6 min read

Cassini Significant Events 02/04/2015 – 02/10/2015

Cassini is currently orbiting Saturn with a 31.9-day period in a plane inclined 19.1 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on Feb. 11 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 .

Regular readers of these significant events reports are familiar with the range of activities Cassini accomplishes on a routine basis. Among them are remote-sensing telescopic observations, rocket engine and thruster firings, direct-sensing magnetospheric instrument observations, command sequence boundaries, and close encounters within the Saturn system. Cassini's Outreach team has created an annotated list of all of this year's past and future milestones, with links to previous years spanning the whole orbital tour. The page may be found here:
http://saturn.jpl.nasa.gov/mission/saturntourdates .

Commands from the on-board S87 sequence orchestrated most of Cassini's activities this week. Saturn loomed ever larger day by day, while the spacecraft was plunging toward its periapsis passage on Tuesday. As always, all images acquired were published on the Cassini website under "Raw Images." And as always, there are many spectacular views among them. They can be found here soon after being sent to Earth:
http://saturn.jpl.nasa.gov/photos/raw .

Wednesday, Feb. 4 (DOY 035)

First up this week was a quick, two-minute storm watch of Saturn by the Imaging Science Subsystem (ISS). ISS then continued observing for an hour, turning to look near Saturn for small objects as part of the satellite orbit campaign. Next, the Composite Infrared Spectrometer (CIRS) took control of spacecraft pointing and stared at Saturn's sunlit C ring for ten hours, obtaining thermal infrared spectra to study the ring particles' composition. All the while, the Visible and Infrared Mapping Spectrometer (VIMS) took advantage of this pointing to make its own observation in ride-along mode. The C ring is the innermost of the easily visible main rings. ISS did another two-minute storm watch, and then this was followed by another hour-long satellite orbit observation. To finish out the busy day, VIMS began calling the shots for eight hours to make a mosaic-scan of the sunlit side of the rings, while CIRS and ISS rode along.

Thursday, Feb. 5 (DOY 036)

As soon as VIMS completed its ring mosaic, ISS carried out another two-minute storm watch observation before the spacecraft turned to face its high-gain antenna dish toward Earth for a nine-hour communications session.

Friday, Feb. 6 (DOY 037)

The spacecraft remained Earth-pointed today while the Magnetospheric and Plasma Science (MAPS) instruments acquired data.

Saturday, Feb. 7 (DOY 038)

ISS spent 13 hours today with its telescopes trained on the bright, narrow F ring to make a movie. This ring occupies the space just outside of the main rings; its speeding particles complete one revolution about Saturn every 14.8 hours.

Sunday, Feb. 8 (DOY 039)

VIMS observed the sunlit rings for five hours while the illumination phase angle varied with the spacecraft's decreasing latitude; CIRS rode along. CIRS then stared at Saturn's dense, sunlit B ring for six hours obtaining thermal infrared spectra to study chemical composition, while VIMS was the rider. Both before and after the CIRS-led observation, ISS squeezed in a two-minute storm watch on the planet. With this observing complete, ISS reacquired and tracked the orbits of known "propeller" features in Saturn’s rings (http://go.usa.gov/YyGR). Finally, ISS, CIRS and VIMS performed a 90-minute observation in the Titan monitoring campaign, while the huge moon was 2.6 million kilometers away.

More than a dozen flight team members worked during the weekend analyzing the latest navigation data, designing another Orbit Trim Maneuver (OTM), and creating its commands. By late in the evening, the maneuver design was reviewed and approved, and the commands were readied for uplink on the following morning.

Monday, Feb. 9 (DOY 040)

VIMS targeted Saturn for 10.5 hours to make mosaics mapping the northern hemisphere. CIRS and ISS rode along, making their own observations, while the Ultraviolet Imaging Spectrograph (UVIS) rode along looking for haze. Next UVIS took control of pointing for three hours to perform a scan of Saturn's thermosphere over the sunlit northern hemisphere. Data from this rare observation will be used to determine the particle density there, as an aid in planning Cassini's 2017 proximal orbits, in which the spacecraft will zoom in between the planet's rings and atmosphere.

Shortly after Cassini turned toward Earth upon completion of these activities, the commands for OTM-403 arrived and were stored aboard. They clocked out a few hours later, turning the spacecraft and firing its small hydrazine-fed rocket thrusters for 25 seconds. This imparted a change in velocity of 29 millimeters per second, fine-tuning Cassini's flight path on approach to Titan for the T-109 encounter on Feb. 12. A flyby page has been published for this encounter:
http://saturn.jpl.nasa.gov/mission/flybys/titan20150212 .

An image featured today shows Saturn's rings as seen through the red filter in ISS's narrow-angle camera: /resources/16158

Tuesday, Jan. 10 (DOY 041)

Today's first science activity following the OTM was another 90-minute Titan monitoring campaign observation. This time, the distance to the target had shrunk to 1.8 million kilometers. After that, ISS spent 5.5 hours observing Saturn's large icy satellite Rhea as it passed within 47,000 kilometers. CIRS, UVIS and VIMS rode along. This flyby of Rhea was an example of a non-targeted encounter, meaning that no OTMs were dedicated to achieving it. As it happened, Cassini passed through the ring plane into Saturn's southern hemisphere during the observation.

VIMS began making mosaics of Saturn's southern hemisphere. Again, CIRS, ISS, and UVIS rode along. About halfway through this regional mapping activity, VIMS turned to observe the red star Alpha Herculis for just over an hour as, by virtue of Cassini's motion, it became occulted by the main rings. CIRS rode along observing this occultation. VIMS then regained control for another 2.75 hours to continue mapping Saturn's southern hemisphere while CIRS, ISS and UVIS rode along. Toward the end of the day, while communicating with Earth again, Cassini passed through the periapsis of its Saturn Orbit #212. Its speed had increased to a maximum of 45,970 kilometers per hour relative to the planet, coming in as close as 355,160 kilometers above the visible limb.

During the past week, the Deep Space Network communicated with and tracked Cassini on seven occasions, using stations in Australia and California. A total of 254 individual commands were uplinked, and about 1,030 megabytes of telemetry data were downlinked and captured at rates as high as 124,426 bits per second.