WASHINGTON — Raytheon Space and Airborne Systems was awarded a $46 million contract modification from the U.S. Air Force Research Laboratory to continue development of an infrared sensor intended for a missile warning system that may succeed the  over-budget and behind-schedule Space Based Infrared System (SBIRS) now in development.

The Air Force several years ago began planning for a so-called third-generation missile warning system even as it continued to fall behind on the development of SBIRS, a program dogged by technical troubles. Lockheed Martin Space Systems of Sunnyvale, Calif., is the prime contractor for the SBIRS program, which consists of dedicated missile warning satellites in geosynchronous orbits and payloads hosted on classified satellites in highly elliptical orbits. The program is more than $7.5 billion over its original cost estimate and its geosynchronous satellites are now more than eight years behind schedule.

Under a program called Third Generation Infrared Surveillance, El Segundo, Calif.-based Raytheon and McLean, Va.-based Science Applications International Corp. (SAIC) are designing and building sensors that could one day perform the missile warning mission. A portion of the SAIC-built sensor will be used in a demonstration when it is hosted on an SES Americom commercial communications satellite set to launch in 2010.

Raytheon delivered its sensor to the Air Force in March 2008. With the contract extension, the company will spend the next 25 months upgrading the sensor to a fully flight-qualified payload and putting it through environmental testing, Doug Marimon, Raytheon’s senior program manager for missile warning, said in an Oct. 29 interview. The Air Force has said it plans to conduct ground testing and algorithm development with the payload, but no plan to fly it in space has been announced.

The Raytheon design uses four infrared focal planes totaling 16 million pixels within a single telescope. This eliminates the need for some of the complex gimbals and steering mechanisms that other missile warning payloads use, Marimon said.

“That simplifies the assembly and test over competing designs, and it drives down cost by getting complexity out of the system,” he said. “It’s a single unblinking eye with a simple, scalable design that can be used for a variety of missions.”

But the Third Generation Infrared Surveillance program faces opposition from some in Congress who believe the Air Force should be focusing its resources on SBIRS. The Air Force requested $143.2 million for the program in 2010. While the Senate fully funded that request, the House of Representatives provided just $39.2 million for the program in its version of the defense appropriations bill. A conference to hammer out the differences between the two spending bills has not yet been scheduled.

Meanwhile, Lockheed Martin has begun a series of tests on the second geosynchronous SBIRS spacecraft that will establish a performance baseline before the craft enters environmental testing, the company announced Oct. 29. The first geosynchronous satellite is now in thermal vacuum testing and is scheduled to launch in 2011.