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Cassini Significant Events 08/06/2014 – 08/12/2014

Cassini is orbiting Saturn with a 31.9-day period in a plane inclined 48 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on August 12 using the 70 meter-diameter Deep Space Network (DSN) station at Goldstone, California. The spacecraft continues to be in an excellent state of health with all of its subsystems operating normally except for the instrument issues described at http://saturn.jpl.nasa.gov/news/significantevents/anomalies. Information on the present position of the Cassini spacecraft may be found on "Eyes on the Solar System".

This week's highlight was the firing of Cassini's bi-propellent-fed main rocket engine on Saturday to perform Orbit Trim Maneuver (OTM)-387. This was the single largest propulsive event remaining in Cassini's mission. It nudged the spacecraft's trajectory to fly by Saturn's largest moon Titan at an altitude of 964.0 kilometers above the surface during the T-104 encounter on August 21. Besides targeting to the correct geometry for science observations, OTM-387 was designed to alter the trajectory so that T-104 and subsequent Titan flybys through T-110 will now lower Cassini’s orbital inclination back down to Saturn’s equatorial plane.

Wednesday, Aug. 6 (DOY 218)

Under control of the on-board S85 command sequence, the Ultraviolet Imaging Spectrograph (UVIS) turned the spacecraft to perform an 11.5-hour series of mosaic scans of Saturn’s magnetosphere. These scans are designed to reveal oxygen in Saturn's vicinity.

One of Cassini's most compelling portraits of Saturn's north polar region was selected as today's NASA's Astronomy Picture of the Day:

Thursday, Aug. 7 (DOY 219)

UVIS carried out a 13.5-hour oxygen search similar to Wednesday’s observation.

All of the opportunities for Cassini's OTMs are identified years in advance. Each such maneuver comes into focus for operations in an encounter-strategy meeting a number of weeks before execution. For OTM 387, this occurred on July 10. The OTM commands were built early this week, and were approved today for uplink to the flight system.

Friday, Aug. 8 (DOY 220)

The file of OTM-387 commands were uplinked today, using one of the DSN's 34 meter-diameter stations in Australia. After a round-trip light time of 2 hours 43 minutes, telemetry confirmed that all 142 individual commands had been properly received. Following this, UVIS made another scan for oxygen; this one lasting 14.5 hours.

Saturday, Aug. 9 (DOY 221)

OTM-387 executed today, turning the spacecraft and firing its main engine for 71 seconds. This produced the desired change in velocity of 12.5 meters per second. An additional OTM opportunity will occur on August 18 in case fine-tuning might be needed on the final approach to the Titan T-104 flyby. Another OTM opportunity will come four days after the encounter to allow for any needed trajectory cleanup.

The large OTM was used to reverse the “cranking direction” of the Titan flybys. The T-104 through T-110 flybys, in addition to providing prime Titan science opportunities, will also supply the trajectory changes to lower Cassini’s orbital inclination back down to Saturn’s equatorial plane. This will enable the final close encounters with Saturn’s icy satellites Dione and Enceladus later next year.

After the OTM, the Cosmic Dust Analyzer (CDA) had the spacecraft turn to an attitude that allowed it to observe dust coming in from outside the Saturnian system. The observation lasted 14 hours.

Sunday, Aug. 10 (DOY 222)

The Composite Infrared Spectrometer (CIRS) trained its telescope on Saturn for 13 hours to map temperatures in the upper troposphere and tropopause. The Visible and Infrared Mapping Spectrometer (VIMS) took advantage of the pointing and took data for a ride-along observation.

Monday, Aug. 11 (DOY 223)

The little moon Prometheus orbits Saturn just inward from the F ring. In an image featured today, its partner Pandora is seen in its orbit just outside the narrow ring. Pandora goes around Saturn once every 15.1 hours, taking a little longer than particles in the F ring. The image may be found here: /resources/16080.

Tuesday, Aug. 12 (DOY 224)

The Imaging Science Subsystem (ISS) made an observation in the satellite orbit campaign, observing objects close to the planet. At its conclusion, ISS looked over at Saturn for a two-minute storm-watch observation. CIRS then stared at the sunlit side of the C ring for 10 hours, obtaining thermal infrared spectra to study ring particle composition. ISS and VIMS rode along. When that observation completed, ISS made another quick storm watch.

Given Cassini's proximity to Saturn's planet-like moon, ISS can detect clouds in Titan's atmosphere and measure their movement over time. A news feature released today shows the evolution of new clouds, and puts them in context with the changing alien seasons: http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20140812.

This week, the DSN communicated with and tracked Cassini on nine routine occasions, using stations in Australia and California. A total of 157 individual commands were uplinked, and about 1,520 megabytes of telemetry data were downlinked at rates as high as 142,201 bits per second. Coherent Doppler-shift data and ranging data were obtained for a total of about 36 hours, and nine hours of Radio Science data were collected for system calibration. In addition to this routine support, Cassini participated in testing the new 34 meter-diameter station in Canberra, Australia, and also carried out an exercise of the DSN's Emergency Control Center at Goldstone, California.