February 21
BBC News - 
The US has struck a defunct spy satellite with a missile fired from a warship, military officials say.
The attempt went ahead from waters on the western side of Hawaii despite earlier concerns that bad weather could delay the operation.
The satellite, known as USA 193, stopped communicating and lost control hours after it was launched in 2006.
Officials say the shootdown was approved amid concerns that fuel on board could pose a threat to humans.
They say the toxic fuel hydrazine could harm or kill humans if inhaled.
It is unclear whether the missile has ruptured the tank. By doing so, the military hoped to disperse as much hydrazine as possible in space before the National Reconnaissance Office (NRO) "bird" falls to Earth.
Officials expect that over 50% of the debris will fall to Earth within the first 15 hours after the strike - or within its first two revolutions of Earth.
The US denied the operation was a response to the anti-satellite test carried out by China last year, which prompted fears of a space arms race.
But Russia has challenged America's rationale for carrying out the action.
Precision needed
Earlier the military said it would destroy the satellite with an SM-3 missile fired from the cruiser USS Lake Erie, which is posted on the western side of Hawaii along with the destroyers USS Decatur and USS Russell.
The US intended to intercept the 2,300kg (5,000lbs) spacecraft - believed by some commentators to be a radar imaging reconnaissance satellite - when it was at an altitude of 240km above the ground.
Hitting USA 193 just at the edge of the Earth's atmosphere minimises the amount of debris that would remain in space.
The missile needs to pierce the satellite's fuel tank, containing more than 450kg (1,000lbs) of toxic hydrazine, which would otherwise be expected to survive re-entry.
With the satellite's thermal control system gone, the fuel would now be frozen solid, allowing the tank to resist the heat of re-entry. If the tank were to land intact, it could leak toxic gas over a wide area.
Window of opportunity
It is unclear whether the missile has ruptured the tank. By doing so, the military hoped to disperse as much hydrazine as possible in space before the National Reconnaissance Office (NRO) "bird" falls to Earth.
Officials expect that over 50% of the debris will fall to Earth within the first 15 hours after the strike - or within its first two revolutions of Earth.
Left to its own devices, about half of the spacecraft would be expected to survive the blazing descent through the atmosphere, scattering debris in a defined "corridor" which runs across the Earth's surface
MORE at BBC