Future human astronauts traveling to Mars would face risks beyond each other's changing moods in cramped quarters. They would also get blasted with extremely high, harmful doses of space radiation, well beyond the lifetime acceptable limits currently used by NASA, according to a new study of data collected by the agency's Curiosity rover on its voyage to Mars. "Previously, there have not been direct measurements of the dose rate in deep space by shielded instruments," said Cary Zeitlin, a scientist at the Southwest Research Institute and the lead author of the study published tomorrow in the journal Science. In other words, even the Curiosity spacecraft's shields — the most advanced built yet for interplanetary travel — could not protect the rover from being dosed with levels of radiation that would substantially increase the long-term risk of cancer and other, shorter-term health effects for human astronauts.
"possibility of damage to the central nervous system."
"Induction of cataracts is also a concern, and so is the possibility of damage to the central nervous system," Zeitlin told The Verge in an email. "There may also be enhanced risk of cardiovascular disease." The grim outlook for a Mars mission comes from one particular instrument aboard the Curiosity rover, the Radiation Assessment Detector (RAD). As the Curiosity rover traveled to Mars on its nearly yearlong flight in late 2011 and most of 2012, the RAD instrument measured the levels of two types of radioactive particles getting through to the inside of the spacecraft.
One type of particle released by powerful solar eruptions, known as a solar energetic particle (SEP), has relatively lower energy, meaning that traditional spacecraft shielding materials such as aluminum are somewhat effective. In order to further bolster astronaut protection, Zeitlin said that it may be necessary to build manned spacecraft to Mars with special "storm shelter" compartments, where astronauts can hide out when they receive warning of incoming SEP blasts.
"you can actually increase the dose by putting the wrong kind of shielding in."
But the Curiosity rover detected another type of particle in high doses that is more difficult to shield against using conventional materials: galactic cosmic rays, which are more energetic and better at penetrating through even the hardest of metals. Worse, "you can actually increase the dose by putting the wrong kind of shielding in," said Mark Looper, a research scientist at The Aerospace Corporation, who was not involved in this particular study but who also studies space radiation and often works with Zeitlin.
That's because galactic cosmic rays can break apart into atomic shrapnel as they pass through certain types of shielding, and this shrapnel can produce more radiation. Looper said hydrogen atoms can serve as an effective defense. "Ideally you'd have a spacecraft shielded by ice," Looper told The Verge. However, noting that this would be unfeasible for many reasons, Looper said that another material, the plastic polyethylene, would also be helpful. "Right now you could build a spacecraft and be confident in its shielding, but it would be hideously expensive," Looper said. "But I have to believe we will do it eventually."