Galileo Mission Status - January 20, 1998
MEDIA RELATIONS OFFICE JET PROPULSION LABORATORY CALIFORNIA INSTITUTE OF TECHNOLOGY NATIONAL AERONAUTICS AND SPACE ADMINISTRATION PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011 http://www.jpl.nasa.gov
Members of the Galileo flight team are analyzing data from a test performed Friday night, which they hope will shed light on the cause of two recent incidents of anomalous behavior by the spacecraft. While the investigation continues, the spacecraft has resumed normal transmission to Earth of pictures and other science information stored on its onboard tape recorder.
While one anomaly occurred during the spacecraft's December 16, 1997 flyby of Europa, and the other after the flyby, both involved the attitude control subsystem, which controls where the spacecraft and scan platform are pointing. Team members suspect the cause may have been one of the spacecraft's two gyroscopes. The gyroscopes are used to point the spacecraft when very precise pointing control and knowledge of the spacecraft's position and orientation are needed, usually for camera and other remote sensing science observations or for maneuvers that adjust the spacecraft's flight path.
The anomalies were not considered serious, but they did cause a temporary slowdown in the rate at which information was transmitted to Earth. That's because the anomalies caused Galileo's radio antenna to point in a direction about 10 degrees from Earth, about eight degrees greater than the normal attitude for ideal data transmission. However, information is now being transmitted at a normal rate once again, thanks to a spacecraft turn performed last week which pointed Galileo's antenna within 3 degrees of Earth, a normal angle.
Galileo has begun sending back to Earth some high-resolution pictures taken during the Dec.16 Europa encounter. That flyby was the closest ever to be performed by Galileo, with the spacecraft dipping down to 200 kilometers (124 miles) above the icy moon's surface. This week, Galileo will also return fields and particles information on the interaction between Europa and Jupiter's magnetic and electric field environment.
A flight path maneuver is planned for Thursday evening, Jan. 22 to prepare for Galileo's upcoming Europa encounter on Feb. 10. Special precautions have been taken in the design of this maneuver to minimize its vulnerability to any gyro problems. Because of its proximity to solar conjunction, when the Sun will be between Galileo and Earth, no data collection is planned except for radio science information.
The spacecraft recently began a two-year extended mission, known as the Galileo Europa Mission, which will include a total of eight Europa flybys, four of Callisto, and one or two of Io, depending on spacecraft health.
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