The little ding that appeared recently on a window in the International Space Station is minor compared to the epic collisions that experts fear will occur as more satellites and debris clutter Earth's orbit.
"We are going to have some massive objects colliding in space and creating big, big field of debris and present a problem for satellites," said Darren McKnight, technical director at Integrity Applications, a Virginia engineering firm that works on government spy satellites. "The problem is it's very, very difficult to predict when that will occur."
Space collisions might be hard to predict, but debris is floating space all the time.
The European Space Agency recently released a photo of a 7 millimeter-diameter chip in the space station's window that it said had been gouged by "a tiny piece of space debris, possibly a paint flake or small metal fragment no bigger than a few thousandths of a millimetre across."
"I am often asked if the International Space Station is hit by space debris," ESA astronaut Tim Peake, who snapped the photo as he travelled 240 miles above the Earth, said in an accompanying statement. "Yes — this is the chip in one of our Cupola windows, glad it is quadruple glazed!"
Though tiny, the object was likely traveling at a speed of around 10 kilometers a second, or more than 22,000 miles per hour, so it struck the window with enormous force.
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NASA estimates that more than 100 million man-made objects the size of a grain of salt are orbiting the planet. About 500,000 objects that are roughly the size of a marble are also believed to be out there, as well as 23,000 objects the size of a softball or larger.
The amount of such fragments has expanded exponentially since the dawn of space exploration in the early 1960s. It has primarily resulted from discarded rocket parts and satellites, as well as from smash-ups between chunks space junk over the years — much of the debris is made up of bits of other debris. This phenomenon is known as the Kessler Syndrome, named for NASA scientist Donald Kessler, who described the effect in 1978.
A computer-generated illustration of space debris in low Earth orbit. (Image via NASA)
A few big hits have occurred. In 2009, a defunct Russian satellite slammed into a working commercial satellite owned by an American company. The crash created 2,000 pieces of debris that were large enough to track, according to NASA. In 2007, China tested a missile on a non-operational weather satellite, which produced 3,000 pieces of junk.
Both crashes also likely produced tens of thousands of smaller items that scientists can't track, which McKnight said could easily damage the International Space Station and other functioning objects in orbit.
The Chinese satellite weighed almost 1,900 pounds. McKnight said that some other clusters of space junk weigh more than 18,000 pounds because they include pieces of Soviet-era rockets. He estimated that there was a one-in-4,000 chance every year of two large discarded Soviet rockets hitting each other and creating more debris.
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"That level of ambiguity is tougher as space becomes more commercialized," said McKnight. "If you lost two satellites due to debris, that might affect share prices. It might make insurance go up."
NASA and other space agencies have instituted measures to crack down on space polluters, including a rule stating that anyone who sends a satellite or other object into space needs to plan on bringing it back down in 25 years. But Jer Chyi Liou, NASA's chief scientist for orbital debris, said only about half of the world's space missions today plan on bringing their spacecraft back in that period, mostly because of money.
"You need to allocate additional fuel to allow you to lower your orbit at the end of the mission," Liou said. "There's a price associated with that."
But even if everyone followed the 25-year rule, the amount of individual pieces of space junk probably wouldn't decline, Kessler said.
"We've already put so much stuff in Earth's orbit that the collision frequency is high enough compared to how fast stuff reenters that you will still have a building up," he said.
So folks have proposed ideas about cleaning up space.
Former NASA scientist Jerome Pearson helped designed a lightweight, towing-cable-like craft called the ElectroDynamic Debris Eliminator, or EDDE, which would use the planet's magnetic pull to corral space junk into a net. He's now the president of STAR Technology and Research, a company that's seeking to capitalize on EDDE. Pearson's plan is to create an orbiting junkyard that could provide materials for future space missions.
"We've got to get rid of that stuff before we have too many collisions," he said. "The best thing to do would be to recycle the stuff. There's a lot of high-grade aluminum up there."
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Others are working on satellites that would attach to debris and carry it back to earth, inflatable attachments that would bump fragments out of orbit, or lasers that would similarly redirect cosmic flotsam.
Liou thinks such efforts are a little premature.
"Orbital debris is a serious problem, but at the same time the sky is not falling," he said. "We do not need active debris removal today. But we need to look into technology for creating new cost effective ways to maybe deal with this problem 10 to 20 years down the road."
Kessler believes the issue is more urgent that that, and thinks the biggest chunks of junk should be retrieved from space as soon as possible to avoid collisions that could create more plumes of space litter. As in the battle against climate change, the quest to clean up space shouldn't be passed on to future generations, he said.
"To me, it's not too different than the same kind of problems that we've had on Earth," he remarked. "We just don't pay attention to what we're doing to the environment. Eventually it becomes non-sustainable."
Follow John Dyer on Twitter: @johnjdyerjr