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Cassini Significant Events 03/30/16 – 04/05/16

Cassini is orbiting Saturn with a period of 31.9 days in a plane inclined 28.8 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on April 6, using one of the 34-meter diameter Deep Space Network 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


Following a series of ring observations, Cassini's highlight this week was a close encounter with Saturn's largest moon Titan. The T-118 flyby on Monday April 4 was at a low enough altitude that Cassini's Ion and Neutral Mass Spectrometer (INMS) was able to directly measure constituents of Titan's upper atmosphere. At the same time, Cassini's Ultraviolet Imaging Spectrograph (UVIS) observed a solar occultation, collecting data about Titan's dense atmosphere by measuring sunlight passing through it. The T-118 Encounter page has more details, and an informative video to illustrate the event:


Wednesday, March 30 (DOY 090)

UVIS concluded an observation of Saturn that it had begun the previous day, and then the Visible and Infrared Mapping Spectrometer (VIMS) carried out an 8.5-hour global mapping of the planet. Meanwhile, the Radio and Plasma Wave Science instrument spent the day at elevated data-collection rates, studying Saturn’s outer magnetosphere .

Thursday, March 31 (DOY 091)

The Imaging Science Subsystem (ISS) made a 90-minute, routine monitoring observation of Titan. VIMS and the Composite Infrared Spectrometer (CIRS) rode along taking data as well.

Still on its way "down" from its apoapsis passage ten days ago, Cassini came within 1.5 million kilometers of Saturn today. At this point VIMS began an eight-hour observation of Saturn's rings, making a mosaic of the sunlit side. CIRS and UVIS rode along. For the next few days, Cassini's Optical Remote-Sensing (ORS, telescopic) instruments would continue making observations of the rings. While a designated-prime instrument controlled spacecraft pointing, other selected ORS instruments rode along, taking data for which space had been allocated on the spacecraft's data recorders.

Friday, April 1 (DOY 092)

Saturn's narrow, complicated F ring was the subject of ISS-led observations for 6.5 hours today. The acquired images will become a movie to help scientists understand the kinematics of that strange ring. Next, CIRS stared at the opaque core of the wide B ring for four hours, capturing spectra at moderate wavelength-resolution, to study its composition and structure.

Acting on commands that were freshly prepared and uplinked by the flight team during today's Deep Space Network communications and tracking session, Cassini turned and fired its small rocket thrusters for 62 seconds. This Orbit Trim Maneuver (OTM)-445 imparted a change in velocity of 63 millimeters per second, adjusting the spacecraft's trajectory for the upcoming Titan encounter.

Next came another 90-minute Titan meteorological campaign observation, with CIRS and VIMS participating as before. Late in the day, CIRS, VIMS, and UVIS then began a six-hour study of the sunlit side of the Cassini Division, which is between Saturn's A ring and B ring, to determine the composition of particles orbiting there.

Saturday, April 2 (DOY 093)

ISS spent two hours today making a high-resolution color mosaic of a portion of the main rings. Next, ISS took images of the continuously changing F ring and the edge of the A ring for an hour, studying their complex dynamics. For the next activity in this "rings segment" of observations, CIRS scanned the rings' sunlit side at far infrared wavelengths for three hours, mapping thermal emission at varying observing geometries.

During the CIRS activity, Cassini passed through the ring plane going south, and then flew through periapsis in its orbit #234 of Saturn. It had come in as close as 308,000 km to the planet's visible edge, going 49,190 km per hour relative to the gas giant.

Finally today, ISS spent 40 minutes tracking known "propeller" features in the rings (

) and making high-resolution images of them. The final science activity for the day was a three-hour VIMS observation to obtain information about the rings' composition.

Sunday, April 3 (DOY 094)

Wrapping up the "rings segment" observations for this orbit, CIRS again spent two hours mapping the rings' thermal emission. Having passed south of the rings now, this time Cassini was observing their dark side. ISS followed up with one more 40-minute retargeting of propellers.

Next, UVIS led all the other ORS instruments in a high-priority experiment: observing a four-hour stellar occultation. Thanks to the spacecraft's motion in Saturn orbit, the star Gamma Orionis passed behind the rings and then Saturn’s atmosphere. In

of Cassini's astonishing view, the bright blue shoulder star of Orion, also known as Bellatrix, was about to go behind Saturn's dusty G ring. The star continued moving toward the right in this view, eventually to probe the space near Saturn at around 2 degrees north latitude. This is the region that Cassini will directly sample in its final five orbits in 2017. The occultation provides scientific information on the atmospheric density, composition, and temperature at that location; the density is relevant to engineering safety considerations for Cassini's final orbits.

As the day ended, Cassini's "eyes" turned to point towards Saturn's largest moon; CIRS started a nearly ten-hour observation mapping temperatures on Titan, with ISS and VIMS riding along.

Monday, April 4 (DOY 095)

A few hours into the CIRS observation, huge Titan loomed closer to Cassini than our own Moon is to Earth, and encounter observations were underway for the T-118 flyby. Today's encounter was an inclined south polar flyby at 990 km altitude. It occurred in the late midnight sector of Saturn’s magnetosphere, where Cassini could explore the polar sector of Titan's induced magnetosphere. Refer to the T-118 flyby page linked above for information about the science data collected. The encounter also provided a planned gravity-assist kick for the spacecraft, increasing Cassini's orbital period from 23.9 days to 31.9 days, and boosting the inclination of the spacecraft's orbit from 21.9 up to 28.8 degrees. Eight more targeted encounters with Titan remain in Cassini's planned mission.

In an image featured today, shadows of the rings make Saturn look misshapen:


Tuesday, April 5 (DOY 096)

Departing Titan, VIMS looked for specular reflections of sunlight, at infrared wavelengths, from Titan's small lakes above 70 degrees north latitude; it also mapped the northern hemisphere at low resolution; CIRS and ISS also participated.

On seven occasions during the week, the Deep Space Network communicated with and tracked Cassini, using stations in Australia and California. A total of 171 individual commands were uplinked, and about 1,882 megabytes of telemetry data were downlinked and captured at rates as high as 142,201 bits per second.

Cassini position on April 5, 2016
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.