It's a measure of how peacefully human beings have used space in the 50-plus years we've been traveling there that we're a whole lot better at putting things into orbit than we are at blowing them back out. That, of course, is a function of practice. Thousands of pieces of machinery have been lofted into space since the launch of Sputnik in 1957 and almost all of them have either tumbled back down on their own or simply remained in orbit.
This week, the Pentagon tried something different. On Wednesday evening, it announced that it successfully launched a sea-based missile and shot down a crippled satellite gliding 150 miles overhead, in a $60 million effort to blast it out of the sky before it could tumble home and hurt someone. It's been a neat little feat on the part of the military planners but that doesn't mean they're telling the whole truth about why they bothered in the first place.
The clay pigeon in the military's cross hairs was an unnamed, 5,000-lb. spy satellite that was launched in 2006 and never quite got its purchase in space, suffering a malfunction almost immediately upon its arrival in orbit. Comparatively low-orbiting craft like this one tumble back to Earth faster than high-orbiting ones, as the upper wisps of the planet's atmosphere produce increasing amounts of drag, pulling the object lower and lower. This one was on a trajectory that would have caused it to begin its terminal plunge sometime in March, sending it on a fiery descent that should have entirely or at least mostly incinerated it.
So why make the effort at such a complicated bit of sharpshooting just to bag a target that was coming down anyway? The Pentagon says it's all about safety. Five thousand pounds of out-of-control satellite can do an awful lot of damage if it drops on the wrong spot. What's more, this particular satellite is carrying a 500-lb. tank of frozen hydrazine fuel nasty stuff if you're unlucky enough to inhale it. Striking the ground at reentry speed, the gas could immediately disperse over a patch of ground as big as two football fields.
None of this, however, was likely to happen. For one thing, 70% of the Earth's surface is water. Even considering that the flight paths of most satellites are designed to carry them over as much land as possible, that's still a lot of uninhabited square mileage lying below. NASA acknowledges that 3,000 satellites and 6,000 pieces of space debris are currently circling the planet a pretty huge swarm of potentially incoming rubbish to justify devoting so much attention to just one.
The hydrazine argument is similarly suspect. It's extremely hard for a spacecraft component to survive reentry even if you want it to. The scientific experiments carried aboard the Apollo lunar modules were powered by radioactive fuel, which was itself encased in heavy ceramic just to ensure that it would survive such an accident. Even then, there were white knuckles whenever one flew since the risk existed that an uncontrolled reentry would crack the cask and leak radiation. The hydrazine tank a hollow vessel is nowhere near as robust and is unlikely to make it through the heat and aerodynamic violence of the plunge that awaits it, meaning that it will spill its contents high in the atmosphere, where it will represent barely a breath of gas that will disperse harmlessly.
The more believable explanation for the duck hunt is that it's been an exercise in politics rather than safety. Washington was none too pleased in January of 2007 when China shot down one of its own weather satellites after it had outlived its usefulness, a bit of technological sword-rattling that proved it could target any other nation's orbiting hardware with equal ease. Beijing too made vague claims of worrying about the public weal, but Washington saw the act more as the political statement it probably was, and concluded correctly that American spy satellites are not quite as safe as they once were. An American shootdown would be one way to return the gesture. The timing is particularly suspicious since Russia and China issued a joint condemnation of the militarization of space only days before the Pentagon went public with its plans. While Beijing's sudden pacifism is hardly credible after it own exercise in cosmic skeet-shooting, neither is the Washington's insistence that there is no linkage between the two events.
Another possibility is that the Pentagon was indeed nervous about something aboard the satellite, but not the tank of fuel. Spy satellites are, by definition, made of secret hardware, and nothing so pleases one military power as the chance to seize and pick over the technology of another. Should American camera and communications components fall into the wrong hands, whatever tactical advantage was gained in developing them would be lost.
With success announced on Wednesday night, the Pentagon is hardly likely to change its explanation now. They say the mission to destroy the satellite been accomplished, and for nowany questions that it's raised may be gone along with it.