Recently, scientists have shown that mice who had a high energy particle beam shot through their brains suffered some loss of curiosity and ability to do work. Now your response might be “well duh, you just shot the mice with a particle beam, of course it’ll have problems.” To most of us it’s just an interesting or slightly cruel science experiment. However to astronauts and the engineerings and scientists looking over them or trying to get them to Mars, it’s a serious concern.
Space is abound with radiation. Every time we send something up there, it will get hit by high energy radiation. We just design equipment to have redundancy and still be able to operate if one system goes down. However we can’t build redundancy into humans. Astronauts on the space station regularlly see flashes in their vision when they close their eyes to go to sleep. Those flashes are due to a high energy radiation particle striking the astronaut’s optic nerve. Luckily a few strikes don’t cause long term harm, as far as we know. Additionally, the space station is protected from the the majority of the harmful radiation by the Earth’s magnetic field, which also protects us here on the ground. But if we send people to Mars, they will spend a few months outside the Earth’s protective field and in direct exposure to whatever is out there. So engineers and scientists are trying to figure out ways to protect human during long space trips.
There are two types of radiation in space, Galactic Cosmic Rays (GCR) and Solar Particle Events (SPE). SPEs are generated by the Sun and consist mostly of electrons, hydrogen nuclei, and helium nuclei. The Sun throws out these particles as part of its regular nuclear fusion process. During solar flares, it gets really bad and becomes a high energy particle bombardment. GCRs are even higher energy particles of all elements up to iron. These particles are stripped of all their electrons and zoom through space at incredible speeds with hugh energy. GCRs comes from outside our solar system. Currently theory says GCRs are created by the destruction of stars and the resulting novas or supernovas that accelerate these particles to extremely high speeds. SUPERNOVAS! That’s pretty damn amazing I think.
So these particles can greatly threaten our future human presence in space outside of Earth’s orbit. Even if we go to the Moon, space radiation will still be a concern because the Moon doesn’t have much of a protective magnetic field. For a Moon base, an “easy” solution would be to build the based underground and let the Lunar dirt protect the astronauts. For space travel though, we can’t bring a huge pile of dirt. On Earth, nuclear reactors and waste are shielded with thick layers of lead, steel, and concrete. All of those materials are incredibly heavy, and not really feasibly to take with on a space trip. A spaceship would require a few inch thick layer of lead or steel, which would make the ship extremely heavy. An alternative is to use water as shielding material. In fact any material with a large amount of hydrogen is a good shielding material. Water is used on earth for nuclear reactors to both cool and shield the radioactive fuel rods. There was even a recent NASA study to examine the use of a water recycling bladder as the external hull of the spacecraft.
Massive spacecraft shielding may not be the only solution for the problem of radiation for travel to other planets. You see the primary problem is how long you spend in the unprotected regions of space between planets. So if you could greatly cut down on the travel time from say here to Mars, then you can get away with much less spacecraft shielding. So there is a trade between more shielding and more fuel for the engines. Now if we had much better engines that can do more with less fuel, that would be the best option. However the current high power engines are typically based on nuclear power, which has its own radiation and other issues. So what’s the answer? Right now with our current technology, most likely a compromise between existing propulsion systems carrying more fuel and a moderate amount of shielding. But there will undoubtedly be some exposure to space radiation, and I’m sure it’s something the astronauts, scientists, and doctors will be expecting and prepared for. Who knows though, one of the current mission concepts for NASA’s Space Launch System has a manned mission to Mars in the 2030-2045 time frame, and by then we may have discovered some brand new propulsion system or way to protect astronauts from radiation either with shielding or maybe a medical alternative that makes humans more resistant to radiation.