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Cassini continues its extended tour of Saturn on March 27 with Rev107, the spacecraftís 108th orbit around the Ringed Planet. Rev107 completes a 180 degree transfer maneuver by the Cassini spacecraft, switching the spacecraft's periapse from the nightside of Saturn to the dayside. Cassini uses two Titan flybys in quick succession, the first shortly before the start of Rev107 (and discussed in the Rev106 Looking Ahead article) and the second shortly after the end of the orbit (to be discussed in the Rev108 article). This maneuver shortens the length of this particular rev to 8 days, but orbits over next few months will last 16 days. During this rev, Cassini only completes half a circuit around Saturn. Rev107 starts as Cassini reaches apoapse, the farthest point in its orbit around Saturn. At this point, Cassini is 1.129 million kilometers (702,000 miles) from the planet. Rev107 is a nearly circular orbit with the periapse distance very close to the apoapse distance. Periapse occurs on March 28.
Following observations from the T51 Titan flyby that occurs eight minutes prior to the start of the Rev107, Cassiniís camera system will focus primarily on Saturnís small satellites and ring system. On March 29, ISS will acquire the first of three astrometric observations during this orbit. Astrometric observations are used to refine our knowledge of the orbital motions of Saturnís various satellites, in this case of Pan, Atlas, Epimetheus, Prometheus, Janus, and Methone. Cassini also will take a time-lapse movie of Saturnís F ring, looking at clumps and gores in the narrow ring as well as the passing satellites Prometheus and Pandora.
On March 30, Cassini ISS will observe the shadow of Mimas as it crosses Saturnís A ring. Such opportunities to observe moon shadows on the ring system will become more common as Saturn approaches equinox, when the Sun crosses the planetís equator and ring plane from the south to the north. ISS also will take another astrometric observation, this time of Daphnis, Pan, Janus, Pandora, and Epimetheus. The Composite Infrared Spectrometer will take several radial scans of the ring system, particularly in the area in Saturnís shadow, to observe the reflection of Saturnís infrared emission.
On March 31, Cassini ISS will be turned to Titan to help improve the calibration of the polarized filters on the narrow angle camera. To do this, ISS will acquire images in these filters as Cassini rotates about the cameraís bore sight. This will reveal the effect of the polarized filters have on our ability to view Titanís surface features through Titanís haze layers. With Kraken Mare near the field of view, scientists can also use this effort to see how using polarization filters effects the appearance of large bodies of liquid methane on Titan. Cassini also will acquire the last of its three astrometric observations on this rev, this time observing Epimetheus, Anthe, Daphnis, Pandora, and Pan. CIRS will also take several temperature scans of the ring system. The spectrometer will perform similar scans on April 1 and 2.
Cassini finishes Rev107 as it approaches Titan for the T52 flyby. Stay tuned next time for details on this exciting flyby.
Image products created in Celestia. All dates in Coordinated Universal Time (UTC).