Ron Wanttaja wrote:
And when you come down, you have to get rid of all the 25,000 FPS. Orbital
spacecraft take some small portion away with rockets, and scrub off the
rest in atmospheric friction. The X-Prize folks have a far simpler
problem. Hopefully, that'll be addressed in the Y-Prize. :-)

Actually, getting rid of that excess velocity by aerobraking is also a bit
of a trick for an X-Prize class vehicle, at least if it's going straight
up and straight down. The problem is that you end up going quite fast
before you hit sensible atmosphere, and the atmosphere is actually pretty
thin, so you have to get rid of a lot of velocity fast (which implies high
g loads and high heating) or you end up at zero altitude with nonzero
speed. This is called "lithobraking" :-)

Coming in from orbit you can decelerate higher up, and take advantage of a
bit of lift to keep you in the thinner part of the atmosphere longer. A
ship like Rutan's can also do this to a certain extent since it will have
a substantial horizontal component of velocity.

.......Andrew
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Andrew Case |
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