WASHINGTON (CNN) -- The U.S. military may try within days to shoot down a failed satellite using a missile launched from a Navy ship, officials announced Thursday.
A Delta II rocket lifts off in December, carrying a reconnaissance satellite that failed hours later.
Gen. James Cartwright, vice chairman of the Joint Chiefs of Staff, told reporters at the Pentagon that the window to accomplish the mission could begin in three to four days, and remain open for seven to eight.
While much space trash and debris have safely crashed to Earth after burning up in the atmosphere on re-entry, authorities said what makes this 5,000-pound satellite different is the approximately 1,000 pounds of frozen toxic hydrazine propellant it carries.
Without any intervention, officials believe the satellite would come down on its own in early March.
If it came down in one piece, nearly half the spacecraft would survive re-entry and the hydrazine -- heated to a gas -- could spread a toxic cloud roughly the size of two football fields, Cartwright said. Learn more about the shoot-down mission »
Hydrazine is similar to chlorine or ammonia in that it affects the lungs and breathing tissue, the general said.
The option of striking the satellite with a missile launched from an Aegis cruiser was decided upon by President Bush after consultation with several government and military officials and aerospace experts, said Deputy National Security Adviser James Jeffrey.
"After further review of this option and, in particular, consideration of the question of saving or reducing injury to human life, the president, on the recommendation of his national and homeland teams, directed the Department of Defense to carry out the intercept," Jeffrey said.
The goal is to hit the satellite just before it enters Earth's atmosphere and blast it apart so that the hydrazine tank explodes. The smaller debris would be more likely to burn up in the atmosphere.
NASA Administrator Michael Griffin said there's nothing the military can do to make the outcome worse.
"If we miss, nothing changes. If we shoot and barely touch it, the satellite is just barely in orbit" and would still burn up somewhat in the atmosphere, Griffin said.
"If we shoot and get a direct hit, that's a clean kill and we're in good shape," he added.
Experts said that with three-quarters of Earth covered in water, there's a 25 percent chance the satellite's remnants will hit land -- and a 1 percent chance they will hit a populated area.
There will be three Navy ships involved in the operation. The USS Lake Erie, an Aegis cruiser, will fire the missile, while trajectory information comes from a second ship. The third ship will be used as a backup, U.S. Navy officials said.
The Lake Erie has long been used as the platform for the sea-based missile defense program.
Cartwright said the satellite stopped working within hours of its launch in December and has not responded to attempts to communicate with it. He brushed off blog theories that the military wants to shoot down the satellite with a missile to destroy any classified data it may have accumulated in its short life, or to prevent other countries from acquiring the technology.
In January 2007, China used a land-based missile to destroy a 2,200-pound satellite that was orbiting 528 miles above Earth.
But the impact left more than 150,000 pieces of debris floating above Earth, NASA estimates. The space agency characterizes nearly 2,600 pieces as "large," meaning greater than 4 inches across, which pose a potential threat to satellites and spacecraft.
China is responsible for 42 percent of all satellite debris in orbit as of January 1, most of it from that Fengyun-C meteorological satellite.
NASA has called it the worst satellite breakup in history. E-mail to a friend
CNN's Mike Mount and Kate Tobin contributed to this report.
All About The Pentagon • U.S. Navy
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.