Galileo Is Preparing for the Next Io Flyby

In this final week before the next Io flyby, the pace of activities picks up considerably. On Monday, four more optical navigation frames are shuttered. These images frame the satellite Callisto and several stars. By comparing the relative positions of Callisto and the stars, ground navigators can help refine the position of the spacecraft, supplementing the usual radiometric tracking data used for orbit determination. Two additional such frames are shuttered on Wednesday.

On Tuesday, the Magnetometer instrument changes its configuration, preparing for the more intense magnetic environment as the spacecraft nears Jupiter.

On Thursday, the sequence of commands that will govern Galileo's activities during next week's flyby will be transmitted to the spacecraft. These commands will be sent from the 70-meter diameter Deep Space Network tracking station located at Robledo, near Madrid, Spain. There are two other such antennas that support the Galileo mission, located at the Goldstone tracking station in the Southern California desert, and also at Tidbinbilla, near Canberra, Australia. For more information about these communications complexes, please visit: http://deepspace.jpl.nasa.gov/dsn/ .

Friday sees the end of playback of the tape-recorded data acquired during the last Io flyby on August 5. This week's data return consists of collections of fragments of observations which were lost in transit during previous playback attempts. Once playback has concluded, routine maintenance of the tape recorder is performed on Saturday, to prepare for the new recording.

Also on Saturday, the final targeting maneuver is executed. This motor burn will fine-tune the trajectory of the spacecraft to reach the desired aim-point 181 kilometers (112 miles) above the surface of Io next Monday. Then at 7:41 p.m. PDT the commands sent to the spacecraft on Thursday take charge, and the encounter is under way! First up is configuration of the Fields and Particles instruments, and the start of twelve days of continuous real-time data collection for those instruments.

The six instruments on Galileo which measure the particles and electromagnetic fields that surround Jupiter and its satellites are the Dust Detector Subsystem, the Energetic Particle Detector, the Heavy Ion Counter, the Magnetometer, the Plasma Subsystem, and the Plasma Wave Subsystem.

On Sunday, the tape recorder is moved to the correct position to start recording for the encounter. Also, the attitude control software is configured to rely on sightings of a single bright star to determine the spacecraft orientation. Ordinarily, three or more stars are used for this determination. However, when Galileo approaches Jupiter, high levels of radiation create electronic noise in the star detector, and only very bright stars can be seen reliably. It then becomes a challenge to find a star that is sufficiently bright and also falls within field of view of the star scanner. During the 48 hours surrounding the closest approach to Jupiter and Io, we will be viewing the star Achernar (Alpha Eridani), which is the sixth brightest star in the catalog we maintain for use by Galileo.

Take a deep breath, we're about to get really busy!