Cassini Significant Events 09/12/07 - 09/18/07

September 21, 2007

(Source: Cassini Project)

The most recent spacecraft telemetry was acquired on Tuesday, Sept. 18, from the Madrid 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

Wednesday, Sept. 12 (DOY 255):

The official port for the S36 Science Operations Plan Update process occurred today. The products were merged and reports delivered to the teams and AACS for end-to-end pointing analysis. This process completes on Friday, Sept. 28.

At the end of the Significant Events report from last week it was stated that the flight team had just held an anomaly resolution meeting, and had selected a plan for recovery of the instruments and the background sequence. The Solid State Power Switch (SSPS) trip on TWTA-B last week was the first switch trip since Nov. 26, 2006. The SSPSs are susceptible to Galactic Cosmic Rays, and trips are predicted to occur at a rate of about two per year. Cassini has now had 21 such trips in 10 years of flight since launch. This particular trip caused a loss of power to a Traveling Wave Tube Amplifier (TWTA), subsequent RF loss, a call to System Fault Protection (SFP), and put the spacecraft in "safe mode".

On Tuesday of last week, as soon as the SSPS trip had been confirmed as the cause of SFP execution, real time commanding was begun to initiate the process of putting the spacecraft back in a nominal operational configuration, and to play back the remaining on-board Iapetus data.
On Wednesday, Sept. 12, commands were sent to power on the Visual and Infrared Mapping Spectrometer (VIMS) and its supplemental heater. This was followed by commands to prepare the spacecraft to execute OTM-128.

Thursday, Sept. 13 (DOY 256):

Orbit Trim Maneuver (OTM) #128 was performed today. This is the cleanup maneuver from the Iapetus encounter on Sept. 10. The main engine burn began at 12:44 PM PDT. Telemetry immediately after the maneuver showed the burn duration was 83.4 seconds, giving a delta-V of 13.48 m/s. All subsystems reported nominal performance after the maneuver.

This OTM was performed before the spacecraft had been fully reconfigured after safing, without a background sequence running. Real time commands were uplinked to set up the initial and final conditions for the burn. Because the reaction wheels (RWA) had been turned off by safing, thrusters were used for both the roll and yaw turns before the OTM. Usually rolls are on RWAs and yaws are on thrusters for a Main Engine maneuver. The OTM block turned the RWAs on following the burn.

Normal operations continued on the ground with meetings being held for an S39 Engineering Activities Review, and a Simulation Coordination meeting for S35. The SIM coordination meeting is for a test of the Titan 38 flyby sequence. AACS requested a test to examine the low altitude flyby on reaction wheels to verify uncertainties in the RWAs and to validate the Kinematic Prediction Tool and Flight Software Development System testing.

Friday, Sept. 14 (DOY 257):

With OTM-128 having been successfully executed, commands were sent to swap from TWTA-A back to TWTA-B. The TWTA RF Loss algorithm causes hardware swaps in both the Telemetry and Command Units and the TWTAs. The swap was successful and the spacecraft is now operating normally on TWTA-B.

At this point the instruments and background sequence are still "off."

On the ground, work continued on the proposed Extended Mission. The second set of Cassini Information Management System extended mission inputs was delivered today. Requests for observations, spacecraft activities, downlinks, OTMs, etc., were submitted for orbits 80 through 102. The Target Working Teams will begin working these segments next week to smooth out conflicts where they occur.

An image of Iapetus is Astronomy Picture of the Day today.

Saturday, Sept. 15 (DOY 258):

Commands were sent to prepare the background sequence for activation, the instruments were powered on, and instrument team members reported that they were ready for the next step.

A 3-D image of Iapetus' equatorial ridge was Astronomy Picture of the Day today.

Sunday, Sept. 16 (DOY 259):

The S33 background sequence was reactivated on Sunday at 259T21:09:36 SCET. Science activities resumed with imaging and Visual and Infrared Mapping Spectrometer Saturn southern hemisphere movies and an Iapetus global color observation, an Ultraviolet Imaging Spectrograph calibration and Saturn mosaic, and the acquisition of some optical navigation images. The spacecraft and instruments have now resumed normal operations.

Monday, Sept. 17 (DOY 260):

Orbit Trim Maneuver (OTM) #129 was performed today. This is the apoapsis maneuver setting up for the Titan 36 encounter on Oct. 2. The reaction control subsystem burn began at 12:45pm PDT. Telemetry immediately after the maneuver showed the burn duration was 79.0 seconds, giving a delta-V of 98.5 mm/sec. All subsystems reported nominal performance after the maneuver.

Command and Data Subsystem (CDS) flight software (FSW) V10 final end-to-end testing was completed Sept. 12. The Software Requirements Certification Review for this FSW was held Sept. 13, and the Uplink Readiness Review was completed today. The uplink to the solid-state recorder is planned for Sept. 24 - 26. Activation and checkout of V10 on-board the spacecraft will start the week of Oct. 7.

The Science Operations Plan Update process for S37 kicked off today. The preliminary port is scheduled for Oct. 2, with the process completing on Oct. 27.

Tuesday, Sept. 18 (DOY 261):

After a delay of one day due to the safing event last week, sequence leads for S34 began uplinking Instrument Expanded Block (IEB) files today in preparation for the start of execution of the sequence on Sept. 22. The remaining IEBs go up tomorrow and the S34 background sequence - part A - will go up on Thursday.

S34 is unique in that it is divided into four parts to allow for the uplink and checkout of the CDS V10 flight software while accommodating as much science as possible, including a Hyperion flyby, around the CDS activities. The final approval meeting was held today for parts A and B of the sequence along with the Hyperion mini-sequence. The CDS activities following part A are performed independent of the background sequence via real time commands. One open issue still to be addressed for S34 is what possible options to pursue if the DAWN project reschedules launch from Sept. 26.