WASHINGTON – Of all the hazards facing a human mission to Mars — something NASA and countless other space buffs would love to see at some point — one of the hardest to solve is the radiation that saturates interplanetary space.
New data, gathered by NASA’s Curiosity rover as it traveled to Mars, have confirmed that interplanetary space is a hostile medium, and suggest that engineers need to find a way to speed up space travel significantly if they hope to reduce radiation exposure.
The new research, which was published online Thursday by the journal Science, is not a game-changer for human spaceflight. But it brings more hard data to a known risk factor, and will help NASA and other space agencies to come up with strategies for making spaceflight safer.
Space is not empty, but rather is saturated with charged particles. Some are flung from the sun in solar flares and coronal mass ejections.
An astronaut protected only by a spacesuit during a spacewalk could become extremely sick if struck by a burst of solar particles.
Those particles pose less of a threat inside a shielded spacecraft. But there are other kinds of particles, called galactic cosmic rays, that are spawned in supernovas around the galaxy and arrive at much higher energies, capable of penetrating thick metal barriers. They are virtually unstoppable.
The effects of interplanetary radiation on the human body are not well understood. Until now, scientists had limited information about how much radiation penetrates a spacecraft during an interplanetary journey. But the Curiosity rover carried along a Radiation Assessment Detector, and it measured the incoming radiation during its 253-day trip to Mars, which began in November 2011.
Curiosity flew to Mars in a spacecraft that had shielding similar to what astronauts would have on the new crew vehicle being developed by NASA. The detector picked up an average of 1.8 millisieverts of radiation per day. A human being on the surface of Earth receives only about 3 millisieverts of radiation in an entire year.
“The radiation environment in deep space is several hundred times more intense than it is on Earth, and that’s even inside a shielded spacecraft,” said Cary Zeitlin, a physicist at the Southwest Research Institute in Boulder, Colorado, and the lead author of the new study.
In a fast-trajectory journey to Mars using existing propulsion, astronauts would travel for about 180 days to the red planet and 180 days home. According to the report, such a trip would expose them to a total of 662 millisieverts during the round-trip journey.
Some space agencies limit astronauts to 1,000 millisieverts during their entire career. NASA’s standard varies from person to person, influenced by age and gender, and it is designed to permit no more than a 3 percent excess risk of death from cancer over the person’s lifetime.
Astronauts would also be exposed to radiation during their stay on Mars (or in orbit around the planet if the mission did not include a landing). So the total radiation exposure during a mission, particularly one lasting about two years, might exceed the official limits set by space agencies.