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Cassini Significant Events 10/21/15 – 10/28/15

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 Oct. 28 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 .

In addition to all the "normal, routine" activities this week, the Cassini flight team, working closely with the Deep Space Network (DSN), took steps to be sure all is ready for the Enceladus flyby E-21 on Wednesday Oct. 28. A superb video was released that sums up the E-21 low-altitude pass, during which the spacecraft will fly through the plume of icy material issuing from strange moon's southern regions. Cassini's in-situ science instruments will be sampling the plume material. The video is linked here, along with seven key facts about the encounter: http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20151026 .

This E-21 encounter is Cassini's final plunge through the visible plume, which is formed from several discrete sources near the south pole of tiny Enceladus. The E-22 encounter, on December 19, will be humanity’s last close look to the enigmatic body until some new mission takes shape and takes flight.

Wednesday, Oct. 21 (DOY 294)

One of Cassini's science instruments, the Magnetospheric Imaging Instrument (MIMI) is designed to make in-situ measurements of the spacecraft's immediate environment, but it also has the unique ability to form remote-sensing-type images of Saturn's magnetic envelope. Today, MIMI had the spacecraft roll about its longitudinal axis for nine hours, continuing a study of Saturn’s inner magnetosphere. This occurred during a routine DSN communications and tracking session, while the spacecraft's high-gain antenna was trained on Earth. MIMI's rolling observation was repeated on the following day during another DSN session.

Around halfway through the MIMI observation today, the spacecraft coasted through apoapsis, marking the start of its Saturn orbit #224. It had reached an altitude of just over two million kilometers from Saturn, and had gradually slowed to 6,126 km per hour relative to the planet.

NASA's Astronomy Picture of the Day today featured one of Cassini's close-ups of Enceladus's north polar terrain: http://apod.nasa.gov/apod/ap151021.html .

Thursday, Oct. 22 (DOY 295)

The Cassini Project's annual essay contest for students in grades 5 through 12 was kicked off this week; "Cassini Scientist for a Day" is described here: http://saturn.jpl.nasa.gov/education/scientistforaday2015 .

Friday, Oct. 23 (DOY 296)

At JPL, Cassini's week-long 67th Project Science Group meeting wrapped up today. There had been 184 individuals, scientists and engineers, in attendance. Meanwhile in Saturn orbit, the Cosmic Dust Analyzer (CDA) controlled the spacecraft's orientation for 13.5 hours to perform an observation of dust grains orbiting Saturn in the retrograde direction. This was the first science activity commanded by the newly-uplinked second half of the S91 ten-week command sequence.

Saturday, Oct. 24 (DOY 297)

The Imaging Science Subsystem (ISS) turned to point its telescopes at Saturn's largest moon Titan for 90 minutes of cloud monitoring. The Composite Infrared Spectrometer (CIRS) and the Visible and Infrared Mapping Spectrometer (VIMS) participated as well. Titan was 2.8 million km away from Cassini. This observation was repeated on Monday, when the hazy moon was at a distance of 2 million km.

Following the Titan monitoring, CIRS took control for 12 hours to study the composition of Saturn’s atmosphere. Before and after CIRS's observation, ISS made two-minute Saturn storm-watch observations. Next, during another DSN session, the sequence of commands onboard Cassini reached a planned pause, which had been reserved for Orbit Trim Maneuver (OTM)-427. Navigation solutions showed that Cassini was close enough to its planned trajectory approaching Enceladus that no propulsive maneuver would be required, and realtime commanding for the OTM was cancelled.

Sunday, Oct. 25 (DOY 298)

ISS performed a 14.75-hour observation of Saturn's small, distant irregular moon, Skathi (also transliterated from the Norse as Scadi). This very dark-surfaced object orbits Saturn in a retrograde and highly inclined orbit that reaches as far as 19.7 million km from the planet. The name refers to a giantess in Norse mythology. Given the parameters of Skathi's orbit, it is possible that it might have formed from material knocked off of Saturn's moon Phoebe by an ancient collision.

Monday, Oct. 26 (DOY 299)

ISS conducted another Saturn storm-watch observation for two minutes, and then made an hour-long observation in the satellite orbit campaign, looking near Saturn for small objects. Next, ISS turned and watched Skathi for another 3.25 hours.

An image featured today shows off one of the most perplexing natural satellites in the known universe, good old Enceladus, which Cassini will be closely encountering on Oct. 28: /resources/16259 .

Tuesday, Oct. 27 (DOY 300)

Today marks 400 days until Cassini begins its series of F-ring orbits, where periapses will occur just outside that thin and ever-changing strand outside the main A ring.

First, ISS performed another 60-minute satellite orbit campaign observation, this time with VIMS participating. Next, ISS and VIMS observed the transit of Saturn's small satellite Janus as it passed in front of much larger Tethys. ISS then turned back to Titan for a 90-minute monitoring observation with CIRS and VIMS riding along; Titan was at a distance of 1.7 million km. Finally, CIRS tracked Saturn's large icy moon Dione for five hours to study the composition of its surface; ISS and VIMS rode along making their own observations.

Throughout the week, and largely independent of which directions the spacecraft was turning to point its other instruments, the Magnetospheric and Plasma Science (MAPS) instruments continued collecting data about the spacecraft's environment.

Also during this week, the Deep Space Network communicated with and tracked Cassini on nine occasions, using DSN stations in Australia and California. A total of 295 individual commands were uplinked, and about 1,590 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 Oct. 27: http://go.nasa.gov/1jOt7EN . 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.