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Cassini continues its exploration of the Saturn system with the 12-day Rev 193, which begins on June 19 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 193 occurs during the first inclined phase, which lasts until March 2015, of the Cassini Solstice Mission. The inclined phase will allow for polar views of Saturn and Titan as well as better vistas of Saturn's rings than those Cassini had while in the earlier, equatorial phase of the Solstice Mission. Thirty-seven ISS observations are planned for Rev 193 with many focused on Saturn's atmosphere and rings.
On June 19, a couple of hour after apoapse, ISS will acquire a quick observation of Saturn using the 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. Two more observations are planned for June 19, four more for June 20 and 21, and six more for June 28 and 29. On June 19, ISS will look for clouds across Titan's Tsegihi region from a distance of 2.35 million kilometers (1.46 million miles). Next, 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. Finally, ISS will acquire a movie of the F ring, observing its various channels and streamers created by the interaction between the ring material and the nearby moon, Prometheus.
On June 21, the camera system will ride along with a Visual and Infrared Mapping Spectrometer (VIMS) stellar occultation observation, as a red, super-giant star, Mu Cephei (also known as Herschel's Garnet Star), is occulted by Saturn's rings. On June 22, ISS will image the outer A ring, where it will be looking at propellers previously imaged by Cassini. Propellers are small voids in Saturn's rings created by the gravitational interaction between large ring particles and the surrounding ring. Later that day, ISS will acquire a distant observation of a crescent Titan. These images will be taken from a distance of 1.94 million kilometers (1.21 million miles) and will be used to study Titan's upper haze layers. ISS will ride along with a VIMS observation of Saturn's south polar aurora. In addition to making a movie of the planet's aurorae, the images will be used to independently measure the rotation period of Saturn's magnetic field.
On June 25 at 05:09 UTC, Cassini will reach periapse for Rev 193 at an altitude of 557,860 kilometers (346,640 miles) from Saturn. On June 23, ISS will image a crescent Mimas at a distance of 846,000 kilometers (526,000 miles). Afterwards, ISS will image the limb of Saturn while the Sun is behind the planet. This provides an excellent opportunity for observing the various haze layers in the planet's upper atmosphere. On June 24, ISS will monitor the south polar plume of Enceladus from a distance of 535,000 kilometers (332,000 miles). On June 25 and 26, ISS will ride along with a pair of VIMS movies of Saturn's north polar region. During the first observation, ISS will acquire three sets of color filter images using the Wide-Angle Camera (WAC) centered on the north pole. During the second, ISS will acquire a two-by-two mosaic of the north polar region. ISS will then take another look at Titan, looking for clouds across the moon's northern trailing hemisphere from a distance of 1.39 million kilometers (0.87 million miles). This observation will also provide a decent opportunity to image Titan's largest hydrocarbon sea, Kraken Mare.
On June 27, ISS will ride along with a pair of Ultraviolet Imaging Spectrometer (UVIS) observations of two icy moons, Dione and Mimas. In both cases, the moons will be at a very low phase angle, allowing researchers to study the brightness and size of the opposition surge on both moons. This can provide an estimate for the grain size and surface roughness of both moons. Next, ISS will stare at the north hemisphere of Saturn, acquiring a nearly full-rotation movie of the clouds in this region. The observation will be useful for making maps of Saturn. On June 28, as Cassini crosses back below the ring plane, it will observe three mutual events involving Saturn's icy satellites. The first two involve Mimas, first as it appears to pass below Enceladus and then as it passes in front of Saturn's rings (with Pandora and Janus making cameo appearances). The third mutual event observation focuses on Enceladus as the small moon Calypso passes behind Enceladus's south polar plume. Between the Mimas and Enceladus observations, ISS will acquire another astrometric observation of Saturn's small, inner moons.
On June 28, ISS will acquire a low-phase movie of Saturn's faint, inner D ring. On June 29 and 30, ISS will acquire three observations of the small, outer satellite, Ijiraq. These observations, combined with the earlier rotational light curves, will be used to determine the rotation period of the small moon. Unlike Saturn's inner moons, its small, outer satellites rotate once about their axis in a much shorter time than it takes for them to go around Saturn. Ijiraq is 12 kilometers (7 miles) across and will be 8.1 million kilometers (5.03 million miles) away.
On July 1, Cassini will reach apoapse, bringing Rev 193 to a close and starting the next orbit, Rev 194, which includes a targeted flyby of Titan.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).