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Cassini continues its exploration of the Saturn system with the 12-day Rev 241, which begins on August 25 at its farthest distance from the planet. This is also called the orbit’s apoapse. At this point, Cassini is 1.50 million kilometers (0.93 million miles) from Saturn’s cloud tops. Rev 241 occurs during the second inclined phase of the Cassini Solstice Mission. Over the next several orbits, Cassini will use encounters with Titan to gradually increase the inclination of its orbit. Nine ISS observations are planned for Rev 241 with the majority focused on Saturn’s rings.
On August 27 and 28, the Composite Infrared Spectrometer (CIRS) will acquire a nearly 36-hour, distant observation of Titan from a distance of 1.11 million kilometers (0.69 million miles). This will allow for thermal measurements of Titan’s north polar region. For its first observation for Rev 241, on August 29, ISS will acquire a 17-hour movie of the F ring, a narrow ring just outside the main ring system. The movie will be used to monitor the creation of clumps and channels, formed by the gravitational interaction between F ring material and nearby moons and moonlets. On August 30, ISS will ride along with the Visual and Infrared Mapping Spectrometer (VIMS) to observe a stellar occultation of the red supergiant star Antares by the rings. Stellar occultations can be used to probe the fine-scale structure of Saturn’s rings. Another stellar occultation, this time of the Mira-variable X Ophiuchi, will be observed on August 31 as Cassini is crossing below the ring plane.
On August 31 at 13:16 UTC, Cassini will reach periapse for Rev 241 at an altitude of 400,480 kilometers (248,850 miles) above Saturn's cloud tops, between the orbits of Dione and Rhea. During periapse, ISS will be conducting a 15-hour-long survey of the propellers in the outer A ring. Propellers are voids in the ring created by the gravity of large, 100 – 1000 meter (328 – 3280 foot) ring particles. Due to the influence of the rings on their motion, these observations are used to keep track of previously discovered propellers, like Earhart and Bleriot. On September 1, ISS will acquire a color scan using the Narrow-Angle Camera (NAC) of the unlit face of the A and B rings. Afterwards, VIMS will observe a solar occultation by the rings. Like the stellar occultations, but using the Sun, this will be used to look at the fine-scale structure of the rings, particularly in the C ring.
On September 2, VIMS will acquire another stellar occultation by the ring system, this time of the red supergiant Betelgeuse. Afterwards, ISS will observe the unlit side of the F ring for 11 hours. On September 4, ISS will ride along with the Ultraviolet Imaging Spectrometer (UVIS) as it acquires scans across Saturn. ISS will perform similar observations on September 5, this time while riding along with CIRS.
On September 6, Cassini will reach apoapse, bringing Rev 241 to a close and starting up the next orbit, Rev 242.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).