Apply shuttle ET foam in a vacuum.

"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
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