ASAT Missile Hits Satellite Target
The U.S. Navy fired a missile just after 10:30 p.m. EST on Wednesday evening, and hit the target of the defunct spy satellite, which was 130 miles above the Pacific Ocean. "The missile's been launched and (it was) a successful intercept," a Pentagon source said. There was no immediate word on whether the fuel tank had been shattered as officials had hoped.
Having lost power shortly after it reached orbit in late 2006, the satellite, known as US 193, was out of control and well below the altitude of a normal satellite. The Pentagon had planned to hit it with an SM-3 missile (Standard Missile-3, built by Raytheon Co.) just before it re-entered Earth's atmosphere.
Challenge of Closing Speed
The high closing speed of more than 22,000 mph may have been a challenge for the Aegis Ballistic Missile Defense System, the combat system built by Lockheed Martin Corp. with powerful computers and radar that detect and track the satellite as it rises above the horizon. All previous tests have involved slower-moving targets.
Challenge of Lack of Heat Signature
The homing system would normally use infrared radiation (heat) to guide the missile to the satellite, but this defunct satellite was not emitting much heat. So the Navy quickly adapted the targeting software for the SM-3 missile interceptors to respond to lower levels of heat emission.
Specifically, the satellite has no heat-generating propulsion system on board, making it more difficult for the missile's heat-seeking system to work. The satellite would have had a heat infrared signature only from the heat of the sun, reduced from what it would be if it were operational. The launch occurred after the spacecraft had been warmed by its transit through daylight.
This hit marks the first time the U.S. has used a tactical missile to destroy a spacecraft, and the fastest target ever hit by the military.
Unlike China’s ASAT Test, Debris Insignificant from U.S. Navy ASAT Missile
Debris in Low Earth Orbit will not be significant, unlike debris from the Chinese ASAT test in January 2007. U.S. Marine Corps Gen. James Cartwright, vice chairman of the Joint Chiefs of Staff, said the intercept would take place at a low enough altitude to minimize orbital debris. Cartwright, along with NASA Administrator Mike Griffin, said that well over 50 percent of the debris from a successful intercept will re-enter and burn up in the atmosphere within two orbits, or 10-15 hours, while the remainder would come down within a matter of weeks. Satellites typically operate at altitudes higher than this debris is expected to reach.
The Chinese ASAT test occurred at an altitude of some 528 miles/850 km and much of the resulting debris will remain in orbit for 20 or more years. The international space station orbits Earth at an altitude of around 199 miles/320 km.
Theresa Hitchens, Director of the World Security Institute's Center for Defense Information, stated in an email to Imaging Notes, "The very low altitude of intercept means that most of the debris will fall very quickly (hours/days) and the chances of creating high velocity debris that kicks out to higher orbits is small. It is not in any way as irresponsible as the Chinese test, which took place at a crowded altitude that is already heavily polluted and where debris will remain for decades. There is no comparison."
She continued, "On the other hand, there is some concern among experts that our debris and impact models may not be as accurate as we had thought – given that the NASA debris model underestimated the amount of debris likely from the Chinese test. The bottom line is that the chances of creating debris that would pose a danger to the International Space Station or Low Earth Orbit sats is probably quite small; it is not non-existent."
Hitchens authored a story about debris from China's ASAT test from January 2007 in the Summer 2007 Imaging Notes:
Code Red? Chinese ASAT Test Raises Debris Threat to EO Sats
Politically, this act may have negative ramifications. Ray Williamson, Executive Director of the Secure World Foundation and Editor of Imaging Notes, stated, "I fear that using a ballistic missile in this manner after the United States roundly chastised the Chinese government for its anti-satellite (ASAT) test just over a year ago sends completely the wrong message to the world community."
Animation Video of Hit
An animation of the missile hitting the satellite, the impact and the debris statistical distribution is available through the following link:
Click here to see the animation.