News | October 29, 2014
Cassini Significant Events 10/22/2014 - 10/28/2014
Cassini is currently orbiting Saturn with a 47.8-day period in a plane inclined 33.1 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on October 29 using two of the 34-meter diameter Deep Space Network (DSN) stations 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/news/significantevents/anomalies. Information on the present position of the Cassini spacecraft may be found on "Eyes on the Solar System".
While Cassini continued its climb outbound from an Oct. 21 periapsis, its close flyby of Saturn's most massive moon Titan this Thursday provided the gravity-assist "kick" to alter the spacecraft's trajectory. Nothing is gained free of charge, so Titan's own orbital momentum was changed as well, but not enough to measure. Per plan, Cassini's orbit period increased by about sixteen days, and its inclination decreased by 7.2 degrees. Each of the next four Titan encounters will continue decreasing Cassini's orbital inclination until it is again in the plane with the rings in April of next year. Meanwhile on Earth, the Cassini Project Science Group's 64th meeting continued its work through Friday at JPL.
Wednesday, Oct. 22 (DOY 295)
The Visible and Infrared Mapping Spectrometer (VIMS) targeted Saturn's south pole for one hour to construct a map of auroral emissions from that region. Next, the Composite Infrared Spectrometer (CIRS) spent 10 hours staring at one location on Saturn to obtain high-signal-to-noise spectral data on the atmosphere's composition. During this time, all the other telescopic remote-sensing instruments -- VIMS, the Ultraviolet Imaging Spectrograph (UVIS), and the Imaging Science Subsystem (ISS) -- also made observations in ride-along mode since they all point in the same direction. At the end of CIRS's observation, VIMS controlled pointing for 55 minutes to add data to its south-polar mapping.
Thursday, Oct. 23 (DOY 296)
All eyes turned to Titan as Cassini closed within 400,000 kilometers of the haze-enshrouded world. ISS, VIMS, and CIRS each had their turn at the helm or riding along, and UVIS also rode along at times. By day's end, the distance had shrunk to only 54,000 kilometers; for comparison, the distance from Earth to our Moon is 384,400 kilometers on average. Finally, the Radio Science team had the spacecraft turn to point its high-gain antenna dish to Titan while transmitting pure radio-frequency tones at S-band (2 GHz), X-band (8 GHz), and Ka-band (32 GHz) as part of the bistatic scattering experiment to probe the surface. On Earth, the DSN's 70-meter and one of the 34-meter diameter stations in Australia began watching for reflections off of Titan's land and seas, considering of course the 90-minute light-time delay. The T-106 flyby page has more information: http://saturn.jpl.nasa.gov/mission/flybys/titan20141024
Friday, Oct. 24 (DOY 297)
Closest approach to Titan came rapidly; by 02:40 Universal Time, the distance had diminished to 1,013 kilometers off the surface -- just barely outside the sensible atmosphere. Unmistakable specular reflections appeared in the DSN's Radio Science receivers, coming and going as Cassini's transmitter illuminated the smooth surface of the lake known as Kraken Mare and its meandering shoreline. To the Radio Science team, these constituted superb measurements to distinguish solid from liquid, determine surface reflectivity, dielectric constant and implied composition, as well as determine surface roughness on the alien world.
Following in kind, VIMS took control of pointing to look for an infrared specular reflection of sunlight off the eastern shore of Kraken Mare while the other telescopic instruments rode along. They monitored for cloud activity as Titan receded, and acquired a new global view of the seas and lakes located at the North Pole. CIRS finished up the day observing Titan in the far- and mid-infrared parts of the spectrum for temperature maps and composition, with VIMS, ISS, and UVIS making use of the pointing as well. By the end of the day Titan was 420,000 kilometers behind the speeding spacecraft.
The 64th meeting of the Cassini Project Science Group concluded at JPL today.
Saturday, Oct. 25 (DOY 298)
Continuing with Titan science, ISS monitored its northern latitudes to track clouds, which have reappeared in recent months, and their evolution as Titan's summer gradually approaches; each of Titan's seasons -- and Saturn's -- lasts more than seven Earth-years. CIRS and VIMS rode along.
Sunday, Oct. 26 (DOY 299)
During Cassini's other activities this week, the Magnetospheric and Plasma Science instruments continued their ongoing campaigns to measure Saturn's and Titan's atmospheric and ionospheric thermal structures, and to study the magnetosphere.
Monday, Oct. 27 (DOY 300)
ISS, CIRS and VIMS performed an observation in the Titan monitoring campaign, now that the huge moon had receded to a distance of 1.5 million kilometers; these observations are normally done at large distances. ISS then observed Saturn's narrow, enigmatic F ring for 12.5 hours to create a low-resolution movie.
The Cassini Navigation team saw their solutions for Cassini's precise orbital path converging based on the past few days of DSN tracking results. Given this latest knowledge, commands were created today for Orbit Trim Maneuver (OTM)-395 and sent to turn the spacecraft and fire its small rocket thrusters for one minute. This OTM provided the desired change in Cassini's velocity of 62 millimeters per second, to clean up small errors in the spacecraft's trajectory following the T-106 encounter.
Featured today, two of Saturn's tiny icy satellites are almost lost in the beauty of a unique image: /resources/16105
Tuesday, Oct. 28 (DOY 301)
The Navigation team used the ISS to take five images of Saturn's small, active moon Enceladus against the background star field for optical navigation purposes. Following this, CIRS stared at the sunlit side of Saturn's rings for 10 hours to obtain thermal infrared spectra for use in studying ring particle composition.
This week, the DSN communicated with and tracked Cassini on seven occasions, using stations in Australia and California. A total of 137 individual commands were uplinked, and about 1425 megabytes of telemetry data were downlinked at rates as high as 110,601 bits per second.