Cassini is currently 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 Feb. 17 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 .
Cassini carried out several entirely different kinds of scientific observations this week while orbiting the ringed gas giant. On Tuesday was the T-117 encounter with Titan, for which the Radio Science Subsystem (RSS) team, along with the Deep Space Network (DSN), had been preparing. It included two uses of the spacecraft's continuous radio signals: first, the DSN observed Cassini going behind Titan, while RSS made high-fidelity recordings of the signal as it was affected by Titan's atmosphere.
After this ingress occultation, Cassini kept its high-gain antenna tracking the limb of Titan so that its signals could be refracted around the body as much as possible. This was followed by observing Cassini’s occultation egress, and then a special bistatic experiment took place. The spacecraft was rotated to the precise orientation in which its radio signals would have the best chance of skipping off small lakes and ponds on the surface of Titan's northern region, before being received on Earth. Indeed, clear specular reflections of the signal were captured, and analysis of them will lead to better understanding Titan's complex surface.
Wednesday, Feb. 10 (DOY 041)
As the day began, Cassini was about two million kilometers from Saturn, well on its way "down" from last week's apoapsis. For 13.5 hours, the Imaging Science Subsystem (ISS) trained its telescopes on Saturn's F ring, constantly taking images to create a movie. Particles making up that bright, narrow ring race around the planet going nearly 60,000 km per hour. The Composite Infrared Spectrometer (CIRS) and the Visible and Infrared Mapping Spectrometer (VIMS) rode along, making observations as well.
Thursday, Feb. 11 (DOY 042)
ISS and CIRS made a 90-minute observation as part of the Titan monitoring campaign, while the planet-like moon was about three million km away on the far side of Saturn. Next, ISS spent 60 minutes looking for objects near the planet, part of the satellite orbit campaign. This pair of observations was repeated before the end of the day, and then again on the following day. The viewing geometry is illustrated here: http://go.nasa.gov/1U8s6po .
Next, VIMS took control of spacecraft pointing for four hours to create a mosaic of the sunlit rings. CIRS rode along making its own observations. Following this, Cassini's Navigation team used ISS to view Saturn's large icy satellite Tethys against the background stars for optical navigation purposes. Finally, late in the day, CIRS began an eight-hour stare at the sunlit side of Saturn's opaque B ring, obtaining spectra at thermal-infrared wavelengths to study the composition of the ring particles; VIMS rode along.
A whimsical "Titan Travel Poster," created by The Studio at JPL, is today's featured image.
Friday, Feb. 12 (DOY 043)
Early in the day, realtime commands were uplinked to adjust the pointing vectors stored aboard the spacecraft, in preparation for Radio Science experiments coming up during Tuesday's Titan encounter T-117. Later, the flight team prepared and approved a set of commands that would be sent to Cassini on the following day to execute Orbit Trim Maneuver (OTM)-442.
At JPL, Cassini's 68th Project Science Group (PSG) meeting wrapped up. The next PSG will be this June at the European Space Agency's European Space Research and Technology Centre (ESTEC), in Noordwijk, the Netherlands.
Saturday, Feb. 13 (DOY 044)
The Ultraviolet Imaging Spectrograph (UVIS) turned to examine Saturn's large icy satellite Dione for nearly two hours. With these observations done, ISS and CIRS spent two hours studying "propellers" in the rings (http://go.nasa.gov/17oqTWF).
When these observations were completed, Cassini turned towards Earth and received the OTM-442 commands. In response, the spacecraft turned and fired its small rocket thrusters for 9.4 seconds to achieve a change in velocity of 15 millimeters per second. This served as a fine adjustment of its course towards Tuesday's Titan encounter T-117.
Sunday, Feb. 14 (DOY 045)
The Magnetospheric Imaging Instrument (MIMI) and the Magnetometer (MAG) began a two-day survey while the Ion and Neutral Mass Spectrometer (INMS) conducted an observation of neutral molecules in Saturn's inner magnetosphere.
UVIS tracked the bright blue star Alpha Virginis (also known as Spica) for 2.5 hours while it was being occulted by Saturn's rings; CIRS rode along. After the star was fully hidden behind the B ring, UVIS turned to Saturn's sunlit northern auroral region, and spent 5.5 hours observing the oval; CIRS and VIMS also made observations. UVIS and CIRS then looked over to Saturn's eastern side for 8.6 hours, while the star rose from behind the atmosphere and proceeded to be occulted again by the rings. Finally, ISS, CIRS, and VIMS conducted one more 90-minute Titan monitoring observation.
Monday, Feb. 15 (DOY 046)
By now, the spacecraft had come much closer to Saturn. The Cosmic Dust Analyzer (CDA) spent two hours collecting and measuring particles of dust while Cassini passed through the ring plane going south. Next, VIMS turned to observe Saturn's small, active moon Enceladus, with ISS, UVIS, and CIRS riding along; for a few hours the spacecraft was chasing along behind Enceladus in its orbit. During this observation, the spacecraft passed periapsis, having come within 173,000 km above the planet's visible limb. Its speed relative to Saturn at that point was 62,351 km per hour.
After observing Enceladus itself, UVIS turned to Saturn's atmosphere to observe the spot where Enceladus leaves a "footprint" visible at UV wavelengths, which is caused by electrodynamic coupling via Saturn's magnetic field. The observation lasted 10.3 hours.
UVIS concluded the day by observing the blue star Gamma Orionis -- Bellatrix -- for 2.5 hours as it entered occultation behind Saturn’s night-side atmosphere.
An image featured today shows an unusual view of Saturn's moon Dione: http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=5301 .
Tuesday, Feb. 16 (DOY 047)
MIMI dictated the spacecraft's attitude for one hour today, so that its Ion and Neutral Camera could view plasma that co-rotates with Saturn, largely driven by the rotating magnetic field. Following this, Cassini had closed the distance to Titan to within 248,000 km, which is much closer than the Earth is to our own Moon. Late in the day, Cassini's closest approach to Titan came at 1,018 km above its atmosphere-enshrouded surface. In addition to the science data obtained during the flyby, Titan's gravitation and orbital momentum launched the spacecraft into a higher-inclination orbit of Saturn, and increased its orbit period as well. The spacecraft's orbit changed from a 16-day period at 17.5 degrees inclination to a 23.9-day period at 21.9 degrees, as measured from Saturn's equatorial plane. The T-117 encounter is further described here: http://saturn.jpl.nasa.gov/mission/flybys/titan20160216 .
On seven 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 five of them. Also this week, the Deep Space Network communicated with and tracked Cassini on eleven occasions, using its stations in Spain and Australia. A total of 189 individual commands were uplinked, and about 1,211 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 Feb. 16, several hours before the T-117 close approach: http://go.nasa.gov/1OdNraY . 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.