NASA's Galileo spacecraft soars above Jupiter's volcanic moon Io in this artist's impression. Photo: NASA/JPL

The first of the next three weeks sees the continued return of science data stored on the spacecraft's onboard tape recorder. In the second and third weeks, the orbital motion of the Earth and Jupiter brings the Sun between the two, creating radio interference and making reliable communications between the spacecraft and Earth impossible. The Sun's effect on Galileo's radio signal gradually increases as the spacecraft moves behind the Sun, and then gradually decreases as the spacecraft emerges from behind the Sun. This geometric situation is known as superior solar conjuction. The spacecraft will emerge just in time to prepare for a close flyby of Ganymede on May 20.

During the week of April 24th, playback is interrupted twice. On Tuesday, April 25 playback is halted to allow the spacecraft to perform a small turn to keep its antenna pointed toward Earth. On Thursday, April 27, playback is interrupted again to perform standard maintenance on the spacecraft's propulsion system. On Friday, April 28 playback is terminated for the duration of the solar conjunction.

Prior to the loss of reliable communications, Galileo returns three observations acquired during its February flyby of Io. The observations are returned by the Photopolarimeter Radiometer (PPR), the Solid-State Imaging camera (SSI), and the Near-Infrared Mapping Spectrometer (NIMS). PPR returns a dayside thermal map of Io. The map is designed to provide information on the thermal properties of Io's surface in the presence of sunlight. NIMS and SSI complete the playback plans by returning additional independent views of Io.