I’ve heard there are materials that can withstand the image sort of the earth’s atmosphere, such as carbon nanotubes and Kevlar. Supposedly, a perfectly constructed bridge of such material could be used as a tether for a space elevator, although challenges exist in reliable construction.

To creatively navigate this issue, my protagonist is starting small – he wants to fly a balloon of such material filled with helium or some such floating gas up through the atmosphere, with a single thread of heat resistant material attached to it.

My questions are:

  • What material could such a balloon be made of that are light enough to float when filled with helium?

  • If helium wouldn’t work, is there another gas that would?

  • If such a balloon could feasibly be constructed, could it rise with a light-weight string of similar material attached? If one balloon is not sufficient, how about many?

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There's a small problem with your helium balloon; helium works as a lifting gas because it's lighter than air, but it's not lighter than space.

Ultimately, helium will rise into the sky to a point where the weight density of the helium is more or less in equilibrium with the surrounding air. I'll spare you the math; this works out to roughly 32km above sea level. By contrast, a geostationary orbit needs to be out at roughly 36,000 km above sea level to be stable. Ultimately, you get to less than 0.1% the height you need with helium because by the time you get to geostationary orbit height, there's no air around for the helium to be lighter than.

You might get a little higher by actually heating the helium, thus reducing its density further, but ultimately the best you're likely to do is get to the top of the atmosphere.

You could of course switch to hydrogen, which has 50% the density of helium and thus double the lifting power, but that still only gets you so far.

So, you could try heating the hydrogen, but I think we all know how that would work out.

In the end, you need to be surrounded by air to get lift from a gas that's lighter than air.

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  • $\begingroup$ Good point. Could you imagine any way in which having cables extending up to 32km would benefit the process of erecting a space elevator? Is gravity less up there? $\endgroup$ – frankbacon322 Sep 24 '18 at 3:56
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    $\begingroup$ @frankbacon322 In theory there is an advantage, in the sense that the cables that reach to 36,000km must reach 32km first. It'd certainly help, as in having a non-zero effect. But if somebody told me they were building a space elevator, and they'd already got 32km up, it'd not encourage me to invest in their company. Every aspect of building a space elevator is harder than that. $\endgroup$ – Cort Ammon Sep 24 '18 at 4:02
  • $\begingroup$ Hm... how about space based solar power from such a height? $\endgroup$ – frankbacon322 Sep 24 '18 at 4:13
  • $\begingroup$ @frankbacon322 my first question would be why not generate the power on the ground? Energy weighs very little (E=mc^2) so getting it up the space elevator is much easier than getting mass up there. Given that solar cells work perfectly well on earth, I'm not convinced that you'd ever recoup the energy cost of hauling the mass of the cells up that high by comparison to some power lines. $\endgroup$ – Tim B II Sep 24 '18 at 4:18
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    $\begingroup$ You also run into a problem with the balloon holding the material expanding and eventually bursting as the material just isn't flexible enough. $\endgroup$ – Shadowzee Sep 24 '18 at 4:19

You probably want to stick with the method proposed in the article you linked in the comments (energy.gov/articles/space-based-solar-power) rather than building a space elevator if you want to generate power.

In terms of small scale experiments, you could use a weather balloon like device to lift something like a cube satellite up fairly high and use that to test the transmission of power from orbit to a ground station. This would let you do preliminary testing without the stricter requirements of proper spaceship launches and it would be much cheaper.

Assuming you wanted to scale this up, with larger satellites and still retain the balloon concept, you might be able to add some small rocket/fuel boosters to your satellite and launch it up higher into orbit which would give you a much longer amount of time before it would fall down.

In terms of a fully functional solar power system in space, your going to need to either construct a space elevator in full scale or stick with the cost of a 100 or more launches to assemble the system in space. There is no easy way for us to get things out of our atmosphere and TimBII's answer covers why balloons can't achieve it.

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  • $\begingroup$ Better make those boosters big. You still need the the delta-V to sustain Low Earth Orbit, which is around 7.8 km/s. In a balloon tied to the earth you are traveling at most 40000km/24h = 0.463 km/s (on the equator). $\endgroup$ – GretchenV Sep 24 '18 at 11:03

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