Cassini Update - June 25, 2015

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Cassini Significant Events
for 06/17/15 - 06/23/15

Cassini is currently orbiting Saturn with a period of 18.9 days in a plane
inclined 0.3 degrees from the planet's equatorial plane. The most recent
spacecraft tracking and telemetry data were obtained on June 24 using
one of the 34-meter diameter Deep Space Network stations in California.
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

Starting in November of next year, Cassini's orbits will be highly elongated
and highly unconventional. From then until the end of mission in September
2017, each orbit will last a little more than a week, and will loop around
Saturn in a plane inclined over 60 degrees from the equatorial plane,
wherein lie the rings. From an apoapsis height of over 1,285,000 kilometers
"above" the planet -- this is more than the distance to Titan's orbit
-- the spacecraft will come in to periapsis just outside of Saturn's narrow
and enigmatic F ring. This repeats until April of 2017, when periapses
will occur closer than ever before, in between the innermost ring and
the gas giant's upper atmosphere. Its speed at that point will be more
than 123,400 kilometers per hour relative to the planet.

These F ring and Proximal orbits were the focus of the 66th Cassini Project
Science Group meeting (PSG), which convened on the Caltech campus in Pasadena
this week. Which instrument will be allocated which portions of which
orbit? Which observations warrant special, advanced preparations? One
of the two main goals for the scientists, mission planners and other flight
team members in the PSG is to approve the "segmentation plans" and "pre-integrated
events" (fondly known as PIEs) for these unique orbits. The other goal
is to approve plans for obtaining the best science data return from the
final, high-speed plunge into Saturn's atmosphere. Known as Cassini's
Grand Finale, it will neatly end nearly 20 years in flight.

Wednesday, June 17 (DOY 168)

The Imaging Science Subsystem (ISS) controlled spacecraft pointing for
nearly four hours today to carry out an observation of Saturn's irregular
moon Albiorix. Named for the king of the world in Gallic mythology, this
moon has a diameter of about 26 kilometers and moves as far as 16.2 million
kilometers away from the planet in an inclined, highly elliptical orbit.
Next, a nine-hour tracking and communications session via the Deep Space
Network (DSN) also served to enhance the Radio Science team's measurements
of the gravity of Saturn's icy moon Dione, which Cassini encountered on
the previous day.

Finally, ISS returned to Albiorix and followed it for another 5.5 hours.
The Ultraviolet Imaging Spectrograph (UVIS) and the Visible and Infrared
Mapping Spectrometer (VIMS) participated with ISS, "riding along" for
both observations. The science teams’ goal for these distant irregular
moons is to obtain information on basic physical properties such as rotation
rate, orientation of the poles, and a rough determination of the objects'
shapes.

Upon completion of the irregular moon observation, UVIS took control for
five hours to make one slow scan across Saturn's visible hemisphere to
form spectral images. VIMS rode along.

Thursday, June 18 (DOY 169)

The Magnetometer (MAG) began a two-day observation of Saturn's magnetic
field; this continued even though spacecraft pointing would change to
accommodate various observations by Cassini's telescopes, the optical
remote-sensing instruments. The first attitude change was for ISS, which
performed a 90-minute haze observation as part of the Titan monitoring
campaign, with VIMS and the Composite Infrared Spectrometer (CIRS) riding
along. UVIS then controlled pointing for 11.75 hours to view Saturn's
aurorae; ISS and VIMS rode along.

During Cassini's close encounter with Saturn's moon Dione last week, Radio
Science -- measuring Dione's mass distribution -- was not the only kind
of scientific investigation. Images and infrared observations covered
the 1,122-kilometer wide icy satellite as well. Today's news feature highlights
the imaging, including one quite extraordinary view of Dione against a
sliver of sunlit rings on Saturn's night side:

http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20150618 .

Friday, June 19 (DOY 170)

ISS made another 90-minute Titan haze observation while CIRS and VIMS
rode along. Next, the Magnetospheric Imaging Instrument (MIMI) began nearly
13 hours of pointing its Ion and Neutral Camera (INCA) at Saturn to make
a remote-sensing observation of Saturn's magnetic field activity. This
kind of imaging is one of many capabilities of this unique science instrument.

Small lakes and vast seas dot the surface of Saturn's largest satellite
Titan. The means by which some of the smaller lakes were formed was the
subject of a news feature released today:

http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20150619 .

Saturday, June 20 (DOY 171)

MIMI controlled pointing for seven hours to make another INCA observation
of Saturn. All the while, MAG proceeded with its own two-day in-situ measurements.
INCA repeated its observation on the following day for 7.25 hours.

Sunday, June 21 (DOY 172)

NASA's Astronomy Picture of the Day today comprises a dozen images of
Saturn, taken from Earth, over the course of 11 years out of the ringed
planet's 29.5-year revolution about the Sun:

http://apod.nasa.gov/apod/ap150621.html .

Monday, June 22 (DOY 173)

The 66th Project Science Group began meeting on the Caltech campus today
with about 150 scientists and engineers in attendance.

Some of Saturn's moons were captured with a perspective that can never
be obtained from Earth, in a unique Cassini ISS image featured today:

http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=5204


Tuesday, June 23 (DOY 174)

MIMI completed its fourth and final INCA stare at Saturn today. This one
lasted 13.5 hours.

During the past week, the DSN communicated with and tracked Cassini on
11 routine occasions, using deep space stations in Spain, California and
Australia. A total of 36 individual commands were uplinked, and about
1,410 megabytes of telemetry data were downlinked and captured at rates
as high as 142,201 bits per second.

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This illustration shows Cassini's position on June 23:
http://go.nasa.gov/1LsMVIN .
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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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