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Cassini continues its series of seven-day-long orbits with Rev79, the spacecraft's 80th orbit around the ringed planet. During this orbit, Cassini's observations focus on Saturn's icy satellites and rings. Cassini begins Rev79 on July 31 at its farthest distance from Saturn, called apoapsis. At this point, Cassini is 1.22 million km (761,000 mi) from Saturn. The first observations of this orbit involve Saturn's small, inner satellites. On August 1, Cassini will search for additional satellites between Mimas and Enceladus. Cassini's cameras have discovered three previously-unseen moons in this region: Anthe, Methone, and Pallene. On August 1 and 2, the spacecraft will also observe various small satellites in the inner part of the Saturn system in order to better constrain the orbital motions of these moons, which can be affected by nearby large satellites. Cassini will also take a look at the F ring as part of a monitoring campaign to look for changes in the various clumps, knots, and gores in the ring caused by gravitational interactions with Prometheus, Pandora, and large chunks within the ring. Finally, on August 2, Cassini will acquire a partial azimuthal scan of the Cassini Division between the A and B rings.
On August 3, Cassini will again focus on Saturn's ring system. ISS will observe a single point in the F ring over a full rotation, looking at how that point (a clump or a gore) changes during a full orbit due to various gravitational interactions. VIMS will observe a stellar occultation of the ring using Gamma Crucis, a red giant star in the constellation Crux. Cassini will also perform Orbital Trim Maneuver number 162, an engine burn designed as cleanup following the T45 flyby during the previous orbit and to help set up the Enceladus flyby scheduled for Rev80. On August 4 Cassini reaches periapse, its closest point to Saturn during Rev79. At that point, Cassini will be 237,537 km (147,599 mi) from Saturn's cloud tops. Near periapse, Cassini will quickly pass high over the north polar region of Saturn before descending below the ring plane 40 minutes before periapse. Prior to closest approach, ISS will perform a non-targeted flyby of Mimas with a distance of 121,951 km (75,777 mi). Closest approach to Mimas occurs while the moon is in the shadow of Saturn, so many of the ISS observations of Mimas occur one to two hours before that time, when Mimas is a bit further away, but in sunlight. These observations provide an excellent opportunity to fill a gap in the ISS map of Mimas, over the northern sub-Saturn hemisphere. Shortly afterward, Cassini's antenna will be pointed at Earth in order to perform a 30-minute-long, radio-science occultation scan of the ring system. Cassini will transmit a signal using its Ka, X, and S bands to Earth, and the effect on the signal by the intervening rings will be measured to determine ring densities at various points in the system.
Following periapse, Cassini continues to target Saturn's ring system. ISS will perform a full, 360-degree azimuthal scan of the 1.475 Rs ringlet in the outer C ring. On August 5, the Composite Infrared Spectrometer (CIRS) will perform a couple of temperature scans of the sunlit side of the rings.
On August 6, Cassini will start to shift its focus to Saturn's icy satellites. First though, ISS will perform another stare at an area in the F ring over a 9.5-hour period. Cassini will then perform several distant icy satellite observations, including Rhea on August 6, Tethys on August 7, and Dione on August 8. Also on August 6, Cassini will observe several small satellites of Saturn to better refine their orbits. Cassini will also image Enceladus and its surrounding space in order to look at the moon's plume structure prior to the August 11 Cassini flyby of that satellite. Finally, Cassini will also search for small satellites between Mimas and Enceladus on two occasions on August 7 and 8.
Cassini begins Rev80 on August 8. During the upcoming orbit, Cassini will encounter the icy satellite Enceladus, this time with close-up observations of the plume vents.
Image products created in Celestia. Mimas basemap by Steve Albers. Saturn basemap by Björn Jónsson.