Cassini Update - November 18, 2015

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Cassini Significant Events
for 11/11/15 - 11/17/15

Cassini is currently orbiting Saturn with a period of 12.7 days in a plane
inclined 1.3 degrees from the planet's equatorial plane. The most recent
spacecraft tracking and telemetry data were obtained on Nov. 18 using
the newest of the Deep Space Network's stations, a 34-meter diameter antenna
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

http://saturn.jpl.nasa.gov/news/significantevents/anomalies

Early on Wednesday, Cassini sped through periapsis, the closest point
in its orbit around Saturn. Later that day it took advantage of a non-targeted
encounter with Saturn's moon Tethys at a distance of 8,900 kilometers.
Then on Thursday, Cassini carried out its targeted encounter T-114 with
Saturn's planet-like moon Titan. By Tuesday, the spacecraft had coasted
all the way "up" to apoapsis.

Cassini's Navigation team used the T-114 flyby for gravity assist, reducing
Cassini's orbit period from 13.9 to 12.7 days. It also ratcheted up the
inclination of Cassini's orbit slightly, from 0.6 to 1.3 degree measured
from Saturn's equatorial ring plane. This small increase portends more
to come. All future targeted Titan encounters will have their effect on
Cassini's orbital inclination, until April 2017, when the inclination
will be over 62 degrees. At that time, the final Titan encounter T-126
will modify Cassini's orbit so its next 22 periapses will occur in between
the rings and Saturn's atmosphere.

Wednesday, Nov. 11 (DOY 315)

While speeding inward towards periapsis, Cassini's Cosmic Dust Analyzer
(CDA) spent 2.5 hours studying in particular the relatively large grains
of dust in that region. The Visible and Infrared Mapping Spectrometer
(VIMS) then took over control of spacecraft pointing to observe the red
star named 30 Piscium for nearly three hours while it was occulted by
Saturn's rings. During this observation, Cassini passed periapsis, having
come within 114,500 km of Saturn's visible edge. Its speed at that point
was 72,026 km per hour relative to the planet.

As soon as the VIMS stellar ring occultation experiment was completed,
CDA took back control in order to sample the faint trail of dust that
shares the orbit of Saturn's moon Pallene. Meteors impacting Pallene,
which is around six km in diameter, dislodge the dust that forms the faint
Pallene ring. This annotated image from 2006 identifies that fine ring:

http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=2313

Immediately following CDA's experiment, Cassini turned to point the optical
remote-sensing instruments -- the telescopes -- to examine Saturn's moon
Tethys, which is around 1,000 km in diameter. For 1.75 hours while the
non-targeted encounter played out, the Imaging Science Subsystem (ISS),
the Composite Infrared Spectrometer (CIRS), the Ultraviolet Imaging Spectrograph
(UVIS), and VIMS, made observations of the satellites' icy surface. They
captured views and measurements of some very curious reddish-color streaks
that Cassini discovered earlier on Tethys's surface. "Non-targeted" means
that no propulsive maneuvers were devoted to achieving the encounter.

Finally, CDA resumed control for 4.25 hours to continue measuring the
relatively large dust grains near periapsis.

High above Titan's south pole, an enormous cloud feature lingers, and
Cassini has been watching it. Today's news feature highlights and discusses
the prominent phenomenon:

http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20151111

Thursday, Nov. 12 (DOY 316)

CIRS and VIMS spent nearly 21 hours taking turns controlling the spacecraft
pointing today, to study the atmosphere of Saturn's largest moon. ISS
rode along, taking advantage of the pointing, and taking images. The infrared
instruments were measuring the temperature and composition of the strange
south-pole cloud mentioned above, as it continues to develop in the advancing
southern autumn.

Only 35 years ago today, the Voyager-1 Spacecraft made its closest approach
to Saturn on a fast but extremely productive flyby of the system. It also
succeeded in conducting solar-occultation and radio-occultation experiments
with Titan; had these experiments failed, Voyager 2 would have been re-targeted
to attempt them, foregoing its ability to encounter Uranus and Neptune.
The successful Voyager-1 encounter provided groundbreaking measurements
of the huge moon's mass, and probed its atmosphere with the occultations.
The dynamics of the encounter then flung the spacecraft on a northerly
course, eventually into interplanetary space. Both Voyagers continue to
communicate with their flight team basically every day via the Deep Space
Network; round-trip light-time to Voyager 1 today is 37 hours 8 minutes.

Friday, Nov. 13 (DOY 317)

The day after the anniversary of Voyager-1's historic encounter, Cassini,
whose instruments were designed with better capabilities for observing
Titan, encountered that body today. Now, of course, Titan is known to
have rivers and lakes on its surface, as well as a complex atmosphere.
The T-114 encounter page has the details, including an animation, of today's
event:

http://saturn.jpl.nasa.gov/mission/flybys/titan20151113 .

Saturday, Nov. 14 (DOY 318)

Cassini's Radar instrument kept the spacecraft's high-gain antenna trained
on Titan for two hours today, collecting data via its passive radiometer
mode, both for science investigation and instrument calibration.

Sunday, Nov. 15 (DOY 319)

ISS took two minutes to make a storm-watch observation on Saturn, and
then viewed Enceladus for 90 minutes to take images for optical navigation
purposes. Next, CIRS observed Saturn's atmosphere for twelve hours, collecting
spectral data to better determine the atmosphere's composition. ISS and
VIMS rode along with CIRS. Following this, ISS made another two-minute
Saturn storm-watch observation. The spacecraft then turned to communicate
with Earth.

Based on the latest iterations of the Navigation team's solutions, the
flight team created and sent up commands to perform Orbit Trim Maneuver
(OTM)-431. This maneuver turned the spacecraft and fired its hydrazine-fed
rocket thrusters for 105 seconds. This provided a change in velocity of
103 millimeters per second needed to clean up Cassini's trajectory following
the T-114 encounter.

Monday, Nov. 16 (DOY 320)

CDA took the reins for 15 hours today to sample dust that orbits Saturn
in the retrograde direction.

Even 35 years ago, Saturn's little icy moon Enceladus was known to be
the most reflective body in our solar system, but the puzzle as to why
remained to be resolved by Cassini. In an image featured today, Enceladus's
high albedo is clear to see:

http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=5272

Tuesday, Nov. 17 (DOY 321)

ISS, CIRS and VIMS performed a 90-minute observation in the Titan monitoring
campaign, from a distance of 1.9 million km. Next came another two-minute
Saturn storm watch by ISS, and then ISS, CIRS and VIMS jointly made an
18-hour observation of Saturn's E ring, seen edge-on. The E ring is formed
by the plume of material issuing from Enceladus's south-pole geysers.

While the E-ring observation was taking place, Cassini coasted through
apoapsis, the high point in its orbit of Saturn. This marked the start
of Orbit #226. The spacecraft had slowed to 6,059 km per hour relative
to Saturn, and reached an altitude of 1.95 million km from the planet.

During the week, the Deep Space Network communicated with and tracked
Cassini on five occasions, using stations in Australia. A total of 13,216
individual commands were uplinked, including commands that will support
Cassini's instruments when the next ten-week command sequence S92 takes
effect. About 1,331 megabytes of telemetry data were downlinked and captured
at rates as high as 110,601 bits per second.

This illustration shows Cassini's position on Nov. 17: http://go.nasa.gov/1jOsKKv
. 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.

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Milestones spanning the whole orbital tour are listed here:
http://saturn.jpl.nasa.gov/mission/saturntourdates .
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For a glossary of technical terms relating to these events, click the
"full story" link on this page:
http://saturn.jpl.nasa.gov/news/significantevents/ .
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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/ .
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Visit the JPL Cassini home page for more information about the Cassini
Project: http://saturn.jpl.nasa.gov/
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