High altitude balloons

[Henning]

Theoretically, given an infinite amount of material, and 1000kg hydrogen, how far into space could you make a balloon go, and how large would the envelope be. Calculate envelope weight using modern commercially available materials technology. What will be the limiting factor on terminal altitude, if any (can it get high and large enough to be affected by solar winds and taken into space?)?

 

[Jim Logajan]

That is what I was wondering about, getting fuel to orbit taking as much advantage as possible of its own lift. Maybe float it as high as possible then drag it further with some rocket device it carried aloft.

The energy saved probably isn't that much. Using high school level physics to get a first order estimate of the potential energy needed to get to a reasonable orbit altitude versus the kinetic energy to maintain a low earth orbit:

Potential energy Ep to raise m kg to a height h meters up:
Ep = m*g*h

Kinetic energy Ek to move m kg to a speed V meters/sec:
Ek = m*V*V/2

For m = 1 kg, g = 9.8 m/sec/sec, h = 400,000 m, (about 248 miles up), V = 7800 m/s (approximate orbital velocity at that altitude) I get:

Ep = 3.9 MJ
Ek = 30.4 MJ

So using a balloon saves on the order of ~10% of the needed energy. Most of the energy needed to get into orbit is in reaching a speed that keeps the spacecraft from crashing into the ground. Sorry to burst your balloon idea.