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

This week Galileo completes the third week of a 100-day continuous survey of the Jovian magnetosphere. The survey is performed by Galileo's suite of Fields and Particles instruments as part of a dual-spacecraft observation campaign with the Cassini spacecraft. Cassini will pass by Jupiter later this year on its way to arrival at Saturn in 2004.

The data collected by Galileo are extremely valuable as it is rare to find two spacecraft in the same region of space, simultaneously examining the same phenomena. During the 100-day survey, Galileo's flight path will take it from the solar wind into the heart of the Jovian magnetosphere, and back out into the solar wind. All the while, Cassini's instruments will provide additional information on the solar wind. The most valuable portion of the dual-spacecraft campaign will be when Galileo finds itself within the Jovian magnetosphere later this year. With the data from both spacecraft, scientists will be able to see how changes in the solar wind can affect the interior of the magnetosphere.

Galileo is completely dedicated to maintaining the continuity of the fields and particles survey. In preparation, all planned data playback from previous encounters was completed several weeks ago. This allows Galileo's tape recorder to be used to record the contents of an onboard data buffer. The data buffer is used to store survey data when radio antennas of the Deep Space Network are being used by other missions. When insufficient time is available for Galileo, the data buffer overflows and the data are lost. To prevent data loss, the contents of the buffer are recorded to the tape recorder for playback at a later time.

Galileo uses its tape recorder only four times this week to maintain a continuous data set, because sufficient antenna time has been allotted on the Deep Space Network. Out of the total 168 hours in the week (24 hours times 7 days), 124 hours of antenna time has been scheduled for use by Galileo.

On Monday, Galileo also performs standard maintenance on its propulsion systems.