Lockheed Martin has adjusted the production schedule for the U.S. Navy's third Mobile User Objective System satellite, shuffling it behind a fourth spacecraft in the five-member fleet after testing uncovered a workmanship issue with the satellite's UHF communications payload, a company official said Wednesday.

Two MUOS satellites in the Lockheed Martin factory in Sunnyvale, Calif. Photo credit: Lockheed Martin
 
The launch of the the MUOS 3 spacecraft was expected in mid-2014 before engineers discovered the payload issue. Lockheed Martin, the Navy's prime contractor for the MUOS program, has accelerated preparations for launching the constellation's fourth spacecraft, according to Mark Valerio, vice president of the company's military space division.

"We found an anomaly with a component in thermal vacuum testing, so we took out of the assembly line," Valerio told Spaceflight Now at the Satellite 2014 conference in Washington.

The suspect component was in the satellite's legacy UHF communications payload, one of two systems carried aboard MUOS satellites to route narrowband voice and data messages between U.S. troops on ships, submarines, airplanes, land vehicles and on foot with handheld terminals.

Valerio declined to say which component showed problems during the thermal vacuum test, which exposes the spacecraft to the temperatures and vacuum conditions it will see in space.

Prepared testimony by the Navy's top space official Wednesday to the strategic forces subcommittee of the Senate Armed Services Committee indicated the problem was rooted in an "insufficient solder volume during the production of the output multiplexer."

The Navy expects no impact to the program's multibillion-dollar budget or delays in completing the deployment of the five-satellite fleet, according to John Zangardi, deputy assistant secretary of the Navy for command, control, communications, computers, intelligence, information operations and space.

Describing the problem as a workmanship issue, Valerio said engineers are sure the issue does not affect other MUOS spacecraft already in orbit or on the ground.

The legacy UHF payload, provided by Boeing, is compatible with existing ground terminals designed to receive and transmit signals through the Navy's UHF Follow-On satellite system, which MUOS was established to replace.

Artist's concept of a MUOS satellite in orbit. Photo credit: Lockheed Martin
 
The next launch of a MUOS satellite is now scheduled for January 2015, and Valerio said the Navy has not decided whether to launch the troubled third MUOS satellite fourth in line or aboard the fifth MUOS launch.

The Navy's new-generation mobile telecom system is set to include four operational satellites, while the fifth craft will serve as an in-orbit spare.

The most powerful configuration of United Launch Alliance's Atlas 5 rocket family is used to launch the MUOS satellites, which weigh nearly 15,000 pounds fueled for liftoff, above the capacity of any other U.S. launcher besides ULA's Delta 4-Heavy rocket.

Featuring giant unfurlable mesh antennas, the MUOS satellites also host modernized wideband code division multiple access payloads to offer users cellphone-like services comparable to 3G technologies in the civilian sector.

The first two MUOS satellites launched in February 2012 and July 2013 are performing well in orbit, according to Lockheed Martin.

Follow Stephen Clark on Twitter: @StephenClark1.