# Capture protons from solar wind

Could it be possible ( using a reasonable amount of energy and ressources ) to capture protons from solar wind on (ex. the moon) in order to produce water for a long term self-sufficient mission. The amount of water should compensate for system losses.

You are free to make assumptions and improve my question as english is not my native language

EDIT: Assuming a proton flux of 2e12 m^-2 s as provided here (https://astronomy.stackexchange.com/questions/18829/composition-and-proton-flux-from-the-solar-wind) we would need to capture an area of 10^6 m^2 in order to get 0.11kg of protons per year ( the mass required to make 1 liter of water )

• To make hydrogen of protons you need electrons too. To make water of hydrogen you need oxygen too.
– Uwe
Commented Mar 3, 2019 at 20:00
• @Uwe there’s plenty of oxygen on the moon, but what could be a source of electrons? Could we get it from solar wind too ? Commented Mar 3, 2019 at 22:00
• density of solar wind: [the density of the solar wind [...] is usually on the order of just a few protons per cubic centimeter][1] [1]: en.wikipedia.org/wiki/Atmosphere_of_the_Moon#Composition
– Kav
Commented Oct 21, 2021 at 15:40

## 3 Answers

Protons are positively charged so it would be quite easy to capture them using a magnetic field. With that said, the density of solar wind is incredibly tenuous by the time it reaches the moon so you'd have trouble accumulating significant mass of hydrogen over a reasonable amount of time. Additionally, you'd still need to liberate oxygen from whatever oxides it is currently residing in on the moon which would be energy intensive.

Finally, there is already an abundance of frozen water in permanently shadowed craters on the moon. In 2009, the Moon Mineralogy Mapper discovered significant evidence for lunar water which was re-confirmed by the LCROSS probe later that year.

There may be a simple way of capturing the protons from the solar wind. It would involve using an electric field to decelerate the protons in order to capture them.

It was proposed to deflect solar wind, using long wire streching out along the vector of solar wind with some current, it generates magnetic field that can pull together some protons towards collector at the end of this wire. This can also be used as a shield from solar wind. It can also generate some power.