1、Lessons Learned Entry: 2116Lesson Info:a71 Lesson Number: 2116a71 Lesson Date: 2009-9-30a71 Submitting Organization: GSFCa71 Submitted by: Jerome Koskoa71 POC Name: Jerry Koskoa71 POC Email: jerome.g.koskonasa.gova71 POC Phone: 301-286-5584Subject: Mission Operations Planning for Irreversible Proces
2、ses Abstract: Many spacecraft include mission operations that implement an irreversible process(s) (e.g. pyro technical deployments) which changes the state or configuration of the spacecraft and its operational capability. If not thought out thoroughly some transitions can have undesirable conseque
3、nces. Consequences may arise due to the untimeliness of the transition or unrelated design features.Description of Driving Event: GSFC built an X-Ray Spectrometer (XRS) which was integrated in Japan with 3 other instruments into the Astro E-2 spacecraft and launched it aboard a Japanese rocket from
4、Japan. The XRS was the primary instrument for this mission which was managed by the Japanese Space Agency (JAXA). Astro E-2 was renamed Suzaku once orbit was obtained as is customary for Japanese missions. The XRS uses calorimetric detectors that must be cooled to near absolute zero (operating at 60
5、mK). This was accomplished by a multi stage Dewar which includes liquid He and solid Ne. Dewar operations are initiated on ascent by blowing pyro valves allowing the He and Ne to vent. The Dewar was also equipped with a pyro driven vent that exposes the Dewar guard vacuum to ambient environment. Thi
6、s design feature was intended to vent the guard vacuum to deep space once on orbit. This would allow any cryogen leakage to be effectively prevented from contaminating this volume. There is another pyro gate valve at the telescopes aperture that protects the internal detectors until on orbit. By blo
7、wing the aperture gate valve the instrument becomes fully operational and is enabled to view its entire desired spectrum. Once the XRS was on orbit it was successfully calibrated and configured Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-for full
8、 operations (i.e. guard vacuum and gate valves blown). However, prior to opening either the aperture valve or the valve to the guard vacuum (i.e. He and Ne are venting) significant science can acquired (although only over a small spectrum) in this configuration. Unfortunately, the space craft design
9、 had a fatal flaw. For most missions that fly cryogens the Dewar comprises the main structural component of the spacecraft. The XRS was buried inside the spacecraft in what turned out to be a confined space. Once integrated into the spacecraft the Dewar was supposed to have been vented to the exteri
10、or of the spacecraft and then overboard. The entire spacecraft exterior was covered with thermal blankets which enclosed the volume that held XRS. The venting He and Ne accumulated in the confined space. Although the confined space was not airtight the venting area provided by the blanket seams rest
11、ricted the venting sufficiently enough to establish a level of atmosphere to pose a contamination issue. When the guard and aperture valves were blown the confined He and Ne were sucked into the guard vacuum shorting out the vacuum causing unacceptable heat loads on the tanks. The cryogens were rapi
12、dly depleted and a planned 3 year mission was over in 19 days with no science having been acquired. It should be noted that Astro E-2, as the name implies, was a “build to print“ reflight of the first Astro which also was launched on a Japanese rocket. It was identically flawed and would have failed
13、 in the fashion but the launch vehicle failed to achieve orbit and was lost. Also notable is the design review process failed to identify the design flaw. This lesson is limited to mission operations planning. The genesis and propagation of the original design flaw is covered in detail in the Astro
14、E-2 Mishap Investigation Board report. There are broader issues with respect to communications and program execution. Lesson(s) Learned: 1) Had mission operations planning considered some science acquisition prior to initiating the Dewar and gate valves some science could have been obtained. 2) If t
15、he fully assembled instrument been tested in an “as flown“ configuration (i.e. confined space was simulated)_ the design flaw would have likely been discovered. Recommendation(s): 1) Mission operations planning should include a thorough analysis of all operations especially irreversible processes un
16、der nominal and anomalous conditions. 2) Mission operations should be fully exercised in test using a “test-as-you-fly fly as you test“. A full up test simulating the actual environmental conditions likely would have detected the design flaw. Evidence of Recurrence Control Effectiveness: Provided by
17、 IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-N/ADocuments Related to Lesson: N/AMission Directorate(s): a71 Space OperationsAdditional Key Phrase(s): a71 Engineering Design (Phase C/D).Spacecraft and Spacecraft Instrumentsa71 Manufacturing and Assemblya71 Integration and TestingAdditional Info: a71 Project: ASTRO E-2Approval Info: a71 Approval Date: 2009-11-12a71 Approval Name: mbella71 Approval Organization: HQProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
