PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011

FOR IMMEDIATE RELEASE                                                November 26, 1990

       The Magellan spacecraft has returned to routine radar mapping of Venus following a weekend incident that caused the loss of data from four mapping orbits.

       Late Friday evening Magellan controllers commanded the spacecraft to update its computer so the radar mapping would precisely match the most recent spacecraft tracking data. Because of an error in the preparation or transmission of the set of commands, the spacecraft received individual commands without adequate time separation.

       Following spacecraft procedures, at 7:11 p.m. PST, the spacecraft's command computer placed the spacecraft in a "safe mode," pointing the high-gain antenna toward Earth and turning off the radar sensor, tape recorders and the high-data rate (1,200 bits per second) transmitter.

       Contact with the spacecraft was not lost and engineering telemetry continued to be received at the lower rate of 40 bits per second.

       At the time of the incident, the spacecraft had just completed mapping over the western part of Aphrodite, the large equatorial upland of Venus. The mapping data was on the tape recorder ready for playback.

       Engineers worked through the night and returned the spacecraft to normal operations. At 8:08 a.m. PST Saturday, the onboard computer sequence resumed with the playback of the mapping orbit obtained immediately before the command error.

       The first star calibration performed after operations resumed showed the spacecraft's pointing error was only 0.06 of a degree away from its target.

       Project flight controllers said the project has received 97.2 percent of the radar image data since planned mapping was started on Sept. 15, keeping the spacecraft on target to meet the project's goal of 70 percent coverage of Venus during the first mapping cycle.


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11/26/90 JJD
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