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February 20, 1999

Mars Climate Orbiter (MCO)

Additional diagnostic telemetry from Inertial Measurement Unit (IMU-A) was downlinked last week in further support of the investigation into noise characteristics of the ring-laser gyro control loops. Similar behavior has now been identified in the Stardust flight spare IMU during ground testing at Honeywell, suggesting it is a design characteristic. Further testing is underway at Honeywell to characterize the circumstances in which the noise phenomena is observed and to identify its cause. Commands were also sent to the spacecraft to obtain some specialized telemetry designed to map the unused space in the telemetry buffer. These maps are being used to formulate a "housekeeping" strategy for managing the buffer free space, limiting its fragmentation.

On Tuesday, Feb. 16, a simple test of the UHF transceiver was performed. With the orbiter in its cruise attitude, the transceiver was powered on and commanded into its nominal receive mode, in which it begins transmitting short "ping" waveforms of 150 millisecond duration every 3 seconds, waiting for the spacecraft to reply. The transceiver was powered for approximately 2 hours; the X-band link with real-time telemetry was maintained throughout this period. A 46 meter radio astronomy station operated by Stanford University was configured to attempt detection of the UHF-band "pings" through several different means. Spacecraft telemetry indicated nominal operation of the transceiver during this period; however, power and temperature telemetry from components located near the UHF antenna displayed an unpredicted pattern of quasi-cyclic noise spikes due to the UHF radio operation. After the transceiver was powered off all real-time telemetry returned to nominal values. The Stanford antenna was unable to detect the "ping" wavetrain in real time (the probability of doing so was not considered to be high for the detection methods attempted). The flight team is currently evaluating telemetry from this test to better understand the apparent interactions observed with the UHF system.

Mars Polar Lander (MPL)

The MPL spacecraft continues to perform well in early cruise. Activity during this past week centered on the attitude control group's work to update the attitude determination and control strategy in early March with a profile and deadband schedule that will allow the star camera to obtain star patterns during the remainder of cruise.

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