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Rev 93: November 12 Ė November 20, 2008
Cassini continues its extended tour of the Saturn system with Rev93, the spacecraftís 94th orbit around the Ringed Planet.
Cassini begins Rev93 on November 12 at its farthest distance from Saturn, called apoapse. At this point, Cassini is 1.28 million km (797,000 mi) from Saturn. The spacecraft is in a high-inclination orbit here, as it is for most of 2008, providing opportunities to view the ring system from high above the ring plane. Such an orbit also provides an opportunity to study the polar regions of Saturn and its satellites.
Cassini ISSís first two observations of Rev93 cover several of Saturnís satellites. On November 13, Cassini will acquire an observation designed to look for clouds in Titan's sub-Saturn hemisphere. Cassini will also observe Saturnís small, inner satellites, including Helene, Anthe, Pallene, and Pan, in order to study the orbital motions of these moons. On November 14, Cassini will acquire a 10-hour-long movie observation of the F ring, and on November 15, Cassini will observe Saturnís north polar region as the Visual and Infrared Spectrometer (VIMS) looks for aurorae.
On November 16, Cassini reaches periapse, its closest point to Saturn on Rev93. At that point, Cassini will be 259,000 km (161,000 mi) from Saturnís center. Near periapse, Cassini will quickly pass high over the north polar region of Saturn before descending below the ring plane 75 minutes before periapse. At this time, Cassini will perform a non-targeted encounter of Tethys at distance of 57,000 km (35,000 mi),however, no images will be acquired. A few hours before periapse, Cassini will make a short movie observation of the F ring, followed by a wide-angle camera mosaic of Saturnís south polar region while VIMS looks for aurorae at this pole.
Cassini encounters Titan on November 19 for the 48th time and the second time this month. The close approach distance is only 1023 km (635 mi). This flyby (known as T47) will allow for imaging of the leading hemisphere of Titan. Inbound to the encounter, when Cassini will observe Titan at moderate phase angles over southwestern Xanadu, the VIMS team will control pointing (or be ďprimeĒ) until one hour before the encounter when the Ultraviolet Imaging Spectrometer (UVIS) Team will take over. During this approach period, ISS will acquire a regional mosaic of Titan covering Hotei Arcus and southeastern Xanadu. VIMS will acquire several observations of Titan at different distances, including a mosaic over Hotei Arcus.
During closest approach on T47, the optical remote sensing instruments on Cassini will be prime. Between one hour and 30 minutes before and after closest approach, the UVIS team will observe a stellar occultation through Titanís atmosphere, using a background star to measure the UV opacity of the upper atmosphere and haze layers. During closest approach, VIMS will acquire a high-resolution, noodle swath across Titanís anti-Saturn hemisphere. The VIMS team hopes to observe the Huygens landing site at 600 meters (0.37 mi) per pixel. Such high resolution would allow scientists to identify different compositional units in the region, such as the dark terrain on which Huygens landed and the brighter, highland area seen to the north of the landing site. VIMS may miss the landing site since the footprint of the VIMS detector is only 64 pixels, or 40 km (25 mi) wide on the surface during the Huygens landing site observation. This projected area is within the uncertainty in our current knowledge of the absolute latitude and longitude of individual surface features due to uncertainties in the pole position and exact spin rate. On the outbound leg of the encounter, CIRS and ISS trade off prime observation time.
Cassini begins Rev94 on November 20. Rev94 includes a close non-targeted encounter of Tethys.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).