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A Lunar Discovery Reveals The Secret To Building Deflector Shields

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Radiation in space is one of the major obstacles to human exploration of the solar system. Astronauts on a round-trip to Mars could be exposed to radiation doses 66,000 times higher than on Earth. But recent research into magnetic fields on the Moon could help us design effective radiation shields.

A new study written by an international team of scientists proposes the creation of "mini-magnetoshperes" that mimic regions on the lunar surface known as "radiation shelters."


These shelters are created by small magnetic fields that—despite their low-intensity compared to the one we have on Earth—prevent high-energy particles from striking the Moon. (They are also responsible for the formation of the wisp-like regions, known as "lunar swirls," that are whiter than the darker, surrounding areas that have been bombarded by radiation.)


While the idea of magnetic shielding for spacecraft is not new, the data gleaned from the lunar surface studies has suggested a more plausible, energy-efficient design:

As noted on the Physics arXiv Blog:

If weak fields can protect parts of the Moon, they ought to be able to do the same for astronauts.

Previous studies of magnetic shields have neglected a crucial ingredient— the natural, low-density plasma that already exists in space.

This plasma is so weak that it consists of just a handful of positive and negative ions in each cubic centimeter of space. But a magnetic field moving through space would sweep these ions ahead of it, causing them to bunch up into a denser region of plasma in front of the spacecraft.

Because of the separation of charge within this plasma, it generates its own electric field. And this turns out to be crucial when it comes to deflecting high-energy particles from the Sun and beyond.

[The authors of the study] point out that it is not necessary for a magnetic shield to stop high-energy particles but merely deflect them. "Much like defending against a charging rugby-footballer, rather than stand in his way to protect the goal line, a better policy is to deflect the player sideways using a small amount of force so he is pushed into touch and out of the field of play," they say.

The electric field provides exactly this force, deflecting high-energy particles and creating a region within the magnetic field that is shielded from them. Because previous studies have never considered this process, they have vastly overestimated the strength of the magnetic field required to provide protection.

The answer…. is to release a gas of say, xenon, into the space around the craft and allow the sun's ultraviolet light to ionize it to form a plasma that then becomes trapped in the magnetic field. They estimate that 0.5 kilograms of xenon would be enough to protect against the two or three storms likely to occur during a six-month trip to Mars.

They go on to show that such a system would provide more than adequate protection for astronauts. Their simulations show that the system would prevent all of the background radiation from entering the radiation shelter inside the spacecraft and that 95 per cent of the high-energy particles (with energies 1 million times higher than the background levels) would be excluded as well.

The authors of the study acknowledge that there are numerous complexities that need to be studied in much more detail before their deflector shield could be built. But, by demonstrating that the power requirements for deflector shields have been dramatically overestimated, their research could enable much more efficient spacecraft designs.

Read the complete study, ''An Exploration of the Effectiveness of Artificial Mini-Magnetospheres as a Potential Solar Storm Shelter for Long Term Human Space Missions," in the journal, Acta Astronautica.


[Source: Physics arXiv Blog]