Deep-space travel bad for astronauts' tickers, say boffins

Deep-space travel could be bad for the heart, report boffins. This has been established by blasting mice with an ion beam from a powerful atom-smasher, causing the luckless murines to develop artery damage of the sort that might result from exposure to powerful cosmic space radiation.

"Cosmic radiation is very different from X-rays and other radiation found on Earth," says Dr Dennis Kucik, pathology prof. "The radiation risks of deep-space travel are difficult to predict, largely because so few people have been exposed."

In fact the only people who have ever travelled beyond the Earth's protective magnetic fields are the 24 US astronauts who landed on or orbited the Moon during the Apollo missions of the 1960s and 70s. It's pretty difficult to draw any conclusions from what happens among such a a small group: but Kucik and his colleagues nonetheless suspected for other reasons that one particular type of cosmic radiation - to wit, the hail of high-energy iron ions which permeates space beyond Earth orbit - could have noticeable health effects once more people go into deep space for longer periods. The scientists thought that iron ions might cause thickening of artery walls, aka atherosclerosis.

In order to test this hypothesis they needed ideally to send some test mice into deep space, but this would naturally be expensive and time-consuming. However, it is possible to generate iron-ion radiation of the sort found out in the big black here on Earth, by using a powerful particle accelerator.

Accordingly Kucik and his colleagues placed a group of mice in a beam of high-velocity iron ions blasted out of a suitable atom-smasher at the Brookhaven lab in New York*. They found that the ion bombardment did indeed cause negative health effects of the sort expected.

"At 13 weeks it was surprising and quite remarkable that we already could see permanent damage — an irreversible thickening of the artery wall where it had been exposed to radiation," says Kucik's fellow boffin Janusz Kabarowski.

The scientists say that high-velocity iron ions are a particular headache for spacecraft and space-suit designers. Other kinds of space radiation can be blocked using shielding: for instance quite thin lead sheets will stop X-rays. But when iron ions hit metallic shields, they can generate secondary radiation on the other side which may be just as bad.

When and if deep-space exploration begins - at the moment US aspirations appear to have slipped back into the 2020s for this - studies like Kucik and Kabarowski's will feed into the design of the ships and the preventive health measures used to protect the astronauts.

The Orion spacecraft, now in ground testing, is the only recent ship intended for deep space. It was meant from the outset for missions beyond low Earth orbit, but the initial focus was on shorter journeys probably within the Earth-Moon system: Orion was conceived under the Bush administration plan which called for a return to the Moon before reaching out for Mars. Most of that plan has now been scrapped, but Orion itself lives on.

Lockheed, manufacturer of the Orion, has said that it could be used for a longer-duration mission to an asteroid as a stepping stone towards a Mars mission: but company spokesmen proposing such a plan did admit that the radiation-exposure issue for such long duration Orion flights "would require further study".

Deep-space ships of the 2020s might use very different propulsion methods, perhaps nuclear powered so as to cut down on journey time. Such ships might have sufficient electricity available on board to employ much more radical radiation shielding methods such as the magnetic forcefield bubbles conceptually outlined as being "relevant to spacecraft" a few years back.

The atomsmasher mouse study paper is published in the journal Radiation Research. ®

Bootnote

*Ignoring the obvious risks that the mice might develop super powers, or perhaps begin glowing green and swell to an enormous size before embarking on a destructive mouse-zilla style rampage.