Lockheed Martin has completed thermal vacuum testing on the fourth satellite scheduled to launch and join the U.S. Navy's Mobile User Objective System (MUOS) constellation. This milestone comes just weeks after the company shipped the third MUOS satellite to Cape Canaveral Air Force Station in anticipation of its January launch.

MUOS operates like a smart-phone cell tower in the sky, vastly improving current secure mobile satellite communications for warfighters on the move. For the first time, MUOS Wideband Code Division Multiple Access technology users will have beyond-line-of-sight capability to transmit and receive voice and data using an Internet Protocol-based system.

The launch of this next satellite, designated MUOS-4 by the Navy and expected in the second half of 2015, will complete the operational constellation and provide global coverage.

"The successful completion of thermal vacuum testing assures that MUOS-4 can endure the extreme hot and cold temperatures it will experience throughout its on-orbit mission life," said Iris Bombelyn, vice president of Lockheed Martin's Narrowband Communications mission area.

"The delivery of this fixed price vehicle shows a clear advantage for block buys to drive down defects and maintain low costs through learning curve advantages."

Completed November 12, thermal vacuum testing was conducted inside the Dual Entry Large Thermal Altitude chamber at Lockheed Martin's Sunnyvale, California satellite integration facility. MUOS-4 now proceeds to final integrated system testing prior to launch later next year.

Lockheed Martin is currently under contract for five MUOS spacecraft. On Nov. 5, MUOS-3 was shipped to Cape Canaveral Air Force Station, Florida in support of a January launch. MUOS-2 was launched and handed over to the Navy for operations in 2013. MUOS-1 was launched and became operational in 2012. MUOS-5 is expected to launch in 2016.