1、Lessons Learned Entry: 0274Lesson Info:a71 Lesson Number: 0274a71 Lesson Date: 1993-07-09a71 Submitting Organization: JPLa71 Submitted by: J. W. HarrellSubject: Mars Observer Payload Data System (PDS) Exposure to Low Temperature Abstract: During thermal vacuum testing of the flight Mars Observer PDS
2、 the subsystem was exposed to a temperature of about -47 degrees Celsius, well below the desired limit of -20 degrees C. The problem was caused by a failure in a temperature controller and was compounded by a chamber operator evaluation error.The recommendations involve use of alarm and “fail safe”
3、 circuits, pretest functional verification of the test facility, procedures required before manual override of “fail safe” devices, and continuous quality assurance monitoring of tests. Description of Driving Event: During testing of the flight Mars Observer PDS (Serial No. 1) in a thermal vacuum ch
4、amber, the subsystem was exposed to a temperature of about -47 degrees Celsius, well below the desired limit of -20 degrees C. The problem was caused by a failure in a temperature controller and was compounded by a chamber operator evaluation error. The failure of the controller during the planned d
5、escent to -20 C was detected by an alarm circuit and a “fail safe“ circuit, both of which functioned properly by closing off the supply of cold gas to the PDS baseplate heat exchanger. The chamber operator overrode the protection circuits, choosing to believe the recently calibrated temperature cont
6、roller rather than the alarms. The subsystem engineer observed from a separate data source that the hardware was exceeding the specified temperature and requested a test termination.Following analysis, evaluation and test facility corrective actions, the test of the PDS was continued and successfull
7、y completed with no further difficulty.Reference(s): PFR #55545 AND #56161 (includes Review Board report)Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Lesson(s) Learned: 1. Environmental testing of flight hardware is a necessary but potentially haz
8、ardous activity in the preparation of a spacecraft or instrument for launch.2. Adherence to proper procedures and alertness by environmental test hardware and facility personnel are important safeguards against facility and/or equipment failure.3. Despite the use of properly calibrated and tested en
9、vironmental test facility protection circuits and alarm systems, overlimit test conditions can still occur.Recommendation(s): 1. Alarm and “fail safe“ circuits must always be utilized with sensors located appropriately on the hardware and test facility to prevent the hardware from exceeding environm
10、ental limits.2. During the pretest functional verification of the test facility controls and alarm systems, attention should be given to the adequacy of transient data sampling and recording to assure timely recognition of “out of tolerance“ test conditions.3. Require communication between test faci
11、lity engineering personnel and cognizant hardware engineering personnel for approval prior to any override of “fail safe“ devices.4. Program offices should give consideration, during the planning and initial stages of a project, to provide continuous quality assurance monitoring of all environmental
12、 tests as an additional safeguard against overlimit test conditions.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Environmenta71 Test & VerificationAdditional Info: Provided by IHSNot for ResaleNo reproductio
13、n or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 1991-09-26a71 Approval Name: Carol Dumaina71 Approval Organization: 125-204a71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
