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 15, 1990


       The Magellan spacecraft today experienced its first loss of signal since it began mapping the planet Venus Sept. 15 with imaging radar, and its third loss since it went into orbit around the planet Aug. 10.

       The 40-minute loss-of-signal began shortly after 9 a.m. PST when the ground station failed to acquire spacecraft communications after the mapping pass of orbit number 825.

       One of the two radio signals was reacquired about 9:40 a.m. but the high-data rate signal was still pointed away from Earth.

       Flight controllers said telemetry signal levels indicated that the high-gain antenna was pointed away from Earth by about one and one-half degrees, which is beyond the limits of the high-data rate communications band but sufficient for communication of engineering data.

       Controllers are commanding the spacecraft's attitude control system to set the bounds higher so that the next star calibration will be able to correct the spacecraft attitude and the exact pointing of the high gain antenna in conjunction with a ground update so that mapping can be resumed.

       The Magellan project lost the spacecraft signal on Aug. 16 for about 11 hours and again on Aug. 21 for 17 hours.

       Occasional minor data losses are expected from time to time when the articulation and attitude control system halts execution. Onboard systems and protective software have been improved to minimize any data losses.

       Controllers said today's problem occurred probably due to spacecraft events similar to those experienced in August. But this time, the spacecraft recovered quickly because of the changes in the safing system implemented after the August problems and mapping is expected to resume within one day.

      


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11/15/90 JJD
#1330