1、Lessons Learned Entry: 0979Lesson Info:a71 Lesson Number: 0979a71 Lesson Date: 2000-04-23a71 Submitting Organization: GSFCa71 Submitted by: Kevin GradySubject: Thruster Plume Impingement Description of Driving Event: On January 11, 2000, while the Terra spacecraft was attempting its first long orbit
2、 raising maneuver, the maneuver was prematurely terminated after 11 seconds of the burn. The burn was halted due to the fact that on-board attitude tolerance limit exceedences were detected. The flight computer correctly aborted the maneuver. There was no time critically for executing the maneuver o
3、n that particular day nor at that particular orbit, therefore a rigorous investigation ensued. This maneuver had been preceded by a calibration burn, which was analyzed and deemed to be nominal.Lesson(s) Learned: Several weeks of investigation proceeded, and a significant amount of analysis and mode
4、ling were performed. It was determined that the impingement of the thruster plumes from two of the attitude thrusters were producing a large torque, by impinging on the Terra solar array. The Terra solar array is a very large flexible blanket type array. The location of the array during the maneuver
5、 resulted in the worse possible orientation for plume interaction, and it also resulted in the largest possible moment arm between the center-of-pressure and center-of-gravity. The combination of these two factors resulted in the larger than expected disturbance torque, which led to the attitude dis
6、turbance and the shutdown of the orbit raising maneuver.Subsequent to numerous analyses and simulations, an optimal orientation for the solar array during the maneuvers was determined, and a modified thruster torque transformation matrix were developed. The torque transformation matrix accounted for
7、 the residual disturbance which was still induced, even with the solar array in the optmized orientation.A series of smaller orbit raising maneuvers were performed to verify the software changes. The maneuvers executed without problems. Long duration maneuvers were then performed. These Provided by
8、IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-maneuvers were likewise successful. Terra reached its operational orbit and began flying in formation with Landsat 7 in February 2000.Upon reviewing the process on why this error was not detected before launch, it
9、was determined that no direct modeling of the plume impingement phenomena was ever performed. Plume effects were accounted for via a design allocation process; however, the torque that was allocated in the design process was inadequate. The allocation was not verified via a closed-loop simulation si
10、mulation.This experience reaffirms the value of performing high fidelity 3-axis simulations prior to launch. This is particularly true as spacecraft grow, and surface areas become larger. The utility of high fidelity 3-axis simulations is unquestionable, and should be performed as a routine and cont
11、inuous part of the spacecraft design process.Recommendation(s): This experience reaffirms the value of performing high fidelity 3-axis simulations prior to launch. This is particularly true as spacecraft grow, and surface areas become larger. The utility of high fidelity 3-axis simulations is unques
12、tionable, and should be performed as a routine and continuous part of the spacecraft design process.Evidence of Recurrence Control Effectiveness: All subsequent orbital raising maneuvers were nominal.Documents Related to Lesson: N/AMission Directorate(s): a71 ScienceAdditional Key Phrase(s): a71 Spa
13、cecrafta71 Test & VerificationAdditional Info: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Approval Info: a71 Approval Date: 2001-08-06a71 Approval Name: Eric Raynora71 Approval Organization: QSa71 Approval Phone Number: 202-358-4738Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
