From: Jet Propulsion Laboratory
Posted: Monday, March 17, 2014
Cassini is orbiting Saturn with a 31.9-day period in a plane inclined 45.5 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on March 11 using one of the 34-meter diameter Deep Space Network (DSN) stations at Goldstone, California. Except for the 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 of the Cassini spacecraft may be found on "Eyes on the Solar System":
Cassini's 100th targeted encounter with Saturn's largest moon Titan was the highlight of the week. Science teams devoted this flyby to an important but rare gravity-field measurement, which was carried out in real time (or as close to real time as the speed of light allows). As planned, the gravity assist from Titan altered Cassini's orbit, bringing the plane of its inclination 2.6 degrees closer to Saturn's equatorial plane. Named T-99, the encounter is described on this page:
Wednesday, March 5 (DOY 064)
The Composite Infrared Spectrometer (CIRS) finished up a 13.5-hour observation of Titan while the hazy world loomed closer and closer.
As the spacecraft closed in on Titan, now less than the distance from Earth to our Moon, the Imaging Science Subsystem (ISS) led an observation lasting three and one-half hours. Next, the on-board S82 command sequence caused Cassini to turn and face its high-gain antenna towards Earth. At that time, a signal from the DSN had just completed its 80-minute propagation across interplanetary space. The spacecraft's receiver locked onto this signal and used it as a precise frequency reference to generate the downlink signal (this is called coherent mode). This special observation continued for 19 hours, using DSN stations in Spain, California, and Australia as the Earth turned. As a result, the Radio Science (RS) team captured highly precise data about the coherent-mode signal's Doppler shift; later analysis will tease out valuable information about Titan's interior structure and other qualities.
Thursday, March 6 (DOY 065)
Cassini's closest approach to Titan occurred as the day shift began at JPL in Pasadena. The RS gravity field measurement continued throughout the day while the flight team worked closely with the DSN stations in real time. Telemetry data (ones and zeroes from the instruments and subsystems) continued coming in along with the RS data.
During the encounter, the Magnetospheric and Plasma Science instruments monitored the Titan environment. In particular, the Magnetometer (MAG) studied the draping and diffusion of the external magnetic field within Titan's upper ionosphere, and over the flank facing away from Saturn.
Friday, March 7 (DOY 066)
As soon as the RS gravity experiment concluded, CIRS had the spacecraft turn so that the instrument could continue to monitor temperatures in Titan's stratosphere. ISS and the Visible and Infrared Mapping Spectrometer (VIMS) made observations as well while CIRS controlled the pointing. Next, CIRS started four hours of ring observations in support of phase- and latitude-mapping to help with modeling the directional emissivity of the ring particles.
Saturday, March 8 (DOY 067)
Cassini's motion in orbit makes it possible to use the light from selected background stars to probe Saturn's rings. First, the familiar bright star Vega (Alpha Lyrae) passed behind Saturn's rings, going from the F ring inward to the D ring. The Ultraviolet Imaging Spectrograph (UVIS) and VIMS took advantage of the fact that this luminous, spectral type-A star is a good target for both instruments to use in probing the rings. Next, VIMS watched as the red star R Lyrae made an ingress occultation, going behind rings F through C. Vega then emerged from behind the planet and UVIS and VIMS observed it passing behind rings C through F. Finally, red R Lyrae came out from behind the planet and was occulted by rings D through F while VIMS again observed. Both of the egress occultations took place while the rings were in Saturn's shadow.
The ISS cameras took exposures for six and three-quarter hours to make a multi-color mosaic of the entire ring system, with close-up views of the edge of Saturn's shadow. CIRS, UVIS, and VIMS also observed. Meanwhile, Cassini coasted through periapsis, its closest point in this orbit at a distance of 859,000 kilometers from the planet. ISS and UVIS made a retargeting effort to spot known propellers in the rings (http://go.usa.gov/YyGR), including the one named Bleriot.
Sunday, March 9 (DOY 068)
CIRS made a four-hour thermal ring-study observation with UVIS riding along. Following this, ISS began taking images for 10 hours and 20 minutes to make a movie of the inner edge of the very distant, inclined, retrograde-orbiting Phoebe Ring.
The flight team sent up the S83 command sequence to Cassini today, using the 70-meter diameter DSN station at Goldstone, California. After a round-trip light time of two hours 37 minutes, each of the 11,057 commands was confirmed as properly received and stored.
Monday, March 10 (DOY 069)
CIRS made another four-hour thermal ring-study observation. Cassini then turned its attention to Saturn's southern polar auroral region. VIMS led a 6.5-hour observation there with CIRS, ISS, and UVIS participating. UVIS then took over and led for another seven hours with CIRS and VIMS riding along.
Saturn's second-largest moon, Rhea, is featured in this image, under nearly full-phase illumination: http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=4993 . The image was also selected for NASA's Image of the Day gallery: http://www.nasa.gov/multimedia/imagegallery/iotd.html .
There was an opportunity to execute Orbit Trim Maneuver (OTM)-374 today to clean up Cassini's trajectory following the T-99 flyby. The encounter was so accurate that the maneuver was unnecessary and flight team canceled the OTM.
Tuesday, March 11 (DOY 070)
Saturn remained the focus of attention as VIMS spent two hours creating a regional map of the planet. ISS then made a scan along the planet's bright limb, with UVIS and VIMS riding. Last, CIRS began a 22 hour observation to map Saturn's atmosphere in the mid-infrared part of the spectrum.Visit the JPL Cassini home page for more information about the Cassini Project: http://saturn.jpl.nasa.gov/
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