The findings could lead to a search for better shields to block the radiation, new propulsion technologies to shorten the trip, or a decision by the space agency to recalibrate the allowable risks for such an ambitious interplanetary mission.
Radiation on the journey to Mars was measured by NASA’s newest Mars rover, Curiosity, which carries an instrument the size of a coffee maker that was originally intended to gauge radiation on the planet’s surface.
Investigators realized that by turning on the instrument right after the rover’s launching in November 2011, they could gather data on the radiation hitting the spacecraft from solar storms and from high-energy cosmic rays that come from outside the galaxy.Continue reading the main story
They determined that “the radiation environment is several hundred times more intense than it is on Earth,” Cary Zeitlin, a scientist at the Southwest Research Institute in Boulder, Colo., said during a NASA news conference on Thursday, “and that’s even inside a shielded spacecraft.” The findings will be published in Friday’s issue of the journal Science.
Radiation dosage is measured in units known as sieverts. A cumulative dose of one sievert is thought to raise the risk of a fatal cancer by about five percentage points.
During Curiosity’s 253-day, 350-million-mile trip, the rover absorbed about half a sievert — an average of 1.8 thousandths of a sievert per day, mostly from cosmic rays. “That could be higher under different circumstances,” Dr. Zeitlin said. The instrument measured radiation from only five solar storms, all modest.
NASA is not planning to send people to Mars until the 2030s, but with current technology, it would take six months to get there and six months to return to Earth. As such, astronauts would absorb about two-thirds of a sievert. By contrast, a person on Earth receives less than a thousandth of a sievert per year from outer space, Dr. Zeitlin said. Americans absorb a few thousandths of a sievert per year, mostly from X-rays and CT scans — still much less than from a Mars trip.
According to the National Cancer Institute, the lifetime risk of dying from cancer is 21 percent; the two-thirds of a sievert from a round-trip mission to Mars would raise that risk by three percentage points, to 24 percent.
The measurements largely agree with earlier estimates and measurements. “These are confirmatory measurements that will help us refine our models,” said Edward J. Semones, the spaceflight radiation health officer at NASA’s Johnson Space Center in Houston.
NASA’s standards currently limit the excess cancer risk for its astronauts to three percentage points.
“We currently would exceed our acceptable limits,” Dr. Semones said.
Advocates for a human mission to Mars say the radiation risk is overblown. “What it shows is that the cosmic ray dose on a Mars mission is not a show-stopper,” Robert Zubrin, founder and president of the Mars Society, said about the new data.
“This is modest proportion of overall risk,” he added. “Therefore, what it means is that we don’t need to delay a humans-to-Mars program until we have a miraculous advanced propulsion system that can get us there faster.”
A spacecraft malfunction during the mission would pose a much greater risk to the astronauts than the radiation, Dr. Zubrin said.
The radiation risk has also not deterred plans by a private group, the Inspiration Mars Foundation, to launch a married couple on a 501-day flyby of Mars in January 2018.
“Those numbers are less than the risk a lot of people take in sports,” said Taber MacCallum, the chief technology officer for the foundation. “They don’t seem that unreasonable to me.”
Another private group, Mars One, which hopes to establish a settlement on Mars in the 2020s, said it had already received thousands of applications.Continue reading the main story