The U.S. will shoot down a damaged spy satellite expected to hit Earth in early March, officials said at a news conference Thursday.
Gen. James Cartwright, Joint Chiefs of Staff vice-chairman, speaks to the media on Thursday.
(CBC)
The satellite, launched in December 2006 and weighing more than 2,000 kilograms, lost power almost immediately and never reached its final orbit.
President George W. Bush, acting on advice of security officials, has decided to try to shoot down the satellite before it enters Earth's atmosphere.
Officials said a missile would be fired from a U.S. navy cruiser off Hawaii next week at the earliest.
The officials said downing the satellite would help ensure it landed in an unpopulated area and help destroy the satellite's thruster tanks. The tanks contain a toxic rocket fuel called hydrazine, which can harm anyone who comes in contact with it, causing a burning sensation similar to chlorine.
Deputy national security adviser James Jeffrey said that if the satellite impacted on land, the hydrazine could spread to an area as large as two football fields.
"The likelihood of it falling in a populated area is small. But there was enough of a risk that the president asked us to review our options," said Jeffrey.
In addition to safety concerns, U.S. officials told the Associated Press earlier that they do not want the satellite to fall into the wrong hands, as it carries a sophisticated and secret imaging sensor.
China drew criticism
But Joint Chiefs of Staff vice-chairman Gen. James Cartwright denied that, saying classified technology is not an issue because the heating that would occur on re-entry would destroy any technology and "would not justify using a missile to shoot it down."
NASA administrator Michael Griffin said the risks to the International Space Station and space shuttle Atlantis was negligible.
It will be the first time the U.S. has ever attempted to shoot a spacecraft down with a surface-to-air missile, Cartwright said.
Last year, China drew criticism from a host of countries, including the U.S., after it used a missile to shoot down an old weather satellite about 865 kilometres above the Earth. The move was widely viewed as one that could lead to the increasing militarization of space.
Cartwright said this case is different because the U.S. is notifying countries and international organizations before attempting to knock out the satellite. He also said the plan to shoot it down as it enters the atmosphere will reduce the potential for debris to remain in orbit.
With files from the Associated Press
The launch of USA-193.
The United States military has announced their intention to use a missile to destroy USA-193, a spy satellite which failed immediately after launch in December 2006. Since launch, the satellite's orbit has decayed and it is approaching the point at which it will re-enter the atmosphere and potentially fall to Earth. The missile will be used as a kinetic anti-satellite weapon (ASAT), and will destroy the satellite through hitting it at high speed.

The satellite potentially has hazardous materials on board, including hydrazine. Ordinarily, the hydrazine would be used as fuel, but since the satellite failed immediately after launch, this was never used. It is expected that about half of the satellite would be capable of surviving re-entry, potentially including the fuel tank. Since hydrazine is toxic, the satellite could pose a severe danger if it hits in a populated area, however it has been considered likely that the tank would probably rupture and explode during re-entry. Destroying the satellite on the grounds of safety is the stated purpose of shooting down the satellite. Officials have denied claims that it is to prevent secrets that the satellite is carrying from falling into the wrong hands, or that it is a demonstration in response to a Chinese ASAT test in January 2007.

The missile which will be used to shoot down the satellite will be a Standard Missile 3 (SM-3), which will be launched from the USS Lake Erie in the North Pacific Ocean. The missile, which was designed to shoot down other missiles, will be modified slightly in order to allow it to recognise USA-193 as its target. 

If the attack is successful, the satellite will be broken into many small pieces. This will eliminate the hazard from the hydrazine and break into small enough pieces that nothing will survive reentry. Officials reported that the likelihood of success was "high". NASA Administrator Michael Griffin said that it was impossible to make the situation any worse. Missing the satellite would change nothing, while a slight blow would still result in the satellite returning to Earth, and a direct hit would destroy the satellite. It is believed that the missile will be aimed directly at the satellite's fuel tank.

While the debris will not pass near enough to the International Space Station to cause disruption, it is not clear whether it could affect spacecraft passing through the lower orbit in which USA-193 currently resides. For this reason, the satellite will not be destroyed until the Space Shuttle ''Atlantis'', which is currently conducting mission STS-122, has landed. The debris caused by the satellite's destruction is expected to re-enter the atmosphere within a few weeks.