WASHINGTON — Two U.S. missile tracking demonstration satellites in June successfully detected and tracked three missiles in the early stages of flight, and later this year will attempt to track missiles as they coast through space following motor burnout.

The Pentagon for decades has operated infrared satellites able to detect potentially threatening missile launches worldwide, but these satellites are only to track missiles in the early boost phase of flight, when their motors produce a significant heat signature. The experimental Space Tracking and Surveillance System (STSS) satellites, on the other hand, are intended to demonstrate so-called birth-to-death missile tracking. As part of a proposed operational constellation, these kinds of satellites would be an important cuing tool for missile defense systems.

After years of delay, the STSS satellites, built by Northrop Grumman Aerospace Systems of Los Angeles, were launched into low Earth orbit last September. The spacecraft were initially dogged by attitude control problems, and on-orbit checkout took longer than anticipated. The satellites’ acquisition sensors, used for initial detection and tracking of missile launches, completed calibration in May, and the satellites observed three U.S. missile tests in June, Debra Christman, a spokeswoman for the U.S. Missile Defense Agency (MDA) said in a July 16 e-mail.

On June 6, the twin STSS satellites observed the debut of the MDA’s two-stage interceptor for the Ground-based Midcourse Defense system as it lifted off from Vandenberg Air Force Base, Calif., and flew over the Pacific Ocean, Christman said. Ten days later, they observed an ICBM test launched from the same location. On June 28, the satellites observed a target missile that was launched from a mobile platform in the Pacific Ocean as part of a test of the Terminal High Altitude Area Defense system.

The data gleaned from the tests have been remarkable, said Gabe Watson, Northrop Grumman’s vice president of missile defense and missile warning programs.


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“These tests in June, the results are outstanding,” Watson said in a July 21 interview. “There were some folks out there who were thinking these things would be launched and never work. We’ve seen that in the press, even.

“I’m really excited that we’re providing objective evidence that this STSS demonstration system is not only working, but if the acquisition sensor data is any kind of leading indicator of what the integrated acquisition and track sensor performance is going to be, this will be revolutionary for the ballistic missile defense system.”

In addition to the acquisition sensors used in the June flight tests, the spacecraft are outfitted with tracking sensors that are still undergoing calibration, Watson said. It is these tracking sensors that will attempt the most difficult part of the demonstration: tracking missiles that have gone cold after their propulsion systems  have shut off. In theory, the low-orbiting STSS craft will be able to track these cold missile bodies against the colder background of deep space.

Calibration of the tracking sensors is nearly complete, and plans call for using them to observe missile flights starting later this year, Watson said.

Last year, the MDA overhauled its entire ballistic missile defense test program, eliminating launches dedicated to the STSS demonstration. The satellites will instead take part in tests with other primary objectives, such as intercept tests involving the emerging U.S. ballistic missile defense system — assuming they are in position to observe these flights when they take place.

The MDA plans to conduct an intercept test of the Airborne Laser Test Bed late this year, and tests of the Aegis Ballistic Missile Defense and Ground-based Midcourse Defense systems early next year, MDA spokesman Rick Lehner said July 22. The satellites may also be used to track the space shuttle and possibly even jet aircraft, Watson said.

Northrop Grumman hopes its work on the STSS satellites will give the company a leg up in the MDA’s planned competition to build an operational constellation of missile tracking satellites. MDA has tapped the Johns Hopkins University Applied Physics Laboratory in Laurel, Md., to lead a prototyping effort for the new Precision Tracking Space System. As many as five industry teams may be chosen in 2011 to provide input for the system’s design.