CICLOPS: Cassini Imaging Central Laboratory for OPerationS

Rev134: Jun 27 - Jul 15 '10
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Cassini closes one chapter and opens another in its journey at the Saturn system with the 18-day-long Rev134, the spacecraft's 135th orbit around the Ringed Planet. On July 1, six years after the spacecraft entered orbit around Saturn, Cassini will begin its second extended mission. This new mission is called the Cassini Solstice Mission since it will extend the life of the project out to Saturn's northern summer solstice in May 2017 before plunging into the planet's atmosphere on September 15, 2017. Cassini begins Rev134 on June 27 at its farthest distance from Saturn, called apoapse. At this point, Cassini is 2.21 million kilometers (1.37 million miles) from Saturn's cloud tops. Cassini is now in an inclined orbit and will take advantage of this opportunity to acquire a number of observations of the unlit face of Saturn's rings. Also, Cassini will fly by Saturn's largest moon Titan for the 72nd time since October 2004.

Cassini's ISS camera system starts its observations for Rev134 a half a day after apoapse by acquiring calibration images for its wide-angle camera (WAC). These images will use the star Spica (Alpha Virginis) to measure the absolute photometry of each filter in the WAC. This is a ride-along observation with the Ultraviolet Imaging Spectrometer (UVIS) which will also be performing instrument calibration using Spica. Two WAC frames using IR5 at different spacecraft positions will be taken. Then a slow scan with multiple filters will be taken so that the star appears to move from left to right. On June 28 and 29, ISS will acquire two movie observations of Saturn's south polar aurora. Each observation begins with the narrow-angle camera (NAC) for small-scale phenomena, then switches to the WAC for an overview of the whole southern hemisphere, and finally returns to the NAC. Also on June 28, Cassini will image Titan from a distance of 3.17 million kilometers (1.97 million miles). Cassini will be searching for clouds across the eastern Aztlan, Quivira, and Fensal regions of Titan in this distant observation. During the previous orbit, a similar observation over this region revealed clouds over southeastern Aztlan around Elba Facula. On June 30, ISS will acquire an astrometric observation of several of Saturn's small, inner satellites in order to improve our knowledge of the motions of these moons. This observation will include images of Epimetheus, Prometheus (albeit while it is in the shadow of Saturn), Janus, Anthe, Methone, Telesto, and Helene.

Between June 30 and July 3, Cassini ISS will acquire five observations of Saturn's B ring in order to track spokes, microscopic dust that is suspended above the ring plane. Observations on July 2 and 3 include ride along images with a Composite Infrared Spectrometer (CIRS) sequence. During these observations, as opposed to a movie, ISS will take advantage of times when the WAC field of view crosses the B ring.

On July 4, Cassini will be closing in on Saturn with three observations. First, with Cassini about 700,000 kilometers (435,000 miles) away from Saturn, ISS will take a number of images of the planet's innermost ring, the D ring. Normally the faintest of Saturn's main rings, the dusty D ring appears brighter at the high-phase-angle, unlit-face geometry that occurs during this observation. Later in the day, Cassini will again look at the main ring system, this time looking at propellers, which are voids in the A ring formed by the gravitational interaction between large ring particles and the surrounding ring. Finally, ISS will ride along with a CIRS observation to image an eclipsed Enceladus.

On July 5 at 05:01 UTC, Cassini will reach the periapse of Rev134, its closest point to Saturn in the orbit. At periapse, the spacecraft will be 118,720 kilometers (73,769 miles) above Saturn's cloud tops. During the hour before periapse, Cassini will perform a close encounter with Daphnis, a small, 9-kilometer (5.6-mile) moonlet within the A ring's Encke Gap. ISS will take a number of clear filter images with the NAC as well as a set of red, green, and blue images. The closest frame will be taken from a distance of 72,816 kilometers (45,245 miles) from Daphnis. At that point, the small moon will appear 20 pixels across. These images will be the closest taken of Daphnis yet.

Cassini encounters Titan on July 7 at 00:22 UTC for the 72nd time. This is the first of 56 Titan flybys planned for the new extended mission, and the last until September 24. The close approach distance for the encounter (known as T71) is 1,005 kilometers (624 miles). This flyby will allow for imaging of the anti-Saturn hemisphere of Titan outbound to the encounter. For much of the inbound segment of the encounter, when only a thin crescent will be visible, the CIRS, RADAR, and Cassini Plasma Spectrometer (CAPS) teams will control spacecraft pointing, or be "prime." First up is CIRS, which will acquire a distant observation of the crescent of Titan, performing monitoring of Titan's atmosphere in the far infrared. RADAR will acquire radiometry data over Titan's sub-Saturn hemisphere. CAPS will study the interaction between Titan and Saturn's magnetosphere.

At closest approach, the Ion and Neutral Mass Spectrometer (INMS) will be prime, directly measuring the composition of Titan's upper atmosphere. This observation is part of a campaign to measure how Titan's atmosphere responds to rising solar activity (solar maximum, or the period of greatest solar activity in the sun's cycle, should occur over the next two years). In addition, INMS is taking this opportunity to measure the dawn atmosphere in the southern hemisphere. RADAR will ride along with INMS in order to acquire a short SAR swath across the southern hemisphere of Titan including portions of Mezzoramia. The magnetometer team members will compare their measurements to those seen during the very close flyby in late June to compare the field geometry of the induced magnetosphere.

Following closest approach, CAPS will again examine the interaction between plasma in Saturn's magnetosphere and Titan. This will be followed by another RADAR radiometry observation, this time covering the anti-Saturn hemisphere. Starting six hours after closest approach, VIMS will acquire three observations of Titan. The first is a mosaic of Titan, designed so that the NAC camera can take a full-disk mosaic of the moon. This mosaic will be taken at a distance of 119,000 to 175,000 kilometers (74,000 to 109,000 miles) from Titan. The other two observations will be centered over western Adiri and will increasingly cover more of the dark region to its west, Belet. These observations are designed to monitor cloud motion and development in the region, assuming there are any clouds. ISS will follow up its T71 observation with two cloud track observations on July 8, when it will be riding along with a CIRS observation, and on July 9, when Cassini is 1.24 million kilometers (770,000 miles) away from the moon.

Finishing up Rev134, ISS will acquire several Saturn monitoring observations between July 9 and 13. These are designed to track cloud features in Saturn atmosphere as well as monitor changes in the planet's atmosphere from seasonal change. This will allow wind speeds at different altitudes to be calculated. The first set of images to be taken during each observation (except for the July 9 UVIS ride along sequence) will cover a variety of WAC filters. Then a sequence of BL1, CB2, MT2, and MT3 images will be taken every 10 minutes.

On July 15, Cassini will reach apoapse on this orbit, bringing it to a close and starting Rev135, the first full orbit of the Cassini Solstice Mission.

Image products created in Celestia. All dates in Coordinated Universal Time (UTC).

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