Starship V2 Versus Space Shuttle Tile damage

[SpaceLizard]

Why do you expect perfect results from what is still an R&D program? The heat shield is probably the most difficult of a all the problems they have to face so I think it's only fair to give them time to figure it out.

The issue I have is two-fold:

The Shuttle TPS didn't ablate.  The waterproofing burned off and tiles got damaged because it was side-mounted and thus in the debris stream from the tank, but the tiles themselves didn't ablate, I don't believe.  That was 50 year old technology.

Second, I think SS should have a lower ballistic coefficient than Shuttle and thus, I presume, a lower heating stress on the TPS.  It's possible that this assumption is incorrect but my thinking is that the SS is bigger but not that different in mass than a Shuttle on-entry (Shuttle usually weighed on the order of 100 metric tons on landing, if I recall correctly).

Ship's tiles aren't ablating the redundant backup layers beneath them exposed by deliberately removed tiles is.

Ship is being made to re-enter in off-nominal and extreme orientations to determine the absolute outer limits of its survivability and therefore experiencing worse heating than it would in normal operations.

[envy887]

Why is SS so charred and discolored compared with Atlantis?

The charring is likely because the tile loss is resulting in a lot of ablation, both of the materials that are intended to ablate, which Shuttle didn't have; and those materials that aren't intended to ablate, which didn't happen on Shuttle because the gaps were filled better and fewer tiles were lost.

Dragon looks like a roasted marshmallow after recovery, and Falcon also chars (in addition to sooting) during reentry. Neither are really affected in their ability to be reused.

The stainless steel rainbow discoloration is simply because Starship has a heat-tolerant structure that operates at higher temps during reentry. This isn't necessarily a problem - actually, it's an indication of unnecessary insulation mass being left off, resulting in a performance improvement.

Ablation is the opposite of "fully and rapidly reusable".

Not necessarily, although it's pretty obvious that SpaceX would prefer to not have anything ablating if possible.

This particular ship wasn't intended to be reusable, or to qualify its design for reuse. The TPS is still in development, and I don't think it's possible to draw any inferences about what the final design will be, except that it's not this one.

[Lee Jay]

Why is SS so charred and discolored compared with Atlantis?

The charring is likely because the tile loss is resulting in a lot of ablation, both of the materials that are intended to ablate, which Shuttle didn't have; and those materials that aren't intended to ablate, which didn't happen on Shuttle because the gaps were filled better and fewer tiles were lost.

So, they need to work on that.

Dragon looks like a roasted marshmallow after recovery, and Falcon also chars (in addition to sooting) during reentry. Neither are really affected in their ability to be reused.

I thought Dragon had an ablative heat shield that isn't designed to be "fully and rapidly reused", and that's why that's okay.

The stainless steel rainbow discoloration is simply because Starship has a heat-tolerant structure that operates at higher temps during reentry. This isn't necessarily a problem - actually, it's an indication of unnecessary insulation mass being left off, resulting in a performance improvement.

But doesn't that mean the oxidation of the stainless is pushing through the tiles and depositing itself on top of the tiles?  Isn't that an indication that the shield has failed to prevent gas flow between the outside and the tank?  Also, if the stainless is oxidizing and that the oxidation is leaving the tank, that means the stainless is ablating and degrading.  Again, that means it's not "fully" reusable.

[Masshole]

Every shuttle flight had tile damage.
EVERY. ONE.

https://i.sstatic.net/9E14m.png

[SpaceLizard]

The stainless steel rainbow discoloration is simply because Starship has a heat-tolerant structure that operates at higher temps during reentry. This isn't necessarily a problem - actually, it's an indication of unnecessary insulation mass being left off, resulting in a performance improvement.

But doesn't that mean the oxidation of the stainless is pushing through the tiles and depositing itself on top of the tiles?  Isn't that an indication that the shield has failed to prevent gas flow between the outside and the tank?  Also, if the stainless is oxidizing and that the oxidation is leaving the tank, that means the stainless is ablating and degrading.  Again, that means it's not "fully" reusable.

Let's try this one more time...
Every StarShip that has flown so far has done so with deliberately missing tiles to test its ability to survive off-nominal situations.
Damage the ships have sustained is therefore not representative of how its heatshield will perform when operational.
Stainless steel ablation was a direct result of deliberately missing tiles which directly exposed the vehicle's bare skin to reentry, and it still landed.

[envy887]

Why is SS so charred and discolored compared with Atlantis?

The charring is likely because the tile loss is resulting in a lot of ablation, both of the materials that are intended to ablate, which Shuttle didn't have; and those materials that aren't intended to ablate, which didn't happen on Shuttle because the gaps were filled better and fewer tiles were lost.

So, they need to work on that.

Dragon looks like a roasted marshmallow after recovery, and Falcon also chars (in addition to sooting) during reentry. Neither are really affected in their ability to be reused.

I thought Dragon had an ablative heat shield that isn't designed to be "fully and rapidly reused", and that's why that's okay.

The stainless steel rainbow discoloration is simply because Starship has a heat-tolerant structure that operates at higher temps during reentry. This isn't necessarily a problem - actually, it's an indication of unnecessary insulation mass being left off, resulting in a performance improvement.

But doesn't that mean the oxidation of the stainless is pushing through the tiles and depositing itself on top of the tiles?  Isn't that an indication that the shield has failed to prevent gas flow between the outside and the tank?  Also, if the stainless is oxidizing and that the oxidation is leaving the tank, that means the stainless is ablating and degrading.  Again, that means it's not "fully" reusable.

Dragon is a production vehicle, so it needs to be "ok", Starship isn't finished with development, so not being "ok" is ok for now. Obviously they need to work on it. It's not "done", nor is it likely to be "done" within the next decade.

"Rapid" and "reuse" are a continuum, not a single point. Dragon is mostly reusable within a few months, although I don't think they reuse the heatshield at all. Starship is aiming for zero-touch turnaround in a few hours, but that's absolutely not going to happen anytime soon. If within the next couple of years they can reuse it like F9, spending a few weeks in the barn between flights getting a fair amount of work done, that would be a pretty big win and more than sufficient for their near-term goals.

5 years from now that might be down to a few days turnaround, and in 10-15 years they might get a same-day reflight. The marginal returns from faster reflights decrease pretty quickly, though. They may never get to same-day reflight, and that would probably be "ok".

[envy887]

The stainless steel rainbow discoloration is simply because Starship has a heat-tolerant structure that operates at higher temps during reentry. This isn't necessarily a problem - actually, it's an indication of unnecessary insulation mass being left off, resulting in a performance improvement.

But doesn't that mean the oxidation of the stainless is pushing through the tiles and depositing itself on top of the tiles?  Isn't that an indication that the shield has failed to prevent gas flow between the outside and the tank?  Also, if the stainless is oxidizing and that the oxidation is leaving the tank, that means the stainless is ablating and degrading.  Again, that means it's not "fully" reusable.

Let's try this one more time...
Every StarShip that has flown so far has done so with deliberately missing tiles to test its ability to survive off-nominal situations.
Damage the ships have sustained is therefore not representative of how its heatshield will perform when operational.
Stainless steel ablation was a direct result of deliberately missing tiles which directly exposed the vehicle's bare skin to reentry, and it still landed.

The skin not only ablated, but burned through, venting the prop tanks in several places. And it still landed.

[DanClemmensen]

The skin not only ablated, but burned through, venting the prop tanks in several places. And it still landed.

I did not see any discussion of this. What did I miss?

[SpaceLizard]

The skin not only ablated, but burned through, venting the prop tanks in several places. And it still landed.

I did not see any discussion of this. What did I miss?

Intermittently from here onward:
https://forum.nasaspaceflight.com/index.php?topic=63578.msg2725473#msg2725473

[catdlr]

The skin not only ablated, but burned through, venting the prop tanks in several places. And it still landed.

I did not see any discussion of this. What did I miss?

Intermittently from here onward:
https://forum.nasaspaceflight.com/index.php?topic=63578.msg2725473#msg2725473

Dan,

I saw that when it was posted.  I didn't feel like commenting on that. I understand the visual of the venting gases at the last moments of the flight, even the very long video of the ship as it's on its belly coming down through the clouds, you can see a steady stream of gases coming off it, streaming out like water coming out of a balloon. But if plasma had burned through into the tank during the reentry, the entire ship would have exploded. I can't explain it. Like Jack would say, "less data is no data."

[envy887]

But if plasma had burned through into the tank during the reentry, the entire ship would have exploded.

The tanks contain pure methane or oxygen. Neither is explosive without the other, so a burn through isn't necessarily any more likely to cause an explosion than opening a vent intentionally, as Starship does quite frequently.

The potential issues are 1) methane can burn with atmospheric oxygen, and 2) the tanks may need some internal pressure for structural stability, and a unintended vent may cause pressure loss. But clearly neither of those rose to the level of being a problem for Flight 11.

[catdlr]

But if plasma had burned through into the tank during the reentry, the entire ship would have exploded.

The tanks contain pure methane or oxygen. Neither is explosive without the other, so a burn through isn't necessarily any more likely to cause an explosion than opening a vent intentionally, as Starship does quite frequently.

The potential issues are 1) methane can burn with atmospheric oxygen, and 2) the tanks may need some internal pressure for structural stability, and a unintended vent may cause pressure loss. But clearly neither of those rose to the level of being a problem for Flight 11.

Got it, thanks. 

ADDED: Having separate header tanks for the final burn ensures a safe landing even if the main tanks are compromised by a hole.

[DanClemmensen]

The skin not only ablated, but burned through, venting the prop tanks in several places. And it still landed.

I did not see any discussion of this. What did I miss?

Intermittently from here onward:
https://forum.nasaspaceflight.com/index.php?topic=63578.msg2725473#msg2725473

Dan,

I saw that when it was posted.  I didn't feel like commenting on that. I understand the visual of the venting gases at the last moments of the flight, even the very long video of the ship as it's on its belly coming down through the clouds, you can see a steady stream of gases coming off it, streaming out like water coming out of a balloon. But if plasma had burned through into the tank during the reentry, the entire ship would have exploded. I can't explain it. Like Jack would say, "less data is no data."

I just reviewed the video. Yes, it looks like burn-through, still venting from the LOX tank, and possibly much larger holes near the center-line on the methane tank, so large that the tank was emptied and no longer venting.  The three Raptors were still firing, but recall that they are using the header tanks, not the main tanks. There is no particular reason for the holes to cause an explosion unless the LOX and methane mix.

It's also quite possible that I am miss-interpreting what I see. I was hoping for an analysis by SpaceX or by one of our better analysts.

[catdlr]

The skin not only ablated, but burned through, venting the prop tanks in several places. And it still landed.

I did not see any discussion of this. What did I miss?

Intermittently from here onward:
https://forum.nasaspaceflight.com/index.php?topic=63578.msg2725473#msg2725473

Dan,

I saw that when it was posted. 

I was hoping for an analysis by SpaceX or by one of our better analysts.

Same conclusion as my previous post: the header tanks save the day when the mains are compromised.

And now, a new thread is exploring crew emergencies in such situations during the flip. 

https://forum.nasaspaceflight.com/index.php?topic=63698.msg2725815#msg2725815

[CJ]

Try searching "elevons"

https://forum.nasaspaceflight.com/index.php?topic=50748.msg2599340#msg2599340

TL;DR the plasma hit the Shuttle hinge at an angle that's easier to shield against.

Thank you VERY much for this. And, yup, I was searching "ailerons" not elevons, oops. And more embarrassingly yet, I thought I was keeping up withe the heat shield thread, but missed those posts.

Thanks again!

[Lee Jay]

The stainless steel rainbow discoloration is simply because Starship has a heat-tolerant structure that operates at higher temps during reentry. This isn't necessarily a problem - actually, it's an indication of unnecessary insulation mass being left off, resulting in a performance improvement.

But doesn't that mean the oxidation of the stainless is pushing through the tiles and depositing itself on top of the tiles?  Isn't that an indication that the shield has failed to prevent gas flow between the outside and the tank?  Also, if the stainless is oxidizing and that the oxidation is leaving the tank, that means the stainless is ablating and degrading.  Again, that means it's not "fully" reusable.

Let's try this one more time...
Every StarShip that has flown so far has done so with deliberately missing tiles to test its ability to survive off-nominal situations.
Damage the ships have sustained is therefore not representative of how its heatshield will perform when operational.
Stainless steel ablation was a direct result of deliberately missing tiles which directly exposed the vehicle's bare skin to reentry, and it still landed.

That has nothing to do with the wide-spread oxidation seen all over the vehicle's heat shield.  If this was only in the spots where tiles were removed, we'd be having a different conversation.

[Lee Jay]

Why is SS so charred and discolored compared with Atlantis?

The charring is likely because the tile loss is resulting in a lot of ablation, both of the materials that are intended to ablate, which Shuttle didn't have; and those materials that aren't intended to ablate, which didn't happen on Shuttle because the gaps were filled better and fewer tiles were lost.

So, they need to work on that.

Dragon looks like a roasted marshmallow after recovery, and Falcon also chars (in addition to sooting) during reentry. Neither are really affected in their ability to be reused.

I thought Dragon had an ablative heat shield that isn't designed to be "fully and rapidly reused", and that's why that's okay.

The stainless steel rainbow discoloration is simply because Starship has a heat-tolerant structure that operates at higher temps during reentry. This isn't necessarily a problem - actually, it's an indication of unnecessary insulation mass being left off, resulting in a performance improvement.

But doesn't that mean the oxidation of the stainless is pushing through the tiles and depositing itself on top of the tiles?  Isn't that an indication that the shield has failed to prevent gas flow between the outside and the tank?  Also, if the stainless is oxidizing and that the oxidation is leaving the tank, that means the stainless is ablating and degrading.  Again, that means it's not "fully" reusable.

Dragon is a production vehicle, so it needs to be "ok", Starship isn't finished with development, so not being "ok" is ok for now. Obviously they need to work on it. It's not "done", nor is it likely to be "done" within the next decade.

"Rapid" and "reuse" are a continuum, not a single point. Dragon is mostly reusable within a few months, although I don't think they reuse the heatshield at all.

The Space Shuttle was reusable within months with a lot of work on the tiles, with 1970s technology.

Starship is aiming for zero-touch turnaround in a few hours, but that's absolutely not going to happen anytime soon. If within the next couple of years they can reuse it like F9, spending a few weeks in the barn between flights getting a fair amount of work done, that would be a pretty big win and more than sufficient for their near-term goals.

I think they need a pathway to full and rapid reusability of the vehicle or it's a failure.  Do they have that pathway or are they trying to invent one as they go?  Otherwise, it's not much different than the Shuttle was.

5 years from now that might be down to a few days turnaround, and in 10-15 years they might get a same-day reflight. The marginal returns from faster reflights decrease pretty quickly, though. They may never get to same-day reflight, and that would probably be "ok".

Regardless, I still don't understand why this one *seems* to perform worse than Shuttle, rather than better.

[SpaceLizard]

The stainless steel rainbow discoloration is simply because Starship has a heat-tolerant structure that operates at higher temps during reentry. This isn't necessarily a problem - actually, it's an indication of unnecessary insulation mass being left off, resulting in a performance improvement.

But doesn't that mean the oxidation of the stainless is pushing through the tiles and depositing itself on top of the tiles?  Isn't that an indication that the shield has failed to prevent gas flow between the outside and the tank?  Also, if the stainless is oxidizing and that the oxidation is leaving the tank, that means the stainless is ablating and degrading.  Again, that means it's not "fully" reusable.

Let's try this one more time...
Every StarShip that has flown so far has done so with deliberately missing tiles to test its ability to survive off-nominal situations.
Damage the ships have sustained is therefore not representative of how its heatshield will perform when operational.
Stainless steel ablation was a direct result of deliberately missing tiles which directly exposed the vehicle's bare skin to reentry, and it still landed.

That has nothing to do with the wide-spread oxidation seen all over the vehicle's heat shield.  If this was only in the spots where tiles were removed, we'd be having a different conversation.

Again, yes it does.
All of the orange areas are flowing directly down stream from the spots where bare steel was deliberately exposed to re-entry.
This is exactly like the metal tiles that were tested on the previous flight.

Edit:
The oxidation is originating from bare steel and flowing over the surface of the tiles staining them as it is caried away.
It is not coming out between the tiles from the steel beneath them.
Pictures of the areas that have flown with deliberately removed tiles:
https://forum.nasaspaceflight.com/index.php?topic=63578.msg2725505#msg2725505

[SpaceLizard]

Again, if the shuttle were treated the way these ships are being treated, (large deliberately removed areas of the heat shield, re-entered at inadvisable angles outside its safe operating envelope), I see no reason why it would look any better if it made it back at all.

The ships are currently being re-entered in prior conditions and heating regimes that shuttle would have never even attempted. Comparison of heat shield performance at this stage is impossible because shuttle never did these things, being mandatorily crewed excluded the possibility.

[Vultur]

Why is SS so charred and discolored compared with Atlantis?

The charring is likely because the tile loss is resulting in a lot of ablation, both of the materials that are intended to ablate, which Shuttle didn't have; and those materials that aren't intended to ablate, which didn't happen on Shuttle because the gaps were filled better and fewer tiles were lost.

Dragon looks like a roasted marshmallow after recovery, and Falcon also chars (in addition to sooting) during reentry. Neither are really affected in their ability to be reused.

The stainless steel rainbow discoloration is simply because Starship has a heat-tolerant structure that operates at higher temps during reentry. This isn't necessarily a problem - actually, it's an indication of unnecessary insulation mass being left off, resulting in a performance improvement.

Ablation is the opposite of "fully and rapidly reusable".

Exactly. On SS the ablative material is a backup. If it ever ablates, that means that the primary TPS failed. It does allow the SS to be recovered, inspected, and reburbished, but that is a (possibly minor) repair, not normal "fully and rapidly reusable" operation.

The current heat shield is not a final, operational "fully and rapidly reusable" one. It's still in development.

I think the system is going to be much more robust than Shuttle because of stainless steel vs aluminum airframe,  but it may never achieve full "gas and go" very rapid reusability. Even if it doesn't, I think it'd still be a dramatic improvement over anything that's yet existed.

OTOH, I don't think SpaceX is going to give up if it doesn't work. They'd try something else. Maybe going back to transpiration cooling, maybe something totally different (rapid swap of heat shield as one piece?).