Cassini Significant Events
06/18/08 - 06/23/08
The most recent spacecraft telemetry was acquired on June 23, from
the Madrid, Spain tracking complex. 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, June 18 (Day of Year (DOY) 170)
AACS is continuing to investigate the significant change in RWA-2
friction test results. This has not affected any overall pointing or
other spacecraft performance to date.
The third and final delivery port of the S44 Science Operations Plan
process occurred today. All files have been received from teams
participating in this sequence. The process will complete on July 7,
when products will be handed over to Uplink Operations for the final
development process. Tomorrow, files will be delivered for port 2
of the S45 process.
Thursday, June 19 (DOY 171)
Part 2 of the S41 background sequence began execution on board the
spacecraft today at 9:47 p.m. PDT.
A kickoff meeting was held today for the fifth and final Live Update
of S41. Science Planning analyzed current targeting based on the
orbit determination solution that the Navigation Team released for
Orbit Trim Manuever (OTM) 59. As a result, the vectors for Saturn,
Enceladus, Janus, Mimas and Tethys on DOY 182 will be updated for six
separate observations. Imaging Science (ISS), the Composite Infrared
Spectrometer (CIRS) and Ultraviolet Imaging Spectrograph (UVIS) have
concurred with the analysis and what will receive an update. The
current plan is to approve the files at a Command Approval Meeting
(CAM) on June 27, and uplink them that same day.
ISS begins observations on DOY 171 by conducting a photometric
stellar calibration. As the spacecraft approaches apoapse, ISS
images Saturn atmospheric dynamics using the narrow- and wide-angle
cameras. Meanwhile, Magnetospheric and Plasma Science (MAPS) teams
add more data to their ongoing campaign to image the dynamics of
Saturn's inner magnetosphere.
Uplink Operations sent commands to the spacecraft today for a Radio
and Plasma Wave Science (RPWS) change from two-antenna to
three-antenna direction finding in survey modes that will execute on
Sunday, and the Radio Science (RSS) Live Movable Block Saturn
Occultation Egress file for execution on Monday. Tomorrow, files
will be sent for the DOY 173 Live Inertial Vector Propagator Update
for Saturn/Tethys, and for OTM-159.
Monday, June 23 (DOY 175)
Non-targeted flybys of Methone and Pan occurred today.
DOY 175 was a very busy day on the spacecraft. It began with the
MAPS instruments performing an auroral crossing experiment. In
high-inclination orbits, such as Cassini's current orbit, the
spacecraft has an opportunity to sample the plasma environment near
Saturn's auroral regions near the poles. Furthermore, this auroral
crossing took place during a spacecraft downlink over the Canberra's
70-meter station. The convergence of a favorable geometry and a
70-meter downlink allowed MAPS instruments, such as RPWS and the
Cassini Plasma Spectrometer, to collect and downlink data at a very
high rate.
The auroral crossing and downlink was briefly interrupted by the
execution of OTM-159. After the maneuver, the spacecraft slewed back
to an Earth-pointed orientation and set up for an RSS Saturn
Occultation. This was the last RSS observation the Cassini Prime
Mission. A Saturn occultation occurs when Saturn blocks the Earth,
as viewed from the spacecraft. This unique geometric configuration
allows RSS to measure Saturn's atmosphere and ionosphere by
continuously sending a radio signal to Earth and measuring changes in
the signal as it passes through Saturn's atmosphere and ionosphere.
While this was going on, the MAPS instruments continued their
auroral-crossing investigation. This was possible because the
spacecraft's orientation allowed it to point the radio transmitter
toward Earth and rotate around the transmitter axis to point the MAPS
instruments at Saturn at the same time.
OTM-159 was performed today. This was the periapsis maneuver setting
up the Titan- 45 encounter on July 29. The Main Engine burn began at
12:45 a.m. PDT. Telemetry immediately after the maneuver showed the
burn duration was 73.5 seconds, giving a delta-V of 12.2 meters per
second. All subsystems reported nominal performance after the
maneuver. Due to the size of this maneuver, and the large costs of
delta V if it were to be executed over the backup pass, the decision
was made to uplink the files early to provide additional uplink
windows should the need arise.
After the successful execution of OTM-159, the main engine cover was
cycled for the 40th time since launch. It was closed to provide
protection from dust hazards that would occur that day, and on June
30, July 7 and July 14. The cover will be opened again on July 21.
At that point, it will have been closed for 25 days.
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