Facts of the Matter
Cosmic rays pose obstacle to space travel
Cosmic rays are not really rays. They are charged particles traveling at near the speed of light. The majority consists of protons and electrons that are ejected from the sun during solar storms.
The less common but more dangerous particles are the extremely energetic nuclei of heavy elements traveling at near light speeds that come from outside the solar system. The highest-energy particles are the rarest but also the most hazardous.
These heavy, high-energy-particles have energies 100 million times higher than those made at the Fermi lab, the world's highest-energy particle accelerator. There, atomic particles are smashed into one another to produce showers of different kinds of subatomic particles.
Fortunately for us, high-energy cosmic ray particles strike air molecules in the upper atmosphere and produce multiple cascades of lower-energy elementary particles. Unfortunately, they do the same thing when they collide with an atom in the body. There, the low-energy particles are far less benign, and they can cause harmful genetic damage that can accumulate quickly.
Blood samples from astronauts to the MIR space station revealed that the frequency of broken and misshapen chromosomes in their blood cells had doubled during their stay of less than four months. They had received a total radiation dose more than seven times the annual limit recommended for nuclear workers.
Ironically, most metals are generally good shields against cosmic radiation, but aluminum, which is valued in the aerospace world for its lightness, is the worst and is virtually ineffective. Plastic is actually a better shield.
Astronauts in low-earth orbit, where the shuttle and ISS operate, get some shielding by the thinnest of atmospheres above them, and also by Earth itself, which blocks part of the sky. They also are exposed for relatively short times.
A trip to Mars will take at least two years, during which time the astronauts will be riddled with both high- and low-energy cosmic radiation. A single coronal mass ejection from a solar storm could be lethal in the short term, and the long-term exposure to high-energy cosmic radiation could cause high rates of cancer and decreased life expectancy for those who would return to Earth.
Electronic equipment is also vulnerable to cosmic radiation. It shut down Cassini spacecraft for 12 hours in September as it was transmitting data about Saturn's moon Iapetus. It was not fully functional for nearly a week.
Because cosmic rays can cause cancer in unprotected astronauts, a better understanding of where and how cosmic rays are accelerated will improve predictions of how many will be encountered as astronauts set sail on the new ocean of space. We do not understand the details of expected risk to astronauts over long time periods, but engineers are looking for creative solutions to the great frontier of space in propulsion, life support, re-entry and others as well as mission goals and plans.
Cosmic radiation might pose the greatest risk to extraterrestrial voyagers and could be the most difficult life support problem to solve.
Richard Brill, professor of science at Honolulu Community College, teaches earth and physical science and investigates life and the universe. E-mail questions and comments to firstname.lastname@example.org