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Cassini Significant Events 09/04/2013 – 09/10/2013

Cassini is orbiting Saturn with a 23.9-day period in a plane inclined 53.4 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on Sept. 11 using the 70-meter diameter Deep Space Network station at Canberra, Australia. Except for some science instrument issues described in previous reports (for more information search the Cassini website for CAPS and USO), the spacecraft continues to be in an excellent state of health with all of its subsystems operating normally. 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/ .

The laws described by Isaac Newton keep Cassini falling freely around Saturn, but flight team engineers still make small adjustments to its path once in a while. Short rocket firings on Aug. 7 and Sept. 8 tweaked the flight path to target to a 1,400-kilometer flyby of Titan on Sept. 12. Along with the scheduled science investigations led by the optical remote sensing instruments, the gravity assist from this huge natural satellite will reshape Cassini's orbit by lowering its inclination and increasing its period. The T94 encounter page has details on the instrument activities: http://saturn.jpl.nasa.gov/mission/flybys/titan20130912/ .

Wednesday, Sept. 4 (DOY 247)

The Cosmic Dust Analyzer completed a 37-hour observation of retrograde-orbiting particles. The Imaging Science Subsystem (ISS) then began a 10.5-hour Titan long range monitoring observation from a distance of 540,000 kilometers. ISS led another of these observations on Friday when the distance to Titan had increased almost two-fold.

Thursday, Sept. 5 (DOY 248)

ISS began a 16.5-hour observation of the irregular moon, Tarvos. This small icy body has a very dark surface and a diameter of about fourteen kilometers. It orbits Saturn once every 926 days at nearly eighteen million kilometers from the planet.

Friday, Sept. 6 (DOY 249)

These evenings Saturn is getting lower in the western sky, but as always it is an extraordinary and memorable sight in a small telescope. Find the very bright planet Venus in the west, then look up to the left from there to identify the much dimmer Saturn.

Saturday, Aug. 7 (DOY 250)

ISS created a 13.5-hour low-resolution movie of the F ring. A previous movie illustrates one of the many reasons why this narrow ring is of interest:

Sunday, Sept. 8 (DOY 251)

The Ultraviolet Imaging Spectrograph (UVIS) observed Saturn's aurora for 15 hours. Next, the flight team sent commands to Cassini to perform Orbit Trim Maneuver 358, which turned the spacecraft and fired its thrusters for 30 seconds. The resulting change in velocity of 33 millimeters per second fine-tuned Cassini's approach to Titan for the T-94 flyby coming up on Sept. 12.

Monday, Sept. 9 (DOY 252)

The Composite Infrared Spectrometer (CIRS) mapped the temperature of the rings in Saturn's shadow in an effort to determine their thermal inertia. Next it turned to map the temperatures in Saturn's north polar region.

When Cassini had its high-gain antenna pointed to Earth and the Deep Space Network began receiving data today, telemetry revealed that one of the spacecraft's solid-state power switches had tripped off, likely the result of being hit by a cosmic-ray particle as happens a couple times a year. This one turned off Cassini's primary deep-space transponder that receives signals from Earth and generates the downlink. An on-board fault-protection algorithm had executed properly, preventing any complications by turning it back on again automatically. Commands were prepared to read out selected memory locations and "clean up" after the event.

A remarkable image from the ISS wide-angle camera showing rings and atmosphere was featured today. A brilliant spot of reflected sunlight can be seen in the lower left; this is the "opposition effect" surge in the B ring's brightness around the point directly opposite the Sun from the spacecraft. The A, B, and C rings (going inward) are clearly visible, but the D ring (interior to the C ring) and the thin F ring (just outside the A ring) do not show up in this low-phase observation. If all goes according to plan, beginning in April 2017 Cassini's periapsis will come within the dark space between the D ring and the atmosphere. The image can be found at: /resources/15886 .

Tuesday, Sept. 10 (DOY 253)

ISS performed an observation in the Satellite Orbit Campaign looking at small objects near Saturn while going through periapsis of Orbit #197, at almost the distance from Saturn as Titan's orbit. Next, it reacquired and tracked the orbits of known "propellers" (http://go.usa.gov/YyGR) in Saturn's rings. Finally, the Visible and Infrared Mapping Spectrometer (VIMS) watched an occultation of the red star W Hydrae for nearly six hours as it passed behind the rings due to spacecraft motion.