1、Lessons Learned Entry: 0350Lesson Info:a71 Lesson Number: 0350a71 Lesson Date: 1994-11-11a71 Submitting Organization: JPLa71 Submitted by: A.G. GussnerSubject: Galileo Spacecraft Telemetry Degradation due to Antenna Multipath Abstract: After Galileo completed its second Earth flyby, communication si
2、gnal levels received on Earth decreased and fluctuated unexpectedly. The cause was determined to be interference that was not detected during test because the test article was not consistent with the orbiter telecommunications functional requirements document.Recommendations involved use of concurre
3、nt engineering, verification of requirements compliance, updating of requirements documents based on hardware ECRs, post test evaluation of non-flight like characteristics, and assuring that hardware used for functional testing properly simulates the characteristics of the flight hardware. Descripti
4、on of Driving Event: After the spacecraft completed its second Earth flyby, communication signal levels received on Earth decreased and fluctuated unexpectedly. The cause was determined to be interference when the Radio Frequency (RF) radiation angle from the boresight of the Low Gain Antenna (LGA-1
5、) to Earth exceeded 90 degrees causing the signal to pass through the High Gain Antenna tip sunshade. The tip sunshade is constructed of 9 conductive ribs and a circumferential wire supporting an RF transparent shade. Phasing of the direct signal with the signal reflected off the 9 conductive ribs o
6、f the sunshade caused multipath signal fluctuations that varied with the rotation of the spacecraft. Since the orbiter telecommunications functional requirements document stated that “the outer portion of the tip sunshade is RF transparent,“ the LGA antenna pattern tests used a totally RF transparen
7、t tip sunshade model, and multipath interference was not detected.Additional Keyword(s): RF Performance VerificationProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Reference(s): ISA# 2125Lesson(s) Learned: Approval of hardware Engineering Change Requ
8、ests (ECRs) which conflict with functional requirements documents, without concurrently updating the requirements documents, can result in subsystem functional testing which does not adequately simulate the characteristics of the flight hardware.Recommendation(s): 1. “Concurrent engineering“ is requ
9、ired between requirements, design, fabrication and test engineering functions.2. Verification of requirements compliance must be performed. Requirements must be adhered to, changed to match hardware characteristics, or waived through the ECR process.3. Requirements documents should be continuously u
10、pdated based on hardware ECRs.4. Post test evaluation of non-flight like characteristics is required.5. Hardware used for functional testing must properly simulate the characteristics of the flight hardware.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Dire
11、ctorate(s): N/AAdditional Key Phrase(s): a71 Communication Systemsa71 Configuration Managementa71 Test & VerificationAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 1994-05-31a71 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-,-,-
