The Invisible Killers
We have the technology to send astronauts to Mars. But can we return them safely to Earth?
- By John F. Ross
- Air & Space magazine, January 2006
(Page 2 of 5)
Cucinotta and Schimmerling are at the forefront of a community of researchers working on what may be the most complex example of risk analysis ever undertaken. The study of space radiation is forging collaborations between researchers in widely different disciplines, from spacecraft engineering to solar physics to molecular biology. But so far, the results have not produced a detailed picture of how space radiation would affect human beings over long periods. And until that information is available, “we just can’t send [astronauts] into space and see what happens,” says Cucinotta. “Until we better understand the risks, NASA won’t send astronauts on long-duration spaceflights.”
The Alpha Beta Gammas
Solar storms, largely unpredictable, are not the only radiation danger in space. Far outside our galaxy, violent events such as the explosions of stars produce particles called cosmic rays. The atoms in cosmic rays are charged, or ionized: Because they have either lost or gained an electron, they carry a negative or positive charge. Heated to very high energies, these particles race through space at extraordinary speeds.
Cosmic rays can be made up of any element on the periodic table up to iron (the table lists elements by increasing atomic weight). Cosmic rays made up of heavy elements are particularly dangerous. A charged particle of iron, for example, slams into atoms in a cell and sends them careening like a cue ball hitting the rack. These newly energized particles hit others, setting off a cascade of destruction. Lead, for instance, while highly effective at shielding bodies against X-rays in the dentist’s chair, is such a heavy element that atoms set loose from it could prove lethal to astronauts using it for shielding.
Other forms of radiation populate deep space and may pose a danger to astronauts: X-rays, alpha-rays, beta-particles, gamma-rays, and neutrons. All contain excess energy and, in an attempt to stabilize themselves, throw off mass or energy. The high energy of these particles enables them not only to travel at or near light speed but also to penetrate shields and burrow deep into human tissue.
In the space between here and Mars, the distribution of cosmic rays is not dense enough to induce acute radiation sickness. But what if the exposure consisted of a low, steady level of ionizing radiation over a two- or three-year mission in deep space? Would that cause subtler health problems? Scientists estimate that an astronaut in a conventional spacecraft on a 900-day Mars mission might encounter as much as 130,000 millirem—a dose equivalent to what you’d be exposed to living 370 years on Earth.
To help build a database that relates levels of radiation exposure with adverse effects, NASA runs the Space Radiation Laboratory at the Department of Energy’s Brookhaven National Laboratory in New York. Adam Rusek oversees the daily operations of the new $34 million facility, which is the only one in the United States devoted exclusively to studying the effects of radiation on living creatures.
The NSRL is housed in an unimpressive low gray building in the woodlands of central Long Island. Here, Rusek and his team of physicists operate a particle accelerator that can replicate deep space’s highly charged subatomic particles, accelerate them to nearly the speed of light, and then slam them into vials of tissue and cells, laboratory animals, and various shielding materials.
Rusek also runs a “summer camp” for biologists to learn the rudiments of particle physics. Sitting in the NSRL’s cramped kitchen, which serves as an informal command center, Rusek comments with a wry grin: “You’d be surprised how many biologists don’t know what a Gaussian wave is.” (It’s a phenomenon of quantum physics.)
To simulate particles found in space, Rusek and his colleagues begin with ordinary materials, such as iron and carbon. They energize the particles by heating them until they are dangerously unstable. During experiments, Rusek mans a computer near the large steel door that marks the opening to the accelerator. From here he operates a Sony webcam that provides views of the 400-square-foot room where the speeding particles end up. Because of the danger involved in the experiments, opening the door can take up to five minutes, requiring an iris scan (to confirm the researchers’ identities), a sign-off from an operator watching on a video camera in another building, and a series of key insertions into a bank of instruments.