I just learned today that besides roving around Mars looking for evidence of past life, the Curiosity mission included a careful measurement of the amount of radiation an astronaut would absorb during a trip to Mars. The instruments were inside the spacecraft, roughly the same environment as astronaut would probably ride in. Curiosity measured the exposure as 1.8 millisieverts per day. That's not so bad. According to NASA, lifetime exposure to 1000 millisieverts has a 5 percent chance of causing a fatal cancer. NASA's current rules limit astronauts to a dose of 660 millisieverts over their careers, which they say has a 3 percent chance of killing people. Using a powerful rocket, the trip to Mars could be made in 180 days. So a round trip could be made within NASA's limits, even allowing a few weeks on the surface and some time to train. Shielding could also block some of the radiation, not to mention that plenty of people would be willing to risk even a 10 percent chance of cancer to be one of the first people on Mars. If this result stands up, the radiation problem is not the obstacle some people feared it would be.
One caution is that Curiosity made the trip during a quiet solar cycle. A major solar storm would increase the exposure, but until a spacecraft with the right instruments flies through one, we won't know exactly how much.
Reference: mystery-sky-lights.blogspot.com
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