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Cassini continues its exploration of the Saturn system with the 9.6-day Rev 244, which begins on September 29 at its farthest distance from the planet. This is also called the orbit’s apoapse. At this point, Cassini is 1.34 million kilometers (0.83 million miles) from Saturn’s cloud tops. Rev 244 occurs toward the end of 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. Ten ISS observations are planned for Rev 244 with the majority focused on Saturn’s rings and polar aurora.
For its first observation for Rev 244, on October 1, ISS will acquire an observation of a crescent Titan from a distance of 1.39 million kilometers (0.86 million miles). This will allow Cassini to monitor changes in its upper haze layers and to look for clouds across its north polar region. ISS will observe a thinner crescent Titan on October 5. For much of the first half of Rev 244, the Ultraviolet Imaging Spectrometer (UVIS) will acquire a series of observations of Saturn’s polar aurora. ISS will ride along with the UVIS observation of the south polar auroral ring on October 4. ISS will also ride along with a UVIS observation of Mimas on October 3, from a distance of 606,000 kilometers (377,000 miles). This is designed to measure Mimas’ opposition surge as Cassini will be nearly exactly between the Sun and Mimas. UVIS will observe a stellar occultation by the rings as the A ring passes in front of the B-type star Sigma Sagittarii.
On October 4 at 00:19 UTC, Cassini will reach periapse for Rev 244 at an altitude of 278,618 kilometers (173,126 miles) above Saturn's cloud tops, between the orbits of Tethys and Dione. On October 5, ISS will observe the small, distant moon Kiviuq from about 10.5 million kilometers (6.50 million miles). This observation will be used to estimate Kiviuq’s shape by measuring its light curve and looking for possible stellar occultations. This observation will last for 13 hours. A similar, day-long observation will be acquired late on October 6 and October 7. On October 6, ISS will be conducting a 100-minute-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.
Immediately after the propeller observation, 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 October 6 and October 8, ISS will look at some of Saturn’s faint, dusty rings. On October 6, the WAC will be used to look at the E ring, a large dusty ring generated from the jets emanating from Enceladus’s south polar region. On October 8, ISS will look at the very faint Phoebe ring, generated by micrometeorite impacts on the distant moon Phoebe.
On October 8, Cassini will reach apoapse, bringing Rev 244 to a close and starting up the next orbit, Rev 245.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).