Let’s Shoot Down a Satellite: An In-Depth Review (Part 1)

Last year, the People's Republic of China used a medium-range ballistic missile to destroy weather satellite Fengyun-1C, a 958-kg spacecraft which had stopped working in 2005. China's anti-satellite (ASAT) exercise caused an international uproar as other nations, including the United States, decried the testing and development of anti-satellite weapons. China's ASAT exercise also littered Earth's atmosphere with shrapnel, a problem for mission managers and satellite operators who must now navigate around even more space junk

At the time of China's anti-satellite test, the United States stated that it also had the technology to shoot down satellites from Earth, but would do so only as a pre-emptive measure if the nation or any of its satellites were threatened. A year later, the need for such a pre-emptive strike arrived, but not because of an international adversary. On Wednesday, February 20, 2008, at approximately 10:26 PM (EST) a U.S. Navy Aegis warship named USS Lake Erie launched a modified tactile Standard Missile-3 (SM-3) at satellite USA-193, which is also know as NROL-21. The initial view of the missile strike indicated that the main threat, the satellite's fuel tank, had been destroyed.

USA-193 (NROL-21) was a bus-sized, 5000-lb. spy satellite launched on December 14, 2006, but which lost contact with ground control soon after reaching orbit. The satellite's intelligence objective remains secret, but some believe the spacecraft was a high-resolution radar satellite designed to produce images for the National Reconnaissance Office (NRO). USA-193 (NROL-21) had a fuel tank filled with 1000 pounds of hydrazine, a lightweight monoprellant which does not require a separate oxidizer. Although the satellite's hydrazine fuel should have been used during its mission, a large quantity remained. And because hydrazine is toxic, the spy satellite could have posed a serious health hazardous if the fuel tank survived re-entry and crashed in a populated area.

Like all objects in a decaying orbit, USA-193 (NROL-21) was being "sucked" into Earth's gravitational field. In order for a spacecraft to remain in orbit, it must periodically turn-on its engines to return to the proper orbiting elevation. If the spy satellite had not been shot down, experts warned that it would re-enter Earth's atmosphere naturally, during the first week of March. It was also estimated that about half of the 5000 pounds (including the fuel tank) would survive the blazing, super-hot decent of re-entry.

If the spy satellite had re-entered Earth's atmosphere naturally, debris would have been scattered over several hundred miles of the planet's surface. Moreover, if the fuel tank itself hit the Earth, 1000 pounds of toxic hydrazine gas would have been scattered over an area about the size of two football fields. The U.S. Centers for Disease Control (CDC) issued a warning to all public health officials, asking them to review health effects related to hydrazine poisoning in order to prepare for a crash of the satellite's fuel tank anywhere in the United States.

After research was completed and experts were consulted, the U.S. government determined that its spy satellite was too dangerous to re-enter Earth's atmosphere. The initial order came from the Pentagon with the President's approval. The military was called in to complete the mission; however, due to the intense international publicity and political ramifications, Defense Secretary Robert Gates was given the job of making the final decision about whether to pull the ASAT trigger.

Editors Note: Click here for Part 2 of this four-part series.

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