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Cassini Significant Events 04/29/2015 – 05/05/2015

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 May 6 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/news/significantevents/anomalies .

This week Cassini's Imaging Science Subsystem (ISS) produced 528 images, and the Visible and Infrared Mapping Spectrometer (VIMS) generated 220 data "cubes." Since 2004 when approach science began, 338,431 images from ISS and 227,975 cubes from VIMS have been returned and processed. Also this week, the command sequence known as S88 completed its 10 weeks of operation on Friday, at which time the on-board S89 sequence seamlessly took control. Work continues on preparing the command sequences S90 and S91.

The trajectory that the Cassini Program adopted in July 2009 benefits from the fortuitous discovery that gravity assists from two Titan flybys, one in November 2016 and another in April 2017, can be used to swing the spacecraft directly onto unprecedented paths closer and closer to Saturn (illustrated here: http://go.nasa.gov/1ElnrYh ).

At a meeting at JPL on Monday, participants looked towards these planned F-ring orbits, proximal orbits, and atmospheric entry (the Grand Finale). Cassini's mission and science planners, navigators, spacecraft engineers and representatives from the science instruments and disciplines discussed known uncertainties in observation timing, and how to selectively control them with propulsive events. At next month's Project Science Group meeting at Caltech in Pasadena, science investigators are expected to make crucial decisions that will enable high-level plans to be finalized, so that increasingly detailed planning for command sequences S97 through S101, which cover these final orbits, can proceed.

Wednesday, April 29 (DOY 119)

The Cosmic Dust Analyzer (CDA) completed a 37-hour retrograde dust observation today. Following this, Cassini turned to face its 4-meter-diameter high-gain dish squarely toward Earth, in time to begin receiving a stream of 6,534 individually time-tagged commands comprising the S89 sequence. At an uplink rate of 500 bits per second, the sequence transmission took just over 41 minutes to begin its interplanetary trek. Telemetry later showed that all the commands were stored in memory, ready to begin executing on May 2.

Thursday, April 30 (DOY 120)

The Ultraviolet Imaging Spectrograph (UVIS), the Composite Infrared Spectrometer (CIRS), and VIMS began a 14.5-hour observation of Saturn’s aurora.

Friday, May 1 (DOY 121)

The S89 command sequence, which was uplinked on Wednesday, began executing on the flight system today; it will orchestrate Cassini's activities for the next 10 weeks. Today's activities included some routine engineering tasks and a science instrument calibration.

The one-way communication time between Earth and Cassini is nearing its yearly minimum. Today it took 75 minutes and 17 seconds at the speed of light; this value is still decreasing as Earth swings around toward Saturn. The minimum communication delay this year will be on May 25, while Saturn is still near its May 22 opposition (when it is highest in Earth's sky at midnight). This view illustrates the planets' positions: https://space.jpl.nasa.gov/cgi-bin/wspace?tbody=1000&vbody=1001&month=5&day=1&year=2015&hour=00&minute=00&fovmul=1&rfov=8&bfov=30&porbs=1&showsc=1&showac=1 (in this view, all planets revolve in a counter-clockwise direction).

Saturday, May 2 (DOY 122)

The Cosmic Dust Analyzer (CDA) began a 13.3-hour observation as part of the retrograde dust campaign.

Sunday, May 3 (DOY 123)

ISS, CIRS and VIMS made a 90-minute observation in the Titan monitoring campaign. The huge hazy moon was 2.3 million kilometers from Cassini's telescopes. Next, ISS turned to Saturn for a two-minute storm-watch observation. ISS then spent 45 minutes looking near the planet for small objects, part of the satellite orbit campaign. As soon as this was complete, CIRS began an 11.5-hour observation of Saturn’s atmosphere in the mid-infrared part of the spectrum, to determine upper troposphere and tropopause temperatures.

Monday, May 4 (DOY 124)

Based on the latest tracking data from the Deep Space Network (DSN) and the Navigation team's latest iteration of Cassini's orbital motion, the flight team sent commands that were created near real time to perform Orbit Trim Maneuver (OTM)-409. This was the Titan T-111 approach maneuver. The spacecraft properly responded by turning and burning its small hydrazine-fed rocket thrusters for 12 seconds to produce a 17-millimeter-per-second change in velocity.

ISS, CIRS and VIMS performed another 90-minute Titan monitoring observation; the distance had decreased to 1.7 million kilometers. Following this, ISS carried out another one-hour satellite orbit observation. Two-minute ISS storm-watch observations occurred four more times this week; two were today, and two more were on Tuesday. VIMS participated in one of them each day.

An image featured this week looks down through Saturn's high atmospheric haze, where some of its Jupiter-like weather patterns can begin to be seen. In the lower right, rings intersect with their own shadows in the atmosphere:
/resources/16186 .

Tuesday, May 5 (DOY 125)

UVIS made radial profiles of Saturn’s atmosphere in an observation lasting 1.25 hours. Next, UVIS, with ISS and VIMS riding along, proceeded to image Saturn's thermosphere for almost five hours. This is the hot region of Saturn's very thin atmosphere up above the planet's visible limb. This observation will help characterize the gas density in that space for proximal orbit planning. Next, ISS, CIRS and VIMS executed another 90-minute Titan monitoring observation. The distance to Titan is closing fast. Today it was 1.1 million kilometers away, but in the first minutes of Friday, May 7 Universal Time, Cassini will be encountering Titan at an altitude of 2,271.5 kilometers above its surface during the T-111 flyby, with CIRS and VIMS as the prime observers. Finally today, VIMS took the helm to start an 18-hour observation of Saturn's faint G ring and its broad E ring. Two other telescopic remote-sensing instruments -- CIRS and UVIS -- participated.

A late-breaking news release was published describing the patterns of eruptions from the south-pole crevasses of the tiny moon Enceladus. Repeated observations and ongoing studies may have yielded a better perspective on the phenomenon, which is illustrated in a short video accompanying the article:
http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20150506 .

During the past week, the DSN communicated with and tracked Cassini on eight occasions, using stations in California and Australia. A total of 6,706 individual commands were uplinked, and about 1,598 megabytes of telemetry data were downlinked and captured at rates as high as 142,201 bits per second.

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/ .