Cassini continues its exploration of the Saturn system with the 19-day Rev167, which begins on May 28 at its farthest distance from the planet. This is also called the orbit's apoapse. At this point, Cassini is 2.20 million kilometers (1.37 million miles) from Saturn's cloud tops. This orbit includes a flyby of Saturn's largest moon, Titan. The flyby will push the spacecraft into a more inclined orbit, from an inclination of 15.8 degrees to 21.1 degrees, relative to the equatorial plane of the planet. Cassini will end up in a orbit inclined by 61.7 degrees by this time next year. This first inclined phase of the mission, a phase which lasts until March 2015, will allow for polar views of Saturn and Titan as well as better vistas of Saturn's rings than those Cassini has viewed while in the earlier, equatorial phase of the Solstice Mission. Fifty-one ISS observations are planned for Rev167, the vast majority dedicated to Saturn and Titan storm cloud monitoring, as well as to a Titan flyby.
ISS begins its observations for Rev167 on May 29, the day after Cassini passes apoapse, with three quick observations of Saturn using the wide-angle camera (WAC). These 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. Nine more such observations are planned between June 1 and June 3, while 12 more will be taken between June 9 and June 17. Between the first two Storm Watch observations, ISS will take a look at Titan from a distance of 3.09 million kilometers (1.92 million miles). The observation is an effort to look for clouds in the moon's atmosphere as part of the "Titan Monitoring Campaign" (TMC). This observation of a gibbous Titan is designed to monitor clouds over the moon's Senkyo dune field. ISS also will be taking shorter-wavelength images to study changes in Titan's upper haze layers. Between the second and third Storm Watch observations, ISS will acquire an astrometric observation of Saturn's small, inner moons, including Epimetheus, Telesto, Atlas, Calypso, Polydeuces, and Daphnis. Astrometric observations are used to improve our understanding of the orbits of these small satellites, which can be influenced by Saturn's larger icy satellites. After the third Storm Watch observation, ISS will acquire a 10-hour, 30-minute light curve of the outer irregular satellite Ymir. Cassini will be at a distance of 15.1 million kilometers (9.40 million miles) from the 18-kilometer-wide (11.2-mile-wide) satellite.
On June 1, ISS will take a TMC observation of Titan that will allow for monitoring of cloud features across the sub-Saturn hemisphere from a distance of 3.08 million kilometers (1.91 million miles). After another storm watch observation, ISS will acquire an astrometric sequence of Saturn's small inner moons, including Epimetheus, Prometheus, Helene, Pallene, Telesto, and Atlas. On June 2, ISS will take another TMC observation of Titan, covering the Fensal-Aztlan dune fields. The TMC observation will be taken from a distance of 2.83 million kilometers (1.76 million miles). Another astrometric observation will follow, including Helene, Pallene, Janus, Pan, and Polydeuces in this set.
On June 5 at 04:53 UTC, Cassini will reach periapse for Rev167 at an altitude of 126,590 kilometers (78,659 miles) from Saturn. ISS observations during the periapse period will be taken during a non-targeted encounter with Mimas and include a pair of observations of propellers in the A ring. The A ring is host to thousands of these propellers, which are gravitationally-formed voids created by large ring particles. These observations, on June 4 and 5, will search for these propellers in the region between the Encke Gap (itself carved by the small moon Pan) and the Keeler Gap (a narrower gap carved by Daphnis). Of particular importance for this observation is to re-image previously observed propellers to better measure their sizes and orbits. On June 5, ISS will ride along with the Composite Infrared Spectrometer (CIRS) to observe a non-targeted encounter with Mimas. At 05:08 UTC, Cassini will pass Mimas at a distance of 43,563 kilometers (27,069 miles). This encounter will allow for imaging of Mimas's north polar region and northern leading hemisphere.
Two days after periapse, Cassini encounters Titan on June 7 at 00:07 UTC for the 85th time. This is the fifth of nine Titan flybys planned for 2012, with the next encounter scheduled for July 24. T84 is a low-altitude flyby with a close-approach altitude of 959 kilometers (595 miles). This flyby will allow for imaging of the Adiri region and the anti-Saturn hemisphere of Titan outbound from the encounter. Before the encounter, CIRS and the Visual and Infrared Mapping Spectrometer (VIMS) will acquire spectral scans and other data of Titan's night side. VIMS will search for specular, or mirror-like, reflections off the northern lakes. CIRS will scan across Titan using its far-infrared and mid-infrared channels as well as perform a limb integration. In a limb integration CIRS stares at Titan's sunlit limb, or edge of the visible disk, to build up high resolution spectra, or values that vary over along at continuum, of Titan's hazes. ISS will ride along to acquire images of Titan's upper haze layers, which are more easily visible at high phase angles.
At closest approach, control of spacecraft pointing will switch to the RADAR instruments. RADAR will acquire a SAR swath that will stretch from northeast of Fensal near 30 degrees north latitude, 15 degrees west longitude; east-by-northeast through a region not previously seen by RADAR near 50 degrees north latitude, 205 degrees west longitude across the mid-northern trailing hemisphere; then back east-southeast to an area just north of Adiri around 10 degrees north latitude, 20 degrees west longitude. This swath will be used to fill a major gap in the RADAR instrument team's coverage in the northern mid-latitudes in the trailing hemisphere. Previous swaths in the northern mid-latitudes, like the first SAR swath on Ta, revealed bland and difficult to interpret terrain. Before closest approach, RADAR will acquire a HiSAR swath around 60 degrees north latitude, 330 degrees west longitude along the southwestern shore of Kraken Mare. After the flyby, the instrument will acquire a HiSAR swath covering Concordia Regio, an area that saw methane rainfall and possible wide-spread flooding in late 2010. Inbound and outbound scatterometry, radiometry and altimetry will also be taken by RADAR. Afterward, CIRS will map surface temperatures across the visible disk to look for diurnal and albedo-related differences while the Ultraviolet Imaging Spectrometer (UVIS) will scan across Titan's sunlit side with its extreme- and far-ultraviolet channels. ISS will ride along during these three observations, searching for clouds across Adiri and western Shangri-La, including over the Huygens probe's landing site. The next day, June 8, ISS will acquire four sets of observations of Titan at distances between 694,490 and 897,900 kilometers (431,540 and 557,530 miles) in order to search for clouds and monitor their development if they are present. These observations will be centered near the western edge of Adiri and the eastern part of the Belet dune sea.
On June 9, ISS will acquire an astrometric sequence of Saturn's small inner moons, including Calypso, Polydeuces, Pan, Daphnis, Prometheus, and Atlas. On June 11, ISS will acquire a TMC observation of Titan, covering the trailing hemisphere. The TMC observation will be taken from a distance of 2.40 million kilometers (1.49 million miles). Another astrometric observation will follow, including Helene, Prometheus, Atlas, Daphnis, Epimetheus, Anthe, Polydeuces, and Calypso in this set. On June 15, ISS will take a TMC observation of Titan, covering the sub-Saturn hemisphere of the large moon from a distance of 3.92 million kilometers (2.43 million miles). After another storm watch observation, ISS will acquire another astrometric sequence, this time imaging Polydeuces, Pan, Janus, Anthe, Calypso, Pallene, and Pandora. Finally, on June 16, ISS will search for Trojan moons at Titan's L5 LaGrangian point, which lies 60 degrees behind Titan on its orbit.
On June 17, Cassini will reach apoapse on this orbit, bringing it to a close and starting Rev168. Rev168 includes numerous ring observations and a non-targeted encounter with Tethys.
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