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Following a series of exciting orbits over the last couple of months, Rev 51, Cassiniís 52nd orbit around Saturn, signals the beginning of a new phase in the Cassini mission, with an increased emphasis in ring observations as the spacecraftís orbit becomes increasingly inclined. Rev51 also includes an important non-targeted encounter with Titan. Cassini begins Rev51 on October 12 at its farthest distance from Saturn, called apoapsis. At this point, Cassini is 2.97 million km (1.85 million mi) from Saturn. During the first week of Rev51, the cameras will not be performing any targeted science observations, as Cassini receives and checks out its new flight software, version 10. The checkout will be complete by October 18 when Cassini observes its first target of Rev51, a movie observation of the Encke Gap in Saturnís A ring.
Over the next four days, Cassini will perform two non-targeted encounters with Hyperion and Titan. Five separate observations are planned of Hyperion over a three-day period, covering most of a single Hyperion rotation. The highest resolution images are planned for October 21 when Cassini is 148,000 km (92,000 mi) away, allowing for observations with a resolution below one kilometer per pixel. In addition to characterizing surface features in areas that may not have been observed at this kind of resolution, these observations will allow Cassini scientists to determine Hyperionís rotational state during the present epoch. Cassini performs a non-targeted encounter with Titan on October 22 when it comes within 440,000 km (273,000 mi) of the haze-shrouded satellite. Several observations are planned during the encounter in order to fill a coverage gap between 250 and 310 degrees longitude within Titanís trailing hemisphere. This area includes the western part of the equatorial dark region named Adiri, shown by the Cassini RADAR experiment to covered in dark, longitudinal dunes. It also includes a bright area between Belet and the dark region named Senkyo. The area may include an impact crater with a dark floor. Finally, these observations may provide the highest resolution observations yet by the ISS instrument of a large, Caspian Sea-sized dark region in the north polar region, thought to be a body of liquid methane and ethane.
Cassini reaches the closest point to Saturn in its orbit, called periapsis, on October 24, when it is 229,000 km (142,000 mi) from the ringed planet. During this periapsis period, Cassini will focus on Saturnís ring system and on satellite photometry. Near periapsis, Saturn will be almost directly between the Sun and Cassini, providing an excellent time to observe Saturnís diffuse rings, like the innermost D ring. The spacecraft will also perform a radial scan, a series of images across the ring system from the innermost D ring out to the F ring, when Cassini is only slightly below the ring plane. Cassini will also conduct a campaign of photometry observations of Saturnís various icy satellites. These observations will help Cassini scientists to characterize the fine-scale structure of these satellitesí surfaces.
As Cassini approaches apoapsis, and the next orbit, the spacecraft will perform a series of observations of Saturn and the ring system with the wide-angle camera. These observations are designed to study the polarimetry (or polarization properties) of Saturnís atmosphere and ring system at moderate phase angles.
On November 5, Cassini begins Rev52, its 53rd orbit around Saturn. The next orbit will include the T37 flyby of Titan; non-targeted flybys of Rhea and Enceladus; and observations of Anthe, a newly-discovered, small satellite between Mimas and Enceladus.