectory would eventually wind up with the nose point forward and the Starship rightside-up.

If the charted numbers (125km entry interface @ 7500m/s) are close to the maximum, that implies an arrival v∞ = 5650m/s.  Here are some windows for both minimum energy and minimum time-of-flight, given that restriction.

Reentry speed is primarily determined by orbital mechanics. Mars has much less mass than Earth, so the velocity of a spacecraft at 100km circular orbit around Mars would be roughly 3.5km/s only. Pathfinder's reentry speed is actually higher than Mars escape velocity, as it uses the Martian atmosphere to aerobreak into landing trajectory. Note while Mars reentry begins at around 130km altitude, the spacecraft would continue to accelerate until about 80km in Pathfinder's case, that's when aerodynamic forces finally displaces orbital mechanic.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 10/07/2021 11:40 pm
Reentry speed is primarily determined by orbital mechanics. Mars has much less mass than Earth, so the velocity of a spacecraft at 100km circular orbit around Mars would be roughly 3.5km/s only. Pathfinder's reentry speed is actually higher than Mars escape velocity, as it uses the Martian atmosphere to aerobreak into landing trajectory. Note while Mars reentry begins at around 130km altitude, the spacecraft would continue to accelerate until about 80km in Pathfinder's case, that's when aerodynamic forces finally displaces orbital mechanic.

Yup.  But it's easy to compute the arrival v∞ if you can specify the altitude where drag becomes non-negligible.  If that's 80km @ 7500m/s, then v∞ is about 5620m/s--a reduction of only about 30m/s from using 125km.

But my question still stands:  Is Pathfinder a good proxy for a vehicle that will probably have a shallower flight-path angle and a radically different TPS?
Title: Re: Starship heat shield
Post by: edzieba on 10/08/2021 08:30 am
At some point, I'd heard somebody suggesting that Starship would do Mars entry with negative lift, so that it could have a flight path angle that would otherwise cause it to skip out of the atmosphere but still stayed at a very high altitude for a long time.  However, I'm unclear on how such a trajectory would eventually wind up with the nose point forward and the Starship rightside-up.
Extensive modelling of such a trajectory here (skip to 30:54 if you don't want to watch the whole thing.): https://youtu.be/ZoSKHzziLKw?t=1854

This was for the old 'Red Dragon' mission concept, but the principle for a cylindrical rather than conical lifting body is the same: roll 'upside down' when negative lift is required, and roll back upright afterwards.
Title: Re: Starship heat shield
Post by: tenkendojo on 10/08/2021 08:37 am
Reentry speed is primarily determined by orbital mechanics. Mars has much less mass than Earth, so the velocity of a spacecraft at 100km circular orbit around Mars would be roughly 3.5km/s only. Pathfinder's reentry speed is actually higher than Mars escape velocity, as it uses the Martian atmosphere to aerobreak into landing trajectory. Note while Mars reentry begins at around 130km altitude, the spacecraft would continue to accelerate until about 80km in Pathfinder's case, that's when aerodynamic forces finally displaces orbital mechanic.

But my question still stands:  Is Pathfinder a good proxy for a vehicle that will probably have a shallower flight-path angle and a radically different TPS?

I can't speak for SS but in terms of Mars lander missions, Pathfinder's entry profile is very atypical: it entered Martian atmosphere very fast from a retrograde orbital direction. It used a specially designed hypersonic parachute to bleed off additional velocity, and employed a lithobreaking airbag to deal with its rather high touchdown velocity (about 12.5m/s verticle velocity at touchdown, and it's horizontal touchdown velocity was even higher IRC, upto 20m/s).

I would think MSL entry profile might be more comparable to SS missions than Pathfinder. For more info, see: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwja9I7psLrzAhVflnIEHaPFDdsQFnoECA4QAQ&url=https%3A%2F%2Fsmartech.gatech.edu%2Fbitstream%2Fhandle%2F1853%2F8390%2FIEEEPaper06ID0076FINAL.pdf&usg=AOvVaw1UBgo8WR90g4Uz8iOp65qS more info
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 10/08/2021 05:42 pm
This was for the old 'Red Dragon' mission concept, but the principle for a cylindrical rather than conical lifting body is the same: roll 'upside down' when negative lift is required, and roll back upright afterwards.

That seems doable for a Dragon, which has a fairly low angle of attack and fairly stubby moments of inertia in the roll and pitch directions.  As a result, it can roll pretty fast, and the stagnation point isn't going to move off of the TPS while you're rolling.

But how can you roll a Starship, which has high angle of attack, hefty pitch moments, and not the most responsive aerocontrols?  And if you can roll it, how do you roll it in such a manner that you keep your free stream stagnation point on the TPS, rather than having it walk around to the unprotected dorsal side of the vehicle?

ISTM that the maneuver that a Starship would need is a combination roll/yaw maneuver, so that the angle of attack stays the same while the lift vector rotates until it's pointing up.  Is that a feasible maneuver with elonerons?

I don't want to haul us too far off-topic here, but this seems on-point to the extent that if you can't model the heat loads and duration of those loads, you really don't know what you need.  Having recently wallowed around in Earth-Mars porkchop plots, it's not super-difficult to find low-energy, fairly long time-of-flight trajectories that keep arrival speeds fairly low, but arrival speed rapidly becomes the primary constraint as you try to shorten time-of-flight.  It'd be nice to work to some kind of figure of merit here.  (And of course by "work", I mean "fool around in a space-nerdy kinda way".)

I guess the other wrinkle here is whether you're designing to direct entry or an aerobrake pass into an eccentric orbit, followed by a lower speed EDL.
Title: Re: Starship heat shield
Post by: eriblo on 10/08/2021 06:48 pm
This was for the old 'Red Dragon' mission concept, but the principle for a cylindrical rather than conical lifting body is the same: roll 'upside down' when negative lift is required, and roll back upright afterwards.

That seems doable for a Dragon, which has a fairly low angle of attack and fairly stubby moments of inertia in the roll and pitch directions.  As a result, it can roll pretty fast, and the stagnation point isn't going to move off of the TPS while you're rolling.

But how can you roll a Starship, which has high angle of attack, hefty pitch moments, and not the most responsive aerocontrols?  And if you can roll it, how do you roll it in such a manner that you keep your free stream stagnation point on the TPS, rather than having it walk around to the unprotected dorsal side of the vehicle?

ISTM that the maneuver that a Starship would need is a combination roll/yaw maneuver, so that the angle of attack stays the same while the lift vector rotates until it's pointing up.  Is that a feasible maneuver with elonerons?

I don't want to haul us too far off-topic here, but this seems on-point to the extent that if you can't model the heat loads and duration of those loads, you really don't know what you need.  Having recently wallowed around in Earth-Mars porkchop plots, it's not super-difficult to find low-energy, fairly long time-of-flight trajectories that keep arrival speeds fairly low, but arrival speed rapidly becomes the primary constraint as you try to shorten time-of-flight.  It'd be nice to work to some kind of figure of merit here.  (And of course by "work", I mean "fool around in a space-nerdy kinda way".)

I guess the other wrinkle here is whether you're designing to direct entry or an aerobrake pass into an eccentric orbit, followed by a lower speed EDL.
The coordinate systems are different. Both maneuvers are rotating the lift vector around the velocity vector at constant AoA. For Starship it is simply a combined retraction/deployment of the fins in diagonal pairs (i.e. right forward/left aft in, left forward/right aft out to rotate to the nose to the right and vice versa). Starship has the added benefit of also being able to quickly do small corrections in total drag/lift and AoA which is a good thing since it will at best be barely passively stable for part of the flight envelope.
Title: Re: Starship heat shield
Post by: edzieba on 10/09/2021 09:19 am
This was for the old 'Red Dragon' mission concept, but the principle for a cylindrical rather than conical lifting body is the same: roll 'upside down' when negative lift is required, and roll back upright afterwards.

That seems doable for a Dragon, which has a fairly low angle of attack and fairly stubby moments of inertia in the roll and pitch directions.  As a result, it can roll pretty fast, and the stagnation point isn't going to move off of the TPS while you're rolling.

But how can you roll a Starship, which has high angle of attack, hefty pitch moments, and not the most responsive aerocontrols?  And if you can roll it, how do you roll it in such a manner that you keep your free stream stagnation point on the TPS, rather than having it walk around to the unprotected dorsal side of the vehicle?

ISTM that the maneuver that a Starship would need is a combination roll/yaw maneuver, so that the angle of attack stays the same while the lift vector rotates until it's pointing up.  Is that a feasible maneuver with elonerons?

I don't want to haul us too far off-topic here, but this seems on-point to the extent that if you can't model the heat loads and duration of those loads, you really don't know what you need.  Having recently wallowed around in Earth-Mars porkchop plots, it's not super-difficult to find low-energy, fairly long time-of-flight trajectories that keep arrival speeds fairly low, but arrival speed rapidly becomes the primary constraint as you try to shorten time-of-flight.  It'd be nice to work to some kind of figure of merit here.  (And of course by "work", I mean "fool around in a space-nerdy kinda way".)

I guess the other wrinkle here is whether you're designing to direct entry or an aerobrake pass into an eccentric orbit, followed by a lower speed EDL.
As eriblo says, roll is about the velocity vector, not around the body axis. See the original BFR presentation at 35:33 :
https://youtu.be/tdUX3ypDVwI?list=PLBQ5P5txVQr9_jeZLGa0n5EIYvsOJFAnY&t=2133
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 10/09/2021 09:24 pm
As eriblo says, roll is about the velocity vector, not around the body axis.

I understand that.  That's fairly easy to do if the AoA is 0º, and only somewhat harder if it's 90º.  But you're doing this because you need lift, and both of those cases have L/D = ~0.  To get lift, you need the AoA between those extremes, so rotating about the velocity vector is essentially a controlled hypersonic spiral.  I'm pretty sure that you can do pitch, roll, and yaw using just the four elonerons, but I'm not sure how much command authority you have if there are errors.  And an error that moves the stagnation point off of the TPS is one that has to be corrected pretty quickly.
Title: Re: Starship heat shield
Post by: eriblo on 10/09/2021 10:30 pm
As eriblo says, roll is about the velocity vector, not around the body axis.

I understand that.  That's fairly easy to do if the AoA is 0º, and only somewhat harder if it's 90º.  But you're doing this because you need lift, and both of those cases have L/D = ~0.  To get lift, you need the AoA between those extremes, so rotating about the velocity vector is essentially a controlled hypersonic spiral.  I'm pretty sure that you can do pitch, roll, and yaw using just the four elonerons, but I'm not sure how much command authority you have if there are errors.  And an error that moves the stagnation point off of the TPS is one that has to be corrected pretty quickly.
The control surfaces will be sized to provide sufficient control authority - that is the sole reason for including them. I personally think the control logic will be significantly easier than most fly-by-wire aircraft which have more control surfaces all of which need to stay within tight speed/altitude/AoA-dependent envelopes. Starship could probably get quite far with just a simple control axis mapping and direct feedback.

As far as I know we have seen no difference between the TPS at different points (except the small radius nose tip) so it is likely that the heating distribution can move around a bit without problem. Getting into an orientation where the stagnation point actually moves off the TPS would be like an airliner flying backwards.

BTW,  0º AoA for Starship would correspond to a deep stall, i.e. just falling with no control input.
Title: Re: Starship heat shield
Post by: equiserre on 10/10/2021 12:48 am
As eriblo says, roll is about the velocity vector, not around the body axis.

I understand that.  That's fairly easy to do if the AoA is 0º, and only somewhat harder if it's 90º.  But you're doing this because you need lift, and both of those cases have L/D = ~0.  To get lift, you need the AoA between those extremes, so rotating about the velocity vector is essentially a controlled hypersonic spiral.  I'm pretty sure that you can do pitch, roll, and yaw using just the four elonerons, but I'm not sure how much command authority you have if there are errors.  And an error that moves the stagnation point off of the TPS is one that has to be corrected pretty quickly.
Radical, are your doubts not solved by watching the simulation of mars edl? It shows all maneuvers in dynamic detail. It checks out. Dont understand your concerns
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 10/10/2021 05:30 am
Radical, are your doubts not solved by watching the simulation of mars edl? It shows all maneuvers in dynamic detail. It checks out. Dont understand your concerns

A simulation from four years ago, built around a carbon composite vehicle, with a single delta wing, with a split flap, and a fixed dihedral?  A simulation that doesn't use the skydiving technique?  I still have some doubts.
Title: Re: Starship heat shield
Post by: Adriano on 10/10/2021 06:43 am
If the starship enters the atmosphere nose first  (AoA=0) and trust controls fail, it can still initiate a rotation using the movable surfaces because the hinges of the forward surfaces are at an angle. If you raise both forward surfaces with AoA =0, you create a lift initiating a pitch rotation, and if you lower one forward surface and raise the other, you will initiate a roll.
Title: Re: Starship heat shield
Post by: JamesH65 on 10/10/2021 08:40 am
Radical, are your doubts not solved by watching the simulation of mars edl? It shows all maneuvers in dynamic detail. It checks out. Dont understand your concerns

A simulation from four years ago, built around a carbon composite vehicle, with a single delta wing, with a split flap, and a fixed dihedral?  A simulation that doesn't use the skydiving technique?  I still have some doubts.

Is your doubt that SpaceX won't have redone the simulations around the latest design?

That would be quite foolish of then, and I don't think they are foolish.
Title: Re: Starship heat shield
Post by: Twark_Main on 10/10/2021 09:35 am
Radical, are your doubts not solved by watching the simulation of mars edl? It shows all maneuvers in dynamic detail. It checks out. Dont understand your concerns

A simulation from four years ago, built around a carbon composite vehicle, with a single delta wing, with a split flap, and a fixed dihedral?

None of those implementation details change the basic mechanics of planning/optimizing the reentry trajectory, which hasn't really changed since Red Dragon. Enter with negative lift to avoid skip-out, roll upright to avoid lithobraking, and bleed off maximum energy aerodynamically before lighting the engines for landing.

A simulation that doesn't use the skydiving technique?

It does use the skydiving technique. Starting at simulation time ~350-400 seconds it's essentially flying sideways.

Or by "doesn't use the skydiving technique" are you saying "doesn't use four control surfaces?" Because if the latter, then you're really just repeating your earlier points.

The current Starship performs better than earlier designs, but nevertheless the "correct" trajectory optimization strategy is essentially unchanged.
Title: Re: Starship heat shield
Post by: ETurner on 10/10/2021 11:51 am
As eriblo says, roll is about the velocity vector, not around the body axis.

I understand that.  That's fairly easy to do if the AoA is 0º, and only somewhat harder if it's 90º.  But you're doing this because you need lift, and both of those cases have L/D = ~0.  To get lift, you need the AoA between those extremes, so rotating about the velocity vector is essentially a controlled hypersonic spiral.  I'm pretty sure that you can do pitch, roll, and yaw using just the four elonerons, but I'm not sure how much command authority you have if there are errors.  And an error that moves the stagnation point off of the TPS is one that has to be corrected pretty quickly.
I don’t see how “rotating about the velocity vector is essentially a controlled hypersonic spiral”. It’s just a roll maneuver. What does “spiral” mean here?
Title: Re: Starship heat shield
Post by: livingjw on 10/10/2021 02:14 pm
StarShip will likely be limited to no lower than ~30-40 degrees during reentry. Control authority will drop to near zero at zero degrees. Also, Max L/D occurs around this AoA range, so there isn't a need to go to lower AoA.

John
Title: Re: Starship heat shield
Post by: brettly2021 on 10/10/2021 02:27 pm
closeup of some discovery spaceshuttle tiles on display at
Air and Space Museum Parkway Chantilly, VA
Tiles are from front side panel , (not very exposed) can see some marks from re=entry, can see some sort of gap filler, some has been worn away during re=entry, exposing some other sort of material between tiles.
If SN20 flies with tiles as they are now, I predict huge number will break/fall off during engine startup on launch,
some more falling off during ascent, will make for an interesting light show during re=entry
Title: Re: Starship heat shield
Post by: Redclaws on 10/10/2021 02:39 pm
closeup of some discovery spaceshuttle tiles on display at
Air and Space Museum Parkway Chantilly, VA
Tiles are from front side panel , (not very exposed) can see some marks from re=entry, can see some sort of gap filler, some has been worn away during re=entry, exposing some other sort of material between tiles.
If SN20 flies with tiles as they are now, I predict huge number will break/fall off during engine startup on launch,
some more falling off during ascent, will make for an interesting light show during re=entry

I think static firing should take care of the “engine startup on launch part”, don’t you think?  Or perhaps the vibrations will be much worse when not held down…. Hmm.
Title: Re: Starship heat shield
Post by: brettly2021 on 10/10/2021 02:48 pm
static fire is extremely short duration, will sn20 be on top of bn4 when bn4 is static fired?
anyhow this interview with elon musk I think only about 2 weeks ago,
https://www.youtube.com/watch?v=4_LAXD-f9e0

at about the 45min mark he brings in the heatshield head guy, who mentions a few interesting things, one of which is they use some factory machines originally from a croatian condensed milk factory in part of proces of the tile making ( he mentions recovering acid and grinding up the fibres).....poor guy looks absolutely exhausted by the way.
Title: Re: Starship heat shield
Post by: rsdavis9 on 10/10/2021 03:24 pm
StarShip will likely be limited to now lower than ~30-40 degrees during reentry. Control authority will drop to near zero at zero degrees. Also, Max L/D occurs around this AoA range, so there isn't a need to go to lower AoA.

John

Just to make sure: 0 deg AoA is when starship is belly flopping with neither nose or tail closer to the oncoming stream of air/plasma?
Title: Re: Starship heat shield
Post by: equiserre on 10/10/2021 04:42 pm
Radical, are your doubts not solved by watching the simulation of mars edl? It shows all maneuvers in dynamic detail. It checks out. Dont understand your concerns

A simulation from four years ago, built around a carbon composite vehicle, with a single delta wing, with a split flap, and a fixed dihedral?  A simulation that doesn't use the skydiving technique?  I still have some doubts.
We are talking about different sims then
Title: Re: Starship heat shield
Post by: Exastro on 10/10/2021 04:54 pm
StarShip will likely be limited to now lower than ~30-40 degrees during reentry. Control authority will drop to near zero at zero degrees. Also, Max L/D occurs around this AoA range, so there isn't a need to go to lower AoA.

John

Just to make sure: 0 deg AoA is when starship is belly flopping with neither nose or tail closer to the oncoming stream of air/plasma?

It's perpendicular to that (per Wikipedia) https://en.wikipedia.org/wiki/Angle_of_attack (https://en.wikipedia.org/wiki/Angle_of_attack): 

(https://upload.wikimedia.org/wikipedia/commons/f/f5/MISB_ST_0601.8_-_Platform_Angle_of_Attack.png)
Title: Re: Starship heat shield
Post by: equiserre on 10/10/2021 05:30 pm
Radical, are your doubts not solved by watching the simulation of mars edl? It shows all maneuvers in dynamic detail. It checks out. Dont understand your concerns

A simulation from four years ago, built around a carbon composite vehicle, with a single delta wing, with a split flap, and a fixed dihedral?  A simulation that doesn't use the skydiving technique?  I still have some doubts.
We are talking about different sims then
The sim in the dearmoon presentation has the present configuration except different fins planform. It's earth edl. Put it the toghether with the one in 2019 which is a mars reentry, and the sim in mk1 starship update, showing final bellyflop with the most actual configuration. You have everything you need.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 10/10/2021 06:53 pm
StarShip will likely be limited to now lower than ~30-40 degrees during reentry. Control authority will drop to near zero at zero degrees. Also, Max L/D occurs around this AoA range, so there isn't a need to go to lower AoA.

John

Just to make sure: 0 deg AoA is when starship is belly flopping with neither nose or tail closer to the oncoming stream of air/plasma?

No, that's 90º AoA.  AoA is relative to the flow.  Flight path angle is relative to the horizon.  So the bellyflop is 90º AoA and 90º flight-path angle.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 10/10/2021 07:31 pm
I don’t see how “rotating about the velocity vector is essentially a controlled hypersonic spiral”. It’s just a roll maneuver. What does “spiral” mean here?

If you just did a roll (i.e., rotation about the x-axis) from a 30º angle of attack, you'd wind up at a -30º angle of attack, which would expose the top of the Starship to high stagnation pressures and heating.

The sim in the dearmoon presentation has the present configuration except different fins planform. It's earth edl. Put it the toghether with the one in 2019 which is a mars reentry, and the sim in mk1 starship update, showing final bellyflop with the most actual configuration. You have everything you need.

OK, I'd forgotten about the DearMoon preso.

I understand how pitch and roll work with the elonerons.  I'm less certain about yaw.  I assume that increasing the dihedral for one forward flap and the opposite rear flap will induce some amount of yaw, but I'm not sure how much control authority there is relative to pitch and roll.

I guess you can perform the maneuver with a series of small roll/pitch/roll/pitch... maneuvers, which means that there's a combination maneuver that will be smooth.  That doesn't require much yaw authority.

I surrender!
Title: Re: Starship heat shield
Post by: ETurner on 10/10/2021 08:01 pm
I don’t see how “rotating about the velocity vector is essentially a controlled hypersonic spiral”. It’s just a roll maneuver. What does “spiral” mean here?

If you just did a roll (i.e., rotation about the x-axis) from a 30º angle of attack, you'd wind up at a -30º angle of attack, which would expose the top of the Starship to high stagnation pressures and heating.
Oops -- terminology blooper. Yes, “roll” would be in body-centered coordinates and neither necessary or wise. What one wants is rotation of the vehicle around the velocity vector (w.r.t. the surrounding air), which redirects the lift vector while making no difference to thermal protection. What can be confusing is that for typical vehicles and typical flight conditions, the nominal body axis and velocity vector roughly coincide.
Title: Re: Starship heat shield
Post by: livingjw on 10/10/2021 08:55 pm
StarShip will likely be limited to now lower than ~30-40 degrees during reentry. Control authority will drop to near zero at zero degrees. Also, Max L/D occurs around this AoA range, so there isn't a need to go to lower AoA.

John

Just to make sure: 0 deg AoA is when starship is belly flopping with neither nose or tail closer to the oncoming stream of air/plasma?

No, 0 degree AoA is when the axis of StarShip is coincident with the direction of flight, just like an aircraft. 90 degree would be full belly flop.

John
Title: Re: Starship heat shield
Post by: ETurner on 10/11/2021 11:05 am
I don’t see how “rotating about the velocity vector is essentially a controlled hypersonic spiral”. It’s just a roll maneuver. What does “spiral” mean here?

If you just did a roll (i.e., rotation about the x-axis) from a 30º angle of attack, you'd wind up at a -30º angle of attack, which would expose the top of the Starship to high stagnation pressures and heating.
Oops -- terminology blooper. Yes, “roll” would be in body-centered coordinates and neither necessary or wise. What one wants is rotation of the vehicle around the velocity vector (w.r.t. the surrounding air), which redirects the lift vector while making no difference to thermal protection. What can be confusing is that for typical vehicles and typical flight conditions, the nominal body axis and velocity vector roughly coincide.
Also, a “barrel roll” in aerobatics is pretty much a rotation around the velocity vector, and definitely not around the vehicle axis (this is an “aileron roll”, which is very different at high AoA!). I had meant “roll” in the former not-wrong sense.
Title: Re: Starship heat shield
Post by: edzieba on 10/11/2021 11:17 am
RVac 6 in tent 1.
A peek into tent 3.
S22 common dome section inside tent 1.
Yes, it is windy today.
As it's technically part of the vehicle TPS: RVac has now gained a metallic skirt.
Title: Re: Starship heat shield
Post by: Modiseus on 10/11/2021 05:10 pm
Vic on the LabPadre discord has found PowerPoint slides about Starship reentry observation:
https://ntrs.nasa.gov/citations/20210020835

The NASA Scientifically Calibrated In Flight Imagery (SCIFLI) team plans to take images of Starship as it reenters using NASAs WB-57F aircraft. Some interesting details can be found in these two slides:

The Starship heatshield is labeled as "Starbrick thermal tiles".

[Starship's heat tiles are called "Starbricks".]

They are targeting a Starship reentry observation opportunity near March 2022.

The slides contain a picture of Spacex's heat simulation software. I have attached the full image that can be found inside the PowerPoint file.
(fun fact: .pptx files are just zip file that can be opened by a software like 7zip or by renaming them to .zip)

zubenelgenubi: Added content in [ ].
Title: Re: Starship heat shield
Post by: eriblo on 10/11/2021 05:48 pm
It is worth noting (especially in this thread) that while the max heating rate due to Raptor toasting looks to be similar to Starship reentry it is unlikely that Super Heavy will need any extra protection:

304l:
Heat capacity: 0.5 J/g/K
Density: 8 g/cm3
Thickness: 4 mm

=> Areal heat capacity: 1.6 J/K/cm2

Max heat rate: 20 W/cm2     =>  Temperature increase:  12.5 K/s
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 10/11/2021 08:23 pm
It is worth noting (especially in this thread) that while the max heating rate due to Raptor toasting looks to be similar to Starship reentry it is unlikely that Super Heavy will need any extra protection:

304l:
Heat capacity: 0.5 J/g/K
Density: 8 g/cm3
Thickness: 4 mm

=> Areal heat capacity: 1.6 J/K/cm2

Max heat rate: 20 W/cm2     =>  Temperature increase:  12.5 K/s
interesting calculation. but wasn't the steel 3 mm or did I miss something?
Title: Re: Starship heat shield
Post by: su27k on 10/12/2021 03:21 am
It is worth noting (especially in this thread) that while the max heating rate due to Raptor toasting looks to be similar to Starship reentry it is unlikely that Super Heavy will need any extra protection:

I think re-entry peak heat rate is a lot higher? It should be over 100 W/cm^2
Title: Re: Starship heat shield
Post by: beelsebob on 10/12/2021 06:21 am
It is worth noting (especially in this thread) that while the max heating rate due to Raptor toasting looks to be similar to Starship reentry it is unlikely that Super Heavy will need any extra protection:

304l:
Heat capacity: 0.5 J/g/K
Density: 8 g/cm3
Thickness: 4 mm

=> Areal heat capacity: 1.6 J/K/cm2

Max heat rate: 20 W/cm2     =>  Temperature increase:  12.5 K/s
interesting calculation. but wasn't the steel 3 mm or did I miss something?
I believe for super heavy it was, and still is intended to be 4mm.  Starship itself has had thinner steel experiments performed, but it doesn’t need to withstand launching with a full starship on top of it, and not getting crushed.
Title: Re: Starship heat shield
Post by: brettly2021 on 10/12/2021 05:55 pm
Red RTV silicone think you could use that inbetween the tiles?
Seems the answer in part is yes, used on shuttle discovery to hold the spacer material in place, only a minimal amount seems to have been used see:
https://airandspace.si.edu/collection-objects/tile-gap-filler-shuttle-sts-114/nasm_A20060583000

Also it seems the filler between tiles is ceramic sheet, I would have thought something flexible would be better.
Something flexible with the consistency and rubberyness of silicone sealers would I think help stop ceramic tile breakage. Maybe there is nothing with that consistency that can handle the temperatures.
The spacer material on shuttle discovery was easily removed, as done per one space walk, seems they were only just held in position.
see
https://www.theguardian.com/science/2005/aug/03/spaceexploration.internationalnews1
Title: Re: Starship heat shield
Post by: brettly2021 on 10/12/2021 06:06 pm
Another bit of evidence for red rtv silicone being used on shuttle tiles:
from antlantis shuttle article here:
http://www.collectspace.com/news/news-021811a.html
I think a better option than those pins on starship, I could be wrong.
Title: Re: Starship heat shield
Post by: edzieba on 10/12/2021 06:37 pm
Red RTV silicone think you could use that inbetween the tiles?
Seems the answer in part is yes, used on shuttle discovery to hold the spacer material in place, only a minimal amount seems to have been used see:
https://airandspace.si.edu/collection-objects/tile-gap-filler-shuttle-sts-114/nasm_A20060583000

Also it seems the filler between tiles is ceramic sheet, I would have thought something flexible would be better.
Something flexible with the consistency and rubberyness of silicone sealers would I think help stop ceramic tile breakage. Maybe there is nothing with that consistency that can handle the temperatures.
The spacer material on shuttle discovery was easily removed, as done per one space walk, seems they were only just held in position.
see
https://www.theguardian.com/science/2005/aug/03/spaceexploration.internationalnews1
The filler bars are not 'ceramic sheet', it's ceramic fibre (mat).
Starship uses two different tile attachment mechanisms. Over most of the surface, mechanical pins are used. Over small areas with high or complex curvature (nose tip, flap edges, flap cover roots,) adhesive bonding almost identical to STS is used (good chance they're using RTV-560, as its flight tested and so known to work).
Title: Re: Starship heat shield
Post by: brettly2021 on 10/14/2021 10:23 am
Its probably time for a flexible sealant purpose built for the job that can withstand very high temps,
both the tiles and sealant start out from the same material ( silica) or perhaps some combination of the two together ( powdered tiles into red silicon mix or something similar). Flexible silicone and fragile tiles is a good combination in my view. I have no idea of the history of how red rtv sealant came about whether is was developed for space program or just happened to suit their use.
Title: Re: Starship heat shield
Post by: brettly2021 on 10/14/2021 10:34 am
seems testing of rtv ( room temperature vulcanising) silicones goes back to the 1960s, this JPL paper maybe around the start of when they were testing them for space use.
https://ntrs.nasa.gov/api/citations/19650020859/downloads/19650020859.pdf
560 silicone is tested at that time, its now over 50years years down the track, surely there are now available better suited materials  or perhaps it really is time for some products to be developed.
Title: Re: Starship heat shield
Post by: WormPicker959 on 10/14/2021 04:08 pm
One thing I noticed in the recent photos from StarshipGazer is that the tiles that are glued on have white side-faces, whereas the black glass coating goes down over the sides in the "standard" tiles. I wonder if that's just that there's gap filler "pre-attached" to the tiles or something? They also look significantly thicker than the standard tiles.

Because so much of this is very similar to STS (RTV, black glass coated silica fibers, etc.), were there tiles on the orbiters that also didn't have a glass coating on the sides? If so, what was the reasoning?

Edit: attached image to show what I mean. There look to be some denoising/image processing artifacts when you zoom in, so the detail is a bit funky in places, but it's pretty clear anyways.
Title: Re: Starship heat shield
Post by: xvel on 10/14/2021 04:49 pm
Maybe it's just manufacturing simplification, mechanically attached tiles have only few shapes and there are lots of them so they are mass produced and then coated, glued tiles have more shapes and there is a lot less of them so maybe they are cnc cut from precoated blanks so sides are left uncoated.
Title: Re: Starship heat shield
Post by: brettly2021 on 10/14/2021 05:42 pm
it appears they have wrapped the white nomex or similar fabric around the edges, if you look the right hand top of same pic you can see more clearly the sides are wrapped in the white material, pic attached, I wonder  what the glue is going underneath?
Title: Re: Starship heat shield
Post by: eriblo on 10/14/2021 06:08 pm
it appears they have wrapped the white nomex or similar fabric around the edges, if you look the right hand top of same pic you can see more clearly the sides are wrapped in the white material, pic attached, I wonder  what the glue is going underneath?
We can be fairly sure it is not Nomex (max temperature 370°C) - "refractory ceramic fiber felt" is likely unspecific enough to be correct, i.e. similar or even identical to what is under the other tiles.
Title: Re: Starship heat shield
Post by: brettly2021 on 10/16/2021 08:53 am
Yes I only said Nomex as I had heard it mentioned in regard space shuttle tiles. I really have no idea what the fabric is.
Title: Re: Starship heat shield
Post by: brettly2021 on 10/16/2021 09:23 am
just a quick bit of research found this article:
https://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts_sys.html
It confirms Nomex used as the tile base on space shuttle tiles ( so basically aramid fibres, I think kevlar is type of aramid fibre) that are made into a felt like material ( a bit less than 1/2" thick in some areas on shuttle).
max temp 500F ( 260degC) but some areas where the nomex is treated can take 800F ( 426degC).
Of course being at bottom of tile temps will be much lower than the front of tiles ( 2,000degC ?).
So its possible it is still some style of Nomex or aramid fibre, definitely possible.
Search for SIPS in article above takes you too relevant info.
Title: Re: Starship heat shield
Post by: eriblo on 10/16/2021 01:27 pm
seems testing of rtv ( room temperature vulcanising) silicones goes back to the 1960s, this JPL paper maybe around the start of when they were testing them for space use.
https://ntrs.nasa.gov/api/citations/19650020859/downloads/19650020859.pdf
560 silicone is tested at that time, its now over 50years years down the track, surely there are now available better suited materials  or perhaps it really is time for some products to be developed.
Technological progress is not only limited by time and effort (i.e. money) but ultimately by the laws of physics. Just because some thing was invented 50 years ago does not automagically mean that it has or even can be improved upon. They are after all using 304l SS which is 100 years old technology...

There might well be incremental improvements and adaption to unique requirements to be done but I would think that the field of high temperature flexible seals and adhesives is fairly mature considering how much money has been spent on optimizing internal combustion engines.
Title: Re: Starship heat shield
Post by: Redclaws on 10/16/2021 01:55 pm
seems testing of rtv ( room temperature vulcanising) silicones goes back to the 1960s, this JPL paper maybe around the start of when they were testing them for space use.
https://ntrs.nasa.gov/api/citations/19650020859/downloads/19650020859.pdf
560 silicone is tested at that time, its now over 50years years down the track, surely there are now available better suited materials  or perhaps it really is time for some products to be developed.
Technological progress is not only limited by time and effort (i.e. money) but ultimately by the laws of physics. Just because some thing was invented 50 years ago does not automagically mean that it has or even can be improved upon. They are after all using 304l SS which is 100 years old technology...

There might well be incremental improvements and adaption to unique requirements to be done but I would think that the field of high temperature flexible seals and adhesives is fairly mature considering how much money has been spent on optimizing internal combustion engines.

For a lot of reasons, the relevant definition of “high temperature” and the desired properties here are pretty different. That doesn’t mean there’s necessarily any low hanging fruit for development, but I think it does mean the automotive seals work is only marginally relevant.
Title: Re: Starship heat shield
Post by: livingjw on 10/16/2021 04:06 pm
seems testing of rtv ( room temperature vulcanising) silicones goes back to the 1960s, this JPL paper maybe around the start of when they were testing them for space use.
https://ntrs.nasa.gov/api/citations/19650020859/downloads/19650020859.pdf
560 silicone is tested at that time, its now over 50years years down the track, surely there are now available better suited materials  or perhaps it really is time for some products to be developed.
Technological progress is not only limited by time and effort (i.e. money) but ultimately by the laws of physics. Just because some thing was invented 50 years ago does not automagically mean that it has or even can be improved upon. They are after all using 304l SS which is 100 years old technology...

There might well be incremental improvements and adaption to unique requirements to be done but I would think that the field of high temperature flexible seals and adhesives is fairly mature considering how much money has been spent on optimizing internal combustion engines.

For a lot of reasons, the relevant definition of “high temperature” and the desired properties here are pretty different. That doesn’t mean there’s necessarily any low hanging fruit for development, but I think it does mean the automotive seals work is only marginally relevant.

How so? They seem pretty relevant to me.

John
Title: Re: Starship heat shield
Post by: eriblo on 10/16/2021 09:23 pm
It is worth noting (especially in this thread) that while the max heating rate due to Raptor toasting looks to be similar to Starship reentry it is unlikely that Super Heavy will need any extra protection:
I think re-entry peak heat rate is a lot higher? It should be over 100 W/cm^2
It would be great if the current Starship tiles are able to handle that kind of heat flux as that would be state-of-the-art. I am no expert but I have wondered quite a bit about this, so here is my "quick" recap for those who are interested:


Reusable radiative/insulative TPS generally consist of an outer layer that can withstand both the temperature, loads and chemical attack at the surface and has a high emissivity in order to effectively re-radiate the incident heat flux. This is backed by one or more insulating layers in order to stop the heat flow from the hot outer layer to the spacecraft shin/structure.

Each layer has to be matched to the next one regarding maximum temperature, mechanical loads and thermal expansion for the desired range of heating profiles (a short high temperature pulse might melt the outer layer(s) but otherwise be fine while a relatively low temperature but long duration one might leave the TPS unscathed but the spacecraft cooked).

Ceramic TPS tiles like those on the Shuttle and (to all appearances) Starship consist of a block of rigidized refractory ceramic fiber coated/impregnated on the outer surface with a high temperature high emissivity glass.


Some examples of the maximum use temperatures (heat flux assumes equilibrium black body radiation at ε=0.9):
 
Original Shuttle HRSI seems to have been limited to 2300 °F (1533 K, 28 W/cm2) due to the pure silica LI-900/-2200 insulation while newer versions like TUFI treated AETB goes up to 1750 K (48 W/cm2). The RCG coating used on these is good for 3000 °F or even 3150 °F.

TUFROC uses a HETC treatment (includes tantalum disilicide for improved thermal and emissive properties) on an intermediate oxidation protected ceramic carbon layer on top of the TUFI/AETB to mange 3000 °F  (1922 K, 70 W/cm2) for ~10 min or up to 3600 °F (2255 K, 132 W/cm2) for ~1 min. This matches the multi-use limit on the Shuttles RCC panels at 3000 °F.


The environmental documents we saw back in the day was for TUFI and RCG coatings if I recall correctly. However, I am not sure if that or the insulation composition is limiting - if it contains silica fibers they will probably be limited to something like the AETB temperatures, say 1650 K - 1750 K. More or less all that we can say about the current Starship tiles is that the insulator is white so it is unlikely to be carbon based. If is only alumina and other higher melting point fibers they might be able to reach ~2000 K before they have to improve significantly on previous work.


AETB - Alumina-Enhanced Thermal Barrier
HETC - High Efficiency Tantalum-based Composite
HRSI - High-temperature Reusable Surface Insulation
LI-900/-2200 - Lockheed Insulation, 9/22 lb/cf
RCG - Reaction Cured Glass
TUFI - TToughened Uni-piece Fibrous Insulation
TUFROC  - Toughened Uni-piece, Fibrous, Reinforced, Oxidization-resistant Composite

Light reading:
https://ntrs.nasa.gov/citations/20160003291
https://patents.google.com/patent/US7314648B1 (TUFROC)
https://patents.google.com/patent/US7767305B1 (HETC)

BTW, the HETC and TUFROC patents mentions short duration testing at over 3800 °F (2366 K, 160 W/cm2) and 300 W/cm2 (2796 K) respectively so it is likely that there is quite a bit of non-reusable margin in these systems.
Title: Re: Starship heat shield
Post by: brettly2021 on 10/18/2021 08:43 am
some excellent links there, though being patents they do try to cover all bases and multiple material combinations,
this article is informative on history of heatshield tiles up to 1980.
https://history.nasa.gov/sts1/pages/tps.html
This is a very obvious statement but the conditions the starship re-enters through,  has the ability to completely destroy the space craft, as has been seen many times in the past. So a bunch of tiles being blown off during venting on the ground, and changes in shape of the stailness during crane movements or tank filling are somewhat concerning. As they are I really expect serious tile damage and detachment during static fire, even though a very short duration test. I wonder if it will be a night time test fire.
Title: Re: Starship heat shield
Post by: kevinof on 10/18/2021 09:07 am
Have I got this right? You are suggesting that SpaceX might do a night time test so as to hide any possible damage from onlookers?

Every failure to date has been in public and never hidden. Plus they have some of the smartest engineers on the planet so I think it's a pretty good bet that they understand about expanding tanks and blowing vents and the re-entry regime and are way ahead of us in their thinking and understanding of the issues.

some excellent links there, though being patents they do try to cover all bases and multiple material combinations,
this article is informative on history of heatshield tiles up to 1980.
https://history.nasa.gov/sts1/pages/tps.html
This is a very obvious statement but the conditions the starship re-enters through,  has the ability to completely destroy the space craft, as has been seen many times in the past. So a bunch of tiles being blown off during venting on the ground, and changes in shape of the stailness during crane movements or tank filling are somewhat concerning. As they are I really expect serious tile damage and detachment during static fire, even though a very short duration test. I wonder if it will be a night time test fire.
Title: Re: Starship heat shield
Post by: cdebuhr on 10/18/2021 01:08 pm
Have I got this right? You are suggesting that SpaceX might do a night time test so as to hide any possible damage from onlookers?

Every failure to date has been in public and never hidden. Plus they have some of the smartest engineers on the planet so I think it's a pretty good bet that they understand about expanding tanks and blowing vents and the re-entry regime and are way ahead of us in their thinking and understanding of the issues.

some excellent links there, though being patents they do try to cover all bases and multiple material combinations,
this article is informative on history of heatshield tiles up to 1980.
https://history.nasa.gov/sts1/pages/tps.html
This is a very obvious statement but the conditions the starship re-enters through,  has the ability to completely destroy the space craft, as has been seen many times in the past. So a bunch of tiles being blown off during venting on the ground, and changes in shape of the stailness during crane movements or tank filling are somewhat concerning. As they are I really expect serious tile damage and detachment during static fire, even though a very short duration test. I wonder if it will be a night time test fire.
That's a bit of a stretch, no?  Given the times of the test windows, and past testing performance, its quite reasonable to idly wonder if testing will happen after dark, impeding the ability of the peanut gallery to watch whats going on.  Jumping from there to the conclusion that SpaceX is trying to hide something just doesn't follow.
Title: Re: Starship heat shield
Post by: kevinof on 10/18/2021 02:09 pm
Hell of a stretch and completely without foundation SpaceX have never hidden anything in Boca and I doubt they could even if they wanted to. They have a history of being open about issues and where they are going with something.

Have I got this right? You are suggesting that SpaceX might do a night time test so as to hide any possible damage from onlookers?

Every failure to date has been in public and never hidden. Plus they have some of the smartest engineers on the planet so I think it's a pretty good bet that they understand about expanding tanks and blowing vents and the re-entry regime and are way ahead of us in their thinking and understanding of the issues.

some excellent links there, though being patents they do try to cover all bases and multiple material combinations,
this article is informative on history of heatshield tiles up to 1980.
https://history.nasa.gov/sts1/pages/tps.html
This is a very obvious statement but the conditions the starship re-enters through,  has the ability to completely destroy the space craft, as has been seen many times in the past. So a bunch of tiles being blown off during venting on the ground, and changes in shape of the stailness during crane movements or tank filling are somewhat concerning. As they are I really expect serious tile damage and detachment during static fire, even though a very short duration test. I wonder if it will be a night time test fire.
That's a bit of a stretch, no?  Given the times of the test windows, and past testing performance, its quite reasonable to idly wonder if testing will happen after dark, impeding the ability of the peanut gallery to watch whats going on.  Jumping from there to the conclusion that SpaceX is trying to hide something just doesn't follow.
Title: Re: Starship heat shield
Post by: Redclaws on 10/18/2021 02:20 pm
some excellent links there, though being patents they do try to cover all bases and multiple material combinations,
this article is informative on history of heatshield tiles up to 1980.
https://history.nasa.gov/sts1/pages/tps.html
This is a very obvious statement but the conditions the starship re-enters through,  has the ability to completely destroy the space craft, as has been seen many times in the past. So a bunch of tiles being blown off during venting on the ground, and changes in shape of the stailness during crane movements or tank filling are somewhat concerning. As they are I really expect serious tile damage and detachment during static fire, even though a very short duration test. I wonder if it will be a night time test fire.

We will literally see it in the morning, *if* they did this, but also, if they did it, they would light the thing up with spotlights like crazy, so *they* could see it.
Title: Re: Starship heat shield
Post by: Tangilinear Interjar on 10/18/2021 02:50 pm
" So a bunch of tiles being blown off during venting on the ground, and changes in shape of the stailness during crane movements or tank filling are somewhat concerning. "

Can someone please share with me anything that supports this continuing notion that the nosecone flexes during lifts and therefore looses tiles?

This seems to be a concept taken as a truth by many on this forum and I can't imagine what has possibly driven it. It makes absolutely no sense.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 10/18/2021 06:37 pm
" So a bunch of tiles being blown off during venting on the ground, and changes in shape of the stailness during crane movements or tank filling are somewhat concerning. "

Can someone please share with me anything that supports this continuing notion that the nosecone flexes during lifts and therefore looses tiles?

This seems to be a concept taken as a truth by many on this forum and I can't imagine what has possibly driven it. It makes absolutely no sense.

"Absolutely no sense"

Your burden of proof is inverted.

Everything flexes.   Engineers have to prove the flex is not enough to cause problems, and with tiles on a curved surface you run right into tolerance problems head-on.

OTOH, OP did use the word 'concern', and I can understand why that might be concerning ;-P

Title: Re: Starship heat shield
Post by: edzieba on 10/18/2021 08:33 pm
Your burden of proof is inverted.
For the claim that tiles are lost when the nose is lifted, the burden of proof is to show tiles have been lost when the nose has been lifted.

Thus far, I cannot recall this being observed. Tiles have been observed as lost during pressurisation tests, but not as a result of a lift (even as just inferred tile loss from before/after photos).
Title: Re: Starship heat shield
Post by: ETurner on 10/18/2021 09:19 pm
Your burden of proof is inverted.
For the claim that tiles are lost when the nose is lifted, the burden of proof is to show tiles have been lost when the nose has been lifted.

Thus far, I cannot recall this being observed. Tiles have been observed as lost during pressurisation tests, but not as a result of a lift (even as just inferred tile loss from before/after photos).
Also, steel below its elastic limit [better: working stress] will stretch very little, and lifting from the nose won’t cause significant bending, either. The change in distance between pins will be very, very, very small.
Title: Re: Starship heat shield
Post by: Okie_Steve on 10/18/2021 10:24 pm
After the test fit full stack a number of tiles were marked with colored tape and some were replaced. I made an (erroneous) post assuming it was a result of the lift and others objected.  After some discussion it was concluded there was no direct evidence of when, where or how the damages actually occurred,  it could well have been preexisting, where upon I retracted my assertion.   :o

Basically some people seem to be making the same assumption I did, but without any more real evidence as to what actually happened.

Wait and see.  ::)
Title: Re: Starship heat shield
Post by: OTV Booster on 10/18/2021 10:27 pm
Your burden of proof is inverted.
For the claim that tiles are lost when the nose is lifted, the burden of proof is to show tiles have been lost when the nose has been lifted.

Thus far, I cannot recall this being observed. Tiles have been observed as lost during pressurisation tests, but not as a result of a lift (even as just inferred tile loss from before/after photos).
Also, steel below its elastic limit will stretch very little, and lifting from the nose won’t cause significant bending, either. The change in distance between pins will be very, very, very small.
If I express concern about tiles getting shed, don't take is as a 'sky is falling' type of concern. It's a mix of I (and everybody else) has never seen anything quite like this and SX has been known to give something a try when their modeling doesn't quite reach far enough. At a minimum the modeling improves.


SX is gluing tiles direct to the skin. IIUC, on the shuttle the felt was attached to the skin (glued?) and the tiles were glued to the felt. This gave some latitude for creep. Where tiles are pinned there are dimples that pop into shape with tank press.  Plenty can go wrong.


I have no idea if 20 will shed tiles when she lights off. It's an open question until it's done. For us and probably SX. That's why they test. They can slag the ship on EDL and it's still a win. They can slag 21 or send it off to the boneyard if 20 shows the design to be hopeless. Then we watch for another design on 22. Or maybe this design only needs refinement and maybe (oh, please, oh please) we'll see 20 or 21 do a clean EDL.


My opinion is that SX will make it work but it will probably take a few tries. This is a HARD problem. In the meantime they have a test platform for every pre EDL thing they need to get working. That includes refueling and sat deployment.
Title: Re: Starship heat shield
Post by: oiorionsbelt on 10/18/2021 11:24 pm
On the way to making a minimum viable heat shield, start with something that fails early, iterate quickly from there.
Title: Re: Starship heat shield
Post by: brettly2021 on 10/19/2021 12:31 pm
All I can say is SpaceX WILL solve the problem, there is no doubt about that, and as per usual I will be amazed once again at how they do it, but what we can see from boca chica there is a big issue with tiles, whatever is the true reasons for cracking/fracturing tiles, all pre-launch, must be a  concern considering the stresses the ship will go through on the way back to earth. I'm just going by what I see in videos/pictures and a little research, yup it will be obvious if the tiles are effected by static fire whether they do it at night or day time, but it would be a little embarrasing if they had a massive detiling event on static fire. What do you people think? Anyone care to guesstimate what percentage of tiles will crack or be damaged during static fire? Its a very very short event.
Title: Re: Starship heat shield
Post by: JamesH65 on 10/19/2021 02:17 pm
All I can say is SpaceX WILL solve the problem, there is no doubt about that, and as per usual I will be amazed once again at how they do it, but what we can see from boca chica there is a big issue with tiles, whatever is the true reasons for cracking/fracturing tiles, all pre-launch, must be a  concern considering the stresses the ship will go through on the way back to earth. I'm just going by what I see in videos/pictures and a little research, yup it will be obvious if the tiles are effected by static fire whether they do it at night or day time, but it would be a little embarrasing if they had a massive detiling event on static fire. What do you people think? Anyone care to guesstimate what percentage of tiles will crack or be damaged during static fire? Its a very very short event.

I'm not seeing why this is either concerning or embarrassing. As you say, SpaceX will figure something out, if there is indeed an issue.
Title: Re: Starship heat shield
Post by: Tangilinear Interjar on 10/19/2021 03:33 pm
I also don't see anything that says they have a big issue with tiles. From what I can see, the tiles are pretty robust, yes some have cracked but how much is that just first generation tiles and how much is it due to technique in applying them?

They are very quickly replaceable, they "seem" to be quick to manufacture and customize, and they are very easily handled. The ones that had to be replaced on the nosecone were rushed into place so inferring to much from that might not be reasonable. However they were all QC'd, repaired/replaced and QC'd again. I didn't see evidence of the body getting QC'd, unlike we now can see in the manufacturing tents, so if we see a number on the body fall off during tests it also won't concern me much. If we see a bunch fall off the nosecone then I would be a bit concerned.

And them getting blasted off due to a nozzle facing the wrong direction is not a failure of the tiles.

This is is a prototype design/development process and a huge part of that process is iterative learning. It's to bad more people haven't been able to participate in such a process. It can be very demoralizing at first when your brilliant idea totally tanks due to some root level oversight but you learn to learn from that kind of thing. Eventually you realize that spending any time worrying about what might go wrong is time wasted that would be better used learning from what actually did go wrong (or right).
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 10/20/2021 04:59 am
TUFROC uses a HETC treatment (includes tantalum disilicide for improved thermal and emissive properties) on an intermediate oxidation protected ceramic carbon layer on top of the TUFI/AETB to mange 3000 °F  (1922 K, 70 W/cm2) for ~10 min or up to 3600 °F (2255 K, 132 W/cm2) for ~1 min. This matches the multi-use limit on the Shuttles RCC panels at 3000 °F.

So if the Starship tiles are TUFROC-like, then from the inside out, we have:

1) The pin.
2) Maybe some kind of gap filler / structural slip / bearing to deal with expansion, contraction, and mechanical stresses.
3) AETB as the bulk of the insulating layer.
4) HETC coated with RCG for high refractory, high emissivity, low absorptivity.

I didn't go back a huge number of pages on the thread, so I apologize if this got answered somewhere:  With advanced TUFROC, the slide deck you linked implied that the pin connected to the ROCCI (the HETC/RCG combo).  Do you think that's what's happening with the pinned tiles for Starship?  Or have they figured out some way to anchor the pin latches in the AETB (or whatever the insulator is)?

The other thing I'm not understanding is how the pin isn't a huge heat conductor through the AETB.  This is one of the reasons why I wondered if the latches were in the AETB, but even then, they should still increase the conductivity of the whole system, and you don't want that.  What am I missing?
Title: Re: Starship heat shield
Post by: tyrred on 10/20/2021 05:09 am
TUFROC uses a HETC treatment (includes tantalum disilicide for improved thermal and emissive properties) on an intermediate oxidation protected ceramic carbon layer on top of the TUFI/AETB to mange 3000 °F  (1922 K, 70 W/cm2) for ~10 min or up to 3600 °F (2255 K, 132 W/cm2) for ~1 min. This matches the multi-use limit on the Shuttles RCC panels at 3000 °F.

So if the Starship tiles are TUFROC-like, then from the inside out, we have:

1) The pin.
2) Maybe some kind of gap filler / structural slip / bearing to deal with expansion, contraction, and mechanical stresses.
3) AETB as the bulk of the insulating layer.
4) HETC coated with RCG for high refractory, high emissivity, low absorptivity.

I didn't go back a huge number of pages on the thread, so I apologize if this got answered somewhere:  With advanced TUFROC, the slide deck you linked implied that the pin connected to the ROCCI (the HETC/RCG combo).  Do you think that's what's happening with the pinned tiles for Starship?  Or have they figured out some way to anchor the pin latches in the AETB (or whatever the insulator is)?

The other thing I'm not understanding is how the pin isn't a huge heat conductor through the AETB.  This is one of the reasons why I wondered if the latches were in the AETB, but even then, they should still increase the conductivity of the whole system, and you don't want that.  What am I missing?

I think you missed the part where these tiles are not TUFROC.
Title: Re: Starship heat shield
Post by: ETurner on 10/20/2021 12:55 pm
The other thing I'm not understanding is how the pin isn't a huge heat conductor through the AETB.  This is one of the reasons why I wondered if the latches were in the AETB, but even then, they should still increase the conductivity of the whole system, and you don't want that.  What am I missing?
Thermal conductance is proportional to conductivity x cross-section.
Pin conductivity is high (metal), but cross-section(pins) << cross-section(tiles), so relative conductance is low.
Also, the pins don’t go all the way through and and probably make poor (point-like) thermal contact with the tiles.
This has come up before.
Title: Re: Starship heat shield
Post by: OTV Booster on 10/20/2021 08:09 pm
The other thing I'm not understanding is how the pin isn't a huge heat conductor through the AETB.  This is one of the reasons why I wondered if the latches were in the AETB, but even then, they should still increase the conductivity of the whole system, and you don't want that.  What am I missing?
Thermal conductance is proportional to conductivity x cross-section.
Pin conductivity is high (metal), but cross-section(pins) << cross-section(tiles), so relative conductance is low.
Also, the pins don’t go all the way through and and probably make poor (point-like) thermal contact with the tiles.
This has come up before.
And, for a metal, SS is a lousy heat conductor.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 10/21/2021 03:58 am
And, for a metal, SS is a lousy heat conductor.

If you were going to have hot spots, you'd want the metal to be a good conductor.
Title: Re: Starship heat shield
Post by: OTV Booster on 10/21/2021 04:09 pm
And, for a metal, SS is a lousy heat conductor.

If you were going to have hot spots, you'd want the metal to be a good conductor.
It's a two edged sword. The pins conduct poorly to the skin, but when the heat impulse does get there it doesn't conduct away and spread out very fast. Grumble, grumble.
Title: Re: Starship heat shield
Post by: marsbase on 10/21/2021 04:17 pm
And, for a metal, SS is a lousy heat conductor.

If you were going to have hot spots, you'd want the metal to be a good conductor.
It's a two edged sword. The pins conduct poorly to the skin, but when the heat impulse does get there it doesn't conduct away and spread out very fast. Grumble, grumble.
The skin is only 4 mm think, much thinner than the length of the pins.  And of course the cryo fuels have chilled the skin from the inside.  So a heat sink is less than 4 mm away from the surface of the skin.
Title: Re: Starship heat shield
Post by: DanClemmensen on 10/21/2021 05:29 pm
And, for a metal, SS is a lousy heat conductor.

If you were going to have hot spots, you'd want the metal to be a good conductor.
It's a two edged sword. The pins conduct poorly to the skin, but when the heat impulse does get there it doesn't conduct away and spread out very fast. Grumble, grumble.
The skin is only 4 mm think, much thinner than the length of the pins.  And of course the cryo fuels have chilled the skin from the inside.  So a heat sink is less than 4 mm away from the surface of the skin.
It's complicated. The pin might have the equivalent of a 4mm x 4mm cross section. The steel under a missing tile might have a cross sectional surface to adjoining steel areas of about 4mm depth  x 500 mm circumference. In addition to the heat transfer into the ship. the cross section into the ship is perhaps equivalent to 300 mm x 300 mm. When the missing tile is over a tank, the heat will transfer to the very cold gas or liquid in the tank convectively: this transfer is overwhelmingly larger that any conduction in the steel.  When the missing tile is not over a tank, things will get interesting. My guess (no data, just a guess) is that convective heat transfer into atmospheric pressured air will easily keep the steel cool, but what about an unpressurized cargo hold?
Title: Re: Starship heat shield
Post by: edzieba on 10/21/2021 06:05 pm
this transfer is overwhelmingly larger that any conduction in the steel.
That's a definitely a 'calculations required' claim.

600-1200kWm^-2 are a rough range for thermal flux during re-entry heating, so ~300mm x 300mm of exposed stainless steel is being bathed by 54-108kW of heating. To stay below ~650°C (significant strength loss beyond that), you have:
An 850K (~650°C and ~-200°C on either side) temperature gradient
A 4mm wall thickness (0.004m)
A 16.2 Wm^-1K^-1 thermal conductivity for 304L
So you can tolerate ~55Wm^-2 in steady-state for bare 304L. That's quite a way from what's necessary to handle EDL, hence why the tiles are installed to start with.
Title: Re: Starship heat shield
Post by: tbellman on 10/21/2021 06:55 pm
When the missing tile is over a tank, the heat will transfer to the very cold gas or liquid in the tank convectively:

Which cold gas or liquid?  The main tanks will be more or less empty at atmospheric entry.  They may be pressurized to make the ship stiff, but otherwise you can't count on there being any propellant left in them.  The landing propellant will be in the header tanks.

There is also the payload bay, which takes up a large portion of the surface area, and inside that you may have live human beings, not cryogenic liquids...
Title: Re: Starship heat shield
Post by: whitelancer64 on 10/21/2021 07:29 pm
TUFROC uses a HETC treatment (includes tantalum disilicide for improved thermal and emissive properties) on an intermediate oxidation protected ceramic carbon layer on top of the TUFI/AETB to mange 3000 °F  (1922 K, 70 W/cm2) for ~10 min or up to 3600 °F (2255 K, 132 W/cm2) for ~1 min. This matches the multi-use limit on the Shuttles RCC panels at 3000 °F.

So if the Starship tiles are TUFROC-like, then from the inside out, we have:

1) The pin.
2) Maybe some kind of gap filler / structural slip / bearing to deal with expansion, contraction, and mechanical stresses.
3) AETB as the bulk of the insulating layer.
4) HETC coated with RCG for high refractory, high emissivity, low absorptivity.

I didn't go back a huge number of pages on the thread, so I apologize if this got answered somewhere:  With advanced TUFROC, the slide deck you linked implied that the pin connected to the ROCCI (the HETC/RCG combo).  Do you think that's what's happening with the pinned tiles for Starship?  Or have they figured out some way to anchor the pin latches in the AETB (or whatever the insulator is)?

The other thing I'm not understanding is how the pin isn't a huge heat conductor through the AETB.  This is one of the reasons why I wondered if the latches were in the AETB, but even then, they should still increase the conductivity of the whole system, and you don't want that.  What am I missing?

I think you missed the part where these tiles are not TUFROC.

eriblo's post does not say that.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 10/21/2021 08:27 pm
I think you missed the part where these tiles are not TUFROC.

eriblo's post does not say that.

I know they're not TUFROC, which is why I said "TUFROC-like".  Is that correct?  Or at least to the extent that they're:

1) Pinned attachments.  (And I'm still confused how the pins are mechanically anchored into the tiles.)
2) RCG of some sort on the outside, with some thin layer of high-heat-capacity refractory substance just below.
3) Then something thicker with very low conductivity below that.
Title: Re: Starship heat shield
Post by: eriblo on 10/21/2021 09:51 pm
I think you missed the part where these tiles are not TUFROC.

eriblo's post does not say that.

I know they're not TUFROC, which is why I said "TUFROC-like".  Is that correct?  Or at least to the extent that they're:

1) Pinned attachments.  (And I'm still confused how the pins are mechanically anchored into the tiles.)
2) RCG of some sort on the outside, with some thin layer of high-heat-capacity refractory substance just below.
3) Then something thicker with very low conductivity below that.
TUFROC has a completely separate ceramic carbon cap on top of a refractory ceramic fiber base (both of which are porous bulk insulators). TUFROC is glued to the spacecraft skin, the pins-connecting-to-embedded-metal-brackets are a completely separate attachment system. We have seen no sign of separate layers beyond the surface coating or any carbon based material so I think the current tiles are much closer to a denser version of TUFI tiles.
Title: Re: Starship heat shield
Post by: Hog on 10/21/2021 10:09 pm
Thermal Protection Materials and
Systems: Past and Future

Sylvia M. Johnson
NASA Ames Research Center
40th International Conference and Exposition
on Advanced Ceramics and Composites
Daytona Beach
January 25, 2015
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 10/21/2021 11:25 pm
TUFROC has a completely separate ceramic carbon cap on top of a refractory ceramic fiber base (both of which are porous bulk insulators). TUFROC is glued to the spacecraft skin, the pins-connecting-to-embedded-metal-brackets are a completely separate attachment system. We have seen no sign of separate layers beyond the surface coating or any carbon based material so I think the current tiles are much closer to a denser version of TUFI tiles.

I'm going off of p. 19 of the preso that you linked up-thread.  That shows both the ROCCI cap and the AETB.

There's a diagram on p. 16 that shows the pin sticking out of the "substrate", but it doesn't specify whether the other end of the pin is anchored in the insulator (which would requiring gluing the tile to the vehicle) or whether it extends all the way through the insulator (which would imply that it's attached to the vehicle).

This is where I'm still confused.  ISTM that there are three ways you can pin the tile on vehicle (everyone's favorite party game):

1) Pin attached to structure, poking all the way through the insulator, and anchored on the ROCCI (or thing on the tiles that's like the ROCCI).  In this, the insulator is just kinda smooshed between the cap and the structure, but prevented from sliding by the pins going through it.  This gives a conductive path through the insulator via the pin but, as ETurner pointed out, if the pin cross section to insulator ratio is low, maybe this isn't a big deal.

2) Something TUFI-like, with the pin attached to the structure, but anchored somewhere in the insulator.  Since the insulator is mechanically weak, I'd imagine that the anchor would have to be wider to distribute the load without the insulator getting crumbly, and the wide anchor would then have an issue with having a lot of area with high conductance.

3) Pin attached to the insulator, and anchored on the ROCCI or ROCCI-like layer, with the insulator glued on.  (Note that I'm ignoring any spacers or slip pads--they could exist in all three cases.)

Both #1 and #3 are consistent with the picture on p. 16.  But I think you're saying that #2 is the mostly likely bet.  That seems most consistent with a unitary tile, but then I don't understand the anchoring method.
Title: Re: Starship heat shield
Post by: daavery on 10/22/2021 01:20 am
https://forum.nasaspaceflight.com/index.php?topic=50748.msg2291774#msg2291774

shows the SPX tiles - they have a Y grooved embed that captures the pin tops  . the embed looks to be a metallic structure that is cast into the base tile.
Title: Re: Starship heat shield
Post by: Slarty1080 on 10/22/2021 01:48 am
https://twitter.com/elonmusk/status/1451354108531728384 (https://twitter.com/elonmusk/status/1451354108531728384)
Title: Re: Starship heat shield
Post by: ETurner on 10/22/2021 02:48 am
https://twitter.com/elonmusk/status/1451354108531728384 (https://twitter.com/elonmusk/status/1451354108531728384)
How can this be reasonable at this late date?
If these are known-bad tiles that they haven’t bothered to replace, that’s sort of almost OK.
But otherwise...??
Title: Re: Starship heat shield
Post by: grndkntrl on 10/22/2021 03:02 am
https://twitter.com/elonmusk/status/1451354108531728384 (https://twitter.com/elonmusk/status/1451354108531728384)
How can this be reasonable at this late date?
If these are known-bad tiles that they haven’t bothered to replace, that’s sort of almost OK.
But otherwise...??

Because:
Quote from: Elon Musk
Shaking out the problems (literally) haha

https://twitter.com/elonmusk/status/1451378080845549570
Title: Re: Starship heat shield
Post by: Toast on 10/22/2021 03:38 am
https://twitter.com/elonmusk/status/1451354108531728384 (https://twitter.com/elonmusk/status/1451354108531728384)
How can this be reasonable at this late date?
If these are known-bad tiles that they haven’t bothered to replace, that’s sort of almost OK.
But otherwise...??

I think we need to define "late date". If this was something like SLS-1 (build it slowly and expensively but get it right the first time) then yes, this would absolutely be concerning. But it's not like that at all--this is a very early prototype (that is being intentionally expended) in a very hardware-rich "try stuff and see what works" style development program.
Title: Re: Starship heat shield
Post by: Coastal Ron on 10/22/2021 03:41 am
How can this be reasonable at this late date?
If these are known-bad tiles that they haven’t bothered to replace, that’s sort of almost OK.
But otherwise...??

We have to remember that the Starship vehicle will NEVER light its engines on the ground for normal flights, because it will normally sit on top of the Booster to get off the ground. So tiles falling off because of a static fire on the ground is not necessarily a bad sign, since that is a condition they are not designed to operate in.

The bigger question is whether the tiles that did fall off during the static fire would have stayed on during a launch on top of the Booster, with the air trying to rip them off...
Title: Re: Starship heat shield
Post by: xvel on 10/22/2021 03:45 am
How can this be reasonable at this late date?
If these are known-bad tiles that they haven’t bothered to replace, that’s sort of almost OK.
But otherwise...??

We have to remember that the Starship vehicle will NEVER light its engines on the ground for normal flights, because it will normally sit on top of the Booster to get off the ground. So tiles falling off because of a static fire on the ground is not necessarily a bad sign, since that is a condition they are not designed to operate in.

The bigger question is whether the tiles that did fall off during the static fire would have stayed on during a launch on top of the Booster, with the air trying to rip them off...

Yes but actually no, point to point starship will launch on it's own and it will have even more engines
Title: Re: Starship heat shield
Post by: chopsticks on 10/22/2021 04:33 am
How can this be reasonable at this late date?
If these are known-bad tiles that they haven’t bothered to replace, that’s sort of almost OK.
But otherwise...??

We have to remember that the Starship vehicle will NEVER light its engines on the ground for normal flights, because it will normally sit on top of the Booster to get off the ground. So tiles falling off because of a static fire on the ground is not necessarily a bad sign, since that is a condition they are not designed to operate in.

The bigger question is whether the tiles that did fall off during the static fire would have stayed on during a launch on top of the Booster, with the air trying to rip them off...

Yes but actually no, point to point starship will launch on it's own and it will have even more engines
We're a long ways from there yet.
Title: Re: Starship heat shield
Post by: ThatOldJanxSpirit on 10/22/2021 07:18 am
https://twitter.com/elonmusk/status/1451354108531728384 (https://twitter.com/elonmusk/status/1451354108531728384)
How can this be reasonable at this late date?
If these are known-bad tiles that they haven’t bothered to replace, that’s sort of almost OK.
But otherwise...??

It is completely reasonable because this is not a ‘late date’. This is an early flight prototype, not a finished product. If tiles fall off they replace them. If tiles keep falling off they tweak the design. That’s the whole point of this development method.
Title: Re: Starship heat shield
Post by: Slarty1080 on 10/22/2021 09:11 am
https://twitter.com/elonmusk/status/1451354108531728384 (https://twitter.com/elonmusk/status/1451354108531728384)
How can this be reasonable at this late date?
If these are known-bad tiles that they haven’t bothered to replace, that’s sort of almost OK.
But otherwise...??

It is completely reasonable because this is not a ‘late date’. This is an early flight prototype, not a finished product. If tiles fall off they replace them. If tiles keep falling off they tweak the design. That’s the whole point of this development method.
The heat tiles will also experience an environment that they would not normally encounter. At launch Starship will be 50m away from the Raptors on Superheavy and when the Raptors on Starship fire up it will be out of the atmosphere. That said, no doubt they will still take a lot of vibration and will need design tweaks etc. But yes its a prototype...
Title: Re: Starship heat shield
Post by: Yggdrasill on 10/22/2021 09:26 am
Six engine static fire may be the most intense event the heat shield will experience, aside from the heating of reentry. When the Starship engines fire up after separation from Super Heavy, the Starship isn't being held back by mounting points to the suborbital launch mount, so the energy goes more into accelerating the Starship instead of twisting and bending the structure, and dynamic loads should be lower. So, if SpaceX gets to the point where they can do a six engine static fire without any tiles falling off, that's probably a good indicator they are attached properly.

I guess we will see if they now attach the other four engines and do another static fire. If they do, and it's a similarly low number of tiles missing, I would think SpaceX has it under control.
Title: Re: Starship heat shield
Post by: Almoturg on 10/22/2021 11:05 am
this transfer is overwhelmingly larger that any conduction in the steel.
That's a definitely a 'calculations required' claim.

600-1200kWm^-2 are a rough range for thermal flux during re-entry heating, so ~300mm x 300mm of exposed stainless steel is being bathed by 54-108kW of heating. To stay below ~650°C (significant strength loss beyond that), you have:
An 850K (~650°C and ~-200°C on either side) temperature gradient
A 4mm wall thickness (0.004m)
A 16.2 Wm^-1K^-1 thermal conductivity for 304L
So you can tolerate ~55Wm^-2 in steady-state for bare 304L. That's quite a way from what's necessary to handle EDL, hence why the tiles are installed to start with.

That's off by ~5 orders of magnitude, you multiplied by 0.004 instead of dividing.

(16.2 Wm^-1K^-1) × (850K) / (0.004m) = 3.4 × 10^6 Wm^-2

so about 300 kW /m^2
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 10/22/2021 02:06 pm
Well, after the 2 engine static fire some tiles fell off. It seems to me that the more catastrophist theory (that a big wave of tiles will fell off) has been proven wrong*. I personally thought that a bit more tiles would fell of.
*But still we have to see a full static fire, but this makes me more confident, expecially because of the already mentioned different conditions during a real orbital launch.

I counted about 10 tiles lacking, but id don't know if the pan covered the entire vehicle. Moreover I'm not a qualified pixel counter. Was the spot that I higlighted absent before the static fire (so it was caused by the vent problem of a few weeks ago)?

Title: Re: Starship heat shield
Post by: brettly2021 on 10/22/2021 03:19 pm
I'm not sure how long the test fire was, maybe 1 at most 2 seconds, but I was expecting more tiles to come loose,
the thing is there will now be considerable cracking of tiles apart from those that fell off. Suspect they will have to go through the coloured tape exercise again, that will give an indication of how many tiles cracked. I suspect quite alot. There is definitely a design issue to be solved here, a very high temp flexible glue would solve the problem, has it been invented yet? sticky glue type aerogel? similar to red rtv in consistency and glueing properties but extreme high temp, I doubt it exists yet.
So how will they solve it? Anyone got any ideas how to solve it ? Maybe red rtv between the Y shaped backing plate and the tile? that might work. A bit of red rtv where the clips make contact with the Y shaped backing plate might also help.
I've always thought silicone solves alot of problems.
Title: Re: Starship heat shield
Post by: edzieba on 10/22/2021 03:25 pm
No need to try and solve issues that haven't actually occurred yet: "considerable cracking of tiles" is pure assumption/guesswork, with the only evidence so far (a high resolution image pan) appears to show only a single visible cracked tile that was not already marked for replacement.
Title: Re: Starship heat shield
Post by: rsdavis9 on 10/22/2021 04:29 pm
Somebody is probably going to say they are going to need massive QA of the tiles so they don't fall off. Maybe they need to make a shaking rig to check the installation.

In real life just static fire new ship and then just replace tiles that fell off.

Anybody got an idea of which is harder for tiles?
1. Max Q airflow
2. Static fire at sea level
3. Engine startup at stage sep

In general is vibration worse than airflow?

Wondering if the shake test on ground is the max and therefore will QA the tiles for them.
 
Title: Re: Starship heat shield
Post by: WormPicker959 on 10/22/2021 04:39 pm
I think the idea of the static fire being a "QA check" really depends on the nature of the failure here. If the problem is with those sites on the ship (whatever tile you put there, however you put it, it'll fall off again), it's a very different problem than a probabilistic one (tiles have p probability of falling off, which is clearly very low). In the latter, just replace those that do until you're confident the odds are > some safety factor; if it's the former, then the QA needs to happen somewhere upstream in the process. Still, if whatever changes necessary to repair that section can be made on the pad, the in situ QA could still be viable...

I wonder if we'll know! We'll see how they go about replacing the tiles, and if they perform static fires after doing so.
Title: Re: Starship heat shield
Post by: Restless on 10/22/2021 05:06 pm
We shouldn't be downplaying the tile problem.
NO tiles should be falling off during static fire. Otherwise, reentry will surely fail. I mean, this is analogous to the spray-on insulation of the SS external tank. NASA knew it was a problem and kept on flying....

But, I'm sure Spacex is working the problem very hard.
Title: Re: Starship heat shield
Post by: Tangilinear Interjar on 10/22/2021 05:18 pm
From what I can see there's only one or two tiles from the upper area that was QC'd that came off. The rest were from areas that didn't have a QC double check. That seems VERY good to me. I expect they will do a close up inspection if not full QC of the whole heat shield prior to launch but it was pointless until after the test fires.

Note that SS21 is getting a full QC on all of its tiles during assembly.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 10/22/2021 05:52 pm
this transfer is overwhelmingly larger that any conduction in the steel.
That's a definitely a 'calculations required' claim.

600-1200kWm^-2 are a rough range for thermal flux during re-entry heating, so ~300mm x 300mm of exposed stainless steel is being bathed by 54-108kW of heating. To stay below ~650°C (significant strength loss beyond that), you have:
An 850K (~650°C and ~-200°C on either side) temperature gradient
A 4mm wall thickness (0.004m)
A 16.2 Wm^-1K^-1 thermal conductivity for 304L
So you can tolerate ~55Wm^-2 in steady-state for bare 304L. That's quite a way from what's necessary to handle EDL, hence why the tiles are installed to start with.

That's off by ~5 orders of magnitude, you multiplied by 0.004 instead of dividing.

(16.2 Wm^-1K^-1) × (850K) / (0.004m) = 3.4 × 10^6 Wm^-2

so about 300 kW /m^2

Good calculation on the heat flux through the SS, but the process is going to be limited by Stefan Boltzmann:

radiative Heat flux going in *both* directions (out/in) of SS sheet:

radiative Flux = emmisitivity_stainless * boltzmann_constant * (Th^4 - Tc^4)

Emissivity of stainless is about 0.6.
Boltzmann_constant = 5.67e-8
Th = 650+273 = 923K
Tc = 100K

Flux = 0.6 * 5.67e-8 * (923^4 - 100^4) = 25kw/m^2

In two directions that's 50kW / m^2.

In other words, to maintain equilibrium temperature of the stainless steel sheet, the impinging heat flux from re-entry must be less than 50kW/m^2.   Otherwise the steel will heat up because it can't radiate the heat fast enough.

The 300kW/m^2 being 6x higher means the conductance of the 304L isn't a limiting factor.


If you don't care about structural strength you can let the stainless steel heat up to 1250degC which would give a net radiative flux of 180kW/m^2 (360kW/m^2 both directions).
Title: Re: Starship heat shield
Post by: AU1.52 on 10/22/2021 05:56 pm
Plus they are still in the developmental stage. If this were happening before or during the 1st manned lunch of Starship (flight 50?) I might be more concerned.


Being able to survive reentry with a few missing tiles well, we may end up calling this a non issue.


Still early days and who know where their heat shield tech will have evolved to in 2 - 3 years from now. It will certainly not stay static.
Title: Re: Starship heat shield
Post by: ETurner on 10/22/2021 06:01 pm
https://twitter.com/elonmusk/status/1451354108531728384 (https://twitter.com/elonmusk/status/1451354108531728384)
How can this be reasonable at this late date?
If these are known-bad tiles that they haven’t bothered to replace, that’s sort of almost OK.
But otherwise...??

It is completely reasonable because this is not a ‘late date’. This is an early flight prototype, not a finished product. If tiles fall off they replace them. If tiles keep falling off they tweak the design. That’s the whole point of this development method.
Yes, this isn’t late as in “too late to succeed” -- flexible development, fast iteration, etc., can deal with the problem.
It is, however, surprisingly late (this is subjective and absolutely true: I’m surprised!) considering the apparent number of design iterations on what looks like a problem that should be readily solved: Make tiles that aren’t cracked (after pre-installation QC) and use fasteners that hold the tiles securely without applying too much stress.

I continue to wonder whether they’ve chosen a design that over-constrains the attachments -- 3 translational constraints per pin is 9 per tile, which is 3 too many for a stress-free kinematic constraint (https://en.wikipedia.org/wiki/Kinematic_coupling#Maxwell_coupling) on the tile positions and orientations. A formally over-constrained design can work (only?) if the pins can absorb manufacturing tolerances and in-use displacements through elastic deformation (acting as springs). [Otherwise, not so good -- strong and stiff pins lead to (unnecessarily) high stress in tiles.]

TL;DR: Should work already, will work eventually, but what seems to be the current design seems questionable.
Title: Re: Starship heat shield
Post by: edzieba on 10/22/2021 06:26 pm
It is, however, surprisingly late (this is subjective and absolutely true: I’m surprised!) considering the apparent number of design iterations on what looks like a problem that should be readily solved
It's literally the first iteration of a full heat-shield installation (and not single small patches), and the first firing of an RVac (which is mechanically coupled directly to the outer skin, rather than just to the thrust puck) attached to Starship. There has been no earlier iteration yet.
Title: Re: Starship heat shield
Post by: wannamoonbase on 10/22/2021 07:42 pm
https://twitter.com/elonmusk/status/1451354108531728384 (https://twitter.com/elonmusk/status/1451354108531728384)
How can this be reasonable at this late date?
If these are known-bad tiles that they haven’t bothered to replace, that’s sort of almost OK.
But otherwise...??

It is completely reasonable because this is not a ‘late date’. This is an early flight prototype, not a finished product. If tiles fall off they replace them. If tiles keep falling off they tweak the design. That’s the whole point of this development method.
Yes, this isn’t late as in “too late to succeed” -- flexible development, fast iteration, etc., can deal with the problem.
It is, however, surprisingly late (this is subjective and absolutely true: I’m surprised!) considering the apparent number of design iterations on what looks like a problem that should be readily solved: Make tiles that aren’t cracked (after pre-installation QC) and use fasteners that hold the tiles securely without applying too much stress.

I continue to wonder whether they’ve chosen a design that over-constrains the attachments -- 3 translational constraints per pin is 9 per tile, which is 3 too many for a stress-free kinematic constraint (https://en.wikipedia.org/wiki/Kinematic_coupling#Maxwell_coupling) on the tile positions and orientations. A formally over-constrained design can work (only?) if the pins can absorb manufacturing tolerances and in-use displacements through elastic deformation (acting as springs). [Otherwise, not so good -- strong and stiff pins lead to (unnecessarily) high stress in tiles.]

TL;DR: Should work already, will work eventually, but what seems to be the current design seems questionable.

I think you're asking a lot, it hasn't been to orbit yet. 

They'll work on it.  I'd look at the % of tiles that popped off, examine each one that failed for a root causes then make any changes.  It could be design, manufacturing, installation or even how the vehicle is handled. 

They'll figure it out, once they get some flying reps.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 10/22/2021 09:01 pm
So:  If there are still cracking/detachment issues after shaking this stuff out, will they delay the orbital test?  I'd say no--an expendable Starship with a modestly reusable SuperHeavy gives Starlink a lower specific launch cost than a state-of-the-art F9.  Plus, they can get lots of data off of the intact tiles and the Starship skin before it fries itself during reentry.
Title: Re: Starship heat shield
Post by: envy887 on 10/22/2021 09:12 pm
We shouldn't be downplaying the tile problem.
NO tiles should be falling off during static fire. Otherwise, reentry will surely fail. I mean, this is analogous to the spray-on insulation of the SS external tank. NASA knew it was a problem and kept on flying....

You shouldn't be overstating the tile problem.

1) Launch on a booster is a very different and probably more challenging environment than a static fire, so the fact that some tiles fall off on a static fire does not necessarily mean they will fall off on an orbital launch attempt.

2) We don't know that losing a few tiles will cause reentry to "surely fail". Shuttle survived reentry with damaged and missing tiles many times, and Starship with its high-temperature-capable structure is almost certainly much more robust to tile failure than Shuttle was.

3) Even if a reentry fails on one of the initial flights, so what? They aren't launching crew, and these aren't $1.5B vehicles. They can lose a few without a problem. In fact, they are already planning to ditch Ship 20 in the ocean. If they get any reentry data at all, the test will be a major success.
Title: Re: Starship heat shield
Post by: edzieba on 10/22/2021 09:30 pm
Before and after composite from RGV and StarshipGazer. From the belly view, I can count 9 lost or partially lost tiles.
Title: Re: Starship heat shield
Post by: Keldor on 10/22/2021 10:35 pm
How can this be reasonable at this late date?
If these are known-bad tiles that they haven’t bothered to replace, that’s sort of almost OK.
But otherwise...??

We have to remember that the Starship vehicle will NEVER light its engines on the ground for normal flights, because it will normally sit on top of the Booster to get off the ground. So tiles falling off because of a static fire on the ground is not necessarily a bad sign, since that is a condition they are not designed to operate in.

The bigger question is whether the tiles that did fall off during the static fire would have stayed on during a launch on top of the Booster, with the air trying to rip them off...

Yes but actually no, point to point starship will launch on it's own and it will have even more engines
We're a long ways from there yet.

Will point to point even need a "full" heat shield?  It's going to be considerably less energetic without Superheavy, and so reentry heating will be significantly reduced.
Title: Re: Starship heat shield
Post by: frith01 on 10/22/2021 10:47 pm
Until there are enough "end-points"  to jump to,  I would expect even the point to point to use Booster.

Even when there are enough end-points, I would see a high value in shipping freight with the passengers as a money-making venture even more lucrative than passengers.  Fexed / UPS  + Government(s) moving stuff = $$.  Plus by-passing jam-packed ports Customs areas = big win.
(Space-X sites would need their own)
Title: Re: Starship heat shield
Post by: brettly2021 on 10/23/2021 09:50 am
Has anyone seen any very closeup shots of the lost tile spaces?
I suspect its tile breakage is the issue, I also suspect the tile is molded around the y shaped metal bracket that the pins slot into. I doubt the pins will come out, so expecting to see the y shaped brackets still in place ( that would mean its tile breakage is the issue). It would be extremely hard to see any cracks except with extreme closeup shots of the tiles. I was possible to see cracking post the lift onto b4 with extreme tile closeup shots.
If its tile breakage away from the steel y shaped support, then I still think a little red rtv between the y shaped supports and the tile material would help. Seems Elon Musk is suggesting weak tiles are weeded out by the vibrations of the test.....maybe true.......or is there a fundamental design issue going on here?
Yup there is alot of conjecture but thats what this site is about!
Title: Re: Starship heat shield
Post by: joek on 10/23/2021 11:26 am
Before and after composite from RGV and StarshipGazer. From the belly view, I can count 9 lost or partially lost tiles.

So what would the defect rate be, which think is an important metric? Someone must have done an estimate of total tile count (but can't find it)... anyone?
Title: Re: Starship heat shield
Post by: rsdavis9 on 10/23/2021 12:13 pm
Before and after composite from RGV and StarshipGazer. From the belly view, I can count 9 lost or partially lost tiles.

So what would the defect rate be, which think is an important metric? Someone must have done an estimate of total tile count (but can't find it)... anyone?

Maybe 10,000 tiles. So 10 out of 10,000 is .1% tile breakage.
This to me means that it isn't a fundamental design issue and is just an "acceptable" failure of installation or manufacture. Something that will be worked out.
Title: Re: Starship heat shield
Post by: grndkntrl on 10/23/2021 12:47 pm
Before and after composite from RGV and StarshipGazer. From the belly view, I can count 9 lost or partially lost tiles.

So what would the defect rate be, which think is an important metric? Someone must have done an estimate of total tile count (but can't find it)... anyone?

Maybe 10,000 tiles. So 10 out of 10,000 is .1% tile breakage.
This to me means that it isn't a fundamental design issue and is just an "acceptable" failure of installation or manufacture. Something that will be worked out.

skylord_luke on /r/SpaceXLounge did a tile count of SN20 around the time of the August full stack, and it came out at ~15,480 ±200: https://www.reddit.com/r/SpaceXLounge/comments/oyrly7/so_i_counted_the_amount_of_tiles_on_starship/

A couple of the folks on twitter who have been doing full models of the ship also gave tile counts, but I can't seem to find those tweets at the moment, although IIRC their counts were pretty close to the above estimate.

So if only 10 tiles are lost, then that's just 0.0646% of the total.
Title: Re: Starship heat shield
Post by: livingjw on 10/23/2021 02:37 pm
How can this be reasonable at this late date?
If these are known-bad tiles that they haven’t bothered to replace, that’s sort of almost OK.
But otherwise...??

We have to remember that the Starship vehicle will NEVER light its engines on the ground for normal flights, because it will normally sit on top of the Booster to get off the ground. So tiles falling off because of a static fire on the ground is not necessarily a bad sign, since that is a condition they are not designed to operate in.

The bigger question is whether the tiles that did fall off during the static fire would have stayed on during a launch on top of the Booster, with the air trying to rip them off...

Yes but actually no, point to point starship will launch on it's own and it will have even more engines
We're a long ways from there yet.

Will point to point even need a "full" heat shield?  It's going to be considerably less energetic without Superheavy, and so reentry heating will be significantly reduced.

Point to Point still needs to get close to orbital speeds, so TPS will be needed.

John
Title: Re: Starship heat shield
Post by: brettly2021 on 10/23/2021 09:44 pm
one lost tile in the wrong place might be all it takes to destroy the craft on re-entry.
Rather critical issue for the time being I would think.
Anyone got extreme closeups of the tiles post static fires?
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 10/23/2021 10:35 pm
I'm still trying to figure out the actual tile structure.  After going back through the last 20 pages or so, I found photographs here (https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=50748.0;attach=2060233;image) and here (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2292797#msg2292797).  From that, I tried to construct a cross-section of one of the pinned tiles, through the center of the pin slot.  Attached.

Some things I'm confused about:

1) What's the deal with the empty space?  Doesn't that make the tile highly prone to cracking?

2) I'm unclear on whether there's a full additional layer of ceramic insulation on the bottom of the y-channel (as I have in the diagram), or whether the y-channel's narrow encapsulation of the metal sits directly on the space / pad / blanket.  Kinda depends on whether the upside-down tile is intact or not.

3) It seems like there's a metallic guide sleeve for the slot in the y-channel that holds the pin.  I can't tell if this sleeve would go all the way to the blanket or not.

Am I barking up the right tree yet?
Title: Re: Starship heat shield
Post by: AU1.52 on 10/23/2021 11:22 pm
Are we sure there is a void ie is there really a back piece of ceramic? It looks like the back indented three sections would get at least partly filled in by the blanket when the tile is fixed to the pins.
Title: Re: Starship heat shield
Post by: CrazyHorse80 on 10/24/2021 07:18 am
Just a random brain fart, but... How cool would it be if they'll rig a Raptor engine on an horizontal support, hook it up to some LOX and LCH4 pipes and fire it up against a vertical standing StarShip with complete heat shield? Could it validate or prove the heat shield concept wrong without requiring an orbital flight, just in case FAA doesn't allow it anytime soon?

EDIT: typo.
Title: Re: Starship heat shield
Post by: brettly2021 on 10/24/2021 09:38 am
I dont know about rear structure of tile, how its connected to y frame,
I am curious about this though:
When the static fires occured there was a type of mist could be seen coming from the tiles, I'm not sure what
that mist was. It seemed to come from all areas of the tiles except maybe the top half of the nosecone.
If the tanks were full it might have been ice from atmospheric water vapour that chilled down due to the cold
fuels in the tanks. Anyone know what it was?
Anyhow led me to an idea ( bit of a crazy idea):
what if the white backing material (whatever it is) was to be drenched with water as the tanks are filling up, assuming it can hold liquid water, lets assume the water then freezes due to cold propellents inside tanks, and you  land up with a very thick layer of ice under the tiles ( assume the expansion of the water doesn't hurt the tiles).
Yup its going to be heavy but....lets assume that water soaked white backing felt makes its too orbit fully saturated with water, or even largely still as ice, once in orbit its cold out there, ice will remain as ice.
So you have taken a good source of water with you too space ( if needed).....but....on re-entry all that water can turn back into liquid and then gas, giving a layer of protection to the tiles as the out-gases absorb energy of re-entry. ( back and sides of tiles might need that black borosilicate( or similar) layer).
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 10/24/2021 09:48 am
I dont know about rear structure of tile, how its connected to y frame,
I am curious about this though:
When the static fires occured there was a type of mist could be seen coming from the tiles, I'm not sure what
that mist was. It seemed to come from all areas of the tiles except maybe the top half of the nosecone.
If the tanks were full it might have been ice from atmospheric water vapour that chilled down due to the cold
fuels in the tanks. Anyone know what it was?
Anyhow led me to an idea ( bit of a crazy idea):
what if the white backing material (whatever it is) was to be drenched with water as the tanks are filling up, assuming it can hold liquid water, lets assume the water then freezes due to cold propellents inside tanks, and you  land up with a very thick layer of ice under the tiles ( assume the expansion of the water doesn't hurt the tiles).
Yup its going to be heavy but....lets assume that water soaked white backing felt makes its too orbit fully saturated with water, or even largely still as ice, once in orbit its cold out there, ice will remain as ice.
So you have taken a good source of water with you too space ( if needed).....but....on re-entry all that water can turn back into liquid and then gas, giving a layer of protection to the tiles as the out-gases absorb energy of re-entry. ( back and sides of tiles might need that black borosilicate( or similar) layer).
I hope there is not such ice layer because it will make planning trajectories difficult due to its unknown mass. And it would take dV away too.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 10/24/2021 10:36 am
Just a random brain fart, but... How cool would it be it they'll rig a Raptor engine on an horizontal support, hook it up to some LOX and LCH4 pipes and fire it up against a vertical standing StarShip with complete heat shield? Could it validate or prove the heat shield concept wrong without requiring an orbital flight, just in case FAA doesn't allow it anytime soon?


Like for every thing of this kind the development and construction of this test rig would take more time than the orbital flight. Moreover, even if the realtor engine exhaust *might* be very roughly in the ballpark for the temperature, and surely low in the velocity, the density and chemical composition are way off. Moreover the mechanism that causes the heating during twenty is the shockwave compression, not a combustion.

edit: fixed quote
Title: Re: Starship heat shield
Post by: Star-Dust on 10/24/2021 01:39 pm
Before and after composite from RGV and StarshipGazer. From the belly view, I can count 9 lost or partially lost tiles.
This is enough damage for re-entry RUD?
Title: Re: Starship heat shield
Post by: Twark_Main on 10/24/2021 03:17 pm
this transfer is overwhelmingly larger that any conduction in the steel.
That's a definitely a 'calculations required' claim.

600-1200kWm^-2 are a rough range for thermal flux during re-entry heating, so ~300mm x 300mm of exposed stainless steel is being bathed by 54-108kW of heating. To stay below ~650°C (significant strength loss beyond that), you have:
An 850K (~650°C and ~-200°C on either side) temperature gradient
A 4mm wall thickness (0.004m)
A 16.2 Wm^-1K^-1 thermal conductivity for 304L
So you can tolerate ~55Wm^-2 in steady-state for bare 304L. That's quite a way from what's necessary to handle EDL, hence why the tiles are installed to start with.

That's off by ~5 orders of magnitude, you multiplied by 0.004 instead of dividing.

(16.2 Wm^-1K^-1) × (850K) / (0.004m) = 3.4 × 10^6 Wm^-2

so about 300 kW /m^2

Surely that should be 3000 kW/m^2, not 300.
Title: Re: Starship heat shield
Post by: wannamoonbase on 10/24/2021 03:19 pm
Before and after composite from RGV and StarshipGazer. From the belly view, I can count 9 lost or partially lost tiles.
This is enough damage for re-entry RUD?

I bet there are engineers inside SpaceX asking the same thing.

Knowing the condition of the heat shield on these first test flights, with only 1 orbit, is going to be a challenge.  Lots of in flight cameras I guess. 

How the entire TPS performs around Max Q is going to be interesting.  Does anyone have an experienced judgement on how it will do at high velocities or is the thunderous loads on the launch stand in the denser atmosphere going to be a bigger challenge.

Seems if they can get a healthy TPS to orbit that. Re-entry maybe the easier part.
Title: Re: Starship heat shield
Post by: Twark_Main on 10/24/2021 03:28 pm

Good calculation on the heat flux through the SS, but the process is going to be limited by Stefan Boltzmann:

[snip]

In other words, to maintain equilibrium temperature of the stainless steel sheet, the impinging heat flux from re-entry must be less than 50kW/m^2.   Otherwise the steel will heat up because it can't radiate the heat fast enough.

This can't be right.

The impinging heat flux would have to be greater than 50 kW/m^2, because otherwise 100% of the heat would be carried away by radiation, leaving 0% left over to be removed by conduction. Given the stated temperature gradient, zero conductive heat flow is clearly non-physical.

I think you must have meant that the net heat flux must be 50 kW/m^2, not the total heat flux.

Also, to "maintain equilibrium temperature" the heat flux can't be "less than" the value either, because in that case the steel will cool down.
Title: Re: Starship heat shield
Post by: Redclaws on 10/24/2021 03:43 pm
Before and after composite from RGV and StarshipGazer. From the belly view, I can count 9 lost or partially lost tiles.
This is enough damage for re-entry RUD?

I would think yes - these are fairly large tiles and therefore fairly large gaps.  But only SpaceX probably has much real idea of it and they’re probably not sure either.  (Well, they might be sure if it’s well outside or well inside predictions, but still…)
Title: Re: Starship heat shield
Post by: OTV Booster on 10/24/2021 04:55 pm
I dont know about rear structure of tile, how its connected to y frame,
I am curious about this though:
When the static fires occured there was a type of mist could be seen coming from the tiles, I'm not sure what
that mist was. It seemed to come from all areas of the tiles except maybe the top half of the nosecone.
If the tanks were full it might have been ice from atmospheric water vapour that chilled down due to the cold
fuels in the tanks. Anyone know what it was?
Anyhow led me to an idea ( bit of a crazy idea):
what if the white backing material (whatever it is) was to be drenched with water as the tanks are filling up, assuming it can hold liquid water, lets assume the water then freezes due to cold propellents inside tanks, and you  land up with a very thick layer of ice under the tiles ( assume the expansion of the water doesn't hurt the tiles).
Yup its going to be heavy but....lets assume that water soaked white backing felt makes its too orbit fully saturated with water, or even largely still as ice, once in orbit its cold out there, ice will remain as ice.
So you have taken a good source of water with you too space ( if needed).....but....on re-entry all that water can turn back into liquid and then gas, giving a layer of protection to the tiles as the out-gases absorb energy of re-entry. ( back and sides of tiles might need that black borosilicate( or similar) layer).
A BOE, shows this much water to be HEAVY. With a 4.5m radius and ~50m of height covered with tiles, ignoring the fin covering and assuming a 1cm layer of water, the water weighs in at ~7t. There's a risk that the freezing water could pop tiles off. It would also be off center mass (which might add passive stability during the belly flop) and would probably lend itself to uneven buildup without a lot of engineering.


Let's take your question one step further and think of 7t as a mass budget for further improvement. The SX team can do a lot with 7t. If a more robust pin and attachment method weighs 1g, with 15,480 tiles, that's only 15.48kg. If it's 5 grams it works out to 77.4kg.


The water idea has a certain attraction but weighs way too much and has other downsides.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 10/24/2021 06:05 pm
Are we sure there is a void ie is there really a back piece of ceramic? It looks like the back indented three sections would get at least partly filled in by the blanket when the tile is fixed to the pins.

Whatever blanket there is isn't going to be soft and fluffy, and therefore isn't going to fill the gaps.  Even if it were, it would be hard to distribute the stresses evenly with that kind of filler.

If there are gaps, it's because SpaceX thinks that they can take a lot of mass out of the TPS by providing them.  My guess is that we'll start to see ceramic support ribs appear between the y-channels until the cracking and tear-offs stop happening.  This is completely consistent with the, "You should take so much stuff out of your design that you have to add some stuff back in" design philosophy.
Title: Re: Starship heat shield
Post by: BT52 on 10/24/2021 07:02 pm
Yeah agree. Especially if initial main feature of bayonet clip design doesn't work. You avoid too much optimization for nothing. So its in a way sad that SpaceX needs build all infrastructure from scratch first and wait for public opinions. Also its rural and natural habitat location doesn't help too much in terms of speedup the process in testing even more. Also transport between facilities at boca are logistical hussle.

So i agree engineers are feeling very angsty about first flight and its ramification so they can get back too work at its heat shield design even further. At end of day they can torch tiles as much they want in lab. All that vibrations, head soaks, acoustics are hard too sim in CFD and NASAs windtunnels. Even if there is a way to test that system without scaling problems.
Title: Re: Starship heat shield
Post by: Slarty1080 on 10/25/2021 08:29 am
Yeah agree. Especially if initial main feature of bayonet clip design doesn't work. You avoid too much optimization for nothing. So its in a way sad that SpaceX needs build all infrastructure from scratch first and wait for public opinions. Also its rural and natural habitat location doesn't help too much in terms of speedup the process in testing even more. Also transport between facilities at boca are logistical hussle.

So i agree engineers are feeling very angsty about first flight and its ramification so they can get back too work at its heat shield design even further. At end of day they can torch tiles as much they want in lab. All that vibrations, head soaks, acoustics are hard too sim in CFD and NASAs windtunnels. Even if there is a way to test that system without scaling problems.
Sad that SpaceX needs to build all infrastructure from scratch first and wait for public opinions? Do you mean that it's a little bit unfortunate that all of their experiments and inevitable mistakes are on public display?

I imagine the engineers are all a bit nervous. They just have to do there best and hope that 1) it's not their bit that fails and 2) that if their bit does fail it's not some sort of school boy error type thing (school boy error in terms of SpaceX rocketry covers a lot of ground).
Title: Re: Starship heat shield
Post by: InterestedEngineer on 10/25/2021 11:37 pm
Before and after composite from RGV and StarshipGazer. From the belly view, I can count 9 lost or partially lost tiles.
This is enough damage for re-entry RUD?

No.  missing tiles are not adjacent, and Superwool backing is sufficient in a small surface area to protect for one re-entry.

Numerous discussions about this in threads above.   Tl;DR SpaceX would no design a system with 10k failure points of which zero are allowed to fail before vehicle loss.   (Space Shuttle and Boeing 737-Max being exceptions to the single point of failure rule.... how did that turn out?)
Title: Re: Starship heat shield
Post by: OTV Booster on 10/26/2021 12:45 am
Yeah agree. Especially if initial main feature of bayonet clip design doesn't work. You avoid too much optimization for nothing. So its in a way sad that SpaceX needs build all infrastructure from scratch first and wait for public opinions. Also its rural and natural habitat location doesn't help too much in terms of speedup the process in testing even more. Also transport between facilities at boca are logistical hussle.

So i agree engineers are feeling very angsty about first flight and its ramification so they can get back too work at its heat shield design even further. At end of day they can torch tiles as much they want in lab. All that vibrations, head soaks, acoustics are hard too sim in CFD and NASAs windtunnels. Even if there is a way to test that system without scaling problems.
Sad that SpaceX needs to build all infrastructure from scratch first and wait for public opinions? Do you mean that it's a little bit unfortunate that all of their experiments and inevitable mistakes are on public display?

I imagine the engineers are all a bit nervous. They just have to do there best and hope that 1) it's not their bit that fails and 2) that if their bit does fail it's not some sort of school boy error type thing (school boy error in terms of SpaceX rocketry covers a lot of ground).
No, BT52 was getting at SX building out then going through the FAA public comment process for an up/down on what's already done.


Wearing my fanboi hat: lead, follow or get out of the way. Wearing my general citizen hat: you want to build without an environmental ok (especially in the midst of a sensitive area), ya pays your money and ya take your chances.


As corporate citizens, SX is in the top tier and my gut says to cut them some slack. Would I feel this way about some other companies? No. I'm conflicted.


Nuff said. Wrong thread for this.
Title: Re: Starship heat shield
Post by: brettly2021 on 10/26/2021 10:38 am
thanks OTV booster for the calcs on crazy water idea. 7 tonnes is quite a bit of water, compared to say 77kg of clips and tiles, is that really all it weighs? 7 tonnes of water though might be rather useful , say , on the moon.
Lets say do both sides of the ship with water/felt and tiles, control issues not such a problem and 14 tonnes of water to play with on the moon.
Title: Re: Starship heat shield
Post by: DistantTemple on 10/26/2021 03:07 pm
thanks OTV booster for the calcs on crazy water idea. 7 tonnes is quite a bit of water, compared to say 77kg of clips and tiles, is that really all it weighs? 7 tonnes of water though might be rather useful , say , on the moon.
Lets say do both sides of the ship with water/felt and tiles, control issues not such a problem and 14 tonnes of water to play with on the moon.
Are you serious? Useable water on the moon would include it being "in" something. Or if ICE, then in convenient blocks-still stored ready for use. Stick on the side of the ship, busily sublimating in the sunlight, most of it above ladder height, and half of it hidden in insulation matting under tiles - is, mmm, inconvenient!
Title: Re: Starship heat shield
Post by: whitelancer64 on 10/26/2021 03:49 pm
thanks OTV booster for the calcs on crazy water idea. 7 tonnes is quite a bit of water, compared to say 77kg of clips and tiles, is that really all it weighs? 7 tonnes of water though might be rather useful , say , on the moon.
Lets say do both sides of the ship with water/felt and tiles, control issues not such a problem and 14 tonnes of water to play with on the moon.

77 kg for only the pin and attachments, if they weigh 5 grams each. The entire heat shield is likely in the 7 metric ton range.
Title: Re: Starship heat shield
Post by: OTV Booster on 10/26/2021 04:08 pm
thanks OTV booster for the calcs on crazy water idea. 7 tonnes is quite a bit of water, compared to say 77kg of clips and tiles, is that really all it weighs? 7 tonnes of water though might be rather useful , say , on the moon.
Lets say do both sides of the ship with water/felt and tiles, control issues not such a problem and 14 tonnes of water to play with on the moon.
No, that 77kg was in addition to what's already there and was strictly a 'for example' type of number. It could be ten times heavier and still be an order of magnitude less than the water.
Title: Re: Starship heat shield
Post by: dwheeler on 10/26/2021 04:12 pm
Before and after composite from RGV and StarshipGazer. From the belly view, I can count 9 lost or partially lost tiles.
This is enough damage for re-entry RUD?

No.  missing tiles are not adjacent, and Superwool backing is sufficient in a small surface area to protect for one re-entry.

Numerous discussions about this in threads above.   Tl;DR SpaceX would no design a system with 10k failure points of which zero are allowed to fail before vehicle loss.   (Space Shuttle and Boeing 737-Max being exceptions to the single point of failure rule.... how did that turn out?)
I'm not nearly as confident as you around this statement. At best I'd say there are probably many single tile losses that might be Ok. But I wouldn't be surprised if there are some single tile losses that could be very bad. And I'd add that some single tile losses might result in loosing adjacent tiles due to aerodynamic force and weakened steel. If nothing else, modeling how the ship reacts to various tile failures seems like a very difficult task.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 10/26/2021 05:46 pm
thanks OTV booster for the calcs on crazy water idea. 7 tonnes is quite a bit of water, compared to say 77kg of clips and tiles, is that really all it weighs? 7 tonnes of water though might be rather useful , say , on the moon.
Lets say do both sides of the ship with water/felt and tiles, control issues not such a problem and 14 tonnes of water to play with on the moon.

77 kg for only the pin and attachments, if they weigh 5 grams each. The entire heat shield is likely in the 7 metric ton range.

I wonder how much the metal in the y-channels weighs.  At a SWAG, I'll bet it's at least 25% of the total tile mass.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 10/26/2021 08:49 pm
Before and after composite from RGV and StarshipGazer. From the belly view, I can count 9 lost or partially lost tiles.
This is enough damage for re-entry RUD?

No.  missing tiles are not adjacent, and Superwool backing is sufficient in a small surface area to protect for one re-entry.

Numerous discussions about this in threads above.   Tl;DR SpaceX would no design a system with 10k failure points of which zero are allowed to fail before vehicle loss.   (Space Shuttle and Boeing 737-Max being exceptions to the single point of failure rule.... how did that turn out?)
I'm not nearly as confident as you around this statement. At best I'd say there are probably many single tile losses that might be Ok. But I wouldn't be surprised if there are some single tile losses that could be very bad. And I'd add that some single tile losses might result in loosing adjacent tiles due to aerodynamic force and weakened steel. If nothing else, modeling how the ship reacts to various tile failures seems like a very difficult task.
I think that the only way to find out whetever one tile loss is fatal or how dangerouse it is is to wait for the first reentry. We are discussing this from a lot of time, and we don't have much added information that could help us in this front. We should beware while discussing this aspect,because in this cases we risk that truth are built in this forum just because many agree and they are riproposed many times.
BTW, I too think that one singular tile lost wound not be very dangerouse, but it's only an opinion.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 10/27/2021 02:58 am
And I'd add that some single tile losses might result in loosing adjacent tiles due to aerodynamic force and weakened steel.

Tiles unzipping is a possible common-mode failure.   When the vent blasted sideways earlier I think it only took 2 columns of tiles with it, right?   So maybe the unzip is self-limiting.

Also something that can be tested in a wind tunnel (assuming wind tunnels can handle flying tile debris).

"Try it and find out" seems reasonable given the few tiles that were lost so far.
Title: Re: Starship heat shield
Post by: BT52 on 10/27/2021 05:33 am
Yeah zip effect is concern. But I have Orthodox idea. Like chain rakes...
https://i.ebayimg.com/images/g/-DIAAOSwcMhblHrZ/s-l640.jpg
Title: Re: Starship heat shield
Post by: brettly2021 on 10/27/2021 11:35 am
Sorry to harp on the water blanket idea, the tiles are good heat insulators, they can get very hot and heat conductance is very slow ( if I've got the right idea), so they would also make good insulators to keep things cool.
Lets say a layer of water ice makes it too the moon ( embedded in the backing fabric)
While on the moon ( or in space) in shade it will stay as ice, exposed to sunlight it will evaporate or sublime, rather than being a bad thing, that gives an easy way to covert it too liquid for use. Just how to capture the evaporated/sublimed water would be tricky problem to solve, probably could be done.
Maybe take out a few tiles, put on a clear window, with tube that takes away evaporated/sublimed water, might not be that hard.
On ascent from earth I think the water would make it to cold space as ice due to insulation of tiles, it would take some energy away from the propellents, so longer propellent filling time might be needed. Gap between the tiles is another issue.

Title: Re: Starship heat shield
Post by: edzieba on 10/27/2021 12:05 pm
Work continues on Ship 21 nosecone.
Two tiles added to the nose section appear to be either missing their black RCG top layer, have a white top layer of unknown composition, or have been painted white over the RCG. It does not appear to just be a reflectance trick as the surrounding tiles at the same or similar sun angle are not the same uniform white.
Title: Re: Starship heat shield
Post by: Yggdrasill on 10/27/2021 12:17 pm
Maybe dummy tiles that will be replaced with the real thing? Makes sense that they might 3D print a unique tile before they make the real one, for instance.
Title: Re: Starship heat shield
Post by: Elmar Moelzer on 10/27/2021 12:29 pm
This might have been covered before (very long thread), but I am wondering why they are not using bigger tiles, at least on the cylindrical section. Would seem like a lot less work for installation and might need less mounting points. Is it a problem with manufacturing them to a bigger size (e.g. more potential waste due to manufacturing faults)?
Title: Re: Starship heat shield
Post by: cdebuhr on 10/27/2021 01:32 pm
Sorry to harp on the water blanket idea, the tiles are good heat insulators, they can get very hot and heat conductance is very slow ( if I've got the right idea), so they would also make good insulators to keep things cool.
Lets say a layer of water ice makes it too the moon ( embedded in the backing fabric)
While on the moon ( or in space) in shade it will stay as ice, exposed to sunlight it will evaporate or sublime, rather than being a bad thing, that gives an easy way to covert it too liquid for use. Just how to capture the evaporated/sublimed water would be tricky problem to solve, probably could be done.
Maybe take out a few tiles, put on a clear window, with tube that takes away evaporated/sublimed water, might not be that hard.
On ascent from earth I think the water would make it to cold space as ice due to insulation of tiles, it would take some energy away from the propellents, so longer propellent filling time might be needed. Gap between the tiles is another issue.
For the record I believe this idea has exactly zero chance of ever being implemented in any practical way.  I think the technical challenges in implementing this in any practical way are far more severe that you realize, and its most likely completely hopeless as a way to get water to the moon (or anywhere really).  But the bigger question here isn't how?, it's why?.  Water is heavy, so ISTM that the most logical thing to do is put it in a tank.  Your 7 tons of water would take up less that one percent of the pressurized volume of Starship.  Alternatively, if you wanted to just ship water to the moon, you'd run into mass limits long before you ever hit volume limits, so just carry it inside (as liquid, in a tank).  Before you embark on the very substantial task of explaining the how of this notion, I would encourage you to think long and hard about the why.
Title: Re: Starship heat shield
Post by: livingjw on 10/27/2021 01:42 pm
Work continues on Ship 21 nosecone.
Two tiles added to the nose section appear to be either missing their black RCG top layer, have a white top layer of unknown composition, or have been painted white over the RCG. It does not appear to just be a reflectance trick as the surrounding tiles at the same or similar sun angle are not the same uniform white.

- Could be a dummy tile blank in the process of being tailor fit or a silica tile before final machining and coating. I would not be surprised if they can do the TUFI coating at Boca Chica now.

- Silica blanks ae 3D milled, not 3D printed.

John
Title: Re: Starship heat shield
Post by: eriblo on 10/27/2021 03:28 pm
This might have been covered before (very long thread), but I am wondering why they are not using bigger tiles, at least on the cylindrical section. Would seem like a lot less work for installation and might need less mounting points. Is it a problem with manufacturing them to a bigger size (e.g. more potential waste due to manufacturing faults)?
They did. It looks like they tended to break.

Most of the smaller TPS patches on the earlier prototypes included larger tiles than the current "standard" tile. It stands to mention that a larger tile will be weaker unless it is made denser (i.e. heavier), have larger gaps between tiles and could be more sensitive to vibrations.
Title: Re: Starship heat shield
Post by: ppb on 10/27/2021 03:45 pm
This might have been covered before (very long thread), but I am wondering why they are not using bigger tiles, at least on the cylindrical section. Would seem like a lot less work for installation and might need less mounting points. Is it a problem with manufacturing them to a bigger size (e.g. more potential waste due to manufacturing faults)?
They did. It looks like they tended to break.

Most of the smaller TPS patches on the earlier prototypes included larger tiles than the current "standard" tile. It stands to mention that a larger tile will be weaker unless it is made denser (i.e. heavier), have larger gaps between tiles and could be more sensitive to vibrations.
And the reason they probably vibrated more is larger flat tiles are not going to tightly fit a curved surface. They could have changed their tile manufacturing process to make them conformally curved, but the simpler solution was to just make them smaller.
Title: Re: Starship heat shield
Post by: OTV Booster on 10/27/2021 09:50 pm
Maybe dummy tiles that will be replaced with the real thing? Makes sense that they might 3D print a unique tile before they make the real one, for instance.
Or maybe a clear sign that SX knows the tile system is less than perfect and are trying different things. If these tiles stay on for launch maybe they've found a hard ceramic coating with high reflectance in visible and high emissivity in IR, like the paint on the LSS mockup.
Title: Re: Starship heat shield
Post by: OTV Booster on 10/27/2021 09:54 pm
This might have been covered before (very long thread), but I am wondering why they are not using bigger tiles, at least on the cylindrical section. Would seem like a lot less work for installation and might need less mounting points. Is it a problem with manufacturing them to a bigger size (e.g. more potential waste due to manufacturing faults)?
They did. It looks like they tended to break.

Most of the smaller TPS patches on the earlier prototypes included larger tiles than the current "standard" tile. It stands to mention that a larger tile will be weaker unless it is made denser (i.e. heavier), have larger gaps between tiles and could be more sensitive to vibrations.
Also, the larger the tile the greater the divergence from the curve of the OML and the more the pointy corners stick out begging for heat buildup.
Title: Re: Starship heat shield
Post by: Twark_Main on 10/27/2021 10:32 pm
And the reason they probably vibrated more is larger flat tiles are not going to tightly fit a curved surface. They could have changed their tile manufacturing process to make them conformally curved, but the simpler solution was to just make them smaller.

It's more likely (by Occam's Razor) that we're seeing a simple direct scaling effect: larger tiles have more mass, but they have the same number of attachment points. That means more stress per attachment point. Simple.


Just as an aside, do we have confirmation that the tiles are flat and not curved? Sorry if I missed it.
Title: Re: Starship heat shield
Post by: Coastal Ron on 10/27/2021 10:54 pm
This might have been covered before (very long thread), but I am wondering why they are not using bigger tiles, at least on the cylindrical section. Would seem like a lot less work for installation and might need less mounting points. Is it a problem with manufacturing them to a bigger size (e.g. more potential waste due to manufacturing faults)?
They did. It looks like they tended to break.

Most of the smaller TPS patches on the earlier prototypes included larger tiles than the current "standard" tile. It stands to mention that a larger tile will be weaker unless it is made denser (i.e. heavier), have larger gaps between tiles and could be more sensitive to vibrations.
Also, the larger the tile the greater the divergence from the curve of the OML and the more the pointy corners stick out begging for heat buildup.

A larger tile could just be longer in the vertical dimension, which would not have the issue of curvature to deal with - in other words, a strip of heat tile instead of a hexagon. This would only work on the body of the Starship that is the same diameter (i.e. not the nose), but that is a lot of space to cover.
Title: Re: Starship heat shield
Post by: Twark_Main on 10/27/2021 11:17 pm
This might have been covered before (very long thread), but I am wondering why they are not using bigger tiles, at least on the cylindrical section. Would seem like a lot less work for installation and might need less mounting points. Is it a problem with manufacturing them to a bigger size (e.g. more potential waste due to manufacturing faults)?
They did. It looks like they tended to break.

Most of the smaller TPS patches on the earlier prototypes included larger tiles than the current "standard" tile. It stands to mention that a larger tile will be weaker unless it is made denser (i.e. heavier), have larger gaps between tiles and could be more sensitive to vibrations.
Also, the larger the tile the greater the divergence from the curve of the OML and the more the pointy corners stick out begging for heat buildup.

A larger tile could just be longer in the vertical dimension, which would not have the issue of curvature to deal with - in other words, a strip of heat tile instead of a hexagon. This would only work on the body of the Starship that is the same diameter (i.e. not the nose), but that is a lot of space to cover.

If it's an issue of simple mass scaling (as I argue above) or an issue of thermal and/or pressure expansion, then longer tiles will have the same flaw.
Title: Re: Starship heat shield
Post by: Elmar Moelzer on 10/28/2021 12:17 am
Also, the larger the tile the greater the divergence from the curve of the OML and the more the pointy corners stick out begging for heat buildup.
Why not make them to fit the curvature?
Title: Re: Starship heat shield
Post by: Sciencefan on 10/28/2021 02:32 am
Larger tiles need bigger gaps for thermal expansion.
Title: Re: Starship heat shield
Post by: Coastal Ron on 10/28/2021 05:15 am
Larger tiles need bigger gaps for thermal expansion.

Or overlapping ends and edges.
Title: Re: Starship heat shield
Post by: daveglo on 10/28/2021 05:18 pm
Larger tiles need bigger gaps for thermal expansion.

Or overlapping ends and edges.
Kind of like . . . scales? :)
Title: Re: Starship heat shield
Post by: ETurner on 10/28/2021 07:00 pm
And the reason they probably vibrated more is larger flat tiles are not going to tightly fit a curved surface. They could have changed their tile manufacturing process to make them conformally curved, but the simpler solution was to just make them smaller.

It's more likely (by Occam's Razor) that we're seeing a simple direct scaling effect: larger tiles have more mass, but they have the same number of attachment points. That means more stress per attachment point. Simple.


Just as an aside, do we have confirmation that the tiles are flat and not curved? Sorry if I missed it.
Larger tiles, larger areas, larger forces, greater bending moments.
Same thickness, more fragile.

Tiny tiles would be blocky and unlikely to break, but not a good choice for other reasons.
Title: Re: Starship heat shield
Post by: grndkntrl on 10/28/2021 07:30 pm
And the reason they probably vibrated more is larger flat tiles are not going to tightly fit a curved surface. They could have changed their tile manufacturing process to make them conformally curved, but the simpler solution was to just make them smaller.

It's more likely (by Occam's Razor) that we're seeing a simple direct scaling effect: larger tiles have more mass, but they have the same number of attachment points. That means more stress per attachment point. Simple.


Just as an aside, do we have confirmation that the tiles are flat and not curved? Sorry if I missed it.
Larger tiles, larger areas, larger forces, greater bending moments.
Same thickness, more fragile.

Tiny tiles would be blocky and unlikely to break, but not a good choice for other reasons.

Yep, it's a trade-off between multiple factors and finding the right balance for what they need.
Title: Re: Starship heat shield
Post by: Coastal Ron on 10/28/2021 08:21 pm
Larger tiles need bigger gaps for thermal expansion.

Or overlapping ends and edges.
Kind of like . . . scales? :)

I would not be surprised if SpaceX has thought of what I'm thinking of and rejected it for good reasons, but what I was thinking of would be something like a 45 degree bevel that allows the bottom of the top tile to overlap the top of the bottom tile, but still leave room for heat expansion of the tile.

We don't see any overlap with the current tiles, so even a small amount of overlap could be an added bonus.

In order to tile the straight bodied part of the Starship, you'd need three separate versions of the tile:

1. A "spine" variant that would be placed in the bottom of the ship when it is falling through the atmosphere. This version would have 45 degree overlaps that stick out and over on the sides, an under slope at the top, and an under slope at the bottom.

2. A "Right side" variant would only be placed on the right side of the body from the "spine" variants, and would have under slope on the side towards the spine, and over slopes on the right side as the body curves "up" the side of the body.

3. Same as 2 above, but the left side variant.

It could be that SpaceX has rejected long tiles because of expansion issues or because they could break more. So consider this more of a thought experiment...  :o
Title: Re: Starship heat shield
Post by: OTV Booster on 10/28/2021 09:28 pm
Also, the larger the tile the greater the divergence from the curve of the OML and the more the pointy corners stick out begging for heat buildup.
Why not make them to fit the curvature?
This is the first full try ala SX modus operandi of just good enough. If they need to do that they will. It's not that big a parts count issue on the cylinder but up on the ogive it might be a complexity they'd like to avoid. That said, there are custom curved tiles in the fin edges. They'll do whatever it takes.
Title: Re: Starship heat shield
Post by: OTV Booster on 10/28/2021 09:37 pm
Larger tiles need bigger gaps for thermal expansion.

Or overlapping ends and edges.
Kind of like . . . scales? :)

I would not be surprised if SpaceX has thought of what I'm thinking of and rejected it for good reasons, but what I was thinking of would be something like a 45 degree bevel that allows the bottom of the top tile to overlap the top of the bottom tile, but still leave room for heat expansion of the tile.

We don't see any overlap with the current tiles, so even a small amount of overlap could be an added bonus.

In order to tile the straight bodied part of the Starship, you'd need three separate versions of the tile:

1. A "spine" variant that would be placed in the bottom of the ship when it is falling through the atmosphere. This version would have 45 degree overlaps that stick out and over on the sides, an under slope at the top, and an under slope at the bottom.

2. A "Right side" variant would only be placed on the right side of the body from the "spine" variants, and would have under slope on the side towards the spine, and over slopes on the right side as the body curves "up" the side of the body.

3. Same as 2 above, but the left side variant.

It could be that SpaceX has rejected long tiles because of expansion issues or because they could break more. So consider this more of a thought experiment...  :o
There's that old bugaboo of swapping out overlapping tiles. If the bevel is mild and the pin short maybe there would be enough slack to lever one side up and pop the latch before the other side starts to bind. Make the bevel too mild and what's the point? Like everything else in this game, it's a balancing act.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 10/28/2021 10:12 pm
Larger tiles need bigger gaps for thermal expansion.

Or overlapping ends and edges.
Kind of like . . . scales? :)

I would not be surprised if SpaceX has thought of what I'm thinking of and rejected it for good reasons, but what I was thinking of would be something like a 45 degree bevel that allows the bottom of the top tile to overlap the top of the bottom tile, but still leave room for heat expansion of the tile.

We don't see any overlap with the current tiles, so even a small amount of overlap could be an added bonus.

In order to tile the straight bodied part of the Starship, you'd need three separate versions of the tile:

1. A "spine" variant that would be placed in the bottom of the ship when it is falling through the atmosphere. This version would have 45 degree overlaps that stick out and over on the sides, an under slope at the top, and an under slope at the bottom.

2. A "Right side" variant would only be placed on the right side of the body from the "spine" variants, and would have under slope on the side towards the spine, and over slopes on the right side as the body curves "up" the side of the body.

3. Same as 2 above, but the left side variant.

It could be that SpaceX has rejected long tiles because of expansion issues or because they could break more. So consider this more of a thought experiment...  :o

Tiles vibrate in 3 dimensions, in the "Z" direction (in/out of the steel) there is probably a lot of play from the compression of the Superwool and the connector.   Overlapping tiles would need a lot of space to prevent collisions during vibrations, it's just not viable.

Think of the tiles as delicate glass inside a cabinet.  In an earthquake, the reason they break is they bounce off each other.   Separate them so they can't easily touch and they are fine.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 10/28/2021 10:20 pm
Or you could do a pull test like they did on the Space Shuttle. Requirement was just north of 100 lbs if I remember right.
1) insert tile, 2) check fit, 3) pull test, done.

John

(thread from prototype discussion thread).

I'm sorry but I have to disagree John.  In high volume manufacturing adding tests is almost never the correct solution.  Elon has some good rants on this topic, and I spent the first 5 years of my career eliminating unneeded tests from a high volume electronics manufacturing line.

Unless the test can be integrated into an application tool that takes near zero additional time, adding a 10 second test to 10,000 tiles isn't the best solution when 7 tiles out of 10,000 failed.   

The static fire test is the best QA method for that kind of failure rate.

The tiles are hand-applied, so not sure what kind of tool would be possible for making the tile application process faster while doing in-situ test.  Perhaps a robot could do a higher quality job.

On repair after landing, a test tool for the repair would probably be a good idea, since there's probably no static fire to check the work.

Title: Re: Starship heat shield
Post by: Alastor on 10/29/2021 12:51 am
Random thought.

It seems implicitly accepted by everyone that cracked tiles will have to be replaced.
But will they really ?

After all, the gaps between tiles are not filled with anything, and the cracks surely leave smaller gaps than that.
So if they see that cracked tiles remain decently attached, I am wondering if really they would require replacement.
Title: Re: Starship heat shield
Post by: Echo_Jex on 10/29/2021 02:01 am
Random thought.

It seems implicitly accepted by everyone that cracked tiles will have to be replaced.
But will they really ?

After all, the gaps between tiles are not filled with anything, and the cracks surely leave smaller gaps than that.
So if they see that cracked tiles remain decently attached, I am wondering if really they would require replacement.

That's a good thought. There may be different inspection criteria for the prototypes in engineering development vs "rapidly reusable" . Like any good inspection, there should be pass, fail, and pass with concerns, called Process Indicators in my line of work. I think your on to something if we were talking about chipped tiles, but cracks in guessing will for the most part travel along lines that intersect with the attachment point holes, and those would need to be addressed
Title: Re: Starship heat shield
Post by: livingjw on 10/29/2021 02:30 pm
Or you could do a pull test like they did on the Space Shuttle. Requirement was just north of 100 lbs if I remember right.
1) insert tile, 2) check fit, 3) pull test, done.

John

(thread from prototype discussion thread).

I'm sorry but I have to disagree John.  In high volume manufacturing adding tests is almost never the correct solution.  Elon has some good rants on this topic, and I spent the first 5 years of my career eliminating unneeded tests from a high volume electronics manufacturing line.

Unless the test can be integrated into an application tool that takes near zero additional time, adding a 10 second test to 10,000 tiles isn't the best solution when 7 tiles out of 10,000 failed.   

The static fire test is the best QA method for that kind of failure rate.

The tiles are hand-applied, so not sure what kind of tool would be possible for making the tile application process faster while doing in-situ test.  Perhaps a robot could do a higher quality job.

On repair after landing, a test tool for the repair would probably be a good idea, since there's probably no static fire to check the work.

I was thinking of a hand held push-pull tool for installing the tile. It would make pushing the tiles on less prone to cracking. Pulling on the tiles after installation could be done with suction. Could be quicker than by hand.

John
Title: Re: Starship heat shield
Post by: livingjw on 10/29/2021 02:33 pm
A cracked tile could possibly leave the tile improperly supported. There is no redundancy in your attachment to the 3 pins.

John
Title: Re: Starship heat shield
Post by: OTV Booster on 10/30/2021 03:21 am
Or you could do a pull test like they did on the Space Shuttle. Requirement was just north of 100 lbs if I remember right.
1) insert tile, 2) check fit, 3) pull test, done.

John

(thread from prototype discussion thread).

I'm sorry but I have to disagree John.  In high volume manufacturing adding tests is almost never the correct solution.  Elon has some good rants on this topic, and I spent the first 5 years of my career eliminating unneeded tests from a high volume electronics manufacturing line.

Unless the test can be integrated into an application tool that takes near zero additional time, adding a 10 second test to 10,000 tiles isn't the best solution when 7 tiles out of 10,000 failed.   

The static fire test is the best QA method for that kind of failure rate.

The tiles are hand-applied, so not sure what kind of tool would be possible for making the tile application process faster while doing in-situ test.  Perhaps a robot could do a higher quality job.

On repair after landing, a test tool for the repair would probably be a good idea, since there's probably no static fire to check the work.
They're still feeling their way through the problem. First find a general solution, then figure out how to automate it with minimal modification.


A robot can replicate more precisely than a human hand but human hand gives good feedback for sensing a hang up during install. Once they have a system that can take advantage of robot replicability and is precise enough to not need a hands sensitivity, they'll have a winner - at least on the install problem.


As for testing...  a robot actuator with three flat 'fingers' to grab three flats on a tile. The ends of the fingers would bend inward to grab under the tile. A plunger in the center of the actuator would press the face of the tile and trap it against the bent ends of the fingers. Arm inserts the symmetrically supported tile onto the pins, then the arm gives a tug, just like ant human would. The tug is the test.


If it's too hard to design the fingers thickness and tip length skinny enough to allow extraction through the inter tile cracks and still have it strong enough to give a meaningful test, make them strictly a holding jig and use a suction cup for the test.


Use a second arm for the suction cup and testing runs parallel with with install. Keep testing until the tile system gives off a warm fuzzy vibe because it's so reliable, then ditch the production testing or find a way to narrow it to suspect tiles.



Title: Re: Starship heat shield
Post by: Bob Niland on 10/30/2021 03:46 pm
Echo_Jex: There may be different inspection criteria for the prototypes in engineering development vs "rapidly reusable".

That suggests some overall context-setting that might be useful on this thread.

As we watch things shake out at Starbase, so to speak, just what are we witnessing? Beats me, really, but they don't seem to be terribly surprised at developments.

Would I be incorrect to presume that at the very least:
☼ Sx used continuously-adapting computer models to develop this tile design, informed by:
☼ stressing R&D installation of R&D samples on R&D mount attachments on a shake table, perhaps with some active substrate flexure,
☼ stressing R&D installation of R&D samples on R&D mount attachments in a hypersonic wind tunnel, perhaps with some active substrate flexure, plus
☼ things learned from actual flight of test materials (e.g. CRS-18)

The above would have been R&D materials and processes. What's at B.C. might represent qualification of production-grade tiles & production-grade installation, and perhaps not so much validation of the basic tile design. And yes, I'm also expecting that the entire life-cycle process for tiles will at some point be automated (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2264287#msg2264287).
Title: Re: Starship heat shield
Post by: livingjw on 10/30/2021 10:53 pm
Echo_Jex: There may be different inspection criteria for the prototypes in engineering development vs "rapidly reusable".

That suggests some overall context-setting that might be useful on this thread.

As we watch things shake out at Starbase, so to speak, just what are we witnessing? Beats me, really, but they don't seem to be terribly surprised at developments.

Would I be incorrect to presume that at the very least:
☼ Sx used continuously-adapting computer models to develop this tile design, informed by:
☼ stressing R&D installation of R&D samples on R&D mount attachments on a shake table, perhaps with some active substrate flexure,
☼ stressing R&D installation of R&D samples on R&D mount attachments in a hypersonic wind tunnel, perhaps with some active substrate flexure, plus
☼ things learned from actual flight of test materials (e.g. CRS-18)

The above would have been R&D materials and processes. What's at B.C. might represent qualification of production-grade tiles & production-grade installation, and perhaps not so much validation of the basic tile design. And yes, I'm also expecting that the entire life-cycle process for tiles will at some point be automated (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2264287#msg2264287).

I assume most of these analyses and tests has been done.

John
Title: Re: Starship heat shield
Post by: Alastor on 10/30/2021 11:51 pm
A cracked tile could possibly leave the tile improperly supported. There is no redundancy in your attachment to the 3 pins.

I'm not sure that's correct.
Remember that the attachement points on the tile's side are linked together through a metallic frame that's encased in the tile.
So depending on where the crack is, there likely are cases where the tile is cracked, but where both halves are still attached to the frame, and thus, to the attachement mechanism.

Of course for the gap to be cracked and for a gap to form, it necessarily means it can somewhat be moved by vibrations, and thus could be damaged by further exposure to that.
another worry I would have intuitively would be that the heat coming through the crack might melt the tile's metallic frame, that's not behind the thermal blanket.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 10/31/2021 05:15 am
I'm not sure that's correct.
Remember that the attachement points on the tile's side are linked together through a metallic frame that's encased in the tile.
So depending on where the crack is, there likely are cases where the tile is cracked, but where both halves are still attached to the frame, and thus, to the attachement mechanism.

Given that loads on the unsupported parts of the tile will generate torques along the y-channel supports, it's more likely that the cracks will be along the channels, rather than across them.  That'll leave a chunk literally flapping in the breeze, which will likely carry it way in short order.

Folks, cracked tiles are bad.  You can argue all you want about how often a missing tile is a catastrophic failure, but I'm pretty sure that the answer is going to be, "Often enough that you really don't want any."  I'm pretty sure that engineering will continue until p(loss of tile) << p(loss of vehicle).

This doesn't necessarily mean that the first launch will be delayed, because getting this puppy to orbit is much, much more important than getting it back down from orbit.  But I doubt that Starship will be considered reliably recoverable until missing tiles are very, very rare.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 11/01/2021 08:30 pm
I'm not sure that's correct.
Remember that the attachement points on the tile's side are linked together through a metallic frame that's encased in the tile.
So depending on where the crack is, there likely are cases where the tile is cracked, but where both halves are still attached to the frame, and thus, to the attachement mechanism.

Given that loads on the unsupported parts of the tile will generate torques along the y-channel supports, it's more likely that the cracks will be along the channels, rather than across them.  That'll leave a chunk literally flapping in the breeze, which will likely carry it way in short order.

Folks, cracked tiles are bad.  You can argue all you want about how often a missing tile is a catastrophic failure, but I'm pretty sure that the answer is going to be, "Often enough that you really don't want any."  I'm pretty sure that engineering will continue until p(loss of tile) << p(loss of vehicle).

This doesn't necessarily mean that the first launch will be delayed, because getting this puppy to orbit is much, much more important than getting it back down from orbit.  But I doubt that Starship will be considered reliably recoverable until missing tiles are very, very rare.

Yes, I agree. SS could withstand a few brocken tiles, but there is a reason because of which it haas a full heat shield and it doesn't lack a few tiles. The inspection that we saw months ago clearly showns that they wnat to find the cracked tiles.  About S20 the most important thing for them like you say is to get it to orbit. I think that s21 and s22 will be the true test beds for the heat shield.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 11/01/2021 09:12 pm
Yes, I agree. SS could withstand a few brocken tiles, but there is a reason because of which it haas a full heat shield and it doesn't lack a few tiles. The inspection that we saw months ago clearly showns that they wnat to find the cracked tiles.  About S20 the most important thing for them like you say is to get it to orbit. I think that s21 and s22 will be the true test beds for the heat shield.

Well, every Starship that gets to orbit will become a test of the heat shield and EDL in general.  S20 is just unlikely to be a successful test.  I'll bet that the same can be said for S21 and S22 as well.
Title: Re: Starship heat shield
Post by: envy887 on 11/01/2021 10:19 pm
I'm not sure that's correct.
Remember that the attachement points on the tile's side are linked together through a metallic frame that's encased in the tile.
So depending on where the crack is, there likely are cases where the tile is cracked, but where both halves are still attached to the frame, and thus, to the attachement mechanism.

Given that loads on the unsupported parts of the tile will generate torques along the y-channel supports, it's more likely that the cracks will be along the channels, rather than across them.  That'll leave a chunk literally flapping in the breeze, which will likely carry it way in short order.

Folks, cracked tiles are bad.  You can argue all you want about how often a missing tile is a catastrophic failure, but I'm pretty sure that the answer is going to be, "Often enough that you really don't want any."  I'm pretty sure that engineering will continue until p(loss of tile) << p(loss of vehicle).

This doesn't necessarily mean that the first launch will be delayed, because getting this puppy to orbit is much, much more important than getting it back down from orbit.  But I doubt that Starship will be considered reliably recoverable until missing tiles are very, very rare.

Yes, I agree. SS could withstand a few brocken tiles, but there is a reason because of which it haas a full heat shield and it doesn't lack a few tiles. The inspection that we saw months ago clearly showns that they wnat to find the cracked tiles.  About S20 the most important thing for them like you say is to get it to orbit. I think that s21 and s22 will be the true test beds for the heat shield.

I think Starship will generally survive TPS failures, but I do not think it will ever be rapidly reusable after a TPS failure, instead requiring at least repairs and possibly scrapping.

Since the goal is rapid reuse, they are doing, and need to do, everything that is reasonably possible to eliminate TPS failures.
Title: Re: Starship heat shield
Post by: DBMandrake on 11/03/2021 09:19 am
I think Starship will generally survive TPS failures, but I do not think it will ever be rapidly reusable after a TPS failure, instead requiring at least repairs and possibly scrapping.

Since the goal is rapid reuse, they are doing, and need to do, everything that is reasonably possible to eliminate TPS failures.
That's also my gut feeling based on no particular expertise...  it certainly has a lot higher chance of surviving a missing tile or two when it's made from stainless steel vs the shuttles aluminium frame but there's no way it would be getting rapidly re-flown afterwards, (even un-manned) as even if the steel didn't melt and lose integrity it could have been considerably weakened by the excessive heat etc... and if they can produce these things like a sausage in a sausage factory why would you want to risk re-flying a damaged one if there are several new ones waiting their turn ? In that case just be glad that it landed in one piece, study the damage to help improve the design and move on.

It sounds crazy but I think you almost want to lose a few tiles on at least some of the first few orbital test flights precisely to see whether it survives or not missing a few tiles. If it survives re-entry and is able to land (later flights when they aren't landing in water) and the damage can then be studied that's a goldmine of data to help work out where the limits are.

If it can consistently survive and land with a few missing tiles and you can later reach a point where tiles don't go missing either that gives a lot of confidence in safety margins vs computer simulations. Losing a tile might not be ideal but it's not necessarily instant loss of mission if they can prove how rugged it is in real life missing tile testing.

If they don't lose any tiles by accident in the first few orbital test flights which land don't be surprised if they launch a test flight with tiles deliberately missing just to see what happens - that seems like the sort of thing SpaceX would try.  ;D
Title: Re: Starship heat shield
Post by: BT52 on 11/03/2021 03:33 pm
In your last case I would do the same. Also later on I would also try wet weather test with full wet saturated underpadding.
Title: Re: Starship heat shield
Post by: sanman on 11/03/2021 10:40 pm
but there's no way it would be getting rapidly re-flown afterwards, (even un-manned) as even if the steel didn't melt and lose integrity it could have been considerably weakened by the excessive heat etc

But does the goal of rapid re-flight then potentially increase the likelihood of overlooking significant damage following return?
Title: Re: Starship heat shield
Post by: Okie_Steve on 11/03/2021 10:46 pm
but there's no way it would be getting rapidly re-flown afterwards, (even un-manned) as even if the steel didn't melt and lose integrity it could have been considerably weakened by the excessive heat etc

But does the goal of rapid re-flight then potentially increase the likelihood of overlooking significant damage following return?

This sounds like a good job for first pass machine vision automatic inspection, maybe via drones for close up views. Flag anything off nominal looking for human review. Missing, damaged or relocated tiles should be fairly easy to quantify.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 11/04/2021 03:52 am
but there's no way it would be getting rapidly re-flown afterwards, (even un-manned) as even if the steel didn't melt and lose integrity it could have been considerably weakened by the excessive heat etc

But does the goal of rapid re-flight then potentially increase the likelihood of overlooking significant damage following return?

I wonder if you could embed strain gauges with passive RFIDs in each tile.  I'll bet that a crack anywhere will change strain in easily-detectable ways.

Not sure if you could keep the RFID from cooking, though.

That said, I still think the ultimate answer is to make cracked tiles really, really rare.
This sounds like a good job for first pass machine vision automatic inspection, maybe via drones for close up views. Flag anything off nominal looking for human review. Missing, damaged or relocated tiles should be fairly easy to quantify.
Title: Re: Starship heat shield
Post by: Oersted on 11/04/2021 05:39 am
I'm sure SpaceX has been simulating the TPS in plasma flow to very great lengths. One of the important factors of those simulations would be the "granularity", or resolution, they have been able to achieve in the simulations.

I am pretty sure the simulations have informed the eventual choice of tile size acceptable for maintaining good shielding, even in the case of a tile loss.

As I see it, the strength of perpendicular versus parallel plasma flows (in relation to the tile surface) must have a great effect.

If the perpendicular flows are very strong, then they would act like a blow torch straight onto the tiles. That wouldn't bode well for skin integrity even in the case of just a single tile loss.

If the parallel plasma flows are much stronger and, in effect, overpower the perpendicular flows, then I could see them shielding an area where a tile has been lost.

Of course the strengths of perpendicular and parallel flows are very much dependent on where on the fuselage the tiles are located.
Title: Re: Starship heat shield
Post by: edzieba on 11/04/2021 08:03 am
If the perpendicular flows are very strong, then they would act like a blow torch straight onto the tiles. That wouldn't bode well for skin integrity even in the case of just a single tile loss.
Two and a half years ago, SpaceX were literally conducting that head-on blowtorch test on tile sections: https://twitter.com/elonmusk/status/1107378575924035584
It is extremely likely that testing with hypersonic flows, tile-outs, etc, have also been conducted on tile sections but not publicly documented.
Title: Re: Starship heat shield
Post by: KBK on 11/04/2021 12:02 pm
Echo_Jex: There may be different inspection criteria for the prototypes in engineering development vs "rapidly reusable".

That suggests some overall context-setting that might be useful on this thread.

As we watch things shake out at Starbase, so to speak, just what are we witnessing? Beats me, really, but they don't seem to be terribly surprised at developments.

Would I be incorrect to presume that at the very least:
☼ Sx used continuously-adapting computer models to develop this tile design, informed by:
☼ stressing R&D installation of R&D samples on R&D mount attachments on a shake table, perhaps with some active substrate flexure,
☼ stressing R&D installation of R&D samples on R&D mount attachments in a hypersonic wind tunnel, perhaps with some active substrate flexure, plus
☼ things learned from actual flight of test materials (e.g. CRS-18)

The above would have been R&D materials and processes. What's at B.C. might represent qualification of production-grade tiles & production-grade installation, and perhaps not so much validation of the basic tile design. And yes, I'm also expecting that the entire life-cycle process for tiles will at some point be automated (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2264287#msg2264287).

I assume most of these analyses and tests has been done.

John

Same here. Perhaps a few more or modifications to said build/test suite/regimen, as we're not directly in situ.. so we don't have the spark in our minds of seeing the whole existing process enchilada.
Title: Re: Starship heat shield
Post by: KBK on 11/04/2021 12:16 pm
I'm sure SpaceX has been simulating the TPS in plasma flow to very great lengths. One of the important factors of those simulations would be the "granularity", or resolution, they have been able to achieve in the simulations.

I am pretty sure the simulations have informed the eventual choice of tile size acceptable for maintaining good shielding, even in the case of a tile loss.

As I see it, the strength of perpendicular versus parallel plasma flows (in relation to the tile surface) must have a great effect.

If the perpendicular flows are very strong, then they would act like a blow torch straight onto the tiles. That wouldn't bode well for skin integrity even in the case of just a single tile loss.

If the parallel plasma flows are much stronger and, in effect, overpower the perpendicular flows, then I could see them shielding an area where a tile has been lost.

Of course the strengths of perpendicular and parallel flows are very much dependent on where on the fuselage the tiles are located.

More resolution in FLIR, might be a good thing. some modification of said gear...something that puts the camera proper in it's sweet zone of sensitivity. This, with regard to frame rate, flow rate and being on a shaker of some sort. Being on a shaker is where an improved frame rate might really be helpful. This one seems to be headed in the right direction but the temperature range is not quite high enough.
 (https://www.flir.ca/discover/instruments/oil-petrochemical/a-flir-infrared-furnace-camera-for-high-temp-industrial-applications-watches-hydro-reformers-at-german-bayernoil-refinery-complex/)
The next problem is that any additional reflecting layer that is designed to be in front of the camera proper, to get the camera into it's sweet spot..that layer would quite likely require some form of temperature control on it's own, as thermals in the reflector would probably slow the temporal resolution. Maybe a liquid cooled lens stack. A coated transparent ceramic, maybe. Even high speed air flow (across the ceramic reflector) might be clean enough to do the trick, to keep that temporal resolution up. Perhaps someone has solved this potential problem already.

To do this sort of temporal resolution test, if it is easy (enough) to arrive at... and then find out if it has any use. There might be useful data in there. Who knows. Again, considering the issue of number of tiles and importance of said tiles, and so on... more varied data might be better, at least at this discovery end of the process.

EG, it might turn out that cooling the edges of a ceramic reflector is the best way to keep the given sheet cooled, without having thermal flutter occur in the lens proper. Where air and fluid would possibly cause enough random fluctuations to make fine resolution and fine temporal resolution (as a related pair) attempts be pretty well useless.

A way around that might be edge cooling, where the thermal changes have a more defined, less random propagation pattern. Then, add in a modifier in the resulting data, where it is akin to optical color shift correction. This is used to correct for VR lenses, to get rid of color aberration across the viewed image. A similar thermal correction might be useful. To only be looked at, if a problem arises, but one should probably have a back up plan for the back up plan, one that looks at potential issues.

Anyway, it's just a quickly rambled thought experiment at this point. A few seconds of thought put into it is probably worth the time it takes.

Doubling the fundamental frame rate limit of FLIR is 'almost' easy...as this can be done via using two cameras with tightly controlled frame capture sequencing and all the rest that follows. Mapping the individual cameras sensitivities out on a calibration set up... and then the resulting correction file for when the cameras are paired. Does the possible loss in that calibration/pairing process warrant the attempt? One might borrow/mine from the 3D camera fields of endeavor for the basic hardware design. Additionally, via the data package... sensitivity across thermals goes up just a hair, it comes along for the ride, if it properly handled, it might be useful. Who knows. Something additional to look at, for future extrapolation. One can half step the thermals as well, via a second thermal filter on the one camera in the given paring. Write it down in the notes.

(my job, for about the past 20 plus years... has principally been about prototype initiation and proofing. A place where the need for custom design and gear is desirable. Hence these sorts of rambles. They are semi-educated guesses, rife with cross insemination, steeped in the lore of actually doing it, every dang day, all day long. Where my inherent over the top ADHD and semi OCD comes in very handy)

Whoops..I also see a potential way to quadruple the resolution of the camera..but that's another ramble...
Title: Re: Starship heat shield
Post by: Slarty1080 on 11/04/2021 04:40 pm
I'm sure SpaceX has been simulating the TPS in plasma flow to very great lengths. One of the important factors of those simulations would be the "granularity", or resolution, they have been able to achieve in the simulations.

I am pretty sure the simulations have informed the eventual choice of tile size acceptable for maintaining good shielding, even in the case of a tile loss.

As I see it, the strength of perpendicular versus parallel plasma flows (in relation to the tile surface) must have a great effect.

If the perpendicular flows are very strong, then they would act like a blow torch straight onto the tiles. That wouldn't bode well for skin integrity even in the case of just a single tile loss.

If the parallel plasma flows are much stronger and, in effect, overpower the perpendicular flows, then I could see them shielding an area where a tile has been lost.

Of course the strengths of perpendicular and parallel flows are very much dependent on where on the fuselage the tiles are located.
I believe they now use adaptive grids in the simulation where the resolution is variable, lower where there is little complexity and much higher where there is more complexity. This video explains it in some detail (13 mins in)
https://www.youtube.com/watch?v=vYA0f6R5KAI  (https://www.youtube.com/watch?v=vYA0f6R5KAI)
Title: Re: Starship heat shield
Post by: OTV Booster on 11/04/2021 11:10 pm
I'm sure SpaceX has been simulating the TPS in plasma flow to very great lengths. One of the important factors of those simulations would be the "granularity", or resolution, they have been able to achieve in the simulations.

I am pretty sure the simulations have informed the eventual choice of tile size acceptable for maintaining good shielding, even in the case of a tile loss.

As I see it, the strength of perpendicular versus parallel plasma flows (in relation to the tile surface) must have a great effect.

If the perpendicular flows are very strong, then they would act like a blow torch straight onto the tiles. That wouldn't bode well for skin integrity even in the case of just a single tile loss.

If the parallel plasma flows are much stronger and, in effect, overpower the perpendicular flows, then I could see them shielding an area where a tile has been lost.

Of course the strengths of perpendicular and parallel flows are very much dependent on where on the fuselage the tiles are located.

More resolution in FLIR, might be a good thing. some modification of said gear...something that puts the camera proper in it's sweet zone of sensitivity. This, with regard to frame rate, flow rate and being on a shaker of some sort. Being on a shaker is where an improved frame rate might really be helpful. This one seems to be headed in the right direction but the temperature range is not quite high enough.
 (https://www.flir.ca/discover/instruments/oil-petrochemical/a-flir-infrared-furnace-camera-for-high-temp-industrial-applications-watches-hydro-reformers-at-german-bayernoil-refinery-complex/)
The next problem is that any additional reflecting layer that is designed to be in front of the camera proper, to get the camera into it's sweet spot..that layer would quite likely require some form of temperature control on it's own, as thermals in the reflector would probably slow the temporal resolution. Maybe a liquid cooled lens stack. A coated transparent ceramic, maybe. Even high speed air flow (across the ceramic reflector) might be clean enough to do the trick, to keep that temporal resolution up. Perhaps someone has solved this potential problem already.

To do this sort of temporal resolution test, if it is easy (enough) to arrive at... and then find out if it has any use. There might be useful data in there. Who knows. Again, considering the issue of number of tiles and importance of said tiles, and so on... more varied data might be better, at least at this discovery end of the process.

EG, it might turn out that cooling the edges of a ceramic reflector is the best way to keep the given sheet cooled, without having thermal flutter occur in the lens proper. Where air and fluid would possibly cause enough random fluctuations to make fine resolution and fine temporal resolution (as a related pair) attempts be pretty well useless.

A way around that might be edge cooling, where the thermal changes have a more defined, less random propagation pattern. Then, add in a modifier in the resulting data, where it is akin to optical color shift correction. This is used to correct for VR lenses, to get rid of color aberration across the viewed image. A similar thermal correction might be useful. To only be looked at, if a problem arises, but one should probably have a back up plan for the back up plan, one that looks at potential issues.

Anyway, it's just a quickly rambled thought experiment at this point. A few seconds of thought put into it is probably worth the time it takes.

Doubling the fundamental frame rate limit of FLIR is 'almost' easy...as this can be done via using two cameras with tightly controlled frame capture sequencing and all the rest that follows. Mapping the individual cameras sensitivities out on a calibration set up... and then the resulting correction file for when the cameras are paired. Does the possible loss in that calibration/pairing process warrant the attempt? One might borrow/mine from the 3D camera fields of endeavor for the basic hardware design. Additionally, via the data package... sensitivity across thermals goes up just a hair, it comes along for the ride, if it properly handled, it might be useful. Who knows. Something additional to look at, for future extrapolation. One can half step the thermals as well, via a second thermal filter on the one camera in the given paring. Write it down in the notes.

(my job, for about the past 20 plus years... has principally been about prototype initiation and proofing. A place where the need for custom design and gear is desirable. Hence these sorts of rambles. They are semi-educated guesses, rife with cross insemination, steeped in the lore of actually doing it, every dang day, all day long. Where my inherent over the top ADHD and semi OCD comes in very handy)

Whoops..I also see a potential way to quadruple the resolution of the camera..but that's another ramble...
I'm looking at this from a photography point of view. And a lifelong infatuation with astronomy where I've learned that all EMR behaves roughly the same if the unit of measure is a wavelength.


The problem of the optics emitting around the wavelength of interest is a common problem in space based astronomy. The solution, as you point out, is to cool the optics so they no longer add noise to the signal. Unless I'm missing something (what, me :P ?) the problem is dynamic range, not frame rate. IIUC, the SN ratio does not change with exposure.


There are some assumption here but they all concern exposures towards the edges of the sensor design. That's one place where the dynamic range takes a hit. The hotter the optics, the more the noise pushes towards sensor saturation. OTOH, adding uniform noise to a weak signal is one way of bringing it up to minimum sensor threshold.


I was thinking of some sort of tunable optical notch filter tuned to the black body of the optics. That lead me to thinking about periodic imaging of a grid target to map heat distortion of the optics then I realized the target is a (mostly) hexagonal grid.


All in all, there are probably easier way to do it, but a fun exercise.

Title: Re: Starship heat shield
Post by: brettly2021 on 11/05/2021 03:36 am
there are plasma wind tunnels for doing testing to
https://www.livescience.com/plasma-tunnel-melts-satellite-model.html

also some tiles being replaced on sn20 near wing a few day ago, the cause might be the static fire but really cause is not known,
I'm asusming related to static fire, so the tally for tile loss goes up quite a bit.....yup its all assumption.
Title: Re: Starship heat shield
Post by: schuttle89 on 11/05/2021 12:33 pm
there are plasma wind tunnels for doing testing to
https://www.livescience.com/plasma-tunnel-melts-satellite-model.html

also some tiles being replaced on sn20 near wing a few day ago, the cause might be the static fire but really cause is not known,
I'm asusming related to static fire, so the tally for tile loss goes up quite a bit.....yup its all assumption.
Just some questions on my end but how would a static fire affect those tiles? Something specific to square on square contact area that makes them more sensitive to shaking? Temperature difference from nearer-to-tank to farther-from-tank causing issues? Both those issues don't seem too stressful compared to the load they're supposed to handle.
Title: Re: Starship heat shield
Post by: markbike528cbx on 11/05/2021 03:58 pm
there are plasma wind tunnels for doing testing to
https://www.livescience.com/plasma-tunnel-melts-satellite-model.html

also some tiles being replaced on sn20 near wing a few day ago, the cause might be the static fire but really cause is not known,
I'm asusming related to static fire, so the tally for tile loss goes up quite a bit.....yup its all assumption.
Just some questions on my end but how would a static fire affect those tiles? Something specific to square on square contact area that makes them more sensitive to shaking? Temperature difference from nearer-to-tank to farther-from-tank causing issues? Both those issues don't seem too stressful compared to the load they're supposed to handle.
Resonances.   
Think of Starship as a guitar string and the tile is stuck on. 
At a node, not much movement, between nodes, there is a lot of movement.
Title: Re: Starship heat shield
Post by: schuttle89 on 11/05/2021 08:23 pm
there are plasma wind tunnels for doing testing to
https://www.livescience.com/plasma-tunnel-melts-satellite-model.html

also some tiles being replaced on sn20 near wing a few day ago, the cause might be the static fire but really cause is not known,
I'm asusming related to static fire, so the tally for tile loss goes up quite a bit.....yup its all assumption.
Just some questions on my end but how would a static fire affect those tiles? Something specific to square on square contact area that makes them more sensitive to shaking? Temperature difference from nearer-to-tank to farther-from-tank causing issues? Both those issues don't seem too stressful compared to the load they're supposed to handle.
Resonances.   
Think of Starship as a guitar string and the tile is stuck on. 
At a node, not much movement, between nodes, there is a lot of movement.

I meant specifically with the tiles in that specific area, as in why would they be replacing a large area on that flat surface as opposed to on the barrel sections?
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 11/05/2021 08:27 pm
I meant specifically with the tiles in that specific area, as in why would they be replacing a large area on that flat surface as opposed to on the barrel sections?

It could be as simple as something that they were working on got ready in time to be tested on SN20.  I'd be a little surprised if everything were completely uniform.  They're looking for flight data.  If they can get flight data from several different sets of tiles at the same time, so much the better.
Title: Re: Starship heat shield
Post by: tgio on 11/06/2021 01:26 am
S21 aft section was moved to the front of the mid bay.

S21's aft section has larger tiles on the bulkhead reinforcement band than on the rest of the section (see attached image from the quoted post). For comparison, the same section on S20 uses the usual smaller tiles. Is there any reason they'd want larger tiles on this area specifically, or might they be thinking of switching to larger tiles and are gathering data with this smaller section first? Could it have something to do with the lack of thermal blanket on the reinforcement band?
Title: Re: Starship heat shield
Post by: AC in NC on 11/06/2021 02:19 am
Is there any reason they'd want larger tiles on this area specifically
Width of the band might be a reason
Title: Re: Starship heat shield
Post by: volker2020 on 11/06/2021 09:33 am
S21 aft section was moved to the front of the mid bay.

S21's aft section has larger tiles on the bulkhead reinforcement band than on the rest of the section (see attached image from the quoted post). For comparison, the same section on S20 uses the usual smaller tiles. Is there any reason they'd want larger tiles on this area specifically, or might they be thinking of switching to larger tiles and are gathering data with this smaller section first? Could it have something to do with the lack of thermal blanket on the reinforcement band?
Good question. By the way, am I the only one, having the impression that the tiles are applied with a higher accuracy than before?
Title: Re: Starship heat shield
Post by: brettly2021 on 11/06/2021 11:41 am
smaller tiles less chance of cracking is my guess, so can use larger tiles on more reinforced areas.
No idea if the wing tiles were cracked during test fire, I expect will see more replacements though.
Title: Re: Starship heat shield
Post by: Tangilinear Interjar on 11/06/2021 01:36 pm
S21 aft section was moved to the front of the mid bay.

S21's aft section has larger tiles on the bulkhead reinforcement band than on the rest of the section (see attached image from the quoted post). For comparison, the same section on S20 uses the usual smaller tiles. Is there any reason they'd want larger tiles on this area specifically, or might they be thinking of switching to larger tiles and are gathering data with this smaller section first? Could it have something to do with the lack of thermal blanket on the reinforcement band?
I suspect it has something to do with the tiles being glued on rather than pinned on.

Since they are going to be glued the manufacturing process is different so the size (and perhaps shape) constraint is different. Therefore you might as well make them bigger so you have less of them to apply. Also your size needs to fit the band width.
Title: Re: Starship heat shield
Post by: Sohl on 11/08/2021 01:24 pm
... By the way, am I the only one, having the impression that the tiles are applied with a higher accuracy than before?

No, I have that impression too.  The tiles seem more consistently fitted and the edges seem better aligned into a smooth surface.
Title: Re: Starship heat shield
Post by: billh on 11/08/2021 03:38 pm
... By the way, am I the only one, having the impression that the tiles are applied with a higher accuracy than before?

No, I have that impression too.  The tiles seem more consistently fitted and the edges seem better aligned into a smooth surface.
Is that true for the nose cone, too? The barrel section is more uniform than the nose cone for SN20, too.
Title: Re: Starship heat shield
Post by: Sohl on 11/08/2021 04:02 pm
...  The tiles seem more consistently fitted and the edges seem better aligned into a smooth surface.
Is that true for the nose cone, too? The barrel section is more uniform than the nose cone for SN20, too.

To my eye in the pictures I've seen, SN21 cone and barrel sections both have a more even, smooth appearance indicating less tile-to-tile variation in mounting, and thus forming a smoother skin.  Not perfect, but a good step forward.  YMMV, since I'm not sure we've had the best lighting angles to emphasize irregularities for SN21 yet. 
Title: Re: Starship heat shield
Post by: Slarty1080 on 11/08/2021 10:10 pm
...  The tiles seem more consistently fitted and the edges seem better aligned into a smooth surface.
Is that true for the nose cone, too? The barrel section is more uniform than the nose cone for SN20, too.

To my eye in the pictures I've seen, SN21 cone and barrel sections both have a more even, smooth appearance indicating less tile-to-tile variation in mounting, and thus forming a smoother skin.  Not perfect, but a good step forward.  YMMV, since I'm not sure we've had the best lighting angles to emphasize irregularities for SN21 yet.
I wonder how much more delay on the part of the FAA it would take to doom SN20 to lawn ornamentation duties and allow SN21 in on the first orbital attempt?
Title: Re: Starship heat shield
Post by: OTV Booster on 11/08/2021 10:38 pm
...  The tiles seem more consistently fitted and the edges seem better aligned into a smooth surface.
Is that true for the nose cone, too? The barrel section is more uniform than the nose cone for SN20, too.

To my eye in the pictures I've seen, SN21 cone and barrel sections both have a more even, smooth appearance indicating less tile-to-tile variation in mounting, and thus forming a smoother skin.  Not perfect, but a good step forward.  YMMV, since I'm not sure we've had the best lighting angles to emphasize irregularities for SN21 yet.
The skin of the SS has noticeably improved with each build although the improvement curve has been flattening of late. No reason not to expect the tiles to follow the same path despite a chorus of "they're not doing it right." It's the SX way.
Title: Re: Starship heat shield
Post by: OTV Booster on 11/08/2021 10:41 pm
...  The tiles seem more consistently fitted and the edges seem better aligned into a smooth surface.
Is that true for the nose cone, too? The barrel section is more uniform than the nose cone for SN20, too.

To my eye in the pictures I've seen, SN21 cone and barrel sections both have a more even, smooth appearance indicating less tile-to-tile variation in mounting, and thus forming a smoother skin.  Not perfect, but a good step forward.  YMMV, since I'm not sure we've had the best lighting angles to emphasize irregularities for SN21 yet.
I wonder how much more delay on the part of the FAA it would take to doom SN20 to lawn ornamentation duties and allow SN21 in on the first orbital attempt?
I'll answer your question with a question. How long before SN21 is ready? They'll do it in a heartbeat if the timing works out.
Title: Re: Starship heat shield
Post by: Slarty1080 on 11/10/2021 04:57 pm
...  The tiles seem more consistently fitted and the edges seem better aligned into a smooth surface.
Is that true for the nose cone, too? The barrel section is more uniform than the nose cone for SN20, too.

To my eye in the pictures I've seen, SN21 cone and barrel sections both have a more even, smooth appearance indicating less tile-to-tile variation in mounting, and thus forming a smoother skin.  Not perfect, but a good step forward.  YMMV, since I'm not sure we've had the best lighting angles to emphasize irregularities for SN21 yet.
I wonder how much more delay on the part of the FAA it would take to doom SN20 to lawn ornamentation duties and allow SN21 in on the first orbital attempt?
I'll answer your question with a question. How long before SN21 is ready? They'll do it in a heartbeat if the timing works out.
IMO SN21 will be ready long before the FAA are, so it seems likely that SN20 will soon be relegated to a static fire and GSE testing role. If it hasn't been already.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 11/10/2021 09:33 pm
IMO SN21 will be ready long before the FAA are, so it seems likely that SN20 will soon be relegated to a static fire and GSE testing role. If it hasn't been already.

They could also get a non-SuperHeavy launch license pretty easily, fill it as full as they can while still having an adequate T/W to launch with just the sea-level engines (I get about 160t of prop for T/W=1.2), and get some decent suborbital reentry data by launching it out to sea.  SWAGging at gravity losses, I get a burnout speed of something like 2200m/s.  Not exactly an orbital reentry, but fast enough to find out if the CFD models are roughly correct, and to see how many tiles fall off.

Update:  Anybody know the details of the mounting of the RVacs?  If you can swap them out for RSLs without having to re-engineer the entire thrust structure, then you can load 960t of prop and expend 7450m/s of delta-v with a launch T/W=1.3.  That's probably good for an entry speed of 6800m/s.  That'll get you some pretty serious data.
Title: Re: Starship heat shield
Post by: Twark_Main on 11/11/2021 07:54 am
Also, the larger the tile the greater the divergence from the curve of the OML and the more the pointy corners stick out begging for heat buildup.
Why not make them to fit the curvature?
This is the first full try ala SX modus operandi of just good enough. If they need to do that they will. It's not that big a parts count issue on the cylinder but up on the ogive it might be a complexity they'd like to avoid. That said, there are custom curved tiles in the fin edges. They'll do whatever it takes.

Even if they used the exact same (single-curved) tiles on the ogive, the overall curvature would still be less wrong than using flat tiles.

So again I ask, why not make the tiles fit the curvature? ???

Is it just so the body flaps (which are flat) can share a common tile SKU with the body/ogive tiles? Or is it the additional manufacturing complexity of making slightly curved tiles? Or is it just that SpaceX hasn't reached that stage yet?
Title: Re: Starship heat shield
Post by: edzieba on 11/11/2021 10:57 am
Why not make them to fit the curvature?
Currently (as per the FDEP report) tiles are milled to final size and shape on a router (cheap and fast, potentially large working volume for multiple tiles processed in parallel). Curved tiles would need a 5-axis CNC (more expensive, slower, more complex fixturing). If the flat tiles are adequate, curved tiles being 'better' is not worth the cost and time expenditure.
Title: Re: Starship heat shield
Post by: OTV Booster on 11/11/2021 04:59 pm
IMO SN21 will be ready long before the FAA are, so it seems likely that SN20 will soon be relegated to a static fire and GSE testing role. If it hasn't been already.

They could also get a non-SuperHeavy launch license pretty easily, fill it as full as they can while still having an adequate T/W to launch with just the sea-level engines (I get about 160t of prop for T/W=1.2), and get some decent suborbital reentry data by launching it out to sea.  SWAGging at gravity losses, I get a burnout speed of something like 2200m/s.  Not exactly an orbital reentry, but fast enough to find out if the CFD models are roughly correct, and to see how many tiles fall off.

Update:  Anybody know the details of the mounting of the RVacs?  If you can swap them out for RSLs without having to re-engineer the entire thrust structure, then you can load 960t of prop and expend 7450m/s of delta-v with a launch T/W=1.3.  That's probably good for an entry speed of 6800m/s.  That'll get you some pretty serious data.
Or maybe add three RVacs to the three outer SL's. Yeah, a major thrust dome and plumbing redesign but as per speculation, something maybe being looked at. Big advantages for the meat haulers. If they're hung up on regulatory, it would keep the game moving.
Title: Re: Starship heat shield
Post by: OTV Booster on 11/11/2021 05:48 pm
Also, the larger the tile the greater the divergence from the curve of the OML and the more the pointy corners stick out begging for heat buildup.
Why not make them to fit the curvature?
This is the first full try ala SX modus operandi of just good enough. If they need to do that they will. It's not that big a parts count issue on the cylinder but up on the ogive it might be a complexity they'd like to avoid. That said, there are custom curved tiles in the fin edges. They'll do whatever it takes.

Even if they used the exact same (single-curved) tiles on the ogive, the overall curvature would still be less wrong than using flat tiles.

So again I ask, why not make the tiles fit the curvature? ???

Is it just so the body flaps (which are flat) can share a common tile SKU with the body/ogive tiles? Or is it the additional manufacturing complexity of making slightly curved tiles? Or is it just that SpaceX hasn't reached that stage yet?
SX will probably do a lot more tile customizing but given the culture, they've got to give the flat ones a try. Easing up to just good enough instead of dropping down from over engineered.
Title: Re: Starship heat shield
Post by: Twark_Main on 11/11/2021 10:59 pm
Why not make them to fit the curvature?
Currently (as per the FDEP report) tiles are milled to final size and shape on a router (cheap and fast, potentially large working volume for multiple tiles processed in parallel). Curved tiles would need a 5-axis CNC (more expensive, slower, more complex fixturing). If the flat tiles are adequate, curved tiles being 'better' is not worth the cost and time expenditure.

It says (https://forum.nasaspaceflight.com/index.php?topic=48412.msg2162595#msg2162595)

Quote
The tiles are shaped to the desired form using a router.

A 5-axis CNC router is also a "router," so it's not clear that this is actually a contradiction.

I find it highly unlikely that SpaceX is using a manual (non-CNC) router for manufacturing the tiles.



Thus far we have 5 votes for "manufacturing complexity" and 4 votes for "not there yet."  ???  8)
Title: Re: Starship heat shield
Post by: Keldor on 11/11/2021 11:47 pm
Why not make them to fit the curvature?
Currently (as per the FDEP report) tiles are milled to final size and shape on a router (cheap and fast, potentially large working volume for multiple tiles processed in parallel). Curved tiles would need a 5-axis CNC (more expensive, slower, more complex fixturing). If the flat tiles are adequate, curved tiles being 'better' is not worth the cost and time expenditure.

It says (https://forum.nasaspaceflight.com/index.php?topic=48412.msg2162595#msg2162595)

Quote
The tiles are shaped to the desired form using a router.

A 5-axis CNC router is also a "router," so it's not clear that this is actually a contradiction.

I find it highly unlikely that SpaceX is using a manual (non-CNC) router for manufacturing the tiles.



Thus far we have 5 votes for "manufacturing complexity" and 4 votes for "not there yet."  ???  8)

For tiles on the body, curvature is quite small.  I don't see why you would need a 5 axis CNC to cut those.

In any case, a 5-axis machine isn't any slower, it just seems that way because you usually use them for more complicated parts.  The speed has to do with how much material has to be removed and how smooth your finish needs to be.  As for cost, I doubt this is really a problem for SpaceX.  They're expensive for mom and pop shops, not for multi-billion dollar companies.

Also, unlike large machinery for manufacturing massive objects like the fuselage of Starship, CNC machines for things the size of tiles are relatively small and portable, and so it's easy to rearrange things if your initial production line isn't optimal.  Contrast this to stacking boosters, where you're essentially building your factory around your production line, meaning that if you later find that your requirements aren't what you thought they were, you're stuck.  Thus, while for stacking it's in your interest to start with very basic techniques and figure out what your factory really needs by testing, you can go straight toward a more or less final production line and simply move things around and replace things that didn't work out easily to optimize the process.
Title: Re: Starship heat shield
Post by: Slarty1080 on 11/12/2021 01:35 am
Also, the larger the tile the greater the divergence from the curve of the OML and the more the pointy corners stick out begging for heat buildup.
Why not make them to fit the curvature?
This is the first full try ala SX modus operandi of just good enough. If they need to do that they will. It's not that big a parts count issue on the cylinder but up on the ogive it might be a complexity they'd like to avoid. That said, there are custom curved tiles in the fin edges. They'll do whatever it takes.

Even if they used the exact same (single-curved) tiles on the ogive, the overall curvature would still be less wrong than using flat tiles.

So again I ask, why not make the tiles fit the curvature? ???

Is it just so the body flaps (which are flat) can share a common tile SKU with the body/ogive tiles? Or is it the additional manufacturing complexity of making slightly curved tiles? Or is it just that SpaceX hasn't reached that stage yet?
SX will probably do a lot more tile customizing but given the culture, they've got to give the flat ones a try. Easing up to just good enough instead of dropping down from over engineered.
Yes and they have a much better grasp of what's needed than we do. I (and probably others) made invalid assumptions about the tiles right from early on. My suggestion that a different tile would be needed for each layer of the nose cone was wrong because I had assumed no long straight lines were allowed between tiles. But long straight lines are allowed between tiles as long as they run circumferentially and not longitudinally. This allows them to get a much better fit with just 3 primary tile types and their corresponding half tiles. 
Whose to say what other assumptions we are making explicitly or implicitly that may be wrong?
Title: Re: Starship heat shield
Post by: brettly2021 on 11/12/2021 01:27 pm
I have been wondering why the nosecone in particular requires glued on tiles ( red rtv silicone as glue?), anyhow scott manley put up a pic of a mach 20 wind tunnel test from the 1970s showing shock wave, and can be clearly seen the high temp shock wave remains very close to the nosecone area, and gradually gets further away from the craft as you go down the length of the craft, same shoud apply to sn20.
Also next static fire, I think we might see some more tile shedding, will find out soon enough.
Title: Re: Starship heat shield
Post by: DanClemmensen on 11/12/2021 01:33 pm
I have been wondering why the nosecone in particular requires glued on tiles ( red rtv silicone as glue?), anyhow scott manley put up a pic of a mach 20 wind tunnel test from the 1970s showing shock wave, and can be clearly seen the high temp shock wave remains very close to the nosecone area, and gradually gets further away from the craft as you go down the length of the craft, same shoud apply to sn20.
Also next static fire, I think we might see some more tile shedding, will find out soon enough.
How relevant is this Shuttle test to Starship? Starship does not have big wings. I thought it would just present its windward side to the direction of travel instead of a nose-up attitude.
Title: Re: Starship heat shield
Post by: abaddon on 11/12/2021 05:25 pm
Looks like the Ship 20 heat shield did pretty well during the full static fire, losing perhaps two dozen tiles?  We might see more when we have closer imaging, but seems unlikely it will be a lot more.
Title: Re: Starship heat shield
Post by: dwheeler on 11/12/2021 05:44 pm
Looks like the Ship 20 heat shield did pretty well during the full static fire, losing perhaps two dozen tiles?  We might see more when we have closer imaging, but seems unlikely it will be a lot more.

Grainy as hell but here's a before an after from the twitter video:
Title: Re: Starship heat shield
Post by: envy887 on 11/12/2021 05:45 pm
I have been wondering why the nosecone in particular requires glued on tiles ( red rtv silicone as glue?), anyhow scott manley put up a pic of a mach 20 wind tunnel test from the 1970s showing shock wave, and can be clearly seen the high temp shock wave remains very close to the nosecone area, and gradually gets further away from the craft as you go down the length of the craft, same shoud apply to sn20.
Also next static fire, I think we might see some more tile shedding, will find out soon enough.
How relevant is this Shuttle test to Starship? Starship does not have big wings. I thought it would just present its windward side to the direction of travel instead of a nose-up attitude.

Very. Starship is going to enter at a higher angle of attack than Shuttle's 40 degrees, but not by much. It certainly won't be broadside (90 degrees AoA) because they it would not generate any lift, and it needs lift.
Title: Re: Starship heat shield
Post by: daveglo on 11/13/2021 04:00 am

Very. Starship is going to enter at a higher angle of attack than Shuttle's 40 degrees, but not by much. It certainly won't be broadside (90 degrees AoA) because they it would not generate any lift, and it needs lift.

Higher AoA?  You bet.  70 degrees per Elon.

https://twitter.com/elonmusk/status/1325937554236043266?s=20
Title: Re: Starship heat shield
Post by: brettly2021 on 11/13/2021 06:09 am
yup a few more tiles lost , you can see the ones under the forward right wing fall off at the 3:29mark in this static fire nasaspaceflight video
https://www.youtube.com/watch?v=9Tzr-d0wGVU
Even at 70deg ( if thats what they go at) AoA shock pattern should be pretty similar, nose will still have bow shock at closest to tiles and therefore hottest. There is an excellent series of lectures on understanding of the plasma during re-entry by Dr Javier Urzay here is his youtube
https://www.youtube.com/channel/UCQ9rIwlFOaslOlwp55s2LWw/videos
( note lecture no.2 sound is not good )
I keep finding more and more excellent reentry videos from 60s to recent ( youtube algorithmn is not helpful) here is a good one from gemini program
https://www.youtube.com/watch?v=1Gyn8Fx2Bfs
Its looking backward can just see rear( top) of capsule in the vid.
Its interesting in that the oxygen ionisation gives pinkish colour and nitrogen gives green later in the reentry
( if I have that correct oxygen much lower temp ionisation), its basically same as the aurora in night sky, though aurora ionisation is different process of course but same colourful effect.
( colours might also be effected by ablative type heatshield)
I really have doubts about the stainless clips and brackets concept.

Title: Re: Starship heat shield
Post by: OV103Fan on 11/13/2021 12:50 pm
It looks like most of the tiles the fell off after the six engine static fire are on the tanks and not the nosecone/barrel section.  Did the tank sections get the same scrutiny and rework that the nose barrel and cone sections did (the green/red/blue tape inspection)?
Title: Re: Starship heat shield
Post by: beelsebob on 11/13/2021 09:28 pm
I have been wondering why the nosecone in particular requires glued on tiles ( red rtv silicone as glue?), anyhow scott manley put up a pic of a mach 20 wind tunnel test from the 1970s showing shock wave, and can be clearly seen the high temp shock wave remains very close to the nosecone area, and gradually gets further away from the craft as you go down the length of the craft, same shoud apply to sn20.
Also next static fire, I think we might see some more tile shedding, will find out soon enough.

Remember though, the Space Shuttle entered at a much more nose down angle than Starship will.  How much of the bow shock being close to the nose cone is due to the tight curvature, and how much is due to it being the first bit of the space shuttle to hit the air.  A blunt reentry capsule shape pushing its bow shock away from it suggests strongly that Starship's much more belly first entry will push the bow shock much further from the nose.
Title: Re: Starship heat shield
Post by: beelsebob on 11/13/2021 09:32 pm
https://forum.nasaspaceflight.com/index.php?topic=54984.msg2310219#msg2310219

In the past when they've applied the blanket it's been one part, hasn't it?  I imagine this is a manufacturing optimisation - it certainly sounds a lot easier to put small sheets on than trying to wrap a giant sheet around it.  I don't see any reason it would improve the actual performance of the heat shield.
Title: Re: Starship heat shield
Post by: BT52 on 11/13/2021 10:10 pm
I would integrate felt into tile itself or even delete it altogether. I guess ice/rain and frost is real concern for interstellar travel. But i m sure jury is still on that assumption.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 11/14/2021 12:00 pm
I have been wondering why the nosecone in particular requires glued on tiles ( red rtv silicone as glue?), anyhow scott manley put up a pic of a mach 20 wind tunnel test from the 1970s showing shock wave, and can be clearly seen the high temp shock wave remains very close to the nosecone area, and gradually gets further away from the craft as you go down the length of the craft, same shoud apply to sn20.
Also next static fire, I think we might see some more tile shedding, will find out soon enough.

There's a quick-and-dirty formula for heating rate (in W/m²) that goes:

q̇ = 1.83E-4v³√(⍴/rnose)

Where v is the current speed, ⍴ is the atmospheric density, and rnose is the nose radius, in meters.  This makes pretty good sense on a sharp-body vehicle at low AoA (where it's tiny, and therefore heating is extreme), and on a blunt-body vehicle (where it's somewhat larger than the radius of the blunt body itself.  But I've fallen and can't get up when trying to describe the nose radius on a high-AoA sorta-but-not-really sharp body.

Anybody know how to take a stab at this for various parts of a reentering Starship?  Best I can figure is to make this related to how much the shock curves around any given surface, but even then it's hard to convert from curvature to nose radius.
Title: Re: Starship heat shield
Post by: Twark_Main on 11/14/2021 04:25 pm
I have been wondering why the nosecone in particular requires glued on tiles ( red rtv silicone as glue?), anyhow scott manley put up a pic of a mach 20 wind tunnel test from the 1970s showing shock wave, and can be clearly seen the high temp shock wave remains very close to the nosecone area, and gradually gets further away from the craft as you go down the length of the craft, same shoud apply to sn20.
Also next static fire, I think we might see some more tile shedding, will find out soon enough.

There's a quick-and-dirty formula for heating rate (in W/m²) that goes:

q̇ = 1.83E-4v³√(⍴/rnose)

Where v is the current speed, ⍴ is the atmospheric density, and rnose is the nose radius, in meters.

I assume ⍴ is given in kg/m3, but what is v? M/s? Km/s? Kph?

Pro-tip: if you want the equation to be independent of the units used (ie the correct way in physics), then put the units where they belong: attached to the empirical constant.

If you're giving v above in m/s, then the equation is:

q̇ = (1.83E-4 kg1/2 m-1/2 ) v³√(⍴/rnose)
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 11/14/2021 10:10 pm
Pro-tip: if you want the equation to be independent of the units used (ie the correct way in physics), then put the units where they belong: attached to the empirical constant.

If you're giving v above in m/s, then the equation is:

q̇ = (1.83E-4 kg1/2 m-1/2 ) v³√(⍴/rnose)

q̇ is in W/m², so I think the coefficient is in kg½m-1, but I was willing to trust the source (which is an FAA tutorial, p. 4.1.7-322 (https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/cami/library/online_libraries/aerospace_medicine/tutorial/media/iii.4.1.7_returning_from_space.pdf)).  And yes, v is in m/s.

But none of that gets me any closer to figuring out how to estimate the nose radius.
Title: Re: Starship heat shield
Post by: Stan-1967 on 11/14/2021 11:56 pm
Pro-tip: if you want the equation to be independent of the units used (ie the correct way in physics), then put the units where they belong: attached to the empirical constant.

If you're giving v above in m/s, then the equation is:

q̇ = (1.83E-4 kg1/2 m-1/2 ) v³√(⍴/rnose)

q̇ is in W/m², so I think the coefficient is in kg½m-1, but I was willing to trust the source (which is an FAA tutorial, p. 4.1.7-322 (https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/cami/library/online_libraries/aerospace_medicine/tutorial/media/iii.4.1.7_returning_from_space.pdf)).  And yes, v is in m/s.

But none of that gets me any closer to figuring out how to estimate the nose radius.


Can you estimate the curvature at any point on the ogive as a parabola?  Wouldn't the focus of the parabola around the axis of symmetry then be your critical radius dimension?

Alternately, if you represent the ogive as a quadratic equation, taking the inverse of the derivative ( tangent line) at any give point gives you a line perpendicular to the ogive tangent at that point.  You could numerically step your way outwards from the axis of symmetry & find the (x,y) coordinates where the adjacent linear equations intersect.  Then the distance from your tangential point on the ogive the intersection of adjacent tangents is your radius.  The radius will be calculated with pythagoreans theorem as the hypotenuse of the X,Y sides.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 11/15/2021 07:54 am
Pro-tip: if you want the equation to be independent of the units used (ie the correct way in physics), then put the units where they belong: attached to the empirical constant.

If you're giving v above in m/s, then the equation is:

q̇ = (1.83E-4 kg1/2 m-1/2 ) v³√(⍴/rnose)

q̇ is in W/m², so I think the coefficient is in kg½m-1, but I was willing to trust the source (which is an FAA tutorial, p. 4.1.7-322 (https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/cami/library/online_libraries/aerospace_medicine/tutorial/media/iii.4.1.7_returning_from_space.pdf)).  And yes, v is in m/s.

But none of that gets me any closer to figuring out how to estimate the nose radius.


Can you estimate the curvature at any point on the ogive as a parabola?  Wouldn't the focus of the parabola around the axis of symmetry then be your critical radius dimension?

Alternately, if you represent the ogive as a quadratic equation, taking the inverse of the derivative ( tangent line) at any give point gives you a line perpendicular to the ogive tangent at that point.  You could numerically step your way outwards from the axis of symmetry & find the (x,y) coordinates where the adjacent linear equations intersect.  Then the distance from your tangential point on the ogive the intersection of adjacent tangents is your radius.  The radius will be calculated with pythagoreans theorem as the hypotenuse of the X,Y sides.

Seems like you need an angle of attack term in there somewhere.  Also, the elonerons are going to change the shock formation a lot.

Ultimately, heating is determined by how far the shock stands off from the surface of the vehicle.  The farther it stands off, the lower the heating.
Title: Re: Starship heat shield
Post by: brettly2021 on 11/15/2021 11:25 am
A little more info on the heatshield tiles, someone made an estimate of the total weight in this thread, found a nice article on the shuttle tiles:
https://science.ksc.nasa.gov/shuttle/technology/sts-newsref/sts-tps.html
Its says shuttle tiles were 9lbs per cubic foot ( might give a rough estimate of total weight) for the lighter version.
( heavier version only around the nose etc which are 22ibs per cubic foot).
Why I dont like the pin/y bracket method of space x:
1. according to article above the tiles on the shuttle they need to be isolated from the vibrations etc, shuttle used isolation pads. The stainless pins are in effect going to transfer vibration to the tile via the Y brackets.
2. The y brackets are just set into the tile at manufacture, so vibration from bracket directly transferred to tile ( tiles are very easily cracked)
3. The stainless clips in effect will magnify the vibrations  ( and if it happens you hit their resonate frequency they will act like little tuning forks).
4. The y brackets so far are not one connected piece, they are three separate pieces set into the slurry at manufacture. That would have to increase chance of cracking in my view.
5. The white blanket might perform some dampening of vibration of pins so thats a positive.
I dont think it will work in long term ( I could be wrong of course!), maybe increase tile density to decrease risk of cracking but weight issues there.

Title: Re: Starship heat shield
Post by: AJW on 11/15/2021 02:37 pm
The tile that I have is just the silica w/o the coating and comes in at 7.5 lbs. per sq. ft. The coating is heavier and the ratio of tile to coating would depend on the exposed surface area, and Shuttle tiles varied widely in shape and size, which is why the overall weight values provided can only be approximate.
Title: Re: Starship heat shield
Post by: Oersted on 11/15/2021 02:49 pm
Why I dont like the pin/y bracket method of space x:
1. according to article above the tiles on the shuttle they need to be isolated from the vibrations etc, shuttle used isolation pads. The stainless pins are in effect going to transfer vibration to the tile via the Y brackets.
2. The y brackets are just set into the tile at manufacture, so vibration from bracket directly transferred to tile ( tiles are very easily cracked)
3. The stainless clips in effect will magnify the vibrations  ( and if it happens you hit their resonate frequency they will act like little tuning forks).
4. The y brackets so far are not one connected piece, they are three separate pieces set into the slurry at manufacture. That would have to increase chance of cracking in my view.
5. The white blanket might perform some dampening of vibration of pins so thats a positive.
I dont think it will work in long term ( I could be wrong of course!), maybe increase tile density to decrease risk of cracking but weight issues there.

I am thinking that the individual tiles are very light, so wouldn't they just "shake long" with whatever frequency is transmitted via the pins? The problem would be to have two substantial bodies starting to vibrate in a disharmonic way: that would expose the connections to a lot of force.

Just my 5 cents.
Title: Re: Starship heat shield
Post by: Oersted on 11/15/2021 02:52 pm
Oh, and of course SpaceX has tested all thinkable issues relating to vibration. That goes without saying. Let's keep the Dunning-Kruger effect in mind... https://en.wikipedia.org/w/index.php?title=Dunning%E2%80%93Kruger_effect&oldid=1053909068
Title: Re: Starship heat shield
Post by: OTV Booster on 11/15/2021 03:12 pm
I have been wondering why the nosecone in particular requires glued on tiles ( red rtv silicone as glue?), anyhow scott manley put up a pic of a mach 20 wind tunnel test from the 1970s showing shock wave, and can be clearly seen the high temp shock wave remains very close to the nosecone area, and gradually gets further away from the craft as you go down the length of the craft, same shoud apply to sn20.
Also next static fire, I think we might see some more tile shedding, will find out soon enough.

Remember though, the Space Shuttle entered at a much more nose down angle than Starship will.  How much of the bow shock being close to the nose cone is due to the tight curvature, and how much is due to it being the first bit of the space shuttle to hit the air.  A blunt reentry capsule shape pushing its bow shock away from it suggests strongly that Starship's much more belly first entry will push the bow shock much further from the nose.
Not all that much. Part of the problem with the pointy end is that all the flow wraps around it. Because it's pointy it's getting radiative heating from all directions and in fairly equal proportions. On the cylinder input from 'adjacent' is from a bit further away. On the nose 'adjacent' still very close.


Edit to add: a blunt body capsule has the same problem where the flow runs off the edge. The flow is close and the radiative input comes equally from a radius with the edge at the focus.
Title: Re: Starship heat shield
Post by: Robotbeat on 11/15/2021 04:26 pm
Did Shuttle ever lose tiles on main engine test? Did it lose any tiles on lift off?
Title: Re: Starship heat shield
Post by: Jcc on 11/15/2021 04:38 pm
Oh, and of course SpaceX has tested all thinkable issues relating to vibration. That goes without saying. Let's keep the Dunning-Kruger effect in mind... https://en.wikipedia.org/w/index.php?title=Dunning%E2%80%93Kruger_effect&oldid=1053909068

No, I don't think they did test every thinkable issue. They have a totally different development methodology compared with other  aerospace companies, where they intentionally "fail early" and resolve issues as they appear. They can do that because the build cost for these early prototypes is so low, and the willingness to accept risk is part of what keeps the cost low. It's a virtuous cycle that worked pretty well for booster reuse, which nobody thought would be possible but they did it.
Title: Re: Starship heat shield
Post by: livingjw on 11/15/2021 04:50 pm
An unexpected vibration can fail a part in very short order. Identification of all possible vibration modes is nearly impossible for a complex design. You will most likely miss a few. Testing, inspection, and analysis is almost always needed to track down unexpected vibration modes. The good news is that there are numerous minor fixes which can usually deal with them once they are identified.

John
Title: Re: Starship heat shield
Post by: daveglo on 11/15/2021 05:33 pm
An unexpected vibration can fail a part in very short order. Identification of all possible vibration modes is nearly impossible for a complex design. You will most likely miss a few. Testing, inspection, and analysis is almost always needed to track down unexpected vibration modes. The good news is that there are numerous minor fixes which can usually deal with them once they are identified.

John
Completely agree.  Solutions such as a slight increase in the gap clearances on tiles in certain locations to allow for greater freedom of movement.  Or slightly increased underlayment blanket thickness to provide more damping (and doesn't change overall mass if you increase the loft of the material).  Maybe even a small geometry change to the tile retention clips to increase clamping force, trading on the risk of increased installation damage. These are all production tolerances that may need adjustment as testing illustrates the weak points.
Title: Re: Starship heat shield
Post by: AJW on 11/15/2021 05:48 pm
Did Shuttle ever lose tiles on main engine test? Did it lose any tiles on lift off?

Columbia lost more than 2000 tiles while just being ferried before the first flight. 
Over 700 lost or damaged tiles on STS-27.
8-10 tiles lost or damaged on STS-134.

This issue was never fully resolved throughout the entire life of the Shuttle and I can't verify this but one report stated that loose tiles, cracked tiles, broken tiles, abraded tiles or missing tiles were part of every shuttle flight.  Lockheed and NASA had decades to find a solution to the tile problem, but they were still unsuccessful.  For Starship, color me wary, but optimistic.


Title: Re: Starship heat shield
Post by: OV103Fan on 11/15/2021 07:43 pm
Did Shuttle ever lose tiles on main engine test? Did it lose any tiles on lift off?

Columbia lost more than 2000 tiles while just being ferried before the first flight. 
Over 700 lost or damaged tiles on STS-27.
8-10 tiles lost or damaged on STS-134.

This issue was never fully resolved throughout the entire life of the Shuttle and I can't verify this but one report stated that loose tiles, cracked tiles, broken tiles, abraded tiles or missing tiles were part of every shuttle flight.  Lockheed and NASA had decades to find a solution to the tile problem, but they were still unsuccessful.  For Starship, color me wary, but optimistic.

Correct me if I'm wrong, but I think tile loss was actually pretty rare after STS1 (which only lost tiles on the leeward side that hadn't been pull tested), with 27R being the only exception I know of.  But yes, damage was certainly a regular occurrence.

I am not aware of any tile loss on the FRFs (Flight Readiness Firings).
Title: Re: Starship heat shield
Post by: Rocket Science on 11/15/2021 10:24 pm
Setting the ferry flight aside because changes were made after. Shuttle lost few if any that were not impact related some were partly damaged... SS may have a resonance challenge for the TPS to overcome and the elasticity of the vehicle on entry is another one even if tank pressure is not lost... YMMV
Title: Re: Starship heat shield
Post by: daveglo on 11/15/2021 10:33 pm
... SS may have a resonance challenge for the TPS to overcome and the elasticity of the vehicle on entry is another one even if tank pressure is not lost... YMMV

Only one way to find out.  Light that candle!   ;D
Title: Re: Starship heat shield
Post by: gosink on 11/15/2021 10:56 pm
With regard to unexpected vibration modes in the 1000's of tiles and other parts, there is an interesting technology called "video magnification".  See the link here:  https://youtu.be/rEoc0YoALt0

It would be easy to set this up and look at the SS in a static fire and see if (what) is amiss.  Actually you'd probably want dozens of videos with zoom lenses.  Super cheap way to look for problems. 
Title: Re: Starship heat shield
Post by: Rocket Science on 11/16/2021 01:48 pm
... SS may have a resonance challenge for the TPS to overcome and the elasticity of the vehicle on entry is another one even if tank pressure is not lost... YMMV

Only one way to find out.  Light that candle!   ;D
A bit more exciting than using my old slide rule at least! ;D
Title: Re: Starship heat shield
Post by: edzieba on 11/16/2021 07:44 pm
... SS may have a resonance challenge for the TPS to overcome and the elasticity of the vehicle on entry is another one even if tank pressure is not lost... YMMV

Only one way to find out.  Light that candle!   ;D
Which SpaceX have done, on multiple static fires and flights, at multiple scales (from small tile patches to whole ring spans to now full coverage). Even Starhopper had a tile patch, so the tile and tile attachment design has been iterating with in-flight testing for over two years now.
Title: Re: Starship heat shield
Post by: Slothman on 11/16/2021 08:16 pm
... SS may have a resonance challenge for the TPS to overcome and the elasticity of the vehicle on entry is another one even if tank pressure is not lost... YMMV

Only one way to find out.  Light that candle!   ;D
Which SpaceX have done, on multiple static fires and flights, at multiple scales (from small tile patches to whole ring spans to now full coverage). Even Starhopper had a tile patch, so the tile and tile attachment design has been iterating with in-flight testing for over two years now.
Iterating lightly, and only really meaningfully in the latest full coverage  tests where reactions in more than 1-way curved surfaces in locations with a great variety of outside factors and potential corelations were tested.

Stuff takes time.
Title: Re: Starship heat shield
Post by: edzieba on 11/16/2021 08:31 pm
... SS may have a resonance challenge for the TPS to overcome and the elasticity of the vehicle on entry is another one even if tank pressure is not lost... YMMV

Only one way to find out.  Light that candle!   ;D
Which SpaceX have done, on multiple static fires and flights, at multiple scales (from small tile patches to whole ring spans to now full coverage). Even Starhopper had a tile patch, so the tile and tile attachment design has been iterating with in-flight testing for over two years now.
Iterating lightly, and only really meaningfully in the latest full coverage  tests
We've gone from the 'bolt through' tiles on Starshopper, through multiple different mounting mechanism (both mechanical and adhesive) with varying backing thickness/presence, varying presence/lack of gap-fillers, etc, various sizes of tiles, plus at least one internal tile frame change. A lot of iteration has already occurred before SpaceX even decided to start increasing the patch size.
The chemically adhered tiles at least were already a pretty high TRL (9) due to decades of operational use on STS, as is the tile composition and manufacture. The new parts are the mechanical mounting and the embedding of that mount inside the tile.
Title: Re: Starship heat shield
Post by: Echo_Jex on 11/16/2021 08:44 pm
With a strong regard towards S20 specifically, and in the reflection of potentially how S21+ tiles will be different by tweaking mechanical tolerances going forward, I think the "tiles fall off too easy" concerns might be more under wraps that these static fires give SX credit for.

S20 was a rushed floor model, with lower grade and QA fail tiles being used due to tile shortages in the days prior to the photo shoot (if this is conjecture let me know, i thought there was something official about tile shortages the night prior to the stack). I know some attempts have been made to QA what they could after installing, but i think many of the tiles that have fallen off were from these prototype tiles.  I strongly agree that S20 tiles are NOT the first round ever of tiles, but from what i am seeing, the equivalent areas from the test articles on S20 are doing far better than the areas that had been uncovered until S20

@edzieba have there been any retrofits on S20 after the photoshoot that would change the observation that S20 heatshield performance is or is not currently representative of the newer models?
Title: Re: Starship heat shield
Post by: edzieba on 11/16/2021 11:06 pm
After the stack photoshoot, Ship 20 was destacked, then the tiles were inspected and damaged/suspect tiles replaced, as well as the untiled areas receiving their tiles.
Title: Re: Starship heat shield
Post by: Robotbeat on 11/16/2021 11:28 pm
I suspect SpaceX will go to at least partly metal tiles eventually, as Elon suggested, altho they might fly orbital for a while with ceramic.
Title: Re: Starship heat shield
Post by: warp99 on 11/17/2021 12:52 am
I suspect SpaceX will go to at least partly metal tiles eventually, as Elon suggested, altho they might fly orbital for a while with ceramic.
Metal tiles would require a lower ballistic coefficient to reduce peak entry temperatures to around 1000C.  So the “Dragon Wing” design with large wings spanning the gap between the forward and aft flaps and extending the overall Starship width to about 25m.  The larger tile area and higher mass of wings and the metal tiles would lead to a significant loss of payload. 

If the ceramic tiles do not work out I suspect the back up plan will be Pica-X tiles with programmed replacement after 8-10 LEO re-entries or a single Earth-Mars return trip.
Title: Re: Starship heat shield
Post by: Robotbeat on 11/17/2021 01:40 am
There are metals with much higher useful temperatures than 1000C.
Title: Re: Starship heat shield
Post by: Rocket Science on 11/17/2021 07:31 am
... SS may have a resonance challenge for the TPS to overcome and the elasticity of the vehicle on entry is another one even if tank pressure is not lost... YMMV

Only one way to find out.  Light that candle!   ;D
Which SpaceX have done, on multiple static fires and flights, at multiple scales (from small tile patches to whole ring spans to now full coverage). Even Starhopper had a tile patch, so the tile and tile attachment design has been iterating with in-flight testing for over two years now.
Iterating lightly, and only really meaningfully in the latest full coverage  tests
We've gone from the 'bolt through' tiles on Starshopper, through multiple different mounting mechanism (both mechanical and adhesive) with varying backing thickness/presence, varying presence/lack of gap-fillers, etc, various sizes of tiles, plus at least one internal tile frame change. A lot of iteration has already occurred before SpaceX even decided to start increasing the patch size.
The chemically adhered tiles at least were already a pretty high TRL (9) due to decades of operational use on STS, as is the tile composition and manufacture. The new parts are the mechanical mounting and the embedding of that mount inside the tile.
Yes I know all this thank you. I stated from the onset a couple more years ago that the TPS was going to be a 'long pole" for this SS design. I just don't post on here much anymore because of all the hand-waving. The other NSF ol' timers will know what I mean...

~Rob
Title: Re: Starship heat shield
Post by: brettly2021 on 11/17/2021 11:55 am
thanks gosink for that excellent video on vibration video techniques, quite amazing.
I am quite interested in the role of water ice shedding during static fire. Its quite common for the ice to break off during engine fire and liftoff from the cold surfaces. Just what is the physical nature of that ice I dont know, from videos it appears to be white rather than clear, so I assume its like compacted snow ( will be related to how the crystals form I guess).
Probably many factors determine how thick this layer gets but its usually very visible at launches. Watching an Atlas5 launch from last year I'm guessing maybe 1cm or so thickness?
https://www.youtube.com/watch?v=g0fdp0evEW4

The amount of ice I assume could be subtantial and usually it easily sheds off the rocket, vibration at initial engine fire seems to remove quite alot.
Starship with the heatshield tiles is a different matter and underlying wool is a different matter. It might land up being trivial but I dont think so.
How will the ice form under the white puffy blankets? or will it form within the blankets also? Will it put pressure on the fragile tiles? The ice will have to exit via the spaces between the tiles.
I think this process can be seen quite clearly during static second fire, on the tiled side you can clearly see what looks like a mist over the tiles, which forms as soon as engine fires, then forms a nice snowy mist, then drops down with gravity on outside of the tiles......but how much ice remains behind the tiles and will that remaining water ice  make it too orbit?
The stainless side of sn20 its much harder see what happens to the ice, but you can make out the ice first making a mist then quickly dropping with gravity. some pics attached




Title: Re: Starship heat shield
Post by: kourgath on 11/18/2021 09:17 am
The image from SpaceX for the static fire may show something interesting. Could it be that we are seeing shockwaves reflected from the ground as each raptor fires up?  This also could be an artefact of imaging but given we are seeing tiles come off there is an argument I’ve seen here that ground firing and firing from the top of the booster at separation could be different.

Just a thought…
Title: Re: Starship heat shield
Post by: edzieba on 11/18/2021 10:36 am
A minor procedure note:
On Ship 21 we see that the majority of tiles have a small 'OK' written on their apex. In the latest NSF video we see a few tiles being drilled out and replaced. The replacement tiles installed already have this 'OK' marking, so that marking is an indicator of a pre-install inspection rather than a post-install inspection. This should be of interest to those estimating post-install inspection coverage as we saw with Ship 20.
Title: Re: Starship heat shield
Post by: RoboGoofers on 11/18/2021 01:55 pm
Is the purpose of the black mesh between the tiles and insulation known, yet? I was thinking that this would be a good way to install various sensors (it doesn't currently appear to be the case, though).

maybe the gap it creates will provide a path for vapor to escape from the insulation? or allows the tiles to move more freely when expanding/contracting?
Title: Re: Starship heat shield
Post by: thebraylonwilliams on 11/18/2021 02:06 pm
I want to say its mainly used as a mounting solution that helps the tiles stay attached during the expanding contracting during reentry. He talks about it in part 2 of the Everyday Astronaut tour of Starbase. I belive its mentioned in part 2.
Title: Re: Starship heat shield
Post by: _MECO on 11/18/2021 05:49 pm
I suspect SpaceX will go to at least partly metal tiles eventually, as Elon suggested, altho they might fly orbital for a while with ceramic.
Metal tiles would require a lower ballistic coefficient to reduce peak entry temperatures to around 1000C.  So the “Dragon Wing” design with large wings spanning the gap between the forward and aft flaps and extending the overall Starship width to about 25m.  The larger tile area and higher mass of wings and the metal tiles would lead to a significant loss of payload. 
Is this where we start entertaining those weird double-fuselage extra wide Starships again? Those were fun.
Title: Re: Starship heat shield
Post by: brettly2021 on 11/19/2021 09:54 am
I'm also curious about that black mesh, also wonder what material it is? Must be heat resistant to suit.
I can only think of it might help keep the white blanket in place? cant see it helping the tiles.It is quite a windy place they are working in.

Last picture posted shows nicely in closeup the snowy mist ( assuming its some sort of water ice) comes out the spaces around the tiles.

Just a note on work safety when those guy drill out the tiles to remove them, you can see the dust fly out in small clouds, those guys should use masks, silicosis is not a nice disease.

I guess there is some possibilty the white mist also contains some dust from the rear of the tiles, but dont think that would be an issue.

Title: Re: Starship heat shield
Post by: brettly2021 on 11/20/2021 07:28 pm
Now I'm a bit confused, I've noticed that this white mist is also coming from the bottom wings on test fire, so I wouldn't think the wings will be all that cold? So shoudn't be any ice on the stainless surface, but there is a considerable amount of white 'mist' also coming out of them.
So what could that be? could it be the white blanket or the tiles themselves?
Title: Re: Starship heat shield
Post by: edzieba on 11/20/2021 08:29 pm
So what could that be?
Dust. Everything on site will end up covered in it. 
Title: Re: Starship heat shield
Post by: William497 on 11/20/2021 08:58 pm
Just curious what happened to elons original plan of transpiration cooling? And why did they decide to go with tiles?
And If they did use transpiration cooling would the leidenfrost effect apply?
Title: Re: Starship heat shield
Post by: eriblo on 11/20/2021 09:17 pm
Just curious what happened to elons original plan of transpiration cooling? And why did they decide to go with tiles?
And If they did use transpiration cooling would the leidenfrost effect apply?
https://twitter.com/elonmusk/status/1107376856175513600
https://twitter.com/elonmusk/status/1107380559834046465
https://twitter.com/elonmusk/status/1154229558989561857
https://twitter.com/elonmusk/status/1176561209971101696
https://twitter.com/elonmusk/status/1228396138870407169
https://twitter.com/elonmusk/status/1228400791880269824
https://twitter.com/elonmusk/status/1314741760568954880

Transpiration cooling is a bit of a misnomer, the majority of the effect is due to cool gas shielding - i.e. exactly the same thing as the Leidenfrost effect (which could be said about standard ablative heat shields as well...).
Title: Re: Starship heat shield
Post by: OTV Booster on 11/20/2021 11:55 pm
So what could that be?
Dust. Everything on site will end up covered in it.
Maybe another mechanism. Speed of sound in stainless would be higher than in air. Maybe a high frequency vibration that loads into the air and creates a local shock. In humid air a shock will look vapor like. I've seen it in pics of aircraft and live in person from the air watching expanding shock domes emitting from detonations.
Title: Re: Starship heat shield
Post by: Skyway on 11/22/2021 04:25 pm
A minor procedure note:
On Ship 21 we see that the majority of tiles have a small 'OK' written on their apex. In the latest NSF video we see a few tiles being drilled out and replaced. The replacement tiles installed already have this 'OK' marking, so that marking is an indicator of a pre-install inspection rather than a post-install inspection. This should be of interest to those estimating post-install inspection coverage as we saw with Ship 20.

I just saw the video you mentioned, and you can clearly see that employees write something in white at the top of each tile after installation (1:25 and 1:38). Wouldn't that be "ok"?
Title: Re: Starship heat shield
Post by: brettly2021 on 11/24/2021 02:00 pm
Just a thought regarding the white mist during static fire.
The tiles are some form of silicon, silicon can be water absorbent ( hydrophyllic), I remember reading somewhere the shuttle tiles were coated to stop water infiltration ( not the black borosilcate coating, but another coating for the white part not covered by black). If the rear of the tiles is not coated to stop water absorbtion, it might make the rear part prone to water absorption and might be possible the white mist ( thinking of the flaps here) is inner most layer of tile being a mix of water and silicone shaking loose.
anyhow it seems the ship is trying to say I can make a misty coating to protect myself during re-entry.
Title: Re: Starship heat shield
Post by: CMac on 11/24/2021 02:23 pm
I happened across this slide-deck for a course:
https://tfaws.nasa.gov/TFAWS12/Proceedings/Aerothermodynamics%20Course.pdf (https://tfaws.nasa.gov/TFAWS12/Proceedings/Aerothermodynamics%20Course.pdf)

It's very interesting but I don't have time to look at the detail. I learned a good bit just by scanning through the slides.
Title: Re: Starship heat shield
Post by: Robotbeat on 11/24/2021 02:31 pm
I happened across this slide-deck for a course:
https://tfaws.nasa.gov/TFAWS12/Proceedings/Aerothermodynamics%20Course.pdf (https://tfaws.nasa.gov/TFAWS12/Proceedings/Aerothermodynamics%20Course.pdf)

It's very interesting but I don't have time to look at the detail. I learned a good bit just by scanning through the slides.
Yeah, I remember that exact presentation. Super helpful!
Title: Re: Starship heat shield
Post by: DanClemmensen on 11/24/2021 04:40 pm
I happened across this slide-deck for a course:
https://tfaws.nasa.gov/TFAWS12/Proceedings/Aerothermodynamics%20Course.pdf (https://tfaws.nasa.gov/TFAWS12/Proceedings/Aerothermodynamics%20Course.pdf)

It's very interesting but I don't have time to look at the detail. I learned a good bit just by scanning through the slides.
WOW! This is the slide deck for a whole course, so the time to actually assimilate it would be weeks. However, it really brings home how complicated TPS can get. One thing to learn quickly: re-entry vehicles are "blunt", not "pointy", for a reason: to generate a big shockwave that moves away from the vehicle as much as quickly as possible. This shockwave carries away almost all of the energy, and the TPS must handle the rest. Oversimplifying,  the leading part of the vehicle is called the "nose" and the "nose diameter" is a fundamental parameter. Thus, the "nose" of a circular capsule (Orion, Dragon, Apollo) is the bottom part that is covered by the heat shield. The "nose" of a vehicle that is not radially symmetric about its velocity vector (Shuttle, Starship) is complicated, and is not simply the pointy front part. The "nose diameter" varies across the vehicle. Still oversimplifying, the "diameter" at a point is the diameter of the section of a sphere that approximates the curvature of the surface at that point.   And that's just in the first few slides.
Title: Re: Starship heat shield
Post by: CMac on 11/25/2021 01:48 pm
Yes, I was interested to see that most of the heat flows into the wake. The small bit extra is turned into radiation or conducted into the tile surface.
There is a time/temperature trade-off between: fast deceleration with high surface temperature or long slow deceleration with better temperature but a higher heat load conducted into the lower layers.
Title: Re: Starship heat shield
Post by: Robotbeat on 12/04/2021 05:02 pm
I hope they try those stainless heatshield tiles they showed before. Those shouldn’t have the brittleness problems. Might still have to use Shuttle-like ceramic tiles for stuff with sharper radiuses like near aero surfaces, but it’s still a big potential improvement.

NASA had been developing Inconel heatshield tiles for X-33/Venturestar, but certain grades of stainless are essentially just as good as Inconel but an order of magnitude cheaper.

(This comparison is for thermocouple sheath use temperature, but I think it is a reasonably good comparison.)
Title: Re: Starship heat shield
Post by: DanClemmensen on 12/04/2021 05:21 pm
I hope they try those stainless heatshield tiles they showed before. Those shouldn’t have the brittleness problems. Might still have to use Shuttle-like ceramic tiles for stuff with sharper radiuses like near aero surfaces, but it’s still a big potential improvement.

NASA had been developing Inconel heatshield tiles for X-33/Venturestar, but certain grades of stainless are essentially just as good as Inconel but an order of magnitude cheaper.

(This comparison is for thermocouple sheath use temperature, but I think it is a reasonably good comparison.)

OK, here's an ignorant question: why not use this more expensive steel for the actual structure, at least in the TPS area of the ship? you would need to insulate on the inside, but that insulation replaces the insulation that is part of the tiles.  Using two types of steel makes it slightly harder to fabricate the 9 m rings, but not much. Insulation in the tank area may require a tank liner layer, but again, you are replacing the multilayer TPS. Qualitatively, it looks like the mass per square meter of skin will go down, not up. (And aesthetically, a silver spaceship is just cool, although Space Patrol black and silver is also pretty cool.)
Title: Re: Starship heat shield
Post by: etudiant on 12/04/2021 05:24 pm
I hope they try those stainless heatshield tiles they showed before. Those shouldn’t have the brittleness problems. Might still have to use Shuttle-like ceramic tiles for stuff with sharper radiuses like near aero surfaces, but it’s still a big potential improvement.

NASA had been developing Inconel heatshield tiles for X-33/Venturestar, but certain grades of stainless are essentially just as good as Inconel but an order of magnitude cheaper.

(This comparison is for thermocouple sheath use temperature, but I think it is a reasonably good comparison.)

Is there any indication of how well that temperature resistance is sustained? Stainless steel is a pretty fluid alloy concept, the stuff evolves even while one looks at it.
Title: Re: Starship heat shield
Post by: OTV Booster on 12/04/2021 05:54 pm
I hope they try those stainless heatshield tiles they showed before. Those shouldn’t have the brittleness problems. Might still have to use Shuttle-like ceramic tiles for stuff with sharper radiuses like near aero surfaces, but it’s still a big potential improvement.

NASA had been developing Inconel heatshield tiles for X-33/Venturestar, but certain grades of stainless are essentially just as good as Inconel but an order of magnitude cheaper.

(This comparison is for thermocouple sheath use temperature, but I think it is a reasonably good comparison.)
You got me thinking. Always dangerous. What do you think of the tiles loosing the vitreous surface and gaining stainless? Thermal expansion would dictate they be separate pieces. Put the bayonet on the back of the stainless and the socket on the skin. Run passthrough holes in the ceramic. Or some variation. Tricky details but the outer surface won't crack from MMOD. It also puts the ceramic in compression where it has its best strength.
Title: Re: Starship heat shield
Post by: samgineer on 12/04/2021 06:31 pm
Just a thought regarding the white mist during static fire.
The tiles are some form of silicon, silicon can be water absorbent ( hydrophyllic), I remember reading somewhere the shuttle tiles were coated to stop water infiltration ( not the black borosilcate coating, but another coating for the white part not covered by black). If the rear of the tiles is not coated to stop water absorbtion, it might make the rear part prone to water absorption and might be possible the white mist ( thinking of the flaps here) is inner most layer of tile being a mix of water and silicone shaking loose.
anyhow it seems the ship is trying to say I can make a misty coating to protect myself during re-entry.

SpaceX use almost exactly same tiles as Shuttle, silica fibre and borosilicate coating. Main difference is Starship ones are thinner and use different waterproofing agent to stop water. Shuttle tiles was quite sensitive to water after multiple landings because it basically burned of waterproofing (i may not be right, I'm not sure), SpaceX may have more durable waterproofing as they changed one from shuttle era.
Title: Re: Starship heat shield
Post by: livingjw on 12/04/2021 10:36 pm
I hope they try those stainless heatshield tiles they showed before. Those shouldn’t have the brittleness problems. Might still have to use Shuttle-like ceramic tiles for stuff with sharper radiuses like near aero surfaces, but it’s still a big potential improvement.

NASA had been developing Inconel heatshield tiles for X-33/Venturestar, but certain grades of stainless are essentially just as good as Inconel but an order of magnitude cheaper.

(This comparison is for thermocouple sheath use temperature, but I think it is a reasonably good comparison.)

And Carbon/Carbon or Carbon/SiC can handle 2900 F or more with proper coatings.

John
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 12/05/2021 05:54 pm
I hope they try those stainless heatshield tiles they showed before. Those shouldn’t have the brittleness problems. Might still have to use Shuttle-like ceramic tiles for stuff with sharper radiuses like near aero surfaces, but it’s still a big potential improvement.

NASA had been developing Inconel heatshield tiles for X-33/Venturestar, but certain grades of stainless are essentially just as good as Inconel but an order of magnitude cheaper.

(This comparison is for thermocouple sheath use temperature, but I think it is a reasonably good comparison.)

Stainless doesn't have very good emissivity, does it?
Title: Re: Starship heat shield
Post by: Twark_Main on 12/05/2021 09:20 pm
Just a thought regarding the white mist during static fire.
The tiles are some form of silicon, silicon can be water absorbent ( hydrophyllic), I remember reading somewhere the shuttle tiles were coated to stop water infiltration ( not the black borosilcate coating, but another coating for the white part not covered by black). If the rear of the tiles is not coated to stop water absorbtion, it might make the rear part prone to water absorption and might be possible the white mist ( thinking of the flaps here) is inner most layer of tile being a mix of water and silicone shaking loose.
anyhow it seems the ship is trying to say I can make a misty coating to protect myself during re-entry.

SpaceX use almost exactly same tiles as Shuttle, silica fibre and borosilicate coating. Main difference is Starship ones are thinner and use different waterproofing agent to stop water. Shuttle tiles was quite sensitive to water after multiple landings because it basically burned of waterproofing (i may not be right, I'm not sure), SpaceX may have more durable waterproofing as they changed one from shuttle era.

The silicone waterproofing was applied to all the tiles, both white and black. It entirely burned off during reentry, so it needed to be reapplied (by hand, one tile at a time) before every launch.

Since the waterproofing burned off during reentry, after the Shuttle landed it couldn't be rained on. If a heavy rain happened, the vehicle would have to be dried out for a month with high-powered lights (https://www.cnn.com/2001/TECH/space/05/30/shuttle.delayed/index.html).

Overall it was an extremely labor-intensive system. There's literally zero chance that Starship could work without dramatic improvements over the Shuttle waterproofing system. It was the exact opposite of "rapid reusability."
Title: Re: Starship heat shield
Post by: Hog on 12/06/2021 07:41 pm
Paper on improvements to the Shuttles DiMethylEthoxySilane (DMES) waterproofing, which took 72 hours to complete and mega humanpower.  IIRC the DMES wasn't simply deposited, sprayed, slathered or painted on, it was injected "intra-tiley" (yes I made that up) into and through the tile in 2 places for each tile.

The stuff off gasses ethanol, considered a pollutant in the workplace.

Space-X will be using methyltrimethoxysilane to waterproof their tiles.
Title: Re: Starship heat shield
Post by: ETurner on 12/06/2021 08:50 pm
I hope they try those stainless heatshield tiles they showed before. Those shouldn’t have the brittleness problems. Might still have to use Shuttle-like ceramic tiles for stuff with sharper radiuses like near aero surfaces, but it’s still a big potential improvement.
[...]
As others have noted, the shielding problem decreases pretty smoothly from the belly to the back. It’s obvious that the present system isn’t optimized for mass, because there’s a literal step function between shielded-like-the-belly and unshielded-like-the-back. So far as I can see, full-thickness tiles are adjacent to bare metal.

We should expect to see something different eventually, and probably not just thinner (and more fragile) tiles toward the edge of the shield. Something like stainless on top of Superwool seems like a better choice, but this “better” may be far from best.

One way or another, thermal protection will taper off rather than cut off.
Title: Re: Starship heat shield
Post by: JamesH65 on 12/07/2021 08:03 am
One way or another, thermal protection will taper off rather than cut off.

Why?
Title: Re: Starship heat shield
Post by: daavery on 12/07/2021 10:42 am
the whole idea is avoid the space shuttle and every tile being unique. using 1 design and thickness of tile allows for bulk manufacturing instead is 100s of unique tile versions
Title: Re: Starship heat shield
Post by: ETurner on 12/07/2021 04:54 pm
One way or another, thermal protection will taper off rather than cut off.

Why?
Because if bare metal is enough on one side of edge, then using full-thickness (= full-mass) worst-case shielding just 10 cm away is a waste. The only argument for an all-or-nothing transition at the edge is to make the shield uniform. [edit: as daavery argues above]

I can see this as a shortcut in a prototype, but not in an optimized production vehicle.

Title: Re: Starship heat shield
Post by: rsdavis9 on 12/07/2021 05:04 pm
One way or another, thermal protection will taper off rather than cut off.

Why?
Because if bare metal is enough on one side of edge, then using full-thickness (= full-mass) worst-case shielding just 10 cm away is a waste. The only argument for an all-or-nothing transition at the edge is to make the shield uniform. [edit: as daavery argues above]

I can see this as a shortcut in a prototype, but not in an optimized production vehicle.

So correct me if I am wrong. I am not a hypersonic flow specialist.

So at the midline we have supersonic flow that piles up and creates a large standoff/stagnation for the super hot gas.
At the edges it comes much closer to the edge because there is a lot less of the cushion to keep the flow away from the metal.

The flow might be cooler by the time it passes the edge and also near the edge their is not as much compression going on. So this would be the reverse of the standoff distance.

So you have 2 effects going on and I would bet the standoff/stagnation distance is the greater?
Title: Re: Starship heat shield
Post by: ETurner on 12/07/2021 05:08 pm
the whole idea is avoid the space shuttle and every tile being unique. using 1 design and thickness of tile allows for bulk manufacturing instead is 100s of unique tile versions

Tapering the shield with a transition thickness or two isn’t anything like the “every tile is unique” Shuttle nightmare. There are already many kinds of tiles on the vehicle (look at the nose, look at the body flaps). Adding (for example) two more kinds could save a significant fraction of the heat shield mass, which would be well worth doing.

Substituting stainless surfaces where heating is lower would be a more substantial departure, but could be a big win for cost, robustness, and maintenance. Stainless on (for example) a thin Superwool insulation layer must be OK near the boundary where a bare stainless pressure vessel surface is OK.

Or am I missing something obvious?
Title: Re: Starship heat shield
Post by: ETurner on 12/07/2021 05:17 pm
One way or another, thermal protection will taper off rather than cut off.

Why?
Because if bare metal is enough on one side of edge, then using full-thickness (= full-mass) worst-case shielding just 10 cm away is a waste. The only argument for an all-or-nothing transition at the edge is to make the shield uniform. [edit: as daavery argues above]

I can see this as a shortcut in a prototype, but not in an optimized production vehicle.

So correct me if I am wrong. I am not a hypersonic flow specialist.

So at the midline we have supersonic flow that piles up and creates a large standoff/stagnation for the super hot gas.
At the edges it comes much closer to the edge because there is a lot less of the cushion to keep the flow away from the metal.

The flow might be cooler by the time it passes the edge and also near the edge their is not as much compression going on. So this would be the reverse of the standoff distance.

So you have 2 effects going on and I would bet the standoff/stagnation distance is the greater?
For something like a sphere (no sharp edges), heating is highest at the stagnation point, and for the same reason, heating is higher on the mid-line than on the sides of a cylinder entering at a high angle of attack.

A bunch of images here (https://www.google.com/search?q=hypersonic+shock+on+a+sphere&tbm=isch) show the shock geometry in the spherical case -- the standoff distance increases away from the stagnation point.
Title: Re: Starship heat shield
Post by: edzieba on 12/07/2021 05:27 pm
IIRC, total mass of the tiles on Starship is estimated as around 9 metric tonnes (assuming density comaprable to the STS tiles that are almost identical to).
Thinning the tiles for optimum mass gains you maybe a few hundred kilograms. That is absolutely not worth the headache of adding extra tile types: manufacturing yet more variants, handling (e.g. crates and packing) for yet more variants, labelling for yet more variants (to avoid mixing with others that share the same peg layout) and/or adding a new peg layout to avoid mixing tiles, extra QC steps to make sure tile types are not mixed, etc.

SpaceX are optimising for cost and complexity, not mass.
Title: Re: Starship heat shield
Post by: Wolfram66 on 12/07/2021 05:32 pm
Has any attempt to use Alumina Al2O3-Al3O2 rather than SiO2 as the tile substrate? They use Alumina in high temperatures ( it is what sapphire is made of) in plasma furnaces and electronics?
Title: Re: Starship heat shield
Post by: eriblo on 12/07/2021 05:45 pm
Has any attempt to use Alumina Al2O3-Al3O2 rather than SiO2 as the tile substrate? They use Alumina in high temperatures ( it is what sapphire is made of) in plasma furnaces and electronics?
I have wondered about this myself, although it stands to mention that AETB tiles are 68% silica, 20% alumina and 12% aluminoborosilicate. I think the problem might be similar to that of ultra-high-temperature ceramics: the higher the temperature tolerance of your material, the harder it is to make into the composition and structure you want...
Title: Re: Starship heat shield
Post by: eriblo on 12/07/2021 06:04 pm
the whole idea is avoid the space shuttle and every tile being unique. using 1 design and thickness of tile allows for bulk manufacturing instead is 100s of unique tile versions

Tapering the shield with a transition thickness or two isn’t anything like the “every tile is unique” Shuttle nightmare. There are already many kinds of tiles on the vehicle (look at the nose, look at the body flaps). Adding (for example) two more kinds could save a significant fraction of the heat shield mass, which would be well worth doing.

Substituting stainless surfaces where heating is lower would be a more substantial departure, but could be a big win for cost, robustness, and maintenance. Stainless on (for example) a thin Superwool insulation layer must be OK near the boundary where a bare stainless pressure vessel surface is OK.

Or am I missing something obvious?
I agree that there can be some optimization of the heat shield edge but also think that will wait until they are optimizing for the last % of payload.
A few things to consider:

There might be limitations regarding total heat conducted into the structure rather than maximum temperature (i.e. you still need the full insulation, just not the temperature tolerance).

The multi-cm edge of the heat shield might detach the flow and very rapidly decrease the transverse convective heat flow.

A thin sheet of stainless backed by insulation will have much lower thermal inertia and will only be able to shed heat by radiation on the outside surface so it will be much more sensitive to fluctuations in heat flow caused by for example local turbulence or shock interactions.
Title: Re: Starship heat shield
Post by: ETurner on 12/07/2021 07:23 pm
IIRC, total mass of the tiles on Starship is estimated as around 9 metric tonnes (assuming density comaprable to the STS tiles that are almost identical to).
Thinning the tiles for optimum mass gains you maybe a few hundred kilograms. That is absolutely not worth the headache of adding extra tile types: manufacturing yet more variants, handling (e.g. crates and packing) for yet more variants, labelling for yet more variants (to avoid mixing with others that share the same peg layout) and/or adding a new peg layout to avoid mixing tiles, extra QC steps to make sure tile types are not mixed, etc.

SpaceX are optimising for cost and complexity, not mass.
I would make that more like “a few tons”. I think that SpaceX could manage to put different tiles on a few vertical bands down the body of the vehicle without being driven mad by the complexity, crates, packing, etc.

How many distinct tile types do they have now? More than I want to count: https://www.teslarati.com/spacex-orbital-starship-raptor-reinstallation/ (https://www.teslarati.com/spacex-orbital-starship-raptor-reinstallation/) To see a broader region with more than a few types, look at the tiles on the ogive.

But maybe they would find two or three more types too difficult, and maybe getting a few more tons to orbit just isn’t worth the effort. We’ll see.

Here is a detail from the image linked above:
Title: Re: Starship heat shield
Post by: ETurner on 12/07/2021 07:35 pm
the whole idea is avoid the space shuttle and every tile being unique. using 1 design and thickness of tile allows for bulk manufacturing instead is 100s of unique tile versions

Tapering the shield with a transition thickness or two isn’t anything like the “every tile is unique” Shuttle nightmare. There are already many kinds of tiles on the vehicle (look at the nose, look at the body flaps). Adding (for example) two more kinds could save a significant fraction of the heat shield mass, which would be well worth doing.

Substituting stainless surfaces where heating is lower would be a more substantial departure, but could be a big win for cost, robustness, and maintenance. Stainless on (for example) a thin Superwool insulation layer must be OK near the boundary where a bare stainless pressure vessel surface is OK.

Or am I missing something obvious?
I agree that there can be some optimization of the heat shield edge but also think that will wait until they are optimizing for the last % of payload.
A few things to consider:

There might be limitations regarding total heat conducted into the structure rather than maximum temperature (i.e. you still need the full insulation, just not the temperature tolerance).

The multi-cm edge of the heat shield might detach the flow and very rapidly decrease the transverse convective heat flow.

A thin sheet of stainless backed by insulation will have much lower thermal inertia and will only be able to shed heat by radiation on the outside surface so it will be much more sensitive to fluctuations in heat flow caused by for example local turbulence or shock interactions.
Thanks, these are all well-grounded points.

I strongly agree with the first (waiting for optimization).
I think saying that “you still need the full insulation, just not the temperature tolerance” is a bit too strong, but points to an important consideration.
The possibility of actual benefits (protective flow detachment) from a multi-cm step at the edge is particularly interesting. It would provide a positive reason for a feature that would otherwise offend engineering esthetics (mine, at least). If there is no thickness taper in the mature design, this seems like the most likely reason.
Title: Re: Starship heat shield
Post by: whitelancer64 on 12/07/2021 07:53 pm
IIRC, total mass of the tiles on Starship is estimated as around 9 metric tonnes (assuming density comaprable to the STS tiles that are almost identical to).
Thinning the tiles for optimum mass gains you maybe a few hundred kilograms. That is absolutely not worth the headache of adding extra tile types: manufacturing yet more variants, handling (e.g. crates and packing) for yet more variants, labelling for yet more variants (to avoid mixing with others that share the same peg layout) and/or adding a new peg layout to avoid mixing tiles, extra QC steps to make sure tile types are not mixed, etc.

SpaceX are optimising for cost and complexity, not mass.

Assuming 9 tons for total TPS weight, if you can reduce the weight of 10% of the tiles by half, that's still 450 kg (992 lb).

That's not trivial.

Mass is still an extremely important aspect of Starship (as it is in all rockets). Every kg they can remove from Starship is a kg that can be added directly to payload.
Title: Re: Starship heat shield
Post by: DanClemmensen on 12/07/2021 08:02 pm
IIRC, total mass of the tiles on Starship is estimated as around 9 metric tonnes (assuming density comaprable to the STS tiles that are almost identical to).
Thinning the tiles for optimum mass gains you maybe a few hundred kilograms. That is absolutely not worth the headache of adding extra tile types: manufacturing yet more variants, handling (e.g. crates and packing) for yet more variants, labelling for yet more variants (to avoid mixing with others that share the same peg layout) and/or adding a new peg layout to avoid mixing tiles, extra QC steps to make sure tile types are not mixed, etc.

SpaceX are optimising for cost and complexity, not mass.

Assuming 9 tons for total TPS weight, if you can reduce the weight of 10% of the tiles by half, that's still 450 kg (992 lb).

That's not trivial.

Mass is still an extremely important aspect of Starship (as it is in all rockets). Every kg they can remove from Starship is a kg that can be added directly to payload.
You just added less than 1% to the payload mass on a  reusable launch (probably more like 0.7% : we'll see). Your cost to do this (design, manufacturing, turnaround/refurbishment) is X, Y, and Z. At $2 million/launch or even $10 million/launch, I don't see how you are going to recover your investment. You only recover it on the edge case where that extra tonne is actually needed for the mission.
Title: Re: Starship heat shield
Post by: Robotbeat on 12/07/2021 08:05 pm
You recover it every tanker refueling or additional secondary payload or higher GTO orbit.
Title: Re: Starship heat shield
Post by: Twark_Main on 12/07/2021 08:10 pm
You recover it every tanker refueling

... but, just like DanClemmensen said, only if the mission you're refueling actually needs the additional single-digit tonnes of propellant.

Title: Re: Starship heat shield
Post by: whitelancer64 on 12/07/2021 08:22 pm
IIRC, total mass of the tiles on Starship is estimated as around 9 metric tonnes (assuming density comaprable to the STS tiles that are almost identical to).
Thinning the tiles for optimum mass gains you maybe a few hundred kilograms. That is absolutely not worth the headache of adding extra tile types: manufacturing yet more variants, handling (e.g. crates and packing) for yet more variants, labelling for yet more variants (to avoid mixing with others that share the same peg layout) and/or adding a new peg layout to avoid mixing tiles, extra QC steps to make sure tile types are not mixed, etc.

SpaceX are optimising for cost and complexity, not mass.

Assuming 9 tons for total TPS weight, if you can reduce the weight of 10% of the tiles by half, that's still 450 kg (992 lb).

That's not trivial.

Mass is still an extremely important aspect of Starship (as it is in all rockets). Every kg they can remove from Starship is a kg that can be added directly to payload.
You just added less than 1% to the payload mass on a  reusable launch (probably more like 0.7% : we'll see). Your cost to do this (design, manufacturing, turnaround/refurbishment) is X, Y, and Z. At $2 million/launch or even $10 million/launch, I don't see how you are going to recover your investment. You only recover it on the edge case where that extra tonne is actually needed for the mission.

Over hundreds of launches, it will add up. The tyranny of the rocket equation never slumbers. Over time, an extra 450 kg of performance reserves would easily save millions of dollars in fuel costs alone.
Title: Re: Starship heat shield
Post by: DanClemmensen on 12/07/2021 08:43 pm
You recover it every tanker refueling or additional secondary payload or higher GTO orbit.
Tanker refuelings are quantized so not quite, unless you have a depot. Even with a depot you are only saving at most 0.7% of the cost (or one launch for every 150 tanker launches, if you prefer). For the rideshare case you will not get the extra tonne of customer payload unless there are an effectively unlimited number of paying customers with satellites of variable sizes in the one-tonne range. If your demand is completely elastic with continuously-variable mass, you get at most 0.7% gain. I'm just not seeing it.  Even for GEO: If the payload is just one tonne too big for me to get to GEO, I will need to refuel in LEO to deliver. But if it were two tonnes too big, I would need to refuel anyway, so it's still an edge case, and that edge will be there somewhere anyway, so we are still talking about 0.7% cost improvement on average.

About GTO: using "Starship economics", does it ever make sense to launch to GTO? (It may: I am very much NOT a rocket scientist.) Might it not be cheaper and simpler to put the payload in a Starship, launch to LEO, refuel, deliver to GEO, and then come home? This assumes a depot or some sort of standard tanker system that provides propellant at $10 million/150 t = $67000/t, not a bespoke tanker for the GEO mission.
Title: Re: Starship heat shield
Post by: whitelancer64 on 12/07/2021 09:10 pm
You recover it every tanker refueling or additional secondary payload or higher GTO orbit.
Tanker refuelings are quantized so not quite, unless you have a depot. Even with a depot you are only saving at most 0.7% of the cost (or one launch for every 150 tanker launches, if you prefer). For the rideshare case you will not get the extra tonne of customer payload unless there are an effectively unlimited number of paying customers with satellites of variable sizes in the one-tonne range. If your demand is completely elastic with continuously-variable mass, you get at most 0.7% gain. I'm just not seeing it.  Even for GEO: If the payload is just one tonne too big for me to get to GEO, I will need to refuel in LEO to deliver. But if it were two tonnes too big, I would need to refuel anyway, so it's still an edge case, and that edge will be there somewhere anyway, so we are still talking about 0.7% cost improvement on average.

About GTO: using "Starship economics", does it ever make sense to launch to GTO? (It may: I am very much NOT a rocket scientist.) Might it not be cheaper and simpler to put the payload in a Starship, launch to LEO, refuel, deliver to GEO, and then come home? This assumes a depot or some sort of standard tanker system that provides propellant at $10 million/150 t = $67000/t, not a bespoke tanker for the GEO mission.

Keep in mind, this is assuming 9 tons for total TPS weight, and that you can only reduce the weight of 10% of the tiles by half.

Both heavily conservative estimates. It's probably true that the weight of a much higher percentage of tiles can be reduced significantly, depending on their location.

Also, the TPS is not the only place where mass savings can be made. Elon Musk originally said he hoped the final mass of Starship would be around 85 tons.

There's lots of room for mass optimization.
Title: Re: Starship heat shield
Post by: Robotbeat on 12/07/2021 09:20 pm
You recover it every tanker refueling

... but, just like DanClemmensen said, only if the mission you're refueling actually needs the additional single-digit tonnes of propellant.
Not if you use a depot, which SpaceX is doing for Artemis.
Title: Re: Starship heat shield
Post by: DanClemmensen on 12/07/2021 09:37 pm
You recover it every tanker refueling or additional secondary payload or higher GTO orbit.
Tanker refuelings are quantized so not quite, unless you have a depot. Even with a depot you are only saving at most 0.7% of the cost (or one launch for every 150 tanker launches, if you prefer). For the rideshare case you will not get the extra tonne of customer payload unless there are an effectively unlimited number of paying customers with satellites of variable sizes in the one-tonne range. If your demand is completely elastic with continuously-variable mass, you get at most 0.7% gain. I'm just not seeing it.  Even for GEO: If the payload is just one tonne too big for me to get to GEO, I will need to refuel in LEO to deliver. But if it were two tonnes too big, I would need to refuel anyway, so it's still an edge case, and that edge will be there somewhere anyway, so we are still talking about 0.7% cost improvement on average.

About GTO: using "Starship economics", does it ever make sense to launch to GTO? (It may: I am very much NOT a rocket scientist.) Might it not be cheaper and simpler to put the payload in a Starship, launch to LEO, refuel, deliver to GEO, and then come home? This assumes a depot or some sort of standard tanker system that provides propellant at $10 million/150 t = $67000/t, not a bespoke tanker for the GEO mission.

Keep in mind, this is assuming 9 tons for total TPS weight, and that you can only reduce the weight of 10% of the tiles by half.

Both heavily conservative estimates. It's probably true that the weight of a much higher percentage of tiles can be reduced significantly, depending on their location.

Also, the TPS is not the only place where mass savings can be made. Elon Musk originally said he hoped the final mass of Starship would be around 85 tons.

There's lots of room for mass optimization.
Hey, I'm easy. If the launch cost is $10 million and the payload mass is somewhere near 150 t, then you will save on the order of $67,000 per launch for every tonne of dry mass you save, TPS or not. let's be generous and give you 100 launches: you save $6.7 million per tonne of dry mass saved. If that dry mass savings does not increase the cost of operations or refurbishment, you will only need to recoup the costs of design and manufacture associated with the mass savings. Note that Elon is aiming for $2 million/launch, not $10 million. Note also that this is tankers and other LEO-type missions, or you won't get the 100-mission reuse.

I'm guessing that there are simpler ways to save $67,000/launch than to remove a tonne of mass. I'm certainly not against mass reduction, but let's keep it in perspective.
Title: Re: Starship heat shield
Post by: Robotbeat on 12/07/2021 09:47 pm
Every such incremental change looks insignificant by itself in isolation but to make the whole thing viable you need enough of them to compound together.

SpaceX isn’t gonna ignore a 1% mass savings if it’s staring them in the face.

Doesn’t mean they’ll do it right away, but probably will eventually.
Title: Re: Starship heat shield
Post by: DanClemmensen on 12/07/2021 09:59 pm
Every such incremental change looks insignificant by itself in isolation but to make the whole thing viable you need enough of them to compound together.

SpaceX isn’t gonna ignore a 1% mass savings if it’s staring them in the face.
Yep, they will analyze any mass saving they can. It's a question of priority. Right now, they need to get to orbit with Starlink satellites. I doubt they will consider any design change for the purpose of mass reduction if it affects the schedule. Clearly, any design change they are required to make for other reasons will take mass into account, so there may be some saving anyway. I would bet that Elon would trade an extra tonne of mass to shorten the schedule by a month. He would probably trade an extra ten tonnes for that month if he knew he would get it back in a year.
Title: Re: Starship heat shield
Post by: ETurner on 12/07/2021 10:08 pm
Another perspective: If the entire vehicle faced the relaxed thermal environment now seen on its sides, the heat shield design would make a different mass/cost/robustness trade-off, maybe not even using tiles. Since half the shielded area is in that kind of relaxed environment -- not stagnation point conditions -- then similar mass/cost/robustness improvements may still be worth pursuing. What if half the tile area could be replaced with a metal TPS solution?

But for now, it makes sense to design for the hard case and use the solution everywhere. Premature optimization is the root of much evil.
Title: Re: Starship heat shield
Post by: Robotbeat on 12/07/2021 10:09 pm
This is the same Elon that deleted the legs and used the highest pressure rocket engine.
Title: Re: Starship heat shield
Post by: DanClemmensen on 12/08/2021 01:01 am
This is the same Elon that deleted the legs and used the highest pressure rocket engine.
That was then. This is now. We are within maybe 3 months of the first flight and Elon says SpaceX is at risk of bankruptcy if the cannot launch Starlink satellites. Deleting the legs in favor of chopsticks was not an apparent schedule risk when that decision was made: different engineering teams. The Raptor choice was also made a long time ago. The current schedule crisis is a short-term problem whose risk is caused by the surprise.
Title: Starship heat shield
Post by: Lars-J on 12/08/2021 04:09 am
Another perspective: If the entire vehicle faced the relaxed thermal environment now seen on its sides, the heat shield design would make a different mass/cost/robustness trade-off, maybe not even using tiles. Since half the shielded area is in that kind of relaxed environment -- not stagnation point conditions -- then similar mass/cost/robustness improvements may still be worth pursuing. What if half the tile area could be replaced with a metal TPS solution?

But for now, it makes sense to design for the hard case and use the solution everywhere. Premature optimization is the root of much evil.

This is the same Elon that deleted the legs and used the highest pressure rocket engine.

The genius is in deciding what parts to prematurely optimize.

SpaceX is known for optimizing for cost instead of performance, but if all your parts are performing so-so, the end result will be underwhelming. You’ve got to pick your battles. SpaceX has always zeroed in to a few small areas to optimize.
Title: Re: Starship heat shield
Post by: brettly2021 on 12/08/2021 10:49 am
With regard tile waterproofing.
Thanks for the info posted and link to a pdf file. I had made a few assumptions on the waterproofing:
the borosilicate ( or similar) black coating already provided a waterproof surface, not the whole tile is coated with the black borosilcate. So only the rear or sides of tiles without borosilcate required waterproofing i.e. the white parts of the tiles which are not visible.
The pdf file posted previously says waterproofing was injected after shuttle flights, which suggests to me its only the
white parts which require waterproofing. If that is correct why not just cover the whole of the tiles with borosilicate?
Maybe it wouldn't be necessary to re-waterproof at all.
Title: Re: Starship heat shield
Post by: edzieba on 12/08/2021 12:08 pm
You recover it every tanker refueling

... but, just like DanClemmensen said, only if the mission you're refueling actually needs the additional single-digit tonnes of propellant.
Not if you use a depot, which SpaceX is doing for Artemis.
Unless each tanker launch is just barely short of the propellant mass required by a few hundred kg and thus requires an additional launch to top-up that last ~1 ton, that doesn't actually save you much money at all. The per-launch costs will dwarf propellant costs for quite some time to come. You need to be operating at much higher flight rates and re-use counts before propellant cost starts to dominate launch costs, and at that point you have to consider whether that extra few hundred kg for edge-cause missions is worth retrofitting your fleet.
why not just cover the whole of the tiles with borosilicate?
The borosilicate glass layer is a thin brittle crust over a stiff but frangible low density ceramic (a bit like an open-cell foam). SpaceX are also applying the pushpins via pressing them into the internal channels straight through the sintered fibre (just letting it crush out of the way rather than needing to mill or cast dedicated channels). The glass is vulnerable to cracks and microfractures, and whilst these can be tolerated for use as a heatshield (a hairline crack in the glass coating does not significantly affect its radiative properties) it will allow water ingress. Coating the entire tile and assuming that the glass coating will remain unfractured to provide the waterproofing is very likely to result in waterlogged tiles.
Title: Re: Starship heat shield
Post by: eriblo on 12/08/2021 12:12 pm
With regard tile waterproofing.
Thanks for the info posted and link to a pdf file. I had made a few assumptions on the waterproofing:
the borosilicate ( or similar) black coating already provided a waterproof surface, not the whole tile is coated with the black borosilcate. So only the rear or sides of tiles without borosilcate required waterproofing i.e. the white parts of the tiles which are not visible.
The pdf file posted previously says waterproofing was injected after shuttle flights, which suggests to me its only the
white parts which require waterproofing. If that is correct why not just cover the whole of the tiles with borosilicate?
Maybe it wouldn't be necessary to re-waterproof at all.
The bulk material of the tile is a low density open "foam" of thin silica fibres. It needs to have some surface uncovered in order for the air inside to escape when exposed to the vacuum of space. Otherwise the surface layer would have to withstand a pressure difference of several atmospheres when the tile is heated. The insulating performance would also be negatively affected.

Silica is naturally hydrophilic due to silanol groups on the surface. Combined with the large surface area the tiles will adsorb a lot of water just from the humidity in the air (porous silica is commonly used as a dessicant). This is a problem because of added weight and that the water will both freeze in space and flash to superheated steam on re-entry which can fracture the tile.

The standard way to prevent this is to replace the silanol groups with something that is hydrophobic. The problem is that these groups will decompose or literally burn up on re-entry so the treatment has to be repeated.
Title: Re: Starship heat shield
Post by: Twark_Main on 12/08/2021 03:54 pm
You recover it every tanker refueling

... but, just like DanClemmensen said, only if the mission you're refueling actually needs the additional single-digit tonnes of propellant.
Not if you use a depot, which SpaceX is doing for Artemis.

Yes, it adds up within that refueling campaign (that's how it went from under 1 tonne to "single-digit tonnes"). But the vast majority of launches won't be.
Title: Re: Starship heat shield
Post by: Robotbeat on 12/08/2021 04:51 pm
You recover it every tanker refueling

... but, just like DanClemmensen said, only if the mission you're refueling actually needs the additional single-digit tonnes of propellant.
Not if you use a depot, which SpaceX is doing for Artemis.

Yes, it adds up within that refueling campaign (that's how it went from under 1 tonne to "single-digit tonnes"). But the vast majority of launches won't be.
This argument that small improvements aren’t worth it just doesn’t hold with reality.

Maybe 99 out of 100 payloads don’t care, but that 1 payload wouldn’t otherwise be launchable.

Maybe you get significantly more delta-v to GTO without refueling.

Maybe WITH refueling you get 1% extra propellant.

In each case it’s still an expected value of 1%.

With that extra performance you can operate at a lower chamber pressure, increasing life of the engine and reducing probability of failure… perhaps also allowing you to have more usable engines (maybe only 20% of Raptors can handle 250bar, but 80% can handle 200 bar and 100% can handle 180 bar). Maybe you can afford fewer engines per booster. Maybe you can afford more propellant for entry/boost back burn or landing hovering, giving you more margin for recovery. Maybe you can forego subcooling. Maybe you can use that extra 1% for better heatshield or structural margins.

It’s still around 1%, so I wouldn’t expect huge improvements, but 1% is not nothing.

It’s probably something they’ll do gradually over time. But the “it’s small so not helpful” is the kind of thinking that someone does when they’re not trying to make a rocket or airplane. The entire vehicle is the compound effect of hundreds of 1% performance improvements.
Title: Re: Starship heat shield
Post by: rakaydos on 12/08/2021 06:53 pm
You recover it every tanker refueling

... but, just like DanClemmensen said, only if the mission you're refueling actually needs the additional single-digit tonnes of propellant.
Not if you use a depot, which SpaceX is doing for Artemis.

Yes, it adds up within that refueling campaign (that's how it went from under 1 tonne to "single-digit tonnes"). But the vast majority of launches won't be.
Depots as a separate starship type would not be able to reenter- the insulation for long term cryo storage on orbit is different from reentry shielding. To be used for the next campaign, the depot will either need to be abandoned, or transfer to a more appropriate departure orbit. More fuel per launch helps to make the second option more viable.
Title: Re: Starship heat shield
Post by: whitelancer64 on 12/08/2021 07:35 pm
You recover it every tanker refueling

... but, just like DanClemmensen said, only if the mission you're refueling actually needs the additional single-digit tonnes of propellant.
Not if you use a depot, which SpaceX is doing for Artemis.

Yes, it adds up within that refueling campaign (that's how it went from under 1 tonne to "single-digit tonnes"). But the vast majority of launches won't be.
Depots as a separate starship type would not be able to reenter- the insulation for long term cryo storage on orbit is different from reentry shielding. To be used for the next campaign, the depot will either need to be abandoned, or transfer to a more appropriate departure orbit. More fuel per launch helps to make the second option more viable.

I doubt there will be a separate variant for depots. A Tanker can be a temporary depot just fine.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 12/08/2021 08:10 pm
You recover it every tanker refueling

... but, just like DanClemmensen said, only if the mission you're refueling actually needs the additional single-digit tonnes of propellant.
Not if you use a depot, which SpaceX is doing for Artemis.

Yes, it adds up within that refueling campaign (that's how it went from under 1 tonne to "single-digit tonnes"). But the vast majority of launches won't be.
Depots as a separate starship type would not be able to reenter- the insulation for long term cryo storage on orbit is different from reentry shielding. To be used for the next campaign, the depot will either need to be abandoned, or transfer to a more appropriate departure orbit. More fuel per launch helps to make the second option more viable.

I doubt there will be a separate variant for depots. A Tanker can be a temporary depot just fine.
I agree that for temporary use a tanker might be fine, but the heat shielding and the flaps add a lot of mass. In the long terma a different version might be better for the tanker, if the demand from customers is enough.
Title: Re: Starship heat shield
Post by: Kazioo on 12/08/2021 08:46 pm
Elon was asked 2 weeks ago about the challenge of long-term storage of cryogenics with all the boil off problems etc. and he said that there will be a Depot variant of Starship with multi-layer thermal insulation. (And let's not forget that this variant is also mentioned in the NASA's official documentation for HLS).

Starship going to Mars will only store propellant in the header tanks. There may be no way to hold larger amounts in the main tanks without insulation, so Depot might be a necessary variant to do refilling at all, not just a nice optimization for later.
Title: Re: Starship heat shield
Post by: whitelancer64 on 12/08/2021 08:52 pm
Elon was asked 2 weeks ago about the challenge of long-term storage of cryogenics with all the boil off problems etc. and he said that there will be a Depot variant of Starship with multi-layer thermal insulation. (And let's not forget that this variant is also mentioned in the NASA's official documentation for HLS).

Starship going to Mars will only store propellant in the header tanks. There may be no way to hold larger amounts in the main tanks without insulation, so Depot might be a necessary variant to do refilling at all, not just a nice optimization for later.

A depot in NRHO might make sense for Artemis, but I don't think the lunar surface landings will be frequent enough to warrant having one. Certainly not in the near term, anyway. But, if NASA's willing to pay for it... *shrug*
Title: Re: Starship heat shield
Post by: Kazioo on 12/08/2021 09:10 pm
I have no idea how big of a problem the boil off will be in shorter time, like a few days or a week, but if it's significant then Starship will need an insulated depot not just for Artemis and Mars, but even for many missions to orbits other than LEO that F9 and FH already can do.

I don't think anyone believes they will be able to do multiple Starship launches per day anytime soon, so even 2 refill launches could mean a week or longer storage that may require a depot.

In other words: if the problem is serious we are no longer talking about depot being a cool feature to have, but a technical necessity for a minimum viable concept that works.

Elon seems to be more convinced about the necessity of a depot than landing thrusters on HLS Starship.
Title: Re: Starship heat shield
Post by: whitelancer64 on 12/08/2021 09:46 pm
I have no idea how big of a problem the boil off will be in shorter time, like a few days or a week, but if it's significant then Starship will need an insulated depot not just for Artemis and Mars, but even for many missions to orbits other than LEO that F9 and FH already can do.

I don't think anyone believes they will be able to do multiple Starship launches per day anytime soon, so even 2 refill launches could mean a week or longer storage that may require a depot.

In other words: if the problem is serious we are no longer talking about depot being a cool feature to have, but a technical necessity for a minimum viable concept that works.

Elon seems to be more convinced about the necessity of a depot than landing thrusters on HLS Starship.

If you point the Starship Tanker's engines at the Sun, you get minimal solar heating on the tanks. The heatshield also provides some insulation. Previous indications were that was sufficient for a significant period of time.

For example, Starship HLS is supposed to have a loiter time of up to several months in NRHO before an Artemis landing.
Title: Re: Starship heat shield
Post by: Asteroza on 12/08/2021 10:33 pm
Functionally it shouldn't be that hard to have a robot arm inchworm along the dorsal spine to a good spot near the nose, deploy an inflatable sunshield tube over the nose, then drag it back over the body to envelope most of the tankage. Need to keep clear of RCS nozzles though. That would allow a stock tanker to run in long term depot mode, assuming the cryocooling system is sized for both cases.

The PR optics of the installed sunshield though...
Title: Re: Starship heat shield
Post by: OTV Booster on 12/09/2021 12:08 am
Short term, a stock SS will do ok for a depot. Long term, not so much. Rad Mod ran numbers for different refueling scenarios and IIRC, stretch tanks and a no return design package made a difference in some. Further down the road it might be reasonable to add active cooling and multiple tankers in popular orbits. Ultimately is would be great to have depots as an available resource rather than a mission specific add on. Especially when launching a clutch of mars bound ships.
Title: Re: Starship heat shield
Post by: eriblo on 12/09/2021 12:27 am
I have no idea how big of a problem the boil off will be in shorter time, like a few days or a week, but if it's significant then Starship will need an insulated depot not just for Artemis and Mars, but even for many missions to orbits other than LEO that F9 and FH already can do.

I don't think anyone believes they will be able to do multiple Starship launches per day anytime soon, so even 2 refill launches could mean a week or longer storage that may require a depot.

In other words: if the problem is serious we are no longer talking about depot being a cool feature to have, but a technical necessity for a minimum viable concept that works.

Elon seems to be more convinced about the necessity of a depot than landing thrusters on HLS Starship.

If you point the Starship Tanker's engines at the Sun, you get minimal solar heating on the tanks. The heatshield also provides some insulation. Previous indications were that was sufficient for a significant period of time.

For example, Starship HLS is supposed to have a loiter time of up to several months in NRHO before an Artemis landing.
The engine section is full of conductive metal ;) My suggestion is to put MLI above the top tank dome and point the nose towards the Sun. The nose will be "hot" (probably no more than warm) but the only heat leak will be the thin barrel wall. If you insulate the last meter above barrel/dome weld even a 300 K temperature difference would be < 1 kW of heating.

Short term, a stock SS will do ok for a depot. Long term, not so much. Rad Mod ran numbers for different refueling scenarios and IIRC, stretch tanks and a no return design package made a difference in some. Further down the road it might be reasonable to add active cooling and multiple tankers in popular orbits. Ultimately is would be great to have depots as an available resource rather than a mission specific add on. Especially when launching a clutch of mars bound ships.
Indeed, for high orbits the nose to sun approach might be enough to avoid boil-off completely but lower down you would have to do your best block the reflected sunlight and thermal emissions from the surface with the heat shield. The crazy thing is that if it is just ~240 W/m2 of thermal emissions (-18 °C, 265 K) like on the night side (of Earth) a heat shield at ~1 W/m2K on top of a 100 K tank wall would have a surface temperature of 220 K and conduct 120 W/m2, while the bare tank wall with an IR reflectivity likely > 80 % would absorb less than half that! Interesting modeling/optimization problem...
Title: Re: Starship heat shield
Post by: OTV Booster on 12/09/2021 12:35 am
Every such incremental change looks insignificant by itself in isolation but to make the whole thing viable you need enough of them to compound together.

SpaceX isn’t gonna ignore a 1% mass savings if it’s staring them in the face.
Yep, they will analyze any mass saving they can. It's a question of priority. Right now, they need to get to orbit with Starlink satellites. I doubt they will consider any design change for the purpose of mass reduction if it affects the schedule. Clearly, any design change they are required to make for other reasons will take mass into account, so there may be some saving anyway. I would bet that Elon would trade an extra tonne of mass to shorten the schedule by a month. He would probably trade an extra ten tonnes for that month if he knew he would get it back in a year.
I keep seeing the differences between the first F9 and the current one. SS will be no different. For now, get the sucker working, then start deploying Starlinks. Then look for .7% mass here and .7% there. They've got a lot on their plate.


As for the number of unique tiles, that is a problem but nothing like the Shuttle. Compared to the Shuttle, the SS is a simple topography. Looking at tiles in the fiddly areas, there is a mix of unique and and duplicate tiles. Many, like the tiles that wrap around an edge are not only there in multiples, they are inherently bi laterally symmetrical. The same tiles can be used on both sides.


Keeping the count as low as possible is an engineering goal. Getting back down in one piece is a mission objective. The number of tiles it takes to meet the objective will define "low as possible".


Methinks the heatshield will be a thorn in the idea of rapid reusability. It is what it is, but it's not the shuttle.
Title: Re: Starship heat shield
Post by: Twark_Main on 12/09/2021 12:46 am
Seems clear that the tiles are limited structurally, not thermally.

If Starship could go the Shuttle route and glue the tiles on with RTG, they could probably make them as thin as they want. But the whole point of Starship is that the steel backside can get hotter than aluminum, so RTG is off the table.

We've all seen the effort required in structurally qualifying the tile attachment mechanism & process. Lots of broken tiles and rework. I doubt SpaceX wants to repeat that process many times over with many different thicknesses.
Title: Re: Starship heat shield
Post by: OTV Booster on 12/09/2021 12:50 am
I have no idea how big of a problem the boil off will be in shorter time, like a few days or a week, but if it's significant then Starship will need an insulated depot not just for Artemis and Mars, but even for many missions to orbits other than LEO that F9 and FH already can do.

I don't think anyone believes they will be able to do multiple Starship launches per day anytime soon, so even 2 refill launches could mean a week or longer storage that may require a depot.

In other words: if the problem is serious we are no longer talking about depot being a cool feature to have, but a technical necessity for a minimum viable concept that works.

Elon seems to be more convinced about the necessity of a depot than landing thrusters on HLS Starship.

If you point the Starship Tanker's engines at the Sun, you get minimal solar heating on the tanks. The heatshield also provides some insulation. Previous indications were that was sufficient for a significant period of time.

For example, Starship HLS is supposed to have a loiter time of up to several months in NRHO before an Artemis landing.
The engine section is full of conductive metal ;) My suggestion is to put MLI above the top tank dome and point the nose towards the Sun. The nose will be "hot" (probably no more than warm) but the only heat leak will be the thin barrel wall. If you insulate the last meter above barrel/dome weld even a 300 K temperature difference would be < 1 kW of heating.

Short term, a stock SS will do ok for a depot. Long term, not so much. Rad Mod ran numbers for different refueling scenarios and IIRC, stretch tanks and a no return design package made a difference in some. Further down the road it might be reasonable to add active cooling and multiple tankers in popular orbits. Ultimately is would be great to have depots as an available resource rather than a mission specific add on. Especially when launching a clutch of mars bound ships.
Indeed, for high orbits the nose to sun approach might be enough to avoid boil-off completely but lower down you would have to do your best block the reflected sunlight and thermal emissions from the surface with the heat shield. The crazy thing is that if it is just ~240 W/m2 of thermal emissions (-18 °C, 265 K) like on the night side (of Earth) a heat shield at ~1 W/m2K on top of a 100 K tank wall would have a surface temperature of 220 K and conduct 120 W/m2, while the bare tank wall with an IR reflectivity likely > 80 % would absorb less than half that! Interesting modeling/optimization problem...
How does it compare on the day side? Would that white thermal paint improve things? It would be great to get rid of the heat shield but if it does away with a deplorable shade it's worth keeping.


At what altitude does earth thermal become insignificant?



Title: Re: Starship heat shield
Post by: ThatOldJanxSpirit on 12/09/2021 03:45 pm
I have no idea how big of a problem the boil off will be in shorter time, like a few days or a week, but if it's significant then Starship will need an insulated depot not just for Artemis and Mars, but even for many missions to orbits other than LEO that F9 and FH already can do.

I don't think anyone believes they will be able to do multiple Starship launches per day anytime soon, so even 2 refill launches could mean a week or longer storage that may require a depot.

In other words: if the problem is serious we are no longer talking about depot being a cool feature to have, but a technical necessity for a minimum viable concept that works.

Elon seems to be more convinced about the necessity of a depot than landing thrusters on HLS Starship.

If you point the Starship Tanker's engines at the Sun, you get minimal solar heating on the tanks. The heatshield also provides some insulation. Previous indications were that was sufficient for a significant period of time.

For example, Starship HLS is supposed to have a loiter time of up to several months in NRHO before an Artemis landing.
The engine section is full of conductive metal ;) My suggestion is to put MLI above the top tank dome and point the nose towards the Sun. The nose will be "hot" (probably no more than warm) but the only heat leak will be the thin barrel wall. If you insulate the last meter above barrel/dome weld even a 300 K temperature difference would be < 1 kW of heating.

Short term, a stock SS will do ok for a depot. Long term, not so much. Rad Mod ran numbers for different refueling scenarios and IIRC, stretch tanks and a no return design package made a difference in some. Further down the road it might be reasonable to add active cooling and multiple tankers in popular orbits. Ultimately is would be great to have depots as an available resource rather than a mission specific add on. Especially when launching a clutch of mars bound ships.
Indeed, for high orbits the nose to sun approach might be enough to avoid boil-off completely but lower down you would have to do your best block the reflected sunlight and thermal emissions from the surface with the heat shield. The crazy thing is that if it is just ~240 W/m2 of thermal emissions (-18 °C, 265 K) like on the night side (of Earth) a heat shield at ~1 W/m2K on top of a 100 K tank wall would have a surface temperature of 220 K and conduct 120 W/m2, while the bare tank wall with an IR reflectivity likely > 80 % would absorb less than half that! Interesting modeling/optimization problem...
How does it compare on the day side? Would that white thermal paint improve things? It would be great to get rid of the heat shield but if it does away with a deplorable shade it's worth keeping.


At what altitude does earth thermal become insignificant?

The white paint makes an enormous difference as this superb video demonstrates.

https://m.youtube.com/watch?v=0J8zviPF2zI
Title: Re: Starship heat shield
Post by: rsdavis9 on 12/09/2021 05:27 pm
Short term, a stock SS will do ok for a depot. Long term, not so much. Rad Mod ran numbers for different refueling scenarios and IIRC, stretch tanks and a no return design package made a difference in some. Further down the road it might be reasonable to add active cooling and multiple tankers in popular orbits. Ultimately is would be great to have depots as an available resource rather than a mission specific add on. Especially when launching a clutch of mars bound ships.

Yea but just think what a LEO gas station for any orbital rocket will enable. Whats  the cost/gal of a fill up with LOX and LCH4 in orbit.
Title: Re: Starship heat shield
Post by: Robotbeat on 12/09/2021 07:22 pm
Every such incremental change looks insignificant by itself in isolation but to make the whole thing viable you need enough of them to compound together.

SpaceX isn’t gonna ignore a 1% mass savings if it’s staring them in the face.
Yep, they will analyze any mass saving they can. It's a question of priority. Right now, they need to get to orbit with Starlink satellites. I doubt they will consider any design change for the purpose of mass reduction if it affects the schedule. Clearly, any design change they are required to make for other reasons will take mass into account, so there may be some saving anyway. I would bet that Elon would trade an extra tonne of mass to shorten the schedule by a month. He would probably trade an extra ten tonnes for that month if he knew he would get it back in a year.
I keep seeing the differences between the first F9 and the current one. SS will be no different. For now, get the sucker working, then start deploying Starlinks. Then look for .7% mass here and .7% there. They've got a lot on their plate.


As for the number of unique tiles, that is a problem but nothing like the Shuttle. Compared to the Shuttle, the SS is a simple topography. Looking at tiles in the fiddly areas, there is a mix of unique and and duplicate tiles. Many, like the tiles that wrap around an edge are not only there in multiples, they are inherently bi laterally symmetrical. The same tiles can be used on both sides.


Keeping the count as low as possible is an engineering goal. Getting back down in one piece is a mission objective. The number of tiles it takes to meet the objective will define "low as possible".


Methinks the heatshield will be a thorn in the idea of rapid reusability. It is what it is, but it's not the shuttle.
Precisely.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 12/09/2021 09:18 pm
Short term, a stock SS will do ok for a depot. Long term, not so much. Rad Mod ran numbers for different refueling scenarios and IIRC, stretch tanks and a no return design package made a difference in some. Further down the road it might be reasonable to add active cooling and multiple tankers in popular orbits. Ultimately is would be great to have depots as an available resource rather than a mission specific add on. Especially when launching a clutch of mars bound ships.

Yea but just think what a LEO gas station for any orbital rocket will enable. Whats  the cost/gal of a fill up with LOX and LCH4 in orbit.

Much though I always enjoy a good "It's a dessert topping!  No, it's a propellant depot!" argument, this seems decidedly off-topic for here.

PS:  All right-thinking people know that it's a dessert topping.
Title: Re: Starship heat shield
Post by: OTV Booster on 12/09/2021 09:59 pm
Short term, a stock SS will do ok for a depot. Long term, not so much. Rad Mod ran numbers for different refueling scenarios and IIRC, stretch tanks and a no return design package made a difference in some. Further down the road it might be reasonable to add active cooling and multiple tankers in popular orbits. Ultimately is would be great to have depots as an available resource rather than a mission specific add on. Especially when launching a clutch of mars bound ships.

Yea but just think what a LEO gas station for any orbital rocket will enable. Whats  the cost/gal of a fill up with LOX and LCH4 in orbit.
A lot less than a rocket big enough to lift all the propellant it needs.
Title: Re: Starship heat shield
Post by: brettly2021 on 12/12/2021 03:02 pm
based on some comments by apollo astronauts, that the first 20sec or so of liftoff is extremely violent, that it would be pretty much impossible to touch any of the dials/instruments even if they wanted to, I'm going to predict the tiles if they fly as they are now during the first flight that maybe 5% to 7% will fall off in first minute of flight, after that I would hesitate to predict.
Title: Re: Starship heat shield
Post by: Blueshift on 12/12/2021 03:55 pm
based on some comments by apollo astronauts, that the first 20sec or so of liftoff is extremely violent, that it would be pretty much impossible to touch any of the dials/instruments even if they wanted to, I'm going to predict the tiles if they fly as they are now during the first flight that maybe 5% to 7% will fall off in first minute of flight, after that I would hesitate to predict.
Given that the level of vibrations is inversely proportional to the number of engines, I would expect a rather smooth ride as long as the booster is burning. But in general I agree, it would be a miracle if the first heat shield arrives in orbit in one piece.
Title: Re: Starship heat shield
Post by: Slothman on 12/12/2021 04:56 pm
based on some comments by apollo astronauts, that the first 20sec or so of liftoff is extremely violent, that it would be pretty much impossible to touch any of the dials/instruments even if they wanted to, I'm going to predict the tiles if they fly as they are now during the first flight that maybe 5% to 7% will fall off in first minute of flight, after that I would hesitate to predict.
Given that the level of vibrations is inversely proportional to the number of engines, I would expect a rather smooth ride as long as the booster is burning. But in general I agree, it would be a miracle if the first heat shield arrives in orbit in one piece.

To that point, I remember crew dragon astronauts saying that the second stage flight is rougher than the booster flight for exactly that reason.
Title: Re: Starship heat shield
Post by: Tangilinear Interjar on 12/13/2021 03:37 pm
But in general I agree, it would be a miracle if the first heat shield arrives in orbit in one piece.

Nope!

It will be because of design, engineering and process.

It always blows my mind how so many people see a little thing like a tile fall off and jump to the conclusion that the whole design is faulty.

It's as if these people have never conceived something, designed and built it only to find out that you missed one (or five) little things. Doesn't mean that the concept is bad, just that there's more to do to get it to do the job as conceived.

I think this quickness to determine something a failure should be called the "Chicken Little Syndrome".
Title: Re: Starship heat shield
Post by: KBK on 12/13/2021 04:08 pm
It's a consideration of magnitude potential in failure for all tiles individually,  calculated as a set. The place where we come to say that a magnitude reduction in peak/transient stressing per tile, is required to get to a situation where all tiles are collectively at a zero failure point.

Ie, that one in a thousand or one in 10,000, really isn't good enough. and that 'problem' will generally show it's face in transient stressing, not just long term stressing.

Where those first seconds of the flight is more akin to chaos in stressing than anything else.

Think freak ocean waves, when searching for a simile of a sort. Which is merely tile reaction to loading, not the loading itself.

The mesh is seemingly a way to deal with some that, for a magnitude reduction when considered across all tiles individually and as a set.

It was not the same as my individual and half arsed solution presented as a 'flyer' (here in this thread), as I do not have the data set that SpaceX has.

I consider the mesh to be a good idea and a decent compromise that will probably get the job done, in all the right ways of: costs, simplicity, potential for failure, energetic dissipation sharing, transient limiting, etc.

the big deal, again, was a full spectrum of tile reduction in transit motion and load and the sharing of that load and the continual dissipation (instead of build) of the given transient loads/motion. to damp out potential in 'freak waves' by a magnitude.

That is the only way, IMO, that the heat shield tiles MIGHT meet the requirement of not even one single tile failure in a given flight.

To some extent, only flying that puppy will really show how effective the mesh might be. Static firing is obviously good, of course.

they may have to resort to a different weave and slightly tighter mesh, to get the job done.  Knot/crossing changes in the mesh can allow for more or less directionality of stress coupling to the blanket (XYZ), and then... a tighter mesh can allow for more effective tip control due to gap and knot placement with regard to tile tip location being less random seeming - with lower value changes. To find that sweet spot, is the deal.

Overall individual and collective tile tip control will show broad jumps in effectiveness as changes in mesh size occur. This is independent of tile attachment problems, and tile manufacturing problems.

It's a messy calculation that will be initially best served via intuition, lore and experience.

Throw some spaghetti at the fridge, see if it sticks.
Title: Re: Starship heat shield
Post by: daavery on 12/13/2021 04:30 pm
something to remember is that so far the static fires have been with mostly empty starship tanks and the actual flight regime will be full tanks and ignition @ MECO altitude for launch phase and partial tanks and ignition of 3 engines on orbit or 2-3 engines on the flip
Title: Re: Starship heat shield
Post by: KBK on 12/13/2021 04:51 pm
something to remember is that so far the static fires have been with mostly empty starship tanks and the actual flight regime will be full tanks and ignition @ MECO altitude for launch phase and partial tanks and ignition of 3 engines on orbit or 2-3 engines on the flip

This, will, of course, change the magnitude peak values of vibration and modes in the tile, blanket, mesh, pin mount, SS tank sheet motion, and resonance modes of each and all individually and in interface, and so on etc.

Mostly of importance is the level change in vibrational modes for the tank sheets themselves.

As for any descent related issues, they will have to wait in line.

(edit): Oh yes. Starship will be on top of the stack, not at the bottom, where the pressures are much higher (at the bottom)(2 pi steradians, half sphere proximity loading, surface effects, etc) .  Relevance in these points is to be considered - but not specifically counted upon for load reduction. Data required....
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 12/13/2021 08:43 pm
It's a consideration of magnitude potential in failure for all tiles individually,  calculated as a set. The place where we come to say that a magnitude reduction in peak/transient stressing per tile, is required to get to a situation where all tiles are collectively at a zero failure point.

Ie, that one in a thousand or one in 10,000, really isn't good enough. and that 'problem' will generally show it's face in transient stressing, not just long term stressing.

Where those first seconds of the flight is more akin to chaos in stressing than anything else.

Think freak ocean waves, when searching for a simile of a sort. Which is merely tile reaction to loading, not the loading itself.

If they really have chaotic vibrational modes, even transient ones, they have much bigger problems than a bunch of cracked tiles.  They almost certainly have many different vibrational modes, but that just means that they have some kind of pink noise, to which the response of the tiles can be tuned.

The tiles are essentially really fragile trusses, supported mostly by the y-channels and the pins that couple the y-channels to the hull, and somewhat by the underlying blanket.  They're going to have a transient response when the vibrations coming through the pins drive them.  But that response is tunable in a lot of different ways, simply by varying the thickness of the tiles at various points in the span between the channels and in the parts that overhang beyond the ends of the channels.

I agree that getting that right is hard, and likely requires lots of data.  But I disagree that you can't get a few orders of magnitude more reliability out of the individual tiles when you finally get it right.  Mechanical engineers do stuff like this all the time; it's the difference between a machine that works fine for thousands of hours and one that shakes itself to pieces in a couple of seconds.  Usually the former started out being the latter, and then somebody tweaked the tuning.
Title: Re: Starship heat shield
Post by: Blueshift on 12/14/2021 12:36 am
But in general I agree, it would be a miracle if the first heat shield arrives in orbit in one piece.

Nope!

It will be because of design, engineering and process.

It always blows my mind how so many people see a little thing like a tile fall off and jump to the conclusion that the whole design is faulty.

It's as if these people have never conceived something, designed and built it only to find out that you missed one (or five) little things. Doesn't mean that the concept is bad, just that there's more to do to get it to do the job as conceived.

I think this quickness to determine something a failure should be called the "Chicken Little Syndrome".
Calm down, you’re barking up the wrong tree. I didn’t write any of this!
Title: Re: Starship heat shield
Post by: brettly2021 on 12/14/2021 11:40 am
that is interesting theory that more engines gives less vibration, I would have thought the opposite.
The three metal supports on each tile ( the y bracket) are not joined, they are three separate pieces of  metal for each
tile, I would have thought the three metal pieces should be joined together it would give less stress on the tiles.
weight of each metal piece is 25g ( 24.68g to be more accurate), so 75g all up for the 'y' bracket metal pieces ( from collected debris boca chica beach post sn11)
Title: Re: Starship heat shield
Post by: OTV Booster on 12/14/2021 04:01 pm
that is interesting theory that more engines gives less vibration, I would have thought the opposite.
The three metal supports on each tile ( the y bracket) are not joined, they are three separate pieces of  metal for each
tile, I would have thought the three metal pieces should be joined together it would give less stress on the tiles.
weight of each metal piece is 25g ( 24.68g to be more accurate), so 75g all up for the 'y' bracket metal pieces ( from collected debris boca chica beach post sn11)
Yes more engines = more vibration, but...
With one engine any vibration peaks are experienced directly. With multiple engines it is unlikely that peaks would directly overlap. As the number of engines goes up the peaks tend to distribute and with different frequencies. There will still be occasional reinforcement between peaks but the overall randomness will smooth things out.


If the engines fall into some sort of  vibrational sync there will be big problems. They'll probably be looking for this.


Maybe they can tune it to play Space Oddity.  ::)
Title: Re: Starship heat shield
Post by: eriblo on 12/14/2021 05:07 pm
[...]
If my speculative labeling of Nic's picture is correct the the vents would be the ~ 2cm diameter holes in each side of the two round posts ~1m from the edge of the TPS. If that is the case it would seem that the jets, helped by the Coandă effect, managed to get under the blanket and produce pressure differential large enough to dislodge some of the tiles (would only require a fraction of an atmosphere).

Maybe it should have been caught before it happened but it would at least be easy to remedy by welding a small ramp next to the vents and perhaps rotating and/or moving them slightly for later prototypes. The only relevance I can see for this failure mode for the rest of the TPS would be the forward facing edges behind the forward fins/ahead of the aft fins on ascent. We will see if they do anything there before launch...
https://twitter.com/NicAnsuini/status/1470454169723191301

Always nice to know when your armchair rocket sciencing is sort of correct - I was wondering since they so far removed the damaged tiles and insulation on S20 but only replaced some of the ones far enough away to not be affected by the header vents.
Title: Re: Starship heat shield
Post by: brettly2021 on 12/17/2021 11:42 am
thats interesting about the vibration modes.
so 75g for one 'y' connector ( y connectors have no join in middle, so technically they are just three separate pieces)
someone posted 15,480 tiles on sn20, lets say 480 or so are glued, and 15,000 use the y pieces.
gives 1.125 tonnes of stainless y pieces, just in case any nerds interested.
dont have a clip to weigh, working on it. ( assuming all y pieces are same size which probably are not).
the one y piece arm I have is 10cm length and 3.5cm width, height about 1.4cm: weight 25g ( just under).
Hole for clip is 7mm by 4mm rectangular

Title: Re: Starship heat shield
Post by: djh on 12/18/2021 12:03 am
Hi there,


Has there been any consideration to vibration-absorbing technology between Stage 1 and Stage 2 to reduce the transmission of launch vibration from Superheavy to Starship?

Having the direct steel-to-steel contact between the top rings of SH and the base skirt of SS is unfortunately an excellent conductor of any energy. But there must be ways to mitigate this transmission. What is done in other engineering fields to absorb energy between two metal surfaces in contact, and could that work here?


Thanks
Title: Re: Starship heat shield
Post by: Malatrope on 12/18/2021 01:11 am
that is interesting theory that more engines gives less vibration, I would have thought the opposite.
The three metal supports on each tile ( the y bracket) are not joined, they are three separate pieces of  metal for each
tile, I would have thought the three metal pieces should be joined together it would give less stress on the tiles.
weight of each metal piece is 25g ( 24.68g to be more accurate), so 75g all up for the 'y' bracket metal pieces ( from collected debris boca chica beach post sn11)

The summation of any group of noisy signals averages out the peaks. I expect the ride on this booster to be smooth as silk.
Title: Re: Starship heat shield
Post by: Vonbraun on 12/18/2021 01:56 pm
On the latest NSF video https://www.youtube.com/watch?v=HHTQATW6C94&t=633s (https://www.youtube.com/watch?v=HHTQATW6C94&t=633s) shows the pan of S21 heat shield and it appears to be heavily damaged from all the manufacturing activities. The hairline fractures are most likely from the flexing action of the skin when transported and lifted. It would point towards the heatshield application and transportation can be done only after the ship can be pressurized rigid, so at a very late stage.

When manufacturing has sequences which can not be broken in separate parallel actions and in this case must be done at extreme heights and awkward positions, it could become a major bottleneck for the manufacturing. Probably a dedicated high bay just for that purpose is needed. Would there be a regulatory safety hassle if starship were pressurized to say, 1.5 bars while work is being done on it? One thing which comes to my mind is that it could require them to pressure test it before applying the shields (as it is considered unsafe to pressure before regulatory testing).

Just talking to keep myself warm.
Title: Re: Starship heat shield
Post by: edzieba on 12/18/2021 03:15 pm
Or alternatively, modify the mounting mechanism to accommodate a small amount of stretch/warp.
Title: Re: Starship heat shield
Post by: ETurner on 12/18/2021 04:45 pm
Or alternatively, modify the mounting mechanism to accommodate a small amount of stretch/warp.
Kinematic coupling.
Title: Re: Starship heat shield
Post by: CrazyHorse80 on 12/19/2021 05:53 am
On the latest NSF video https://www.youtube.com/watch?v=HHTQATW6C94&t=633s (https://www.youtube.com/watch?v=HHTQATW6C94&t=633s) shows the pan of S21 heat shield and it appears to be heavily damaged from all the manufacturing activities. The hairline fractures are most likely from the flexing action of the skin when transported and lifted. It would point towards the heatshield application and transportation can be done only after the ship can be pressurized rigid, so at a very late stage.

When manufacturing has sequences which can not be broken in separate parallel actions and in this case must be done at extreme heights and awkward positions, it could become a major bottleneck for the manufacturing. Probably a dedicated high bay just for that purpose is needed. Would there be a regulatory safety hassle if starship were pressurized to say, 1.5 bars while work is being done on it? One thing which comes to my mind is that it could require them to pressure test it before applying the shields (as it is considered unsafe to pressure before regulatory testing).

Just talking to keep myself warm.

When I watched the video myself, I was thinking about writing this exact same post... I am leaning toward thinking this is a temporary solution until the new wide bay will be done and they'll set up, there or in the high bay, a zone for the heat shield assembly with various floors where workers could easily access all of the fully assembled ship from the tip of the cone to the aft without having to use a manlift. So that this will be the last assembly stop before being redy to flight. Even if they will find a better mounting mechanism, the tiles just seem to be too brittle to have them mounted at the beginning of the assembly line.
Title: Re: Starship heat shield
Post by: brettly2021 on 12/19/2021 09:19 am
from that video there is no way you can determine if there are hairline cracks, to see a hairline crack you need much more high resolution images, I think what you refer to as  hairline cracks in that video , are in fact chalk marks by the installers, just what they mean I have no idea.
Title: Re: Starship heat shield
Post by: eriblo on 12/19/2021 10:24 am
from that video there is no way you can determine if there are hairline cracks, to see a hairline crack you need much more high resolution images, I think what you refer to as  hairline cracks in that video , are in fact chalk marks by the installers, just what they mean I have no idea.
I think the first reasonable assumption is that the chalk is used to mark cracks. In any case the marked tiles tend to have either a big X or have the OK mark scratched out suggesting they will all be replaced.
Title: Re: Starship heat shield
Post by: Tangilinear Interjar on 12/19/2021 04:06 pm
The hairline fractures are most likely from the flexing action of the skin when transported and lifted. It would point towards the heatshield application and transportation can be done only after the ship can be pressurized rigid, so at a very late stage.

How do you jump to the conclusion that the flexing of a very stiff stainless steel can is the likely cause as opposed to something like maybe the pounding them on with a fist?
Title: Re: Starship heat shield
Post by: OTV Booster on 12/19/2021 04:55 pm
The hairline fractures are most likely from the flexing action of the skin when transported and lifted. It would point towards the heatshield application and transportation can be done only after the ship can be pressurized rigid, so at a very late stage.

How do you jump to the conclusion that the flexing of a very stiff stainless steel can is the likely cause as opposed to something like maybe the pounding them on with a fist?
A meat hammer (fist) does a good job of impact distribution. Just as important, an experienced tradesman develops a fine tactile sense of limits. Screw up a couple and the feel is there. Few screwups follow. If it takes too much force to install a tile the problem most likely will be clips and/or Y bracket being misaligned, out of spec or damaged. The tile not being square to the surface when hit could mess it up too. That counts as a screwup and should go away with experience.


IMO, if the chalk marks represent cracks, there is a design or environmental problem. If the cracks really are coming from the meat hammers and everything is in spec, it's a design that can not be installed manually without special tools. If it's not from the meat hammers it's something in the environment and transport is a good target for the hairy eyeball.
Title: Re: Starship heat shield
Post by: Keldor on 12/19/2021 06:45 pm
The hairline fractures are most likely from the flexing action of the skin when transported and lifted. It would point towards the heatshield application and transportation can be done only after the ship can be pressurized rigid, so at a very late stage.

How do you jump to the conclusion that the flexing of a very stiff stainless steel can is the likely cause as opposed to something like maybe the pounding them on with a fist?
A meat hammer (fist) does a good job of impact distribution. Just as important, an experienced tradesman develops a fine tactile sense of limits. Screw up a couple and the feel is there. Few screwups follow. If it takes too much force to install a tile the problem most likely will be clips and/or Y bracket being misaligned, out of spec or damaged. The tile not being square to the surface when hit could mess it up too. That counts as a screwup and should go away with experience.


IMO, if the chalk marks represent cracks, there is a design or environmental problem. If the cracks really are coming from the meat hammers and everything is in spec, it's a design that can not be installed manually without special tools. If it's not from the meat hammers it's something in the environment and transport is a good target for the hairy eyeball.

One thing to note amout "experienced trademan" is that going into SN20, these didn't really exist.  The team's full experience at this point was installing maybe a thousand tiles on the patches on the earlier prototypes, and they had never installed them in the tricky regions like the nose and edges of the fins.  It was a learning experience for everyone, and that's fine - this is one of the reasons we build prototypes.
Title: Re: Starship heat shield
Post by: KBK on 12/20/2021 12:27 pm
from that video there is no way you can determine if there are hairline cracks, to see a hairline crack you need much more high resolution images, I think what you refer to as  hairline cracks in that video , are in fact chalk marks by the installers, just what they mean I have no idea.
I think the first reasonable assumption is that the chalk is used to mark cracks. In any case the marked tiles tend to have either a big X or have the OK mark scratched out suggesting they will all be replaced.

Possibly positioning error, instead. A pointing toward gap error in evenness for the given tile in-situ final mount. the direction the tile needs to move in, for further inspection... and possibly followed up rumination on what may be the causal factors. To have a solid indelible mark on the given tiles, so this can be further monitored, as time passes, as the body of the ship is moved about. Something like that.....maybe....
Title: Re: Starship heat shield
Post by: Vonbraun on 12/20/2021 03:41 pm
I see very few X shaped chalk marks. Most are oriented > or < shaped, some are Y shaped, bending towards the center trough the pins. We have previously seen cracks without marks and they are exactly like that. I think they are finding out by inspecting them early on, before the cracks are seen by naked eye?. Ultrasound inspection or something like that?

What makes me believe they are mostly from flexing is that the markings increase dramatically to the unsupported top. It could be that the lower portions are yet to be marked, but if i were tasked for this kind of inspection, i would start from easy and work towards hard spots.

Also would anybody allow this many damaged tiles to be manifested from an improper assembly? Surely you would test it ad nauseum at the pin prototyping & mounting method stage? Perhaps they have let their trainers loose and given them something to do instead of brewing coffee? Personally i would use a wooden stress relief board and not hit the tiles straight with my fists like how they are doing now. Anyway this kind of damage should appear more uniform across the body and maybe not this widespread. Alleviating all possible sources of future problems is of course a key in space flight manufacturing.
Title: Re: Starship heat shield
Post by: OTV Booster on 12/20/2021 06:01 pm
The hairline fractures are most likely from the flexing action of the skin when transported and lifted. It would point towards the heatshield application and transportation can be done only after the ship can be pressurized rigid, so at a very late stage.

How do you jump to the conclusion that the flexing of a very stiff stainless steel can is the likely cause as opposed to something like maybe the pounding them on with a fist?
A meat hammer (fist) does a good job of impact distribution. Just as important, an experienced tradesman develops a fine tactile sense of limits. Screw up a couple and the feel is there. Few screwups follow. If it takes too much force to install a tile the problem most likely will be clips and/or Y bracket being misaligned, out of spec or damaged. The tile not being square to the surface when hit could mess it up too. That counts as a screwup and should go away with experience.


IMO, if the chalk marks represent cracks, there is a design or environmental problem. If the cracks really are coming from the meat hammers and everything is in spec, it's a design that can not be installed manually without special tools. If it's not from the meat hammers it's something in the environment and transport is a good target for the hairy eyeball.

One thing to note amout "experienced trademan" is that going into SN20, these didn't really exist.  The team's full experience at this point was installing maybe a thousand tiles on the patches on the earlier prototypes, and they had never installed them in the tricky regions like the nose and edges of the fins.  It was a learning experience for everyone, and that's fine - this is one of the reasons we build prototypes.
Yes and no. Manual trades do amazing cross pollination. Installing door panels on a 70's vintage Ford product, with wire bayonet clips amazingly like the tiles, is very educational. Somehow I became the go to guy for power windows at a Lincoln Mercury dealer. Tiles and door panels are different but have similarities. When I spoke of experienced tradesmen I meant just that - not experienced thermal tile installers.


Of course, actually installing a thermal tile gets major bonus points. Screw one up and a lifetime of experience smacking things into place kicks in to modify the next try.


If the working guys are breaking the tiles I guarantee they're muttering under their breaths about idiot engineers and the instructions they got to smack the tiles onto the clips.



Title: Re: Starship heat shield
Post by: brettly2021 on 12/21/2021 09:14 am
I've had a bit of a look at the tile markings, attached is photo in the negative which shows them fairly clearly.
Each tile has 6 points ( hexagonal) but the 'y' brackets have only 3 pieces, so when installing you need to know where the y bracket is located so the pins line up. I think its probably as simple as that. Its possible some of the pins dont line up exactly and may account for some of the markings. I doubt its related to cracking at all, probably just the guys find it easier to know where the y bracket is before popping into place. Sort of done in a shorthand manner, that is clear to the guy installing. Looks like hierogliphics for aliens to us.
Also a pic showing see through tile on how the metal pieces are arranged ( note its not a 'y' bracket just three pieces of metal embedded into the tile). Why they are not joined in the middle, as that would give more strength and less cracking might be related to expansion of the metal at high temps, better if they are not joined?
Title: Re: Starship heat shield
Post by: livingjw on 01/05/2022 03:20 pm
I noticed that the SN20 tiles over the lift brackets were removed as a single collection of tiles. It looked like they were fastened to a plate.

John
Title: Re: Starship heat shield
Post by: edzieba on 01/05/2022 04:34 pm
Yes. We saw the plate with the clips installed briefly before it was tiled over.
Oddly, they drilled out the clip areas on the tiles (necessary for removal) before conducting the static fire. Seems like it was just a fit check of the tile panels, and that it coincided with the static fire before they could finish removing them again was just a coincidence (rather than an intentional install for testing in static fire conditions).
Title: Re: Starship heat shield
Post by: Gunner on 01/05/2022 05:48 pm
Good to see a couple posts.  Haven't been any since Dec 21.  I was thinking maybe there was a new thread.  Just the holidays I guess ;)
Title: Re: Starship heat shield
Post by: brettly2021 on 01/28/2022 11:39 am
yup this thread sure has gone quiet so I might just bring up an idea I previously mentioned about ice formation on the skin of the rocket during refuelling. I was just watching this onboard camera of the mars rover ula launch, it clearly shows that ice formed during fuelling quite easily makes it into orbit.
https://www.youtube.com/watch?v=NAkEOHhYuSo (https://www.youtube.com/watch?v=NAkEOHhYuSo)

This layer of ice ( I'm not sure how thick it gets but reasonably thick i'm guessing a 1cm or more...just a guess) will be lying behind the tiles, during take off some falls off( a large proportion I'm guessing again), but since the tiles are over the top of the ice layer its probably not desireable for the ice to break off as tile damage may occur.
So my guess is the layer under the tiles ( the fluffy white stuff.....whatever it is!) may play a role in stopping the ice from breaking apart in big junks. I'm guessing the ice becomes intertwined with the fluffy white stuff, and puts some limit on the size of crystal growth. We have been seeing a white powdery looking mist coming off between the tiles during static fires, my guess, is its ice powder being shaken loose from the white fluffy padding layer.
Its probably playing quite an important role in reducing tile breakage.

Whatever ice is left behind in the white fluffy layer would almost certainly make it to space ( my guess), its protected thermally by the tiles, and probably structurally protected by the white fluffy stuff.
During re-entry is all this water going to sublimate/evaporate as the rear of the tiles heat up, and what effect will it then have on plasma layer? I wonder if it will create any issues, I realise there is a method of cooling during re-entry by outgassing into the plasma stream ( I think thats the case) but would energetic hydrogen/oxygen ions  be a source of concern?

Title: Re: Starship heat shield
Post by: sebk on 01/28/2022 11:54 am
To have any non trivial thickness of ice to develop on a surface this surface needs to see free airflow, so there's a flow of humidity which then condenses out. If you block air movement (for example by putting on tiles and under-tile padding) you are blocking humidity inflow and there wont be any thick ice layer.
Title: Re: Starship heat shield
Post by: Craigles on 01/28/2022 07:21 pm
(clip ...)
During re-entry is all this water going to sublimate/evaporate as the rear of the tiles heat up, and what effect will it then have on plasma layer?
(clip ...)
Great question!

Unpredictable.

The effect on the boundary layer heat transfer, from ice sublimation behind the tiles, will be largely unpredictable as the mass of the H2O there will also be largely unpredictable.  Sometimes at launch we see lots of ice, depending on weather and elapsed time. Other times we see less ice. Both the heat transfer effect and cooling effect will be good things to measure from the first flight. As I understand it (better source, anybody?), NASA is helping by sending a chaser jet to Hawaii to observe this re-entry in the infra-red. That possible concern with "energetic hydrogen/oxygen ions" (steam) should be testable in the lab, for example with a hydrox welding torch.
Title: Re: Starship heat shield
Post by: OTV Booster on 01/29/2022 03:27 pm
To have any non trivial thickness of ice to develop on a surface this surface needs to see free airflow, so there's a flow of humidity which then condenses out. If you block air movement (for example by putting on tiles and under-tile padding) you are blocking humidity inflow and there wont be any thick ice layer.
As the air under the tiles chills during propellant loading it will contract and as it migrates downward through the fiber layer more air will be drawn in at the top of the tile. Moisture will condense out and freeze. As the padding fills with frozen water (solid? fluffy?) the convection behind the tile will slow and probably stop at some point.


ISTM that this will be the mechanism. The open issues seems be the texture of the ice and how much it takes to clog the padding. The added weight of ice makes the 1.5 T/W look like a smart margin. Even fluff starts adding up.   
Title: Re: Starship heat shield
Post by: BT52 on 01/29/2022 03:34 pm
Sorry what is metric T/W ?
Title: Re: Starship heat shield
Post by: eriblo on 01/29/2022 04:22 pm
Sorry what is metric T/W ?
Thrust to weight ratio.
Title: Re: Starship heat shield
Post by: eriblo on 01/29/2022 04:47 pm
To have any non trivial thickness of ice to develop on a surface this surface needs to see free airflow, so there's a flow of humidity which then condenses out. If you block air movement (for example by putting on tiles and under-tile padding) you are blocking humidity inflow and there wont be any thick ice layer.
As the air under the tiles chills during propellant loading it will contract and as it migrates downward through the fiber layer more air will be drawn in at the top of the tile. Moisture will condense out and freeze. As the padding fills with frozen water (solid? fluffy?) the convection behind the tile will slow and probably stop at some point.

ISTM that this will be the mechanism. The open issues seems be the texture of the ice and how much it takes to clog the padding. The added weight of ice makes the 1.5 T/W look like a smart margin. Even fluff starts adding up.
30 °C air can hold 30 g/m3 of water vapor. Cooling it down to 100 K increases the density ~3x. So a 5 cm layer cooling down and drawing in more air as the density increases will contain a maximum of ~5 g/m2 of water for a grand total of < 10 kg for the whole heat shield. The bare steel surface can potentially collect much more but it will still be more or less identical to the frost on other launch vehicles such as F9 - relatively fluffy and easily dislodged on takeoff.

As has been stated before the potential for hydrophilic insulation/tiles materials to adsorb significant amounts of water over longer timescales or from precipitation is a much larger worry. The concern for the tiles have been that freezing water (on orbit) and steam (during reentry) can fracture them. I have not heard of reactive Hydrogen species being a specific problem, the surface coating is already designed to withstand chemical attack from the plasma.
Title: Re: Starship heat shield
Post by: ETurner on 01/30/2022 09:04 am
Quick launch after propellant loading can help a lot. Less time to build up ice = less ice.
Title: Re: Starship heat shield
Post by: brettly2021 on 01/31/2022 04:18 am
This might have seemed obvious to some but not to me till recently:
the whole design of the tile system is based around keeping the tiles away from the cool surface of the tank, in comparison with space shuttle where the tiles were not in contact ( as far as I know) with super chilled surfaces.
To me this now seems obvious in retrospect........doh!
Have to keep in mind this technology was developed for space shuttle.
Some tiles on nosecone are being red siliconed in place same as procedure on space shuttle i.e. no superchilled surface to deal with, so have to assume the red silicone not suited to superchilled temps.
So this whole design of white fluffy air filled matting, stainless steel( ss) clips extended out to mate with ss plates in the tiles, all designed to keep the tiles away from the superchilled surface ( i forget exact temp they go down to but its very cold to add more propellent).
Which raises some rather interesting questions about the ice layer that forms ( white fluffy mat is filled with ambient air ).
If the surface of the ship is cold enough it wont just be water ice forming, depending on the temperature/pressure there might be nitrogen or carbon dioxide as soilds also. Someone would have to check the temps at which they become solids.
 I know nitrogen stays liquid to very cold temps/pressures, carbon dioxide ( dry ice) i'm guessing not as low temp/pressure to become solid.
In that movie I posted last post you can see at 3min31sec at fairing deploy, a large shock goes through the rocket, and you get a really nice ice cloud leave the rocket due to the shock ( similar to ice cloud seen at static fire of starship). That might be a method to use to make ice cloud at will in space.
So there is that process where musk has mentioned that cold gas can be sprayed during re-entry to protect some sensitive parts such as hinges of wings which are a bit exposed.
So now I'm thinking why have these tiles got spaces between them ( albeit small) probably to allow these ice particles to escape from behind the tiles, though this will also produce a cooling effect during re-entry as the ice escapes, heats up rapidly and forms free radicals in the plasma stream, the colour of the plasma should represent these free radicals
( atoms that have lost their electrons...from memory) and whatever atmospherice gases are out there at given height.
So the composition of the ice has some effect also on cooling effect, as long as they keep some distance in front of the ship as it re-enters, if the plasma sits on the surface of the tiles due to the ice coming out might be some issues.
So they have the basic design and mechanism worked out, but I believe there are some weaknesses in the design that could be improved on.
I think the ss embedded into the silica tiles is bad bad idea, I think better approach would be to make a an ss mesh ( light weight framework) of suitable shape that the tiles can be red siliconed onto. As long as the ice can still finds its way  between the tiles.
They will no doubt be testing in those plasma wind tunnels to find better solutions.
The desingn of an ss mesh to glue the tiles to would be intereting project, lots of different ways it could be done.
I will try find time to draw a pic of what I"m thinking. Maybe they have already tried this idea and found not feasible.
Title: Re: Starship heat shield
Post by: brettly2021 on 01/31/2022 04:50 am
something like this:
Title: Re: Starship heat shield
Post by: eriblo on 01/31/2022 07:48 am
The tiles on the tip of the nose are "red siliconed" directly to the surface of the LOX header tank so it would seem like the cold is not a problem.
Title: Re: Starship heat shield
Post by: brettly2021 on 01/31/2022 11:19 am
interesting eriblo,
here is pick of how the metal supports are embedded into the tiles, side view of tile

Title: Re: Starship heat shield
Post by: edzieba on 01/31/2022 11:28 am
No need to go chasing non-problems. Ice on the surface of or behind the tiles (in the batting) in and of itself is not an issue. It will not be forming in sufficient volume to mechanically displace the tiles, and sublimation will be sufficiently slow (and with enough gaps around the tiles) that gas pressure will not be building up and popping tiles off. For the silicone-mounted areas, ice formation behind the tiles is prevented by the silicone impregnated felt beneath the tiles eliminating any air volume, along with the silicone-impregnated gap fillers between the tiles.
Ice formation inside the tiles themselves is the primary concern, as both the ice formation and the gas generated by its sublimation are capable of fracturing the tiles. But that's solved by waterproofing the tiles, as was done for STS.
Title: Re: Starship heat shield
Post by: brettly2021 on 01/31/2022 11:50 am
some really good info there, just wondering if the header tank does still chill outside metal or if design was changed
after the test in 2020 where that design failed ( no expert here just trying to make sense of the design)

Title: Re: Starship heat shield
Post by: brettly2021 on 01/31/2022 12:21 pm
sn21 appears white fluffy all way to the top, no red silicone, alot of guessing on my behalf going on here, but I liked my theory! way biased!
Title: Re: Starship heat shield
Post by: brettly2021 on 02/03/2022 10:51 am
ship 21 appears to be some red silicone used on a small section of tiles, a narrow band, i'm guessing that section not in contact with cold liquids? anyone can line up that section with inside liquids?
Title: Re: Starship heat shield
Post by: eriblo on 02/03/2022 01:18 pm
ship 21 appears to be some red silicone used on a small section of tiles, a narrow band, i'm guessing that section not in contact with cold liquids? anyone can line up that section with inside liquids?
I had actually forgotten about that when talking about tiles glued to cryogenic tank walls before:

The pre-tiled ship sections do not have last few rows of tiles at the edges so that they can welded together. They are also missing some of the studs in this area and I believe that they have been gluing at least two rows of tiles per joint (2-3 of which are in the tank sections). There is also glued tiles on top of the doubling band used to reinforce the aft bulkhead joint where the wall transitions from pressurized tank to stringer reinforced aft skirt (which is what you marked in the screenshot).
Title: Re: Starship heat shield
Post by: brettly2021 on 02/06/2022 04:02 pm
I've given some thought to improve starship tile system and cracking problem.
( theres quite a bit of detail in the structure but for brevity will post basics)
Came up with this:
 A backing plate which tiles are red siliconed to. Backing plate can pop onto existing three pins on via 3 lugs.
Backing plate material of suitable material ( carbon fibre or aluminium or stainless or phenolic resin).
Design of backing plate so that its very stiff structurally but lightweight. Red silicone ample proportion to give soft base for tile ( maybea few mm thickness).
One form either the whole backing plate is ablative material such as phenolic resin, if tile falls off there is some secondary system to save the ship, or just a thin layer of phenolic resin.



Title: Re: Starship heat shield
Post by: livingjw on 02/07/2022 02:33 am
I've given some thought to improve starship tile system and cracking problem.
( theres quite a bit of detail in the structure but for brevity will post basics)
Came up with this:
 A backing plate which tiles are red siliconed to. Backing plate can pop onto existing three pins on via 3 lugs.
Backing plate material of suitable material ( carbon fibre or aluminium or stainless or phenolic resin).
Design of backing plate so that its very stiff structurally but lightweight. Red silicone ample proportion to give soft base for tile ( maybea few mm thickness).
One form either the whole backing plate is ablative material such as phenolic resin, if tile falls off there is some secondary system to save the ship, or just a thin layer of phenolic resin.

Sounds like it would be too heavy and where did the batting insulation go? Without the batting, you will have to thicken the ceramic tile. Also the temperature at the tank tile interface might be too high for the silicone adhesive.

John
Title: Re: Starship heat shield
Post by: edzieba on 02/07/2022 09:41 am
I've given some thought to improve starship tile system and cracking problem.
( theres quite a bit of detail in the structure but for brevity will post basics)
Came up with this:
 A backing plate which tiles are red siliconed to. Backing plate can pop onto existing three pins on via 3 lugs.
Backing plate material of suitable material ( carbon fibre or aluminium or stainless or phenolic resin).
Design of backing plate so that its very stiff structurally but lightweight. Red silicone ample proportion to give soft base for tile ( maybea few mm thickness).
One form either the whole backing plate is ablative material such as phenolic resin, if tile falls off there is some secondary system to save the ship, or just a thin layer of phenolic resin.
Why? What problem is this trying to solve, and why does it solve it? It adds extra mass and extra points of failure, but does not appear to eliminate any mass or eliminate any points of failure.
Title: Re: Starship heat shield
Post by: envy887 on 02/07/2022 12:12 pm
I've given some thought to improve starship tile system and cracking problem.
( theres quite a bit of detail in the structure but for brevity will post basics)
Came up with this:
 A backing plate which tiles are red siliconed to. Backing plate can pop onto existing three pins on via 3 lugs.
Backing plate material of suitable material ( carbon fibre or aluminium or stainless or phenolic resin).
Design of backing plate so that its very stiff structurally but lightweight. Red silicone ample proportion to give soft base for tile ( maybea few mm thickness).
One form either the whole backing plate is ablative material such as phenolic resin, if tile falls off there is some secondary system to save the ship, or just a thin layer of phenolic resin.
Why? What problem is this trying to solve, and why does it solve it? It adds extra mass and extra points of failure, but does not appear to eliminate any mass or eliminate any points of failure.

Most of the tile failures seem to be the attachment points separating from the bulk of the tile, or the entire tile cracking around the attachments. Adhering the entire back of the tile to a solid surface would spread those concentrated loads out over the surface and should reduce cracking and pull-out. It would also allow that exacting and time-consuming adhesive step to be done in a factory instead of on the vehicle, as the whole assembly would simply snap on to the welded mounting points.

But it does look heavy, especially once you consider the extra tile thickness needed to keep the silicone adhesive below its failure temperature. SpaceX seems to be trying to eliminate the adhesive as much as possible.
Title: Re: Starship heat shield
Post by: edzieba on 02/07/2022 01:32 pm
I've given some thought to improve starship tile system and cracking problem.
( theres quite a bit of detail in the structure but for brevity will post basics)
Came up with this:
 A backing plate which tiles are red siliconed to. Backing plate can pop onto existing three pins on via 3 lugs.
Backing plate material of suitable material ( carbon fibre or aluminium or stainless or phenolic resin).
Design of backing plate so that its very stiff structurally but lightweight. Red silicone ample proportion to give soft base for tile ( maybea few mm thickness).
One form either the whole backing plate is ablative material such as phenolic resin, if tile falls off there is some secondary system to save the ship, or just a thin layer of phenolic resin.
Why? What problem is this trying to solve, and why does it solve it? It adds extra mass and extra points of failure, but does not appear to eliminate any mass or eliminate any points of failure.

Most of the tile failures seem to be the attachment points separating from the bulk of the tile, or the entire tile cracking around the attachments. Adhering the entire back of the tile to a solid surface would spread those concentrated loads out over the surface and should reduce cracking and pull-out. It would also allow that exacting and time-consuming adhesive step to be done in a factory instead of on the vehicle, as the whole assembly would simply snap on to the welded mounting points.

But it does look heavy, especially once you consider the extra tile thickness needed to keep the silicone adhesive below its failure temperature. SpaceX seems to be trying to eliminate the adhesive as much as possible.
That seems like a "fix the tiles" problem (e.g. adding a fibre reinforced core to the sintered preform, or using a more fractal metal insert to spread loads more evenly) rather than an "add a whole extra attachment mechanism" problem.

::EDIT::

And that's if the problem is even down to the embedded pin catches, and not some other mechanism. RCG coating thickness, RCG coating cure cycle, thermal soak between process steps, tile corner and vertex radius, etc, could all contribute to residual stress that could result in cracking regardless of attachment. Before deploying a Rube-Goldberg glue-on-pins-on-felt-on-mat 'fix', best to correctly identify the actual problem first.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/08/2022 10:10 am
This system an idea to replace the  three embedded stainless pieces in each tile, the idea is to match weight of the three embedded pieces with new piece a backing plate ( no change in weight).........doable? yes I believe so.
I was assuming the TILE thickness would not require changing in order to protect red rtv....that might be a problem.
Backing plate would have to be engineered really well and 3d printed most likely only way to achieve low weight.
Not sure if carbon fibre can be 3d printed, it might not be suitable material anyhow.
The backing plate would be largely hollow, similar to how bone is structure, or bone of a birds wing, not just a a lump of metal or other material. I believe there are some ai type programs that can work out best hollow type structure to give required stiffness and lightweight and strength in areas where needed.

There would be some issues depending on material used for example if aluminium was used ( 3d printed), aluminium/stainless would see corrosion at the mounting points would require non-conductive inserts where the pins click into the new backing plate.
Might even be possible to add the felt backing in factory to each tile ( I see on starship 21 I think it was, they referred to the white fluffy backing as felt in chalk on the ship) before laying the tile.
The biggest issue would be if the thickness of the tiles as they are is enough for red rtv? as envy88 has made me aware, didn't think of that!
 
Title: Re: Starship heat shield
Post by: eriblo on 02/08/2022 02:08 pm
The tiles that are glued directly to the stainless steel are thicker - they join seamlessly side by side with the standard mounted tile + felt system. They might be closer to the standard tiles in some low heat areas on the fins/fairings.

The bulk tile material can likely handle >1500 K, the felt is similar or better, the steel should be good to at least 700 K indefinitely (probably more than 900 K at the low durations/cycles involved) and the brackets/mounting pins should be similar or better (they can use a different alloy and are fine with annealed material properties). They should all be ok down to 0 K.

The RTV silicone is the most temperature limited part of the system. The upper limit is likely <600 K and it looks like SpaceX have judged it sufficient at LOX temperatures as well but it is likely quite brittle at that point.

That means that gluing tiles to a mounting plate trades all the extra weight of the mounting system for easier installation with regard to just gluing tiles directly - an option that has already been replaced by the current system for most of the surface. As other have stated any added mass has to be weighted against just reinforcing the current tiles.
Title: Re: Starship heat shield
Post by: edzieba on 02/09/2022 09:32 am
The bulk tile material can likely handle >1500 K, the felt is similar or better
Felt is worse. Uncoated tiles would also not fare well.

Whilst the tiles look like a big block of insulator with a thin cosmetic coating, in terms of functionality during re-entry (enormous radiative heat loading, plus plasma impingement) they're more like a thin glass sheet doing most of the work reflecting and reradiating heat, and the tile body just handling what heat conducts through that layer. The unsintered felt is not suitable on its own as an exposed bare TPS.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/09/2022 12:33 pm
I'm not sure if I would agree with edzeiba, you are saying that the black ceramic glass coating which is maybe as thick as a human hair is doing most of the work?? I find that hard to believe ( said with max smart ( agent 86)voice)
I view the tile system as a weakness in the design of starship so far, it might even be as important as finding a solution to injector plate instability was to apollo, if they cant get the thing back on the ground in one piece reliably that is a huge issue. At the moment it appears the tile system is not the centre of attention for SpaceX, but I suspect it will be at some stage and I'm guessing the system will undergo alot of change. Which is good for armchair scientists ( or even proper scientists/engineers) as it may not as yet be determined what the reliable tile system will look like, its an opportunity to speculate and put some ideas out there.
So with that in mind: let me speculate.
How about this idea:
Use the ice build up during fueling for cooling during re-entry, if not enough water in atmosphere during fueling add some to get a good ice layer in the felt ( or whatever is directly against the hull) in future.
That cold ice will make it to space, then use that ice during re-entry to cool the tiles, in particular the rear of the tiles.
So with my back plate idea, the rear of the backplate might be designed to be cooled by evaporating/sublimating ice,
keeping the temp of the backplate down ( that h2o as gas then exits between the tiles) then ionised and help cooling the compressed gas infront of heat shield.
So if the backplate is cooled sufficiently red rtv silicone might not be a problem. How about mix some white silicone heat paste in with the red rtv ? And improve heat transfer across the rtv ( ok thats a bit experimental).
The rear of the backplate would probably have something like fins or large surface area for cooling by water evap/sublimation. Something along those lines.
There are lots of possibilities here to explore I dont think the final design is set in stone for spacex, will be interesting to see what happens on test flight.

Picture attached: say backing plate is aluminium or similar, 4 different ideas for cooling the rear of the  plate of aluminium ( side touching onto felt)
1 to 3 : take a piece of aluminium plate cnc out channels  so that steam/gas is directed to the extremity of the tile in tortuous path
4 : bit different idea the plate, really its two plates held together by many small columns, steam/gas directed to the edges exit via holes then directed into slots between tiles ( but with some angle to help go into the oncoming
 rare-ified air stream ( if that makes sense, harder to make but would work pretty good I think if can be made light enough).
Title: Re: Starship heat shield
Post by: Redclaws on 02/09/2022 01:00 pm
I'm not sure if I would agree with edzeiba, you are saying that the black ceramic glass coating which is maybe as thick as a human hair is doing most of the work?? I find that hard to believe ( said with max smart ( agent 86)voice)

The incredulity here shows a high degree of confidence in a simplistic understanding…. What does “most of the work” even mean?  It’s all necessary.

But as the rejection of heat is essentially a boundary effect, and reusable heat shield systems are strongly motivated to reject as much as possible, in some sense it does “most of the work”.  The outer layer still gets very hot, though, so insulation behind it is critical for keeping that high heat out of the rest of the system.  All components are essential though it’s true the engineering constraints may be harsher for that outer layer.

Whatever you find hard to believe or not, this is how it works.  Whether or not it will work well enough is a different issue, but it’s certainly a valid design *approach*.
Title: Re: Starship heat shield
Post by: eriblo on 02/09/2022 01:11 pm
The bulk tile material can likely handle >1500 K, the felt is similar or better
Felt is worse. Uncoated tiles would also not fare well.

Whilst the tiles look like a big block of insulator with a thin cosmetic coating, in terms of functionality during re-entry (enormous radiative heat loading, plus plasma impingement) they're more like a thin glass sheet doing most of the work reflecting and reradiating heat, and the tile body just handling what heat conducts through that layer. The unsintered felt is not suitable on its own as an exposed bare TPS.
Yes, the tile coating can withstand higher temperatures - possibly up to 2000 K. The tiles are usually limited by the maximum temperature of the bulk silica fiber material which is the reason for TUFROC where a layer of higher temperature carbon-based insulator is put in between the coating and the silica insulator.

I have not talked about using felt instead of tiles, just about the capabilities of the materials. There are felt compositions with less or no silica that are rated for > 1700 K which is much higher than the tile insulator (unless they have innovated beyond the original shuttle derived material). The reason for not using this composition for tiles would be precisely the need to sinter the fibers together to rigidize the insulation so it can support the glass coating.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/09/2022 01:38 pm
so my backplate concept 4, a bit more detail only showing right hand side in any detail, nothing to scale.
Title: Re: Starship heat shield
Post by: livingjw on 02/09/2022 02:59 pm
so my backplate concept 4, a bit more detail only showing right hand side in any detail, nothing to scale.

- Now it appears that you have added even more structure and less insulation. You have pushed the silicone into an even hotter environment. The silicone adhesive is near its maximum temperature limit when it is behind the tile insulation.

- I would suggest looking at the many NASA papers and slide presentations on the Shuttel TPS. That would give you a pretty good idea as to the temperature limits and depth of insulation required for reentry.

John
Title: Re: Starship heat shield
Post by: brettly2021 on 02/09/2022 05:10 pm
yup just nutting out some ideas.

These tiles are really quite curious material, what puzzles me is this:
the videos showing the tiles coming straight out of an oven and the corners cooling off immediately so they can be picked up by hand to me is very curious behaviour.
this video is particularly informative
https://www.youtube.com/watch?v=CchPemGaEmw (https://www.youtube.com/watch?v=CchPemGaEmw)

Tiles are 90plus percent air.
The thermal conductivity of both air and the silica fibres are low, as is the specific heat, but exposing to air the corners will cool off very very quickly indeed. This seems counter-intuitive to me. In this video link its described as the tile in insulating itself from his hand at the 3:43 mark.
So the speed at which heat is transferred is very very slow, yet the corners cool immediately?
Can anyone explain that in terms of physics in some detail?
Title: Re: Starship heat shield
Post by: Robotbeat on 02/09/2022 05:25 pm
yup just nutting out some ideas.

These tiles are really quite curious material, what puzzles me is this:
the videos showing the tiles coming straight out of an oven and the corners cooling off immediately so they can be picked up by hand to me is very curious behaviour.
this video is particularly informative
https://www.youtube.com/watch?v=CchPemGaEmw (https://www.youtube.com/watch?v=CchPemGaEmw)

Tiles are 90plus percent air.
The thermal conductivity of both air and the silica fibres are low, as is the specific heat, but exposing to air the corners will cool off very very quickly indeed. This seems counter-intuitive to me. In this video link its described as the tile in insulating itself from his hand at the 3:43 mark.
So the speed at which heat is transferred is very very slow, yet the corners cool immediately?
Can anyone explain that in terms of physics in some detail?
cools off quickly at the surface due to radiative and convective effects. Internal heat transfer is slow. Corners have the most surface area for a given mass.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/09/2022 05:35 pm
ok so I just learn  the borosilicate glass coating emits back a large proportion of the heat, not sure exact amount but it means only 10 or 20% or so continues into the tile, so Edzieba is correct that it does most of the work, now I understand apologies for doubting edzieba ( or as max would say.....sorry about that chief)

So since air can cool the edges what effect would an aluminium heatsink have if it was in contact with the tile and could remove heat? What if that heatsink was extremely cold? would it cool more than just air?
Would it cool enough so that the rear of the tile was kept under the suitable operating temperature of red rtv?
If yes then my backplate idea will have some validity.
Title: Re: Starship heat shield
Post by: xvel on 02/09/2022 05:39 pm
If you imagine a point inside that cube, that point thas some heat capacity, all points in that cube have the same heat capacity because it is homogenous material, how fast particular point will lose temperature depends on how close it is to surface of that cube, points in the middle of that cube are far away from surface so they loose heat slowly, points close to a middle of one particular side of that cube will loose heat quicker (there is less material to insulate from cold air for those), points close to corners are close to 3 sides of that cube so they'll lose the temperature the fastest.
Title: Re: Starship heat shield
Post by: DanClemmensen on 02/09/2022 05:51 pm
Warning dumb question from a non-rocket-scientist:  As I understand it, re-entry aerobraking is used to dissipate the kinetic energy of the vehicle. Most of the energy is converted to heat in the bow shockwave, and some of this heat gets transferred to the skin of the vehicle by several methods. Several methods are used to prevent the heat from damaging the structure, including insulation, ablation, and (in theory) transpiration. Ablation and transpiration work by expending mass to carry away the heat.

So here is the question: can a vehicle use its engines to inject mass to create a buffer between the bow shock and the vehicle? Orient the vehicle to enter tail first, and then fire up the engines to create as cool an exhaust as they are capable of at as low a thrust as they can. For a methalox engine, this might be done by using only the LOX and just enough methane to drive the turbopump. This exhaust would push the bow shock out and would also carry away heat the way the ablated material does in an ablative heat shield. The bow shock provides deceleration by pushing the exhaust back against the tail.
Title: Re: Starship heat shield
Post by: xvel on 02/09/2022 06:00 pm
Warning dumb question from a non-rocket-scientist:  As I understand it, re-entry aerobraking is used to dissipate the kinetic energy of the vehicle. Most of the energy is converted to heat in the bow shockwave, and some of this heat gets transferred to the skin of the vehicle by several methods. Several methods are used to prevent the heat from damaging the structure, including insulation, ablation, and (in theory) transpiration. Ablation and transpiration work by expending mass to carry away the heat.

So here is the question: can a vehicle use its engines to inject mass to create a buffer between the bow shock and the vehicle? Orient the vehicle to enter tail first, and then fire up the engines to create as cool an exhaust as they are capable of at as low a thrust as they can. For a methalox engine, this might be done by using only the LOX and just enough methane to drive the turbopump. This exhaust would push the bow shock out and would also carry away heat the way the ablated material does in an ablative heat shield. The bow shock provides deceleration by pushing the exhaust back against the tail.

You would need to take that additional fuel to orbit first right? so your payload would need to shrink...

But there was (and maybe still is) considered something similar for starship, https://en.wikipedia.org/wiki/Transpiration_cooling, but not with engines but with bleeding methane through starship skin.
There are many ways to get rid of heat, only question is what is the lightest solution.
Title: Re: Starship heat shield
Post by: DanClemmensen on 02/09/2022 06:46 pm
Warning dumb question from a non-rocket-scientist:  As I understand it, re-entry aerobraking is used to dissipate the kinetic energy of the vehicle. Most of the energy is converted to heat in the bow shockwave, and some of this heat gets transferred to the skin of the vehicle by several methods. Several methods are used to prevent the heat from damaging the structure, including insulation, ablation, and (in theory) transpiration. Ablation and transpiration work by expending mass to carry away the heat.

So here is the question: can a vehicle use its engines to inject mass to create a buffer between the bow shock and the vehicle? Orient the vehicle to enter tail first, and then fire up the engines to create as cool an exhaust as they are capable of at as low a thrust as they can. For a methalox engine, this might be done by using only the LOX and just enough methane to drive the turbopump. This exhaust would push the bow shock out and would also carry away heat the way the ablated material does in an ablative heat shield. The bow shock provides deceleration by pushing the exhaust back against the tail.

You would need to take that additional fuel to orbit first right? so your payload would need to shrink...

But there was (and maybe still is) considered something similar for starship, https://en.wikipedia.org/wiki/Transpiration_cooling, but not with engines but with bleeding methane through starship skin.
There are many ways to get rid of heat, only question is what is the lightest solution.
You need to take some mass to orbit in any event: TPS tiles, transpiration cooling mass and equipment, ablative heat shield, whatever. The question is: how much? In theory (and only in theory) the amount of heat carried away is roughly proportional to the amount of mass use to carry that heat, in addition to a huge and scary number of other factors. The potential advantage of using engine exhaust is that you don't need the mass of a separate mass-injection system.
Title: Re: Starship heat shield
Post by: Robotbeat on 02/09/2022 07:01 pm
Sometimes the drag produced by the vehicle actually goes down when you burn the engines. And, of course, rocket exhaust is hot…
Title: Re: Starship heat shield
Post by: edzieba on 02/09/2022 09:02 pm
So here is the question: can a vehicle use its engines to inject mass to create a buffer between the bow shock and the vehicle? Orient the vehicle to enter tail first, and then fire up the engines to create as cool an exhaust as they are capable of at as low a thrust as they can.
Yes, Falcon 9 does this during the Entry Burn (as a welcome side-effect of burning to decelerate). However:
Sometimes the drag produced by the vehicle actually goes down when you burn the engines. And, of course, rocket exhaust is hot…
Firing engines directly into the bow shock collapses the bow shock and allows the superheated plasma that it kept at bay to move into contact with the vehicle wherever it is not being directly displaced by exhaust gas.

As an analogy: consider hiding behind an umbrella from an extreme torrential downpour in hurricane force winds. The umbrella is your bow shock, pushing most of the water away but there is still plenty soaking through or splashing back off the displaced droplets to the side or just getting past as the umbrella canopy flops about in the onslaught. Now point a high pressure high flow air nozzle up the shaft of the umbrella: directly above the nozzle the stream of air is really effective at pushing the droplets away, great! But it's also blasted away your umbrella canopy, so all the rest of the rain is now hitting you unimpeded.

The alternatives are to use a low velocity low pressure flow (very low throttle, akin to transpiration cooling from a single source) or to put your engines around the periphery of the vehicle and fire slightly outwards. The former doesn't allow you to produce much thrust at all, and whilst it no longer completely disrupts the bow shock it still reduces the amount of drag, which means you are expending propellent to decelerate less. The latter 'inflates' the bow shock, decelerating you without increasing entry plasma infringement and your propulsion effectiveness is only reduced slightly by cosine losses (and the expanded shock increases drag too). This was the original design for ITS back when it was akin to a scaled-up Dragon 2 - with Red Dragon being a sub-scale test mission.
Max Fagin's theses is an excellent source of information for retropropulsion effects: https://docs.lib.purdue.edu/open_access_theses/1199/
Title: Re: Starship heat shield
Post by: DanClemmensen on 02/09/2022 09:15 pm
Sometimes the drag produced by the vehicle actually goes down when you burn the engines. And, of course, rocket exhaust is hot…
Reducing the drag is not an inherent problem. It just increases the amount of time it takes to dissipate the kinetic energy of reentry and reduces peak thermal input rate, while providing more time to dissipate the heat. We will end up at the same terminal velocity in any case, and as soon as the velocity gets low enough we will no longer need the exhaust buffer so we shift to a ventral-first approach and increase drag.

Yes, the exhaust is higher temperature than ambient, but if it is almost all oxygen it's not at the temperature of exhaust intended for thrust.
Title: Re: Starship heat shield
Post by: hkultala on 02/09/2022 09:37 pm
Warning dumb question from a non-rocket-scientist:  As I understand it, re-entry aerobraking is used to dissipate the kinetic energy of the vehicle. Most of the energy is converted to heat in the bow shockwave, and some of this heat gets transferred to the skin of the vehicle by several methods. Several methods are used to prevent the heat from damaging the structure, including insulation, ablation, and (in theory) transpiration. Ablation and transpiration work by expending mass to carry away the heat.

So here is the question: can a vehicle use its engines to inject mass to create a buffer between the bow shock and the vehicle? Orient the vehicle to enter tail first, and then fire up the engines to create as cool an exhaust as they are capable of at as low a thrust as they can. For a methalox engine, this might be done by using only the LOX and just enough methane to drive the turbopump. This exhaust would push the bow shock out and would also carry away heat the way the ablated material does in an ablative heat shield. The bow shock provides deceleration by pushing the exhaust back against the tail.

Oxygen-rich exhaust might probably be much more destructive to the vehicle than any aerodynamic loads from the aerobraking.  Hot oxygen is very chemically extremely corrosive.

So oxygen-rich exhaust makes absolutely zero sense.
Title: Re: Starship heat shield
Post by: Oersted on 02/09/2022 11:21 pm

So oxygen-rich exhaust makes absolutely zero sense.


You can perhaps even say it would be adding fuel to the fire.
Title: Re: Starship heat shield
Post by: edzieba on 02/09/2022 11:29 pm

So oxygen-rich exhaust makes absolutely zero sense.


You can perhaps even say it would be adding fuel to the fire.
What would be fuel-rich exhaust. Oxygen-rich exhaust attaching vehicle components would be adding fire to the fuel.
Title: Re: Starship heat shield
Post by: livingjw on 02/10/2022 12:16 am
- Adding Oxygen to a fire creates a blow torch.

- In the limit, with perfect insulation behind the outer surface, the temperature reaches what is called adiabatic or equilibrium wall temperature.  In essence all of the heat being radiated and convected onto the surface is re-radiated by the outer wall. No heat gets through the insulation. This is close to what we are trying to accomplish with TPS insulation. What heat gets through the TPS must be soaked up into the structure and any fluid behind it. It is only when the surface temperature exceeds known material limits that we should resort to ablation or transpiration cooling. Mass is too precious to throw away unless absolutely necessary. See the rocket equation.

John
Title: Re: Starship heat shield
Post by: brettly2021 on 02/10/2022 08:02 am
thanks xvel for explanation of cooling of tile edges out of oven.
There are many videos of people heating these tiles with blow torch, seems there are alot of the shuttle type tiles out there. So if I understand this correctly, the heat transfer is extremely slow, you heat up a part of the tile with torch and basically just that part gets hot.
So heat from the inside of tile takes quite a while to reach the outside ,a slow process, but once the heat reaches the edges its easily taken away by air ( in the case of the videos showing cool edges appear almost immediately).
With that in mind I suspect a heatsink of say aluminium might be quite effective in removing the heat that has reached the surface of the tile.........it might be relatively easy to cool the rear of the tile just going by the videos.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/10/2022 08:10 am
well seems I aint so crazy afterall, appears Musk has already commented on water cooling during re-entry some time back:
https://www.teslarati.com/spacex-ceo-elon-musk-starship-transpiring-steel-heat-shield-interview/


Title: Re: Starship heat shield
Post by: edzieba on 02/10/2022 11:25 am
thanks xvel for explanation of cooling of tile edges out of oven.
There are many videos of people heating these tiles with blow torch, seems there are alot of the shuttle type tiles out there. So if I understand this correctly, the heat transfer is extremely slow, you heat up a part of the tile with torch and basically just that part gets hot.
So heat from the inside of tile takes quite a while to reach the outside ,a slow process, but once the heat reaches the edges its easily taken away by air ( in the case of the videos showing cool edges appear almost immediately).
With that in mind I suspect a heatsink of say aluminium might be quite effective in removing the heat that has reached the surface of the tile.........it might be relatively easy to cool the rear of the tile just going by the videos.
Adding a heatsink just means that all that heat you have been so carefully trying to avoid reaching the vehicle body is given a conduction path that dumps it into the vehicle body, defeating the entire point of the TPS. Because the only way to sink that heat is for it to go from a hot thing (the tile) to a cold thing (the vehicle).
Title: Re: Starship heat shield
Post by: livingjw on 02/10/2022 03:48 pm
well seems I aint so crazy afterall, appears Musk has already commented on water cooling during re-entry some time back:
https://www.teslarati.com/spacex-ceo-elon-musk-starship-transpiring-steel-heat-shield-interview/

Water wicking TPS concept goes back to the 1960s. Lockheed might have been the first one to propose it. I believe water wicking is used near the engines in the Falcon 9. Again, should only used when necessary.

John
Title: Re: Starship heat shield
Post by: livingjw on 02/10/2022 03:53 pm
thanks xvel for explanation of cooling of tile edges out of oven.
There are many videos of people heating these tiles with blow torch, seems there are alot of the shuttle type tiles out there. So if I understand this correctly, the heat transfer is extremely slow, you heat up a part of the tile with torch and basically just that part gets hot.
So heat from the inside of tile takes quite a while to reach the outside ,a slow process, but once the heat reaches the edges its easily taken away by air ( in the case of the videos showing cool edges appear almost immediately).
With that in mind I suspect a heatsink of say aluminium might be quite effective in removing the heat that has reached the surface of the tile.........it might be relatively easy to cool the rear of the tile just going by the videos.
Adding a heatsink just means that all that heat you have been so carefully trying to avoid reaching the vehicle body is given a conduction path that dumps it into the vehicle body, defeating the entire point of the TPS. Because the only way to sink that heat is for it to go from a hot thing (the tile) to a cold thing (the vehicle).

Your don't need to add a heat sink. You already have one. Cooling the rear of the tile is what the stainless steel wall does in conjunction with any fluid behind it. Whatever gets through the TPS goes into the vehicle.

Guys, this isn't any different than insulating a house. Whatever heat gets through the insulation heats or cools the inside of the house.

John
Title: Re: Starship heat shield
Post by: brettly2021 on 02/11/2022 04:13 am
This process is going to be happening anyhow,  there will be ice there and probably quite alot of it since the felt and tiles will restrict ice breaking off , so the rear of the tiles will be heating the felt, the ice in the felt will turn to steam or gas, I'm guessing most of it will be steam. During re-entry the steam and ice will be mixing in the felt, probably will get a sort of slushy ice at some stage, mix of ice/water and some steam thrown in.
That steam will need to go somewhere, only pathway is eventually to go out through the tile gaps or edges where tiles end. I think it would be hard to deny this process is going to happen of its own volition.
Even when the tanks are empty its still going to be damn cold, more than cold enough for the ice to remain in situ in the felt. I think its only 5 or 6 minute re-entry where temps are high?
So with that in mind I've done another backingplate mod, the whole reason being to stop cracking of tiles by allowing red rtv and nice solid backplate to keep the tiles safe ( it might even be possible to make the tiles thinner by using this type of backing plate as some heat energy will be transferred away in per diagram.
This time backing plate has needle like prongs which go down into the felt ( not as far as the hull though), they assist heat transfer to create steam from the ice, the steam then leaves via the spaces between the tiles.
As the steam exits it comes into contact of the side of the hot tiles, steam would I guess become superheated and eventually when temp is high enough it will dissasociate into H and O ions, then ions will get stripped of their electrond and plasma form.
Its probably not necessary for the steam to be directed out of the tile gaps, as you dont want to loose water too fast,
letting the steam find its own tortuous path out might be ok.
Note the diagram is not to scale, backingplate would not be that bulky or large or heavy.
Title: Re: Starship heat shield
Post by: edzieba on 02/11/2022 08:46 am
No. You're adding a bunch of extra unnecessary hardware, encouraging mass to accumulate behind the tiles (ice), and trying to actively make the TPS system worse (sinking heat to the hold side).
Moving heat to the cold side of your TPS is actively making your TPS worse. The whole point of your TPS is to prevent heat from getting to the cold side.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/11/2022 09:34 am
Yup if the felt discourages ice buildup, these are just thought experiments.
Since we can see from the static fires that there is ice there in the felt and comes out as a white cloud, as it does on the non-tiled side, I'm not encouraging ice build up, its already there!
I dont think SpaceX current tile design with embedded stainless will be reliable and tiles will crack or be lost during first test flight,  hence having a go at nutting out some alternate designs. I understand your concern about the design, the tiles will do their job regardless of whats behind them, bleeding off a bit of heat energy at the rear to lower temp for red rtv attachment and assisting cooling at the front of the tiles at same time, I think is not a bid idea.
I could be wrong, but you would have to convince me some physics why it wouldn't work.
Title: Re: Starship heat shield
Post by: Doom2pro on 02/11/2022 11:38 am
If only the heating material was plasma like they could magnetically repell it...
Title: Re: Starship heat shield
Post by: edzieba on 02/11/2022 01:15 pm
Yup if the felt discourages ice buildup, these are just thought experiments.
Since we can see from the static fires that there is ice there in the felt and comes out as a white cloud, as it does on the non-tiled side, I'm not encouraging ice build up, its already there!
Not a given. Boca Chica is a dusty place, and dust will also be liberated on engine startup.
Quote
bleeding off a bit of heat energy at the rear to lower temp for red rtv attachment and assisting cooling at the front of the tiles at same time, I think is not a bid idea.
It is a bad idea. The entire purpose of the tiles is to have the maximum thermal resistance achievable between the outer surface and the inner surface. Any conduction path added to the inner surface is completely opposite to the entire purpose of the TPS.
It's akin to taking a nice pair of oven mitts, and putting some electric heaters inside to stop your hands getting cold. It's solving a problem that doesn't exist whilst simultaneously making the overall system less effective.
Title: Re: Starship heat shield
Post by: Oersted on 02/11/2022 08:40 pm
Yup if the felt discourages ice buildup, these are just thought experiments.
Since we can see from the static fires that there is ice there in the felt and comes out as a white cloud, as it does on the non-tiled side, I'm not encouraging ice build up, its already there!
I dont think SpaceX current tile design with embedded stainless will be reliable and tiles will crack or be lost during first test flight,  hence having a go at nutting out some alternate designs. I understand your concern about the design, the tiles will do their job regardless of whats behind them, bleeding off a bit of heat energy at the rear to lower temp for red rtv attachment and assisting cooling at the front of the tiles at same time, I think is not a bid idea.
I could be wrong, but you would have to convince me some physics why it wouldn't work.

You do realise SpaceX has a big team of top world experts making these tiles, right? Don't suffer from the Dunning Kruger effect.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/12/2022 10:21 am
Still no physics to say why it wont work? Some heat transfer calculations might be useful.
Yup I realise spacex/tesla has top scientists, thats why I'm so surprised at the stainless embedded in the tiles.
Lets see how the tiles go during ascent and re-entry.
Title: Re: Starship heat shield
Post by: ETurner on 02/12/2022 10:42 am
Still no physics to say why it wont work? Some heat transfer calculations might be useful.
There’s no point in analyzing a design that gets the parts backward. Maybe read more and write less?
Title: Re: Starship heat shield
Post by: cdebuhr on 02/12/2022 02:50 pm
Still no physics to say why it wont work? Some heat transfer calculations might be useful.
There’s no point in analyzing a design that gets the parts backward. Maybe read more and write less?
Emphasis mine.  Excellent advice in almost any circumstance.  To this I would also add the old rule that if someone thinks they've got some new concept, design, or principal that going to change everything, or at least is a significant advancement, and the general response is along the lines of "nope - that'll never work", then the onus is on the originator of the idea (looking at you, brettly2021) to demonstrate otherwise with physics, calculations, working models, etc.  It has to be this way.  We're it otherwise hardworking professionals in every field would never get anything done, as they'd have to spend all their time refuting (with physics, calculations, non-working models, etc.) "new" ideas brought to them by the mighty horde of those who ... write more and read less.
Title: Re: Starship heat shield
Post by: OTV Booster on 02/12/2022 05:01 pm
Still no physics to say why it wont work? Some heat transfer calculations might be useful.
Yup I realise spacex/tesla has top scientists, thats why I'm so surprised at the stainless embedded in the tiles.
Lets see how the tiles go during ascent and re-entry.
/s
Maybe they can put the tiles on the inside of the tank and the propellant on the outside - somehow. Then the tiles would be protected from ice AND excess heat! Show me the numbers that say it won't work. Grumble, grumble, mumble, mumble.


/end sarcasm.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/13/2022 05:14 pm
Thus far seems alot of negativity towards the idea, which is a shame. At this time it appears that in order to get the backing plate system to work ( to produce steam behind the tiles during re-entry) would require significantly thinner tiles than currently used. But the unexpected result of the design is this: shuttle tiles were cooled down post flight, they still contained alot of heat after landing ( not sure what method they used: water sprayed? ), this sytem would possibly create a passive cooling mechanism for the tiles post re-entry, I will know more after I do some calculations, I'm puting together data from research papers at present.
something else I wasn't aware of is the flow over the ship crosses from laminar to turbelant flow and has a large effect on temperatures.
I'll put up some info as I go along the data and calcs process:
this paper from nasa langely
https://pdfs.semanticscholar.org/4015/416b29f262013a20a9b515784cff30f84940.pdf?_ga=2.55780777.328901456.1644666594-1633489343.1644666594
Its got some real world data from flight shuttle flight sts-96, which will be useful. For example pic attached shows temp of tiles during re-entry vertical axis is temp degF horizontal axis is time in seconds ( temp probe located on botton of wing...aileron in this case.....). Time zero is at 400,000ft which they call start of the re-entry interface.

 


Title: Re: Starship heat shield
Post by: brettly2021 on 02/13/2022 06:42 pm
these lectures probably already posted, but excellent sources of info from the guys that did the calcs for apollo/shuttle
https://ocw.mit.edu/courses/aeronautics-and-astronautics/16-885j-aircraft-systems-engineering-fall-2005/video-lectures/lecture-12/
Title: Re: Starship heat shield
Post by: edzieba on 02/13/2022 07:15 pm
At this time it appears that in order to get the backing plate system to work ( to produce steam behind the tiles during re-entry)
You don't want to do this, at all. Gas pressure generated behind the tiles is trying to push the tiles off, which is bad.

The STS tiles were not actively cooled, and certainly not by water spray (the rewaterproofing guys would have chased after anyone who proposed to do so and club them before they could train any nozzles on the unprotected tiles).
Title: Re: Starship heat shield
Post by: BT52 on 02/13/2022 10:33 pm

At this time it appears that in order to get the backing plate system to work ( to produce steam behind the tiles during re-entry)

I respect your eutusiasm and all. But Why Engineer something that even shuttle dint need. Beauty of this system is totally pasive and damm effective. General concept is almost surely right direction. At least for current state in material science. IMO
Title: Re: Starship heat shield
Post by: brettly2021 on 02/14/2022 09:02 am
there is a good reason to re-engineer, the stainless steel plates ( 3x) that are embedded into the tiles are the current method of having a type of backing plate. I believe the design is very much flawed. I'm quite convinced spacex will do away with those 3 stainless mounting brackets. Thats my whole purpose of discussing this. The tiles have very little expansion as far as I'm aware, will be quite different to the stainless expansion, and the tiles are fragile. There is a method to increase density of the rear of tiles which was used on shuttle, which is probably what space x has done,
to overcome the issues but I really think its a bad method and wont be used for long.  Hence the reason for discussing backing plate ideas. It certainly is an interesting way to learn about the tiles/heat transfer etc. I'm a novice, knowledge is not great but is increasing.
I think I was misled by a youtube video which said the tiles were actively cooled after landing, I think that is wrong.
There will be a much better form of attachment/backing plate designed by SpaceX, why not put some ideas out there of different ways to do it?
The steam formation is what I consider something that will be an issue when the tile heat reaches the felt backing,
I'm suggesting it will likely happen, why not discuss it? I might be wrong but it appears at this stage there is ice formation in the felt backing, as its clearly visible during  test fires ( although one person is suggesting its just dust, problem is its same white cloud visible on the tile side and the non-tile side of the starship ....very much doubt its dust, there will be some dust but the white cloud would not be white if it was just dust)
I'm not sure as yet but its possible steam will form very late in re-entry,  since the heat takes so long to get to the back of the tiles, I will have some data soon on that.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/14/2022 09:59 am
some data from sts-5 from this paper:
https://www.nasa.gov/centers/dryden/pdf/88780main_H-2553.pdf
interesting paper too, showing hypothetical temps of tile system for shuttle with loss of various numbers of tiles.
The pic below shows peak heating period is between 80-50km between time of 6.5min to 20min after start descent, boy that thing looses alot of height in first 6 mins.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/14/2022 10:14 am
the shuttle tile system was tile/rtv/sip/al : tile then red silicone then felt pad then aluminium structure.
They suggest in that paper in last post that at time 15min mark aluminium and red rtv reach peak temp of 50degC and aluminium skin reach same 50degC . They say max structural limit of aluminium as 117 degC  ( not melting point!).
Anyhow for that particular location ( wing base centre not leading edge) the temp is way way below boiling point of water, so will be no issue with steam formation at all. Other locations may differ somewhat, I thought someone had given some really high temps for the back of tiles/aluminium surface but appears not that hot in this area anyhow.
I know the leading edges get really hot not relevant for majority of tiles though.
If this is typical of the majority of the tiles.
I'm thinking very light very thin carbon fibre backing plate, with its rigity and some forms very high temp resistance, would probably suit. 3D printed to get lightest weight/thinest design might just do that job, and could probably match the weight of the 3 stainless pieces being used at present.
Amateur here though, could be wrong.
Title: Re: Starship heat shield
Post by: livingjw on 02/14/2022 12:47 pm
the shuttle tile system was tile/rtv/sip/al : tile then red silicone then felt pad then aluminium structure.
They suggest in that paper in last post that at time 15min mark aluminium and red rtv reach peak temp of 50degC and aluminium skin reach same 50degC . They say max structural limit of aluminium as 117 degC  ( not melting point!).
Anyhow for that particular location ( wing base centre not leading edge) the temp is way way below boiling point of water, so will be no issue with steam formation at all. Other locations may differ somewhat, I thought someone had given some really high temps for the back of tiles/aluminium surface but appears not that hot in this area anyhow.
I know the leading edges get really hot not relevant for majority of tiles though.
If this is typical of the majority of the tiles.
I'm thinking very light very thin carbon fibre backing plate, with its rigity and some forms very high temp resistance, would probably suit. 3D printed to get lightest weight/thinest design might just do that job, and could probably match the weight of the 3 stainless pieces being used at present.
Amateur here though, could be wrong.

Shuttle tiles were bonded onto the aluminum. You missed the red silicone between the aluminum skin and the SIP.

SS skins will have max allowable temperatures much higher than the shuttle's aluminum skin. Probably somewhere in the range of 400-500 C.

John
Title: Re: Starship heat shield
Post by: Slarty1080 on 02/14/2022 01:14 pm
there is a good reason to re-engineer, the stainless steel plates ( 3x) that are embedded into the tiles are the current method of having a type of backing plate. I believe the design is very much flawed. I'm quite convinced spacex will do away with those 3 stainless mounting brackets. Thats my whole purpose of discussing this. The tiles have very little expansion as far as I'm aware, will be quite different to the stainless expansion, and the tiles are fragile. There is a method to increase density of the rear of tiles which was used on shuttle, which is probably what space x has done,
to overcome the issues but I really think its a bad method and wont be used for long.  Hence the reason for discussing backing plate ideas. It certainly is an interesting way to learn about the tiles/heat transfer etc. I'm a novice, knowledge is not great but is increasing.
I think I was misled by a youtube video which said the tiles were actively cooled after landing, I think that is wrong.
There will be a much better form of attachment/backing plate designed by SpaceX, why not put some ideas out there of different ways to do it?
The steam formation is what I consider something that will be an issue when the tile heat reaches the felt backing,
I'm suggesting it will likely happen, why not discuss it? I might be wrong but it appears at this stage there is ice formation in the felt backing, as its clearly visible during  test fires ( although one person is suggesting its just dust, problem is its same white cloud visible on the tile side and the non-tile side of the starship ....very much doubt its dust, there will be some dust but the white cloud would not be white if it was just dust)
I'm not sure as yet but its possible steam will form very late in re-entry,  since the heat takes so long to get to the back of the tiles, I will have some data soon on that.
I imagine every effort will be made to minimise ice build up behind the tiles as it will add mass. But assuming that there is at least a little, what's going to happen to it? Firstly strong vibration will loosen it and break it up and air flow in the lower atmosphere will blow it out during launch. Any that remains after that will sublimate into the vacuum. There really is no chance of steam forming very late in re-entry.
Title: Re: Starship heat shield
Post by: eriblo on 02/14/2022 01:43 pm
there is a good reason to re-engineer, the stainless steel plates ( 3x) that are embedded into the tiles are the current method of having a type of backing plate. I believe the design is very much flawed. I'm quite convinced spacex will do away with those 3 stainless mounting brackets. Thats my whole purpose of discussing this.
I think I speak for many when I say that I do not quite share your conviction :) Remember SpaceX engineers (some of which have decades of experience with these TPS materials and designs) have spent many thousands of hours designing and testing different configurations - of which we have only seen a handful.
The tiles have very little expansion as far as I'm aware, will be quite different to the stainless expansion, and the tiles are fragile. There is a method to increase density of the rear of tiles which was used on shuttle, which is probably what space x has done, to overcome the issues but I really think its a bad method and wont be used for long.  Hence the reason for discussing backing plate ideas.
I do not think we have ever had the chance to see a tile fail from CTE mismatch as opposed to installation or vibration.
Title: Re: Starship heat shield
Post by: daavery on 02/14/2022 02:06 pm
there is a good reason to re-engineer, the stainless steel plates ( 3x) that are embedded into the tiles are the current method of having a type of backing plate. I believe the design is very much flawed. I'm quite convinced spacex will do away with those 3 stainless mounting brackets. Thats my whole purpose of discussing this. The tiles have very little expansion as far as I'm aware, will be quite different to the stainless expansion, and the tiles are fragile.

the 3 steel plates form a 3 point kinematic mount that easily deals with thermal expansion and mechanical vibration. ther is no need for a backing plate or bonding
Title: Re: Starship heat shield
Post by: edzieba on 02/14/2022 02:18 pm
there is a good reason to re-engineer, the stainless steel plates ( 3x) that are embedded into the tiles are the current method of having a type of backing plate. I believe the design is very much flawed.
Then rather than trying to propose solutions to non-problems, you should instead be concentrated on providing some evidence that your belief has any resemblance to reality. That some cracked tiles have 3-fold patterns is not much evidence on its own when the tiles themselves have 3-fold symmetry (as a subset of having 6-fold symmetry).
Title: Re: Starship heat shield
Post by: Tangilinear Interjar on 02/14/2022 03:32 pm
there is a good reason to re-engineer, the stainless steel plates ( 3x) that are embedded into the tiles are the current method of having a type of backing plate. I believe the design is very much flawed. I'm quite convinced spacex will do away with those 3 stainless mounting brackets. Thats my whole purpose of discussing this. The tiles have very little expansion as far as I'm aware, will be quite different to the stainless expansion, and the tiles are fragile.

the 3 steel plates form a 3 point kinematic mount that easily deals with thermal expansion and mechanical vibration. ther is no need for a backing plate or bonding

Further, if there's a problem with differential expansion of the three embedded plates and the tile it would sure be easier to simply engineer a variation of the plate that mitegated the difference. Perhaps a ceramic one.

Years ago a coworker described a particular type of engineer as a guy who would scratch his back by reaching between his legs, technically it could be done but why choose the hardest way possible.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/14/2022 05:55 pm
well this certainly got the thread going again, thanks john my mistake, yup missed that rtv onto the aluminium,
yes the starship stainless temp can withstand much higher than space shuttle aluminium.
Just some more real world data for space shuttle, from sts-1 flight the aluminium skin temps on the wing bottom only got to 50degC ( pic attached from this paper) from nasa dryden
https://ntrs.nasa.gov/api/citations/19820015617/downloads/19820015617.pdf

 I think the space shuttle tiles probably thicker than starship so rear side of tile will be over 50degc, no idea what temp it will go to, unless some data turns up on starship tiles testing. Doesn't matter if my ideas are right or wrong, just interesting process and way of learning in my view.
Well I've certainly learned alot and will look forward to see what developments happen with the tile attachments methods in future.
Title: Re: Starship heat shield
Post by: BT52 on 02/14/2022 06:17 pm
I can speak for us all. As ex-technician and engineer myself. I can see young guys urge to complicate things as much as possible, unnecessarily. So as technician-first and mine scrappy upbringing i can see shortcuts and make problems much simple and easy. Most hard solutions are simple ones. And that takes yrs of experience OR you grew up with that mentality from young age.

SpaceX can ate humble pie for sure. Even Elon himself. Witch is rare and valuable. But anyway more u think about it more make sense. Those tiles are quite well thought out. Bayonet clips needs some work, sure. Same for jigs and floor workers. 

I see biggest problem in mechanical coupling/clipping. More precisely i have in mind exact assembly step when felt sheet is applying. There those clips can and will be inevitable become bended, twisted. Solution for that? Ideally robot can fix this/sewing machine analogy come to mind. But... I would eliminate it if possible or glue it to the individually tile itself and leave those nice snap on bayonet clips for main hull as is.

Kinematic coupling makes totally sense. Bracket can be so easily adapted that is almost funny. Although for real i dint really saw it on ship atm. Full free motion sys at least. Although they could tried couple sys already and i missed it.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 02/14/2022 11:59 pm

The bulk tile material can likely handle >1500 K, the felt is similar or better, the steel should be good to at least 700 K indefinitely (probably more than 900 K at the low durations/cycles involved) and the brackets/mounting pins should be similar or better (they can use a different alloy and are fine with annealed material properties). They should all be ok down to 0 K.


> brackets/mounting pins should be 900K or better

There's very little load on the brackets/mounting pins.  They should be able to hit 1200-1400K if made of the same grade of stainless.  Sure they can't carry much load at that temperature, but they don't have to, unlike the tank.
Title: Re: Starship heat shield
Post by: livingjw on 02/15/2022 02:10 pm

.... I think the space shuttle tiles probably thicker than starship so rear side of tile will be over 50degc, no idea what temp it will go to....


Rear side temperature will go to what they are designed to go to. This will be determined by SpaceX considering the maximum usable temperature of the skin and the effect of the heat that gets through on the gas and inards of the vehicle. It will be in the hundreds of degrees C.

John
Title: Re: Starship heat shield
Post by: brettly2021 on 02/15/2022 07:09 pm
just watching everyday astronaut interview pt2 with Musk, he talks a bit about the heatshield tiles, on thing he mentions is that hot ullage gas goes into the tank, so the inside of the tank has some temperature at some stage.
I think the word he used is ullage ( I had to look it up).
Title: Re: Starship heat shield
Post by: brettly2021 on 02/16/2022 10:01 am
I'm not sure of the relationship between tile thickness and peak temp on back side, lets say as a guess its linear relationship, then if the shuttle tiles reach 50degC peak at rear, and if the starship tiles are say 1/3 the thickness, then maybe ( 3 times shuttle temp)150degC rear side temp of tiles.......probably way out. Can only guesstimate.
I'm going to take a guess at around 100degC or just under.
Another thought, since the tiles are pushed into the pins which sort of latches them, why not have the pins such that when you push them on they latch, if you push them in again they de-latch and spring back out. Would make replacement super fast.
Title: Re: Starship heat shield
Post by: edzieba on 02/16/2022 12:37 pm
I'm not sure of the relationship between tile thickness and peak temp on back side, lets say as a guess its linear relationship, then if the shuttle tiles reach 50degC peak at rear, and if the starship tiles are say 1/3 the thickness, then maybe ( 3 times shuttle temp)150degC rear side temp of tiles.......probably way out. Can only guesstimate.
I'm going to take a guess at around 100degC or just under.
Thickness is not the only factor. Re-entry profile and thus total thermal load and thermal soak time are also major factors in maximum backside temperature.
Quote
Another thought, since the tiles are pushed into the pins which sort of latches them, why not have the pins such that when you push them on they latch, if you push them in again they de-latch and spring back out. Would make replacement super fast.
If you're replacing a tile, you do not care about damaging it so drilling through to reach the latch is not an issue. However, a delatchable tile introduces an unnecessary risk of delatching unintentionally e.g. on encountering a pressure that would not damage the time but provides sufficient force to delatch.
Title: Re: Starship heat shield
Post by: rakaydos on 02/16/2022 01:37 pm
just watching everyday astronaut interview pt2 with Musk, he talks a bit about the heatshield tiles, on thing he mentions is that hot ullage gas goes into the tank, so the inside of the tank has some temperature at some stage.
I think the word he used is ullage ( I had to look it up).
Autogenous pressurization of the tanks. Hot gas oxygen in the liquid oxygen tank, to fill the volume and push the LOX into the pumps. Same with methane gas in the liquid methane tank.

This has nothing to do with the heat shied.
Title: Re: Starship heat shield
Post by: t3kboi on 02/16/2022 02:23 pm
there is a good reason to re-engineer, the stainless steel plates ( 3x) that are embedded into the tiles are the current method of having a type of backing plate. I believe the design is very much flawed. I'm quite convinced spacex will do away with those 3 stainless mounting brackets. Thats my whole purpose of discussing this. The tiles have very little expansion as far as I'm aware, will be quite different to the stainless expansion, and the tiles are fragile. There is a method to increase density of the rear of tiles which was used on shuttle, which is probably what space x has done,
to overcome the issues but I really think its a bad method and wont be used for long.  Hence the reason for discussing backing plate ideas. It certainly is an interesting way to learn about the tiles/heat transfer etc. I'm a novice, knowledge is not great but is increasing.
I think I was misled by a youtube video which said the tiles were actively cooled after landing, I think that is wrong.
There will be a much better form of attachment/backing plate designed by SpaceX, why not put some ideas out there of different ways to do it?
The steam formation is what I consider something that will be an issue when the tile heat reaches the felt backing,
I'm suggesting it will likely happen, why not discuss it? I might be wrong but it appears at this stage there is ice formation in the felt backing, as its clearly visible during  test fires ( although one person is suggesting its just dust, problem is its same white cloud visible on the tile side and the non-tile side of the starship ....very much doubt its dust, there will be some dust but the white cloud would not be white if it was just dust)
I'm not sure as yet but its possible steam will form very late in re-entry,  since the heat takes so long to get to the back of the tiles, I will have some data soon on that.

Yes, please inspire discussion about this - but in this thread, we want to examine and discuss the approach that SpaceX is actually using, and the results from observing their manufacturing and testing of what is actually on the starships.

So... just start a new thread for speculation about mitigation of possible failures in the current design.

NSF is all about signal to noise.  In its own thread, you will get discussion from people who are interested in your ideas.   Continuing to argue/refute/justify yourself here, where there is a demonstrated antipathy to your ideas, is a waste of everyone's time, and is bringing the signal level way down.

Like this post I am making - it is unnecessary noise, and does not contribute anything to the actual subject.

Title: Re: Starship heat shield
Post by: OTV Booster on 02/16/2022 04:40 pm
I'm not sure of the relationship between tile thickness and peak temp on back side, lets say as a guess its linear relationship, then if the shuttle tiles reach 50degC peak at rear, and if the starship tiles are say 1/3 the thickness, then maybe ( 3 times shuttle temp)150degC rear side temp of tiles.......probably way out. Can only guesstimate.
I'm going to take a guess at around 100degC or just under.
Another thought, since the tiles are pushed into the pins which sort of latches them, why not have the pins such that when you push them on they latch, if you push them in again they de-latch and spring back out. Would make replacement super fast.
Using your logic, that would be not 50deg C but 323deg K. I don't know one way or the other if it works that way.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/18/2022 12:04 pm
cyro test of sn20 if you go to this video:
https://youtu.be/J9VxcPhTqHU?t=787
starting at 13:07 ( put vid in hd and slow it down) its becomes clear that a white vapour is being dispelled between the tile gaps ( vertical row of tiles on right), white vapour is also coming off the exposed ice not covered with tiles, can only assume same process is occuring behind the tiles as with the exposed tiles. I suggest its pretty good evidence that there is ice behind the tiles in the felt. Assuming its sublimation of the ice giving rise to the vapour.
Title: Re: Starship heat shield
Post by: RoboGoofers on 02/18/2022 07:17 pm
please just start a new thread of your own.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/19/2022 10:34 am
Thread was started to discuss the nature and geometry of the tiles.
I'm quite fascinated by these tiles, how they behave and their properties. So have gone back to the youtube video showing the shuttle tiles being taken out of the oven and picked up by hand. I've gone through the video and used the timestamps to try and get some 'feel' for how they operate.
Video can be viewed here:
https://www.youtube.com/watch?v=Pp9Yax8UNoM (https://www.youtube.com/watch?v=Pp9Yax8UNoM)
Two small cubes are 9lb per sq foot, large rectangular piece under cubes is 22 lb per sq foot ( substantially denser).
Oven temp is 2300degF cubes been in there for a couple of hours so should have a fairly uniform temp throughout.
Lab guy mentions that the cubes are approx 2200degF when taken out of oven.
Picture attached shows the cubes being removed from oven, first fraction of a second when removed you can see already the edges and corners have cooled substantially. After 2 seconds corners edges well defined cool spots.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/19/2022 10:46 am
the video does some reveal some interesting aspects of the tiles. There are a number of modes of heat transfer at play.
The heat within the tile you could say is a type of conductive heat transfer but would also involve radiant heat transfer.
( Convection probably not relevant within the tile). Next pic shows where the tile is picked up by fingers at each corner occurs 9 sec after taken out of oven, very short time period. What is interesting is the heat pattern left on the rectangular large base tile. As the tile is lifted off the base there is a flare of bright light, which at 9.2sec you can see leaves a fuzzy edged square somewhat larger than the small cube, at 9.75sec a well defined bright coloured square is left on the bottom tile where the cube was sitting.
So there is radiant heat leaving both the top cube and bottom rectangular tile and interacting. Since the operators hands are not burned the radiant heat appears to not be acting over a very large distance ( absorbed quite efficiently by the air I assume).

Title: Re: Starship heat shield
Post by: brettly2021 on 02/19/2022 10:51 am
Next sequence shows the outline of the cube where it was removed from base tile changing colour, from bright white to red to a dull red almost black, this occurs over a period of approx 13 seconds. The colour of course gives some indication of the temperature.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/19/2022 10:57 am
last sequence show cooling off of the small cube, over a period of 24 seconds, you can see the corners and edges continue to cool and change to blackish colour. I was curious as to why the corners and edges cool off more rapidly and I think I have a reasonable explanation:
The heat inside the cube can be visualised as a sphere, where the heat from the centre conducts outwards in all directions at the same rate. It takes longer for the heat too reach the edges than the face of the cube, and longer for the heat to reach the vertices ( corners) than it takes to reach the edges. This seems pretty obvious and the rate of heat transfer is very very slow through the cube.
But at the surface radiant heat transfer can occur to the surrounding air, that rate of heat transfer is much faster than the rate at which heat transfers through the cube.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/19/2022 11:06 am
So the sphere in cube pic above, in the top pic its easy to see that the middle of the face of each side recieves heat from centre of cube before the edge or corner, it just takes longer for the heat to get there ( edges/corners) as its further distance from the centre , so you could look at it this way:
it takes longer for radiant heat ( taken away from surface) to be replaced by heat within from within the cube at the edges and corners and hence are cooler. The vertices ( corners are coolest points )
This might seem obvious in hindsight but took me a while to understand what was going on.
Although this is somewhat different process to what occurs when tiles are on the shuttle or starship, the heat transfer is from one side of tile too the other, it useful for predicting hot/cool spots  on the rear of the tiles. Since at present rear of tiles is not uniform flat surface there will be a temperature profile at the rear of the tiles, depending on distance from heat source.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/19/2022 11:12 am
Regarding heat transfer within the tiles, I dont think it would be simply coduction. Since there is silica fibres and majority of the tile is made of air ( or whatever gas is present during manufacture process), it wont be just conduction via the fibres. I'm guessing it might go a bit like this:
conduction across tiny fibre then radiant transfer across air, then absorption into next fibre, then conduction and radiant transfer, would be quite complex I think.
Title: Re: Starship heat shield
Post by: CMac on 02/19/2022 11:53 am
Have a look at https://en.wikipedia.org/wiki/Heat_equation (https://en.wikipedia.org/wiki/Heat_equation)

There is a combination of heat capacity of the material and conductivity of the material. Probably very large % is radiant transfer between fibers. Convection cannot happen in small voids and conductivity of air is very low. Conduction along fibers is along long random paths while radiative path is direct.

Think about a hot teaspoon - approximately one dimensional problem. You lift out of hot water after being fully immersed. Then you hold one end in your fingers (not so hot as to burn). Heat quickly leaves the metal at that end, into your finger (and transported away by blood flow). You feel this as very hot. It feels like it cools down a bit when that end of spoon cools down, but the other end is actually still quite hot. It takes time for heat to transfer along the spoon and the rate of transfer depends on the differences in temperature along the spoon. The hottness you feel is related to the rate of energy transfer into your finger.

Note that air does not absorb much radiative heat at all. The heat loss from the cube is largely radiated out to the walls and people in the room. Some convection too but at high temperature, I guess the radiative component is much larger.
Title: Re: Starship heat shield
Post by: livingjw on 02/19/2022 03:12 pm
I did this model of the LI-900 material a couple of years ago. Pretty good fit of the thermal conductivity as a function of pressure and temperature. Pressure is in bars, temperature in degrees K.

Note: this thermal conductivity model will work for transient heat transfer problems. I just showed how it works with steady state heat transfer. Reentry is obviously going to be transient.

BTW, LI-900 density is ~9 lb per cubic foot, (not sq foot)

John
Title: Re: Starship heat shield
Post by: Redclaws on 02/19/2022 03:22 pm
last sequence show cooling off of the small cube, over a period of 24 seconds, you can see the corners and edges continue to cool and change to blackish colour. I was curious as to why the corners and edges cool off more rapidly and I think I have a reasonable explanation:
The heat inside the cube can be visualised as a sphere, where the heat from the centre conducts outwards in all directions at the same rate. It takes longer for the heat too reach the edges than the face of the cube, and longer for the heat to reach the vertices ( corners) than it takes to reach the edges. This seems pretty obvious and the rate of heat transfer is very very slow through the cube.
This is pretty well correct, except for that last sentence.

But at the surface radiant heat transfer can occur to the surrounding air, that rate of heat transfer is much faster than the rate at which heat transfers through the cube.

This does not obviously follow.  The transfer rate to the outside doesn’t need to be faster than the internal rate for the differential to occur - it could be much slower and the exact same differential would occur, it would just be relatively smaller.  The size of the differential between different parts of the cube will be a function of the relative rate within the cube vs transfer to the outside, true enough, but its *existence* is not.  The rate of heat transfer within the cube is not infinite, therefore any loss to the outside will result in a temperature differential that looks like this.
Title: Re: Starship heat shield
Post by: equiserre on 02/19/2022 10:01 pm
Please please Starship heat shield only. Dont ruin one of the 4 or 5 good threads.
Title: Re: Starship heat shield
Post by: ETurner on 02/19/2022 10:09 pm
Please please Starship heat shield only. Dont ruin one of the 4 or 5 good threads.
Could use some thread trimming at this point.
Title: Re: Starship heat shield
Post by: livingjw on 02/20/2022 01:54 am
The attached NASA 2012 paper is great for those interested in estimating tile thickness required to maintain skin and tank temperatures during reentry. It develops a simple rapid method for estimating tile thickness and shows how it correlates with much more detailed methods. Answers are within 10-20 % before any corrections are made. With corrections, it looks like it could be kept to below 10% error. Good rapid robust method.

John
Title: Re: Starship heat shield
Post by: brettly2021 on 02/21/2022 03:22 am
excellent feedback thankyou, will go over those papers shortly,  shuttle tiles and starship tiles seem to be the same material, I think very relevant.
Title: Re: Starship heat shield
Post by: livingjw on 02/21/2022 01:40 pm
From latest pictures on L2, it appears that the gap between tiles is 2-3 popsicle stick thicknesses. These guys know high tech!
 :^)

John
Title: Re: Starship heat shield
Post by: edzieba on 02/21/2022 03:03 pm
From latest pictures on L2, it appears that the gap between tiles is 2-3 popsicle stick thicknesses. These guys know high tech!
 :^)

John
Or possible 1 carpenter's pencil.
Title: Re: Starship heat shield
Post by: livingjw on 02/21/2022 08:45 pm
From latest pictures on L2, it appears that the gap between tiles is 2-3 popsicle stick thicknesses. These guys know high tech!
 :^)

John
Or possible 1 carpenter's pencil.

Sure looked like one.

John
Title: Re: Starship heat shield
Post by: WiresMN on 02/21/2022 10:43 pm
From latest pictures on L2, it appears that the gap between tiles is 2-3 popsicle stick thicknesses. These guys know high tech!
 :^)

John
Or possible 1 carpenter's pencil.

Sure looked like one.

John

Do you know how much those tile grout line spacers cost at home depot. This is SpaceX not NASA.   ;D

I love the use what you have approach.  It reminds me of a farmer I worked for. Bailing wire was a luxury item.
Title: Re: Starship heat shield
Post by: brettly2021 on 02/28/2022 04:02 am
last cyro test on s21 a few days ago, no cold vapour appears to come out between the tiles, thought video is not very close up, so seems possible as someone mentoned previously ( sorry cant remember who it was) that the backing felt might have a hydrophobic outer coating, to prevent ice build up behind tiles.
There is one area that does have vapour coming out between the tiles during cyro test, have pointed arrow towards it.
there is not a huge amount of vapour coming off the exposed cold areas either, so guessing it was low humidity day
Title: Re: Starship heat shield
Post by: brettly2021 on 03/03/2022 04:53 am
just having a look at John L's papers, really nice work. What I think is interesting is that what appears on the surface to be a simple tile, in order to  predict its nature mathematically is an extremely complex matter.
The formulas etc given in the nasa paper in last link put up by John is a work of art and would require some time to understand it well. Thanks John for simplifying it down to something that is much easier to understand in your paper.
Would you be able to comment on the graph attached, I'm trying to understand it.
 Lets say thickness of tile is 2cm
then some results are ( just approximate):
outside max: 330degC ( 600K) gives inner max of -60degC ( diff: 270degC)
                    530degC ( 800K) gives inner max of 280degC ( diff: 250degC)
                    730degC ( 1000k) gives inner max of 560degC ( diff: 170degC)
                    930degC ( 1200k) gives inner max of approx 780degC ( extrapolated) ( diff: 150degC)
where diff : is difference between outer and inner wall max temps.
Would you agress with this interpretation of your graph and would anyone know the exact thickness of the majority of tiles on the underbelly of the starship?
sorry only degC makes sense to me.
Title: Re: Starship heat shield
Post by: livingjw on 03/03/2022 06:31 pm
just having a look at John L's papers, really nice work. What I think is interesting is that what appears on the surface to be a simple tile, in order to  predict its nature mathematically is an extremely complex matter.
The formulas etc given in the nasa paper in last link put up by John is a work of art and would require some time to understand it well. Thanks John for simplifying it down to something that is much easier to understand in your paper.
Would you be able to comment on the graph attached, I'm trying to understand it.
 Lets say thickness of tile is 2cm
then some results are ( just approximate):
outside max: 330degC ( 600K) gives inner max of -60degC ( diff: 270degC)
                    530degC ( 800K) gives inner max of 280degC ( diff: 250degC)
                    730degC ( 1000k) gives inner max of 560degC ( diff: 170degC)
                    930degC ( 1200k) gives inner max of approx 780degC ( extrapolated) ( diff: 150degC)
where diff : is difference between outer and inner wall max temps.
Would you agress with this interpretation of your graph and would anyone know the exact thickness of the majority of tiles on the underbelly of the starship?
sorry only degC makes sense to me.

You appear to be reading it correctly. Remember this is a steady state case and will be worse than the reentry heating pulse.

Tile plus felt insulation, is probably between 2 and 3 inches (5-7.6 cm).

See the following for some recent discussion:
https://forum.nasaspaceflight.com/index.php?topic=55857.msg2345990#msg2345990
Title: Re: Starship heat shield
Post by: brettly2021 on 03/06/2022 10:29 am
thanks for feedback and link, if anyone knows the actual thickness of a belly tile, your graph will show us the actual rear temperature, at the moment looks like its going to be pretty darn hot.
Title: Re: Starship heat shield
Post by: Keldor on 03/06/2022 05:34 pm
thanks for feedback and link, if anyone knows the actual thickness of a belly tile, your graph will show us the actual rear temperature, at the moment looks like its going to be pretty darn hot.

Well, looking up the stats for 304 and 310 stainless steel alloys, the annealing temperature is typically a bit above 1000C for 90 minutes, followed by water or air quenching.  It's hard to judge one long annealing bake versus 100 or so short reentry moments of peak heating over the lifetime of a vehicle, but it seems reasonable that peak heating could approach these sorts of temperatures.  Pretty darn hot indeed.
Title: Re: Starship heat shield
Post by: edzieba on 03/06/2022 09:07 pm
thanks for feedback and link, if anyone knows the actual thickness of a belly tile, your graph will show us the actual rear temperature, at the moment looks like its going to be pretty darn hot.
Note that the graph is for steady-state conditions, whereas EDL is a limited heat-pulse. Once heating stops, heat soaked into the insulator is now being conducted away to both faces rather than just the inner face in the steady-state regime (with the hottest region near the outer skin also being closest to the new cold surface), and you have a limited amount of energy being input into the system rather than the unlimited quantity of the steady state model.
Title: Re: Starship heat shield
Post by: eriblo on 03/06/2022 10:48 pm
thanks for feedback and link, if anyone knows the actual thickness of a belly tile, your graph will show us the actual rear temperature, at the moment looks like its going to be pretty darn hot.
Note that the graph is for steady-state conditions, whereas EDL is a limited heat-pulse. Once heating stops, heat soaked into the insulator is now being conducted away to both faces rather than just the inner face in the steady-state regime (with the hottest region near the outer skin also being closest to the new cold surface), and you have a limited amount of energy being input into the system rather than the unlimited quantity of the steady state model.
The model looks like it is for steady state with a conducted heat load of 909 W/m2. The heat capacity of a 4 mm SS hull is about 16kJ/m2K so it would heat up at a rate of ~200K/h for these thickness and temperature combinations...

So unless I am mistaken these particular graphs have almost no relevance ro temperatures during EDL.
Title: Re: Starship heat shield
Post by: livingjw on 03/07/2022 01:00 pm
thanks for feedback and link, if anyone knows the actual thickness of a belly tile, your graph will show us the actual rear temperature, at the moment looks like its going to be pretty darn hot.
Note that the graph is for steady-state conditions, whereas EDL is a limited heat-pulse. Once heating stops, heat soaked into the insulator is now being conducted away to both faces rather than just the inner face in the steady-state regime (with the hottest region near the outer skin also being closest to the new cold surface), and you have a limited amount of energy being input into the system rather than the unlimited quantity of the steady state model.
The model looks like it is for steady state with a conducted heat load of 909 W/m2. The heat capacity of a 4 mm SS hull is about 16kJ/m2K so it would heat up at a rate of ~200K/h for these thickness and temperature combinations...

So unless I am mistaken these particular graphs have almost no relevance ro temperatures during EDL.

- It was just an example to demonstrate the use of the Li-900 model. I had the steady state example around for a hypersonic cruiser model I was working on. In that situation the heat flux into the vehicle was absorbed by an internal thermal management system which ultimatly dumped it into the fuel.

- For reentry you should implement the NASA report model I posted.

John
Title: Re: Starship heat shield
Post by: brettly2021 on 03/08/2022 03:05 am
I posted a graph for space shuttle a few pages back, showed the peak heating region lasted for about 14minutes for shuttle, assuming will be similar for starship, so although referred to as a heat pulse, that is a significant amount of time where high temperatures are sustained.
Title: Re: Starship heat shield
Post by: schuttle89 on 03/08/2022 04:15 pm
I posted a graph for space shuttle a few pages back, showed the peak heating region lasted for about 14minutes for shuttle, assuming will be similar for starship, so although referred to as a heat pulse, that is a significant amount of time where high temperatures are sustained.
I could be very off on this as I took literally only one aerospace engineering class as an elective, but it seems to me that starship will renter slightly faster than the shuttle as it has significantly less cross range. Or I guess maybe a better way to say it is as a question: how does the difference in shape between shuttle and starship change the thermal load the heat shield experiences? Less or more total heat flux? Greater or lesser peak flux? I know there is speculation up thread, so is it safe to assume the shuttle is a good model?
Title: Re: Starship heat shield
Post by: jpo234 on 03/08/2022 04:49 pm
Interesting yet unconfirmed post from Avalaerion (https://www.reddit.com/user/Avalaerion/):
Within the next few years we will see metallic/ceramic alloy tiles. From the trials I have seen they look really futuristic. The surface when polished looks rainbow shimmery, like silicon solar cells, or labradorite (https://www.reddit.com/r/spacex/comments/so3e8g/comment/hzughex/)
Title: Re: Starship heat shield
Post by: brettly2021 on 03/09/2022 10:21 am
reason I posted regarding the 14minute period peak heating region ( from 80k to 50km) of the shuttle is that some posters mentioned that the tiles see a heat pulse, in my mind the word 'pulse' is associated with a very short time frame, the pulse of a heart for example is very quick, pulses in electronics tend to be very quick. Since the period of peak heating will be what I consider a fairly long period ( on the order of almost 1/4 of an hour) I just wanted to clear up exactly what the other contributors are meaning by a heat 'pulse'. Pulse is probably not the best descriptor for it.
How close it will be to starship peak heating period I cannot say.
Title: Re: Starship heat shield
Post by: sebk on 03/09/2022 10:43 am
Pulse is a physical/engineering term. Don't confuse it with common meanings.

Because of very low thermal conductivity you get relatively modest stream of energy passing through the shield. This energy then slowly heats up what's behind the shield.

For example assume 500m^2 of surface (~heat shield size). Assume 1kW/m^2 heat pass rate. Assume 1000s long heat pulse:

500 [m^2] * 1 [kW/m^2] * 1000 [ s] = 500 000 [ kW*s = kJ]

Assume the mass behind is 100t (100Mg = 100 000kg) and let's go with stainless steel specific heat of 0.5kJ/kg.K.
500 000 [kJ] / 100 000 [kg] / 0.5 [kJ/kg.K] = 10 K -- the over 15 minutes of heating would warm up the entire structure by 10K on average, without the heat being dumped anywhere.
Title: Re: Starship heat shield
Post by: Redclaws on 03/09/2022 11:24 am
reason I posted regarding the 14minute period peak heating region ( from 80k to 50km) of the shuttle is that some posters mentioned that the tiles see a heat pulse, in my mind the word 'pulse' is associated with a very short time frame, the pulse of a heart for example is very quick, pulses in electronics tend to be very quick. Since the period of peak heating will be what I consider a fairly long period ( on the order of almost 1/4 of an hour) I just wanted to clear up exactly what the other contributors are meaning by a heat 'pulse'. Pulse is probably not the best descriptor for it.
How close it will be to starship peak heating period I cannot say.

Pulse is being used in a technical sense here to indicate that a steady state is not reached.  Basically it’s short *enough* in duration that one should not model it as a steady state.  That’s all it means.
Title: Re: Starship heat shield
Post by: livingjw on 03/09/2022 01:23 pm
The NASA paper on transient heat pulse is clearly defined on pages 4 and 28 with diagrams and times.

John
Title: Re: Starship heat shield
Post by: brettly2021 on 03/10/2022 09:09 am
very interesting, I see page 28 reference does make it fairly clear, in particular that graph, using that graph ( figure 17) and using the equivalent heating pulse square ( area under the graph), it goes from 200sec to 1400 sec, which is 20minute time period .

That paper is really something, figure 16 and equation 27  they have discovered an interesting correlation ( I cant say I understand the relevance of the correlation)  the fact that they made some discovery using mathematics is quite an impressive achievement).
Title: Re: Starship heat shield
Post by: brettly2021 on 03/10/2022 09:15 am
anyone know what caused the temperature to jump back up shown in fig 17 by red circle.
Title: Re: Starship heat shield
Post by: livingjw on 03/10/2022 02:49 pm
anyone know what caused the temperature to jump back up shown in fig 17 by red circle.

Could be the S turns to manage flight path.

John
Title: Re: Starship heat shield
Post by: InterestedEngineer on 03/10/2022 06:30 pm
Simulation video shows tile vibration up close.  Start at about 4:30 or so.

Realistic or no?

https://www.youtube.com/watch?v=NOT4-XwU9qQ
Title: Re: Starship heat shield
Post by: eriblo on 03/10/2022 07:53 pm
Simulation video shows tile vibration up close.  Start at about 4:30 or so.

Realistic or no?

https://youtube.com/watch?v=NOT4-XwU9qQ
I wonder if it is intentional or just an artifact of the camera shake implementation - in any case I would say not realistic.

The tiles are light and fairly rigidly attached to the hull so large scale movement like that in the video would likely require vibration amplitudes of 100's of gs. Any resonant frequencies would be much higher.
Sideways movement like that - i.e. a large fraction of the attachment pin length - would also lead to metal fatigue within minutes although I suspect the tiles would completely crumble away before that.

In reality the tiles are obviously not expected to move more than a mm or so as there are no gap fillers in between them and tiles contacting each other would rapidly damage them.
Title: Re: Starship heat shield
Post by: Keldor on 03/10/2022 09:04 pm
Simulation video shows tile vibration up close.  Start at about 4:30 or so.

Realistic or no?

https://youtube.com/watch?v=NOT4-XwU9qQ
I wonder if it is intentional or just an artifact of the camera shake implementation - in any case I would say not realistic.

The tiles are light and fairly rigidly attached to the hull so large scale movement like that in the video would likely require vibration amplitudes of 100's of gs. Any resonant frequencies would be much higher.
Sideways movement like that - i.e. a large fraction of the attachment pin length - would also lead to metal fatigue within minutes although I suspect the tiles would completely crumble away before that.

In reality the tiles are obviously not expected to move more than a mm or so as there are no gap fillers in between them and tiles contacting each other would rapidly damage them.

It could also be an optical illusion caused by the virtual camera just happening to line up with the edges of the tiles in such a way that a tiny bit of camera movement (the camera shake in this case) reveals or hides the white backing.  That camera shake is pretty substantial on this scale, representing the camera moving around by a few inches, and it's done by translating the camera, not rotation as would be seen in a real life camera (you can tell because there's no shake on the Earth, just the rocket).
Title: Re: Starship heat shield
Post by: Redclaws on 03/10/2022 09:10 pm
Simulation video shows tile vibration up close.  Start at about 4:30 or so.

Realistic or no?

https://www.youtube.com/watch?v=NOT4-XwU9qQ

This looks to me like the simulation is showing the ship shaking under thrust.  Nothing tile specific.
Title: Re: Starship heat shield
Post by: r8ix on 03/10/2022 09:38 pm
Simulation video shows tile vibration up close.  Start at about 4:30 or so.

Realistic or no?

https://www.youtube.com/watch?v=NOT4-XwU9qQ

This looks to me like the simulation is showing the ship shaking under thrust.  Nothing tile specific.

The skin's a bit wrinkly, too. Heatshield is shaking monolithically relative to the ship. Both are likely due to simulation errors / simplifications / assumptions.
Title: Re: Starship heat shield
Post by: IWanda on 03/25/2022 08:29 pm
I noticed in a recent NSF daily update youtube video that the tiles on the top of the "bulge" that hold the upper flap/fin are much thicker than most tiles (estimating 3-4x) (sorry no link, can't find which day).  I assume they are the same material, so the model must have much more heating at that point.  Is it expected to be that different?
Title: Re: Starship heat shield
Post by: livingjw on 03/26/2022 12:35 am
I noticed in a recent NSF daily update youtube video that the tiles on the top of the "bulge" that hold the upper flap/fin are much thicker than most tiles (estimating 3-4x) (sorry no link, can't find which day).  I assume they are the same material, so the model must have much more heating at that point.  Is it expected to be that different?

It has a smaller radius and protrudes from the surface so the BL will be thin and the shock close.

John
Title: Re: Starship heat shield
Post by: su27k on 04/09/2022 02:52 am
https://twitter.com/RGVaerialphotos/status/1512604307195150336

Quote
Tile RUD
Title: Re: Starship heat shield
Post by: su27k on 04/09/2022 02:55 am
https://twitter.com/RGVaerialphotos/status/1512531763457040384

Quote
S24 nose cone close ups

Title: Re: Starship heat shield
Post by: su27k on 04/17/2022 12:48 pm
https://twitter.com/RGVaerialphotos/status/1514974518686715906

Quote
Aft static aero leading edge
Title: Re: Starship heat shield
Post by: BT52 on 04/17/2022 02:46 pm
What are those seals made from?
Title: Re: Starship heat shield
Post by: Twark_Main on 04/19/2022 06:04 am
What are those seals made from?

ITAR-ium? ;)

If anything is "dual use," it's steerable re-targetable reentry vehicles.
Title: Re: Starship heat shield
Post by: brettly2021 on 04/21/2022 09:05 am
some nice detail in that photo:
green arrow can see fibrous material rapped around the edges of the tiles as tile spacer.
red arrow can see the material is very fibrous: I wonder if its asbestos based?
can also see that tiles are likely just bonded directly to the aluminium frame ( rtv glue?)
Title: Re: Starship heat shield
Post by: brettly2021 on 04/21/2022 09:08 am
closeup showing the fibrous nature of the filler material ( I've noticed this fibre sticking out in other photos also)
Title: Re: Starship heat shield
Post by: eriblo on 04/21/2022 10:43 am
some nice detail in that photo:
green arrow can see fibrous material rapped around the edges of the tiles as tile spacer.
red arrow can see the material is very fibrous: I wonder if its asbestos based?
can also see that tiles are likely just bonded directly to the aluminium frame ( rtv glue?)
If by "asbestos based" you mean "made from high temperature ceramic fibers" then that is most likely the case, just like the white insulation and the tiles themselves. The exact composition might be the same or optimized for each application, we have no way of knowing unless they tell us.

If you mean that they are using actual asbestos then obviously no from the way they are handling it. I also believe that asbestos has a lower temperature limit than many safer alternative fibers.

I am curious about why you think the structure is aluminium instead of stainless steel?
Title: Re: Starship heat shield
Post by: brettly2021 on 04/22/2022 10:38 am
I think your right it could well be stainless steel, more likely than aluminium, I was simply thinking at the time of the shuttle tile under surface, no other reason than that.
They were drilling tiles without masks not so long ago, alot of dust was produced,  I mentioned on here the risk of silicosis at the time, they changed to mask wearing soon after.
So there is no guarentee safe work practices indicate its not asbestos.
Title: Re: Starship heat shield
Post by: edzieba on 04/22/2022 10:57 am
Nothing to indicate it is Asbestos either, and no good reason to use Asbestos for TPS either (as far as I am aware Asbestos has not been used for spacecraft TPS).
The current tiles are very, very close to the STS tiles in composition and method of manufacture. The adhesion mechanism for non-pin tiles is also very similar (RTV Silicone backing with inter-tile batting), so it is very likely the gap-fillers are also the same or very similar silica fibre pads.
Title: Re: Starship heat shield
Post by: brettly2021 on 04/23/2022 03:29 pm
some sound reasoning there, I wonder what effect ( if any) those rather long fibres sticking out will have on the plasma?
Title: Re: Starship heat shield
Post by: eriblo on 04/23/2022 03:51 pm
some sound reasoning there, I wonder what effect ( if any) those rather long fibres sticking out will have on the plasma?
They will melt away within seconds of entry interface.
Title: Re: Starship heat shield
Post by: su27k on 04/29/2022 04:11 am
S21's heat shield being dismantled

https://twitter.com/RGVaerialphotos/status/1519839018795638784
Title: Re: Starship heat shield
Post by: su27k on 05/15/2022 09:15 am
https://twitter.com/NicAnsuini/status/1524830414581420041

Quote
T I L E S

- @NASASpaceflight
Title: Re: Starship heat shield
Post by: KBK on 05/17/2022 03:15 pm
Pardon the moment of idiotic ideas, as an intrusion. this may have been considered before, and probably has.

If the problem is the flap junction, then a micro ridge, of the right shape (along the length of the gap), can disturb the flow around that gap, possibly, just enough.. so as to lower the danger provided by said gap.

Flutter, resonance, thermal accumulation (in all possible forms and ways, with the in situ mess), etc, are all additional problems (there are notable potential issues to cover) that need be considered but there may be some merit to it. A couple of percentage points may make all the difference in the world, depending on what the simulated/experimental/real-world data says.

i see that  the mesh used to support the overall stability of the tiles is still there. in the video of the star ship 24? in the given bay, where we had a good close look...which was in the Tim Dodd video of recent, I thought that the mesh 'resonance and vibration support/stability' methodology had been abandoned for going back to a pure gluing or elastic support of the underlying thermal Blanket.

Which I thought would lead to problems, problems that might make it the more error prone path than something like a separate 'away from the mount pins in all ways' corner support for the tiles, as i had earlier suggested, where the corners (adjacent to one another), in order to prevent 'moving living near chaotic patterns' akin to cymatics, freak waves, etc..the threat of tile corners slapping each other... had to have some sort of secondary connected support in their motions. I suggested a mounting pad of a sort, shaped in a certain way. Where individual 'separate from the mount pins' support for vibration control is enacted, and the comers move slightly with respect one another, in a paired or shared motion, thus helping reduce tile slapping under complex load. Critically, this includes corner damping and is thus is a two-fer, which is just good engineering if one can pull it off. a subtle continual draining of the vibration load can go a long long way. Reduction of capacity to emerge into complex building resonance. In most cases a slight drain is all it takes. https://www.youtube.com/watch?v=S-PJMycvmA8

I said so and provided a quick idea on that, as it was, as a post and set of thoughts.. just me trying to properly and (as much as possible) attempt to fully define the emergent problem at hand..and in that.. proffer a quickly idealized solution. (I spent some good 20 years working on this area, across other industries and applications)

But the idea of the mesh (which appeared soon after), I thought was a brilliant and simple way past the complexity and residual issues of individual thermal pad underlying supports that achieve a similar thing.

The mesh's effectiveness is TBD, but it is still a great idea, in all ways it could be. Because there are so many tiles under such a complex load, a magnitude better level of functionality in the real world might be achieved by some very minimal changes in vibrational/damping issues.

It's a threshholding issue, about the overall ship surviving, or not. As subtle change in overall tile stability can possibly make huge differences (magnitudes) in overall ship 'success'. And if it works, seek more overhead. As one should, relatively speaking, never stop seeking more overhead when dealing with space.

Just like the control of the booster proper, re grid fins. Damping of resonance(through the various encountered atmospheric envelopes), just enough damping, is all that is required for controlling the ship. Elon went into this a bit, near the end of the recent Tim Dodd video.

They don't need total control or gross control, they just need enough continual minimal damping in order to get the job done, and the result is magnitudes better, overall, compared to no controls, and the excess mass of too large a grid, etc. Micro correction within a window of application. And they probably think they have enough complex overhead in their emergent ideas on grid fin application.

Tile stability, as a complex integrated issue - is similar.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 05/27/2022 04:40 pm
Ooops, vent causes tiles to fly in the breeze

https://twitter.com/kspaceacademy/status/1530209785500557315
Title: Re: Starship heat shield
Post by: JCopernicus on 05/27/2022 06:19 pm
Ooops, vent causes tiles to fly in the breeze

https://twitter.com/kspaceacademy/status/1530209785500557315

I thought those were birds on first watch.  ;D
Title: Re: Starship heat shield
Post by: brettly2021 on 05/28/2022 03:45 pm
heres an interesting homemade tps tile:
https://www.youtube.com/watch?v=E7MxSIkpcrk
Title: Re: Starship heat shield
Post by: edzieba on 05/29/2022 11:39 am
heres an interesting homemade tps tile:
https://www.youtube.com/watch?v=E7MxSIkpcrk
Well, it has the shape in common, I guess. But that's about it.
Title: Re: Starship heat shield
Post by: Bob Shaw on 05/29/2022 11:56 am
Nothing to indicate it is Asbestos either, and no good reason to use Asbestos for TPS either (as far as I am aware Asbestos has not been used for spacecraft TPS).
The current tiles are very, very close to the STS tiles in composition and method of manufacture. The adhesion mechanism for non-pin tiles is also very similar (RTV Silicone backing with inter-tile batting), so it is very likely the gap-fillers are also the same or very similar silica fibre pads.

When I was attending the Cosmonauts exhibition at the Science Museum in London I chatted with the Curator of the event. He said they'd had a difference of opinion - cultural - with the Russians as the Vostok and Voskhod capsules were shedding asbestos. The Russians thought nothing of it, the Londoners were unhappy! During the exhibition itself the flown vehicles were safely behind glass!

There are many photographs showing fibrous material flaking off the early Soiviet vehicles post-landing, so yes, asbestos has been flown in space as part of TPS.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 05/29/2022 10:09 pm
Nothing to indicate it is Asbestos either, and no good reason to use Asbestos for TPS either (as far as I am aware Asbestos has not been used for spacecraft TPS).
The current tiles are very, very close to the STS tiles in composition and method of manufacture. The adhesion mechanism for non-pin tiles is also very similar (RTV Silicone backing with inter-tile batting), so it is very likely the gap-fillers are also the same or very similar silica fibre pads.

When I was attending the Cosmonauts exhibition at the Science Museum in London I chatted with the Curator of the event. He said they'd had a difference of opinion - cultural - with the Russians as the Vostok and Voskhod capsules were shedding asbestos. The Russians thought nothing of it, the Londoners were unhappy! During the exhibition itself the flown vehicles were safely behind glass!

There are many photographs showing fibrous material flaking off the early Soiviet vehicles post-landing, so yes, asbestos has been flown in space as part of TPS.

Whatever the material is, it's not being treated specially by SpaceX, as they have the stuff flapping all over the place and being installed/scrapped by people who are not using respirators or bunny suits.

There's only one kind of material that meets temperature specs and generally-safe-for-humans requirements, and is used all over oil country such as Texas and is relatively low cost and relatively light.   That's why that's the most likely material.

It's a safe form of mineral wool, only been around in the last 25 years or so.  A half a dozen manufacturers judging by Google.
Title: Re: Starship heat shield
Post by: su27k on 05/30/2022 03:33 am
Interesting thread about Shuttle tiles, hopefully Starship tiles can avoid the complex procedure related to water intrusion:

https://twitter.com/DrPhiltill/status/1530776472675405824

Quote
Another interesting fact: a lot of the darker, new tiles (the replacements) are located over antennas, which we sometimes used as convenient access points for airframe structural inspections between flights. /1



2/ You can tell these are the antenna locations by the four white chevrons painted onto the tiles around each antenna. We used those to align ground-testing antennas to verify the comm/nav systems worked before the next flight.



3/ Another interesting fact: each tile has a hole in it with a white circle painted around the hole so technicians could find it. That hole was used to inject water-proofing spray into the inside of every single tile before each rollout to the launch pad. I marked a few examples:



4/ Oh, but why did we have to spray water-proofing spray inside each and every Space Shuttle tile before every launch? Those tiles protect against the super hot plasma during re-entry from space, and we know there isn’t any water up there! I’m glad you asked…



5/ The problem was that the Space Shuttle had to sit through frequent rainstorms while it was on the launch pad, and if rain seeped into the tiles then it would add a huge amount of weight to the vehicle, which could prevent it from achieving the desired orbit.



6/ But why weren’t the tiles simply sealed so the rain couldn’t get in? I mean, if you had to cut a hole in the surface to inject the water-proofing spray, then the water shouldn’t be able to get in anyhow, right? Well no, because we couldn’t actually seal the tiles. Why not?…



7/ Because the tiles were 90% hollow and were filled with air, and when the Space Shuttle flew up into the vacuum of space, the air needed to easily get out of the tiles or then pressure would make them explode and then they would not protect the Shuttle during landing.



8/ But why were they 90% hollow? Because the whole point of them was to be excellent insulators during hot re-entry from space. They were made of tiny silica fibers that barely touched each other so heat could barely conduct through them.



9/ Here’s an interesting video on how they were made. They were such good insulators you could heat them to glowing-hot while holding them in your hand. newsflare.com/video/173291/w…



10/ So then, if they had to let air out while launching, and the coating couldn’t keep water out, then why have the coating? Two reasons. 1st, to be a smooth surface so the plasma would flow without turbulence over the surface during entry to minimize heating. And…



11/ 2nd, to have high emissivity in the desired wavelengths so heat that *did* get into the tiles from the hot plasma would radiate back to space more easily than go into the skin of the Space Shuttle. Thus, they were black over the hotter parts, white over the cooler parts.



12/ So they were hollow, filled with air that needed to get out while the Shuttle was “going uphill”, but they had to be coated which would restrict the air getting out. So the coating was simply left off near the base of every tile, allowing the air an escape path.



13/ So that escape path for the air meant that the rain could get into the tiles before launch, weighing the vehicle down tremendously, and that would have been a giant problem!



14/ Part of the reason this problem was so giant was that the silica fibers that make up the body of each tile are hydrophilic — “water loving”. Water clings to it. Any water that got into a tile would never want to come out again. It would become happy water inside its new home.



15/ Materials are sometimes classified as hydrophobic — water tries to get away from it — or hydrophilic — water clings to it. The coating on this leaf is hydrophobic, so water beads-up and wants to run off the leaf. (Source: https://scitechdaily.com/more-efficient-thermal-cooling-method-bioinspired-by-plants/amp/)



16/ The fibers in jeans are hydrophilic, so if you go snow skiing you get wet. That’s why, back in the day, we used Scotchgard on jeans to go skiing. Scotchgard is hydrophobic. It’s pretty much the same thing we sprayed into Shuttle tiles.



17/ Remember learning about a meniscus back in high school or college chemistry lab? It’s that curve of the water inside a glass container. That’s because glass is hydrophilic, so water loves it and wants to climb up the sides of the glass. Shuttle tile fibers are silica (glass).



18/ After installing the tiles, we could not get access to the uncoated parts of the tile to spray “Scotchgard” into each tile to keep the rain out, so they had to poke the little holes in the coating of each tile (in the little circles in this picture) to inject the spray. But…



19/ …now your gonna ask, why not just spray in the Scotchgard BEFORE installing the tiles, when we still had access to the uncoated parts near the base of each tile? Wouldn’t that be easier than injecting each tile one-by-one AFTER installation? Well…



20/ The problem was that the “Scotchgard” burns out of the tiles during that super hot re-entry. It was vaporized by the heat and then it escaped from the tiles the same way the air escaped. So we had to reinject it into every tile all over again before every flight.



21/ So we had hollow tiles for heat protection, high emissivity coating on the tiles, a gap in the coating to let the air out, Scotchgard for inside the tiles to keep the rain out, and tiny holes to spray the Scotchgard in after every landing before going back out to the pad. BUT



22/ There was still one problem. Sometimes the Shuttle came back from a mission, freshly burned-out from all its Scotchgard, and before it was towed back to the hangar a thunderstorm rolled in and the tiles got soaked full of water. Florida weather changes fast.



23/ So then we are back to square one: how do we get those tons of water to come back out of the hydrophilic tiles before spraying in the new Scotchgard? Heat lamps did not work. It just moved the water around the outside of the vehicle to the cold side, never leaving the tiles.



24/ I used to be a Space Shuttle comm/nav engineer and later became a physicist. My first physics project at NASA was to study how to get water out of the Space Shuttle tiles. I did experiments filling them with water and sucking it back out using a vacuum hose on the same holes.



25/ It was a really cool condensed matter project because the water droplets did a directed (but randomized) walk through the fibers, with denser fibers holding the water more tightly so it was diffusion thru random potential wells. It resulted in stretched exponential curves.



26/ In the end we used those results to help decide how long to suck on the tiles before removing the suction cups and moving on to the next batch of tiles. The system could suck the Shuttle dry in a few days, whereas heat lamps took months and still couldn’t get the water out.



27/ So when I look at Shuttle tiles I think of those 2 things: the white chevrons marking the comm/nav antennas which I worked on for 10 years as part of the launch team, then the tiny holes where we sucked water out after (later) becoming a physicist. Fond memories! /end
Title: Re: Starship heat shield
Post by: edzieba on 05/30/2022 11:32 am
A minor correction on the STS tile waterproofing:
The tiles were initially impregnated with methyltrimethoxysilane (MTMS) during manufacture, and this provided waterproofing through to the first flight and entry, and which point the MTMS burnt off during entry. Subsequent to this, a rewaterproofing agent needed to be applied after every flight.
Initially, rewaterproofing was performed by spray-on fluoropolymer (Scotchguard), with the idea that it could be sprayed on rapidly after landing to minimise the chance of water ingress. This proved inadequate, as too much Scotchguard would interact with and degrade the Silicone used to adhere the gap-fillers between the tiles, and too little provided inadequate protection and led to water ingress into the tiles.
As a replacement for the Scotchguard, hexamethyldisilazane (HDMS) was applied through vapour diffusion, to provide good penetration into the tile. As a rewaterproofing agent it worked well, but it was found the catalyst used in the HDMS degraded the silicone under the base of the tile (that attached it to the Orbiter), meaning all treated tiles needed to be replaced and a new rewaterproofing agent found.
That new agent was dimethylethoxysilane (DMES), which needed to be injected rather than diffused into the tiles. This was laborious (poking a needle into each tile and injecting sly enough to not fracture the tile) but it worked and did not degrade the silicone, so was the rewaterproofing agent for the rest of the life of STS.

Manufacture of Starship's tiles impregnates them with MTMS during manufacture (as per the FDEP report (https://prodenv.dep.state.fl.us/DepNexus/public/electronic-documents/FLR000231449/facility!search) on the tile facility waste handling), with the rewaterproofing method currently unknown.
Title: Re: Starship heat shield
Post by: rsdavis9 on 05/30/2022 12:03 pm
So in the new tile loss video from the cryo testing/pipe rupture were the tiles pin attached or glued on?
Just wondering if gluing versus mechanical is showing up as better/worse.
Title: Re: Starship heat shield
Post by: JayWee on 05/30/2022 03:04 pm
A minor correction on the STS tile waterproofing:
The tiles were initially impregnated with methyltrimethoxysilane (MTMS) during manufacture, and this provided waterproofing through to the first flight and entry, and which point the MTMS burnt off during entry. Subsequent to this, a rewaterproofing agent needed to be applied after every flight.
Initially, rewaterproofing was performed by spray-on fluoropolymer (Scotchguard), with the idea that it could be sprayed on rapidly after landing to minimise the chance of water ingress. This proved inadequate, as too much Scotchguard would interact with and degrade the Silicone used to adhere the gap-fillers between the tiles, and too little provided inadequate protection and led to water ingress into the tiles.
As a replacement for the Scotchguard, hexamethyldisilazane (HDMS) was applied through vapour diffusion, to provide good penetration into the tile. As a rewaterproofing agent it worked well, but it was found the catalyst used in the HDMS degraded the silicone under the base of the tile (that attached it to the Orbiter), meaning all treated tiles needed to be replaced and a new rewaterproofing agent found.
That new agent was dimethylethoxysilane (DMES), which needed to be injected rather than diffused into the tiles. This was laborious (poking a needle into each tile and injecting sly enough to not fracture the tile) but it worked and did not degrade the silicone, so was the rewaterproofing agent for the rest of the life of STS.

Manufacture of Starship's tiles impregnates them with MTMS during manufacture (as per the FDEP report (https://prodenv.dep.state.fl.us/DepNexus/public/electronic-documents/FLR000231449/facility!search) on the tile facility waste handling), with the rewaterproofing method currently unknown.
Why can't the MTMS be used as rewaterproofing agent?
Title: Re: Starship heat shield
Post by: Genial Precis on 05/30/2022 05:21 pm
Having to re-waterproof the tiles between flights seems like a big hairy deal, if not a showstopper, for rapid reuse. I wonder if we won't see either a ceramic coating on the fibers or a change to the composition of the fibers which causes them to develop a hydrophobic surface.

The rare earth oxides are all hydrophobic (https://www.nature.com/articles/nmat3545.pdf) but not superhydrophobic (contact angle 100-120 degrees) and a cerium oxide coating survived 1000 C in air in the linked Nature report. Cerium is cheap, which is good, and I wonder if a cerium oxide doped fiber might regenerate a cerium oxide coating when heated, which would both save the effort of applying the coating and make it self-healing.

The article is from 2013 so there may be better materials since, or not. Avoiding this waterproofing and re-waterproofing process, especially as something to be done after every flight, seems important. And that definitely disqualifies organic coatings on the fibers, however applied, as they'll all burn off much the same.
Title: Re: Starship heat shield
Post by: DanClemmensen on 05/30/2022 05:52 pm
Having to re-waterproof the tiles between flights seems like a big hairy deal, if not a showstopper, for rapid reuse. I wonder if we won't see either a ceramic coating on the fibers or a change to the composition of the fibers which causes them to develop a hydrophobic surface.
Yes. It looks to me that it kills truly rapid reuse, unless the inspection and re-waterproofing process can be fully automated. Starship's geometry is a lot simpler than the shuttle's, and automation has become much more sophisticated during the last 20 years,  so it might be possible. I'm guessing that inspection and re-waterproofing can be automated but tile replacement will remain at least semi-manual for a long while.
Title: Re: Starship heat shield
Post by: Genial Precis on 05/30/2022 06:32 pm
Haha, forget that bit about rare earth oxides. Apparently it's since been discovered (https://www.sciencedirect.com/science/article/pii/S2589004221016618) that they aren't intrinsically hydrophobic; they're only hydrophobic when they've had a few minutes to adsorb VOCs from the air. Which may be good enough, or not, but I don't want to misattribute the mechanism.
Title: Re: Starship heat shield
Post by: Chris Bergin on 05/30/2022 08:25 pm
New video by our team on this:

A deep dive on how Starship will survive the brutal forces of atmospheric reentry.

Video and Pictures from Mary (@BocaChicaGal) and Nic (@nicansuini). Edited by Brady (@theFavoritist).

https://www.youtube.com/watch?v=0ktFGqC764w
Title: Re: Starship heat shield
Post by: Dancing Dog on 05/31/2022 02:42 am
It looks like a lot of this was discussed here 6 months ago, https://forum.nasaspaceflight.com/index.php?topic=50748.msg2318162#msg2318162 (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2318162#msg2318162) if anyone is interested. The glassy black surface seems to itself be waterproof.
Title: Re: Starship heat shield
Post by: edzieba on 05/31/2022 06:58 am
The glass coating is waterproof. But the glass coating is only on one face, it does not protect the tile from water ingress (the sintered silica sucks up moisture like a sponge) in the same way an umbrella will not protect you from getting wet in a sauna.
Title: Re: Starship heat shield
Post by: Barley on 05/31/2022 02:55 pm
Starship has a lower surface area/volume ratio than the shuttle because it is larger and has a more compact shape.

If the weight of absorbed water is the only problem SS may be able to dispense with waterproofing, or accept imperfect waterproofing.  This would be particularly true for tanker flights since these have excess fuel that could be used to adjust for an unknown mass of absorbed water.

OTOH if boiling or freezing water destroys tiles this would not help.
Title: Re: Starship heat shield
Post by: edzieba on 06/01/2022 06:44 am
OTOH if boiling or freezing water destroys tiles this would not help.
Water ingress causes exactly this.
From "Orbiter Thermal Protection System Lessons Learned" (https://doi.org/10.2514/6.2011-7308):
Quote
After the 2nd flight of Columbia inspection of the Orbiter indicated that in-plane failures of six HRSI tiles had
occurred on the right wing glove area. The depth of the missing material corresponded to the burnout zone of the
factory waterproofing or the 1050 F line. In addition, the surface coating of 12 tiles on the body flap showed
evidence of bubbling. Based on these observations and previous results from the ground test program, it was
concluded that water penetration had occurred on the tiles before the flight and the rewaterproofing application
technique required improvement. The mechanism involved in this failure is postulated as follows. Water from
rainstorms entered an area of the tiles before lift-off. During ascent, a small amount of water in the tile was
vaporized, and the remainder cooled rapidly because of the rapid decrease in pressure. When the vehicle went to
orbital conditions, the water changed to ice, which contracted and fractured the tile. The steam generated in the tile
during entry then completed the fracture of the tile.
Title: Re: Starship heat shield
Post by: greybeardengineer on 06/01/2022 12:57 pm
Shuttle tiles fit extremely tightly together and were attached to the vehicle with adhesive.

Most Starship tiles have a deliberate inter tile gap to allow thermal expansion and are attached with mechanical devices whose retention force and range and spring constant of "play" can be defined as necessary. This scheme likely tolerates freezing and boiling of intruding moisture and resultant stress on individual tiles much better than the orbiter's.
Title: Re: Starship heat shield
Post by: edzieba on 06/01/2022 02:06 pm
Shuttle tiles fit extremely tightly together and were attached to the vehicle with adhesive.

Most Starship tiles have a deliberate inter tile gap to allow thermal expansion and are attached with mechanical devices whose retention force and range and spring constant of "play" can be defined as necessary. This scheme likely tolerates freezing and boiling of intruding moisture and resultant stress on individual tiles much better than the orbiter's.
The fracturing was internal to the tile, attachment method or abutment would be irrelevant to that failure mechanism.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/01/2022 09:44 pm
Starship has a lower surface area/volume ratio than the shuttle because it is larger and has a more compact shape.

If the weight of absorbed water is the only problem SS may be able to dispense with waterproofing, or accept imperfect waterproofing.  This would be particularly true for tanker flights since these have excess fuel that could be used to adjust for an unknown mass of absorbed water.

OTOH if boiling or freezing water destroys tiles this would not help.

If the tiles are that permeable, then boiling is probably irrelevant, it won't cause damage.   At high enough altitude (> 60km) the moisture will boil off (or sublime if frozen), and thus only slightly impact Starship fuel usage since staging doesn't happen until about that altitude.  The water mass will probably be there for the entire Booster burn but it's probably rounding error given Booster + full Starship is on the order of 1800 tons.  I doubt 2 tons of water will matter, that's equivalent to a 1-2 engine outage on the Booster which is already planned for.

Freezing, OTOH.  Fortunately, unlike Challenger, the damage will be obvious.

And since freezing happens every time we see a cryo test, my guess is, not a problem.   Let's see what the shortest time between a BC rainstorm and cryotest is.  Has this happened yet?
Title: Re: Starship heat shield
Post by: sebk on 06/02/2022 10:26 am
Tiles installed on Ships which didn't return from space are waterproofed. So it's not a concern for cryo testing of new vehicles.

Also, during ascent part of the water would evaporate, but the rest would freeze. Evaporation cools it and once the temperature is at 273.16K freezing starts. Large fraction of the water which soaked unprotected tiles would freeze on ascent.
Title: Re: Starship heat shield
Post by: MichaelBlackbourn on 06/02/2022 01:33 pm
Maybe that’s a feature. An extra 2 tons of energy absorbing ablative material for active cooling on the way down.
Title: Re: Starship heat shield
Post by: Hog on 06/02/2022 03:24 pm
Starship has a lower surface area/volume ratio than the shuttle because it is larger and has a more compact shape.

If the weight of absorbed water is the only problem SS may be able to dispense with waterproofing, or accept imperfect waterproofing.  This would be particularly true for tanker flights since these have excess fuel that could be used to adjust for an unknown mass of absorbed water.

OTOH if boiling or freezing water destroys tiles this would not help.

If the tiles are that permeable, then boiling is probably irrelevant, it won't cause damage.   At high enough altitude (> 60km) the moisture will boil off (or sublime if frozen), and thus only slightly impact Starship fuel usage since staging doesn't happen until about that altitude.  The water mass will probably be there for the entire Booster burn but it's probably rounding error given Booster + full Starship is on the order of 1800 tons.  I doubt 2 tons of water will matter, that's equivalent to a 1-2 engine outage on the Booster which is already planned for.

Freezing, OTOH.  Fortunately, unlike Challenger, the damage will be obvious.

And since freezing happens every time we see a cryo test, my guess is, not a problem.   Let's see what the shortest time between a BC rainstorm and cryotest is.  Has this happened yet?
Not following your Challenger bit.  What freezing damage was hidden during a Challenger (OV-099) flight?
Title: Re: Starship heat shield
Post by: rsdavis9 on 06/02/2022 03:55 pm
Starship has a lower surface area/volume ratio than the shuttle because it is larger and has a more compact shape.

If the weight of absorbed water is the only problem SS may be able to dispense with waterproofing, or accept imperfect waterproofing.  This would be particularly true for tanker flights since these have excess fuel that could be used to adjust for an unknown mass of absorbed water.

OTOH if boiling or freezing water destroys tiles this would not help.

If the tiles are that permeable, then boiling is probably irrelevant, it won't cause damage.   At high enough altitude (> 60km) the moisture will boil off (or sublime if frozen), and thus only slightly impact Starship fuel usage since staging doesn't happen until about that altitude.  The water mass will probably be there for the entire Booster burn but it's probably rounding error given Booster + full Starship is on the order of 1800 tons.  I doubt 2 tons of water will matter, that's equivalent to a 1-2 engine outage on the Booster which is already planned for.

Freezing, OTOH.  Fortunately, unlike Challenger, the damage will be obvious.

And since freezing happens every time we see a cryo test, my guess is, not a problem.   Let's see what the shortest time between a BC rainstorm and cryotest is.  Has this happened yet?
Not following your Challenger bit.  What freezing damage was hidden during a Challenger (OV-099) flight?

Freezing/cold O-rings?
Title: Re: Starship heat shield
Post by: Robotbeat on 06/02/2022 04:06 pm
Was due to temperature, not freezing. Different phenomenon.
Title: Re: Starship heat shield
Post by: warp99 on 06/02/2022 11:11 pm
Shuttle tiles fit extremely tightly together and were attached to the vehicle with adhesive.

Most Starship tiles have a deliberate inter tile gap to allow thermal expansion and are attached with mechanical devices whose retention force and range and spring constant of "play" can be defined as necessary. This scheme likely tolerates freezing and boiling of intruding moisture and resultant stress on individual tiles much better than the orbiter's.
Shuttle tiles were spaced apart to allow for thermal expansion during entry and had gap fillers fitted which made the tile surface look smooth from a distance. 

Starship tiles have a larger gap because they also have to allow for the tank surface contracting when filled with cryogenic liquid and are mostly clipped in place although nose and flap leading edge tiles are glued.  They also have gap fillers.  The material composition of the tile fibers is very similar although there is much less optimisation of the tiles shape and thickness so manufacturing is easier.

In summary Starship tiles have all the same issues and benefits as shuttle tiles.  We will have to see if SpaceX can come up with better and cheaper solutions than NASA to these issues. 

I am of the view that they can - but they will not be able to achieve the hoped for flight cadence from the ship.  Frequent booster flights seem more achievable.
Title: Re: Starship heat shield
Post by: sebk on 06/03/2022 09:40 am
My take is they're going with what's known to work first, despite its known drawbacks. Then, they will optimize it, but also develop entirely new solutions (after all there were pretty specific job postings indicating they seriously look at stuff like metallic heat shields). R'n'D takes time, though.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/03/2022 04:37 pm
Could they ensure that Starship is kept sheltered before launch to prevent the absorption of rain? I know it would be a massive undertaking but it should at least theoretically be possible to have some sort of movable structure to keep the rain off. It can't be that much more crazy than ideas like using chopsticks to snatch a Starship out of the air.
Title: Re: Starship heat shield
Post by: DanClemmensen on 06/03/2022 04:43 pm
Could they ensure that Starship is kept sheltered before launch to prevent the absorption of rain? I know it would be a massive undertaking but it should at least theoretically be possible to have some sort of movable structure to keep the rain off. It can't be that much more crazy than ideas like using chopsticks to snatch a Starship out of the air.
A baggie. A really big baggie.
Title: Re: Starship heat shield
Post by: launchwatcher on 06/04/2022 07:30 pm
Could they ensure that Starship is kept sheltered before launch to prevent the absorption of rain? I know it would be a massive undertaking but it should at least theoretically be possible to have some sort of movable structure to keep the rain off. It can't be that much more crazy than ideas like using chopsticks to snatch a Starship out of the air.
A baggie. A really big baggie.
Minotaur has something like that - the first stage sheds what looks like a shrink-wrapped plastic skin at launch time.
Title: Re: Starship heat shield
Post by: DanClemmensen on 06/04/2022 07:56 pm
Could they ensure that Starship is kept sheltered before launch to prevent the absorption of rain? I know it would be a massive undertaking but it should at least theoretically be possible to have some sort of movable structure to keep the rain off. It can't be that much more crazy than ideas like using chopsticks to snatch a Starship out of the air.
A baggie. A really big baggie.
Minotaur has something like that - the first stage sheds what looks like a shrink-wrapped plastic skin at launch time.
I was trying to be funny, but I do note that the chopsticks could probably be used to to install the baggie.  Not sure how to keep moisture from condensing into/onto the tiles during cryogenic propellant loading, though.
Title: Re: Starship heat shield
Post by: BT52 on 06/04/2022 11:01 pm
Well theoretically u could made "vacuum" bag recirculation then. Witch adds whole plethora failure of modes and makes me cringe from problems u create. And increased cost of lunch, more systems to maintain and unavoidable additional weight at lunch for edge case. SS Roof and tight lunch windows and monitoring weather conditions should suffice. Unless you guys were thinking about huge tarp for SS during "out" of hangar scenario.

Anyway I guess they tested worse case scenario with current fibre structure and tweak its density  to reduce capillary effect. They probably want retain tile structural integrity even if you renter with frozen core of tiles.

I was just thinking out load. Would you boil off some water if you rotate ship belly towards sun?  I know tall task. Given exposed area is ceramic and heat transfer is not so ideal. Orbital material science is not mine area of knowledge so i don't know for sure.
Title: Re: Starship heat shield
Post by: edzieba on 06/05/2022 12:35 am
Sublimating trapped water is a hazard, the sublimation rate needs to be controlled and low enough for the gas produced not to do any damage itself. Even assuming that the water freezing did not already cause damage.

The tiles will need rewaterproofing after each entry. The batting may or may not need rewaterproofing depending on what temperature it reached (the heat is what bakes out the waterproofing in the first place).

There is currently a mesh layer between the batting and tiles. Switch this for woven 'bubbler' hose and you can keep the batting and tiles flooded with dry Nitrogen to minimise condensation during tanking. That doesn't solve the rewaterproofing issue though, and you'd go through a lot of nitrogen (and a LONG time) to dry out the tiles if they became waterlogged. STS used direct radiant heat to dry tiles if they were exposed to moisture before the orbiter could be moved under cover and rewaterproofed, but even that took weeks.
Title: Re: Starship heat shield
Post by: Dancing Dog on 06/05/2022 03:51 am
Given that this has been a known issue since before the start of the program, it's literally a "bet the company" program, and SpaceX almost certainly has former STS heat shield experts on staff, I think "I don't know how we'll avoid re-waterproofing 18k tiles after every flight" is not something they're saying in the offices at Boca Chica. I suspect the issue was resolved before the first Starbrick (not "tile") left the Bakery.
Title: Re: Starship heat shield
Post by: MGoDuPage on 06/05/2022 06:53 am
Given that this has been a known issue since before the start of the program, it's literally a "bet the company" program, and SpaceX almost certainly has former STS heat shield experts on staff, I think "I don't know how we'll avoid re-waterproofing 18k tiles after every flight" is not something they're saying in the offices at Boca Chica. I suspect the issue was resolved before the first Starbrick (not "tile") left the Bakery.

This is an excellent point, thanks for bringing it up.

Not only is it excellent as it relates to the re-waterproofing tiles issue, but as it relates to almost everything for the entire SS/SH project. Not that they had every conceivable problem pre-solved before they even launched the project, but at least enough so that they didn’t see any insurmountable obstacles from the get going. I’d never thought of it that way, but now that it’s laid out like this, it seems obvious in retrospect. That includes the idea of onboarding former STS engineers to provide insight from the Shuttle Era.

As a layperson, it also got me viewing the SS/SH for what it really is spiritually: a hybrid between the best elements of STS & Falcon 9, but ALSO with:

1) the benefit of hindsight/“lessons learned” from both systems,

2) an additional 10 years of advances in the world of aerospace design development, & manufacturing.

3) the project being driven by a maniacal personality focused on setting Mars

4) existing within the setting of a private company that is neither hamstrung by the whims of Congress, nor obsessed with juicing short term performance at the expense of long term success just to boost quarterly profit, but that DOES know that if this project fails, it will be an existential threat to the company’s very existence.


Bottom Line: Viewing it this way, I REALLY like their chances. Maybe not to nail 100% of all innovative elements perfectly. But at least enough such that they’re virtually guaranteed to cut launch costs by half while also revolutionizing some other logistical element (capacity; range) of space flight.
Title: Re: Starship heat shield
Post by: JamesH65 on 06/06/2022 01:37 pm
Given that this has been a known issue since before the start of the program, it's literally a "bet the company" program, and SpaceX almost certainly has former STS heat shield experts on staff, I think "I don't know how we'll avoid re-waterproofing 18k tiles after every flight" is not something they're saying in the offices at Boca Chica. I suspect the issue was resolved before the first Starbrick (not "tile") left the Bakery.

Quite. Although I would say maybe not completely resolved, but certainly a long way to the end goal. I would certainly think that some of the commentators here worrying about it should definitely consider that they may not be the experts here.
Title: Re: Starship heat shield
Post by: dwheeler on 06/06/2022 03:18 pm
Given that this has been a known issue since before the start of the program, it's literally a "bet the company" program, and SpaceX almost certainly has former STS heat shield experts on staff, I think "I don't know how we'll avoid re-waterproofing 18k tiles after every flight" is not something they're saying in the offices at Boca Chica. I suspect the issue was resolved before the first Starbrick (not "tile") left the Bakery.

Quite. Although I would say maybe not completely resolved, but certainly a long way to the end goal. I would certainly think that some of the commentators here worrying about it should definitely consider that they may not be the experts here.

Ok. No commenting on anything unless you're a SpaceX engineer then. Time to shut down NSF...  ::)
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/07/2022 05:38 am
Given that this has been a known issue since before the start of the program, it's literally a "bet the company" program, and SpaceX almost certainly has former STS heat shield experts on staff, I think "I don't know how we'll avoid re-waterproofing 18k tiles after every flight" is not something they're saying in the offices at Boca Chica. I suspect the issue was resolved before the first Starbrick (not "tile") left the Bakery.

Quite. Although I would say maybe not completely resolved, but certainly a long way to the end goal. I would certainly think that some of the commentators here worrying about it should definitely consider that they may not be the experts here.

I would love it if the commentators did some math, such as estimating how many grams of water a tile could hold, then estimating how many grams that is on the starship's entire set of tiles, then estimate the sublimation rate at various altitudes to see how much water is left after staging (where that mass starts to matter).   You could also estimate the flux  of outgassing and see if that might affect the tile's mechanical properties.  All that data is easily available or easily derived.

You could also dig into the BC weather history and find out if any cryo tests happened within a day of the last rainstorm and then figure out how many tiles were lost and compare that to other tests that were not preceded by rain.  That might tell you whether freezing of water in a tile is a problem or not.

But all that would take actual work.

If one is going to make an assertion that is contrary to Elon's engineering plans, the burden is on you to at least do some math to show you have a point.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/07/2022 05:58 am
As an example it rained lightly in BC on 5/29 and they did a cryotest on on S24 on 6/02.  Unless tiles dry out in 3 days, if they were waterlogged that water froze.

Keep in mind the ship is only partially tiled, there's tons of places for rain to collect.  Any water proofing is probably irrelevant with that much side and blanket area exposed.

Source:   https://www.timeanddate.com/weather/@4675354/historic?month=5&year=2022

and the S24/B7 updates thread.

If you think frozen water is a problem for the tiles you should go back to the last 10 or so cryo tests on starship and check when it last rained.  It rains a lot on the Gulf, I suspect you'll find more than I just found by some very casual homework.
Title: Re: Starship heat shield
Post by: sebk on 06/07/2022 09:39 am
Tiles currently installed are impregnated  ::)

So whatever rain falling on Sn 20 or Sn 24 is not relevant.

The problem discussed is should they and if yes then how would they  be waterproofed after orbital entry.

Title: Re: Starship heat shield
Post by: JamesH65 on 06/07/2022 02:17 pm
Given that this has been a known issue since before the start of the program, it's literally a "bet the company" program, and SpaceX almost certainly has former STS heat shield experts on staff, I think "I don't know how we'll avoid re-waterproofing 18k tiles after every flight" is not something they're saying in the offices at Boca Chica. I suspect the issue was resolved before the first Starbrick (not "tile") left the Bakery.

Quite. Although I would say maybe not completely resolved, but certainly a long way to the end goal. I would certainly think that some of the commentators here worrying about it should definitely consider that they may not be the experts here.

Ok. No commenting on anything unless you're a SpaceX engineer then. Time to shut down NSF...  ::)

Way to miss the point. There are too many people on here saying, in effect, "That will never work". I have no problem with commenting, but I do have a problem with people thinking they know better than SpaceX. That's offensive to the engineers at SpaceX, who they are effectively calling incompetent.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/07/2022 03:33 pm
Tiles currently installed are impregnated  ::)

I forgot, is that a guess based on EPA/MSDS disclosures from the Florida facility, or is it a "the shuttle did it that way" guess?  And the water repellent applies to *all* the surfaces? (I don't know).

SuperWool blankets have a water absorption ratiing of ~20% by weight.   there's on the order of 750m^2 of tile (pi*4.5*50) backed by wool.

Assuming iit's 50mm superwool that's 37.5 cubic meters of superwool, at 128kg/m^3 = 4.8T of superwool, or about 1T of water absorbed.  Rounding error for the first 3 minutes of flight.

All that wool was wide open to the rain for numerous cryotests.   Didn't seem to bother anything as far as freezing goes.

So, why are tiles different than the superwool?

https://www.goodfellow.com/DocumentHandler/177/superwool-ht.pdf?download=1
https://pure.strath.ac.uk/ws/portalfiles/portal/90853154/Edet_etal_Electrochem_2019_Poster_Investigation_of_water_absorption_profile_of_mineral_wool.pdf
Title: Re: Starship heat shield
Post by: edzieba on 06/07/2022 03:50 pm
Tiles currently installed are impregnated  ::)

I forgot, is that a guess based on EPA/MSDS disclosures from the Florida facility, or is it a "the shuttle did it that way" guess?  And the water repellent applies to *all* the surfaces? (I don't know).
Both: the EPA document revealed they are doing it 'the shuttle way' - MTMS impregnation during manufacture.
Quote
SuperWool blankets have a water absorption ratiing of ~20% by weight.   there's on the order of 750m^2 of tile (pi*4.5*50) backed by wool.

Assuming iit's 50mm superwool that's 37.5 cubic meters of superwool, at 128kg/m^3 = 4.8T of superwool, or about 1T of water absorbed.  Rounding error for the first 3 minutes of flight.

All that wool was wide open to the rain for numerous cryotests.   Didn't seem to bother anything as far as freezing goes.

So, why are tiles different than the superwool?

https://www.goodfellow.com/DocumentHandler/177/superwool-ht.pdf?download=1
https://pure.strath.ac.uk/ws/portalfiles/portal/90853154/Edet_etal_Electrochem_2019_Poster_Investigation_of_water_absorption_profile_of_mineral_wool.pdf
It's unknown what the batting composition is (superwool, kaowool, and other ASF & RCF products have been assumed, but no confirmation), but waterproofing impregnation could be done at manufacture or post manufacture, and like the tiles would need rewaterproofing after exposure to elevated temperatures.
Title: Re: Starship heat shield
Post by: brettly2021 on 06/07/2022 09:12 pm
elon musk states in recent everyday astronaut video that the tiles will expand and fill the gaps, so should be no problem for hot gas entry between tiles, I think he got that one wrong, I remember when I was researching a bit on the shuttle tiles one reason the material was so suitable was the lack of thermal expansion, I wont be bothered going back to find the data, if others want to debate it the info is out there, but expansion should be negligible.
Title: Re: Starship heat shield
Post by: Bob Niland on 06/07/2022 10:35 pm
elon musk states in recent everyday astronaut video that the tiles will expand and fill the gaps, so should be no problem for hot gas entry between tiles, I think he got that one wrong, I remember when I was researching a bit on the shuttle tiles one reason the material was so suitable was the lack of thermal expansion, I wont be bothered going back to find the data, if others want to debate it the info is out there, but expansion should be negligible.
Expansion at gaps aide, the hazards associated with gaps are substantially different for shuttle & Starship. The thermal resilience of the orbiter's aluminum (7075?) skin was dramatically lower than is expected for Starship's 304L stainless steel.
Personally, what I'm more concerned with, at this late date in SS iterations, is how easy it seems to be for the tiles to shake loose.
Title: Re: Starship heat shield
Post by: DanClemmensen on 06/07/2022 10:53 pm
elon musk states in recent everyday astronaut video that the tiles will expand and fill the gaps, so should be no problem for hot gas entry between tiles, I think he got that one wrong, I remember when I was researching a bit on the shuttle tiles one reason the material was so suitable was the lack of thermal expansion, I wont be bothered going back to find the data, if others want to debate it the info is out there, but expansion should be negligible.
Expansion at gaps aide, the hazards associated with gaps are substantially different for shuttle & Starship. The thermal resilience of the orbiter's aluminum (7075?) skin was dramatically lower than is expected for Starship's 304L stainless steel.
Personally, what I'm more concerned with, at this late date in SS iterations, is how easy it seems to be for the tiles to shake loose.
I wonder if they are now thinking about using a deliberate internal Impulse ("boom") as a way to test the tiles. Does it just shake off loose tiles, or does it loosen tiles that are otherwise tight? If it works, it allows a single test to test all the tiles instead of requiring individual testing.
Title: Re: Starship heat shield
Post by: dwheeler on 06/08/2022 01:59 pm
Given that this has been a known issue since before the start of the program, it's literally a "bet the company" program, and SpaceX almost certainly has former STS heat shield experts on staff, I think "I don't know how we'll avoid re-waterproofing 18k tiles after every flight" is not something they're saying in the offices at Boca Chica. I suspect the issue was resolved before the first Starbrick (not "tile") left the Bakery.

Quite. Although I would say maybe not completely resolved, but certainly a long way to the end goal. I would certainly think that some of the commentators here worrying about it should definitely consider that they may not be the experts here.

Ok. No commenting on anything unless you're a SpaceX engineer then. Time to shut down NSF...  ::)

Way to miss the point. There are too many people on here saying, in effect, "That will never work". I have no problem with commenting, but I do have a problem with people thinking they know better than SpaceX. That's offensive to the engineers at SpaceX, who they are effectively calling incompetent.

It was argued that the current SS tiles are the same material and use the same initial waterproofing technique, ( impregnating the tiles as part of the manufacturing process), as the Shuttle tiles. The Shuttle tiles needed to be re-impregnated after each re-entry which was a huge effort. So people were simply speculating on how SpaceX is going to avoid that huge effort. No one is calling the SpaceX engineers incompetent. People are just curious so want to discuss the problem. NSF has literally hundreds of pages of threads where people are discussing/speculating/wondering how SpaceX is tackling various problems.
Title: Re: Starship heat shield
Post by: Alvian@IDN on 06/08/2022 02:14 pm
elon musk states in recent everyday astronaut video that the tiles will expand and fill the gaps, so should be no problem for hot gas entry between tiles, I think he got that one wrong, I remember when I was researching a bit on the shuttle tiles one reason the material was so suitable was the lack of thermal expansion, I wont be bothered going back to find the data, if others want to debate it the info is out there, but expansion should be negligible.
Expansion at gaps aide, the hazards associated with gaps are substantially different for shuttle & Starship. The thermal resilience of the orbiter's aluminum (7075?) skin was dramatically lower than is expected for Starship's 304L stainless steel.
Personally, what I'm more concerned with, at this late date in SS iterations, is how easy it seems to be for the tiles to shake loose.
Didn't everybody already knows the whole S24 pipe coming lose? It's really not a tile problems

S24's second & third cryoproof also completely disproven this assumptions. Zero tile coming loose
Title: Re: Starship heat shield
Post by: chopsticks on 06/08/2022 02:32 pm
There's an alleged SpaceX insider who periodically leaks info on the SpaceX subreddit who posted something that caught my eye.

https://www.reddit.com/r/spacex/comments/uli9ix/comment/ib5hxzo/?utm_source=share&utm_medium=web2x&context=3

Quote
Not sure. I've raised this with SpaceX indirectly and this observation is part of a design hold point until actual flights provide information on behavior of the tiles at launch and subsequent speeds. Redesign would be a major delay. Shuttle tiles did not have cryogenics in the tank behind them. The tiles on the Shuttle were also sealed with both woven fiberglass caulking strips and silicone sealant to mitigate weather and plasma intrusion as u/flshr19 will confirm.

Secondly, I'm not happy with the bayonet fittings or 'tile pins' holding the tile on. They are like a steel rawlplug with one way toothed ridging that requires destruction to remove the tile. Still, the anchor sockets in the tile rip out still attached to the bayonet fitting and the tile falls off.

There is another product on the market, and I won't promote it but if you want to see it it is here which is like steel velcro and probably better suited to thermal heating and tile replacement.

Going forward, the current tiles are the best and lightest thermal cladding available. Metallic forms carry a severe weight penalty, so it is up to the design team to finesse their tile, anchor points, reinforcing mesh, and felt insulation for all weather, all heat load situations.

This is the link to the "steel velcro" mentioned:

https://www.metaklett.de/en/technologie.html

Looks interesting.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/08/2022 04:51 pm
Based on the preponderance of evidence, I believe SpaceX has completely abandoned any waterproofing on tiles and the heat shield in general, including scotch-guard or other water proofing chemicals.

From WaPo article

Quote
Early in the shuttle's history, NASA discovered that the porous tiles tended to suck up moisture like a sponge, then crack in the freezing void of space.

The other way to solve expansion/contraction problems from changes caused by freezing water is loose mechanical tolerances.

Space Shuttle did not have loose mechanical tolerances.  That wasn't the design philosophy and you can't do that with aluminum or the materials available for backing in the 1970s.  The tiles were packed together and sealed, leaving little room for expansion that occurs when water freezes.

SpaceX, OTOH, has loose tolerances all over the place - in the super-wool padding, in the bayonet fastener, and between the tiles.   The padding deals with any plasma leaks resulting from those loose tolerances, as well as a skin that can handle 750degC.

They have already tested freezing in live testing, via cryogenic testing after the Starship getting wet.   What remains to prove is whether or not the tiles and padding were waterpoofed.   They *could* have been, but based on the design approach I don't think they are using the waterproofing they have on their MSDS disclosures.

Can't think of another way to find out (on our end) other than an updated disclosure form from the Florida facility, insider gossip, or a reflown Starship that has sat out in the weather.


https://www.washingtonpost.com/wp-srv/articles/A38144-2003Feb6.html
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/08/2022 05:26 pm
Shuttle tiles did not have cryogenics in the tank behind them. The tiles on the Shuttle were also sealed with both woven fiberglass caulking strips and silicone sealant to mitigate weather and plasma intrusion as u/flshr19 will confirm.

He doesn't say what the root problem is, just another "I don't like the design" comment.

The lack of tight tolerances + cryogenic behind them go together.   Tight tolerances don't like freezing water, or the expansion of steel as it goes from -200degC to 750degC

Quote
Secondly, I'm not happy with the bayonet fittings or 'tile pins' holding the tile on. They are like a steel rawlplug with one way toothed ridging that requires destruction to remove the tile. Still, the anchor sockets in the tile rip out still attached to the bayonet fitting and the tile falls off.

I don't see a problem with destruction for removing a tile.  It's the way drywall and siding works on my house.  It's annoying when I have to repair something, but not intolerable.   With half of the surface not covered with tiles, access to most systems doesn't require removal anyways.  Wish I could say the same about my house plumbing and electrical.

Every tile removal we've witnessed so far was for damaged tiles.  It doesn't seem bad that you have to break what is already broken.

I think the author implied a mechanical weakness argument but didn't come out and say it.

Quote
There is another product on the market, and I won't promote it but if you want to see it it is here which is like steel velcro and probably better suited to thermal heating and tile replacement.

Looks interesting but how do you peel a rigid item?   See the pictures on the mfgr's website.  All velcro I know about involves a bend radius for removal.  Ceramics and glass have zero bend radius.   the steel velcro probably doesn't have the degrees of freedom that the triple bayonet system has, so will be more rigid and promote cracking.

Quote
Going forward, the current tiles are the best and lightest thermal cladding available. Metallic forms carry a severe weight penalty, so it is up to the design team to finesse their tile, anchor points, reinforcing mesh, and felt insulation for all weather, all heat load situations.

Can't argue with that. 

Quote
This is the link to the "steel velcro" mentioned:

https://www.metaklett.de/en/technologie.html

Looks interesting.
Title: Re: Starship heat shield
Post by: chopsticks on 06/08/2022 07:46 pm
Looks interesting but how do you peel a rigid item?   See the pictures on the mfgr's website.  All velcro I know about involves a bend radius for removal.  Ceramics and glass have zero bend radius.   the steel velcro probably doesn't have the degrees of freedom that the triple bayonet system has, so will be more rigid and promote cracking.

I think the OP's thought was that this steel velcro *would provide enough degrees of freedom. The advantages I see in this method of tile placement is 1 - probably simpler to install, and 2 - less thermal penetration (no thermal path like the exisiting pins).

As far as removing them, presumably it would be the same (why remove a tile if it isn't broken?) and if it's broken anyway, perhaps you could peel it off from the back.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/08/2022 09:02 pm
I think the OP's thought was that this steel velcro *would provide enough degrees of freedom. The advantages I see in this method of tile placement is 1 - probably simpler to install, and 2 - less thermal penetration (no thermal path like the exisiting pins).

As far as removing them, presumably it would be the same (why remove a tile if it isn't broken?) and if it's broken anyway, perhaps you could peel it off from the back.

If the plan is to hook the steel velcro to the "felt" backing you will get amazing thermal properties and lots of movement freedom but I doubt there is sufficient strength in "felt" backing to hold on to those tiles.  Right now the "felt" backing is held on by some sort of mesh and the compression of the tiles against the pins.   The mfgr calls this "hybrid" configuration.

If the plan is to use the mfgrs steel-steel mode you well get far more thermal coupling than three pins.  The mfgr calls this "Entenkopf" configuration.

The pins have very little thermal coupling to the Starship, as thermal coupling is proportional to surface area and the pins are tiny in relation to the size of the tile.  The math for this was done way above in the thread.

So thermal and removal don't make sense as a reason to switch to "steel velcro".  Which are the reasons he cited in his post.

There may be enough degrees of freedom in the "Entenkopf" configuration, I don't know.

https://www.metaklett.de/en/technologie.html
Title: Re: Starship heat shield
Post by: mmeijeri on 06/08/2022 09:07 pm
If the plan is to use the mfgrs steel-steel mode you well get far more thermal coupling than three pins.  The mfgr calls this "Etenkopf" configuration.

[snip]

https://www.metaklett.de/en/technologie.html

At first I was puzzled by the name Etenkopf, but then I clicked the link. It's Entenkopf with an 'n', which is German for duck head.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/08/2022 09:15 pm
It's unknown what the batting composition is (superwool, kaowool, and other ASF & RCF products have been assumed, but no confirmation), but waterproofing impregnation could be done at manufacture or post manufacture, and like the tiles would need rewaterproofing after exposure to elevated temperatures.

We know from observation that they are taking no safety precautions when handling the "felt blanket".

We also know that it needs to have a useful temperature in excess of 750degC.

This considerably narrows the choices down to... superwool.

Superwool:  Human safe, working temperature 1300degC
Kaowool:  can cause cancer from fine particles:   1100 degC
Other ASF&RFC products:  Many cause cancer or severe lung irritation.  Cite one that doesn't.

http://www.lloyd-ris.co.uk/pdfs/datasheets/607%20Products%20MSDS.pdf
https://www.insulationindustries.com.au/wp-content/uploads/2022/05/MSDS_-_Kaowool_Blanket_and_Bulk_Products.pdf
Title: Re: Starship heat shield
Post by: livingjw on 06/08/2022 09:52 pm
It's unknown what the batting composition is (superwool, kaowool, and other ASF & RCF products have been assumed, but no confirmation), but waterproofing impregnation could be done at manufacture or post manufacture, and like the tiles would need rewaterproofing after exposure to elevated temperatures.

We know from observation that they are taking no safety precautions when handling the "felt blanket".

We also know that it needs to have a useful temperature in excess of 750degC.

This considerably narrows the choices down to... superwool.

Superwool:  Human safe, working temperature 1300degC
Kaowool:  can cause cancer from fine particles:   1100 degC
Other ASF&RFC products:  Many cause cancer or severe lung irritation.  Cite one that doesn't.

http://www.lloyd-ris.co.uk/pdfs/datasheets/607%20Products%20MSDS.pdf
https://www.insulationindustries.com.au/wp-content/uploads/2022/05/MSDS_-_Kaowool_Blanket_and_Bulk_Products.pdf

My money is on an alumina fiber product like Saffil. Its good to 1650 C, ~3000 F.

John
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/08/2022 11:35 pm
It's unknown what the batting composition is (superwool, kaowool, and other ASF & RCF products have been assumed, but no confirmation), but waterproofing impregnation could be done at manufacture or post manufacture, and like the tiles would need rewaterproofing after exposure to elevated temperatures.

We know from observation that they are taking no safety precautions when handling the "felt blanket".

We also know that it needs to have a useful temperature in excess of 750degC.

This considerably narrows the choices down to... superwool.

Superwool:  Human safe, working temperature 1300degC
Kaowool:  can cause cancer from fine particles:   1100 degC
Other ASF&RFC products:  Many cause cancer or severe lung irritation.  Cite one that doesn't.

http://www.lloyd-ris.co.uk/pdfs/datasheets/607%20Products%20MSDS.pdf
https://www.insulationindustries.com.au/wp-content/uploads/2022/05/MSDS_-_Kaowool_Blanket_and_Bulk_Products.pdf

My money is on an alumina fiber product like Saffil. Its good to 1650 C, ~3000 F.

John

Nice find!

Saffil:   Human safe, working temperature 1650C  (looks to be as safe or safer than Superwool)

MSDS:  https://www.unifrax.com/wp-content/uploads/2018/08/Unifrax-SDS-Saffil-V2.00-GB-en-160811.pdf

product brief:  http://www.lloyd-ris.co.uk/pdfs/datasheets/saffil%20blanket%5B1%5D.pdf

and a general overview of related material:  https://www.unifrax.com/product-category/blankets/?productcategory=236

Title: Re: Starship heat shield
Post by: edzieba on 06/09/2022 10:36 am
Based on the preponderance of evidence, I believe SpaceX has completely abandoned any waterproofing on tiles and the heat shield in general, including scotch-guard or other water proofing chemicals.

From WaPo article

Quote
Early in the shuttle's history, NASA discovered that the porous tiles tended to suck up moisture like a sponge, then crack in the freezing void of space.

The other way to solve expansion/contraction problems from changes caused by freezing water is loose mechanical tolerances.

Space Shuttle did not have loose mechanical tolerances.  That wasn't the design philosophy and you can't do that with aluminum or the materials available for backing in the 1970s.  The tiles were packed together and sealed, leaving little room for expansion that occurs when water freezes.

SpaceX, OTOH, has loose tolerances all over the place - in the super-wool padding, in the bayonet fastener, and between the tiles.   The padding deals with any plasma leaks resulting from those loose tolerances, as well as a skin that can handle 750degC.

They have already tested freezing in live testing, via cryogenic testing after the Starship getting wet.   What remains to prove is whether or not the tiles and padding were waterpoofed.   They *could* have been, but based on the design approach I don't think they are using the waterproofing they have on their MSDS disclosures.

Can't think of another way to find out (on our end) other than an updated disclosure form from the Florida facility, insider gossip, or a reflown Starship that has sat out in the weather.


https://www.washingtonpost.com/wp-srv/articles/A38144-2003Feb6.html
The tile cracking caused by water-impregnated tiles undergoing freeze/sublimation/boil cycles duringascent & descent is independent of attachment mechanism. A tile floating freely unattached to any vehicle would have the same issues.
If SpaceX does not rewaterproof tiles (and does not immediately place a landed Starship in a desiccating environment until liftoff, because atmospheric moisture exists regardless of inclement weather) then the tiles will need to be considered single-use items. Rewaterproofing is not optional.
Title: Re: Starship heat shield
Post by: RoboGoofers on 06/09/2022 01:40 pm
Based on the preponderance of evidence, I believe SpaceX has completely abandoned any waterproofing on tiles and the heat shield in general, including scotch-guard or other water proofing chemicals.

From WaPo article

Quote
Early in the shuttle's history, NASA discovered that the porous tiles tended to suck up moisture like a sponge, then crack in the freezing void of space.

The other way to solve expansion/contraction problems from changes caused by freezing water is loose mechanical tolerances.

Space Shuttle did not have loose mechanical tolerances.  That wasn't the design philosophy and you can't do that with aluminum or the materials available for backing in the 1970s.  The tiles were packed together and sealed, leaving little room for expansion that occurs when water freezes.

SpaceX, OTOH, has loose tolerances all over the place - in the super-wool padding, in the bayonet fastener, and between the tiles.   The padding deals with any plasma leaks resulting from those loose tolerances, as well as a skin that can handle 750degC.

They have already tested freezing in live testing, via cryogenic testing after the Starship getting wet.   What remains to prove is whether or not the tiles and padding were waterpoofed.   They *could* have been, but based on the design approach I don't think they are using the waterproofing they have on their MSDS disclosures.

Can't think of another way to find out (on our end) other than an updated disclosure form from the Florida facility, insider gossip, or a reflown Starship that has sat out in the weather.


https://www.washingtonpost.com/wp-srv/articles/A38144-2003Feb6.html
The tile cracking caused by water-impregnated tiles undergoing freeze/sublimation/boil cycles duringascent & descent is independent of attachment mechanism. A tile floating freely unattached to any vehicle would have the same issues.
If SpaceX does not rewaterproof tiles (and does not immediately place a landed Starship in a desiccating environment until liftoff, because atmospheric moisture exists regardless of inclement weather) then the tiles will need to be considered single-use items. Rewaterproofing is not optional.
What I wonder is what is the time scale for how long the tiles can sit without rewaterproofing before it becomes a problem? Hours, days, or weeks?
If it's days or longer, then they might be working with the specification that "well, we'll be doing rapid relaunch, so it's not a problem."
After all, shuttle was exposed to humidity for a much longer time between launches.

It will take them years to get to that launch cadence but they're not going to keep any of the existing starships anyway, and it'll probably be years before they have a finalized design. So until then, as long as they aren't carrying any downmass, losing a starship on decent is acceptable (and instructive).
Title: Re: Starship heat shield
Post by: DanClemmensen on 06/09/2022 02:00 pm
What I wonder is what is the time scale for how long the tiles can sit without rewaterproofing before it becomes a problem? Hours, days, or weeks?
If it's days or longer, then they might be working with the specification that "well, we'll be doing rapid relaunch, so it's not a problem."
After all, shuttle was exposed to humidity for a much longer time between launches.

It will take them years to get to that launch cadence but they're not going to keep any of the existing starships anyway, and it'll probably be years before they have a finalized design. So until then, as long as they aren't carrying any downmass, losing a starship on decent is acceptable (and instructive).
I still think they can take a (ahem) prophylactic approach and cover the Starship in a thin flexible conformal sheath each time it lands, which can be filled if needed with dry nitrogen.
Title: Re: Starship heat shield
Post by: edzieba on 06/09/2022 02:39 pm
After all, shuttle was exposed to humidity for a much longer time between launches.
The Orbiter also had the tiles re-waterproofed.
And in events where rain occurred before the Orbiter could be brought under cover and re-waterproofing performed, a protracted drying period of weeks was required to drive out the absorbed moisture.
Title: Re: Starship heat shield
Post by: JamesH65 on 06/09/2022 04:29 pm
So, SpaceX need to develop a waterproof tile that doesn't suffer this fate. Have they already done this? Seems like it would be high on the development schedule as its pretty much needed for high turnaround reusability. Is everyone assuming they haven't bothered or forgot to think about this?
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/09/2022 04:47 pm
After all, shuttle was exposed to humidity for a much longer time between launches.
The Orbiter also had the tiles re-waterproofed.
And in events where rain occurred before the Orbiter could be brought under cover and re-waterproofing performed, a protracted drying period of weeks was required to drive out the absorbed moisture.

Since that's 100% opposite of SpaceX's MO, that's not likely.

I'm in the midst of 2-3 pages of google search results, and nothing indicates that there's a problem with taking an untreated tile, soaking it in water, and throwing in the freezer.   Just that tiles "pop off" the shuttle, which could be from internal fractures or low tolerances.   And it was something like 6 out of 33,000 tiles that made them paranoid.  I don't think Starship will care about 6 tiles popping off unless they are contiguous.   Starship has a non-fragile layered system, with the next layer down being capable of taking 1300degC (or 1650degC) and the layer below that 750degC.

Apparently one can buy tiles.  So running a kitchen-top experiment is not beyond the realm of possibilities here.

There's also some work that was never flown that made the tiles permanently water proof using non-organic flourinated compounds.

We are also rehashing something that was discussed 2 years ago.  Worth reading the two pages after this post:

https://forum.nasaspaceflight.com/index.php?topic=50748.280
Title: Re: Starship heat shield
Post by: dwheeler on 06/09/2022 04:48 pm
So, SpaceX need to develop a waterproof tile that doesn't suffer this fate. Have they already done this? Seems like it would be high on the development schedule as its pretty much needed for high turnaround reusability. Is everyone assuming they haven't bothered or forgot to think about this?

I don't think anyone is assuming that. Why would you think that?
Title: Re: Starship heat shield
Post by: edzieba on 06/09/2022 05:20 pm
I'm in the midst of 2-3 pages of google search results, and nothing indicates that there's a problem with taking an untreated tile, soaking it in water, and throwing in the freezer.   Just that tiles "pop off" the shuttle, which could be from internal fractures or low tolerances.
See my post on the previous page of this thread, linking to the relevant document and quoting the relevant section (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2373374#msg2373374). The issue is nothing to do with tile attachment, the failure occurs within the body of the tile.
Title: Re: Starship heat shield
Post by: Barley on 06/09/2022 06:02 pm
So, SpaceX need to develop a waterproof tile that doesn't suffer this fate. Have they already done this? Seems like it would be high on the development schedule as its pretty much needed for high turnaround reusability. Is everyone assuming they haven't bothered or forgot to think about this?

I think SpaceX is willing to try things that may or may not work to see what happens.  Like carbon fiber BFR.
And they are willing to work with things that do not work perfectly.  Like fairing recovery.
And once they have something that kinda' works they will try to make it better.  Like F9 block 5.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/09/2022 06:21 pm
It's unknown what the batting composition is (superwool, kaowool, and other ASF & RCF products have been assumed, but no confirmation), but waterproofing impregnation could be done at manufacture or post manufacture, and like the tiles would need rewaterproofing after exposure to elevated temperatures.

We know from observation that they are taking no safety precautions when handling the "felt blanket".

We also know that it needs to have a useful temperature in excess of 750degC.

This considerably narrows the choices down to... superwool.

Superwool:  Human safe, working temperature 1300degC
Kaowool:  can cause cancer from fine particles:   1100 degC
Other ASF&RFC products:  Many cause cancer or severe lung irritation.  Cite one that doesn't.

http://www.lloyd-ris.co.uk/pdfs/datasheets/607%20Products%20MSDS.pdf
https://www.insulationindustries.com.au/wp-content/uploads/2022/05/MSDS_-_Kaowool_Blanket_and_Bulk_Products.pdf

My money is on an alumina fiber product like Saffil. Its good to 1650 C, ~3000 F.

John

Nice find!

Saffil:   Human safe, working temperature 1650C  (looks to be as safe or safer than Superwool)

MSDS:  https://www.unifrax.com/wp-content/uploads/2018/08/Unifrax-SDS-Saffil-V2.00-GB-en-160811.pdf

product brief:  http://www.lloyd-ris.co.uk/pdfs/datasheets/saffil%20blanket%5B1%5D.pdf

and a general overview of related material:  https://www.unifrax.com/product-category/blankets/?productcategory=236

Saffil FTW on tensile strength:  20x better than SuperWool

Saffil tensile Strength:  1500 kPa
SuperWool tensile stength:  70kPa

https://www.azom.com/properties.aspx?ArticleID=1720

Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/09/2022 06:47 pm
I'm in the midst of 2-3 pages of google search results, and nothing indicates that there's a problem with taking an untreated tile, soaking it in water, and throwing in the freezer.   Just that tiles "pop off" the shuttle, which could be from internal fractures or low tolerances.
See my post on the previous page of this thread, linking to the relevant document and quoting the relevant section (https://forum.nasaspaceflight.com/index.php?topic=50748.msg2373374#msg2373374). The issue is nothing to do with tile attachment, the failure occurs within the body of the tile.

Thanks for the reference.

Quoting from the paper:  https://sci-hub.se/https://doi.org/10.2514/6.2011-7308

Quote
Originally it was intended that the re-waterproofing needed to
be completed quickly for turnaround activities so spray on type materials were investigated as the factory
waterproofing burns out at temperatures above 1050 F. The first spray that was used was a fluro-polymer or
Scotchgard, which provided a thin film of low surface energy on the exterior surface of the tile glass coating. It was
recognized that this treatment would not provide an impervious barrier to water and that its effects would be highly
dependent on the surface tension of the water and resultant contact angle.

After the 2nd flight of Columbia inspection of the Orbiter indicated that in-plane failures of six HRSI tiles had
occurred on the right wing glove area. The depth of the missing material corresponded to the burnout zone of the
factory waterproofing or the 1050 F line. In addition, the surface coating of 12 tiles on the body flap showed
evidence of bubbling.

I confirm that your assertion is correct, there was internal destruction (see the "burnout zone" observation and bubbling).  It wasn't structural (though they had those problems too).

However, the destruction rate was very low.

6 tiles, as long as they are not contiguous, won't bother Starship at all.   For Orbiter, it could and was a catastrophe. 

Defense in depth helps a lot.   Nomex that backed the Orbiter tiles burns at 370degC.   Aluminum can only withstand 250degC.  Saffil on Starship can withstand 1650degC.   Starship's skin can withstand 750degC.   Missing tiles are largely irrelevant to Starship, just a maintenance problem.

This why I maintain that Starship's true "heat" shield is the "felt backing" (probably Saffil).  The tiles are there to hold on the backing and for a high emissivity to take maximum advantage of Stefan-Boltzmann.

SpaceX is unlikely to depend on a system that must be perfect every time and requires delicate indoor treatment processes.  They demonstrate this by manufacturing Starship in open-air tents and buildings, and leaving Starships half-tiled out in the rain and then running cryo tests on them.

Quote
To eliminate tile fracturing while the vehicle was on orbit the attitude was changed to provide a
favorable Sun attitude to drive out the water before ice damage could occur. The activity proved successful as post
flight evaluations revealed that no tiles underwent fracturing.

That seems like a mitigation SpaceX would easily adopt,.  Let's look for that in the first flights (if there's a cam for it)
Title: Re: Starship heat shield
Post by: edzieba on 06/10/2022 10:58 am
This why I maintain that Starship's true "heat" shield is the "felt backing" (probably Saffil).  The tiles are there to hold on the backing and for a high emissivity to take maximum advantage of Stefan-Boltzmann.
The 'true' heatshield is the thin borosilciate glass coating on the outer surface of the tiles. That is what radiates the majority of incoming energy from entry away from the vehicle again, and resists the chemical attach from the ionised atmosphere molecules in the entry plasma (e.g. superheated oxygen). The sintered silica tile body that the glass is coated onto supports that coating with low mass (lower than a solid glass sheet of comparable strength) and reduced conduction from the backside of that high temperature glass coating to the vehicle. The mats behind the tiles provide some mechanical isolation to the tile body, and allows the pin latching mechanism to work (needs to push 'in' slightly further than the final latched position in order to latch), and allows the tile backside surface to not need to be exactly conformal the the tank wall - i.e. the backside can be flat rather than a hollow sphere or cylinder section. Without that outer glass layer, the rest of the materials would be exposed to a much total higher energy, would absorb a dramatically higher proportion of that energy, and be under attack from high energy particles attempting to decompose the insulating fibres.
Title: Re: Starship heat shield
Post by: CMac on 06/10/2022 04:01 pm
You could even argue that the true heat shield is the shockwave. Something like 90 or 99% of the heating goes into the wake, never getting near the vehicle.
However from a direct heating point of view, that's a great point. The thin surface layer gets really hot and radiates most of the incident energy back out as a blazing bright light.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/10/2022 04:41 pm
This why I maintain that Starship's true "heat" shield is the "felt backing" (probably Saffil).  The tiles are there to hold on the backing and for a high emissivity to take maximum advantage of Stefan-Boltzmann.
The 'true' heatshield is the thin borosilciate glass coating on the outer surface of the tiles. That is what radiates the majority of incoming energy from entry away from the vehicle again, and resists the chemical attach from the ionised atmosphere molecules in the entry plasma (e.g. superheated oxygen). The sintered silica tile body that the glass is coated onto supports that coating with low mass (lower than a solid glass sheet of comparable strength) and reduced conduction from the backside of that high temperature glass coating to the vehicle. The mats behind the tiles provide some mechanical isolation to the tile body, and allows the pin latching mechanism to work (needs to push 'in' slightly further than the final latched position in order to latch), and allows the tile backside surface to not need to be exactly conformal the the tank wall - i.e. the backside can be flat rather than a hollow sphere or cylinder section. Without that outer glass layer, the rest of the materials would be exposed to a much total higher energy, would absorb a dramatically higher proportion of that energy, and be under attack from high energy particles attempting to decompose the insulating fibres.

Right, what you describe concerning heat removal is Stefan-Boltzmann (SB) at work.   Emissivity times temperature to the fourth power.

And you are correct averaged over the entire surface area of the Starship, SB removes a majority of the heat.

For Orbiter, that would apply also to every square inch, since there's no multi-layer defense.   Lose one tile, bad stuff happens.

For Starship, it does not apply to every square inch.  A few missing tiles cracked from being frozen while full of water (which is all the Space Shuttle ever experienced) is a non-event, because of layered defense.

Thus, SpaceX, as clearly shown by their operations, doesn't care whether Starship gets wet, and doesn't care very much about water proofing tiles.
Title: Re: Starship heat shield
Post by: edzieba on 06/10/2022 06:27 pm
For Starship, it does not apply to every square inch.  A few missing tiles cracked from being frozen while full of water (which is all the Space Shuttle ever experienced) is a non-event, because of layered defense.
Often asserted, yet to be proven. If heating of the stainless structure reduced strength beyond the minimum required, the tank will fail, and potentially the vehicle (due to semiballoon construction). That temperature is higher than that which would cause damage to the STS orbiter, but remains lower than the temperatures reached during EDL (or no TPS would be required in the first place). And because someone will probably bring up the STS-27 missing tile: That area had a substantial thickness of Aluminium behind it (~5mm Aluninium access panel, gapped over the Aluminium structure itself), rather than the ~3mm Stainless single-layer tank skin of Starship.
In addition, tiles in the highest heating areas of Starship (nose tip, flap roots) are adhered with RTV silicone in the same manner as on STS, without backing felt.
Quote
Thus, SpaceX, as clearly shown by their operations, doesn't care whether Starship gets wet, and doesn't care very much about water proofing tiles.
This assertion does not follow even if a single or small number of tile failures is tolerable: tile failure from water intrusion is a known failure mode. Absence of re-waterproofing is not going to affect a handful of isolated tiles, it will affect all tiles.

Current operations also do not provide insight into SpaceX's re-waterproofing solution, as they have yet to require re-waterproofing. The tiles are impregnated with MTMS to provide waterproofing from time of manufacture, but re-waterproofing is something that needs to occur after EDL (where the MTMS burns off). Since no Starship has yet to perform EDL, we have no public insight into this. And as we know the first Starship to return from orbit will be intentionally expended, and it is likely that the initial few Starships to return will not be re-used (as pace of development is likely to make them obsolete before they leave the pad) it may be some time before we see what SpaceX have planned for rewaterproofing.
Title: Re: Starship heat shield
Post by: Barley on 06/10/2022 06:42 pm
Starship can tolerate heat shield issues in another way:  For the bulk of missions (tankers, satellite deployments) a SS is returning empty and there is an acceptable loss rate, balance the costs of better protection v. replacement cost.  At that point they can still try to improve, but they don't need to improve.

Only a few missions will have valuable down mass or crew.  They may take special precautions.  They may test those on some, but not all, less critical reentries.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/11/2022 07:23 pm
This why I maintain that Starship's true "heat" shield is the "felt backing" (probably Saffil).  The tiles are there to hold on the backing and for a high emissivity to take maximum advantage of Stefan-Boltzmann.
The 'true' heatshield is the thin borosilciate glass coating on the outer surface of the tiles. That is what radiates the majority of incoming energy from entry away from the vehicle again, and resists the chemical attach from the ionised atmosphere molecules in the entry plasma (e.g. superheated oxygen). The sintered silica tile body that the glass is coated onto supports that coating with low mass (lower than a solid glass sheet of comparable strength) and reduced conduction from the backside of that high temperature glass coating to the vehicle. The mats behind the tiles provide some mechanical isolation to the tile body, and allows the pin latching mechanism to work (needs to push 'in' slightly further than the final latched position in order to latch), and allows the tile backside surface to not need to be exactly conformal the the tank wall - i.e. the backside can be flat rather than a hollow sphere or cylinder section. Without that outer glass layer, the rest of the materials would be exposed to a much total higher energy, would absorb a dramatically higher proportion of that energy, and be under attack from high energy particles attempting to decompose the insulating fibres.

I dived into Stefan-Boltzmann and heat flux equations, made a spreadsheet, and came to some conclusions.

In reaching these conclusions, I'm assuming a sandwich of tile, Saffil, and 304L stainless steel.  The tile and Saffil conduct some heat to the Starship skin and the 304L stainless emits the heat into the interior of the Starship.   Depending on the circumstances, the outer layer of either Saffil or tile emits a much larger chunk of heat away from Starship.

Conclusion 1: The tiles provides a heat flux reduction between 3x-5x averaged over the whole heat shield as compared to Saffil only.
Conclusion 2: Missing tiles don't matter as far protection of the stainless steel goes, the flux in that area of the heat shield rises 3x-5x but the temperature of the 304L stainless in that area only rises about 190degC, and is well away from its maximum operating temperature of 870degC.   The Saffil, assuming it remains mechanically intact, acts as a good backup protection against heat damage to the stainless steel if there is a tile failure.
Conclusion 3: The Saffil would reach its maximum operating temperature before the stainless would reach its max operating temperature.   There's redundancy in the Saffil layer.
Conclusion 4: Saffil emits enough heat away from Starship to be equivalent to tile emissions but at a slightly but not substantially higher temperature.

Spreadsheet at https://docs.google.com/spreadsheets/d/1nMR6EvrKo87L-QiZtSMF-_w3q4-uKHJY1FRuPTAQvjE/edit?usp=sharing

Discussion:
When you have one side of an object very hot known temperature, an insulator in the middle, and emission as the main carrier of heat on the inside, you can set the heat fluxes equal to each other and arrive at equilibrium values for the inside temperature.


q_insulation = k_insulation *(Toutside -Tinside)/thickness = SB_constant*emitter_constant*Tinside^4


For one insulation layer and one emitting layer this provides an easy analytical solution to finding equilibrium temperature.   For example at Saffil's maximum operating temperature of 1600degC, the stainless steel behind it will reach a temperature of 620degC, well within its maximum operating temperature of 870degC.   Assuming the outer surface does not get hotter than what tiles can manage (1260degC), the stainless steel would reach a temperature of 550degC.

For two insulation layers (Tile + Saffil) I was unable to create an analytical solution so I just solved numerically assuming conservation of energy.   At the tile's maximum operating temperature of 1260degC, the temperature at the outer surface of the Saffil reaches 610degC and the temperature of the stainless reaches 360degC.   

Assuming an average of of 850degC external temperature over the entire heat shield of the starship, the Saffil reaches an external temperature of 455degC and the stainless steel reaches a temperature of 300degC.


Assumptions:
I guessed at 1" tiles, 1" Saffil blanket, and used the available data sheets for both.  References in the spreadsheet.
Alumina has a surprisingly high emissivity of 0.75->0.90 depending what data source you look at.  Saffil is almost all alumina, but I did not find a specification specifically for Safill.  I used the lower number for alumina of 0.75.


I do not know the thickness of the tiles.  Any pixel counters figure that out yet?


Title: Re: Starship heat shield
Post by: edzieba on 06/11/2022 08:41 pm
Sadly EDL behaviour is not that simple to model. As well as radiant heating, you also have hot gas diffusion and catalytic heating, and the proportion and energy of each will vary with velocity and altitude. Unlike the glass coating, fibre mats (and particularly flexible fibre mats) are highly porous, can have fibres that are mobile (i.e. move around when gas impinges on them) and have an extremely high surface area for a given mass. That surface area works directly against you for the chemical effects in particular: if your saffil mat reacts and erodes faster than it can heart up, it's not able to do its job of reducing thermal conductivity.

Flexible high temperature battens were available for STS, were used on STS for backside TPS, and were the underlay for the HRSI and FRCI tiles. They were not ignored in favour of the headache of the tiles on the underside just for fun, but because they were not sufficient.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/11/2022 09:30 pm
Sadly EDL behaviour is not that simple to model. As well as radiant heating, you also have hot gas diffusion and catalytic heating, and the proportion and energy of each will vary with velocity and altitude. Unlike the glass coating, fibre mats (and particularly flexible fibre mats) are highly porous, can have fibres that are mobile (i.e. move around when gas impinges on them) and have an extremely high surface area for a given mass. That surface area works directly against you for the chemical effects in particular: if your saffil mat reacts and erodes faster than it can heart up, it's not able to do its job of reducing thermal conductivity.

That sounds correct for Orbiter and in English, but a sensitivity analysis on the conductivity of Saffil's says otherwise.

I agree we cannot count on Saffil operating at its specified thermal conductivity.  So how much worse can it get before the steel exceeds its operating temperature?

I created a row titled "tattered Saffil", and I had to make the conductivity of Saffil 6 times worse than the specification in order heat the stainless steel to its maximum operating temperature, at the same maximum radiative flux that the tile would have at its maximum operating temperature.

I think that the huge difference between Orbiter and Starship is the max operating temperature of 304L stainless is 870degC and aluminum is 200degC.

That's not a 4.35x difference, because that is not taking Stefan Boltzmann into account.  That 4.35x difference in temperature radiates a heck of a lot more of the heat into the interior of starship, and thus makes any insulation in the way far more effective.   It takes very little insulation between the stainless steel and the shockwave to drop the temperature down low enough for the stainless to handle it.

The actual ratio in S-B terms is 34 times the radiative capability of the stainless steel over aluminum.

34 times the radiative flux changes everything.   That's 34 times the temperature drop over a given insulation material.

It doesn't take very much insulation to protect small areas of stainless steel from its maximum temperature.

It does take a good average tile coverage to prevent all the prop from boiling off, however (at a guess, I haven't calculated the thermal mass of the propellant, we are still on "does one tile even matter"
Title: Re: Starship heat shield
Post by: edzieba on 06/12/2022 01:27 am
The obvious question you should be asking yourself is why SpaceX are not just covering Starahip - or anyone else covering any other vehicle for that matter, the product being over half a century old - with secured-in-place mats. Because if the tiles are just providing an aerosurface or just holding the mats on, there are lighter and less complex methods than RCG-coated sintered-silica tiles.
Radiative transfer alone is not sufficient to model re-entry.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/12/2022 04:38 am
The obvious question you should be asking yourself is why SpaceX are not just covering Starahip - or anyone else covering any other vehicle for that matter, the product being over half a century old - with secured-in-place mats. Because if the tiles are just providing an aerosurface or just holding the mats on, there are lighter and less complex methods than RCG-coated sintered-silica tiles.

Several reasons to be using tiles and not just Saffil matts:

1.  3x-5x less heat transfer into the interior of Starship so as to not boil off all the starship fuel.  I have yet to calculate how much heat flux Starsip can actually handle into the interior and not boil everything off, this might be a minor deal or a big deal.
2.  Secure the mats.   Whatever method secures the mats has to be light, strong, and withstand 1300degC+, and withstand more air movement than the mats can..   We've investigated what materials can do that in threads far above, there's nothing lighter than coated sintered tiles that we could find (or SpaceX for that matter)
3.  As you pointed out, protection from plasma etching.
4.  Redundancy.   There's no redundancy if there are just mats.
5.  Replacement of small simple parts when failures or damage occur.

Quote
Radiative transfer alone is not sufficient to model re-entry.

Radiative transfer modeling is necessary but not sufficient, and points out where weakness and redundancies might exist.   6x is a lot of redundancy for small tile-size spots on the skin.

I modeled Orbiter's radiative transfer.  There's very little redundancy anywhere.  One tile fails at wrong time/place, catastrophe happens, just based on a simple best-case radiative transfer model, and not counting all the other valid issues you bring up.

Starship is an order of magnitude improvement in heat shield capability over the Orbiter, simply because of the stainless steel's ability to withstand and radiate heat.   I didn't fully realize what a big deal that was until I did the math.   Temperature to the fourth power is a gigantic lever.   There's also the fact that modern human-safe high temp insulation exists now, and it didn't prior to about 1976 or so (more widely late 1980s)

The issues you bring up, alas, require finite element analysis, which SpaceX being experts at, is likely being done.   But simple equations can tell us that there's a lot of redundancy in terms of thermal characteristics of Starship, much more than for Orbiter.
Title: Re: Starship heat shield
Post by: edzieba on 06/12/2022 08:10 am
1.  3x-5x less heat transfer into the interior of Starship so as to not boil off all the starship fuel.  I have yet to calculate how much heat flux Starsip can actually handle into the interior and not boil everything off, this might be a minor deal or a big deal.
On entry, the main tank volumes will be empty of liquids, and at moderate gas pressure required for structural stability.
Quote
2.  Secure the mats.   Whatever method secures the mats has to be light, strong, and withstand 1300degC+, and withstand more air movement than the mats can..   We've investigated what materials can do that in threads far above, there's nothing lighter than coated sintered tiles that we could find (or SpaceX for that matter)
The fibres the non-woven matting are made from can be woven into fibres, and used to stitch to backside support posts (e.g. the existing clip stanchions). This is how existing heatproof blankets are mounted.
Quote
There's also the fact that modern human-safe high temp insulation exists now, and it didn't prior to about 1976 or so (more widely late 1980s)
Saffil mat dates from the early 70s.


The tiles are the primary TPS, the mat's purpose is primarily mechanical. There are large areas of the vehicle with tiles only but no mat underlay, and zero areas of the vehicle with mat only and no tile overlay. Not even on the backshell, even the transition region is fully tiled.
Title: Re: Starship heat shield
Post by: sebk on 06/14/2022 08:58 pm
The obvious question you should be asking yourself is why SpaceX are not just covering Starahip - or anyone else covering any other vehicle for that matter, the product being over half a century old - with secured-in-place mats. Because if the tiles are just providing an aerosurface or just holding the mats on, there are lighter and less complex methods than RCG-coated sintered-silica tiles.
Radiative transfer alone is not sufficient to model re-entry.

TBE Shuttle  leeward side was covered by mats (but very different from Saffil) and they were handling temperatures stainless steel is supposed to handle uncovered.

Also various inflatable heat shield prototypes were made from fabric not tiles. And they were supposed to handle re-entry "head on" so with temperatures around 1200°C
Title: Re: Starship heat shield
Post by: Asteroza on 06/15/2022 02:42 am
The obvious question you should be asking yourself is why SpaceX are not just covering Starahip - or anyone else covering any other vehicle for that matter, the product being over half a century old - with secured-in-place mats. Because if the tiles are just providing an aerosurface or just holding the mats on, there are lighter and less complex methods than RCG-coated sintered-silica tiles.
Radiative transfer alone is not sufficient to model re-entry.

TBE Shuttle  leeward side was covered by mats (but very different from Saffil) and they were handling temperatures stainless steel is supposed to handle uncovered.

Also various inflatable heat shield prototypes were made from fabric not tiles. And they were supposed to handle re-entry "head on" so with temperatures around 1200°C

I'm pretty sure the inflatable heatshields were one use only, and many had a hard center/disk that handles the initial shockwave. I think some of them worked by some sort of charring layer protection as well?
Title: Re: Starship heat shield
Post by: edzieba on 06/15/2022 08:42 am
Yes, HIAD used a fabric backing to carry an ablative TPS.

Backshell environment is a quite different environment to the primary TPS, which is why you can have vehicles with complex to manufacture cast-in-place ablator shells on one face, and 'slopped on with a spatula' ablative coatings on the backshell. And why Saffil mats are adequate for the STS orbiter upper surface, but not for the lower surface or surfaces between the two thermal regimes. NASA replaced as much of the LRSI tiles as they could with FIB, but only in areas where it could handle the reentry environment.
Title: Re: Starship heat shield
Post by: adrianwyard on 06/23/2022 02:42 am
Is there any consensus on what SpaceX will likely do to keep the tiles attached during dynamic events? If not, what are the options?

Would simply bonding them (a la Shuttle) be so bad? And a related question: why might they be trying to make the pin method work instead?
Title: Re: Starship heat shield
Post by: Redclaws on 06/23/2022 03:09 am
Because bonding them is intrinsically harder for maintenance than pins.  That seems like enough answer by itself, doesn’t it?
Title: Re: Starship heat shield
Post by: adrianwyard on 06/23/2022 03:30 am
That was my guess too. And the SpaceX MO is to try the ideal method first to see if that works as is, i.e. "can we just slap on a new tile when one's needed?" But the pin attachments we've seen so far are clearly not working that well.
Title: Re: Starship heat shield
Post by: adrianwyard on 06/23/2022 03:59 am
Related note: a pin attachment allows for quick-and-easy replacement of tiles, but there's no provision for repairing the mat. Surely we can't assume mats never need repairing? What if a tile is lost on ascent and the mat has to deal with the full heat flux on return?

I wonder how big the mats are, and how they deal with the seams. If mat repairs are tolerable, then bond the tile, and replace its mat too when needed. But if you have to replace mats seam to seam that'll involve a lot of tiles.

Perhaps one compromise is to produce large panels of tiles bonded to their underlying mat that can be replaced as a unit. A single panel design would cover a lot of the area...
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/23/2022 04:19 am
Related note: a pin attachment allows for quick-and-easy replacement of tiles, but there's no provision for repairing the mat. Surely we can't assume mats never need repairing? What if a tile is lost on ascent and the mat has to deal with the full heat flux on return?

I wonder how big the mats are, and how they deal with the seams. If mat repairs are tolerable, then bond the tile, and replace its mat too when needed. But if you have to replace mats seam to seam that'll involve a lot of tiles.

Perhaps one compromise is to produce large panels of tiles bonded to their underlying mat that can be replaced as a unit. A single panel design would cover a lot of the area...

IF a tile is lost and the mat in the open area is damaged, then my guess, since one doesn't want mat seams right at tile seams, is to replace the 6 surrounding tiles as well and patch the mat with a circle patch.

So a spot damaged mat involves replacing 7 tiles.

Not great, but not horrible.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/23/2022 04:19 am
That was my guess too. And the SpaceX MO is to try the ideal method first to see if that works as is, i.e. "can we just slap on a new tile when one's needed?" But the pin attachments we've seen so far are clearly not working that well.

Why do you think they are not "working well"?   Need to define "working well".
Title: Re: Starship heat shield
Post by: adrianwyard on 06/23/2022 04:38 am
I'd say the pins are working well if all tiles stay firmly attached during all normal spacecraft operations, starting with static fire.
Title: Re: Starship heat shield
Post by: DanClemmensen on 06/23/2022 04:44 am
I'd say the pins are working well if all tiles stay firmly attached during all normal spacecraft operations, starting with static fire.
I'd say the tiles are working well if a minor sudden internal overpressure event  ("THUMP") fails to dislodge any tiles. We saw such an event on S24, apparently accidentally induced, and some tiles fell off. Maybe they should do it on purpose.
Title: Re: Starship heat shield
Post by: ThatOldJanxSpirit on 06/23/2022 05:33 am
I'd say the pins are working well if all tiles stay firmly attached during all normal spacecraft operations, starting with static fire.
I'd say the tiles are working well if a minor sudden internal overpressure event  ("THUMP") fails to dislodge any tiles. We saw such an event on S24, apparently accidentally induced, and some tiles fell off. Maybe they should do it on purpose.

If speculation that this was a header tank autogenous pressurisation line failure is correct this would hardly be a minor event. Rather than overpressure damage it was more likely the result of the pipe whipping the the vehicle side.
Title: Re: Starship heat shield
Post by: DanClemmensen on 06/23/2022 05:36 am
I'd say the pins are working well if all tiles stay firmly attached during all normal spacecraft operations, starting with static fire.
I'd say the tiles are working well if a minor sudden internal overpressure event  ("THUMP") fails to dislodge any tiles. We saw such an event on S24, apparently accidentally induced, and some tiles fell off. Maybe they should do it on purpose.
If speculation that this was a header tank autogenous pressurisation line failure is correct this would hardly be a minor event. Rather than overpressure damage it was more likely the result of the pipe whipping the the vehicle side.
Clearly, if they want to use a deliberate "thump" to test the tiles they will find a non-destructive way to do it.
Title: Re: Starship heat shield
Post by: edzieba on 06/23/2022 10:42 am
Because bonding them is intrinsically harder for maintenance than pins.  That seems like enough answer by itself, doesn’t it?
They already bond the tiles on the nose, flap edges, flap base, joints between ring segments, etc.
Bonding tiles is known to work (flight proven on STS), but is messy, slow, and expensive both to install and to maintain. The pinned connections are intended to be faster, cheaper, and easier to install and maintain. Pins are used where they can (large areas of simply geometry) and not used where they can't. Time will tell whether the pins achieve their design goals, but adhesive remains as a fallback option if necessary - albeit an undesirable one - but continued iteration on the pin system is more likely.
If speculation that this was a header tank autogenous pressurisation line failure is correct this would hardly be a minor event. Rather than overpressure damage it was more likely the result of the pipe whipping the the vehicle side.
Clearly, if they want to use a deliberate "thump" to test the tiles they will find a non-destructive way to do it.
Only if there are any 'thump' sources that are liable to occur without more critical damage. e.g. the header tank line failure would have already been a loss-of-vehicle failure due to not having a header tank available for the landing burn, regardless of tile condition.
Title: Re: Starship heat shield
Post by: dwheeler on 06/23/2022 02:11 pm
Because bonding them is intrinsically harder for maintenance than pins.  That seems like enough answer by itself, doesn’t it?
They already bond the tiles on the nose, flap edges, flap base, joints between ring segments, etc.
Bonding tiles is known to work (flight proven on STS), <snip>

Except tiles were never bonded to a cryogenic tank on STS. This is new territory...
Title: Re: Starship heat shield
Post by: DanClemmensen on 06/23/2022 02:45 pm
If speculation that this was a header tank autogenous pressurisation line failure is correct this would hardly be a minor event. Rather than overpressure damage it was more likely the result of the pipe whipping the the vehicle side.
Clearly, if they want to use a deliberate "thump" to test the tiles they will find a non-destructive way to do it.
Only if there are any 'thump' sources that are liable to occur without more critical damage. e.g. the header tank line failure would have already been a loss-of-vehicle failure due to not having a header tank available for the landing burn, regardless of tile condition.
IF they chose to do a deliberate "thump" (an idle armchair idea, not something SpaceX ever mentioned) then it would use a carefully engineered system that has little risk of damage. It might be designed for use only during the manufacturing test, or to be used after any tile work during refurbishment, or even used each time the tanks are filled. As much as possible of the mass of the system would be on the ground, not in the Starship.
Title: Re: Starship heat shield
Post by: edzieba on 06/23/2022 03:30 pm
If speculation that this was a header tank autogenous pressurisation line failure is correct this would hardly be a minor event. Rather than overpressure damage it was more likely the result of the pipe whipping the the vehicle side.
Clearly, if they want to use a deliberate "thump" to test the tiles they will find a non-destructive way to do it.
Only if there are any 'thump' sources that are liable to occur without more critical damage. e.g. the header tank line failure would have already been a loss-of-vehicle failure due to not having a header tank available for the landing burn, regardless of tile condition.
IF they chose to do a deliberate "thump" (an idle armchair idea, not something SpaceX ever mentioned) then it would use a carefully engineered system that has little risk of damage. It might be designed for use only during the manufacturing test, or to be used after any tile work during refurbishment, or even used each time the tanks are filled. As much as possible of the mass of the system would be on the ground, not in the Starship.
You missed my point: what potential sources of a 'thump' exist that would not otherwise result in LoV or LoM? Or in other words, is this a scenario that needs to be tested for in the first place?
For example: testing for tile adhesion against flowing saltwater is not a useful test to conduct, because if the vehicle is experiencing flowing saltwater at all then something has already gone very wrong and tile adhesion is no longer a concern.
Title: Re: Starship heat shield
Post by: rsdavis9 on 06/23/2022 04:44 pm
They already bond the tiles on the nose, flap edges, flap base, joints between ring segments, etc.
Bonding tiles is known to work (flight proven on STS), but is messy, slow, and expensive both to install and to maintain. The pinned connections are intended to be faster, cheaper, and easier to install and maintain. Pins are used where they can (large areas of simply geometry) and not used where they can't. Time will tell whether the pins achieve their design goals, but adhesive remains as a fallback option if necessary - albeit an undesirable one - but continued iteration on the pin system is more likely.


An interesting question/observation will be what we see after their first orbital test:
Do they do more pin tiles.
Or do they do more glued tiles.

I for one bet they will do more of the tile surface with pins.
For example the joint between segments would seem to be a place pins would be easier than gluing.

Quote
Except tiles were never bonded to a cryogenic tank on STS. This is new territory...

And the " joints between ring segments" is glued on cryogenic and so far they haven't fallen off.
 
Title: Re: Starship heat shield
Post by: adrianwyard on 06/23/2022 05:07 pm
Do we know how the pins have been mechanically attached to the tiles to date? I've read a few guesses but nothing definitive.

The tiles appear to be just as brittle as those on the Shuttle, so spreading the connecting load over much of the tiles interior seems necessary.

...Bench-testing pin attachments with representative loads seems pretty easy, so it's unclear why they're installing a design that falls of the test vehicles during static fires, etc. My only guess is they want practice at acreage installation right now, knowing the pin/tile design will need to change.
Title: Re: Starship heat shield
Post by: whitelancer64 on 06/23/2022 05:23 pm
Do we know how the pins have been mechanically attached to the tiles to date? I've read a few guesses but nothing definitive.

The tiles appear to be just as brittle as those on the Shuttle, so spreading the connecting load over much of the tiles interior seems necessary.

...Bench-testing pin attachments with representative loads seems pretty easy, so it's unclear why they're installing a design that falls of the test vehicles during static fires, etc. My only guess is they want practice at acreage installation right now, knowing the pin/tile design will need to change.

If the pin attachment design needed to change, it would have by now. The "acreage" testing was done long ago, they've completed tiling multiple test vehicles and Starships, that have undergone full cryo testing, the test flights, etc. A few tiles getting damaged or falling off here and there does not warrant a complete redesign of the system. At worst it means a few specific areas might need tweaking.
Title: Re: Starship heat shield
Post by: adrianwyard on 06/23/2022 06:37 pm
Hopefully you are correct and it's no more than tweaking.  But the current state, i.e. 'a few tiles getting damaged or falling off here and there' does not make for a fully and rapidly reusable vehicle.

To be fair, seeing these problems on actual hardware is less shocking when you factor in SpaceX's hardware rich design approach. There are other aspects that are also not yet matured, e.g. orbital refueling mechanisms, ship catch pins/attachments.
Title: Re: Starship heat shield
Post by: wannamoonbase on 06/23/2022 07:36 pm
Do we know how the pins have been mechanically attached to the tiles to date? I've read a few guesses but nothing definitive.

The tiles appear to be just as brittle as those on the Shuttle, so spreading the connecting load over much of the tiles interior seems necessary.

...Bench-testing pin attachments with representative loads seems pretty easy, so it's unclear why they're installing a design that falls of the test vehicles during static fires, etc. My only guess is they want practice at acreage installation right now, knowing the pin/tile design will need to change.

If the pin attachment design needed to change, it would have by now. The "acreage" testing was done long ago, they've completed tiling multiple test vehicles and Starships, that have undergone full cryo testing, the test flights, etc. A few tiles getting damaged or falling off here and there does not warrant a complete redesign of the system. At worst it means a few specific areas might need tweaking.

I think you maybe wrong with the idea, that if there needs to be changes it would have been done by now.  Starship has not gone through a full stack static fire, reached LEO or attempted a re-entry. 

SpaceX is always trying to find the minimal viable product.  I think they maybe busy with everything needed to reach orbit and may also be waiting to see it this design works and when things fail, if they fail, before putting resources in the heatshield.

S24 is likely highly instrumented and if there are problems SpaceX will know exactly what forces create it and they can adapt to that. 

I think they will get it all sorted but that the heatshield is the single biggest risk item to the success of this project.
Title: Re: Starship heat shield
Post by: whitelancer64 on 06/23/2022 07:47 pm
Do we know how the pins have been mechanically attached to the tiles to date? I've read a few guesses but nothing definitive.

The tiles appear to be just as brittle as those on the Shuttle, so spreading the connecting load over much of the tiles interior seems necessary.

...Bench-testing pin attachments with representative loads seems pretty easy, so it's unclear why they're installing a design that falls of the test vehicles during static fires, etc. My only guess is they want practice at acreage installation right now, knowing the pin/tile design will need to change.

If the pin attachment design needed to change, it would have by now. The "acreage" testing was done long ago, they've completed tiling multiple test vehicles and Starships, that have undergone full cryo testing, the test flights, etc. A few tiles getting damaged or falling off here and there does not warrant a complete redesign of the system. At worst it means a few specific areas might need tweaking.

I think you maybe wrong with the idea, that if there needs to be changes it would have been done by now.  Starship has not gone through a full stack static fire, reached LEO or attempted a re-entry. 

SpaceX is always trying to find the minimal viable product.  I think they maybe busy with everything needed to reach orbit and may also be waiting to see it this design works and when things fail, if they fail, before putting resources in the heatshield.

S24 is likely highly instrumented and if there are problems SpaceX will know exactly what forces create it and they can adapt to that. 

I think they will get it all sorted but that the heatshield is the single biggest risk item to the success of this project.

Then let me be very clear: none of the testing we have seen to date indicates the need for a tile attachment design change. The vast majority of heat shield tiles remained on the Starship, even in the very earliest tests when many were broken or fell off. During the most recent tests we have seen only a very few break or fall off. It's not a systemic problem.
Title: Re: Starship heat shield
Post by: wannamoonbase on 06/23/2022 08:34 pm
Do we know how the pins have been mechanically attached to the tiles to date? I've read a few guesses but nothing definitive.

The tiles appear to be just as brittle as those on the Shuttle, so spreading the connecting load over much of the tiles interior seems necessary.

...Bench-testing pin attachments with representative loads seems pretty easy, so it's unclear why they're installing a design that falls of the test vehicles during static fires, etc. My only guess is they want practice at acreage installation right now, knowing the pin/tile design will need to change.

If the pin attachment design needed to change, it would have by now. The "acreage" testing was done long ago, they've completed tiling multiple test vehicles and Starships, that have undergone full cryo testing, the test flights, etc. A few tiles getting damaged or falling off here and there does not warrant a complete redesign of the system. At worst it means a few specific areas might need tweaking.

I think you maybe wrong with the idea, that if there needs to be changes it would have been done by now.  Starship has not gone through a full stack static fire, reached LEO or attempted a re-entry. 

SpaceX is always trying to find the minimal viable product.  I think they maybe busy with everything needed to reach orbit and may also be waiting to see it this design works and when things fail, if they fail, before putting resources in the heatshield.

S24 is likely highly instrumented and if there are problems SpaceX will know exactly what forces create it and they can adapt to that. 

I think they will get it all sorted but that the heatshield is the single biggest risk item to the success of this project.

Then let me be very clear: none of the testing we have seen to date indicates the need for a tile attachment design change. The vast majority of heat shield tiles remained on the Starship, even in the very earliest tests when many were broken or fell off. During the most recent tests we have seen only a very few break or fall off. It's not a systemic problem.

I agree that currently there does not appear to be a need for design change.  But they need to get to a point where zero tiles fall off. 

Any number of lost tiles greater than zero is a problem.  But until they have flight experience no one knows for sure. 
Title: Re: Starship heat shield
Post by: whitelancer64 on 06/23/2022 08:59 pm
I just think there's way too much "OMG a couple tiles fell off, time to scrap everything and redesign the entire heat shield" going on here, and not enough, "Hey, only a couple tiles fell off, looks like SpaceX has nearly got the heat shield system down pat."

Frankly of all the issues that SpaceX has to deal with, I have always considered the heat shield to be a very minor concern.
Title: Re: Starship heat shield
Post by: wannamoonbase on 06/23/2022 09:33 pm
I just think there's way too much "OMG a couple tiles fell off, time to scrap everything and redesign the entire heat shield" going on here, and not enough, "Hey, only a couple tiles fell off, looks like SpaceX has nearly got the heat shield system down pat."

Frankly of all the issues that SpaceX has to deal with, I have always considered the heat shield to be a very minor concern.

Well it's a minor concern right up to entry interface.  If they get to that point they have proven a lot of things.

Getting Superheavy successfully off the ground and to MECO makes me anxious every time I think about it.

If they get into orbit then they can worry about the heatshield. 

Title: Re: Starship heat shield
Post by: livingjw on 06/23/2022 09:44 pm
I just think there's way too much "OMG a couple tiles fell off, time to scrap everything and redesign the entire heat shield" going on here, and not enough, "Hey, only a couple tiles fell off, looks like SpaceX has nearly got the heat shield system down pat."

Frankly of all the issues that SpaceX has to deal with, I have always considered the heat shield to be a very minor concern.

Minor? By far the most expensive aspect of the Space Shuttle was TPS maintenance. It consumed ~20,000 man-hours per flight.

John
Title: Re: Starship heat shield
Post by: Hog on 06/23/2022 09:44 pm
I just think there's way too much "OMG a couple tiles fell off, time to scrap everything and redesign the entire heat shield" going on here, and not enough, "Hey, only a couple tiles fell off, looks like SpaceX has nearly got the heat shield system down pat."

Frankly of all the issues that SpaceX has to deal with, I have always considered the heat shield to be a very minor concern.

Well it's a minor concern right up to entry interface.  If they get to that point they have proven a lot of things.

Getting Superheavy successfully off the ground and to MECO makes me anxious every time I think about it.

If they get into orbit then they can worry about the heatshield.
Isn't it required, orbit or not? 
 
I was under the impression that SS's heatshield is a make or break deal for quick-turnaround reuseability?
Title: Re: Starship heat shield
Post by: whitelancer64 on 06/23/2022 09:53 pm
I just think there's way too much "OMG a couple tiles fell off, time to scrap everything and redesign the entire heat shield" going on here, and not enough, "Hey, only a couple tiles fell off, looks like SpaceX has nearly got the heat shield system down pat."

Frankly of all the issues that SpaceX has to deal with, I have always considered the heat shield to be a very minor concern.

Minor? By far the most expensive aspect of the Space Shuttle was TPS maintenance. It consumed ~20,000 man-hours per flight.

John

Which is completely irrelevant to Starship. Their tiles are not made of the same material, are not installed in the same way, and are not 24,500 unique shapes. The game changer is the fact that over 90% of the Starship tiles are the exact same shape. We have seen Starship tile replacement done by people just going up in a scissor lift.
Title: Re: Starship heat shield
Post by: whitelancer64 on 06/23/2022 09:56 pm
I just think there's way too much "OMG a couple tiles fell off, time to scrap everything and redesign the entire heat shield" going on here, and not enough, "Hey, only a couple tiles fell off, looks like SpaceX has nearly got the heat shield system down pat."

Frankly of all the issues that SpaceX has to deal with, I have always considered the heat shield to be a very minor concern.

Well it's a minor concern right up to entry interface.  If they get to that point they have proven a lot of things.

Getting Superheavy successfully off the ground and to MECO makes me anxious every time I think about it.

If they get into orbit then they can worry about the heatshield.

Honestly, even the first reentry doesn't worry me. Humanity has been doing heat shields on spacecraft for a long time, with very few failures. The only one that comes to mind is Columbia, and that wasn't a problem with the heat shield design per se. The Shuttles had a lot of near-disasters due to debris strikes, something that Starship does not really have to deal with. Other than that I'm not sure if a heat shield has ever been the cause of a failure during reentry. More relevantly, SpaceX hasn't had any big heat shield issues during reentry with the Dragons.

As an aside, I have always considered in orbit refueling to be the number one problem they need to solve, and way too many people, both here and elsewhere, consider that practically a fait accompli.
Title: Re: Starship heat shield
Post by: Hog on 06/23/2022 10:51 pm
I just think there's way too much "OMG a couple tiles fell off, time to scrap everything and redesign the entire heat shield" going on here, and not enough, "Hey, only a couple tiles fell off, looks like SpaceX has nearly got the heat shield system down pat."

Frankly of all the issues that SpaceX has to deal with, I have always considered the heat shield to be a very minor concern.

Minor? By far the most expensive aspect of the Space Shuttle was TPS maintenance. It consumed ~20,000 man-hours per flight.

John

Which is completely irrelevant to Starship. Their tiles are not made of the same material, are not installed in the same way, and are not 24,500 unique shapes. The game changer is the fact that over 90% of the Starship tiles are the exact same shape. We have seen Starship tile replacement done by people just going up in a scissor lift.
We have seen shuttle tile install with installers standing on the ground.
Some are the same material.
The large acreage SS tiles are the same shape, which of course has advantages, but is physical maintenance  really a "game changer" one of them? The shape of the tiles didn't create all the human-hours for STS maintenance.
Different, yes, completely irrelevant, far from it.
Title: Re: Starship heat shield
Post by: whitelancer64 on 06/23/2022 11:06 pm
I just think there's way too much "OMG a couple tiles fell off, time to scrap everything and redesign the entire heat shield" going on here, and not enough, "Hey, only a couple tiles fell off, looks like SpaceX has nearly got the heat shield system down pat."

Frankly of all the issues that SpaceX has to deal with, I have always considered the heat shield to be a very minor concern.

Minor? By far the most expensive aspect of the Space Shuttle was TPS maintenance. It consumed ~20,000 man-hours per flight.

John

Which is completely irrelevant to Starship. Their tiles are not made of the same material, are not installed in the same way, and are not 24,500 unique shapes. The game changer is the fact that over 90% of the Starship tiles are the exact same shape. We have seen Starship tile replacement done by people just going up in a scissor lift.
We have seen shuttle tile install with installers standing on the ground.
Some are the same material.
The large acreage SS tiles are the same shape, which of course has advantages, but is physical maintenance  really a "game changer" one of them? The shape of the tiles didn't create all the human-hours for STS maintenance.
Different, yes, completely irrelevant, far from it.

Compared to the very time consuming and labor intensive maintenance that was required for the Shuttle tiles, yes, it is a game-changer.

The shape of the tiles makes it far, far easier to replace a tile. You don't need to make a new one every time, you can just take one from a pile of spares.
Title: Re: Starship heat shield
Post by: Slarty1080 on 06/24/2022 01:18 am

it seems to me that the tile design and application method really is a game changer it terms of speed and cost. The space shuttle was measured in the number of tiles/man/week, Starship is tiles/man/minute

https://en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_system#Slow_tile_application (https://en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_system#Slow_tile_application)

https://www.reddit.com/r/SpaceXLounge/comments/m4ii51/video_of_spacex_installing_starship_heat_shield/ (https://www.reddit.com/r/SpaceXLounge/comments/m4ii51/video_of_spacex_installing_starship_heat_shield/)
Title: Re: Starship heat shield
Post by: Redclaws on 06/24/2022 01:29 am
I just think there's way too much "OMG a couple tiles fell off, time to scrap everything and redesign the entire heat shield" going on here, and not enough, "Hey, only a couple tiles fell off, looks like SpaceX has nearly got the heat shield system down pat."

Frankly of all the issues that SpaceX has to deal with, I have always considered the heat shield to be a very minor concern.

Well it's a minor concern right up to entry interface.  If they get to that point they have proven a lot of things.

Getting Superheavy successfully off the ground and to MECO makes me anxious every time I think about it.

If they get into orbit then they can worry about the heatshield.

Honestly, even the first reentry doesn't worry me. Humanity has been doing heat shields on spacecraft for a long time, with very few failures. The only one that comes to mind is Columbia, and that wasn't a problem with the heat shield design per se. The Shuttles had a lot of near-disasters due to debris strikes, something that Starship does not really have to deal with. Other than that I'm not sure if a heat shield has ever been the cause of a failure during reentry. More relevantly, SpaceX hasn't had any big heat shield issues during reentry with the Dragons.

As an aside, I have always considered in orbit refueling to be the number one problem they need to solve, and way too many people, both here and elsewhere, consider that practically a fait accompli.

While a heat shield has rarely been the cause of failure, consider that might be partly because they receive an enormous amount of attention.  The idea that they’re challenging is coming from somewhere.  In carefully engineered systems designed with a decent domain understanding, the failures don’t necessarily come more from the “hard” parts.  The problem is known so the failures come from oversights or unknowns rather than intrinsic difficulties.
Title: Re: Starship heat shield
Post by: darkenfast on 06/24/2022 02:28 am
We've seen how quickly tiles can be installed on SS. We've seen some tiles fall off. The number of tiles falling off seems to be decreasing.

Overall, the steel/matting/pin-secured-tile-system seems to be working. It probably needs to do better for routine reuse.

Maybe the next iteration of SS models (I forget which number that will be), will show up with a different pattern/number/shape of pins. Those pins are installed by robotic machinery. We won't know until the Watchers spot it.

If that happens, it will be a lesson in just just how valuable the SpaceX system of "How to mass-produce a big rocket" is. My opinion is that the whole of what is going on at Boca Chica and the other SpaceX sites is more impressive than the vehicles!

Remember: They're not reusing the first few rockets anyway, just getting a lot of data.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/24/2022 04:05 am
The only one that comes to mind is Columbia, and that wasn't a problem with the heat shield design per se. The Shuttles had a lot of near-disasters due to debris strikes, something that Starship does not really have to deal with.

It was absolutely a design problem with the Orbiter.  Thousands of single points of failure - a design problem that couldn't be fixed with the tech available at the time.

Stainless steel completely changes the design.  There are few single points of failure in the Starship's heat shield system (maybe around the "wings" that impact the plasma flow and don't have a mat backing, even then not sure, we can't do fluid simulations, SpaceX are experts).

Orbiter, OTOH, had hundreds to thousands of single points of failure - tiles in critically hot places that if damaged/fell off, meant breakup on re-entry.

I don't think 1100degC at the stainless steel in a single hot spot will cause a Starship to break up unless it's at a critical stress point.  It may take i out of commission (or they may weld a patch around it).   The pins will routinely see that kind of temperature - and shrug it off, as they aren't a high stress point.

I did the math a few pages back.  TL;DR the huge difference a little bit of insulation makes when operating temperature of underlying structure is 870degC vs. 250degC.    take that ratio in kelvin, to the *fourth* power (Stefan-Boltzmann). Starship hotspots can withstand 35 times the heat flux of the Orbiter.

Title: Re: Starship heat shield
Post by: edzieba on 06/24/2022 11:48 am
I just think there's way too much "OMG a couple tiles fell off, time to scrap everything and redesign the entire heat shield" going on here, and not enough, "Hey, only a couple tiles fell off, looks like SpaceX has nearly got the heat shield system down pat."

Frankly of all the issues that SpaceX has to deal with, I have always considered the heat shield to be a very minor concern.

Minor? By far the most expensive aspect of the Space Shuttle was TPS maintenance. It consumed ~20,000 man-hours per flight.

John

Which is completely irrelevant to Starship. Their tiles are not made of the same material, are not installed in the same way, and are not 24,500 unique shapes. The game changer is the fact that over 90% of the Starship tiles are the exact same shape. We have seen Starship tile replacement done by people just going up in a scissor lift.
- The tiles are made of the same material: sintered Silica fibres, coated with borosilicate glass, then impregnated with MTMS (methyltrimethoxysilane) for initial waterproofing. They are nearly identical to the STS tiles in composition, though not in shape.
- The pinned tiles are attached differently, but the bonded tiles are attached very similarly to the STS tiles: adhesive bonded to a refractory felt backer that is adhesive bonded to the vehicle skin, with refractory felt packets between tiles (also adhesive bonded). On past Starships we saw them using the same distinctive red Dowsil RTV silicone that was use don STS, but recent vehicles have switched to a white adhesive. This may be a new adhesive formulation, or may just the the same silicone but without the pigment as a special order for SpaceX (who like having a black & white colourscheme).
- Whilst the majority of the tile acreage (barrel sections) is composed of the identical pinned tiles, there are also a series of varying size and geometry pinned tiles for the nose, and a large number of unique tile designs for the flap roots, flap tips, nose, etc. These are all bonded rather than pinned, too - like on STS.


The big challenge with STS was not the unique tiles or their bonding, but because of re-waterproofing. After every entry, the waterproofing burnt off and the tiles went from hydrophobic to extremely hydrophilic (to the extend they would 'suck up' ambient humidity, not just rainwater). Wet tiles are bad not because of mass, but because the process of sublimation, freezing, and re-sublimation during ascent, coast, and entry results in internal tile fracturing. That is a known and recorded phenomena, and is independent of tile attachment method. Thus, re-waterproofing is mandatory.
The big timesink for STS' TPS was that re-waterproofing. I went over the history of re-waterproofing agents a mere two pages ago:
The tiles were initially impregnated with methyltrimethoxysilane (MTMS) during manufacture, and this provided waterproofing through to the first flight and entry, and which point the MTMS burnt off during entry. Subsequent to this, a rewaterproofing agent needed to be applied after every flight.
Initially, rewaterproofing was performed by spray-on fluoropolymer (Scotchguard), with the idea that it could be sprayed on rapidly after landing to minimise the chance of water ingress. This proved inadequate, as too much Scotchguard would interact with and degrade the Silicone used to adhere the gap-fillers between the tiles, and too little provided inadequate protection and led to water ingress into the tiles.
As a replacement for the Scotchguard, hexamethyldisilazane (HDMS) was applied through vapour diffusion, to provide good penetration into the tile. As a rewaterproofing agent it worked well, but it was found the catalyst used in the HDMS degraded the silicone under the base of the tile (that attached it to the Orbiter), meaning all treated tiles needed to be replaced and a new rewaterproofing agent found.
That new agent was dimethylethoxysilane (DMES), which needed to be injected rather than diffused into the tiles. This was laborious (poking a needle into each tile and injecting sly enough to not fracture the tile) but it worked and did not degrade the silicone, so was the re-waterproofing agent for the rest of the life of STS.
The big timesinks of TPS refurb were waiting for the tiles to dry out if they had been exposed to moisture between landing and being rolled back to a controlled environment, and the actual process of injecting every tile individually with DMES. Whilst replacement of individual tiles meant installing a cut-to-size replacement, tile replacement was not what the majority of time was spent on, particularly by the end of the programme when the switch had been made to r-ewaterproofing agents that did not degrade the adhesives.

For Starship, we've seen that pin-attached tile replacement is fast but destructive (i.e. the removed tile is destroyed during removal). Bonded tile replacement would presumably be no slower than for STS once they get the hang of it. But we do not know what their re-waterproofing solution is, nor how fast or how effective it is, because no vehicle yet has experienced the high temperatures that would require re-waterproofing.
They may have a brand new re-waterproofing agent they hope will work that will be easy and fast (and above all, cheap) to apply and can be done fast enough after return to avoid the need for drying.
They may think they have solved the problems with one of the previously attempted re-waterproofing solutions, possibly by switching to an adhesive that is less susceptible to chemical damage from those agents.
They may even not have a definite chosen solution yet, but expect the combination of low flight rates (leaving ample time for the painful for tried-and-tested method of DMES injection to be performed) and lack of reflight (because a returned Starship will have been obsoleted and replaced with the improved model before it has even left the pad) to allow the problem to be kicked down the road for quite some time before it becomes an actual issue.
Title: Re: Starship heat shield
Post by: volker2020 on 06/24/2022 12:45 pm
I just think there's way too much "OMG a couple tiles fell off, time to scrap everything and redesign the entire heat shield" going on here, and not enough, "Hey, only a couple tiles fell off, looks like SpaceX has nearly got the heat shield system down pat."

Frankly of all the issues that SpaceX has to deal with, I have always considered the heat shield to be a very minor concern.

Minor? By far the most expensive aspect of the Space Shuttle was TPS maintenance. It consumed ~20,000 man-hours per flight.

John
My impression was, that the Shuttle had flight cost of around 1 Billion per start. But 20,000 man hours, paying them 100$ per hour does only bring me to  2.000.000$. There must be some other expensive items on the way.
Title: Re: Starship heat shield
Post by: livingjw on 06/24/2022 05:00 pm
I just think there's way too much "OMG a couple tiles fell off, time to scrap everything and redesign the entire heat shield" going on here, and not enough, "Hey, only a couple tiles fell off, looks like SpaceX has nearly got the heat shield system down pat."

Frankly of all the issues that SpaceX has to deal with, I have always considered the heat shield to be a very minor concern.

Minor? By far the most expensive aspect of the Space Shuttle was TPS maintenance. It consumed ~20,000 man-hours per flight.

John
My impression was, that the Shuttle had flight cost of around 1 Billion per start. But 20,000 man hours, paying them 100$ per hour does only bring me to  2.000.000$. There must be some other expensive items on the way.

Sorry, I meant maintenance expense. It also took months which represents loss of productivity. Throwing away hardware is always going to very expensive. Also, a lot of the shuttle expense is overhead.

John
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/24/2022 06:50 pm
The big challenge with STS was not the unique tiles or their bonding, but because of re-waterproofing. After every entry, the waterproofing burnt off and the tiles went from hydrophobic to extremely hydrophilic (to the extend they would 'suck up' ambient humidity, not just rainwater). Wet tiles are bad not because of mass, but because the process of sublimation, freezing, and re-sublimation during ascent, coast, and entry results in internal tile fracturing. That is a known and recorded phenomena, and is independent of tile attachment method. Thus, re-waterproofing is mandatory.

From the Space Shuttle white paper your provided

Quote
Originally it was intended that the re-waterproofing needed to
be completed quickly for turnaround activities so spray on type materials were investigated as the factory
waterproofing burns out at temperatures above 1050 F. The first spray that was used was a fluro-polymer or
Scotchgard, which provided a thin film of low surface energy on the exterior surface of the tile glass coating. It was
recognized that this treatment would not provide an impervious barrier to water and that its effects would be highly
dependent on the surface tension of the water and resultant contact angle.

After the 2nd flight of Columbia inspection of the Orbiter indicated that in-plane failures of six HRSI tiles had
occurred on the right wing glove area. The depth of the missing material corresponded to the burnout zone of the
factory waterproofing or the 1050 F line. In addition, the surface coating of 12 tiles on the body flap showed
evidence of bubbling.

So they'll spray on Scotch Guard.   Kind of like airplanes in the winter get routine de-icer treatments. 

18 damaged tiles when you have a single point of failure design like Orbiter is catastrophic, and leads to all sorts of paranoid time consuming design choices (that failed anyways).

Such is the nature of critical systems that have single points of failure.  It's why any sane engineer avoids them if at all possible.

Starship doesn't have a single point of failure problem on its heat shield, The time to replace 18 tiles is far smaller than the time to wield a syringe on 20,000 tiles.   So they will just live with the slight amount of damage potential from water in the tiles.
Title: Re: Starship heat shield
Post by: DanClemmensen on 06/24/2022 07:03 pm

Starship doesn't have a single point of failure problem on its heat shield, The time to replace 18 tiles is far smaller than the time to wield a syringe on 20,000 tiles.   So they will just live with the slight amount of damage potential from water in the tiles.

It's now 30 or more years later, and Starship is geometrically far less complicated than STS. It's likely that the syringe job can be automated. They might decide to use the syringe on the glued-on tiles and count on replacing the pinned-on tiles as needed.

I feel the TPS is still the most problematical part of the SS and the most likely to slow the turnaround, even if they can automate syringing of the glued-on tiles and inspection of all the tiles. There would also be mess made if you ever need to land in a rainstorm.
Title: Re: Starship heat shield
Post by: rsdavis9 on 06/24/2022 07:30 pm
Maybe they have a design of the tile that allows the tile to get wet and allows the resulting steam to escape without damage?
Porous enough to allow escape of steam as gas.
Tight enough to prevent ingress of hot reentry gas.

It also seems that this would something you can easily model and also easy to test on the ground in a test jig.

Any thoughts?
Any body got some spare tiles? Mount them to a steel plate and soak and heat up with a torch.
I think nomad might have some...
 
Title: Re: Starship heat shield
Post by: BT52 on 06/24/2022 07:45 pm
Thats 1000% what they did. Still then u define restrictions into system. Also u define "safe" and operational windows.
Heat shield is quite overengineered for a reason. Ofc they would like to make it lighter and thinner but i m sure structural integrity and reuse takes main attention in that case for sure. I speculate the porosity, thickness and tile gaps play role in that scenario discussed above.
Title: Re: Starship heat shield
Post by: edzieba on 06/24/2022 08:10 pm
18 damaged tiles when you have a single point of failure design like Orbiter is catastrophic, and leads to all sorts of paranoid time consuming design choices (that failed anyways).
The '18 tiles' is merely how many tiles they found fractured and identified the problem from, not how many tiles will fail from an inadequate waterproofing job. Concluding "if you spray Starship with Scotchguard only 18 tiles will fail" from that is false logic.
Quote
Starship doesn't have a single point of failure problem on its heat shield
Often asserted, yet to be proven. SpaceX cover large acreages of the ship with continuous tiles even when leaving a small hole would make things a lot easier (e.g. covering the lift points, covering downward-facing sensors and antennae, etc), so they clearly think that the tiles are all needed. SpaceX are not in the habit of installing a part if they could instead eliminate that part.
Quote
The time to replace 18 tiles is far smaller than the time to wield a syringe on 20,000 tiles.
Again, that false '18 tiles' figure. And we do not yet know if DMES re-waterproofing is the solution chosen by SpaceX, only that it is one option that has been proven to work successfully.

The full section which you quoted a small proton of, which highlights that "use less Scotchguard" and "use more scotchguard" both resulted in failures, and why DMES injection was settled on after trying other more convenient methods that proved inadequate in actual flight testing:
Quote
Thermal protection system anomalies due to moisture absorption that have occurred during flight test led to
many changes to the way tiles were rewaterproofed. Originally it was intended that the re-waterproofing needed to
be completed quickly for turnaround activities so spray on type materials were investigated as the factory
waterproofing burns out at temperatures above 1050 F. The first spray that was used was a fluro-polymer or
Scotchgard, which provided a thin film of low surface energy on the exterior surface of the tile glass coating. It was
recognized that this treatment would not provide an impervious barrier to water and that its effects would be highly
dependent on the surface tension of the water and resultant contact angle.
After the 2nd flight of Columbia inspection of the Orbiter indicated that in-plane failures of six HRSI tiles had
occurred on the right wing glove area. The depth of the missing material corresponded to the burnout zone of the
factory waterproofing or the 1050 F line. In addition, the surface coating of 12 tiles on the body flap showed
evidence of bubbling. Based on these observations and previous results from the ground test program, it was
concluded that water penetration had occurred on the tiles before the flight and the rewaterproofing application
technique required improvement. The mechanism involved in this failure is postulated as follows. Water from
rainstorms entered an area of the tiles before lift-off. During ascent, a small amount of water in the tile was
vaporized, and the remainder cooled rapidly because of the rapid decrease in pressure. When the vehicle went to
orbital conditions, the water changed to ice, which contracted and fractured the tile. The steam generated in the tile
during entry then completed the fracture of the tile.
Prior to the 3rd flight of Columbia an auxiliary pressurization and nozzle system was developed for application of
the Scotchgard. This technique improved the penetration effectiveness of the material into the tile. In addition the
amount of Scotchgard that was applied was increased by a factor of four in an attempt to prevent water absorption.
The post flight inspection after the 3rd flight of Columbia found that several non-densified LRSI and HRSI tile
were missing in the forward fuselage area and body flap areas. In contrast to the STS-2 flight anomaly, complete
loss of the tiles occurred during the mission. After extensive testing the failure was attributed to excessive quantities
of Scotchgard carrier agent that caused swelling of the RTV bond between the tile and the SIP, failing the tile-to-SIP
bondline. The rewaterproofing procedures for STS-4 were modified to reduce the amount of Scotchgard application.
[...]
The flight test program revealed that the film type rewaterproofing was inadequate so activities were undertaken
to develop an internal rewaterproofing system that could return the tile to a factory waterproof state. A commercial
disilazane material was selected as the most promising. This material has a vapor pressure at room temperature that
allows the vapors to penetrate the interior of the tile by means of vapor diffusion. Although ammonia is formed by
the reaction of this product, the amount produced is minimal and the vapors could be handled by adequate
ventilation. This method worked fine until it was discovered that reversion or softening of the RTV-577 screed,
which is used to fair out the underlying structure, could occur. During the STS-41G mission the V070-394504-372
tile was lost, Figure 8, at some point during the reentry phase. The loss occurred at the RTV bondline of the tile to
the underlying RTV-577 screed. The catalyst that was used in the silane tile waterproofing solution was found
through test to be the culprit. Over 4000 tiles were removed and replaced over areas of RTV-577 to preclude further
issues from this chemical reaction. In addition a new waterproofing agent, DimethylEthoxySilane (DMES), was
developed for use during rewaterproofing. Over the remainder of the Space Shuttle program, DMES was proven to
be a very successful waterproofing agent although it was expensive, labor intensive, and generated toxic vapors that
required bay closure to perform the task.

Maybe they have a design of the tile that allows the tile to get wet and allows the resulting steam to escape without damage?
The damage is not just from steam, but from internal ice formation. The tiles are already porous to water vapour: that's the problem, not the solution.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/24/2022 08:34 pm
18 damaged tiles when you have a single point of failure design like Orbiter is catastrophic, and leads to all sorts of paranoid time consuming design choices (that failed anyways).

The '18 tiles' is merely how many tiles they found fractured and identified the problem from, not how many tiles will fail from an inadequate waterproofing job. Concluding "if you spray Starship with Scotchguard only 18 tiles will fail" from that is false logic.

Spray on Scotchgard is literally what they did for the first two shuttle flights.   It's not false logic to conclude that the damage yield is 18/20,000 tiles. It's just observation/estimation of a minor (in percentage terms) problem.   Although not minor, if that's 18 single points of failure.

Starship doesn't have a single point of failure problem on its heat shield

Often asserted, yet to be proven. SpaceX cover large acreages of the ship with continuous tiles even when leaving a small hole would make things a lot easier (e.g. covering the lift points, covering downward-facing sensors and antennae, etc), so they clearly think that the tiles are all needed. SpaceX are not in the habit of installing a part if they could instead eliminate that part.

They cover those because (a) there's no mat backing those areas, (b) lift points are one critical piece that shouldn't go above 870degC as they are high stress, and (c) sensors and antennae aren't stainless steel and can't handle 870degC.

There *are* a few single remaining points of failure on Starship, the lift points being one of them (you wouldn't want them breaking when being caught by chopsticks).  The other is I suspect that part of the flaps are going to impinge on the plasma flow, which raises heat levels considerably (you see how thick some of those tiles are?)  I suspect the number of single failure points is in the single digits, not in the thousands like Orbiter.

They may even re-inject those few tiles or apply special waterproof treatments at those few single points after every flight.   Just not 20,000 tiles.

As far as "proven", we all eagerly await the first flights.  Meanwhile we have design analysis, cryotests being done on tiles soaked in rain, and knowledge that SpaceX is world-class when it comes to finite element analysis and related disciplines, as well as a fanatacism for smooth operations and high reuse rates.

I still want to buy a space shuttle tile, soak it in water for an hour, and throw it in my freezer to see what happens.  I'm quite sure SpaceX has done this, many times.

Title: Re: Starship heat shield
Post by: edzieba on 06/24/2022 08:57 pm
18 damaged tiles when you have a single point of failure design like Orbiter is catastrophic, and leads to all sorts of paranoid time consuming design choices (that failed anyways).

The '18 tiles' is merely how many tiles they found fractured and identified the problem from, not how many tiles will fail from an inadequate waterproofing job. Concluding "if you spray Starship with Scotchguard only 18 tiles will fail" from that is false logic.

Spray on Scotchgard is literally what they did for the first two shuttle flights.   It's not false logic to conclude that the damage yield is 18/20,000 tiles. It's just observation/estimation of a minor (in percentage terms) problem.
First one flight after rewaterproofing: you don't rewaterproof for the first every launch because the factory waterproofing has not burnt off yet. The first ever flight was protected by the factory MTMS waterproofing treatment. The NASA document even states outright that the failure on the second flight was at the burnout line of the factory waterproofing (said burnout occurring on the first flight).
Quote
They cover those because (a) there's no mat backing those areas, (b) lift points are one critical piece that shouldn't go above 870degC as they are high stress, and (c) sensors and antennae aren't stainless steel and can't handle 870degC.
The mat is not the primary TPS. It's a good insualtor agaisnt conductive heat transfer, but that's not the sort of heat transfer you experience during EDL. That's instead radiative (first portion of EDL with highest energy and greatest velocity lost) and later convective (later portion where velocity has slowed). The mats lack the borosilicate glass coating that rejects the majority of radiative heat transfer, and lack the gas impermeability of the borosilicate glass coating that prevents hot gas infiltration (convective heat transfer).

The mats alone are not sufficient protection, which is why the entire vehicle TPS is covered in tiles and bare mats are used nowhere.
Quote
There *are* a few single remaining points of failure on Starship, the lift points being one of them (you wouldn't want them breaking when being caught by chopsticks).
The lift points are used for the sling eyes, not by the chopsticks.
Quote
They may even re-inject those few tiles or apply special waterproof treatments at those few single points after every flight.   Just not 20,000 tiles.
The water infiltration failure mode has nothing to do with how much heating they receive during entry, the majority of the failure occurs during ascent. Any tile heated above the waterproofing burnout temperature will need rewaterproofing.
Quote
Meanwhile we have design analysis, cryotests being done on tiles soaked in rain
Unless SpaceX went and secretly took a blowtorch to the side of the vehicle prior to cryoproofing, those tiles would still have had their factory MTMS waterproofing in place. This is why we do not know what rewaterproofing method SpaceX are using yet: they have yet to have had any times that need rewaterproofing outside of their labs.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/25/2022 03:31 am
18 damaged tiles when you have a single point of failure design like Orbiter is catastrophic, and leads to all sorts of paranoid time consuming design choices (that failed anyways).

The '18 tiles' is merely how many tiles they found fractured and identified the problem from, not how many tiles will fail from an inadequate waterproofing job. Concluding "if you spray Starship with Scotchguard only 18 tiles will fail" from that is false logic.

Spray on Scotchgard is literally what they did for the first two shuttle flights.   It's not false logic to conclude that the damage yield is 18/20,000 tiles. It's just observation/estimation of a minor (in percentage terms) problem.
First one flight after rewaterproofing: you don't rewaterproof for the first every launch because the factory waterproofing has not burnt off yet. The first ever flight was protected by the factory MTMS waterproofing treatment. The NASA document even states outright that the failure on the second flight was at the burnout line of the factory waterproofing (said burnout occurring on the first flight).
Quote
They cover those because (a) there's no mat backing those areas, (b) lift points are one critical piece that shouldn't go above 870degC as they are high stress, and (c) sensors and antennae aren't stainless steel and can't handle 870degC.
The mat is not the primary TPS. It's a good insualtor agaisnt conductive heat transfer, but that's not the sort of heat transfer you experience during EDL. That's instead radiative (first portion of EDL with highest energy and greatest velocity lost) and later convective (later portion where velocity has slowed). The mats lack the borosilicate glass coating that rejects the majority of radiative heat transfer, and lack the gas impermeability of the borosilicate glass coating that prevents hot gas infiltration (convective heat transfer).

The mats alone are not sufficient protection, which is why the entire vehicle TPS is covered in tiles and bare mats are used nowhere.
Quote
There *are* a few single remaining points of failure on Starship, the lift points being one of them (you wouldn't want them breaking when being caught by chopsticks).
The lift points are used for the sling eyes, not by the chopsticks.
Quote
They may even re-inject those few tiles or apply special waterproof treatments at those few single points after every flight.   Just not 20,000 tiles.
The water infiltration failure mode has nothing to do with how much heating they receive during entry, the majority of the failure occurs during ascent. Any tile heated above the waterproofing burnout temperature will need rewaterproofing.
Quote
Meanwhile we have design analysis, cryotests being done on tiles soaked in rain
Unless SpaceX went and secretly took a blowtorch to the side of the vehicle prior to cryoproofing, those tiles would still have had their factory MTMS waterproofing in place. This is why we do not know what rewaterproofing method SpaceX are using yet: they have yet to have had any times that need rewaterproofing outside of their labs.

Show us the math.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/25/2022 03:53 am

The mat is not the primary TPS. It's a good insualtor agaisnt conductive heat transfer, but that's not the sort of heat transfer you experience during EDL. That's instead radiative (first portion of EDL with highest energy and greatest velocity lost) and later convective (later portion where velocity has slowed). The mats lack the borosilicate glass coating that rejects the majority of radiative heat transfer, and lack the gas impermeability of the borosilicate glass coating that prevents hot gas infiltration (convective heat transfer).

Correct(1), so the danger of heating a spot of stainless steel past 870degC is in the radiative dominated portion of reentry, where there is the highest energy conditions for heating.  The convective heating is done at much lower energies and thus doesn't involve danger of heating to  870degC.  I suspect the bare stainless can handle the convective heating all by itself.

Now, go look up the emissivity  of the borosilicate glass coating vs. the Saffil.  They are only different by about 20% (as opposed to stainless steel which is 2.5x).   This is what is involved in the "rejection" of radiative heat.

The glass will be radiating about as efficient as humans can make material, and the Saffil about 20% less so.   Since there's a factor of 34 in the small-spot safety of stainless steel over aluminum, that is quite sufficient for small-number-of-tiles loss.

I did the math above,  If you think the math is wrong do some math to show why it is wrong, don't just use words.  Back them up.   Math his how engineering disputes are supposed to done.


(1) see https://en.wikipedia.org/wiki/Atmospheric_entry#Reentry_heating
Title: Re: Starship heat shield
Post by: edzieba on 06/25/2022 12:57 pm

The mat is not the primary TPS. It's a good insualtor agaisnt conductive heat transfer, but that's not the sort of heat transfer you experience during EDL. That's instead radiative (first portion of EDL with highest energy and greatest velocity lost) and later convective (later portion where velocity has slowed). The mats lack the borosilicate glass coating that rejects the majority of radiative heat transfer, and lack the gas impermeability of the borosilicate glass coating that prevents hot gas infiltration (convective heat transfer).

Correct(1), so the danger of heating a spot of stainless steel past 870degC is in the radiative dominated portion of reentry, where there is the highest energy conditions for heating.  The convective heating is done at much lower energies and thus doesn't involve danger of heating to  870degC.  I suspect the bare stainless can handle the convective heating all by itself.

Now, go look up the emissivity  of the borosilicate glass coating vs. the Saffil.  They are only different by about 20% (as opposed to stainless steel which is 2.5x).   This is what is involved in the "rejection" of radiative heat.

The glass will be radiating about as efficient as humans can make material, and the Saffil about 20% less so.   Since there's a factor of 34 in the small-spot safety of stainless steel over aluminum, that is quite sufficient for small-number-of-tiles loss.

I did the math above,  If you think the math is wrong do some math to show why it is wrong, don't just use words.  Back them up.   Math his how engineering disputes are supposed to done.


(1) see https://en.wikipedia.org/wiki/Atmospheric_entry#Reentry_heating
Very well, some napkin math to see if we're even vaguely in the correct ballpark:

Confining to the convective regime and imagining that somehow the TPS disappears after the radiative regime with no heat transfer to the steel:
Stainless steel heat capacity: ~500J/kg.K
Heat flux as re-entry heating becomes dominated by convective rather than radiative heating (https://www.researchgate.net/figure/Typical-convective-and-radiative-fluxes-encountered-during-Earth-reentry-and-their_fig95_338868244): ~3MW/m2
Mass of 1 square metre of Stainless Steel of thickness 3mm: ~23.6kg
Temperature rise per second per square metre of exposed Stainless Steel in convective heating regime: ~250K
Therefore, exposed Stainless will exceed 870°C (assuming starting from ~-300°C for the LOX tank wall) in ~5 seconds of exposure in the convective heating regime. This ignores that it also needs to survive the radiative regime, and chemical attack (and additional heating) from the surrounding plasma.

So no, your "suspicion" that "bare stainless can handle the convective heating all by itself" is not correct, by a rather large margin. Extended over the entire entry regime, we can make that a pretty definite conclusion. We can also conclude the same from SpaceX application of TPS, which does not leave any Stainless steel exposed to the forward direction. Nor do they leave any of the mats exposed.

---

If instead you want 'the math' of why spray application (or no application) of rewaterproofing is not a viable option, that would be within NTRS' now redacted archives. Ideally if someone has a copy of:

Hill, W. L., and S. M. Mitchell, "Certification of Rewaterproofing Agent for Shuttle Thermal Protection Systems," 199th Am. Chem. Soc. ConE, Boston, Massachusetts, April 1990.

which may also be:

Hill WL, Mitchell SM. Rewaterproofing agent for the Shuttle thermal protection system Polymeric Materials Science and Engineering, Proceedings of the Acs Division of Polymeric Materials Science and Engineering. 62: 668-672.

That would likely be helpful.

But we also have the existence-proof that spray-application was not sufficient to prevent water ingress into tiles, and that water ingress did result in tile failure. Those are both things that actually happened, in actual flight testing, with actual tiles. The same composition tiles as are currently fitted to Starship. This is not some theoretical potential concern, it's an issue identified from prior flight data of items currently installed in vehicles about to fly.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/25/2022 09:47 pm
Very well, some napkin math to see if we're even vaguely in the correct ballpark:

Confining to the convective regime and imagining that somehow the TPS disappears after the radiative regime with no heat transfer to the steel:
Stainless steel heat capacity: ~500J/kg.K
Heat flux as re-entry heating becomes dominated by convective rather than radiative heating (https://www.researchgate.net/figure/Typical-convective-and-radiative-fluxes-encountered-during-Earth-reentry-and-their_fig95_338868244): ~3MW/m2
Mass of 1 square metre of Stainless Steel of thickness 3mm: ~23.6kg
Temperature rise per second per square metre of exposed Stainless Steel in convective heating regime: ~250K
Therefore, exposed Stainless will exceed 870°C (assuming starting from ~-300°C for the LOX tank wall) in ~5 seconds of exposure in the convective heating regime. This ignores that it also needs to survive the radiative regime, and chemical attack (and additional heating) from the surrounding plasma.

So no, your "suspicion" that "bare stainless can handle the convective heating all by itself" is not correct, by a rather large margin. Extended over the entire entry regime, we can make that a pretty definite conclusion. We can also conclude the same from SpaceX application of TPS, which does not leave any Stainless steel exposed to the forward direction. Nor do they leave any of the mats exposed.

That is not an equilibrium calculation (not a conservation of energy calculation, in other words), and you didn't use Stefan Boltzmann at all, and since S-B has a temperature to the fourth power term, your estimates are extremely far off.   Furthermore your input of 3MW/m^2 is not likely to be correct because that heat flux would melt the tiles, insulation, and aluminum of the orbiter.  You need to sanity check your napkin math against a known working implementation and verify that your math is correct.

A square meter of SS sheet, which has an emissivity of 0.35, at 870 degC will radiate 34KW/m^2 in both directions, for a total emission of 68kW/m^2.  this is is 2 orders of magnitude difference from 3MW/m^2, so by your analysis the SS will flash into plasma within ~10-15 seconds.

Let's do the same analysis for the Orbiter heat shield, which has a known max temperature of 1260degC, and an emissivity of 0.95 (but only emits in one direction, outwards).  The equilibrium temperature by solving the S-B equations is 300kW/m^2, or still off by an order of magnitude.   Using your data, the tiles will flash into plasma, but take a bit longer to do so.

The temperature required for the 3MW/m^2 to go somewhere is, solving S-B, the emissions temperature for tile needs to be 2460degC, which is more than 1,000 degC larger than their specification.

So if at equilibrium (i.e. conservation of energy, the 3MW/m^2 has to go *somewhere*), the tiles would turn into plasma, then we have a GIGO problem.

Where does the 3MW/m^2 go in the ideal case of the tiles all functional?   That's the math you have to solve. If one gets a nonsense answer then the analysis is not correct.

I suspect the 3MW/m^2 reflects a very steep entry angle common for ablative reentries.  In the paper you cite, see figure 5 that shows the different trajectories.  I suspect Figure 3, where one might get a 3MW figure at 11km/sec, is for steep rentry angle, not shallow reentry angle.  The figure is from 1969, and since all missions at that time were ablative/steep entries, that is the most likely explanation,

Furthermore, from the paper you cite:
Quote
the heat flux on the afterbody was about 5 times lower than on the forebody (about 20 W/cm2 as compared to 100 W/cm2

That would indicate that the backside heating, which SpaceX has clearly stated doesn't require heat tiles, would be 600kw/m^2, whose two-way emission temperature would be 1700degC, which would melt the stainless steel.

Again, this demonstrates that the 3MW/m^2 (which by the graph for LEO re-entry should be 1MW/m^2) is not a valid value for a shallow reentry.

Or, the simple model of heat flux/emission for calculating the equilibrium temperature is missing a *huge* heat sink. Possibly, but do the math to show how something *works* on orbiter before saying it won't work on Starship.   I did the math using S-B equilibrium and I got fairly reasonable answers for Orbiter, with an equilibrium heat flux of 300kW/m^2 for 5 inch tiles (i.e. maximum, not average)

https://docs.google.com/spreadsheets/d/1nMR6EvrKo87L-QiZtSMF-_w3q4-uKHJY1FRuPTAQvjE/edit?usp=sharing

It would be nice to find what the heat flux for the Orbiter shallow reentry was, but I've not found a good reference yet.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/25/2022 10:46 pm
I found an old interesting paper on validation of an FEM model based on data from STS-5.

The heat fluxes all sub 100kW/m^2 except for Figure 19, the surface heating rates of WS328 (the wing), which exceeds 1MW/m^2 for about 200 seconds, and the temperature hits 1000degC (figure 28) (and stays there for quite a bit longer than the heat flux)

Where did all that energy go?  S-B doesn't account for it in a straightforward calculation.

Perhaps heat soak in the tiles takes up more energy than I suspected

https://www.nasa.gov/centers/dryden/pdf/88035main_H-1236.pdf

(not OCR'd, unfortunately)
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/26/2022 09:32 pm
Very well, some napkin math to see if we're even vaguely in the correct ballpark:

Confining to the convective regime and imagining that somehow the TPS disappears after the radiative regime with no heat transfer to the steel:
Stainless steel heat capacity: ~500J/kg.K
Heat flux as re-entry heating becomes dominated by convective rather than radiative heating (https://www.researchgate.net/figure/Typical-convective-and-radiative-fluxes-encountered-during-Earth-reentry-and-their_fig95_338868244): ~3MW/m2
Mass of 1 square metre of Stainless Steel of thickness 3mm: ~23.6kg
Temperature rise per second per square metre of exposed Stainless Steel in convective heating regime: ~250K
Therefore, exposed Stainless will exceed 870°C (assuming starting from ~-300°C for the LOX tank wall) in ~5 seconds of exposure in the convective heating regime. This ignores that it also needs to survive the radiative regime, and chemical attack (and additional heating) from the surrounding plasma.

So no, your "suspicion" that "bare stainless can handle the convective heating all by itself" is not correct, by a rather large margin. Extended over the entire entry regime, we can make that a pretty definite conclusion. We can also conclude the same from SpaceX application of TPS, which does not leave any Stainless steel exposed to the forward direction. Nor do they leave any of the mats exposed.
I suspect the 3MW/m^2 reflects a very steep entry angle common for ablative reentries.  In the paper you cite, see figure 5 that shows the different trajectories.  I suspect Figure 3, where one might get a 3MW figure at 11km/sec, is for steep rentry angle, not shallow reentry angle.  The figure is from 1969, and since all missions at that time were ablative/steep entries, that is the most likely explanation,

I have confirmation that 3MW/m^2 is for steep reentry profiles, which Orbiter and Starship cannot do.

Here's a great paper on calculating the first-order effects of various trajectories of reentry:

https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/cami/library/online_libraries/aerospace_medicine/tutorial/media/iii.4.1.7_returning_from_space.pdf

Figure 4.1.7-15 shows the heating rate for different entry angles @ 8km/sec.  For 85 degrees, the peak heating rate is 1.2MW, which corresponds reasonably closely to the source you were citing - ablative materials for steep reentry angles.

For a shallow angles, the same figure shows a peak heating rate of 600kw for a 15 degree angle.   So for a simple 2m cone half the heating rate, and not too far off the S-B equilibrium calculations I've done.  (2x instead of 10x).

Keep in mind this was for a generic cone reentry vehicle with nose radius of 2m.   SS or Orbiter will be more complex, but the effective nose radius is larger and that variable is  in the denominator, so the heating will be less than the simple model in the paper.

I strongly recommend reading this paper, it's appropriate material for this forum and sufficient for first-order estimates of Starship heat shield requirements.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/27/2022 06:10 am
Cross post from thread on research paper on Starship reentry trajectory and heat fluxes.   A really good read.

https://forum.nasaspaceflight.com/index.php?topic=56619.0

Key picture of heat flux contours attached to this post.

Related to heat shield, the peak heating in hotspots doesn't exceed 300-400kW/m^2, but average on the main body area is very low at about less than 100kW/m^2.   The location of the hotspots (nose, forward end of canards) is not unexpected.

 At less than 100KW/m^2 on the main portion of the body, the equilibrium S-B temperature is about 900degC at an emissivity of 0.95.  At Saffil's emissivity of 0.75 and an insulation factor 25 times worse than its specification the equilibrium temperature at the stainless steel doesn't exceed 870degC, so there's a ton of redundancy on the main body.   Lots of tiles on the main body can be lost, as long as the Saffil doesn't fly off the steel will be fine.

The hot spots, look to be less than 5% of the total surface area.    They are already in spots that use glue instead of mechanical attachment (tip of nose, curved area at interface of canards and body).  Those are likely single points of failure and cannot be allowed to fail from lack of water proofing, failure of the glue, etc.   They are also spots not cooled by underlying cryogenic fuel.  (nose cone tanks might be?)

A key modeling lesson is that the hotspots have 3-5x more heat flux than the average.

Overall, the implications on maintenance are good.  about 5% of the protected surface area needs similar paranoia to that of the Space Shuttle, the rest does not, and a tile-loss-yield of 0.1% shouldn't bother the main body.


Title: Re: Starship heat shield
Post by: JayWee on 06/27/2022 06:22 am
That seems quite low heating - is it because Starship is fluffy compared to the Shuttle?
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/27/2022 06:59 am
That seems quite low heating - is it because Starship is fluffy compared to the Shuttle?

Read the linked post, it's got tons of details.   

Peak heating is similar, average is 1/3 less than Shuttle.

My guess is lower ballistic coefficient than Shuttle, an angle of attack of 80 degrees vs 30 degrees reduces hot spots, and average higher altitude for bleeding off energy.

I think lower BC corresponds to "fluffy", so yes, Starship is more fluffy.

Speaking of BC, I found this estimate of BCs amongst different space worthy vehicles:

https://space.stackexchange.com/questions/48798/design-of-starship-fins
Title: Re: Starship heat shield
Post by: Slothman on 06/27/2022 06:39 pm
How do these hotspots, coefficients and all change if starship comes in with the flaps all the way back? Would they do that? Or will they always come in "arms and legs fully spread"? I would think that offering less head-on surface reduces the heating, at the expense of not decelerating as fast, which might be desired?
Maybe they come in with the flaps half way actuated, so they have some stability control in all directions?
Title: Re: Starship heat shield
Post by: Robotbeat on 06/27/2022 07:48 pm
How do these hotspots, coefficients and all change if starship comes in with the flaps all the way back? Would they do that? Or will they always come in "arms and legs fully spread"? I would think that offering less head-on surface reduces the heating, at the expense of not decelerating as fast, which might be desired?
Maybe they come in with the flaps half way actuated, so they have some stability control in all directions?
nah, it makes heat worse if you come in without flaps extended.
Title: Re: Starship heat shield
Post by: eriblo on 06/27/2022 08:27 pm
The payload mass is going to be the biggest factor for flap position (in order to trim center of drag to match center of mass). Apart from that you want maximum extension for maximum drag and lift (with some reserve for control).

There might be a double whammy for re-entry heating with heavier payloads as it means both higher mass and smaller area with less extension of the aft flaps.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/27/2022 09:51 pm
The payload mass is going to be the biggest factor for flap position (in order to trim center of drag to match center of mass). Apart from that you want maximum extension for maximum drag and lift (with some reserve for control).

There might be a double whammy for re-entry heating with heavier payloads as it means both higher mass and smaller area with less extension of the aft flaps.

Yes.  re-entry with humans or other valuable cargo is only going to happen when the tile bugs are thoroughly worked out and characterized.

There's a lot of cargo-and-fuel-to-LEO flights before that happens, so they'll have tons of data.
Title: Re: Starship heat shield
Post by: Cheapchips on 07/05/2022 05:55 am
What paint could they be using between the edge tiles on S24?  They presumably don't want it cooking off during re-entry.   
Title: Re: Starship heat shield
Post by: edzieba on 07/05/2022 10:21 am
What paint could they be using between the edge tiles on S24?  They presumably don't want it cooking off during re-entry.
Could be:
Ablative: cooking off during re-entry is the design goal
Cosmetic: cooking off during re-entry is mere visual inconvenience (see: paint damage during F9 re-entry)
Radiative (temperature control in orbit): also does not need to survive re-entry
Radiative (during re-entry): here's the only case where the coating needs to survive (enough of) re-entry to do its job
Title: Re: Starship heat shield
Post by: InterestedEngineer on 07/05/2022 06:34 pm
What paint could they be using between the edge tiles on S24?  They presumably don't want it cooking off during re-entry.
Could be:
Ablative: cooking off during re-entry is the design goal
Cosmetic: cooking off during re-entry is mere visual inconvenience (see: paint damage during F9 re-entry)
Radiative (temperature control in orbit): also does not need to survive re-entry
Radiative (during re-entry): here's the only case where the coating needs to survive (enough of) re-entry to do its job

I think you mean the black painted area behind the forward fins, right?  See red box in attached pic.  That looks new.

That might indicate their simulations show enough heat will get on stainless steel around the fins to be worrisome, but given stainless steel's emissivity of 0.35, painting it black might double or 2.5x the emissivity, bringing the temperature into a reasonable range.   That paint effectively doubled the radiative capability of the stainless steel @870degC from 34kW/m^2 to greater than 68kW/m^2.

I'd also guess it's somewhat of a test.  From the simulation of the paper in the thread above, they may be able to reduce some of the surface area of the tile/blanket and turn it into highly emissive paint, as a good chunk of the currently tiled surface is estimated at < 70kW/m^2

from this website, the 2x increase in emissivity might be pessimistic, as there are modern coatings that are as good as the tiles themselves, so 2.7x.

https://www.acktar.com/products-services/high-emissivity-materials/




Title: Re: Starship heat shield
Post by: Tangilinear Interjar on 07/07/2022 03:36 pm
While there may be some performance improvements by painting some areas, it's clear from looking at how and where they painted that most of the paint is for aesthetic reasons.
Title: Re: Starship heat shield
Post by: Robotbeat on 07/07/2022 03:44 pm
While there may be some performance improvements by painting some areas, it's clear from looking at how and where they painted that most of the paint is for aesthetic reasons.
I don't agree (in part because it doesn't seem that aesthetic of a paint pattern). It seems quite likely that analysis showed they might need more thermal protection, so they added some to maximize the chance it survives reentry.

It could also be for analysis purposes. If they have high resolution tracking cameras following the vehicle's reentry from a chase plane (like was sometimes done with Shuttle or Falcon 9), having black, high-emissivity paint anywhere it might get hot and surrounding, that allows them to map the temperature distribution accurately with infrared (etc) cameras. Shiny stainless steel does not allow that.
Title: Re: Starship heat shield
Post by: Reynold on 07/07/2022 07:02 pm
While there may be some performance improvements by painting some areas, it's clear from looking at how and where they painted that most of the paint is for aesthetic reasons.
I don't agree (in part because it doesn't seem that aesthetic of a paint pattern). It seems quite likely that analysis showed they might need more thermal protection, so they added some to maximize the chance it survives reentry.

It could also be for analysis purposes. If they have high resolution tracking cameras following the vehicle's reentry from a chase plane (like was sometimes done with Shuttle or Falcon 9), having black, high-emissivity paint anywhere it might get hot and surrounding, that allows them to map the temperature distribution accurately with infrared (etc) cameras. Shiny stainless steel does not allow that.

I think I recall that there was a NASA project funding item someone noticed many months ago for what looked like thermal reentry analysis for an undescribed object doing reentry near Hawaii, and it was speculated that this was for NASA looking at the Starship reentry.  This would make sense both for SpaceX, so they don't have to build a dedicated system to watch this, and NASA, to help refine their models of different aerodynamic shapes doing reentry.  All of NASA's existing data is probably either on capsules, or the Space Shuttle. 
Title: Re: Starship heat shield
Post by: edzieba on 07/08/2022 10:56 am
While there may be some performance improvements by painting some areas, it's clear from looking at how and where they painted that most of the paint is for aesthetic reasons.
I don't agree (in part because it doesn't seem that aesthetic of a paint pattern). It seems quite likely that analysis showed they might need more thermal protection, so they added some to maximize the chance it survives reentry.

It could also be for analysis purposes. If they have high resolution tracking cameras following the vehicle's reentry from a chase plane (like was sometimes done with Shuttle or Falcon 9), having black, high-emissivity paint anywhere it might get hot and surrounding, that allows them to map the temperature distribution accurately with infrared (etc) cameras. Shiny stainless steel does not allow that.

I think I recall that there was a NASA project funding item someone noticed many months ago for what looked like thermal reentry analysis for an undescribed object doing reentry near Hawaii, and it was speculated that this was for NASA looking at the Starship reentry.  This would make sense both for SpaceX, so they don't have to build a dedicated system to watch this, and NASA, to help refine their models of different aerodynamic shapes doing reentry.  All of NASA's existing data is probably either on capsules, or the Space Shuttle.
The slide deck (https://ntrs.nasa.gov/api/citations/20210020835/downloads/GCD_2021%20APR_SCIFLI_SpaceX%20ACO%20poster.pptx.pdf) literally has 'Starship' in the title, the body, and is plastered with pictures of it. No speculation required.

Starship is projected to enter over the Pacific Missile Range due to the existing extensive tracking and measurement capabilities of that range. WB-57 observations would be nice, but still mainly viewing from 'below' during most of EDL - by the time Starship has descended below the WB-57's maximum altitude it will be almost if not already (for the first test with limited downmass) subsonic.
Title: Re: Starship heat shield
Post by: DanClemmensen on 07/08/2022 01:16 pm
While there may be some performance improvements by painting some areas, it's clear from looking at how and where they painted that most of the paint is for aesthetic reasons.
I don't agree (in part because it doesn't seem that aesthetic of a paint pattern). It seems quite likely that analysis showed they might need more thermal protection, so they added some to maximize the chance it survives reentry.

It could also be for analysis purposes. If they have high resolution tracking cameras following the vehicle's reentry from a chase plane (like was sometimes done with Shuttle or Falcon 9), having black, high-emissivity paint anywhere it might get hot and surrounding, that allows them to map the temperature distribution accurately with infrared (etc) cameras. Shiny stainless steel does not allow that.

I think I recall that there was a NASA project funding item someone noticed many months ago for what looked like thermal reentry analysis for an undescribed object doing reentry near Hawaii, and it was speculated that this was for NASA looking at the Starship reentry.  This would make sense both for SpaceX, so they don't have to build a dedicated system to watch this, and NASA, to help refine their models of different aerodynamic shapes doing reentry.  All of NASA's existing data is probably either on capsules, or the Space Shuttle.
The slide deck (https://ntrs.nasa.gov/api/citations/20210020835/downloads/GCD_2021%20APR_SCIFLI_SpaceX%20ACO%20poster.pptx.pdf) literally has 'Starship' in the title, the body, and is plastered with pictures of it. No speculation required.

Starship is projected to enter over the Pacific Missile Range due to the existing extensive tracking and measurement capabilities of that range. WB-57 observations would be nice, but still mainly viewing from 'below' during most of EDL - by the time Starship has descended below the WB-57's maximum altitude it will be almost if not already (for the first test with limited downmass) subsonic.
Starship's ventral-forward attitude means that the dorsal surface is fairly visible after Starship passes the observer, I think. do we know where the WB-57 will be located?
Title: Re: Starship heat shield
Post by: marsbase on 07/08/2022 02:03 pm
While there may be some performance improvements by painting some areas, it's clear from looking at how and where they painted that most of the paint is for aesthetic reasons.
I don't agree (in part because it doesn't seem that aesthetic of a paint pattern). It seems quite likely that analysis showed they might need more thermal protection, so they added some to maximize the chance it survives reentry.

It could also be for analysis purposes. If they have high resolution tracking cameras following the vehicle's reentry from a chase plane (like was sometimes done with Shuttle or Falcon 9), having black, high-emissivity paint anywhere it might get hot and surrounding, that allows them to map the temperature distribution accurately with infrared (etc) cameras. Shiny stainless steel does not allow that.

I think I recall that there was a NASA project funding item someone noticed many months ago for what looked like thermal reentry analysis for an undescribed object doing reentry near Hawaii, and it was speculated that this was for NASA looking at the Starship reentry.  This would make sense both for SpaceX, so they don't have to build a dedicated system to watch this, and NASA, to help refine their models of different aerodynamic shapes doing reentry.  All of NASA's existing data is probably either on capsules, or the Space Shuttle.
The slide deck (https://ntrs.nasa.gov/api/citations/20210020835/downloads/GCD_2021%20APR_SCIFLI_SpaceX%20ACO%20poster.pptx.pdf) literally has 'Starship' in the title, the body, and is plastered with pictures of it. No speculation required.

Starship is projected to enter over the Pacific Missile Range due to the existing extensive tracking and measurement capabilities of that range. WB-57 observations would be nice, but still mainly viewing from 'below' during most of EDL - by the time Starship has descended below the WB-57's maximum altitude it will be almost if not already (for the first test with limited downmass) subsonic.
Starship's ventral-forward attitude means that the dorsal surface is fairly visible after Starship passes the observer, I think. do we know where the WB-57 will be located?
There will be many military satellites focused on that Starship flight. Nobody has more to gain from Starship than the US military.
Title: Re: Starship heat shield
Post by: wannamoonbase on 07/08/2022 02:51 pm
While there may be some performance improvements by painting some areas, it's clear from looking at how and where they painted that most of the paint is for aesthetic reasons.
I don't agree (in part because it doesn't seem that aesthetic of a paint pattern). It seems quite likely that analysis showed they might need more thermal protection, so they added some to maximize the chance it survives reentry.

It could also be for analysis purposes. If they have high resolution tracking cameras following the vehicle's reentry from a chase plane (like was sometimes done with Shuttle or Falcon 9), having black, high-emissivity paint anywhere it might get hot and surrounding, that allows them to map the temperature distribution accurately with infrared (etc) cameras. Shiny stainless steel does not allow that.

I think I recall that there was a NASA project funding item someone noticed many months ago for what looked like thermal reentry analysis for an undescribed object doing reentry near Hawaii, and it was speculated that this was for NASA looking at the Starship reentry.  This would make sense both for SpaceX, so they don't have to build a dedicated system to watch this, and NASA, to help refine their models of different aerodynamic shapes doing reentry.  All of NASA's existing data is probably either on capsules, or the Space Shuttle.
The slide deck (https://ntrs.nasa.gov/api/citations/20210020835/downloads/GCD_2021%20APR_SCIFLI_SpaceX%20ACO%20poster.pptx.pdf) literally has 'Starship' in the title, the body, and is plastered with pictures of it. No speculation required.

Starship is projected to enter over the Pacific Missile Range due to the existing extensive tracking and measurement capabilities of that range. WB-57 observations would be nice, but still mainly viewing from 'below' during most of EDL - by the time Starship has descended below the WB-57's maximum altitude it will be almost if not already (for the first test with limited downmass) subsonic.
Starship's ventral-forward attitude means that the dorsal surface is fairly visible after Starship passes the observer, I think. do we know where the WB-57 will be located?
There will be many military satellites focused on that Starship flight. Nobody has more to gain from Starship than the US military.

SpaceX and NASA might disagree.  SpaceX has bet nearly everything on Starship being successful. 

It will be one of the most monitored launches ever. 

I have total faith in Superheavy being able to work and even recovery with the chopsticks. 

Starship can get to orbit, I believe that as well.  The heatshield on such a large vehicle with control surfaces, that has been the biggest unknown in my mind since the start of this development effort.
Title: Re: Starship heat shield
Post by: marsbase on 07/08/2022 04:33 pm
There will be many military satellites focused on that Starship flight. Nobody has more to gain from Starship than the US military.

SpaceX and NASA might disagree.  SpaceX has bet nearly everything on Starship being successful. 

It will be one of the most monitored launches ever. 

I have total faith in Superheavy being able to work and even recovery with the chopsticks. 

Starship can get to orbit, I believe that as well.  The heatshield on such a large vehicle with control surfaces, that has been the biggest unknown in my mind since the start of this development effort.
I agree that the heatshield functioning is the part of Starship I worry about most.  And let me re-word my earlier comment"
"There will be many military satellites focused on that Starship flight. Not all of them will be American."
Title: Re: Starship heat shield
Post by: Slarty1080 on 07/10/2022 08:34 am
There will be many military satellites focused on that Starship flight. Nobody has more to gain from Starship than the US military.

SpaceX and NASA might disagree.  SpaceX has bet nearly everything on Starship being successful. 

It will be one of the most monitored launches ever. 

I have total faith in Superheavy being able to work and even recovery with the chopsticks. 

Starship can get to orbit, I believe that as well.  The heatshield on such a large vehicle with control surfaces, that has been the biggest unknown in my mind since the start of this development effort.
I agree that the heatshield functioning is the part of Starship I worry about most.  And let me re-word my earlier comment"
"There will be many military satellites focused on that Starship flight. Not all of them will be American."
Yes in theory it should all work fine. But the trouble is that in theory practice and theory are the same. But in practice they are often different. Lets hope that any problems uncovered can be easily resolved an there aren't any seriously hairy gotyas lurking.
Title: Re: Starship heat shield
Post by: KBK on 07/11/2022 01:22 pm
They are at the 'real world test required', in order to go forward with heat shield design.

Launch that sucker, see what happens, then huddle, ruminate, and re-imagine on whatever level required.

I've looked at the sides of ship 24 in some of those more recent images (past few days) and it says that the blanket & mesh idea wants to work but localized disturbances are wreaking havoc.

will the mesh be even enough, over such a large area?
can two layers of mesh make this function?
Can these two given layers be aligned in such a way to make it even enough, with enough support?
will the mesh size ratios have to be tuned?

The 'problem' as it were, is to get support at the tips of the tiles, in conjunction with associated adjacent tips, but to not translate, as much as possible, that shared support to anywhere near the mount pins.

To gain a form of damped flexibility on/in those corners to 'follow the round' as it were, of the curve, but with all the other caveats in play - doing their concurrent thing. This is why I originally suggested a backing support of some sort that had a shaped end that pushed into the blanket, at the corner. This, of course, adds on a few extra problems in build and potential for issue, in order to address the paired complex movement/vibration problem of mount pins vs corner support (in complex analysis of the corner/meet/motion problem).

Which is why I suggested a test section of a curve, with a vibration mount and high speed camera/laser analysis, to get the corner support or mesh layering as close as possible to what is thought to be needed. To find the peak effect damping valley, in some way, before flight. How much useful data that would produce, is debatable.. but it's a viable avenue for analysis, from what I can see. And comes at quit minimal cost, effort, and losses in time.

This situation came about, where such tests would have been the more viable path, due to the slow down in flight testing over the past year. Normally, their iteration rate would have made this borderline in effectiveness via swamping such thinking by the sheer number of flights taking place (akin to raptor production). But that's hindsight, 'n all that...

With the flight test iterations (numerically, etc) now sort of set in stone, a test jig might be the more viable way to go, now ...or still...

There's a lot of stuff up in the air, here, so it's no small wonder that some of this like the heat shield, is giving more grief than desired.

To get to maximum distillation of the problem at hand...Everything comes down to the effective damping and control of the position of those tile corners in conjunction with one another (each tri-corner 'meet up').

Another thing/problem/solution might end up being the specific shape of the outer edges of the tiles, re 90 degrees or with some sort of bevel to those edges. the air/plasma/thermal flow can be converted, possibly, to being some of the damping and flutter/vibration control. Possibly. Very debatable for at least a few seconds, anyway.

~~~~~~~~~~~~~~~

An idea comes: a bump or attachment of some sort, UNDER the blanket, attached to the stainless hull itself, that changes the pressure and stress loading of the tri-corner areas.

The more I think of it..that might be the way to go. Thus, no excessive contoured/shaped tile mount but more vibrational control and dissipation available at the exact tri-corner area. the benefit of it being on the hull itself and away from the thermal loading issues. Additionally, more precision is guaranteed. The hardware for pin mounting is already in play and highly precise, etc.

It seems so smart that it's making me feel stupid for not seeing it before.

Which is always a good sign re viability.

This deletes the problematic mesh, and puts all the control of corners on the blanket's complex aspects. Which is simplified and more ideal. All while gaining separation from the pin mounts, for halving the motional range problems, thus likely taking the entire shield below the overall vibration or motion threshold problem range.

Re-distilling that scenario, simplified... puts the question down to: blanket vibration or resilience or flexibility and vibration/dissipation/absorption ~vs~ the tile mechanical stress load limits.

So, the physical engineering problem devolves down to being the hull attached bump shape and so on..vs the development or finding of the exact right blanket.

One set of niggling points remains, though. The vibration modes of the hull itself. How much that plays into it. The idea behind the mesh or external to the hull support of the tri-corners, is part of the game of avoiding and damping the peak and average hull vibration modes, vs the potential tile vibration modes, or their damping vs external expected forces.

But, I think that the right blanket vs the right pin lengths and shapes (damping mechanism within the pin design itself? this is possible), might help deal with all that. Delete the part (the mesh or any external tile mount scenario), simplify.

To help speed up the mental iteration process by adding in an idea (just came) that is known to be effective, a stress loaded legged spider of a sort for the tri-corner support item. the stressed legs of the tri-corner bump would deal with some dissipation of hull vibration. That weld is no more risky than a pin mount weld, which there are many thousands of.

Think of a spider with three shaped legs, all evenly spaced, with the spider body being the weld point, and each leg being (possibly, think through and test a few designs) stressed against the hull. This creates a possible corner motion trap under the blanket, for some minimal form of two axis damping of the individual tiles in the tri-corner.

Additionally, shaping a bevel into the underside of the tile edges in the appropriate areas adds into the scenario of the dual axis vibration trap with even (lower peak loading on small areas of the tile) loading and control of position for said corner problem. Where, as the tiles expand from the thermal load, they are herded into perfect alignment with respect to one another and the damping also increases (changes in parameters, anyway), etc.

Very much a 'crap, why did I not see this before' kinda thing, which hints strongly toward it's ultimate viability.

This looks to be a final functional long term viable solution for the heat shield problem, and I'd take a bet on that one. I was thinking the mesh might (and I'm really not fond of maybe scenarios) work but those two recent images up the side of the tile layout of ship 24, really put the tile problem back on the table for me.

I'd love to work with spacex, I think I can help....but it seems inordinately hard to get their attention. I could have done this months ago, If was standing in front of that ship.
Title: Re: Starship heat shield
Post by: DanClemmensen on 07/11/2022 04:20 pm
...
~~~~~~~~~~~~~~~
An idea comes: a bump or attachment of some sort, UNDER the blanket, attached to the stainless hull itself, that changes the pressure and stress loading of the tri-corner areas.
Stamp the stainless steel to form a tile-shaped flat surface for each tile. Probably easier, lighter. and stronger than adding bumps. Do this as a post-processng step when forming the rings. It does make adding stringers more complicated, but not my much.
Title: Re: Starship heat shield
Post by: robot_enthusiast on 07/12/2022 03:06 am
...
~~~~~~~~~~~~~~~
An idea comes: a bump or attachment of some sort, UNDER the blanket, attached to the stainless hull itself, that changes the pressure and stress loading of the tri-corner areas.
Stamp the stainless steel to form a tile-shaped flat surface for each tile. Probably easier, lighter. and stronger than adding bumps. Do this as a post-processng step when forming the rings. It does make adding stringers more complicated, but not my much.
I take it you've never tried popping a dent out of a car. With material that thin a small amount of internal pressure will pop the skin right back to the shape it started. If there's a tile on top then it would be destroyed.
Title: Re: Starship heat shield
Post by: OTV Booster on 08/07/2022 02:24 pm
This is a bit off the wall, but does anybody have a clue about the reflectivity or absorbance of the tiles at various radio frequencies?
Title: Re: Starship heat shield
Post by: InterestedEngineer on 08/07/2022 02:43 pm
This is a bit off the wall, but does anybody have a clue about the reflectivity or absorbance of the tiles at various radio frequencies?

There's no metal in the tiles save the bracket, which behind it has a pile of stainless steel.  Ceramic is non-conductive.

No conductivity, no effect on RF (unless there's a ceramic between two conductors, then maybe some existing waveguide effect gets modified.

So the effect of the tiles on RF should be about zero.
Title: Re: Starship heat shield
Post by: edzieba on 08/08/2022 11:34 am
This is a bit off the wall, but does anybody have a clue about the reflectivity or absorbance of the tiles at various radio frequencies?
I can't find an actual transmissivity spectrum of the STS tiles (which the Starships tiles are near identical to in composition) but there were L-band antennae installed under the tiles, so its reasonable to assume that at least UHF and below are reasonably unimpeded.
Title: Re: Starship heat shield
Post by: Cheapchips on 08/10/2022 07:03 am
Did S24 manage to keep all it's tiles during the two engine static fire?  I couldn't see any falling in the NSF footage.

That's a step forward in terms of quality control if it managed to retain them?
Title: Re: Starship heat shield
Post by: adrianwyard on 09/11/2022 07:44 am
Before/After:
https://twitter.com/RGVaerialphotos/status/1568237736867291145
Title: Re: Starship heat shield
Post by: Restless on 09/12/2022 05:36 am
I believe there were about 30 tiles lost. On the basis that the rigors of launch and re-entry are on the order of a hundred times that of a static fire, we could expect a loss of 3000 tiles and probable loss of the Starship as well. A more secure method of attaching tiles needs to be developed which, I'm sure Spacex is working on.
Title: Re: Starship heat shield
Post by: Nevyn72 on 09/12/2022 06:58 am
I believe there were about 30 tiles lost. On the basis that the rigors of launch and re-entry are on the order of a hundred times that of a static fire, we could expect a loss of 3000 tiles and probable loss of the Starship as well. A more secure method of attaching tiles needs to be developed which, I'm sure Spacex is working on.

Wow, I had to duck to avoid all the handwaving in that post!  :o

Care to elaborate on how you arrived at the figure of 100 times more rigorous conditions during launch and re-entry?
What process would result in such an increase causing a similarly sized increase in the number of tiles being damaged?
Title: Re: Starship heat shield
Post by: Skyrunner on 09/12/2022 07:52 am
I believe there were about 30 tiles lost. On the basis that the rigors of launch and re-entry are on the order of a hundred times that of a static fire, we could expect a loss of 3000 tiles and probable loss of the Starship as well. A more secure method of attaching tiles needs to be developed which, I'm sure Spacex is working on.

Many tiles were hit by the aggregate coming out of the newly poured concrete ring around the stand. Please enlighten me how that equates to orbital re-entry?

That newly poured concrete might benefit from martyte to prevent concrete "erosion". Or weld extra covers around the suborbital stand to protect the flaps from debris. Ideas anyone?
Title: Re: Starship heat shield
Post by: JamesH65 on 09/13/2022 05:49 pm
I believe there were about 30 tiles lost. On the basis that the rigors of launch and re-entry are on the order of a hundred times that of a static fire, we could expect a loss of 3000 tiles and probable loss of the Starship as well. A more secure method of attaching tiles needs to be developed which, I'm sure Spacex is working on.

Er, no?

Why do you think orbital reentry will be any worse than a static fire?
Title: Re: Starship heat shield
Post by: DusanC on 09/15/2022 07:50 am
There is a major redesign of tiles that I haven't noticed before  ??? , their sides are now beveled.
I wonder if:
1. There will be another type of tile that goes between them? or
2. There won't be any tiles between these? This solution would be for higher thermal loads than possible with plain stainless but lower than fully tiled. Mass optimization maybe?

(https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=54984.0;attach=2127012;image)
Title: Re: Starship heat shield
Post by: sebk on 09/15/2022 08:45 am
Those are likely not tiles at all, but antenna (or other instrumentation) covers for a ship which according to rumors it's not going to have a heatshield at all. Installing such stuff paints the said rumors more likely.
Title: Re: Starship heat shield
Post by: DusanC on 09/15/2022 09:20 am
Those are likely not tiles at all, but antenna (or other instrumentation) covers for a ship which according to rumors it's not going to have a heatshield at all. Installing such stuff paints the said rumors more likely.

You're right, their placement on windward side threw me off.

Here's the same pattern on ship 24 leeward side.

(https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=56074.0;attach=2125844;image)
Title: Re: Starship heat shield
Post by: OTV Booster on 09/15/2022 10:18 pm
Those are likely not tiles at all, but antenna (or other instrumentation) covers for a ship which according to rumors it's not going to have a heatshield at all. Installing such stuff paints the said rumors more likely.
Yeah, rumor of no tiles. Why have mounting pins if tiles aren't planned? Each one of those nubbins will collect heat and melt. The ones on the centerline may even reach through or distort the shock front. It's interesting to speculate the impact all this would have in a sorta academic way but I doubt they're going to actually test it. Whatever it would do, it would not be good. Something else is going on.


We all know how adverse I am to speculating ::)  but I'm gonna go out on a limb. Major tile changes coming up. Form factor will have little or no change but the materials and/or metal inserts will change. Or there's a world wide tile shortage.

Title: Re: Starship heat shield
Post by: chopsticks on 09/15/2022 10:42 pm
Occam's razor: The pins are there because the temporary switch to no tiles hadn't been planned before this nosecone was already made and had the pins welded on. They used the next nosecone in line which was this one.
Title: Re: Starship heat shield
Post by: litton4 on 09/16/2022 09:47 am
Occam's razor: The pins are there because the temporary switch to no tiles hadn't been planned before this nosecone was already made and had the pins welded on. They used the next nosecone in line which was this one.

If they attempt re-entry in this configuration, surely the pins will destroy the smooth plasma flow around the vehicle?

(and don't call me Shirley)

Unless they plan for this to be a destructive re-entry all along...
Title: Re: Starship heat shield
Post by: edzieba on 09/16/2022 11:03 am
Recent S25 stacking - The tile gap between sections is a lot wider than we've seen previously. Before, ring segments gaps have omitted one row of complete tiles (but attached via adhesive rather than pins) and one row of half-tiles (attached by adhesive) on either side of the gap, making for a '3 tile wide' gap. Here, that gap looks closer to 5-7 tiles.

Occam's razor: The pins are there because the temporary switch to no tiles hadn't been planned before this nosecone was already made and had the pins welded on. They used the next nosecone in line which was this one.
Alternative cut of the razor: the pins are installed but tiles aren't because they intend to install the tiles but the tiles are not ready to be installed yet (e.g. major changes to tile manufacture interrupting production, like moving sites, replacing equipment, changing fibre suppliers or bringing fibre manufacture in-house, etc).
Title: Re: Starship heat shield
Post by: chopsticks on 09/16/2022 12:41 pm
Occam's razor: The pins are there because the temporary switch to no tiles hadn't been planned before this nosecone was already made and had the pins welded on. They used the next nosecone in line which was this one.

If they attempt re-entry in this configuration, surely the pins will destroy the smooth plasma flow around the vehicle?

(and don't call me Shirley)

Unless they plan for this to be a destructive re-entry all along...

Expendable.
Title: Re: Starship heat shield
Post by: chopsticks on 09/16/2022 12:50 pm
Alternative cut of the razor: the pins are installed but tiles aren't because they intend to install the tiles but the tiles are not ready to be installed yet (e.g. major changes to tile manufacture interrupting production, like moving sites, replacing equipment, changing fibre suppliers or bringing fibre manufacture in-house, etc).

Could easily be that as well. The reason I said that was because S27 skipped the part in production where they weld the pins on (didn't receive any). I can't remember what I heard that though.
Title: Re: Starship heat shield
Post by: woods170 on 09/16/2022 12:54 pm
Occam's razor: The pins are there because the temporary switch to no tiles hadn't been planned before this nosecone was already made and had the pins welded on. They used the next nosecone in line which was this one.

If they attempt re-entry in this configuration, surely the pins will destroy the smooth plasma flow around the vehicle?

(and don't call me Shirley)

Unless they plan for this to be a destructive re-entry all along...

Emphasis mine.

Without the heat shield tiles in place the reentry will destroy the vehicle regardless.
Title: Re: Starship heat shield
Post by: Hamish.Student on 09/16/2022 01:50 pm
Those are likely not tiles at all, but antenna (or other instrumentation) covers for a ship which according to rumors it's not going to have a heatshield at all. Installing such stuff paints the said rumors more likely.
   
 
Would someone please provide a summary of the rumours? I looked back a few pages and didn't find anything. Cheers!
Title: Re: Starship heat shield
Post by: OTV Booster on 09/16/2022 04:06 pm
Recent S25 stacking - The tile gap between sections is a lot wider than we've seen previously. Before, ring segments gaps have omitted one row of complete tiles (but attached via adhesive rather than pins) and one row of half-tiles (attached by adhesive) on either side of the gap, making for a '3 tile wide' gap. Here, that gap looks closer to 5-7 tiles.

Occam's razor: The pins are there because the temporary switch to no tiles hadn't been planned before this nosecone was already made and had the pins welded on. They used the next nosecone in line which was this one.
Alternative cut of the razor: the pins are installed but tiles aren't because they intend to install the tiles but the tiles are not ready to be installed yet (e.g. major changes to tile manufacture interrupting production, like moving sites, replacing equipment, changing fibre suppliers or bringing fibre manufacture in-house, etc).
Another thought. Maybe tile application is planned as an early move to the new building and things are lagging. No idea why this specific operation would be moved early. Just looking at possibilities.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/16/2022 04:15 pm
Occam's razor: The pins are there because the temporary switch to no tiles hadn't been planned before this nosecone was already made and had the pins welded on. They used the next nosecone in line which was this one.
Naw, doesn't make sense. Besides screwing up reentry, naked pins can't be doing anything good for ascent. Lots of drag and breakup of laminar flow. Judging by past performance, if SX didn't want tiles all of a sudden they would scrap the pinned pieces and move on.
Title: Re: Starship heat shield
Post by: Hog on 09/16/2022 05:53 pm
Occam's razor: The pins are there because the temporary switch to no tiles hadn't been planned before this nosecone was already made and had the pins welded on. They used the next nosecone in line which was this one.
Naw, doesn't make sense. Besides screwing up reentry, naked pins can't be doing anything good for ascent. Lots of drag and breakup of laminar flow. Judging by past performance, if SX didn't want tiles all of a sudden they would scrap the pinned pieces and move on.
How long exactly would ascent performance be affected to any major degree?  Launch, get up and out of most of the atmosphere then begin to lay over and really pour on the acceleration. AIUI the atmospheric portion of ascent is a small portion of the total acceleration plot of an orbital vehicle.

Any chance these exposed pins would begin to ablate?  It might be nice to know how melting pins material(stainless?) affects "downstream" TPS.
Title: Re: Starship heat shield
Post by: Slothman on 09/16/2022 05:57 pm
Hey, maybe exposed pins can BE the TPS. They are sacrificial matter that slowly evaporates, keeping the plasma from the actual hull. Naturally not reusable, but then again, the first orbital test flight wasn't supposed to be recovered anyways.
Title: Re: Starship heat shield
Post by: Robotbeat on 09/16/2022 06:35 pm
Hey, maybe exposed pins can BE the TPS. They are sacrificial matter that slowly evaporates, keeping the plasma from the actual hull. Naturally not reusable, but then again, the first orbital test flight wasn't supposed to be recovered anyways.
Nah. They’ll probably actually make the problem worse by creating little hot spots on the flow around them.
Title: Re: Starship heat shield
Post by: Hog on 09/16/2022 06:48 pm
Hey, maybe exposed pins can BE the TPS. They are sacrificial matter that slowly evaporates, keeping the plasma from the actual hull. Naturally not reusable, but then again, the first orbital test flight wasn't supposed to be recovered anyways.
Nah. They’ll probably actually make the problem worse by creating little hot spots on the flow around them.
If the pins remain as part of the design, we are bound to find out.
Title: Re: Starship heat shield
Post by: Keldor on 09/16/2022 10:34 pm
It seems to me that the most likely explanation for the pins without tiles on ship 26 is simply that they've changed up the assembly order a bit.  It's even possible that they've decided that they can't do a static fire from the suborbital pad without damaging tiles due to the acoustics, and so have opted to not install them until after the static fire campaign is complete.
Title: Re: Starship heat shield
Post by: Robotbeat on 09/16/2022 11:19 pm
It seems to me that the most likely explanation for the pins without tiles on ship 26 is simply that they've changed up the assembly order a bit.  It's even possible that they've decided that they can't do a static fire from the suborbital pad without damaging tiles due to the acoustics, and so have opted to not install them until after the static fire campaign is complete.
I would think that you're likely to risk losing tiles during launch if you can't static fire on the suborbital pad without damaging tiles. Even if the acoustic environment is a bit different for orbital launch, I would hope the tiles aren't so marginal that a stress test like that would cause them to fail.

...it's a sign they'll need to improve the robustness of the system. A truly robust TPS is obviously going to have to handle ground testing and such, not just the exact flight environment.

This is why my working speculative theory is they've made significant improvements to the TPS attachment method or the tiles or something since SN24 but they might not be ready to deploy those improvements until SN28 or SN29 or something.
Title: Re: Starship heat shield
Post by: Nevyn72 on 09/16/2022 11:33 pm
Remember it's not a case of not installing tiles on the pins on S26, they were installed (on the nose at least) and later removed...

The question is why?
Title: Re: Starship heat shield
Post by: Robotbeat on 09/17/2022 12:51 am
Remember it's not a case of not installing tiles on the pins on S26, they were installed (on the nose at least) and later removed...

The question is why?
Wasted mass if they're not planning on recovering the stage.
Title: Re: Starship heat shield
Post by: chopsticks on 09/17/2022 02:20 am
Occam's razor: The pins are there because the temporary switch to no tiles hadn't been planned before this nosecone was already made and had the pins welded on. They used the next nosecone in line which was this one.
Naw, doesn't make sense. Besides screwing up reentry, naked pins can't be doing anything good for ascent. Lots of drag and breakup of laminar flow. Judging by past performance, if SX didn't want tiles all of a sudden they would scrap the pinned pieces and move on.


Yeah, it does make sense. You're missing the bit about it being expendable. If the pins are already there, who cares? It's not being recovered anyway. As far as laminar flow is concerned, I really don't see the small aerodynamic hit on the way up as being a very big deal. And they may end up scrapping it as you say but based on their past performance, they may end up just using what they have if it's more convenient.
Title: Re: Starship heat shield
Post by: eriblo on 09/17/2022 03:17 pm
Those are likely not tiles at all, but antenna (or other instrumentation) covers for a ship which according to rumors it's not going to have a heatshield at all. Installing such stuff paints the said rumors more likely.
   
 
Would someone please provide a summary of the rumours? I looked back a few pages and didn't find anything. Cheers!
Don't know if you know about it but this site has some useful articles  ;)

https://www.nasaspaceflight.com/2022/09/starship-next-phase-of-testing/
Quote
As previously reported, Ship 26 and Ship 27 may be undergoing a radical change in plans, omitting thermal protection system (TPS) tiles and not installing aerodynamic flaps. So far, this seems to be holding true with parts of Ship 26 seen now bare of tiles and on stand-by at Starbase’s ring yard for stacking.

Ship 27 parts are also proceeding similarly to Ship 26 parts. In some cases, there seems to be a strange mix-match of parts for these vehicles.

https://www.nasaspaceflight.com/2022/08/booster-7-additional-tests/
Quote
While all of this is happening, workers have been seen doing unusual work on future Starship vehicles and more concretely on Ship 26.

Workers were seen removing Thermal Protection System (TPS) tiles and blankets from Ship 26’s nosecone, while some of its barrel sections, which were supposed to receive the installation pins for the TPS tiles, are already staged outside in the ring yard ready for stacking.

While there has not been any official reason provided, some indications point to SpaceX trying to fast-track Ship 26 and Ship 27 builds by not installing TPS tiles or even flaps in order to quickly deliver Starlink v2 satellites into orbit, which the company may need in order to accelerate deployment once Starship proves itself worthy of going into orbit.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/17/2022 04:42 pm
Occam's razor: The pins are there because the temporary switch to no tiles hadn't been planned before this nosecone was already made and had the pins welded on. They used the next nosecone in line which was this one.
Naw, doesn't make sense. Besides screwing up reentry, naked pins can't be doing anything good for ascent. Lots of drag and breakup of laminar flow. Judging by past performance, if SX didn't want tiles all of a sudden they would scrap the pinned pieces and move on.
How long exactly would ascent performance be affected to any major degree?  Launch, get up and out of most of the atmosphere then begin to lay over and really pour on the acceleration. AIUI the atmospheric portion of ascent is a small portion of the total acceleration plot of an orbital vehicle.

Any chance these exposed pins would begin to ablate?  It might be nice to know how melting pins material(stainless?) affects "downstream" TPS.
To be straight up, I've got no numbers and no firm answers. Just things to consider. Laying over for a horizontal component is mission dependent. Historically it often starts within 10's of seconds after liftoff. MaxQ changes accordingly. MaxQ is enough of a force to be reconned with that most if not all launches throttle down through it. Atmospheric transit may account for a small portion of the total acceleration but that says nothing about its portion of the total energy expenditure. Unless SX has modeled naked pins during liftoff, they don't have answers either. Like I said, I see nothing good coming from it. And I do see many possible gotcha's.

Your point about ablating pin interaction with downstream tiles caught me by surprise. We've seen barrel sections without tiles too and just assumed that no mix n match was in the works. My bad. Either way, I see no good coming from it.

My guess is that new tiles are expected to come on line or these pieces without tiles will be manufacturing pathfinders at best. Either way, I don't expect them to fly.


Edit: last sentence was unclear. I don't expect them to fly if they stay untiled.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/17/2022 04:52 pm
It seems to me that the most likely explanation for the pins without tiles on ship 26 is simply that they've changed up the assembly order a bit.  It's even possible that they've decided that they can't do a static fire from the suborbital pad without damaging tiles due to the acoustics, and so have opted to not install them until after the static fire campaign is complete.
Now that is good thinking.

Didn't we see them removing tiles? Which piece was it? Removing tiles might fit with a change in testing.


Edit: Answerd by Nevyn72
Title: Re: Starship heat shield
Post by: Robotbeat on 09/17/2022 05:04 pm
You can model the pins without too much difficulty. Max-Q is near transonic region, not hypersonic, so it’s easier to model.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/17/2022 05:35 pm
Those are likely not tiles at all, but antenna (or other instrumentation) covers for a ship which according to rumors it's not going to have a heatshield at all. Installing such stuff paints the said rumors more likely.
   
 
Would someone please provide a summary of the rumours? I looked back a few pages and didn't find anything. Cheers!
Don't know if you know about it but this site has some useful articles  ;)

https://www.nasaspaceflight.com/2022/09/starship-next-phase-of-testing/ (https://www.nasaspaceflight.com/2022/09/starship-next-phase-of-testing/)
Quote
As previously reported, Ship 26 and Ship 27 may be undergoing a radical change in plans, omitting thermal protection system (TPS) tiles and not installing aerodynamic flaps. So far, this seems to be holding true with parts of Ship 26 seen now bare of tiles and on stand-by at Starbase’s ring yard for stacking.

Ship 27 parts are also proceeding similarly to Ship 26 parts. In some cases, there seems to be a strange mix-match of parts for these vehicles.

https://www.nasaspaceflight.com/2022/08/booster-7-additional-tests/ (https://www.nasaspaceflight.com/2022/08/booster-7-additional-tests/)
Quote
While all of this is happening, workers have been seen doing unusual work on future Starship vehicles and more concretely on Ship 26.

Workers were seen removing Thermal Protection System (TPS) tiles and blankets from Ship 26’s nosecone, while some of its barrel sections, which were supposed to receive the installation pins for the TPS tiles, are already staged outside in the ring yard ready for stacking.

While there has not been any official reason provided, some indications point to SpaceX trying to fast-track Ship 26 and Ship 27 builds by not installing TPS tiles or even flaps in order to quickly deliver Starlink v2 satellites into orbit, which the company may need in order to accelerate deployment once Starship proves itself worthy of going into orbit.
Hmmm. Maybe I'll have to eat my words. Low throttle well before MaxQ. Maybe even for a while after MaxQ. No fins. No tiles. Lots of margin. And ammo in their FCC arguments about bandwidth.


No attempt at EDL makes no sense from a testing perspective but it ties the whole thing up with a bow from a StarLink perspective. 
Title: Re: Starship heat shield
Post by: Keldor on 09/17/2022 07:40 pm
Remember it's not a case of not installing tiles on the pins on S26, they were installed (on the nose at least) and later removed...

The question is why?

Hmm...  Another possibility is that S26 is in the process of being scrapped, similar to what they did with S16 after S15 flew.  In this case, they might just have to strip the TPS for environmental reasons, since we can probably expect it to have a lot of the same potential health issues from exposure as asbestos.
Title: Re: Starship heat shield
Post by: sebk on 09/17/2022 08:37 pm
No. They proceeded with the construction, but stripped of tiles.
Title: Re: Starship heat shield
Post by: John-H on 09/18/2022 12:08 am
My fearless prediction is that they will launch at least a few expendable, much lighter Starships.

John
Title: Re: Starship heat shield
Post by: darkenfast on 09/18/2022 08:38 am
Forgive if this has been mentioned above and I missed it, but could the "tileless" Ships be scheduled for shipment to KSC, for fit-checks, tile installation practice or whatever? It might make sense to do the tiles there, especially if shipping involves laying the Ship down on its side. I know it seems a little early, but it was just a thought.
Title: Re: Starship heat shield
Post by: Nightstalker89 on 09/18/2022 09:00 am
Until they catch a booster, why expend resources on putting tiles on the ships, just expend them and move on.  Once they catch a few boosters then concentrate on ship reuse.  Classic agile development technique.  Only work on what you need today to get the fastest viable product to market.  After that refine.  The current ships with tiles are just development lead products to see where the team working on that in parallel may need to refine their portion of the product.
Title: Re: Starship heat shield
Post by: JamesH65 on 09/18/2022 04:11 pm
In this case, they might just have to strip the TPS for environmental reasons, since we can probably expect it to have a lot of the same potential health issues from exposure as asbestos.

I don't think we have seen evidence for that, have we? Asbestos has a very specific hook like shape which makes it nasty, does the material used for the tiles have the same structure?
Title: Re: Starship heat shield
Post by: DanClemmensen on 09/18/2022 04:16 pm
Until they catch a booster, why expend resources on putting tiles on the ships, just expend them and move on.  Once they catch a few boosters then concentrate on ship reuse.  Classic agile development technique.  Only work on what you need today to get the fastest viable product to market.  After that refine.  The current ships with tiles are just development lead products to see where the team working on that in parallel may need to refine their portion of the product.
It's a tradeoff. They have a limited number of approved launches, so they need to test the TPS on every launch. The resources needed to test EDL are different than the resources to test launch, and except for the very first launch the EDL test can be deferred for days or weeks, so there is not even a short-term resource allocation problem.
Title: Re: Starship heat shield
Post by: eriblo on 09/18/2022 04:40 pm
Until they catch a booster, why expend resources on putting tiles on the ships, just expend them and move on.  Once they catch a few boosters then concentrate on ship reuse.  Classic agile development technique.  Only work on what you need today to get the fastest viable product to market.  After that refine.  The current ships with tiles are just development lead products to see where the team working on that in parallel may need to refine their portion of the product.
They explicitly started with the Starship part of the system because that was going to take the most effort and the whole reusable system was the minimum viable product - they already had unrivaled launch capabilities.

Now with Starlink V2 needing launches ASAP they might have a reason for a few expendable launches but I highly doubt it would have anything to do with speeding up the rest of the program.
Title: Re: Starship heat shield
Post by: robot_enthusiast on 09/18/2022 07:51 pm
Until they catch a booster, why expend resources on putting tiles on the ships, just expend them and move on.  Once they catch a few boosters then concentrate on ship reuse.  Classic agile development technique.  Only work on what you need today to get the fastest viable product to market.  After that refine.  The current ships with tiles are just development lead products to see where the team working on that in parallel may need to refine their portion of the product.
They explicitly started with the Starship part of the system because that was going to take the most effort and the whole reusable system was the minimum viable product - they already had unrivaled launch capabilities.

Now with Starlink V2 needing launches ASAP they might have a reason for a few expendable launches but I highly doubt it would have anything to do with speeding up the rest of the program.
I would have to disagree with the sentiment that it will not speed up the rest of the program. They appear to have paused further development of the heat shield until they get flight data to work off of to continue improving the design. Because of this it appears that their choices are to pause production for months after the first flight while improvements are implemented, or continue production without heat shields and continue developing SH and stage 0. Going to the effort of installing a heat shield on S26 & 27 would only give them redundant data at the cost of pulling resources from other areas and extending the production timeline.
Title: Re: Starship heat shield
Post by: edzieba on 09/19/2022 10:27 am
On the subject of the tiles themselves: can anyone remember the last time tiles were installed on any vehicle?
Looking back over the archived photos, S25 appears to have been fully tiles (prior to stacking) in late July, and S26 had been partially tiled for some time before the tiles were removed in August.

I'm going to place my bet as: Tile block upgrade is occurring, S26 and later will receive new tiles (which may be visually identical) before flight if tile production has restarted in time to provide full tile coverage, and ships will only launch untiled if there are not sufficient tiles available to complete coverage in time (rather than launching partially tiled, those tiles can be 'stolen' to more rapidly complete tiling of the next ship).
Title: Re: Starship heat shield
Post by: StarshipTrooper on 09/19/2022 03:16 pm
It could be that they can build a Superheavy quicker than they can a fully tiled and finned Starship. So to get up to pace for launching StarLinks they needed to speed up the upper stage production.
Title: Re: Starship heat shield
Post by: ppb on 09/19/2022 04:05 pm
It could be that they can build a Superheavy quicker than they can a fully tiled and finned Starship. So to get up to pace for launching StarLinks they needed to speed up the upper stage production.
And they may still get valuable data that anchors their aero heating and structural models for a bare SS on reentry. They may even have enough torque authority from ACS only and no flaps to trim their preferred attitude during the critical phase of reentry.

Minimum viable product includes a minimum viable heat shield.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/19/2022 09:12 pm
It could be that they can build a Superheavy quicker than they can a fully tiled and finned Starship. So to get up to pace for launching StarLinks they needed to speed up the upper stage production.
As an alternative, put more resources into SS and build fewer boosters. The last Elon mentioned long term SS to booster ratio it was 10:1.


Edit to add: until they can grab a booster they'll need one per launch. Even then the changes will come so thick and fast they may not bother (StarLink being the joker). It may be a year or two before we see a full stack launched with already flown stages.


Time, time, time See what's become of me
While I looked around for my possibilities
I was so hard to please...
     Simon & Garfunkel
Title: Re: Starship heat shield
Post by: john smith 19 on 09/20/2022 08:10 pm
Hmm...  Another possibility is that S26 is in the process of being scrapped, similar to what they did with S16 after S15 flew.  In this case, they might just have to strip the TPS for environmental reasons, since we can probably expect it to have a lot of the same potential health issues from exposure as asbestos.
Highly unlikely.

The well known safety issues around Asbestos would force similar safety requirements around stuff that was even similar to it in structure.

That said most of this stuff is dangerous if it's finely powdered and get airborn. Asbestos OTOH is naturally fibrous, so it's difficult to process without it getting airborn.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 09/21/2022 02:40 am
Zack Golden reasonably arrives at the conclusion that the tile damage from the 6 engine Raptor test was caused by debris from the test stand.

Implications for taking off from Mars, but not for taking off from Earth.

https://youtu.be/mJV-dWMy9Vo
Title: Re: Starship heat shield
Post by: john smith 19 on 09/21/2022 07:40 am
Zack Golden reasonably arrives at the conclusion that the tile damage from the 6 engine Raptor test was caused by debris from the test stand.

Implications for taking off from Mars, but not for taking off from Earth.
Which suggests that there should be action around the base to either strengthen the concrete or overlay it with steel plate preping for the next flight.

That should be pretty visible. Has anyone seen this?
Title: Re: Starship heat shield
Post by: oiorionsbelt on 09/21/2022 11:03 pm
Zack Golden reasonably arrives at the conclusion that the tile damage from the 6 engine Raptor test was caused by debris from the test stand.

Implications for taking off from Mars, but not for taking off from Earth.
Which suggests that there should be action around the base to either strengthen the concrete or overlay it with steel plate preping for the next flight.

That should be pretty visible. Has anyone seen this?
  "the next flight" will see Starship atop the booster not on the suborbital pad. Static fires of course.....
Title: Re: Starship heat shield
Post by: RamsesBic on 09/22/2022 12:03 am
Zack Golden reasonably arrives at the conclusion that the tile damage from the 6 engine Raptor test was caused by debris from the test stand.

Implications for taking off from Mars, but not for taking off from Earth.
Which suggests that there should be action around the base to either strengthen the concrete or overlay it with steel plate preping for the next flight.

That should be pretty visible. Has anyone seen this?
  "the next flight" will see Starship atop the booster not on the suborbital pad. Static fires of course.....

Don't forget S25. It has to go through ambient, cryo, thrust and static fire tests too. The sub-orbital pads need an upgrade if they want to SF 6 Raptors again.
Title: Re: Starship heat shield
Post by: john smith 19 on 09/22/2022 07:37 am
  "the next flight" will see Starship atop the booster not on the suborbital pad. Static fires of course.....
Then I guess the question becomes "Does the launch pad differ from the static fire pad?" IE Heavier concrete layers, steel plates laid down etc.

That would suggest that unexpected high levels of pad debris was the issue with the missing tiles.
Title: Re: Starship heat shield
Post by: john smith 19 on 09/22/2022 07:40 am
Zack Golden reasonably arrives at the conclusion that the tile damage from the 6 engine Raptor test was caused by debris from the test stand.

Implications for taking off from Mars, but not for taking off from Earth.
Which suggests that there should be action around the base to either strengthen the concrete or overlay it with steel plate preping for the next flight.

That should be pretty visible. Has anyone seen this?
  "the next flight" will see Starship atop the booster not on the suborbital pad. Static fires of course.....

Don't forget S25. It has to go through ambient, cryo, thrust and static fire tests too. The sub-orbital pads need an upgrade if they want to SF 6 Raptors again.
And if Raptors ongoing development work include upgrading the thrust level without it whatever debris got blown up by them starting up is going to happen worse, without something being done to the pad.

So has anyone noticed anything?
Title: Re: Starship heat shield
Post by: Barley on 09/22/2022 03:03 pm
  "the next flight" will see Starship atop the booster not on the suborbital pad. Static fires of course.....
Then I guess the question becomes "Does the launch pad differ from the static fire pad?" IE Heavier concrete layers, steel plates laid down etc.

That would suggest that unexpected high levels of pad debris was the issue with the missing tiles.

IIUC It looks to me that the super-heavy pad has a much taller "milk stool", eyeballing it 6m to 30m, at least for some of the mockups.  So perhaps they've already learned the lessons and made the changes.

OTOH they will need somewhere to static fire SS (Static firing Starship atop the booster is not a good idea) so some changes may be needed to the static fire pad.
Title: Re: Starship heat shield
Post by: RamsesBic on 09/22/2022 03:58 pm
  "the next flight" will see Starship atop the booster not on the suborbital pad. Static fires of course.....
Then I guess the question becomes "Does the launch pad differ from the static fire pad?" IE Heavier concrete layers, steel plates laid down etc.

That would suggest that unexpected high levels of pad debris was the issue with the missing tiles.

IIUC It looks to me that the super-heavy pad has a much taller "milk stool", eyeballing it 6m to 30m, at least for some of the mockups.  So perhaps they've already learned the lessons and made the changes.

OTOH they will need somewhere to static fire SS (Static firing Starship atop the booster is not a good idea) so some changes may be needed to the static fire pad.
The risk of debris hitting tiles when the ship is stacked on the booster is near zero.
The booster has no tiles that need protecting.
The "problem" is static fire tests of ships on the sub-orbital stands. I am sure they are going to do something to solve the problem before the next SF test with 6 Raptors. Installing better mounts for cameras on the legs of the stand might also give them better images and avoid causing unintentional brush fires.
Title: Re: Starship heat shield
Post by: adrianwyard on 09/22/2022 04:07 pm
*Technically* I suppose they could suspend Starship from the chopsticks at the correct height for the QD to attach. With no booster below that would give plenty of clearance for a static fire and guarantee no debris would reach the tiles  :) (This is joke.)

I find it fascinating we've not seen any evidence of flame diverters (which they use at MacGregor) for the test mount or main launch table. Even rolling in a small one like used for the V2 would presumably help?

Either way the key challenge for the heat shield is not static fire debris but launch vibration. (Mars landings are of course another matter entirely.)
Title: Re: Starship heat shield
Post by: RamsesBic on 09/22/2022 04:18 pm
An alternate method could be to shield the ship rather than protect the ground. It could for example be a much wider ring on top of the stand, or protecting walls around the ship (the lower sections at least.
I am pretty sure they are giving all such alternatives careful thought and will chose the most practical.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/22/2022 05:19 pm
So, we're seeing static fire tile damage that looks to be unavoidable without heroic efforts. An alternative reason for tile challenged builds? Do all the ground testing without tiles then install tiles before mounting SS on SH?


It looks like they are planning on some throwaways to get StarLink v2 going but maybe this makes makes long term sense.
Title: Re: Starship heat shield
Post by: adrianwyard on 09/22/2022 05:55 pm
Adding bespoke debris/blast shields to the test mount to protect the flaps and lower edge of the starship doesn't sound that difficult in the scheme of things. Then any resulting tile loss would be due to startup vibrations, so somewhat indicative of what will happen on an actual flight.
Title: Re: Starship heat shield
Post by: RamsesBic on 09/22/2022 05:57 pm
So, we're seeing static fire tile damage that looks to be unavoidable without heroic efforts. An alternative reason for tile challenged builds? Do all the ground testing without tiles then install tiles before mounting SS on SH?


It looks like they are planning on some throwaways to get StarLink v2 going but maybe this makes makes long term sense.

I would not call some upgrade of a stand a "heroic effort" by any means.
Title: Re: Starship heat shield
Post by: john smith 19 on 09/22/2022 07:56 pm

I find it fascinating we've not seen any evidence of flame diverters (which they use at MacGregor) for the test mount or main launch table. Even rolling in a small one like used for the V2 would presumably help?

Either way the key challenge for the heat shield is not static fire debris but launch vibration. (Mars landings are of course another matter entirely.)
I remember seeing images of this and have always wondered why they were'nt more use than huge, heavy flame trenches.

Thanks for providing the image.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 09/22/2022 07:58 pm

I find it fascinating we've not seen any evidence of flame diverters (which they use at MacGregor) for the test mount or main launch table. Even rolling in a small one like used for the V2 would presumably help?

Either way the key challenge for the heat shield is not static fire debris but launch vibration. (Mars landings are of course another matter entirely.)
I remember seeing images of this and have always wondered why they were'nt more use than huge, heavy flame trenches.

Thanks for providing the image.

Because you can't easily service underneath a stand which has flame trenches.

That conversation really belongs in the Facilities and Fleets section, here's a convenient link to the start of that conversation:

https://forum.nasaspaceflight.com/index.php?topic=54355.msg2411243#msg2411243
Title: Re: Starship heat shield
Post by: AC in NC on 09/22/2022 11:59 pm
So, we're seeing static fire tile damage that looks to be unavoidable without heroic efforts. An alternative reason for tile challenged builds? Do all the ground testing without tiles then install tiles before mounting SS on SH?
It looks like they are planning on some throwaways to get StarLink v2 going but maybe this makes makes long term sense.
I would not call some upgrade of a stand a "heroic effort" by any means.
OK.  But that has absolutely nothing to do with what OTV said.
Title: Re: Starship heat shield
Post by: Dr.Unhold on 09/23/2022 12:20 pm
I believe this argument has been made several times before on this thread, but in the light of all the talk about focussing on optimizing the test stand to avoid damages:
The ground tests on sub-par stands also serve as good testing grounds for landing/starting on unprepared terrain. Certainly, SS is a long way away from regularly landing in such environments (maybe moon being an exception). But think about what you can learn early on about making your engines/vehicle more robust. You might even pick up some easy fixes that substantially reduce the damages in these kind of environments, when you have experience (=data). And how to collect better data on this than on a ship that might not even fly, sits on the ground and can be easily inspected..
So the process of finding a good enough (sub-)orbital test stand and launch pad has synergies with arriving at a more robust system.
Title: Re: Starship heat shield
Post by: OTV Booster on 09/23/2022 09:04 pm
Adding bespoke debris/blast shields to the test mount to protect the flaps and lower edge of the starship doesn't sound that difficult in the scheme of things. Then any resulting tile loss would be due to startup vibrations, so somewhat indicative of what will happen on an actual flight.
How indicative is an open question. Being close to the ground is acoustically different than being on top of SH. There's a lot of acoustic energy being reflected back up. It's conceivable that when stacked during an SH live fire a whole new set of problems will show up. I hope not but that's why the test.
Title: Re: Starship heat shield
Post by: john smith 19 on 09/24/2022 02:32 pm
I believe this argument has been made several times before on this thread, but in the light of all the talk about focussing on optimizing the test stand to avoid damages:
The ground tests on sub-par stands also serve as good testing grounds for landing/starting on unprepared terrain. Certainly, SS is a long way away from regularly landing in such environments (maybe moon being an exception). But think about what you can learn early on about making your engines/vehicle more robust. You might even pick up some easy fixes that substantially reduce the damages in these kind of environments, when you have experience (=data). And how to collect better data on this than on a ship that might not even fly, sits on the ground and can be easily inspected..
So the process of finding a good enough (sub-)orbital test stand and launch pad has synergies with arriving at a more robust system.
That is a very interesting trade.

On the one hand it improves your chance of a rugged TPS for the Mars landing, but on the other it could seriously damage an otherwise perfectly good SS that could make orbit and land safetly on a concrete pad, but now won't  :(

Also you get that  TPS testing for free (apart from the pad repairs). 

OTOH the key goal right now is simply to get to (and back from) orbit in the first place.

That has to be the enabling step to get every SS programme moving.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 09/24/2022 04:05 pm
I believe this argument has been made several times before on this thread, but in the light of all the talk about focussing on optimizing the test stand to avoid damages:
The ground tests on sub-par stands also serve as good testing grounds for landing/starting on unprepared terrain. Certainly, SS is a long way away from regularly landing in such environments (maybe moon being an exception). But think about what you can learn early on about making your engines/vehicle more robust. You might even pick up some easy fixes that substantially reduce the damages in these kind of environments, when you have experience (=data). And how to collect better data on this than on a ship that might not even fly, sits on the ground and can be easily inspected..
So the process of finding a good enough (sub-)orbital test stand and launch pad has synergies with arriving at a more robust system.
That is a very interesting trade.

On the one hand it improves your chance of a rugged TPS for the Mars landing, but on the other it could seriously damage an otherwise perfectly good SS that could make orbit and land safetly on a concrete pad, but now won't  :(

Also you get that  TPS testing for free (apart from the pad repairs). 

OTOH the key goal right now is simply to get to (and back from) orbit in the first place.

That has to be the enabling step to get every SS programme moving.

Starting to get OT here, but at what point in this hypothesis does Gwynn Shotwell call up Musk as ask "hey about those Starlink v2 satellites we need to make revenue next year", they build a more robust test stand so they can test actual orbital launches
Title: Re: Starship heat shield
Post by: john smith 19 on 09/24/2022 04:30 pm

Starting to get OT here, but at what point in this hypothesis does Gwynn Shotwell call up Musk as ask "hey about those Starlink v2 satellites we need to make revenue next year", they build a more robust test stand so they can test actual orbital launches
Hasn't she already done so?

That was my point. Leave the sub orbital stand alone and if damages a SS that's a learning experience, or upgrade  and push harder to get to orbit to begin with.

My instinct is that the importance of TPS exceeds engines. There's a Raptor (or  should we call it Raptor II?) thrust level that will get SS to orbit. Anything above that --> more payload. A design that's not hitting 100% of theoretical performance is not a show stopper.

But underperfoming TPS --> Vehicle will (or probably will) fail to survive re-entry. And that stops everything, unless you want to sacrifice every SS.

BTW I just remembered that someone can only have 5 launches from this site.  Has anyone tracke how many they have left?  I would have guessed they would have pushed for at least 12 to allow (potentially) 1 a month to iterate the design.
Title: Re: Starship heat shield
Post by: eriblo on 09/24/2022 05:48 pm
I personally think the "Mars does not have landing pads/launch pads/whatever so Starship won't need it" meme is a bit premature, especially with regard to TPS.

Permanent and expanding presence on Mars requires that Starship is fully successful on Earth first and that the tech is somewhat transferable, not the other way around.

We do not even know if the current TPS is at all relevant to Mars launches. If it works well on Earth it will probably work for Mars EDL as well, especially for slow-transfer-and-quite-possibly-one-way cargo Starships.

However, returning from Mars will be a tougher entry than any crewed vehicle has done so far. I fully expect the crew transfer ships to have a heavily modified if not completely different TPS.

Title: Re: Starship heat shield
Post by: OTV Booster on 09/24/2022 10:35 pm

Starting to get OT here, but at what point in this hypothesis does Gwynn Shotwell call up Musk as ask "hey about those Starlink v2 satellites we need to make revenue next year", they build a more robust test stand so they can test actual orbital launches
Hasn't she already done so?

That was my point. Leave the sub orbital stand alone and if damages a SS that's a learning experience, or upgrade  and push harder to get to orbit to begin with.

My instinct is that the importance of TPS exceeds engines. There's a Raptor (or  should we call it Raptor II?) thrust level that will get SS to orbit. Anything above that --> more payload. A design that's not hitting 100% of theoretical performance is not a show stopper.

But underperfoming TPS --> Vehicle will (or probably will) fail to survive re-entry. And that stops everything, unless you want to sacrifice every SS.

BTW I just remembered that someone can only have 5 launches from this site.  Has anyone tracke how many they have left?  I would have guessed they would have pushed for at least 12 to allow (potentially) 1 a month to iterate the design.
Uh, I thought that was five launches per year. Does anybody have that at their fingertips?
Title: Re: Starship heat shield
Post by: john smith 19 on 09/25/2022 07:12 am

Uh, I thought that was five launches per year. Does anybody have that at their fingertips?
Sorry, that indeed should have been 5/year. That could seem generous in early development, but now with whole stage 1s and 2s built it would seem quite restrictive.

Could they have just one left that they are holding in reserve to try and make orbit before the year ends? Not quite a SS to Mars, but a good way to close out 2022. In which case they'd want every possible failure mode closed off (AFAP) before using it.
Title: Re: Starship heat shield
Post by: tbellman on 09/25/2022 10:59 am
Sorry, that indeed should have been 5/year. That could seem generous in early development, but now with whole stage 1s and 2s built it would seem quite restrictive.

Could they have just one left that they are holding in reserve to try and make orbit before the year ends? Not quite a SS to Mars, but a good way to close out 2022. In which case they'd want every possible failure mode closed off (AFAP) before using it.

Which universe are you from where 5 - 0 = 1?  There hasn't been a single orbital launch of Starship, or even attempt at orbital launch, so how could there be only one left out of five?
Title: Re: Starship heat shield
Post by: DanClemmensen on 09/25/2022 02:07 pm
Sorry, that indeed should have been 5/year. That could seem generous in early development, but now with whole stage 1s and 2s built it would seem quite restrictive.

Could they have just one left that they are holding in reserve to try and make orbit before the year ends? Not quite a SS to Mars, but a good way to close out 2022. In which case they'd want every possible failure mode closed off (AFAP) before using it.

Which universe are you from where 5 - 0 = 1?  There hasn't been a single orbital launch of Starship, or even attempt at orbital launch, so how could there be only one left out of five?
The 5/yr is a count of SH launches, not orbital launches. If they launched an SH 100 meters in the air with no SS on top to test a chopstick catch, it would still count as an SH launch. I suspect this is the reason they will only do full-up orbital launches of SH. The distinction is academic unless they want to start hopping SH out to a floating platform, in which case they will probably try for a change to the rule.
Title: Re: Starship heat shield
Post by: john smith 19 on 09/26/2022 07:31 am
The 5/yr is a count of SH launches, not orbital launches. If they launched an SH 100 meters in the air with no SS on top to test a chopstick catch, it would still count as an SH launch. I suspect this is the reason they will only do full-up orbital launches of SH. The distinction is academic unless they want to start hopping SH out to a floating platform, in which case they will probably try for a change to the rule.
That is what I thought.

So has anyone been keeping count which ones would could toward the limit?
Title: Re: Starship heat shield
Post by: DanClemmensen on 09/26/2022 01:36 pm
The 5/yr is a count of SH launches, not orbital launches. If they launched an SH 100 meters in the air with no SS on top to test a chopstick catch, it would still count as an SH launch. I suspect this is the reason they will only do full-up orbital launches of SH. The distinction is academic unless they want to start hopping SH out to a floating platform, in which case they will probably try for a change to the rule.
That is what I thought.

So has anyone been keeping count which ones would could toward the limit?
There have been no SH launches, so the count is zero. It's not a launch unless it leaves the pad.

In addition to 5/yr SH, They are also allowed to do 12/yr SS launches that do no include an SH. There has not been an SS launch this year. A full stack launch is an SH launch, not an SS launch.
Title: Re: Starship heat shield
Post by: john smith 19 on 09/26/2022 02:27 pm
There have been no SH launches, so the count is zero. It's not a launch unless it leaves the pad.

In addition to 5/yr SH, They are also allowed to do 12/yr SS launches that do no include an SH. There has not been an SS launch this year. A full stack launch is an SH launch, not an SS launch.
Thanks for that. 

It clearly means that SX is not limited by having run out of takeoff opportunities at the site. They could (in principle) stack an SS and SH tomorrow and take a shot at orbit.

It looks as if the TPS is proving more difficult to perfect than expected.
Title: Re: Starship heat shield
Post by: Robotbeat on 09/26/2022 02:29 pm
The TPS isn’t stopping them from doing an orbital attempt. They don’t need to recover Starship intact for the first several dozen launches.
Title: Re: Starship heat shield
Post by: DanClemmensen on 09/26/2022 02:49 pm
There have been no SH launches, so the count is zero. It's not a launch unless it leaves the pad.

In addition to 5/yr SH, They are also allowed to do 12/yr SS launches that do no include an SH. There has not been an SS launch this year. A full stack launch is an SH launch, not an SS launch.
Thanks for that. 

It clearly means that SX is not limited by having run out of takeoff opportunities at the site. They could (in principle) stack an SS and SH tomorrow and take a shot at orbit.

It looks as if the TPS is proving more difficult to perfect than expected.
Sorry, not tomorrow. They need both the FCC temporary frequency licenses and the actual FAA launch license. Both of these are routine and they don't take long, but they do result in public notices that we all get to see, just like at KSC. More than a day but less than a week(?)
Title: Re: Starship heat shield
Post by: Vultur on 09/26/2022 02:57 pm
I think the actual pacing item is prep of the booster itself ("robustness upgrades" for B7) + static fires, nothing to do with heat shield.
Title: Re: Starship heat shield
Post by: john smith 19 on 09/27/2022 07:08 am
Sorry, not tomorrow. They need both the FCC temporary frequency licenses and the actual FAA launch license. Both of these are routine and they don't take long, but they do result in public notices that we all get to see, just like at KSC. More than a day but less than a week(?)
And thanks for this as well. That gives a future timeline. I'm guessing those timescales would lengthen once we start getting closer to the Christmas period.

I guess the obvious question remains "Is the tile material, or how they are mounted?"

Title: Re: Starship heat shield
Post by: john smith 19 on 09/27/2022 07:15 am
The TPS isn’t stopping them from doing an orbital attempt. They don’t need to recover Starship intact for the first several dozen launches.
Stage 2 reusability is the key distinguising feature of SS over F9. Without it you just have a very much larger, very much more complicated F9 architecture.

With it everything changes. All future SS programmes become possible. Provided it can demonstrate adequte levels of reliability and reasonable replacement costs.
Title: Re: Starship heat shield
Post by: john smith 19 on 09/27/2022 07:20 am
I think the actual pacing item is prep of the booster itself ("robustness upgrades" for B7) + static fires, nothing to do with heat shield.
This seems doubtful.  :(

Having gone through so many iterations of Raptor it should be possible to deliver enough of a standard version that can run for what, about 10 mins total? That would get them early data on TPS under actual operating conditions.

It's a cliche but once you get to LEO you are "Halfway to anywhere." Payload can always be increased but if you can't survive reentry

TPS is looking like the long pole in the tent.
Title: Re: Starship heat shield
Post by: edzieba on 09/27/2022 01:37 pm
I think the actual pacing item is prep of the booster itself ("robustness upgrades" for B7) + static fires, nothing to do with heat shield.
This seems doubtful.  :(

Having gone through so many iterations of Raptor it should be possible to deliver enough of a standard version that can run for what, about 10 mins total? That would get them early data on TPS under actual operating conditions.

It's a cliche but once you get to LEO you are "Halfway to anywhere." Payload can always be increased but if you can't survive reentry

TPS is looking like the long pole in the tent.
If you can't survive re-entry then SpaceX "merely" have a F9-style partially reusable vehicle capable of super-heavy-lift at a lower cost/kg than F9. Starship recovery and re-use are desirable in the long term for further cost reduction and for improved schedule (not needing to build an additional 6 engines between launches), but a partially reusable Starship + Super Heavy stack is still a viable system for payloads of sufficient mass and value.

I doubt SpaceX would deliberately remove TPS or flaps for a test launch, as any post-mission recovery testing is essentially 'free', but if the choice was not flying or flying a vehicle with TPS known to be sub-par, they'd still fly and get what data they can get for the phases of EDL it survives rather than waiting for a perfected vehicle.
Title: Re: Starship heat shield
Post by: rsdavis9 on 09/27/2022 01:43 pm
I think the actual pacing item is prep of the booster itself ("robustness upgrades" for B7) + static fires, nothing to do with heat shield.
This seems doubtful.  :(

Having gone through so many iterations of Raptor it should be possible to deliver enough of a standard version that can run for what, about 10 mins total? That would get them early data on TPS under actual operating conditions.

It's a cliche but once you get to LEO you are "Halfway to anywhere." Payload can always be increased but if you can't survive reentry

TPS is looking like the long pole in the tent.
If you can't survive re-entry then SpaceX "merely" have a F9-style partially reusable vehicle capable of super-heavy-lift at a lower cost/kg than F9. Starship recovery and re-use are desirable in the long term for further cost reduction and for improved schedule (not needing to build an additional 6 engines between launches), but a partially reusable Starship + Super Heavy stack is still a viable system for payloads of sufficient mass and value.

I doubt SpaceX would deliberately remove TPS or flaps for a test launch, as any post-mission recovery testing is essentially 'free', but if the choice was not flying or flying a vehicle with TPS known to be sub-par, they'd still fly and get what data they can get for the phases of EDL it survives rather than waiting for a perfected vehicle.

two comments:
1. Maybe they are leaving tps (and did I just hear copv's off of booster?) off so they can ship to Florida?
2. If SS reentry never works they have all the above advances over f9 and a much faster launch cadence then f9 because of no droneships.

edit: added reentry
Title: Re: Starship heat shield
Post by: john smith 19 on 09/27/2022 03:00 pm
Over the years there have been many attempts at improving flying efficiency by delaying the point on the chord of a wing where airflow goes turbulent.

This has created specifications for how smooth a surface (any surface) has to be in order to retain laminar flow.

This document, from the British "Aeronautical Research Council Reports & Memoranda" gives some figures for what has to be done. Which also implies that there will be trouble if they cannot be met, or maintained.  :(

Obviously this work was done from the PoV of subsonic vehicles. Above M1 it's unlikely that the limits would be less stringent, and quite plausible they would be more so.
Title: Re: Starship heat shield
Post by: Robotbeat on 09/27/2022 03:04 pm
Laminar flow over wings has nothing to do with Starship. That only matters if you’re trying to get good lift to drag ratio, which makes no difference to Starship as the Elonerons basically act as big drag brakes.

Why the frowny face? LOL no concern trolling here…
Title: Re: Starship heat shield
Post by: OTV Booster on 09/27/2022 04:46 pm
I think the actual pacing item is prep of the booster itself ("robustness upgrades" for B7) + static fires, nothing to do with heat shield.
This seems doubtful.  :(

Having gone through so many iterations of Raptor it should be possible to deliver enough of a standard version that can run for what, about 10 mins total? That would get them early data on TPS under actual operating conditions.

It's a cliche but once you get to LEO you are "Halfway to anywhere." Payload can always be increased but if you can't survive reentry

TPS is looking like the long pole in the tent.
If we unwind a year or so, NSF consensus (and Musk statements?) had TPS as the long pole. No surprises here.

Title: Re: Starship heat shield
Post by: OTV Booster on 09/27/2022 04:55 pm
I think the actual pacing item is prep of the booster itself ("robustness upgrades" for B7) + static fires, nothing to do with heat shield.
This seems doubtful.  :(

Having gone through so many iterations of Raptor it should be possible to deliver enough of a standard version that can run for what, about 10 mins total? That would get them early data on TPS under actual operating conditions.

It's a cliche but once you get to LEO you are "Halfway to anywhere." Payload can always be increased but if you can't survive reentry

TPS is looking like the long pole in the tent.
If you can't survive re-entry then SpaceX "merely" have a F9-style partially reusable vehicle capable of super-heavy-lift at a lower cost/kg than F9. Starship recovery and re-use are desirable in the long term for further cost reduction and for improved schedule (not needing to build an additional 6 engines between launches), but a partially reusable Starship + Super Heavy stack is still a viable system for payloads of sufficient mass and value.

I doubt SpaceX would deliberately remove TPS or flaps for a test launch, as any post-mission recovery testing is essentially 'free', but if the choice was not flying or flying a vehicle with TPS known to be sub-par, they'd still fly and get what data they can get for the phases of EDL it survives rather than waiting for a perfected vehicle.
It's unclear if you're addressing the general case or the TPS naked builds we're seeing. If the latter, there's discussion in the StarLink thread that suggests that there might be a push to get some sats up via SS. If this is correct, some quick n dirty launches sans TPS might be in the works. There are good arguments both ways.
Title: Re: Starship heat shield
Post by: Robotbeat on 09/27/2022 06:17 pm
If the current Starships in the pipeline are not intended to be the operational design anyway, there may not be a lot lost by making them expendable.
Title: Re: Starship heat shield
Post by: Action on 09/27/2022 08:51 pm
Laminar flow over wings has nothing to do with Starship.

Not sure if this is what john smith 19 was getting at, but heat transfer goes way up when the flow goes turbulent, which is why surface roughness is an issue for reentry.  Smooth is good.

This is a known problem with fragile-tile systems like Shuttle and was studied extensively.  However it is also suspected to be a problem with transpiration cooled systems because the points where coolant is injected into the boundary layer may introduce turbulence.

Either way, I think this is just a "you really need more heat shield than you would if you assumed laminar flow" and not a fatal problem with careful engineering.
Title: Re: Starship heat shield
Post by: john smith 19 on 09/28/2022 07:22 am
Laminar flow over wings has nothing to do with Starship. That only matters if you’re trying to get good lift to drag ratio, which makes no difference to Starship as the Elonerons basically act as big drag brakes.

Why the frowny face? LOL no concern trolling here…
Given the organization that did the work deals with aircraft and helicopters they normally talk in terms of wings, but in truth it's an issue with every part of an airborne vehicle.

The difference in heat transfer between laminar flow and turbulent flow can be be in the range 4x-10x. Or have you forgotten this?

Of course you can just assume worst case heat transfer on all tiles and just make them 10x the thickness that a laminar flow assumption gives you, but given the amount of skin that has to be wrapped with them that's going to start having an effect on payload, given the 1:1 struture to payload trade for stage 2's. I'm not sure how much peoples ability to identify where the laminar-to-turbulent point is has improved since Shuttle was designed. For a symentrical body it should be easier, but the more bumps, humps and protruberances you add the tougher it gets to model. It's not just the gross changes, it's all the little corners. For example, one of the worst hot spots on the shuttle was the corner area between the OMS pods and the rest of the rear engine section.

Turbulent flow also makes it more likely you'll get one of those tiles fluttering. Those forces can be quite high and  if one tile is ripped off you've now got a hole for flow to stagnate in. How serious this is depends on wheather it's virtually impossible, and needs no mitigation, or it's viewed as possible and something is done about it.

I'll give one last data point. The Piaggio P.180 is an aluminum alloy turboprop business aircraft. Laminar flow was a design goal. It's mfg said the wing manages to maintain laminar flow over 20% of the fuselage and double the chord of other aircarft of its size. They also said its skin is accurate to 0.010" which is part of how it achieves that flow. This is technology was available (at that scale) in the mid 1980's.

I thought the report was quite relevant, given this threads title.
Title: Re: Starship heat shield
Post by: john smith 19 on 09/28/2022 07:28 am
and not a fatal problem with careful engineering.
That would be a fair description of the Shuttles safety record regarding its heat shield.
Title: Re: Starship heat shield
Post by: Action on 09/28/2022 07:47 pm
and not a fatal problem with careful engineering.
That would be a fair description of the Shuttles safety record regarding its heat shield.

Yeah, they worked around it at great cost.

When they did lose a Shuttle due to the heat shield failing and the wings falling off, it was another thing that caused the problem.
Title: Re: Starship heat shield
Post by: Hog on 09/29/2022 01:46 am
and not a fatal problem with careful engineering.
That would be a fair description of the Shuttles safety record regarding its heat shield.

Yeah, they worked around it at great cost.

When they did lose a Shuttle due to the heat shield failing and the wings falling off, it was another thing that caused the problem.
Ya, a chunk the "heat shield" of the External Tank was run into by the RCC wing leading edge "heat shield" of the Orbiter at over 500 mph closure.   "RCC is hard and stout and afterall, it was JUST foam. Just a possible issue with processing for next mission, no safety of flight issue."    Ya-but-no.
Title: Re: Starship heat shield
Post by: chopsticks on 09/29/2022 04:50 am


and not a fatal problem with careful engineering.
That would be a fair description of the Shuttles safety record regarding its heat shield.

Yeah, they worked around it at great cost.

When they did lose a Shuttle due to the heat shield failing and the wings falling off, it was another thing that caused the problem.
Ya, a chunk the "heat shield" of the External Tank was run into by the RCC wing leading edge "heat shield" of the Orbiter at over 500 mph closure.   "RCC is hard and stout and afterall, it was JUST foam. Just a possible issue with processing for next mission, no safety of flight issue."    Ya-but-no.


He's not wrong.
Title: Re: Starship heat shield
Post by: john smith 19 on 09/29/2022 08:28 am
Ya, a chunk the " heat shield" of the External Tank was run into by the RCC wing leading edge "heat shield" of the Orbiter at over 500 mph closure.   "RCC is hard and stout and afterall, it was JUST foam. Just a possible issue with processing for next mission, no safety of flight issue."    Ya-but-no.
Always you must watch the assumptions.  :(

Had that foam hit the RCC at the RCC's design operating temperature a) the foam would be a squidgy fluid lump b) The RCC would not have been brittle. One of RCC's much launded properties is how it gets stronger as it gets hotter (provided of course there's no O2 about, or the oxidation resistant skin is intact)

Instead the fairly brittle RCC (at near room temperature) got hit by a lump of rigid foam at about (IIRC) M2. The old story about the wood splinters found buried in the side of an armoured car after a hurricane comes to mind.

WRT to this thread that event chain cannot happen.

The question becomes what could damage the SS TPS, and what standards does it need to be made to reduce turbulence issues?
Title: Re: Starship heat shield
Post by: Action on 09/29/2022 01:25 pm
and not a fatal problem with careful engineering.
That would be a fair description of the Shuttles safety record regarding its heat shield.

Yeah, they worked around it at great cost.

When they did lose a Shuttle due to the heat shield failing and the wings falling off, it was another thing that caused the problem.
Ya, a chunk the "heat shield" of the External Tank was run into by the RCC wing leading edge "heat shield" of the Orbiter at over 500 mph closure.   "RCC is hard and stout and afterall, it was JUST foam. Just a possible issue with processing for next mission, no safety of flight issue."    Ya-but-no.

I didn't mean to be cheering for the Shuttle solution.  There were several large problems with their approach.  I just meant to say it wasn't fragile tiles or turbulent flow that got them, it was having a large TPS acreage exposed on the way up where stuff could fall on it.

Bringing it back on topic, Starship has lessened this problem by its configuration, but not eliminated it.
Title: Re: Starship heat shield
Post by: john smith 19 on 09/29/2022 03:21 pm
I didn't mean to be cheering for the Shuttle solution.  There were several large problems with their approach.  I just meant to say it wasn't fragile tiles or turbulent flow that got them, it was having a large TPS acreage exposed on the way up where stuff could fall on it.
Actually it was fragile tile and turbulent flow. RCC panels were only on the wing leading edge and nose. Everything else were either various kinds of blanket topside, or tiles bottom side. But all of them were backed by the skin, which would have given them some "bounce." The wing leading edge had nothing behind it. . If it had it (arguably) would have survived the impact. That cavity acted as a trap for very high speed airflow. The rest is history.
Quote from: Action
Bringing it back on topic, Starship has lessened this problem by its configuration, but not eliminated it.
Since the TPS is on SS, not SH there is nothing above that to shed stuff to hit its tiles, apart from a) Hail stones on the way up (does anyone seriously think they would launch during a hail storm?) b) Metorites

Of course on orbit it's a different story...
 This is where having a standard shaped tile (or at least a very restricted number of different types) makes on-orbit repair possible.
Title: Re: Starship heat shield
Post by: Action on 09/29/2022 03:49 pm
Quote from: Action
Bringing it back on topic, Starship has lessened this problem by its configuration, but not eliminated it.
Since the TPS is on SS, not SH there is nothing above that to shed stuff to hit its tiles, apart from a) Hail stones on the way up (does anyone seriously think they would launch during a hail storm?) b) Metorites

The TPS acreage on Starship is large and exposed on the way up.  It's not cozied up next to an ET known for having things fall off it, but it is out there in the airstream.  Ice could fall off Starship and hit the flaps (not sure what we're calling them these days) quite easily.  Tiles shed from high up could hit areas lower down.  I think I'd ignore things like birdstrikes as being beyond what this level of technology can reasonably be expected to deal with.  Anyway, it's definitely a better plan than Shuttle, but it still has the same problem.

The only way to 100% solve this problem is to have the heatshield covered or in a controlled environment on the way up.  Dragon, for example, has its heatshield on the bottom where nothing can bang into it.

[Edit: Spelling]
Title: Re: Starship heat shield
Post by: john smith 19 on 09/30/2022 08:57 am
The TPS acreage on Starship is large and exposed on the way up.  It's not cozied up next to an ET known for having things fall off it, but it is out there in the airstream.  Ice could fall off Starship and hit the flaps (not sure what we're calling them these days) quite easily.  Tiles shed from high up could hit areas lower down.  I think I'd ignore things like birdstrikes as being beyond what this level of technology can reasonably be expected to deal with.  Anyway, it's definitely a better plan than Shuttle, but it still has the same problem.

The only way to 100% solve this problem is to have the heatshield covered or in a controlled environment on the way up.  Dragon, for example, has its heatshield on the bottom where nothing can bang into it.

[Edit: Spelling]
Practically that only works if the heatshield is underneath the vehicle, like a Bono plug nozzle design. Wrapping the whole S2 in a shroud strong enough to avoid damage is going to add a lot of mass to S2 and probably make slying off a failed S1 impossible.  :(

IRL in the 3rd decade of the 21st century SS will have Vehicle Health Monitoring sensors to continuously monitor tank pressure and temperature (puncture shows as falling pressure. Tile damage should show as hot spot boiling off too much propellant), probably as part of a suite of skin monitors, or some kind of deployable boom.

The Shuttle programme developed a bunch of concepts for this, most of which were never used, but they do exist and have been discussed.

I'd like to remind people of Mary Shafer's words. Mary was a Flight Engineer at NASA Dryden during a lot of test flying programmes. Every one was flown by a top class pilot after extensive preparation but there was casualty rate of about one pilot death a year throughout the 1950's. Her comment was "Insisting on perfect safety is for people who don't have the balls to live in the real world."

Everything has a level of risk. Normally this is a subject only actuaries concern themselves with. Some of those risks can be reduced, some cannot. Going to orbit, for a long time to come is going to be substantially more risky than taking a commercial airline flight or similar scheduled transport.
Title: Re: Starship heat shield
Post by: Skyway on 09/30/2022 10:07 am
I'd like to remind people of Mary Shafer's words. Mary was a Flight Engineer at NASA Dryden during a lot of test flying programmes. Every one was flown by a top class pilot after extensive preparation but there was casualty rate of about one pilot death a year throughout the 1950's. Her comment was "Insisting on perfect safety is for people who don't have the balls to live in the real world."

Everything has a level of risk. Normally this is a subject only actuaries concern themselves with. Some of those risks can be reduced, some cannot. Going to orbit, for a long time to come is going to be substantially more risky than taking a commercial airline flight or similar scheduled transport.

Thanks for the collaboration and just to try to clarify the matter, I must say that Safety is not the same today as it was in the 50s. Today such a sentence sounds like complete nonsense, due to the current stage of maturity of the concept.

There is a balance point, and it is not constant. And precisely because it is not constant, the search for Safety is uninterrupted, always leading to endless changes in systems, procedures, and training throughout the operation.

I agree with the meaning of what you said. The tendency of many people to want to "manage" a risk using the most radical and guaranteeing measure possible is utopian and therefore does not exist in reality.

Risks exist, but they are managed. I only disagree with the way in which the statement that some risks cannot be reduced was made. It makes it appear that risks that cannot be reduced are simply accepted, which is not the case if the score for the probability X severity ratio for that risk is high.

If a risk scores high in this ratio and it cannot be reduced, then the operation does not continue. And this is true as far as SpaceX and especially NASA are concerned.

As for mitigating the risk of tile loss during take-off, it doesn't have to be radical. A vehicle airworthiness reliability study in the event of such a system failure to a greater extent than is regularly experienced on flights would already manage this risk. A system such as the aforementioned vehicle health monitoring system that would abort takeoff when detecting this type of occurrence would be suitable as well. In-orbit repair measures... various possibilities that do not involve adding weight to the vehicle.
Title: Re: Starship heat shield
Post by: Skyway on 09/30/2022 10:21 am
Quote from: Action
Bringing it back on topic, Starship has lessened this problem by its configuration, but not eliminated it.
Since the TPS is on SS, not SH there is nothing above that to shed stuff to hit its tiles, apart from a) Hail stones on the way up (does anyone seriously think they would launch during a hail storm?) b) Metorites

The TPS acreage on Starship is large and exposed on the way up.  It's not cozied up next to an ET known for having things fall off it, but it is out there in the airstream.  Ice could fall off Starship and hit the flaps (not sure what we're calling them these days) quite easily.  Tiles shed from high up could hit areas lower down.  I think I'd ignore things like birdstrikes as being beyond what this level of technology can reasonably be expected to deal with.  Anyway, it's definitely a better plan than Shuttle, but it still has the same problem.

The only way to 100% solve this problem is to have the heatshield covered or in a controlled environment on the way up.  Dragon, for example, has its heatshield on the bottom where nothing can bang into it.

[Edit: Spelling]

The thermal protection of the Dragon capsule is at the bottom for the sake of aerodynamic design.

The capsule was designed in that way, taking into account its use as the "nose" of the rocket on the way up, but mainly to have better balance (control) and less exposure of the capsule body during re-entry. Therefore, the thermal protection is in the "fit" with the trunk.

It doesn't stay there to be protected along the way up. This is a good consequence of other requirements. And it is also a fact that the edge of the thermal protection is exposed, and damage there would potentially cause many controllability problems during re-entry.

Wanting to protect the thermal protection during ascent is the same as putting grilles on the air intake of commercial aircraft engines. It's a very exaggerated measure compared to the probability of significant damage, and it ends up adding other failure modules that were previously non-existent.

In addition to being an immense effort focused on just one of the vehicle's operational risks, in an ocean of so many others as or more severe and/or probable.

Risk is managed surgically, not with a sledgehammer.

EDIT: Just to add that I'm talking about Dragon's heat shield. The Capsule has thermal protection on its body as well.
Title: Re: Starship heat shield
Post by: Action on 09/30/2022 02:13 pm
The TPS acreage on Starship is large and exposed on the way up.  It's not cozied up next to an ET known for having things fall off it, but it is out there in the airstream.  Ice could fall off Starship and hit the flaps (not sure what we're calling them these days) quite easily.  Tiles shed from high up could hit areas lower down.  I think I'd ignore things like birdstrikes as being beyond what this level of technology can reasonably be expected to deal with.  Anyway, it's definitely a better plan than Shuttle, but it still has the same problem.

The only way to 100% solve this problem is to have the heatshield covered or in a controlled environment on the way up.  Dragon, for example, has its heatshield on the bottom where nothing can bang into it.

[Edit: Spelling]
Practically that only works if the heatshield is underneath the vehicle, like a Bono plug nozzle design. Wrapping the whole S2 in a shroud strong enough to avoid damage is going to add a lot of mass to S2 and probably make slying off a failed S1 impossible.  :(

You can always have the second stage go up in a fairing.  The X-37B does it that way, and Dreamchaser is intended to I believe.  If you attach the fairing to the first stage like the Rocket Lab Neutron, it shouldn't even cost much payload.

But yes, putting the heatshield on the bottom is probably the most sensible way to do it.  It's definitely simpler and lends itself to easier reentry modes.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/01/2022 07:15 am
You can always have the second stage go up in a fairing.  The X-37B does it that way, and Dreamchaser is intended to I believe.  If you attach the fairing to the first stage like the Rocket Lab Neutron, it shouldn't even cost much payload.
This is the dictionary use of "stage," not the common one, IE a stage that is required to deliver substantial velocity to get to orbit. Neither of your examples does so. They are basically passive payloads during ascent. You might like to consider how they would work if they carry crew and there is an emergancy. What happens then?

For an actual example in this context you would be looking at versions of the Centaur, that used an extended payload fairing to protect the boiloff insulation on the LH2 tank during ascent.

Quote from: Action
But yes, putting the heatshield on the bottom is probably the most sensible way to do it.  It's definitely simpler and lends itself to easier reentry modes.
Then that would not be the design SX is going with. It would be a totally different vehicle.
Title: Re: Starship heat shield
Post by: Skyway on 10/01/2022 10:15 am
You can always have the second stage go up in a fairing.  The X-37B does it that way, and Dreamchaser is intended to I believe.  If you attach the fairing to the first stage like the Rocket Lab Neutron, it shouldn't even cost much payload.

They are payloads, not stages.

The Soyuz is also a spacecraft that is launched inside a fairing, but it is not for the protection of any heat shield. It's simply because it was also thought of as payload, even with humans inside.

Is it possible to cover a stage with a fairing? Yes, it is possible. But is it beneficial? In the case of Starship, no.

Simply because there isn't a problem in Starship that requires this kind of solution.
Title: Re: Starship heat shield
Post by: Action on 10/01/2022 06:13 pm
Quote from: Action
But yes, putting the heatshield on the bottom is probably the most sensible way to do it.  It's definitely simpler and lends itself to easier reentry modes.
Then that would not be the design SX is going with. It would be a totally different vehicle.

Yes, of course.  Well, not totally different - the same engines and the same basic structure in a different shape. 

I've said before that SpaceX erred when they moved from carbon fiber and no longer had any practical diameter limit, not reconsidering sideways reentry followed by a mode switch to land vertically.  They've been banging their heads against propellant management and heat shield problems for the last three years, and those problems were entirely optional.

I mostly agree that shrouding the second stage somehow is probably not the best idea.
Title: Re: Starship heat shield
Post by: Action on 10/01/2022 06:15 pm
You can always have the second stage go up in a fairing.  The X-37B does it that way, and Dreamchaser is intended to I believe.  If you attach the fairing to the first stage like the Rocket Lab Neutron, it shouldn't even cost much payload.

They are payloads, not stages.

That makes no difference to the argument.  They're sideways reentering vehicles with fragile heat shield technology, just like Starship.  So they go up protected.
Title: Re: Starship heat shield
Post by: Skyway on 10/01/2022 06:52 pm
You can always have the second stage go up in a fairing.  The X-37B does it that way, and Dreamchaser is intended to I believe.  If you attach the fairing to the first stage like the Rocket Lab Neutron, it shouldn't even cost much payload.

They are payloads, not stages.

That makes no difference to the argument.  They're sideways reentering vehicles with fragile heat shield technology, just like Starship.  So they go up protected.

So it's your understanding that these vehicles are launched inside fairings, not for aerodynamic reasons, but to spare their "fragile" thermal protection. That's it?

A risk is created of something colliding with the thermal shield where there was no such risk before, to protect that thermal shield from collisions.

OK.
Title: Re: Starship heat shield
Post by: Action on 10/01/2022 07:01 pm
So it's your understanding that these vehicles are launched inside fairings, not for aerodynamic reasons, but to spare their "fragile" thermal protection. That's it?

I don't recall saying that that was the only reason, but I note that Dynasoar, which had a much tougher heatshield proposed IIRC, was supposed to go up exposed to the airflow.

But yeah, fair enough.  Enclosing them in a fairing also has aerodynamic and structural benefits.

[Edit: Clarified to say that I think there can be more than one reason to go up shrouded.]
Title: Re: Starship heat shield
Post by: eriblo on 10/01/2022 07:24 pm
So it's your understanding that these vehicles are launched inside fairings, not for aerodynamic reasons, but to spare their "fragile" thermal protection. That's it?

I don't recall saying that that was the only reason, but I note that Dynasoar, which had a much tougher heatshield proposed IIRC, was supposed to go up exposed to the airflow.

But yeah, fair enough.  Enclosing them in a fairing also has aerodynamic and structural benefits.

[Edit: Clarified to say that I think there can be more than one reason to go up shrouded.]
How is enclosing an almost optimally bullet shaped spacecraft (that has to withstand atmospheric reentry) with a larger fairing going be an improvement?
Title: Re: Starship heat shield
Post by: Skyway on 10/01/2022 07:32 pm
So it's your understanding that these vehicles are launched inside fairings, not for aerodynamic reasons, but to spare their "fragile" thermal protection. That's it?

I don't recall saying that that was the only reason, but I note that Dynasoar, which had a much tougher heatshield proposed IIRC, was supposed to go up exposed to the airflow.

But yeah, fair enough.  Enclosing them in a fairing also has aerodynamic and structural benefits.

[Edit: Clarified to say that I think there can be more than one reason to go up shrouded.]

The point is that you are claiming these vehicles are launch inside fairings also to protect their thermal protection systems. This statement is not consistent with reality.

What if I told you that the fairing has nothing to do with the thermal protection systems of these vehicles?

What if I told you that the vehicle you use as a basis for comparison (X-20) was a 5-ton, 6-meter-wide vehicle and that it didn't have a fairing big enough in the 60's to take it inside?

It's all about aerodynamic load. The relation between lift, drag, laminar flow, turbulent flow, and attachment points. Also, the impact of those things on the rocket's performance is huge.
Title: Re: Starship heat shield
Post by: Action on 10/01/2022 07:32 pm
So it's your understanding that these vehicles are launched inside fairings, not for aerodynamic reasons, but to spare their "fragile" thermal protection. That's it?

I don't recall saying that that was the only reason, but I note that Dynasoar, which had a much tougher heatshield proposed IIRC, was supposed to go up exposed to the airflow.

But yeah, fair enough.  Enclosing them in a fairing also has aerodynamic and structural benefits.

[Edit: Clarified to say that I think there can be more than one reason to go up shrouded.]
How is enclosing an almost optimally bullet shaped spacecraft (that has to withstand atmospheric reentry) with a larger fairing going be an improvement?

It's a benefit for X-37B and Dreamchaser.  Ask Skyway - he's the one who brought it up.  That's not a relevant benefit for Starship, or at least it's a pretty minor benefit.

I've also been clear in stating I think this is an inferior option.  It is though, for completeness, another way of protecting a fragile side-mount heat shield. 
Title: Re: Starship heat shield
Post by: Skyway on 10/01/2022 07:40 pm

It's a benefit for X-37B and Dreamchaser.  Ask Skyway - he's the one who brought it up...

Not true.

You cited these vehicles as an example before anyone else. I just answered it.

https://forum.nasaspaceflight.com/index.php?topic=50748.3140

You can always have the second stage go up in a fairing.  The X-37B does it that way, and Dreamchaser is intended to I believe.  If you attach the fairing to the first stage like the Rocket Lab Neutron, it shouldn't even cost much payload.

But yes, putting the heatshield on the bottom is probably the most sensible way to do it.  It's definitely simpler and lends itself to easier reentry modes.



Title: Re: Starship heat shield
Post by: Action on 10/01/2022 07:43 pm

It's a benefit for X-37B and Dreamchaser.  Ask Skyway - he's the one who brought it up...

Not true.

You cited these vehicles as an example before anyone else. I just answered it.

https://forum.nasaspaceflight.com/index.php?topic=50748.3140

You can always have the second stage go up in a fairing.  The X-37B does it that way, and Dreamchaser is intended to I believe.  If you attach the fairing to the first stage like the Rocket Lab Neutron, it shouldn't even cost much payload.

But yes, putting the heatshield on the bottom is probably the most sensible way to do it.  It's definitely simpler and lends itself to easier reentry modes.

You brought up the aerodynamics of the situation as an additional justification for the fairings in those cases.  I'm sorry, I don't mean to be argumentative.
Title: Re: Starship heat shield
Post by: Skyway on 10/01/2022 07:49 pm

You brought up the aerodynamics of the situation as an additional justification for the fairings in those cases.  I'm sorry, I don't mean to be argumentative.

Fair enough. That's ok.
Title: Re: Starship heat shield
Post by: chopsticks on 10/01/2022 08:56 pm


I've said before that SpaceX erred when they moved from carbon fiber and no longer had any practical diameter limit, not reconsidering sideways reentry followed by a mode switch to land vertically.  They've been banging their heads against propellant management and heat shield problems for the last three years, and those problems were entirely optional.



Huh?

 Starship was always going to re-enter side on when it was going to be made from carbon fibre. The exact landing maneuver was never very clear but I'm sure it would have involved some sort of flip and burn, therefore not making prop management any different.

The switch to stainless steel has nothing at all to do with the heat shield being on the side, it was always this way.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/02/2022 08:57 am

I've also been clear in stating I think this is an inferior option.  It is though, for completeness, another way of protecting a fragile side-mount heat shield.
Which begs the question how fragile are these tiles to begin with.

The patent on which they are based suggests a 2 component design with a thickish "top hat" around a rigid ceramic foam core. This is a physically seperate part, although it's not clear if the core is formed in-situ or they are mechanically fitted together.

The Shuttle tiles also used a ceramic foam core but their skin was a very thin, fragile glass for thermal emissitivty. This could be cracked quite easily. It was also mostly on the top only. On later flights in high damage areas NASA eveloped a graded tile coating that ran more deeply into the tile itself but added weight.

My instinct is that SS tiles are substantially tougher than Shuttle era tiles. Their all-over outside coating should also make them basically waterproof. However that still leaves moisture absorption (Shuttle foam was open cell, although at least one contract bidder proposed closed cell, like a form of Autoclaved Aerated Concrete).

Wheather this water vapor is an actual threat, or evaporate harmlessly at some stage in the flight, depends on the relative sizes of several different phenomena that occure during ascent and descent.

It's not clear what their areal weight is relative to shuttle tiles. With the closing of the Shuttle TPS database you can't look the numbers up any more either.  :(
Title: Re: Starship heat shield
Post by: edzieba on 10/02/2022 11:40 am
You're thinking of TUFROC, which is not what SpaceX are using.
SpaceX's tiles (seen thus far) are the same construction as the STS tiles: silica fibres are sintered into a brick, the brick is cut down to size, a thin Borosilicate glass coating is applies to some (front and part of each side) surfaces, and the finished tile is impregnated in its initial waterproofing agent (that burns off on first exposure to high temperature).
They are not multi-part, and they do not have an all-over RCG coating.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/03/2022 07:51 am
You're thinking of TUFROC, which is not what SpaceX are using.
SpaceX's tiles (seen thus far) are the same construction as the STS tiles: silica fibres are sintered into a brick, the brick is cut down to size, a thin Borosilicate glass coating is applies to some (front and part of each side) surfaces, and the finished tile is impregnated in its initial waterproofing agent (that burns off on first exposure to high temperature).
They are not multi-part, and they do not have an all-over RCG coating.
In that case they will have the fragility of Shuttle tiles, being about 95% air and hydroscopic.

What's likely going kill turnaround time with this technology is the waterproofing, or rather the re-waterproofing, as the original stuff burnt off after one application. It was also pretty toxic and every single tile needed to be individually injected.  Great for employing lots of staff. Not so great for cost control.  :(

 I believe SX have found something better and TBH it should be a stage in the production process for new tiles, but something is going to have to be done about doing it after X number of landings (I'm hoping the new stuff lasts more than one landing, but I don't think anyone knows).

Ames had developed a hydrophobic transition metal coating designed to make the tiles permanently waterproof, but it was never flight tested. Operationally that would be the Holy Grail for this stuff. Waterproof-for-life.  The Applied Physics group at NASA also developed faster ways to dry the tiles and ways to form the tiles without machining  and at a larger size than the standard 6"x6" size were developed.

BTW IIRC basic Shuttle tile density was 12lb/CuFt. That's 192.63Kg M^-3. IE an SG of 0.19263 relative to water.
Title: Re: Starship heat shield
Post by: AnalogMan on 10/03/2022 12:06 pm
From earlier in this thread:
A Density comparison between chalk and Shuttle Orbiter tiles.

Chalk 156 lb/ft3 typically (varies from ~ 112 to 168 lb/ft3)

Shuttle Orbiter tiles:

LI-900 (black tiles on underside) 9 lb/ft3
LI-2200 (black higher strength around windows & landing gear doors) 22 lb/ft3

FRCI-12 (improved tiles to replace some LI tiles) 12 lb/ft3

LRSI-9  (white tiles on upper surfaces) 9 lb/ft3
LRSI-12 (white tiles on upper surfaces) 12 lb/ft3

BRI-18 (strongest & toughest tile produced, replacement for critical areas)  18 lb/ft3

Water 62.4 lb/ft3
Styrofoam packaging and insulation typically 1 to 2 lb/ft3

Conversion to metric:

1 lb/ft3 is equivalent to 0.016 g/cm3 or 16.0 kg/m3
Title: Re: Starship heat shield
Post by: Action on 10/03/2022 12:42 pm

You brought up the aerodynamics of the situation as an additional justification for the fairings in those cases.  I'm sorry, I don't mean to be argumentative.

Fair enough. That's ok.

Thank you.
Title: Re: Starship heat shield
Post by: Action on 10/03/2022 12:57 pm


I've said before that SpaceX erred when they moved from carbon fiber and no longer had any practical diameter limit, not reconsidering sideways reentry followed by a mode switch to land vertically.  They've been banging their heads against propellant management and heat shield problems for the last three years, and those problems were entirely optional.

Huh?

Starship was always going to re-enter side on when it was going to be made from carbon fibre. The exact landing maneuver was never very clear but I'm sure it would have involved some sort of flip and burn, therefore not making prop management any different.

The switch to stainless steel has nothing at all to do with the heat shield being on the side, it was always this way.

I don't want to derail the heatshield thread with that point, but I will briefly explain it.  My understanding is that carbon fiber limited SpaceX in the size and shape of vehicle they could propose, because of the need for a very large curing oven among other things.  So they proposed a long and skinny second stage that looked like most modern expendable rockets.  If you have to have a long and skinny second stage, side entry kind of makes sense.  When they switched to steel, they no longer had to have that shape and could have rethought reentry and landing.
Title: Re: Starship heat shield
Post by: livingjw on 10/03/2022 06:09 pm


I've said before that SpaceX erred when they moved from carbon fiber and no longer had any practical diameter limit, not reconsidering sideways reentry followed by a mode switch to land vertically.  They've been banging their heads against propellant management and heat shield problems for the last three years, and those problems were entirely optional.

Huh?

Starship was always going to re-enter side on when it was going to be made from carbon fibre. The exact landing maneuver was never very clear but I'm sure it would have involved some sort of flip and burn, therefore not making prop management any different.

The switch to stainless steel has nothing at all to do with the heat shield being on the side, it was always this way.

I don't want to derail the heatshield thread with that point, but I will briefly explain it.  My understanding is that carbon fiber limited SpaceX in the size and shape of vehicle they could propose, because of the need for a very large curing oven among other things.  So they proposed a long and skinny second stage that looked like most modern expendable rockets.  If you have to have a long and skinny second stage, side entry kind of makes sense.  When they switched to steel, they no longer had to have that shape and could have rethought reentry and landing.

Starship needs a small ballistic coefficient and a an L/D max in the range of 0.5-1.0 to control heating and g loads. This requires a lot of reentry area. I don't see how this can be accomplished with an axial layout without compromising ascent performance. Care to provide a sketch and some numbers?

John
Title: Re: Starship heat shield
Post by: Action on 10/03/2022 06:55 pm


I've said before that SpaceX erred when they moved from carbon fiber and no longer had any practical diameter limit, not reconsidering sideways reentry followed by a mode switch to land vertically.  They've been banging their heads against propellant management and heat shield problems for the last three years, and those problems were entirely optional.

Huh?

Starship was always going to re-enter side on when it was going to be made from carbon fibre. The exact landing maneuver was never very clear but I'm sure it would have involved some sort of flip and burn, therefore not making prop management any different.

The switch to stainless steel has nothing at all to do with the heat shield being on the side, it was always this way.

I don't want to derail the heatshield thread with that point, but I will briefly explain it.  My understanding is that carbon fiber limited SpaceX in the size and shape of vehicle they could propose, because of the need for a very large curing oven among other things.  So they proposed a long and skinny second stage that looked like most modern expendable rockets.  If you have to have a long and skinny second stage, side entry kind of makes sense.  When they switched to steel, they no longer had to have that shape and could have rethought reentry and landing.

Starship needs a small ballistic coefficient and a an L/D max in the range of 0.5-1.0 to control heating and g loads. This requires a lot of reentry area. I don't see how this can be accomplished with an axial layout without compromising ascent performance. Care to provide a sketch and some numbers?

John

A capsule shape on top of a regular super heavy seems like the obvious alternative.  I believe Stoke Space Technologies is proposing something vaguely like it.

It would not have the same cross-range and it would have moderately higher-g reentry, if you feel those things are very important.  The trade would be that you get better structural mass fraction, easier reentry more amenable to tougher heatshield solutions, and no mode switch on landing.
Title: Re: Starship heat shield
Post by: schuttle89 on 10/04/2022 12:48 am


I've said before that SpaceX erred when they moved from carbon fiber and no longer had any practical diameter limit, not reconsidering sideways reentry followed by a mode switch to land vertically.  They've been banging their heads against propellant management and heat shield problems for the last three years, and those problems were entirely optional.

Huh?

Starship was always going to re-enter side on when it was going to be made from carbon fibre. The exact landing maneuver was never very clear but I'm sure it would have involved some sort of flip and burn, therefore not making prop management any different.

The switch to stainless steel has nothing at all to do with the heat shield being on the side, it was always this way.

I don't want to derail the heatshield thread with that point, but I will briefly explain it.  My understanding is that carbon fiber limited SpaceX in the size and shape of vehicle they could propose, because of the need for a very large curing oven among other things.  So they proposed a long and skinny second stage that looked like most modern expendable rockets.  If you have to have a long and skinny second stage, side entry kind of makes sense.  When they switched to steel, they no longer had to have that shape and could have rethought reentry and landing.

Starship needs a small ballistic coefficient and a an L/D max in the range of 0.5-1.0 to control heating and g loads. This requires a lot of reentry area. I don't see how this can be accomplished with an axial layout without compromising ascent performance. Care to provide a sketch and some numbers?

John

A capsule shape on top of a regular super heavy seems like the obvious alternative.  I believe Stoke Space Technologies is proposing something vaguely like it.

It would not have the same cross-range and it would have moderately higher-g reentry, if you feel those things are very important.  The trade would be that you get better structural mass fraction, easier reentry more amenable to tougher heatshield solutions, and no mode switch on landing.
The goal is landing on Mars and Earth with the same second stage. I have not seen a capsule concept that is capable of that. (To be very fair I haven't looked very hard but I do pay attention here and have never seen one proposed)
Title: Re: Starship heat shield
Post by: edzieba on 10/04/2022 08:13 am
Very early ('Big Falcon Rocket' era) Starship designs were essentially scaled up Dragons utilising supersonic retropropulsion to expand the bow shock (works with canted-out engines, direct firing ones disrupt the shock) as Red Dragon was intended to demonstrate. Part of what killed Red Dragon was that the Starship design changed to sideways entry with aerodynamic lifting, so that demo mission became internally redundant.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/04/2022 09:30 am
Starship needs a small ballistic coefficient and a an L/D max in the range of 0.5-1.0 to control heating and g loads. This requires a lot of reentry area. I don't see how this can be accomplished with an axial layout without compromising ascent performance. Care to provide a sketch and some numbers?

John
Well lifting capsule designs IE with offset Cg, like Apollo managed 0.3. I think up to 0.5 is viable, but it gets tough about that.

I think people's intuition about entry is quite badly skewed by seeing the final stages of the Shuttle landings. Most of Shuttle's decelleration took place (IIRC) around 46deg to the airflow. This is very high AoA compared to normal aircraft's level flight (IIRC standard commercial airline climb out is about 7deg) and SS is going to come in at about 70deg?

These are the sort of attitudes you see combat aircraft do at air shows when they want to show off their vectoring engine nozzles.   8) People see these displays and ask "How can an aircraft stay in the air like that?"
Title: Re: Starship heat shield
Post by: Action on 10/04/2022 01:40 pm
I have not seen a capsule concept that is capable of that. (To be very fair I haven't looked very hard but I do pay attention here and have never seen one proposed)

In addition to the Dragon-based proposals, I think Gary Hudson proposed a system based on Phoenix to do that.
Title: Re: Starship heat shield
Post by: livingjw on 10/04/2022 01:45 pm
I have not seen a capsule concept that is capable of that. (To be very fair I haven't looked very hard but I do pay attention here and have never seen one proposed)

In addition to the Dragon-based proposals, I think Gary Hudson proposed a system based on Phoenix to do that.

Phoenix? What is that? Do you have a reference?

John
Title: Re: Starship heat shield
Post by: Action on 10/04/2022 01:50 pm
Phoenix? What is that? Do you have a reference?

John

Phoenix was Hudson's name for a family of SSTO proposals, all of which were Bono-style big-capsule shapes, though they were small by the standards of SSTO proposals.

I can't find a free copy of the paper about using it for Mars, but the citation is: HUDSON, GARY. "Employing a chemical rocket VTOVL SSTO for high velocity Mars round trip travel." 24th Joint Propulsion Conference. 1988.
Title: Re: Starship heat shield
Post by: livingjw on 10/04/2022 06:25 pm
Phoenix? What is that? Do you have a reference?

John

Phoenix was Hudson's name for a family of SSTO proposals, all of which were Bono-style big-capsule shapes, though they were small by the standards of SSTO proposals.

I can't find a free copy of the paper about using it for Mars, but the citation is: HUDSON, GARY. "Employing a chemical rocket VTOVL SSTO for high velocity Mars round trip travel." 24th Joint Propulsion Conference. 1988.

- Found the Phoenix papers. Gumdrop/capsule approach doesn't scale well for large, heavy, low ballistic coefficient vehicles. In order to handle the heating with known TPS you will need Shuttle, or lower, ballistic coefficient. To manage g's and atmospheric variations you will need the ability to generate an L/D of 0.5-1.0. A capsule shaped Starship design would need a diameter of ~26m to match Starship's sideways approach. Not very good for ascent aerodynamics.

- SSTO is a non-starter with current technology. You have to shave design margins pretty slim and payload fractions will be around 1% of gross, if all goes well. Any hiccups in development and you have no payload at all.

John
Title: Re: Starship heat shield
Post by: sevenperforce on 10/04/2022 07:55 pm
Very early ('Big Falcon Rocket' era) Starship designs were essentially scaled up Dragons utilising supersonic retropropulsion to expand the bow shock (works with canted-out engines, direct firing ones disrupt the shock) as Red Dragon was intended to demonstrate. Part of what killed Red Dragon was that the Starship design changed to sideways entry with aerodynamic lifting, so that demo mission became internally redundant.
Was there any proposal for getting around cosine losses or were they just going to grit their teeth and bear it?
Title: Re: Starship heat shield
Post by: Action on 10/04/2022 07:58 pm
- Found the Phoenix papers. Gumdrop/capsule approach doesn't scale well for large, heavy, low ballistic coefficient vehicles. In order to handle the heating with known TPS you will need Shuttle, or lower, ballistic coefficient. To manage g's and atmospheric variations you will need the ability to generate an L/D of 0.5-1.0. A capsule shaped Starship design would need a diameter of ~26m to match Starship's sideways approach. Not very good for ascent aerodynamics.

- SSTO is a non-starter with current technology. You have to shave design margins pretty slim and payload fractions will be around 1% of gross, if all goes well. Any hiccups in development and you have no payload at all.

John

To the contrary, I think the big capsule shape is quite scalable; I'm not sure why you'd think otherwise.  You have the picture right - it would look like a regular rocket with a hammerhead fairing, maybe a little more conical than cylindrical.  Certainly entities like Boeing, Grumman, and Chrysler thought the big capsule made sense and proposed tremendously large vehicles with immense payloads.  They should have no problem achieving 3-g reentries, usually proposing cg-offsets or small aerodynamic features.  Maybe you think you need better than that, but I'm not sure why you would.  Plus, with lower total heat reentries they're amenable to ablatives, convection cooling, transpiration, or even heat sink heat shields.

The SSTO part of the Phoenix paper is not what I meant to point to - it's not terribly relevant to the current discussion.  Suffice it to say, if it was feasible to perform the proposed mission with a capsule-style SSTO, it would surely be feasible to perform it with a capsule-style second stage of a TSTO which would have much bigger margins.  Otherwise, I think the paper is kind of neat.  It reads like a first draft of the Starship architecture, with an RLV refueled in LEO and then sent to Mars and back.  It predates a lot of the thinking on Mars in situ resource utlization, so it suggests some scheme with the Martian moons, but I can't really fault the guy for not inventing everything.  Clearly he was born thirty years too soon.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/04/2022 08:21 pm

- SSTO is a non-starter with current technology. You have to shave design margins pretty slim and payload fractions will be around 1% of gross, if all goes well. Any hiccups in development and you have no payload at all.

John
With the understanding you are talking about rocket based VTOVL SSTO.

Excellent find about the table of ballistic coefficients BTW.
Title: Re: Starship heat shield
Post by: livingjw on 10/04/2022 09:32 pm

- SSTO is a non-starter with current technology. You have to shave design margins pretty slim and payload fractions will be around 1% of gross, if all goes well. Any hiccups in development and you have no payload at all.

John
With the understanding you are talking about rocket based VTOVL SSTO.

Excellent find about the table of ballistic coefficients BTW.

- SSTO by any known means is pretty iffy. I have modeled all the various approaches over the years for the USAF.

- Best (largest payload to empty wt. & lowest growth factor) SSTO approaches my team modeled over the years were:
    - VTOHL (or VTOVL) tri-propellant (LOx, LCH4, LH2) rocket
    - VTOHL (or VTOVL) tri-propellant (LOx, LCH4, LH2) rocket-scramjet

- All HTO concepts always faired poorly due to their large heavy wings, propulsion systems and takeoff gear. They have great EIsp but horrible ln(Mi/Mf).   DV = g EIsp x ln(Mi/Mf).   

- All SSTO concepts require the best available technology and have relatively low TRLs. They are risky propositions.

John
Title: Re: Starship heat shield
Post by: livingjw on 10/05/2022 12:08 am
- Found the Phoenix papers. Gumdrop/capsule approach doesn't scale well for large, heavy, low ballistic coefficient vehicles. In order to handle the heating with known TPS you will need Shuttle, or lower, ballistic coefficient. To manage g's and atmospheric variations you will need the ability to generate an L/D of 0.5-1.0. A capsule shaped Starship design would need a diameter of ~26m to match Starship's sideways approach. Not very good for ascent aerodynamics.

- SSTO is a non-starter with current technology. You have to shave design margins pretty slim and payload fractions will be around 1% of gross, if all goes well. Any hiccups in development and you have no payload at all.

John

To the contrary, I think the big capsule shape is quite scalable; I'm not sure why you'd think otherwise.  You have the picture right - it would look like a regular rocket with a hammerhead fairing, maybe a little more conical than cylindrical.  Certainly entities like Boeing, Grumman, and Chrysler thought the big capsule made sense and proposed tremendously large vehicles with immense payloads.  They should have no problem achieving 3-g reentries, usually proposing cg-offsets or small aerodynamic features.  Maybe you think you need better than that, but I'm not sure why you would.  Plus, with lower total heat reentries they're amenable to ablatives, convection cooling, transpiration, or even heat sink heat shields.

The SSTO part of the Phoenix paper is not what I meant to point to - it's not terribly relevant to the current discussion.  Suffice it to say, if it was feasible to perform the proposed mission with a capsule-style SSTO, it would surely be feasible to perform it with a capsule-style second stage of a TSTO which would have much bigger margins.  Otherwise, I think the paper is kind of neat.  It reads like a first draft of the Starship architecture, with an RLV refueled in LEO and then sent to Mars and back.  It predates a lot of the thinking on Mars in situ resource utilization, so it suggests some scheme with the Martian moons, but I can't really fault the guy for not inventing everything.  Clearly he was born thirty years too soon.

- I should have been clearer. As the vehicle mass and volume grows (assuming constant vehicle density), the capsule shape will get flatter to maintain ballistic coefficient. This is the direct result of the cube-square relationship between volume and area. Fine for reentry but, it makes ascent through an atmosphere harder and harder.

- My primary concern is ascent. The supersonic drag of a capsule shaped vehicle with a 26 m diameter will be ~10x larger on ascent than Starship (see attached diagram). Some of this can be offset by lowering thrust to weight of the booster, but at the expense of gravity losses. It will have higher losses and thus will require higher propellant mass ratio.

- The diagram shows a capsule design with the same volume and reentry area as the Starship. Each square is 3 meters. I superimposed the capsule's circular reentry area on top of the Starship sideview. I sketched in a 520m^2 rectangle to show that it more or less matches the Starship dimensions. I hope this helps.

John
Title: Re: Starship heat shield
Post by: HMXHMX on 10/05/2022 03:09 am
This thread is not the place to discuss Phoenix; one of these days I may start a thread somewhere at NSF to talk about my designs/ideas from decades past...but not today.  I will note a few quick points to get them on the record.

Several Phoenix vehicles (including the one in the Mars paper) were dual-fuel, mixed-mode.  Some were single-fuel, mixed-mode (variable LH2 mix ratios).  Most would have used active cooling base TPS; one of the benefits of active cooling is it can be used during ascent to alleviate base heating and also can be dialed up when conducting an entry from hyperbolic (or GTO) orbits.  I also proposed running the engines in gas generator mode during entry – essentially a "supersonic retro-propuslion" approach to reduce base heating on entry by blowing off the shock.  This approach also has the potential to increase L/D by reducing drag.

Most all concepts also would have used nose-mounted "aerospikes" (not aerospike engines, but drag reduction devices similar to that used on Trident).  Such spikes can reduce supersonic drag by as much as 75%. 

And the mass fraction argument won't be settled until someone flies one.

Back on topic!
Title: Re: Starship heat shield
Post by: edzieba on 10/05/2022 08:18 am
Very early ('Big Falcon Rocket' era) Starship designs were essentially scaled up Dragons utilising supersonic retropropulsion to expand the bow shock (works with canted-out engines, direct firing ones disrupt the shock) as Red Dragon was intended to demonstrate. Part of what killed Red Dragon was that the Starship design changed to sideways entry with aerodynamic lifting, so that demo mission became internally redundant.
Was there any proposal for getting around cosine losses or were they just going to grit their teeth and bear it?
Deceleration was intended to be more from the 'inflated' shock rather than the retropropulsion, so the angle was a feature rather than a bug.

Though remember that this design was dropped because it traded poorly against an unpowered aerodynamic lifting entry (propellant mass vs. structural mass), at least at Starship's scale. Might trade better at a different scale, and there is a gulf between vehicles the size of Starship, and the largest viable pure drag capsule for Mars entry (MSL is close to that limit) where retropropulsion, inflatable decelerators, negative lift trajectories, etc, can play in the trade space.
Title: Re: Starship heat shield
Post by: Action on 10/05/2022 01:15 pm
- I should have been clearer. As the vehicle mass and volume grows (assuming constant vehicle density), the capsule shape will get flatter to maintain ballistic coefficient. This is the direct result of the cube-square relationship between volume and area. Fine for reentry but, it makes ascent through an atmosphere harder and harder.

- My primary concern is ascent. The supersonic drag of a capsule shaped vehicle with a 26 m diameter will be ~10x larger on ascent than Starship (see attached diagram). Some of this can be offset by lowering thrust to weight of the booster, but at the expense of gravity losses. It will have higher losses and thus will require higher propellant mass ratio.

- The diagram shows a capsule design with the same volume and reentry area as the Starship. Each square is 3 meters. I superimposed the capsule's circular reentry area on top of the Starship sideview. I sketched in a 520m^2 rectangle to show that it more or less matches the Starship dimensions. I hope this helps.

John

Understood, thank you.  You won't need to maintain the same ballistic coefficient exactly, because you have a flatter bottom with a higher coefficient of drag.  You also get a better mass fraction to work with from a more structurally efficient shape, so it's lighter per unit volume.  And nothing stops you from using extra aerodynamic features to increase that drag as Starship does, so generally I'd envision a steeper cone for similar descent aerodynamic performance.  Besides, ascent drag losses are relatively small on such large vehicles. 

Even if you are skeptical about all the above, if Starship's engines and mass fraction work as advertised it has performance to spare.  Performance that could reasonably be allocated to safety and reliability, and perhaps more importantly, development time.  If the second stage was VTVL, it would be flying by now, and we wouldn't have this heatshield thread.

I've derailed the thread enough.  I'll let this go.  Thanks all.
Title: Re: Starship heat shield
Post by: edzieba on 10/05/2022 03:15 pm
If the second stage was VTVL, it would be flying by now
The second stage IS VTVL, and it HAS been flying.
Title: Re: Starship heat shield
Post by: sevenperforce on 10/05/2022 03:50 pm
Very early ('Big Falcon Rocket' era) Starship designs were essentially scaled up Dragons utilising supersonic retropropulsion to expand the bow shock (works with canted-out engines, direct firing ones disrupt the shock) as Red Dragon was intended to demonstrate. Part of what killed Red Dragon was that the Starship design changed to sideways entry with aerodynamic lifting, so that demo mission became internally redundant.
Was there any proposal for getting around cosine losses or were they just going to grit their teeth and bear it?
Deceleration was intended to be more from the 'inflated' shock rather than the retropropulsion, so the angle was a feature rather than a bug.

Though remember that this design was dropped because it traded poorly against an unpowered aerodynamic lifting entry (propellant mass vs. structural mass), at least at Starship's scale. Might trade better at a different scale, and there is a gulf between vehicles the size of Starship, and the largest viable pure drag capsule for Mars entry (MSL is close to that limit) where retropropulsion, inflatable decelerators, negative lift trajectories, etc, can play in the trade space.
I meant cosine losses on ascent. Or was it expected to have separate engines for orbital insertion? And if so, where would they have been placed?
Title: Re: Starship heat shield
Post by: Action on 10/05/2022 05:33 pm
If the second stage was VTVL, it would be flying by now, and we wouldn't have this heatshield thread.

If the second stage was [conventional] VTVL [as described on the past few pages], it would be flying [regularly, more than once] by now, and we wouldn't have this heatshield thread.
Title: Re: Starship heat shield
Post by: inaccurate_reality on 10/05/2022 07:48 pm
Sorry if it's come up before, but has there been discussion of larger, slab-like TPS tiles to replace hundreds of individual tiles?

I suppose the obvious problem is thermal expansion, which is way more manageable with a small hexagonal tile than a single rectangular tile that stretches across the entire ship. But the upside is, assuming the tiles follow the shuttle recipe exactly and need to be replaced with waterproofed ones every flight, the replacement process for large portions of the ship - anything with simple geometry over a large area, is arguably faster
Title: Re: Starship heat shield
Post by: john smith 19 on 10/05/2022 07:56 pm
- SSTO by any known means is pretty iffy. I have modeled all the various approaches over the years for the USAF.
I've always found that any modelling's realism is only as good as the realism of the assumptions used to set it up. GIGO is eternal :(
Quote from: livingjw
- Best (largest payload to empty wt. & lowest growth factor) SSTO approaches my team modeled over the years were:
    - VTOHL (or VTOVL) tri-propellant (LOx, LCH4, LH2) rocket
    - VTOHL (or VTOVL) tri-propellant (LOx, LCH4, LH2) rocket-scramjet
The SCramjet result is truly astonishing given AFAIK the best T/W of one of these is 4:1, and they need a big rocket to get they up to operating speed.
 :) 
Quote from: livingjw
- All HTO concepts always faired poorly due to their large heavy wings, propulsion systems and takeoff gear. They have great EIsp bu

t horrible ln(Mi/Mf).   DV = g EIsp x ln(Mi/Mf).   
With the understanding that you are talking about air breathing HTO. AFAIK there is no reason an HTO would have any better Isp than a VTO rocket.
But when the Isp is 6x the best rocket Isp available you can now afford those wings  :)

Quote from: livingjw
- All SSTO concepts require the best available technology
True.
Quote from: livingjw
and have relatively low TRLs. They are risky propositions.
John
Although there has been significant work by some companies to raise those TRL's.

But then there's actual risk in development and there's perceived risk.

SS's perceived risk is viewed as low.  Time will tell wheather that perception is accurate.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/05/2022 08:07 pm
Sorry if it's come up before, but has there been discussion of larger, slab-like TPS tiles to replace hundreds of individual tiles?
Some earlier in the thread.  There was a NASA Tech Brief from the 80's or 90's that described a method of slip casting the tiles over a porous mold that was under a slight vacuum to draw the water through it. This allowed near net shape slabs to match contours without machining. The test pieces were IIRC 18"x18" IE 9 standard tiles in 1. Apparently there not worried about thermal effects at this scale.
Quote from: inaccurate_reality
I suppose the obvious problem is thermal expansion, which is way more manageable with a small hexagonal tile than a single rectangular tile that stretches across the entire ship. But the upside is, assuming the tiles follow the shuttle recipe exactly and need to be replaced with waterproofed ones every flight, the replacement process for large portions of the ship - anything with simple geometry over a large area, is arguably faster
Waterproofing something so large is likely to be tricky. The small tiles each had a specific injection hole through the thin, brittle glass coating for injection of the waterproofing compound. I'd find it very doubtful that one hole would allow the fluid to penetrate a significantly bigger area. My instinct would be you'd need multiple holes.
Title: Re: Starship heat shield
Post by: schuttle89 on 10/05/2022 08:27 pm
If the second stage was VTVL, it would be flying by now, and we wouldn't have this heatshield thread.

If the second stage was [conventional] VTVL [as described on the past few pages], it would be flying [regularly, more than once] by now, and we wouldn't have this heatshield thread.
So how would this craft scrub off velocity? A capsule? Which earlier in the thread was shown to have to be huge and cause other problems. Otherwise you're back to this whole heat shield issue. Also you're assuming that the reason starship isn't flying right now is the heat shield (it could be gse, ffa approval, raptor 2 problems or anything else). There are thousands of pages on this part of the website talking about design tradeoffs. People argue about one part and ignore everything else that has to work in sync to make the whole system work.
Title: Re: Starship heat shield
Post by: livingjw on 10/06/2022 02:41 am
- This is really not the place for this alternative design discussion, so let me end with one of our reports that covers quite a few alternative designs, unfortunately it does not include a SSTO VTHL or VTVL rocket. Wish it did.

John

Title: Re: Starship heat shield
Post by: john smith 19 on 10/06/2022 07:33 am
- This is really not the place for this alternative design discussion, so let me end with one of our reports that covers quite a few alternative designs, unfortunately it does not include a SSTO VTHL or VTVL rocket. Wish it did.

John
Thanks for this. What a very interesting collection of authors in one place :)
Title: Re: Starship heat shield
Post by: octavo on 10/06/2022 07:48 am
- This is really not the place for this alternative design discussion, so let me end with one of our reports that covers quite a few alternative designs, unfortunately it does not include a SSTO VTHL or VTVL rocket. Wish it did.

John
Thanks for this. What a very interesting collection of authors in one place :)

Thank you both for all of your informative posts over the years - I mostly lurk, but wanted to say I enjoy reading both of your posts, wherever I find them. The armchair engineers who are convinced their pet idea is a better solution than the team at SpaceX have been able to come up with never fail to stagger me with their hubris.
Title: Re: Starship heat shield
Post by: edzieba on 10/06/2022 09:42 am
Sorry if it's come up before, but has there been discussion of larger, slab-like TPS tiles to replace hundreds of individual tiles?

I suppose the obvious problem is thermal expansion, which is way more manageable with a small hexagonal tile than a single rectangular tile that stretches across the entire ship. But the upside is, assuming the tiles follow the shuttle recipe exactly and need to be replaced with waterproofed ones every flight, the replacement process for large portions of the ship - anything with simple geometry over a large area, is arguably faster
The big problem is not breaking the thing. A large shell made of sintered ceramic is incredibly fragile. I'd be willing to bet it would not even come vaguely close to being self-supporting. If you embed a structural support into it, you are now adding non-functional dry mass. Even if you try and get away with only external handling equipment (e.g. similar to how the STS orbiter payload bay doors required external frames if opened in a 1g environment) then you need to figure out how to attach it to the tank wall in a way that supports it across the entire surface (so a lot of blind attachment points. And ones that need to be unlatched remotely if you ever want to remove it intact) without restraining it when it expands and contracts between cryogenic and re-entry conditions. Along with all the dewatering and waterproofing issues mentioned. And the difficulty in fabricating such an item - first, construct the world's largest monolithic 2200°C furnace...

You earn yourself a lot of extra headaches, for no real benefit.
Title: Re: Starship heat shield
Post by: RamsesBic on 10/06/2022 10:12 am
Sorry if it's come up before, but has there been discussion of larger, slab-like TPS tiles to replace hundreds of individual tiles?

I suppose the obvious problem is thermal expansion, which is way more manageable with a small hexagonal tile than a single rectangular tile that stretches across the entire ship. But the upside is, assuming the tiles follow the shuttle recipe exactly and need to be replaced with waterproofed ones every flight, the replacement process for large portions of the ship - anything with simple geometry over a large area, is arguably faster
The big problem is not breaking the thing. A large shell made of sintered ceramic is incredibly fragile. I'd be willing to bet it would not even come vaguely close to being self-supporting. If you embed a structural support into it, you are now adding non-functional dry mass. Even if you try and get away with only external handling equipment (e.g. similar to how the STS orbiter payload bay doors required external frames if opened in a 1g environment) then you need to figure out how to attach it to the tank wall in a way that supports it across the entire surface (so a lot of blind attachment points. And ones that need to be unlatched remotely if you ever want to remove it intact) without restraining it when it expands and contracts between cryogenic and re-entry conditions. Along with all the dewatering and waterproofing issues mentioned. And the difficulty in fabricating such an item - first, construct the world's largest monolithic 2200°C furnace...

You earn yourself a lot of extra headaches, for no real benefit.

I could add to that. If you were to make the worlds largest furnace and make that shield, how would you fit it to the ship without cracking it? You can't bake it with the ship - the steel would melt.
If any section of that shield breaks off during re-entry the size of the gap would very likely be orders of magnitude larger than any tile.
Title: Re: Starship heat shield
Post by: RamsesBic on 10/06/2022 10:19 am
A question: If we suppose that too many tiles fall off the ship and it does not survive re-entry, would adding a thin ablative layer under the tiles (replacing or in addition to the thermal blankets) be too heavy? Too expensive? Is it even possible?
Title: Re: Starship heat shield
Post by: edzieba on 10/06/2022 10:39 am
A question: If we suppose that too many tiles fall off the ship and it does not survive re-entry, would adding a thin ablative layer under the tiles (replacing or in addition to the thermal blankets) be too heavy? Too expensive? Is it even possible?
Since you don't know a-priori which tile will fail, and at what point in the EDL sequence (e.g. worst case is the tile fails before entry starts), then you'd need to apply an ablative heatshield across the entire vehicle capable of surviving the entire EDL sequence. At that point, you've added the mass of an entire second TPS to the vehicle.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/06/2022 11:00 am
A question: If we suppose that too many tiles fall off the ship and it does not survive re-entry, would adding a thin ablative layer under the tiles (replacing or in addition to the thermal blankets) be too heavy? Too expensive? Is it even possible?
Well there is a flexible version of both SIRCA and PICA ablatives that can be cut with a (sharp) knife. This makes working around holes, hatches etc much quicker and easier.

So it's a possible option that's not necessaily even very labor intensive.

But how long's it going to last? How thick should it be? Just to give some perspective the amount of kinetic and potential energy you need to lose dropping from LEO is about 11.4x that you need to lose from about M6 (roughly the F9's S1 staging velocity). So if F9 S1 needs a 1mm thick layer SS will need 11.4mm. Of course you could then run probabilistic risk assessment, IE lots of monte carlo runs, to decide where the most likely/most serious tile losses would be and just put some under those areas.

The benefit of a few standard size tiles is their interchanagability. Logically you'd have sensors to monitor tile damage and replace those from a small(ish) stock carried on board.

But it's complicated.  :( Totally passive (but likely quite heavy) system of sub-tile ablative Vs monitoring and sensors and some kind of tile replacement process on orbit before you start entry?

Also while such ablatives exist how do you attach them to SS? AFAIK they are usually attached to aluminum structures, not steel. Usually (AFAIK) by some kind of adhesive. However a significant part of that surface is going to be at cryogenic temperatures, possibly after a minimum of at least a 3 month (but maybe up to 6?) cold soak. Maybe there's an OTS adhesive that can handle that combo already.

My instinct is they will ignore this issue and focus on just getting a vehicle to orbit with the standard TPS as designed.

Obviously that first vehicle when it goes up will a)Be completely automated b) Have lots of sensors. c) Assuming it lands safetly be studied in minute detail.

Until that happens planning a backup TPS, with no solid idea of how the baseline TPS will fail to begin with, seems a bit premature.  :(
Title: Re: Starship heat shield
Post by: john smith 19 on 10/06/2022 11:07 am
Since you don't know a-priori which tile will fail, and at what point in the EDL sequence (e.g. worst case is the tile fails before entry starts), then you'd need to apply an ablative heatshield across the entire vehicle capable of surviving the entire EDL sequence. At that point, you've added the mass of an entire second TPS to the vehicle.
That would be the worst case scenario.  :(

I guess to get a baseline for this you'd need to find out how much ablative is burnt off the Dragon heat shield on reentry. It's the only one that runs the full range orbital velocity to zero.

Anyone have any numbers for this?
Title: Re: Starship heat shield
Post by: edzieba on 10/06/2022 12:35 pm
Since you don't know a-priori which tile will fail, and at what point in the EDL sequence (e.g. worst case is the tile fails before entry starts), then you'd need to apply an ablative heatshield across the entire vehicle capable of surviving the entire EDL sequence. At that point, you've added the mass of an entire second TPS to the vehicle.
That would be the worst case scenario.  :(

I guess to get a baseline for this you'd need to find out how much ablative is burnt off the Dragon heat shield on reentry. It's the only one that runs the full range orbital velocity to zero.

Anyone have any numbers for this?
Dragon TPS would has a more benign re-entry environment than Starship sees.

For ablative TPS, entry trajectory is designed to reduce total thermal input, with high peak temperatures being acceptable. Too much total heat soaks through the TPS and the system fails, but higher peak heat for a short time means less total ablation and less heat soak. That's the sort of trajectory Dragon flies, which is limited more by crew (and structural) desired g tolerance than peak heating.

For a radiative TPS (like Starship's) the goal is to keep peak heating within acceptable limits, with total thermal input being much less of an issue. That's the sort of trajectory Starship flies. Flying PICA-X in the same environment is liable to burn through a much thicker layer whilst also heating up the backside to a higher temperature.
Title: Re: Starship heat shield
Post by: RamsesBic on 10/06/2022 01:01 pm
Hmmm... So it is the tiles or nothing? No back-up possible.
I think the ship can survive losing a few tiles here and there, but we have to see if that is true or just what we hope for.

Btw, there are two types of lost tiles. Those lost on launch (could in theory be repaired on orbit) and those lost at some point during re-entry, which would just need some help to make it down.

Or will losing cargo ships now and then be acceptable and the cost of doing business?
Title: Re: Starship heat shield
Post by: livingjw on 10/06/2022 02:50 pm
Hmmm... So it is the tiles or nothing? No back-up possible.
I think the ship can survive losing a few tiles here and there, but we have to see if that is true or just what we hope for.

Btw, there are two types of lost tiles. Those lost on launch (could in theory be repaired on orbit) and those lost at some point during re-entry, which would just need some help to make it down.

Or will losing cargo ships now and then be acceptable and the cost of doing business?

There are other TPS technologies. One that I have studied is C/Sic composite shells (one to two feet on a side) mechanically fixed, backed with Saffil or similar insulation. They come in at about the same weight. Advanced Carbon/carbon shells also would work. Both would be more expensive and lower TRL in this application. SpaceX's current approach is coming along, and it certainly is repairable. Durability yet to be fully demonstrated. I expect to see incremental improvements to their current TPS approach.

John
Title: Re: Starship heat shield
Post by: john smith 19 on 10/06/2022 03:16 pm
Dragon TPS would has a more benign re-entry environment than Starship sees.

For ablative TPS, entry trajectory is designed to reduce total thermal input, with high peak temperatures being acceptable. Too much total heat soaks through the TPS and the system fails, but higher peak heat for a short time means less total ablation and less heat soak. That's the sort of trajectory Dragon flies, which is limited more by crew (and structural) desired g tolerance than peak heating.

For a radiative TPS (like Starship's) the goal is to keep peak heating within acceptable limits, with total thermal input being much less of an issue. That's the sort of trajectory Starship flies. Flying PICA-X in the same environment is liable to burn through a much thicker layer whilst also heating up the backside to a higher temperature.
I'm aware of the difference between an ablative and a radiative TPS, as well as the difference in the form of the heat pulse they are designed to cope with.

But given we know the approximate density of PICAX with the thickness lost on a Dragon reentry we can start to get an idea of what sort of mass such a backup would add to the SS empty weight.

It won't be accurate, that's a given. But it is a place to start.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/06/2022 03:31 pm
Hmmm... So it is the tiles or nothing? No back-up possible.
Not at all, but a)No previous vehicle has had a 2nd heatshield behind the first b)Any option adds weight, so the question is do you really need it?
Quote from: RamsesBic
I think the ship can survive losing a few tiles here and there, but we have to see if that is true or just what we hope for.
You're probably right. It comes down to 2 questions. Where is the tile(s) lost and whenin the trajectory. If it's a single tile from the top side (as it comes in side on) just as it's horizontal speed drops to near zero to an Earth landing then the answer is probably yes. Lose it from the lower side as it start to decellerate (IE at near orbital speed) and it probably won't.
Quote from: RamsesBic
Btw, there are two types of lost tiles. Those lost on launch (could in theory be repaired on orbit) and those lost at some point during re-entry, which would just need some help to make it down.

Or will losing cargo ships now and then be acceptable and the cost of doing business?
Actually tiles could be lost any time during the ascent trajectory, not just launch.

In practice with the amount of cargo Musk plans to send to mars (about 9 for every passenger carrier IIRC) the answer would have to be yes.  :(

Except since the same design is also the passenger carrier then if it does happen then it's going to have to be fixed and proved to be fixed, as they will not be astronaughts, they will be "spaceflight participants" as the FAA calls them. Lower levels of risk will be expected (by the FAA if no one else) and also demonstrated either by a lot of flights or a detailed mathematical analysis whose assumptions can be justified.
Title: Re: Starship heat shield
Post by: RamsesBic on 10/06/2022 04:38 pm
Hmmm... So it is the tiles or nothing? No back-up possible.
Not at all, but a)No previous vehicle has had a 2nd heatshield behind the first b)Any option adds weight, so the question is do you really need it?

a) I am aware of that. Starships are already using thermal blankets and nets, that is more than one is it not?
b) It would add weight, but the question is what would be preferable? Not adding weight or losing a ship?

Quote from: john smith 19
Quote from: RamsesBic
I think the ship can survive losing a few tiles here and there, but we have to see if that is true or just what we hope for.
You're probably right. It comes down to 2 questions. Where is the tile(s) lost and whenin the trajectory. If it's a single tile from the top side (as it comes in side on) just as it's horizontal speed drops to near zero to an Earth landing then the answer is probably yes. Lose it from the lower side as it start to decellerate (IE at near orbital speed) and it probably won't.
Quote from: RamsesBic
Btw, there are two types of lost tiles. Those lost on launch (could in theory be repaired on orbit) and those lost at some point during re-entry, which would just need some help to make it down.

Or will losing cargo ships now and then be acceptable and the cost of doing business?
Actually tiles could be lost any time during the ascent trajectory, not just launch.

In practice with the amount of cargo Musk plans to send to mars (about 9 for every passenger carrier IIRC) the answer would have to be yes.  :(

Except since the same design is also the passenger carrier then if it does happen then it's going to have to be fixed and proved to be fixed, as they will not be astronaughts, they will be "spaceflight participants" as the FAA calls them. Lower levels of risk will be expected (by the FAA if no one else) and also demonstrated either by a lot of flights or a detailed mathematical analysis whose assumptions can be justified.

Maybe I should have said "before re-entry" rather than launch.

I am assuming that the system will improve as the number of flights increases such that when humans are to board a ship the problem would be negligible.
Title: Re: Starship heat shield
Post by: OTV Booster on 10/06/2022 05:12 pm
Re: loosing tiles. I can't put my finger on it but there has been a NASA paper linked on NSF showing a relationship between radius of curvature and shock stand-off.


Assume the very tippy tip tile on the nose were lost. The radius of curvature would normally be the nose radius. Remove the tile and the radius of curvature that is of interest would be the top edge of the next tile down on the centerline. This edge is sharp and the radius of curvature of the shock front would be correspondingly small. My guess is that there would be some risk of shock impingement where the tile is missing. If the shock does not impinge and the shock stand-off distance small, heat input might be mitigated by any cryo cooling the header tank would give. Then the problem becomes landing propellant loss.


The entire centerline would be a concern with the the (I'm at a loss for the correct word) point towards the bottom of the ogive that is the first point of atmospheric 'contact' being of special concern. Moving away from the centerline, the shock stand-off distance increases and the risk associated with tile loss goes down.


This looks like a map for a backup TPS system, if future experience warrants. All the fiddly shapes, including the fins, makes my brain hurt but there may be a similar map here too. Key point: a backup TPS need not be full sized or of constant thickness.

Title: Re: Starship heat shield
Post by: DanClemmensen on 10/06/2022 05:22 pm
Re: loosing tiles. I can't put my finger on it but there has been a NASA paper linked on NSF showing a relationship between radius of curvature and shock stand-off.


Assume the very tippy tip tile on the nose were lost. The radius of curvature would normally be the nose radius. Remove the tile and the radius of curvature that is of interest would be the top edge of the next tile down on the centerline. This edge is sharp and the radius of curvature of the shock front would be correspondingly small. My guess is that there would be some risk of shock impingement where the tile is missing. If the shock does not impinge and the shock stand-off distance small, heat input might be mitigated by any cryo cooling the header tank would give. Then the problem becomes landing propellant loss.


The entire centerline would be a concern with the the (I'm at a loss for the correct word) point towards the bottom of the ogive that is the first point of atmospheric 'contact' being of special concern. Moving away from the centerline, the shock stand-off distance increases and the risk associated with tile loss goes down.


This looks like a map for a backup TPS system, if future experience warrants. All the fiddly shapes, including the fins, makes my brain hurt but there may be a similar map here too. Key point: a backup TPS need not be full sized or of constant thickness.
SS does not enter "nose" first. It enters belly first. All references to "nose radius" in the re-entry literature refer to the curvature of the entering body in its direction of travel. If the tippy-tip TPS falls off, I don't know how to calculate the "radius" of the result. The Starship nose is sticking out toward the side of the plasma flow.
Title: Re: Starship heat shield
Post by: RamsesBic on 10/06/2022 06:10 pm
The nose cone has glued tiles, just as the Shuttle had. Those don't fall off, unless they were not glued properly. (Anyone watching Starbase live today would have seen how hard it is to remove glued tiles. Chisel and big hammer needed.)

The ones most in danger imho are in the middle of the ship, held by studs. If one is not flush enough to the ones around it that corner could break off. If a tiles is not installed the correct way it could fall off too.

What no one can know for sure, until at least the first orbital flight, is whether or not losing one tile causes the loss of others around it. I don't know what kind of forces the plasma can exert on a tile, besides the heat. Is it capable of getting under the next tile and flicking it out?
Title: Re: Starship heat shield
Post by: Hog on 10/06/2022 06:23 pm
The nose cone has glued tiles, just as the Shuttle had. Those don't fall off, unless they were not glued properly. (Anyone watching Starbase live today would have seen how hard it is to remove glued tiles. Chisel and big hammer needed.)

The ones most in danger imho are in the middle of the ship, held by studs. If one is not flush enough to the ones around it that corner could break off. If a tiles is not installed the correct way it could fall off too.

What no one can know for sure, until at least the first orbital flight, is whether or not losing one tile causes the loss of others around it. I don't know what kind of forces the plasma can exert on a tile, besides the heat. Is it capable of getting under the next tile and flicking it out?
Emphasis mine.
During STS times this was known as the "zipper effect".
Title: Re: Starship heat shield
Post by: edzieba on 10/07/2022 07:51 am
Re: loosing tiles. I can't put my finger on it but there has been a NASA paper linked on NSF showing a relationship between radius of curvature and shock stand-off.


Assume the very tippy tip tile on the nose were lost. The radius of curvature would normally be the nose radius. Remove the tile and the radius of curvature that is of interest would be the top edge of the next tile down on the centerline. This edge is sharp and the radius of curvature of the shock front would be correspondingly small. My guess is that there would be some risk of shock impingement where the tile is missing. If the shock does not impinge and the shock stand-off distance small, heat input might be mitigated by any cryo cooling the header tank would give. Then the problem becomes landing propellant loss.


The entire centerline would be a concern with the the (I'm at a loss for the correct word) point towards the bottom of the ogive that is the first point of atmospheric 'contact' being of special concern. Moving away from the centerline, the shock stand-off distance increases and the risk associated with tile loss goes down.


This looks like a map for a backup TPS system, if future experience warrants. All the fiddly shapes, including the fins, makes my brain hurt but there may be a similar map here too. Key point: a backup TPS need not be full sized or of constant thickness.
SS does not enter "nose" first. It enters belly first. All references to "nose radius" in the re-entry literature refer to the curvature of the entering body in its direction of travel. If the tippy-tip TPS falls off, I don't know how to calculate the "radius" of the result. The Starship nose is sticking out toward the side of the plasma flow.
Starship entry AoA is ~70°. The nose still still be first, and since the nose itself has an angle of ~60°, the stagnation point will just be a little to the nadir of the very tippy top.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/07/2022 08:25 am
Starship entry AoA is ~70°. The nose still still be first, and since the nose itself has an angle of ~60°, the stagnation point will just be a little to the nadir of the very tippy top.
Indeed. SS's entry is quite Shuttle like.  I'm reminded that Reinforced Carbon Carbon was only used on two areas of the Shuttle TPS, the wing leading edges and the nose area.

Obviously Musk is expecting the heating levels will be low enough not to need such extreme materials. That said based on the table given a couple of pages back SS's ballistic coefficient is only about 8%[EDIT lower ] than that of Shuttle. I guess changing the angle from 46 to 70 degrees will make quite a difference to peak temperatures.
Title: Re: Starship heat shield
Post by: woods170 on 10/07/2022 10:12 am
The nose cone has glued tiles, just as the Shuttle had. Those don't fall off, unless they were not glued properly. (Anyone watching Starbase live today would have seen how hard it is to remove glued tiles. Chisel and big hammer needed.)

The ones most in danger imho are in the middle of the ship, held by studs. If one is not flush enough to the ones around it that corner could break off. If a tiles is not installed the correct way it could fall off too.

What no one can know for sure, until at least the first orbital flight, is whether or not losing one tile causes the loss of others around it. I don't know what kind of forces the plasma can exert on a tile, besides the heat. Is it capable of getting under the next tile and flicking it out?
Emphasis mine.
During STS times this was known as the "zipper effect".

The "zipper effect" was a concern during shuttle development. But flight experience proved that the "zipper effect" was highly unlikely to be triggered by a lost tile. Increased turbulence and thermal loading to the exposed side of the next tile was observed, but was not strong enough to force the debonding of that next tile. STS-27 being the best observations of this lack of zipper effect.
Title: Re: Starship heat shield
Post by: RamsesBic on 10/07/2022 10:51 am
The nose cone has glued tiles, just as the Shuttle had. Those don't fall off, unless they were not glued properly. (Anyone watching Starbase live today would have seen how hard it is to remove glued tiles. Chisel and big hammer needed.)

The ones most in danger imho are in the middle of the ship, held by studs. If one is not flush enough to the ones around it that corner could break off. If a tiles is not installed the correct way it could fall off too.

What no one can know for sure, until at least the first orbital flight, is whether or not losing one tile causes the loss of others around it. I don't know what kind of forces the plasma can exert on a tile, besides the heat. Is it capable of getting under the next tile and flicking it out?
Emphasis mine.
During STS times this was known as the "zipper effect".

The "zipper effect" was a concern during shuttle development. But flight experience proved that the "zipper effect" was highly unlikely to be triggered by a lost tile. Increased turbulence and thermal loading to the exposed side of the next tile was observed, but was not strong enough to force the debonding of that next tile. STS-27 being the best observations of this lack of zipper effect.

Good to know. Thanks.
But Starship uses studs and the Shuttle used glue, so the result might not be the same.
Title: Re: Starship heat shield
Post by: eriblo on 10/07/2022 11:35 am
The nose cone has glued tiles, just as the Shuttle had. Those don't fall off, unless they were not glued properly. (Anyone watching Starbase live today would have seen how hard it is to remove glued tiles. Chisel and big hammer needed.)

The ones most in danger imho are in the middle of the ship, held by studs. If one is not flush enough to the ones around it that corner could break off. If a tiles is not installed the correct way it could fall off too.

What no one can know for sure, until at least the first orbital flight, is whether or not losing one tile causes the loss of others around it. I don't know what kind of forces the plasma can exert on a tile, besides the heat. Is it capable of getting under the next tile and flicking it out?
Emphasis mine.
During STS times this was known as the "zipper effect".

The "zipper effect" was a concern during shuttle development. But flight experience proved that the "zipper effect" was highly unlikely to be triggered by a lost tile. Increased turbulence and thermal loading to the exposed side of the next tile was observed, but was not strong enough to force the debonding of that next tile. STS-27 being the best observations of this lack of zipper effect.

Good to know. Thanks.
But Starship uses studs and the Shuttle used glue, so the result might not be the same.
That glue the part of the TPS with the lowest temperature limit (which was fine as the aluminum structure beneath was even worse). The studs will likely be fine from a temperature standpoint.

Dynamic pressure from a high velocity gas flow getting in behind the tiles can dislodge then as we saw with the cold gas thrusters but that was a Mach 2-3 (?) stream of higher than sea level density nitrogen. Hopefully they have done the numbers and tested the tiles for Max-Q and reentry conditions...
Title: Re: Starship heat shield
Post by: Reynold on 10/07/2022 03:17 pm
Hmmm... So it is the tiles or nothing? No back-up possible.
I think the ship can survive losing a few tiles here and there, but we have to see if that is true or just what we hope for.

I think part of the idea of the SS construction is that IS the backup.  Note that before Columbia, STS-27 lost tiles and had the aluminum skin melt but fortunately there was a stainless steel mounting plate for the structure underneath and that saved it.

If you need still another backup heat shield in addition to the stainless steel and the thermal tiles, you probably want to improve the thermal tiles and fastening process in some way rather than add another redundancy.  Or stick to doing reentry on Dragons, and accept a 1 in 10 vehicle loss on cargo runs of Starship. 
Title: Re: Starship heat shield
Post by: Hog on 10/07/2022 04:09 pm
Hmmm... So it is the tiles or nothing? No back-up possible.
I think the ship can survive losing a few tiles here and there, but we have to see if that is true or just what we hope for.


I think part of the idea of the SS construction is that IS the backup.  Note that before Columbia, STS-27 lost tiles and had the aluminum skin melt but fortunately there was a stainless steel mounting plate for the structure underneath and that saved it.

If you need still another backup heat shield in addition to the stainless steel and the thermal tiles, you probably want to improve the thermal tiles and fastening process in some way rather than add another redundancy.  Or stick to doing reentry on Dragons, and accept a 1 in 10 vehicle loss on cargo runs of Starship.

Added a picture of the "melty" portion of Orbiter Vehicle (OV-104) Discovery following the tile loss.
xxxxxxxxxxxxxxxx


That 1/9 LOC/V(Loss of Crew/Vehicle) was approx the same safety stats for STS-5 through STS-9(STS-5 and STS-6 saw crew size jump from 2=left seated Commander and right seated Pilot up to 4 with 2 mission specialists seated behind the Commander/pilot. Then for STS-7 and STS-8 saw the 4 crew on the flight deck with a 5th crewmember down in the mid-deck and for STS-9 saw 4 on the flight deck and 2 in the mid-deck for a crew of 6), the ejection seat system was called the SR-1 system and used the Shuttle Ejection Escape Suit(SEES) (S1030A) which was a derivation of the David Clark Company's USAF S1030 pressure suits used in the Mach 3+ Blackbird series of recon., interceptor and NASA research planes.  The SR-1 seat system and the SEES pressure suits used for flights STS-1 through STS-4 improved the LOC/V rates up to 1 loss in 12 attempts  My times have changed, of course these LOCV rates were NOT known at the time and were calculated once STS had retired.
With President Reagan pronouncing the Space Shuttle as "OPERATIONAL" for STS-5, the SR-1 system was disabled on OV-102 Columbia with the crew wearing those blue cotton flight suits along with basic lightweight helmets and masks which by design, would supply oxygen to crewmembers from their carry along PEAPs(personal Egress Air Packs). the masks and PEAPs were designed to supply breathable air to the astronauts to enable them to escape the orbiter vehicle during emergency escapes from the crew compartment down to the mid-deck, out along the crew access arm and to the slide baskets and finally to the bunkers to shelter in place, or to awaiting M-113 armoured tracked tanks to evacuate them in case of casualties that had a time constraint(Golden Hour).
Following her 2nd operational mission(STS-9) Columbia entered an 18 month period back at her birthplace of Palmdale California beginning January 1984 back in California,undergoing modifications that removed the Orbiter Flight Test hardware and updating her to similar specifications as those of its sister orbiters.  OV-102 Columbia had the remnants of the SR-1 ejection system removed and the program moved forward with a "shirt-sleeves" internal operational environment.

attachments
1) astronauts at the bottom of the slidewires escape system wearing the  Shuttle Ejection Escape Suit
2) John Young sporting a SEES
3) The "melty" portion of Atlantis following STS-27
Title: Re: Starship heat shield
Post by: Hog on 10/07/2022 04:33 pm
The nose cone has glued tiles, just as the Shuttle had. Those don't fall off, unless they were not glued properly. (Anyone watching Starbase live today would have seen how hard it is to remove glued tiles. Chisel and big hammer needed.)

The ones most in danger imho are in the middle of the ship, held by studs. If one is not flush enough to the ones around it that corner could break off. If a tiles is not installed the correct way it could fall off too.

What no one can know for sure, until at least the first orbital flight, is whether or not losing one tile causes the loss of others around it. I don't know what kind of forces the plasma can exert on a tile, besides the heat. Is it capable of getting under the next tile and flicking it out?
Emphasis mine.
During STS times this was known as the "zipper effect".

The "zipper effect" was a concern during shuttle development. But flight experience proved that the "zipper effect" was highly unlikely to be triggered by a lost tile. Increased turbulence and thermal loading to the exposed side of the next tile was observed, but was not strong enough to force the debonding of that next tile. STS-27 being the best observations of this lack of zipper effect.
Not sure if considered a part of Shuttle's development period or not, but the "zipper effect", or the lack thereof, was accentuated by media reports of "supposed tile losses" during OV-102 Columbia's transit atop the Shuttle Carrier Aircraft from California to Florida.  What appeared to be larger sections of tiles that were lost during this SCA transit, were actually tile spacers that were installed onto the orbiter vehicle specifically for the delivery flight.  While SOME tiles were indeed lost, the vast volumes of lost tiles due to this "zipper effect" were incorrect and hugely overstated.  To the un-knowing, the off-nominal appearing "false tiles" appeared like missing or damaged tiles which combined with earlier worries from NASA engineers about the possibility of the "zipper effect" seemed to propagate the apparent myth of the "zipper effect".  Another case or knowing "just enough to be dangerous".  There's a LOT of this in the world of spaceflight enthusiasm.

There was a huge push to get the Thermal Protection System(TPS) installed on Columbia as the launch date was looming, so these "false tile sections" were fashioned onto Columbia specifically for her cross country SCA flight to Florida. The remaining tiles would be installed at KSC at the rate of 1.7 tiles per person per week.

attachments
1)Columbia tile situation upon arrival at KSC
2) tile history slide
3) Columbia delivery flight
Title: Re: Starship heat shield
Post by: OTV Booster on 10/07/2022 06:22 pm
Re: loosing tiles. I can't put my finger on it but there has been a NASA paper linked on NSF showing a relationship between radius of curvature and shock stand-off.


Assume the very tippy tip tile on the nose were lost. The radius of curvature would normally be the nose radius. Remove the tile and the radius of curvature that is of interest would be the top edge of the next tile down on the centerline. This edge is sharp and the radius of curvature of the shock front would be correspondingly small. My guess is that there would be some risk of shock impingement where the tile is missing. If the shock does not impinge and the shock stand-off distance small, heat input might be mitigated by any cryo cooling the header tank would give. Then the problem becomes landing propellant loss.


The entire centerline would be a concern with the the (I'm at a loss for the correct word) point towards the bottom of the ogive that is the first point of atmospheric 'contact' being of special concern. Moving away from the centerline, the shock stand-off distance increases and the risk associated with tile loss goes down.


This looks like a map for a backup TPS system, if future experience warrants. All the fiddly shapes, including the fins, makes my brain hurt but there may be a similar map here too. Key point: a backup TPS need not be full sized or of constant thickness.
SS does not enter "nose" first. It enters belly first. All references to "nose radius" in the re-entry literature refer to the curvature of the entering body in its direction of travel. If the tippy-tip TPS falls off, I don't know how to calculate the "radius" of the result. The Starship nose is sticking out toward the side of the plasma flow.
No, please. I understand SS will not reenter nose first. Reread the my post with the assumption of a realistic AoA.

AIUI, SS is intended to reenter with an AoA of ~70deg. This moves the point of first contact from the centerline of the barrel up onto the ogive. At this point there are two radii to consider. Up/down and left/right, and it gets complicated.

At the edge where the tippy tip tile is missing a new up/down radius is introduced along the centerline. Flow will 'flow' over the lip and most likely down to the newly exposed surface. The shock will most probably also make an adjustment around the lip but my dedicated CFD computer is down right now (/s) and I can't tell if there will be any shock impingement. Greatest danger might be the side face of the tile opposite the flow.

Down on the barrel, let's assume an AoA of 90deg. It makes the visualization easier. The shock front is closest along the centerline and compressive force and it's heating are greatest. Surface flow is from the centerline to the sides. Remove one centerline tile.

The compressive forces stay the same but are now on the skin, not a tile. AIUI, the shock front would dimple in at a rate determined by the radius of curvature of the tile edge. Here it gets interesting. With the shock front dimpling in and the missing tile forming a pocket, there may be a Venturi effect with the semi trapped flow excessively heating the adjacent tile edges. This effect decreases as the missing tile distance from the centerline increases.

This is admittedly all a mind experiment. The only number I have is 42, and Elon's already used it on SS.
Title: Re: Starship heat shield
Post by: OTV Booster on 10/07/2022 06:33 pm
The nose cone has glued tiles, just as the Shuttle had. Those don't fall off, unless they were not glued properly. (Anyone watching Starbase live today would have seen how hard it is to remove glued tiles. Chisel and big hammer needed.)

The ones most in danger imho are in the middle of the ship, held by studs. If one is not flush enough to the ones around it that corner could break off. If a tiles is not installed the correct way it could fall off too.

What no one can know for sure, until at least the first orbital flight, is whether or not losing one tile causes the loss of others around it. I don't know what kind of forces the plasma can exert on a tile, besides the heat. Is it capable of getting under the next tile and flicking it out?
I've a hunch they'll start glueing the centerline tiles too. That'll suck for repair but the need for repair will go down. ISTM that the possibility of a missing tile starting a cascade is highest in the centerline. See previous post.
Title: Re: Starship heat shield
Post by: OTV Booster on 10/07/2022 06:35 pm
Re: loosing tiles. I can't put my finger on it but there has been a NASA paper linked on NSF showing a relationship between radius of curvature and shock stand-off.


Assume the very tippy tip tile on the nose were lost. The radius of curvature would normally be the nose radius. Remove the tile and the radius of curvature that is of interest would be the top edge of the next tile down on the centerline. This edge is sharp and the radius of curvature of the shock front would be correspondingly small. My guess is that there would be some risk of shock impingement where the tile is missing. If the shock does not impinge and the shock stand-off distance small, heat input might be mitigated by any cryo cooling the header tank would give. Then the problem becomes landing propellant loss.


The entire centerline would be a concern with the the (I'm at a loss for the correct word) point towards the bottom of the ogive that is the first point of atmospheric 'contact' being of special concern. Moving away from the centerline, the shock stand-off distance increases and the risk associated with tile loss goes down.


This looks like a map for a backup TPS system, if future experience warrants. All the fiddly shapes, including the fins, makes my brain hurt but there may be a similar map here too. Key point: a backup TPS need not be full sized or of constant thickness.
SS does not enter "nose" first. It enters belly first. All references to "nose radius" in the re-entry literature refer to the curvature of the entering body in its direction of travel. If the tippy-tip TPS falls off, I don't know how to calculate the "radius" of the result. The Starship nose is sticking out toward the side of the plasma flow.
Starship entry AoA is ~70°. The nose still still be first, and since the nose itself has an angle of ~60°, the stagnation point will just be a little to the nadir of the very tippy top.
Stagnation point! That's the term I was looking for. Thanks.
Title: Re: Starship heat shield
Post by: adrianwyard on 10/07/2022 08:35 pm
The nose cone has glued tiles, just as the Shuttle had. Those don't fall off, unless they were not glued properly. (Anyone watching Starbase live today would have seen how hard it is to remove glued tiles. Chisel and big hammer needed.)

The ones most in danger imho are in the middle of the ship, held by studs. If one is not flush enough to the ones around it that corner could break off. If a tiles is not installed the correct way it could fall off too.

What no one can know for sure, until at least the first orbital flight, is whether or not losing one tile causes the loss of others around it. I don't know what kind of forces the plasma can exert on a tile, besides the heat. Is it capable of getting under the next tile and flicking it out?
I've a hunch they'll start glueing the centerline tiles too. That'll suck for repair but the need for repair will go down. ISTM that the possibility of a missing tile starting a cascade is highest in the centerline. See previous post.
If glue turns out to be necessary to fix most tiles I wonder if it would make sense to switch to larger replaceable units, e.g. an entire barrel-section's worth of glued tiles on a lightweight structure. This is far from a 'rapidly reusable' ideal TPS but I could imagine a large supply of barrel sections being on hand, so if a Starship lands with a couple of broken tiles on the belly, you swap out its entire section in less time than a custom repair. It's far from ideal, and doesn't address the complex geometry sections but it would address ~70% of the TPS area?
Title: Re: Starship heat shield
Post by: RamsesBic on 10/07/2022 09:09 pm
The nose cone has glued tiles, just as the Shuttle had. Those don't fall off, unless they were not glued properly. (Anyone watching Starbase live today would have seen how hard it is to remove glued tiles. Chisel and big hammer needed.)

The ones most in danger imho are in the middle of the ship, held by studs. If one is not flush enough to the ones around it that corner could break off. If a tiles is not installed the correct way it could fall off too.

What no one can know for sure, until at least the first orbital flight, is whether or not losing one tile causes the loss of others around it. I don't know what kind of forces the plasma can exert on a tile, besides the heat. Is it capable of getting under the next tile and flicking it out?
I've a hunch they'll start glueing the centerline tiles too. That'll suck for repair but the need for repair will go down. ISTM that the possibility of a missing tile starting a cascade is highest in the centerline. See previous post.
If glue turns out to be necessary to fix most tiles I wonder if it would make sense to switch to larger replaceable units, e.g. an entire barrel-section's worth of glued tiles on a lightweight structure. This is far from a 'rapidly reusable' ideal TPS but I could imagine a large supply of barrel sections being on hand, so if a Starship lands with a couple of broken tiles on the belly, you swap out its entire section in less time than a custom repair. It's far from ideal, and doesn't address the complex geometry sections but it would address ~70% of the TPS area?
Thermal expansion and contraction would crack such sections.
Title: Re: Starship heat shield
Post by: adrianwyard on 10/08/2022 01:14 am
If the idea had merit I'm confident SpaceX engineers could work up expansion joints. The bigger question is how much weight would such a panelized approach add?
Title: Re: Starship heat shield
Post by: BT52 on 10/08/2022 04:29 am
If the idea had merit I'm confident SpaceX engineers could work up expansion joints. The bigger question is how much weight would such a panelized approach add?

Yeah i got similar idea. But with bottom mesh as support and tiles are glued on it. Sorta strapping mechanism.

No matter how you put it. Bayonet clip with steel  frame inside tile should be still more weight efficient.

Ofc most efficient is just glue all of it directly on shell... But Shuttle showed that this is tough cookie to maintain and quick turn around is not really possible. That's why we both juggling with other means to quickly remove panels and cure them in more clean, assessable and controlled environment.



Title: Re: Starship heat shield
Post by: john smith 19 on 10/08/2022 06:46 am

Thermal expansion and contraction would crack such sections.
If the skin were aluminum and they didn't use a stress isolation pad yes.

But SS is steel. I can't recall if it's TCE is 1/3 or 1/10 that of aluminum. It's definitely a lot lower.

Maybe low enough not to be a problem.

Truth is without a test flight to orbit and at least an attempt to get back to ground we lack any solid data.  :(
Title: Re: Starship heat shield
Post by: DanClemmensen on 10/08/2022 02:30 pm
The nose cone has glued tiles, just as the Shuttle had. Those don't fall off, unless they were not glued properly. (Anyone watching Starbase live today would have seen how hard it is to remove glued tiles. Chisel and big hammer needed.)

The ones most in danger imho are in the middle of the ship, held by studs. If one is not flush enough to the ones around it that corner could break off. If a tiles is not installed the correct way it could fall off too.

What no one can know for sure, until at least the first orbital flight, is whether or not losing one tile causes the loss of others around it. I don't know what kind of forces the plasma can exert on a tile, besides the heat. Is it capable of getting under the next tile and flicking it out?
I've a hunch they'll start glueing the centerline tiles too. That'll suck for repair but the need for repair will go down. ISTM that the possibility of a missing tile starting a cascade is highest in the centerline. See previous post.
If glue turns out to be necessary to fix most tiles I wonder if it would make sense to switch to larger replaceable units, e.g. an entire barrel-section's worth of glued tiles on a lightweight structure. This is far from a 'rapidly reusable' ideal TPS but I could imagine a large supply of barrel sections being on hand, so if a Starship lands with a couple of broken tiles on the belly, you swap out its entire section in less time than a custom repair. It's far from ideal, and doesn't address the complex geometry sections but it would address ~70% of the TPS area?
Thermal expansion and contraction would crack such sections.
How does thermal expansion compare with expansion due to pressurization? I would think that pressurization would cause more on a tank that large.
Title: Re: Starship heat shield
Post by: RamsesBic on 10/08/2022 03:29 pm
A ship with about atmospheric pressure is built with rather large gaps between the tiles. At operational pressure (6 bar) it will expand - that is fine for the tiles, the gaps might increase a bit.
But when it is re-entring the atmosphere (still at 6 bar internal pressure) and the temperature reaches its maximum those gaps will narrow to be almost zero due to expansion of the tiles. This is the part that would cause a very large tile to crack when it has nowhere to expand.
Of course the very large tile would also have trouble when the ship goes from 1 bar to 6 bar.

Another question is how would you install such a big tile? How many studs would you need? Will you use a frame? Then how much weight will it add? It is already hard to install a small tile with 3 holes onto 3 studs.

How much would get exposed if such a very large tile is lost?

I really can't see any benefits from using very large tiles (or shields if you prefer).

I am still not giving up on the present tiles. We just have to wait and see.
Title: Re: Starship heat shield
Post by: sebk on 10/11/2022 05:03 pm
Re: loosing tiles. I can't put my finger on it but there has been a NASA paper linked on NSF showing a relationship between radius of curvature and shock stand-off.


Assume the very tippy tip tile on the nose were lost. The radius of curvature would normally be the nose radius. Remove the tile and the radius of curvature that is of interest would be the top edge of the next tile down on the centerline. This edge is sharp and the radius of curvature of the shock front would be correspondingly small. My guess is that there would be some risk of shock impingement where the tile is missing. If the shock does not impinge and the shock stand-off distance small, heat input might be mitigated by any cryo cooling the header tank would give. Then the problem becomes landing propellant loss.


The entire centerline would be a concern with the the (I'm at a loss for the correct word) point towards the bottom of the ogive that is the first point of atmospheric 'contact' being of special concern. Moving away from the centerline, the shock stand-off distance increases and the risk associated with tile loss goes down.


This looks like a map for a backup TPS system, if future experience warrants. All the fiddly shapes, including the fins, makes my brain hurt but there may be a similar map here too. Key point: a backup TPS need not be full sized or of constant thickness.
SS does not enter "nose" first. It enters belly first. All references to "nose radius" in the re-entry literature refer to the curvature of the entering body in its direction of travel. If the tippy-tip TPS falls off, I don't know how to calculate the "radius" of the result. The Starship nose is sticking out toward the side of the plasma flow.
No, please. I understand SS will not reenter nose first. Reread the my post with the assumption of a realistic AoA.

AIUI, SS is intended to reenter with an AoA of ~70deg. This moves the point of first contact from the centerline of the barrel up onto the ogive. At this point there are two radii to consider. Up/down and left/right, and it gets complicated.

At the edge where the tippy tip tile is missing a new up/down radius is introduced along the centerline. Flow will 'flow' over the lip and most likely down to the newly exposed surface. The shock will most probably also make an adjustment around the lip but my dedicated CFD computer is down right now (/s) and I can't tell if there will be any shock impingement. Greatest danger might be the side face of the tile opposite the flow.

Down on the barrel, let's assume an AoA of 90deg. It makes the visualization easier. The shock front is closest along the centerline and compressive force and it's heating are greatest. Surface flow is from the centerline to the sides. Remove one centerline tile.

The compressive forces stay the same but are now on the skin, not a tile. AIUI, the shock front would dimple in at a rate determined by the radius of curvature of the tile edge. Here it gets interesting. With the shock front dimpling in and the missing tile forming a pocket, there may be a Venturi effect with the semi trapped flow excessively heating the adjacent tile edges. This effect decreases as the missing tile distance from the centerline increases.

This is admittedly all a mind experiment. The only number I have is 42, and Elon's already used it on SS.

Actually, on the center-spot (or center line at 90° AoA) behind the stagnation point there would be no local shock even if a tile fell off. The bow shock would be around half a meter away (bow shock standoff is about 1/9 of the radius of the curvature) and behind the shock you have stagnation point, i.e. the point where there's no major air movement. There will be turbulence and stuff (unless things are so smooth the flow is laminar) but they will be subsonic.

But as you'd start moving to the side, you'd start getting air movement again. If you'd move totally to the side you'd actually get supersonic flow (in the order of Mach 2.5 if I remember correctly; I could be badly wrong, though). So somewhere on the side of the barrel, likely at some point between 30° and 60° to the side you actually get supersonic flow behind the bow shock too. So that's the place where there's potential for shock impingement onto the skin if a tile is missing. OTOH heating would be less there, because bow shock standoff is significantly larger back there, and the flow has lower pressure (so it's colder and contains less heat to transfer).

You could (extremely roughly!) think about the skin of the vehicle and bow shock forming a kind of a nozzle through which the stagnation point air expands to escape behind the sides of the reentering vehicle.
Title: Re: Starship heat shield
Post by: edzieba on 10/11/2022 06:11 pm
The bow shock would be around half a meter away (bow shock standoff is about 1/9 of the radius of the curvature) and behind the shock you have stagnation point, i.e. the point where there's no major air movement.
The problem is that once a tile is removed (or the TPS otherwise mechanically disrupted) you no longer have a radius equal to the radius of the vehicle. You have a radius equal to the lip of the edge of the adjacent tiles, which is a few mm at most. The shock in that region is then happy to reattach to the surface of the vehicle and allow hot gas to impinge on the vehicle.
Title: Re: Starship heat shield
Post by: eriblo on 10/11/2022 09:09 pm
The bow shock would be around half a meter away (bow shock standoff is about 1/9 of the radius of the curvature) and behind the shock you have stagnation point, i.e. the point where there's no major air movement.
The problem is that once a tile is removed (or the TPS otherwise mechanically disrupted) you no longer have a radius equal to the radius of the vehicle. You have a radius equal to the lip of the edge of the adjacent tiles, which is a few mm at most. The shock in that region is then happy to reattach to the surface of the vehicle and allow hot gas to impinge on the vehicle.
No, as sebk stated the relevant radius of curvature has to do with how the gas flows around the vehicle and this will not change drastically for disruptions that are significantly smaller than the shock standoff distance.

The dangers are shocks in the local (up to supersonic) flow and increased heat transfer downstream due to turbulence. The space shuttle flew experiments to study this where one tile had an up to 0.5 inch tall ridge with radii of a few mm (see for example the attached pdf) which did not suffer any damage.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/12/2022 10:44 am
The dangers are shocks in the local (up to supersonic) flow and increased heat transfer downstream due to turbulence. The space shuttle flew experiments to study this where one tile had an up to 0.5 inch tall ridge with radii of a few mm (see for example the attached pdf) which did not suffer any damage.
Interesting paper. 

But note those tile locations were selected to avoid damage to begin with. That's not to say things could have been much more serious in other locations.

What is good new s was that all predicted temperatures were substantially higher than the actual results.

So the design tool results were conservative and while you can't be quite sure how much lower the actual temperatures will be, you can be sure they will be lower.

In fact the difference looks big enough that there may be a systemantic element that needs to be found to improve the match.

The joker in the pack is to what exten those tools are "first principles" or wheather they use fudge factors drawn from wind tunnel models of Shuttle. Obviously if the latter then transferring the results to SS will be very doubtful.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 10/12/2022 11:33 pm
The bow shock would be around half a meter away (bow shock standoff is about 1/9 of the radius of the curvature) and behind the shock you have stagnation point, i.e. the point where there's no major air movement.
The problem is that once a tile is removed (or the TPS otherwise mechanically disrupted) you no longer have a radius equal to the radius of the vehicle. You have a radius equal to the lip of the edge of the adjacent tiles, which is a few mm at most. The shock in that region is then happy to reattach to the surface of the vehicle and allow hot gas to impinge on the vehicle.
No, as sebk stated the relevant radius of curvature has to do with how the gas flows around the vehicle and this will not change drastically for disruptions that are significantly smaller than the shock standoff distance.

The dangers are shocks in the local (up to supersonic) flow and increased heat transfer downstream due to turbulence. The space shuttle flew experiments to study this where one tile had an up to 0.5 inch tall ridge with radii of a few mm (see for example the attached pdf) which did not suffer any damage.

A void and a protuberance are not the same thing when it comes to hypersonic flow. 

So while the paper is interesting, it doesn't apply to missing tiles.
Title: Re: Starship heat shield
Post by: OTV Booster on 10/13/2022 02:20 am
Re: loosing tiles. I can't put my finger on it but there has been a NASA paper linked on NSF showing a relationship between radius of curvature and shock stand-off.


Assume the very tippy tip tile on the nose were lost. The radius of curvature would normally be the nose radius. Remove the tile and the radius of curvature that is of interest would be the top edge of the next tile down on the centerline. This edge is sharp and the radius of curvature of the shock front would be correspondingly small. My guess is that there would be some risk of shock impingement where the tile is missing. If the shock does not impinge and the shock stand-off distance small, heat input might be mitigated by any cryo cooling the header tank would give. Then the problem becomes landing propellant loss.


The entire centerline would be a concern with the the (I'm at a loss for the correct word) point towards the bottom of the ogive that is the first point of atmospheric 'contact' being of special concern. Moving away from the centerline, the shock stand-off distance increases and the risk associated with tile loss goes down.


This looks like a map for a backup TPS system, if future experience warrants. All the fiddly shapes, including the fins, makes my brain hurt but there may be a similar map here too. Key point: a backup TPS need not be full sized or of constant thickness.
SS does not enter "nose" first. It enters belly first. All references to "nose radius" in the re-entry literature refer to the curvature of the entering body in its direction of travel. If the tippy-tip TPS falls off, I don't know how to calculate the "radius" of the result. The Starship nose is sticking out toward the side of the plasma flow.
No, please. I understand SS will not reenter nose first. Reread the my post with the assumption of a realistic AoA.

AIUI, SS is intended to reenter with an AoA of ~70deg. This moves the point of first contact from the centerline of the barrel up onto the ogive. At this point there are two radii to consider. Up/down and left/right, and it gets complicated.

At the edge where the tippy tip tile is missing a new up/down radius is introduced along the centerline. Flow will 'flow' over the lip and most likely down to the newly exposed surface. The shock will most probably also make an adjustment around the lip but my dedicated CFD computer is down right now (/s) and I can't tell if there will be any shock impingement. Greatest danger might be the side face of the tile opposite the flow.

Down on the barrel, let's assume an AoA of 90deg. It makes the visualization easier. The shock front is closest along the centerline and compressive force and it's heating are greatest. Surface flow is from the centerline to the sides. Remove one centerline tile.

The compressive forces stay the same but are now on the skin, not a tile. AIUI, the shock front would dimple in at a rate determined by the radius of curvature of the tile edge. Here it gets interesting. With the shock front dimpling in and the missing tile forming a pocket, there may be a Venturi effect with the semi trapped flow excessively heating the adjacent tile edges. This effect decreases as the missing tile distance from the centerline increases.

This is admittedly all a mind experiment. The only number I have is 42, and Elon's already used it on SS.

Actually, on the center-spot (or center line at 90° AoA) behind the stagnation point there would be no local shock even if a tile fell off. The bow shock would be around half a meter away (bow shock standoff is about 1/9 of the radius of the curvature) and behind the shock you have stagnation point, i.e. the point where there's no major air movement. There will be turbulence and stuff (unless things are so smooth the flow is laminar) but they will be subsonic.

But as you'd start moving to the side, you'd start getting air movement again. If you'd move totally to the side you'd actually get supersonic flow (in the order of Mach 2.5 if I remember correctly; I could be badly wrong, though). So somewhere on the side of the barrel, likely at some point between 30° and 60° to the side you actually get supersonic flow behind the bow shock too. So that's the place where there's potential for shock impingement onto the skin if a tile is missing. OTOH heating would be less there, because bow shock standoff is significantly larger back there, and the flow has lower pressure (so it's colder and contains less heat to transfer).

You could (extremely roughly!) think about the skin of the vehicle and bow shock forming a kind of a nozzle through which the stagnation point air expands to escape behind the sides of the reentering vehicle.
The CFD system is still down <g> so I'm trying to use my head and model this one air particle at a time. Again assume a 90deg. AoA for simplicity.


The heatshield is in vacuum so there are no aerodynamics. Then it encounters one particle of air directly on the centerline. The particle hits and that is one tiny bit of compressive heating to both the heatshield and the particle. The energetic particle is now conceptually sharing a frame of reference with the ship and being hot and energetic, rebounds.


A key concept here is 'mean free space' between air particles. As the air gets denser the mean free space goes down and a rebounding particle has an increasing chance of impacting an incoming* particle of air. When a rebounding particle hits an incoming particle a nascent shock wave forms.


That first partial that impacts an incoming particle would bounce back towards the ship and contribute again to compressive heating. The particle it impacted would also rebound and have some chance of hitting yet another incoming particle and the process would cascade. This is all at the stagnation point.


To one side or the other the process would follow this pattern but with a radial component. This is what forms the flow under the shock. Particles are always bleeding in from the shock and adding to the flow. Particles are always piling up and entering the ships frame of reference. This pileup is the shockwave.


Not sure where this is going. Gotta think on it some more. Somebody point me in the right direction if I'm off base.


* Really just unlucky enough to be in the way.
Title: Re: Starship heat shield
Post by: Nomadd on 10/13/2022 02:40 am
 I heard that 24 and 25 will have tiles but 26, 27 and 28 will be operational Starlink missions with no tiles. The only thing that makes sense to me is that there's a major shakeup with the heat shield that won't be ready for a while but they still want to get some Starlinks launched.
 Then again, not all that much makes sense to me.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/13/2022 06:59 am

The CFD system is still down <g> so I'm trying to use my head and model this one air particle at a time. Again assume a 90deg. AoA for simplicity.


The heatshield is in vacuum so there are no aerodynamics. Then it encounters one particle of air directly on the centerline. The particle hits and that is one tiny bit of compressive heating to both the heatshield and the particle. The energetic particle is now conceptually sharing a frame of reference with the ship and being hot and energetic, rebounds.


A key concept here is 'mean free space' between air particles. As the air gets denser the mean free space goes down and a rebounding particle has an increasing chance of impacting an incoming* particle of air. When a rebounding particle hits an incoming particle a nascent shock wave forms.


That first partial that impacts an incoming particle would bounce back towards the ship and contribute again to compressive heating. The particle it impacted would also rebound and have some chance of hitting yet another incoming particle and the process would cascade. This is all at the stagnation point.


To one side or the other the process would follow this pattern but with a radial component. This is what forms the flow under the shock. Particles are always bleeding in from the shock and adding to the flow. Particles are always piling up and entering the ships frame of reference. This pileup is the shockwave.


Not sure where this is going. Gotta think on it some more. Somebody point me in the right direction if I'm off base.


* Really just unlucky enough to be in the way.
What you're kind of describing is quite similar to how the effect of a neutron moderator was worked out from first principles in a book called "Elementary Pile Theory"

It's about momentum transfer between two bodies. In your scenario you would start by picturing it from the PoV, or frame of reference of SS, and then move to considering how both bodies react to their impact and recoil in the frame of reference of them  moving against the Earth.

You're starting at Newtonian flow (straight line impacts, like rays of light) then as the density rises into (IIRC) slip flow. so you need to consider what the Knusden number is. This is the area where "Temperature" is measuring the average speed of molecules. This is also where you have 7-11 species airflow models as the "airflow" can have multiple temperaturs. NASA's Chul Park would be a relevant author here.
Title: Re: Starship heat shield
Post by: sebk on 10/13/2022 02:20 pm
Re: loosing tiles. I can't put my finger on it but there has been a NASA paper linked on NSF showing a relationship between radius of curvature and shock stand-off.


Assume the very tippy tip tile on the nose were lost. The radius of curvature would normally be the nose radius. Remove the tile and the radius of curvature that is of interest would be the top edge of the next tile down on the centerline. This edge is sharp and the radius of curvature of the shock front would be correspondingly small. My guess is that there would be some risk of shock impingement where the tile is missing. If the shock does not impinge and the shock stand-off distance small, heat input might be mitigated by any cryo cooling the header tank would give. Then the problem becomes landing propellant loss.


The entire centerline would be a concern with the the (I'm at a loss for the correct word) point towards the bottom of the ogive that is the first point of atmospheric 'contact' being of special concern. Moving away from the centerline, the shock stand-off distance increases and the risk associated with tile loss goes down.


This looks like a map for a backup TPS system, if future experience warrants. All the fiddly shapes, including the fins, makes my brain hurt but there may be a similar map here too. Key point: a backup TPS need not be full sized or of constant thickness.
SS does not enter "nose" first. It enters belly first. All references to "nose radius" in the re-entry literature refer to the curvature of the entering body in its direction of travel. If the tippy-tip TPS falls off, I don't know how to calculate the "radius" of the result. The Starship nose is sticking out toward the side of the plasma flow.
No, please. I understand SS will not reenter nose first. Reread the my post with the assumption of a realistic AoA.

AIUI, SS is intended to reenter with an AoA of ~70deg. This moves the point of first contact from the centerline of the barrel up onto the ogive. At this point there are two radii to consider. Up/down and left/right, and it gets complicated.

At the edge where the tippy tip tile is missing a new up/down radius is introduced along the centerline. Flow will 'flow' over the lip and most likely down to the newly exposed surface. The shock will most probably also make an adjustment around the lip but my dedicated CFD computer is down right now (/s) and I can't tell if there will be any shock impingement. Greatest danger might be the side face of the tile opposite the flow.

Down on the barrel, let's assume an AoA of 90deg. It makes the visualization easier. The shock front is closest along the centerline and compressive force and it's heating are greatest. Surface flow is from the centerline to the sides. Remove one centerline tile.

The compressive forces stay the same but are now on the skin, not a tile. AIUI, the shock front would dimple in at a rate determined by the radius of curvature of the tile edge. Here it gets interesting. With the shock front dimpling in and the missing tile forming a pocket, there may be a Venturi effect with the semi trapped flow excessively heating the adjacent tile edges. This effect decreases as the missing tile distance from the centerline increases.

This is admittedly all a mind experiment. The only number I have is 42, and Elon's already used it on SS.

Actually, on the center-spot (or center line at 90° AoA) behind the stagnation point there would be no local shock even if a tile fell off. The bow shock would be around half a meter away (bow shock standoff is about 1/9 of the radius of the curvature) and behind the shock you have stagnation point, i.e. the point where there's no major air movement. There will be turbulence and stuff (unless things are so smooth the flow is laminar) but they will be subsonic.

But as you'd start moving to the side, you'd start getting air movement again. If you'd move totally to the side you'd actually get supersonic flow (in the order of Mach 2.5 if I remember correctly; I could be badly wrong, though). So somewhere on the side of the barrel, likely at some point between 30° and 60° to the side you actually get supersonic flow behind the bow shock too. So that's the place where there's potential for shock impingement onto the skin if a tile is missing. OTOH heating would be less there, because bow shock standoff is significantly larger back there, and the flow has lower pressure (so it's colder and contains less heat to transfer).

You could (extremely roughly!) think about the skin of the vehicle and bow shock forming a kind of a nozzle through which the stagnation point air expands to escape behind the sides of the reentering vehicle.
The CFD system is still down <g> so I'm trying to use my head and model this one air particle at a time. Again assume a 90deg. AoA for simplicity.


The heatshield is in vacuum so there are no aerodynamics. Then it encounters one particle of air directly on the centerline. The particle hits and that is one tiny bit of compressive heating to both the heatshield and the particle. The energetic particle is now conceptually sharing a frame of reference with the ship and being hot and energetic, rebounds.


A key concept here is 'mean free space' between air particles. As the air gets denser the mean free space goes down and a rebounding particle has an increasing chance of impacting an incoming* particle of air. When a rebounding particle hits an incoming particle a nascent shock wave forms.


That first partial that impacts an incoming particle would bounce back towards the ship and contribute again to compressive heating. The particle it impacted would also rebound and have some chance of hitting yet another incoming particle and the process would cascade. This is all at the stagnation point.


To one side or the other the process would follow this pattern but with a radial component. This is what forms the flow under the shock. Particles are always bleeding in from the shock and adding to the flow. Particles are always piling up and entering the ships frame of reference. This pileup is the shockwave.


Not sure where this is going. Gotta think on it some more. Somebody point me in the right direction if I'm off base.


* Really just unlucky enough to be in the way.


Your understanding is pretty good.

Just few additions:

To actually have a shock formed, its standoff distance must be incomparably larger than the mean free path of air molecules. Otherwise it will be "too blurred", i.e. the variance of actual free paths of actual particles will be too large. Once would hit another just after a millimeter while another would fly freely for half a meter.

So the bigger the reentering object and lower its curvature, the earlier will the shock form. That's why you could have the bow shock of our solar system forming in a gas so rarefied that human scale objects could fly through thousands km per second without forming anything.

Another part is that those molecules will emit thermal photons, i.e. they will lose energy via radiation. And to make things even more interesting depending on their states they may be also absorb or not photons which fly around them.

The interactions are complex, you get multiple blurry layers differing by temperature and actual chemical species present (the temperatures are high enough to cause ionization not to even mention chemical reactions which would be rare in calmer conditions). For example, simplifying air to just nitrox, you'd have O2, N2, O, N, O+, N+, O3-, O3,  various species of NOx, (NO2, N2O4, NO+, N2O, etc...), even some O+2 and N+2, etc...

The net effect is that the bow shock itself is about 8000K hot, but between it and the vehicle nose things get a lot cooler, so the skin could be for example at 1260K.

NB, there's an interesting phenomenon that if the air is rarefied enough that the bow shock doesn't form, you get extremely high temperatures very close to the skin. The effect is that the skin will absorb much higher fraction of the heat when there's no bow shock, than when there's the cushion formed by the bow shock and the layers behind. So for example in Shuttle you'd already get high heating and plasma visible behind the windows while the braking force was like 0.1g or so.

Title: Re: Starship heat shield
Post by: OTV Booster on 10/13/2022 05:44 pm
Re: sebk and one particle at a time.


Yeah, was trying to keep it simple and add complexities one at a time. The early example of a single partial impact is what happens before a bow shock forms. All heating is applied directly to the skin.


I was thinking about the various species. They're there, they're important but ISTM, irrelevant in assessing the flow impact of a missing tile. Thermal and chemical, but not flow.


Something I'm chewing on is charges. That first partial, it's gonna hit hard. Not only will it break apart into constituent atoms, it will also most probably shed an electron or two. In the grand scheme of things charge will be conserved but are there local effects?  If there are, this might affect flow.


You also touched on stand-off distance and shock development. For argument, let's assume particles are evenly distributed and there is no issue with 'mushiness' in the shock structure. At a high mean free space (thin atmosphere) that first secondary impact would stand off quite a bit. From here several things happen simultaneously an I'm unclear on what dominates, and how much everything contributes to shock stand-off throughout reentry.


1) As secondary rebounds increase with decreasing MFS (Mean Free Space) the density of the stagnation gasses increase which would increase the stand-off distance.


2) As the above happens and MFS is decreasing, more particles are interacting with the rebounds, increasing the density (correct word?) and energy of the shock. My first thought is that would press the shock closer but on rethink, I'm not so sure.


3) As velocity bleeds off into denser air the MFS decreases but the MFS itself interacts with the slowing ship such that the TIME between between particle impacts may be lower and the stand-off distance affected. My brain hurts.


You mentioned a tentative mach 2.5 on the stagnation layer velocity. Is this in relation to the ship surface or the surrounding medium? Would it be an overall velocity or differential through its thickness? Slow at the ship and fast at the shock or visa versa? I'm sure it's something you read and half remember, so maybe I'm just being cruel in asking :D
Title: Re: Starship heat shield
Post by: john smith 19 on 10/13/2022 08:07 pm
Re: sebk and one particle at a time.


Yeah, was trying to keep it simple and add complexities one at a time. The early example of a single partial impact is what happens before a bow shock forms. All heating is applied directly to the skin.


I was thinking about the various species. They're there, they're important but ISTM, irrelevant in assessing the flow impact of a missing tile. Thermal and chemical, but not flow.


Something I'm chewing on is charges. That first partial, it's gonna hit hard. Not only will it break apart into constituent atoms, it will also most probably shed an electron or two. In the grand scheme of things charge will be conserved but are there local effects?  If there are, this might affect flow.
"Real gas effects" is the general term for this stuff.  Historically they used a 7 element model for reentry from orbital velocity, about 7900m/s.  At this speed ionization was not considered but you do get dissociation where O2 -> O + O and N2 -> N + N. This absorbs substantial energy and as was noted there is also photon emission. Whether they make to the skin or are aborbed in the gas layer can have significant effects.  Given that temperature is a measure of a particles velocity an O2 "particle" is heavier than an O, so it's temperature will be lower. This is why the early ICBM warhead studies about enormous temperatures (able to melt tungsten for example) were so misleading.

An analytical model for this was developed in the late 50's by Lighhill, but it only dealt with a single gas. This has recently been extended to cope with air. I've added a file on it. It claims to be within 4% of the full calculated solution up to 12000k. Good luck.
Title: Re: Starship heat shield
Post by: Nomadd on 10/21/2022 04:23 am
 I found a 16 square ft. piece of white, 5/8" thick, lined fuzzy insulation that I think is heat tile underlayment. The storm last week was kind enough to blow it onto public land.
 I'm trying to think of a few tests to do.
Title: Re: Starship heat shield
Post by: eriblo on 10/21/2022 09:55 am
The easiest that come to mind (if you have a decent scale) is to weight it to get the density. Soak it in water to see how hydrofilic/fobic it is. Bake it for a bit in an oven - weight changes might be to small to measure but any smoke or changes in texture/color would suggest some organic components/treatments. Repeat water testing after baking.
Obviously: seeing what it takes to melt/burn it.

These results will of course be mostly boring "nothing happens" if it is a good TPS material.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/21/2022 10:43 pm
These results will of course be mostly boring "nothing happens" if it is a good TPS material.
Should be "nothing happens."

If something does then things become more interesting and you'd wonder why SX went with a material that displayed those properties.

But 16Sq Ft is kind of a large thing to be blowing round. So either a)It's really light (like it's mostly air) or b)That storm was very serious  :(

TBH I could believe either.
Title: Re: Starship heat shield
Post by: RamsesBic on 10/22/2022 09:14 am
I have been thinking about the way the TPS tiles are made and how they are attached to the hull.
If I understand the way the tiles are made, they are baked (sintered) with a Y shaped frame on the back that has 3 holes for the studs that are welded to the hull by robots.

So I asked myself why do it in 2 steps? Why not sinter the tile with a frame that already has 3 studs fixed to the frame, no holes needed, then have the robots weld the tile with studs to the hull?

To do that the studs on the tile need to be electrically wired to make the welding possible. Then as much of that wiring as possible could be pulled away (or left in place). I was thinking the frame would include the wires.

I have seen how studs are welded, but I don't know if that can be done while a stud is behind a tile.

If a tile is cracked it will have to be removed as they do now, but the studs have to also be cut off to make place for a new tile.

Just a thought that maybe others can improve...or debunk.
Title: Re: Starship heat shield
Post by: OTV Booster on 10/22/2022 05:06 pm
I have been thinking about the way the TPS tiles are made and how they are attached to the hull.
If I understand the way the tiles are made, they are baked (sintered) with a Y shaped frame on the back that has 3 holes for the studs that are welded to the hull by robots.

So I asked myself why do it in 2 steps? Why not sinter the tile with a frame that already has 3 studs fixed to the frame, no holes needed, then have the robots weld the tile with studs to the hull?

To do that the studs on the tile need to be electrically wired to make the welding possible. Then as much of that wiring as possible could be pulled away (or left in place). I was thinking the frame would include the wires.

I have seen how studs are welded, but I don't know if that can be done while a stud is behind a tile.

If a tile is cracked it will have to be removed as they do now, but the studs have to also be cut off to make place for a new tile.

Just a thought that maybe others can improve...or debunk.
Cabling large enough to carry welding current for the pins would leave holes or gaps in the tiles that would negate the tiles purpose. Leaving the cables in place would create a thermal path to the pins and underlying surface. If the cables stay in place the weight increase would most likely at least double the weight of each tile.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/22/2022 05:36 pm

So I asked myself why do it in 2 steps? Why not sinter the tile with a frame that already has 3 studs fixed to the frame, no holes needed, then have the robots weld the tile with studs to the hull?
AIUI these tiles are designed to be removed from those mouting studs if they need to be replaced.

What you're suggesting would likely weld the tile to the stud, as well as the stud to the hull.

Coming up with a design that only welds the stud to the hull and leaves the actual attachment mechanism undamaged is likely to prove more trouble than any benefits to replacing the current system.

Stud welding in industry is highly automated. Each one taking a few seconds and often done at more than one at a time.
Title: Re: Starship heat shield
Post by: RamsesBic on 10/22/2022 08:57 pm

So I asked myself why do it in 2 steps? Why not sinter the tile with a frame that already has 3 studs fixed to the frame, no holes needed, then have the robots weld the tile with studs to the hull?
AIUI these tiles are designed to be removed from those mouting studs if they need to be replaced.

What you're suggesting would likely weld the tile to the stud, as well as the stud to the hull.

Coming up with a design that only welds the stud to the hull and leaves the actual attachment mechanism undamaged is likely to prove more trouble than any benefits to replacing the current system.

Stud welding in industry is highly automated. Each one taking a few seconds and often done at more than one at a time.

The studs would not be welded to the tile, but be part of the frame just as the holes are now.

When it comes to removing tiles I have noted they drill holes, then use those to break the tile in pieces then they remove the frame that was holding the tile last. With the tiles I am thinking of it would only add one step - grind off 3 studs.

The system I am envisioning would also be automated but instead of just welding studs the robot arm would place the tile, with its 3 built in studs, in its exact position then run the current through the frame on the back which would weld the tips of the studs to the hull, then pick up the next tile and repeat.

What I am not sure about is if to weld any stud there is a minimum thickness of the electrical wire used for the welding? Would it be possible to use the metal of the frame itself as a section of such a wire?

This system would also make it easier to leave all tiling until the ship is fully stacked. Then the robot would run all over the ship in one go. It can be mounted on a frame that can move it vertically and horizontally. Rotating the ship would also help.

The point of doing the tiling last is there will be no need to glue tiles at the junctions between sections the way they must at present. That would leave gluing to the tip of the nose cone and parts of the flaps. Maybe also the perimeter of the tiling surface. (Tiles are glued between sections because there is no way the studs on one side will perfectly aligned with studs on an adjacent section.)

But it all depends on the welding of the studs when installing the tile. If that for some reason can't be done then my idea is dead in the water. The wire needed for the welding has to be narrow enough to fit between any two tiles without causing damage. An alternative is to have 3 holes on the surface of each tile that connects the wires needed to the built in studs. When they have been welded the wire would be removed as the robot arm moves off the tile. Those holes would not be much more than the gaps between tiles - maybe less. They could even be at a slight angle to reduce exposure on reentry. Robots are good at doing that kind of exact movements and accurate placement.

If SpaceX wants to produce a ship every 3 days doing tiles by hand the way they are installed today will be very hard in the long run.
Title: Re: Starship heat shield
Post by: OTV Booster on 10/23/2022 02:04 am

So I asked myself why do it in 2 steps? Why not sinter the tile with a frame that already has 3 studs fixed to the frame, no holes needed, then have the robots weld the tile with studs to the hull?
AIUI these tiles are designed to be removed from those mouting studs if they need to be replaced.

What you're suggesting would likely weld the tile to the stud, as well as the stud to the hull.

Coming up with a design that only welds the stud to the hull and leaves the actual attachment mechanism undamaged is likely to prove more trouble than any benefits to replacing the current system.

Stud welding in industry is highly automated. Each one taking a few seconds and often done at more than one at a time.
IIRC, we've seen a bot welding the pins but I don't think we saw in enough detail to know exactly what technique was being used - or did we?


There was something recent about laser welding but I think that was about the rings. Does anybody have a handle on this?
Title: Re: Starship heat shield
Post by: OTV Booster on 10/23/2022 02:54 am

So I asked myself why do it in 2 steps? Why not sinter the tile with a frame that already has 3 studs fixed to the frame, no holes needed, then have the robots weld the tile with studs to the hull?
AIUI these tiles are designed to be removed from those mouting studs if they need to be replaced.

What you're suggesting would likely weld the tile to the stud, as well as the stud to the hull.

Coming up with a design that only welds the stud to the hull and leaves the actual attachment mechanism undamaged is likely to prove more trouble than any benefits to replacing the current system.

Stud welding in industry is highly automated. Each one taking a few seconds and often done at more than one at a time.

The studs would not be welded to the tile, but be part of the frame just as the holes are now.

When it comes to removing tiles I have noted they drill holes, then use those to break the tile in pieces then they remove the frame that was holding the tile last. With the tiles I am thinking of it would only add one step - grind off 3 studs.

The system I am envisioning would also be automated but instead of just welding studs the robot arm would place the tile, with its 3 built in studs, in its exact position then run the current through the frame on the back which would weld the tips of the studs to the hull, then pick up the next tile and repeat.

What I am not sure about is if to weld any stud there is a minimum thickness of the electrical wire used for the welding? Would it be possible to use the metal of the frame itself as a section of such a wire?

This system would also make it easier to leave all tiling until the ship is fully stacked. Then the robot would run all over the ship in one go. It can be mounted on a frame that can move it vertically and horizontally. Rotating the ship would also help.

The point of doing the tiling last is there will be no need to glue tiles at the junctions between sections the way they must at present. That would leave gluing to the tip of the nose cone and parts of the flaps. Maybe also the perimeter of the tiling surface. (Tiles are glued between sections because there is no way the studs on one side will perfectly aligned with studs on an adjacent section.)

But it all depends on the welding of the studs when installing the tile. If that for some reason can't be done then my idea is dead in the water. The wire needed for the welding has to be narrow enough to fit between any two tiles without causing damage. An alternative is to have 3 holes on the surface of each tile that connects the wires needed to the built in studs. When they have been welded the wire would be removed as the robot arm moves off the tile. Those holes would not be much more than the gaps between tiles - maybe less. They could even be at a slight angle to reduce exposure on reentry. Robots are good at doing that kind of exact movements and accurate placement.

If SpaceX wants to produce a ship every 3 days doing tiles by hand the way they are installed today will be very hard in the long run.
Have you ever looked at a welder? Even the smallest home hobby unit has cables as thick as a finger.


Have you ever used a surface grinder? What you call "only one step" would be no more than an irritation on earth but on orbit or transit to mars this would be a major operation and a space suit devouring risk. Admittedly, a safer specialized grinder could be designed and a robot could do the work but there's no reason to think that SX needs to pivot to another design - yet.


Yes, the tiles and bayonet clips have been a problem. If you've been following this since the first test tiles were installed you'll know that shedding tiles is not as bad as it once was. They need to keep working the problem and refine the design. If they can't make it work they'll look in other directions.
Title: Re: Starship heat shield
Post by: RamsesBic on 10/23/2022 08:34 am

Have you ever looked at a welder? Even the smallest home hobby unit has cables as thick as a finger.


Have you ever used a surface grinder? What you call "only one step" would be no more than an irritation on earth but on orbit or transit to mars this would be a major operation and a space suit devouring risk. Admittedly, a safer specialized grinder could be designed and a robot could do the work but there's no reason to think that SX needs to pivot to another design - yet.


Yes, the tiles and bayonet clips have been a problem. If you've been following this since the first test tiles were installed you'll know that shedding tiles is not as bad as it once was. They need to keep working the problem and refine the design. If they can't make it work they'll look in other directions.

I know that those welding wires are thick (I have done some DIY welding), that is why I am asking those who might know more than me. But don't forget that the gaps between tiles are a few mm (I can only compare the size of the gaps on photos to those of a tile).
My alternative is to use holes in the tiles that connect directly to the studs. Their small size would be of the same order as the gaps and could easily be tested in a lab to show if they would add to the risks.

You mention replacing tiles in space. I would counter that with the cases when workers have had to use crowbars and chisels to remove tiles. Doing that in space will be a challenge to say the least.

I know that the installation of tiles has improved a great deal and am pretty sure they will do fine. But what I was looking at was how to automate and simplify the process (and reduce the number of tiles cracked during installation). SpaceX's tile experts could I am sure find better modifications. This idea I had was just one way. One I think could be used and improved on - that's all. (To SpaceX: if you use it or a variant of it give a donation to some charity)
It might sound like a complicated method, but really is not, and the benefits of removing the need to glue half the glued tiles is not negligible either.

BTW, if the robots used today welded the studs after stacking the ship they would avoid glueing all those tiles at the section junctions. Anyone who has watched the tiling knows using glue takes at least 10 times longer and is pure hell to remove. (I would hate to see an astronaut try using solvents in space to remove the glue behind a tile)
Title: Re: Starship heat shield
Post by: OTV Booster on 10/23/2022 06:58 pm

Have you ever looked at a welder? Even the smallest home hobby unit has cables as thick as a finger.


Have you ever used a surface grinder? What you call "only one step" would be no more than an irritation on earth but on orbit or transit to mars this would be a major operation and a space suit devouring risk. Admittedly, a safer specialized grinder could be designed and a robot could do the work but there's no reason to think that SX needs to pivot to another design - yet.


Yes, the tiles and bayonet clips have been a problem. If you've been following this since the first test tiles were installed you'll know that shedding tiles is not as bad as it once was. They need to keep working the problem and refine the design. If they can't make it work they'll look in other directions.

I know that those welding wires are thick (I have done some DIY welding), that is why I am asking those who might know more than me. But don't forget that the gaps between tiles are a few mm (I can only compare the size of the gaps on photos to those of a tile).
My alternative is to use holes in the tiles that connect directly to the studs. Their small size would be of the same order as the gaps and could easily be tested in a lab to show if they would add to the risks.

You mention replacing tiles in space. I would counter that with the cases when workers have had to use crowbars and chisels to remove tiles. Doing that in space will be a challenge to say the least.

I know that the installation of tiles has improved a great deal and am pretty sure they will do fine. But what I was looking at was how to automate and simplify the process (and reduce the number of tiles cracked during installation). SpaceX's tile experts could I am sure find better modifications. This idea I had was just one way. One I think could be used and improved on - that's all. (To SpaceX: if you use it or a variant of it give a donation to some charity)
It might sound like a complicated method, but really is not, and the benefits of removing the need to glue half the glued tiles is not negligible either.

BTW, if the robots used today welded the studs after stacking the ship they would avoid glueing all those tiles at the section junctions. Anyone who has watched the tiling knows using glue takes at least 10 times longer and is pure hell to remove. (I would hate to see an astronaut try using solvents in space to remove the glue behind a tile)
Absolutely agree that the pin welding would best be done on the stacked ship. Conjecture: the current method is a SpaceX 'good enough' for current testing needs. I haven't been following closely but it appears that barrel fabrication easily outstrips stacking so they weld the pins while the barrels are waiting to stack. That'll change as the fabrication process matures.


They really need at least one launch and EDL attempt before they can have a clue on refinement or pivot to something different. Once they have a better idea of where they're going they'll refine the mounting process. We'll need to keep our eyes open for tile fabrication and installation changes following first launch. Unfortunately, the new factory will hide much (but not all) of what they do.


Your idea on welding cable holes in the tiles kicked off a thought. There has been talk of small holes to allow injection of hydrophobic chemicals. There are latches that are very robust that release easily when pressed by a thin stiff wire. This might be two birds with one stone.


Your idea for welding the pins pre installed on the tiles, is IMO, a non starter for so many reasons. Ignoring the difficulties of the cable size, think of the Y bracket and the three pins as one mostly conductive circuit. If current is applied directly to one pin there is a ground path through the pin to the hull. There is also a ground path from the pin to the Y bracket and on to the other two pins. The powered pin would weld to the hull and the Y bracket and the Y bracket would weld to the other two pins, and those pins would weld to the hull.


If the power is applied directly to the Y bracket it's essentially the same problem with the small advantage that all three pins might do a more even but still shitty weld at both ends. With so many paths and semi gaps it would be impossible to replicate conditions from one weld to the next. No replication, no consistency.


To make the problem worse, all the work is hidden and no visual inspection is possible. And because the Y bracket would be welded to the pins, tile removal would be more difficult than it is now. 


Then there is that thermal blanket underlayment. It would have to be preinstalled and the pins (bayonet clips really) designed to pierce through it with a highly reduced footprint at the contact point. That's bad for weld integrity. The blanket could have holes prepunched to allow passage of the pins with full sized bases. Making that floppy squirmy blanket line up consistently would be another can of worms. Not impossible but definitely a new set of problems.


In the end your pin concept would most likely create more problems than it fixes. It has all the hallmarks of an idea you're in love with and not to be discarded lightly. That happens here. Please, please, think about divorce. It'll be better for the children.


IANARS or a master welder. The opinions expressed above are those of the author and not NSF...
Title: Re: Starship heat shield
Post by: RamsesBic on 10/23/2022 08:48 pm
 ;) Don't worry, I am not fixating on my idea. Just wanted to throw it out there and see if others could make something of it. I just need convincing.

I admit that using the Y frame to assist in leading the current was not that great. The other one with the three holes is better. BTW, the holes would get almost closed during reentry due to tile expansion - they would also release some of the tension.
Can't the welds be tested by measuring conductivity and resistance once the pin is welded? How is it done at present? Is someone checking using X-ray every single stud? (I have never seen it done)

As to making the tile with the pins fixed when it leaves the oven, what would be different compared to the tile leaving it with the 3 holes (in the Y frame)? I am assuming the holes are made of some metal, just as the studs would.

The thermal blankets are needed to reduce vibrations, but they could also be to act as last resort if a tile is lost, I guess. They could be cut to the right size and made part of a tile's back side. Maybe slightly wider to avoid gaps. That would btw replace the need to add those blankets by hand, and having to push them over the studs, which in turn risks bending a stud here or there.

I will stop here. I think I have stated all the points I wanted to make.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/23/2022 09:40 pm

They really need at least one launch and EDL attempt before they can have a clue on refinement or pivot to something different. Once they have a better idea of where they're going they'll refine the mounting process.
A full flight to orbit would shake out a lot of issues.

Your idea on welding cable holes in the tiles kicked off a thought. There has been talk of small holes to allow injection of hydrophobic chemicals. There are latches that are very robust that release easily when pressed by a thin stiff wire. This might be two birds with one stone.
At the back end of the X33 programme the metal tiles were being mounted by (IIRC) 4 screws, 1 at each corner, with a superalloy cap backed by high temperature insulation. However at the very end of one of the reports there were notes about a better proposal. An adaptation of some kind of commercial tool. Very thin head that could slide between the tiles and squeeze some kind of spring that would allow the tile to come off very easily while being very light as well.

Unfortunately that's all I can remember about it.  :( .  IIRC the actual TPS contractor was Rohr, who are (or were) quite big in building parts of ships.
Title: Re: Starship heat shield
Post by: OTV Booster on 10/23/2022 10:22 pm
;) Don't worry, I am not fixating on my idea. Just wanted to throw it out there and see if others could make something of it. I just need convincing.

I admit that using the Y frame to assist in leading the current was not that great. The other one with the three holes is better. BTW, the holes would get almost closed during reentry due to tile expansion - they would also release some of the tension.
Can't the welds be tested by measuring conductivity and resistance once the pin is welded? How is it done at present? Is someone checking using X-ray every single stud? (I have never seen it done)

As to making the tile with the pins fixed when it leaves the oven, what would be different compared to the tile leaving it with the 3 holes (in the Y frame)? I am assuming the holes are made of some metal, just as the studs would.

The thermal blankets are needed to reduce vibrations, but they could also be to act as last resort if a tile is lost, I guess. They could be cut to the right size and made part of a tile's back side. Maybe slightly wider to avoid gaps. That would btw replace the need to add those blankets by hand, and having to push them over the studs, which in turn risks bending a stud here or there.

I will stop here. I think I have stated all the points I wanted to make.
A misconception. The holes will not close on heating. They will enlarge. This is any material. The mean space between molecules becomes greater over the entire object. All dimensions increase.


The current Y bracket, or at least the last one I remember seeing, has three slots for the clips, not holes. The tile can expand over the clips without binding and cracking. If not the Y bracket, some other mechanism is needed to allow for the expansion differences of tile and hull. Three clips without this would lead to failure, most probably of all the tiles.


I was also wondering about how they test clip welds. It may be that they did extensive testing to find the exact setting needed for a good weld and measure current draw during the weld process to point out anomalies. I'm old school enough that I always want to see my work product. Even dogs and cats do it.  :D  This, and every other test I can think of other than imaging of some sort becomes murky through two interfaces (pin to hull and pin to Y bracket).


The thermal blanket is a, well, thermal blanket. It is a backup. TBH, I don't know if there is anything solid on this or if it's NSF lore. AIUI, it also reduces scuffing from vibration as you point out, and it is (speculated? known?) that it puts a bit of springiness behind the tile to keep the pins mechanically loaded, which sorta overlaps on the vibration thing.


Think through the idea of a patchwork thermal blanket a bit larger than a tile. Lay down tile number 1. Assume the intended gap is 5mm. Assume the extra fringe of blanket is 10mm. Lay down tile number 2. Hmm. It overlaps the fringe of tile 1 but it's fringe can only lap on top of tile 1. Ah ha! We can modify the blanket to stay flush on three faces and extend out 10mm on three faces. We now have a tile that can only go on with only one specific orientation. Bummer. It just got more complicated.


Next, picture loosing one tile. Hmmm. The blanket is pinched under three tiles and being held in place but is flapping in the breeze around half its circumference. And why exactly is this a good thing?


To my knowledge, however imperfect, I know if no time a stud was bent while pushing the blanket over them. It looks to be roughly the texture of a dense fiberglass insulation batt.


Really, honest to mergatroid,  cross my heart and pinky promise, welding the pins as you suggest would make it harder, more expensive, and more prone to breakage. Did I mention it wouldn't work?


Are you sure you aren't in love with this idea? I know a good counselor...


In a more serious vein, you're new here. I strongly suggest starting at the beginning of this thread and at least skimming through to see what the discussion has covered. It's a lot to digest but if you're here because you're curious about the topic, you will come away from your reading with a reasonable education on the general issues and the specifics of what SX has has done to address these issues. And you would be doing the rest of us a curtesy by not hammering on something that has already been hammered to death. You haven't done that last. You've hit on something new. Bravo!
Title: Re: Starship heat shield
Post by: Nomadd on 10/23/2022 10:43 pm
 Still not sure what this stuff is, but it held back two minutes of butane fury without getting warm on the far side.
 The metalic film didn't last long, but the stuffing seemed kind of ablative.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 10/23/2022 11:24 pm
Still not sure what this stuff is, but it held back two minutes of butane fury without getting warm on the far side.
 The metalic film didn't last long, but the stuffing seemed kind of ablative.

Butane torch goes to something like 1400degC.

I don't think a mineral wool like Superwool is ablative.  That makes this stuff better than Superwool.

A super high temperature version of something like Nomex?  It can't be organic, the molecular bonds can't be made strong enough.
Title: Re: Starship heat shield
Post by: RamsesBic on 10/23/2022 11:29 pm
;) Don't worry, I am not fixating on my idea. Just wanted to throw it out there and see if others could make something of it. I just need convincing.

I admit that using the Y frame to assist in leading the current was not that great. The other one with the three holes is better. BTW, the holes would get almost closed during reentry due to tile expansion - they would also release some of the tension.
Can't the welds be tested by measuring conductivity and resistance once the pin is welded? How is it done at present? Is someone checking using X-ray every single stud? (I have never seen it done)

As to making the tile with the pins fixed when it leaves the oven, what would be different compared to the tile leaving it with the 3 holes (in the Y frame)? I am assuming the holes are made of some metal, just as the studs would.

The thermal blankets are needed to reduce vibrations, but they could also be to act as last resort if a tile is lost, I guess. They could be cut to the right size and made part of a tile's back side. Maybe slightly wider to avoid gaps. That would btw replace the need to add those blankets by hand, and having to push them over the studs, which in turn risks bending a stud here or there.

I will stop here. I think I have stated all the points I wanted to make.
A misconception. The holes will not close on heating. They will enlarge. This is any material. The mean space between molecules becomes greater over the entire object. All dimensions increase.


The current Y bracket, or at least the last one I remember seeing, has three slots for the clips, not holes. The tile can expand over the clips without binding and cracking. If not the Y bracket, some other mechanism is needed to allow for the expansion differences of tile and hull. Three clips without this would lead to failure, most probably of all the tiles.


I was also wondering about how they test clip welds. It may be that they did extensive testing to find the exact setting needed for a good weld and measure current draw during the weld process to point out anomalies. I'm old school enough that I always want to see my work product. Even dogs and cats do it.  :D  This, and every other test I can think of other than imaging of some sort becomes murky through two interfaces (pin to hull and pin to Y bracket).


The thermal blanket is a, well, thermal blanket. It is a backup. TBH, I don't know if there is anything solid on this or if it's NSF lore. AIUI, it also reduces scuffing from vibration as you point out, and it is (speculated? known?) that it puts a bit of springiness behind the tile to keep the pins mechanically loaded, which sorta overlaps on the vibration thing.


Think through the idea of a patchwork thermal blanket a bit larger than a tile. Lay down tile number 1. Assume the intended gap is 5mm. Assume the extra fringe of blanket is 10mm. Lay down tile number 2. Hmm. It overlaps the fringe of tile 1 but it's fringe can only lap on top of tile 1. Ah ha! We can modify the blanket to stay flush on three faces and extend out 10mm on three faces. We now have a tile that can only go on with only one specific orientation. Bummer. It just got more complicated.


Next, picture loosing one tile. Hmmm. The blanket is pinched under three tiles and being held in place but is flapping in the breeze around half its circumference. And why exactly is this a good thing?


To my knowledge, however imperfect, I know if no time a stud was bent while pushing the blanket over them. It looks to be roughly the texture of a dense fiberglass insulation batt.


Really, honest to mergatroid,  cross my heart and pinky promise, welding the pins as you suggest would make it harder, more expensive, and more prone to breakage. Did I mention it wouldn't work?


Are you sure you aren't in love with this idea? I know a good counselor...


In a more serious vein, you're new here. I strongly suggest starting at the beginning of this thread and at least skimming through to see what the discussion has covered. It's a lot to digest but if you're here because you're curious about the topic, you will come away from your reading with a reasonable education on the general issues and the specifics of what SX has has done to address these issues. And you would be doing the rest of us a curtesy by not hammering on something that has already been hammered to death. You haven't done that last. You've hit on something new. Bravo!

I have been following for over 2 years. I just don't jump in that often.
Title: Re: Starship heat shield
Post by: Thrustpuzzle on 10/24/2022 01:19 am
At the back end of the X33 programme the metal tiles were being mounted by (IIRC) 4 screws, 1 at each corner, with a superalloy cap backed by high temperature insulation. However at the very end of one of the reports there were notes about a better proposal. An adaptation of some kind of commercial tool. Very thin head that could slide between the tiles and squeeze some kind of spring that would allow the tile to come off very easily while being very light as well.
Unfortunately that's all I can remember about it.  :( .  IIRC the actual TPS contractor was Rohr, who are (or were) quite big in building parts of ships.
Your memory was exactly on point both on the mounting description and the proposal for improved versions. This is the report (https://www.researchgate.net/publication/255921834_Development_of_metallic_thermal_protection_systems_for_the_reusable_launch_vehicle) you were thinking of.

Quote
The most innovative and effective modification, however, is the use of quick release fasteners.   The fastener uses a simple wire clip that snaps into a groove of a stud attached to the structure.  The fastener is released by sliding a special “scissors-like” tool into the gap between panels and squeezing the ends of the wire together.  A thin slot or notch in the gap cover allows the tool to be inserted into the gap.  When the panels heat up and expand the gaps begin to close and the slots slide over the adjacent panels.  This fastener concept has no loose parts, is quick and simple to operate, and eliminates the costly and troublesome fastener access tubes  and  covers.
Title: Re: Starship heat shield
Post by: chopsticks on 10/24/2022 02:57 am


Still not sure what this stuff is, but it held back two minutes of butane fury without getting warm on the far side.
 The metalic film didn't last long, but the stuffing seemed kind of ablative.

Which side is the back side here? Does the other side have the same metallic film or is it just fluffy?
Title: Re: Starship heat shield
Post by: Nomadd on 10/24/2022 05:20 am


Still not sure what this stuff is, but it held back two minutes of butane fury without getting warm on the far side.
 The metalic film didn't last long, but the stuffing seemed kind of ablative.

Which side is the back side here? Does the other side have the same metallic film or is it just fluffy?
Just fluffy. There's some extremely fine powder coming out when it's abused. I decided to keep it in a plastic bag and take precautions when I handle or torture it.

 It's probably just coincidence that I developed the ability to shoot flames from my eyes after I touched it.
Title: Re: Starship heat shield
Post by: livingjw on 10/24/2022 01:44 pm


Still not sure what this stuff is, but it held back two minutes of butane fury without getting warm on the far side.
 The metalic film didn't last long, but the stuffing seemed kind of ablative.

Which side is the back side here? Does the other side have the same metallic film or is it just fluffy?
Just fluffy. There's some extremely fine powder coming out when it's abused. I decided to keep it in a plastic bag and take precautions when I handle or torture it.

 It's probably just coincidence that I developed the ability to shoot flames from my eyes after I touched it.

Any sign that it was "needled" into a blanket or just straight mat?

John
Title: Re: Starship heat shield
Post by: Nomadd on 10/24/2022 04:09 pm
Any sign that it was "needled" into a blanket or just straight mat?
John
Straight mat.
Title: Re: Starship heat shield
Post by: john smith 19 on 10/25/2022 07:02 pm
Still not sure what this stuff is, but it held back two minutes of butane fury without getting warm on the far side.
 The metalic film didn't last long, but the stuffing seemed kind of ablative.
A quick check says butane combustion can hit 1430c/2606F.  Not bad as a 1 shot emergancy tactic to get back to the surface.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 10/25/2022 08:34 pm
Still not sure what this stuff is, but it held back two minutes of butane fury without getting warm on the far side.
 The metalic film didn't last long, but the stuffing seemed kind of ablative.

I'm surprised, it doesn't act like Saffil or Superwool:

https://www.youtube.com/watch?v=m9gjcnc6IAw
Title: Re: Starship heat shield
Post by: RamsesBic on 10/25/2022 08:48 pm
Still not sure what this stuff is, but it held back two minutes of butane fury without getting warm on the far side.
 The metalic film didn't last long, but the stuffing seemed kind of ablative.

I'm surprised, it doesn't act like Saffil or Superwool:

https://www.youtube.com/watch?v=m9gjcnc6IAw

I find it odd that he uses the torch at a short distance and concentrated on one point when blasting the steel, but at 3 times the distance and moving in circles for the matt. I would have liked him to show what happens if it is given the same treatment as the steel. I would have to guess the result would not be as impressive or he would have. (But it shows anyway that such materials are good insulators)
Title: Re: Starship heat shield
Post by: eriblo on 10/25/2022 09:17 pm
Yes, Superwool Plus has a classification temperature of 1200°C and the HT version is 1300°C so it might be able to just about handle the melting point of the steel - but the torch is quite a bit hotter than that. He has to move it quickly as the felt is made of thin fibres and the bulk density of the steel is 50x - 100x larger.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 10/25/2022 10:26 pm
Yes, Superwool Plus has a classification temperature of 1200°C and the HT version is 1300°C so it might be able to just about handle the melting point of the steel - but the torch is quite a bit hotter than that. He has to move it quickly as the felt is made of thin fibres and the bulk density of the steel is 50x - 100x larger.

I was hoping to find a superwool/saffil "test with a torch" that showed what failure looked like to see if it mirrored what @Nomadd got, but haven't found one.

In this video the hand below the pad contraindicates testing to failure.
Title: Re: Starship heat shield
Post by: Nomadd on 10/25/2022 11:56 pm
 I'm starting to lean toward the stuff I found being cryo insulation from the tower. I see some blowing loose up there and the sheet was about the right width to wrap around the big lines.

https://youtu.be/wxDI5AyUDPs
Title: Re: Starship heat shield
Post by: john smith 19 on 10/26/2022 07:13 pm
Yes, Superwool Plus has a classification temperature of 1200°C and the HT version is 1300°C so it might be able to just about handle the melting point of the steel - but the torch is quite a bit hotter than that. He has to move it quickly as the felt is made of thin fibres and the bulk density of the steel is 50x - 100x larger.
IIRC Saffill is rated up to 1600c. Unfortunately no one seems to be able to weave it (or maybe no one has ever tried?) Normally used as a felt or batting.

Saffil was designed to replace Asbestos (without killing people). In the 50's there was a certain amount of work on fiber reinforced phenolic composite ("Durestos"). Asbestos was stiffer than glass fibre (not sure if Saffil is or not).

There are some ways the operating temperature of polymers could be pushed above 500c, but that's another conversation.
Title: Re: Starship heat shield
Post by: Taxidermista on 11/16/2022 09:54 pm
I was hoping to find in this thread some discussion about the recently tested LOFTID inflatable shield and the feasibility of a future application on a Starship but surprisingly couldn't find any. Is that option an unreasonable one?
Title: Re: Starship heat shield
Post by: adrianwyard on 11/16/2022 11:06 pm
It's hard to see how something like LOFTID could be made 'rapidly reusable', so is not a good fit for Starship as currently conceived. It will have its uses though, I'm sure.
Title: Re: Starship heat shield
Post by: Nomadd on 11/28/2022 02:09 am
 A couple of fin fairings and a piece of something that I'm not sure about sitting out back.
Title: Re: Starship heat shield
Post by: RamsesBic on 11/28/2022 10:15 am
A couple of fin fairings and a piece of something that I'm not sure about sitting out back.

It looks like the frames of the tiles stick out on the sides.
Title: Re: Starship heat shield
Post by: edzieba on 11/28/2022 10:46 am
That would likely be how the rails are inserted after sintering - rather than needing the rails to survive sintering furnace temperatures without deformation inside the tile preforms. The tiles are quite friable, so little mechanical force would be needed to push them in without any prior milling of channels.
How to get through the Borosilicate glass coating without fracturing it would be the tricky bit. Could be a hairline gap masked off during the glass application process, could be a milled slot in just the glass layer to allow insertion, or very careful insertion right through the unmodified glass layer to avoid spreading cracks.
Title: Re: Starship heat shield
Post by: BT52 on 11/28/2022 11:04 am
Agree with u. This is done mechanically. Sharp  and good  fixture. Depends how brittle material is really.

Or less likely. During suntering there are preinstalled ceramic inserts before baking process. Those are removed atfer coating. Or are even pull out with steel profile that goes inside as we see from picture.
Title: Re: Starship heat shield
Post by: RamsesBic on 11/28/2022 11:16 am
That would likely be how the rails are inserted after sintering - rather than needing the rails to survive sintering furnace temperatures without deformation inside the tile preforms. The tiles are quite friable, so little mechanical force would be needed to push them in without any prior milling of channels.
How to get through the Borosilicate glass coating without fracturing it would be the tricky bit. Could be a hairline gap masked off during the glass application process, could be a milled slot in just the glass layer to allow insertion, or very careful insertion right through the unmodified glass layer to avoid spreading cracks.

After watching tiles being cracked and removed, the frames many times are the last to be romoved and are Y-shaped. Can't see how you can insert a Y-shaped frame after sintering.
Title: Re: Starship heat shield
Post by: edzieba on 11/28/2022 11:20 am
That would likely be how the rails are inserted after sintering - rather than needing the rails to survive sintering furnace temperatures without deformation inside the tile preforms. The tiles are quite friable, so little mechanical force would be needed to push them in without any prior milling of channels.
How to get through the Borosilicate glass coating without fracturing it would be the tricky bit. Could be a hairline gap masked off during the glass application process, could be a milled slot in just the glass layer to allow insertion, or very careful insertion right through the unmodified glass layer to avoid spreading cracks.

After watching tiles being cracked and removed, the frames many times are the last to be romoved and are Y-shaped. Can't see how you can insert a Y-shaped frame after sintering.
One arm at a time, meeting in the centre. The frames are what are retained by the clip pins, so tiles that have fractured are easier to remove 'around' the mounted frame, which will hold to the clip pins all on its own. Whole tiles being removed have holes drilled to access the pins, which are than released from the frame internally and the whole tile assembly removed.
Title: Re: Starship heat shield
Post by: Nomadd on 11/28/2022 11:52 am
A couple of fin fairings and a piece of something that I'm not sure about sitting out back.

It looks like the frames of the tiles stick out on the sides.

The frames use to be shorter and completely buried. They were where most of the ones I saw failed.
They were three separate pieces instead of Ys originally. I'm not sure about these.
Title: Re: Starship heat shield
Post by: Tangilinear Interjar on 11/29/2022 03:01 pm
Regarding the visible mounting support in those tiles; my money is on there being a standard sintered tile part that's probably the exact size of the main hex tiles. That component is either coated and baked to make a standard tile or it's machined to a smaller size or different shape for the other tiles as a secondary process before being coated and baked.

These particular tiles are small enough that the metal was cut exposed on the edges and for whatever reason the glass coating doesn't adhere to the metal well.

From a manufacturability perspective having a single high production process that makes all the tile blanks and then customizing just a few makes the most sense.

As for the little bit of exposed metal, I doubt that it matters considering where it is and that it's edge on.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 11/29/2022 04:49 pm
As for the little bit of exposed metal, I doubt that it matters considering where it is and that it's edge on.

Stainless steel can handle the temperatures the tile requires without melting (1250degC).

That temperature does dramatically reduce SS strength - permanently.  But a lot of strength is not needed, the tiles are already extremely fragile.

So exposed metal doesn't matter much.
Title: Re: Starship heat shield
Post by: edzieba on 11/30/2022 09:39 am
Regarding the visible mounting support in those tiles; my money is on there being a standard sintered tile part that's probably the exact size of the main hex tiles. That component is either coated and baked to make a standard tile or it's machined to a smaller size or different shape for the other tiles as a secondary process before being coated and baked.

These particular tiles are small enough that the metal was cut exposed on the edges and for whatever reason the glass coating doesn't adhere to the metal well.

From a manufacturability perspective having a single high production process that makes all the tile blanks and then customizing just a few makes the most sense.

As for the little bit of exposed metal, I doubt that it matters considering where it is and that it's edge on.
From the FDEP report on the tile manufacturing facility: The tile billets are moulded, then sintered, then cut in half face-to-face or back-to-back (i.e. billets are double-thickness), then trimmed to size, then the RCG coating is applied (with further heating).
Title: Re: Starship heat shield
Post by: equiserre on 11/30/2022 09:44 pm
A couple of fin fairings and a piece of something that I'm not sure about sitting out back.

Great photos, Nomadd! the fin fairing tiles seem to be of a completely different design from the main body tiles?  And no red adhesive is to be seen. Can someone sum up what they are and how are they attached?
Title: Re: Starship heat shield
Post by: edzieba on 12/01/2022 08:04 am
A couple of fin fairings and a piece of something that I'm not sure about sitting out back.

Great photos, Nomadd! the fin fairing tiles seem to be of a completely different design from the main body tiles?  And no red adhesive is to be seen. Can someone sum up what they are and how are they attached?
SpaceX switched from red RTV to white some months ago (either a switch in formulation, or just a big enough order they could request a different pigment). They've also gotten better at applying it without as much smear.
Title: Re: Starship heat shield
Post by: su27k on 12/24/2022 03:03 am
Not sure if this has been posted before or not, old news from 2021, seems likely this is related to Starship heat shield: SpaceX wins Air Force manufacturing research contract for hypersonic vehicle thermal shields (https://spacenews.com/spacex-wins-air-force-manufacturing-research-contract-for-hypersonic-vehicle-thermal-shields/)

Quote from: SpaceNews
The Air Force Research Laboratory awarded SpaceX an $8.5 million contract to investigate advanced materials and manufacturing techniques for heat shields that protect hypersonic vehicles in flight.

Heat protection is a critical technology to shield hypersonic vehicles from the intense heat experienced when flying at more than five times the speed of sound.

The contract was from the AFRL Materials and Manufacturing Directorate for a project called “multipurpose thermal protection systems for hypersonics.”

Anyway, AFRL has recently extended the contract (Award ID FA865021C5253) to add an additional $8M for "Multipurpose Thermal Protection Systems for Hypersonics Add Work"
Title: Re: Starship heat shield
Post by: FutureSpaceTourist on 12/29/2022 04:46 am
twitter.com/drchriscombs/status/1608207918310252544

Quote
Notice how w each iteration we see a higher % of tiles that are a custom fit to their unique location. Was probably inevitable

I know they wanted to simplify things but I’ve got a feeling the tile layout is basically gonna look like the shuttle when it’s done #starship #SpaceX

https://twitter.com/drphiltill/status/1608236249386717184

Quote
Having worked on and around Space shuttle tiles, I can tell you there’s a thing known as “step and gap” (important for laminar flow and heat transfer), and the tiles in this picture don’t yet demonstrate mastery of that topic (to say the least).

twitter.com/stuck4ger/status/1608280328187133952

Quote
Isn’t Starships’s reentry AOA around 60 deg (2X the Shuttle)? Are step inconsistencies as important at those extreme alphas? I was told Soviet fighters had much worse surface tolerances than American fighters because they didn’t see the need to over design for the mission.

https://twitter.com/drphiltill/status/1608291129451069440

Quote
I don’t know. I agree that their requirements are likely a lot different.
Title: Re: Starship heat shield
Post by: meekGee on 12/29/2022 07:06 pm
I thought that because SS is not a rigid structure, gaps are inevitable and not as controlled as they were in Shuttle.

There was something a year or so ago about part of the mitigation being the hexagonal shape, since it discouraged plasma flow in the gaps.  Also the Stainless skin of course.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 12/30/2022 05:27 pm
An interesting paper on gaps in heat shields, via numerical simulation:

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0117012 (https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0117012)

Some interesting quotes:

Quote
Heat flux ratio in the gap decreases as Mach number increases, because the boundary layer tends to be thinner and air flowing into the gap decreases as Mach number increases.

The faster you go the more gap you can have (by a few mm)

Quote
The heat flux ratio is basically U-shaped distribution along the surface of a gap.

The axis being vertical: heat flux ratio to a standard flat surface, and horizontal: the length along the gap. Note at higher mach numbers there's a bigger spike but in the gap the heat decreases. Post gap there's a heat increase but it's not a square function.

Note his is for flat surfaces.  The complexities of flows around the flaperons is probably why they fill in the gaps in those areas.

Quote
Thus, setting chamfer in the windward can reduce the gap effect coefficient, which is a valid method for reducing the gap local aerodynamic heating environment.

I can't recall, are the edges of the tiles chamfered?

TL;DR - the gaps in the main body are fine.  Any refinement is due to updated CFD modeling, which SpaceX is a world class expert at.
Title: Re: Starship heat shield
Post by: eriblo on 12/30/2022 06:38 pm
My understanding is that the Orbiters were as smooth as possible to delay the boundary layer tripping from laminar flow to turbulent as long as possible (in both time and space).

This can decrease the peak temperature and total heat load for the flat surfaces downstream of the stagnation points along the nose and leading edges.

Starship currently has the same TPS design on the whole surface (the exception being small radii and compound curvatures). This suggest that it is overkill with regard to the increased heat transport from surface irregularities.

The Starship architecture as a whole is of course not quite as sensitive to a (initially?) slightly less mass optimized heat shield...
Title: Re: Starship heat shield
Post by: InterestedEngineer on 01/13/2023 08:03 am
Quote
https://twitter.com/ringwatchers/status/1613691353472405504

Before/after pics of black paint being added.

Black paint can change stainless steel's Stefan Boltzman emission constant from 0.35 to 0.98 or so, so 2.5x more watts emitted per unit area.

Which adds margin for any area that is exposed to moderate amounts of reentry heat.
Title: Re: Starship heat shield
Post by: Oersted on 01/14/2023 10:47 am
Open question: would each and every tile carry an RFID chip (or similar) to help identify problems during the upcoming orbital mission? Could be helpful to see if/when and where tiles come off during all phases of the flight.
Title: Re: Starship heat shield
Post by: eriblo on 01/15/2023 01:54 pm
Open question: would each and every tile carry an RFID chip (or similar) to help identify problems during the upcoming orbital mission? Could be helpful to see if/when and where tiles come off during all phases of the flight.
There might be RFID tags that can survive the temperatures involved but I think it would require quite a bit of work. It would also be tricky to read them as they are mounted on a curved metal surface.

Other options would be a wire/fiber optic mesh behind the insulation as well as cameras inside the tanks or mounted on the flaps.

I think the only TPS related sensors we have seen are the handfull of likely temperature sensors mounted on the ventral side of the nose cone/payload bay.

One thing I could see on the first flight is a simple free flying or tethered 360 camera deployed from the aft skirt after SECO. There has been talk of something like that on Polaris Dawn and it should require a minimum of effort.
Title: Re: Starship heat shield
Post by: Slothman on 01/15/2023 06:05 pm
Open question: would each and every tile carry an RFID chip (or similar) to help identify problems during the upcoming orbital mission? Could be helpful to see if/when and where tiles come off during all phases of the flight.
There might be RFID tags that can survive the temperatures involved but I think it would require quite a bit of work. It would also be tricky to read them as they are mounted on a curved metal surface.

Other options would be a wire/fiber optic mesh behind the insulation as well as cameras inside the tanks or mounted on the flaps.

I think the only TPS related sensors we have seen are the handfull of likely temperature sensors mounted on the ventral side of the nose cone/payload bay.

One thing I could see on the first flight is a simple free flying or tethered 360 camera deployed from the aft skirt after SECO. There has been talk of something like that on Polaris Dawn and it should require a minimum of effort.

I mean.. it would be significantly difficult to read RFID chips in flight, which is apparently where the question was going, talking about detecting *when* tiles fall off, meaning having a constant connection to each tile. That's just insane. You would need a reader probably under the tiles or inside the barrel every couple inches.

At most I could imagine a 1-wire detection circuit per tile but even that is way overkill for a reusable starship.
Title: Re: Starship heat shield
Post by: meekGee on 01/15/2023 06:29 pm
Open question: would each and every tile carry an RFID chip (or similar) to help identify problems during the upcoming orbital mission? Could be helpful to see if/when and where tiles come off during all phases of the flight.
I think much can be learned using IR cameras looking at the inside of the skin.

To elaborate:

Because of the aspect ratio of the skin, temperature variations on the outside will imprint nicely on the inside.  Not exactly 1:1 but with some modeling you can reconstruct exactly what's happening on the outside, including tile temperature, plasma flow between tiles, etc.

You will know what happened at each location, and when, and the recording continues even as tiles fail, all the way until the vehicle fails.

And you'll even have a record of that, which will be so awesome. (With stainless, it might actually glow before failing)
Title: Re: Starship heat shield
Post by: DanClemmensen on 01/15/2023 06:49 pm
Open question: would each and every tile carry an RFID chip (or similar) to help identify problems during the upcoming orbital mission? Could be helpful to see if/when and where tiles come off during all phases of the flight.
I do not know of an RF system that could operate "over the air" near a big stainless steel tank. There might conceivably be a way to use some sort of skin effect to transmit along the surface of the tank. A network of thousands of these would be a challenge. the bigger question is "why?". Addition of the tranceiver and sensors to the tile would change its physical characteristics, probably making it more delicate and less insulating, not to mention being a manufacturing nightmare.
Title: Re: Starship heat shield
Post by: BT52 on 01/15/2023 07:09 pm
I think temp probes (or cameras  inside tank  as from AA video WHERE Musk mentioned it as possibility) and raw TELESCOPE video analysis are enough  of indication. And same goes for both ascent and descend ofc. 

If u lose tile at ascent and descent both are viable test situations worth to test it. And its effects i.e. hot spots will be seen indirectly via temperature at ship tank skin anyway. At ascent u will not seen immediately necessary  but at orbit they  will definitely took its look how many tiles they lost IMO
Title: Re: Starship heat shield
Post by: OTV Booster on 01/15/2023 08:45 pm
Open question: would each and every tile carry an RFID chip (or similar) to help identify problems during the upcoming orbital mission? Could be helpful to see if/when and where tiles come off during all phases of the flight.
There might be RFID tags that can survive the temperatures involved but I think it would require quite a bit of work. It would also be tricky to read them as they are mounted on a curved metal surface.

Other options would be a wire/fiber optic mesh behind the insulation as well as cameras inside the tanks or mounted on the flaps.

I think the only TPS related sensors we have seen are the handfull of likely temperature sensors mounted on the ventral side of the nose cone/payload bay.

One thing I could see on the first flight is a simple free flying or tethered 360 camera deployed from the aft skirt after SECO. There has been talk of something like that on Polaris Dawn and it should require a minimum of effort.

I mean.. it would be significantly difficult to read RFID chips in flight, which is apparently where the question was going, talking about detecting *when* tiles fall off, meaning having a constant connection to each tile. That's just insane. You would need a reader probably under the tiles or inside the barrel every couple inches.

At most I could imagine a 1-wire detection circuit per tile but even that is way overkill for a reusable starship.
I've brought this up in the past and gotten no traction. Acustic sensing. It probably wouldn't work when the main engines are firing but otherwise a network of mic's and some serious DSP's behind them could conceivably localize to individual tiles and with a good signal library, pin down what happened.


We've all heard how that hull rings when beaten by a hammer. It transmits sounds quite well. Every material has a characteristic acoustic signature. I doubt there is anything on the starship that would sound like a cracking tile except... a cracking tile. There is a lot of other noise but that's what DSP's are for. They pull small signal out of big noise.


Cracking is only one failure mode and even it has subcategories. How fine a discrimination is possible is an open question but at a gross level of tagging failures, I think it would work.


Any sonar operators out there? :D
Title: Re: Starship heat shield
Post by: Oersted on 01/16/2023 06:11 am
Tile detachment detection with that kind of granularity would primarily be for the initial test flights. Hopefully wouldn't be needed on a mature launch system.
Title: Re: Starship heat shield
Post by: Asteroza on 01/16/2023 06:33 am
Tile detachment detection with that kind of granularity would primarily be for the initial test flights. Hopefully wouldn't be needed on a mature launch system.

Why not, in the case of advanced vehicle health management being a normal thing? Knowing you have a busted tile provides at least a chance to deal with it, if you have a means to do so...
Title: Re: Starship heat shield
Post by: Oersted on 01/16/2023 09:04 am
Just a resource and construction issue. Pretty normal to have highly instrumented experimental vehicles and production vehicles less so.
Title: Re: Starship heat shield
Post by: NH22077 on 01/16/2023 07:06 pm
Open question: would each and every tile carry an RFID chip... Snip
There might be RFID tags that can survive the temperatures... Snip

One thing I could see on the first flight is a simple free flying or tethered 360 camera deployed from the aft skirt after SECO....
Snip
I've brought this up in the past and gotten no traction. Acustic sensing. It probably wouldn't work when the main engines are firing but otherwise a network of mic's and some serious DSP's behind them could conceivably localize to individual tiles and with a good signal library, pin down what happened.

We've all heard how that hull rings when beaten by a hammer. It transmits sounds quite well. Every material has a characteristic acoustic signature. I doubt there is anything on the starship that would sound like a cracking tile except... a cracking tile. There is a lot of other noise but that's what DSP's are for. They pull small signal out of big noise.

Cracking is only one failure mode and even it has subcategories. How fine a discrimination is possible is an open question but at a gross level of tagging failures, I think it would work.

Any sonar operators out there? :D


Phill,
  Not a sonar op, but a live sound engineer.
The DSP will need to know what tiles cracking while the vehicle is at hypersonic velocity sounds like. Which would require a full size vehicle. Put into a supersonic wind tunnel to get the data the DSP will require. They might get away with putting the top 1/3 of a SS. Nosecone flaps & a straight ring or 2 under it. With the bottom wielded shut with a circular plate.
  And do the same with engine section and lower flaps with the top sealed, the engine skirt open. 
   The problem is I have never heard of a supersonic wind tunnel big enough. And using a 1/10 scale model would sound different. Maybe they could extrapolate the tonal differences. I don't know.

eriblo, I like the idea of deploying a cubesat or two with cameras.

Ned

Title: Re: Starship heat shield
Post by: edzieba on 01/17/2023 11:12 am
Not necessary to know the actual sound, but a calibration session would be noted applying some test sound (ideally an impulse. A hammer would not be unreasonable) in known locations to allow the time difference and reflections recorded by the transducers to be mapped to physical locations. This is a hobby-level operation, many people have DIYed touch-sensitive objects by applying contact mics to objects and calibrating desired interaction areas. It's also something SpaceX themselves have done, using the accelerometers on board CRS-7 as contact mics in order to localise the strut failure.
Acoustic monitoring would give you a map of tile events, through it would not provide information of why a given tile failed without more localised instrumentation (e.g. temperature probes, strain gauges on tile pins, etc). Remote sensing from the test range equipment would only provide exterior temperatures (which can be mapped to flow discontinuities too) but not temperatures of components beneath the surface. Though both would give a map of likely tile loss areas in order to more accurately target future instrumentation installations.
Title: Re: Starship heat shield
Post by: Tangilinear Interjar on 01/17/2023 03:18 pm
Y'all are making a pretty big assumption that one of these very light weight, super insulated tiles with a veeeery thin glass layer, and is as isolated from the ship as possible (in most places) with a layer of fluffy insulation that probably works as a pretty good acoustic insulator as well, will actually make much sound at all when it cracks.

I'd be very surprised if the breaking sound signature was even within 20 dB of the ambient background noise.
Title: Re: Starship heat shield
Post by: edzieba on 01/17/2023 05:13 pm
Y'all are making a pretty big assumption that one of these very light weight, super insulated tiles with a veeeery thin glass layer, and is as isolated from the ship as possible (in most places) with a layer of fluffy insulation that probably works as a pretty good acoustic insulator as well, will actually make much sound at all when it cracks.

I'd be very surprised if the breaking sound signature was even within 20 dB of the ambient background noise.
Maybe not the sound of a tile breaking, but the sound of the metal insert within a tile rattling around on or tearing off the metal (and welded directly to the skin) mounting pegs will. A cracked tile that remain in place and otherwise in large chunks is likely still mostly effective as TPS (once the vehicle decelerates enough for airflow to slow enough for it to fall off, its done its job) but a tile that fails so catastrophically that it affects TPS effectiveness is of more interest for that sort of vehicle-did-not-survive telemetry.
Title: Re: Starship heat shield
Post by: OTV Booster on 01/17/2023 06:30 pm
Open question: would each and every tile carry an RFID chip... Snip
There might be RFID tags that can survive the temperatures... Snip

One thing I could see on the first flight is a simple free flying or tethered 360 camera deployed from the aft skirt after SECO....
Snip
I've brought this up in the past and gotten no traction. Acustic sensing. It probably wouldn't work when the main engines are firing but otherwise a network of mic's and some serious DSP's behind them could conceivably localize to individual tiles and with a good signal library, pin down what happened.

We've all heard how that hull rings when beaten by a hammer. It transmits sounds quite well. Every material has a characteristic acoustic signature. I doubt there is anything on the starship that would sound like a cracking tile except... a cracking tile. There is a lot of other noise but that's what DSP's are for. They pull small signal out of big noise.

Cracking is only one failure mode and even it has subcategories. How fine a discrimination is possible is an open question but at a gross level of tagging failures, I think it would work.

Any sonar operators out there? :D


Phill,
  Not a sonar op, but a live sound engineer.
The DSP will need to know what tiles cracking while the vehicle is at hypersonic velocity sounds like. Which would require a full size vehicle. Put into a supersonic wind tunnel to get the data the DSP will require. They might get away with putting the top 1/3 of a SS. Nosecone flaps & a straight ring or 2 under it. With the bottom wielded shut with a circular plate.
  And do the same with engine section and lower flaps with the top sealed, the engine skirt open. 
   The problem is I have never heard of a supersonic wind tunnel big enough. And using a 1/10 scale model would sound different. Maybe they could extrapolate the tonal differences. I don't know.

eriblo, I like the idea of deploying a cubesat or two with cameras.

Ned
With an array of mic's it should be possible to pin down the physical source of transients. Combined with high speed video/LiDAR would that be enough to start building a library?


Would the tile-bracket-pins-hull acoustic path give a signal independent of external atmospherics?
Title: Re: Starship heat shield
Post by: OTV Booster on 01/17/2023 06:40 pm
Not necessary to know the actual sound, but a calibration session would be noted applying some test sound (ideally an impulse. A hammer would not be unreasonable) in known locations to allow the time difference and reflections recorded by the transducers to be mapped to physical locations. This is a hobby-level operation, many people have DIYed touch-sensitive objects by applying contact mics to objects and calibrating desired interaction areas. It's also something SpaceX themselves have done, using the accelerometers on board CRS-7 as contact mics in order to localise the strut failure.
Acoustic monitoring would give you a map of tile events, through it would not provide information of why a given tile failed without more localised instrumentation (e.g. temperature probes, strain gauges on tile pins, etc). Remote sensing from the test range equipment would only provide exterior temperatures (which can be mapped to flow discontinuities too) but not temperatures of components beneath the surface. Though both would give a map of likely tile loss areas in order to more accurately target future instrumentation installations.
I think you just answered my questions. Thank you.


It sounds like a combination of IR cameras and mics would touch a lot of bases.


Monitoring the tiles is important for development and ongoing operations. For development learning the reason for failure is top priority. For ops, it's most important to know you had an oops.


Hmmm. A name for the SX softball team? Noopsoops!
Title: Re: Starship heat shield
Post by: OTV Booster on 01/17/2023 06:50 pm
Y'all are making a pretty big assumption that one of these very light weight, super insulated tiles with a veeeery thin glass layer, and is as isolated from the ship as possible (in most places) with a layer of fluffy insulation that probably works as a pretty good acoustic insulator as well, will actually make much sound at all when it cracks.

I'd be very surprised if the breaking sound signature was even within 20 dB of the ambient background noise.
My musicians ear tells me that cracking ceramic is a sharp transient with little or no ring. Not much area under that waveform but quite a bit of amplitude.


The pins give an acoustic path but in the end we will never unless it's tried.


The sound you hear is the frantic scurrying of SX lurkers digging out SS accelerometer data.
Title: Re: Starship heat shield
Post by: adrianwyard on 01/17/2023 08:27 pm
I'll admit this is an interesting discussion, but to point out the obvious: job #1 should be demonstrating an attachment mechanism that can keep the tiles in place for repeated static fires and/or wind tunnel testing. No harm developing a fancy way to detect when/where they fail in flight too, but if they stay on during ground tests this may not be needed...
Title: Re: Starship heat shield
Post by: Hog on 01/18/2023 01:05 pm
After viewing a few of the latest videos of working with and removing TPS tiles, it appears as a labour intensive system.  It will be very interesting to see what Space X goes with when SS/SH enters it's operational phase.  In the meantime, some flight testing of the TPS will be very exciting!
Title: Re: Starship heat shield
Post by: Nomadd on 02/04/2023 05:00 pm
 Paid the old homestead a visit today and cleaned up the mudflats some.
Title: Re: Starship heat shield
Post by: BT52 on 02/04/2023 06:27 pm
OMG very nice.

So how u can sinter with metal inserts? Got no idea how they do that...

Seems to me texture implies not machining is needed. Also that would be preferred methodology to ease mass production.

 
Title: Re: Starship heat shield
Post by: matthewkantar on 02/04/2023 07:12 pm
Nice that SpaceX’s mom wrote their name on it.

Edit: it seems like the metal insert is steel, but not a stainless alloy?
Title: Re: Starship heat shield
Post by: InterestedEngineer on 02/04/2023 08:50 pm
Nice that SpaceX’s mom wrote their name on it.

Edit: it seems like the metal insert is steel, but not a stainless alloy?

It is stainless.  It looks stainless, and it's been sitting in a salty estuary for a while.

Aluminum would have had a telltale corrosion, as would almost any other metal besides stainless.  The tiny streak in the faster looks like very mild stainless corrosion to me.
Title: Re: Starship heat shield
Post by: RamsesBic on 02/04/2023 08:51 pm
OMG very nice.

So how u can sinter with metal inserts? Got no idea how they do that...

Seems to me texture implies not machining is needed. Also that would be preferred methodology to ease mass production.

I have been told the brackets are pushed inside after the tile has been sintered. On some images you can see the edge of the bracket sticking a mm or so out of the side. 3 brackets per tile.
Title: Re: Starship heat shield
Post by: eriblo on 02/04/2023 11:57 pm
OMG very nice.

So how u can sinter with metal inserts? Got no idea how they do that...

Seems to me texture implies not machining is needed. Also that would be preferred methodology to ease mass production.
I have been told the brackets are pushed inside after the tile has been sintered. On some images you can see the edge of the bracket sticking a mm or so out of the side. 3 brackets per tile.
By someone who would know or who is speculating? This would seem like the absolutely worst way to do this from what we know about the tiles..
Title: Re: Starship heat shield
Post by: RamsesBic on 02/05/2023 12:50 am
OMG very nice.

So how u can sinter with metal inserts? Got no idea how they do that...

Seems to me texture implies not machining is needed. Also that would be preferred methodology to ease mass production.
I have been told the brackets are pushed inside after the tile has been sintered. On some images you can see the edge of the bracket sticking a mm or so out of the side. 3 brackets per tile.
By someone who would know or who is speculating? This would seem like the absolutely worst way to do this from what we know about the tiles..

By one of the regulars here.
Title: Re: Starship heat shield
Post by: Nomadd on 02/05/2023 01:26 am
OMG very nice.

So how u can sinter with metal inserts? Got no idea how they do that...

Seems to me texture implies not machining is needed. Also that would be preferred methodology to ease mass production.

I have been told the brackets are pushed inside after the tile has been sintered. On some images you can see the edge of the bracket sticking a mm or so out of the side. 3 brackets per tile.
It does look like there's a path through the material where the bracket was pushed in.
Title: Re: Starship heat shield
Post by: eriblo on 02/05/2023 01:24 pm
OMG very nice.

So how u can sinter with metal inserts? Got no idea how they do that...

Seems to me texture implies not machining is needed. Also that would be preferred methodology to ease mass production.
I have been told the brackets are pushed inside after the tile has been sintered. On some images you can see the edge of the bracket sticking a mm or so out of the side. 3 brackets per tile.
It does look like there's a path through the material where the bracket was pushed in.
Is there a visible difference between the original and fracture surfaces on the tile? What does the tile "channel" surface look like? Are the brackets free to move or are they rigidity attached to the tile? Can a metal object like a nail be pushed into the tile without excessive fracturing?

The reason I have been sceptical of the "pushed into the sintered tile" claim is that I thought the tiles would be too brittle/fragile. Most people would not buy the explanation of glassware with embedded objects to be "you just have to push them in carefully...".

If the brackets are embedded before sintering they have to withstand temperatures of 2300 °F for silica tiles and up to 2600 °F for something like AETB. The former should be doable with some steels or nickel alloys while the latter would be difficult.

If the brackets are added after sintering I would expect the channel to either be cut separately by a saw or vibrating tool or by vibrating the bracket while it is inserted. It would then be free to move unless cemented in place afterwards. Independent movement is not a drawback with regard to thermal expansion as long as it is small enough for the holes line up.
Title: Re: Starship heat shield
Post by: Nomadd on 02/05/2023 03:24 pm
 I have no idea how they make it, but the white stuff is very light and crumbly in it's final form. The brackets are pretty tight and don't seem like they can move around. The channel is packed with white powder, but I can't tell if that's just a result of the insertion, or they pack it in manually.

 I'm trying to think of a vibrator where I could control axis, amplitude, waveform and frequency for experimentation.
 Or maybe just strap em on a speaker with AC/DC playing.
Title: Re: Starship heat shield
Post by: Ben Baley on 02/05/2023 06:41 pm
It seems to me that the easiest way to insert the bracket would be to machine a channel slightly smaller than the bracket and then insert them. That way they would be wedged in there and as long as the size difference is properly controlled would allow for a tight fit without overstressing and cracking the tile
Title: Re: Starship heat shield
Post by: edzieba on 02/05/2023 08:07 pm
- Press cleaned Silica fibres (cleaning occurs at Cidco Road) into mould to create tile preform
- Sinter tile preform in furnace
- Mill sintered preform to size and shape, split preform (double-sided, flat-face to flat-face, so front and backside can be milled to shape) into individual tile blanks
- Press mounting plates into tile blank - the tiles are very frangible, little force is needed and no pre-milling.
- Apply RCG coating
- Sinter RCG coating (singe-sided heating, tile backside not heated to avoid insert damage, helps that the tiles are such good insulators)
- Infiltrate with waterproofing agent (MTMS).

In composition, the tiles are nearly identical to the STS tiles (sintered Silica 'foam' with Borosilicate glass coating). STS tiles did not have the inserts, and were a different shape without the rear cavities. The Silicone-adhered tiles on Starship are even closer to STS, lacking the metal inserts and having conformal backsides rather than the hollowed-out backs of the pin attached tiles.
Title: Re: Starship heat shield
Post by: Oersted on 02/06/2023 10:49 am
So, the hollowed-out backsides are what permit the brackets to slide in?
Title: Re: Starship heat shield
Post by: Oersted on 02/06/2023 10:53 am
Paid the old homestead a visit today and cleaned up the mudflats some.

Would love to see the tile from a couple of other angles, Nomadd, I have a hard time understanding the geometry of it.

Nice find!
Title: Re: Starship heat shield
Post by: RamsesBic on 02/06/2023 11:02 am
Paid the old homestead a visit today and cleaned up the mudflats some.

Would love to see the tile from a couple of other angles, Nomadd, I have a hard time understanding the geometry of it.

Nice find!

Nomadd posted pictures already. See https://forum.nasaspaceflight.com/index.php?topic=50748.3260
Title: Re: Starship heat shield
Post by: edzieba on 02/06/2023 12:36 pm
So, the hollowed-out backsides are what permit the brackets to slide in?
No, they just save mass. And save on Silica, which reduces cost (and the reduced overall thickness may also speed up sintering time, which will also save cost).
Title: Re: Starship heat shield
Post by: Oersted on 02/06/2023 01:50 pm
Paid the old homestead a visit today and cleaned up the mudflats some.

Would love to see the tile from a couple of other angles, Nomadd, I have a hard time understanding the geometry of it.

Nice find!

Nomadd posted pictures already. See https://forum.nasaspaceflight.com/index.php?topic=50748.3260

I didn't find any more pics of that tile in your link.
Title: Re: Starship heat shield
Post by: RamsesBic on 02/06/2023 02:47 pm
Paid the old homestead a visit today and cleaned up the mudflats some.

Would love to see the tile from a couple of other angles, Nomadd, I have a hard time understanding the geometry of it.

Nice find!

Nomadd posted pictures already. See https://forum.nasaspaceflight.com/index.php?topic=50748.3260

I didn't find any more pics of that tile in your link.

Not sure what images you hope to see beyond those. It is not like SpaceX allows photographers into their tile production factory.
Title: Re: Starship heat shield
Post by: Oersted on 02/06/2023 03:46 pm
RamsesBic, I refer you to reply #3311 in this thread, where a fellow called Nomadd posted a pic of a broken tile he found near the SpaceX facilities in Boca Chica. I just asked him if he would mind posting a few more pics, from different angles, of that broken tile.
Title: Re: Starship heat shield
Post by: whitelancer64 on 02/06/2023 04:11 pm
Paid the old homestead a visit today and cleaned up the mudflats some.

Would love to see the tile from a couple of other angles, Nomadd, I have a hard time understanding the geometry of it.

Nice find!

Assuming you still have it in your possession, I would also be very interested in the weight of this tile fragment.
Title: Re: Starship heat shield
Post by: OTV Booster on 02/06/2023 06:22 pm
Am I missing something? The tiles are sintered? This is the first I've heard of this.


Sintering is a pressure process. Even if the tile material were sintered I don't see how the glaze could be sintered on.


Can somebody unconfuse me?




Title: Re: Starship heat shield
Post by: eriblo on 02/06/2023 06:54 pm
Am I missing something? The tiles are sintered? This is the first I've heard of this.


Sintering is a pressure process. Even if the tile material were sintered I don't see how the glaze could be sintered on.


Can somebody unconfuse me?
Sintering involves pressure and/or heat. Materials like these are sintered at high temperatures at atmospheric pressure just like pottery.
Title: Re: Starship heat shield
Post by: OTV Booster on 02/07/2023 07:53 pm
Am I missing something? The tiles are sintered? This is the first I've heard of this.


Sintering is a pressure process. Even if the tile material were sintered I don't see how the glaze could be sintered on.


Can somebody unconfuse me?
Sintering involves pressure and/or heat. Materials like these are sintered at high temperatures at atmospheric pressure just like pottery.
Never heard the term used that way. For ceramics, the familiar term is baking or firing.


Broadly speaking, my familiarity with sintering involves pressure which generally results in heat but heat can be added. Individual particles fuse at the point of contact without general melting, creating a matrix with open spaces throughout.


Hmmm, that last does describe the tile material, so I'll just shut up and grok. Live and learn.


BTW, the glaze would not be an open matrix. In the pottery world, goop with glass in it is painted on and fired high enough that the glass softens and runs together into a solid layer. Porcelain can be thought of as all glaze with no substrate.
Title: Re: Starship heat shield
Post by: edzieba on 02/08/2023 09:57 am
Am I missing something? The tiles are sintered? This is the first I've heard of this.


Sintering is a pressure process. Even if the tile material were sintered I don't see how the glaze could be sintered on.


Can somebody unconfuse me?
Sintering involves pressure and/or heat. Materials like these are sintered at high temperatures at atmospheric pressure just like pottery.
Never heard the term used that way. For ceramics, the familiar term is baking or firing.


Broadly speaking, my familiarity with sintering involves pressure which generally results in heat but heat can be added. Individual particles fuse at the point of contact without general melting, creating a matrix with open spaces throughout.


Hmmm, that last does describe the tile material, so I'll just shut up and grok. Live and learn.


BTW, the glaze would not be an open matrix. In the pottery world, goop with glass in it is painted on and fired high enough that the glass softens and runs together into a solid layer. Porcelain can be thought of as all glaze with no substrate.
Sintering using mechanical pressure is unsuitable for the the tiles, as pre-crushing the porous tile renders it ineffective in terms of its desired insulating properties. There are also plenty of ceramics and metallics that are vacuum sintered - e.g. tungsten carbide tooling inserts - or sintered at atmospheric pressure (though not always in regular air).
Title: Re: Starship heat shield
Post by: InterestedEngineer on 02/22/2023 12:42 am
This video, at the 6:49 -> 7:15 mark, shows the mesh that holds down the blanket gets easily melted by the sparks / blast flying off from the welder that is taking apart a ring:

https://www.youtube.com/watch?v=WWA5NRWfhYE

It reminds me of what plastic might look like after melting it.

It'll be interesting seeing a tile repair with melted material behind it getting replaced after a reentry.

Snapshot of video with the welder part way down its cut.
Title: Re: Starship heat shield
Post by: RamsesBic on 02/22/2023 12:50 am
Does the plastic mesh have any function other than keeping the thermal blankets from getting loose before the tiles are added?
Title: Re: Starship heat shield
Post by: InterestedEngineer on 02/22/2023 06:15 am
Does the plastic mesh have any function other than keeping the thermal blankets from getting loose before the tiles are added?

After watching the blowtorch melt the mesh, I'd say the answer is "no".

I thought the mesh might have a high enough operating temperature to keep flapping down in the event of a lost tile, but the video falsifies that hypothesis.
Title: Re: Starship heat shield
Post by: edzieba on 02/22/2023 08:36 am
The same gas-axe also chews right through the felt pads with impunity. Contrary to some oft-repeated claims, refractory wools are great at handling radiant heat, but not so great at dealing with direct impingement heating.
Title: Re: Starship heat shield
Post by: JCopernicus on 02/22/2023 10:16 am
Why don't they cover the mount in the heat shield material on the ship?

My first guess is that the thrusters are a lot hotter than the re entry temps?

And if so then I just answered my own question?
Title: Re: Starship heat shield
Post by: Slothman on 02/22/2023 10:23 am
Why don't they cover the mount in the heat shield material on the ship?

My first guess is that the thrusters are a lot hotter than the re entry temps?

And if so then I just answered my own question?

I think it might be more about accoustic vibrations shattering the tiles
Title: Re: Starship heat shield
Post by: RamsesBic on 02/22/2023 11:28 am
Why don't they cover the mount in the heat shield material on the ship?

My first guess is that the thrusters are a lot hotter than the re entry temps?

And if so then I just answered my own question?

I think it might be more about accoustic vibrations shattering the tiles

Acoustic vibrations are just molecules moving in waves with wavelengths we can hear.
As I understand this, the difference between the exhaust from the Raptors and the reentry atmospheric heating has to do with the number of molecules hitting the surface and their speed.
The exhaust has many more molecules per second. The atmosphere fewer molecules but at higher speeds.
The tiles can handle few molecules per second, but not as many as in the exhaust.
Title: Re: Starship heat shield
Post by: edzieba on 02/22/2023 12:25 pm
Just for fun:
Air density at 100km above surface: ~6x10-7 kg/m3
Entry velocity: ~8km/s
1s of entry flight impacts an 8km long column of air
1 m2 of entering vehicle will meet 8000 cubic metres of air during 1s of entry
8000 m3 of air will mass ~4.8g
Entry plasma mass flow: ~0.005kg/s

Booster aft end area: ~18m2
Raptor propellant consumption: ~650kg/s each
33 raptors per booster: 21450 kg/s
Mass flow rate per square metre of booster: ~1200kg/s

About a factor of 2.4 million difference. A gentle hypersonic plasma tickling vs. a meaty combustion-product pummelling.

(Yes, peak flow would be later during entry, I'm not breaking out the calculator during my lunch break).
Title: Re: Starship heat shield
Post by: InterestedEngineer on 02/22/2023 06:45 pm
Just for fun:
Air density at 100km above surface: ~6x10-7 kg/m3
Entry velocity: ~8km/s
1s of entry flight impacts an 8km long column of air
1 m2 of entering vehicle will meet 8000 cubic metres of air during 1s of entry
8000 m3 of air will mass ~4.8g
Entry plasma mass flow: ~0.005kg/s

Booster aft end area: ~18m2
Raptor propellant consumption: ~650kg/s each
33 raptors per booster: 21450 kg/s
Mass flow rate per square metre of booster: ~1200kg/s

About a factor of 2.4 million difference. A gentle hypersonic plasma tickling vs. a meaty combustion-product pummelling.

(Yes, peak flow would be later during entry, I'm not breaking out the calculator during my lunch break).

Nice math, thanks!

Converting into watts/m2:

Rentry:  0.5 * .005kg/s * (8,000m/s)2 = 160kW/m2
Booster Aft KE:  0.5 * 21450 kg/s * (3,200 m/s)2 = 110GW/m2
Booster Aft Thermal:  0.4 * 110GW = 44GW
Booster Total: 154GW

about 1 million factor difference in total energy flux.
Title: Re: Starship heat shield
Post by: Robotbeat on 02/24/2023 08:43 pm
Had a random idea:
Orbital thermal protection system that can tolerate a class of Kindergartners throwing rocks at it. Should be a thing. ASTM standard Kindergartners.
Title: Re: Starship heat shield
Post by: Robotbeat on 02/24/2023 08:58 pm
Just for fun:
Air density at 100km above surface: ~6x10-7 kg/m3
Entry velocity: ~8km/s
1s of entry flight impacts an 8km long column of air
1 m2 of entering vehicle will meet 8000 cubic metres of air during 1s of entry
8000 m3 of air will mass ~4.8g
Entry plasma mass flow: ~0.005kg/s

Booster aft end area: ~18m2
Raptor propellant consumption: ~650kg/s each
33 raptors per booster: 21450 kg/s
Mass flow rate per square metre of booster: ~1200kg/s

About a factor of 2.4 million difference. A gentle hypersonic plasma tickling vs. a meaty combustion-product pummelling.

(Yes, peak flow would be later during entry, I'm not breaking out the calculator during my lunch break).
Earth scale height is about 8.5km (meaning each change in 8.5km altitude results in a change in density by about a factor of e, 2.718…)

If peak reentry heating occurs at 50km, that’s a factor of e^5.88=358… but we can use sea level pressure as a reference point as well, to double-check.

6e-7kg/m^3*e^(5.88) =2.1e-4kg/m^3. Calculating from sea level which has a density of 1.2g/liter = 3.3e-3kg/m^3… factor of like 16 off LOL.so let’s pick somewhere logarithmically in the middle, like a favor of 4 larger than 2.1e-4g/L, like 8.4e-4g/L.

Wolfram Alpha says it’s 10.e-3g/L at 50km, so that little interpolation exercise worked.

Anyway, the point is that reentry heating at the same speed is about twice as intense energy-wise at 50km than at 100km.

That reduces the difference in energy flux a bit. But actually… the energy is not efficiently transferred into the ground.
Title: Re: Starship heat shield
Post by: kraisee on 02/24/2023 09:55 pm
Ever since I realized this system would have a huge re-entry footprint (Ahhh, the 12m BFR!) I have been wondering if the metallic thermal-protection concept that was intended for X-33/VentureStar might be suitable for use on Starship?

One of the key benefits of the "hot metal" heat shield was that it was explicitly designed to be robust, intended to survive minor debris strikes that would typically damage tiles, and even work in situations involving small MMOD hits.

Being that it forms a second layer that would vent to vacuum, that is not in continual contact with the primary structure of the vehicle, it was also intended to serve as a moderately good sun shield layer to help with storing cryogens on the vehicle.

A variant designed specifically for Starship with all those features, might be worth the weight penalty - which I understand wasn't actually that bad.

Ross.
Title: Re: Starship heat shield
Post by: warp99 on 02/24/2023 10:35 pm
Ever since I realized this system would have a huge re-entry footprint (Ahhh, the 12m BFR!) I have been wondering if the metallic thermal-protection concept that was intended for X-33/VentureStar might be suitable for use on Starship?

One of the key benefits of the "hot metal" heat shield was that it was explicitly designed to be robust, intended to survive minor debris strikes that would typically damage tiles, and even work in situations involving small MMOD hits.

Being that it forms a second layer that would vent to vacuum, that is not in continual contact with the primary structure of the vehicle, it was also intended to serve as a moderately good sun shield layer to help with storing cryogens on the vehicle.

A variant designed specifically for Starship with all those features, might be worth the weight penalty - which I understand wasn't actually that bad.

Ross.
The issue with metal tiles is the lower service temperature compared with ceramic fiber tiles.  For example niobium can tolerate up to 1300C and a niobium+hafnium+titanium alloy up to 1480C but actual service temperatures for repeated re-entries are likely 300C below these numbers.  Coated alumina+silica ceramic tiles can work up to 1250C on a repeated basis and show less erosion from oxygen plasma. 

The relatively high expansion coefficient also requires the tiles to be overlapped at the edges rather than butted together with gap fillers.  In order to use metal tiles on Starship the ballistic coefficient would need to be lowered likely using oversized chines aka wings.  This is possibly the source of Elon's cryptic comment a few years ago that they were looking at Dragon wings for Starship.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 02/24/2023 10:46 pm
Ever since I realized this system would have a huge re-entry footprint (Ahhh, the 12m BFR!) I have been wondering if the metallic thermal-protection concept that was intended for X-33/VentureStar might be suitable for use on Starship?

One of the key benefits of the "hot metal" heat shield was that it was explicitly designed to be robust, intended to survive minor debris strikes that would typically damage tiles, and even work in situations involving small MMOD hits.

Being that it forms a second layer that would vent to vacuum, that is not in continual contact with the primary structure of the vehicle, it was also intended to serve as a moderately good sun shield layer to help with storing cryogens on the vehicle.

A variant designed specifically for Starship with all those features, might be worth the weight penalty - which I understand wasn't actually that bad.

Ross.
The issue with metal tiles is the lower service temperature compared with ceramic fiber tiles.  For example niobium can tolerate up to 1300C and a niobium+hafnium+titanium alloy up to 1480C but actual service temperatures for repeated re-entries are likely 300C below these numbers.  Coated alumina+silica ceramic tiles can work up to 1250C on a repeated basis and show less erosion from oxygen plasma. 

The relatively high expansion coefficient also requires the tiles to be overlapped at the edges rather than butted together with gap fillers.  In order to use metal tiles on Starship the ballistic coefficient would need to be lowered likely using oversized chines aka wings.  This is possibly the source of Elon's cryptic comment a few years ago that they were looking at Dragon wings for Starship.

I don't think metal tiles can be made lighter than ceramic.

Ceramic tiles also have a pretty good heat capacity, they can take spikes of joules well above the average rate and not be damaged.  Metal cannot.
Title: Re: Starship heat shield
Post by: Robotbeat on 02/24/2023 11:06 pm
Ever since I realized this system would have a huge re-entry footprint (Ahhh, the 12m BFR!) I have been wondering if the metallic thermal-protection concept that was intended for X-33/VentureStar might be suitable for use on Starship?

One of the key benefits of the "hot metal" heat shield was that it was explicitly designed to be robust, intended to survive minor debris strikes that would typically damage tiles, and even work in situations involving small MMOD hits.

Being that it forms a second layer that would vent to vacuum, that is not in continual contact with the primary structure of the vehicle, it was also intended to serve as a moderately good sun shield layer to help with storing cryogens on the vehicle.

A variant designed specifically for Starship with all those features, might be worth the weight penalty - which I understand wasn't actually that bad.

Ross.
Completely agree, Ross. And I've tried to convince SpaceX folk to consider this approach, including trying to hook them up with the X-33 heatshield developers.
Title: Re: Starship heat shield
Post by: kraisee on 02/24/2023 11:52 pm
Ever since I realized this system would have a huge re-entry footprint (Ahhh, the 12m BFR!) I have been wondering if the metallic thermal-protection concept that was intended for X-33/VentureStar might be suitable for use on Starship?

One of the key benefits of the "hot metal" heat shield was that it was explicitly designed to be robust, intended to survive minor debris strikes that would typically damage tiles, and even work in situations involving small MMOD hits.

Being that it forms a second layer that would vent to vacuum, that is not in continual contact with the primary structure of the vehicle, it was also intended to serve as a moderately good sun shield layer to help with storing cryogens on the vehicle.

A variant designed specifically for Starship with all those features, might be worth the weight penalty - which I understand wasn't actually that bad.

Ross.
The issue with metal tiles is the lower service temperature compared with ceramic fiber tiles.  For example niobium can tolerate up to 1300C and a niobium+hafnium+titanium alloy up to 1480C but actual service temperatures for repeated re-entries are likely 300C below these numbers.  Coated alumina+silica ceramic tiles can work up to 1250C on a repeated basis and show less erosion from oxygen plasma. 

The relatively high expansion coefficient also requires the tiles to be overlapped at the edges rather than butted together with gap fillers.  In order to use metal tiles on Starship the ballistic coefficient would need to be lowered likely using oversized chines aka wings.  This is possibly the source of Elon's cryptic comment a few years ago that they were looking at Dragon wings for Starship.

I only get on NSF periodically, so this may have been answered before, but does the NSF community actually know what the peak heating for Starship entry - Earth and Mars - looks like?

Starship has a fairly high entry surface area to weight ratio, which is the same general 'feature' that made the metallic TPS viable for X-33/VS. Can Starship fly entry trajectories that keep peak heating below the 1480C you mention?


Metallic TPS might be one option, perhaps.   Maybe another variant of PICA-X could be developed.   I don't really care what the solution ends up being, only the ceramic tiles genuinely scare me as a long-term solution.

My concern is that a ceramic TPS Starship will *ALWAYS* be vulnerable to damage.   We learned that pretty convincingly on Shuttle.   To my mind that screams a critical accident becomes a "when", not an "if".

We don't really know what the acoustic launch environ on the Red planet is, because nobody has ever tried it, so there are unk-unk risks there.   And there are lots of dust/stone particles on the Martian surface that rocket engines will clearly kick around, and there is always a possibility of one or more bouncing back and hitting the TPS with significant force - especially given just how near the ground the TPS is, on a Mars-landed Starship.

Failures of Starship during re-entry - especially ones that could have been corrected early in the development phase - could seriously harm Mars colonization efforts.   Perhaps existentially.

Given the huge performance Starship has, my question boils down to whether even an extra couple of tons of tougher TPS would really be a *BAD* trade to consider?

Ross.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 02/25/2023 02:50 am

My concern is that a ceramic TPS Starship will *ALWAYS* be vulnerable to damage.   We learned that pretty convincingly on Shuttle.   To my mind that screams a critical accident becomes a "when", not an "if".

Ross.

Why do you think tile damage on a Starship will lead to the same outcome as the Shuttle.

Hint:  Do the math.

Title: Re: Starship heat shield
Post by: eriblo on 02/25/2023 03:40 pm
There seems to be a widespread belief that Starship has a low ballistic coefficient. I guess it is based on the large and fluffy appearance?  ::)


Shuttle orbiter: ~350 m2 projected, reentry mass 85 t - 105 t.

Perpendicular ballistic coefficient:
240 kg/m2 - 300 kg/m2

At 40° pitch:
380 kg/m2 - 470 kg/m2


Starship: ~580 m2 projected (flaps akimbo), reentry mass 150 t - 300 t.

Perpendicular ballistic coefficient:
260 kg/m2 - 520 kg/m2

At 70° pitch:
280 kg/m2 - 550 kg/m2

The reference area for Starship will actually be significantly smaller as the flaps will have some dihedral and a cylindrical body has roughly half the drag of a flat bottomed one.

While many reentries will be empty and relatively light the heat shield will be designed for the heaviest case.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 02/25/2023 04:13 pm
There seems to be a widespread belief that Starship has a low ballistic coefficient. I guess it is based on the large and fluffy appearance?  ::)


Shuttle orbiter: ~350 m2 projected, reentry mass 85 t - 105 t.

Perpendicular ballistic coefficient:
240 kg/m2 - 300 kg/m2

At 40° pitch:
380 kg/m2 - 470 kg/m2


Starship: ~580 m2 projected (flaps akimbo), reentry mass 150 t - 300 t.

Perpendicular ballistic coefficient:
260 kg/m2 - 520 kg/m2

At 70° pitch:
280 kg/m2 - 550 kg/m2

The reference area for Starship will actually be significantly smaller as the flaps will have some dihedral and a cylindrical body has roughly half the drag of a flat bottomed one.

While many reentries will be empty and relatively light the heat shield will be designed for the heaviest case.

How did you get 580m projected?

4.5m * pi * 50m = 706 m2

Which doesn't include flaps
Title: Re: Starship heat shield
Post by: eriblo on 02/25/2023 04:56 pm
There seems to be a widespread belief that Starship has a low ballistic coefficient. I guess it is based on the large and fluffy appearance?  ::)


Shuttle orbiter: ~350 m2 projected, reentry mass 85 t - 105 t.

Perpendicular ballistic coefficient:
240 kg/m2 - 300 kg/m2

At 40° pitch:
380 kg/m2 - 470 kg/m2


Starship: ~580 m2 projected (flaps akimbo), reentry mass 150 t - 300 t.

Perpendicular ballistic coefficient:
260 kg/m2 - 520 kg/m2

At 70° pitch:
280 kg/m2 - 550 kg/m2

The reference area for Starship will actually be significantly smaller as the flaps will have some dihedral and a cylindrical body has roughly half the drag of a flat bottomed one.

While many reentries will be empty and relatively light the heat shield will be designed for the heaviest case.

How did you get 580m projected?

4.5m * pi * 50m = 706 m2

Which doesn't include flaps
Projected as in the shadow cast on a perpendicular surface. I.e. 9 m * 50 m minus nose taper plus flaps. Did a quick and dirty outline trace on Rafael's SNx drawing.
Title: Re: Starship heat shield
Post by: Robotbeat on 02/25/2023 05:12 pm
I think Starship might be on the heavier side at first, but operationally could be 85 tonnes empty eventually. 300t is too high. Not sure if it’ll ever do that much.
Title: Re: Starship heat shield
Post by: rsdavis9 on 02/25/2023 05:49 pm
I think Starship might be on the heavier side at first, but operationally could be 85 tonnes empty eventually. 300t is too high. Not sure if it’ll ever do that much.

with 100t return payload?
Title: Re: Starship heat shield
Post by: eriblo on 02/25/2023 05:51 pm
I think Starship might be on the heavier side at first, but operationally could be 85 tonnes empty eventually. 300t is too high. Not sure if it’ll ever do that much.

with 100t return payload?
I used 120 t dry + 30 t landing propellant and residuals + 150 t payload.

30 t is about what the estimate is for the current header tanks but it is quite a bit more than needed for landing on Earth (and less than what you need for Mars).
Title: Re: Starship heat shield
Post by: Robotbeat on 02/25/2023 07:38 pm
Again, I don’t think they’ll be doing a 300t entry from orbit (at least not without some aero upgrades). Either the returned payload will be small or they’ll make big strides on reducing dry mass of the stage (and landing propellant) or both. They hope to get stage dry mass down to 85 tonnes, may need only like 5-10 tons of propellant for terminal landing, and the payload may only be about 60 tons when returning from orbit, so could be just 150 tonnes.
Title: Re: Starship heat shield
Post by: eriblo on 02/25/2023 09:41 pm
Again, I don’t think they’ll be doing a 300t entry from orbit (at least not without some aero upgrades). Either the returned payload will be small or they’ll make big strides on reducing dry mass of the stage (and landing propellant) or both. They hope to get stage dry mass down to 85 tonnes, may need only like 5-10 tons of propellant for terminal landing, and the payload may only be about 60 tons when returning from orbit, so could be just 150 tonnes.
Does not make much sense to design a reusable vehicle that can not land with its maximum payload. Especially not when the ultimate goal is to land as much payload as possible...
Title: Re: Starship heat shield
Post by: Michael S on 02/25/2023 09:58 pm
Again, I don’t think they’ll be doing a 300t entry from orbit (at least not without some aero upgrades). Either the returned payload will be small or they’ll make big strides on reducing dry mass of the stage (and landing propellant) or both. They hope to get stage dry mass down to 85 tonnes, may need only like 5-10 tons of propellant for terminal landing, and the payload may only be about 60 tons when returning from orbit, so could be just 150 tonnes.
Does not make much sense to design a reusable vehicle that can not land with its maximum payload. Especially not when the ultimate goal is to land as much payload as possible...
…on Mars. 
The impression I’ve gotten from Robotbeat, is this has been a discussion for returning to Earth.  In the near term, what use case is there to land with the maximum payload on Earth?
Title: Re: Starship heat shield
Post by: marsbase on 02/25/2023 10:01 pm
Does not make much sense to design a reusable vehicle that can not land with its maximum payload. Especially not when the ultimate goal is to land as much payload as possible...
There is a max launch payload, a max landing payload for Earth, and max landing payloads for Luna and Mars.  They are not all the same. If you are designing to be able to land on Earth the same max payload you launch, then you are designing in a reduced max launch payload. 
Title: Re: Starship heat shield
Post by: Robotbeat on 02/25/2023 10:34 pm
Again, I don’t think they’ll be doing a 300t entry from orbit (at least not without some aero upgrades). Either the returned payload will be small or they’ll make big strides on reducing dry mass of the stage (and landing propellant) or both. They hope to get stage dry mass down to 85 tonnes, may need only like 5-10 tons of propellant for terminal landing, and the payload may only be about 60 tons when returning from orbit, so could be just 150 tonnes.
Does not make much sense to design a reusable vehicle that can not land with its maximum payload. …
Obviously it does, for the very reason this discussion started (easier on the heatshield design). In fact, it’s not uncommon for aircraft to have different take-off max weight and landing max weight. They add a fuel dump. (Shuttle, in fact, was going to have that for Centaur missions before Challenger blew up and changed the risk profile for flights with crew, which was of course all Shuttle flights.)
Title: Re: Starship heat shield
Post by: RoboGoofers on 02/25/2023 11:51 pm
Ever since I realized this system would have a huge re-entry footprint (Ahhh, the 12m BFR!) I have been wondering if the metallic thermal-protection concept that was intended for X-33/VentureStar might be suitable for use on Starship?

One of the key benefits of the "hot metal" heat shield was that it was explicitly designed to be robust, intended to survive minor debris strikes that would typically damage tiles, and even work in situations involving small MMOD hits.

Being that it forms a second layer that would vent to vacuum, that is not in continual contact with the primary structure of the vehicle, it was also intended to serve as a moderately good sun shield layer to help with storing cryogens on the vehicle.

A variant designed specifically for Starship with all those features, might be worth the weight penalty - which I understand wasn't actually that bad.

Ross.
The issue with metal tiles is the lower service temperature compared with ceramic fiber tiles.  For example niobium can tolerate up to 1300C and a niobium+hafnium+titanium alloy up to 1480C but actual service temperatures for repeated re-entries are likely 300C below these numbers.  Coated alumina+silica ceramic tiles can work up to 1250C on a repeated basis and show less erosion from oxygen plasma. 

The relatively high expansion coefficient also requires the tiles to be overlapped at the edges rather than butted together with gap fillers.  In order to use metal tiles on Starship the ballistic coefficient would need to be lowered likely using oversized chines aka wings.  This is possibly the source of Elon's cryptic comment a few years ago that they were looking at Dragon wings for Starship.
They also need a solution that can work for Mars return reentry.
Title: Re: Starship heat shield
Post by: Dancing Dog on 02/26/2023 01:59 am
Quote
Dragon wings for Starship

This could refer to moving the hinges of the upper flaps behind the midline, or possibly the swing-out tower landing hooks (but the hooks would be OT, I suppose).
Title: Re: Starship heat shield
Post by: r8ix on 02/26/2023 03:45 am
I doubt I can find the source anymore, but I've heard 150t up and 50t down as the cargo specs.
Title: Re: Starship heat shield
Post by: Nomadd on 02/26/2023 03:57 am
 I'd think they'd need full payload landing capability for an abort or refueling failure, but that would only be leo speed.
 Handling an unplanned Mars evacuation might be a requirement, which they might not want to be payload limited.
Title: Re: Starship heat shield
Post by: eriblo on 02/26/2023 03:48 pm
Again, I don’t think they’ll be doing a 300t entry from orbit (at least not without some aero upgrades). Either the returned payload will be small or they’ll make big strides on reducing dry mass of the stage (and landing propellant) or both. They hope to get stage dry mass down to 85 tonnes, may need only like 5-10 tons of propellant for terminal landing, and the payload may only be about 60 tons when returning from orbit, so could be just 150 tonnes.
Does not make much sense to design a reusable vehicle that can not land with its maximum payload. Especially not when the ultimate goal is to land as much payload as possible...
…on Mars. 
The impression I’ve gotten from Robotbeat, is this has been a discussion for returning to Earth.  In the near term, what use case is there to land with the maximum payload on Earth?
As Nomadd mentions a lower maximum down mass means significant higher risk of loss of payload and vehicle for late aborts or any failure that prevents payload deployment. Remember that Starship will have a significant fraction of max LEO payload launches.
Title: Re: Starship heat shield
Post by: eriblo on 02/26/2023 03:48 pm
Does not make much sense to design a reusable vehicle that can not land with its maximum payload. Especially not when the ultimate goal is to land as much payload as possible...
There is a max launch payload, a max landing payload for Earth, and max landing payloads for Luna and Mars.  They are not all the same. If you are designing to be able to land on Earth the same max payload you launch, then you are designing in a reduced max launch payload.
I am not sure I follow your logic. Maximum launch payload is determined by launch vehicle performance. Maximum landed payload on Earth is determined by heat shield performance (among other things).

Yes, if you go for the absolutely minimum performance heat shield you might gain a few tonnes of payload but it might also be the case that other factors already mean that you can land with more payload mass than you can launch.
Title: Re: Starship heat shield
Post by: eriblo on 02/26/2023 03:48 pm
Again, I don’t think they’ll be doing a 300t entry from orbit (at least not without some aero upgrades). Either the returned payload will be small or they’ll make big strides on reducing dry mass of the stage (and landing propellant) or both. They hope to get stage dry mass down to 85 tonnes, may need only like 5-10 tons of propellant for terminal landing, and the payload may only be about 60 tons when returning from orbit, so could be just 150 tonnes.
Does not make much sense to design a reusable vehicle that can not land with its maximum payload. …
Obviously it does, for the very reason this discussion started (easier on the heatshield design). In fact, it’s not uncommon for aircraft to have different take-off max weight and landing max weight. They add a fuel dump. (Shuttle, in fact, was going to have that for Centaur missions before Challenger blew up and changed the risk profile for flights with crew, which was of course all Shuttle flights.)
I'll concede that Starship does not have to be able to land with maximum (reusable) payload but I think that SpaceX has higher ambitions.

If the standard heat shield is only good for reduced mass LEO reentries it would be workable but it would involve higher risk when launching heavy payloads (likely mass limiting crewed launches). It would also mean that they need a higher performance version sooner rather than later for MEO/HEO/Cislunar.

There is also the reusability dimension - they want a heat shield that can do hundreds of reentries with minimum refurbishment which  suggests a bit of margin for the odd slightly heavy or fast one.

Regarding the aircraft analogy - they are certified to land at any weight they are allowed to take off at, it might just be at a lower vertical speed. This is not the case for Starship as it has a maximum take off weight of ~1500 t.
Title: Re: Starship heat shield
Post by: eriblo on 02/26/2023 04:14 pm
I doubt I can find the source anymore, but I've heard 150t up and 50t down as the cargo specs.
See if you can find a better one than the often misquoted 2017 presentation which is "Typical [Mars to Earth] return payload 50 t" which was dv limited.

EDIT: Put a strike through misremembered statements.
Title: Re: Starship heat shield
Post by: Robotbeat on 02/26/2023 04:27 pm
That’s inserting quite a lot of unwritten words into that slide.
Title: Re: Starship heat shield
Post by: Tangilinear Interjar on 02/26/2023 04:30 pm

Regarding the aircraft analogy - they are certified to land at any weight they are allowed to take off at, it might just be at a lower vertical speed. This is not the case for Starship as it has a maximum take off weight of ~1500 t.

Definitely wrong on this one 👆

It's very common for an aircraft to have a different maximum takeoff weight than it's maximum landing weight. In fact it's also common to have an even greater taxi weight!
Title: Re: Starship heat shield
Post by: marsbase on 02/26/2023 05:05 pm
Does not make much sense to design a reusable vehicle that can not land with its maximum payload. Especially not when the ultimate goal is to land as much payload as possible...
There is a max launch payload, a max landing payload for Earth, and max landing payloads for Luna and Mars.  They are not all the same. If you are designing to be able to land on Earth the same max payload you launch, then you are designing in a reduced max launch payload.
I am not sure I follow your logic. Maximum launch payload is determined by launch vehicle performance. Maximum landed payload on Earth is determined by heat shield performance (among other things.)
Here you say that maximum launch payload is determined by launch vehicle performance. But above you imply that the maximum launch payload should be determined by the weight that can be landed on Earth.   Which is it?
Title: Re: Starship heat shield
Post by: eriblo on 02/26/2023 05:43 pm
That’s inserting quite a lot of unwritten words into that slide.
You are correct, I checked with the presentation and Elon does not say that so I might be conflating later and different context statements. My apologies.

I will note that it is the BFR version and that it notes "Typical" rather than "Maximum" return payload.
Title: Re: Starship heat shield
Post by: eriblo on 02/26/2023 05:49 pm

Regarding the aircraft analogy - they are certified to land at any weight they are allowed to take off at, it might just be at a lower vertical speed. This is not the case for Starship as it has a maximum take off weight of ~1500 t.

Definitely wrong on this one 👆

It's very common for an aircraft to have a different maximum takeoff weight than it's maximum landing weight. In fact it's also common to have an even greater taxi weight!
It is called an "Overweight landing". No pilot is going to take the scenic route to get rid of fuel if they get a fire alarm and smoke right after take off.
Title: Re: Starship heat shield
Post by: eriblo on 02/26/2023 05:59 pm
Does not make much sense to design a reusable vehicle that can not land with its maximum payload. Especially not when the ultimate goal is to land as much payload as possible...
There is a max launch payload, a max landing payload for Earth, and max landing payloads for Luna and Mars.  They are not all the same. If you are designing to be able to land on Earth the same max payload you launch, then you are designing in a reduced max launch payload.
I am not sure I follow your logic. Maximum launch payload is determined by launch vehicle performance. Maximum landed payload on Earth is determined by heat shield performance (among other things.)
Here you say that maximum launch payload is determined by launch vehicle performance. But above you imply that the maximum launch payload should be determined by the weight that can be landed on Earth.   Which is it?
I am saying that it makes sense to design a reusable launch vehicle so that landed payload mass is equal to or greater than launched payload mass.

I sounds like you are saying that landed payload mass had to be smaller than launched payload mass?
Title: Re: Starship heat shield
Post by: Robotbeat on 02/26/2023 06:09 pm

Regarding the aircraft analogy - they are certified to land at any weight they are allowed to take off at, it might just be at a lower vertical speed. This is not the case for Starship as it has a maximum take off weight of ~1500 t.

Definitely wrong on this one 👆

It's very common for an aircraft to have a different maximum takeoff weight than it's maximum landing weight. In fact it's also common to have an even greater taxi weight!
It is called an "Overweight landing". No pilot is going to take the scenic route to get rid of fuel if they get a fire alarm and smoke right after take off.
And then you’d potentially have to rebuild the landing gear as it would be potentially yielded.
Title: Re: Starship heat shield
Post by: Robotbeat on 02/26/2023 06:14 pm
Does not make much sense to design a reusable vehicle that can not land with its maximum payload. Especially not when the ultimate goal is to land as much payload as possible...
There is a max launch payload, a max landing payload for Earth, and max landing payloads for Luna and Mars.  They are not all the same. If you are designing to be able to land on Earth the same max payload you launch, then you are designing in a reduced max launch payload.
I am not sure I follow your logic. Maximum launch payload is determined by launch vehicle performance. Maximum landed payload on Earth is determined by heat shield performance (among other things.)
Here you say that maximum launch payload is determined by launch vehicle performance. But above you imply that the maximum launch payload should be determined by the weight that can be landed on Earth.   Which is it?
I am saying that it makes sense to design a reusable launch vehicle so that landed payload mass is equal to or greater than launched payload mass.


Actually, it does make sense for the same reason it makes sense for airliners to demonstrably have a higher safe take-off weight than landing weight. And Shuttle Centaur was to have a fuel dump port for much the same reason.

SpaceX may want variants of Starship that can land heavy payloads, but that may require larger aerosurfaces, etc.

Not sure why you’re being so stubborn about this, seeing as multiple sources show that it’s common for take off weight to exceed landed weight, that this would’ve applied to Shuttle and will likely apply to at least some variants of Starship. Can you explain your motivation as to why you insist on this, essentially crippling the ascent payload of Starship so that it could always land with whatever it’s max ascent payload is?
Title: Re: Starship heat shield
Post by: marsbase on 02/26/2023 06:41 pm
Does not make much sense to design a reusable vehicle that can not land with its maximum payload. Especially not when the ultimate goal is to land as much payload as possible...
There is a max launch payload, a max landing payload for Earth, and max landing payloads for Luna and Mars.  They are not all the same. If you are designing to be able to land on Earth the same max payload you launch, then you are designing in a reduced max launch payload.
I am not sure I follow your logic. Maximum launch payload is determined by launch vehicle performance. Maximum landed payload on Earth is determined by heat shield performance (among other things.)
Here you say that maximum launch payload is determined by launch vehicle performance. But above you imply that the maximum launch payload should be determined by the weight that can be landed on Earth.   Which is it?
I am saying that it makes sense to design a reusable launch vehicle so that landed payload mass is equal to or greater than launched payload mass.

I sounds like you are saying that landed payload mass had to be smaller than launched payload mass?
I think you want to design the launch vehicle to lift as much payload as possible.  There will be times, maybe with crewed flights or with a very expensive payload, when you will launch with less than max payload in order to be able to land in an abort condition and salvage the payload.  But you would not design the launch vehicle around that limitation because you will not always want to adhere to it.
Title: Re: Starship heat shield
Post by: Asteroza on 02/27/2023 12:20 am
Does not make much sense to design a reusable vehicle that can not land with its maximum payload. Especially not when the ultimate goal is to land as much payload as possible...
There is a max launch payload, a max landing payload for Earth, and max landing payloads for Luna and Mars.  They are not all the same. If you are designing to be able to land on Earth the same max payload you launch, then you are designing in a reduced max launch payload.
I am not sure I follow your logic. Maximum launch payload is determined by launch vehicle performance. Maximum landed payload on Earth is determined by heat shield performance (among other things.)
Here you say that maximum launch payload is determined by launch vehicle performance. But above you imply that the maximum launch payload should be determined by the weight that can be landed on Earth.   Which is it?
I am saying that it makes sense to design a reusable launch vehicle so that landed payload mass is equal to or greater than launched payload mass.

I sounds like you are saying that landed payload mass had to be smaller than launched payload mass?
I think you want to design the launch vehicle to lift as much payload as possible.  There will be times, maybe with crewed flights or with a very expensive payload, when you will launch with less than max payload in order to be able to land in an abort condition and salvage the payload.  But you would not design the launch vehicle around that limitation because you will not always want to adhere to it.

Wait, doesn't that by definition mean a starship launch payload mass exceeding recoverable mass is just an expendable starship that sometimes you get lucky recovering?

You're boned if you have to abort, so that isn't a reusable starship.
If you don't abort, maybe you might be able to land with no return mass later, maybe not.
If you must refuel to land, I guess you can call that reusable, just not in one go...
Title: Re: Starship heat shield
Post by: Robotbeat on 02/27/2023 02:27 am
That’s playing weird games with words to try to salvage a disproven point.

Shuttle was gonna have a fuel dump for Centaur missions to enable abort. Something similar could be done for Starship.
Title: Re: Starship heat shield
Post by: eriblo on 02/27/2023 10:06 am

Regarding the aircraft analogy - they are certified to land at any weight they are allowed to take off at, it might just be at a lower vertical speed. This is not the case for Starship as it has a maximum take off weight of ~1500 t.

Definitely wrong on this one 👆

It's very common for an aircraft to have a different maximum takeoff weight than it's maximum landing weight. In fact it's also common to have an even greater taxi weight!
It is called an "Overweight landing". No pilot is going to take the scenic route to get rid of fuel if they get a fire alarm and smoke right after take off.
And then you’d potentially have to rebuild the landing gear as it would be potentially yielded.
No, the analogy is that an overweight airliner crashes and burns just like how a full Starship crashes and burns because the heat shield can not handle the additional mass.

Inspecting and potentially repairing the landing gear would be like a full Starship reentering just fine but requiring inspections and possibly extra refurbishment which is crazy talk ::)
Title: Re: Starship heat shield
Post by: eriblo on 02/27/2023 10:15 am
[...]

Not sure why you’re being so stubborn about this, seeing as multiple sources show that it’s common for take off weight to exceed landed weight, that this would’ve applied to Shuttle and will likely apply to at least some variants of Starship. Can you explain your motivation as to why you insist on this, essentially crippling the ascent payload of Starship so that it could always land with whatever it’s max ascent payload is?
Not sure why you’re being so stubborn about this, seeing as aircraft can always land at their take off weight in a contingency, that the one case where this would’ve applied to Shuttle was deemed to risky and we do not actually know whether this will apply to any variants of Starship. Can you explain your motivation as to why you insist on this, essentially crippling the landing payload of Starship so that it can't land with whatever it’s max ascent payload is?
Title: Re: Starship heat shield
Post by: eriblo on 02/27/2023 10:36 am
To recap the recent discussion:

I did a simplistic calculation of the ballistic coefficient of Starship with no and full payload to show that it is not necessarily that much lower than the Space Shuttle.

There were objections to the full payload case based on the opinion that Starship will only be able to reenter with a fraction of the full payload mass.

Then there was some back and forth regarding aircraft analogies and the importance of maximizing upmass.


Reduced or full payload does not matter all that much for the original argument regarding ballistic coefficient. Starship has a ballistic coefficient at best slightly lower and in many cases quite possibly larger than the Shuttle and it will have less lift so there is no reason to expect an easier reentry.
Title: Re: Starship heat shield
Post by: Robotbeat on 02/27/2023 12:42 pm
It has been established multiple times now that it’s pretty normal for nominal take off weight to exceed nominal allowed landing weight.

I think if you assume Starship will reenter at like 300 tons, you’ll be disappointed. I think this is very unlikely until aero improvements are made. Likely the ballistic coefficient will be very similar to Shuttle.
Title: Re: Starship heat shield
Post by: edzieba on 02/27/2023 01:03 pm
There seems to be a widespread belief that Starship has a low ballistic coefficient. I guess it is based on the large and fluffy appearance?  ::)


Shuttle orbiter: ~350 m2 projected, reentry mass 85 t - 105 t.

Perpendicular ballistic coefficient:
240 kg/m2 - 300 kg/m2

At 40° pitch:
380 kg/m2 - 470 kg/m2


Starship: ~580 m2 projected (flaps akimbo), reentry mass 150 t - 300 t.

Perpendicular ballistic coefficient:
260 kg/m2 - 520 kg/m2

At 70° pitch:
280 kg/m2 - 550 kg/m2

The reference area for Starship will actually be significantly smaller as the flaps will have some dihedral and a cylindrical body has roughly half the drag of a flat bottomed one.

While many reentries will be empty and relatively light the heat shield will be designed for the heaviest case.
Your estimates seem to diverge quite a bit from CALT's: https://forum.nasaspaceflight.com/index.php?topic=56619.0
Title: Re: Starship heat shield
Post by: chopsticks on 02/27/2023 01:10 pm
Yes, if you expect to land Starship with 100 tonnes (or whatever max ascent payload is) the CG is going to be way different then when empty. The neutral skydiver fall/re-entry profile will no longer be neutral (in comparison to when empty), and the flaps will have to compensate for this (if they even can at all!) thereby giving you less margin on either end of the flight envelope.

This doesn't even take into account the extra mass and propellant needed for the landing burn, which would again affect the CG (likely larger header tanks as an example).

IMO a different version of Starship will probably be necessary for landing substantial downmass.
Title: Re: Starship heat shield
Post by: eriblo on 02/27/2023 01:46 pm
There seems to be a widespread belief that Starship has a low ballistic coefficient. I guess it is based on the large and fluffy appearance?  ::)


Shuttle orbiter: ~350 m2 projected, reentry mass 85 t - 105 t.

Perpendicular ballistic coefficient:
240 kg/m2 - 300 kg/m2

At 40° pitch:
380 kg/m2 - 470 kg/m2


Starship: ~580 m2 projected (flaps akimbo), reentry mass 150 t - 300 t.

Perpendicular ballistic coefficient:
260 kg/m2 - 520 kg/m2

At 70° pitch:
280 kg/m2 - 550 kg/m2

The reference area for Starship will actually be significantly smaller as the flaps will have some dihedral and a cylindrical body has roughly half the drag of a flat bottomed one.

While many reentries will be empty and relatively light the heat shield will be designed for the heaviest case.
Your estimates seem to diverge quite a bit from CALT's: https://forum.nasaspaceflight.com/index.php?topic=56619.0
In what way? For Starship they have 140 t, 545 m2 of "waterline" area and a ballistic coefficient of 275 kg/m2 at presumably 70° of pitch.

For Shuttle they have 441 kg/m2.

I would say that the numbers agree surprisingly well?

EDIT to add:
They also conclude that Starship will have similar or higher peak temperatures (but lower total heat loads) compared to Shuttle. This shows that their lower ballistic coefficient can not compensate for the lower lift and is in line with the original point I was making.
Title: Re: Starship heat shield
Post by: sebk on 02/27/2023 02:53 pm

Regarding the aircraft analogy - they are certified to land at any weight they are allowed to take off at, it might just be at a lower vertical speed. This is not the case for Starship as it has a maximum take off weight of ~1500 t.

Definitely wrong on this one 👆

It's very common for an aircraft to have a different maximum takeoff weight than it's maximum landing weight. In fact it's also common to have an even greater taxi weight!
It is called an "Overweight landing". No pilot is going to take the scenic route to get rid of fuel if they get a fire alarm and smoke right after take off.
And then you’d potentially have to rebuild the landing gear as it would be potentially yielded.
No, the analogy is that an overweight airliner crashes and burns just like how a full Starship crashes and burns because the heat shield can not handle the additional mass.

Inspecting and potentially repairing the landing gear would be like a full Starship reentering just fine but requiring inspections and possibly extra refurbishment which is crazy talk ::)

Heatshield is not 0-1 the same way landing gear isn't. There's necessarily quite bit of margin between operational load and actual failure load.

Reentering just fine but being unable to fly again without repairs is actually quite likely contingency option.
Title: Re: Starship heat shield
Post by: Tangilinear Interjar on 02/27/2023 03:40 pm

Regarding the aircraft analogy - they are certified to land at any weight they are allowed to take off at, it might just be at a lower vertical speed. This is not the case for Starship as it has a maximum take off weight of ~1500 t.

Definitely wrong on this one 👆

It's very common for an aircraft to have a different maximum takeoff weight than it's maximum landing weight. In fact it's also common to have an even greater taxi weight!
It is called an "Overweight landing". No pilot is going to take the scenic route to get rid of fuel if they get a fire alarm and smoke right after take off.
And then you’d potentially have to rebuild the landing gear as it would be potentially yielded.

You can also takeoff with more weight than the aircraft is certified for, but then you are out of certification. Same as landing with too much weight, it's pretty simple, aircraft are NOT always certified to land with the same weight as they are certified to takeoff with.

BTW the second or third thing that a pilot will do in an emergency return to airport is hit the fuel dump. In a non time critical emergency they will in fact loiter over a specified area to dump fuel.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 03/07/2023 03:47 am
The emissive (ablative?) paint is flaking off a bit on S24:

https://twitter.com/cnunezimages/status/1632856594672222208
Title: Re: Starship heat shield
Post by: xvel on 03/07/2023 03:43 pm
The emissive (ablative?) paint is flaking off a bit on S24:

https://twitter.com/cnunezimages/status/1632856594672222208

I'm pretty sure this is just a paint and has nothing to do with heat shielding
Title: Re: Starship heat shield
Post by: InterestedEngineer on 03/07/2023 03:51 pm
The emissive (ablative?) paint is flaking off a bit on S24:

https://twitter.com/cnunezimages/status/1632856594672222208

I'm pretty sure this is just a paint and has nothing to do with heat shielding

Why would they only paint next to the heat shield were heat can still be high?

Paint can be a heat shield, using two different methods:

1.  The emissivity of stainless steel is 0.35.  A black paint, the special kinds, can get to 0.99, same as the tiles.  This nearly triples the watts being emitted from a hot section of steel.
2.  Ablative


Either of those count towards managing the heat of reentry, and thus count as a heat shield
Title: Re: Starship heat shield
Post by: Twark_Main on 03/08/2023 04:25 am
The emissive (ablative?) paint is flaking off a bit on S24:

https://twitter.com/cnunezimages/status/1632856594672222208

I'm pretty sure this is just a paint and has nothing to do with heat shielding

Why would they only paint next to the heat shield were heat can still be high?

Paint can be a heat shield, using two different methods:

1.  The emissivity of stainless steel is 0.35.

Where are you seeing that?

NASA says (https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf) the emissivity of stainless is <.15 unless the surface has a sandblasted finish. AFAIK Starship does not have a sandblasted finish.

This only reinforces your main point, of course.
Title: Re: Starship heat shield
Post by: livingjw on 03/08/2023 12:38 pm
I think the paint is just for "pretty".

John
Title: Re: Starship heat shield
Post by: BT52 on 03/08/2023 01:35 pm
I think the paint is just for "pretty".

John

Maybe. But i would totally argue that form follow the function is just too strong in spaceX ethos. Jusk check out how Falcon 9 boosters look after couple reentries.
Title: Re: Starship heat shield
Post by: marsbase on 03/08/2023 02:45 pm
I think the paint is just for "pretty".

John

Maybe. But i would totally argue that form follow the function is just too strong in spaceX ethos. Jusk check out how Falcon 9 boosters look after couple reentries.
Soot on the F9 first stage is an advertisement for reusability.  On the Starship booster they are just using paint to make clean lines that look well "engineered".  In neither case is form following function.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 03/08/2023 02:53 pm
I think the paint is just for "pretty".

John

Maybe. But i would totally argue that form follow the function is just too strong in spaceX ethos. Jusk check out how Falcon 9 boosters look after couple reentries.
Soot on the F9 first stage is an advertisement for reusability.  On the Starship booster they are just using paint to make clean lines that look well "engineered".  In neither case is form following function.

If the temperature in those areas just windward of the heat shield will get into the 400-500degC range (plausible), why not paint them with a high emissivity paint?  It's easily available.

https://acktar.com/products-services/high-emissivity-materials/

Otherwise there's zero reason to paint at all.  "best part is no part".

My guess is they are running an experiment (that has already failed).
Title: Re: Starship heat shield
Post by: InterestedEngineer on 03/08/2023 02:55 pm


Where are you seeing that?

NASA says (https://ntrs.nasa.gov/api/citations/19840015630/downloads/19840015630.pdf) the emissivity of stainless is <.15 unless the surface has a sandblasted finish. AFAIK Starship does not have a sandblasted finish.

This only reinforces your main point, of course.

I googled it of course.

https://www.flukeprocessinstruments.com/en-us/service-and-support/knowledge-center/infrared-technology/emissivity-metals


I didn't bother to check for what wavelengths.  NASA probably did, so I'll take their numbers.
Title: Re: Starship heat shield
Post by: OTV Booster on 03/09/2023 02:07 pm
The emissive (ablative?) paint is flaking off a bit on S24:

https://twitter.com/cnunezimages/status/1632856594672222208 (https://twitter.com/cnunezimages/status/1632856594672222208)

I'm pretty sure this is just a paint and has nothing to do with heat shielding

Why would they only paint next to the heat shield were heat can still be high?

Paint can be a heat shield, using two different methods:

1.  The emissivity of stainless steel is 0.35.  A black paint, the special kinds, can get to 0.99, same as the tiles.  This nearly triples the watts being emitted from a hot section of steel.
2.  Ablative


Either of those count towards managing the heat of reentry, and thus count as a heat shield
A possible alternative: Elon is big on visuals.
Title: Re: Starship heat shield
Post by: chopsticks on 03/09/2023 02:32 pm


Otherwise there's zero reason to paint at all.  "best part is no part".

I think I'm going to barf if I hear this one more time.

You realize that they painted B4's engine bells, too right?

Pray tell, what was "the necessary part" in this case?
Title: Re: Starship heat shield
Post by: JamesH65 on 03/09/2023 02:45 pm
I suspect the conversation went as follows:

Elon: Hmm, those jagged edges of the tiles make it look unfinished.
Someone else: We don't want to make and attach half tiles just to make it look nice!
Elon: Just paint on a straight black edge, it will look fine from a distance.
Title: Re: Starship heat shield
Post by: wannamoonbase on 03/09/2023 08:34 pm
Heat shields are tough, time consuming and expensive. 

SpaceX is going to have to improve this whole process a lot, but first, gotta fly!
Title: Re: Starship heat shield
Post by: dondar on 03/12/2023 10:29 am
I think the paint is just for "pretty".

John
is this really a paint? looks to be a goo they used as the base to clue tiles on. (it is quite thick as you can see in the damaged spots.The form indicates initial design specs.
Title: Re: Starship heat shield
Post by: xvel on 03/12/2023 05:48 pm
I think the paint is just for "pretty".

John
is this really a paint? looks to be a goo they used as the base to clue tiles on. (it is quite thick as you can see in the damaged spots.The form indicates initial design specs.

I think you are quite wrong, most of the tiles are not glued but mechanically attached and those that are glued are glued directly with something like high temperature rtv sillicone, and this was painted after the tiles were attached

https://twitter.com/NicAnsuini/status/1533077216036274179

photo before painting
Title: Re: Starship heat shield
Post by: uhrflieger on 03/17/2023 05:23 am
3 years ago I was able to follow the extensive discussion about the absolute avoidance of straight joints. 
https://forum.nasaspaceflight.com/index.php?topic=50748.msg2073366#msg2073366
https://twitter.com/elonmusk/status/1107379727302451200
Now I've been wondering for quite some time about the practical implementation of the problem where the creative tile shapes discussed here have not been used.  Instead, dead-straight joints were arranged in the nose cone area.  Sorry I haven't gone through all the >170 pages here yet, can someone please give me a link if this has already been discussed and justified here?
Title: Re: Starship heat shield
Post by: Crispy on 03/17/2023 08:24 am
Now I've been wondering for quite some time about the practical implementation of the problem where the creative tile shapes discussed here have not been used.  Instead, dead-straight joints were arranged in the nose cone area.  Sorry I haven't gone through all the >170 pages here yet, can someone please give me a link if this has already been discussed and justified here?

The nose cap tiles (and other "non-standard" areas with aligned joints like the flap hinges) are glued instead of bracketed, and have a filler between them to keep the hot gas out.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 05/06/2023 04:54 am
Do we have a consensus guess for the maximum entry speed that Starship must handle?  Do you think it'll be higher or lower than 11km/s?

Am I correct in assuming that, from a thermal standpoint, it doesn't matter much whether the entry is on Earth or Mars?  (Constraining the amount of permissible negative lift needed to keep the vehicle in the atmosphere on Mars is another story...)
Title: Re: Starship heat shield
Post by: whitelancer64 on 05/06/2023 05:28 am
Do we have a consensus guess for the maximum entry speed that Starship must handle?  Do you think it'll be higher or lower than 11km/s?

Am I correct in assuming that, from a thermal standpoint, it doesn't matter much whether the entry is on Earth or Mars?  (Constraining the amount of permissible negative lift needed to keep the vehicle in the atmosphere on Mars is another story...)

Higher than 11 km/s by definition. Minimum velocity on a free return trajectory from Mars is 11.4 km/s but is typically around 12-13ish km/s (NASA limited studies for human missions to a maximum reentry velocity of 16 km/s).

The exact velocity is heavily dependent on the Hohmann transfer window and the dV of the initial orbit injection burn.

Heat loads are significantly higher on Earth than on Mars, due to the higher velocity of entry. Mars entry velocity is typically around 4.5-7.5ish km/s for the various probes NASA has sent.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 05/06/2023 06:16 am
Heat loads are significantly higher on Earth than on Mars, due to the higher velocity of entry. Mars entry velocity is typically around 4.5-7.5ish km/s for the various probes NASA has sent.

I was looking for an apples-to-apples, entry-speed-normalized answer to that question.  I'm assuming that heat loads for an 11.4km/s entry speed (not v∞) on Earth and Mars should be roughly the same.  (If you know the entry speed, you can figure out the v∞, a vice versa.)  The Mars entry trajectory will stabilize lower in the atmosphere, but the differences in composition should have only a small effect, correct?

Good point about needing to be able to cover the free return case.

I'm fooling with this because I want to be able to constrain arrival v∞ in both directions.  That seems to be more of a gating item on time of flight than the departure v∞.  However, if you're flying a with a full load of prop, you can keep some propulsive braking prop.  But that of course limits your departure speed in a different way...
Title: Re: Starship heat shield
Post by: steveleach on 05/06/2023 09:38 am
Heat loads are significantly higher on Earth than on Mars, due to the higher velocity of entry. Mars entry velocity is typically around 4.5-7.5ish km/s for the various probes NASA has sent.

I was looking for an apples-to-apples, entry-speed-normalized answer to that question.  I'm assuming that heat loads for an 11.4km/s entry speed (not v∞) on Earth and Mars should be roughly the same.  (If you know the entry speed, you can figure out the v∞, a vice versa.)  The Mars entry trajectory will stabilize lower in the atmosphere, but the differences in composition should have only a small effect, correct?

Good point about needing to be able to cover the free return case.

I'm fooling with this because I want to be able to constrain arrival v∞ in both directions.  That seems to be more of a gating item on time of flight than the departure v∞.  However, if you're flying a with a full load of prop, you can keep some propulsive braking prop.  But that of course limits your departure speed in a different way...
If entry speed is your limiting factor then wouldn't it be best to include a braking burn almost by definition?

Take whatever dv you have available above that which gives the max entry speed, and divide it across acceleration and braking.
Title: Re: Starship heat shield
Post by: sebk on 05/06/2023 12:21 pm
Heat loads are significantly higher on Earth than on Mars, due to the higher velocity of entry. Mars entry velocity is typically around 4.5-7.5ish km/s for the various probes NASA has sent.

I was looking for an apples-to-apples, entry-speed-normalized answer to that question.  I'm assuming that heat loads for an 11.4km/s entry speed (not v∞) on Earth and Mars should be roughly the same.  (If you know the entry speed, you can figure out the v∞, a vice versa.)  The Mars entry trajectory will stabilize lower in the atmosphere, but the differences in composition should have only a small effect, correct?

Not really.

Mars has different atmospheric composition which, among other things, means:

* A higher Mach number (for the same velocity). Your 12.5km/s Mach 46 Earth atmosphere entry is Mach 60 in CO2 atmosphere.
* Very different radiative environment in and behind the bow shock.

The net result is that even Mars ballistic entries are considered worse than Earth ones at the same speed.

But all of this is minor.

The major part is that at Mars you must do negative lifting entry at anything even similar to Earth's LEO entry, not to mention interplanetary entry. And the thing is at high Mach numbers your L:D ratio is severely limited. This dictates high g-loads. And high g-loads mean ~proportionally higher heating rates.

IOW At Earth you could limit your heating rate by skidding on top of the atmosphere for quite a while. Not so much on Mars where you must accept high g-load and accompanying heating rate.
Title: Re: Starship heat shield
Post by: livingjw on 05/06/2023 03:11 pm
Heat loads are significantly higher on Earth than on Mars, due to the higher velocity of entry. Mars entry velocity is typically around 4.5-7.5ish km/s for the various probes NASA has sent.

I was looking for an apples-to-apples, entry-speed-normalized answer to that question.  I'm assuming that heat loads for an 11.4km/s entry speed (not v∞) on Earth and Mars should be roughly the same.  (If you know the entry speed, you can figure out the v∞, a vice versa.)  The Mars entry trajectory will stabilize lower in the atmosphere, but the differences in composition should have only a small effect, correct?

Not really.

Mars has different atmospheric composition which, among other things, means:

* A higher Mach number (for the same velocity). Your 12.5km/s Mach 46 Earth atmosphere entry is Mach 60 in CO2 atmosphere.
* Very different radiative environment in and behind the bow shock.

The net result is that even Mars ballistic entries are considered worse than Earth ones at the same speed.

But all of this is minor.

The major part is that at Mars you must do negative lifting entry at anything even similar to Earth's LEO entry, not to mention interplanetary entry. And the thing is at high Mach numbers your L:D ratio is severely limited. This dictates high g-loads. And high g-loads mean ~proportionally higher heating rates.

IOW At Earth you could limit your heating rate by skidding on top of the atmosphere for quite a while. Not so much on Mars where you must accept high g-load and accompanying heating rate.

Max L/D changes hardly at all after Mach ~4.  Max L/D of ~1 should be achievable throughout Mars entry.

John
Title: Re: Starship heat shield
Post by: sebk on 05/06/2023 04:22 pm
Yes, Starship according to various reports has L:D from 0.5 to 0.8.

At reportedly nominal 60° AoA I'd expect L:D ~0.5

Still, at Earth, due to lower curvature you could skim the atmosphere for quite a bit without even trying to produce lift. You could fly for about 2800km (with half of that in a densest zone providing ~90% of braking) with zero lift and stay with g-loads below 1. So you could start your reentry at over 12km/s and without any lift and without exceeding 1g slow down enough to capture.

If you tried the same exercise at Mars, at 12km/s you'd just reduce your velocity to 11.75km/s or so and wouldn't be appreciably closer to capture.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 05/06/2023 05:22 pm
Answers the questions I had about how SpaceX might monitor Mars aerocapture/entry

https://www.jpl.nasa.gov/images/pia22317-marco-being-tested-in-sunlight
Title: Re: Starship heat shield
Post by: eriblo on 05/06/2023 08:02 pm
I did some simplified sims a while ago - as stated above entries at Mars are generally gentler because they are slower. At the same entry velocity the peak temperature and g-forces are higher due to the smaller radius and gravity.

A 6 km/s entry at Mars has about the same peak temperature as an 8 km/s entry at Earth. If you have a 5 g0 limit the max entry speed at Mars is 12 km/s and at Earth it is 15 km/s.

I expect an fully reusable tile bases heat shield to be good for LEO and multi-pass cis-lunar as well as slow Mars transfer and Mars Orbit. For fast Mars transfers and Earth return I think they will need an ablative heat shield.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 05/06/2023 08:31 pm
I did some simplified sims a while ago - as stated above entries at Mars are generally gentler because they are slower. At the same entry velocity the peak temperature and g-forces are higher due to the smaller radius and gravity.

A 6 km/s entry at Mars has about the same peak temperature as an 8 km/s entry at Earth. If you have a 5 g0 limit the max entry speed at Mars is 12 km/s and at Earth it is 15 km/s.

I expect an fully reusable tile bases heat shield to be good for LEO and multi-pass cis-lunar as well as slow Mars transfer and Mars Orbit. For fast Mars transfers and Earth return I think they will need an ablative heat shield.

How did you you simulate maximum heating and what was the criteria for "max entry speed"?
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 05/06/2023 09:41 pm
Yes, Starship according to various reports has L:D from 0.5 to 0.8.

At reportedly nominal 60° AoA I'd expect L:D ~0.5

Still, at Earth, due to lower curvature you could skim the atmosphere for quite a bit without even trying to produce lift. You could fly for about 2800km (with half of that in a densest zone providing ~90% of braking) with zero lift and stay with g-loads below 1. So you could start your reentry at over 12km/s and without any lift and without exceeding 1g slow down enough to capture.

If you tried the same exercise at Mars, at 12km/s you'd just reduce your velocity to 11.75km/s or so and wouldn't be appreciably closer to capture.

Ultimately, all I'm trying to get is a maximum value for arrival v∞ for both Mars and Earth.

There will be a maximum allowable entry speed:

vEntryMax = min(vMaxThermal, vMaxAccel)

where:

1) vMaxThermal is the speed that results in the maximum allowable heat pulse at some magic altitude.  The magic altitude will be different for Earth and Mars, but my assumption is that vMaxThermal at that magic altitude will be the same.  I don't know how to compute this. 

I'm also not sure that this normalization of the problem to a single entry speed at some planet-dependent magic altitude is valid.  I see that, just above, eriblo doesn't think this is true.  Why?

2) vMaxAccel is the maximum allowable speed that keeps the payload and/or crew from being crushed from lift acceleration while maintaining Starship at the magic altitude:

maxLiftAccel = vMaxAccel²/rMagic - g
where
rMagic = magicAltitude + rBody
and
g = μ/rMagic²

So the constraint is:

vMaxAccel <= sqrt(rMagic*maxLiftAccel + μ/rMagic)

I'm guessing that maxLiftAccel will be about 3 gees (29.4m/s²).

Once we've computed vEntryMax, we can set the hyperbolic periapse to rMagic and solve for the arrival v∞:

vInfinity = sqrt(vEntryMax² - 2μ/rMagic)

Clarification:  I expect that vMaxThermal will be the limiting condition for Earth, but vMaxAccel will limit Mars entry.
Title: Re: Starship heat shield
Post by: sebk on 05/07/2023 09:15 pm
I think for thermal you have 2 primary constraints, not 1:

1. Heat pulse, i.e. the one you mentioned. This is the amount of energy which gets to your ship.
2. Peak heating. This is the maximum heating rate. Among other things this dictates skin temperature.

Ablative heat shields are primarily concerned with the first (1). But non-ablative ones are concerned with both (1 & 2), and it's easier to adjust them for 1 if a need arises (generally you improve the insulation layer). But adjusting for a higher peak heating (2) essentially means coming up with a different material which is not an easy change, and often means redoing your heatshield from scratch. And If you ramp peak heating just a tad too much we're simply out of known materials at all.

The thing about (2) is that it depends not just on velocity. It depends on deceleration as well. If you replace 2g braking with 4g braking you essentially doubled your peak heating.

At the same time you have likely reduced(!) heat pulse! This is counterintuitive, because kinetic energy to lose is the same regardless of how quickly you drop it. But the thing is, at certain point the more rarefied the ambient atmosphere the larger fraction of heat gets to the vehicle (and less is taken away by the ambient air). So when you pass entry interface heating initially grows much faster than deceleration. Just look at Shuttle reentry heating and deceleration profiles. Or some (SpaceX?) materials about Starship reentry. You're dropping speed slowly while heating is already high.

So if you have an ablative heatshield, you want to punch through the too thin air fast into high deceleration region. Total heat pulse is less that way, so you need less material to ablate. And you don't care that much about peak heating (within limits), as the temperature is primarily set by your ablative material's phase changes.

But if you have non-ablative heatshield, you prefer skidding on top of the atmosphere. The heat pulse is larger (often significantly), but you keep peak heating in check by keeping the whole kinetic energy drop rate in check. But if you have to generate more (negative) lift to hold onto a small low planet, you need to increase drag according to L:D ratio of your vehicle, which means higher deceleration which means higher kinetic energy drop rate and higher heating.

Title: Re: Starship heat shield
Post by: TheRadicalModerate on 05/08/2023 04:23 am
But if you have non-ablative heatshield, you prefer skidding on top of the atmosphere. The heat pulse is larger (often significantly), but you keep peak heating in check by keeping the whole kinetic energy drop rate in check. But if you have to generate more (negative) lift to hold onto a small low planet, you need to increase drag according to L:D ratio of your vehicle, which means higher deceleration which means higher kinetic energy drop rate and higher heating.

I'd been assuming that the actual deceleration was negligible compared to the lift-induced acceleration.  That's clearly not true, per your L/D reasoning, which seems sound to me.  I think that blows up my "magic altitude, same thermal" assumption.

That's not fatal to getting clean entry speeds for both Mars and Earth, but it does mean that you need to make an analysis of each out whole cloth, rather than breaking this into easily-separable thermal and lift-based pieces.
Title: Re: Starship heat shield
Post by: hoku on 05/12/2023 06:18 am
"Apparently all the Starship thermal protection system tiles started washing up on South Padre Island yesterday (~3 weeks post launch)"

https://twitter.com/DrChrisCombs/status/1656762126151700480 (https://twitter.com/DrChrisCombs/status/1656762126151700480)
Title: Re: Starship heat shield
Post by: RamsesBic on 05/12/2023 01:10 pm
Starship Gazer took this image of the back side of a tile. It is the first I have seen so clearly.
Title: Re: Starship heat shield
Post by: Oersted on 05/12/2023 03:04 pm
"Apparently all the Starship thermal protection system tiles started washing up on South Padre Island yesterday (~3 weeks post launch)"

https://twitter.com/DrChrisCombs/status/1656762126151700480 (https://twitter.com/DrChrisCombs/status/1656762126151700480)

Good material for a trencadís project.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 05/12/2023 03:07 pm
"Apparently all the Starship thermal protection system tiles started washing up on South Padre Island yesterday (~3 weeks post launch)"

https://twitter.com/DrChrisCombs/status/1656762126151700480 (https://twitter.com/DrChrisCombs/status/1656762126151700480)

Good material for a trencadís project.

I would love it if someone ran some experiments on the pieces.  Here are some suggestions:

1.  Soak in water and then freeze and thaw to see if they disintegrate from ice expansion.
2.  Take a blowtorch to them to see how well they resist heat transfer
Title: Re: Starship heat shield
Post by: Robotbeat on 05/12/2023 03:39 pm
If China doesn’t have somebody down there in South Texas hunting for heat shield tiles, then they are incompetent.
Title: Re: Starship heat shield
Post by: edzieba on 05/12/2023 04:31 pm
If China doesn’t have somebody down there in South Texas hunting for heat shield tiles, then they are incompetent.
They're sintered silica fibre tiles with a Borosilicate RCG surface layer. The geometry and attachment method is novel (but also already public knowledge), the composition is not. China can already manufacture their own (https://www.mdpi.com/2079-6412/13/2/463/pdf).
China have no need to scrabble in the dirt to gather something they can already make.
Title: Re: Starship heat shield
Post by: Robotbeat on 05/12/2023 08:46 pm
If China doesn’t have somebody down there in South Texas hunting for heat shield tiles, then they are incompetent.
They're sintered silica fibre tiles with a Borosilicate RCG surface layer. The geometry and attachment method is novel (but also already public knowledge), the composition is not. China can already manufacture their own (https://www.mdpi.com/2079-6412/13/2/463/pdf).
China have no need to scrabble in the dirt to gather something they can already make.
Sure, but you would likely not get approval to sell heatshield tiles direct to China.
Title: Re: Starship heat shield
Post by: hoku on 05/14/2023 08:00 am
Flotsam heat shield tiles from SN-24 collected at South Padre Island beaches are now up for bid on eBay (some are mis-identified as SN-11?).
Title: Re: Starship heat shield
Post by: drzerg on 05/14/2023 11:52 am
They are still property of spacex. But they obligated to clear the debris on their own cost.
Title: Re: Starship heat shield
Post by: Nomadd on 05/14/2023 02:54 pm
Flotsam heat shield tiles from SN-24 collected at South Padre Island beaches are now up for bid on eBay (some are mis-identified as SN-11).
There were plenty of SN11 tiles picked up. I've used some myself.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 05/14/2023 10:41 pm
Flotsam heat shield tiles from SN-24 collected at South Padre Island beaches are now up for bid on eBay (some are mis-identified as SN-11).
There were plenty of SN11 tiles picked up. I've used some myself.

Nomadd:

Have you tried a soak/freeze cycle to see how bad they fall apart when frozen while wet?

I would love to hear the result of that experiment.
Title: Re: Starship heat shield
Post by: Nomadd on 05/15/2023 12:22 am
Flotsam heat shield tiles from SN-24 collected at South Padre Island beaches are now up for bid on eBay (some are mis-identified as SN-11).
There were plenty of SN11 tiles picked up. I've used some myself.

Nomadd:

Have you tried a soak/freeze cycle to see how bad they fall apart when frozen while wet?

I would love to hear the result of that experiment.
Never thought of that. Maybe on my next visit to the storehouse. i'm wandering around Ireland for some reason at the moment.
Title: Re: Starship heat shield
Post by: Oersted on 05/15/2023 01:23 pm
Ireland is perfect for a soak/freeze cycle...  :)
Title: Re: Starship heat shield
Post by: neoforce on 05/15/2023 05:18 pm
Flotsam heat shield tiles from SN-24 collected at South Padre Island beaches are now up for bid on eBay (some are mis-identified as SN-11).
There were plenty of SN11 tiles picked up. I've used some myself.

Maybe you should consider selling some of them.  lots of bids and high prices. 
Title: Re: Starship heat shield
Post by: Robotbeat on 05/15/2023 08:09 pm
They are still property of spacex. But they obligated to clear the debris on their own cost.
Im not sure that it is. It didn’t go to space, so the usual OST provision may not apply.
Title: Re: Starship heat shield
Post by: drzerg on 05/15/2023 10:28 pm
They are still property of spacex. But they obligated to clear the debris on their own cost.
Im not sure that it is. It didn’t go to space, so the usual OST provision may not apply.

Good catch! So what legal status of raptors lying on the ocean floor in the international waters are?

p.s. sorry. Just realized that it is off topic.
Title: Re: Starship heat shield
Post by: edzieba on 05/16/2023 08:26 am
They are still property of spacex. But they obligated to clear the debris on their own cost.
Im not sure that it is. It didn’t go to space, so the usual OST provision may not apply.
The Space Liability Convention still applies to launch vehicles that do not reach orbit (or above the Karman line), so SpaceX would be liable for cleanup. Ownership is undefined beyond 'Objects launched into reach Outer Space' - could be interpreted as covering attempted but failed launches to Outer Space, or could be interpreted as only objects that actually reach Outer Space are covered, leaving a grey area for suborbital rocket bodies and failed launches. Presumably all parties would - if ever challenged - wish the interpretation to cover suborbital objects too (to dissuade theft and aid recovery of items from failed launches, e.g. the Discoverer 2 situation) but this would to be clarified unless challenged.
Maritime law on salvage (flotsam vs. jetsam, etc) has already not been broadly interpreted as applying to aircraft, so there is little basis in attempting to apply it to spacecraft either.
Title: Re: Starship heat shield
Post by: Robotbeat on 05/16/2023 01:32 pm
You are posting your supposition about the law as if it is fact. The clear wording of the law does not say it applies to failed launches which never reach space.
Title: Re: Starship heat shield
Post by: edzieba on 05/16/2023 01:51 pm
You are posting your supposition about the law as if it is fact. The clear wording of the law does not say it applies to failed launches which never reach space.
The clear working of the law is in fact clear, Article I Parts (b) and (d) (https://www.unoosa.org/pdf/gares/ARES_26_2777E.pdf):
Quote
(b) The term "launching" includes attempted launching;
[...]
(d) The term "space object" includes component parts of
a object as well as its launch vehicle and parts threof.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 05/16/2023 03:46 pm
You are posting your supposition about the law as if it is fact. The clear wording of the law does not say it applies to failed launches which never reach space.
The clear working of the law is in fact clear, Article I Parts (b) and (d) (https://www.unoosa.org/pdf/gares/ARES_26_2777E.pdf):
Quote
(b) The term "launching" includes attempted launching;
[...]
(d) The term "space object" includes component parts of
a object as well as its launch vehicle and parts threof.

I asked this question in the licenses thread, where it is more on topic than here.

Please take the legal discussions over there:

https://forum.nasaspaceflight.com/index.php?topic=58853.msg2487242#msg2487242
Title: Re: Starship heat shield
Post by: Robotbeat on 05/16/2023 03:52 pm
You are posting your supposition about the law as if it is fact. The clear wording of the law does not say it applies to failed launches which never reach space.
The clear working of the law is in fact clear, Article I Parts (b) and (d) (https://www.unoosa.org/pdf/gares/ARES_26_2777E.pdf):
Quote
(b) The term "launching" includes attempted launching;
[...]
(d) The term "space object" includes component parts of
a object as well as its launch vehicle and parts threof.
I stand corrected! Thank you.
Title: Re: Starship heat shield
Post by: FutureSpaceTourist on 05/22/2023 06:24 am
Elon liked this tweet:

https://twitter.com/iniallanderson/status/1660391871900729345

Quote
Awesome video here of someone torching a piece of Starship Heatshield Tile! Look how quickly that heat is dissipated! 🔥
📸: @ Keith Yates | facebook.com/groups/1541938…
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 06/27/2023 11:06 pm
I think for thermal you have 2 primary constraints, not 1:

1. Heat pulse, i.e. the one you mentioned. This is the amount of energy which gets to your ship.
2. Peak heating. This is the maximum heating rate. Among other things this dictates skin temperature.

Ablative heat shields are primarily concerned with the first (1). But non-ablative ones are concerned with both (1 & 2), and it's easier to adjust them for 1 if a need arises (generally you improve the insulation layer). But adjusting for a higher peak heating (2) essentially means coming up with a different material which is not an easy change, and often means redoing your heatshield from scratch. And If you ramp peak heating just a tad too much we're simply out of known materials at all.

The thing about (2) is that it depends not just on velocity. It depends on deceleration as well. If you replace 2g braking with 4g braking you essentially doubled your peak heating.

At the same time you have likely reduced(!) heat pulse! This is counterintuitive, because kinetic energy to lose is the same regardless of how quickly you drop it. But the thing is, at certain point the more rarefied the ambient atmosphere the larger fraction of heat gets to the vehicle (and less is taken away by the ambient air). So when you pass entry interface heating initially grows much faster than deceleration. Just look at Shuttle reentry heating and deceleration profiles. Or some (SpaceX?) materials about Starship reentry. You're dropping speed slowly while heating is already high.

So if you have an ablative heatshield, you want to punch through the too thin air fast into high deceleration region. Total heat pulse is less that way, so you need less material to ablate. And you don't care that much about peak heating (within limits), as the temperature is primarily set by your ablative material's phase changes.

But if you have non-ablative heatshield, you prefer skidding on top of the atmosphere. The heat pulse is larger (often significantly), but you keep peak heating in check by keeping the whole kinetic energy drop rate in check. But if you have to generate more (negative) lift to hold onto a small low planet, you need to increase drag according to L:D ratio of your vehicle, which means higher deceleration which means higher kinetic energy drop rate and higher heating.

First, I never thanked you for this post.  It's a very clear problem statement, and I refer back to it quite often.

So how do things change if Starship intends to aerocapture instead of doing a direct EDL?  (This question applies for both Mars and Earth entry.)

I can think of a few of things:

1) You don't have to kill all the speed in a single direct EDL.  You only need enough to get you captured into an eccentric orbit.  That presumably makes the path through the atmosphere shorter, which reduces the heat pulse.

2) The Starship can cold-soak or barbecue roll to radiate away the heat pulse before beginning the actual EDL.

3) You also obviously get a chance to null out any guidance irregularities, allowing changes to both periapse altitude and inclination post-aerocapture.

4) The radius of curvature of the path requiring negative lift can be substantially greater, resulting in lower lift, which in turn reduces the amount of drag that's required.

It's #4 that I'm most curious about.  (See attachment.)  The deeper you can dip into the atmosphere before pulling out, the larger the radius of curvature of the path where substantial drag is produced.  But that means that the Starship has to endure a very brief period of high drag, and therefore high peak heating.  You obviously can't exceed a dynamic pressure that causes so high a peak heating that the tiles fail, but they're not going to soak at that temperature for very long.  This is the kinda-in-between case between pure peak heating and total heat pulse.

Is there a pony in here somewhere?  As always, the name of the game is the highest tolerable arrival v∞.
Title: Re: Starship heat shield
Post by: Asteroza on 06/28/2023 12:33 am
Heat pulse cooling post aerocapture is still non-trivial. You gotta deploy radiators fairly quickly once you pull out of the reentry dive, plus do a burn at apogee to keep you out of atmosphere for the period necessary to get cooling into a stable state in your elliptical loiter orbit until you decide to come down for another atmosphere run or EDL.

There's also the weird trade space of skip glide reetries post-aerocapture, where the heat pulse problem magnifies but you may be able to reduce peak heating.
Title: Re: Starship heat shield
Post by: livingjw on 06/28/2023 06:54 pm
Heat pulse cooling post aerocapture is still non-trivial. You gotta deploy radiators fairly quickly once you pull out of the reentry dive, plus do a burn at apogee to keep you out of atmosphere for the period necessary to get cooling into a stable state in your elliptical loiter orbit until you decide to come down for another atmosphere run or EDL.

There's also the weird trade space of skip glide reetries post-aerocapture, where the heat pulse problem magnifies but you may be able to reduce peak heating.

Why would you need to deploy radiators? Post-aerocapture the heat will radiate away from the tiles and also into the tanks. Tanks would be vented to control pressure. I don't see how radiators would help.

John
Title: Re: Starship heat shield
Post by: sebk on 06/28/2023 07:23 pm
I think for thermal you have 2 primary constraints, not 1:

1. Heat pulse, i.e. the one you mentioned. This is the amount of energy which gets to your ship.
2. Peak heating. This is the maximum heating rate. Among other things this dictates skin temperature.

Ablative heat shields are primarily concerned with the first (1). But non-ablative ones are concerned with both (1 & 2), and it's easier to adjust them for 1 if a need arises (generally you improve the insulation layer). But adjusting for a higher peak heating (2) essentially means coming up with a different material which is not an easy change, and often means redoing your heatshield from scratch. And If you ramp peak heating just a tad too much we're simply out of known materials at all.

The thing about (2) is that it depends not just on velocity. It depends on deceleration as well. If you replace 2g braking with 4g braking you essentially doubled your peak heating.

At the same time you have likely reduced(!) heat pulse! This is counterintuitive, because kinetic energy to lose is the same regardless of how quickly you drop it. But the thing is, at certain point the more rarefied the ambient atmosphere the larger fraction of heat gets to the vehicle (and less is taken away by the ambient air). So when you pass entry interface heating initially grows much faster than deceleration. Just look at Shuttle reentry heating and deceleration profiles. Or some (SpaceX?) materials about Starship reentry. You're dropping speed slowly while heating is already high.

So if you have an ablative heatshield, you want to punch through the too thin air fast into high deceleration region. Total heat pulse is less that way, so you need less material to ablate. And you don't care that much about peak heating (within limits), as the temperature is primarily set by your ablative material's phase changes.

But if you have non-ablative heatshield, you prefer skidding on top of the atmosphere. The heat pulse is larger (often significantly), but you keep peak heating in check by keeping the whole kinetic energy drop rate in check. But if you have to generate more (negative) lift to hold onto a small low planet, you need to increase drag according to L:D ratio of your vehicle, which means higher deceleration which means higher kinetic energy drop rate and higher heating.

First, I never thanked you for this post.  It's a very clear problem statement, and I refer back to it quite often.

So how do things change if Starship intends to aerocapture instead of doing a direct EDL?  (This question applies for both Mars and Earth entry.)

I can think of a few of things:

1) You don't have to kill all the speed in a single direct EDL.  You only need enough to get you captured into an eccentric orbit.  That presumably makes the path through the atmosphere shorter, which reduces the heat pulse.

2) The Starship can cold-soak or barbecue roll to radiate away the heat pulse before beginning the actual EDL.

3) You also obviously get a chance to null out any guidance irregularities, allowing changes to both periapse altitude and inclination post-aerocapture.

4) The radius of curvature of the path requiring negative lift can be substantially greater, resulting in lower lift, which in turn reduces the amount of drag that's required.

It's #4 that I'm most curious about.  (See attachment.)  The deeper you can dip into the atmosphere before pulling out, the larger the radius of curvature of the path where substantial drag is produced.  But that means that the Starship has to endure a very brief period of high drag, and therefore high peak heating.  You obviously can't exceed a dynamic pressure that causes so high a peak heating that the tiles fail, but they're not going to soak at that temperature for very long.  This is the kinda-in-between case between pure peak heating and total heat pulse.

Is there a pony in here somewhere?  As always, the name of the game is the highest tolerable arrival v∞.

Generally braking force (at a fixed velocity) is ~linear with atmospheric density, so over a single scale height the force will change by a factor of e. In effect about 3/4 (more precisely 73.1%) of the whole braking will occur in a 1 scale height band of the atmosphere, 88% will take 2 scale heights band, and 3 scale heights will cover over 95% of braking.

If your velocity is closeish to parabolic, your ballistic braking path through a single scale height band (i.e. responsible for about 3/4 of braking) will be very roughly 2x the horizon distance from 2x scale height (if I'm not badly mistaken). Plugging in Mars radius (3389.5km) and atmospheric scale height (11.1km) we get ~777km path for ~3/4 of aerocapture ∆v. If speeds are deeper into the hyperbolic territory the path will get shorter, down to about 660km at really high speeds. So say ~730-750km of path staying withing one scale height. This means ~1000km path equivalent for 100% ∆v. But remember that said 660~777km path still has a factor of e difference in density, so the peak deceleration would be √e ≈ 1.6x higher than average over that single scale height band.

So all in all, if you don't produce lift, for Mars your peak deceleration will be about 1.6x the uniform deceleration you'd need to achieve your target ∆v over 1000km path.

NB, on Earth this equivalent ballistic braking path is ~1250km.
Title: Re: Starship heat shield
Post by: TheRadicalModerate on 06/28/2023 11:53 pm
Heat pulse cooling post aerocapture is still non-trivial. You gotta deploy radiators fairly quickly once you pull out of the reentry dive, plus do a burn at apogee to keep you out of atmosphere for the period necessary to get cooling into a stable state in your elliptical loiter orbit until you decide to come down for another atmosphere run or EDL.

There's also the weird trade space of skip glide reetries post-aerocapture, where the heat pulse problem magnifies but you may be able to reduce peak heating.

Why would you need to deploy radiators? Post-aerocapture the heat will radiate away from the tiles and also into the tanks. Tanks would be vented to control pressure. I don't see how radiators would help.

John

It does bring up some interesting questions about how to cool the payload bay / garage / crew module.  I guess they could sink that heat into the main tanks as well.

It'd be an interesting calculation to figure out how many tonnes of prop you lose dealing with the heat pulse.  Of course, you'd need to know what the heat pulse was in the first place.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 06/29/2023 12:55 am
.

4) The radius of curvature of the path requiring negative lift can be substantially greater, resulting in lower lift, which in turn reduces the amount of drag that's required.

It's #4 that I'm most curious about.  (See attachment.)  The deeper you can dip into the atmosphere before pulling out, the larger the radius of curvature of the path where substantial drag is produced.  But that means that the Starship has to endure a very brief period of high drag, and therefore high peak heating.  You obviously can't exceed a dynamic pressure that causes so high a peak heating that the tiles fail, but they're not going to soak at that temperature for very long.  This is the kinda-in-between case between pure peak heating and total heat pulse.

Is there a pony in here somewhere?  As always, the name of the game is the highest tolerable arrival v∞.

Here's a possible but very small pony:

http://mae-nas.eng.usu.edu/MAE_5420_Web/section3/appendix3.pdf

Rough back of the envelope calculations say there's about 8GJ of heat capacity for the tiles of Starship (LI-2200).

So some of that heat capacity is available for the "deep dip" the heat radiating capability of the tiles can be exceeded for however much heat capacity is left before Bad Stuff Happens.

Let's say there's 4GJ left.   For 300t vehicle running at 7km/sec that's a deltaV of 2m/sec.   

A tiny, tiny little pony.   Might be better off looking at film cooling hot spots with CH4.
Title: Re: Starship heat shield
Post by: Asteroza on 06/29/2023 01:08 am
Heat pulse cooling post aerocapture is still non-trivial. You gotta deploy radiators fairly quickly once you pull out of the reentry dive, plus do a burn at apogee to keep you out of atmosphere for the period necessary to get cooling into a stable state in your elliptical loiter orbit until you decide to come down for another atmosphere run or EDL.

There's also the weird trade space of skip glide reetries post-aerocapture, where the heat pulse problem magnifies but you may be able to reduce peak heating.

Why would you need to deploy radiators? Post-aerocapture the heat will radiate away from the tiles and also into the tanks. Tanks would be vented to control pressure. I don't see how radiators would help.

John

Well, I suppose that's a question of how much you're willing to vent. If you need to do an apogee burn anyways and using primary propellant tanks as a temporary heatsink, I suppose you could try to kill two birds with one stone by using gaseous RCS to both relieve pressure and do the burn... not the most efficient method but it is expedient plus uses existing equipment. Hrm, I wonder if you could front end the inputs to RCS with a vortex tube cooler to get some free cooling with your burn...

But the impression I get is you will end up needing to run the cryocooler to deal with the remaining heat to prevent all the propellant going to gas and exceeding tank pressure, plus the Raptors expect liquid propellants so you can't let it all go to gas even if you could keep it in the tank. Well, assuming you don't offload any remaining propellant to some other storage system, since Starship isn't ideal for long term propellant storage anyways. The consensus is Starship will have a cryocooler for interplanetary cruise, but a cooler sized for that is much smaller than one trying to overcome structural heat pulses.
Title: Re: Starship heat shield
Post by: livingjw on 06/29/2023 04:25 pm
Heat pulse cooling post aerocapture is still non-trivial. You gotta deploy radiators fairly quickly once you pull out of the reentry dive, plus do a burn at apogee to keep you out of atmosphere for the period necessary to get cooling into a stable state in your elliptical loiter orbit until you decide to come down for another atmosphere run or EDL.

There's also the weird trade space of skip glide reetries post-aerocapture, where the heat pulse problem magnifies but you may be able to reduce peak heating.

Only a small fraction (~5%?) of the heat makes it into the tanks.

Why would you need to deploy radiators? Post-aerocapture the heat will radiate away from the tiles and also into the tanks. Tanks would be vented to control pressure. I don't see how radiators would help.

John

Well, I suppose that's a question of how much you're willing to vent. If you need to do an apogee burn anyways and using primary propellant tanks as a temporary heatsink, I suppose you could try to kill two birds with one stone by using gaseous RCS to both relieve pressure and do the burn... not the most efficient method but it is expedient plus uses existing equipment. Hrm, I wonder if you could front end the inputs to RCS with a vortex tube cooler to get some free cooling with your burn...

But the impression I get is you will end up needing to run the cryocooler to deal with the remaining heat to prevent all the propellant going to gas and exceeding tank pressure, plus the Raptors expect liquid propellants so you can't let it all go to gas even if you could keep it in the tank. Well, assuming you don't offload any remaining propellant to some other storage system, since Starship isn't ideal for long term propellant storage anyways. The consensus is Starship will have a cryocooler for interplanetary cruise, but a cooler sized for that is much smaller than one trying to overcome structural heat pulses.


Only a small fraction (~5%?) of the heat makes it into the tanks.

John
Title: Re: Starship heat shield
Post by: brussell on 07/14/2023 04:52 pm
What exactly is the TPS material in Starship?

Apologies in advance since it's probably been discussed to no end already, but this thread is gigantic and I couldn't find it.
Title: Re: Starship heat shield
Post by: rsdavis9 on 07/14/2023 10:36 pm
What exactly is the TPS material in Starship?

Apologies in advance since it's probably been discussed to no end already, but this thread is gigantic and I couldn't find it.

Some kind of fused/sintered silica.
Same as or very similar to the space shuttle tiles.

Light weight and insulating and able to get hot.
Title: Re: Starship heat shield
Post by: edzieba on 07/17/2023 05:15 pm
What exactly is the TPS material in Starship?

Apologies in advance since it's probably been discussed to no end already, but this thread is gigantic and I couldn't find it.
Sintered silica fibre bricks, with an outer coating of borosilicate reaction-cured glass, methyl-trimethoxy silane (MTMS) waterproofing agent [1], with embedded metallic 'track' inserts (metal unknown [2]) used to latch onto the pins for the flat tiles - the curved tiles (e.g. for the nose tip, flap leading edges, etc) that are glued in place using silicone adhesive lack the metal inserts.

[1] This is burnt off on first entry, the rewaterproofing agent SpaceX intend to use after recovery is unknown.
[2] On that note: does anyone who picked up one of the scattered tiles from OFT-1 happen to have access to an XRF gun?

Source is an FDEP report on the tile manufacturing facility in Florida (attached).
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 07/17/2023 07:02 pm
I think for thermal you have 2 primary constraints, not 1:

1. Heat pulse, i.e. the one you mentioned. This is the amount of energy which gets to your ship.
2. Peak heating. This is the maximum heating rate. Among other things this dictates skin temperature.

Ablative heat shields are primarily concerned with the first (1). But non-ablative ones are concerned with both (1 & 2), and it's easier to adjust them for 1 if a need arises (generally you improve the insulation layer). But adjusting for a higher peak heating (2) essentially means coming up with a different material which is not an easy change, and often means redoing your heatshield from scratch. And If you ramp peak heating just a tad too much we're simply out of known materials at all.

The thing about (2) is that it depends not just on velocity. It depends on deceleration as well. If you replace 2g braking with 4g braking you essentially doubled your peak heating.

At the same time you have likely reduced(!) heat pulse! This is counterintuitive, because kinetic energy to lose is the same regardless of how quickly you drop it. But the thing is, at certain point the more rarefied the ambient atmosphere the larger fraction of heat gets to the vehicle (and less is taken away by the ambient air). So when you pass entry interface heating initially grows much faster than deceleration. Just look at Shuttle reentry heating and deceleration profiles. Or some (SpaceX?) materials about Starship reentry. You're dropping speed slowly while heating is already high.

So if you have an ablative heatshield, you want to punch through the too thin air fast into high deceleration region. Total heat pulse is less that way, so you need less material to ablate. And you don't care that much about peak heating (within limits), as the temperature is primarily set by your ablative material's phase changes.

But if you have non-ablative heatshield, you prefer skidding on top of the atmosphere. The heat pulse is larger (often significantly), but you keep peak heating in check by keeping the whole kinetic energy drop rate in check. But if you have to generate more (negative) lift to hold onto a small low planet, you need to increase drag according to L:D ratio of your vehicle, which means higher deceleration which means higher kinetic energy drop rate and higher heating.

First, I never thanked you for this post.  It's a very clear problem statement, and I refer back to it quite often.

So how do things change if Starship intends to aerocapture instead of doing a direct EDL?  (This question applies for both Mars and Earth entry.)

I can think of a few of things:

1) You don't have to kill all the speed in a single direct EDL.  You only need enough to get you captured into an eccentric orbit.  That presumably makes the path through the atmosphere shorter, which reduces the heat pulse.

2) The Starship can cold-soak or barbecue roll to radiate away the heat pulse before beginning the actual EDL.

3) You also obviously get a chance to null out any guidance irregularities, allowing changes to both periapse altitude and inclination post-aerocapture.

4) The radius of curvature of the path requiring negative lift can be substantially greater, resulting in lower lift, which in turn reduces the amount of drag that's required.

It's #4 that I'm most curious about.  (See attachment.)  The deeper you can dip into the atmosphere before pulling out, the larger the radius of curvature of the path where substantial drag is produced.  But that means that the Starship has to endure a very brief period of high drag, and therefore high peak heating.  You obviously can't exceed a dynamic pressure that causes so high a peak heating that the tiles fail, but they're not going to soak at that temperature for very long.  This is the kinda-in-between case between pure peak heating and total heat pulse.

Is there a pony in here somewhere?  As always, the name of the game is the highest tolerable arrival v∞.


I wonder if since SS will be the first vehicle heading to mars with a reusable heat shield it will not do a capture burn, but instead only aerobrake.
IIRC all missions to mars have either 1) directly plunged in the atmosphere and EDLed, because they had ablative heat shields   2)did a capture burn aided by aerobraking

This maneuver would save a lot of dV, but the heating pulse and peak heating would need to be carefully studied. Also SS could aerobrake in a very  elliptical orbit, but that orbit might be month long, and so they would probably want to get deeper in the atmosphere to scrub more velocity.
Title: Re: Starship heat shield
Post by: edzieba on 07/18/2023 11:24 am
I think for thermal you have 2 primary constraints, not 1:

1. Heat pulse, i.e. the one you mentioned. This is the amount of energy which gets to your ship.
2. Peak heating. This is the maximum heating rate. Among other things this dictates skin temperature.

Ablative heat shields are primarily concerned with the first (1). But non-ablative ones are concerned with both (1 & 2), and it's easier to adjust them for 1 if a need arises (generally you improve the insulation layer). But adjusting for a higher peak heating (2) essentially means coming up with a different material which is not an easy change, and often means redoing your heatshield from scratch. And If you ramp peak heating just a tad too much we're simply out of known materials at all.

The thing about (2) is that it depends not just on velocity. It depends on deceleration as well. If you replace 2g braking with 4g braking you essentially doubled your peak heating.

At the same time you have likely reduced(!) heat pulse! This is counterintuitive, because kinetic energy to lose is the same regardless of how quickly you drop it. But the thing is, at certain point the more rarefied the ambient atmosphere the larger fraction of heat gets to the vehicle (and less is taken away by the ambient air). So when you pass entry interface heating initially grows much faster than deceleration. Just look at Shuttle reentry heating and deceleration profiles. Or some (SpaceX?) materials about Starship reentry. You're dropping speed slowly while heating is already high.

So if you have an ablative heatshield, you want to punch through the too thin air fast into high deceleration region. Total heat pulse is less that way, so you need less material to ablate. And you don't care that much about peak heating (within limits), as the temperature is primarily set by your ablative material's phase changes.

But if you have non-ablative heatshield, you prefer skidding on top of the atmosphere. The heat pulse is larger (often significantly), but you keep peak heating in check by keeping the whole kinetic energy drop rate in check. But if you have to generate more (negative) lift to hold onto a small low planet, you need to increase drag according to L:D ratio of your vehicle, which means higher deceleration which means higher kinetic energy drop rate and higher heating.

First, I never thanked you for this post.  It's a very clear problem statement, and I refer back to it quite often.

So how do things change if Starship intends to aerocapture instead of doing a direct EDL?  (This question applies for both Mars and Earth entry.)

I can think of a few of things:

1) You don't have to kill all the speed in a single direct EDL.  You only need enough to get you captured into an eccentric orbit.  That presumably makes the path through the atmosphere shorter, which reduces the heat pulse.

2) The Starship can cold-soak or barbecue roll to radiate away the heat pulse before beginning the actual EDL.

3) You also obviously get a chance to null out any guidance irregularities, allowing changes to both periapse altitude and inclination post-aerocapture.

4) The radius of curvature of the path requiring negative lift can be substantially greater, resulting in lower lift, which in turn reduces the amount of drag that's required.

It's #4 that I'm most curious about.  (See attachment.)  The deeper you can dip into the atmosphere before pulling out, the larger the radius of curvature of the path where substantial drag is produced.  But that means that the Starship has to endure a very brief period of high drag, and therefore high peak heating.  You obviously can't exceed a dynamic pressure that causes so high a peak heating that the tiles fail, but they're not going to soak at that temperature for very long.  This is the kinda-in-between case between pure peak heating and total heat pulse.

Is there a pony in here somewhere?  As always, the name of the game is the highest tolerable arrival v∞.


I wonder if since SS will be the first vehicle heading to mars with a reusable heat shield it will not do a capture burn, but instead only aerobrake.
IIRC all missions to mars have either 1) directly plunged in the atmosphere and EDLed, because they had ablative heat shields   2)did a capture burn aided by aerobraking

This maneuver would save a lot of dV, but the heating pulse and peak heating would need to be carefully studied. Also SS could aerobrake in a very  elliptical orbit, but that orbit might be month long, and so they would probably want to get deeper in the atmosphere to scrub more velocity.
That technique is known as 'aerocapture', and the major barrier is knowing atmosphere state at time of entry in order to properly plot a trajectory to scrub just enough velocity to enter the target orbit (too much = early entry at an uncontrolled location on an undesired trajectory, too little  = escape). Proposals to solve that problem include a swathe of probes sent ahead by a few hours to map multiple runs through the atmosphere to map density & temperature, and pre-placing Mars weather satellites to continuously measure the atmosphere in order to build and regularly update a volumetric atmospheric model.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 07/18/2023 01:31 pm
I think for thermal you have 2 primary constraints, not 1:

1. Heat pulse, i.e. the one you mentioned. This is the amount of energy which gets to your ship.
2. Peak heating. This is the maximum heating rate. Among other things this dictates skin temperature.

Ablative heat shields are primarily concerned with the first (1). But non-ablative ones are concerned with both (1 & 2), and it's easier to adjust them for 1 if a need arises (generally you improve the insulation layer). But adjusting for a higher peak heating (2) essentially means coming up with a different material which is not an easy change, and often means redoing your heatshield from scratch. And If you ramp peak heating just a tad too much we're simply out of known materials at all.

The thing about (2) is that it depends not just on velocity. It depends on deceleration as well. If you replace 2g braking with 4g braking you essentially doubled your peak heating.

At the same time you have likely reduced(!) heat pulse! This is counterintuitive, because kinetic energy to lose is the same regardless of how quickly you drop it. But the thing is, at certain point the more rarefied the ambient atmosphere the larger fraction of heat gets to the vehicle (and less is taken away by the ambient air). So when you pass entry interface heating initially grows much faster than deceleration. Just look at Shuttle reentry heating and deceleration profiles. Or some (SpaceX?) materials about Starship reentry. You're dropping speed slowly while heating is already high.

So if you have an ablative heatshield, you want to punch through the too thin air fast into high deceleration region. Total heat pulse is less that way, so you need less material to ablate. And you don't care that much about peak heating (within limits), as the temperature is primarily set by your ablative material's phase changes.

But if you have non-ablative heatshield, you prefer skidding on top of the atmosphere. The heat pulse is larger (often significantly), but you keep peak heating in check by keeping the whole kinetic energy drop rate in check. But if you have to generate more (negative) lift to hold onto a small low planet, you need to increase drag according to L:D ratio of your vehicle, which means higher deceleration which means higher kinetic energy drop rate and higher heating.

First, I never thanked you for this post.  It's a very clear problem statement, and I refer back to it quite often.

So how do things change if Starship intends to aerocapture instead of doing a direct EDL?  (This question applies for both Mars and Earth entry.)

I can think of a few of things:

1) You don't have to kill all the speed in a single direct EDL.  You only need enough to get you captured into an eccentric orbit.  That presumably makes the path through the atmosphere shorter, which reduces the heat pulse.

2) The Starship can cold-soak or barbecue roll to radiate away the heat pulse before beginning the actual EDL.

3) You also obviously get a chance to null out any guidance irregularities, allowing changes to both periapse altitude and inclination post-aerocapture.

4) The radius of curvature of the path requiring negative lift can be substantially greater, resulting in lower lift, which in turn reduces the amount of drag that's required.

It's #4 that I'm most curious about.  (See attachment.)  The deeper you can dip into the atmosphere before pulling out, the larger the radius of curvature of the path where substantial drag is produced.  But that means that the Starship has to endure a very brief period of high drag, and therefore high peak heating.  You obviously can't exceed a dynamic pressure that causes so high a peak heating that the tiles fail, but they're not going to soak at that temperature for very long.  This is the kinda-in-between case between pure peak heating and total heat pulse.

Is there a pony in here somewhere?  As always, the name of the game is the highest tolerable arrival v∞.


I wonder if since SS will be the first vehicle heading to mars with a reusable heat shield it will not do a capture burn, but instead only aerobrake.
IIRC all missions to mars have either 1) directly plunged in the atmosphere and EDLed, because they had ablative heat shields   2)did a capture burn aided by aerobraking

This maneuver would save a lot of dV, but the heating pulse and peak heating would need to be carefully studied. Also SS could aerobrake in a very  elliptical orbit, but that orbit might be month long, and so they would probably want to get deeper in the atmosphere to scrub more velocity.
That technique is known as 'aerocapture', and the major barrier is knowing atmosphere state at time of entry in order to properly plot a trajectory to scrub just enough velocity to enter the target orbit (too much = early entry at an uncontrolled location on an undesired trajectory, too little  = escape). Proposals to solve that problem include a swathe of probes sent ahead by a few hours to map multiple runs through the atmosphere to map density & temperature, and pre-placing Mars weather satellites to continuously measure the atmosphere in order to build and regularly update a volumetric atmospheric model.

Thanks for the insight.
I wonder why such precise information on the state of the atmosphere is needed for aerocapture, that does not need to be extremely precise, but is not needed for standard EDL. The landing ellipse for Perseverance was about 7 miles, and that precision is not due to the sckycrane that only separates at 1.3 miles. Is the upper athmospere of mars so much turbolent and unpredictable and so an EDL is easier to perform accurately because it can go in the lower atmosphere?
Another example: the Orion capsule performs a skip reenty, on Earth. That meneuver is used to increase the accuracy of the landing, and is similar to aerocapture. Orion doesn't employ any probes sent in advance.
Title: Re: Starship heat shield
Post by: edzieba on 07/18/2023 02:18 pm
I think for thermal you have 2 primary constraints, not 1:

1. Heat pulse, i.e. the one you mentioned. This is the amount of energy which gets to your ship.
2. Peak heating. This is the maximum heating rate. Among other things this dictates skin temperature.

Ablative heat shields are primarily concerned with the first (1). But non-ablative ones are concerned with both (1 & 2), and it's easier to adjust them for 1 if a need arises (generally you improve the insulation layer). But adjusting for a higher peak heating (2) essentially means coming up with a different material which is not an easy change, and often means redoing your heatshield from scratch. And If you ramp peak heating just a tad too much we're simply out of known materials at all.

The thing about (2) is that it depends not just on velocity. It depends on deceleration as well. If you replace 2g braking with 4g braking you essentially doubled your peak heating.

At the same time you have likely reduced(!) heat pulse! This is counterintuitive, because kinetic energy to lose is the same regardless of how quickly you drop it. But the thing is, at certain point the more rarefied the ambient atmosphere the larger fraction of heat gets to the vehicle (and less is taken away by the ambient air). So when you pass entry interface heating initially grows much faster than deceleration. Just look at Shuttle reentry heating and deceleration profiles. Or some (SpaceX?) materials about Starship reentry. You're dropping speed slowly while heating is already high.

So if you have an ablative heatshield, you want to punch through the too thin air fast into high deceleration region. Total heat pulse is less that way, so you need less material to ablate. And you don't care that much about peak heating (within limits), as the temperature is primarily set by your ablative material's phase changes.

But if you have non-ablative heatshield, you prefer skidding on top of the atmosphere. The heat pulse is larger (often significantly), but you keep peak heating in check by keeping the whole kinetic energy drop rate in check. But if you have to generate more (negative) lift to hold onto a small low planet, you need to increase drag according to L:D ratio of your vehicle, which means higher deceleration which means higher kinetic energy drop rate and higher heating.

First, I never thanked you for this post.  It's a very clear problem statement, and I refer back to it quite often.

So how do things change if Starship intends to aerocapture instead of doing a direct EDL?  (This question applies for both Mars and Earth entry.)

I can think of a few of things:

1) You don't have to kill all the speed in a single direct EDL.  You only need enough to get you captured into an eccentric orbit.  That presumably makes the path through the atmosphere shorter, which reduces the heat pulse.

2) The Starship can cold-soak or barbecue roll to radiate away the heat pulse before beginning the actual EDL.

3) You also obviously get a chance to null out any guidance irregularities, allowing changes to both periapse altitude and inclination post-aerocapture.

4) The radius of curvature of the path requiring negative lift can be substantially greater, resulting in lower lift, which in turn reduces the amount of drag that's required.

It's #4 that I'm most curious about.  (See attachment.)  The deeper you can dip into the atmosphere before pulling out, the larger the radius of curvature of the path where substantial drag is produced.  But that means that the Starship has to endure a very brief period of high drag, and therefore high peak heating.  You obviously can't exceed a dynamic pressure that causes so high a peak heating that the tiles fail, but they're not going to soak at that temperature for very long.  This is the kinda-in-between case between pure peak heating and total heat pulse.

Is there a pony in here somewhere?  As always, the name of the game is the highest tolerable arrival v∞.


I wonder if since SS will be the first vehicle heading to mars with a reusable heat shield it will not do a capture burn, but instead only aerobrake.
IIRC all missions to mars have either 1) directly plunged in the atmosphere and EDLed, because they had ablative heat shields   2)did a capture burn aided by aerobraking

This maneuver would save a lot of dV, but the heating pulse and peak heating would need to be carefully studied. Also SS could aerobrake in a very  elliptical orbit, but that orbit might be month long, and so they would probably want to get deeper in the atmosphere to scrub more velocity.
That technique is known as 'aerocapture', and the major barrier is knowing atmosphere state at time of entry in order to properly plot a trajectory to scrub just enough velocity to enter the target orbit (too much = early entry at an uncontrolled location on an undesired trajectory, too little  = escape). Proposals to solve that problem include a swathe of probes sent ahead by a few hours to map multiple runs through the atmosphere to map density & temperature, and pre-placing Mars weather satellites to continuously measure the atmosphere in order to build and regularly update a volumetric atmospheric model.

Thanks for the insight.
I wonder why such precise information on the state of the atmosphere is needed for aerocapture, that does not need to be extremely precise, but is not needed for standard EDL. The landing ellipse for Perseverance was about 7 miles, and that precision is not due to the sckycrane that only separates at 1.3 miles. Is the upper athmospere of mars so much turbolent and unpredictable and so an EDL is easier to perform accurately because it can go in the lower atmosphere?
Another example: the Orion capsule performs a skip reenty, on Earth. That meneuver is used to increase the accuracy of the landing, and is similar to aerocapture. Orion doesn't employ any probes sent in advance.
EDL spends a decent amount of time in the lower atmosphere, which is more 'stable' (e.g. for Mars a 1 Pa variance at 20km is a 1% change in pressure, a 1 Pa variance at 60km is a 100% variance in pressure), and for EDL a velocity residual has less of an effect on final trajectory than for aerocapture (an extra 100m/s may land you a few km down your landing ellipse, but an extra 100m/s after capture may be an escape trajectory or need 100m/s extra deltaV to correct).

On Earth, we have an extensive network of weather satellites measuring atmospheric properties at high fidelity and updating those measurements regularly, along with a vast network of ground stations to augment those satellites, and the ability to release balloons for even more measurements. Mars currently has none of that.
Title: Re: Starship heat shield
Post by: drzerg on 07/18/2023 07:43 pm
If starship could produce enough lift there will be margin of error that could be fixed by manuvering.
Title: Re: Starship heat shield
Post by: OTV Booster on 07/19/2023 05:02 pm
I think for thermal you have 2 primary constraints, not 1:

1. Heat pulse, i.e. the one you mentioned. This is the amount of energy which gets to your ship.
2. Peak heating. This is the maximum heating rate. Among other things this dictates skin temperature.

Ablative heat shields are primarily concerned with the first (1). But non-ablative ones are concerned with both (1 & 2), and it's easier to adjust them for 1 if a need arises (generally you improve the insulation layer). But adjusting for a higher peak heating (2) essentially means coming up with a different material which is not an easy change, and often means redoing your heatshield from scratch. And If you ramp peak heating just a tad too much we're simply out of known materials at all.

The thing about (2) is that it depends not just on velocity. It depends on deceleration as well. If you replace 2g braking with 4g braking you essentially doubled your peak heating.

At the same time you have likely reduced(!) heat pulse! This is counterintuitive, because kinetic energy to lose is the same regardless of how quickly you drop it. But the thing is, at certain point the more rarefied the ambient atmosphere the larger fraction of heat gets to the vehicle (and less is taken away by the ambient air). So when you pass entry interface heating initially grows much faster than deceleration. Just look at Shuttle reentry heating and deceleration profiles. Or some (SpaceX?) materials about Starship reentry. You're dropping speed slowly while heating is already high.

So if you have an ablative heatshield, you want to punch through the too thin air fast into high deceleration region. Total heat pulse is less that way, so you need less material to ablate. And you don't care that much about peak heating (within limits), as the temperature is primarily set by your ablative material's phase changes.

But if you have non-ablative heatshield, you prefer skidding on top of the atmosphere. The heat pulse is larger (often significantly), but you keep peak heating in check by keeping the whole kinetic energy drop rate in check. But if you have to generate more (negative) lift to hold onto a small low planet, you need to increase drag according to L:D ratio of your vehicle, which means higher deceleration which means higher kinetic energy drop rate and higher heating.

First, I never thanked you for this post.  It's a very clear problem statement, and I refer back to it quite often.

So how do things change if Starship intends to aerocapture instead of doing a direct EDL?  (This question applies for both Mars and Earth entry.)

I can think of a few of things:

1) You don't have to kill all the speed in a single direct EDL.  You only need enough to get you captured into an eccentric orbit.  That presumably makes the path through the atmosphere shorter, which reduces the heat pulse.

2) The Starship can cold-soak or barbecue roll to radiate away the heat pulse before beginning the actual EDL.

3) You also obviously get a chance to null out any guidance irregularities, allowing changes to both periapse altitude and inclination post-aerocapture.

4) The radius of curvature of the path requiring negative lift can be substantially greater, resulting in lower lift, which in turn reduces the amount of drag that's required.

It's #4 that I'm most curious about.  (See attachment.)  The deeper you can dip into the atmosphere before pulling out, the larger the radius of curvature of the path where substantial drag is produced.  But that means that the Starship has to endure a very brief period of high drag, and therefore high peak heating.  You obviously can't exceed a dynamic pressure that causes so high a peak heating that the tiles fail, but they're not going to soak at that temperature for very long.  This is the kinda-in-between case between pure peak heating and total heat pulse.

Is there a pony in here somewhere?  As always, the name of the game is the highest tolerable arrival v∞.


I wonder if since SS will be the first vehicle heading to mars with a reusable heat shield it will not do a capture burn, but instead only aerobrake.
IIRC all missions to mars have either 1) directly plunged in the atmosphere and EDLed, because they had ablative heat shields   2)did a capture burn aided by aerobraking

This maneuver would save a lot of dV, but the heating pulse and peak heating would need to be carefully studied. Also SS could aerobrake in a very  elliptical orbit, but that orbit might be month long, and so they would probably want to get deeper in the atmosphere to scrub more velocity.
That technique is known as 'aerocapture', and the major barrier is knowing atmosphere state at time of entry in order to properly plot a trajectory to scrub just enough velocity to enter the target orbit (too much = early entry at an uncontrolled location on an undesired trajectory, too little  = escape). Proposals to solve that problem include a swathe of probes sent ahead by a few hours to map multiple runs through the atmosphere to map density & temperature, and pre-placing Mars weather satellites to continuously measure the atmosphere in order to build and regularly update a volumetric atmospheric model.
Going a tad in the OT direction: if the first mission plans on long distance excursions a minimal StarLink constellation makes sense. If low enough, the sats get good data for a broad picture of the state of the atmosphere. Not sure if this is good enough for an aerobreaking map. It's in the right direction.
Title: Re: Starship heat shield
Post by: Asteroza on 07/19/2023 10:38 pm
Going a tad in the OT direction: if the first mission plans on long distance excursions a minimal StarLink constellation makes sense. If low enough, the sats get good data for a broad picture of the state of the atmosphere. Not sure if this is good enough for an aerobreaking map. It's in the right direction.

What level of mapping would be required to sufficiently inform both design phase heatshield tweaking, and arrival phase EDL tweaking? As in, updated atmosphere mapping might be serviceable with a pair of cubesats, but live EDL mapping might require a small swarm of cubesats to get sufficient fast coverage?
Title: Re: Starship heat shield
Post by: Hog on 07/20/2023 10:51 pm
If starship could produce enough lift there will be margin of error that could be fixed by manuvering.
And maneuvering can get you cross-range.  Nothing like some high hypersonic moves while making plasma.  I'm a fan.
Title: Re: Starship heat shield
Post by: sebk on 07/21/2023 01:46 pm
I think for thermal you have 2 primary constraints, not 1:

1. Heat pulse, i.e. the one you mentioned. This is the amount of energy which gets to your ship.
2. Peak heating. This is the maximum heating rate. Among other things this dictates skin temperature.

Ablative heat shields are primarily concerned with the first (1). But non-ablative ones are concerned with both (1 & 2), and it's easier to adjust them for 1 if a need arises (generally you improve the insulation layer). But adjusting for a higher peak heating (2) essentially means coming up with a different material which is not an easy change, and often means redoing your heatshield from scratch. And If you ramp peak heating just a tad too much we're simply out of known materials at all.

The thing about (2) is that it depends not just on velocity. It depends on deceleration as well. If you replace 2g braking with 4g braking you essentially doubled your peak heating.

At the same time you have likely reduced(!) heat pulse! This is counterintuitive, because kinetic energy to lose is the same regardless of how quickly you drop it. But the thing is, at certain point the more rarefied the ambient atmosphere the larger fraction of heat gets to the vehicle (and less is taken away by the ambient air). So when you pass entry interface heating initially grows much faster than deceleration. Just look at Shuttle reentry heating and deceleration profiles. Or some (SpaceX?) materials about Starship reentry. You're dropping speed slowly while heating is already high.

So if you have an ablative heatshield, you want to punch through the too thin air fast into high deceleration region. Total heat pulse is less that way, so you need less material to ablate. And you don't care that much about peak heating (within limits), as the temperature is primarily set by your ablative material's phase changes.

But if you have non-ablative heatshield, you prefer skidding on top of the atmosphere. The heat pulse is larger (often significantly), but you keep peak heating in check by keeping the whole kinetic energy drop rate in check. But if you have to generate more (negative) lift to hold onto a small low planet, you need to increase drag according to L:D ratio of your vehicle, which means higher deceleration which means higher kinetic energy drop rate and higher heating.

First, I never thanked you for this post.  It's a very clear problem statement, and I refer back to it quite often.

So how do things change if Starship intends to aerocapture instead of doing a direct EDL?  (This question applies for both Mars and Earth entry.)

I can think of a few of things:

1) You don't have to kill all the speed in a single direct EDL.  You only need enough to get you captured into an eccentric orbit.  That presumably makes the path through the atmosphere shorter, which reduces the heat pulse.

2) The Starship can cold-soak or barbecue roll to radiate away the heat pulse before beginning the actual EDL.

3) You also obviously get a chance to null out any guidance irregularities, allowing changes to both periapse altitude and inclination post-aerocapture.

4) The radius of curvature of the path requiring negative lift can be substantially greater, resulting in lower lift, which in turn reduces the amount of drag that's required.

It's #4 that I'm most curious about.  (See attachment.)  The deeper you can dip into the atmosphere before pulling out, the larger the radius of curvature of the path where substantial drag is produced.  But that means that the Starship has to endure a very brief period of high drag, and therefore high peak heating.  You obviously can't exceed a dynamic pressure that causes so high a peak heating that the tiles fail, but they're not going to soak at that temperature for very long.  This is the kinda-in-between case between pure peak heating and total heat pulse.

Is there a pony in here somewhere?  As always, the name of the game is the highest tolerable arrival v∞.


I wonder if since SS will be the first vehicle heading to mars with a reusable heat shield it will not do a capture burn, but instead only aerobrake.
IIRC all missions to mars have either 1) directly plunged in the atmosphere and EDLed, because they had ablative heat shields   2)did a capture burn aided by aerobraking

This maneuver would save a lot of dV, but the heating pulse and peak heating would need to be carefully studied. Also SS could aerobrake in a very  elliptical orbit, but that orbit might be month long, and so they would probably want to get deeper in the atmosphere to scrub more velocity.
That technique is known as 'aerocapture', and the major barrier is knowing atmosphere state at time of entry in order to properly plot a trajectory to scrub just enough velocity to enter the target orbit (too much = early entry at an uncontrolled location on an undesired trajectory, too little  = escape). Proposals to solve that problem include a swathe of probes sent ahead by a few hours to map multiple runs through the atmosphere to map density & temperature, and pre-placing Mars weather satellites to continuously measure the atmosphere in order to build and regularly update a volumetric atmospheric model.

Thanks for the insight.
I wonder why such precise information on the state of the atmosphere is needed for aerocapture, that does not need to be extremely precise, but is not needed for standard EDL. The landing ellipse for Perseverance was about 7 miles, and that precision is not due to the sckycrane that only separates at 1.3 miles. Is the upper athmospere of mars so much turbolent and unpredictable and so an EDL is easier to perform accurately because it can go in the lower atmosphere?
Another example: the Orion capsule performs a skip reenty, on Earth. That meneuver is used to increase the accuracy of the landing, and is similar to aerocapture. Orion doesn't employ any probes sent in advance.
EDL spends a decent amount of time in the lower atmosphere, which is more 'stable' (e.g. for Mars a 1 Pa variance at 20km is a 1% change in pressure, a 1 Pa variance at 60km is a 100% variance in pressure), and for EDL a velocity residual has less of an effect on final trajectory than for aerocapture (an extra 100m/s may land you a few km down your landing ellipse, but an extra 100m/s after capture may be an escape trajectory or need 100m/s extra deltaV to correct).

The obvious solution is not to try a so marginal capture than 0.1km/s error leaves you in a heliocentric orbit (or on the other extreme causes a deorbit). The useful range of post capture velocities (in Mars centered inertial coordinate system) is 3.5km/s to 4.9km/s. So just aim for 4.2km/s and your margin of error is 0.7km/s (or if your expected error is asymmetric aim for the post-capture velocity with the biggest asymmetric margin). The capturing pass would go down to some 20-40km above standard datum, and there the error would be <=10% which is OK for entry interface velocities up to 4.2 + 10*0.7 = 11.2[km/s] which is more than needed (capturing at anything above ~10km/s would be adventurous anyway).

Sure, post-capture phasing would be "fun" but it's doable in a few sols. The conops would be to have the capture central point at the latitude of the planned landing site. Then the initial post-capture orbit would have periapsis around that point in the atmosphere. So first order of work is to raise periapsis above the atmosphere. Then you determine when landing point would be passing under your periapsis point (they have the same latitude, so they must coincide every ~24.5 hours) and on one of the early periapsis passes you change your orbital period to have an integer number of cycles until the landing spot does coincide with your periapsis point (you look ahead a few sols, so you could chose the coincidence point with the smallest dV to reach it). Then, you just wait the calculated number of cycles (minus ~half), do the deorbit burn (~half a cycle before landing) and perform EDL.
Title: Re: Starship heat shield
Post by: FutureSpaceTourist on 07/29/2023 06:20 am
https://twitter.com/rgvaerialphotos/status/1685091648991068160

Quote
So that's how you remove a heat tile.
Title: Re: Starship heat shield
Post by: eeergo on 11/18/2023 01:48 pm
Heatshield performance at launch still looks like it needs relevant redesign. Note the tiles are primarily -but noy only- missing at welded sutures and flaps, and this happened during apparently nominal liftoff/first stage flight conditions (probably still subsonic?).

https://twitter.com/johnkrausphotos/status/1725877991312376190
Title: Re: Starship heat shield
Post by: flexbuffchest on 11/18/2023 02:20 pm
Heatshield performance at launch still looks like it needs relevant redesign. Note the tiles are primarily -but noy only- missing at welded sutures and flaps, and this happened during apparently nominal liftoff/first stage flight conditions (probably still subsonic?).

https://twitter.com/johnkrausphotos/status/1725877991312376190
I wouldn't put too much stock into missing tiles on this test. Doesn't sound like SpaceX really worried about them at all.

https://twitter.com/CSI_Starbase/status/1725891849225679047
Title: Re: Starship heat shield
Post by: tenkendojo on 11/18/2023 03:17 pm
https://twitter.com/rgvaerialphotos/status/1685091648991068160

Quote
So that's how you remove a heat tile.
Wow imagine in-orbit EVA tile replacement. Gonna be heck of a debris cloud.
Title: Re: Starship heat shield
Post by: eeergo on 11/18/2023 04:50 pm
Heatshield performance at launch still looks like it needs relevant redesign. Note the tiles are primarily -but noy only- missing at welded sutures and flaps, and this happened during apparently nominal liftoff/first stage flight conditions (probably still subsonic?).
I wouldn't put too much stock into missing tiles on this test. Doesn't sound like SpaceX really worried about them at all.

There was clearly some "worrying" since they went to the trouble of replacing some single lost ones, and R&R'ing quite some more due to unspecified reasons, plus performing lots of detailing work overall. If they expected dozens of them to fall right off at the beginning of flight, they would have dedicated much less time and effort.
Title: Re: Starship heat shield
Post by: RamsesBic on 11/20/2023 12:38 pm
Heatshield performance at launch still looks like it needs relevant redesign. Note the tiles are primarily -but noy only- missing at welded sutures and flaps, and this happened during apparently nominal liftoff/first stage flight conditions (probably still subsonic?).
I wouldn't put too much stock into missing tiles on this test. Doesn't sound like SpaceX really worried about them at all.

There was clearly some "worrying" since they went to the trouble of replacing some single lost ones, and R&R'ing quite some more due to unspecified reasons, plus performing lots of detailing work overall. If they expected dozens of them to fall right off at the beginning of flight, they would have dedicated much less time and effort.

Not really. The tile installers have their work to do, but it is not the first priority - just check how often a tile is missing for weeks. The ship was never expected to "land". It was to be destroyed no matter what, so losing a few tiles was never a big worry. They are introducing new methods of testing the adhesion of the tiles for coming ships (using suction cups to pull at them). I wish they were able to weld the studs and installing the tiles AFTER stacking the whole ship - much harder for the robots, but it is just an engineering problem. That would reduce the need to use glue as much. Automating the whole process would be a good goal.
Title: Re: Starship heat shield
Post by: rsdavis9 on 11/20/2023 02:17 pm

I wish they were able to weld the studs and installing the tiles AFTER stacking the whole ship - much harder for the robots, but it is just an engineering problem. That would reduce the need to use glue as much. Automating the whole process would be a good goal.

YES!

Even using the stud installer for "gap" tiles would be another way. So pre tile sections and then once sections are welded together use a stud installer and install the gap tiles without glue.
Title: Re: Starship heat shield
Post by: eriblo on 11/20/2023 02:28 pm

I wish they were able to weld the studs and installing the tiles AFTER stacking the whole ship - much harder for the robots, but it is just an engineering problem. That would reduce the need to use glue as much. Automating the whole process would be a good goal.

YES!

Even using the stud installer for "gap" tiles would be another way. So pre tile sections and then once sections are welded together use a stud installer and install the gap tiles without glue.
That works for the cylindrical barrel welds but you also have the glued tiles on the highly curved parts of the hull (nose, flap edges and roots). It will be much harder to implement studded tiles there and it might be undesirable to start with - glued tiles can have the gaps filled much more easily which could be necessary where the tangential flow is high and the radius of curvature is small. As long as there are any glued tiles you need to solve it anyway.
Title: Re: Starship heat shield
Post by: Barley on 11/20/2023 04:39 pm

Even using the stud installer for "gap" tiles would be another way. So pre tile sections and then once sections are welded together use a stud installer and install the gap tiles without glue.
That works for the cylindrical barrel welds but you also have the glued tiles on the highly curved parts of the hull (nose, flap edges and roots). It will be much harder to implement studded tiles there and it might be undesirable to start with - glued tiles can have the gaps filled much more easily which could be necessary where the tangential flow is high and the radius of curvature is small. As long as there are any glued tiles you need to solve it anyway.
True, but if fewer tiles have to be glued they can use heavier glues, tiles or backers to solve it for the remainder that really need glue.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 11/20/2023 04:58 pm
Any guesses about why many more tiles fell of from S25 than S24?

Lower aero loads? Less precise installation?
Title: Re: Starship heat shield
Post by: abaddon on 11/20/2023 05:05 pm
Any guesses about why many more tiles fell of from S25 than S24?

Lower aero loads? Less precise installation?
Are we sure we know how many tiles fell from each?

As for a guess why; IFT-1 had a very "gentle" (slow) start sequence that was aimed at reducing stress on the vehicle but ended up being much worse for the pad.  IFT-2 started much more quickly, so likely more stress on the vehicle, possibly more vibrations and more tiles falling off.  IFT-1 also lifted off with fewer Raptors lit and then lost raptors pretty quickly, so likely lower aero loads even at the low altitudes where we can see missing tile spots.
Title: Re: Starship heat shield
Post by: scaesare on 11/20/2023 05:15 pm
Any guesses about why many more tiles fell of from S25 than S24?

Lower aero loads? Less precise installation?
Are we sure we know how many tiles fell from each?

As for a guess why; IFT-1 had a very "gentle" (slow) start sequence that was aimed at reducing stress on the vehicle but ended up being much worse for the pad.  IFT-2 started much more quickly, so likely more stress on the vehicle, possibly more vibrations and more tiles falling off.  IFT-1 also lifted off with fewer Raptors lit and then lost raptors pretty quickly, so likely lower aero loads even at the low altitudes where we can see missing tile spots.

Do we know for a fact taht the liftoff profile of IFT-1 was deliberately a "very "gentle" (slow) start sequence that was aimed at reducing stress on the vehicle", and not a result of the early engine failures?

There were already 3 engines out as it cleared the tower... that's down 1.5 millon pounds of thrust...
Title: Re: Starship heat shield
Post by: abaddon on 11/20/2023 05:23 pm
Do we know for a fact taht the liftoff profile of IFT-1 was deliberately a "very "gentle" (slow) start sequence that was aimed at reducing stress on the vehicle", and not a result of the early engine failures?
Yes, I believe we do, although I don't have a citation handy.  To be clear it wasn't the "liftoff profile" it was the startup sequence I am referring to.
Title: Re: Starship heat shield
Post by: adrianwyard on 11/20/2023 05:48 pm
Do we know if the overall TPS relies on the steel structure/prop soaking some of the heat? My guess is no: the tiles themselves are good insulators, as is the blanket underneath, and not much would make it through the pins.

If no, then I wonder if they'd be better of making the heat shield in large detachable sections of tiles that could be replaced en masse. Maybe 10-15 or so sections: 4x flaps, several for nose curves, large for barrel sections.

This would allow for offline waterproofing* pull-testing and detailed post flight testing. You could also iterate the attachment/composition. You'd keep a supply of spares ready to go. And of course leave the TPS off if not needed.

As the system improved you'd replace fewer sections after each flight.

There would surely be a weight penalty for the structure the tiles are attached to. If it can't be light this is a non-starter.
_______
* AFAIK all tiles will need this after each flight - a significant maintenance step.
Title: Re: Starship heat shield
Post by: Alberto-Girardi on 11/20/2023 08:53 pm
From Every Day Astronaut tracking video it seems that the bigger tile fall off occurs way after liftoff, during the roll program (not implying that there is any relation between the two things).

https://www.youtube.com/watch?v=Iv5AMNYGql4

(the video from 9:25 onwards is especially interesting)
Title: Re: Starship heat shield
Post by: brettly2021 on 11/24/2023 09:32 am
Do away with those stupids  SS clips, a thin smear of red silicone will be fine, also get rid of the fishing net type material beihnd the tiles.........problem solved. The SS clips also have stainless pieces embedded in the tile, get rid of it and will also save quite a bit of weight. No need for the clips its over enginered.
Predicated a long  time ago it would be problemmatic.
Title: Re: Starship heat shield
Post by: eriblo on 11/24/2023 09:59 am
Do away with those stupids  SS clips, a thin smear of red silicone will be fine, also get rid of the fishing net type material beihnd the tiles.........problem solved. The SS clips also have stainless pieces embedded in the tile, get rid of it and will also save quite a bit of weight. No need for the clips its over enginered.
Predicated a long  time ago it would be problemmatic.
Are you missing a sarcasm marker? A disproportionately large fraction of the tiles that fell off where glued...
Title: Re: Starship heat shield
Post by: brettly2021 on 11/25/2023 02:41 pm
yes a stupid post on my behalf perhaps, also the temp of the SS will be problem for silicone,
heres a better idea:
velcro made from material that can handle the temps...........or similar to velcro, the SS clips are just not good.
heres pic of early in flight showing approx 100 cells gone........need to zoom to count them.
Title: Re: Starship heat shield
Post by: meekGee on 11/25/2023 02:57 pm
yes a stupid post on my behalf perhaps, also the temp of the SS will be problem for silicone,
heres a better idea:
velcro made from material that can handle the temps...........or similar to velcro, the SS clips are just not good.
heres pic of early in flight showing approx 100 cells gone........need to zoom to count them.
Yup you got it, problem solved.
Title: Re: Starship heat shield
Post by: midaswelby on 12/06/2023 07:25 pm
Cross posting this, correctly I hope.  My thought was that the size of the TPS tiles being reduced also reduces several issues, such as strength of the tile, gap size and spacing, geometry in non-symmetrical areas of the vehicle, etc .  Notice the frames already attached in the image, suggesting more frame and less tile body might also be beneficial.  Obviously, far greater number of tiles to manufacture and mount, but I thought it interesting to consider the possibilities of this new approach. 

https://twitter.com/labpadre/status/1732419872079204851

https://twitter.com/labpadre/status/1732419872079204851

Quote
New in the Ring Yard: A test barrel with what appears to be pins arranged for much smaller TPS tiles. Current theory is that these might be placed over the ship section seams instead of using glued-on tiles.

@CosmicalChief
@Ringwatchers
Title: Re: Starship heat shield
Post by: wannamoonbase on 12/08/2023 03:04 pm
Cross posting this, correctly I hope.  My thought was that the size of the TPS tiles being reduced also reduces several issues, such as strength of the tile, gap size and spacing, geometry in non-symmetrical areas of the vehicle, etc .  Notice the frames already attached in the image, suggesting more frame and less tile body might also be beneficial.  Obviously, far greater number of tiles to manufacture and mount, but I thought it interesting to consider the possibilities of this new approach. 

https://twitter.com/labpadre/status/1732419872079204851

https://twitter.com/labpadre/status/1732419872079204851

Quote
New in the Ring Yard: A test barrel with what appears to be pins arranged for much smaller TPS tiles. Current theory is that these might be placed over the ship section seams instead of using glued-on tiles.

@CosmicalChief
@Ringwatchers

Interesting development.  Will be interesting to see where this goes.

I wonder if there is also some manufacturing advantages.  Yes it's more tiles but maybe there are some ways to make smaller tiles faster and more consistent. More automated, less scrap, maybe.

Tighter gaps seems important too.

Anyway, it's good to see some iteration on the heat shield.
Title: Re: Starship heat shield
Post by: BT52 on 12/08/2023 04:49 pm
I would say so yes. Like in chip production and its wafer reduction scraps. Smaller tiles can make usage of existing furnaces much more efficient. But overall cost of production with hand labour will go up. So its paramount to use totally robotic assembly and attachment checks. Although for prototyping hand labour make sense ofc. Because they are not even close to be locked in final alpha design. Even tho they have imbedded foretaught with its designs. The later is very important and i like that.

I would go further and develop glue on tiles and make it that way. Wings (elerons) and nose already use it. I would just scrap it. Pick and place machines with already preapplied glue tiles would be scary fast.

Furthermore too satisfied tolerance stack up make tiles wedge shape or  what else. Or even make some grove as aero shield between seems. Klyo wool can be scraped or just used on edges in preaplied form on tile itself as sealant. Like muffin paper cup if u think about it. 
Title: Re: Starship heat shield
Post by: InterestedEngineer on 02/08/2024 05:06 pm
From the WB-57 footage, the heat shield isn't looking so good.  Snapshot from 13:04:42

Title: Re: Starship heat shield
Post by: Hog on 02/09/2024 06:19 pm
I find it very interesting that even after all these years, the Thermal Protection System(TPS) remains such a challenge. Darned laws of thermodynamics, but I'm sure they'll get there.
Title: Re: Starship heat shield
Post by: wannamoonbase on 02/09/2024 06:41 pm
I find it very interesting that even after all these years, the Thermal Protection System(TPS) remains such a challenge. Darned laws of thermodynamics, but I'm sure they'll get there.

I've always considered the heat shield the single most critical element of Starship.

I think the smaller tiles we've seen a good step forward.  They will solve the problem but it's anyone's guess how long it will take.

I think the pace of progress has been waiting for flights, they were focused on getting to the point of flying.  Now that they are flying it will develop.
Title: Re: Starship heat shield
Post by: alang on 02/10/2024 05:55 pm
"I've always considered the heat shield the single most critical element of Starship."

This has problem answered many times, so please delete if necessary:
I've always assumed that the heat shield of the moving surfaces to be the most critical element of Starship, especially the area where the surfaces hinge. Is it known if the moving surfaces with be locked into a particular orientation during entry, because if they are not then there are effectively many more heat shield and reentry heating profiles to be modelled and tested than if they are fixed for a period.
Title: Re: Starship heat shield
Post by: eriblo on 02/10/2024 06:10 pm
"I've always considered the heat shield the single most critical element of Starship."

This has problem answered many times, so please delete if necessary:
I've always assumed that the heat shield of the moving surfaces to be the most critical element of Starship, especially the area where the surfaces hinge. Is it known if the moving surfaces with be locked into a particular orientation during entry, because if they are not then there are effectively many more heat shield and reentry heating profiles to be modelled and tested than if they are fixed for a period.
The reason they have moving surfaces is to trim and steer during EDL so they will be moving. Starship is also, unlike capsules, at best marginally stable in several axis so it would most likely tumble without active control.
Title: Re: Starship heat shield
Post by: matthewkantar on 02/10/2024 09:15 pm
The tiles on the control surfaces are not mounted directly to tanks containing cryogenic propellants. The tanks move with pressurization and changes in temperature, they expose the tile system to cycles of extreme cold, and pretty dang hot sitting in the Texas sun.

It might be harder to model the air flow, but getting em to stay put should be easier.
Title: Re: Starship heat shield
Post by: ETurner on 02/11/2024 09:19 pm
I find it very interesting that even after all these years, the Thermal Protection System(TPS) remains such a challenge. Darned laws of thermodynamics, but I'm sure they'll get there.
But the TPS hasn't even got hot yet.
I don't get it.
Title: Re: Starship heat shield
Post by: eriblo on 02/11/2024 09:24 pm
I find it very interesting that even after all these years, the Thermal Protection System(TPS) remains such a challenge. Darned laws of thermodynamics, but I'm sure they'll get there.
But the TPS hasn't even got hot yet.
I don't get it.
Short version: gluing glass to stainless steel is difficult.
Title: Re: Starship heat shield
Post by: Kspbutitscursed on 02/11/2024 09:38 pm
I find it very interesting that even after all these years, the Thermal Protection System(TPS) remains such a challenge. Darned laws of thermodynamics, but I'm sure they'll get there.
But the TPS hasn't even got hot yet.
I don't get it.
Short version: gluing glass to stainless steel is difficult.
well on most of the tiles they are machanically attached via the pins on the vehicles
Title: Re: Starship heat shield
Post by: Crispy on 02/13/2024 07:02 am
YouTube channel "Breaking Taps" has a a great video where he puts a shuttle tile fragment and a S24 tile in a scanning electron microscope to compare. He also makes his own tile to explain the process.
https://youtu.be/SI7mpjHGiFU?si=xT_attV5AObnFdSL
Title: Re: Starship heat shield
Post by: whitelancer64 on 02/13/2024 03:25 pm
I find it very interesting that even after all these years, the Thermal Protection System(TPS) remains such a challenge. Darned laws of thermodynamics, but I'm sure they'll get there.
But the TPS hasn't even got hot yet.
I don't get it.
Short version: gluing glass to stainless steel is difficult.
well on most of the tiles they are machanically attached via the pins on the vehicles

Which actually is a fair point. I don't think any of the glued tiles have come off, only the ones mechanically attached with pins.
Title: Re: Starship heat shield
Post by: eriblo on 02/13/2024 03:51 pm
I find it very interesting that even after all these years, the Thermal Protection System(TPS) remains such a challenge. Darned laws of thermodynamics, but I'm sure they'll get there.
But the TPS hasn't even got hot yet.
I don't get it.
Short version: gluing glass to stainless steel is difficult.
well on most of the tiles they are machanically attached via the pins on the vehicles
Which actually is a fair point. I don't think any of the glued tiles have come off, only the ones mechanically attached with pins.
It was the other way around on S25, most if the lost tiles looked to be glued.
Title: Re: Starship heat shield
Post by: equiserre on 02/13/2024 04:35 pm
I find it very interesting that even after all these years, the Thermal Protection System(TPS) remains such a challenge. Darned laws of thermodynamics, but I'm sure they'll get there.
But the TPS hasn't even got hot yet.
I don't get it.
Short version: gluing glass to stainless steel is difficult.
well on most of the tiles they are machanically attached via the pins on the vehicles
Which actually is a fair point. I don't think any of the glued tiles have come off, only the ones mechanically attached with pins.
It was the other way around on S25, most if the lost tiles looked to be glued.
Yes, but interestingly not in the nose?
Title: Re: Starship heat shield
Post by: Brigantine on 02/14/2024 08:06 am
The static fire test stand is lower to the ground than the OLM, and even then the full stack doesn't have tiles near the aft end.

If a static fire test was shaking tiles lose on the nose, that would need more explaining than damaged tiles close to the forcing.

It will be interesting to see whether the tiles lost on the actual flight has the same pattern re glued vs pinned (less vibration, more aerodynamic forces)- and then whether the Masseys static fire test stand impacts differently to the suborbital stand. (is it higher?)
Title: Re: Starship heat shield
Post by: catdlr on 02/17/2024 08:50 pm
The Science of SpaceX Starship’s Thermal Tiles


https://www.youtube.com/watch?v=SI7mpjHGiFU
Title: Re: Starship heat shield
Post by: Nascat on 02/24/2024 01:59 pm
Hello, I’ve been finding tiles from SN25 in the Caribbean. I’ve also found others that I don’t think are from SN25, can anyone help me identify these? The heat scorched one is really cool! Thanks
Title: Re: Starship heat shield
Post by: catdlr on 02/24/2024 10:51 pm
Hello, I’ve been finding tiles from SN25 in the Caribbean. I’ve also found others that I don’t think are from SN25, can anyone help me identify these? The heat-scorched one is really cool! Thanks

NASCAT,
Nice find(s).  You could do some research on NOAA for sea current patterns and you might discover how floating items can land in areas far away.  Here on the West Coast, we continually get items from Japan.  May I ask where you are located, and where you are on vacation or live there?

BTW, welcome to the forum.

Best
Tony
Title: Re: Starship heat shield
Post by: Kazioo on 03/17/2024 08:52 pm
IFT-3's slow motion video shows that even the air drag during the rocket's ascent is enough to rip some tiles off.
But I think that was on the flap, so I assume it's the glue not being strong enough.
Title: Re: Starship heat shield
Post by: InterestedEngineer on 03/17/2024 08:54 pm
Here's my estimate of tile loss for IFT-3 during launch - 8 tiles.

Much improvement, and the distribution and location of these losses would not be mission critical

From Everyday Astronaut's "cosmic perspective" video.



Title: Re: Starship heat shield
Post by: StraumliBlight on 03/17/2024 09:55 pm
Here's my estimate of tile loss for IFT-3 during launch - 8 tiles.

Much improvement, and the distribution and location of these losses would not be mission critical

From Everyday Astronaut's "cosmic perspective" video.

Two intact (https://www.reddit.com/r/Damnthatsinteresting/comments/1bgxbwq/i_got_a_souvenir_from_the_3rd_spacex_starship/) tiles (https://www.reddit.com/r/SpaceXMasterrace/comments/1bevzly/got_mine_im_the_latest_happy_owner_of_a_fully/) were found after launch.
Title: Re: Starship heat shield
Post by: Metalskin on 03/18/2024 02:08 am
I'm not familiar with the tides, currents, etc. So I am curious if it's possible that these could have washed up, after having detached themselves after the booster entered the water?
Title: Re: Starship heat shield
Post by: InterestedEngineer on 03/18/2024 02:19 am
I'm not familiar with the tides, currents, etc. So I am curious if it's possible that these could have washed up, after having detached themselves after the booster entered the water?

let's make that more complete:  after entering the water at over 1000km/hour

I suspect not.
Title: Re: Starship heat shield
Post by: EspenU on 03/18/2024 02:25 am
I'm not familiar with the tides, currents, etc. So I am curious if it's possible that these could have washed up, after having detached themselves after the booster entered the water?
The booster doesn't have tiles though. So unless they are from a previous launch, they would have to come from the ship during launch.
Title: Re: Starship heat shield
Post by: ETurner on 03/18/2024 10:49 am
Two intact (https://www.reddit.com/r/Damnthatsinteresting/comments/1bgxbwq/i_got_a_souvenir_from_the_3rd_spacex_starship/) tiles (https://www.reddit.com/r/SpaceXMasterrace/comments/1bevzly/got_mine_im_the_latest_happy_owner_of_a_fully/) were found after launch.
Looking at the beautiful picture above, 4.jpeg, how did the tile come off the vehicle?
Ceramic cracked and failed? --- no, it's intact.
Adhesive failure? --- no, this isn't a glued tile.
Metal piece pullout? --- no, they're still in place.
Pin welded to vehicle failed? --- seems unlikely!
Design that still doesn't result in the tile clipping onto the pin with reasonably attentive installation? --- surely not!
Tile manufactured and thrown into the sea to confuse NSF readers? --- by nefarious forces?
Title: Re: Starship heat shield
Post by: warp99 on 03/18/2024 11:30 am
Two intact (https://www.reddit.com/r/Damnthatsinteresting/comments/1bgxbwq/i_got_a_souvenir_from_the_3rd_spacex_starship/) tiles (https://www.reddit.com/r/SpaceXMasterrace/comments/1bevzly/got_mine_im_the_latest_happy_owner_of_a_fully/) were found after launch.
Looking at the beautiful picture above, 4.jpeg, how did the tile come off the vehicle?
Ceramic cracked and failed? --- no, it's intact.
Adhesive failure? --- no, this isn't a glued tile.
Metal piece pullout? --- no, they're still in place.
Pin welded to vehicle failed? --- seems unlikely!
Design that still doesn't result in the tile clipping onto the pin with reasonably attentive installation? --- surely not!
Tile manufactured and thrown into the sea to confuse NSF readers? --- by nefarious forces?
I appreciate the poetry but 

1.  The first tile shows signs of being glued on despite being specifically designed to clip on

2.  The second tile shows absolutely no sign of scarring or pullout damage around the slots - but it does have a series of dents around all three retention slots as if the end of a stud had been banging on the metal bracket with the vibration during launch - implying that the clips were not engaged on all three slots and friction from compression of the tile material and presumably positive airflow pressure was holding it on during launch until it wasn't 

So these are easy fixes with a QA procedure that does vacuum pulls on the tiles - I seem to have read about that process being used on another vehicle somewhere?!
Title: Re: Starship heat shield
Post by: Sciencefan on 03/18/2024 11:55 am
Two intact (https://www.reddit.com/r/Damnthatsinteresting/comments/1bgxbwq/i_got_a_souvenir_from_the_3rd_spacex_starship/) tiles (https://www.reddit.com/r/SpaceXMasterrace/comments/1bevzly/got_mine_im_the_latest_happy_owner_of_a_fully/) were found after launch.
Looking at the beautiful picture above, 4.jpeg, how did the tile come off the vehicle?
Ceramic cracked and failed? --- no, it's intact.
Adhesive failure? --- no, this isn't a glued tile.
Metal piece pullout? --- no, they're still in place.
Pin welded to vehicle failed? --- seems unlikely!
Design that still doesn't result in the tile clipping onto the pin with reasonably attentive installation? --- surely not!
Tile manufactured and thrown into the sea to confuse NSF readers? --- by nefarious forces?

This is just a single tile. Likely pins were damaged or adhesive remains on the ship.
Title: Re: Starship heat shield
Post by: ETurner on 03/18/2024 11:56 am
Two intact (https://www.reddit.com/r/Damnthatsinteresting/comments/1bgxbwq/i_got_a_souvenir_from_the_3rd_spacex_starship/) tiles (https://www.reddit.com/r/SpaceXMasterrace/comments/1bevzly/got_mine_im_the_latest_happy_owner_of_a_fully/) were found after launch.
Looking at the beautiful picture above, 4.jpeg, how did the tile come off the vehicle?
...
Design that still doesn't result in the tile clipping onto the pin with reasonably attentive installation? --- surely not!
...
...
So these are easy fixes with a QA procedure that does vacuum pulls on the tiles - I seem to have read about that process being used on another vehicle somewhere?!
So we're going with a failure of "reasonably attentive installation" + lack of QC.
This does seem like the best explanation.
Title: Re: Starship heat shield
Post by: ETurner on 03/18/2024 12:06 pm
This is just a single tile. Likely pins were damaged or adhesive remains on the ship.
4.jpg was obviously attached by pins, so no adhesive. Weak pins (realistically, weak welds) is consistent with what we see, but seems unlikely, I think SpaceX has got welding down pat.
Title: Re: Starship heat shield
Post by: TergenFlerg on 03/18/2024 12:08 pm
Two intact (https://www.reddit.com/r/Damnthatsinteresting/comments/1bgxbwq/i_got_a_souvenir_from_the_3rd_spacex_starship/) tiles (https://www.reddit.com/r/SpaceXMasterrace/comments/1bevzly/got_mine_im_the_latest_happy_owner_of_a_fully/) were found after launch.
Looking at the beautiful picture above, 4.jpeg, how did the tile come off the vehicle?
Ceramic cracked and failed? --- no, it's intact.
Adhesive failure? --- no, this isn't a glued tile.
Metal piece pullout? --- no, they're still in place.
Pin welded to vehicle failed? --- seems unlikely!
Design that still doesn't result in the tile clipping onto the pin with reasonably attentive installation? --- surely not!
Tile manufactured and thrown into the sea to confuse NSF readers? --- by nefarious forces?
I appreciate the poetry but 

1.  The first tile shows signs of being glued on despite being specifically designed to clip on

2.  The second tile shows absolutely no sign of scarring or pullout damage around the slots - but it does have a series of dents around all three retention slots as if the end of a stud had been banging on the metal bracket with the vibration during launch - implying that the clips were not engaged on all three slots and friction from compression of the tile material and presumably positive airflow pressure was holding it on during launch until it wasn't 

So these are easy fixes with a QA procedure that does vacuum pulls on the tiles - I seem to have read about that process being used on another vehicle somewhere?!

The first tile has sand on it, not glue.
Title: Re: Starship heat shield
Post by: DanClemmensen on 03/18/2024 12:44 pm
This is just a single tile. Likely pins were damaged or adhesive remains on the ship.
4.jpg was obviously attached by pins, so no adhesive. Weak pins (realistically, weak welds) is consistent with what we see, but seems unlikely, I think SpaceX has got welding down pat.
I thought the pin was welded to the ship. If the weld fails, the pin would still be attached to the tile, which is not the case here. It appears that the tile pulled cleanly away from all three pins, which means the press-fit detention clip system failed. That system needs some attention, either a more positive one-way clip configuration, or a fool-proof non-invasive inspection system, or both.
Title: Re: Starship heat shield
Post by: pospa on 03/18/2024 01:21 pm

Two intact (https://www.reddit.com/r/Damnthatsinteresting/comments/1bgxbwq/i_got_a_souvenir_from_the_3rd_spacex_starship/) tiles (https://www.reddit.com/r/SpaceXMasterrace/comments/1bevzly/got_mine_im_the_latest_happy_owner_of_a_fully/) were found after launch.
What is exact weight of complete hexagonal tile?
Title: Re: Starship heat shield
Post by: StraumliBlight on 03/18/2024 01:26 pm
What is exact weight of complete hexagonal tile?

The tile weighs 381 g (https://www.tiktok.com/@ellieinspace3/video/7347131142996266283).
Title: Re: Starship heat shield
Post by: rsdavis9 on 03/18/2024 01:49 pm
A long time ago I pixel counted a tile as 24.35cm flat to flat(instead of point to point). Anybody know what the size is?

EDIT:
We heard in the broadcast that there are 18000 tiles. So 18000*.381kg=6.8t
Title: Re: Starship heat shield
Post by: pospa on 03/18/2024 02:15 pm
A long time ago I pixel counted a tile as 24.35cm flat to flat(instead of point to point). Anybody know what the size is?

EDIT:
We heard in the broadcast that there are 18000 tiles. So 18000*.381kg=6.8t

Yeah, that would be minimum, just for tiles. Its likely couple of tons more as you need to count in also:
- 3 metal pins / tile (~54 000 pcs)
- thermal resistant blanket under tiles (~1 inch thick)
- adhesive wherever pins are not used (edges, corners, nose cone, welds between ring sections, etc.)

All in all my gues of total TPS weight on Starship is something between 8 - 10 tons.
Title: Re: Starship heat shield
Post by: Nomadd on 03/18/2024 05:22 pm
 I can't remember all the specifics, but I came up with 26 ounces a square foot using a complete tile I found, not including underlayment or pins.
Title: Re: Starship heat shield
Post by: DanClemmensen on 03/18/2024 05:29 pm
I can't remember all the specifics, but I came up with 26 ounces a square foot using a complete tile I found, not including underlayment or pins.
What's that in long tons per acre?   :D
26 oz/ft2 = 8 kg/m2