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Cassini Significant Events 06/22/16 – 06/28/16

Cassini is orbiting Saturn with a period of 23.9 days in a plane inclined 43 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on June 29, using the 70-meter diameter Deep Space Network station 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/anomalies .

Cassini sped inbound this week towards a June 30 periapsis passage. Along the way, it made different kinds of observations of Saturn's rings. The optical remote-sensing instruments viewed the rings from their sunlit side and then from their dark side. The Cosmic Dust Analyzer directly observed ring-plane dust as it encountered the instrument, and two occultation experiments tracked bright stars while the rings passed in front of them, attenuating the starlight and revealing ring detail.

Wednesday, June 22 (DOY 174)

The reflecting telescope Cassini uses in its Imaging Science Subsystem (ISS) has an aperture of just less than 8 inches, smaller than many modern amateur telescopes. Today ISS trained this “Narrow-Angle Camera” on Saturn's largest moon Titan for 90 minutes of meteorological monitoring. The Visible and Infrared Mapping Spectrometer (VIMS) rode along. After a calibration activity, ISS spent 60 minutes with the satellite orbit campaign, looking near Saturn for small objects. VIMS and the Composite Infrared Spectrometer (CIRS) rode along for this observation.

Next, ISS began an observation lasting about 23 hours, watching the bright arc of material in Saturn's faint G ring, while it was sunlit from behind; CIRS and VIMS participated. The small moon Aegaeon occupies this region, and might be a source of ring material. Objects in this arc take about 19 hours to circle the planet.

The flight team uplinked Cassini’s S95 command sequence today. After a round-trip time of 150 minutes at the speed of light, telemetry confirmed that all 9,323 individual commands had been properly received.

Thursday, June 23 (DOY 175)

VIMS took control of spacecraft pointing for seven hours today to observe the sunlit face of Saturn's rings. ISS, CIRS and the Ultraviolet Imaging Spectrograph (UVIS) participated as riders.

The Cassini Project Science meeting (PSG) #69 wrapped up today at the European Space Research and Technology Centre (ESTEC) in Noordwijk, the Netherlands. The end-of-mission plans were a key focus of discussion.

Friday, June 24 (DOY 176)

ISS, CIRS and VIMS made another 90-minute Titan monitoring observation.

Saturday, June 25 (DOY 177)

UVIS, CIRS and VIMS observed Saturn’s northern aurora for nearly 10 hours. Next, VIMS trained its optics on the bright red-giant star Antares -- Alpha Scorpii -- for just over 10 hours. Despite city lights, this red star is visible to the unaided eye these evenings near Saturn, but is not to be confused with the brighter red object Mars a little to its right. From Cassini's point of view, distant Antares passed slowly behind Saturn's semi-transparent A ring. ISS, CIRS and UVIS, observed the stellar ring occultation along with VIMS. In this illustration of Cassini's view, Antares can be seen on the left, going behind Saturn's F ring before moving into the A ring, all a result of the spacecraft's motion.

Following the occultation, Cassini's Navigation team took control of ISS for 90 minutes to make images of Saturn's small, low-density moon Hyperion against the background stars for optical navigation purposes.

Finally near the end of the day, VIMS, CIRS, ISS and UVIS targeted the zero-phase point on Saturn's rings for 5.5 hours. The viewing geometry had the Sun directly behind Cassini, so that the "opposition effect" brightening could be seen where Cassini's shadow would be, were it able to cast a clear shadow that far. This VIMS image from 2013 illustrates the effect: /resources/15962 .

Sunday, June 26 (DOY 178)

The zero-phase ring observation, which wrapped up early today, was the final science observation to be commanded from Cassini's on-board S94 sequence. S95, which had been uplinked on Wednesday, began its 74-day run with an observation of Saturn's rings led by ISS. The observing geometry of this multi-wavelength series of images reproduced that of a similar set of multi-filter photometric observations of Saturn's rings made by the Hubble Space Telescope (HST) from the vicinity of Earth. Analysis of this dataset will allow for a more direct comparison between HST and Cassini ISS imaging. CIRS and UVIS participated in the 5.5-hour observation.

Next, CIRS led five hours of observing thermal emissions from Saturn's rings, part of a long-term campaign to collect data at a variety of phase angles and elevation angles. Today's observation, with UVIS riding along, made multiple radial scans of the main rings at low-phase and low-elevation angles.

Monday, June 27 (DOY 179)

ISS turned to view Saturn's faint D ring, the one closest to the planet, which Cassini will soon be skirting. This five-hour observation took advantage of the low elevation angle to increase the signal-to-noise level for measuring such a tenuous ring. The images captured will be made into a movie, which will allow scientists to improve the time baseline for observations of the ring’s vertical corrugations and other dynamic features.

The Cosmic Dust Analyzer (CDA) turned to sample small particles while Cassini flew through the ring plane today, going rapidly southward towards a June-30 periapsis. After this two-hour activity, ISS made another observation of the D ring, this one from even closer range than the previous one. Today's lasted 5.75 hours, with participation from VIMS and UVIS.

In 300 days from now, Cassini will begin its series of 22 Proximal Orbits, in which the spacecraft will repeatedly pass in between Saturn's D ring and atmosphere.

Tuesday, June 28 (DOY 180)

With its view from below the rings looking back up north now, CIRS observed spectra from the narrow Encke-gap region in Saturn's A ring for 4.25 hours, to study the composition and structure of this unique region. The stunningly different viewing geometry is illustrated here.

Following the CIRS observation, VIMS tracked the star beta Pegasi for 5.5 hours while it passed behind Saturn's A ring and Cassini Division and skimmed inside the outer edge of the B ring.

An image featured this week shows a unique view of Saturn's small active moon Enceladus, with a dark Saturn in the background: /resources/17381 .

A new section on the Cassini website offers a great way to explore the spacecraft and all its components: https://saturn.jpl.nasa.gov/the-journey/the-spacecraft .

On five occasions during the week, while Cassini's optical instruments were pointing at or near Saturn, ISS carried out two-minute Saturn storm-watch observations.

The Deep Space Network communicated with and tracked Cassini on five days this week, using stations in Australia. A total of 9,355 individual commands were uplinked, and about 982 megabytes of telemetry data were downlinked and captured at rates as high as 142,201 bits per second.

An illustration of Cassini's path up to mid-day June 28, 2016.