For NASA, sending astronauts to Mars brings not only technological challenges, but biological and psychological ones as well.
Unlike robots and machines, humankind has a low tolerance for radiation and is affected by the psychological stress of working in a remote, high-risk environment.
A trip to Mars and landing on its surface is the ultimate goal of NASA's Orion mission, which makes its first unmanned test flight next year. A manned mission to recover an asteroid is slated for 2021, with the goal of a Mars landing expected at least a decade later.
With its current technology, it would take NASA six months to send an astronaut to Mars and back. A landing would add several months to that timeline.
"If you go to deep space like to the moon, asteroid or Mars you're above not only Earth's atmosphere but also the Earth's magnetic field, which provides radiation protection," said astronaut Stan Love, who is working on crew survivability with NASA.
"So when you get out into interplanetary space, you're really getting exposed to radiation," he said.
NASA research has shown that its current shielding technology would not protect astronauts on a mission to Mars from either short- or long-term health effects. The result would be an increase in the likelihood of developing fatal cancers.
In an article published today in the periodical Science, lead scientist Cary Zeitlin inferred from data culled from the Mars Curiosity rover that a yearlong round trip to Mars would expose astronauts to as much radiation as getting a whole-body CT scan once every five to six days.
NASA has dodged a radiation disaster before, Love said. That could have happened on one of NASA's Apollo missions if a solar flare had occurred. Radiation poisoning from such an event "would have killed the crew," he said.
A NASA-led study published last year also found that astronauts risk getting Alzheimer's disease during prolonged missions. The study suggested that prolonged radiation exposure will speed up changes in the brain associated with Alzheimer's. For now, the survivability of astronauts is an issue that offers more questions than answers.
"The technological obstacles of Orion are pretty challenging because it requires the development of new technologies, but the physiological ones are sufficiently challenging, too," said John Charles, chief of the international science office of NASA's human research program. "This has been the topic of a lot of research and planning for several decades."
Radiation is but one of the challenges facing the Orion program. Others include osteoporosis and changes to the eyes from living in a prolonged state of weightlessness. Some astronauts who have completed prolonged stays in the International Space Station have needed eyeglasses upon return to Earth. Some of the vision changes have been temporary, others permanent.
"The changes in the shape of the eye we hypothesize are related to fluid shifting in the body related to weightlessness in the absence of effective gravity," said Charles. "There might be an increase in intracranial pressure in the cerebral spinal fluid, and this may have be affecting some astronauts after months in space flight."
Some of the stressors facing astronauts in a mission to Mars will be psychological.
"We've identified a set of risks to astronauts' safety and health in long-duration flight, and the most worrisome are the psychological aspects of being isolated and being away from home in a highrisk environment for an expanded length of time," Charles said.
The distance between Earth and Mars means that as a spacecraft gets closer to Mars, it will take longer to communicate with home.
"If you're in the middle of your mission, you will be 20 minutes away, by radio, from one-way communication," Charles said. "So there is going to be a high degree of autonomy astronauts will be dependent only on themselves for whatever information and skills they need."
Call The Bee's Edward Ortiz, (916) 321-1071. Follow him on Twitter @edwardortiz.