PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011

FOR IMMEDIATE RELEASE                                                December 18, 1990

       One of two radar data tape recorders aboard the Magellan spacecraft, now orbiting the planet Venus, will be turned off on Dec. 22 because of an increasingly high error rate, it was reported Tuesday.

       While the effects of the error rate on that recorder may be corrected with equipment on the ground, controllers said the process is too time consuming. Instead, they want to determine the exact cause of the problem and devise a better solution.

       Magellan can operate with a single tape recorder and still achieve the primary mission objective of acquiring more than 70 percent of the Venus map during the first 243-day cycle, said project manager Tony Spear at NASA's Jet Propulsion Laboratory.

       This will leave small data gaps on each orbit, but the areas missed can be mapped during an extended mission.

       The tape recorder will be inoperative for an unspecified period of time while engineers study the problem. There will be a loss of some radar data on each mapping pass, but it will not seriously affect the overall mission, Spear said.

       At the present time, both recorders A and B, each with a 1.8 billion bit capacity, are being used to record the data from the Magellan imaging radar. Recorder A will be shut down while an investigative team diagnoses the problem, Spear said.

       Use of the single recorder strategy will result in three 40 kilometer (25 mile) gaps in each mapping pass. With one recorder, some data is lost each time the tape stops and reverses to begin use of the next track. With two recorders, the second tape picks up the data lost during that period.

       In early 1991, controllers will decide whether to stay in the single tape recorder strategy, go back to the original two tape plan or use a 5-track strategy. The last-mentioned approach would use one track of recorder A to buffer the tape reversals of recorder B on each orbit.

       The investigative team is made up of experts from JPL, its primary spacecraft contractor Martin-Marietta Corp., and Odetics, manufacturer of the recorders.

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


12/18/90 JJD