US Navy shoots down failing satellite on first try

The Pentagon said tonight it had successfully shot down a dying spy satellite, according to broadcast reports.

Rather than risk the chance a large piece of or the fuel from a failing spy satellite falling on populated areas the government last week decided the best course of action was to shoot the satellite down. The physics of such a shot were complicated as the satellite was traveling at about 17,000mph at about 114 miles up and the missile moves at about 5,000mph for a closing rate of over 20,000mph. The Navy had a less than 10 second window to hit the satellite as it passed overhead of its ships in the Pacific Ocean.

Early reports did not indicate how much of the satellite would now enter the atmosphere, but sources indicated the Navy said most of the debris would now fall over the Pacific Ocean.

Military officials wanted to shoot down the satellite before March 1, when the satellite was widely predicted to start entering the atmosphere and breaking up.As we reported earlier the exact size of the satellite and how much of it might actually make it through reentry and hit anyone or anything on the ground was up for debate.

Most space experts, however don't believe such plummeting debris really pose much danger but now that the military is apparently intent on shooting this one down, perhaps we don't know the whole story. He says that satellites come out of orbit and fall back to Earth harmlessly on average once a year, Dr Ruediger Jehn, a space debris analyst at the European Space Agency told the BBC last month.

Normally, when US spy satellites reach the end of their lives, they are disposed of through a controlled re-entry and dumped in the Pacific Ocean, so that no-one can learn their secrets. But, Dr Jehn says older satellites are often more difficult to de-orbit properly. "When they re-enter they usually burn up in the atmosphere because a lot of heat has developed and there is a lot of friction," he told the BBC. "Only heat-resistant or very heavy objects will survive. There is a risk in this case that something will hit the ground, but given that the Earth is so big, the probability in this case that someone will be hit is really remote."

The AP said details about the missile and the targeting were not immediately available. But the decision involves several U.S. agencies, including the National Security Agency, the Department of Homeland Defense and the State Department.Shooting down a satellite is particularly sensitive because of the controversy surrounding China's anti-satellite test last year, when Beijing shot down one of its defunct weather satellites, drawing immediate criticism from the U.S. and other countries, the AP stated.Aviation Week said Aerospace Corp., a California-based research organization that regularly advises the Defense Department, has assembled some basic data about falling satellites and what can be done about them.

"For an orbiting object, shooting it down actually breaks the object into many pieces, some of which could be hazardous to other satellites," says the Aerospace Corp. "Many of the fragments will survive re-entry, but be spread over a much larger area. The pros and cons for a specific case would need to be examined."Re-entering objects, including major items such as satellites, platforms and rocket bodies, have dropped 5,400 metric tons of material on the Earth in the past 40 years, the research group says.

The concern is that the spacecraft carries a full tank of hydrazine - a toxic propellant - that would have been used to reposition the satellite in orbit. Government analysts say the odds are that the tank will crack open during re-entry or than it will land in the ocean, which makes up 70% of the area where the breaking up satellite might land, Aviation Week reported.

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