A Mars trip may pose severe radiation risks, possibly making a human mission there in the near-future impossible. One possible solution to the dilemma could be the development of nuclear rockets.
Curiosity, NASA's agile Mars rover, has returned data from its Radiation Assessment Detector (RAD). This device was designed to measure radiation levels on the surface of the Red Planet, but that's not all it accomplished.
"...[W]e realized about a year and a half before launch that taking measurements during the cruise phase on the way to Mars in deep space would be not so different than... a future human astronaut might experience in their spacecraft on their way to Mars. So we turned RAD on about 10 days after the launch of Curiosity and we took about seven months of data," Donald Hassler, RAD director, said. During the trip, the RAD was mounted between Curiosity's heat shield and the decent module.
On or near the Earth, our planet's magnetic field protects us from cosmic rays and radiation from the Sun. At greater distances from our home world, radiation hits spacecraft full-force. The new data from Curiosity suggested that an astronaut's exposure to radiation during a 12-to-17 month-long trip to Mars would be greater than space agencies allow over an astronaut's entire career.
One way to deal with the problem of radiation exposure is to get there faster. A safer trip to Mars could be accomplished using a nuclear rocket, according to NASA's Chris Mooore. Such a journey would only take six months.
"It's a long-range technology-development activity, and it will probably be many years before that is ready," Moore said. "But it is part of our mission architecture for sending humans to Mars, is to use nuclear rockets," Moore said.
During the trip, Curiosity measured 1.8 millisieverts (mSv) of radiation per day. This is equivalent to receiving a full CT scan ever four to five days, according to Cary Zeitlin of the Southwest Research Institute. At these levels, even the shortest trip to Mars would expose an astronaut to between 540 and 780 mSv of radiation. Being exposed to 1,000 mSv over a career as an astronaut will increase that person's risk of developing a fatal case of cancer by five percent. NASA only allows three percent additional risk.
Shielding could provide some protection for astronauts, but that comes at the cost of weight, so the journey takes longer, exposing the crew to longer exposures. If you cut back on shielding, you subject the astronauts to greater levels of exposure, even if for a shorter time.
From November 2011 to August 2012, as Curiosity traveled to Mars, the Sun was giving off comparatively low amounts of radiation. This means that the RAD measurements were likely lower than normal, and astronauts on the way to Mars might be in even more trouble than we think.
