Cassini is orbiting Saturn with a period of 23.9 days in a plane inclined 21.9 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on March 9, using the 70-meter diameter Deep Space Network 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 stored on board Cassini in the S93 sequence controlled the spacecraft's activities while orbiting Saturn this week. Meanwhile, Sequence Implementation Process teams continued working on the 10-week command sequences S94, which will begin executing on April 18, and S95, which starts on June 26. Tasks have also been scheduled for S96, which goes active early in September. Five sequences remain to be worked after that, before the end of the mission in September 2017.
Wednesday, March 2 (DOY 062)
Cassini's Magnetospheric and Plasma Science (MAPS) instruments spent the day collecting in-situ data from the spacecraft's immediate environment, out near apoapsis of its Saturn orbit.
An image featured today shows some of Cassini's highest-resolution views of the surface of Saturn's huge planet-like moon Titan. The Synthetic Aperture Radar image covers roughly 500 kilometers on a side, with insets revealing changes that have been detected in one of Titan's great lakes: http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=5312 .
A few days later, the same image was featured as NASA's Astronomy Picture of the Day: .
Thursday, March 3 (DOY 063)
The Imaging Science Instrument (ISS) led an observation in the Titan monitoring campaign while the target was 2.4 million km from Cassini. The Composite Infrared Spectrometer (CIRS) and the Visible and Infrared Mapping Spectrometer (VIMS) rode along taking data as well. After this 90-minute observation, ISS looked for one hour towards small objects near Saturn, as part of the satellite orbit campaign. As soon as this was done, the Navigation team pointed ISS to Saturn's moon Iapetus while it was in the neighborhood of two million km from the spacecraft. The exposure allowed background stars to be seen behind the two-toned moon, so it can be used for optical navigation purposes. Finally, CIRS took over spacecraft pointing and began a 23-hour long observation of Saturn to study the composition of its atmosphere. VIMS and the Ultraviolet Imaging Spectrograph (UVIS) rode along. The spectacular view from Cassini in its inclined orbit is illustrated here: http://go.nasa.gov/1LRXFlN .
A meeting of the science teams for the Cassini Plasma Spectrometer (CAPS) and the Ion and Neutral Mass Spectrometer (INMS) was held at the Institute of Planetology and Astrophysics in Grenoble, France, from March 1 through today. The meeting included talks on recent science results from Titan, Saturn’s magnetosphere, and icy satellites, as well as planning for Cassini's proximal orbits in 2017. Other key topics included analysis of data from the E-21 Enceladus flyby, the results of which are still being analyzed.
Friday, March 4 (DOY 064)
Upon completion of the CIRS activity, ISS made another one-hour satellite orbit campaign observation. Next, VIMS spent 6.5 hours making a mosaic of Saturn's rings, with CIRS riding along.
Saturday, March 5 (DOY 065)
Saturn is a fine sight in any small telescope for early morning viewers these days; the bright off-white planet twinkles much less than stars do, and appears to the upper-left of the red star Antares. The planet's rings are tilted down 26 degrees, almost as wide-open as they ever are, from Earth's point of view.
Sunday, March 6 (DOY 066)
ISS, CIRS and VIMS performed another 90-minute Titan monitoring observation, from a range of 1.4 million km. Next, ISS spent 14 hours observing Saturn's narrow, ever-changing F ring to create a movie. CIRS and VIMS then observed Titan for eight hours to study the composition of its dense atmosphere.
Monday, March 7 (DOY 067)
CIRS and VIMS observed the sunlit side of Saturn's opaque B ring, obtaining spectra at thermal-infrared wavelengths to study ring-particle composition. Next, ISS and VIMS made another long-range, long-duration Titan monitoring observation. It lasted nine hours, and was repeated on the following day.
Saturn's icy moon Rhea is half the size of our own Moon, and Tethys is even smaller. In an image featured today, both Rhea and Tethys grace the gas giant's sky: http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=5311 .
Tuesday, March 8 (DOY 068)
UVIS turned to stare at the distant but bright star Alpha Virginis, also known as Spica, for 87 minutes while Saturn's large icy moon Dione occulted the star. This stellar occultation helps in the search for any volatiles and plumes that might be coming from Dione.
Cassini's radio signal is always very weak by the time it has propagated to Earth. In milliwatts, it's 2.5X10e-15 mw, 15 places to the right of the decimal point, after being collected by a 70-meter diameter Deep Space Network (DSN) station. After the big Cassegrain reflector antenna has concentrated it, the first electronics the signal encounters is a low-noise amplifier (LNA). The LNA is normally cooled with liquid helium to just a few Kelvins above absolute zero, to be sure it contributes little noise while amplifying the signal to useable levels. Today, the LNA in the Australian 70-m station failed, so Cassini's signal could not be captured. Therefore, a large portion of telemetry data from science observations during the past 1.5 days was unfortunately lost.
With a system as complex as a deep space tracking station, these occasional outages are a part of any flight project’s life. When particularly valuable data is on Cassini’s solid state recorders, the flight team will often take special steps like protecting the data until is has been played back or by playing it back twice. The operations team is currently considering such options for the March 11 UVIS observation of Enceladus occulting Epsilon Orionis: http://saturn.jpl.nasa.gov/mission/flybys/enceladus20160311/ .
On three occasions during the week, when the optical instruments were pointing at or near Saturn, ISS made two-minute Saturn storm-watch observations; VIMS rode along with two of them. Also this week, the Deep Space Network communicated with and tracked Cassini on four occasions, using its stations in Australia and California. A total of 133 individual commands were uplinked, and about 579 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 March 8: http://go.nasa.gov/1OdMS0L . The format shows Cassini's path over most of its current orbit up to today; looking down from the north, all depicted objects (except the background stars of course) revolve counter-clockwise, including Saturn along its orange-colored orbit of the Sun.