A reconnaissance satellite under construction in an undated photo

Courtesy National Reconnaissance Office

How did the U.S. shoot down its spy satellite?

On Feb. 14, 2008, President George W. Bush announced the United States would shoot down its own USA 193 spy satellite. The U.S. lost contact with the satellite only a few hours after its launch in December 2006 by the National Office of Reconnaissance (NRO). A year later, USA 193 entered into a decaying orbit -- moving toward Earth -- and would re-enter the Earth's sometime in March 2008, out of any kind of human control. A missile fired from the U.S.S. Lake Erie hit the satellite at 10:26 p.m. on Feb. 20, successfully destroying the errant bird [source: Gray].

Government officials say that if the gas canister containing 1,000 pounds (453.6 kg) of unspent hydrazine fuel survived the missile strike, made it back to Earth and leaks, it could have posed a health risk. The gas is like chlorine, and causes the same type of lung and throat irritation effects as chlorine -- prolonged exposure can mean death. A similar gas canister withstood re-entry following the Columbia space shuttle disaster in 2003. While it didn't land in an area where it endangered lives, it could have. "This is all about trying to reduce the danger to human beings," said Deputy National Security Adviser, James Jeffrey [source: The New York Times]. Pentagon officials are confident the fuel tank was destroyed along with the rest of the satellite [source: CNN].

Not everyone buys the United States' reason for firing on the satellite. Once plans were announced, both Russia and China cried foul, calling the plan a threat to space security and thinly disguised tests of the United States' missile defense systems. The two nations saw the mission as an opportune way for America to show "its capability to destroy other countries' satellites" [source: AP].

Other organizations viewed the missile strike with a critical eye. "There has to be another reason behind this," Michale Krepon, of the Henry L. Stinson Center on arms control, told The Washington Post. "In the history of the space age, there has not been a single human being who has been harmed by objects falling from space."

In other words, some speculate the world is watching a chess game play out above the Earth's atmosphere. In January 2007, China shot down an old weather satellite 537 miles (864 km) into space. Back then, the roles were reversed -- the United States filed a formal complaint with the United Nations about China's reckless behavior.

Regardless of the motives behind what has come to be called in defense circles, "the shot," was an apparent success. So how exactly did the United States pull it off? Read about that on the next page.

The Aegis class Navy cruiser U.S.S. Lake Erie test fires a SM-3 missile off the coast of Hawaii in December 2003.

U.S. Navy via Getty Images

Spy Satellite Missile

One could make the argument that the Cold War arms race between the United States and the Soviet Union was a good thing, at least in one case. If it weren't for the development of ballistic missiles, there would have been no need to develop anti-ballistic missiles. And without the latter, there was no way to tell where the two-ton (1,800 kg), highly classified spy satellite that the U.S. Navy shot down might land.

The Pentagon modified an existing missile system, and the Navy spent three weeks making modifications to the Block III, a Raytheon SM-3 antiballistic missile. The missile launched from the U.S.S. Lake Erie, a guided missile cruiser in the Pacific Ocean near Hawaii, hitting the satellite at 10:26 p.m. Eastern Standard Time (EST) Feb. 20. The Navy had a very short window to make the strike; the missile had to be fired sometime between 9 p.m. EST on Feb. 20 [source: ABC News] and 10:30 p.m. EST on Feb. 21, 2008 [source: Wired]. It was the first time the United States attempted to use a tactical missile to take out a spacecraft [Business Day].

The Raytheon SM-3 isn't designed to explode upon impact; rather, the missile destroys whatever it hits using brute force, like a bullet. It contains a heat-seeking component, which guided it to the wayward spy satellite. The Navy launched the Block III so that it traveled in the opposite direction of the USA 193, in order to produce a head-on (collinear) collision. The closing velocity of the impact -- which in this case is the sum of the two objects' velocities -- is estimated around 22,000 miles per hour (35,406 km/h) [source: Department of Defense].

The USA 193 spy satellite was about the size of a school bus and weighed 5,000 pounds (2,268 kg) -- a sizeable target -- if it had re-entered Earth's atmosphere intact, its course would have become erratic. The Union of Concerned Scientists said before the launch that the missile had "no better than a 50 percent chance of hitting its target" [source: The Washington Post], although the Block III is a highly accurate missile. As of November 2007, the system had hit 11 of its last 13 targets [source: Wired].

One of the greatest challenges of "the shot" was the brief window of time that the Navy had to take it. When China shot down its weather satellite in January 2007, the altitude (nearly 600 miles (966 km) above sea level) caused the debris created by the impact to hang around in space. While the space junk shouldn't enter our atmosphere -- and pose a threat to life on Earth -- it does present a problem for space travel. The debris can collide with functioning spacecraft, including those that bear human passengers.

To reduce the chance that the debris from the USA 193 will stay in space, the United States chose to shoot it down once it reaches an altitude of about 150 miles (241 km) [source: The Washington Post]. According to the Reuters news agency, the Block III missile hit USA 193 at an altitude of 153 miles (246 km) above the Earth. The window for a perfectly successful shot was narrow. The New York Times put it this way before Wednesday night's successful mission: "If they fire too late, the satellite will enter the atmosphere and start hurtling in unpredictable directions. If they fire too soon, space debris could spread and threaten the International Space Station and other satellites." The Navy had a back-up plan in the event of a missed target: It had two more ships ready to fire. "The worst is that we miss, and then we have a known situation, which is where we are today," said the Joint Chiefs' Gen. Cartwright [source: Department of Defense].

For more information on spacecraft and other related topics, visit the next page.

Lots More Information

Related HowStuffWorks ArticlesMore Great LinksSources
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