From: hal@finney.org
Date: Wed Mar 14 2001 - 11:47:50 MST
Mike Lorrey writes:
> A new NASA program is the Ultra Long Duration Balloon, which can carry
> up to 1600 kg at an altitude minimum of 33.5 km for periods of up to 100
> days. What is the mass fraction required to launch from the 33.5 km
> altitude at the equator and gain a 200 km orbit? (btw: what is the
> equation to use to calculate mass fractions? Spike, can you post up your
> spreadsheet?
I don't know the answer, but I do know that getting to altitude is a small
part of the problem of reaching earth orbit. LEO velocity is 7.5E3 m/s.
Putting 1 kg into this orbit takes 1/2 mv^2 or 2.8E7 Joules. Raising 1 kg
by 33.5 km adds 9.8 * 33.5E3 Joules or 3.3E5 Joules, just over 1% of the
needed energy to reach orbit. So you haven't gained much.
Hal
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