Bush orders US Navy to shoot down rogue spy sat

Nonetheless, it was confirmed that the warships would not fire until the space shuttle Atlantis returns to Earth on 20 Feb. NASA chief Michael Griffin said the risk from the interception to astronauts remaining in orbit aboard the International Space Station would be negligible - actually less than that caused by a routine shuttle mission.

The US administration's repeated insistence that the shootdown is motivated by purely humanitarian concerns seems rather dubious. At least 27 satellites re-entered the atmosphere last year, and more than 100 other items big enough to show on radar.

As for the hydrazine, tanks of nasty rocket fuel come down routinely, often intact or nearly so: a Delta-II second stage tank landed in fairly good condition in Texas in 1997, for example. The Delta-II second stage uses a hydrazine-based fuel, and equally toxic/corrosive dinitrogen tetroxide as oxidiser. The motor is restartable, used to provide multiple controlled burns for precise orbital positioning after the first stage drops away. Such a tank would seldom be entirely empty before it fell back to Earth: and yet nobody considers it normal to worry about Delta-II second stages, scores of which have come down over the years.

Indeed, another Delta-II blew up just seconds above the pad in '97, scattering debris all over Cape Canaveral. Tons of toxic fuel and oxidiser - the entire contents of the second stage - went everywhere. The US government's advice to local residents on that occasion? Stay indoors until the afternoon.

A hydrazine tank is also known to have survived the Columbia space shuttle disaster, as NASA's Griffin admitted last night - again, leading to no ill effects.

Against this sort of background, the idea that the descending satellite's little manoeuvring tank is a serious concern - serious enough to mobilise the US fleet with specially modified missiles - doesn't seem terribly plausible.

So why are the Americans so keen to shoot the satellite down? Well, it might be just to see whether they can; and to show that China isn't alone in being able to knock down spacecraft. That view is being taken by several analysts.

Others suggest the shootdown effort is more in the nature of seizing an opportunity. Normally, testing a missile-defence interceptor requires the use of an extremely expensive target. In this case, the target is effectively free - why not take the chance to improve America missile-defence gear? Not exactly killing two birds with one stone, but you get the idea.

Neither of these motivations really seem sufficient to justify the inevitable diplomatic costs. China and Russia are sure to see the move as provocative, and it could lead to further militarisation of space. The US - far and away the major military/intelligence space user - has a lot more to lose here than its adversaries do.