From: Jet Propulsion Laboratory
Posted: Tuesday, October 21, 2008
The most recent spacecraft telemetry was acquired on Oct. 14 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/operations/present-position.cfm.
Wednesday, Oct. 8 (DOY 282):
Port 2 spacecraft activity sequence files for the S48 sequence were delivered today as part of the Science Operations Plan development process. The merged products and Science Planning (SP) assessment will be released tomorrow.
Cassini is currently in a part of Extended Mission that is proving to be a challenge for the flight team. From the Navigation (NAV) perspective, the Enceladus 6, Titan 46 combination is unique even among the existing three double flybys. It is almost a pi-transfer from E6 ~periapsis to T46 ~ apoapsis, but without a maneuver in between. From a science perspective, Radio Science (RSS) made the case that Titan must be targeted, rather than Enceladus, due to attitude and timing sensitivity of the occultation and bi-static experiments at closest approach. The Inertial Vector Definition (IVD) pointing designs for RSS are built into the S45 background sequence and cannot be updated at this late stage. On the other hand, it has been pointed out that E6 presents the last opportunity for lit viewing of the tiger stripes and the "skeet shoot" planned by Imaging Science (ISS) is unique in its implementation.
After some discussions between NAV, SP, and Uplink Operations (ULO), it looks like performing a live Inertial Vector Propagator (IVP) update for E6 pointing vectors can be accommodated. This allows NAV to continue targeting to T46 and gives some amount of flexibility to E6 instrument pointing.
The current best-available prediction using the orbit determination (OD) solution following Orbit Trim Maneuver (OTM) #166 shows the E6 flyby altitude is 15 km lower and occurs 0.26 sec later than on the trajectory for which the observations were designed. The actual live update will use a special OD released by NAV on Monday, Oct. 20. The first uplink window for the update is on Oct. 28. That gives the team eight days - including weekends - to obtain the OD, and analyze the product to determine if an update is indeed necessary. If so, they will need to build the products updating vectors for near closest approach, have them approved, and get them on the spacecraft in time for the E6 flyby on Halloween, Oct. 31.
For more information on pi-transfers and the "skeet-shoot" technique used by ISS, look up the Cassini Significant Events Reports covering Sept. 14, 2006, and Aug. 15, 2008.
Thursday, Oct. 9 (DOY 283):
Non-targeted flybys of Telesto and Janus occurred today. On Thursday the spacecraft encountered Enceladus for the E5 targeted flyby at an altitude of only 25 km, making it the closest flyby of the Cassini mission. Closest approach occurred at approximately 12:31 PM PDT, at a speed of 17.7 km/sec, latitude 28 degrees S, and longitude 97 degrees W. Just 29 seconds after closest approach, Cassini flew directly over the South Pole at an altitude of 339 kilometers. The flyby focused on Magnetosphere and Plasma Science (MAPS) instruments that sniffed and tasted the composition of the icy plumes emanating from the southern pole of Enceladus. See the Enceladus E5 mission description for full details of the science activities occurring during the flyby: http://saturn.jpl.nasa.gov/multimedia/products/mission_descriptions.cfm
Friday, Oct. 10 (DOY 284):
Following the E5 flyby, Spacecraft Operations (SCO) performed a checkout of Sun Sensor Assembly #B as part of normal maintenance.
The Main Engine (ME) cover was opened on October 10, 2008. This was cycle #47.
Beginning today, Cassini outreach will be at the Division of Planetary Sciences conference at Cornell University, Ithaca, NY, supporting outreach activities for that week-long event. Cornell University's Herbert F. Johnson Museum of Art is currently featuring Spectacular Saturn: Images from the Cassini-Huygens Mission, on display from September 20 through January 4. This exhibit displays over fifty images of the planet Saturn, its rings, and satellites. Image selection, by Cornell members of the Cassini project, was made from almost two hundred thousand images that have been transmitted to Earth since the Cassini spacecraft arrived at Saturn in 2004. A 1/10th scale model of the Cassini spacecraft is also on view as well as historical books about Saturn from the Kroch Rare Book and Manuscript collection. The exhibit will next travel to the Smithsonian Air and Space Museum in Washington, D.C. where it will appear until May 2009.
Following the Enceladus flyby, the spacecraft spent nearly 13 hours today at Earth-point to downlink the science data collected during the flyby. During the downlink, SCO opened the main engine cover in preparation for the upcoming OTM-167, and RSS used the time at Earth point to acquire Ka-band frequency data for improving Saturn gravitational field models, as well as performing an Operations Readiness Test (ORT) to demonstrate DSN and RSS preparedness to support the orbit 89 rings occultation experiment on DOY-291. Friday concluded with the Ultraviolet Imaging Spectrograph (UVIS) turning back toward a fleeting Enceladus to map the particle composition of the E ring in the immediate vicinity of Enceladus. These observations will test the connection between changes in the E rings and plume eruptions.
Saturday, Oct. 11 (DOY 285):
SCO and ULO uplinked commands today for OTM-167, to clear the on-board error logs, and install Instrument Expanded Block (IEB) files for ISS and VIMS in support of S45. The final approval meeting for S45 is scheduled for Oct. 14, and execution begins on Saturday, Oct. 18. The remaining seven IEB files will be uplinked on Monday, Oct. 13.
Sunday, Oct. 12 (DOY 286):
The imaging team had control of the spacecraft for all of Sunday, performing a variety of activities. Observations began with a continuation of the long ring spoke movie from the previous day, and narrow angle camera small satellite images for orbital determination. Next was a coordinated Optical Remote Sensing (ORS) activity of Tethys observations for longitudinal and phase angle coverage. The cameras then pointed toward the rings for long term temporal monitoring of the F ring. This was followed by a short one-hour activity continuing coverage for small satellite orbital determination. The last imaging activity on Sunday was a coordinated ORS observation of Dione for longitudinal and phase angle coverage.
Before the day was finished, the spacecraft turned toward Earth to play back science data to Canberra stations. During the downlink, the flight team performed Orbit Trim Maneuver #167. This was the cleanup maneuver from the Enceladus 5 encounter on Oct. 9. The main engine burn began at 6:15 PM PDT. Telemetry immediately after the maneuver showed the burn duration was 20.04 seconds, giving a delta-V of 3.33 m/s, as planned. All subsystems reported nominal performance after the maneuver.
Monday, Oct. 13 (DOY 287):
A close-up image of Enceladus was Astronomy Picture of the Day today. Check it out at: http://antwrp.gsfc.nasa.gov/apod/ap081013.html
New images from Cassini reveal a giant cyclone at Saturn's north pole, and show that a similarly monstrous cyclone churning at Saturn's south pole is powered by Earth-like storm patterns. The new-found cyclone at Saturn's north pole is only visible in the near-infrared wavelengths because the north pole is in winter, and thus in darkness to visible-light cameras. For the complete story go to: http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=876
Cycle #48 of the Main Engine (ME) cover began today when it was closed at the end of the OTM-167 backup uplink window for a dust hazard coming up on Oct. 17. It will be reopened on the 17th after the hazard has passed and before the OTM-168 prime uplink window.
Tuesday, Oct. 14 (DOY 288):
An AACS Reaction Wheel Assembly (RWA) friction test for prime wheels number 1, 2 and 4 was executed Oct. 14. In this test, performed every three months, the RWAS are normally spun up to 900 rpm in both directions and timed as they are allowed to spin down to 0 rpm. This time the coast down was started at +/-1200 rpm. This was in response to the last friction test, performed June 18, where RWA-2 had a significant worsening in the run-down time. This change should start the rundown outside of the drag torque spike area, enabling a clean viscous friction coefficient measurement, which was impossible with the observed drag torque spikes, and redistribute the lubricant. SCO will be analyzing the results this week.
Another beautiful close-up image of Enceladus, showing detail of one of the tiger stripes, was Astronomy Picture of the Day today. Check it out at: http://antwrp.gsfc.nasa.gov/apod/ap081014.html
Visit the JPL Cassini home page for more information about the Cassini Project: http://saturn.jpl.nasa.gov/
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