The US has decided to shoot down one of its intelligence satellites, which is in a wayward orbit and is due to hit earth next month.
President George W Bush ordered the Pentagon to shoot down the satellite through a Navy missile just before it reenters earth's atmosphere.
Though the Pentagon has not announced the exact date of the operation, the satellite will be attempted to be brought down in the next several days using a missile from one of the Aegis ships.
"This is all about trying to reduce the danger to human beings," Deputy National Security Advisor James Jeffries said.
However, in a briefing, the Vice Chair of the Joint Chiefs of Staff General James Cartwright did not guarantee the success of the operation.
"We are better off taking the attempt than not," he said.
A missile known as Standard Missile 3 would be fired in an attempt to intercept the satellite just before it re-enters Earth's atmosphere, he said, warning that it would be 'next to impossible' to hit it afterwards because of atmospheric disturbances.
Cartwright said the missile 'has the ability to get up just beyond the atmosphere, so it has the kinetic energy to be able to reach this satellite as it prepares to reenter. We believe that the window for this activity will start here in the next three or four days and will be open for about maybe as many as seven or eight days.'
The second goal is to directly hit the fuel tank in order to minimise the amount of fuel that returns to Earth.
"Much of this depends on the heating of the atmosphere. So we are trying to build, knowing that, where would the best position be from the Earth to launch a missile to intercept that would drive this down into the ocean. And that's our objective: get rid of the hydrazine and have this fall in the ocean," Cartwright said.
Meanwhile, the administrator of the NASA Michael Griffin argued that it is simply not possible to predict whether it will land in the middle of the Pacific or in a populated area.
"Neutral (situation) is if we miss. Nothing changes. If we shoot and barely touch it, the satellite is, at this point, just barely in orbit. Almost anything that you do to it when it is just barely in orbit is going to cause it to reenter within the next couple of orbits. If we shoot and get a direct hit, then that's a clean kill, and we are in good shape," he said.
"So there is almost nothing we can do here that makes it worse. Almost everything we can do technically makes it better," he added.
Cartwright rejected any comparison between the operation and China's testing an anti-satellite weapon last year.
"What is different here is, one, we are notifying, which is required by treaties and law. And we started that notification well over a month ago and we are continuing to keep people informed and we have a consequence management plan that is in place that we will execute," he said.
"The second here is, in looking at comparisons, this is right at the surface of the atmosphere, so to speak. Other intercepts that have occurred have occurred substantially higher than the space station, as an example.
"That means the debris is there for 20 to 40 years and has to migrate down through both manned space platforms and unmanned space platforms. That will not be the case here," the top Pentagon official added.