USAF: AEHF-1 Engine Failure An Anomaly

Preliminary findings of an investigation into a malfunction on the Pentagon’s newest communications satellite, worth more than $2 billion, indicate that an onboard engine failure was an anomaly and not the result of a design failure. This is clearing the way for the second of the Advanced Extremely High Frequency (AEHF) satellites to be slated for launch as early as March 2012. AEHF-1’s liquid apogee engine (LAE), which was designed by IHI Aerospace of Japan, failed to fire as planned, leaving the spacecraft in a low orbit. The LAEs, however, performed as expected, and the culprit could be a problem in the fuel system feeding those engines. “It was a unique issue to Vehicle 1. It was a manufacturing issue in the propulsion system,” says David Madden, director of the U.S. Air Force’s Military Satellite Communications directorate here. “When you do a lot to a system over a long period of time you potentially induce issues. . .This was an issue of a vehicle that was being worked on over a 10-year period of time.” Madden says the problem was with “workmanship”, but declined to identify the root cause because the findings haven’t yet been fully disclosed to the Air Force’s top leaders. AEHF-1 is now in the midst of a long-duration orbit-raising process. This process is on a revised schedule to place the satellite in its operational orbit at 68-deg. West by next summer. This alternate path was the result of a serendipitous pre-launch decision and the output of a collaboration among the top orbital mechanics specialists in the country. Six 5-lb. thrusters on the reaction engine assembly were used to lift the satellite beyond the atmosphere. Now, zenon-fueled, electric ion thrusters, also called Hall Current Thrusters (HCTs), are being fired for about 10 hr. per day (during a 17-hr. orbit). Each of the HCTs produces about 0.06 lb. of thrust and together they raise the spacecraft’s perigee about 50 km. (31 mi.) per day. Madden says it will take up to eight months to reach geosynchronous orbit about 22,000 mi. over Earth The original plan called for about three months of orbit raising, but an additional three months will likely be needed for testing prior to operational use. The HCTs were originally added to the satellite only for the purpose of periodically “shaking” it to ensure that helium in the fuel tanks doesn’t settle, potentially entering the fuel lines. “Those 5-lb. thrusters saved the day because they weren’t designed to be used for what we used them for.” This long route to orbit will not compromise the mission life of 14 years. “The location of where the satellite was intended to go was primarily to cover the northern pole. We filled our xenon tanks to the max because that is a challenging orbit to maintain,” he says, noting that normally the fuel tanks would not have been full enough to conduct this orbit-raising operation as well as support a full life in orbit. AEHF-1 testing will take place with the satellite in its eventual parking location over Thule Air Base, Greenland, Madden says. By not placing the satellite in a test position, officials estimate they can save about 10-15 lb. of fuel. Once declared operational, the spacecraft will provide secure, high-speed connectivity between nuclear forces and the national command authority. AEHF-2 has been manufactured and tested, and is in storage at Lockheed Martin’s Sunnyvale, Calif., facility. Madden says some limited additional testing may be needed if senior Air Force officials opt to check out any potential mishap scenarios prior to launch. However, hardware changes are unlikely. Immediately following the orbit-raising problem with AEHF-1, officials tabled the launch plan for the second spacecraft, fearing a design problem that could plague each unit. This, however, now appears unlikely, Madden says. AEHF-3 is currently in a vacuum chamber undergoing environmental testing. Madden says he has a handshake agreement with Lockheed Martin to purchase AEHF-4, which could be finalized by the first week of December. He is proposing a bulk buy of the next two AEHF satellites. This could save as much as 25-30% of per-unit cost in future buys, he says, by taking advantage of larger orders for parts and by providing stability to the industrial base underpinning the manufacture of the AEHF.