USAF: AEHF-1 Engine Failure An Anomaly

Posted: November 23, 2010 in Uncategorized
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From Aviation Week:

AEHF-1’s liquid apogee engine (LAE) has been given a clean bill of health.  The fuel system that feeds the LAE…not so fast.

Described as “an anomaly and not the result of a design failure,” the second Advanced Extremely High Frequency (AEHF) satellite could be launched “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. “

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.

Workmanship is often code for an error with the installation.  Too much tape, too little, inadvertently kinking a line, that sort of stuff.  In this case, it sounds like the workmanship issue is being used to describe a quality control type problem during the manufacturing (versus assembly) of the fuel system (and a part of the overall LAE propulsion system).  Normally such an error would be caught during some testing, unless the manufactured piece(s) were not tested as required.  So much speculation, so little time!

If it’s unique to AEHF-1, it means the problem is known and won’t be duplicated with AEHF-2, 3, or 4.  The great news is AEHF-1 got lucky and avoided being stranded due to the presence of

…zenon-fueled, electric ion thrusters, also called Hall Current Thrusters (HCTs), (which) 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.

These firings will continue every orbit and will be centered on apogee.  The goal is to raise AEHF-1’s perigee and lower the inclination on the way towards its mission orbit.

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.”

Normally, unintended consequences are a bad thing.  Not in the case of AEHF-1 and the HCTs.

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.

Hardware changes are unlikely if the issue is positively attributed to the aforementioned workmanship issue.  Otherwise, hardware changes are likely.

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.

The handshake could perhaps be more accurately described as an agreement in principle between the Air Force and Lockheed.  That’s because Lockheed won’t do at-risk work on a system valued at approximately $2billion and the Air Force won’t ask them to do so.

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Comments
  1. […] thanks to a fortuitous event, the presence of super-low thrust Hall Current Thrusters, AEHF-1 will be able to get to where it’s supposed to go; it’ll just take a year longer than […]

  2. […] It’s turns out to be the same end-item, a blocked fuel line for the liquid apogee engine (the little fella on the right) that industry (and the Air Force) announced in February 2011 and was likely known in 2010. […]

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