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#41
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"Derek Lyons" wrote in message ... "Jeff Findley" wrote: Exactly. And the ET, as designed and built, needs its aluminum-lithium structure to remain cold since it's quite a bit stronger at LH2/LOX temperatures than even at room temperature. Add to that the effects of aerodynamic heating, and you'll find that you really do need the foam on the outside. In other words, George (incorrectly) stated as a general principle something that appears to be Shuttle specific. Other vehicles have the same issue to deal with if they use cryogenic propellants and metallic tanks that are integral structural components. They may not have to deal with the aerodynamic heating issue as much because their nose is a payload shroud, not a LOX tank. But in general, you can make your metallic cryogenic tanks lighter by insulating the outside rather than the inside. You also don't have to worry about the insulation coming loose and being ingested by the LH2/LOX intakes. Jeff -- Remove icky phrase from email address to get a valid address. |
#42
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Alex Terrell wrote:
The pre-launch reason to have foam there is to prevent ice buildup on the outside of the tank. Because, if you think foam shedding is bad for Shuttle Tiles and RCC leading edge sections, you should see what ten pounds of nice solid liquid-hydrogen subchilled water ice will do to any surface of the shuttle... If this is the major reason, why not ditch the foam 30 seconds before launch. Ice build up after that would be negligible. This was tried on an Ariane stage, which ended up heavier and less reliable with the detachable foam than it was with the replacement, glued on permanently fixed foam, according to Henry. -george william herbert |
#43
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Carsten A. Arnholm wrote:
George William Herbert wrote: The pre-launch reason to have foam there is to prevent ice buildup on the outside of the tank. Because, if you think foam shedding is bad for Shuttle Tiles and RCC leading edge sections, you should see what ten pounds of nice solid liquid-hydrogen subchilled water ice will do to any surface of the shuttle... Foam on the outside does both jobs. Foam on the inside of the tanks would help prevent water ice buildup on the outside, but not help with ascent heating. External ablative shielding plus internal foam would do both better than we get right now, but would be heavier. Even better would be to put the actual space vehicle in a position where falling objects will not hit it. That means on the top and not on the side, under or whatever. It was clear shortly after Columbia burned up that nobody was ever going to build a new vehicle that way ever again. That's not the question. The issue at hand is whether people properly understand the factors that led to the external foam on the ET or not. If you don't understand them, you're going to get something else wrong somewhere else, eventually... -george william herbert / |
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