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Monday, May 4, 2009

Tracking and demobilizing debris in space


SINGAPORE — The 25 radar and optical telescope centers around the world that help the U.S. Armed Forces track debris in space have become increasingly busy in the past couple of years as man-made junk orbiting Earth proliferates, posing a growing danger to both civilian and military use of space.

There is even talk now of extending mundane rubbish collection into space to remove the biggest and most dangerous junk — old spacecraft and parts of rockets that loft satellites into orbit. The main conclusion of an international conference on space debris held at the European Space Agency headquarters in Darmstadt, Germany, early last month was that active remediation measures must be devised and implemented to prevent further spread of junk.

At a separate conference held around the same time in the United States, Vice Adm. Carl Mauney, deputy commander of the U.S. Strategic Command, noted that 10 countries now had space-launch capabilities, compared to just three — the U.S., Russia and Europe — a decade or so ago. They include Japan, China, India and Israel, all of which have launch facilities that other countries pay to use in putting satellites into orbit.

China announced earlier this year that it would complete its own satellite navigation system by 2015, making it independent of foreign technology, such as the U.S. Global Positioning System and similar space-based networks being developed by Europe and Russia. To do this, Beijing said it would launch 30 more satellites, to add to five already in orbit.

As many as 900 satellites orbit the Earth. About two-thirds of them are civilian and provide services such as weather forecasting, navigation, telecommunications, earth observation and scientific research. The military satellites perform a wide range of functions, from spying or spotting ballistic launches to enabling soldiers to communicate with commanders wherever they are in the world.

The first-ever accidental collision between two orbiting satellites last February underscored as well as amplified the problem of space junk. The collision, 776 km above Siberia, between America's privately owned Iridium communication satellite and a Russian military satellite generated thousands of pieces of new orbiting debris.

Even before the accident, the military-run Space Surveillance Network (SSN) of the U.S. was tracking, correlating and cataloging about 12,500 space objects larger than 5 to 10 centimeters in various orbits up to 36,000 km above the Earth. The SSN is the main source of space debris information for spacecraft and satellite operators, although other countries also monitor space junk or plan to do so in the next few years to protect their satellites.

Traveling at orbital speeds of 27,000 kilometers per hour, even tiny bits of debris can knock out a satellite by destroying a critical component. Any item larger than 10 cm could smash a satellite into many pieces.

In January 2007, China tested an anti-satellite weapon by destroying one of its own spacecraft with a ground-based missile. The collision occurred at an altitude of 862 km, adding over 2,500 trackable objects to the SSN catalog and increasing its size by 25 percent.

A month later, the explosion of a Russian rocket stage in space created over 1,000 pieces of orbiting debris that could threaten other spacecraft. In February 2008, the U.S. shot down what it said was a malfunctioning American spy satellite with a missile fired from a ship. The hit was at an altitude of 249 km, low enough for all of the 170 fragments cataloged to burn up in Earth's atmosphere by the end of the year.

Since the start of the space age, there have been over 4,900 rocket launches to carry satellites and other payloads into orbit. About half the objects in the SSN catalog originate from in-orbit breakups, including about 200 explosions usually caused by onboard fuel. About a quarter of the cataloged objects are old satellites. The remainder are either spent rocket bodies or related equipment.

The European Space Agency estimates that there are now around 20,000 pieces of orbiting space debris larger than 10 cm, 600,000 bits bigger than 1 cm, and over 300 million larger than 1 millimeter. Last month, a close approach by a bit of junk measuring about 1 cm forced the crew of the International Space Station to shelter in their Russian Soyuz escape capsule. The manned modules of the station are protected by debris shields that work like bulletproof vests. They are designed to absorb the impact of orbiting junk — but only up to 1 cm in size.

What worries operators and major users of satellites in Asia and elsewhere, is that as space debris accumulates, collision fragments will start colliding with large intact objects, creating a dangerous cascading process in orbits between 800 and 1,400 km high, where many navigation and remote-sensing satellites are positioned.

Hence the need for the rubbish collection service to remove the big objects. Of course, this would be expensive and there are questions over how it would be done and who would pay.

Meanwhile, the United Nations Committee on the Peaceful Uses of Outer Space has issued a seven-point set of guidelines to minimize proliferation of orbiting junk. However, the prospect of international cooperation to create a system of space traffic management similar to that which regulates movement of aircraft seems a long way off.

Michael Richardson is a visiting senior research fellow at the Institute of South East Asian Studies in Singapore.


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