Space junk

At the 6th European Conference on Space Debris being held in the German city of Darmstadt from April 22 to 25, experts associated with the European Space Agency (ESA) are discussing the problem of waste in orbit around Earth.

One concern is the potential hazards of space debris returning to Earth. But the more pressing problem is that if a functional satellite or space station collides with even a small bit of space junk, it could be completely destroyed.

Collisional cascading

The first collision in space was between a satellite belonging to the United States and another belonging to Russia. The kiss of death occurred at 790 kilometers (491 miles) above Siberia.

"It was really just a matter of time," said Heiner Klinkrad, head of ESA's Space Debris Office. He explained that the space around Earth is full of objects - from tiny screws that have come undone, to rocket fragments and defunct satellites.

Such items comprise what is known as space debris. As the amount of debris increases, more collisions create more debris. Preventing this "collisional cascading" is a focus of the conference in Germany.

"It's mainly the large pieces that cause long-term problems," said Klinkrad. He added that even the smallest fragments can be problematic.

"We can assume that if a 10-centimeter (4-inch) object strikes a satellite, its functioning days are over."

Such fragments have the power of a hand grenade in the weightlessness of outer space, where when objects go flying, they don't come to a stop.

Low risk for earth

The Space Surveillance Network (SSN) has catalogued 13,000 larger pieces of space debris currently floating around Earth. It's estimated there are up to 700,000 objects around 1 centimeter (0.4 inch) in size up there.

The layperson might ask if this mass of space debris will fall back on the Earth. Frank-Jürgen Diekmann, head of ESA's observational satellite mission Envisat, doesn't think so. "The likelihood of something arriving to Earth without burning up isn't exactly zero, but it is very, very low," he said.

According to Kinkrad's estimates, at least two meter-long (3-foot-long) items pass from space to Earth's atmosphere every week. But the researchers are more concerned about protecting expensive satellites.

More than 6,000 satellites have been launched into space since 1957, and around 1,000 are still being used for research, military and telecommunications purposes. "Only about 6 or 7 percent of all objects up there are operational satellites," Klinkrad said.

Calculations are key to preserving these functional satellites. Their orbits are compared with known items in the SSN catalogue, and a risk calendar is planned for every week in order to plan evasive maneuvers.

Getting the big picture

Keeping track of what debris is in orbit is extremely difficult. The equipment is hard to come by and only the U.S. and Russia possess enough of it to carry out effective investigations. European space researchers are dreaming about creating their own debris monitoring system. Klinkrad pointed out that this would help in the reliability of movements to avoid collisions.

The topic has been on the ESA's radar for at least 20 years. But it's only recently that the 18 European member countries have organized to take on the issue politically. Basic building blocks should soon be in place for such a European system, although anything rivaling the U.S. or Russian systems won't be realistic until at least 2015.

The majority of evasive maneuvers programmed are for satellites to avoid collisions with tiny space fragment debris. But each move costs valuable fuel - which can shorten the lifespan of satellites, these days typically around 12 years.

'Common sense'

In March of 2009, even the International Space Station had to turn 180 degrees to avoid fragments from a Chinese weather satellite that passed dangerously close to the manned station.

Klinkrad said that 20 to 30 percent of all risky flybys are the result of a single war game exercise. For example, in January 2007 China blew up one of its satellites with a mid-range rocket. Although the reasons are not known, the results are certainly lasting. There are 2,300 fragments of debris still in orbit around earth.

The Inter-Agency Debris Coordination Committee is seeking international cooperation to address the problem. Klinkrad said openness is the best policy where such debris is concerned, but added that the lack of a legal framework complicates matters.

"At the moment the only thing forbidding people from blowing up their own satellites is common sense," Klinkrad said.

Futuristic solutions

So, what is the best way to deal with space junk? If the satellite's orbit is near the Earth, scientists can create a controlled crash. "One can burn some fuel to push the satellite down, to where the atmosphere captures it and it incinerates upon re-entry," Klinkrad said.

Klinkrad and Diekmann both said they could imagine creating a towing service, where items would be gathered from orbit for disposal. But that's still a long way off, they said.