Lockheed Martin Space Systems said Sept. 6 it has completed thermal vacuum testing of the U.S. Navy’s first Mobile User Objective System (MUOS) satellite, putting the behind-schedule spacecraft on pace to launch during the first quarter of 2012.

“Thermal vacuum testing of the first MUOS satellite was completed later than originally planned as the team worked to validate the performance of this state-of-the-art spacecraft,” Lockheed Martin said in a press release. “While issues with specific legacy payload components were encountered during the test, Lockheed Martin was able to resolve each issue prior to completing thermal vacuum testing and entering final integration system testing in preparation for delivery.”

Lockheed Martin was awarded a $2.1 billion contract in September 2004 to build the first two MUOS satellites; options for three additional satellites boosted the total potential value to $3.26 billion. The fifth satellite in the series, which is intended to replace the Navy’s aging Ultra High Frequency Follow-On constellation, was ordered in February.

The program has encountered multiple delays, putting launch of the first satellite roughly two years behind schedule. Navy officials said last year they expected the first MUOS satellite to launch this September and enter service before the end of 2011.