From: Jet Propulsion Laboratory
Posted: Saturday, June 26, 2010
The most recent spacecraft telemetry was acquired on June 22 from the Deep Space Network tracking complex at Goldstone, California. The Cassini spacecraft is in an excellent state of health and all subsystems are operating normally. Information on the present position and speed of the Cassini spacecraft may be found on the "Present Position" page at: http://saturn.jpl.nasa.gov/mission/presentposition/
Wednesday, June 16 (DOY 167)
At a NASA Honor Awards ceremony at JPL last week, two members of the Cassini Flight team were honored with NASA medals, one the Exceptional Achievement Medal, and the other the Exceptional Service Medal.
The Cosmic Dust Analyzer (CDA) V10.0.4 flight software checkout sequence, which was uplinked last Friday, began execution today.
Port 2 Spacecraft Activity Sequence Files were delivered today as part of the S64 Sequence Implementation Process.
Five instrument expanded block files were uplinked to the spacecraft today in support of the S61 sequence. Proper receipt and registration of all files has been confirmed.
Cassini is once again Astronomy Picture of the Day (APOD). Actually, Cassini is "in" Astronomy Picture of the Day. In celebration of APOD's 15th anniversary, a picture was posted consisting of over 5,000 APOD pictures from the last 15 years. By zooming in, each individual "pict-xel" and the picture in it can be seen. At least three Cassini images are part of the composite. To go to the image, link to: http://antwrp.gsfc.nasa.gov/apod/ap100616.html
Thursday, June 17 (DOY 168)
Orbit Trim Maneuver (OTM) #253 was performed today. This was the approach maneuver setting up for the Titan 70 encounter on June 20. The reaction control subsystem burn began at 8:29 PM PDT. Telemetry immediately after the maneuver showed a burn duration of 18.875 seconds, giving a delta-V of 0.025 m/s. All subsystems reported nominal performance after the maneuver.
The final handoff package of the Equinox Mission was transferred to Uplink Operations today as the final step in the Science Operations Plan process for S63. The kickoff meeting for the last development process for S63 is scheduled for next Tuesday.
All teams approved S61 for uplink to the spacecraft today at the sequence approval meeting. The background sequence is scheduled for radiation on June 21.
As part of the Postdoc Seminar Series at JPL, a presentation was given today on The Enceladus Torus, Saturn's Vaporous "Ring." In addition to Saturn's well-known rings, the kind made of solid material, there is another sort of ring made of gas. Saturn's "torus" seems to come from two main sources: water vapor from Enceladus' plumes and H from Saturn's upper atmosphere. The water vapor torus was discovered via hydroxide detection in the early '90s, but Cassini's detection of an atomic oxygen component prompted scientists to revisit the problem. The torus, it turned out, was much wider than previously thought, with atomic oxygen detected out to 25 RS. Part of this presentation described the various processes that may be responsible for the breadth of the cloud, and in particular how collisions among the torus molecules are key to the expansion. More broadly, it was described how Saturn's torus resembles an astrophysical accretion disk and why collisions constrain, rather than expand, Saturn's main rings.
Cassini will take its lowest dip through the atmosphere of Titan in the evening of June 20. Titan's atmosphere applies torque to objects flying through it, much the same way the flow of air would wiggle your hand around if you stuck it outside a moving car window. Cassini mission planners and engineers at the NASA Engineering and Safety Center in Hampton, Va., have analyzed the torque applied by the atmosphere in detail to make sure the spacecraft can fly safely at an altitude of 880 kilometers above the surface. For the full details of this feature link to: http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20100617/
Friday, June 18 (DOY 169)
Sun Sensor Assembly (SSA) B was powered on and the Main Engine cover was closed today for a potential dust hazard on June 19. The SSA will be powered off via real time command and the main engine cover opened on June 20.
The Radio Science and Cassini Plasma Spectrometer (CAPS) Saturn occultation Live Movable Block began execution today.
A non-targeted flyby of Rhea occurred today, and non-targeted flybys of Pan and Polydeuces will occur Saturday, June 19.
Just before the Titan 70 flyby, Radio Science (RSS) took center stage on June 18 and 19 with ansa-to-ansa ring occultation observations spanning the entire ring system on ingress and egress. RSS also observed the occultation of Earth by Saturn's ionosphere and atmosphere on ingress & egress to measure vertical profiles of electron density in the ionosphere, and of density, pressure, and temperature in the neutral atmosphere.
CAPS led pointing for the Magnetospheric and Plasma Science rings and satellite campaign observations to study the interaction between the magnetospheric hot ion and electron distributions, rings, and icy satellites. The goal was to measure properties of a statistically significant number of satellite L shell crossings distributed among the satellites, and in longitudinal distance from the satellites.
Sunday, June 20 (DOY 171) On June 20, Cassini flew by Titan at an altitude of 880 km, the closest encounter with Titan to date, at a speed of 5.9 km/sec. T70 closest approach occurred at 7:44pm PDT, latitude 82 degrees N. The spacecraft Inertial Reference Unit-B and the Accelerometer were powered on for a couple of hours around the flyby. Due to the low altitude, an extra 2-hour DSN pass was added to capture near real-time telemetry at closest approach. The High Gain Antenna-to-Earth flyby attitude allowed flight team members to acquire 27 minutes of real-time engineering data and confirm that the flyby was as expected. The real-time data and the playback data showed higher than expected thruster firings, possibly indicating that higher than predicted atmospheric density was encountered. Data analysis will be ongoing for the next few weeks. It was possible to receive this real time telemetry because the minimum torque attitude, necessary to go as low as 880 km, was almost the same as the High Gain Antenna to Earth attitude. In a blog post entitled, "Super Swooper: Cassini wraps up its lowest pass through Titan atmosphere," the Cassini Spacecraft Operations Team manager talks about sitting on the edge of her seat during the lowest dip through the atmosphere and keeping an eye on her computer screen. Her post may be seen at http://blogs.jpl.nasa.gov/?p=66
T70 was the Titan flyby in Extended Mission with the highest priority for the Magnetometer (MAG). The measurements obtained by MAG will provide important pieces of evidence in favor or against the presence of an internally generated magnetic field.
For this flyby the Ultraviolet Imaging Spectrograph (UVIS) performed a stellar occultation on the outbound leg from Titan. Occultations are the most valuable Titan observations for UVIS because they provide detailed vertical profiles of nitrogen in the extreme ultraviolet channel during solar occultation, and of hydrocarbons, hydrogen cyanide, and aerosols in the far ultraviolet channel during stellar occultations. These profiles probe altitudes between 300 km and 2400 km, which fill the gap between the Composite Infrared Spectrometer (CIRS) and Ion and Neutral Mass Spectrometer measurements. Much of the chemistry and aerosol formation occurs in this vertical region. Observations taken over the course of the mission will collectively provide coverage at many latitudes and local times and these will be used to study meridional and local variations in the upper atmosphere. Knowledge of these variations is important for understanding the meridional circulation and other dynamical and chemical processes. This experiment was self-calibrating. The information came from a ratio of signal during occultation to signal of the unocculted sun or star just before or after occultation.
The Visual and Infrared Mapping Spectrometer (VIMS) rode along with UVIS just after closest approach for the stellar occultation, then obtained data for a mosaic of Adiri at 20 km per pixel. Imaging Science (ISS) rode along with VIMS to observe Adiri at moderate resolutions, and monitored Titan to track clouds and their evolution for an extra two days after the Titan encounter.
The Radio and Plasma Wave Science instrument measured thermal plasmas in Titan's ionosphere and surrounding environment, searched for lightning in Titan's atmosphere, and investigated the interaction of Titan with Saturn's magnetosphere
Monday, June 21 (DOY 172)
The S61 background sequence was uplinked to the spacecraft today. It has been confirmed to be onboard and registered. The sequence will begin execution on Friday, June 25.
Tuesday, June 22 (DOY 173) The Science and Sequence Update Process for S63, the final sequence in the Equinox Mission, kicked off today. The process will run for approximately 11 weeks and conclude in early September.
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