An artist's concept of NASA's Galileo spacecraft in orbit around Jupiter. Photo: NASA/JPL

This week Galileo's efforts continue on maintaining the continuity of a Fields and Particles instrument survey of the Jovian magnetosphere. The survey data are very valuable as they are Galileo's contribution to a dual-spacecraft observation campaign to examine the influence of the solar wind on the Jovian magnetosphere. Two engineering activities are performed during the week. On Friday, the spacecraft performs standard maintenance on its propulsion systems. On Sunday, the spacecraft executes a small turn to keep its radio antenna pointed toward Earth.

The Fields and Particles instruments on Galileo are the Dust Detector, Energetic Particle Detector, Heavy Ion Counter, Magnetometer, Plasma Detector, and Plasma Wave instrument. The second participant in this dual-spacecraft observation campaign is the Cassini spacecraft. Cassini will pass by Jupiter in December, enroute to arrival at Saturn in 2004. The rarity of having two spacecraft in position to collaborate in observing the same phenomena makes the data gathered by both spacecraft extremely valuable.

Galileo is using its onboard tape recorder to store survey data that cannot be immediately transmitted to Earth. The tape recorder is necessary because Galileo's main computer memory (circa 1980s) is configured to store only about 7 hours of survey data. When the radio antennas of the Deep Space Network (DSN) are being used by other spacecraft and Galileo's data buffer is near capacity, Galileo dumps the contents of the data buffer onto the tape recorder to prevent buffer overflow and data loss. When the next DSN antenna scheduled for Galileo comes along, the survey data that have been stored on the tape recorder are retrieved, packaged and transmitted to Earth.

This week, Galileo uses its tape recorder 10 times to store survey data, and is able to play back data for approximately 80 hours.