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How effective would this be or would the Earth's magnetic field make it useless? Would it take too long for this to be of any use?

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    $\begingroup$ I'm curious, what is a "magnetic scoop"? Can you add a link or two showing that such a thing exists, at least in theory? $\endgroup$ – uhoh Oct 12 '19 at 13:05
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    $\begingroup$ Where is this hydrogen coming from? $\endgroup$ – Steve Linton Oct 12 '19 at 18:54
  • $\begingroup$ Magnetic hydrogen would be helpful. $\endgroup$ – Uwe Oct 12 '19 at 21:05
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    $\begingroup$ @Uwe ionised would do. $\endgroup$ – Steve Linton Oct 12 '19 at 21:09
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Scoping is an interesting idea if you can fuse hydrogen as fuel as you go along, but not so much if you just want to tank it.

Setting aside how the scoop itself works, there’s a problem scooping up stationary gas: you have to bring it up to your speed if you want to put it in a tank and keep it there.

Essentially, you need a way to take your newly acquired fuel up to your orbital speed. That takes most of the energy and $\Delta v$ it would have taken to lift it from the ground; you save only the gravitational potential, which isn’t a large fraction if you’re close enough to Earth to catch something.

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  • $\begingroup$ "That takes most of the energy and Δ𝑣 it would have taken to lift it from the ground..." I'm not sure this is true. For an ion engine the "exhaust velocity is much higher than orbital velocity, so the momentum lost due to drag collecting gas is likely to be a lot less than the momentum gained by accelerating the ions to 100 keV. Can you make a quantitative argument to support your answer? Also energy is not the relevant thing here, ion propulsion always requires a large source of energy, whether solar or RTG or otherwise. $\endgroup$ – uhoh Oct 13 '19 at 6:30
  • $\begingroup$ One way you could support your argument is to point out that for every atom of hydrogen collected you may need to slow down a zillion atoms of nitrogen (assuming Earth orbit), and that would indeed be prohibitive. To counter that though, proposing to try to find a way to use nitrogen would be around that, as would orbiting around a another planet or very large moon with a lot more hydrogen in its upper atmosphere, or even just stay very high where H and He are plentiful! en.wikipedia.org/wiki/… $\endgroup$ – uhoh Oct 13 '19 at 6:33

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