REG NASA-LLIS-0409-1996 Lessons Learned - Voyager Gyro Swap During Launch Phase (1977).pdf

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1、Lessons Learned Entry: 0409Lesson Info:a71 Lesson Number: 0409a71 Lesson Date: 1996-06-24a71 Submitting Organization: JPLa71 Submitted by: J.A. RobertsSubject: Voyager Gyro Swap During Launch Phase (1977) Abstract: Because the Voyager 2 failure protection logic was unnecessarily enabled during launc

2、h, transient gyro outputs triggered a series of alarming “gyro swaps.” Careful attention should be given to preclude the possibility of spurious inputs triggering unwanted events when the protection logic is enabled.Description of Driving Event: (Relevant Historical Lesson(s) Learned)Voyager 2 exper

3、ienced gyro control problems during launch because its failure protection logic was enabled. Attitude control required data about all three spacecraft axes: roll (R), pitch (P), and yaw (Y). The three 2-axis gyros on Voyager provided data, respectively, about the R-P, P-Y, and Y-R axes. Thus any two

4、 gyros together provided the required three axis data, plus a fourth, redundant set of data about an axis common to both gyros. The third gyro acted as backup. The gyros, not needed until just before separation from the Titan/Centaur, were left “on“ and thus warmed up during launch to ensure immedia

5、te readiness.The failure protection logic, also left enabled during launch, sensed failure by comparing the output of the axis common to both controlling gyros. If not equal, the “back-up“ replaced one controlling gyro. If still not equal, the gyros were switched again. Continued inequality among al

6、l possible gyro pairs caused the logic to look elsewhere for the problem.It was understood a priority that the gyro output would “saturate“ during launch, and that this saturation output would be at equal limiting values, thus ensuring a valid logic comparison. Instead, however, the output oscillate

7、d significantly, causing a mis-comparison. Telemetry then indicated the Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-series of “gyro swaps“ as the failure protection logic attempted unsuccessfully to pair gyros having equal output. This led Missio

8、n Operations to suspect a major failure on Voyager 2.Lesson(s) Learned: It is suggested that failure protection logic be enabled only when the protected components or subsystems are required for spacecraft operation. Careful attention should be given to preclude the possibility of spurious inputs tr

9、iggering unwanted events when the protection logic is enabled.Recommendation(s): The gyros were not used for attitude control until just before separation from the Centaur. Thus, the failure protection logic function was not needed until that time. To prevent a recurrence of the Voyager 2 experience

10、, the failure protection logic was disabled on Voyager 1* during periods of launch vehicle thrusting.* Voyager 1 was launched after Voyager 2.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Flight Equipmenta71

11、SpacecraftAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 1996-10-16a71 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-,-,-