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Cassini continues its exploration of the Saturn system with the 12-day Rev 242, which begins on September 6 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 242 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. Sixteen ISS observations are planned for Rev 242 with most focused on Saturn’s atmosphere.
For its first observation for Rev 242, on September 7, ISS, using its Narrow-Angle Camera (NAC), will ride along with the Visual and Infrared Mapping Spectrometer (VIMS) as it observes Saturn’s north polar aurorae. Afterwards, ISS, this time using its Wide-Angle Camera (WAC), will ride along with the Composite Infrared Spectrometer (CIRS) as it maps Saturn’s northern hemisphere with its mid-infrared sensor. ISS will monitor Saturn’s day-side clouds every two hours. ISS will perform similar WAC cloud monitoring during a VIMS north pole movie on September 9. On September 8, ISS will ride along with the Ultraviolet Imaging Spectrometer (UVIS) in order to perform WAC photometry of Saturn’s atmosphere. Photometry is the measurement of an object’s brightness with changing lighting conditions. Similar photometry will be acquired during a VIMS observation of Saturn’s northern hemisphere on September 10 and during a UVIS observation on September 11. On September 10, ISS will acquire an observation of Titan from a distance of 1.80 million kilometers (1.12 million miles). Images from this observation will be used to monitor clouds in Titan’s atmosphere across its northern, sub-Saturn hemisphere.
On September 12 at 11:49 UTC, Cassini will reach periapse for Rev 242 at an altitude of 400,420 kilometers (248,810 miles) above Saturn's cloud tops, between the orbits of Dione and Rhea. On September 11, ISS will acquire a 12-frame WAC mosaic across portions of Saturn’s northern hemisphere from a distance of 580,000 kilometers (360,000 miles). The mosaic will run from Saturn’s north pole to near its equator along its western limb. On September 12, ISS will ride along with UVIS as it observes Saturn’s south polar aurorae. On September 13, the camera system will again ride along with UVIS to observe a crescent Saturn. ISS will acquire a mosaic of parts of illuminated crescent of Saturn on September 14. Also on September 14, ISS will observe a crescent Titan from a distance of 1.51 million kilometers (0.94 million miles). Finally, ISS will acquire another Saturn south polar aurorae observation from a distance of 1.08 million kilometers (0.67 million miles).
On September 17, ISS will acquire a 16-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. After the F ring movie, ISS will acquire a quick observation of Saturn using the Wide-Angle Camera (WAC). This observation is part of a series of “Storm Watch” sequences designed to take advantage of short, two-minute segments when the spacecraft turns to point the optical remote sensing (ORS) instruments back at Saturn, as a waypoint between observations. They include blue, clear, two methane band, and one full-frame, continuum band filter images. On September 18, ISS will acquire a distant observation of Jupiter from a distance of 1.49 billion kilometers (926 million miles). While this is too distant to show Jupiter in much detail, with the planet’s signature belts and zones just barely resolvable in NAC images at this distance, the moderate phase angle makes this astronomical observation unique compared to the views achieved from Earth. This 14 hour observation will be used for photometry and polarimetry of Jupiter’s atmosphere.
On September 18, Cassini will reach apoapse, bringing Rev 242 to a close and starting up the next orbit, Rev 243. This orbit will include a targeted encounter with Titan.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).