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Oberg says Chinese Satellite Killer has Limited Powers

You may know James Oberg as NBC News' space analyst using his 22 years experience in NASA mission control to add context to technical issues. In another of his frequent contributions to the IEEE Spectrum blog he puts some perspective on China's anti-satellite technology.

The missile used to destroy the satellite was a 'kinetic kill' device - it had no explosives. The satellite was destroyed by the force of the collision.

Oberg points out that the head-on collision between the missile and its target sums the velocity of the two objects. The satellite's LEO orbit speed is around 28 000 km/hr, adding the missile's speed "creates a hypersonic shock wave that propagates from the inside of the target outward and, at the outer edge, shreds the target into metallic confetti that moves away at up to hundreds of meters per second."

He goes on to say the satellite was an easy target whose position, orbit and velocity were known in advance.

"The Chinese targeted a low-orbiting, obsolete, weather satellite, where the kinetic kill energy was very great. However, the really strategic satellites fly much higher—the navigation network is 20 000 km up, and the communications constellations are in a geosynchronous arc at 40 000 km. At geosynchronous altitudes, the orbital velocities are so much lower that the impact energy would be only about a tenth as high as in last week's test.

Distance introduces a second burden: terminal navigation. When a target satellite is close to the Earth, ground radars can track it and relay final course corrections, both to the rocket during its ascent and to the kill vehicle, once it has been deployed on its hoped-for collision course. Radar operates at an inverse fourth power law, which means that for the Chinese system to aim many times farther than low Earth orbit—as it would have to do to track objects geosyncronously—the demands on a ground-based radar would be simply impossible."

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