1、Lessons Learned Entry: 0423Lesson Info:a71 Lesson Number: 0423a71 Lesson Date: 1996-07-10a71 Submitting Organization: JPLa71 Submitted by: J.A. RobertsSubject: Viking Navigation - Unexpected Non-gravitational Acceleration Due to Lander Outgassing (1975) Abstract: Immediately after the launch of Viki
2、ng I, large and unexpected non-gravitational accelerations were detected and attributed to outgassing from porous materials (e.g., parachute, blankets, etc.) in the lander. A midcourse correction made to preclude large targeting errors upon Mars Encounter.Every spacecraft design should be reviewed f
3、or its potential for outgassing (and its impact on the navigation strategy and the spacecraft) throughout flight. Description of Driving Event: (Relevant Historical Lesson(s) Learned)Immediately after the launch of Viking I, large and unexpected non-gravitational accelerations were seen when the Dop
4、pler observations of the spacecraft were processed for orbit determination. These perturbations to the spacecraft dynamics were confirmed by observations of the attitude-control limit-cycle motion. Spacecraft team analysis identified the cause as the venting of outgassing products from porous materi
5、als (e.g., parachute, blankets, etc.) in the lander. There was considerable uncertainty in the expected duration of the effect. This uncertainty raised the possibility of large targeting errors at Mars; consequently, the effect was included in the design of the midcourse correction made shortly afte
6、r departure from Earth. The effect appeared to cease 1 to 2 months after launch, and did not in fact significantly increase targeting errors. The same effect was observed on Viking II.Lesson(s) Learned: Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,
7、Every spacecraft design should be reviewed for its potential for outgassing at any time during flight.Recommendation(s): The magnitude of the resulting non-gravitational accelerations should be estimated and compared with the navigation requirements on non-gravitational accelerations. If these requ
8、irements are exceeded, re-design of the navigation strategy and/or the spacecraft may be required.Evidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): N/AAdditional Key Phrase(s): a71 Flight Equipmenta71 Parts Materials & Processesa71 SpacecraftAdditional Info: Approval Info: a71 Approval Date: 1995-09-21a71 Approval Name: Carol Dumaina71 Approval Organization: JPLa71 Approval Phone Number: 818-354-8242Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
