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Cassini Significant Events 08/10/16 - 08/16/16
Cassini is orbiting Saturn with a period of 12 days in a plane inclined 53.7 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data
were obtained on Aug. 17, using two DSN stations in Australia: the 70-meter aperture, plus one of the 34-meter diameter stations. 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.
Spanning Earth and Saturn, the Cassini spacecraft itself operationally "met" with a European Space Agency (ESA) antenna for the first time for science support. During Wednesday’s
Titan T-122 encounter, ESA's 35-meter diameter Deep Space Antenna (DSA)-3, in Malargüe, Argentina, joined forces with one of NASA's 34-meter Deep Space Network antennas in Australia. Together they measured the line-of-sight component of Cassini's speed to
uncanny precision, performing the mission's final gravity measurement of Titan. ESA's DSAs will participate with Cassini several more times before the end of the mission in September next year.
Cassini scientists participated in the Roadmaps to Ocean Worlds (ROW) science meeting, and the Outer Planets Assessment Group (OPAG) meeting this week. Both were in Flagstaff,
Arizona, where attendees heard reports on outer solar system missions including Cassini, and discussed future missions and plans.
Meanwhile, Cassini's science and engineering teams met and continued working on future command sequences. Tasks have been scheduled for development of the S98 sequence, which
will begin controlling Cassini next February.
Wednesday, Aug. 10 (DOY 223)
Cassini coasted swiftly past Saturn's enigmatic largest moon Titan today, executing carefully laid-out observations during the T-122 targeted encounter. The direct-sensing
Magnetospheric and Plasma Science (MAPS) instruments, and the telescopic Optical Remote Sensing instruments all participated. In addition, and for one last time in Cassini's tour of Saturn, the spacecraft was commanded to keep its high-gain antenna dish squarely
tracking Earth throughout the flyby. This enabled the Radio Science team's final direct measurement of Titan’s gravity field, adding to knowledge of mass distribution on and within Titan. The whole time, Cassini was receiving (and phase-locked onto) a stable
reference-frequency signal from the Deep Space Network (DSN) station in Australia, so that the downlink signal from Cassini could have its Doppler shift very accurately measured. More details on the encounter may be found here:
https://saturn.jpl.nasa.gov/news/2926/t-122-last-opportunity-to-probe-titans-deep-structure .
As planned, gravity assist from the T-122 Titan flyby decreased the period of Cassini's orbit of Saturn to 12 days. It also ratcheted up the orbit's inclination by another
4.5 degrees, to 53.7 degrees off the equatorial plane. On average during the mission, targeted Titan encounters have been occurring about once an orbit. Now, though, it will be four orbits before the next one, T-123.
Of note during today's encounter, Cassini's Cosmic Dust Analyzer (CDA) used its only opportunity to conduct a new "dust occultation" technique, observing the interaction with
nanometer-scale dust downstream of Titan’s atmosphere.
As posted above, this was the first time ESA’s tracking assets have provided science support for the Cassini mission. These cross agency activities are one of the cornerstones
of international space exploration collaboration. This was also a notable achievement for ESA in its own right as supporting Cassini is the first time ESA has tracked a deep space mission more than a billion kilometers away. This required both hardware and
software upgrades that performed perfectly:http://www.esa.int/Our_Activities/Operations/Estrack/Most_distant_catch_for_ESA_station .
Receding from the encounter, the Imaging Science Subsystem (ISS) spent six hours acquiring global-scale imaging of Titan’s trailing hemisphere at mid-northern latitudes, which
will provide important constraints for the cloud monitoring campaign. The Visible and Infrared Mapping Spectrometer (VIMS), the Ultraviolet Imaging Spectrograph (UVIS), and the Composite Infrared Spectrometer (CIRS) rode along with ISS.
Exciting new findings on Titan’s surface by Cassini's Radar scientists, based on previous close flybys, was in the news today: https://saturn.jpl.nasa.gov/news/2927/cassini-finds-flooded-canyons-on-titan
.
Thursday, Aug. 11 (DOY 224)
Finishing up the long series of encounter observations, VIMS looked for specular reflections of sunlight coming off lakes near Titan's north pole. After this observation finished,
CIRS and VIMS turned and observed Saturn’s atmosphere for 13 hours in an effort to determine upper troposphere and tropopause temperature.
Friday, Aug. 12 (DOY 225)
ISS, CIRS and VIMS observed Saturn's strange, narrow F-ring for 13.5 hours today.
Saturday, Aug. 13 (DOY 226)
ISS controlled spacecraft pointing for 14.7 hours to observe Saturn’s shadow on the distant, dusty Phoebe ring. Two hours into the observation, Cassini passed through apoapsis,
marking the start of its Saturn Orbit# 240. It had reached a height of 1.5 million kilometers from the planet, slowing to 11,904 km per hour relative to Saturn.
Sunday, Aug. 14 (DOY 227)
There was an opportunity to fire the spacecraft's rocket thrusters today to clean up any trajectory errors induced by Wednesday's T-222 encounter. But Cassini's navigation
team determined that the flight path was remaining close enough to the planned reference trajectory, so this was not needed. Orbit Trim Maneuver (OTM)-458 was therefore cancelled.
ISS, CIRS and VIMS performed a 90-minute observation in the Titan monitoring campaign, now that the range to Titan had reached 1.58 million km from the spacecraft. Next, ISS
and VIMS spent 60 minutes making another observation in the satellite orbit campaign, observing small objects near the planet. These two observations repeated on the following day. Finally today, CIRS and VIMS obtained 10 hours' worth of thermal infrared spectra
of Saturn's sunlit rings, to study ring particle composition.
Monday, Aug. 15 (DOY 228)
VIMS spent seven hours observing the sunlit rings, complementing a set of observations at various latitudes and sunlight phase angles.
Perspective makes two of Saturn's very different moons appear close together in today's featured image: https://saturn.jpl.nasa.gov/resources/7402 .
Tuesday, Aug. 16 (DOY 229)
UVIS, CIRS and VIMS studied Saturn’s northern aurora for just over 10 hours today. Finally, ISS and CIRS carried out a two-hour "propeller" (http://go.nasa.gov/17oqTWF) re-targeting
observation.
On three days this week, while Cassini's optical instruments were already pointing at or near Saturn, ISS carried out two-minute Saturn storm-watch observations. The DSN communicated
with and tracked Cassini via 15 sessions with the DSN this week, using stations in Spain, California and Australia. ESA tracked Cassini on one occasion from Argentina. A total of 24 individual commands were uplinked, and about 1,570 megabytes of telemetry
data were downlinked and captured at rates as high as 142,201 bits per second.
Cassini's path up to mid-day Aug. 16 is illustrated here; the green ellipse of Cassini's path can be seen foreshortened to its smaller, 12-day orbit:http://go.nasa.gov/1WFnGci.
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Milestones spanning the whole orbital tour are listed here:
https://saturn.jpl.nasa.gov/mission/saturn-tour/tour-dates/ .
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Information on the present position and speed of the Cassini spacecraft may be found on the "Present Position" page at:
https://saturn.jpl.nasa.gov/mission/saturn-tour/where-is-cassini-now/ .
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