Air Force Devises Backup Plan to Salvage Ailing Satellite
WASHINGTON — A propulsion system glitch aboard the U.S. Air Force's first Advanced Extremely High Frequency secure communications satellite has forced the service to devise a new orbit-raising plan utilizing smaller thrusters that will delay the craft's arrival at its operating orbit by six months to seven months, according to a service official.
The satellite's operational service life is not expected to be reduced as a result of the revised plan, said Dave Madden, director of the Air Force's Military Satellite Communications Systems Wing.
After years of delay, the Air Force on Aug. 14 launched AEHF-1 aboard an Atlas 5 rocket, which placed the satellite into an elliptical orbit ranging in altitude from 230 kilometers at perigee to 36,000 kilometers at apogee as planned, Madden said during an Aug. 30 media briefing. [Photo of the Atlas 5 rocket launch.]
Ground controllers initiated the orbit-raising sequence Aug. 15, but the hydrazine engine automatically shut down when an anomaly was detected, Madden said. Operators tried the maneuver two days later with the same result, and the engine is now considered a failure, Madden said.The deployment mission profile called for the satellite to then use its hydrazine-fueled liquid apogee engine to climb to an altitude of 19,000 kilometers at perigee over a span of 30 days. Then the satellite's electronic thrusters were to fully circularize the orbit over another 90 days.
The Air Force Space and Missile Systems Center, Aerospace Corp., and AEHF prime contractor Lockheed Martin Space Systems developed a backup plan to use one of the satellite's other propulsion systems to get it to its proper orbit, albeit later than planned, Madden said. The satellite has another propulsion system that is fueled by the same tank as the liquid apogee engine but produces only one-twentieth of the thrust. Engineers believe this system can be used to boost the spacecraft to 19,000 kilometers at perigee in seven months to eight months, Madden said.
Operators began executing the plan Aug. 29, firing the smaller thrusters for 40 minutes and raising the satellite's perigee to 950 kilometers. It was essential to raise the satellite as quickly as possible because it was losing about 2.5 kilometers of altitude per day because of atmospheric drag and the spacecraft had already had to be maneuvered to dodge an oncoming piece of debris, Madden said.
AEHF-1's revised orbit-raising plan will not consume any more fuel than the original plan, meaning the satellite is still expected to operate for 14 years as designed. However, the Air Force could decide it needs to have AEHF-1 in service sooner than now scheduled, and accelerating the orbit-raising sequence would burn more fuel and reduce the satellite's useful life, Madden said.
The Air Force has not yet identified the cause of the engine failure and hopes to do so within a month, Madden said. This is a critical step because the second AEHF satellite is slated for launch in February and it may require new hardware or additional testing, Madden said. If the launch of AEHF-2 is delayed significantly, finding a new slot on the Air Force's manifest could be difficult, Madden said. The service plans to launch the first Space Based Infrared System missile warning satellite right after AEHF-2, and NASA has reserved more than three months on the range starting in August to launch the Juno mission to Jupiter and the $2.5 billion Mars Science Laboratory.
The Air Force plans to buy four AEHF satellites from Sunnyvale, Calif.-based Lockheed Martin Space Systems at a total cost of $9.9 billion. The company may incur some financial penalty as a result of the AEHF-1 problem, but Madden said he could not yet provide specifics.