By Irene Klotz

CAPE CANAVERAL, Fla. (Reuters) - A propulsion system problem has left a U.S. military communications satellite short of its intended orbit, leaving a key communications network over the Middle East, Africa and Asia without a spare, officials said on Tuesday.

The satellite, known as MUOS-5, is the second spacecraft built by Lockheed Martin Corp that has fallen short of its mission goals within the past two weeks.

On July 25, the military called off efforts to recover a Lockheed Martin weather satellite that had suffered a power system failure two years into its five-year design life.

Lockheed did not immediately respond to requests for comment.

The Mobile User Objective System, or MUOS, satellite was intended to serve as an on-orbit spare, so there is no immediate impact to operations, Steven Davis, spokesman with the Space and Naval Warfare Systems Command, said in a statement.

The four-member MUOS constellation provides ultra high frequency communications for the U.S. military over an area that includes Africa, the Middle East and Asia. The system works like a high-speed global cellular network for secure voice, data and video communications for mobile U.S. forces.

The $340 million spacecraft was successfully delivered into its initial orbit by a United Launch Alliance Atlas 5 rocket on June 24 and was expected to boost itself into a test location 22,000 miles (35,400 km) above Hawaii by July 3, Davis said. United Launch Alliance is a partnership of Lockheed Martin and Boeing.

Attempts to raise the satellite's orbit were halted on June 29, leaving the spacecraft in a highly elliptical, rather than circular orbit.

"The satellite remains in a stable intermediate orbit since experiencing the anomaly," Davis said.

Investigators traced the problem to a propulsion system failure, but Davis declined to release additional information about the problem, the satellite's current altitude and what options, if any, exist for using the satellite in its present orbit or changing the orbit.

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The satellite's onboard thrusters are built by Aerojet Rocketdyne Holdings Inc.

"The MUOS team is continuing to evaluate the situation, considering alternate orbit adjustment options, calculating mission impact and investigating all options before proceeding,” Davis said.

(Reporting by Irene Klotz; Editing by Sandra Maler)