Cassini Significant Events 10/08/08 - 10/14/08
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
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