From: Jet Propulsion Laboratory
Posted: Thursday, April 5, 2012
The most recent spacecraft tracking and telemetry data were collected March 14 using the Deep Space Network's 70 meter Station 43 at Canberra, Australia. The Cassini spacecraft is in an excellent state of health. All subsystems are operating normally except for the issues being worked with the Cassini Plasma Spectrometer and the Ultrastable Oscillator. 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/.
There were two Earth-based highlights this week. First, a review with JPL upper management Thursday of a recommendation made by the Cassini Project, the NASA Engineering and Safety Center, and the CAPS instrument team resulted in the decision to proceed with turning the Cassini Plasma Spectrometer (CAPS) back on. (Recall the instrument was turned off last June due to concerns over some problems internal to the instrument and others associated with Radioisotope Thermoelectric Generator #3.) Commands to turn CAPS on were prepared and approved, and will be sent to the spacecraft on March 16.
Second, the Cassini Mission was named the recipient of the top group honor from the Smithsonian's National Air and Space Museum, the Trophy for Current Achievement. Representatives from Cassini will receive the trophy on March 21 at a black-tie dinner in Washington, D.C. The full story appears here: http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20120314/.
Wednesday, March 7 (DOY 067)
The Optical Remote Sensing (ORS) instruments were pointed toward Saturn for the Ultraviolet Imaging Spectrograph (UVIS) and Imaging Science Subsystem (ISS) to measure and monitor the planet's aurorae.
The Sequence Implementation Process leads released Instrument Expanded Block command files in support of the S73 background sequence for the team to review.
The Downlink Ground Systems team set up a second Distributed Object Manager server and a client workstation for testing version A19.0 of the Advanced Multi-mission Operations System.
Thursday, March 8 (DOY 068)
ISS made an observation of Saturn's small irregular moon Jarnsaxa, which is about 6 kilometers in diameter, to characterize its rotation.
A graphic was published today showing Cassini's trajectories for upcoming targeted encounters of the icy moon Enceladus out through October 2015, which will include passes through the icy plumes for in-situ sampling by Cassini's direct-sensing instruments. It also illustrates the previous flybys E-12 through E-16. It can be viewed here: http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=4472
Friday, March 9 (DOY 069)
The small, dark irregular moon Mundilfari, which is about the same size as Jarnsaxa, was ISS's target for characterizing its rotation.
The closest approach to Titan for this orbit of Saturn occured today, a "non-targeted" flyby at a distance of 864,013 kilometers. Titan Monitoring Campaign observations were performed today and will continue over the next few days.
Today's routine communications through the Deep Space Network were interrupted as planned when Cassini turned to use its High-Gain Antenna (HGA) as a shield for two hours while it passed through the potentially hazardous E ring. The backup Sun Sensor Assembly (SSA), whose aperture faces forward through the HGA, was powered on for this event and then back off again when no adverse effects were noted on the prime (or the backup) SSA from the dust hazard.
Saturday, March 10 (DOY 070)
If you noticed the Moon tonight, the creamy-white planet just up to its left was indeed Saturn, 1.33 billion kilometers from Earth.
Cassini passed through Saturn periapsis early today, going by at 68,215 kilometers per hour.
Orbit Trim Maneuver #312 was timed to occur right at periapsis to take advantage of the orbital "leverage" uniquely available there, minimizing propellant use. Firing the main engine provided a delta-V of 3.6 meters per second, targeting to the Enceladus E-17 flyby coming up on March 27. This maneuver was large enough to satisfy the requirement for at least a 5 second burn in any 400 day period for propellant line flushing.
Analysis for the February 6 Y-thruster calibration was completed and documented. Results indicate that thrust mismatches are smaller than 2 percent.
The Attitude and Articulation Control Subsystem (AACS) executed a Reaction Wheel Assembly (RWA) bias maneuver to adjust wheel speeds while Cassini was on Earth point and being tracked by the Deep Space Network.
Cassini took advantage of three sequential non-targeted encounters today and turned the ORS instruments to Enceladus, then to Titan, and then to the large icy moon Rhea. The Rhea observations provided for regional mapping and a search for ring particles. Commands had been sent last week to update instrument pointing for the Rhea observations. See the feature, "Cassini Captures New Images of Icy Moon": http://saturn.jpl.nasa.gov/news/cassinifeatures/feature20120312/
Sunday, March 11 (DOY 071)
UVIS performed an instrument calibration by observing the well-characterized star Spica (alpha Virginis). The Composite Infrared Spectrometer (CIRS) then observed Saturn for 12 hours, measuring oxygen compounds (H2O, CO2) in the stratosphere.
From Cassini's vantage point, Rhea transited in front of Dione while ISS observed for orbit determination purposes.
Following the recent RWA-driven pointing for science data collection, AACS performed another RWA bias maneuver while being tracked from Earth.
Monday, March 12 (DOY 072)
ISS observed a transit of Enceladus across Titan, again for orbit determination purposes. The Cosmic Dust Analyzer (CDA) performed a 13.5 hour observation of dust moving in a retrograde direction about Saturn.
The feature "Cassini Spies Wave Rattling Jet Stream on Jupiter" was published today, based on data collected when Cassini flew by Jupiter in 2000: http://saturn.jpl.nasa.gov/news/newsreleases/newsrelease20120313/
Tuesday, March 13 (DOY 073)
The Magnetometer executed an 8 hour calibration while the spacecraft was rolling about its X-axis.
The Mission Planning Team delivered updates to its software today. One update incorporated a new leap-seconds file into the software. The other corrected a Daylight Saving Time bug in Deep Space Network tracking pass scheduling. A Saturn atmosphere model was delivered for use in spacecraft analyses for the "proximal orbits" planned to begin in 2017. Periapsis for these 6.5-day orbits will be much closer than a spacecraft has ever come to Saturn before - passing between the upper atmosphere and the D ring's inner edge.
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