From: Jet Propulsion Laboratory
Posted: Saturday, July 7, 2012
The most recent spacecraft tracking and telemetry data were collected on July 2 by the Deep Space Network's 34 meter Station 55 at Madrid, Spain. Aside from the Cassini Plasma Spectrometer, which is off, and the Ultrastable Oscillator (see the Jan. 5, 2012 Significant Events), the Cassini spacecraft is in an excellent state of health with all its subsystems functioning 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/
Now that Cassini's orbit is inclined 21 degrees out of Saturn's equatorial plane, many different observations of the splendid ring system have been taking center stage. Thursday's Radio Science ring occultation experiment, in which the Deep Space Network (DSN) itself comprised part of the science instrumentation, was not the least of them. Leading up to Thursday, the DSN participated in three Operations Readiness Tests to help ensure the successful Radio Science data capture.
Wednesday, June 27 (DOY 179)
The Imaging Science Subsystem (ISS), Composite Infrared Spectrometer (CIRS), and Visible and Infrared Mapping Spectrometer (VIMS) completed a 15 hour Titan observation as part of the Long Range Monitoring Campaign.
The ISS narrow-angle camera pointed to the F ring ansa and took 45 images while ring material passed through the field of view. The images will be used to make a movie of the narrow ring to monitor its time variable structure. Resolution was roughly twice as good as typical F ring observations. A previous F ring movie may be seen here: http://saturn.jpl.nasa.gov/video/videodetails/?videoID=241
Thursday, June 28 (DOY 180)
ISS observed the ansa of Saturn's innermost ring, the D ring, for the full orbital period of its particles -- about 5 hours. One goal was to monitor corrugations in the outer part of this ring. These corrugations, which arose after a disturbance in 1983, are discussed at more length here: http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=3664 Another goal of this moderately high phase observation was to see patterns generated by resonances with Saturn's magnetic field.
The Radio Science Subsystem team performed an ingress occultation experiment, probing Saturn's rings using Cassini's three radio-frequency bands: S, X, and Ka. Since the Ultrastable Oscillator (USO) is inoperative, the DSN provided the reference frequency via uplink. The spacecraft's downlink was received and recorded at 70- and 34 meter stations at Canberra, Australia. This was the second of four such experiments designed to sample new values of ring opening angles, about 12.5 to 13.5 degrees. The experiments are expected to yield radial profiles of ring structure, shedding more light on the variability with ring longitude, opening angle, and wavelength of dynamical features such as waves, wakes, edges, gaps, and narrow ringlets. In addition, measurements of the strength and shape of the collective forward scattering of Cassini's radio energy will shed more light on physical properties of ring features such as particle sizes, aggregate sizes or wakes, wake orientation, packing fraction, and ring thickness.
The feature "Cassini Finds Likely Subsurface Ocean on Saturn Moon" was released today. It may be viewed here: http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20120628/ Friday, June 29 (DOY 181)
The flight team uplinked a command that will turn on Cassini's S-band transmitter during a special USO test Tuesday night.
The F ring's structure has been seen to vary during Cassini's mission, so detailed measurements of it are valuable. The Ultraviolet Imaging Spectrograph (UVIS) observed a grazing occultation as the bright star Sirius passed behind the F ring and the outer A ring due to Cassini's motion. This observation measured the distribution and sizes of individual ring particles to a scale of one meter and larger.
VIMS obtained high-resolution spectral observations of the sunlit side of the rings at a moderately low phase angle, running roughly parallel to the planet's shadow across the rings to minimize the effect of scattered light from Saturn.
ISS searched for moonlets in the Cassini Division, which separates the A ring from the B ring.
Saturday, June 30 (DOY 182)
ISS took a 10.5 hour movie of the outer B ring to study edge waves that have been previously detected there. ISS then stared at the D ring ansa for about 5 hours, examining the corrugation patterns from a different viewing geometry to help quantify the amplitude of vertical motions in this region. This lower phase angle observation helped probe the distribution of larger particles, complementing the data obtained from Thursday's observation. Larger particles in this ring may be the source of the fine dust seen in higher-phase images.
Sunday, July 01 (DOY 183)
Today and yesterday ISS led observations in the Titan Monitoring Campaign.
UVIS, with VIMS and CIRS riding along (taking advantage of pointing), observed Saturn's polar aurora with repeated slews across the auroral oval for 12 hours.
Monday, July 02 (DOY 184)
Final preparations involving the Cassini Spacecraft Operations Office, Radio Science Subsystem team, Realtime Operations team, and the DSN were made today for the test late tomorrow night with Deep Space Transponder B, the spacecraft's redundant radio receiver, to troubleshoot the apparently anomalous Ultrastable Oscillator.
UVIS, with VIMS as a rider, observed Saturn's aurora for 14.5 hours. ISS, CIRS and VIMS then monitored Titan at a distance of 3.1 million kilometers.
Tuesday, July 03 (DOY 185)
ISS tracked the orbits of individual known "propeller" shaped features in the rings. UVIS, with VIMS riding along, then started a 23.5 hour observation of Saturn's auroral oval. Videotaping for the 2012 Cassini Scientist for a Day essay contest took place today. Four Cassini flight team members introduced the contest and advocated their chosen targets for the upcoming contest. Videos will be edited over the next few weeks in preparation for announcing the contest on the Cassini website in mid-August.
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