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Could we capture hydrogen from the solar wind instead of importing it or getting it from local sources ie water on mars or the lunar ice? Would it be worth the time vs energy used to get it?

Basically my thought is to Terraform someplace like Venus that is missing hydrogen and you were going to build a massive solar shade to cool the planet. Could you capture the hydrogen that would be hitting the shade. You could use the hydrogen to create any number of items (fuel, water, etc.) instead of importing it.

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  • $\begingroup$ Many of the protons will stop in a thin sheet of material and stay embedded in it for a short time then diffuse out. Maybe some will diffuse inward rather than outwards and can be captured as hydrogen gas behind the film. Of course the stopping protons do damage and the material will eventually break down, but if it could be melted and reformed regularly I think you can have a giant sheet of "proton catching film". I don't know though if it's practical compared to mining water from a passing comet, since there are lots and lots of comets! $\endgroup$
    – uhoh
    Aug 11 '20 at 18:32
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    $\begingroup$ Does a magnetic collector make more sense? The real question is solar wind mass flux in kg/km^2*year $\endgroup$
    – ikrase
    Aug 11 '20 at 19:19
  • $\begingroup$ Sun will lose about a third of its mass in the next 7billion years. This can be calculated to a kg/m2/year value. $\endgroup$
    – peterh
    Aug 11 '20 at 20:34
  • $\begingroup$ The protons could be focused and then trapped by magnetic field. The magnetic field can be generated easily by superconductors. $\endgroup$
    – peterh
    Aug 11 '20 at 20:36
  • $\begingroup$ I did a little calculation and I got 300kg/year/sq km. It can be converted to 2700 kg of water. It is about twice on the orbit of the Venus (about 5500kg). Doing this on the whole Venusian surface, with a mega satellite-system which also solves the problem of the shading, we would require only about a million of years to increase the average Venusian water level with a m. $\endgroup$
    – peterh
    Aug 11 '20 at 20:55
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The solar wind has a typical velocity and density of a few hundred km/s and a few tens of particles per cubic centimeter. See here for example.

So, a 10000km by 10000km square trap would intercept something in the ballpark of $10^{26}$ protons per second (area times velocity times density, taking care to adjust units). This is just about 1kg of hydrogen. Gathering enough for terraforming a planet would take a tediously long time.

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I asked a similar question earlier: Ramscoop for a space station or lunar base?. Going by the answers to that question, the solar wind isn't dense enough for this to be practical.

On the other hand, I've since found a scientific study about this idea. The study claims that it could be used to terraform Mars (as opposed to Venus) in less than 50 years, though that sounds a bit implausible to me.

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  • $\begingroup$ The study is not refereed, but it uses a magnetic trap 0.5 million kilometers across which would produce 1000-2000 tons/hour of hydrogen. Later it says this "can be scaled easily" to produce enough for terraforming, with no numbers that I can see, $\endgroup$ Aug 12 '20 at 7:14
  • $\begingroup$ Can be scaled easily? Perhaps a bit optimistic @SteveLinton, what do you think? $\endgroup$
    – GdD
    Aug 12 '20 at 8:10
  • $\begingroup$ I think the whole idea is impractical. You're far better with comets or water from Ceres. $\endgroup$ Aug 12 '20 at 8:17

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