The Next Generation of Human Spaceflight

GW Johnson · Post by **GW Johnson** » Mon Sep 27, 2010 5:42 pm

On windows: the shuttle windows are 3-layers. The outer layer is the same quartz crystal material as was the windscreen on X-15. It's good to about 2300F before it cracks from a solid phase change (actual melting is about 3200 F, these two temperatures are the same as any other SiO2 ceramic material). In the atmosphere, you get temperatures like that 2300 F phase-change point when you are exposed to hypersonic flow between about M6 and M7. That is why reentry (starting about M25) is so tough.

As for "glass", amorphous SiO2 softens dramatically at about 900 F, because it's a supercooled liquid, not a solid at all. That's the forming temperature for glass blowing. Solid SiO2-as-quartz stays strong to much higher temperatures. Unfortunately, no other materials are ready.

GIThruster · Post by **GIThruster** » Mon Sep 27, 2010 5:59 pm

Diamond windows exist but you'd have to have a really good reason to pay for them over quartz:

http://www.diamond-materials.com/windows_en.htm

Diamond's melting point is highly pressure dependent but is very high, so it can enable hotter windows, and as said earlier, it is the most thermally conductive material in existence. Build some heat pipes into the frame and you can have an extremely high temperature window, but why bother when you can use it for diamond cameral lenses all over a future spacecraft?

rjaypeters · Post by **rjaypeters** » Mon Sep 27, 2010 6:46 pm

GIThruster wrote:...but why bother when you can use it for diamond cameral lenses all over a future spacecraft?

You are right, the cameras will never fail! Please see my earlier comment about passive safety.

GW Johnson · Post by **GW Johnson** » Mon Sep 27, 2010 7:42 pm

Don't get me wrong, I like real windows to look out of, especially in vehicles. It's just that reentry is a real beast for transparencies of any size. Maybe in the future, better materials will be found. There's always hope.

rjaypeters · Post by **rjaypeters** » Mon Sep 27, 2010 8:17 pm

GW Johnson: I understand, but transparencies for reentering vehicles have existed since the Shuttle program (well, earlier, but the Shuttle was the first winged reentry vehicle that flew through reentry). I don't see any good reason for accepting less on the next program.

Are there good, overriding, reasons not to have windows at least for the pilot?

ladajo · Post by **ladajo** » Mon Sep 27, 2010 9:19 pm

Would you call it flying or a computer controlled attempt not to tumble?

93143 · Post by **93143** » Mon Sep 27, 2010 9:51 pm

Buran only made one orbital flight before the program fizzled - launch, orbit, reentry, runway landing. There was no one on board.

As for windows, could you run water through gaps in a sandwich structure, or would the resulting thermal gradients be too high?

rjaypeters · Post by **rjaypeters** » Mon Sep 27, 2010 9:56 pm

ladajo wrote:Would you call it flying or a computer controlled attempt not to tumble?

YES!

rjaypeters · Post by **rjaypeters** » Mon Sep 27, 2010 10:06 pm

93143 wrote:...could you run water through gaps in a sandwich structure, or would the resulting thermal gradients be too high?

Good idea. Doesn't have to be water, just transparent under our conditions. Another layer of complication for us, though.

ladajo · Post by **ladajo** » Mon Sep 27, 2010 10:52 pm

rjaypeters wrote:
ladajo wrote:Would you call it flying or a computer controlled attempt not to tumble?
YES!

Ok, I'll call it a slightly guided mach 20 brick.

rjaypeters · Post by **rjaypeters** » Mon Sep 27, 2010 11:08 pm

ladajo wrote:Ok, I'll call it a slightly guided mach 20 brick.

Oh, Netizen, you wrong the Shuttle! Everytime it had a chance, it landed on the runway!
Also, we would do well to remember the courage of John Young and Robert Crippen (the first).

IntLibber · Post by **IntLibber** » Mon Sep 27, 2010 11:34 pm

rjaypeters wrote:
GIThruster wrote:...but why bother when you can use it for diamond cameral lenses all over a future spacecraft?
You are right, the cameras will never fail! Please see my earlier comment about passive safety.

Anybody piloting a reentry vehicle ought to be able to fly on instruments alone or they shouldn't be in the pilots seat.

GIThruster · Post by **GIThruster** » Mon Sep 27, 2010 11:35 pm

rjaypeters wrote:
93143 wrote:...could you run water through gaps in a sandwich structure, or would the resulting thermal gradients be too high?
Good idea. Doesn't have to be water, just transparent under our conditions. Another layer of complication for us, though.

Not an informed question. You need to understand heat-pipes. You can form both the windows or lenses out of diamond as well as the heat-pipes. You design the pipes around the delta temp you're looking at but most assuredly, you're not looking at water for high temps.

hanelyp · Post by **hanelyp** » Tue Sep 28, 2010 2:22 am

93143 wrote:As for windows, could you run water through gaps in a sandwich structure, or would the resulting thermal gradients be too high?

I expect you could do better with transpiration cooling outside the window.

As for materials, how does sapphire (Al2O3) compare at high temperatures? Tech for producing sheets of this material is fairly mature.

93143 · Post by **93143** » Tue Sep 28, 2010 3:07 am

GIThruster wrote:Not an informed question.

I'd post a more detailed retort but I left my fluid mechanics, gaskinetic theory and heat transfer textbooks at the lab.

Also, who said anything about heat pipes?

hanelyp wrote:I expect you could do better with transpiration cooling outside the window.

I'm not sure I like the idea of a porous transparency exposed to hypersonic flow...

Sapphire melts above 2000ºC, and is being considered for armour applications. Not sure how its mechanical properties behave as you start to approach the melting point...