1、Public Lessons Learned Entry: 6696 Lesson Info: Lesson Number: 6696 Lesson Date: 2012-8-28 Submitting Organization: JPL Submitted by: David Oberhettinger Subject: Verify Test Equipment Functionality Before Testing Abstract: A failure in the system-level testing of the MSL Robotic Arm was traced to G
2、SE wiring that was mis-connected. Because re-test was not feasible, the functionality was verified by analysis. For system-level thermal testing during ATLO, the functionality of all GSE instrumentation should be unequivocally verified prior to closing the chamber doors. Description of Driving Event
3、: System Thermal Test (STT) of the Mars Science Laboratory (MSL) rover was conducted during Assembly, Test, and Launch Operations (ATLO) at the NASA/Caltech Jet Propulsion Laboratory (JPL) in March 2011. One of the components tested during this system-level, low temperature, low pressure test is the
4、 percussive drill at the end of the MSL Robotic Arm (RA), located at the front of the rover and used to take rock samples on Mars. This is a complex mechanism, with three cold-sensitive actuators in the drill, another five in the RA, and a total of sixteen in the Sample Acquisition/Sample Processing
5、 and Handling (SA/SPaH) subsystem. One objective of the STT is to verify at the operational temperature, by means of a Drill Force Transducer, the calibrated force applied by the RA against the drill bit. The force is verified during the test by a load cell (Figure 1) embedded in a ground support eq
6、uipment (GSE) preload plate (Figure 2) that is integrated into the rover STT GSE (Figure 3). Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Figure 1. Load cell (i.e., single-axis force sensor) embedded in the (GSE) RA Preload Plate Assembly Figure 2
7、. Fully assembled RA Preload Plate Assembly mounted on the STT support frame (white GSE test fixture) Figure 3. Full view of the MSL rover and the RA Preload Plate Assembly, both mounted on the rover STT support frame (white GSE test fixture) in the test chamber During the test, the RA was commanded
8、 to apply an increasing preload, in increments of 50 N, to 300 N. However, the load cell embedded in the preload plate did not register an increase in force. (Prior to delivery to ATLO, the load cell had been calibrated and its functionality verified.) The proximate cause of the test failure was the
9、 incorrect connection of the AC power leads to the amplifier unit supplied with the load cell (Reference (1). This occurred during ATLO integration of the STT electrical ground support equipment (EGSE) hardware, and it resulted in no power being sent to the load cell. The root cause was inadequate i
10、nstructions and procedures for unit assembly prior to STT. A contributing cause was that the GSE load cell functionality was not adequately verified prior to starting STT. Specifically, a step to verify the load cell was performed after it was integrated into the STT GSE in the test chamber, but the
11、 data obtained during this verification was erroneously interpreted to conclude that the load cell worked. The verification of the Drill Force Transducer at temperature was accomplished by force measurements, using the deflection of the Drill Bit Box (given its known spring constant) and the gravity
12、 vector on the drill as the turret rotated. References: 1. “Preload plate single axis force sensor giving erroneous readings during STT,“ JPL Problem/Failure Report No. 48193, March 21, 2011. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Lesson(s)
13、Learned: Once EGSE has been integrated with flight hardware, the spacecraft has been placed in a thermal-vacuum chamber, and the testing reveals that EGSE was not properly configured to test the functionality of one of the components, it may not be feasible to interrupt system-level testing to corre
14、ct the test configuration error. For the MSL Drill Force Transducer, verification was accomplished by analysis, but this practice is not generally considered as satisfactory as verification by test. Recommendation(s): For system-level thermal testing during ATLO, it is important to unequivocally ver
15、ify the functionality of all GSE instrumentation prior to closing the chamber doors. Evidence of Recurrence Control Effectiveness: JPL has referenced this lesson learned as additional rationale and guidance supporting Paragraph 6.12.5.3 (“Engineering Practices: Protection and Security of Flight Hard
16、ware”) in the Jet Propulsion Laboratory standard “Flight Project Practices, Rev. 7,” JPL DocID 58032, September 30, 2008. Documents Related to Lesson: N/A Mission Directorate(s): Exploration Systems Science Additional Key Phrase(s): Integration and Testing Additional Categories.Ground Equipment Addi
17、tional Categories.Hardware Additional Categories.Spacecraft Additional Categories.Test & Verification Additional Info: Project: Mars Science Laboratory Approval Info: Approval Date: 2012-09-17 Approval Name: mbell Approval Organization: HQ Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
