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Cassini begins the 28-day Rev146 on March 6 at its farthest distance from Saturn, called apoapse. At this point, Cassini is 3.21 million kilometers (1.99 million miles) from Saturn's cloud tops. The spacecraft is in the middle of the first equatorial phase of the Cassini Solstice Mission, a phase which lasts until May 2012. During this phase, the spacecraft's orbits lie within the equatorial plane of the planet and within the ring plane as well as the orbital plane of most of Saturn's major moons. This equatorial orbit allows Cassini to image Titan's equatorial region and Saturn's atmosphere unobstructed by its rings. In fact, with the exception of distant Skathi observations on March 16 and 30 designed to study how the small moon's brightness changes as it rotates, all the ISS observations for Rev146 will be targeted at Titan and Saturn. On March 20 at 11:45 UTC, Cassini will reach the periapse of Rev146. At a distance of 224,280 kilometers (139,360 miles), this will be the closest point to Saturn in this orbit.
Cassini ISS begins its observations of Saturn for Rev146 two hours after apoapse on March 6. ISS will acquire 22, six-image, north-south mosaic strips using its narrow-angle camera. For each frame of these mosaics, CB2, GRN, and BL1 filtered images will be acquired. From this data, a new, high-resolution map of Saturn can be constructed. On March 8, ISS will image Titan from a distance of 2.94 million kilometers (1.83 million miles). On this occasion, the spacecraft will image the satellite's trailing hemisphere. Researchers will be interested in looking at the region between "Okavango" and South Senkyo for the first time since last September. Next, ISS will observe Saturn over a period of 18 hours, taking a set of wide-angle-camera images (WACs) every two hours, in order to monitor the large northern storm system. A similar monitoring observation, this time two hours long, will be taken on March 14 and will include two image sequences. On March 8, the Ultraviolet Imaging Spectrometer (UVIS) will acquire an extreme- and far-ultraviolet, east-west scan across the visible disk of Saturn. ISS will ride along with this observation, taking NAC and WAC photometry and polarimetry images. UVIS and ISS will acquire similar observations several more times on this orbit: on March 11, 17, 19, and 21. On March 9, ISS will image Titan again, this time from a distance of 3.65 million kilometers (2.27 million miles). The view this time will allow ISS to take a look at southern Senkyo, allowing researchers to monitor surface features and clouds in this region.
Starting March 9, Cassini ISS will begin a series of cloud tracking observations on Saturn. Each observation will last five hours. There are six observations planned: one on March 9, three on March 10, one on March 13, and one on March 14. Each sequence will start out with a set of 13 WAC frames using various color filters including RED, GRN, and BL1 for true color composites, followed by sequences of BL1, CB2, MT2, and MT3 frames from the narrow-angle camera taken every 10 minutes in order to track cloud speeds. While the WACs will certainly show some portions of the large, northern storm or its long tail, the NACs are more focused. For example, those taken on March 9 and those taken during the first sequence on March 10 will be focused on clouds between 25 and 45 degrees south. For reference, the large storm is centered between 34 and 44 degrees north. The other two sequences on March 10 will focus on clouds between 5 degrees south and 15 degrees north. The observations on March 13 and 14 will focus on the great northern storm.
Interspersed with these Saturn cloud tracking observations, Cassini ISS will acquire two more cloud monitoring observations of Titan. These observations are planned for March 11 and 29. The first observation will focus on the sub-Saturn hemisphere of Titan and will be taken from a distance of 2.91 million kilometers (1.81 million miles). On March 29, ISS will image the Fensal-Aztlan region of Titan from a distance of 2.95 million kilometers (1.83 million miles). Finally, on March 18, ISS will acquire yet another Saturn observation, this time looking for lightning on Saturn's night side.
On April 3, Cassini will reach apoapse on this orbit, bringing it to a close and starting Rev147. The Saturn and Titan show continues with nine of the twelve observations dedicated to the two largest bodies in the Saturnian system. A Titan flyby (T75) is planned for April 19.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).