Space Matter is a weekly column that delves into space science and the mechanics of spaceflight. From the latest discoveries in the universe around us to the fits and starts of rocket test flights, you’ll find analysis, discussion and an eternal optimism about space and launching ourselves into the cosmos.
I’ve previously discussed the challenges of getting to Mars and landing on Mars; it’s not going to be easy to get humans to the surface of the red planet. And that’s not even considering the discussion of what will happen to our bodies on the way. There have been studies documenting the psychological challenges of long-term spaceflight, and we’ve been studying the effects of zero-g on the human body for years on the International Space Station. But what about space radiation?
Radiation is a huge problem in space travel. The only reason it’s not a huge problem on Earth is because our planet is protected by a giant magnetic field that extends out into space; it’s what makes life on Earth possible. It protects our delicate planet from the ravages of space radiation.
There are two types of space radiation that anyone outside the Earth’s magnetic field has to worry about. The first are called galactic cosmic rays, or GCR radiation. These originate outside our solar system and travel through our galaxy at close to the speed of light. It’s likely that these high-energy particles originate in the massive explosions of supernovae, though there is still some disagreement on this matter. These particles are composed of every element from hydrogen to uranium; their distinguishing feature is that they’re ionized, meaning their electrons have been stripped, so they hold a charge. That charge is what makes them interact with (and repelled by) Earth’s (charged) magnetic field.
This X-ray/UV image of our Sun shows the active weather regions as blue-white areas. Photo courtesy of NASA/JPL-Caltech/GSFC/JAXA
The second type of radiation comes from our Sun, and it’s much more common: solar particles. Our Sun, and all other stars, actually has its own weather. Sunspots are one form this weather takes. What we need to worry about, though, are solar proton events. These occur during solar weather activity (such as solar flares—but they don’t occur during every solar flare) and consist of charged particles (protons again!) that are unleashed into space by the sun’s magnetic field. We’re protected from these particles by our planet’s magnetic field, but strong solar proton events can be associated with geomagnetic storms, which wreak havoc on the electrical grid.
Outside the protection of the Earth’s magnetic field, these two types of radiation can be a serious threat to astronauts. What’s more, our own magnetic field poses a threat in and of itself. The Earth is surrounded by radiation belts, called the Van Allen belts, which trap radiation particles—they’re part of how our planet is shielded from these particles. Galactic cosmic rays and charged solar particles fly through space straight into the Van Allen belts—which means that there are basically giant belts of radioactive death circling our planet (too much?) These belts aren’t static, but there usually are two of them (sometimes three). The inner Van Allen belt begins about 600 miles above the surface of the Earth; the outer Van Allen belt extends to almost 40,000 miles out. For comparison’s sake, the International Space Station, in low-Earth orbit, is 220 miles above the Earth’s surface, while the Moon is 238,900 miles from the Earth.
Astronaut Buzz Aldrin on the Moon during Apollo 11. Photo courtesy of NASA
“But we’ve been to the Moon,” you might be asking. We’ve sent a total of nine manned missions around or onto the Moon (Apollo 8, 10, 11, 12, 13, 14, 15, 16, and 17), through the Van Allen radiation belts. This is actually a major factor in the conspiracy theory that the Moon landings were faked—astronauts would die after passing through the Van Allen belts.
Well, no, not quite. The Van Allen radiation belts are very dangerous, but there are ways around them. For one, they’re not a sphere encompassing the planet. Think of the belts surrounding the Earth as a giant donut, where Earth is the donut hole.
This image cutaway shows the Van Allen radiation belts surrounding the Earth. Photo courtesy of NASA
The team in charge of Apollo’s trajectory studied the Van Allen belts closely and charted a flight path that would allow the spacecrafts to bypass the thickest parts of the belt. In fact, Apollo missed the inner belt completely and sped quickly through very thin areas of the outer belt. The short duration of exposure to the belts meant that the spacecraft’s aluminum shielding was enough to protect the astronauts. Presumably, NASA could chart a similar trajectory for a Mars mission.
The problem is what happens once astronauts travel through the radiation belts on are their way to their next destination. The Moon missions consisted of three days of travel each way, plus a few days on the surface or in orbit. Mars missions will consist of a minimum of nine months of travel one-way. A low dose of radiation might not have noticeable effects, but when these accumulate, astronauts may run into serious medium- and long-term health problems.
You can bet that NASA and other private spaceflight companies are working hard to mitigate this risk, from nutritional supplements to counteract the effects of radiation to improving spacecraft shielding to better protect astronauts from radiation. It’s important to note, though, that while we’re well on our way, we haven’t solved the space radiation problem yet.
Top photo courtesy of NASA/JPL-Caltech/GSFC/JAXA
Swapna Krishna is a freelance writer, editor and giant space/sci-fi geek.