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Cassini continues its extended tour of the Saturn system with the 17.6-day-long Rev128, the spacecraft's 129th orbit around the Ringed Planet. Cassini begins Rev128 on March 12 at its farthest distance from Saturn, called apoapse. At this point, Cassini is 2.39 million kilometers (1.48 million miles) from Saturn's cloud tops. Between the excitement of the previous orbit with its double flybys of Rhea and Helene, and the next orbit with its flybys of Dione and Titan, Rev128 is comparatively quiet. While Cassini will not fly by any moons during this orbit, it will take advantage of its position near Saturn's ring plane to image a number of mutual events between two or more moons.
Cassini's ISS camera starts its observations for Rev128 a few hours after apoapse by imaging Dione transit across the south polar region of Titan. At the time of the occultation, Dione will be 2.21 million kilometers (1.38 million miles) from the spacecraft, while Titan will be 3.56 million kilometers (2.21 million miles) away. On March 16, ISS will image Titan at a distance of 1.93 million kilometers (1.2 million miles). Titan will be at high phase angles, allowing for monitoring of the satellite's atmospheric haze layers.
On March 20 at 21:21 UTC, Cassini will reach the periapse of Rev128, its closest point to Saturn in the orbit. At periapse, the spacecraft will be 115,500 kilometers (71,800 miles) above Saturn's cloud tops.
After periapse, Cassini will conduct several observation campaigns, such as monitoring clouds on Titan, taking astrometric images of Saturn's small satellites, and imaging mutual events between two or more satellites. On March 22, 24, and 25, ISS will image Titan's trailing and sub-Saturn hemispheres in order to monitor cloud motions, if they are visible. These images will be taken from distances ranging from 2.01 million to 3.06 million kilometers (1.25 million to 1.9 million miles). On five occasions between March 22 and March 27, ISS will acquire astrometric observations known as SATELLORBs of several of Saturn's small satellites, including Calypso, Hyperion, Pallene, Telesto, Polydeuces, Janus, Methone, Anthe, Pandora, and Helene. Astrometric observations add more data points for the calculations of the complex orbits of many of these bodies. This complexity results from the small moons' proximity to much larger moons.
Between March 23 and 28, Cassini will observe five satellite mutual events. On March 23, Cassini will image Dione occult the northern, leading hemisphere of Tethys. Dione will be 1.2 million kilometers (745,000 miles) away, while Tethys will be 1.76 million kilometers (1.09 million miles) away. On March 24, Cassini will image Rhea nearly occult Epimetheus. Rhea will be 1.24 million kilometers (770,000 miles) away, while Epimetheus will be 1.62 million kilometers (1 million miles) away. On March 26, Cassini will image Dione occult the northern, sub-Saturn hemisphere of Tethys. Dione will be 1.96 million kilometers (1.22 million miles) away, while Tethys will be 2.4 million kilometers (1.49 million miles) away. On March 27, Cassini will image a collection of Saturn's moons in a single narrow-angle camera field of view. Janus, Helene, and Epimetheus will pass in front of Titan during this observation, while Telesto will be visible above Titan, and Calypso below. On March 28, Cassini will image Rhea as it occults Prometheus and nearly occults Janus, which passes over Rhea's north pole. Rhea will be 1.9 million kilometers (1.18 million miles) away from Cassini as the moon passes in front of the rings.
Cassini will acquire two observations that are different from these observation campaign groupings. On March 24, ISS will take a 12-frame, wide-angle-camera mosaic of most of the inner Saturn system, out to the orbit of Dione. This observation is intended as part of a campaign to map the vertical structure of the E ring, Saturn's faint, outer ring. On March 29, ISS will look at the outer, irregular satellite Bebhionn from a distance of 9.94 million kilometers (6.18 million miles).
Cassini reaches apoapse on March 29, bringing Rev128 to an end and starting Rev129. During Rev129, Cassini will perform targeted flybys of Dione and Titan.
Image products created in Celestia. All dates in coordinated Universal Time (UTC).