Re: cheap space flight

Forrest Bishop (
Sun, 17 Nov 1996 20:33:57 -0800

Since we have lots of experts on the list, a question: stratospheric
baloons fly pretty high, 30-40 km. Assuming a 1 ton baloon payload
sure defines a gigantic hydrogen baloon), which drags a solid (Al,
perchlorate, resin) booster, made from light compound with a very small

payload (50 kg?), let's say 20 km high up, then igniting the booster to

travel the rest of the way to LEO.
Does this make sense, weight-wise? What are pros, what are cons?

[[I did a study design on this about 20 years ago, using a two-stage
hybrid (read cheap) (solid hydrocarbon, LOX) on a high altitude
The specific impulse is much better than an all-solid.
The all up mass (less balloon) was on the order of 500 Kg, payload
on the order of 5 Kg.
I did use a hydrogen balloon, BTW.
The number one advantage is the reduction of atmospheric drag,
an open air, spherical tankage design and the attendant structural
mass reduction. The chamber pressure also does not have to be run
up to the bleeding edge, saving a lot of pump mass and such.
The nozzles can be fixed, high expansion bells. If I remember, my
second stage nozzle was an ablator nearly the volume of the LOX tank.

The “free” altitude is of secondary interest.

The launch coordinates are hard to control, and the platform is a long
from a service facility. The balloon is hard to recover. The all-up
is quite limited, unless one develops a giant (reuseable?) balloon

All in all, a reasonable proposition, and I think I’ve heard of similar
proposals. Whether it can compete with subsonic aircraft launchers
like the Pegasus is doubtful.