Posted on August 23 2016
If you were lucky, in mid-August you might have had clear skies for viewing the Perseid meteor shower. As Earth passed through a field of comet tail debris, bits of dust, sand, and the occasional pebble sent streaks of light across the sky as they burned up in the atmosphere. Comet fragments and other meteoroids are naturally occurring materials that orbit the sun. There are other things that can also put on a brief, zooming light show as they get vaporized, and these come from our own hands. Space junk, properly called “orbital debris,” flies about the earth in ever greater amounts. It’s estimated there are 7,000 metric tons of it, and it comes in a variety of sizes.
The big stuff, whole satellites that have gone dead, upper stages of launch vehicles, items jettisoned during spacecraft separation procedures, etc, are fairly easily tracked. The smaller stuff, of course, is harder to “see.” NASA tracks debris down to about 4 inches in diameter (think softball) and the Department of Defense watches for things as small as 2 inches across. Naturally, the junk ranges from that size on down to dust. Of all these size categories, there are probably 500,000 pieces larger than a marble, 20,000 of which are greater than softball-size. The really small stuff probably numbers in the tens of millions. And you do have to sweat the small stuff — bits of junk down to the size of a grain of sand or a paint fleck can do real damage when they come winging in at 17,500 mph!
NASA avoids collisions the best it can, but accidents happen. A dead Russian satellite encountered a U.S. commercial communications satellite in 2009, killing it. The problem isn’t just that such meet-ups destroy expensive machinery, but they also result in….more debris! The collision just mentioned generated an estimated 2,000 more things to keep track of, and plenty of stuff too small to follow. And China’s clever 2007 experiment to see if it could destroy a satellite with a missile in space worked just dandy. It created 3,000 more things to duck. NASA has a protocol for its most valuable assets — flights with humans aboard — that calls for moving out of the way when known debris is predicted to enter a certain envelope around a spacecraft. It’s serious business, adjusting the location of something like the International Space Station, but the damage a chunk of old satellite would do could be catastrophic. About once a year, astronauts aboard the station have to take a bit of evasive action when something gets too close. If there’s not enough time to move the station out of the way, astronauts must shelter in place in a specially armored compartment. An even more perilous scenario could unfold if a spy satellite suddenly went dark thanks to a beaning from space debris. If any one of several countries assumed their satellite had been taken down intentionally, international relations could get sticky, or worse.
In time, orbital debris will slow in speed, and gravity will draw it back into the atmosphere where it will momentarily flare as it gets atomized. Depending upon its altitude, an object may take a few years, a few decades, or over a century to get pulled back down. In the meantime, space agencies have to keep firing new satellites and stations into space. To protect astronauts from objects too small to track, space capsules and stations are shielded, but such armor is only good for collisions with things a half-inch across or smaller. There is plenty out there that’s too small to monitor, but too big for the shields. That’s where you have to depend on the immense volume of space and the small probability of a chance meeting.
Never ones to leave things to chance, NASA is constantly looking for methods of sweeping away orbital debris. One experimental design had balloons setting off explosions high in the atmosphere. It was hoped that the force would push a portion of the atmosphere farther into space where it might encounter debris and slow it down, hastening its fall toward Earth. It was a good theory, but it just couldn’t be conducted in large enough volume to be effective. A new approach that is in its early stages is the deployment of little self-powered “blankets.” Able to navigate to the coordinates of known orbital debris, these 1-meter-square wrappable panels would maneuver to a target, hug it, and fire thrusters to drag it down to lower altitude before releasing it to fall to a fiery death. The “blanket” would then head out for another victim. Thousands of such items, called Brane Craft, could be sent up on a single rocket flight to get busy on clearing space of a lot of loose cannons.
Similar to new procedures for products down here on Earth’s surface, space agencies are also working on rules that would require nations or space companies to design in end-of-life mechanisms to ensure satellite disposal into the atmosphere. Like mandatory recycling plans to keep landfills from overflowing, space manufacturers are having to take responsibility for their creations. Though oceanic and space trash problems are different animals, unwanted materials anywhere cause problems of safety. The “space” in space is much greater than in the oceans, and the pieces of dreck floating in water probably outnumber those found in space by billions of times. Still, it’s a testament to humankind’s ability to muck things up that we have managed to foul both the surface and the celestial ceiling of our planet. Cleaning up either one is proving to be an onerous and costly task.