[SatNews] Lockheed Martin (NYSE: LMT) has received a $339.6-million contract option from the U.S. Navy for the fifth satellite in the Mobile User Objective System (MUOS) constellation.

MUOS will replace the current Ultra High Frequency Follow-On (UFO) system and provide assured communications, including simultaneous voice, video and data, for mobile warfighters. The first MUOS satellite is currently undergoing thermal vacuum testing at Lockheed Martin's facilities in Sunnyvale. One of the programs most critical milestones, the test will verify spacecraft functionality and performance in a vacuum environment where the satellite is thoroughly tested at the extreme hot and cold temperatures it will experience in space. The first MUOS satellite, along with the associated ground system, is scheduled for delivery in mid-2011. The second satellite is also proceeding steadily in the production flow. The team is preparing to mate the communications system module with the satellite's propulsion core, allowing the team to begin environmental testing of the fully integrated satellite in preparation for delivery in 2012.