WASHINGTON — The military will attempt to shoot down a crippled spy satellite some time in the next two weeks, senior officials said on Thursday, laying out a high-tech plan to intercept the large spacecraft over the Pacific Ocean just before it tumbles uncontrollably back to earth with toxic fuel aboard.
Only twice in history has any nation shot an actual satellite down: China did it last year, and the United States more than 20 years ago.
President Bush ordered the action to prevent any possible contamination from that hazardous rocket fuel on board, and not out of any concern that parts of the spacecraft might survive and its secrets be revealed, officials said. The challenging mission to demolish it instead on the fringes of space will rely on an unforeseen use of ship-based weapons developed to defend against ballistic missile attacks. That makes it a real-world test both of the nation’s antiballistic missile systems and its antisatellite capabilities, even though the Pentagon said that they were not using the exercise to test their most exotic weapons or send a message to any adversaries.
The three-ship convoy assigned the task will stalk the satellite’s orbital path across the northern Pacific Ocean, tracking the satellite as it circles the globe 16 times a day.
The sensors and weapons involved in the operation, modified from anti-aircraft defenses for use as a shield against incoming missiles and put aboard Navy cruisers, have not been used except in carefully controlled tests.
This time their target is not an incoming warhead or a dummy test target, but a doomed experimental satellite the size of a school bus and weighing 5,000 pounds. It went dead shortly after being launched in December 2006. It contains a half-ton of hydrazene, a rocket fuel that officials said can burn the lungs and even is deadly in extended doses.
The fuel tank is believed sturdy enough to survive re-entry, based on studies of the fuel tank that fell to earth after the shuttle Columbia disaster in 2003. Officials said that the slushy frozen fuel would have then been released wherever it came down.
The military and NASA have calculated that the best opportunity to shoot down the satellite with an interceptor missile is just before it re-enters the atmosphere and starts to tumble and break apart on a random path toward the surface, an opportunity that begins in three to four days, and extends for eight days after that. At that point, its debris would quickly be dragged out of orbit.
In many ways, the task resembles shooting down an intercontinental nuclear missile, although in this case the target is larger, its path is better known, and if a first shot misses, it will continue to circle the earth for long enough to allow a second or even a third try.
The weapon of choice, after modifications that are still under way, is the Standard Missile 3 carried by the Navy’s Aegis cruisers, originally fielded for use against airplanes, cruise missiles and the like. The defensive missiles and supporting radar were already being modified and tested to shoot down enemy warheads, so the software is now being reprogrammed to home in on the radar and other signatures of a large satellite instead of a ballistic missile, officials said. Although White House, military and NASA officials described the president’s decision as motivated solely by wanting to avoid a spread of toxic fuel in an inhabited area, it has implications for missile defense and antisatellite weapons.
“This is all about trying to reduce the danger to human beings,” said James Jeffrey, the deputy national security adviser.
Even so, the ramifications of the operation are diplomatic as well as military and scientific, in part because the United States criticized China last year when Beijing used a defunct weather satellite as a target in a test of an antisatellite system.
The United States has opposed calls for a treaty limiting antisatellite or other weapons in space. On Thursday, officials pledged that the United States will remain wholly within compliance of treaties requiring the notification of other nations before it launches a missile at the disabled satellite.
The American military shot down a satellite in September 1985, as a test of an earlier antisatellite system under development. In that experiment, an F-15 Eagle fighter aircraft fired a missile armed with a “kill” vehicle.
This mission, though, would be the first attempt to use a tactical missile designed to defend against warheads to bring down a satellite in space. The task is made easier by the large size of the satellite, and by the fact that its orbits are being tracked and plotted in advance — as opposed to the more unexpected path of attack of an adversary’s warhead.
Gen. James Cartwright, the vice chairman of the Joint Chiefs of Staff, said that if the first missile failed to strike the satellite, an assessment would be made within days, and that two more missiles are ready. He described little down-side in attempting to destroy the satellite.
“If we fire at the satellite, the worst is that we miss, and then we have a known situation, which is where we are today,” General Cartwright said. “If we graze the satellite, we’re still better off, because likely we’ll still bring it down sooner, and therefore more predictably. If we hit the hydrazine tank, then we’ve improved our potential to mitigate that threat. So the regret factor of not acting clearly outweighed the regret factors of acting.”
Officials said the space shuttle mission now under way will have ended before the order is given to launch a missile at the satellite. While the international space station remains occupied, its orbit is higher than that of the dead satellite.
“We looked very carefully at increased risks to shuttle and station, and broadly speaking, they are negligible,” said Michael Griffin, the NASA administrator.
A Congressional Democrat considered one of the party’s experts on missile defense agreed that the United States had to take responsibility for any threat posed by the satellite, but she warned that the nation needed to be open in the effort as it will be a precedent for other countries.
“Just like our partners in space, we need to be responsible for the risks we create,” said Representative Ellen O. Tauscher of California, who is chairwoman of the House strategic forces subcommittee. “This can’t be a demonstration of an offensive capability.”
Jeffrey G. Lewis, an arms control specialist at the New America Foundation, warned that China would cite the intercept to justify the antisatellite test it conduct last year.
“The politics are terrible,” Mr. Lewis said. “It will be used by the Chinese to excuse their hit-to-kill test. And it really strengthens the perceived link between antisatellite systems and missile defenses. We will be using a missile defense system to shoot down a satellite.”
In January 2007, the Chinese fired an SC-19 missile at a target satellite, which was orbiting 475 miles overhead. About 1,600 pieces of debris, the remnants of the destroyed satellite, were detected soon after that test.
The United States is heavily dependent on satellites for military communications, reconnaissance and targeting, and the Bush administration criticized the Chinese test as a destabilizing development. Pentagon officials said at the time that they suspected the purpose of the test was to give the Chinese military the ability to blind American imaging satellites and hamper American military operations if there were to be a confrontation over Taiwan.
At the same time, the United States has resisted suggestions that a new arms control regime be negotiated to govern space weapons, and it has asserted its sovereign right to defend its own access to space and to deny it to others in future wars.
On Thursday, American officials said there was no comparison between the Chinese test and American plans to down the dead satellite. The Chinese test was conducted at a far higher altitude than the near-earth orbit of the failing American satellite. Debris from the Chinese test, officials said, may orbit and pose a threat to space vehicles for decades, while the debris from the American satellite, if hit by the missile, should fall within weeks.
But David C. Wright, of the Union of Concerned Scientists, said the American satellite is far larger than the one destroyed by China, and he predicted that the missile strike could produce 100,000 pieces of debris, some smaller than a marble but still dangerous to vehicles in space.
He agreed with Pentagon assessments that most of the debris would fall into the atmosphere within weeks. However, he said a risk remained that some debris could be kicked into a higher orbit by the impact of the missile striking from below.
Specialists who follow spy satellite operations have speculated that the problem satellite, managed by the National Reconnaissance Office, is an experimental imagery device built by Lockheed Martin and launched from Vandenberg Air Force Base in California aboard a Delta II rocket. Shortly after it reached orbit, ground controllers lost the ability to control it and were unable to regain communication.
The largest uncontrolled re-entry by an American spacecraft was that of Skylab in 1979. Controllers changed the 78-ton abandoned space station’s orientation to vary atmospheric drag to shift its entry point. Much of the craft fell into the Indian Ocean, as predicted, but some pieces traveled farther than expected, falling harmlessly in Western Australia.