[For trouble viewing the images/movies on this page, go here]
Cassini continues its exploration of the Saturn system with the 9.5-day Rev187, which begins on April 17 at its farthest distance from the planet. This is also called the orbit's apoapse. At this point, Cassini is 1.30 million kilometers (0.81 million miles) from Saturn's cloud tops. Rev 187 occurs nearly a year into the first inclined phase of the Cassini Solstice Mission, a phase which lasts until March 2015. 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. Nineteen ISS observations are planned for Rev 187 with the majority focused on Saturn's atmosphere and rings.
The day after apoapse, ISS will take a pair of 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 storm watch observations are planned for this orbit. Between the two Storm watch observations on April 18, 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. On April 20 and 21, ISS will ride along with a pair of Ultraviolet Imaging Spectrometer (UVIS) observations of Saturn's south polar aurora. In addition to making a movie of the planet's aurorae, the images will be used to independently measure the rotation period of Saturn's magnetic field.
On April 22 at 02:17 UTC, Cassini will reach periapse for Rev 187 at an altitude of 316,700 kilometers (196,790 miles) from Saturn. During the periapse period, except for the Titan observation on the 22nd, ISS will be mostly inactive. On April 21, UVIS will observe a solar occulation by Saturn, which can be used to probe the structure of the planet's upper haze layers. On April 22, UVIS will observe Saturn's northern auroral oval, while the Visual and Infrared Mapping Spectrometer (VIMS) will observe a pair of stellar occultations by Saturn's rings of two red giant stars, R Carinae and Gamma Crucis. Late in the day on April 22, ISS will acquire an observation of Titan, looking for clouds across the moon's northern trailing hemisphere. It will be taken from a distance of 1.20 million kilometers (0.74 million miles).
Late on April 23, ISS will acquire an observation of 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. Afterward, ISS will ride along as UVIS observes a stellar occultation by Saturn's rings of the B-type star, Beta Librae. Afterward, ISS will acquire another astrometric observation of Saturn's small, inner moons. Finally, on April 25, ISS will acquire an observation of the small, outer satellite, Tarvos. The observation is designed to allow researchers to measure the length of its day. Given its small size and great distance from Saturn, Tarvos doesn't rotate synchronously like Saturn's closer and larger icy moons. Tarvos is 15 kilometers (9 miles) across and will be 8.97 million kilometers (5.58 million miles) away.
On April 26, Cassini will reach apoapse on this orbit, bringing it to a close and starting Rev188.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).