1、Lessons Learned Entry: 1197Lesson Info:a71 Lesson Number: 1197a71 Lesson Date: 2002-04-25a71 Submitting Organization: JPLa71 Submitted by: Eric D. Archer/David OberhettingerSubject: Deep Space 2 Telecom Hardware-Software Interaction (1999) Abstract: Because the final subsystem thermal test of the De
2、ep Space 2 telecommunications subsystem was deleted, an important hardware-software interaction was missed.To fully validate performance, test integrated software and hardware over the flight operational temperature range. Description of Driving Event: During post launch bench thermal testing of the
3、 Deep Space 2 (DS-2) telecommunications subsystem (TS), it was discovered that the DS-2 transmit frequency was out of specification when the flight spare electronics was exposed to low temperatures ( -80 C). Upon investigation, a previously unknown hardware-software interaction was discovered.Provid
4、ed by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-D In the design of the TS, the flight software commands a temperature measurement of the master crystal oscillator. This measurement is made to adjust the oscillator frequency to compensate for previously cha
5、racterized, temperature induced, frequency drifts. The software then refers to a lookup table, and applies the appropriate compensation needed to keep the oscillator frequency within specification over the flight allowable operational temperature. Troubleshooting indicated that, due to a programming
6、 error, the software fails to power a sensor ASIC during the period when temperature should be measured by the device. This error was not apparent during ambient testing because the software defaults to a fixed level of compensation at room temperature.During assembly and test of the DS-2 flight har
7、dware, a decision was made to delete TS bench thermal testing because of tight schedule constraints. Previous bench thermal tests of the flight subassembly hardware were believed to have been adequate and to have measured performance representative of the final delivered subsystem. The subassembly t
8、ests, however, did not exercise the flight software. Because the final subsystem test was deleted, an important hardware-software interaction was missed.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-The frequency drift was sufficient to cause a 0.5
9、dB degradation of the DS-2 downlink signal from Mars Global Surveyor-an inconsequential effect given the large design margin in the downlink budget.Reference: Jet Propulsion Laboratory Problem/Failure Report No. Z50019, February 4, 1999.Additional Key Words: telecomm subsystem, power-on testing, sof
10、tware test, frequency excursion, end-to-end testLesson(s) Learned: Hardware subassembly thermal tests may not be indicative of subsystem or higher level performance.Recommendation(s): To fully validate performance, test integrated software and hardware over the flight operational temperature range.E
11、vidence of Recurrence Control Effectiveness: The issue of “test as you fly, and fly as you test“ has been resolved under JPL Corrective Action Notice No. Z69165.Documents Related to Lesson: N/AMission Directorate(s): a71 Exploration Systemsa71 Aeronautics ResearchAdditional Key Phrase(s): a71 Commun
12、ication Systemsa71 Softwarea71 Spacecrafta71 Test & Verificationa71 Test ArticleAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 2002-05-06a71 Approval Name: Carol Dumaina71 Approval Organization: JPLa71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
