QUOTE (DonPMitchell @ Aug 2 2006, 08:32 AM)
Is it feasible?
I have done a few back of the envelope calculations and I get the feeling it might be "pie in the sky" if you can excuse the pun.
It is important to remember two relevant facts.
1. The bouyancy of the atmosphere at 65,000 m (200,00ft) is very small.
2. Getting a payload to that altitude only represents about 8% of the energy needed to achieve a stable minimum orbit. Each kilogram of mass to orbit from there still needs an additional 70 megajoules, or, for the MER buffs, about 20,000 W.h. If we assume an average of say 400W.h per day for the MERs that is how much each will have collected in total in 50 sols. (Slight adjustment after checking calcs)
I have assumed that
(1) solar cell efficiency is 20% (10% if you assume they are in the Earths shadow for 1/2 the time)
(2) ion drive efficiency is 50%
(3) that cargo represents 50% of total mass, this is probably optimistic
(4) that 50% of energy is lost through air resistance.
With these assumptions you would need 40 sq meters /kg to supply enough energy to get each kg to orbit in (say)3 days. A 5,000kg payload would need a solar cell area of 200,000 sq meters. This of course would be limited to an equal mass as the payload and include to balloon and fuel as well.
I have not bothered to calculate the volume of a balloon needed at 65,000 m to support such a mass, but I will add that any publication that still persists in using feet and pounds as units in a scientific field is doomed to crash anyway.