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Cassini Significant Events 08/19/15 – 08/25/15

Cassini is currently orbiting Saturn with a period of 21.8 days in a plane inclined 0.5 degree from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on Aug. 25 using the 70-meter diameter DSN station in 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 .

Cassini spent this week coasting "uphill" in Saturn's equatorial plane, slowing constantly as it headed towards an Aug. 28 apoapsis. Most of the spacecraft's activities were orchestrated by timed commands in the S90 sequence that is stored onboard. Back on Earth, Sequence Implementation (SIP) teams worked on preparations for the 10-week command sequences S91, S92 and S93. The latter will be installed on the spacecraft next February. Part of preparing these clockwork command sequences involves scheduling the necessary time on Deep Space Network (DSN) antennas, based on negotiations among all the other users of DSN resources.

Wednesday, Aug. 19 (DOY 231)

Today, Cassini's Visible and Infrared Mapping Spectrometer (VIMS) called the shots for 10.6 hours to make a global map of Saturn while the planet completed nearly one full rotation; the Composite Infrared Spectrometer (CIRS) took advantage of the spacecraft's pointing, and rode along taking data as well.

As soon as the global mapping was finished, the Imaging Science Subsystem (ISS) turned towards Saturn's largest moon Titan, and spent 90 minutes monitoring its thick, hazy atmosphere from a distance of 1.7 million kilometers. This observation was repeated on Friday, on Saturday, and again on Monday, all from comparable distances. CIRS and VIMS participated today; only VIMS rode along on subsequent days. These 90-minute observations will help make up for the unusual fact that (per plan) the entire 10-week S90 command sequence includes no close encounters of Titan.

Throughout the week, and largely independent of which direction the spacecraft was turning to point its telescopes, the Magnetospheric and Plasma Science (MAPS) instruments continued collecting data in an ongoing survey of Saturn's magnetosphere.

Thursday, Aug. 20 (DOY 232)

ISS took the reins for 7.75 hours today to make observations all along Saturn's bright crescent limb, with CIRS and VIMS riding along. The viewing geometry is illustrated here: https://space.jpl.nasa.gov/cgi-bin/wspace?tbody=699&vbody=-82&month=8&day=20&year=2015&hour=08&minute=00&fovmul=1&rfov=15&bfov=30&brite=1&showsc=1&showac=1 .

Next, the Ultraviolet Imaging Spectrograph (UVIS) took over for 12 hours to make spectral images of Saturn's sunlit parts in the extreme- and far-ultraviolet parts of the spectrum. ISS rode along.

This news feature on Cassini's final close encounter with Dione was released today: http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20150820 .

Friday, Aug. 21 (DOY 233)

Commands in S90 turned Cassini to point its high-gain antenna to Earth early today, beginning a nine-hour, two-way tracking and communications session with the DSN; one of the 35-meter diameter stations in Australia had been scheduled months in advance, as usual. The flight team uplinked commands to execute Orbit Trim Maneuver (OTM)-419, which had the spacecraft turn and fire its small monopropellant rocket thrusters for 56 seconds. This provided 56 millimeters per second of velocity change to clean up the trajectory following last Monday's D5 encounter with Saturn's moon Dione.

After the OTM was over, ISS resumed observations of Saturn. Its narrow-angle camera stared at the southern night-side auroral oval for nearly four hours, while UVIS and VIMS rode along.

Saturday, Aug. 22 (DOY 234)

CIRS began a period of 22 hours mapping Saturn in the mid-infrared part of the spectrum to measure upper troposphere and tropopause temperatures. VIMS rode along.

Sunday, Aug. 23 (DOY 235)

VIMS mapped the aurorae across Saturn's south polar region for 6.3 hours, with ISS, CIRS, and UVIS riding along. UVIS then continued the auroral observations for another 6.3 hours, making repeated slow slews across the auroral oval. CIRS and VIMS were the riders.

Monday, Aug. 24 (DOY 236)

ISS trained its narrow-angle camera on Saturn's southern aurorae for 16 hours today, with UVIS and VIMS also taking data as riders.

Cassini scientists attended the Outer Planets Assessment Group (OPAG) meeting at APL in Laurel, Maryland, which took place today through Wednesday, Aug. 26. OPAG was established by NASA in late 2004 to identify scientific priorities and pathways for exploration in the outer solar system.

Play between sunlight and Saturn-light gives Saturn's small moon Enceladus an unusual appearance in an image highlighted today:
/resources/16224 .

NASA's Astronomy Picture of the Day featured Cassini's view of Dione today:
http://apod.nasa.gov/apod/ap150824.html .

Tuesday, Aug. 25 (DOY 237)

CIRS finished up this week's science observations by staring at Saturn for 12.3 hours to determine the atmosphere's composition; UVIS and VIMS participated.

Today marks the 34th anniversary of Voyager-2's fast flyby of Saturn. Some of the world's leading planetary scientists who currently head science teams on Cassini were also working on investigations of the ringed planet back when Voyager-1 and Voyager-2 encountered Saturn in 1980 and 1981.

During the past week, the DSN communicated with and tracked Cassini on seven occasions, using DSN stations in California and Australia. A total of 136 individual commands were uplinked, and about 1,298 megabytes of telemetry data were downlinked and captured at rates as high as 124,426 bits per second.

This illustration shows Cassini's position on Aug. 25: http://go.nasa.gov/1LhJ6Xy . The format shows Cassini's path over most of its current orbit up to today; looking down from the north, all depicted objects revolve counter-clockwise, including Saturn along its orange-colored orbit of the Sun.

Milestones spanning the whole orbital tour are listed here: http://saturn.jpl.nasa.gov/mission/saturntourdates .

Information on the present position and speed of the Cassini spacecraft may be found on the "Present Position" page at:
http://saturn.jpl.nasa.gov/mission/presentposition/ .