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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:
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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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