5. The Mission Poses Psychological and Physiological Challenges
Separation, the effects of long-term weightlessness on the body, and group dynamics all must be addressed. What will be the psychological impact of seeing the Earth as a tiny star-like dot, with no hope of rescue? Studies such as the Mars 500 experiment in Russia have taken a look at how crews might cope with long-term isolation, but of course, a rescue for earthbound astronauts is only a stone’s throw away. NASA studies have also found that the most effective problem-solving groups are often combinations of men and women, providing the right mixture of action and caution.
4. Length of Manned Mission is Daunting For Humans
The Apollo missions to the Moon lasted only a week; typical crews on the International Space Station rotate about every six months. Just traveling to Mars and back could take up to two years, and the window for an optimal Earth departure opens every 26 months. Plus, we would want to stay there for a bit, rather than just “plant a flag” and return. All told, a Mars mission might last 24 to 36 months, far longer than any manned mission to date. Perhaps spacecraft equipped with nuclear-fusion drives could cut down the travel time, but such technology is always said to be “20 years in the future.” Or perhaps supplies would be sent via automated landers well ahead of the astronauts, who would then set up an Antarctica-style base camp for crews to rotate through.
3. Sustainability and Recycling Technology Must Be Improved
Improvements must be made in our ability to "live off the land" and recycle material in a closed system. Astronauts would have to drink recycled urine and grow what food they could. The one great resource available throughout the inner solar system is sunlight, though even that is less intense at Mars. Again, the International Space Station has provided an excellent test bed for recycling, but even the ISS must be resupplied via spacecraft several times a year. Collectively, the ISS has been continuously inhabited since October 2000.
2. The High Cost Causes Political Uncertainty
Mars Science Laboratory cost $2.5 billion in U.S. dollars; a manned Mars program would cost many times that amount; one figure commonly mentioned is $20 billion, but it could be far more than that. Do we have the political will to carry out a manned interplanetary mission over several presidential administrations? Could it be an international effort like the ISS? While it’s true that international cooperation built the International Space Station, it was Cold War rivalry that sent men to the Moon. One plus with large-scale endeavors such as the Apollo missions or sending rovers to Mars is that all of that money is spent right here on Earth. These types of missions also always spur innovation. Still, it’s unsure that countries and corporations like Space X will be all that interested in purely scientific expeditions in the long run. If the history of the space age is any guide, military and economic goals are the prime drivers, with science and exploration along for the ride. The Obama Administration announced in 2010 that a target for NASA’s new Multi-Purpose Crew Vehicle may be an Earth-crossing asteroid, but the MPCV may not leave the launch pad until 2016 at the earliest.
1. Solar Radiation Poses Serious Threat to Astronauts
The amount of radiation exposure that astronauts would be exposed to on a journey to Mars alone, let alone the return trip, is a major concern that must be addressed. On Earth, we are protected from cell-damaging cosmic rays by a blanketing atmosphere; even astronauts in low Earth orbit enjoy some protection from the magnetic field surrounding the planet. Astronauts on an interplanetary mission would be totally exposed; perhaps they could carry some sort of lead shielding or water-jacketing around crew compartments, although that would come with a huge mass penalty in increased fuel. Even then, really energetic cosmic rays would zip right through almost unimpeded; Apollo astronauts reported periodic flashes in their vision as cosmic rays interacted inside the fluid in their eyeballs. Any successful mission to Mars would be an astronaut’s last journey into space, as they would have exceeded the maximum limit for a lifetime of radiation exposure. One school of thought is that it may be better to send 40- or 50-year-olds who have already had children, as they will likely succumb to natural causes before the radiation exposure catches up to them. The Mars Science Laboratory also carries an experiment on board known as RAD, or the Radiation Assessment Detector which seeks to characterize the radiation environment both during its journey and during its primary mission of one Martian year (687 days) on Mars.
As during Apollo, making the journey during a period of solar minimum could minimize solar radiation, but there’s no guarantee that the Sun wouldn’t throw off an out-of-season flare unannounced. Paradoxically, when solar wind pressure is at an ebb in the inner solar system, cosmic ray penetration also increases. Astronauts would have scant warning from solar observatories that the really energetic gamma and X-rays were inbound; exposure could be limited somewhat by having a heavily shielded “storm shelter” for use in such situations. Another idea includes having a second spacecraft flying in tandem as a sort of “solar storm occulting disk” or having the water-jacketing protecting the spacecraft serve double duty as recycled water for consumption. A manned mission to Mars would be a technical tour-de-force, but as the great interest in the landing of Curiosity has demonstrated, it would also engage the imagination of mankind like no other space mission before it.