The Mobile User Objective System satellite now will enter its first system checkouts before moving on to an environmental test.
The MUOS craft will support the military's UHF satellite communications by providing warfighters on the move with assured communications that include simultaneous voice, video and data.
Lockheed Martin is under contract to deliver five MUOS satellites.
The first MUOS satellite and associated ground system already provide legacy UHF communications capability. The second has finished system testing and will be launched in July. The third is progressing through environmental testing.
There are four satellites plus an on-orbit spare.
"MUOS-4 is gleaning the benefits of the lessons learned from the first three vehicles," said Iris Bombelyn, vice president of Lockheed Martin's Narrowband Communications mission area. "We continue to focus on reducing risk, maintaining efficient operations and delivering a flawless vehicle to our customer.
"Our execution on the ground is complemented by our performance on orbit, where our first satellite is already in position and performing exceptionally.
The multi-beam assembly, which is connected to the communications module, carries 16 ultra-high frequency antennas for distributed communications coverage.