Cassini Significant Events -- for 09/22/05 - 09/28/05

September 30, 2005

(Source: NASA/JPL)


The most recent spacecraft telemetry was acquired Wednesday, September 21,
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, September 22 (DOY 265):

A decision was made today to cancel Orbit Trim Maneuver (OTM) #34.
Originally planned for Friday, September 23, the OTM was determined to be
unnecessary because it wasn't required to stay on tour, and its cancellation
actually resulted in a delta-V savings through OTM-36.

OTM-34 was intended to be the final "targeting" maneuver for the Hyperion
flyby. In place of the OTM, a live update will be performed updating two
instances of the same Hyperion Inertial Vector Propagator (IVP) vector to
adjust the spacecraft pointing to accommodate the slightly different than
planned trajectory. The update will be uplinked to the spacecraft on
Saturday.

Uplink operations sent commands to the spacecraft this evening to perform a
Reaction Wheel Assembly (RWA) bias to adjust the RWA spin rates. This
command is normally included in the OTM mini-sequence. Since the OTM was
cancelled, the commands were sent separately.

Additional files uplinked today included a Live IVP update for Tethys, RADAR
commands in support of the live update, and commands to change the
configuration of the Ion and Neutral Mass Spectrometer after the Hyperion
flyby.

Instrument Operations (IO) Multi-Mission Image Processing Laboratory (MIPL)
personnel supported an optical navigation image downlink designated as
critical, in support of the Hyperion flyby. This involved insuring that the
images got to the Navigation team within 20 minutes of receipt. Special
staffing by both Cassini and multi-mission personnel was used to monitor the
automated system and perform a parallel contingency process. The automated
system again flawlessly delivered the data within minutes.

Friday, September 23 (DOY 266):

Non-targeted flybys of Calypso, Mimas, Prometheus, and Tethys occurred
today. The Tethys flyby was at 1500 km, closer than most non-targeteds.

Amongst the many exciting activities at the end of this week are the two
most hazardous dust crossings of the tour as the spacecraft passes through
the E Ring. Neither of these crossings is considered to be particularly
risky, but they are the two "dustiest" that the spacecraft will experience.
Spacecraft Operations will have Cassini assume a protective attitude by
pointing the High Gain Antenna in the ring particle ram direction and will
command the main engine cover to be deployed or "closed" to protect the
engines.

Cassini's first passive RADAR observations of Saturn's atmosphere are taking
place today near Saturn periapsis, both pre- and post- Tethys flyby. These
observations will probe the deepest atmospheric levels yet.

The Tethys and Hyperion flybys were the subject of a StarDate radio
broadcast today.

Saturday, September 24 (DOY 267):

The new Hyperion live IVP update was uplinked to the spacecraft today. It
will begin execution on DOY 268/2216.

A non-targeted flyby of Titan occurred today.

Sunday, September 25 (DOY 268):

Cassini performed a targeted encounter of Hyperion today. This is the only
close flyby of this satellite in the tour.

Monday, September 26 (DOY 269):

IO/MIPL successfully transitioned to the MIPL D34 Operations system that had
been delivered back in August. To avoid undue disruptions and operational
risk, the implementation date was delayed until after the recent critical
OPNAV images were obtained, after the Tethys and Hyperion fly-bys, and at
the end of a carry-over segment. Besides changing pointers, a hardware
configuration was changed to eliminate two servers in order to lower FY 06
costs.

Science Planning hosted the S18 Science Operations Plan Update process
kickoff meeting.

Cassini Radio Science conducted a Hyperion Mass Determination experiment on
DOY 268-269, Sunday and Monday. This Hyperion targeted flyby was the only
opportunity during the Cassini tour to conduct such an observation. The
observation consisted of two segments: an "inbound" segment, which was
covered by Goldstone's DSS-25 and DSS-26 stations, and an "outbound"
segment, which was covered by Madrid's DSS-55. Hyperion Closest Approach
(C/A) occurred around 269/03:44 ERT/UTC. The first segment completed
approximately 6 hours before C/A, and the second started approximately 1
hour and 45 minutes after C/A.

For the first segment, approximately 2 hours of coherent Doppler X-up/X-down
and X-up/Ka-down were expected, and all data were successfully acquired.
Monopulse was enabled at both antennas throughout the observation, and
performed nominally. A Track Level Compensation (TLC) table, which corrects
for track unevenness, was used at DSS-25. For the second segment, about 1
hour and 20 minutes of coherent Doppler data were expected, but
unfortunately, all data were lost due to a hardware failure at Madrid.
Attempts were made by the station personnel to fix the problem, but up until
the end of the pass, the complex was still down.

Tuesday, September 27 (DOY 270):

The S15 background sequence was given final approval today. The sequence
and associated Instrument Expanded Blocks will be sent to the spacecraft
beginning on October 3.

During today's DSS-14 70m playback of Hyperion data, a telemetry outage
occurred between 16:41:46 and 16:53:50 UTC ERT, during which an outbound
RADAR scatterometry observation was being played back. The data still
exists on board the SSRs, so Mission Planning, Science Planning, SCO, and
the sequence leads are looking into possible options for getting the data
down. UPDATE: It was decided to uplink commands to the spacecraft to move
the SSR-B pointers to enable the team to downlink the data. Those commands
will be sent Thursday. (Actually, as I write this it IS Thursday, so I can
tell you more.) Telemetry indicates that the pointers moved to the correct
location. Now all we have to do is wait for the playback, which won't occur
for a few days.

Wednesday, September 28 (DOY 271):

Orbit trim maneuver #35 (OTM-35) was successfully completed today. This
"cleanup maneuver" both corrects small trajectory errors due to the Saturn
periapsis passage and Hyperion-1 flyby, as well as targets to the moon Dione
for a 500 km altitude flyby on October 11. The reaction control system burn
began at 10:30 am PDT. A "quick look" immediately after the maneuver showed
the burn duration was 321.3 seconds, giving a delta-V of approximately 294
mm/s. All subsystems reported nominal performance after the maneuver.

On Monday of this week, the teams addressed the possible cancellation of
OTM-36. It was determined that if OTM-35 was successful, then OTM-36 would
not be necessary. The current spacecraft trajectory is accurate enough that
the decision was made to go ahead and cancel this maneuver.

A command approval meeting was held today for the eight IEBs to be uplinked
to the spacecraft in support of S15. All were approved to go.

A member of the Cassini Plasma Spectrometer (CAPS) instrument team gave a
Tour Science Talk today. The presentation covered recent CAPS science
results.

A Delivery Coordination Meeting was held for the Maneuver Automation
Subsystem version 5.1.

The S17 Science Operations Plan Update Project Briefing and Waiver
Disposition Meeting was held today. The close-out product is being prepared
for this process and will be handed off to the sequence leads on Friday.
This sequence will now pass on to the Science and Sequence Update Process
that will kick off next Monday.

The Satellite Orbiter Science Team held a Tethys and Hyperion science data
review to discuss the first look at the science data from these flybys and
to discuss the press release plans.