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Cassini continues its exploration of the Saturn system with the 13-day Rev 229, which begins on December 26 at its farthest distance from the planet. This is also called the orbit’s apoapse. At this point, Cassini is 1.90 million kilometers (1.18 million miles) from Saturn’s cloud tops. Rev 229 occurs toward the end of the second Equatorial phase of the Cassini Solstice Mission. During this 10-month phase, which ends during the next orbit, Cassini orbits within the orbital plane of Saturn’s rings, allowing for frequent encounters with Saturn’s icy satellites. Twelve ISS observations are planned for Rev 229 with the majority focused on Saturn’s atmosphere and distant observations of Titan.
For its first observation of Rev 229, on December 27, Cassini will perform an observation of Titan from a distance of 2.52 million kilometers (1.57 million miles). This observation will be used to monitor clouds on Titan, in this case looking for clouds across the moon’s sub-Saturn hemisphere. Similar cloud monitoring observations will be acquired on December 28, December 30, and December 31. The closest of these will be taken on December 31 from a distance of 1.10 million kilometers (0.69 million miles), when ISS will be observing the Fensal-Aztlan region of Titan. A follow-up haze monitoring observation of a crescent Titan will be taken on January 3 at a distance of 1.39 million kilometers (0.86 million miles).
On December 28, ISS will acquire astrometric observations 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. Targets for these observations include Polydeuces, Calypso, Telesto, Helene, Epimetheus, Atlas, and Methone. ISS will acquire a similar observation on December 30.
On December 28, immediately after the astrometric observation, ISS will acquire a quick observation of Saturn using the Wide-Angle Camera (WAC). This observation is 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. These sequences include blue, clear, two methane band, and one full-frame, continuum band filter images. Two more Storm Watch observations will be taken on December 29 and another will be taken on December 30.
On January 1 at 10:39 UTC, Cassini will reach periapse for Rev 229 at an altitude of 94,760 kilometers (58,880 miles) from Saturn's cloud tops, just outside the orbits of Janus and Epimetheus. The only ISS observation planned for the periapse period will involve the camera system monitoring Enceladus’s south polar plume, the source of the diffuse E ring.
On December 26, Cassini will reach apoapse, bringing Rev 229 to a close and starting up the next orbit, Rev 230. During the next orbit, Cassini will start to climb out of Saturn’s ring plane with a flyby of Titan. The spacecraft will also perform close encounters with Mimas, Daphnis, and Telesto, performing imaging along the way.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).