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Cassini continues its exploration of the Saturn system with the 9.6-day Rev 246, which begins on October 8 at its farthest distance from the planet. This is also called the orbit’s apoapse. At this point, Cassini is 1.34 million kilometers (0.83 million miles) from Saturn’s cloud tops. Rev 246 occurs toward the end of the second inclined phase of the Cassini Solstice Mission. During this phase, Cassini will use encounters with Titan to gradually increase the inclination of its orbit. Seventeen ISS observations are planned for Rev 246 with the majority focused on Saturn’s icy satellites.
For its first observation for Rev 246, on October 20, ISS will acquire an astrometric observation of Saturn’s small, inner moons. Astrometric observations are used to improve our understanding of the orbits of these small satellites, which can be influenced by Saturn’s larger icy moons as well as each other. Careful measurements of the positions of these moons are important for later imaging of them at much closer distances during the F ring orbits starting next month. Another astrometric observation will be taken on October 21. Immediately after both astrometric observations, ISS will acquire quick observations of Saturn using the Wide-Angle Camera (WAC). These observations are part of a series of “Storm Watch” sequences designed to take advantage of short, two-minute segments when the spacecraft turns to point the optical remote sensing (ORS) instruments back at Saturn, as a waypoint between observations. They include blue, clear, two methane band, and one full-frame, continuum band filter images. Another storm watch observation will be acquired on October 27.
On October 20, ISS will ride along with the Visual and Infrared Mapping Spectrometer (VIMS) to observe a stellar occultation of the red giant star Lambda Velorum, in the constellation Vela, by the rings. Stellar occultations can be used to probe the fine-scale structure of Saturn’s rings. On October 21, ISS will acquire a high-resolution, color scan of the main rings using a string of Narrow-angle Camera (NAC) pointings from the F ring to C ring.
On October 23 at 03:40 UTC, Cassini will reach periapse for Rev 246 at an altitude of 278,600 kilometers (173,100 miles) above Saturn's cloud tops, between the orbits of Tethys and Dione. During the periapse period, ISS and the rest of the remote sensing instruments will be focused on Saturn’s various icy satellites. On October 22, ISS will observe Rhea, Tethys (twice), Enceladus, and Mimas (as a ride along observation with the Composite Infrared Spectrometer). These observations will be used to map color variations across the north polar regions of these moons. The closest of these is an observation of Mimas, when Cassini will encounter the moon at a distance of 175,750 kilometers (109,210 miles). On October 23, ISS will observe a crescent Dione from a distance of 539,000 kilometers (335,000 miles) in order to search for possible plume activity at the satellite.
On October 25, ISS will observe the small, distant moon Erriapus from a distance of 14.6 million kilometers (9.09 million miles). This observation will be used to estimate Erriapus’s shape and north pole direction by measuring its light curve. This observation will last for 31 hours. On October 27, ISS will observe a half-phase Titan at a distance of 1.20 million kilometers (1.15 million miles). This observation will be used to monitor clouds across Fensal-Aztlan region of Titan. Later on October 27 and into Rev 247, ISS will acquire a movie observation of the F ring that will run for 18 hours.
On October 27, Cassini will reach apoapse, bringing Rev 246 to a close and starting up the next orbit, Rev 247, when Cassini will perform a distant encounter with Titan.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).