Friday, June 25, 2004

Balloons in Space?

DefenseTech links to an article about a "near-space" balloon that was badly damaged by 20-25 knot (23-26 mph) wind. This balloon is meant to go the 100,000 ft and hover over a battlefield to collect intelligence or serve as a communications hub. Which brings up a simple question: if the balloon can't handle a pidly ~25 mph wind, how exactly is it supposed to stay together on the way to 100,000 ft?

There is a very good reason that there have been very few balloons or airships since the 1930s. They just aren't very robust in bad weather. The idea for this particular one is that at 100,000 ft the conditions are pretty calm, but the damn thing still has to be tough enough to make it that high. So that's a little questionable, but apparently the company is working on the idea of eventually building up to the point of having a BALLOON GO TO SPACE!?!?!!!

----- This is Earth calling JP Aerospace, where are you? Over. -------
----- Could you repeat, Houston. We seem to have our heads in a place where the sun does not shine. ------

The guy from JP explains how it would work like this:

"What if you flatten it out and give it a little bit of aerodynamic shape, and point it up a little bit so you have some of that thrust turned into lift?" Powell asked. "As you climb up, your drag is dropping, and now you're accelerating. The question comes, can you get aerodynamically clean enough, while still supporting the lift enough to slowly get faster and faster ... to get all the way to orbit? Is there a drag-power combination to do that? We think there is. It looks like there's a wide margin."

Wow, let's go over a few of the problems with this concept. First and foremost, what do you make the thing out of? It has to be able to be strong enough to handle the aerodynamic loads, plus any gust conditions, on ascent. Light as possible to accelerate the vehicle. And it must be able to handle the thermal loads from going very fast. Even at high altitude, where the air is thin and cold, at high speeds the friction makes things hot enough to melt most materials (drag increases with the square of velocity). Unless these guys have access to the stuff that UFO's are made of, it will be a bit of a problem.

Next you can't count on purely the buoyant force to make it to space, as beyond a certain altitude, what's inside the vehicle will become more dense than what is outside, reversing the acceleration. The propulsion system would have to be light, and it would have to be attached to structure that could handle the thrust loads.

The placement of the payload for the vehicle would have a similar problem. Wherever it is attached will have to be strong enough, which will make the vehicle heavy and impair its performance again.

As an orbital vehicle, the idea of a frickin' balloon is fundamentally unserious. It might be a concept worth exploring only to determine where the biggest problem areas are such that they could be worked on, but it will not be technically feasible in the foreseeable future.

4 comments:

Anonymous said...

Couldn't they just make it out of unobtanium? ;-)
Kim

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