CICLOPS: Cassini Imaging Central Laboratory for OPerationS

Rev281-282: Jun 26 '17 - '00
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Cassini continues its exploration of the Saturn system with the 6.5-day Rev 281, which begins on June 26 at its farthest distance from the planet. This is also called the orbit’s apoapse. At this point, Cassini is 1.21 million kilometers (0.75 million miles) from Saturn’s cloud tops. Rev 281 is the 11th of 22 proximal orbits that will take place between April 2017 and the end of the mission in September. During these orbits, Cassini’s closest approach to Saturn occurs between the ring system and Saturn’s atmosphere. Eight ISS observations are planned for Rev 281, with the majority focused on Saturn’s atmosphere.

On June 27, Cassini’s Optical-Remote-Sensing instruments will observe a pair of stellar occultations by Saturn and its main rings. First, the Ultraviolet Imaging Spectrometer (UVIS) will watch as Beta Canis Majoris passes behind Saturn. This will allow UVIS to observe the structure of Saturn’s south-polar, upper atmosphere. Afterward, ISS will ride along as the Visual and Infrared Mapping Spectrometer (VIMS) observes Sirius as it passes behind the main rings. On June 28, VIMS will acquire several mosaics of Saturn’s north polar region and northern hemisphere to track cloud motion on Saturn’s nightside.

On June 29 at 22:14 UTC, Cassini will reach periapse for Rev 281 at an altitude of 3,595 kilometers (2,234 miles) above Saturn’s cloud tops. Inbound on this periapse pass, UVIS will observe the limb of Saturn to measure airglow and hydrocarbons in Saturn’s upper atmosphere. The Composite Infrared Spectrometer (CIRS) will map the temperature and composition of the vortex at Saturn’s north pole. As Cassini approaches Saturn, ISS will acquire a noodle of Wide-Angle Camera (WAC) images of Saturn’s atmosphere, running from 80 degrees North Latitude to 17 degrees North Latitude. At periapse, the spacecraft will rotate so that the High-Gain Antenna (HGA) is pointed in the RAM direction, protecting the rest of the spacecraft from inner D ring particles. ISS will continue to acquire WACs in this new orientation through closest approach to Saturn. Early on June 30, VIMS will acquire mosaics of Saturn’s unlit, south polar region.

On June 30, ISS will image a crescent Titan from 1.94 million kilometers (1.21 million miles) away to continuing monitoring seasonal changes to its upper haze layers. On July 1, UVIS will observe a pair of stellar occultations by Saturn’s atmosphere of Zeta Orionis and Episilon Orionis, two of the three stars that make up Orion’s belt. VIMS will acquire a pole-to-pole mosaic of Saturn’s nightside. Later on July 1, ISS will observe the bright limb of Saturn to monitor changes in the planet’s upper haze layers. On July 2, ISS will observe the distant, outer moon Bebhionn from 9.66 million kilometers (6.00 million miles) away. On July 3, ISS will image the outer A ring at high phase angles.

On July 3, during the A ring observation, Cassini will reach apoapse, bringing Rev 281 to a close and starting up the next orbit, Rev 282. At this point, Cassini is 1.21 million kilometers (0.75 million miles) from Saturn’s cloud tops. Eleven ISS observations are planned for this orbit, with the majority focused on Saturn’s main rings. On July 4, Cassini’s Optical-Remote-Sensing instruments will observe a pair of stellar occultations by Saturn and its main rings. First, ISS will ride along as the Visual and Infrared Mapping Spectrometer (VIMS) observes Sirius as it passes behind the main rings. Afterward, Ultraviolet Imaging Spectrometer (UVIS) will watch as Beta Canis Majoris passes behind Saturn. This will allow UVIS to observe the structure of Saturn’s south-polar, upper atmosphere. CIRS will also acquire temperature measurements of the lit face of Saturn’s rings during a pair of observations. ISS will ride along with the second of these covering the C and D rings. On July 5, ISS will image a crescent Titan from 1.94 million kilometers (1.21 million miles) away to continuing monitoring seasonal changes to its upper haze layers.

On July 6 at 09:36 UTC, Cassini will reach periapse for Rev 282 at an altitude of 3,615 kilometers (2,246 miles) above Saturn’s cloud tops. Inbound on this periapse pass, CIRS will acquire a temperature map of the boundary of Saturn’s shadow on the main rings. Afterwards, UVIS will observe a stellar occultation by the main rings of the B-type star Kappa Canis Majoris. Next, ISS will acquire a short, color radial scan across the lit face of the B and C rings. ISS will also conduct a survey of the propellers in the outer A ring. Propellers are voids in the ring created by the gravity of large, 100 – 1000-meter (328 – 3280 foot) ring particles. Due to the influence of the rings on their motion, these observations are needed to keep track of previously discovered propellers, like Earhart and Bleriot. ISS will then observe the edge of the A ring. Afterward, ISS will ride along as VIMS observes the red supergiant star Gamma Crucis passing behind the main rings. Finally, UVIS and ISS will acquire a scan across the C ring, studying small-scale structures in the rings.

During the ring plane cross a few minutes before closest approach, the spacecraft will rotate so that the High-Gain Antenna (HGA) is pointed in the RAM direction, protecting the rest of the spacecraft from inner D ring particles. During the ring plane crossing right before periapse, Cassini’s high-gain antenna will be pointed in the direction the spacecraft is moving to shield it from ring particles. It will then turn to acquire a RADAR scatterometry scan across the main ring system, measuring cm-scale roughness from the A ring down to the C ring.

On July 6, the Radio Science Subsystem (RSS) will perform a radio occultation of the rings by transmitting a signal to Earth through the rings. Changes in the strength of the received signal can provide information about the fine-scale structure of the rings. Afterwards, ISS will ride along with a CIRS observation of the unlit side of the A ring. On July 8, ISS will observe the distant, outer moon Bebhionn from 9.93 million kilometers (6.17 million miles) away.

On July 7, Cassini will reach apoapse, bringing Rev 282 to a close and starting up the next orbit, Rev 283, when Cassini will perform a non-targeted encounter with Titan.

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



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