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FOR IMMEDIATE RELEASE                                                February 28, 1991

       The initial actions taken to protect the Magellan spacecraft from the sun's heat as it orbits Venus have been successful, project officials at the Jet Propulsion Laboratory said today.

       Magellan, mapping Venus with imaging radar, has been orbiting with direct sunlight on portions of the spacecraft containing critical components since January 26 due to changes in the geometry of Venus, Earth and the sun.

       "The Magellan spacecraft is in a phase of the mission that was predicted to create a thermal challenge for the flight team due to the heat of the sun reaching some components," said Ken Ledbetter, Martin Marietta, spacecraft team chief.

       Throughout most of its time since last August, Magellan had passed through the shadow of Venus somewhere in its orbit. In one previous episode of full sun throughout its orbit, Magellan was cooled for two hours out of every three because the spacecraft body was in the shadow of the antenna during playback.

       Two actions are now being taken to prevent excess heating of spacecraft components. One is to shorten each 37-minute mapping swath by 10 minutes to assume the playback attitude causing a slight loss in mapping data; the other is to turn the solar panels 90 degrees for about 5 minutes at the beginning and end of each mapping pass to reduce the reflection of sunlight from the mirrored solar cells onto the spacecraft.

       "The plan has been very successful," said Project Manager Tony Spear. "The spacecraft components began cooling and remained well within pre-set limits." Spear added that he was dismayed by reports that the spacecraft was overheating. "Magellan has never overheated," he said, "and we will always take steps to make sure it does not."

       "Most spacecraft components have begun to cool significantly," said Ledbetter.

       The alarm limit is the level at which flight controllers flag the temperature to spacecraft engineers so that corrective action can be considered. This limit is always below the temperature at which overheating will occur.

       Today Magellan began a period when a portion of the orbit passes through the shadow of Venus. That will help cool the spacecraft as the length of time in the Venus shadow increases. This period of shadow will continue through March into early April.

       Magellan has mapped more than 58 percent of Venus to date. A similar mapping pattern on Earth would stretch eastward from Los Angeles to Manila.

       "When the first cycle ends May 15, more than 80 percent of Venus will have been mapped," Spear said, "well over the primary mission requirement of 70 percent."

       JPL manages the Magellan mission for NASA's Office of Space Science and Applications.


2/27.91 JJD