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Cassini continues its exploration of the Saturn system with the 32-day Rev 205, which begins on May 31 at its farthest distance from the planet. This is also called the orbit's apoapse. At this point, Cassini is 3.01 million kilometers (1.86 million miles) from Saturn's cloud tops. Rev 205 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. Thirty-seven ISS observations are planned for Rev 205 with the majority focused on Saturn's atmosphere and on Titan during the T102 flyby.
An hour into the orbit on May 31, ISS will image Titan, looking for clouds across its northern sub-Saturn hemisphere, at a distance of 3.92 million kilometers (2.43 million miles). Between June 1 and June 8, ISS will observe Titan six more times, monitoring Titan's northern hemisphere for clouds. The closest of these observations will be taken on June 8 at a distance of 1.58 million kilometers (0.98 million miles). On June 12 and 14, ISS will observe the outer satellite, Erriapus, from a distance of 13.1 million kilometers (8.14 million miles). Combined with earlier sequences, this observation will be used to determine where its rotational axis points and to model its shape. On June 16 at 11:30 UTC, Cassini will reach periapse for Rev 204 at an altitude of 752,340 kilometers (467,480 miles) from Saturn's cloud tops. During periapse, ISS will ride along with the Ultraviolet Imaging Spectrometer (UVIS) to observe Saturn's south polar aurorae.
Cassini encounters Titan on June 18 at 13:28 UTC for the 103rd time. This is the sixth of eleven Titan flybys planned for 2014, with the next encounter scheduled for July 20. T102 has a relatively high close-approach altitude of 3,658 kilometers (2,273 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 five-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 two more CIRS observations, one focused on Titan's surface and the other on the limb of the moon.
The main focus of the flyby is the Radio Science Subsystem (RSS) observation at closest approach. In the two hours before and after closest approach, RSS will be used to acquire bistatic and radio occultation observations. Both before and after closest approach, RSS will acquire bistatic observations, bouncing radio signals off Titan's surface that will then be received back on Earth. This experiment is used to study the physical properties of Titan surface, whether the area studied is liquid or solid, reflectivity at microwave wavelengths, and its dielectric constant from which its composition and roughness can be estimated. Before closest approach RSS will examine a portion of eastern Tsegihi, just east and south of Shiwanni Virgae. As Cassini departs from Titan, RSS will acquire a bistatic observation of the southern shore of Ligeia Mare, a Lake Superior-sized sea of liquid hydrocarbons in Titan's north polar region. That swath will extend to the northern half of neighboring Kraken Mare. At closest approach, RSS will acquire a radio occultation of Titan's atmosphere, sending a signal through it that will then be acquired back on Earth. By studying variations in the strength of the signal, information about Titan's atmosphere like density, tropospheric wind and temperature profiles, and variations due to seasonal change can be gleaned. 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 global mapping mosaic, covering much of the visible crescent. The mosaic will also include a pair of long stares at Titan's north pole.
On June 20, ISS will acquire a pair of quick observations of Saturn using the Wide-Angle Camera (WAC). These two observations are 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. Eight more storm watch observations will be taken between June 21 and June 30. On June 20, ISS will observe the shadow of Saturn on the faint Phoebe ring. The Phoebe ring, a vast region of small, dust-sized particles generated by micrometeorites impacts on the distant moon Phoebe, more than fills the field-of-view of the Wide-Angle Camera (WAC). To determine the optical density of the rings, researchers will compare the background brightness of the ring in sunlight to areas in the shadow of Saturn, where there is no direct sunlight.
On June 21, 23, and 24, ISS will ride along with UVIS and the Visual and Infrared Spectrometer (VIMS) as they observe occultations by Saturn's rings of two stars, first of the blue subgiant star Gamma Columbae, then on the 23rd and 24th of the red giant star L2 Puppis. On June 22, ISS will acquire a movie of the F ring, observing its various channels and streamers created by the interaction between the ring material and the nearby moon, Prometheus. On June 24, 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 taken on June 26 and June 30. On June 30, ISS will take a look at Titan, searching for clouds across the northern hemisphere. This observation will be taken from a distance of 3.93 million kilometers (2.44 million miles).
On July 2, Cassini will reach apoapse, bringing Rev 205 to a close and starting up the next orbit, Rev 206, which will include another targeted flyby of Titan.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).