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Cassini continues its exploration of the Saturn system with the 24-day Rev 196, which begins on August 5 at its farthest distance from the planet. This is also called the orbit's apoapse. At this point, Cassini is 2.03 million kilometers (1.26 million miles) from Saturn's cloud tops. Rev 196 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-four ISS observations are planned for Rev 196 with most focused on Saturn's atmosphere and rings.
On August 10, five days after apoapse, ISS will ride along with an Ultraviolet Imaging Spectrometer (UVIS) observation of a crescent Iapetus. While the moon will be too distant (4.91 million kilometers or 3.05 million miles away) to observe surface features in any detail, Iapetus will be occulting the bright B-type star Bellatrix, the "right shoulder" of the constellation Orion. UVIS will use the occultation to measure the density of any gasses that might exist in the vicinity of the distant, icy moon. Afterward, ISS will ride-along as UVIS performs a limb-to-limb scan across Saturn using its extreme- and far-ultraviolet channels. ISS will acquire a set of narrow-angle (NAC) and wide-angle (WAC) photometry images of the planet during the scan. On August 12 and 13, ISS will ride-along with the Composite Infrared Spectrometer (CIRS) for three observations of Saturn's dayside atmosphere and north polar aurorae.
On August 14, ISS will acquire a pair of quick observations of Saturn using the WAC. These observations are 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. Fourteen more are planned between August 17 and August 29. Between these first two storm watch observations, 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. Another astrometric observation will be acquired on August 22. On August 15, ISS will look for clouds across Titan's northern sub-Saturn hemisphere from a distance of 2.22 million kilometers (1.38 million miles).
On August 17 at 15:35 UTC, Cassini will reach periapse for Rev 196 at an altitude of 1,054,300 kilometers (655,110 miles) from Saturn. Earlier that day, 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. An hour and a half after periapse, ISS will ride-along with the Visual and Infrared Spectrometer (VIMS) as it observes an occultation by Saturn's rings of the red-giant star W Hydrae. On August 18, ISS will ride-along with CIRS as it observes the rings at near zero phase. These observations are useful for understand grain size variations across the various areas of the ring sytem.
On August 20, ISS will look for clouds across Titan's sub-Saturn hemisphere from a distance of 1.33 million kilometers (0.82 million miles). Afterward, 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. Similar movies will be acquired on August 24, 26, and 28. On August 22, ISS will again look for clouds across Titan's Tsegihi region from a distance of 1.57 million kilometers (0.98 million miles). On August 29, ISS will ride-along with the VIMS as it observes an occultation by Saturn's rings of the red-giant star Beta Andromedae.
On August 29, Cassini will reach apoapse, bringing Rev 196 to a close and starting up the next orbit, Rev 197, which will include a targeted flyby of Titan.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).