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Life on Earth is protected by Earth's magnetic field, which deflects high energy charged particles that arrive from the sun and from outside the solar system. This prevents damage to organisms.

For a habitat in orbit around the sun, how much energy would be required to generate a magnetic field providing sufficient protection for the inhabitants (humans, animals, plants) from direct damage from charged particles?

Would it be possible to power this magnetic field using only solar power? That is, can sufficient solar power be gathered by a habitat? I'm interested in the range of sizes of habitat (if any) for which this would be possible.

I understand this is likely to be different for different sized orbits, due to different levels of charged particle bombardment and different amounts of sunlight available. Assume a roughly circular orbit. This can be somewhat closer to or further from the sun than Earth is, or potentially at the same distance as Earth, if one of these options allows for the possibility of a solution.

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closed as off-topic by a CVn, Vulcronos, Garoal, DonyorM, bowlturner Sep 27 '14 at 12:31

  • This question does not appear to be about worldbuilding, within the scope defined in the help center.
If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ This questions would be a better fit on physics.stackexchange. This question assume nothing about our world is different and is at heart, a hypothetical physics question based on the real world. $\endgroup$ – Vulcronos Sep 26 '14 at 20:49
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    $\begingroup$ I'm voting to close this as "not about worldbuilding". While the question may come up during worldbuilding efforts, this is really at the core just a physics question. (How strong a magnetic field would be needed to bring charged particle levels to safe levels, and how much power would be needed to project that field; the rest is simple math.) We should be careful to not bite off more than we can chew; some questions are simply clearly a better fit for other sites in the network, and I believe this is one of them. Try Physics. $\endgroup$ – a CVn Sep 26 '14 at 20:49
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We need some facts to get this right.

Solar Energy from the Sun at 1 AU

Wikipedia says that we receive about 1361 watts per meter squared. (The power flux through a given bit of space varies with the sun's solar cycles, but I'm ignoring that.)

Needed Energy for the Magnetic Field

Once again, wikipedia suggests that the largest threats to "deep space" travel are protons, helium nuclei, and HZE nuclei. NASA (and wikipedia) also suggest various ways to overcome this. Specifically for magnetic shielding, your power consumption will look like 10 gigawatts to 10 kilowatts, depending on your design.

Solar Cell Efficiency

Solar cells have a demonstrated maximum efficiency of 44.7% The maximum thermodynamic limit is around 86%. Let's assume you have those nice ones that were actually made.

The Calculation

(10 kw / 1.361 kw/m^2)*(1/.447) = ~32.843 m^2

If you go for the 10 kilowatt design, you need ~32 square meters of very high-end solar panels. That's about a 5.73m x 5.73m square, which is large, but doable. For reference, the solar array on the ISS puts out ~84 kw and has ~73m of solar panels.

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Solar wind is the least dangerous thing the sun emits. Anything outside the earth's magnetosphere for very long would require shielding for the higher energy charged particles emitted during solar flares and other CME events.

According to Wikipedia solar energy at 1AU is 1367 watts per square meter. That's a lot of energy. The next question: is it even possible to build a (launchable) electromagnet array capable of deflecting X-Rays and Gamma Rays? I don't know enough about the physics of magnet fields to answer this part of the question.

On the surface, you have a relatively large energy budget (you get 854 KW from just a 25 x 25 meter array (at 100% efficiency)). So it really comes down to building and launching the magnets.

Then you probably want to give some consideration to the crew living in such a high magnetic flux environment. Though, you also have a really big space budget. The magnets could be placed by trusses or booms at some distance away from the crew module so that it sits in the magnetic null. Again, no idea how far away that would be but it seems probably no more than 10s or 100s of meters.

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I don't believe that an enclosed habbitat would actually need a magnetic field to survive. The main danger of the solar wind is stripping the atmosphere of the earth away. Inside a ship with metal ways, there is no danger of that. I believe that ships walls alone provide sufficient protection from solar winds to allow the ship to survive. As long as the ship isn't close enough to the sun to melt, the metal should be enough. We already send astronauts to the moon and ships out of the solar system. Purely metalic shielding can be designed without the need to a magnetic field.

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    $\begingroup$ Actually, purely metallic shielding is not enough for any long-term spaceflight. I'd have to look up exact numbers, but the Apollo astronauts were, during a single lunar mission, exposed to a significant fraction of a (lifetime, IIRC) safe radiation dose, and absence of a magnetic field for protection against the sun's more damaging output is a serious concern if you're going to Mars. Humans are fragile, machines can be constructed to take quite a beating. $\endgroup$ – a CVn Sep 26 '14 at 19:14
  • $\begingroup$ @MichaelKjörling What kind of radiation? Not all radiation is stopped by a magnetic field which is why I said: Purely metalic shielding can be designed, it isn't there yet but I am confident that we can use just metal. I have heard people planning the eventual mars mission and there is no mention of magnetics fields to protect the astronauts. $\endgroup$ – Vulcronos Sep 26 '14 at 19:24
  • $\begingroup$ No, not magnetic shields for protection, but I've seen at least one fairly serious suggestion (though it was many years ago now) that a part of a Mars-mission spacecraft should be built with much heavier materials and used during periods of high solar activity (CMEs, IIRC). While this doesn't disprove your point, such additional shielding is very heavy which is why it would be done for only a small portion of even the inhabitable part of the spacecraft. $\endgroup$ – a CVn Sep 26 '14 at 20:09

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