Following on to @zoomer0056's line of observation, Elon does what Elon finds cool. Always think of him as a highly-gifted teenager with science fiction dreams.
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zoomer0056
Active Member
I gotta check my words before hitting the Post reply button.A Shortfall of Gravitas
As in lack off, not minor reduction in altitude
I don't think they named any of the Falcon 9's, did they? Just SN's.
But SpaceX did give names to the Crew Dragon capsules: Endeavour, Freedom, Endurance. So I am expecting that crewed Starships will also get named.
Yes, heatshield reuse seems like perhaps the major challenge in Starship development at this time. Catching boosters and ships almost seems more of a solvable problem.
TunaBug
Member
I'm curious to know what they actually expect from a "fully reusable" heatshield. Two flights? Three flights? I have assumed that the design of the tiles and their attachment, which seems to be that they just snap on, maybe whack them once with a rubber mallet, is that they are intended to be trivially replaced after some number of flights. Or in other words, if they really thought that the tiles' life would match the starship then wouldn't the attachment be more permanent?
Why don't they make the attachment permanent for now just to shake out the rest of the starship design? If they are intended to be replaceable then figure that out later once they're actually re-using the starships?
Heat shield is one of the hardest parts and they aren't reusing the Ship even if it works, so they want to test the intended design, not one that might survive better but isn't fit for purpose.
Belly flop and flip have already been tested as has reaching space so heat shield is almost the last item on the list.
Assume that they have done tests and simulations and have found that the best lifetime they can expect is short enough to justify an easy means of replacement. Naturally, they want as many flights as they can get, but they need a recovered Starship to inspect before they can begin the cycle of evaluation and refinement. Let's also remember that these are early days for Starship heat shields. The operational heat shield may look nothing like the heat shield we see today.
TunaBug
Member
That's what I was trying to convey, but I clearly fumbled that. I agree that the current design seems optimized for easy replacement. In other words, they've decided that a cheaply/quickly replaced heatshield is better than a large, heavy, good for 100 flights heatshield. Excellent. And the tiles keep falling off during ascent. Not excellent.
Nobody cares how many times you can re-use the heatshield until you can re-use the rest of the starship, too. The heatshield only matters once they get the entire ship to the point that a used heatshield is what is keeping them from re-launching the entire ship. And there are a lot of other systems that still need to be proven out, not just the heatshield. I wouldn't redesign the whole thing: just glue the existing tiles on so that they stop falling off during ascent. Worry about the retention mechanism later.
Ah, but the click-on heat tile system isn't broken, so it doesn't need fixing. Yet. They're losing fewer tiles on each flight, and I seem to recall almost no loss on IFT-3. At least in the area visible during reentry. So SpaceX will undoubtedly wait to see how the click-on system does after they've completed one or two stable reentries. For now, they're making progress with their chosen approach.
Good question.
It would seem that much of the heat shield issue is losing tiles... both here on Starship and on the Shuttle before it. It would be interesting to know, for the tiles that don't fall off, what the "wear" on them is. Actually, the shuttle might be an interesting datapoint here... what was the lifetime for the tiles that stayed attached... I'm sure it was different for the high-temp areas (leading edges, etc...) where they used carbon-carbon... but how long would a "normal" tile last?
Also, regarding attachment method... in addition to ease if installation/replacement, I wonder if adhesive has its own drawbacks for something expected to be reused a significant number of times... Thermal expansion is something I wonder about, but we have seen them glue some on, so I'm not sure....
One hundred missions, with refurbishment. The refurbishment was mostly just a waterproofing. The big problem with Shuttle tiles was their uniqueness, combined with the fact that they repaired tiles instead of replacing them. Apparently, repairing a tile could take a couple days because of the need to cure the material. Tiles did fall off sometimes, and sometimes they had to be removed so that underlying structure could be accessed.
I don't know if Starship's heat tiles are hydrophilic, and I guess nobody knows what sort of inspection regime will be required for them between flights.
If damage to tiles is a constant issue, then you'd want to be able to replace a tile here or there almost constantly, and do it quickly. For all I know, they'll be able to automate inspection and replacement of the click-on tiles. I suspect that would be much more difficult with adhesives involved.
Seems like I saw a thread about the effect of water on the Starship tiles... at NSF maybe.
I did see one video where a guy who found one washed up at the beach and weighed it before and after it dried out, and it did seem to have absorbed some water... dunno if that would impact performance though.
Consider the phase transitions possible during ascent, on orbit, and during reentry. In vacuum would it freeze? During reentry would it flash over to gas? Perhaps SpaceX chose such thin tiles to facilitate exfiltration of moisture during ascent and while on orbit at a pace that won't produce damage.
Edit: Here's a tidbit that I found on the NSF forums. Emphasis is mine.
Edit 2: Apparently, early Space Shuttle flights would do a "rotisserie roll" to make sure any moisture had been baked off. STS-2 had a couple tiles' surface coating damaged because of retained moisture. I assume that's why NASA went to a waterproof coating. To their credit, they tried Scotchgard before switching to the toxic stuff. It'll be interesting to see what happens with Starship's tiles.
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Just duct tape the damn thing and be done with it. Home Depot has a sale going on right now.
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