Reuters February 21, 2008
Spy satellite poses challenges
Shooting down an errant US spy satellite hurtling through space with a tank of toxic fuel presents a challenge for a Navy defence system designed to take out slower, lower-flying ballistic missiles, officials say.
In an operation that could last just minutes from launch to intercept, Navy officials hope a missile fired from a ship and travelling at six times the speed of sound will hit the bus-sized satellite about 220 kilometres above Earth with a nonexplosive "kinetic kill vehicle."
The Aegis ballistic-missile defence system has successfully intercepted incoming missiles in 12 of 14 test flights, according to a Navy document.
That is an 85.7% success rate for a system that uses infrared sensors to search for a missile-shaped target heated by its supersonic travel through layers of atmosphere.
But the satellite, which became disabled soon after its 2006 launch, is flying dead in space, generating no heat. It is also moving faster than the missile system's usual target at 8-10 km per second or up to 35,000 kilometres per hour.
At 2,270 kilograms, the USA 193 satellite is a much bigger target than a ballistic missile's warhead. But officials say the Navy will try to strike the fuel tank to destroy its nearly 450 kilograms toxic payload of unspent hydrazine fuel.
The Navy appeared to sound a note of caution this week.
"Certainly, we're looking for a successful mission. But that, in and of itself, is a high achievement," a Navy official told reporters at a briefing.
High confidence
Senior Pentagon officials have expressed high confidence in the mission. Independent experts also say the Navy has a good chance of destroying the satellite with one missile.
David Mosher of the Rand Corp said the military would carefully select the time of the intercept to maximize its chance of success and minimize the risk to populations below.
"This thing's going several times faster than any target they've tested the system against. But it's also many times bigger than targets they've tested against," said John Pike of the on-line think-tank GlobalSecurity.org.
Sometime in the next 10 days or so, the Navy will launch a three-stage missile from the guided-missile cruiser USS Lake Erie in the Pacific Ocean, with its targeting software altered to look for the satellite instead of an incoming missile.
Another guided missile cruiser, the USS Decatur, will be on hand for a possible second shot if the first attempt fails.
Once above the atmosphere, the Navy said the missile's kinetic warhead will open its infrared "eyes," scan for the satellite and alter course to intercept it just beyond the system's usual 110-120 kilometres altitude range.
The Navy will rely on the heat of the sun to warm the satellite's cold body to a temperature that can be picked up by the warhead's sensor. The launch is expected near sunset in the Pacific, after the spacecraft has been warmed by its transit through daylight.
Analysts say the altitude should allow debris from the collision to fall from space within days or weeks, limiting the risk of possible damage to other space vehicles. The plan is for the debris to fall over open ocean and alerts have been issued to shipping traffic.
Once the warhead finds the satellite, its infrared sensor will try to aim directly for the fuel tank and could transmit a video image of the approach to the point of collision back to Navy officials on Earth.
The system would then scan the collision's debris field to determine the success of the strike. If the missile misses its target, it will continue travelling into space.
© Copyright 2008, Reuters
