Following the publication of his report, Kessler became the seer of space junk, and the snowball effect he described was dubbed the “Kessler syndrome.” For many years, however, his work remained mainly of interest to scientists and space agencies.
That quickly changed five years ago. In 2007, China conducted an anti-satellite weapon test, which destroyed a decommissioned weather satellite, turning it into 150,000 pieces larger than 1 cm across. And two years later a defunct Russian communications satellite called Cosmos 2251 struck an Iridium communications satellite some 500 miles (800 km) above the Earth. Just as Kessler predicted, the catastrophic collisions spawned tens of thousands of new pieces of debris, some of which were large enough to take out other satellites, and large numbers of smaller pieces big enough to cause significant damage. It was a piece from the Cosmos satellite that struck the ISS in March. The Kessler syndrome has long since ceased to be a merely theoretical doomsday scenario.
Today, low Earth orbit is something of a space junkyard: out-of-commission satellites, discarded bits of rocket stages, and fragments of spacecraft circle the planet like zombies roaming a shopping centre. And though large collisions of the sort that destroyed the Iridium satellite are rare, the growing debris cloud poses an increasingly real threat to spacecraft.
Last year a US National Research Council study carried out by a group led by Kessler, reported that when a number of reasonable assumptions are fed into computer models, "the current orbital debris environment has already reached a ‘tipping point’." According to this scenario the numbers of objects, as well as their mass, had reached a level at which frequent collisions and spacecraft failures were now increasingly likely.
There is no shortage of good, or at least novel, ideas for removing space junk, ranging from Death Star-style lasers that would vaporize debris, to space-borne sweeping contraptions reminiscent of an illustration by W. Heath Robinson, the English cartoonist best known for his drawings of eccentric, ingenious and unnecessarily complex machines. Other concepts, no less creative, have included space nets, giant lassos, adhesive blankets, and low-power lasers to gently nudge debris away from collision paths.
One recent proposal that attracted some attention, though has no funding as of yet, is for a design that works in a way reminiscent of sticky flypaper. It would involve sending room-sized, adhesive-covered foam balls into space. Proposed by Sean Shepherd, a librarian from New Mexico, the balls would collect around 30 items of rubbish, before being guided by remote control towards the atmosphere to burn up.
In 2009, the Defense Advanced Research Projects Agency (Darpa), the Pentagon’s far-out research arm, took a serious look at the various proposals. The agency looked at, among other ideas, spacecraft equipped with magnets that would gather up debris, umbrella-shaped “sweepers” and a space tow truck that would drag junk into Earth’s orbit so that it would be incinerated.
Its report, called Catcher’s Mitt, concluded that many of the proposals were unrealistic with existing technologies. For example, the lasers required for most of the laser-based schemes are decades away from development. And "tens to hundreds" of ground-based lasers would need to be operated over a year to remove a single object, the report concluded.
It also found the greatest threat to operational spacecraft comes from medium-sized debris because there is so much of it and it often can't be detected from the ground. For these reasons the report recommended governments should concentrate on “pre-emptive removal” of large objects. Three years after its publication, none of the proposals have been funded.