The Pentagon's one-time attempt to shoot down a satellite

As we reported earlier, rather than take the chance a large piece of falling spy satellite will hit something or spread toxic fuel, the Pentagon is planning to shoot it down. It will be a first of its kind procedure.

Gen. James Cartwright, vice chairman of the Joint Chiefs of Staff, said at a briefing this afternoon that the window of opportunity for such a shootdown will open in the next three or four days and last for seven or eight days. He did not say whether the Pentagon has decided on an exact launch date.

A Navy missile known as Standard Missile 3, built by Raytheon, will be used in an attempt to intercept the satellite just prior to it re-entering Earth's atmosphere. It would be "next to impossible" to hit the satellite after that because of atmospheric disturbances, Cartwright said.

Software associated with the Standard Missile 3 has been modified to enhance the chances of the missile's sensors recognizing that the satellite is its target; he noted that the missile's designed mission is to shoot down ballistic missiles, not satellites.

Here is the official Department of Defense statement on the planned attack:

An uncontrollable U.S. experimental satellite which was launched in December 2006 is expected to reenter Earth's atmosphere between the end of February and early March. Because the satellite was never operational, analysis indicate that approximately 2,500 pounds of satellite mass will survive reentry, including 1,000 pounds of propellant fuel (hydrazine), a hazardous material.

Although the chances of an impact in a populated area are small, the potential consequences would be of enough concern to consider mitigating actions. Therefore, the President has decided to take action to mitigate the risk to human lives by engaging the non-functioning satellite. Because our missile defense system is not designed to engage satellites, extraordinary measures have been taken to temporarily modify three sea-based tactical missiles and three ships to carry out the engagement.

Based on modeling and analysis, our officials have high confidence that the engagement will be successful. As for when this engagement will occur, we will determine the optimal time, location, and geometry for a successful engagement based on a number of factors. As the satellite's path continues to decay, there will be a window of opportunity between late February and early March to conduct this engagement. The decision to engage the satellite has to be made before a precise prediction of impact location is available.

Contact with hydrazine is hazardous. Direct contact with skin or eyes, ingestion or inhalations from hydrazine released from the tank upon impact could result in immediate danger. If this operation is successful, the hydrazine will then no longer pose a risk to humans.

The U.S. government has been and continues to track and monitor this satellite. Various government agencies are planning for the reentry of the satellite. In the event the engagement is not successful, all appropriate elements of the U.S. Government are working together to explore options to mitigate the danger to humans and to ensure that all parties are properly prepared to respond. In the unlikely event satellite pieces land in a populated area, people are strongly advised to avoid the impact area until trained hazardous materials (HAZMAT) teams are able to properly dispose of any remaining hydrazine.