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. 8 using the 70-meter diameter DSN station in Australia. 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 .
Commands in Cassini's memory comprising the 10-week-long S90 sequence continued controlling the spacecraft's activities this week, while the spacecraft looped inwards toward Saturn and flew through periapsis, all the while conducting scientific observations of Saturn and its moons Titan, Dione and Enceladus.
Wednesday, Sept. 2 (DOY 245)
Under control of its electrically-driven reaction wheels as usual, Cassini turned to point its largest telescope, a 50-centimeter aperture Cassegrain, towards Saturn today. This telescope, one of the nine whose apertures are co-aligned on Cassini, comprises the optics of the Composite Infrared Spectrometer (CIRS). The instrument scanned the gas giant for 22 hours in the mid-infrared part of the spectrum, mapping temperatures in Saturn's upper troposphere and its tropopause. The viewing angle CIRS enjoyed (illustrated here https://space.jpl.nasa.gov/cgi-bin/wspace?tbody=699&vbody=-82&month=9&day=2&year=2015&hour=00&minute=00&rfov=90&fovmul=-1&bfov=30&showsc=1&showac=1 ) is never possible for an observer here on Earth, or in Earth orbit. The Visible and Infrared Mapping Spectrometer (VIMS) made observations as well while riding along.
A news feature released today describes new findings about the material making up Saturn's rings, and in particular some important differences within the broad A ring: http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20150902/ .
Thursday, Sept. 3 (DOY 246)
CIRS spent 7.5 hours examining one spot on Saturn, collecting high-quality spectral data to derive the atmosphere's chemical composition. VIMS and the Ultraviolet Imaging Spectrograph (UVIS) rode along while CIRS controlled pointing.
Friday, Sept. 4 (DOY 247)
Cassini's Navigation team used the Imaging Science Subsystem (ISS) today to take images of Saturn's large, two-tone moon Iapetus against a background of stars, for optical navigation purposes. ISS then pointed its cameras to Saturn for five hours, tracking features to measure wind velocities, with UVIS and VIMS riding along. Next, CIRS spent six hours on a compositional measurement similar to the previous day's, with UVIS participating. Finally, ISS took control again for another five-hour wind observation with VIMS and UVIS riding.
Some flight team members surprised hundreds of people on the Pasadena sidewalk with telescopic views of Saturn and Titan this evening. Given that the rings are tilted a wide 24 degrees as seen from Earth this year, Saturn's appearance is stunning in telescopes of almost any size.
Saturday, Sept. 5 (DOY 248)
ISS turned its attention to Titan for 90 minutes to monitor the huge moon's atmospheric haze, with CIRS and VIMS riding along; this observation was repeated on the following day as well. With today’s activity completed, UVIS took the reins for 10.5 hours to perform a slow scan across Saturn’s illuminated area, forming extreme- and far-ultraviolet spectral images. CIRS and ISS rode along taking data.
Sunday, Sept. 6 (DOY 249)
ISS performed imaging at selected latitudes on Saturn for 10.7 hours, covering a range of emission angles while the planet rotated one full time. All the other optical remote-sensing (ORS) instruments, CIRS, VIMS, and UVIS, rode along.
Monday, Sept. 7 (DOY 250)
Cassini's Ion and Neutral Mass Spectrometer (INMS) took observations of the torus about Saturn in which Titan revolves. Overlapping this, VIMS spent 13.7 hours mapping Saturn's sunlit equatorial regions while the planet rotated one full turn again. CIRS and ISS rode along. The Magnetospheric and Plasma Science (MAPS) instruments continued their ongoing magnetosphere survey.
Using one of the 34-meter diameter Deep Space Network (DSN) stations in Australia late today, the flight team uplinked commands to Cassini for the science instruments to use once the S91 command sequence takes control, starting on Sept. 21. After a round-trip time of 2 hours 50 minutes, telemetry showed that each of the 271 individual commands had been properly received across the solar system.
One of the filters that ISS can rotate into its optical path selects for an infrared wavelength that the gas methane (CH4) absorbs. An image of Saturn and Dione using this filter was featured today: /resources/16238 .
Tuesday, Sept. 8 (DOY 251)
Cassini came within about 42,000 kilometers of Saturn's moon Dione, an encounter designated as "non-targeted" because no propulsive maneuvers were in the plan to achieve it. ISS and the other ORS instruments spent eight hours making high-priority observations, which included mapping regions of interest on Dione's surface, and studying its thermally anomalous areas. Some of the parts mapped have a highly degraded appearance, similar to craters on Enceladus's northern hemisphere. Cassini will be making one more passage of this moon at a similar distance, three weeks from now; there are no more close, targeted encounters of Dione to be had.
Next, ISS turned to observe Saturn's small, active moon Enceladus and the plumes of icy material that stream from crevasses near its south pole. ISS led a total of five hours of observations, with CIRS, UVIS, and VIMS participating at various times. One objective of the Enceladus observations was to monitor the plume's brightness at different parts of its orbit about Saturn. This provides information on the processes that generate the plume, and will help constrain models of Enceladus's interior. Another objective was to study the body's leading hemisphere, the side that faces forward in it 1.37-day trip in orbit around the planet. This region is dominated by terrain altered by tectonic processes.
During one of the Enceladus observations today, Cassini flew through the point of periapsis in its own orbit of Saturn, coming within 230,000 kilometers of the gas giant's visible limb and going 56,084 kilometers per hour relative to the planet. This point had been slated for an opportunity to fire Cassini's rocket thrusters to put the spacecraft on track for its T-113 targeted encounter with Titan on Sept. 28. However, navigation solutions based on the latest DSN tracking data showed the spacecraft to be basically right on target for the 1,036-kilometer altitude flyby, so Orbit Trim Maneuver (OTM)-420 was cancelled.
During the past week, the Deep Space Network communicated with and tracked Cassini on seven occasions, using DSN stations in Australia and Spain. A total of 13 individual commands were uplinked, and about 1,402 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 Sept. 8: http://go.nasa.gov/1LhJgxZ . 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.