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

our draft

       The Magellan spacecraft was back to routine radar mapping of Venus Monday following a command error incident during the weekend that caused the loss of four mapping orbits, project officials reported.

       A Magellan Project spokesman at NASA's Jet Propulsion Laboratory said the command error caused the spacecraft to enter a safe mode at 7:11 p.m. PST Friday.

       The routine command was to update the spacecraft's computer for radar pointing. A timing procedure was not followed and the command files were transmitted too close together.

       As a result the spacecraft's computer invoked a safing procedure which include pointing the high-gain antenna toward Earth, turning off the radar sensor, tape recorders and the high-data rate transmitter.

       Contact with the spacecraft was not lost and engineering telemetry was transmitted at 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 prior to the command error.

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

       Even with the loss, project flight controllers said the project has received 97.2 percent of the radar image data since planned mapping was started on Sept. 15.


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11/26/90 JJD
#1333