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Cassini continues its exploration of the Saturn system with the 21-day Rev170, which begins on August 2 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. Rev170 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-three ISS observations are planned for Rev170, the vast majority focused on Saturn's atmosphere.
ISS begins its observations for Rev170 on August 2, a couple of hours after apoapse, with 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. Another is planned for August 3, plus four more on August 8 and 9. Thirteen are planned between August 15 and 23. On August 9, ISS will acquire a time-lapse movie of the F ring that will include the Encke Gap as well.
On August 13 at 01:32 UTC, Cassini will reach periapse for Rev170 at an altitude of 286,380 kilometers (177,950 miles) from Saturn. During the periapse period, the Ultraviolet Imaging Spectrograph (UVIS) will observe an occultation of the star Kappa Orionis by Dione, and ISS will ride along. During the occultation of Kappa Orionis, UVIS will be measuring the density of gasses in Dione's vicinity while ISS will obtain color images at a distance of 709,470 kilometers (440,840 miles).
The periapse period observations continue with high resolution imaging of the F ring late on August 12. Afterward, during periapse early on August 13, ISS will image the C ring of Saturn in search of small, embedded moonlets. Much later that day, ISS will ride along with UVIS to observe Mimas at a very low phase angle. The ISS images will provide global color imaging of Mimas' sub-Saturn hemisphere from a distance of 802,000 kilometers (500,000 miles). Afterward, ISS will acquire another time-lapse movie of the F ring.
On August 17, ISS will ride along with the Composite Infrared Spectrometer (CIRS) to image Saturn's atmosphere. ISS will acquire a set of images every few hours for 10 hours. These images will be used to track clouds in Saturn's atmosphere. On August 19, ISS will take a look at Titan from a distance of 3.45 million kilometers (2.15 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 sub-Saturn hemisphere. ISS also will be taking shorter-wavelength images to study changes in Titan's upper haze layers. On August 21, ISS will image Titan's sub-Saturn hemisphere again, this time from a distance of 3.50 million kilometers (2.17 million miles). On August 19, ISS will acquire a five-hour observation of Saturn's atmosphere. Researchers will use clouds visible in these images to measure wind speeds and directions at different latitudes on the giant planet. Five more of these short movies of Saturn will be taken between August 19 and 23.
On August 23, Cassini will reach apoapse on this orbit, bringing it to a close and starting Rev171.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC). Dione basemap by Steve Albers.