Earth & Sky : Space

Earth & Sky : Space Wanted: Garbage collectors in space

By Stephen Ornes / September 21, 2011

Using telescopes on Earth, space agencies track large pieces of debris orbiting the planet. Most of the garbage is in low-Earth orbit, or LEO, which extends as high as 2,000 kilometers (1,243 miles) above Earth’s surface. This is an artist’s conception of space junk; the sizes of the pieces are greatly exaggerated.

Credit: ESA

Every messy kid gets told to clean up his or her room. City governments send out trucks and crews to clean up roads and parks. Now, scientists say if we want to keep our astronauts and satellites safe, it’s time to clean up space, and soon.

A sprawling garbage heap floats high above Earth. It contains fragments of broken-down satellites and pieces of used rockets, as well as a few unusual objects like gloves and cameras accidentally dropped by astronauts. The problem isn’t going away; it’s getting worse. The number of pieces of space garbage gets larger every year. Around the world, space agencies worry about the trash because even small bits of litter — no larger than the fingernail on your pinkie — can cause serious damage to satellites or spacecraft.

In a recent study, engineer Hugh Lewis and his colleagues from the University of Southampton in England ran some calculations on space junk. In August, they reported that the growth of space junk could slow down if every year about 10 large pieces were removed. (The largest piece of space junk is about the size of a refrigerator.)

If a broken or defunct satellite doesn’t fall back toward Earth and burn up in the atmosphere, it continues to whiz around our planet. It may crash into another satellite or used rocket and break into smaller pieces. These pieces are called orbital debris.

In February 2009, a Russian satellite and a U.S. satellite plowed into each other over northern Siberia. The collision resulted in more than 2,000 new pieces of space junk that continue to orbit Earth. NASA’s Orbital Debris Program Office tracks the larger of these pieces to make sure they don’t smash into other satellites. In March of this year, scientists saw that the International Space Station was headed toward a four-inch piece of space garbage left over from the 2009 collision. They sounded the alarm, and in April the space station changed its course to avoid the debris. This was the fifth time in less than three years that the station has changed its course to stay safe from floating debris.

Not all space junk stays in space. In January 2001, this heavy chunk of a Delta 2 rocket fell to earth about 240 kilometers (150 miles) from Saudi Arabia’s capital, Riyadh. Credit: NASA Orbital Debris Program Office

Another situation, related to greenhouse gas emissions, is lengthening how long any piece of space trash remains in orbit.

As things in orbit push through Earth’s atmosphere, they slow down. This braking action, called friction, not only lowers the orbit of space junk but also increases the chance it will burn up as it slows down. Friction is currently the only thing that removes space junk from orbit. But as more emissions of carbon dioxide, a greenhouse gas, rise into the upper atmosphere, this gas cools off a layer called the thermosphere. As a result, the thermosphere is becoming less dense. (Density is the amount of matter packed into a particular volume, and materials with more density are thicker. Maple syrup, for example, is denser than water.) The drop in density means there’s less friction on space junk, allowing the trash to orbit longer. And this increases its opportunity to hit something.

The recommendation by Lewis and his team to send up space-garbage collectors is easier said than done. Scientists can’t remove 10 pieces a year because “we don’t know how to clean up even one,” Nicholas Johnson told Science News. Johnson is the scientist in charge of NASA’s Orbital Debris Program Office, which keeps track of large pieces of debris and helps spacecraft and satellites avoid dangerous situations. He said that even though a space cleanup is “desirable,” it’s not going to happen in the next few years. “There’s nothing on the horizon” for a space trash pickup program, he said.

Right now, the risk of a serious collision is low. Since people began sending rockets into space, Johnson said only two operational satellites have ever been damaged. He said it’s possible that a dangerous or deadly collision could occur, but the chance of that happening is small.

For now, Johnson told Science News, his team’s near-term priority is tracking smallish pieces of space debris. There are more of them, they’re harder to see from Earth and they’re more likely to cause trouble.“If we’re going to lose spacecraft in the next two decades,” Johnson said, “we’re [probably] going to lose them to small things we [currently] can’t track.”