Spacecraft data nail down radiation risk for humans going to Mars

Astronauts traveling to Mars on any of the current space-flight vehicles would receive a dose of radiation higher than NASA standards permit, according to a study of the radiation environment inside the craft that carried the Curiosity rover to the planet.

The study, reported in Science1, is the first to use radiation data recorded by a robotic craft en route to Mars. It is also the first to rely on measurements from a radiation detector in space that has shielding similar to what might be used on missions carrying humans, says physicist Sheila Thibeault of NASA’s Langley Research Center in Virginia, who was not involved in the study.

Previous calculations of exposure were extrapolations, notes study co-author Cary Zeitlin of the Southwest Research Institute in Boulder, Colorado. Those studies used detectors in space that either had no shielding or were aboard Mars-bound craft whose instruments were not switched on until they reached the planet.

The measurements made by the Mars Science Laboratory (MSL) mission, which landed Curiosity in August 2012, are at the high end of those extrapolations and therefore are not a big surprise, Zeitlin says. But scientists could not be certain that the extrapolations were accurate until they examined the data detected by the spacecraft, he adds. “Models are all well and good, but there’s no substitute for data.”

Zeitlin and his colleagues analysed the radiation recorded by a small detector on board the craft that was active during most of the 253-day cruise to Mars. Although the craft was not uniformly protected from exposure to Galactic cosmic rays and charged particles from the Sun, the MSL’s shielding on average approximated that of human space-flight missions.

The results suggest that astronauts on a Mars-bound mission that was using a current propulsion system would receive 0.66 sieverts of radiation during the voyage to and from the planet. But the study does not take into account additional radiation to which the humans would be exposed once they arrived on the Martian surface, for what might be an extended stay. Exposure to a radiation dose of 1 sievert is associated with a 5% increase in the risk of developing a fatal cancer.

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