Radiation: a space travel hazard?

Space travel is, not unnaturally a key part of much science fiction, but a recent article in the journal Science raised an important issue: radiation. Based on data from Curiosity, travelling to and from Mars employing the same type of trajectory as Curiosity (a standard orbital transfer trajectory) a person going there and back would receive approximately 660 millisieverts of radiation. For comparison the average person gets just under 4 millisieverts per annum, although a CT scan can give you 8. Space agencies limit astronauts to 1000 millisieverts during their entire career. There appear to be two views to this. The first is radiation is probably still the least of an astronaut’s worries. The second it, radiation could get worse than this.

There are two sorts of radiation that are relevant: protons expelled from the sun, which may be in great blobs of plasma, and cosmic rays, from the rest of the universe (and probably originating in supernovae). On earth, we are protected from the sun’s emissions by the earth’s magnetic field, which diverts charged particles, but on an average space ship, there will be no such protection, nor will there be such protection on the surface of Mars. There is less you can do about cosmic rays because they have so much energy. So what can be done to protect the intrepid space traveller?

The first step is obvious: get there faster. Think of crossing the Atlantic. Curiosity was about the slowest you could travel and still get there, and could be compared with crossing the Atlantic in a Viking longboat. Jet planes make what was then a highly risky and very prolonged trip rather ordinary now. Curiosity took so long because chemical propulsion does not provide enough power, so the first step is to devise better propulsion systems. The second step is to provide the astronauts with protection against such radiation, which should include shielding at a minimum. Once at Mars, the atmosphere will provide some shielding, because while the pressure is low, there is still a fairly thick layer, and of course, while inside a building, or even in a suit, there is protection. A massive solar flare would go through a simple wall or a suit, but such flares are detectable and the astronaut should get a couple of days warning. On Mars, getting underground provides any amount of shielding.

Several science fiction books have a lead-shielded zone in their space ship to protect themselves. Actually, plenty of water would do a fairly good job, and of course you have to take plenty of water anyway. Design features help, and do we want to take a huge mass of lead for no other purpose? In my novel, Red Gold, the setting of which involved the colonization of Mars, I proposed two fusion-powered ships, the fusion units to provide electricity and energy for materials production once there. The ships were each about twenty million tonne mass fully laden so they were not small, but they had to be about that big to carry enough stuff required to make a settlement work and give two hundred settlers a reasonable lifestyle. The mass provided some shielding, but the large disks also had large magnetic fields. How much good that would do is debatable. However, I also proposed a massive space station at the Mars sun L1 position, which is the nul gravitational point between Mars and the sun, and that was intended to generate a massive magnetic field powered by solar energy and superconductors. The concept was if charged particles were even given a small nudge, from that distance they would miss Mars. Finally, I had my key settlement underground. I suppose one can debate the effectiveness of these schemes, but I think that if we are going to colonize Mars we have to consider radiation, and I think part of the point of fiction is to alert readers to some of the relevant issues. Meanwhile, I gather there is a Dutch reality TV program intending to send a very limited number of people on a one-way trip to Mars. Read what I think is a dead minimum that should be taken, and see if you would want to be part of that TV show.

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