Despite the Shuttle heading into the final stages of its operational lifetime, the upcoming debut of the Advanced Health Management System (AHMS) on STS-116 has been pursued for many years, according to its project leader.
One of the new upgrades to the main engine controllers will fly in monitor-only mode on Discovery, before becoming an active part of the Shuttle on STS-118.
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The three flight progressive inclusion into the SSME (Space Shuttle Main Engine) system is one of the final major modifications to the reliable power packs that were to play a role in the Shuttle’s replacement, Ares I, before it was replaced by the J-2X.
Still, according to Jeff Spencer, project leader at the Marshall Space Flight Center (MSFC), where the AHMS was developed, it’s been a long time coming.
‘The Space Shuttle Main Engine Project has, for many years, pursued a reliable means to monitor high-pressure turbo machinery health in real time,’ said Spencer, to MSFC’s Marshall Star. ‘The system upgrade provides that capability and, in doing so, will significantly improve shuttle flight safety.’
The upgrade – first noted on this site – is a modification of the existing main engine controller, the on-engine computer used for monitoring the health of the high-pressure fuel turbopump and the high-pressure oxidizer turbopump, which rotate at approximately 35,000 revolutions and 28,000 revolutions per minute, respectively.
The AHMS upgrade uses data from three existing sensors, or accelerometers, mounted on the high-pressure turbopumps to measure how much each pump is vibrating.
Changes include the addition of advanced digital signal processors, radiation-hardened memory and new software. The passive system will run on all three of STS-117’s engines, before being placed into an active role on STS-118.
‘The system will fly first on STS-116 with a single controller in monitor-only mode on one engine,’ added Spencer. ‘This will limit new hardware and software to the least possible risk, preclude the risk of an erroneous shutdown and allow integration risks to be evaluated.’
Explaining the system, Spencer noted that with the AHMS, output data from the accelerometers is routed to the new digital signal processors installed in the main engine controller. The processors analyze the sensor readings 20 times per second, looking for vibration anomalies that indicate impending failure of rotating turbopump components such as blades, impellers, inducers and bearings.
If the magnitude of any vibration anomaly exceeds safe limits, the upgraded main engine controller immediately shuts down the unhealthy engine.
While the only SSME failure occurred on STS-51F, when at T+645 seconds the number one engine shut down prematurely due to a sensor problem, causing an Abort To Orbit (ATO), STS-93 with Columbia was also highly eventful, when during ascent two of three main engine controllers failed. (Both videos are on our Video Section)
Data from the passive flights of the AHMS system on STS-116 and STS-117 will go towards the scheduled inclusion of the system with Endeavour on STS-118 next year.
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