From: Jet Propulsion Laboratory
Posted: Monday, October 29, 2001
The Conclusion of the Io 32 Encounter
The sequence of commands that governed the spacecraft activities during last Monday's flyby of Io is still in control, winding down in its closing days. Data are still being collected and added to the tape recorder. Playback of this encounter's data does not begin until near the end of the week.
Most of Monday was set aside as a backup opportunity to execute the post-encounter maneuver which occurred last Friday. However, the Navigation Team did such a great job of delivering the Galileo spacecraft to the desired location and time for the Io flyby that the need for a potentially large maneuver was reduced to a mere shadow of its possible self, and the Friday activity did the job quite well. We hit the mark on where and when we wanted to be at Io to within 3.5 kilometers (2.1 miles) of the expected 181 kilometers (112 miles) from the surface of the volcanic satellite, and got there only 0.7 seconds late!
From Monday through Thursday, the spacecraft is occupied with the continuous collection of real-time data about the energetic particles and electromagnetic fields that surround Jupiter. The instruments participating in this data collection are the Dust Detector Subsystem, the Energetic Particle Detector, the Heavy Ion Counter, the Magnetometer, the Plasma Subsystem, and the Plasma Wave Subsystem. When complete, this data set will span 12 days and cover the region from the Io torus to the bow shock region, where the solar wind begins to win its constant struggle with Jupiter's magnetic field. Whenever ground communications antennas are not scheduled to listen to Galileo, the data are stored in on-board computer memory and periodically dumped onto the tape recorder for later playback. Two aspects of this continuous data collection are important to scientists. First, the time continuity of the data provides the scientists with a good look at how the environment is constantly changing and evolving. Second, the spatial continuity gives the scientists a picture of the large-scale structure of the environment, as Galileo passes from the distant reaches of the Jupiter system down through the close-in, high-radiation environment, and back out the other side.
But all good things must come to an end, and on Thursday, this data survey ends for all but the Magnetometer and the Dust Detector, which continue to collect data for another three days. When the bits are no longer devoted to the real-time data, the spacecraft can look to the tape recorder and begin sending its data to the eager flight team here on Earth.
The first priority in the playback data is to sample all of the images captured by the Solid State Imaging camera (SSI) over the past week. During recent orbits, radiation-induced problems in the camera have rendered many of the pictures unusable. A recent change to the spacecraft's computer software appears to have kept the problem from recurring during this flyby. We won't be certain until the spacecraft completes a first pass through the tape, returning some imaging data from each recorded frame. The second pass through the recorded data should begin late Sunday or early Monday, and will start returning the full set of data from all of the instruments.
On Friday, routine maintenance of the spacecraft propulsion system is performed.
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