1、Lessons Learned Entry: 0639Lesson Info:a71 Lesson Number: 0639a71 Lesson Date: 1999-10-14a71 Submitting Organization: JPLa71 Submitted by: D. OberhettingerSubject: DS1 Ion Engine Shut-Down Anomaly (1998) Abstract: Shortly after the successful demonstration of solar electric propulsion (SEP) aboard D
2、eep Space 1 began, the xenon ion engine shut down unexpectedly- likely due to a “grid short.” Although the engine was later restarted using other procedures, immediate use of a “grid clear circuit” was deemed as too risky. Since grid shorts are likely to occur during future missions that use SEP tec
3、hnology, conduct further study of grid clear circuits and provide a pre-planned operational procedure for detecting and clearing critical anomalies, including SEP grid shorts.Description of Driving Event: The Deep Space 1 (DS1) mission successfully demonstrated the use of an ion engine as a primary
4、spaceflight propulsion system. A few minutes after startup in November 1998, DS1s xenon ion engine shut down unexpectedly. The problem was believed to be a “grid short,“ a common problem in ion propulsion. Repeated attempts to restart the engine that same day were unsuccessful.Solar electric propuls
5、ion (SEP) imparts a small thrust by passing ions through two closely spaced, charged grids (Figure 1). Should a loose conductive flake bridge the gap between the positive and negative charged grids, it could short the grids leading to automatic shutdown of the engine. Molybdenum flakes commonly peel
6、 off the grids late in the ion engines life. Given the early occurrence of the DS1 anomaly, however, it is possible that a conductive contaminant was introduced during assembly or launch operations.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-refe
7、r to D descriptionD DS1 Xenon Ion Engine Ion propulsion systems in commercial satellites incorporate a “grid clear circuit,“ like a patio bug zapper, that is believed to be capable of clearing grid shorts by producing a brief high current that eliminates the conductive source. DS1 was designed with
8、a relatively low power version of this circuit. After the anomaly, DS1 operators executed preplanned low risk contingency evaluation procedures. It was decided not to take the risk associated with the immediate use of the “grid clear circuit.“Approximately two weeks after the engine shutdown anomaly
9、 an engine start planned for evaluation purposes resulted in successful engine operation. Activities during this two-week period are believed to have induced thermal cycling of the grids which removed the short. Since this early anomaly, engine operation has been normal.Additional Keyword(s): debri
10、s, contamination, fault protection, New Millennium, short circuit, NSTAR, Mission OperationsLesson(s) Learned: The “grid clear“ approach to recovery from a solar electric propulsion (SEP) grid short, a failure mode that is likely to occur during an extended mission, requires additional evaluation be
11、fore it can be judged as an acceptable risk.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Recommendation(s): 1. Provide a pre-planned operational procedure for detecting and clearing time-critical and mission-critical anomalies, including SEP grid
12、shorts.2. Perform a study to determine how well grid clear circuits work. The study should identify the amount of current needed to clear grid shorts caused by various materials.3. Ensure that downlinked data on the operational condition of SEP systems include measurements of the current to the grid
13、s, and the voltage between them, to permit in-flight analysis of a possible grid short.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): a71 Exploration Systemsa71 Sciencea71 Aeronautics ResearchAdditional Key Phrase(s): a71 Flight Operationsa71
14、 Risk Management/Assessmenta71 SpacecraftAdditional Info: Approval Info: a71 Approval Date: 1999-11-02a71 Approval Name: Carol Dumaina71 Approval Organization: 301-450a71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
