1、Lessons Learned Entry: 0641Lesson Info:a71 Lesson Number: 0641a71 Lesson Date: 1999-12-01a71 Submitting Organization: HQa71 Submitted by: Pete RutledgeSubject: Mars Climate Orbiter Mishap Investigation Board - Phase I Report Description of Driving Event: Graphic of the Mars Climate Orbiter Spacecraf
2、t in orbit around the EarthThe Mars Climate Orbiter (MCO) Mission objective was to orbit Mars as the first interplanetary weather satellite and provide a communications relay for the Mars Polar Lander (MPL) which is due to reach Mars in December 1999. The MCO was launched on December 11, 1998, and w
3、as lost sometime following the spacecrafts entry into Mars occultation during the Mars Orbit Insertion (MOI) maneuver. The spacecrafts carrier signal was last seen at approximately 09:04:52 UTC on Thursday, September 23, 1999.Lesson(s) Learned: The MCO Mishap Investigation board (MIB) has determined
4、 that the root cause for the loss of the MCO spacecraft was the failure to use metric units in the coding of a ground software file, “Small Forces,“ used in trajectory models. Specifically, thruster performance data in English units instead of metric units was used in the software application code t
5、itled SM_FORCES (small forces). A file called Angular Momentum Desaturation (AMD) contained the output data from the SM_FORCES software. The data in the AMD file was required to be in metric units per existing software interface documentation, and the trajectory modelers assumed the data was provide
6、d in metric units per the Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-requirements.During the 9-month journey from Earth to Mars, propulsion maneuvers were periodically performed to remove angular momentum buildup in the on-board reaction wheels
7、(flywheels). These Angular Momentum Desaturation (AMD) events occurred 10-14 times more often than was expected by the operations navigation team. This was because the MCO solar array was asymmetrical relative to the spacecraft body as compared to Mars Global Surveyor (MGS) which had symmetrical sol
8、ar arrays. This asymmetric effect significantly increased the Sun-induced (solar pressure-induced) momentum buildup on the spacecraft. The increased AMD events coupled with the fact that the angular momentum (impulse) data was in English, rather than metric, units, resulted in small errors being int
9、roduced in the trajectory estimate over the course of the 9-month journey. At the time of Mars insertion, the spacecraft trajectory was approximately 170 kilometers lower than planned. As a result, MCO either was destroyed in the atmosphere or re-entered heliocentric space after leaving Mars atmosph
10、ere.The Board recognizes that mistakes occur on spacecraft projects. However, sufficient processes are usually in place on projects to catch these mistakes before they become critical to mission success. Unfortunately for MCO, the root cause was not caught by the processes in-place in the MCO projec
11、t.A summary of the findings, contributing causes and MPL recommendations are listed below. These are described in more detail in the body of this report along with the MCO and MPL observations and recommendations.Root Cause: Failure to use metric units in the coding of a ground software file, “Small
12、 Forces,“ used in trajectory modelsContributing Causes:1. Undetected mismodeling of spacecraft velocity changes2. Navigation Team unfamiliar with spacecraft3. Trajectory correction maneuver number 5 not performed4. System engineering process did not adequately address transition from development to
13、operations5. Inadequate communications between project elements6. Inadequate operations Navigation Team staffing7. Inadequate training8. Verification and validation process did not adequately address ground softwareRecommendation(s): Provided by IHSNot for ResaleNo reproduction or networking permitt
14、ed without license from IHS-,-,-1. Verify the consistent use of units throughout the MPL spacecraft design and operations2. Conduct software audit for specification compliance on all data transferred between JPL and Lockheed Martin Astronautics3. Verify Small Forces models used for MPL4. Compare pri
15、me MPL navigation projections with projections by alternate navigation methods5. Train Navigation Team in spacecraft design and operations6. Prepare for possibility of executing trajectory correction maneuver number 57. Establish MPL systems organization to concentrate on trajectory correction maneu
16、ver number 5 and entry, descent and landing operations8. Take steps to improve communications9. Augment Operations Team staff with experienced people to support entry, descent and landing10. Train entire MPL Team and encourage use of Incident, Surprise, Anomaly process11. Develop and execute systems
17、 verification matrix for all requirements12. Conduct independent reviews on all mission critical events13. Construct a fault tree analysis for remainder of MPL mission14. Assign overall Mission Manager15. Perform thermal analysis of thrusters feedline heaters and consider use of pre-conditioning pul
18、ses16. Reexamine propulsion subsystem operations during entry, descent, and landingEvidence of Recurrence Control Effectiveness: N/ADocuments Related to Lesson: N/AMission Directorate(s): a71 ScienceAdditional Key Phrase(s): a71 Configuration Managementa71 Flight Operationsa71 Flight Equipmenta71 Mi
19、shap Reportinga71 Softwarea71 SpacecraftProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-a71 Test & VerificationMishap Report References: Mars Climate Orbiter Mishap Investigation Board Phase I ReportAdditional Info: Approval Info: a71 Approval Date: 1999-12-01a71 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-,-,-
