Let me dog this some more.
http://science.nasa.gov/science-news/science-at-nasa/2004/17feb_radiation/
Posted on
February 17, 2004...
Here's the meat of the article:
"We're not sure," says Cucinotta. According to a 2001 study of people exposed to large doses of radiation--
e.g., Hiroshima atomic bomb survivors and, ironically, cancer patients who have undergone radiation therapy--the added risk of a 1000-day Mars mission lies somewhere between 1% and 19%. "The most likely answer is 3.4%," says Cucinotta, "but the error bars are wide."
The odds are even worse for women, he adds. "Because of breasts and ovaries, the risk to female astronauts is nearly double the risk to males."
Researchers who did the study assumed the Mars-ship would be built "mostly of aluminum, like an old Apollo command module," says Cucinotta. The spaceship's skin would absorb about half the radiation hitting it. "If the extra risk is only a few percent we're OK. We could build a spaceship using aluminum and head for Mars." (Aluminum is a favorite material for spaceship construction, because it's lightweight, strong, and familiar to engineers from long decades of use in the aerospace industry.)
"But if it's 19% our 40something astronaut would face a 20% + 19% = 39% chance of developing life-ending cancer after he returns to Earth. That's not acceptable."
I would argue shaving 20 years off the life of a handful of people to push the human race into intrastellar colonization is better than the millions of person-years shaved off annually by private insurance companies or McDonald's for corporate profits.
Are there any results yet? It's only been six years.
The vast majority of radiation is absorbed in transit. If you remove the possibility of a return trip, you remove a lot of the radiation risk.