Cassini took advantage of its rapidly changing views in the Saturn system again this week, coasting all the way through its short and highly-inclined orbit of Saturn. Most of the spacecraft's activities were controlled by the S95 sequence, which has been running the show since late last June. Instrument commands were loaded aboard the spacecraft this week, getting ready for the September 8 start of the S96 sequence. Meanwhile, work continued on preparing the S97 and S98 sequences, and events have been scheduled for S99. S101 will be Cassini's final ten-week command sequence, which will begin executing in July 2017.
Thursday, Aug. 25 (DOY 238)
The Cosmic Dust Analyzer (CDA) began a 37-hour observation as part of the campaign to measure particles of dust that orbit Saturn in the retrograde direction.
While CDA was collecting dust, Cassini coasted through apoapsis, having reached 1.56 million kilometers from Saturn, and slowing to 11,903 km/hour with respect to the planet. This marked the start of Cassini's orbit #241 about Saturn.
Today marks 35 years since a spacecraft other than Cassini has encountered Saturn. Voyager 2 flew rapidly through the Saturn system and on towards Uranus and Neptune on August 25, 1981. Along with Voyager 1, which sped by Saturn in November 1980, the twin Voyager spacecraft scrutinized the solar system's outer planets, answering scientific questions and raising many more. Cassini's mission and its scientific instrumentation were designed to address many of the questions raised by Voyager, including the nature of haze-enshrouded Titan, the highly reflective little moon Enceladus, and puzzles found in the ring system: http://go.nasa.gov/2bgZTKH.
Saturday, Aug. 27 (DOY 240)
VIMS and the Composite Infrared Spectrometer (CIRS) began a 35-hour study of the composition of Titan's atmosphere.
During Cassini's Proximal Orbits next year (/resources/17365), the spacecraft's speed will be changing rapidly as the spacecraft zips through periapsis going nearly 125,000 km per hour with respect to the planet. Today, Deep Space Network (DSN) stations in Australia teamed with the European Space Agency's Deep Space Antenna facility in Malargüe, Argentina, to carry out a test. The DSN's altered the usual uplink reference signal causing the spacecraft's downlink signal to go through the same dynamics that will be caused by the Doppler effect during the Proximal orbits. The stations demonstrated that there should be no difficulty meeting the Proximal Orbits' requirements.
Saturn is still well-placed for viewing in just about any sort of telescope these evenings. The beautiful ringed planet is near the redder objects Mars and Antares located in the constellation Scorpio in the southwest part of the sky.
CIRS, VIMS, and the Ultraviolet Imaging Spectrograph (UVIS) spent six hours staring at the outer edge of Saturn's broad, opaque B ring, gathering spectral data to learn about the ring material's composition. Following this, ISS began an observation of Saturn's narrow, bright F ring that would last nearly 17 hours. CIRS and VIMS rode along.
The phenomena of brightened reflection at high-phase-angle lighting is evident in the image highlighted today. It's visible as the bright spot where the Cassini Spacecraft's shadow would be seen, if the spacecraft were large enough to produce one: /resources/17491.
VIMS controlled spacecraft pointing for just over seven hours today, to watch as the red star alpha Scorpii, commonly known as Antares, passed behind Saturn's A and B rings, as well as the Cassini Division, before the line of sight to the star was cut off by the disk of Saturn. Just under 90 minutes later, the star reappeared just inside Saturn's closest ring, the D ring. VIMS then proceeded to track the star as it moved out beyond the F ring, as a result of Cassini's motion in orbit. Stellar ring occultations like this one are valuable for measuring the ring system's properties.
The Deep Space Network communicated with and tracked Cassini via six sessions this week, using stations in California and Australia. The European Space Agency's antenna in Malargüe, Argentina participated once as well. A total of 9.284 individual commands were uplinked, and about 1,036 megabytes of telemetry data were downlinked and captured at rates as high as 142,201 bits per second.
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 August 31, using the 70-meter diameter DSN station 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/anomalies
Milestones spanning the whole orbital tour are listed here: https://saturn.jpl.nasa.gov/mission/saturn-tour/tour-dates.
Information on the present position and speed of the Cassini spacecraft may be found on the "Present Position" page at: