From: Jet Propulsion Laboratory
Posted: Monday, February 18, 2013
The Cassini spacecraft is orbiting Saturn with a period of 13.3 days in a plane inclined 53 degrees from the planet's equatorial. The most recent spacecraft tracking and telemetry data were collected on Feb. 13 by the 34-meter Deep Space Network station at Madrid, Spain. Except for some science instrument issues described in previous reports, 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:
Cassini's Sequence Implementation teams continued working on the ten-week command sequences S78 and S79. These sequences will go active on Cassini in March and June respectively. The teams also continued planning for the 2016 start of Cassini's F-ring and Proximal Orbits phase. Meanwhile, commands from the on-board S77 sequence controlled the spacecraft's activities in flight. A web page has been published detailing Cassini's next targeted encounter, the Titan T-89 flyby, coming up on Feb. 17. The T-89 flyby will focus on a Radio Science measurement of Titan's gravity field. The web page may be viewed here: http://saturn.jpl.nasa.gov/mission/flybys/titan20130217/
Wednesday, Feb. 6 (DOY 037)
The Imaging Science Subsystem (ISS) completed a 21-hour observation of the half-kilometer wide satellite Aegaeon in the tenuous G ring. The Composite Infrared Spectrometer (CIRS) then began a 14.5-hour mid-infrared map of Saturn to determine upper troposphere and tropopause temperatures.
Today and on two other occasions this week, the Attitude and Articulation Control Subsystem (AACS) team executed Reaction Wheel Assembly bias maneuvers to adjust the wheel speeds, using thrusters to stabilize the spacecraft.
Thursday, Feb. 7 (DOY 038)
AACS rotated the spacecraft about its X, Y and Z axes to calibrate its prime inertial reference unit, which generates attitude information based on hemispherical resonator gyroscopes.
Telemetry data were unexpectedly absent from the Visible and Infrared Mapping Spectrometer (VIMS) in downlink received through the Deep Space Network (DSN) today. The Cassini anomaly response operations plan was subsequently invoked.
Cassini passed through apoapsis, having coasted to 1.7 million kilometers from the planet and slowing to 10,890 kilometers per hour relative to Saturn. This marked the beginning of Cassini's orbit #181.
Friday, Feb. 8 (DOY 039)
DSN stations in California and Spain conducted two-way communications with Cassini on seven occasions this week. During three of these, they also participated in operations readiness tests, preparing for the real-time Radio Science measurement of Titan's gravity field during the T-89 close encounter on Feb. 17.
Saturday, Feb. 9 (DOY 040)
ISS made an observation in the satellite orbit campaign looking at small satellites near Saturn and then began a 16-hour F ring observation.
Sunday, Feb. 10 (DOY 041)
The Ultraviolet Imaging Spectrograph (UVIS) performed a 12.5-hour observation of Saturn's southern aurora to help identify spatial and temporal intensity variations and allow comparison of post-equinox and pre-equinox trends.
The Spacecraft Operations office finalized installation of the new AACS A8.9.0 flight software by overwriting the old version on the solid state recorders and setting flags that mark all copies of the software as equivalent.
Monday, Feb. 11 (DOY 042)
About 200 scientists from around Europe and the United States convened at JPL for the 59th Cassini-Huygens Project Science Group meeting. Workshops, team meetings, and plenary sessions filled out the week.
After conducting an anomaly meeting, the flight team approved commands to power VIMS off and back on. The commands were sent late in the day, and telemetry indicated a normal power-on reset occurred as planned after a round-trip light time of 2 hours 39 minutes.
The Magnetometer performed an eight hour calibration while rotating the spacecraft about its X axis. ISS, CIRS and the freshly restarted VIMS then jointly observed the rings for five hours to search for periodicities in the spokes.
An image featured today shows Saturn's 1,528-kilometer-diameter moon Rhea. Cassini will have a close encounter with Rhea (R4) early next month (March 6). The image may be seen here: http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=4738
Tuesday, Feb. 12 (DOY 043)
ISS observed the ringlets in the Encke Gap for nearly six hours to watch material as it revolves through, measuring the ringlets' time-variable structures. CIRS and VIMS took data, riding along with ISS's control of spacecraft pointing. All the observations executed normally and returned the expected science data in telemetry, providing welcome evidence that VIMS is back in its normal state following the anomaly response.
CIRS observed the rings for eight hours, scanning across their lit side along the ingress boundary of Saturn's shadow, to map out ring temperatures from several different viewing geometries. By modeling the temperature decrease within the shadow as ring particles were cut off from sunlight, scientists will be able to determine their thermal inertia as a function of distance from Saturn. (Thermal inertia is another diagnostic measure of ring particle composition and structure.)
The flight team designed and approved commands for an Orbit Trim Maneuver (OTM340), the approach maneuver for the Feb.17 Titan T-89 encounter. The commands were uplinked and verified on board. Late in the day the reaction-control subsystem thrusters fired for 26.3 seconds, providing the Cassini spacecraft a delta-V (velocity change) of 32 mm/s.
Visit the JPL Cassini home page for more information about the Cassini Project: http://saturn.jpl.nasa.gov/
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