This Week on Galileo - September 8-14, 1997
Galileo spends the last week of cruise recovering from juggled playback plans, observing the Great Red Spot and preparing for its next encounter with the Jupiter system, scheduled to start late Saturday, September 13 (Pacific Daylight Time), with its closest flyby of Callisto on September 16 (Pacific Daylight Time).
Late last week, changes were made to the playback schedule to allow the return of mission-unique calibration data from the Photopolarimeter Radiometer (PPR) instrument. This schedule change allowed the tape recorder to move further along the tape than originally planned. The schedule change was needed to prevent the PPR data from being overwritten by recorded observations planned later this week. The first few hours of this week have no active playback. During this time, the tape is repositioned to the location required to complete the final set of recording and playback commands.
Once restarted, this week's playback activity is again interrupted by plans to turn the spacecraft for another series of Great Red Spot and general Jupiter atmosphere observations at high-solar phase angles (when the spacecraft is on the dark side of Jupiter and only a small part of Jupiter, as seen by Galileo, appears to be lit by the sun). These observations will permit the science community to determine the light scattering characteristics of Jupiter's upper atmosphere and infer information about the particle size distribution of Jupiter's atmosphere at high altitudes.
Prior to and just after the recording activities of this week, the playback schedule contains a couple of image of Jupiter's atmosphere taken by the Solid State Imaging (SSI) camera. These images were taken at high solar-phase angles and will provide data that is important for interpreting images that contain Jupiter's dark limb. The darkening of Jupiter's limb is partly due to the amount of light that is scattered by the particles in Jupiter's upper atmosphere. Particles that scatter a lot of sunlight will make Jupiter's limb appear darker than particles that scatter less light. By knowing which particles are typical of Jupiter's upper atmosphere, it will be easier for scientists to interpret all images of Jupiter's limb. This in turn will make it easier for them to study the different cloud levels of Jupiter's atmosphere.
The remaining items on this week's playback schedule come from the series of atmospheric observations performed during the week. All observations were made at a solar phase angle of 145 degrees and all by the Near Infrared Mapping Spectrometer (NIMS). They include three observations of a hotspot/plume head cloud region, two observations of the Great Red Spot, and one each of southern and northern hemisphere regions, and an equatorial region.
The playback schedule ends on Friday in preparation for the start of the Callisto - Orbit 10 encounter. The commands for the first part of the encounter are transmitted to the spacecraft on Thursday of this week. Commands for the last orbit trim maneuver (basically, fine-tuning the spacecraft's flight path) prior to the encounter are scheduled to be sent to the spacecraft on Friday.
Don't forget about Galileo's next encounter! It starts here at this site (well, at Jupiter, really) with the return of Today on Galileo on Saturday, 13 September.