You can see it early on some evenings: a glowing dot streaking halfway up the twilight sky, with occasional flashes of light sparkling its path. Those flashes foretell the doom of satellite USA 193. It's tumbling in orbit as the outer wisps of the earth's atmosphere jar its path; as it falls, facets of the craft catch the dying sunlight. USA 193 is doomed. It will plunge to earth sometime in the next two weeks. And the United States has decided to mount a $74 million effort to fragment it before it lands. The first attempt to do this may come as early as Thursday.
Why? Conspiracy theorists have had a field day speculating on possible secret reasons behind the Bush administration's decision to launch up to three SM-3 Standard missiles from U.S. Navy warships somewhere west of Hawaii to hit the satellite.
The suspicions are understandable. USA 193, weighing around 5,000 pounds, is the size of a school bus. But the odds against the satellite's hitting a person are literally millions to one. Three-quarters of the earth's surface is water. Ninety-five percent is uninhabited. Suppose USA 193's debris were to cover a few square miles, which is a plausible estimate. The earth's surface is 197 million square miles—all but one-20th of which is uninhabited. As National Security Council spokesman Gordon Johndroe said on Jan. 20, announcing USA 193's impending demise, "The likely percentage of this satellite or any debris falling into a populated area is very small."
History validates this confidence. In the 50 years of satellite launches, some 17,000 objects have plunged back to earth, according to the Pentagon. The biggest were the 78-ton U.S. Skylab, which came down in 1979, and the 100-ton Soviet Mir space station, which fell in 2001. By one independent count there were, last year alone, some 42 "major re-entries"—which is to say, big things hurtling down. Nine of those were satellites; perhaps a dozen were the upper stages of rockets that had lofted satellites into orbit. There has never been a report of a human being struck by space debris.
The detailed rationale given by administration officials for the shoot-down makes little more sense. USA 193 carries on board a tank of hydrazine, the fuel U.S. satellites use to change orbit in space. This fuel is contained in a spherical steel tank about three feet in diameter. After the space shuttle Columbia was destroyed while re-entering the atmosphere in 2003, its hydrazine tank was found, breached but intact, in a wooded area of Texas. Hydrazine is moderately toxic, with effects akin to chlorine gas. The hydrazine cloud from USA 193's tank would, if released, diffuse over an area of roughly two football fields. The cloud would dissipate in minutes. Nevertheless, we are told, that is the risk that impelled President Bush to order the satellite's midair destruction. Arguing against this are the facts of physics. The roughly 1,000 pounds of hydrazine in the tank is pressurized to a frozen slush. When heated, hydrazine turns into a gas. When USA 193 re-enters, friction from the atmosphere will roast the satellite to 7,500 degrees centigrade, hotter than the surface of the sun. Those who remember Charles's Law from high school will recall that gas expands on heating. The overwhelming probability is that the hydrazine tank—which is designed to withstand the zero temperature of space, not the superheating of re-entry—will simply explode as the hydrazine expands. (Why didn't Columbia's tank burst? Most likely because, as Gen. James Cartwright, vice chairman of the Joint Chiefs of Staff, explained in the Pentagon's Feb. 14 briefing on the planned shoot-down, "they'd burned most of it" on their mission. "So it [had] almost no hydrazine left." In other words, the tank was almost empty.)
Might there be other explanations for the administration's concerns? Spy satellite technologies and capabilities are, along with code-breaking techniques, the crown jewels of U.S. intelligence. So little is known for certain about USA 193. But we do know it was a test vehicle for the next generation of American spy satellites. These future satellites will be, it is hoped, highly capable; USA 193 was reportedly equipped with radars able to picture the earth in minute detail day and night, even through cloud cover. It also reportedly carried gear enabling the intel community to detect electronic transmissions, plus other test equipment for its planned successors. Cartwright said at the Pentagon briefing that "our assessment is high probability that … this would not be of intelligence value." But it is known that the U.S. has been working for years to find a way to make its spy satellites "stealthy"—meaning hard to detect by radars on earth—so they can achieve surprise as they wing overhead perhaps a dozen times a day. The predictability of a satellite's orbital path is a weakness of space surveillance. There is ample evidence that the bad guys have long since learned to hide stuff when they know a U.S. satellite is due over the horizon. A stealthy satellite, maneuvered by its hydrazine-fueled jets into a new orbit, could catch the bad guys unawares. Technologies that made USA 193 stealthy—a shape designed to fool probing radars, a covering to evade other ground-based sensors—are secrets the U.S. might well be ready to spend $74 million to protect.
Then there is the intriguing question of USA 193's power source. Most satellites in the earth's orbit spread giant solar panels—wings the size of football fields—to turn the sun's radiation into electrical power. But those panels illuminate the bird to any radar. No satellite with solar panels can be stealthy. USA 193 failed within seconds of entering initial orbit after its liftoff from Vandenberg Air Force Base in California on Dec. 14, 2006. If it had survived, would it have unfurled solar panels? That's unclear, but it seems unlikely. What was the power source, then? Soviet satellites were commonly powered by miniature nuclear reactors. When the Soviets' Cosmos 954 satellite crashed to earth near Great Slave Lake in Canada in 1978, it spread radioactive debris for some miles. And by one count there are more than 50 nuclear reactors or reactor cores from defunct satellites still orbiting the earth. The U.S. uses nuclear reactors to power satellites sent on distant space probes, but has not—to the best of my knowledge—used them to power spy satellites in earth orbit for some 20 years. At the Pentagon briefing, all questions about USA 193's technologies were passed off to the National Reconnaissance Office, the supersecret agency that runs the U.S. spy satellite programs. The NRO is saying nothing. So the question remains: is USA 193 the first of a new generation of spy satellites powered by nuclear reactors? Could that, along with the risk from hydrazine, explain the administration's determination to destroy the bird?
Unfortunately, we don't know—not yet anyway. What is certain is that USA 193's failure is yet another blow to a U.S. spy satellite effort that was already in deep trouble. The details are arcane, but in essence, the older generation of American spy satellites—birds with names like Keyhole, Lacrosse and Chalet—are coming to the ends of their operational lives, and the U.S. has nothing to replace them with. USA 193 was the sole survivor of an ambitious plan to develop a new family of satellites; the concept was called "Future Imagery Architecture." But that program collapsed a couple of years ago under the weight of technical overreaching and multibillion-dollar cost overruns. The United States has not, thus far, come up with a program to replace it. Those flashes in the evening sky as the doomed USA 193 passes overhead signal the death of more than just one satellite.