Satellite Shootdown Comments
People are looking for ulterior motives for the shootdown because the official explanation – preventing a thousand pounds of hydrazine falling from the sky – seems a bit thin.
Hydrazine is highly dangerous stuff. It’s unstable, corrosive and explodes easily. That means that the fuel tanks for hydrazine are made extra tough. Unfortunately, the strength that lets the fuel tank carry hydrazine safely into space also means that the tank is tough enough to survive catastrophic reentry. When the shuttle broke apart on reentry a few years ago, the hydrazine tank was one of the few items to survive the fall unscathed. In that case, however, the tank contained only a few pounds of hydrazine. In this case, the tank is full. The risk is that the equivalent of a 1000-pound bomb could end up crashing down into a populated area.
Lots of debris falls from space every year – the boosters that carry satellite up come down pretty quickly. Elderly satellites are deorbited without much notice. The difference is that these are usually controlled reentries, where the impact point is planned (usually in water) and there is a degree of control as to the timing. This is an uncontrolled reentry. It’s possible to predict where impact will occur with some accuracy, but a number of factors can through the prediction off. Presumably, the U.S. predicts it will fall near or close to a populated area. Usually these things fall into water – it covers ¾ of the planet’s surface – or an unpopulated area. I know of only one reported case where someone was hit by a piece of a falling satellite, when a 20 pound chunk of aluminum from a Chinese CBERS satellite hit a boy in Shaanxi province – the press reported that he suffered a “fractured toe.”
The hydrazine explanation seems far-fetched, but the alternative explanations make even less sense. The U.S. doesn’t need to do this to impress the Chinese. They were already impressed by earlier successful tests, including the last one where an SM-3 missile launched from an Aegis cruiser hit a warhead 87 miles above the Pacific Ocean. This didn’t get a lot of public attention, but the Chinese military was sure to have followed it closely, if only because the U.S. has a cooperative missile defense program using Aegis with Japan, which the Chinese think could be used to defend Taiwan.
This test and China’s ASAT test really aren’t comparable. This is a ballistic missile defense test rather than an anti-satellite test. An anti-satellite test would have attacked the target while it was in orbit. A BMD test attacks when the target is in reentry. Hitting the target at a lower altitude reduces the risk of debris. One of the problems with the China ASAT test (aside from not telling anyone in advance) is that it left a large debris cloud orbiting the earth. The debris from this Aegis test will be at a lower altitude and be more quickly drawn into the earth's atmosphere, where they will burn up.
Success is likely in this effort, but not assured. Of the ten Aegis tests, eight resulted in hits. There is also the possibility that the satellite will behave erratically as it hits the atmosphere, making it a more difficult target. Variants of the SM-3 missile can be used against aircraft or ships, but these variants carry explosive warheads with proximity fuses (meaning the warhead only as to get near the target, not actually hit it). The missile defense variant uses a ‘kinetic’ warhead, basically a large lump of metal that crashed into the target. It will be moderately embarrassing if it misses.
The notion that secret high tech gizmos would fall into the wrong hands has some merit, but not enough to justify a shoot-down. There are always pieces of wreckage when a satellite falls to the ground. When they fall in the Canadian Arctic, the U.S. and Canada collect the pieces. When a nuclear powered satellite built by the Soviet Union crashed in Canada in the 1970s, the Soviets said they didn’t want the pieces back. When a Chinese rocket carrying a Western-owned communications satellite blew up shortly after launch, the Chinese carefully collected all the pieces and tried to examine them before turning them back, but the most sensitive items were charred and cracked beyond recognition. The probability of gaining useful information from the crash is low, as the best technology would have to survive reentry and the debris would have to fall in an opponent-controlled area. The probability of surviving reentry and landing in a hostile controlled area are too low to explain the decision to shoot down.
The one scenario that doesn’t get as much attention is planetary defence, possibly because it sounds silly. The notion that the U.S. should add intercepting meteorites or asteroids before they strike the earth to its defense missions seems pretty far-fetched. These events are so rare as to be improbable. On the other hand, supporters say, an asteroid strike wiped out the dinosaurs, drastically changed the environment, created a year-long winter and so on. It still sounds far-fetched. On the other hand, a 200-foot wide meteorite that struck Tunguska Siberia in 1908 had the effect of a nuclear explosion (without the radiation aftereffects). If there was warning that a similar event was about to occur over a populated area, it would be nice to have the ability to stop it. It's not worth spending much time worrying about being hit by asteroids, however, or even by satellites, but having spent all that money on missile defense, it’s nice that it finally has some practical use.