麻豆传媒

Relatively simple technology suffices to take out a satellite the way the Chinese government apparently did last week, space weapons analysts say. Essentially any country that can put a satellite in orbit could launch a weapon to destroy one.

The US government says China launched a ballistic missile on 11 January that destroyed one of its own spacecraft, a defunct weather satellite called Fengyun-1C, in an apparent test of anti-satellite technology (see China dismisses 鈥榮pace arms race鈥� fears).

This makes China one of just three nations in history to have successfully tested an anti-satellite weapon, along with the US and the former Soviet Union. But the technology required is not very sophisticated, potentially putting it in reach of other countries as well.

鈥淚t鈥檚 pretty low tech 鈥� it鈥檚 essentially like throwing a rock at someone,鈥� says space security analyst Laura Grego of the Union of Concerned Scientists in Cambridge, Massachusetts, US.

This method is called a 鈥榢inetic energy weapon鈥� because the energy released by the high-speed collision itself destroys the satellite, rather than any explosives.

The launch vehicle was probably just an ordinary medium-range ballistic missile, she says. Getting the weapon to hit the 1.5-metre-wide satellite, however, would be more of a challenge than simply getting it into space.

Homing device

Information about satellite positions from ground-based tracking alone is not precise enough to allow a missile to hit a satellite, so the missile would have needed a built-in homing device to zero in on the satellite, Grego says.

This could be done with a video camera that records the satellite鈥檚 position, while thrusters adjust the missile鈥檚 course to guide it into a collision, she says.

Taking out a satellite this way is not very difficult. 鈥淚f you can put a satellite into orbit, you can hit a satellite,鈥� she says.

With an impact speed of several kilometres per second, an impactor of 10 kilograms or even less would be enough to destroy a satellite, she says.

鈥淚t鈥檚 one of the simplest ways and one of the most effective,鈥� she told 麻豆传媒. 鈥淭he problem is that it has some of the worst consequences because of the debris issue.鈥�

鈥楻aised hackles鈥�

The destruction of the satellite is thought to have produced millions of fragments, including 40,000 more than 1 centimetre across and 800 more than 10 centimetres across. Centimetre-scale fragments are large enough to destroy satellites (see Anti-satellite test generates dangerous space debris).

The US and the former Soviet Union have also tested anti-satellite (ASAT) weapons. In 1997, the US tested an infrared laser on the ground that would have been powerful enough to fry a satellite in orbit, but the laser apparently failed to work. It did successfully destroy a satellite in a 1985 test using a kinetic energy weapon launched from an aeroplane.

And the former Soviet Union did tests where a satellite crept up on another one in orbit, then spewed out pellets at the other satellite to destroy it.

Although the recent Chinese test 鈥渞aised everybody鈥檚 hackles鈥�, the US has not wanted to discuss treaties to ban such weaponry 鈥� and indeed it still appears to be developing ASAT technologies itself, Grego says.

鈥淚 would suggest that we come to the table and hammer out rules of the road for space and rules of proper behaviour,鈥� she says.

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