From: Jet Propulsion Laboratory
Posted: Tuesday, May 29, 2012
The most recent spacecraft tracking and telemetry data were collected on May 23 using the Deep Space Network's 70 meter Station 14 at Goldstone, California. Aside from the Ultrastable Oscillator (see the Jan. 5, 2012 Significant Events), the Cassini spacecraft is in an excellent state of health with all its subsystems operating normally. Information on the present position of the Cassini spacecraft may be found on the "Present Position" page at: http://saturn.jpl.nasa.gov/mission/presentposition/.
This week's highlight was the Titan encounter (T-83), which included acquiring another high-resolution Synthetic Aperture Radar (SAR) image strip about 6,000 kilometers long. Among ongoing observations in the days before Tuesday morning's encounter, the Ultraviolet Imaging Spectrograph (UVIS) continued its series of observations, with the Visible and Infrared Mapping Spectrometer (VIMS), the Imaging Science Subsystem (ISS), and the Composite Infrared Spectrometer (CIRS) riding along, to study Saturn's aurora with slews and fixed pointings at the auroral oval.
Wednesday, May 16 (DOY 137)
Today, as on nearly every day, the Realtime Operations Team sent commands to reset the command-loss timer, which is one of several fault-protection programs running aboard the spacecraft.
The Radio Science Subsystem performed periodic instrument maintenance activities on the Radio Frequency Instrument Subsystem.
Thursday, May 17 (DOY 138)
Today and the next day, ISS led the pointing with CIRS and VIMS also taking measurements in the Titan Monitoring Campaign, watching cloud formations at different phase angles and ranges.
Friday, May 18 (DOY 139)
Commands were sent to overlay telemetry-rate commands in the S73 sequence. This was necessary because Deep Space Network (DSN) antenna allocations were incomplete even as S73 began executing last month. Other command data sent to Cassini made a "live" update to the Inertial Vector Propagator to refine pointing directions for Saturn's satellite Methone. Finally, commands were sent that would perform Orbit Trim Maneuver (OTM) 322 the next day.
Saturday, May 19 (DOY 140)
Nearing periapsis, the Cassini Plasma Spectrometer (CAPS) led spacecraft pointing for Magnetospheric and Plasma Science (MAPS) measurements of the equatorial inner magnetosphere.
OTM-322, the T-83 approach maneuver, executed during its backup window. This was a reaction control subsystem thruster burn with a duration of 73.5 seconds, providing approximately 83 millimeters per second delta-V. The maneuver was delayed to the backup window to allow orbit determination solutions more time to converge.
Sunday, May 20 (DOY 141)
There were three major observing campaigns today. First came high spatial resolution optical studies of Tethys, the third major moon out from Saturn. CIRS took the lead in mapping its leading hemisphere to confirm the previously detected thermal anomaly, to determine thermal surface properties inside and outside of the anomaly, and to characterize the anomaly's shape and spatial extent. The higher daytime temperatures provided enough signal for CIRS to use its FP3 (focal-plane 3) high spatial resolution detector. The CIRS scans allowed ISS and VIMS to mosaic the surface to contribute to a global map of the moon; UVIS rode along to measure variations in Tethys' albedo across its surface.
Going 68,460 kilometers per hour relative to Saturn while viewing Tethys, Cassini passed through periapsis just outside the orbit of Mimas, the innermost of Saturn's major satellites.
ISS then viewed the tiny moon Methone, for which new pointing vectors were uplinked Friday. This close flyby, less than 2,000 kilometers, offered the first opportunity to characterize Methone's geology, to obtain compositional information, and to understand the relationship of the moon to Saturn's ring system. Its orbit lies about 8,500 kilometers outside that of Mimas.
Finally, CAPS took control and turned Cassini to an attitude that allowed optimal measurements of ions and electrons in Saturn's inner magnetosphere. These observations were taken in parallel with higher time resolution measurements by all the MAPS instruments. These latter observations, performed roughly every six months on equatorial orbits, are for the purpose of studying long-term solar cycle and seasonal variability in Saturn's magnetosphere. They are also used to investigate magnetospheric periodicities and their coupling to the ionosphere.
Monday, May 21 (DOY 142)
The image "Serene Scene" with Saturn and Tethys was featured here today: http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=4527.
Cassini pointed the Optical Remote Sensing instruments to the growing disk of Titan to start conducting many observations, which are detailed on the T-83 encounter page (see below).
Tuesday, May 22 (DOY 143)
During the Titan encounter today, the spacecraft rotated repeatedly about all three axes to aim its telescopes, point the large dish antenna for Radar observations, and expose in-situ instruments in desired directions. For closest approach, attitude control switched from reaction wheels to thrusters for increased control authority over atmosphere-generated torques around closest approach. Full information may be found here on the T-83 encounter page: http://saturn.jpl.nasa.gov/mission/flybys/titan20120522/.
By flying closely over Titan's north pole, gravity enabled an "elastic collision" connecting Cassini with some of Titan's orbital momentum. The result of this gravity-assist flyby increased the inclination of the spacecraft's orbit plane from near-equatorial (0.4 degrees) to 15.8 degrees. This is the first of eight gravity-assisted steps that will bring Cassini's inclination to a maximum of 61.7 degrees above the equatorial plane about a year from now. More information on the inclined orbits, and on Methone, may be found here: http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20120521/.
The DSN's 70 meter aperture stations in Madrid, Spain, and Goldstone, California, captured every bit of telemetry that was stored on the solid-state recorders during T-83, while providing Doppler and ranging data for navigation. At the same time, both stations participated in an Operations Readiness Test (ORT) preparing for an upcoming Radio Science ring and atmosphere occultation experiment, which is possible to do now that Cassini's orbital plane has been rotated somewhat out of the ring plane. Cassini's S-band (2 GHz), X-band (8 GHz), and Ka-band (32 GHz) transmissions were received during the ORT.
// end //