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Growing threat from space debris

dpa logodpa 15/04/2017 Joachim Baier

Space debris poses a serious threat to spacecraft and the European Space Agency has called an international conference to discuss the growing problem.

Space debris is a growing problem, with disused satellites, rocket remains and millions of smaller pieces of junk all capable of damaging spacecraft and even destroying them.

"We will increasingly be confronted with collisions in the future," says Holger Krag, 43, who heads the Space Debris Office at the European Space Agency.

"The critical altitude lies between 800 and 1000 kilometres from the earth's surface. Congestion is already extreme there," Krag says.

Space junk has been created primarily by more than 250 breakups and explosions. There are about 18,000 fragments large enough to be tracked by detection systems.

However, even smaller pieces can be dangerous. Estimates say there are more than 750,000 objects measuring between one and 10 centimetres in diameter.

With potential collision speeds of up to 40,000 kilometres per hour, these pieces are capable of exerting the kind of force given off by a hand grenade.

The Seventh European Conference on Space Debris takes place at ESA mission control in Darmstadt between April 18 and 21. There, 400 participants will seek solutions to the problem.

The gathering is the largest and most important of its kind and has taken place every four years since 1993. Thus far, no binding rules have been decided on.

"We will compare notes," says Krag, who is chairing the conference, which was oversubscribed. Participants include engineers, scientists, managers, industrial concerns, universities and decision-makers from countries prominently involved in space travel.

The issue will only become more urgent. The number of rockets and satellites being launched into space is set to increase in the foreseeable future, as the traditional state-run space agencies are joined by commercial companies.

"Mega constellations of this kind is one of the priority issues at our conference on space debris," says Manuel Metz of the German Aerospace Centre.

"No one had this kind of space-travel boom on their radar just four years ago," Metz says, pointing to plans for commercial missions from as early as next year.

"They are on the threshold. Inexpensive space travel is possible."

Krag is also concerned about projects planned by the likes of Samsung and Google, some of which will require a large number of satellites.

"We're talking about several thousand per mission," he says, pointing out that, throughout the history of space travel, "around 7000 satellites have been launched".

This is known as the "Kessler syndrome". Posited by NASA scientist Donald Kessler in 1978, the idea refers to an unpredictable chain reaction of collisions caused by a high density of objects in low earth orbit.

Such collisions could generate innumerable high-speed fragments that could paralyse further work in this region.

Several approaches have been suggested, including drawing the pieces down into the atmosphere and having them burn out over the Pacific.

Having control over the satellites is key to disposal, Krag says, pointing out that hauling in a lost satellite with a grapple arm is "a huge challenge" and something still well in the future.

But he has some reassurance for those of us down on earth. The chance of being hit by a piece of space debris is small, even though theoretically possible. "The probability is tiny," Krag says.

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