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Cassiniís orbits around Saturn tighten even further as the spacecraft starts its 72nd orbit around the Ringed Planet, the 7.1-day-long Rev71. The shorter orbit lends itself to a more dedicated set of observations, including imaging of Saturnís atmosphere, rings, and several of its moons, including Mimas and Titan. Cassini begins Rev71 on June 5 at its farthest distance from Saturn, called apoapsis. At this point, Cassini is 1.27 million km (786,000 mi) from Saturn. The high inclination of this orbit allows for detailed study of Saturnís ring system and northern hemisphere from high above the ring plane. On June 7, Cassini ISS will acquire a partial, medium-resolution azimuthal scan of the inner Cassini Division. The next day, Cassini will acquire two observations of the north polar region in order to look for auroras and lightning. On June 7, Cassini performs several observations of Saturnís small, inner satellites. The observations are designed to study the orbits of these objects and how they might evolve over short periods due to perturbations from the other satellites in the system. Early on June 9, Cassini reaches periapse, its closest point to Saturn on Rev71. At that point, Cassini 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 15 minutes before periapse. Prior to periapse, Cassini will observe Mimasí northern sub-Saturn hemisphere from a distance of 248,000 km (154,000 mi). An hour after closest approach, Cassini ISS will acquire a high-resolution radial scan of the main ring system, from the C ring to the F ring, near the edge of Saturnís shadow on the rings. Shortly afterward, Cassini will acquire a high-resolution azimuthal scan covering the 1.47 Rs ringlet in the outer C ring. (ďRsĒ is shorthand for ďSaturn radii.Ē Saturnís equatorial cloud tops lie at one Rs, or one Saturn radius, from the planetís center, a distance of about 60,270 km or 37,450 mi.)
On June 10, Cassini ISS will acquire a 17-frame, 3-hour-long movie sequence looking at spokes in the B ring. Also on that day, Cassini will observe the area around Enceladus with the narrow-angle camera, looking at scattered light (but not Enceladus itself). These observations are taken to improve the characterization of stray light from the camera optics with the ultimate goal of obtaining higher quality images of the moon's icy plumes. Cassini will also observe the leading hemisphere of Titan, including eastern Xanadu and Fensal-Aztlan from a distance of 1.11 million km (691,000 mi). Finally, also on June 10, Cassini will observe several of Saturnís small satellites as part of the Imaging Teamís continuing orbit determination campaign. On June 11, ISS will perform several dark current calibration sequences. These calibration images are needed to characterize possible changes in the properties of the narrow-angle cameraís CCD detector. The Ultraviolet Imaging Spectrometer (UVIS) will also be calibrating their High-Speed Photometer. ISS will also acquire additional orbit determination images of several of Saturnís small satellites on June 11.
Cassini begins the following orbit, Rev72, on June 12. Rev72 includes distant observations of Rhea, Mimas, Titan, and Saturnís atmosphere and rings.
Image products created in Celestia. Mimas basemap by Steve Albers.