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February 26, 1999

Mars Climate Orbiter (MCO)

MCO continued nominal operations in its current cruise configuration. Commands were transmitted on Friday of last week (Feb. 19) to downlink some telemetry data from the Pressure Modulator Infrared Radiometer (PMIRR) which were not returned after a brief power on of the instrument conducted earlier. All telemetry continue to indicate PMIRR is in excellent health. The flight team is now preparing the command sequence for the orbiter's second course correction, TCM-2, scheduled to take place early on the morning of Mar. 4.

Subsequent analysis of acceptance test data recorded from all of the Inertial Measurement Units onboard MCO, Mars Polar Lander, and STARDUST by the vendor indicate that the behavior in the laser intensity monitor data observed onboard MCO is present in all units. No changes in the y-axis LIM telemetry from MCO have occurred over the last two weeks; the spacecraft's autopilot continues to perform well, with no anomalous behavior seen in response to the LIM noise phenomena.

During further investigation of last week's test of the UHF transceiver, the flight team has identified the cause of noise spikes observed in nearby instrumentation during "ping" transmissions. A review of pre-launch Electromagnetic Interference (EMI) test data with a similar spacecraft configuration has found the shielding and implementation of the affected sensors results in a susceptibillty to interference at UHF-band frequencies that was apparently not replicated with adequate fidelity. Additional analysis of spacecraft telemetry from the test further confirms that no overstressing of any components occurred. The team is now identifying work-around options for UHF relay operations with the lander at Mars.

Mars Polar Lander (MPL)

MPL experienced another week of largely quiescent operation. Today commands are being sent to open the descent engine values and vent the propellant lines to space. This event is timed such that the navigation team has approximately two weeks to observe any resulting effect on the flight path prior to the TCM-2, scheduled for Mar. 15. The attitude control group has completed its analysis leading to a revised attitude profile and deadband schedule for later cruise. During the following week the uplink products needed for implemetation will be built and tested, aiming toward a date of Mar. 9 for radiation.

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