1、Lessons Learned Entry: 0612Lesson Info:a71 Lesson Number: 0612a71 Lesson Date: 1999-03-04a71 Submitting Organization: JPLa71 Submitted by: J. Slonski/D. OberhettingerSubject: Fault Protection of Wax Thermal Actuator Applications (1998) Abstract: Eighteen days after launch of Deep Space 1, a spurious
2、 signal issued by the power distribution logic re-powered the primary heaters on the wax thermal actuators that had been used to release the DS1 solar arrays. The resulting short-circuit current could easily have damaged the power subsystem and jeopardized the mission. Power distribution circuitry s
3、hould be designed to preclude inadvertent powering of wax thermal actuator heaters. Wax actuator circuitry should be designed to prevent a failure that leaves actuator heaters powered for an excessive period of time.Description of Driving Event: refer to D descriptionD Wax thermal actuators are high
4、 reliability devices used to trigger spacecraft deployment mechanisms. Following launch, the Deep Space 1 (DS-1) solar arrays were released by powering the primary heaters in four high output paraffin (HOP) actuators. The HOP heaters were powered for three minutes and, as designed, the HOPs activate
5、d in 70-90 seconds after the heaters were powered. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-The secondary heaters in the HOPs were not powered.Eighteen days later, a spurious signal issued by the power distribution logic re-powered the primary
6、 HOP heaters. After ten minutes of heating, telemetry indicated a short in a HOP that caused the current to increase by approximately 6 amps. Over the next few minutes, all four primary heater circuits failed open, and evidence derived from telemetry indicated that at least three of the four primary
7、 heaters bridged to their corresponding secondary heaters.A trace rated for only 1.6 amps in the power distribution circuit board could easily have been damaged by the short-circuit current of 6 amps. Had this resulted in an open circuit in the power distribution board instead of the HOP, the missio
8、n could clearly have been jeopardized.Additional Keyword(s): Wax Actuator, HOP Actuator, Electrical Short, PyroReference(s): JPL Incident Surprise Anomaly (ISA) No. Z50426Lesson(s) Learned: Wax thermal actuators have failure modes that can cause collateral damage.Recommendation(s): 1. Power distribu
9、tion circuitry should be designed to preclude inadvertent powering of wax thermal actuator heaters.2. Wax thermal actuator drive circuitry should be designed to prevent a failure that leaves actuator heaters powered for an excessive period of time.Evidence of Recurrence Control Effectiveness: N/ADoc
10、uments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-a71 Parts Materials & ProcessesAdditional Info: Approval Info: a71 Approval Date: 1999-03-15a71 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-,-,-
