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Cassini reaches a milestone orbit on January 9 with Rev100, the spacecraft's 101st orbit around the Ringed Planet.
Cassini begins Rev100 at its farthest distance from Saturn, called apoapse. At this point, Cassini is 1.18 million km (738,000 mi) from Saturn. The spacecraft is in a high-inclination orbit, providing an opportunity to study the rings and the polar regions of Saturn and its satellites. On the first day of Rev100, ISS will observe Titan and the faint E ring. The Titan observation, acquired from a distance of 1.47 million km (912,000 mi), will be used to study cloud features on the moon's trailing hemisphere.
For the next three days of this revolution, ISS will focus on Saturn's rings and small satellites. The small satellite observations -- planned for January 10, 11, and 12 -- are astrometric sequences designed to improve our knowledge of the orbits of these objects. The moons to be imaged include: Calypso, Atlas, Epimetheus, Pandora, Prometheus, Pan, and Daphnis. On January 10, ISS will take a radial scan consisting of 15 narrow-angle-camera (NAC) footprints across the main ring system (see ID#3858 for an example of an earlier radial scan). On January 11, the NAC will take an 11-hour, 212-frame movie of the narrow F ring. The next day, ISS will observe the shadow of Epimetheus as it crosses the outer A ring.
On January 14, Cassini reaches periapse, its closest point to Saturn on Rev100. At this point, Cassini will be 548,000 km (341,000 mi) from Saturn's center. Before periapse, ISS will acquire a full longitudinal scan of the unlit face of the F ring (see ID#4974 for a similar scan taken in 2007). Right at periapse and just as Cassini crosses the ring plane, the spacecraft will turn its cameras to a crescent Rhea. The high-phase angle observation, in addition to being useful for photometry purposes, is designed to look for possible rings in orbit around the icy satellite. Following the Rhea sequence, ISS will observe the Strange Ringlet, a narrow ring in the inner Cassini Division.
The next day, January 15, ISS will take a 27-frame, wide-angle-camera mosaic of the illuminated side of Saturn's ring system. ISS will also search for clouds on the sub-Saturn hemisphere of Titan from a distance of 1.3 million km (811,000 mi).
On January 16, ISS will observe Titan's sub-Saturn hemisphere followed by a mini-movie of Prometheus. ISS also will image the shadow of Epimetheus as it crosses the outer A ring. On January 17, Cassini will turn its cameras to the tiny moon Anthe, taking almost 40 images of the satellite, though it will be too far away to resolve any surface features. ISS also will take an astrometric sequence, this time involving Atlas, Pan, Prometheus, Telesto, and Anthe. To conclude a busy day, the Composite Infrared Spectrometer will make a temperature map of the illuminated side of the rings.
On January 18, ISS will once again observe Titan, this time looking at the moon's leading hemisphere from a distance of 1.6 million km (995,000 mi). The instrument will also take a number of wide-angle camera calibration frames with the shutter closed to measure darkness levels on the camera's charged-coupled device (CCD) sensor and maintain the related calibration software. Finally, the Visual and Infrared Mapping Spectrometer and ISS will take a mosaic of Saturn as Cassini approaches the ring plane (see ID#5155 for a similar, recent mosaic). As Rev100 draws to a close on January 19, ISS will take a look at Dione's leading hemisphere from a distance of 1.25 million km (774,000 mi).
Cassini reaches apoapse on January 19, beginning Rev101.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).