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Cassini Significant Events 08/26/15 – 09/01/15

Cassini is currently orbiting Saturn with a period of 21.9 days in a plane inclined 0.4 degree from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on Sept. 1 using the 70-meter diameter DSN station in Spain. 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 .

This illustration shows Cassini's position on Sept. 1: http://go.nasa.gov/1LhJfdi. 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.

Cassini passed apoapsis late on Friday in its orbit of the ringed planet. Gradually, the spacecraft then began the plunge down its 2.7 million-kilometer-high roller coaster in Saturn’s ring plane. It will continue to gather speed until the next periapsis passage on September 8. Commands stored on Cassini in the S90 sequence controlled all of the robot's activities this week, apart from the few routine commands that the flight team sent in real time.

Wednesday, Aug. 26 (DOY 238)

The spacecraft turned to point its telescopes to Saturn's largest moon, and for 90 minutes the Imaging Science Subsystem (ISS) led an observation in the Titan meteorology campaign. Convective clouds are expected to appear in its thick atmosphere soon, as summer deepens in Titan's northern hemisphere. (None have been seen at low latitudes for more than three years now; only the thick, ever-present haze remains.) Cassini was about 1.5 million kilometers away from the planet-like moon; the Visible and Infrared Mapping Spectrometer (VIMS) also took data while ISS controlled pointing.

When Titan monitoring was done, ISS turned and tracked Saturn's small irregular moon Hati for just over six hours. This object has a diameter of about six kilometers and occupies a retrograde, inclined orbit that reaches as far as 19.8 million kilometers from Saturn. It rotates more rapidly than any other object observed in the Saturn system, with a period of only 5.5 hours. The name Hati honors a giant wolf in Norse mythology.

The next observation on Cassini's list devoted six days to the Cosmic Dust Analyzer (CDA), which today began making one observation after another, collecting data on the Saturn dust stream. ISS rode along and took images during some parts of CDA's activity. The dust-stream observation was a high-priority special request that had been planned into the S90 command sequence; the CDA team's goal is to detect Saturn’s rotation period and other periods in dust stream data. CDA has previously found periodicities that correlate with Saturn's kilometer-wavelength radio-frequency emissions. The team has also tentatively identified frequencies that correlate with certain moons' orbital periods. Clearly identifying such periodicities would provide a direct indication of the source of the particles, for example whether they come from Saturn's active moon Enceladus and/or others.

Thursday, Aug. 27 (DOY 239)

A remarkable video, which was created earlier this year by researchers at the University of Arizona, appears on the Cassini website. It uses imaging and spectral data from the Cassini Orbiter and the Huygens Probe to zoom all the way in to Titan's surface:

Friday, Aug. 28 (DOY 240)

CDA continued its special direct-sensing observations while Cassini coasted through apoapsis late in the day, which marked the start of its Saturn Orbit #221. The spacecraft had slowed to 5,823 kilometers per hour relative to the planet.

Saturday, Aug. 29 (DOY 241)

Even while Cassini kept its primary axis aligned with the high-gain antenna pointing to Earth for communications and tracking, CDA controlled the spacecraft's secondary pointing axis so that it could continue to collect important data uninterrupted.

Sunday, Aug. 30 (DOY 242)

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

Monday, Aug. 31 (DOY 243)

An image featured today captures Saturn's moon Dione as it transits in front of the giant planet:
/resources/16237 .

Tuesday, Sept. 1 (DOY 244)

Today marks 600 days until the start of the Proximal Orbit phase, when Cassini's orbits will bring it repeatedly through the space in between Saturn's atmosphere and innermost rings.

CDA completed its prolonged Saturn dust stream observation. Right on its heels, the Ultraviolet Imaging Spectrograph (UVIS) began a 15-hour observation of Saturn in the extreme- and far-ultraviolet parts of the spectrum. ISS rode along taking data while UVIS made a slow scan across Saturn's sunlit portion; the viewing geometry is illustrated here: https://space.jpl.nasa.gov/cgi-bin/wspace?tbody=699&vbody=-82&month=9&day=1&year=2015&hour=12&minute=00&fovmul=1&rfov=10&bfov=30&brite=1&showsc=1&showac=1 .

During the past week, the Deep Space Network communicated with and tracked Cassini on three occasions, using DSN stations in California, Australia, and Spain. A total of eight individual commands were uplinked, and about 520 megabytes of telemetry data were downlinked and captured at rates as high as 110,601 bits per second.