1、Lessons Learned Entry: 0412Lesson Info:a71 Lesson Number: 0412a71 Lesson Date: 1996-06-26a71 Submitting Organization: JPLa71 Submitted by: J.A. RobertsSubject: Voyager-Power Subsystem Coded Commands Interface with the Computer Command Subsystem (CCS) (1975) Abstract: Because, the interface circuit b
2、etween the Voyager CCS and Power subsystems was not electrically isolated, spacecraft system noise prevented reliable commanding from CCS to Power. This was not discovered until system-level test, and circuit modifications were difficult. Lesson recommendations pertain to system level requirements,
3、design, and early compatibility testing for interface circuits.Description of Driving Event: (Relevant Historical Lesson(s) Learned)A digital, coded interface was utilized on Voyager for the first time, at JPL, for transferring basic commands between CCS and Power. It was not until the Proof Test Mo
4、dule Spacecraft System Test Phase, in the Spacecraft Assembly Facility, that an incompatibility appeared that prevented reliable commanding from CCS to Power. The problem was caused by spacecraft system noise that resulted in spurious triggering of interface circuit elements. Circuit modifications,
5、in this case, were troublesome.This configuration was adopted late in the subsystem design phase. For simplicity, an existing power supply was used for this circuitry which resulted in the signal return being common with the spacecraft 30V power return.Additional Keyword(s): Electrical IsolationsRef
6、erence(s): Voyager PFR 39934, 39935, 39940, 39948 SSEF #343.2Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Lesson(s) Learned: The system test phase is too late to discover hardware interface incompatibilities after subsystems have completed qualifi
7、cation testing.Recommendation(s): 1. Coded interface circuits should employ isolated power supply and grounding schemes.2. System level requirements must be generated for the design of grounding of interfaces.3. Compatibility tests, using representative equipment (prototype or breadboard) should be
8、conducted as early as possible for subsystems having new, or complex interfaces. Where noise immunity is critical, injection of noise on the signal lines may be necessary to demonstrate that adequate margin exists.These tests (and the design/analysis that precedes them) should account for the fact t
9、hat differences will exist between subsystem and system configurations. The noise characteristics in the lab may be different than the system configuration, for example.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s
10、): a71 Spacecrafta71 Test & VerificationAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 1996-04-04a71 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-,-,-
