Tracking Missiles in Stereo

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WASHINGTON — If names made any difference, the Pentagon’s Brilliant Eyes missile defense venture would have been a shining success.

But that 1980s Star Wars offshoot flopped in 1994, and it took 15 more years and a program with the plain-Jane name of STSS to finally launch a pair of smart missile-tracking satellites.

The two STSS — Space Tracking and Surveillance System — satellites went into low Earth orbit Sept. 25. They fly in tandem about 1,350 kilometers above the Earth and a couple thousand kilometers apart. In that configuration, they provide a stereo view of the missiles and warheads they track.

If they perform as planned, the pair will be able to detect missile launches and then track the missiles and their warheads through the boost, midcourse and terminal phases of flight.

No other sensor system can do that, said Gabe Watson, STSS program manager for the satellites’ contractor, Northrop Grumman Aerospace Systems of Redondo Beach, Calif. The satellites and a ground-based computer also are designed to quickly tell warheads from decoys.

Each satellite has two sensors. First, an acquisition sensor detects the short-wave infrared signature produced by the hot exhaust of a missile launch. As the missile passes through boost phase, the second sensor takes over using midwave infrared to track upper stages of rockets and the small engines of post-boost vehicles.

Finally, the sensor uses long-wave infrared to continue tracking as the missile and warheads enter the midcourse of their trajectory.

This is the most difficult part of the tracking task. Rocket motors have shut down and there are no bright infrared signatures to focus on. The satellites must be able to spot cold objects coasting through cold space. The sensors they use are sensitive enough to detect objects that are just a few degrees above the absolute zero of space, Watson said.

While tracking, the satellites transmit data about their targets to a Missile Defense Integration and Operations Center at Schriever Air Force Base, Colo. There, a mission data processor combines data from both satellites to produce a stereo or 3-D picture of the incoming missile.

The mission data processor also uses the satellite data to distinguish warheads from decoys, Watson said.

As it is processed, the tracking information is fed to ground-based radars, enabling them to quickly zero in on incoming missiles and warheads so that missile interceptors can be launched to destroy them.

“The ability to do cold-body tracking and ground-data processing is unique. It’s a first for the country,” Watson said.

The objective of STSS is to substantially shorten the time it takes to target and destroy incoming warheads. However, citing the sensitivity of the information, Watson declined to say how quickly after a launch the STSS could provide accurate targeting data for an interceptor launch.

The two STSS satellites in orbit are demonstrators intended to work for two to four years, long enough to find out whether the STSS concept will work.

Missile Defense Agency officials said they will spend the next six months checking out the satellites before testing them against dedicated targets and targets of opportunity.

An STSS that can detect and track missile launches worldwide would require a constellation of 18 to 30 satellites. The U.S. Defense Department has not yet decided whether to build such a system.

For now, the United States relies on Defense Support Program (DSP) satellites to detect missile launches. Twenty-three DSP satellites have been launched since 1970, and six to 10 are believed to still be working.

But those are missile-warning satellites only, Northrop spokesman Bob Bishop said. They cannot track missiles through their full trajectory, as STSS is expected to do. It has been a long struggle to get the two STSS satellites into space.

Their ancestor, Brilliant Eyes, was conceived in the mid-1980s but canceled in 1994 after the threat of Soviet missile attacks subsided. It was replaced with a similar but scaled-down program called the Space Based Infrared System-Low.

SBIRS-Low was killed in 2002 after estimated costs escalated from $10 billion to $23 billion, and schedule and performance problems cropped up. STSS was created from SBIRS-Low’s ashes, and Northrop was awarded an $869 million contract to salvage two SBIRS-Low demonstration satellites. Those are the two now in orbit.

STSS has had problems of its own. Launches scheduled in 2006 and 2007 were scrubbed because of technical difficulties. A launch finally scheduled for last April was then delayed until September.

The delays were caused by production, integration and testing snags, Watson said. Such delays are not unusual, he said. “These were first-of-a-kind systems. There is no other capability like this.”