Space debris removal sorely needed

BERLIN (Feb 12, 2014): The region of space within 2,000 kilometres of the Earth's surface is dangerously littered with junk and needs to be cleaned up.
In February 2009, for example, a derelict Russian satellite, Cosmos 2251, collided with the American satellite Iridium 33 about 800 kilometres over Siberia. They shattered into thousands of pieces that now orbit the Earth.
The largest 2,200 or so from that collision have been catalogued. The International Space Station has had to manoeuvre several times to evade flying debris.
Two years earlier, in January 2007, China conducted an anti-satellite test in which it used a missile to destroy an old weather satellite at an altitude of some 850 kilometres, scattering more than 3,000 substantially sized pieces of spacecraft into low Earth orbit.
"Taken together, the fragments produced by these two events represent about a third of all the objects in space that we can track from the ground," said Heiner Klinkrad, head of the European Space Agency's (ESA) Space Debris Office.
According to Klinkrad, nearly 6,500 tons of junk are orbiting the Earth. The US Air Force's Space Surveillance Network (SSN) can detect and track pieces of debris with a diameter of approximately 10 centimetres at least - about the size of an orange.
In January it reported 16,674 objects, 9,464 of which were fragments. The number was 4,699 before China shot its satellite to pieces.
"It's assumed the Americans actually observe about 22,000 objects" with the SSN's worldwide network of 30 radar and optical telescopes, said Manuel Metz, a space debris expert for the German Aerospace Centre.
Not publicly catalogued are US military items and those of unknown origin, he explained. Even very small fragments orbiting the Earth pack enormous destructive power since they can smash into each other at relative speeds of about 50,000 kilometres an hour.
"An aluminium ball just a centimetre in diameter has the energy of a mid-size car travelling at about 50 kilometres an hour when it strikes a satellite," Klinkrad noted. An object with a diameter of 10 centimetres would rip a satellite apart.
"Catastrophic collisions in which a satellite disintegrates now occur on an average of every five to nine years," said Carsten Wiedemann, a senior scientist at the Institute of Aerospace Systems at Germany's Brunswick University of Technology.
The frequency could increase. Some 900 to 1,000 active satellites are currently orbiting the Earth. They keep telephone systems running, aid weather forecasting, transmit television signals and enable navigation devices to determine their position.
The ESA puts the price of replacing them at about 100 billion euros (136 billion US dollars), and the economic impact of losing them would be far higher.
At the Sixth European Conference on Space Debris, held in April 2013 at ESA's European Space Operations Centre in Darmstadt, Germany, more than 350 participants from around the world agreed there was an urgent need to remove space debris.
There are several ideas on how to do this. One is attaching solar sails to orbiting rubbish in order to drag it down into Earth's atmosphere, where friction from air would cause it to burn up. Another possible method is attaching an electrodynamic tether to a satellite slated for de-orbiting.
The electrical power generated while the tether moves through the Earth's magnetic field could be used to force the satellite down. Or "remover satellites" might serve as space-rubbish collectors either by capturing debris with their robotic arms or diverting it downward into the atmosphere.
The use of ground-based lasers to knock objects out of orbit is "probably still a long way off," according to Metz.
"If enough money were made available, the technology for some solutions actually ought to be within reach," Klinkrad remarked, adding that a number of obstacles, including legal ones, remained, however.
"We can't simply go up there and remove satellites and upper rocket stages that don't belong to us." What is more, he said, the world's militaries are closely monitoring developments on removing space debris because the same technologies could be used to knock out functioning satellites.
Doing nothing would likely be too risky for satellites, Klinkrad said. The hazards are known and everyone wants clean orbital paths, yet hardly anyone is willing to pay for it. "It's just another environmental problem." – DPA