(Agencies)
Updated: 2008-02-15 06:39

WASHINGTON -- President Bush has ordered the Pentagon to use a Navy missile to attempt to destroy a broken US spy satellite and thereby minimize the risk to humans from its toxic fuel by intercepting it just before it re-enters the atmosphere, officials said Thursday.

A spy satellite in an undated image. A US intelligence satellite has lost power and could fall to Earth sometime in February or March, a government official said on Saturday. [Agencies]

The effort  will be undertaken because of the potential that people in the area where the satellite would otherwise crash could be harmed, the officials said.

Deputy National Security Adviser James Jeffrey, briefing reporters at the Pentagon, did not say when the attempted intercept would be conducted, but the satellite is expected to hit Earth during the first week of March.

"This is all about trying to reduce the danger to human beings," Jeffrey said.

Gen. James Cartwright, vice chairman of the Joint Chiefs of Staff, said at the same briefing that the "window of opportunity" for such a shootdown, presumably to be launched from a Navy ship, will open in the next three or four days and last for seven or eight days. He did not say whether the Pentagon has decided on an exact launch date.

Cartwright said this will be an unprecedented effort; he would not say exactly what are the odds of success.

"This is the first time we've used a tactical missile to engage a spacecraft," Cartwright said.

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After extensive study and analysis, US officials came to the conclusion that, "we're better off taking the attempt than not," Cartwright said.

He said a Navy missile known as Standard Missile 3 would be fired in an attempt to intercept the satellite just prior to it re-entering Earth's atmosphere. It would be "next to impossible" to hit the satellite after that because of atmospheric disturbances, Cartwright said.

A second goal, he said, is to directly hit the fuel tank in order to minimize the amount of fuel that returns to Earth.

Software associated with the Standard Missile 3 has been modified to enhance the chances of the missile's sensors recognizing that the satellite is its target; he noted that the missile's designed mission is to shoot down ballistic missiles, not satellites. Other officials said the missile's maximum range, while a classified figure, is not great enough to hit a satellite operating in normal orbits.

"It's a one-time deal," Cartwright said when asked whether the modified Standard Missile 3 should be considered a new US anti-satellite weapon technology.

Cartwright also said that if an initial shootdown attempt fails, a decision will be made whether to take a second shot.

Jeffrey said members of Congress were briefed on the plan earlier Thursday and that diplomatic notifications to other countries would be made before the end of the day.

The military will have to choose a time and a location that will avoid to the greatest degree any damage to other satellites in the sky. Also, there is the possibility that large pieces could remain, and either stay in orbit where they can collide with other satellites or possibly fall to Earth.

It is not known where the satellite will hit. But officials familiar with the situation say about half of the 5,000-pound spacecraft is expected to survive its blazing descent through the atmosphere and will scatter debris. The officials spoke on condition of anonymity because of the sensitivity of the matter.

The satellite is outfitted with thrusters and small engines used to position it in space. They contain the toxic rocket fuel hydrazine, which can cause harm to anyone who contacts it. Officials have said there is about 1,000 pounds of propellent on the satellite.

Known by its military designation US 193, the satellite was launched in December 2006. It lost power and its central computer failed almost immediately afterward, leaving it uncontrollable. It carried a sophisticated and secret imaging sensor.