Thursday, February 12, 2009

2009: first collision between two earth satellites

An American commercial communications satellite was destroyed in a collision with a defunct Russian military satellite in what NASA said was the first such accident in orbit, raising new concerns about the dangers of space debris.

The crash, which happened Tuesday, involved one of the satellites owned by Iridium Satellite LLC and a crippled Russian Cosmos satellite that apparently stopped functioning years ago.

The collision created two large clouds of debris floating roughly 480 miles above Siberia, and prompted space scientists and engineers to assess the likelihood of further collisions.

Cosmos satellites have caused a number of scary incidents over the years, including a 1991 collision between one defunct model and debris from another; a near-collision with the space shuttle the same year; and another that crashed into Canadian wilderness in 1978.

The accident could have implications for US space budgets and policy, partly because it comes amid a Pentagon campaign to increase spending on systems to protect US.high-tech space hardware by keeping better track of the thousands of pieces of debris and other satellites circling the Earth. As more and more satellites are launched, the challenges of keeping them from hitting debris or each other are growing. Military planners also worry about enemies jamming, disabling or potentially even ramming US satellites.

Industry officials say Iridium has identified the Russian craft as a Cosmos series satellite launched in 1993, weighing more than a ton and including an onboard nuclear reactor. That couldn't be independently verified. Experts have said the chance of radioactive debris surviving a fall through the atmosphere and reaching inhabited areas is very small.

More than 220 active commercial satellites now orbit the globe, in addition to hundreds of military, spy and scientific satellites. Commercial satellites provide businesses with everything from data and video transmissions to support for consumer navigation devices.

The Russian craft was being monitored by Pentagon organizations that keep track of space debris in order to prevent in-orbit collisions from damaging or destroying both commercial and government satellites. The National Aeronautics and Space Administration and the Pentagon track more than 10,000 pieces of high-speed debris, some no larger than a football.

Pentagon officials will face questions about how they missed such an impending collision with an intact satellite. Commercial satellites are routinely repositioned to avoid potential collision with smaller pieces of debris.

Pentagon brass, satellite industry executives and NASA leaders for years have publicly expressed concern about the dangers of orbital debris. But the odds of a direct hit between satellites were considered so small as to be basically unthinkable. The ground-based and space-based reconnaissance tools available to the Pentagon generally were considered adequate to keep close track of larger objects.

Recently, US and European operators began reviewing contingency plans to move some telecommunications satellites away from a pair that are malfunctioning. Space collision worries gained momentum in January 2007, when China used a relatively simple antisatellite weapon to knock down one of its aged weather satellites.

When satellites reach the end of their useful lives they often are parked in remote orbits where they are unlikely to endanger working satellites. But if a satellite's onboard computers or other systems fail, or it runs out of battery power, it can be difficult for ground operators to maintain control.

Iridium uses more than 60 satellites to provide voice and data services for about 300,000 subscribers globally. It said the collision has "minimal impact" on service due to its backup capacity. (info from The Wall Street Journal)

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