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Cassini continues its exploration of the Saturn system with the 32-day Rev 206, which begins on July 2 at its farthest distance from the planet. This is also called the orbit's apoapse. At this point, Cassini is 2.92 million kilometers (1.81 million miles) from Saturn's cloud tops. Rev 206 occurs during the first inclined phase, which lasts until March 2015, of the Cassini Solstice Mission. The inclined phase allows 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. Fifty-four ISS observations are planned for Rev 206 with the majority focused on Saturn's rings and on Titan during the T103 flyby.
An hour into the orbit on July 2, ISS will image Titan, looking for clouds across its northern sub-Saturn hemisphere, at a distance of 3.89 million kilometers (2.42 million miles). Immediately afterward, ISS will acquire a quick observation of Saturn using the Wide-Angle Camera (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. Six more storm watch observations will be taken between July 3 and July 15. Another eight will be taken between July 25 and August 2. Afterward, ISS will ride-along with the Composite Infrared Spectrometer (CIRS) in order to image Saturn while CIRS stares at the planet's limb. This series of images includes a set of red, green, and blue filter images for true-color composites. On July 3, ISS will again observe Titan, this time from a distance of 3.79 million kilometers (2.35 million miles). Titan's northern sub-Saturn hemisphere will be visible.
On July 6, ISS will observe the G ring arc, created by micrometeorites blasting material off the small moon Aegaeon, as well as the Anthe ring arc. On July 7 and 8, ISS will spend a full day observing the outer satellite, Kiviuq, from a distance of 14.7 million kilometers (9.16 million miles). Combined with earlier sequences, this observation will be used to determine where its rotational axis points and model its shape. The observation will also be used to measure its surface color, which can be used to constrain its surface composition. On July 13, 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. Another astrometric observation will be taken on July 25. On July 14, ISS will observe a pair of mutual events involving first Tethys, and then Rhea as small moons appear to pass in front of them. Also on July 14, ISS will acquire a pair of observations of Saturn's faint rings, include a movie of the inner D ring.
On July 18 at 05:26 UTC, Cassini will reach periapse for Rev 206 at an altitude of 839,900 kilometers (521,890 miles) from Saturn's cloud tops. On July 16, ISS will image the outer A ring, where it will be looking at propellers previously imaged by Cassini. Propellers are small voids in Saturn's rings created by the gravitational interaction between large ring particles and the surrounding ring. Afterwards, ISS will ride along with the Visual and Infrared Mapping Spectrometer (VIMS) as it observes the rings. ISS will take a set of color filter images with the Wide-angle camera (WAC) across a portion of the unlit face of Saturn's rings. Next, on July 16 and July 17, ISS will again ride along with VIMS as they observe a pair of stellar occultations by the rings, first of Vega (Alpha Lyrae) and then of R Lyrae, a faint, red giant star in the constellation Lyra. VIMS will observe another stellar occulation by Saturn's rings on July 25, this time involving the red-giant star L2 Puppis. On July 17 and 18, ISS will acquire a pair of movies of the B ring and the Encke Gap in the outer A ring.
Cassini encounters Titan on July 20 at 10:41 UTC for the 104th time. This is the seventh of eleven Titan flybys planned for 2014, with the next encounter scheduled for August 21. T103 has a relatively high close-approach altitude of 5,103 kilometers (3,171 miles). Inbound, ISS will observe Titan's southern, sub-Saturn hemisphere. Outbound, ISS will be able to observe a crescent Titan over its northern, sub-Saturn hemisphere. Observations for this encounter will start with ISS riding along with the Composite Infrared Spectrometer (CIRS) as it measures Titan's atmospheric and surface temperatures in the mid-infrared. The observation will include stares at the beginning and ending of the observation for ISS to acquire NAC images of Titan. Next, ISS will acquire a global mapping mosaic of Titan. This eight-frame mosaic will cover much of the visible face of Titan and will be centered just south of eastern Aztlan near Nath. The images from this mosaic will have a resolution around 1.49 kilometers (0.93 miles) per pixel. Afterward, ISS will ride along with a CIRS observation focused on Titan's surface as well as two VIMS cloud monitoring and surface mapping observations. The CIRS observations are part of a campaign to measure stratospheric temperatures as the seasons change from northern spring to summer.
Afterwards, ISS will ride along with UVIS as that instrument observes a stellar occultation when Titan passes in front of the star Alpha Eridiani. For UVIS, stellar occultations are used to provide high-resolution profiles of the hydrocarbons and haze in Titan's atmosphere as well as a temperature and pressure profile. While the Ion and Neutral Mass Spectrometer (INMS) can directly provide such information during close flybys, UVIS can probe deeper into Titan atmosphere, down to an altitude of 200 kilometers (124 miles), well below the minimum altitude Cassini can safely approach Titan. Ingress will be over Titan's southern mid-latitudes while egress will be over its northern mid-latitudes. The slow speed of the occultation will improve the quality of the data and its spatial resolution. During closest approach, UVIS will observe a solar occultation, when Titan's atmosphere blocks the Sun. Like the stellar occultation, this will be used to probe the temperature and pressure of Titan's atmosphere even deeper into its atmosphere. UVIS, before the ingress portion of the stellar occultation, will also perform scans with its extreme- and far-ultraviolet channels, looking particularly at the limb near the same latitude as the solar occultation.
After closest approach, CIRS will acquire more data about Titan's upper haze layers - its structure, temperature, and composition. ISS will ride along. ISS will also have a seven-frame, global-mapping mosaic, covering much of the visible crescent. The observation will also include a pair of long stares at Titan's north pole. On the day following the encounter, July 21 and July 22, ISS will acquire a series of cloud monitoring observations that will be focused on Titan's north polar region.
On July 25, ISS will acquire a color, radial scan of Saturn's rings. Compared to similar observations taken before, this will have higher resolution and will be taken from a higher elevation above the ring plane. On July 26 and July 28, ISS will observe the distant moon, Ijiraq, in order to measure its pole position, the direction the north pole points to in the sky, and its rotational period. Ijiraq will be 11.2 million kilometers (6.94 million miles) away during the observation on July 28. On July 31 and August 2, ISS will observe Titan's northern, trailing hemisphere from a distance of 3.71 million kilometers (2.30 million miles) and 3.88 million kilometers (2.41 million miles), respectively.
On August 3, Cassini will reach apoapse, bringing Rev 206 to a close and starting up the next orbit, Rev 207, which will include another targeted flyby of Titan.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).