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20 Feb 2008 18:23
The United States Defence Department said on Wednesday that the window of opportunity is now open for it to try to shoot down a failing spy satellite.
The navy is planning to hit the satellite with a heat-seeking missile as early as Wednesday night, but officials had been waiting for the space shuttle Atlantis to return to Earth so it would not be hit by falling debris.
“We’re now into the window,” a senior defence official told a news conference minutes after the shuttle landed.
He said it will remain open until at least February 29 and that the decision to attempt a shot will depend on conditions in the atmosphere, such as sea levels, winds and other variables.
“We’re watching weather today,” he said. The ground rules of the news conference were that the official could not be quoted by name.
The military will be making decisions each day on whether to proceed with an attempt—and criteria could change several times each day, he said.
The opportunity to attempt a shot will be available only seconds each day.
The attempted shootdown was approved by President George Bush out of concern that toxic fuel on board the satellite could crash to Earth, the Defence Department has said.
China and Russia have expressed concern at the planned shootdown, saying it could harm security in outer space.
Officials will know nearly immediately whether the missile has hit the satellite, but it will take a day or two to know whether the fuel tank has been destroyed, officials said.
The military has readied a three-stage navy missile, designated the SM-3, which has chalked up a high rate of success in a series of missile defence tests since 2002. In each case it targeted a short- or medium-range ballistic missile, never a satellite.
A hurry-up programme to adapt the missile for this anti-satellite mission was completed in a matter of weeks; navy officials say the changes will be reversed once this satellite is down.
The government issued notices to aviators and mariners to remain clear of a section of the Pacific Ocean beginning at 3.30am GMT on Thursday, indicating the first window of opportunity to launch an SM-3 missile from a navy cruiser, the USS Lake Erie, in an effort to hit the wayward satellite.
Having lost power shortly after it reached orbit in late 2006, the satellite is out of control and well below the altitude of a normal satellite. The Pentagon wants to hit it with an SM-3 missile just before it re-enters Earth’s atmosphere, in that way minimising the amount of debris that would remain in space.
Left alone, the satellite would be expected to hit Earth during the first week of March. About half of the 2Â 250kg spacecraft would be expected to survive its blazing descent through the atmosphere and it would scatter debris over several hundred kilometres.
Adding to the difficulty of the shootdown mission, the missile will have to do better than just hit the bus-sized satellite, a navy official said on Tuesday. It needs to strike the relatively small fuel tank aboard the spacecraft in order to accomplish the main goal, which is to eliminate the toxic fuel that could injure or even kill people if it reached Earth.
The official described technical aspects of the missile’s capabilities on condition that he not be identified.
Also complicating the effort will be the fact that the satellite has no heat-generating propulsion system on board. That makes it more difficult for the navy missile’s heat-seeking system to work, although the official said software changes had been made to compensate for the lack of heat.
The Pentagon press secretary, Geoff Morrell, said Defence Secretary Robert Gates was briefed on the shootdown plan on Tuesday by the two officers who will advise him on exactly when to launch the missile—General Kevin Chilton, head of Strategic Command, and General James Cartwright, vice-chairperson of the Joint Chiefs of Staff, who held Chilton’s post until last summer.—Sapa-AP
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