### Author Topic: Starship heat shield  (Read 1217386 times)

#### Slarty1080

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##### Starship heat shield
« 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

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.
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#### Eylrid

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##### Re: Starship heat shield
« Reply #1 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

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

#### rakaydos

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##### Re: Starship heat shield
« Reply #2 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.

#### DusanC

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##### Re: Starship heat shield
« Reply #3 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

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

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.
« Last Edit: 04/26/2020 01:17 pm by DusanC »

#### Karloss12

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##### Re: Starship heat shield
« Reply #4 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

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

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.
« Last Edit: 04/26/2020 01:28 pm by Karloss12 »

#### SteveU

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##### Re: Starship heat shield
« Reply #5 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

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.
"Better a diamond with a flaw than a pebble without." - Confucius

#### DusanC

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##### Re: Starship heat shield
« Reply #6 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?
« Last Edit: 04/26/2020 01:42 pm by DusanC »

#### Karloss12

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##### Re: Starship heat shield
« Reply #7 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

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.
« Last Edit: 04/26/2020 01:52 pm by Karloss12 »

#### Karloss12

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##### Re: Starship heat shield
« Reply #8 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.

#### wannamoonbase

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##### Re: Starship heat shield
« Reply #9 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.
« Last Edit: 04/26/2020 02:39 pm by wannamoonbase »
Wildly optimistic prediction, Superheavy recovery on IFT-4 or IFT-5

#### rakaydos

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##### Re: Starship heat shield
« Reply #10 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.

#### joek

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##### Re: Starship heat shield
« Reply #11 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, Sylvia M. Johnson, NASA Ames Research Center, 25-Jan-2015.
« Last Edit: 04/26/2020 04:33 pm by joek »

#### joek

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##### Re: Starship heat shield
« Reply #12 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.

#### livingjw

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##### Re: Starship heat shield
« Reply #13 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
« Last Edit: 04/26/2020 04:15 pm by livingjw »

#### WormPicker959

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##### Re: Starship heat shield
« Reply #14 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>

#### xvel

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##### Re: Starship heat shield
« Reply #15 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)
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#### samgineer

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##### Re: Starship heat shield
« Reply #16 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), 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.
« Last Edit: 04/26/2020 05:34 pm by samgineer »

#### livingjw

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##### Re: Starship heat shield
« Reply #17 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

#### Coastal Ron

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##### Re: Starship heat shield
« Reply #18 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.
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#### livingjw

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##### Re: Starship heat shield
« Reply #19 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
« Last Edit: 04/26/2020 05:48 pm by livingjw »