The U.S. Department of Defense said its officials believe a missile hit a stray spy satellite and destroyed its hydrazine tank last week.
The Defense Department said that analysis of the debris shows that the satellite's tank was destroyed by a missile last week, reducing or eliminating the risk that hydrazine would pose a threat to humans. Defense decided to shoot down the satellite, which failed to function soon after its launch in December 2006. Experts believed the satellite would fall to Earth by early March if no action was taken.
Since the satellite's communications system failed, no one could control exactly where or when it would land. Though military leaders had first indicated that falling debris posed little threat to humans, they later determined that a 1,000 pound tank of hydrazine fuel could pose a threat if the fuel landed in populated areas.
A modified tactical Standard Missile-3 fired from the USS Lake Erie hit the satellite and it appears the tank exploded.
Military officials said observers at Vandenberg Air Force Base, Calif., are tracking less than 3,000 pieces of debris, and that all pieces are smaller than a football.
"The vast majority of debris has already re-entered or will shortly re-enter the Earth's atmosphere in the coming days and weeks," the Pentagon said in a statement. "To date, there have been no reports of debris landing on Earth and it is unlikely any will remain intact to impact the ground."
U.S. Strategic Command continues to monitor the debris and will issue notifications if it creates any ground or orbital risk.
"By all accounts this was a successful mission. From the debris analysis, we have a high degree of confidence the satellite's fuel tank was destroyed and the hydrazine has been dissipated," Gen. James E. Cartwright, vice chairman of the Joint Chiefs of Staff, said in a statement released Monday. "The successful satellite engagement was truly a collaborative effort from across the U.S. government, the armed forces, industry, and academia working together to reduce the risk to human life."