Cassini Significant Events 10/28/15 – 11/03/15

Cassini is currently orbiting Saturn with a period of 13.9 days in a plane inclined 0.6 degree from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on Nov. 4 using one of the 34-meter diameter DSN stations 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 .

For the final time in the foreseeable future, the ejecta plume of Saturn's small icy moon Enceladus was directly sampled. This Wednesday, Cassini flew directly through the plume with its dust analyzer and mass spectrometer oriented to maximize sample acquisition. The E-21 encounter went just as planned, and immediately afterwards the Deep Space Network provided flawless tracking and telemetry capture; digital data from all the scientific observations are in the science teams' hands now.

Cassini's navigation team quickly analyzed the line-of-sight radiometric tracking data, which consists of Doppler-shift and range, and determined that the spacecraft was satisfactorily close to its intended flight path. Work was therefore suspended on the realtime task of creating commands for Orbit Trim Maneuver (OTM)-428 to fire the rocket thrusters thus allowing more time to return the flyby data.

Wednesday, Oct. 28 (DOY 301)

Cassini turned to point the Imaging Science Subsystem (ISS)'s telescopes toward Saturn's irregular satellite Bestla while it was nearly eight million kilometers away from the spacecraft. This object, which is only about six km in diameter, was described in the report for Sept. 22 of this year (http://go.nasa.gov/1Ncx4Kz). The observation lasted five hours; the Visible and Infrared Mapping Spectrometer (VIMS) also observed while riding along.

As the distance from Cassini to Enceladus shrank to less than that from Earth to our own Moon, five hours were given over to the Cosmic Dust Analyzer (CDA). Following this observation, the Ion and Neutral Mass Spectrometer (INMS), plus CDA and all the optical remote-sensing instruments, which are ISS, VIMS, the Composite Infrared Spectrometer (CIRS), and the Ultraviolet Imaging Spectrograph (UVIS), took full advantage of today's very close approach to Enceladus, and the flight through its plume of ejected material. The Magnetospheric and Plasma Science (MAPS) instruments participated as well: the Magnetometer, the Radio and Plasma Wave Science instrument, and the Magnetospheric Imaging Instrument. The E-21 Encounter page discusses the scientific objectives and the observations from today's flyby: http://saturn.jpl.nasa.gov/mission/flybys/enceladus20151028 .

During Cassini's observations on approach to Enceladus, the spacecraft flew through periapsis in its Saturn orbit #224. Coming within 114,800 km of Saturn's visible limb, it had reached a speed of 71,971 km per hour relative to the planet.

This illustration shows the viewing geometry from Cassini just three minutes after its closest approach to Enceladus, and the lowest-ever flight through the icy southern plume: http://go.nasa.gov/1WzZvXZ. An illustration from 2012 illustrates the positioning of all of Cassini's entrances into Enceladus's plumes, including this final one, E-21: /resources/15472 .


Thursday, Oct. 29 (DOY 302)

Today, ISS led a 2.5-hour optical remote-sensing observation of Enceladus's plume with VIMS and UVIS participating. Next, UVIS called the shots and observed the bright blue star Zeta Orionis, which is part of Orion's belt, for 2.75 hours as it sank behind Saturn's atmosphere. VIMS rode along. This kind of observation can help determine the abundance of atomic and molecular hydrogen, and some light hydrocarbons, in Saturn's upper atmosphere. Following this stellar occultation, ISS observed Bestla again for 8.5 hours, with VIMS riding along.

Friday, Oct. 30 (DOY 303)

UVIS conducted an observation of Saturn's south-pole aurora for 11.3 hours. It made repeated slow slews of its field of view across the auroral oval during the first half of the observation to look for faint emissions from the dark side. During the second half, UVIS stared at the dark limb; CIRS, ISS and VIMS were riders. MAPS instruments then began a campaign to observe the structure and dynamics of Saturn's magnetotail at low latitudes and moderate distances downstream. Finally, ISS spent 90 minutes observing Enceladus against the background stars for optical navigation purposes.

A news feature released today looks back at the Enceladus E-21 encounter. It features an image of the crescent Enceladus taken on encounter day, appearing to hang above Saturn's rings, while the dusty F ring is brightly sunlit from behind: http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20151030 .

Saturday, Oct. 31 (DOY 304)

ISS conducted a 90-minute Titan monitoring campaign observation at a range of 1.4 million km, with CIRS and VIMS riding along. This was repeated on the following day from a slightly greater distance from Titan. Following today's, UVIS carried out another Saturn southern pole auroral observation. This one lasted 12 hours, while CIRS, ISS and VIMS again rode along.

Sunday, Nov. 1 (DOY 305)

CDA observed interstellar dust for 14.5 hours today.

Monday, Nov. 2 (DOY 306)

An image featured today shows the surface of Titan, looking down through its hazy atmosphere, where two dark dune-fields can be seen: /resources/16270 .


Tuesday, Nov. 3 (DOY 307)

During the week, the Deep Space Network communicated with and tracked Cassini on six occasions, using DSN stations in all three DSN complexes: Australia, Spain and California. A total of 14 individual commands were uplinked, and about 1,778 megabytes of telemetry data were downlinked and captured at rates as high as 110,601 bits per second.

This illustration shows Cassini's position on Nov. 3: http://go.nasa.gov/1j91Ufe . 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.