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Cassini continues its exploration of the Saturn system with the 22-day Rev 219, which begins on July 16 at its farthest distance from the planet. This is also called the orbit's apoapse. At this point, Cassini is 2.67 million kilometers (1.66 million miles) from Saturn's cloud tops. Rev 219 occurs during the second Equatorial phase of Cassini's extended-extended mission. During this 10-month phase, Cassini will orbit within the orbital plane of Saturn's rings, allowing for frequent encounters with Saturn's icy satellites. Twenty-five ISS observations are planned for Rev 219 with the majority focused on Saturn's atmosphere and icy satellites.
For ISS's first observation of Rev 219, on July 19, the camera system 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. Three more astrometric observations will be acquired on July 21, 22, and 26. Immediately afterward, ISS will acquire a quick observation of Saturn using the Wide-Angle Camera (WAC). This observation is part of a series of "Storm Watch" observation sequences designed to take advantage of short, two-minute segments when the spacecraft turns the optical remote sensing (ORS) instruments back to Saturn as a waypoint between other experiments' observations. These sequences include blue, clear, two methane band, and one full-frame, continuum band filter images. Four more will be acquired between July 20 and 22, while another four will be taken after periapse between July 28 and August 1. After the July 19 storm watch observation, ISS will spend 17 hours observing the E and G rings, dusty rings that are more visible at high phase angles. Cassini will acquire a similar observation on July 31.
On July 25, Cassini will perform a non-targeted encounter with Titan. Cassini will pass within 730,000 kilometers (454,000 miles) of Titan. ISS will acquire a pair of observations of Titan in the days leading up to the encounter as well as one an hour later. The first two observations will be acquired on July 21 and 22. The July 21 observation will be taken from a distance of 2.76 million kilometers (1.72 million miles), while the July 22 observation will be taken from a distance of 2.26 million kilometers (1.40 million miles). Along with the observation on July 25th, these observations will be used to look for clouds and surface changes across the sub-Saturn and leading hemispheres.
On July 27 at 05:49 UTC, Cassini will reach periapse for Rev 219 at an altitude of 223,100 kilometers (138,600 miles) from Saturn's cloud tops, between the orbits of Enceladus and Tethys. During the periapse period, Cassini's ISS will acquire several observations of Saturn's icy satellites. On July 26, ISS will ride along with Composite Infrared Spectrometer (CIRS) to observe Rhea's leading hemisphere from a distance of 300,000 kilometers (186,000 miles). Next, ISS will acquire a pair of observations of a half-phase and crescent Dione from a distance of 65,000 kilometers (40,000 miles). Mosaics from these two short observations will cover the bright icy canyons of Dione's trailing hemisphere. On July 27, during periapse, Cassini will observe Enceladus's trailing hemisphere from a distance of 111,420 kilometers (69,230 miles). This hemisphere is covered in young, tectonically-refreshed terrain with more craters visible near the north pole and in the northern mid-latitudes.
On July 28, ISS will observe the Phoebe Ring, a faint, dusty ring that lies between 100 and 270 times Saturn's radius from Saturn (for comparison, Cassini will be 17 Saturn radiis from Saturn during the observation). Cassini will be observing the edge of Saturn's shadow on the very faint ring. On July 29, ISS will observe a crescent Enceladus from a distance of 1.31 million kilometers (0.81 million miles) to monitor plume and jet activity at the moon's south pole. On August 6, ISS will observe the distant, outer moon Hyrrokkin from a distance of 12.9 million kilometers (8.06 million miles). This observation will be used to better constrain this 8-kilometer or 5-mile-wide moon's pole direction and shape.
On August 7, Cassini will reach apoapse, bringing Rev 219 to a close and starting up the next orbit, Rev 220, which will include a targeted flyby of Dione.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).