1、Lessons Learned Entry: 0573Lesson Info:a71 Lesson Number: 0573a71 Lesson Date: 1997-08-07a71 Submitting Organization: JPLa71 Submitted by: K. Clark / D. OberhettingerSubject: Power Bus/GSE Sneak Paths May Energize Spacecraft in the Ground Test Environment (1995) Abstract: Due to the Mars Global Surv
2、eyor electrical power system design, a sneak path through GSE energized the spacecraft power bus, even though spacecraft battery power was disconnected. Locate the power interrupt on the positive side of the power system, design electronic subsystems and GSE for testability, and design circuits and
3、interfaces to avoid sneak paths.Description of Driving Event: The Mars Global Surveyor (MGS) electrical power system (EPS) design featured a switch on the negative leg of the battery for interrupting battery power. When this switch was opened to place the EPS (and thus the spacecraft) in the unpower
4、ed state, a blue light on the ground support equipment (GSE) power bus monitor remained lit, indicating that the spacecraft power bus was still energized.Examination of the design revealed that a residual voltage of almost 2 volts could be expected due to sneak paths both through the GSE grounding s
5、ystem and within the spacecraft telemetry system. Telemetry and control circuitry in the battery charger assembly (BCA), power supply electronics (PSE), and signal conditioning units (SCUs) provides multiple high impedance paths that bypass the main enable plug and the remote power switch and are ma
6、nifested only in the ground test environment. In this specific design, these paths are necessary for normal flight operation of the power subsystem and command and data handling (C a higher voltage could have caused:1. A stressed or blown spacecraft fuse which could have remained undetected.2. Inadv
7、ertent powering of the spacecraft bus without the knowledge of the test crew due to ground equipment.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-3. Burnt connector pins caused by scooping of the “D“-type connector shell during mate or demate.Refe
8、rence(s): PFR #B0JK79Lesson(s) Learned: With certain spacecraft power designs, sneak paths through GSE may energize the spacecraft power bus, even with spacecraft battery power disconnected.Recommendation(s): 1. Locate the power interrupt (e.g., the Main Enable Plug) in the positive side of the powe
9、r system with appropriate safety features.2. Design electronic subsystems and GSE for testability; design circuits and interfaces to avoid sneak paths which energize the spacecraft when it is intended to be in an unpowered configuration.Evidence of Recurrence Control Effectiveness: N/ADocuments Rela
10、ted to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): N/AAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 1997-10-22a71 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-,-,-
