MARS SURVEYOR 98 MISSION STATUS
January 9, 1999
Mars Polar Lander continues to operate in its planned initial attitude and is in excellent health. During the past two days a series of commands to update parameters in the spacecraft's onboard file system have been transmitted successfully. These updates completed modifications to the fault protection system configuration begun earlier this week, and made some changes to the way the lander's autopilot transitions between different acitivities (e.g., slew maneuver to attitude "hold" transition). The fault protection system is now set up so that it will respond correctly to any fault identifications within the attitude determination and control system; these responses had been disabled the day after launch so that diagnostic activities could be conducted. The changes made to the autopilot are designed to temporarily correct for an anomaly identified earlier in its operation, prior to uplink of a software patch to the spacecraft with a comprehensive fix, scheduled for Monday (Jan. 11).
Two days ago another minor software anomaly was discovered onboard the lander, in which the thermal control software task failed to turn off a heater circuit in one subregion of the vehicle. This heater was subsequently turned off via real-time command. The cause of the anomaly was traced to an incorrect re-configuration of the thermal control software by the fault protection system, following the processor restart that occurred early on Weds. morning (see Jan. 6 status report). A software patch to prevent any reoccurrence has been developed and is currently undergoing testing, prior to being uplinked along with the autopilot software patch on Monday.
Additional diagnostic images from the primary ("A" side) star camera were returned yesterday, allowing characterization of the star field and lighting conditions viewed from the current attitude. Further diagnostic image acqusition is scheduled for early next week, in which the lander will slew to several different atittudes in the vicinity of its current attitude, so that images can be obtained under different lighting conditions to support further analysis.
The next major activity scheduled is the first Trajectory Correction Manuever (TCM-1), which will take place on Monday, Jan. 18. Post-launch navigation estimates of the flight path indicate that, as with the orbiter, a highly accurate injection was achieved. The preliminary estimate for the magnitude of the TCM-1 course correction is approximately 15 m/s, most of which is needed to remove the bias inserted into the launch vehicle injection targeting to satisfy planetary protection constraints (the spacecraft is initially targeted away from Mars to minimize the chances that the upper stage will be placed on a trajectory leading to an accidental impact).
During the investigation of the lander software bugs described above, the flight team has found that orbiter flight software needs to be updated as well, due to the design commonality between the two spacecraft. These bugs have not manifested themselves on the orbiter thus far, and the team believes the orbiter is at very low risk for any occurrences. The orbiter is operating on reaction wheel control at this time, whereas the autopilot bug only applies to certain scenarios involving reaction jet control which are never used on the orbiter in its nominal mission, but would be used in some cases by fault protection if called upon. Likewise, the thermal software bug only manifests itself following resets of the flight computer, none of which have occurred on the orbiter. Software patches to remedy these deficiencies are in preparation for the orbiter, and will be tested and uplinked following completion of the lander software updates.
The next significant event scheduled for the orbiter is its second course correction, TCM-2, planned for Monday, Jan. 25. The flight team is continuing to proceed with TCM-2 preparations, which will pick up following the completion of TCM-1 by the lander.
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