News | August 1, 2013
Cassini Significant Events 07/24/2013 - 07/30/2013
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 July 31 using one of the 34-meter diameter Deep Space Network stations 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 of the Cassini spacecraft may be found on the "Present Position" page at:
The Titan T-93 encounter on Friday was the highlight of Cassini's activities this week. As usual, during the encounterCassini's attitude control system used its electrically driven reaction wheels to rotate the spacecraft and point the science instruments. Mission designers also used the flyby as an "elastic collision" with the massive revolving moon to increase Cassini’s orbit period and decrease its inclination with respect to Saturn's equatorial plane. More detail may be found on the T-93 page:
Wednesday, July 24 (DOY 205)
The Ultraviolet Imaging Spectrograph (UVIS) completed an interplanetary hydrogen search. Next, it began a high-priorityextreme-ultraviolet (EUV) and far-ultraviolet (FUV) observation of Saturn. Since all the optical instrument boresights are aligned, the Imaging Science Subsystem (ISS), the Visible and Infrared Mapping Spectrometer (VIMS) and the Composite Infrared Spectrometer (CIRS) also took data. VIMS then observed Saturn's northern hemisphere to make mosaics of the latitudes where storms are typically seen. After eight hours, VIMS observed an atmospheric occultation as the red star W Hydrae passed behind Saturn's limb due to thespacecraft's motion. After the occultation, UVIS resumed its study of Saturn in the EUV and FUV parts of the spectrum.
Thursday, July 25 (DOY 206)
UVIS made another observation in the interplanetary hydrogen search campaign. The spacecraft then turned to train its optical remote-sensing instruments on Titan, which was looming larger as the T93 encounter observations began.
Friday, July 26 (DOY 207)
Cassini flew by Saturn's largest moon, going 20,880 kilometers per hour relative to Titan, and coming as close as 1400 kilometers above its atmosphere-enshrouded surface. Data from all the observations were stored on the solid-state recorder for later playback to Earth. As Cassini departed, its orbit had been reshaped by Titan's gravitation and momentum precisely as planned; its period increased to 23.9 days and its inclination reduced to 53.4 degrees.
Saturday, July 27 (DOY 208)
Cassini turned to point its high-gain antenna to Earth and began playing back telemetry from the Titan T93 encounter. Twenty minutes later the 70-meter diameter Deep Space Network (DSN) antenna in Australia began preparing to track Cassini. In one more hour the giant DSN aperture was pointing squarely to Saturn in the east, just in time as the signal from Cassini finished crossing the distance; within minutes, the stream of telemetry from Cassini -- forming a perfect copy of the bits Cassini recorded -- was in the hands of the instrument science teams and the spacecraft operations engineers. After another ten minutes, the DSN station activated its 18 kilowatt transmitter to begin sending a stable reference signal, commands, and ranging tones; a round-trip light-time later Cassini's navigation team started receiving their precise measurements of spacecraft velocity and distance, data which are especially important right after a Titan flyby. This was one of eight routine communications periods carried out this week using DSN stations in Australia and Spain.
Already more than half a million kilometers from the fast receding giant moon, ISS had the spacecraft turn to monitor Titan's high southern latitudes, in which winter is approaching, to track clouds and watch them evolve. For the remainder of the day, the Radio Science team conducted an operations readiness test with one of the 34-meter diameter DSN stations at Madrid, Spain, preparing for a ring occultation experiment on Aug. 8.
An image taken by Cassini's ISS in 2006 was featured today as NASA's Astronomy Picture of the Day. The extraordinary view has Titan and Enceladus, which is a tenth the diameter of Titan, both backlit by the Sun with Saturn's backlit rings in between them: http://apod.nasa.gov/apod/ap130729.html .
Sunday, July 28 (DOY 209)
UVIS picked up where it left off on Wednesday, observing Saturn in the EUV and FUV. Each observation comprised one slow scan across Saturn's illuminated hemisphere to form spectral images. ISS rode along to take one polarimetry measurement during each scan using its wide-angle camera, and CIRS took data as well. The observation was repeated the following day.
Monday, July 29 (DOY 210)
The Navigation team used ISS to obtain five images of Saturn's satellite Rhea against the background stars for optical navigation purposes. Meanwhile, a crescent view of Enceladus was the subject of a recently acquired image that was featured today:
Tuesday July 30 (DOY 211)
ISS made an observation in the Titan monitoring campaign, and then UVIS completed its last EUV-FUV observation of Saturn for now, with ISS and CIRS again riding along.
Back on Earth, the Mission Planning Forum received a Mission Design presentation regarding options available for the F-ring and Proximal Orbits (FRPO) phase, which will begin in 2016. Among the discussions were the number of FRPO orbits to execute, and how close each of their periapses and ring-plane crossings would be allowed to come to Saturn's atmosphere and inner D-ring region, respectively. In a separate meeting, the first commands for the S80 sequence were approved for transmission. Five files of instrument-expanded blocks, totaling 7093 individual commands, will be sent to Cassini beginning mid-day Saturday Aug. 3.