Readings taken on the mission to drop Curiosity on Mars have shown that humans making the same trip would be bombarded by dangerous levels of radiation.
Long-term population studies have shown exposure to radiation increases a person’s lifetime cancer risk. Exposure to a dose of 1 Sv, accumulated over time, is associated with a 5 percent increase in risk for developing fatal cancer.
NASA has established a 3 percent increased risk of fatal cancer as an acceptable career limit for its astronauts currently operating in low-Earth orbit. The RAD data showed the Curiosity rover was exposed to an average of 1.8 milliSieverts of GCR per day on its journey to Mars. Only about 5 percent of the radiation dose was associated with solar particles because of a relatively quiet solar cycle and the shielding provided by the spacecraft.
It isn’t just a simple matter of building a bigger shield, though. Cosmic rays are difficult to guard against because the more robust the shield is, the more dangerous it might actually become:
Shielding just doesn’t work well for those kinds of particles, at least in the kinds of quantities that we could put on a space vehicle. Part of why shielding against them is so hard is that GCRs carry so much energy that when they hit the shielding, they produce a huge cascade of secondary radiation, which in turn produces additional radiation, etc, producing a large cone of spreading radiation that can work its way right through the shield. In fact, the shield can make a GCR more dangerous, since there are many more particles in the secondary cascade, so the probability of getting hit by a particle (although of somewhat lower energy) is much larger.
It’s mind-boggling when you think about the vast number of technological advances we need to make to achieve safe space-flight and, say, colonization of Mars. Lets hope that the size of the task ahead isn’t enough to deter us.
Published on June 1st, 2013