The Pentagon says it can confirm that the operation to destroy a disabled spy satellite with a missile fired from Earth was a success.
Officials said they were also confident that a hazardous fuel tank on board the craft - USA 193 - was destroyed.
The missile was fired from a warship in waters west of Hawaii last week.
Operatives had only a 10-second window to hit the satellite which went out of control shortly after it was launched in December 2006.
Officials were worried its hydrazine fuel could pose a deadly threat to humans if the craft was left to crash into the Earth.
Graphic of how the satellite was hit
"By all accounts this was a successful mission," said Gen James E Cartwright, vice-chairman of the Joint Chiefs of Staff.
BROKEN SATELLITE
Owner: National Reconnaissance Office
Mission: Classified
Launched: 14 Dec 2006
Weight: 2,300 kg (5,000lbs)
1,134kg (2,500lbs) could survive re-entry
Carrying hydrazine thruster fuel
"From the debris analysis, we have a high degree of confidence the satellite's fuel tank was destroyed and the hydrazine has been dissipated."
The Pentagon statement said a modified tactical Standard Missile-3 (SM-3), was fired from the USS Lake Erie.
Tracking debris
US space specialists continue to track less than 3,000 pieces of debris from the destroyed satellite, all smaller than a football.
The statement said most of the debris had already re-entered the Earth's atmosphere or would do so in the coming days and weeks.
Officials said there had been no reports of debris landing on Earth and it was unlikely any would remain intact to hit the ground.
The controversial operation was criticised by China and Russia. Russia suspects the operation was a cover to test anti-satellite technology under the US missile defence programme.
The US denied the operation was a response to an anti-satellite test carried out by China last year, which prompted fears of a space arms race.
Toxic satellite mission 'success'
Meteor Showers
2008 Meteor Showers
Meteor Shower Best Date Constellation to
look towards ZHR Originates From
Quadrantids January 4 Bootes 120 not known
Lyrids April 22 Lyra 20 Comet Thatcher
Pi-Puppids April 23 Puppis variable not known
Eta-Aquarid May 5 Aquarius 60 Halley's Comet
June Bootids June 27 Bootes variable not known
South.Delta-Aquarids July 28 Aquarius 20 not known
Perseids August 12 Perseus 90 Comet Swift-Tuttle
Aurigids September 1 Auriga variable not known
Draconids October 8 Draco variable not known
Orionids October 21 Orion 20 Halley's Comet
S. Taurid November 5 Taurus 10 not known
N. Taurid November 12 Taurus 15 not known
Leonids November 17 Leo 15 Comet Temple-Tuttle
Alpha-Monocerotids November 21 Monoceros variable not known
Dec Phoenicids December 6 Phoenix variable not known
Puppid/Velids December 6 Puppis 10 not known
Geminids December 13 Gemini 120 Asteroid 3200 Phaethon
Ursid December 22 Ursa Minor 10 not known
Space War: Satellite 'Kill' Would Prove U.S. Capability
The looming U.S. Navy attempt to shoot down a dying satellite could demonstrate an anti-satellite capability for its missile defense system.
A successful kill would mark the first time the United States uses a tactical missile to destroy a spacecraft — assuming that the ship-based missile defense system can handle the high closing speed of more than 22,000 mph.
"Everything becomes much more stressful at these large closing speeds," said Geoffrey Forden, MIT physicist and space expert. "But if they do hit it, that'd be very impressive, and that'd be proof that it has ASAT [anti-satellite] capability."
How it would work
The Navy looks to rely on its Aegis Ballistic Missile Defense System based on U.S. cruisers and destroyers, which was developed to protect U.S. forces and allies against short- and medium-range ballistic missiles. The interceptors rely on kinetic energy from their combined mass and speed to smash into their targets.
Three naval ships stand ready in the North Pacific Ocean to each take a shot with a modified Standard Missile-3 (SM-3). If the first attempt misses, the other two ships can take turns as backups.
The modified SM-3 interceptors will supposedly be able to identify the falling U.S. spy satellite based on changes in their targeting software. However, Forden expressed caution as to whether the Aegis system can score a successful satellite kill at such high closing speeds — previous tests involved much slower-moving targets.
"I'll be very surprised if it works," Forden said, pegging the chances at "less than 50-50."
The United States has managed to take out satellites with other weapon systems in the past. An F-15 Eagle fired a missile-launched kill vehicle that struck and destroyed a target satellite in 1985. SPACE.com's Leonard David also noted a 1986 "Star Wars" test by the Strategic Defense Initiative Organization involving the first space-to-space intercept of a target.
Not alone
The United States is not alone in its anti-satellite tests. China used a missile to shoot down an old weather satellite a year ago, leaving a cloud of debris that will present a low-risk threat to other satellites and space missions for up to 20 years.
A U.S. intercept of its falling spy satellite would happen low enough to avoid debris endangering the International Space Station, and would only occur after space shuttle Atlantis has safely landed.
Success for the United States would boost the perceived capabilities of the Aegis system, but could also heighten international concern over U.S. missile defense systems being used to target satellites.
"All along, other countries have said missile defense has offensive capabilities, and in fact is better suited for such," noted Joan Johnson-Freese, Naval War College security expert, in an e-mail to SPACE.com. "While the U.S. has ignored/downplayed those concerns, this test will basically prove that those concerns were valid."
Senior U.S. officials apparently tried to allay such concerns at the Feb. 14 press briefing by emphasizing that the missile modifications would be difficult to make on a fleet-wide basis.
Concerns remain
Yet Johnson-Freese also observed that the U.S. Navy's three potential attempts "equates to lots of target practice — without international condemnation," because the U.S. has declared the falling satellite a threat to public safety. That still has not prevented China and Russia from expressing their concerns.
Forden pointed out that the U.S. interception attempt could also help legitimize the earlier Chinese anti-satellite test which was heavily criticized by the U.S. and other countries. Setting a precedent now could open the door for future anti-satellite tests by other countries, added Johnson-Freese.
A slight chance also exists that China might be tempted to test its proven anti-satellite capability again, should the U.S. attempts fail to destroy the falling satellite.
"China has said it would take preventive measures, and that's the only thing that makes sense," Forden said.
