Lockheed Martin Space Systems of Sunnyvale, Calif., has won a $58 million contract modification from the U.S. Air Force to support the launch and test of missile warning satellites and sensors as part of the Space Based Infrared System (SBIRS) program, the Pentagon said Jan. 29.

The modification covers the fourth in a series of SBIRS sensors hosted aboard classified satellites operating in highly elliptical orbit, as well as the fourth dedicated SBIRS satellite, which will operate in geosynchronous orbit, Lockheed Martin spokesman Michael Friedman said via email.

Friedman said the dedicated satellite, known as GEO-4, is on schedule for launch in 2015. The elliptical-orbit sensor is slated for delivery to its host satellite that same year, he said.

To date, one dedicated satellite and two elliptical-orbit sensors have been launched as part of the SBIRS program. Friedman said the third elliptical-orbit sensor is slated for delivery to its host satellite this year.

In a separate Jan. 31 notice, the Pentagon said the Air Force was awarding Lockheed Martin a $68.8 million contract for on-orbit support of the GPS satellite constellation.