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Cassini Significant Events 03/25/2015 – 03/31/2015

Cassini is currently orbiting Saturn with a 28-day period in a plane inclined 0.3 degree from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on April 1 using one of the 34-meter diameter Deep Space Network (DSN) stations in Spain. 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's first targeted, close encounter with Saturn's enigmatic moon Iapetus, which has a diameter of 1,469 kilometers, was on Sept. 10, 2007, during the prime mission. The late author Sir Arthur C. Clarke electronically attended the public event that was held at JPL while hard-won images, and other data, were arriving from 1,500 million kilometers away. The original news feature may be seen here:
http://go.nasa.gov/1GhtSgE . This week the strange moon again became the subject of Cassini's telescopes at great length, if not close proximity, during a non-targeted encounter -- meaning that no special propulsive maneuvers were required. Once this campaign began, the spacecraft looked away only to take care of some relatively short calibrations, engineering events, and communications sessions with the flight team via the DSN.

Wednesday, March 25 (DOY 084)

The Composite Infrared Spectrometer (CIRS) wrapped up a 21-hour long observation of Saturn, during which it gathered spectra to better understand the atmosphere's composition. The Visible and Infrared Mapping Spectrometer (VIMS) acquired data in ride-along mode while CIRS was in control. When this was finished, the Imaging Science Subsystem (ISS) took over spacecraft pointing for two minutes to make a storm-watch observation on Saturn. Next, ISS turned to frame an image that included Saturn's largest satellite Titan, smaller Rhea, and yet-smaller Mimas, and snapped the rare portrait. This image is intended to be used for both science and outreach purposes. With this observation completed, Cassini's Navigation team then used ISS to capture some images of the moon Iapetus against its background of stars, for optical navigation purposes.

Thursday, March 26 (DOY 085)

Today, all of Cassini's optical remote-sensing (ORS) instruments: ISS, CIRS, VIMS, and the Ultraviolet Imaging Spectrograph (UVIS), began a campaign, which would last the rest of the week, to track and observe Saturn's unique, two-tone satellite Iapetus. Today's ISS-led observation lasted 7.75 hours.

Friday, March 27 (DOY 086)

A CIRS-led Iapetus observation today lasted six hours. It obtained thermal-infrared spectra for a study of surface emissivity, while the other ORS instruments rode along. Next it was ISS's turn to lead the others for Iapetus observations lasting nearly 33 hours.

Saturday, March 28 (DOY 087)

Passing the apoapsis of its orbit about Saturn, today Cassini marked the start of Orbit #214. The spacecraft had slowed to 5,367 kilometers per hour relative to the planet, and climbed out to 3.2 million kilometers. Iapetus's orbit lies 3.56 million kilometers from Saturn; after today's apoapsis, the spacecraft came within one million kilometers of the icy body. Still a thousand times more distant than the 2007 encounter, this was well within range for the ORS instruments' powerful telescopes.

Sunday, March 29 (DOY 088)

In 1671 when astronomer Jean-Dominique Cassini discovered Iapetus, it disappeared from his view when it was east of Saturn in its 79-day orbit of the ringed giant. He made an educated conjecture as to why, which later proved correct: its leading hemisphere was dark. Today, the object slowly turned parts of its bright and dark hemispheres, its high-contrast spots and high mountains, into view while the ORS instruments observed from Cassini the spacecraft. ISS took the driver's seat again today, for observations that would last a good 45 hours; the remaining ORS instruments rode along.

Monday, March 30 (DOY 089)

Viewing Iapetus has been only one of the benefits of Cassini's return to Saturn's equatorial plane. A news feature published today elaborates:
http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20150330 .

Just outside of Saturn's main rings -- the A, B, and C rings -- is the realm of the narrow, ever-changing F ring along with several interesting small satellites. Today's featured image is centered on one of them, Epimetheus:
/resources/16175 .

Tuesday, March 31 (DOY 090)

Iapetus remained at the center of the ORS instruments' attention today, and again the following day. In total this week, ISS captured and returned 898 images, and VIMS created and sent back 653 cubes (every pixel in a VIMS "cube" consists of 352 spectral channels). And as always, the latest images from Cassini appear promptly on the Raw Images web page. For at least the next few days from now, many extraordinary views of this unusual body may be seen by clicking "Browse Latest 500" on this page:
http://saturn.jpl.nasa.gov/photos/raw .

Today marks 600 days until Cassini's Titan encounter T-125, when a gravity assist will set the spacecraft onto its series of F-ring orbits, during which periapsis will occur just outside that narrow ring; in fact Cassini will be very near the distance from Saturn as is Epimetheus. Following the completion of the F-ring orbits will be a series of proximal orbits known as Cassini's Grand Finale. For reference, see this feature, which illustrates the final F-ring orbit and all the proximal orbits:
http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20140630 .

During the past week, the DSN communicated with and tracked Cassini on five occasions, using stations in California, Australia and Spain. A total of nine individual commands were uplinked, and about 910 megabytes of telemetry data were downlinked and captured at rates as high as 142,201 bits per second.

This illustration shows Cassini's position on March 31: https://space.jpl.nasa.gov/cgi-bin/wspace?tbody=-82&vbody=1001&month=3&day=31&year=2015&hour=23&minute=55&fovmul=1&rfov=40&bfov=30&brite=1&showsc=1&showac=1 .

Milestones spanning the whole orbital tour are listed here: http://saturn.jpl.nasa.gov/mission/saturntourdates .

Information on the present position and speed of the Cassini spacecraft may be found on the "Present Position" page at:
http://saturn.jpl.nasa.gov/mission/presentposition/ .