Permanent Human Settlement of the Earth, Space and Ocean Frontiers

Tuesday, June 06, 2006

The Gamble of Space Radiation

If you venture into space, you are going to get zapped by increased radiation. For those of us who live on the earth’s surface, we are protected by the earth’s relatively thick atmosphere and by the ever-present magnetosphere which both shields and redirects radiation away from us. All around us beneath our feet and drifting about in the air are natural sources of radiation and we certainly take a dose from those sources, but nothing like the radiation in space.
For example, if you are an astronaut in the International Space Station, you will receive over 365 times the radiation in one day as those on the earth’s surface get from natural sources. In other words, spending one day on the ISS is equivalent to one year exposure to natural background sources of radiation walking about on planet earth. And if you launch yourself away from the low earth orbit of the space station, which generally speaking, orbits beneath the protection of the magnetosphere, the exposure jumps four times that. Further, the difference between the lower energy radiation in low earth orbit is much better understood than the high energy-high mass radiation of interplanetary space.
The key question from all this is: so what?
Cancer is the answer, of course. Yesterday we discussed the massive particles of deep space and their potential destruciton of the sentitive regions of the inner brain. Today we will discuss a better understood risk. An increased exposure to ionizing radiation subsequently increases cancer risk. But what kind of risks are we talking about? On this question there is a wide range of disagreement.
NASA’s position is that it is well within acceptable limits. To a government agency, that means that it is within acceptable legal limits of exposing the work force to ionizing radiation. The EPA has set the limit on that: no one is legally permitted to receive a dose of radiation on the job that would increase their risk of death by cancer by greater than 15%. NASA has determined that a stint of duty on the ISS increases the cancer death risk by less than 5%.
But along comes Dr. Marco Durante of the Federico II University in Naples. He has conducted a lengthy study on MIR astronauts for the ESA. He has determined in a study of eight astronauts who had spent 70 days or longer on Mir, he found three with chromosomal abnormalities that might be precancerous. From this he calculates that there is a 20 per cent higher risk of dying from cancer. This, of course, is above US government limits of acceptable risk, and that is only 70 days below the protective layer of the magnetosphere compared to a 1000 days Mars trip - all of it in deep, unprotected space.
Further, Dr. Durante has also determined than on any Mars mission, half of the crew would die of radiation induced cancer upon return from the mission. As far as I can determine, no US Government source has made any comments on this as of this writing.
I have made a dedicated effort to keep this blog readable, and I have been promising for the last three entries to discuss what we may be able to do about the space radiation. So, unless I run into some more irresistible data, I will bring that long promised essay on those countermeasures to you tomorrow! Be patient – and stop smoking!
(Why? Cancer is the answer. If you smoke, you increase your cancer rate to ten times that of the astronaut corps! Why? Naturally occurring radioactive polonium bioaccumulates in the tobacco plant leaves and the smoker bathes his lungs in it each and every day. Not a good idea.)