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Cassini continues its exploration of the Saturn system with the 21-day Rev171, which begins on August 23 at its farthest distance from the planet. This is also called the orbit's apoapse. At this point, Cassini is 2.55 million kilometers (1.58 million miles) from Saturn's cloud tops. Rev171 is near the start of the first inclined phase of the Cassini Solstice Mission, a phase which lasts until March 2015. 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-five ISS observations are planned for Rev171, the vast majority focused on Saturn's atmosphere.
ISS begins its observations for Rev171 on August 24, a day after apoapse, with a pair of quick observations of Saturn using the wide-angle camera (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. Eleven more are planned between September 4 and 8.
On August 25, ISS will ride along with an Ultraviolet Imaging Spectrometer (UVIS) observation of Saturn, acquiring wide-angle photometry and polarimetry. ISS will acquire a similar observation on August 28. On August 27, ISS will acquire a series of images of Saturn using the WAC. These images will be used to measure wind speeds in Saturn's atmosphere by tracking the motion of various clouds. Three more observations of this type will be acquired on August 28 and 30. Also on August 28, ISS will image a crescent Titan from a distance of 1.26 million kilometers (0.79 million miles). ISS will take another look at Titan on August 31 from a distance of 1.17 million kilometers (0.73 million miles). Titan will be at half phase at the time, providing a view of the moon's southern trailing hemisphere. Also on August 31, ISS will ride along with the Composite Infrared Spectrometer (CIRS) to observe Saturn's south polar region in order to monitor aurorae in the planet's upper atmosphere.
On September 3 at 07:39 UTC, Cassini will reach periapse for Rev171 at an altitude of 287,180 kilometers (178,450 miles) from Saturn. During the periapse period, ISS will observe the south polar plume of Enceladus from a distance of 375,000 kilometers (233,000 miles). ISS will also ride along with the Visual and Infrared Spectrometer (VIMS) in order to acquire numerous WAC image sets of Saturn's atmosphere. These images will be focused on Saturn's northern hemisphere near 35 degrees north latitude.
On September 4, ISS will take a look at Titan from a distance of 2.05 million kilometers (1.27 million miles). The observation is an effort to look for clouds in the moon's atmosphere as part of the "Titan Monitoring Campaign" (TMC). This observation of a gibbous-phase Titan is designed to monitor clouds over the moon's Fensal-Aztlan region. ISS also will be taking shorter-wavelength images to study changes in Titan's upper haze layers. On September 5, ISS will acquire a five-hour movie of Saturn's faint, inner, D ring. On September 7, ISS will image Titan again, covering its eastern Xanadu region from a distance of 2.31 million kilometers (1.43 million miles). Later that day, ISS will acquire a 10-hour light curve observation of the small, outer moon, Bestla. Similar observations of Bestla, designed to measure the moon's rotational period, are planned for September 8 and 9. On September 8, ISS will acquire an astrometric observation of Saturn's small, inner moons including Pandora, Epimetheus, Anthe, Pan, Prometheus, Pallene, Helene, Daphnis, Methone and Atlas. Astrometric observations are used to improve our understanding of the orbits of these small satellites, which can be influenced by Saturn's larger icy satellites. Between September 10 and 13, ISS will acquire four TMC observations of a half-phase Titan, covering its southern, anti-Saturn hemisphere. These observations will be acquired from distances ranging from 1.49 to 1.73 million kilometers (0.93 to 1.07 million miles).
On September 13, Cassini will reach apoapse on this orbit, bringing it to a close and starting Rev172. Rev172 includes a flyby of Titan.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).