Space-based missile defences could result in swarms of dangerous debris that make low-Earth orbits permanently unusable, a prominent US astronomer has warned.
Joel Primack of the University of California at Santa Cruz told a UN Educational, Scientific and Cultural Organization conference on Friday that the orbiting anti-missile battle stations proposed by the US could result in so much space junk that other satellites could not operate.
Primack uses satellites in his cosmological research and helped organise the American Physical Society鈥檚 Forum on Physics and Society. Earlier in April, China called for a ban on the deployment of destructive weapons in space, at an international disarmament conference in Beijing.
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Most critics of the US military鈥檚 missile defence programme have focused on trials of ground-based interceptors, which have destroyed dummy warheads in four out of six trials. But neither target nor interceptor reach orbital velocity, so most of the debris they produce would fall to the ground.
Primack鈥檚 concerns focus on space-based interceptors and high-energy lasers that the Missile Defense Agency is developing to target missiles in their vulnerable boost phase, and on measures other countries might take to block their deployment.
Kinetic energy
The most dangerous type of space debris are particles smaller than about 10 centimetres, which are too small to track from the ground but could carry as much kinetic energy as a safe dropped from a three-storey building. NASA estimates low-Earth orbit 鈥� about 320 to 800 kilometres 鈥� already contains 100,000 particles between one and 10 centimetres. Most of these were produced by explosions of the spent upper stages of rockets.
The sheer scale of a space-based missile defence system would raise the risk, Primack told New 杏吧原创: 鈥淭he basic scale of any military activity in space aimed at shooting down missiles is thousands of objects,鈥� because they have to be ready to take action anywhere.
Deploying that many lasers or interceptors would mean increasing launch rates by at least a factor of 10. The Missile Defense Agency plans to begin testing a space-based 鈥渒inetic energy kill vehicle鈥� by 2006; tests of a space-based laser would not start until at least 2012. Although the tests will produce debris, much may fall back to the ground, depending on the trajectory.
The worst scenario would be an attempt to disable US orbital defences. 鈥淚t鈥檚 easy to attack satellites 鈥� basically you put gravel into orbit,鈥� says Primack. A multitude of small, untrackable objects would hit existing satellites and spent boosters, destroying them and producing an increasing cascade of debris.
鈥淥nce we fill space with debris, it鈥檚 permanent,鈥� Primack warns. NASA says debris below 600 km will fall within several years, but objects in 1000-km orbits will survive for a century or more.
