1、Lessons Learned Entry: 0640Lesson Info:a71 Lesson Number: 0640a71 Lesson Date: 1999-10-21a71 Submitting Organization: JPLa71 Submitted by: M. Landano/R. Ross, Jr./D. OberhettingerSubject: Inadequate Venting Analysis for the WIRE Spacecraft (1999) Abstract: Past analyses of electronic, mechanical, an
2、d optical hardware performance have sometimes focused on steady state characteristics to the exclusion of known transients. As indicated in the Wide-Field Infrared Explorer (WIRE) mission loss scenario, spacecraft venting configurations designed for steady state flow rates may experience large unexp
3、ected blow-down impulses, or even nominal cryogen flows sufficient to cause mission loss or degradation. Secondly, the inability of the WIRE spacecraft to counteract accelerated venting rates suggests a marginal attitude control system authority. Third, the unavailability of definitive cryostat temp
4、erature data during the anomalous venting period hampered early, real-time identification of the root problem (premature cover deployment). Consider all venting mission sequences, plus the possibility of unplanned worst-case venting scenarios, in the spacecraft system design. Design the thrust neutr
5、alizing capability of the attitude control system to encompass transient venting-induced torque. Ensure that the electronics monitoring spacecraft health supply data during critical operational sequences.Description of Driving Event: Shortly after separation of the Wide-Field Infrared Explorer (WIRE
6、) spacecraft from the launch vehicle, venting of the secondary cryogen tank was commanded, as planned, to dissipate the heat absorbed by the cryogen since termination of ground cooling. Venting this small amount of hydrogen gas was expected to induce some tumbling of the spacecraft. This tumbling wa
7、s also expected to be quickly dampened by the attitude control system as the solid hydrogen reached equilibrium with the low space-ambient temperature. Instead, the spacecraft was observed to be tumbling too fast to be countered by the reaction wheels and magnetic torquers-an out-of-control conditio
8、n.A NASA review board determined (reference 1) that an error in the design of the pyro electronics caused premature release of the telescope cover when the secondary cryogen tank was vented. The Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-cover r
9、elease permitted a large heat load into the cryostat that caused greater and more prolonged cryogen venting then expected following the transient associated with secondary vent actuation.A “T“ fitting had been placed at the vent outlet to balance the thrust induced to the spacecraft by the gas flow
10、expected from the planned venting sequence. However, design analysis did not consider the torque effects of worst case transient flows caused by one side of the “T“ pointing directly at a connector (added as a late design modification during integration). The combined applied torque to the spacecraf
11、t from the initial secondary vent transient and the effects of early cover release was greater than the attitude control system capability.An independent analysis performed by a member of the WIRE JPL Review Board (reference 1, appendix E, p. 91) indicated the possibility that the normal secondary v
12、ent actuation transient could have exceeded attitude control capability. This could significantly impact early science return since it would take many days to reestablish a stable spacecraft attitude. Venting analyses performed during the design phase considered only the steady state cryogen flows e
13、xpected during primary mission science pointing.However, the premature release of the instrument cover, and resultant boil-off of the cryogen required for telescope operation, was determined by the review board to be the direct cause of the WIRE mission loss (references 1 and 2). It was also determi
14、ned that the design characteristics of the cryogen tank vent outlet prevented timely control of spacecraft attitude following the cover release anomaly, and the venting-induced torque deterred any productive efforts to save the mission.Additional Keyword(s): WIRE failure, thrust vector, thrust neutr
15、alizer, telemetry, angular velocity, roll rate, magnetic torquer, spacecraft spin, torque rod, impingement, subsystem and instrument developmentReference(s):1. WIRE Mishap Investigation Board Report, NASA, June 8, 1999.2. Transient Performance of the WIRE Pyro Electronics, Lesson Learned No. 0634, A
16、ugust 12, 1999.Lesson(s) Learned: 1. Past analyses of electronic, mechanical, and optical hardware performance have sometimes focused on steady state characteristics to the exclusion of known transients. As indicated in the WIRE scenario, spacecraft venting configurations designed for steady state f
17、low rates may experience large unexpected blow-down impulses, or even nominal cryogen flows sufficient to cause mission loss or degradation.2. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-3. The inability of the WIRE spacecraft to counteract accel
18、erated venting rates suggests a marginal attitude control system authority.4. 5. The unavailability of definitive cryostat temperature data during the anomalous venting period hampered early, real-time identification of the root problem (premature cover deployment).Recommendation(s): 1. Consider all
19、 venting mission sequences, plus the possibility of unplanned worst-case venting scenarios, in the spacecraft system design.2. The thrust neutralizing capability of the attitude control system should be designed to encompass transient venting-induced torque.3. Ensure that the electronics monitoring
20、spacecraft health supply data during critical operational sequences.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): a71 ScienceAdditional Key Phrase(s): a71 Cryogenic Systemsa71 Energetic Materials - Explosive/Propellant/Pyrotechnica71 Flight
21、Equipmenta71 Mishap Reportinga71 SpacecraftMishap Report References: WIRE Mishap Investigation Board ReportProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Additional Info: Approval Info: a71 Approval Date: 1999-11-02a71 Approval Name: Carol Dumaina71 Approval Organization: 301-450a71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
