News | October 22, 2014
Cassini Significant Events 10/15/2014 - 10/21/2014
Cassini is orbiting Saturn with a 31.9-day period in a plane inclined 40.3 degrees from the planet's equatorial plane. The most recent spacecraft tracking and telemetry data were obtained on October 21 using the 70-meter diameter Deep Space Network (DSN) station in Australia. 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".
The Cassini Spacecraft continued increasing its speed until passing periapsis on Tuesday. As it climbs outbound from Saturn again, Cassini will encounter Titan on Oct. 24, going 20,000 kilometers per hour relative to the atmosphere-enshrouded moon. During the flyby, the Radio Science team will be conducting a bistatic scattering experiment, constantly slewing the spacecraft's attitude to illuminate parts of Titan's surface with radio waves, much like a searchlight. The reflected signals will be seen on the distant Earth using the DSN Snapshots of this fast-moving geometry are explained in a video slide show released this week: http://saturn.jpl.nasa.gov/mission/flybys/titan20141024
Meanwhile back at JPL, Cassini's 64th Project Science Group drew more than 200 of the Project's scientists to the campus for workshops and team meetings. The major task at hand is hammering out plans to best capture the unprecedented observing geometries and opportunities which will begin in 2016 with the F Ring and Proximal Orbits phase, leading to Cassini's Grand Finale in 2017.
Wednesday, Oct. 15 (DOY 288)
Today while the flight team was observing Cassini's 17th launch anniversary, the Composite Infrared Spectrometer (CIRS) completed an observation that had its 19-inch aperture telescope trained on the sunlit side of the rings for a total of 10 hours, obtaining thermal infrared spectral data. This will be used in studying ring particle composition. The Visible and Infrared Mapping Spectrometer (VIMS) was riding along. As soon as CIRS finished, VIMS began controlling the spacecraft's attitude to make a mosaic of the sunlit rings. This took six hours to complete; CIRS took data during this time as a ride-along observer. Before turning away from the vicinity of Saturn, ISS took two minutes to make a storm-watch observation on the planet. ISS repeated a similar short storm-watch observation on each subsequent day this week.
An unexplained feature in one of Titan's great lakes was the subject of NASA's Astronomy Picture of the Day today: http://apod.nasa.gov/apod/ap141015.html
Cassini had scheduled a 3.5-hour period with the DSN's Australian 70-meter station today, but it was given over to the STEREO-B mission to aid in their emergency situation. This is an infrequent occurrence, but when any one of the dozens of spacecraft that the DSN serves is having problems, the other DSN users are called upon to help out, even if it causes some data to be lost.
Thursday, Oct. 16 (DOY 289)
The Imaging Science Subsystem (ISS), with VIMS riding along, carried out a 90-minute observation as part of the Titan monitoring campaign. This one was from a distance of 1.89 million kilometers; similar observations were repeated on Sunday and Monday. Finally, UVIS began a 27-hour long observation of Saturn's aurora in the planet's high northern latitudes. CIRS and VIMS took advantage of the pointing and acquired data in ride-along mode.
Based on Cassini's observations of Saturn's 396-kilometer wide icy satellite Mimas and the way it wobbles, researchers have learned that there's some unusual structure below its heavily cratered surface.
It's been a long time since Cassini's close encounter with Saturn's low-density, spongy-appearing, 180-kilometer long moon Hyperion. In the intervening years, scientists have learned from the encounter data that the spacecraft had pulled off swarms of electrons from it during the flyby.
Friday, Oct. 17 (DOY 290)
When UVIS completed its aurora observation, the Navigation team spent 90 minutes using ISS to take images of Hyperion against the background stars, for optical navigation purposes. Finally, ISS took control of pointing for six hours to create a color scan of the sunlit rings. CIRS and VIMS rode along.
Saturday, Oct. 18 (DOY 291)
CIRS mapped Saturn’s northern hemisphere in the far-infrared part of the spectrum for 11.5 hours in an effort to determine temperatures in the upper troposphere and tropopause; ISS and VIMS rode along. CIRS then turned to the rings for seven hours to create a far-infrared map of ring temperatures in Saturn’s shadow. This observation will help determine the ring particles' thermal inertia.
Sunday, Oct. 19 (DOY 292)
UVIS observed Saturn's 1,528-kilometer wide satellite Rhea for four hours to measure the ultraviolet albedo of its leading hemisphere; ISS and VIMS rode along. After a Titan monitoring observation, ISS turned towards the giant planet for 80 minutes to make an observation in the satellite orbit campaign. After this was finished, CIRS spent four hours observing the sunlit side of the rings in the thermal infrared, to study particle composition. VIMS rode along. Finally, ISS reacquired and tracked the orbits of known "propeller" features (http://go.usa.gov/YyGR) in Saturn’s rings, while CIRS rode along.
Monday, Oct. 20 (DOY 293)
The 64th meeting of the Cassini Project Science Group convened at JPL today. Meanwhile the spacecraft flew through Saturn's ring plane going south. VIMS targeted Saturn along with the other telescopic, remote-sensing instruments riding along -- ISS, CIRS, and UVIS -- to make observations along Saturn's bright limb for 12 hours. These observations will be used to create a movie. Next, the 10-week long S86 command sequence came to a programmed quiet period reserved for an Orbit Trim Maneuver (OTM). The flight team sent up commands near real time to perform OTM-394, which turned the spacecraft and fired its small rocket thrusters for 32 seconds. This imparted the desired change in velocity of 35 millimeters per second for a fine adjustment to the spacecraft's trajectory approaching Titan for this week's T-106 encounter.
An image featured today captures several clumps in Saturn's narrow, ever-changing F ring, along with the satellite Pandora just outward from the ring, and Atlas on the ring's inward side:
Tuesday, Oct. 21 (DOY 294)
VIMS spent 5.75 hours leading the other remote-sensing instruments in creating mosaics to map the region of Saturn's southern hemisphere. CIRS interest was the limb itself, while UVIS was looking for aurorae in the high southern latitudes. Next, UVIS observed for 80 minutes while the bright blue star Alpha Lyra (popularly known as Vega), emerged from behind Saturn's nighttime atmosphere. VIMS rode along for this stellar atmospheric occultation. When this observation was done, UVIS made repeated slews over a two-hour period across Saturn's southern auroral oval. Finally, VIMS led a 4.5-hour stare at the south auroral region, while the other optical remote-sensing instruments rode along. During this observation Cassini passed through periapsis of its Saturn orbit at an altitude of 627,000 kilometers above the clouds, going 34,320 kilometers per hour relative to the planet.
As usual during all of Cassini's other activities this week, the Magnetospheric and Plasma Science instruments continued their ongoing campaigns to measure Saturn's atmospheric and ionospheric thermal structure, and to study the magnetosphere.
This week, the DSN communicated with and tracked Cassini on six occasions, using stations in Australia and California. A total of 203 individual commands were uplinked, and about 1,630 megabytes of telemetry data were downlinked at rates as high as 110,601 bits per second. The round-trip light time for communications is now three hours.
NASA's Astronomy Picture of the Day today featured a beautiful image of Mimas, with Titan in the background, that Cassini obtained during its close flyby in 2010: http://apod.nasa.gov/apod/ap141021.html.