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May 1, 1998

John McNamee
Mars Surveyor 98 Project Manager

Orbiter solar thermal vacuum (STV) testing was resumed April 27 in order to calibrate the Pressure Modulator Infrared Radiometer (PMIRR) instrument. All spacecraft and instrument STV test objectives were completed successfully (including the calibration of PMIRR) on April 28. A system aliveness test was conducted following STV with no anomalies and the go ahead was given to remove the spacecraft from the thermal vacuum chamber.

The earlier PMIRR failure in STV was determined definitively to be a mechanical failure of the optical chopper assembly, however the exact failure mechanism (debris, power transients, etc.) has not been determined. The damaged chopper assembly will be removed from the PMIRR instrument and replaced with the flight spare. This swap can be accomplished without removing PMIRR from the spacecraft. The damaged chopper will be examined for the exact cause of the failure.

Lander integration and test activities are proceeding on schedule with no significant problems. Lander solar thermal vacuum testing in the cruise configuration is scheduled to begin on May 14.

The pyroshock and vibration re-test of the engineering qualification model Thermal Evolved Gas Analyzer (TEGA) Tunable Diode Laser (TDL) design fix was performed successfully. Subsequently, the flight TDL passed vibration re-testing with no problems. (Note: Pyroshock re-testing was performed only on the engineering qualification model due to potential cumulative effects of this testing on the flight instrument). The flight TEGA is on schedule for integration with the lander spacecraft in June.

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