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Radiation


 
written by Kian Cochrane on June 11, 2003 | contact me
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Radiation
Radiation
Credit: Unknown
Radiation hazards in space have not been a major concern as of today, as space mission have seldom been for longer than a few months, and mostly behind the protective shield of the Earth. On a mission to Mars, however, protection against radiation hazards is necessary to ensure a healthy crew.

Excessive exposure to radiation causes a variety of effects, ranging from flu-like symptoms to hair loss to cancer and mutations. Extreme cases lead to death. Since radiation dose is cumulative, one who has survived a large radiation dose is less likely to survive another. It is clear that the applicable radiation hazards and shielding methods must be analyzed if a manned Martian mission is to ever take place.

Every second, the Sun emits countless numbers of highly radioactive particles called the solar wind. The activity of the solar wind fluctates in eleven-year cycles. During the peak of these cycles, called the solar maximum, there is the potential for a solar storm, an event in which the solar wind increases by several orders of magnitude for a short period of time. We usually don't worry about solar wind or solar storms here on Earth, because the strong magnetic field and thick atmosphere associated with Earth blocks and deflects most of the solar wind. Even during a solar storm, the worst effect on Earth is the temporary disruption of radio communications. When leaving this protective barrier, Man must make his own shielding system, for neither space nor Mars has any substantial shielding effect.

The solar wind consists mostly of fast heavy ions, a dangerous radiation that combines damaging ability with penetration ability, a combination seldom seen when dealing with radiation. Shielding containing hydrogen atoms would be ideal for this kind of radiation, as hydrogen atoms do a good job of shielding without creating much secondary radiation. Water, plastics, and liquid hydrogen are three common materials that contain enough hydrogen to serve as effective shields. Since the astronauts need water, and the spacecraft needs liquid hydrogen, using these required commodities as shielding would allow spacecraft designers to kill two birds with one stone. Such a shield would protect the astronauts except in the case of a solar storm. A small room in the spacecraft could be much more heavily shielded than the rest of the craft and serve as a shelter during a solar storm. Luckily, solar storm particles travel much slower than radio waves, so astronauts could be alerted of solar storms via radio, giving the astronauts a few minutes to seek shelter. With proper shielding and early detection of solar storms, astronauts should not receive a deadly or even unhealthy radiation dose during a Martian mission.

While on Mars, the radiation problems remain largely unchanged; there is no appreciable magnetic field or thick atmosphere to attenuate the solar wind. However, there is an almost limitless source of shielding material on the surface: the Martian regolith. Martian shelters can easily have enough regolith piled on them to shield the inhabitants, or the shelters can be built underground. Since weight is of little concern for an immobile shelter, and regolith is plentiful and free, entire shelters can be completely shielded from the solar wind and solar storms.

If Mars is to be terraformed, people must be protected from radiation even when outside and in shirtsleeves. It is estimated that an atmosphere of at least 390 mb on Mars would provide enough protection from radiation in non-solar-storm conditions. Mars will still lack a magnetic field, so there must be shelters and early warning systems in place for protection against solar storms. Such an atmosphere would likely have to exist anyway on a terraformed Mars, so radiation exposure is not a major obstacle for terraforming Mars.

In conclusion, many grave radiation hazards exist in a Martian mission, both in the spacecraft and on the surface. Fortunately, these problems can be solved using the same method we use to solve problems here on Earth: cleverness and good engineering.

Works Cited:

1) NASA Bioastronautics Data Book

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