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Cassini begins the 18-day Rev157 on November 15 at its farthest distance from Saturn, called apoapse. At this point, Cassini is 2.38 million kilometers (1.48 million miles) from Saturn's cloud tops. The spacecraft is in the middle of the first equatorial phase of the Cassini Solstice Mission, and this phase lasts until May 2012. During this phase, the spacecraft's orbits lie within the equatorial plane of the planet, providing opportunities to encounter Saturn's numerous moons, image the rings edge-on, and to look at Saturn's cloud tops without the rings obscuring the view. Seventeen ISS observations are planned for Rev157, the majority of which are designed to monitor cloud systems in Saturn's atmosphere.
ISS begins its observations for Rev157 six days after apoapse with a lengthy, eight-hour observation of Suttungr, one of Saturn's small, distant satellites. This observation will be taken from a distance of 17.3 million kilometers (10.8 million miles), and when combined with additional observations of this irregular satellite, is designed to measure Suttungr's brightness at different phase angles. These measurements can provide information about the nature of its surface (whether it is rough or smooth for example) even if Cassini never approaches within millions of kilometers of it. On November 23, ISS will perform a trio of quick observations of Saturn and its northern hemisphere storm. These are 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. These images can be used to track the progress of the northern hemisphere storm that began in early December 2010. Nine more such observations are planned between November 25 and 30. Also on November 23, ISS will image Titan's Fensal-Aztlan region from a distance of 2.03 million kilometers (1.26 million miles) in an effort to look for clouds in the moon's atmosphere.
On November 24 at 04:32 UTC, Cassini will reach periapse for Rev157 at a distance of 136,040 kilometers (84,530 miles). The day after periapse, Cassini ISS will image a series of faint ring arcs produced by micrometeorite impacts on Saturn's smaller moons. First Cassini will observe Aegaeon and the G ring arc, followed by Pallene and Anthe. Afterward, Cassini will turn its cameras toward Thrymr, another one of Saturn's distant, irregular satellites. This observation is designed to measure the rotational period of this moon by studying regular variations in the brightness of the satellite. This observation will be taken from a distance of 14.8 million kilometers (9.2 million miles).
On November 27, ISS, riding along with the Composite Infrared Spectrometer (CIRS), will acquire a 15-hour observation of Saturn's largest moon, Titan. At its closest, Cassini will be 748,420 kilometers (465,050 miles) from the moon. Images from this observation will focus on monitoring cloud motions (presuming that there are clouds, which have been rare since last year's Arrow Storm) across Titan's Shangri-La and Xanadu regions. On November 29, ISS will acquire an astrometric observation of Saturn's small, inner moons, including Pandora, Epimetheus, Pan, Aegaeon, and Methone (with larger Enceladus and Mimas making cameos).
On December 3, Cassini will reach apoapse on this orbit, bringing it to a close and starting Rev158. Rev158 includes a pair of targeted flybys of Titan and Dione.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).