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Cassini moves into the next phase of its journey with Rev 75, its 76th orbit around Saturn, and the first full orbit of the Cassini Equinox Mission. During this orbit, Cassiniís observations focus on Saturnís rings, as well as its satellites Enceladus and Dione. Cassini begins Rev75 on July 3 at its farthest distance from Saturn, called apoapsis. At this point, Cassini is 1.25 million km (779,000 mi) from the planet. The first observations during this orbit involve Saturnís rings. The Composite Infrared Spectrometer (CIRS) performs a scan of the rings over the unlit side on July 4. ISS will acquire wide-angle camera (WAC) support images during the scan (the geometry of the left ansa half of this observation is shown in the graphic at left). A similar scan is performed on July 6 when Cassini is closer to Saturn and at high latitude. ISS will again acquire support imaging with the goal of acquiring two-frame mosaics over both ends of the ring system. The other observation before periapse is an ISS/Visual and Infrared Mapping Spectrometer (VIMS) movie of the F ring, looking at channels and clumps in that irregular ring. On July 7, Cassini reaches periapse, its closest point to Saturn on Rev75. At that point, the spacecraft will be 163,000 km (101,000 mi) from Saturnís cloud tops. Near periapse, Cassini will quickly pass high over the north polar region of Saturn before descending below the ring plane 25 minutes before periapse. On that day, Cassini will observe Enceladus at distances ranging from 215,000 to 328,000 km (135,000 to 204,000 mi). This long CIRS stare continues after Enceladus enters eclipse, as Saturn passes in front of the Sun from Enceladusí perspective. The ISS images near the beginning of the observation will cover the moonís northern trailing hemisphere, similar to ISS views acquired during the previous orbit.
After it dives below the ring plane, the spacecraft turns its attention back to the ring system. On July 8, VIMS and ISS will acquire a 7.5-hour-long time-lapse movie of the B ringís sunlit side. Scientists plan to use these images to study spokes, which are seen commonly in the B ring of late. Later that day, Cassini will also observe Dione from a distance of 1.04 million km (647,000 mi) using ISS and the Ultraviolet Imaging Spectrometer (UVIS). These observations will allow for study of Dioneís leading hemisphere.
Cassini begins Rev76 on July 10. Rev76 includes distant observations of Janus, Rhea, Enceladus, Mimas, and Saturnís atmosphere.
Image products created in Celestia. Enceladus basemap by Steve Albers.