Cassini's "background" command sequence, S101, made its appearance on the flight team's development schedule this week. S101 will be the last sequence for the Saturn-orbiting mission. It will conclude with instrument and telecommunications activities carefully selected for returning the best scientific measurements while Cassini makes its plunge into the gas giant next September. Meanwhile, commands from the on-board S97 sequence continued to control the Saturn Orbiter this week.
Wednesday, Dec. 7 (DOY 342)
Cassini's Imaging Science Instrument (ISS) spent eight hours tracking Saturn's small, distant, irregular moon Erriapus, which seems to have the unusually low rotation period of 28 hours. Today's observation will supply nearly full-phase light curves, which will help scientists confirm and refine this parameter and others, such as its shape. The body was named after a giant in Gaulish mythology. Only about eight kilometers in diameter, it has a very dark surface. It reaches as far as 25.6 million km from Saturn in its inclined, prograde orbit.
As of today, ISS has acquired and returned about 386,000 images during the mission. The instrument itself was the topic of a write-up today:https://saturn.jpl.nasa.gov/imaging-science-subsystem .
With ISS's observation of Erriapus completed, most of Cassini's science instruments stood down from making observations for a few days, in recognition that telecommunications would be hampered by the Sun. This page elaborates, and offers a nice video illustration of Cassini's final superior conjunction: https://saturn.jpl.nasa.gov/resources/7568 .
The Cassini Project Scientist gave a presentation to the National Academies of Science, Engineering, and Medicine in Irvine, California, about the importance of large strategic science missions.
Thursday, Dec. 8 (DOY 343)
Slowing with respect to Saturn, Cassini coasted through apoapsis today, and then began speeding up for the inbound leg of Orbit #252.
The Deep Space Network (DSN), which is Cassini's massive "other half," is the subject of a feature article today:https://saturn.jpl.nasa.gov/news/2976/cassinis-largest-science-instrument .
Friday, Dec. 9 (DOY 344)
The spacecraft assumed an attitude that keeps its High-Gain Antenna (HGA) pointed towards Earth as Saturn came within two degrees of the Sun as seen in Earth's sky. The attitude also favors the Cosmic Dust Detector (CDA) as it continued to sample interstellar dust during this conjunction period.
Sunday, Dec. 11 (DOY 346)
The spacecraft turned to orient the HGA into the "dust ram" direction, and maintained that orientation for two hours while making another high-speed pass through Saturn's ring plane. Today's ring-plane crossing occurred at about the same radial distance from the F ring as last week's, when the HGA was not used as a shield. The difference will let the Radio and Plasma Wave Science instrument (RPWS) team compare results, and cross-calibrate them with CDA's data. Later in the mission, the HGA-to-dust-ram attitude will be required for safeguarding the spacecraft during some ring-plane crossings.
Right after crossing Saturn's ring plane today, Cassini sped through periapsis and began slowing on its climb towards another appointment with apoapsis next Thursday.
Today, many Cassini scientists began attending the fall 2016 meeting of the American Geophysical Union in San Francisco. The Cassini project scientist and deputy project scientist gave presentations on the mission's scientific discoveries, and the upcoming science of the Grand Finale.
Monday, Dec. 12 (DOY 347)
Enlarging this image, featured today on the Cassini website, reveals the little moon Daphnis as it raises wakes in the outer part of Saturn's A ring:https://saturn.jpl.nasa.gov/resources/7566 .
NASA saw fit to offer Cassini's recent view of Saturn's north polar region as the Astronomy Picture of the Day today:http://apod.nasa.gov/apod/ap161212.html .
Tuesday, Dec. 13 (DOY 348)
Today marks 7,000 days since Cassini's launch in October of 1997.
The DSN communicated with and tracked Cassini 11 times this week, using stations in Spain, California and Australia. The Radio Science team continued conducting a study of the near-Sun environment while the spacecraft is close to superior conjunction. A total of 410 individual commands were uplinked, while only about 700 megabytes of telemetry data were downlinked and captured at rates as high as 66,360 bits per second.
Cassini is executing its set of F-ring-grazing orbits of Saturn, with a period of 7.2 days in a plane inclined 63.7 degrees from the planet's equatorial plane. These 20 orbits are nearly identical with Cassini's nearest point at about 150,000 km and furthest point at about 1.28 million km from Saturn. Speeds relative to Saturn at those points (periapsis and apoapsis), are close to 76,150 km per hour and 9,000 km per hour respectively.
The most recent spacecraft tracking and telemetry data were obtained on Dec. 13, using the 70-meter diameter DSN station 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 athttp://saturn.jpl.nasa.gov/anomalies .
Cassini's path up to mid-day Dec. 13 is illustrated in this image:http://go.nasa.gov/2epgosm . At that time, the countdown clock in Mission Control was showing 275 days until the end of the mission.