MARS SURVEYOR 98 MISSION STATUS
January 6, 1999
8:00 A.M. (PST)
Liftoff occurred successfully at 12:21 PST on Sunday, Jan. 3. Following separation from the upper stage, the spacecraft initiated its onboard sequence designed to obtain knowledge of the vehicle orientation, then slew to an orientation suitable for radio contact with ground stations in the Deep Space Network. After observing several unsuccessful attempts by the spacecraft to establish attitude knowledge via its prime and back-up stellar sensors (star cameras), the MPL flight team executed its pre-planned contingency plan for this scenario. Ten hours after launch (22:20 PST), the flight team succeeded in commanding the lander into an attitude allowing stable communcation, although at relatively low signal levels. Subsequent analysis of telemetry data indicated that the spacecraft was in excellent health, the only exception being the inability of either star camera to identify a star pattern allowing attitude determination.
During the following day commands were prepared to perform a diagnostic slew in a direction which would improve the received radio signal level. This slew maneuver was executed successfully at approximately 14:00 PST, moving the spacecraft to an attitude yielding a substantial improvement in signal level, then back to its previous attitude. Subsequently, a stored star camera image and related telemetry obtained just prior to link stabilization on the night of Jan. 3 were transmitted back to Earth for analysis. Further evaluation of telemetry data obtained while the vehicle was in the "test" attitude showed it could operate safely there, without violating any power or thermal constraints. As a result, new commands were prepared to slew the lander back to the "test" attitude and to remain there. These commands were radiated to the spacecraft and executed at 09:40 PST on Tuesday, Jan. 5
The flight team then went to work on three fronts. First, a series of parameter updates to the onboard fault protection software system was developed that would ensure an appropriate response to any subsequent safing events, given the current spacecraft attitude and configuration. Second, commands for several additional slew maneuvers were built that would allow more accurate calibration of the lander's orientation and further improve the reliability of the ground/space radio link. In a parallel third effort, development personnel from the Guidance and Control subsystem formed a team to investigate and diagnose star camera behavior. Preliminary analysis of the star camera telemetry indicated that the lack of pattern recognition by the camera was probably due to stray light entering the lens from reflective surfaces in its vicinity. Although each star camera lens is protected by baffles, it was suspected that the baffles were not attenuating stray light from the fringes of the field of view as well as expected. A second look at our plans to experimentally search for the planned initial post-launch attitude brought forth the realization that this attitude would also shade the spacecraft surfaces near the fields of view of both star cameras.
The fault protection updates were uplinked early this morning (Wed, Jan 6, at about 03:00 PST. Upon re-enabling some of the fault protection software, the spacecraft unexpectly reentered the post-launch attitude acquisition sequence, in which the prime star camera successfully recognized a star pattern and determined the lander's orientation. The spacecraft then slewed itself (as it should) to the planned post-launch attitude, while the star camera continuing to indicate that it was viewing a star field and functioning nominally. The flight team then performed the complete, planned post-launch checkout of all lander subsystems, and found the lander was, in fact, healthy and operating in its intended post-launch configuration. The cause of this course of events is now understand and corrective action, in the form of completing our update of the fault protection system configuration, will be completed later today.
Further evaluation of diagnostic telemetry recorded onboard since launch and returned this morning is ongoing. The star camera investigation team is continuing to scrutinize the available diagnostic telemetry and evaluate the orientation envelope within which the camera is not exposed to excessive stray light levels. In addition, the Guidance and Control group has determined the cause of two minor anomalies noted in the operation of lander's autopilot yesterday and today, and is working to uplink a software patch to the lander that will correct the cause.
Mars Climate Orbiter continues to perform well in early cruise. The spacecraft has been in a quiescent mode of operation this past week, to allow the flight team to concentrate on MPL launch support early cruise operations. Development of the second MCO sequence will begin toward the end of this week, and is scheduled for uplink on Jan. 12
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