# How much power would a spacecraft's magnetic shield require?

I've read over the decades that a magnetic shield might protect a spacecraft from cosmic radiation. Its a fascinating idea that might only be theory or science fiction at the moment. In regards to that here is an article on that topic in case someone isn't sure what I mean.

The article even mentions simulations about midway into the article. Does anyone know if research has continued?

My big question though, is how much electrical power would be required to protect a space vessel in this way? How large would the field be in order to be useful?

Better yet, please use some practical objects that anyone can wrap their head around: What if you were using similar technology to protect the Apollo Command Module? Or the Discovery One from 2001 (140 meters long).

In laymans terms, how much electrical power would it take to create a magnetic shield?

Yes, the research on shielding from energetic particles of solar wind plasma using dipole magnetic field continues, and perhaps the best indication of that is the filing of the Spacecraft shield patent (1) in 2010, roughly 2 years after the publication of the Plasma Physics and Controlled Fusion journal (2) that was noticed by the author of that Physics World article (3) that you link to, as well as several other similar ones, e.g. in Universe Today (4).

One look at Ruth Bamford's recent publication (5), the lead researcher and the first quoted author of the said publication that prompted all those news articles, shows this scientist's involvement with several space exploration concept projects, so I'd wager that research seems very much alive. For example, this article titled Conceptual Space Vehicle Architecture for Human Exploration of Mars (6) from 2012 already displays involvement by Boeing and ULA, among others, so that's research that's already at least partially sponsored by the big space industry players.

As for the required size and power, most indicative source is mentioned patent (application number US 12/990,420)(1), quoting:

In order to provide an effective shield, the strength of the shield magnetic field at the source is preferably at least 1×10−4 Tesla. To obtain a boundary between the shield magnetic field and a typical solar wind background magnetic field of around 1×10−7 Tesla (perhaps 5×10−8 to 5×10−6 Tesla depending on the conditions of the solar wind) at a distance of up to a few hundred metres from the spacecraft a field strength of less than 0.1 Tesla at the magnetic field source will generally be sufficient. Allowing for effects of field persistence in the plasma environment, average electrical power from about 100 W to 10 kW, and more preferably from about 500 W to 5 kW may be provided by the power supply to drive the magnetic field source to generate the shield magnetic field.

And the size of functional elements is described in the Universe Today article (4) as "no bigger than a large desk". Of course, these quoted power requirements do seem high, but the shield wouldn't have to be active all the time at its maximum power, and its output could be variable to match observational data by remote observatories feeding data on solar flux to the spacecraft that such dipole magnetic field would be shielding beforehand. If I remember correctly, larger Solar flares reach Earth on average in about a day and a half, so that's roughly ⅔ AU per day. And of course, at distances to the Sun where there is much danger from solar weather, there's also plenty of solar power that can be tapped into by using photovoltaics. For comparison, International Space Station's solar arrays, while large and heavy, are capable of 120 kW of generating capacity.

So it does seem feasible that future long-duration manned missions outside the Earth's magnetic field could use their own, portable and active magnetic field, and protect the crew from exposure to charged high-energy particles of Solar winds with it. Possibly on top of using biological shielding by surrounding crew compartments with layers of water and propellants, like e.g. in this Conceptual Design of Crew Exploration Lander for Asteroid Ceres and Saturn Moons Rhea and Iapetus (7).

1. Google Patents: Spacecraft shield, US 20110049303 A1, Ruth Bamford, Robert Bingham, 2010
2. The interaction of a flowing plasma with a dipole magnetic field: measurements and modelling of a diamagnetic cavity relevant to spacecraft protection, R. Bamford et al., Plasma Physics and Controlled Fusion, 2008 (PDF)
3. Physics World: Magnetic shield could protect spacecraft, Nov. 6, 2008
4. Universe Today: Ion Shield for Interplanetary Spaceships Now a Reality, Nov. 4, 2008
5. Google Scholar: Ruth Bamford, STFC, RAL Space, Rutherford Appleton Laboratory, U.K
6. Conceptual Space Vehicle Architecture for Human Exploration of Mars, with Artificial Gravity and Mini-Magnetosphere Crew Radiation Shield, M. Benton et al., AIAA Meeting Papers, 2012
7. Conceptual Design of Crew Exploration Lander for Asteroid Ceres and Saturn Moons Rhea and Iapetus, M. Benton, American Institute of Aeronautics and Astronautics, 2010 (PDF)
• I had not considered the concept of solar arrays to generate power in this application. But the idea of using biological shielding is fascinating as well. Thanks for providing sources! Feb 23, 2014 at 21:38
• The use of superconductors may reduce power consumption if the superconductor is thermally well isolated and the power requirement for keeping the conductor cold is sufficiently small. But the cooling may require the use of mechanical moving parts, a problem for long time reliabilty.
– Uwe
Mar 27, 2017 at 18:34

It's Monday, so let me rain on this parade a little.

Current magnetic shield designs are adequate to protect against ionizing radiation from the sun. They aren't sufficient to protect against galactic cosmic radiation, which has a lot more energy in each particle. To effectively block that would take a shield with energy 100x greater. If Bamford's shield parameters from TildalWave's answer are used, then 500 kW of power would be needed. It can't be modulated according to current needs, it has to always be at that power level, because GCR fluctuates only very slowly, over the solar cycle, it isn't a matter of occasional storms like solar ionizing radiation. The mass and energy needs of such a system are prohibitive. The effect over time on human health of exposure to a magnetic field of such strength is unknown.

The health effect of cosmic rays at the levels in interplanetary space is not known. Exposure for a year or two may only increase the chances of cancer, or it could be debilitating, if not immediately then a few years down the road. Once we have much more data, it may turn out to be adequate to use a weaker magnetic field that diverts only particles with energies below 500 MeV, for instance - that would be the majority of particles. Or it might not.

Edit: To clarify the potential danger of GCR, here is a table taken from the document the 2nd link goes to, which is an excellent, up to date summary of the matter:

The shielding postulated to calculate the last column is 3 g/cm2 of aluminum... plus the flesh of your body surrounding the important bits. Which is to say, they are assuming that if a 400 MeV proton hits a molecule in one of your muscles, that isn't really important, they are only considering the 'blood forming organs' (which doesn't include your brain). That alone, I think, communicates how much our knowledge of this is preliminary.

It is also critical to bear in mind that this shielding is calculated to help because it is so thin. Because that means that most particles will simply pass right through the whole ship practically as though it wasn't even there. Once one of those particles hits the nucleus of an atom in its path, that's when the real trouble begins. They smash new particles off the that nucleus, multiplying the problem. From Appendix E of NASA's "Space Settlements: A Design Study" (which is an excellent introduction):

There are three mechanisms that are important in mass shielding. First, a charged particle excites electrons for many hundreds of angstroms about its trajectory. This excitation extracts kinetic energy at a roughly constant rate for relativistic particles and acts as a braking mechanism. For relativistic protons in low-Z matter this "linear energy transfer" is $2 MeV/g*cm^-2$ of matter. If the thickness of the mass shield is great enough a particle of finite kinetic energy is stopped. This is the least effective shielding mechanism in matter for relativistic particles.

The second mechanism is nuclear attenuation. For silicon dioxide the average nuclear cross section is 0.4 barn ($10^{-24}\ cm^2$). Thus if a charged particle traverses far enough in the shield (composed of silicon dioxide) it collides with a nucleus and loses energy by inelastic collisions with the nuclear matter. The measure of how far a particle must travel to have a substantial chance of nuclear collision is the mean free path, which for silicon dioxide is $106 g/cm^2$ . This mechanism is an exponential damper of primary beam particles.

Opposing the beam clearing tendency of nuclear attenuation is the creation of energetic secondary particles. For each nuclear collision there is beam loss from nuclear excitation, and beam enhancement (though with overall energy degradation through the increase of entropy) from the secondaries emitted by the excited nuclei. These secondary particles are, of course, attenuated themselves by further nuclear collisions with roughly the same mean free path as the primary particles

So, in all of the parts of the hypothetical ship where there is more stuff than the 3 g/cm2 of aluminum between you and space, there is a much higher chance that you will be struck by damaging particles from those directions, unless the solid stuff in between is at least a couple of meters thick. It might take 5 meters of stuff before the cascade of particles generated by such collisions peters out due to its kinetic energy having been dispersed.

So, maybe you could spend 10 years in deep space and get only the maximum allowable radiation for the career of an astronaut according to NASA, which means you don't have to worry about anything more than a higher chance of cancer, and cataracts. Or maybe that point of view is way too sunny. We really don't know. From the Eugene Parker article above:

One estimate from NASA is that about one third of the DNA in an astronaut’s body would be cut by cosmic rays every year.

• It wasn't especially clear to me from this answer, but the related question linked in comments seems to clarify that that's really only applicable outside the heliosphere, and that shielding for travel within the solar system can probably be left at the parameters given. Can you clarify or rebut this within the answer? Apr 7, 2015 at 0:36
• What is it on Earth, then, if not the magnetic field, that shields us from galactic ionizing radiation? Why wouldn't an astronaut carrying a refrigerator magnet in his pocket (several orders of magnitude stronger than Earth's field) have all the protection he needs? Jun 20, 2016 at 16:26
• @Lotharyx It is the atmosphere. The article linked to in paragraph 3 explains it well at the beginning. The incoming particles collide with the molecules of the atmosphere, shatter them, create more particles, which collide again, and that cascade disperses the energy well before it reaches the ground. We have about 1 kg of air over every cm2 of the Earth, some large fraction of that would be needed over every cm2 of a crew module to protect it that way. Jun 20, 2016 at 16:45
• so much rain, so many parades! 1, 2 ;-)
– uhoh
Feb 19, 2019 at 0:40

This might be of interest: CERN, in collaboration with the European Space Radiation Super Conducting Shield project are using advances in super conductor technology to develop a super conducting magnetic field to protect spacecraft and their occupants. The aim is to create a magnetic field 3,000 times stronger than the Earth's to protect astronauts in a region of diameter ten meters enclosing the spacecraft or habitat.

I can't find details of the power requirements. But the mass is 53.8 tons for the "Pumpkin configuration" and it is passively cooled so the main power would just be to generate and maintain the magnetic field in the super conducting magnets. I've put a section about it here in my Case for Moon First, with the cites I was able to find, but I didn't find that much so far.