1、 Public Lessons Learned Entry: 3339Lesson Info:a71 Lesson Number: 3339 a71 Lesson Date: 2010-07-25 a71 Submitting Organization: KSC a71 Submitted by: Annette Pitt Subject: Space Shuttle Fuel Cell System Missing Critical Instrumentation Forces Turnaround Testing Complexities Abstract: As originally d
2、esigned, the Shuttle Orbiters fuel cells did not adequately monitor the health and status of individual cells. Even though the fuel cells were previously modified to add the Cell Performance Monitor (CPM) capability (which provided aggregate substack 32 cells voltages to each fuel cell), they still
3、did not provide the visibility the ground needed to determine that the individual cells (96 cells per fuel cell) for each fuel cell were healthy. This resulted in the premature termination of STS-83 mission. For new spacecraft systems design and development, it is critical that a worst-case scenario
4、 evaluation be performed on critical flight systems so that health status is available at the level required to determine the systems health. Description of Driving Event: The Space Shuttle Orbiter Fuel Cell Systems as originally designed and developed lacked critical downlinked instrumentation that
5、 provided the health and status of each individual cell (96 cells per fuel cell, 3 fuel cells per ship set). An improvement modification was made early in the program to add a Cell Performance Monitor (CPM) to each fuel cell. The CPM provides a comparison voltage between 16-cell half-stacks for each
6、 32-cell substack (three 32-cell substacks per fuel cell). During the STS-83 mission, one of the fuel cells exhibited a degraded substack 3 (CPM channel 3) voltage measurement, having a steady slope toward the CPM limit of 150 millivolts. Due to limited instrumentation (i.e., the ability to monitor
7、the 96 individual cell-voltages), the abnormal readings were interpreted as a worst-case scenario, the failure of a single cell. The fuel cell was to shut down and “safed“ approximately 48 hours into the flight, requiring the mission to be terminated early. After the early termination of STS-83, the
8、 Program designed and tested a fuel-cell monitoring system (FCMS). This system finally provided individual cell-health monitoring capability. If the FCMS had been available for STS-83, it may have precluded the shutdown of the fuel cell and may have allowed the mission to complete its planned durati
9、on. Lesson(s) Learned: Based on the STS-83 experience, adequate health status information for critical systems must be provided for worst-case scenario resolutions. In the case of the Orbiter fuel cells, it was determined that individual cell health status is mandatory to preclude premature mission
10、termination. It should be noted that attempts had been made prior to FCMS to develop, qualify, and certify single-cell health monitoring. Previous attempts were considered too costly. In light of the failure and the added cost to re-fly the STS-83 mission, the prudent choice should have been to impl
11、ement a design enhancement sooner. Recommendation(s): For new spacecraft systems design and development, it is critical that a worst-case Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-scenario evaluation be performed on critical flight systems so t
12、hat health status is available at the level required to determine the systems health. This health and status must be provided via downlink to ground systems support personnel. Evidence of Recurrence Control Effectiveness: Several instances of CPM erratic behavior on various fuel cells during various
13、 missions have resulted in the implementation of flight rules requiring in-flight FCMS data acquisition and analysis to ensure fuel-cell health and continued operation. Documents Related to Lesson: Click here to download Corrective Action Record Problem No: 83RF01 document Mission Directorate(s): a7
14、1 Exploration Systems a71 Space Operations Additional Key Phrase(s): a71 1.Launch Systems a71 1.Long term sustainability and maintenance planning a71 1.Engineering design and project processes and standards a71 1.Vehicle concepts a71 1.DDT/E a71 1.Crew operations and support concepts a71 1.Ground pr
15、ocessing and manifesting a71 1.Logistics and maintenance a71 1.Risk Management/Assessment a71 1.Orbiting Vehicles a71 1.Ground support systems a71 1.Launch support systems Additional Info: a71 Project: Space Shuttle Program Approval Info: a71 Approval Date: 2010-12-03 a71 Approval Name: mbell a71 Approval Organization: HQ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
