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Cassini continues its exploration of the Saturn system with the 14-day Rev175, which begins on November 19 at its farthest distance from the planet. This is also called the orbit's apoapse. At this point, Cassini is 1.97 million kilometers (1.22 million miles) from Saturn's cloud tops. Rev175 occurs six months into 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 Rev175, the vast majority focused on Saturn's atmosphere as a well as on a Titan flyby on November 29.
ISS begins its observations for Rev175 the day after apoapse with a pair of observation of a gibbous Titan from a distance of 2.53 to 2.61 million kilometers (1.57 to 1.92 million miles). These observations are designed to look for clouds in the moon's atmosphere as part of the "Titan Monitoring Campaign" (TMC). These two observations are designed to monitor clouds over the moon's southern and trailing hemispheres. ISS also will be taking shorter-wavelength images to study changes in Titan's upper haze layers. ISS will image Titan again on November 22 and 23 covering the southern and sub-Saturn hemispheres once more.
On November 20 and 23, ISS will ride along with Ultraviolet Imaging Spectrometer (UVIS) scans of Saturn. The camera system will then acquire a series of WAC images of Saturn in order to measure wind speeds over a period of 5 hours. Similar sets will be taken on November 21, 23, and 24. On November 24, ISS will ride along with a Composite Infrared Spectrometer (CIRS) 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. ISS's observations of the aurora will continue into a pair of Visual and Infrared Mapping Spectrometer (VIMS) observations of the planet's south pole on November 24 and 25.
On November 27 at 02:15 UTC, Cassini will reach periapse for Rev175 at an altitude of 355,680 kilometers (221,010 miles) from Saturn. During the periapse period on November 26, ISS will image the limb of Saturn while the Sun is behind the planet. This will provide an excellent opportunity for observing the various haze layers in the planet's upper atmosphere. Early on the 27th, ISS will acquire a short movie of the planet's north polar region. Researchers will be looking to see if there is a north polar vortex to match the one observed at the south pole earlier in the mission. In addition, spring has progressed far enough that the entirety of the hexagonal jet stream that lies near 77 degrees North latitude will be in sunlight. The hexagon should fill the Wide-angle-camera (WAC) images for this observation. Later on the 27th, ISS will ride along with VIMS in order to acquire a WAC mosaic of Saturn's northern hemisphere and north polar region.
Two days after periapse, Cassini encounters Titan on November 29 at 08:57 UTC for the 89th time. This is the final Titan flyby planned for 2012, with the next encounter scheduled for February 17. T88 is a low-altitude flyby with a close-approach altitude of 1014 kilometers (630 miles). This flyby will allow for imaging of the Adiri region and the southern anti-Saturn hemisphere of Titan outbound from the encounter. Before the encounter, CIRS will acquire spectral scans and other data of Titan's night side and narrow crescent. CIRS will scan across Titan in order to map stratospheric temperatures. The instrument will also make scans along the limb of Titan to measure aerosol and chemical abundances at different altitudes above the moon's surface. ISS will ride along to acquire images of Titan's upper haze layers, which are more easily visible at high phase angles.
At closest approach, the VIMS team will be prime. VIMS will acquire image spectral cubes of several surface features as Cassini makes it pass over Titan. It will first image Mackay Lacus, a large lake or marsh land on the leading hemisphere side of the north pole. The lake was first seen by RADAR in July 2006. VIMS's data could be used to determine the depth of liquids within Mackay Lacus. Next, VIMS will look at Tortola Facula, an area of rough terrain in the northwestern part of the Shangri La sand dune sea, and finally will look at Santorini Facula, an impact crater south of Tortola. As Cassini departs from Titan, CIRS will map surface temperatures across the visible disk to look for diurnal and albedo-related differences while VIMS will perform global mapping at high and medium resolution. ISS will ride along during these observations, searching for clouds across Adiri and the southern anti-Saturn hemisphere, including over the Huygens landing site.
On December 2, ISS will acquire four 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. After the second Saturn storm watch observation, 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. Also on December 2, ISS will look for propellers within the Saturn's outer A ring.
On December 3, Cassini will reach apoapse on this orbit, bringing it to a close and starting Rev176.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).