If the Moon or Mars will we . . .

> Lifting a small rocket by balloon is okay, but small rockets won't
go far or carry much. A typical lift-off mass for the shuttle is
over 2000 tons. At sea level that would require a displaced buoyant
air mass of about 2 million cubic meters. Above sea level,
significantly larger volumes would be required.
>
> Another way to think of this is, how much farther is 80,000 ft.
from the center of Earth? Earth's radius is about 20,718,750 feet,
so 80,000 ft. is less than 1/2 of 1 percent, which is not much
compared to all of the trouble of trying to lift a big rocket?
>
> Jay Huebner

As you point out, the miniscule difference in gravity or potential
energy isn't the advantage of using a balloon. At 80000 feet, you
are above most of the atmosphere, nearly in vacuum. Instead of
needing two types of rocket engine (one for low atmosphere and a
different one for high atmosphere/vacuum) you only need one type of
engine. And your rocket launch will experience much less friction
than a launch from the ground.

Al pointed out that most of the energy required for orbital flight
is to acquire horizontal velocity; he then directly equated this
with fuel. A quick glance at the rocket equation shows that this is
not strictly correct. Most of the fuel is used simply to lift the
fuel itself to 80000 feet.

Ed