(Chris your editor: My question is not can people go, but would you go if you had the stated "39% chance of developing life-ending cancer after he returns to Earth"?)

February 17, 2004: NASA has a mystery to solve: Can people go to Mars, or not?

"It's a question of radiation," says Frank Cucinotta of NASA's Space Radiation Health Project at the Johnson Space Center. "We know how much radiation is out there, waiting for us between Earth and Mars, but we're not sure how the human body is going to react to it."

NASA astronauts have been in space, off and on, for 45 years. Except for a few quick trips to the moon, though, they've never spent much time far from Earth. Deep space is filled with protons from solar flares, gamma rays from newborn black holes, and cosmic rays from exploding stars. A long voyage to Mars, with no big planet nearby to block or deflect that radiation, is going to be a new adventure.

NASA weighs radiation danger in units of cancer risk. A healthy 40-year-old non-smoking American male stands a (whopping) 20% chance of eventually dying from cancer. That's if he stays on Earth. If he travels to Mars, the risk goes up.

The question is, how much?

"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."

The error bars are large, says Cucinotta, for good reason. Space radiation is a unique mix of gamma-rays, high-energy protons and cosmic rays. Atomic bomb blasts and cancer treatments, the basis of many studies, are no substitute for the "real thing."

The rest is here: http://science.nasa.gov/headlines/y2004/17feb_radiation.htm?aol3366