MUOS-5 orbit raising problem identified as propulsion failure
The June 29 anomaly that halted the fifth Mobile User Objective System (MUOS-5) satellite from reaching its targeted geostationary orbit (GEO) has been determined to be due to an issue with the orbit raising propulsion system. The Navy, however, has not identified an exact cause for the failure.
MUOS-5 was successfully launched June 24 and placed into a geostationary transfer orbit (GTO) of 2,379 by 22,219 miles (3,829 by 35,758 kilometers) with an inclination of 19.1 degrees. Over the next couple of weeks, it was expected to use its onboard engines to circularize its orbit from its initial elliptical one. A total of seven burns were expected to take place to accomplish this task. About halfway through the planned series of burns, an anomaly halted this operation.
“The satellite remains in a stable intermediate orbit since experiencing the anomaly,” said Steven Davis of the U.S. Navy’s Space and Naval Warfare Systems Command. “The MUOS team is continuing to evaluate the situation, considering alternative orbit adjustment options, calculating mission impact and investigating all options before proceeding.”
This is the fifth satellite in the MUOS constellation and considered an on-orbit spare. The four other satellites are positioned equidistantly around Earth at GEO. Each has a single BT-4 main engine, which uses hydrazine fuel and nitrogen tetroxide. Additionally, for attitude control, the spacecraft are equipped with 18 monopropellant hydrazine thrusters.
The raising of MUOS-5’s orbit was originally expected to be completed by July 3 for the spacecraft to enter a test location approximately 22,300 miles (35,900 kilometers) above Hawaii. According to Spaceflight Now, since early July, hobbyist observers have reported the spacecraft to have a perigee of around 9,471 miles (15,242 kilometers) with an inclination of 9.8 degrees.
Davis said the delay in MUOS-5 reaching its test location has no impact upon current legacy or Wideband Code Division Multiple Access (WCDMA) satellite communications.
“MUOS-1 through MUOS-4 are in orbit and are currently supporting operations via their legacy payloads, providing UHF satellite communications for the Department of Defense,” Davis said.
If the spacecraft can be deemed able to continue raising its orbit, the vehicle will ultimately be circularized at GEO with an inclination of 5 degrees. After initial tests, it will then be maneuvered to a position near MUOS-4, over the Pacific Ocean.
Users of the MUOS system are able to connect with “smartphone-like” capabilities, which includes voice, text, video, and data transmission on a high-speed Internet Protocol-based system.
Each of the five MUOS satellites was built by Lockheed Martin. They have a 14-meter-diameter reflecting mesh antenna and are equipped with both WCDMA and UHF supporting hardware.
Derek Richardson has a degree in mass media, with an emphasis in contemporary journalism, from Washburn University in Topeka, Kansas. While at Washburn, he was the managing editor of the student run newspaper, the Washburn Review. He also has a website about human spaceflight called Orbital Velocity.