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Cassini continues its exploration of the Saturn system with the 33-day Rev 200, which begins on December 17 at its farthest distance from the planet. This is also called the orbit's apoapse. At this point, Cassini is 2.64 million kilometers (1.64 million miles) from Saturn's cloud tops. Rev 200 occurs during the first inclined phase, which lasts until March 2015, of the Cassini Solstice Mission. The inclined phase will allow for polar views of Saturn and Titan as well as better vistas of Saturn's rings than those Cassini had while in the earlier, equatorial phase of the Solstice Mission. Forty-three ISS observations are planned for Rev 200 with most focused on Saturn's atmosphere and rings as well as Titan during the T97 flyby.
The first observation for the camera system, ISS, will be acquired on December 18. ISS will acquire a movie of Saturn's B ring, looking for dust spokes. Four more spoke movies will be acquired during Rev 200, on December 23, January 5, 11, and 14. On December 19, ISS will examine Titan's haze layers at a distance of 3.75 million kilometers (2.33 million miles). On December 20 and 21, ISS will observe the small, outer moons Tarvos and Skathi from a distance of 21.2 million kilometers (13.1 million miles) and 17.1 million kilometers (10.6 million miles), respectively, in order to measure their rotational period and determine in what direction their north pole points. While most moons of Saturn have days that match their orbital period, Tarvos, Skathi, and the other small outer moons typically have days lasting a few hours to one Earth day (compared to orbital periods exceeding one Earth year). Both will be too far away to observe any surface features, so their days will be calculated by observing slight variations in its apparent brightness as it rotates. The north pole position can be determined by the lightcurve found during this observation by comparing with others acquired previously. On December 22, ISS will acquire a cloud and haze monitoring observation of Titan from a distance of 2.82 million kilometers (1.75 million miles). Observations like this one are designed to track changes in the distribution of cloud across Titan as well as to monitor changes to its haze layers.
On December 25, ISS will acquire an astrometric observation of Saturn's small, inner moons. Astrometric observations are used to improve our understanding of the orbits of these small satellites, which can be influenced by Saturn's larger icy moons. Two more astrometric observations will be acquired on December 27 and January 3. Immediately afterward, ISS will acquire a quick observation of Saturn using the WAC. This observation is part of a series of 'Storm Watch' observation sequences designed to take advantage of short, two-minute segments when the spacecraft turns the optical remote sensing (ORS) instruments back to Saturn as a waypoint between other experiments' observations. These sequences include blue, clear, two methane band, and one full-frame, continuum band filter images. Two more will be taken later on December 26 and 27, while another eight will be taken between January 3 and January 14. On December 29, ISS will observe the tiny moon, Aegaeon, and its accompanying ring arc in the G ring as they orbit Saturn for 15 hours. On December 30, ISS will observe the outer moon, Siarnaq to determine its pole direction.
Cassini encounters Titan on January 1 at 22:00 UTC for the 98th time. This is the first of eleven Titan flybys planned for 2014, with the next encounter scheduled for February 2, 2014. T97 has a close-approach altitude of 1,400 kilometers (870 miles). This flyby will allow for imaging of the north polar region and northern anti-Saturn hemisphere inbound to the encounter and the southern anti-Saturn hemisphere of Titan on the outbound leg. Before the encounter on December 31, ISS will acquire four cloud monitoring observations. Early on January 1, ISS will ride-along with the Composite Infrared Spectrometer (CIRS) as it stares at Titan in order to acquire mid-infrared spectral and temperature information about Titan's atmosphere. Afterward, ISS will acquire a monitoring mosaic of Titan. This nine-frame mosaic will cover much of the visible face of Titan at a resolution of 1.5 kilometers (0.9 miles) per pixel. Next, CIRS will stare at Titan, acquiring compositional information about the moon's atmosphere, and then the Ultraviolet Imaging Spectrometer (UVIS) will perform several far- and extreme-ultraviolet scans across the moon.
During closest approach, VIMS will be the prime instrument with ISS riding along. VIMS will acquire several images of an area of small lakes on the leading hemisphere side of the north pole. VIMS will be mapping the distribution of both filled lakes and empty lakes coated with evaporites. These evaporites appear bright at VIMS' longer wavelengths. At closest approach, VIMS will acquire a noodle-like image strip across the northern anti-Saturn hemisphere and Shangri-La, a dark, sand-dune filled region that lies along Titan's equator. The swath will cut across Mindanao Facula just before closest approach. After the closest approach period, CIRS and UVIS will acquire more data about Titan's upper haze layers - its structure, temperature, and composition - as well as the now-cooling south polar vortex.
On January 3 at 11:34 UTC, Cassini will reach periapse for Rev 200 at an altitude of 1.04 million kilometers (0.64 million miles) from Saturn's cloud tops. A few hours after periapse, ISS will ride along with VIMS as it observes the F ring and the main ring system occult the M-type, red-giant star R Lyrae. Occultations like this one are used to understand the structure of Saturn's ring system and to look for any changes that might occur due to meteor impacts or slight changes in Saturn's gravity field. On January 5, ISS will try to image the edge of Saturn's shadow on the diffuse ring that lies along the orbit of Phoebe. On January 11, ISS will take a look at Saturn's faint rings from near the ring plane and at a high phase angle, which should make the dust in the rings make them appear brighter than they otherwise would. On January 15, ISS will acquire a rotational light curve of the small, outer moon, Tarqeq from a distance of 14.1 million kilometers (8.74 million miles).
On January 19, Cassini will reach apoapse, bringing Rev 200 to a close and starting up the next orbit, Rev 201, which will include another targeted flyby of Titan.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).