Cassini Significant Events -- 06/01/06 - 06/07/06

June 9, 2006

(Source: Cassini Project)


The most recent spacecraft telemetry was acquired Wednesday, June 7, from
the Goldstone tracking stations. The Cassini spacecraft is in an excellent
state of health and is operating normally. Information on the present
position and speed of the Cassini spacecraft may be found on the "Present
Position" web page located at
http://saturn.jpl.nasa.gov/operations/present-position.cfm .

Thursday, June 1 (152):

The Science Operations Plan Update process for S24 kicked off today. The
process will continue for approximately five weeks, and then will be handed
off to Uplink Operations for final development.

Friday, June 2 (DOY 153):

A friction test of the backup reaction wheel - number 3 - was completed
today. Unlike the test for the primary wheels, which is performed every
three months, the test for the backup wheel is performed every six months.
The results were unchanged from those obtained in January 2006 and showed no
significant change since early 2004.

After the Monopropellant Tank Assembly recharge performed in April of this
year, ACS and the Navigation team noticed that the ACS Flight Software (FSW)
determination of delta V was always a factor of 1.10 to 1.16 larger than
that of their Navigation counterparts. A review of the pre-launch ground
based thruster test data indicated that at a feed pressure of 400 psia, the
thrusters' tail off time constant is 48.6+or-4.4 msec. ACS FSW had a
thruster tail-off time constant of 65 msec based on the pre-recharge
pressures. A revised tail off time constant of 43 msec instead of 65 msec
could best explain the 1.10 to 1.16-discrepancy factor. To correct the
problem, the spacecraft team uplinked the revised value to the FSW today.

Saturday, June 3 (DOY 153):

The last activity to be performed for S20 was an end of sequence Reaction
Wheel Assembly (RWA) bias. The S21 background sequence began execution on
June 3 at 2006-154T02:39:00. It will run for about 44 days and will
conclude on July 17. The DSN will be supporting Cassini for 48 tracks over
three complexes. Nearly 40% of these tracks will be over 70 meter antennas.
The sequence contains the Titan 15 targeted flyby, four Orbit Trim Maneuvers
(OTM) numbers 63-66, one live update of Hyperion and Enceladus for the
Ultraviolet Imaging Spectrograph (UVIS), Imaging Science Subsystem (ISS) and
Composite Infrared Spectrometer (CIRS), a ring plane crossing, one each Sun
and Earth occultations by Titan, and a dust hazard for 12 minutes on June
30. Watch for the team to close the main engine cover again for this last
event.

The S21 background sequence began with a standard turn to Earth to downlink
data. The first science activity in S21 was a UVIS observation looking for
Saturn Aurorae. This was followed by the Cassini Plasma Spectrometer (CAPS)
taking control of spacecraft pointing, placing it in a unique orientation to
support the Magnetospheric and Plasma Science (MAPS) instruments' study of
the structure and dynamics of Saturn's Magnetotail at low latitudes and
moderate distances downstream. CAPS also performed a series of spacecraft
rolls to allow full spatial coverage for the MAPS instruments.

Monday, June 5 (DOY 156):

The Cosmic Dust Analyzer (CDA) instrument team successfully uploaded their
new version 10.4 FSW to the spacecraft today. FSW checkout is scheduled for
June 13.

Optical Navigation (Opnav) images were scheduled for acquisition today. The
Navigation team using the ISS cameras took images of Saturn's moons against
the background star field to help determine the spacecraft trajectory as
well as the orbits of the satellites. After the Opnavs, UVIS searched for
Saturn Aurorae. The ISS team took a series of images of a unique geometric
event, the transit of one Saturnian moon, Telesto, across another moon,
Rhea. CAPS then became the prime instrument and continued the Saturn
Magnetotail campaign. The day ended with another series of Opnav images.

Tuesday, June 6 (DOY 157):

The Integrated Test Laboratory concluded a test today of CDS partition 5
playback of Ion and Neutral Mass Spectrometer (INMS) and Magnetometer
Subsystem data during the T16 flyby. The final test report is still pending
but so far nothing anomalous has been reported.

At the end of May, a situation arose where it looked like one or more
activities during the S22, Rev 27, Saturn segment might have to be
sacrificed. The issue had to do with spending about six hours in the
region of less than 300 RPM for the reaction wheels between DOY 227-229.
Uplink Operations, Science Planning, Spacecraft Operations and the
scientists working with various instrument team representatives have been
able to reduce significantly the period of concern with the proposal to add
RWA biases during the DOY 227 and 229 downlink tracks and change the initial
downlink secondary attitude on the DOY 229 track. ACS presented the final
proposal to project management today and it was approved without any loss to
the scheduled observations. Many thanks to all who were involved with
solving this problem!

Wednesday, June 7 (DOY 158):

Cassini flight team members were awarded several NASA Honor Awards at a
ceremony held today at JPL. Group achievement awards went to Radar
Instrument Operations and the Radio Science Subsystem teams as well as the
Huygens Ground Doppler and Huygens Probe Earth-Detection Team. The Cassini
Literacy Program also received an award for its Reading, Writing and Rings
literacy program for 1-4th grade students. In addition to the group awards,
several individuals received the Exceptional Achievement Medal at the
ceremony.

Orbit Trim Maneuver (OTM) # 63 was performed today. This apoapse maneuver
sets up for the Titan 15 encounter on July 2. This maneuver fulfills the
requirement of the FR10B52 propellant line flushing flight rule. The main
engine burn began at 5:45 PM PDT. Telemetry immediately after the maneuver
showed the burn duration was 12 seconds, giving a delta-V of approximately
1.9 m/s. All subsystems reported nominal performance after the maneuver.

A Cassini in-reach talk was given today on the Cassini RADAR Observations of
Longitudinal Dunes. The speaker oriented his audience by starting with the
types of dunes seen on Earth and the processes that create them. He then
moved on to what has been observed so far on Titan.





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