Airship to Orbit question

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Chance - 13 Dec 2005 22:02 GMT

I was reading about the airship to orbit idea, and how it is probably
impossible. This got me to thinking, are there any materials like
carbon nanotubes that could concievably be used produce a large volume
vacuum container or "balloon"? I recently asked one of those
ask-a-physicist sites and was told that an airtight "ballon" with a
volume of near vacuum should float even higher than a hydrogen balloon,
but that no existing materials are at the same time strong enough and
light enough to ever produce such a device. Such a device should be
much simpler and cheaper to create than a space elevator, and could
(hopefully) be mass produced. So is this is just a crazy idea, or is
it possible?

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Cray74@gmail.com - 15 Dec 2005 14:31 GMT

> I recently asked one of those
> ask-a-physicist sites and was told that an airtight "ballon" with a
> volume of near vacuum should float even higher than a hydrogen balloon,

Getting to orbit is not just a matter of altitude. In fact, the only
reason rockets climb is to get above the atmosphere to avoid
aerodynamic drag.

The reason that aerodynamic drag is of concern to rockets is because
orbital velocity around Earth is 17500mph. That's about the bare
minimum speed you need to "miss the horizon" as gravity pulls you back
down to Earth. Even in the upper fringes of the atmosphere (50-60
miles), aerodynamic drag would be a severe problem at 17500mph.

Balloons can help minimize the aerodynamic drag issue by providing a
high altitude launch platform for rockets, but climbing to orbital
altitudes is only a small portion of the effort of getting to orbit.
The real effort is reaching orbital velocity.

As a practical issue for such a "vacuum balloon" (besides materials
strength) is that the material of the balloon's skin still has weight.
Your balloon won't be able to climb all the way to minimal orbital
altitudes (~100 miles) because of its own weight. Actually, the balloon
would be lucky to reach 40 miles. Even at 20-25 miles you'd have a nice
drag reduction.

Mike Miller

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Space Forum / Space Flight / December 2005

Airship to Orbit question