Re: >H Open Air Space Habitats

Carl Feynman (
Mon, 03 Mar 1997 06:27:53 -0500

Forrest Bishop wrote:
>>As this is an "open-air" design, the ends only have to come up from the
cylinder wall
>>about 150 kilometers, and can be very thin near the top, as will be the
I wrote:
>That gives an atmospheric half-life of only 60,000 years.
Forrest Bishop wrote:
>[[Only 60,000 years eh?. BTW, I just guessed at the height. Did you use a
>planetary or planar gas kinetic equation for this?

Here's how I did it. My trusty chart of the 1958 ICAO Standard Atmosphere
says that about 10^-10 of the mass of the atmosphere is above 150 km. I
assumed that all the air above that height was expanding freely horizontally
into vacuum, which would give it a velocity equal to the speed of sound, or
282 m/s at that altitude. Thus, 10^-10 of the atmosphere disappears in a
time equal to the time required for sound to cross the width of the ring.
The rest is multiplication. (hmmm... missed a factor of two there; should
be half the width of the ring, because it's spilling off both sides.)

Obviously the dynamics of the gas is a little more complex than this. But I
don't think I'm off by more than a small factor.