Visualization of debris in Earth orbit, 2010.
Until February 10, 2009, the concept that space garbage was a problem was mostly just a concept.
That day, somewhere 500 miles above the Siberian tundra, the communications satellite Iridium 33 was flying north at about 18,000 miles per hour, relaying phone conversations around the globe. Hurtling east, in an uncontrolled orbit and at the same speed, was a long-retired Russian communication platform called Cosmos 2251. Despite the vigilance of a phalanx of debris tracking radar on the ground, no one predicted that they would collide. When they did, the impact turned the two satellites into about 2,100 pieces that would come to spread out in their own orbits around the Earth. Besides those who lost their phone calls, few on Earth would have known anything happened. But in space, where each piece of the debris now posed a threat to a growing population of orbiting stuff, the risks of space trash had suddenly become dangerously real.
On Tuesday, the Inter-Agency Space Debris Coordination Committee (IADC) released a study that claims debris collisions in space are expected to become a persistent threat over the next two hundred years. This means that satellites, spaceships, and any other flying objects that fly at altitudes fit to observe the Earth are at higher risk than ever of being crushed by a free-floating, planet-encircling trash flotilla.
That cloud of garbage could hinder not only our future of space travel but the networks we depend on for mobile phones, television, radio, weather tracking, surveillance, GPS navigation, and research. Some scientists now talk of having reached a tipping point. In a worst case scenario, runaway pieces of debris as small as 10 cm could cause a catastrophic domino effect, with each new junk projectile leading to yet more destructive trash that could eventually pulverize everything in orbit.
So far, efforts to stem space trash—like an international rule that any new hardware in low Earth orbit be de-orbited and burn up in the atmosphere after 25 years of life—have had limited success. "We're certainly not at 90% compliance with the 25-year rule yet, and we see explosion events on average about three times a year," explained Dr Hugh Lewis, who detailed the research findings at the 6th European Conference on Space Debris in Darmstadt, Germany, on Monday. "Explosion events" are orbital break-ups of spacecraft that help contribute to the mounting pile of orbiting debris.
The "energy flash" of a hypervelocity impact during a simulation of a piece of orbital debris hitting a spacecraft in orbit.
Runaway pieces of debris could cause a catastrophic domino effect, with each new junk projectile leading to yet another and another, eventually pulverizing everything in orbit.
"The problem is exponential," says Opher Doron, General Manager of Israeli Aerospace Industry's space division. "There is genuine concern in the satellite community that if things aren't watched carefully, and if we have a few more accidents, it will be uninhabitable in those [satellite] belts. And it's very difficult to go to other places." Aside from UN recommendations, there aren't any current international regulations related to space debris or stipulations for national responsibility. "People are looking at it and studying it, but there are very few solutions."
Potentially lethal objects in the cosmic scrapyard, which now circles the entire Earth like a giant version of the Great Pacific Garbage Patch, include inactive satellite parts, pieces of rocket stages, and other now-useless shards of machines that were once in orbit. Even seemingly innocuous objects like paint chips can be problematic: in 1983, a .2-mm paint chip left a near-catastrophic crater on the Space Shuttle's windshield (see the photo below). The presence of asteroids or comets doesn't make things any safer. Though there have only been a few space collisions in the past -- most notably that 2009 satellite collision -- the new research suggests that crashes could become as regular as every five to ten years.
The most alarming, immediate threat of a space junk collision is that a piece of debris could come crashing down to Earth. Given Earth's scale and the good chances that most things burn up on re-entry to the atmosphere, it's still a very small risk. Roughly once every day, a piece of American space debris falls from orbit and burns up; but once a week or so, an object too big or dense to burn will survive and fall to Earth.
It's unusual for humans to ever see these objects, but it happens; NASA puts the chances that a piece of space trash will hit a human at 1 in 3,200. In 1997, Lottie Williams was strolling in a park in Tulsa, OK, when she saw a fiery streak in the sky and felt something hit her on the shoulder. It was a metal strip from a Delta II rocket, about the weight of "an empty soda can," she said. In 2001, another piece of a Delta rocket, this time a much larger one, landed in the desert of Saudi Arabia, about 240 km from the capital Riyadh, to the surprise of nearby farmers.
On January 21, 2001, a Delta 2 third stage rocket reentered the atmosphere over the Middle East.
The bigger catastrophes happen up in space. There, the threat of collision isn't as simple as a sole object-to-object crash. There's a theory among physicists called the Kessler Syndrome (also known as collisional cascading) that posits that dense objects could yield a cascade of collisions, each one gaining more debris and becoming harder to break up. The theory was named for NASA scientist Donald Kessler, who, in his 1978 paper “Collision Frequency of Artificial Satellites: The Creation of a Debris Belt,” argued that this domino effect of space collisions would mean "an exponential increase in the number of objects with time, creating a belt of debris around the Earth.”
The paper established Kessler's reputation but meant relatively little for NASA policy. That changed with the collision on February 10, 2009—some three decades after the paper's publication. New attention was paid to a 2006 NASA model that suggested that even if no new launches took place starting then, the space environment would continue to contain the then-known population until about 2055, at which point it would increase on its own. Efforts were redoubled at space agencies around the world to cut down on space debris; in 2010, NASA and DARPA sponsored a conference to find new techniques for preventing and cleaning up space trash.
There are more than 21,000 orbital debris larger than 10 cm flying around in Earth orbit. And that doesn't count the estimated half-million smaller pieces the size of a marble or larger, which can be as dangerous to spacecraft as a missile.
Meanwhile, a U.S. military unit called the Space Surveillance Network, based at California’s Vandenberg Air Force Base, upgraded its systems for monitoring space junk. Before the incident, the network's ground-based radar (which can track objects as small as 3 mm) had been following 120 active satellites and worrying about an average of five potential collisions, or “conjunctions,” per day. By early 2010, according to Wired that year, the network was keeping a close eye on 1,000 active satellites, 3,700 inactive satellites and rocket pieces, and another 15,300 objects the size of a fist or larger—revealing a new daily average of 75 possible collisions. Now it's estimated there are more than 21,000 orbital debris larger than 10 cm flying around in Earth orbit. And that doesn't count the danger posed by the estimated half-million smaller pieces of debris the size of a marble or larger, which can be as dangerous to satellites as a missile.
In fact it was an actual missile that accelerated much of our space mess. When China's Fengyun-1C anti-satellite missile test took out a Chinese weather satellite on January 11, 2007, the result wasn't just a brief but global condemnation of the militiarization of space (Beijing, which had been advocating to ban space weapons, swore that the test was peaceful). The long-term effects of the explosion were bigger: it caused the largest recorded creation of space debris in history, with an estimated 150,000 debris particles now flying around the Earth in uncontrolled orbits. America's own debris-creating high-altitude missile tests P78-1 (1985) and USA-193 (2008) may not have created as much debris (and certainly didn't come in for as much criticism), but all these tests demonstrate again just how much space trash is—to use that hackneyed environmental mantra—everyone's responsibility.
By 2011, the U.S. National Research Council warned NASA that the amount of space debris orbiting the Earth was at a critical level, in terms that Donald Kessler had used in 1979. Some models, it warned, demonstrated that orbital garbage "has reached a tipping point, with enough currently in orbit to continually collide and create even more debris, raising the risk of spacecraft failures."
Leave no trace (in space)
Since 2009, scientists have made several not-so-modest proposals for eradicating space debris in order to prevent future collisions. The most obvious example (and probably the most reasonable) is to launch smaller satellites in lower altitudes. Cheap and tiny CubeSats and PhoneSats—with brains amounting in some cases to little more than an Android phone—will mean fewer chances for collision, not to mention more affordable launches and greater accessibility for a broader range of scientists.
While that solution for the space debris problem is fairly pedantic, other potential solutions sound like something out of Armageddon. There is a space harpoon in the works, for instance, which would include a propulsion pack tied to a hook that would be launched at debris and then pulled towards Earth so the space junk could burn up in the atmosphere. There's just one risk: the harpoon's impact could pierce satellite fuel tanks, which cause the debris in the first place. But the harpoon's engineers at Astrium, a British company, insiste their design's crushable cylinder will prevent tank puncture.
Videos of the space harpoon and giant claw
Meanwhile, as Brian Merchant reported last month, the Swiss government is currently building a giant satellite claw called Cleanspace One, nicknamed the "janitor satellite." Cleanspace One is going to match the orbits of derelict satellites and grab them, not unlike the arcade game we used to waste tokens on to capture that damned Beanie Baby, but with greater success.
Other debris reduction tactics include using a giant fishing net to capture the debris, which was described in the recent IMAX documentary Space Junk 3D, or using tungsten dust to drag on the orbits of decomissioned satellites and bring them down to the atmosphere. Lasers are a possibility. NASA, which now spends tens of millions of dollars on space debris research and is required by the Obama adminstration's National Space Policy to strengthen measures "to limit orbital debris", is developing a study to determine if a ground-based laser could be used to blast the junk and slow its orbit, allowing gravity to then pull the debris into the atmosphere and vaporize it, before future space exploration is further imperiled.
An impact crater on one of the windows of the Space Shuttle
Challenger following a collision with a paint chip during STS-7.
For NASA personnel, it's not a theoretical fear or a threat only to satellites: even a tiny fragment of trash could rip through the Space Station like a terrorist's bomb, a 10-centimeter sphere of aluminum equal to an estimated 7 kilograms of TNT. When a tiny piece of space debris passed within 1,000 miles of the ISS in July 2011, astronauts took refuge inside escape pods, in the event of a catastrophic collision at 17,000 miles per hour.
"This is not a U.S. problem," Marshall Kaplan, a space debris expert, told Space.com recently. He worries about the high costs of cleanup, not to mention legal restrictions, which prohibit the U.S., perpatrator of 29 percent of space junk, from going around cleaning up Russian debris (37 percent) or Chinese trash (28 percent). "It's everybody's problem. And most of the people that produced the debris, the serious offenders, like Russia, China and the United States, are not going to spend that kind of money," says Kaplan. "It's just not a good investment."
To the list of things to be worried about—alongside the future of space exploration or the chance that we'll get hit by an asteroid—we can add something much less sexy and more mundane: our old tendency to not clean up after our mess.
More on trash, in space and otherwise: