Cassini Significant Event Report

For Week Ending 12/12/97

MSO Significant Events input for week of Friday 12/05 through Thursday 12/11:

Spacecraft Status:

Most recent Spacecraft status is from the DSN tracking pass on Thursday, 12/11, over Canberra.

The Cassini spacecraft is in an excellent state of health and is operating nominally. The C5 sequence continues to execute onboard the spacecraft. Early-cruise spacecraft configuration activities are nearly complete.

Inertial attitude control is being maintained using the spacecraft's hydrazine thrusters (RCS system). The spacecraft continues flying in a High Gain Antenna-to-Sun attitude. It will maintain the HGA-to-Sun attitude, except for needed trajectory correction maneuvers, for the first 14 months of flight.

Communication with Earth during early cruise is via one of the spacecraft's two low-gain antennas; the antenna selected depends on the relative geometry of the Sun, Earth and the spacecraft.

Spacecraft Activity Summary:

The 28-day Magnetospheric Imaging Instrument (MIMI) decontamination activity, begun on 11/21, continued nominally through the week.

On Friday, 12/05, the Solid State Recorder (SSR) record and playback pointers were reset, according to plan. This housekeeping activity, done approximately weekly, maximizes the amount of time that recorded engineering data is available for playback to the ground should an anomaly occur on the spacecraft.

From Saturday, 12/06, through Tuesday, 12/09, there were no changes in spacecraft configuration.

Finally on Wednesday, an update of the of RPWS Maintenance Flight Software was successfully uplinked to the SSR. RPWS antenna-deploy software, which was no longer needed, was replaced with RPWS instrument-maintenance software on the prime Solid State Recorder (SSR-B). RPWS Science data collection software was placed on SSR-A. Each SSR now contains identical software in all 4 flight software partitions, providing a prime copy and 3 backup copies of CDS, AACS, and instrument flight software on each SSR. This activity completed the planned SSR software configuration for early cruise.

On Thursday, 12/11, the SSR record and playback pointers were reset, according to plan.

Upcoming spacecraft events:

Events for the week of 12/12 through 12/18 include: continuation of the MIMI decontamination activity, a reset of the SSR pointers (12/17) and the UVIS-only Periodic Instrument Maintenance (PIM) (12/17 through 12/18).

DSN Coverage:

Being past the L+30 point in its mission, Cassini no longer requires continuous DSN coverage. Over the past week Cassini had 4 DSN track periods. In the coming week, there will be 6 DSN passes, portions of which occur each day from Friday 12/12 through Thursday 12/18.

Additional information about Cassini-Huygens is online at

Cassini will begin orbiting Saturn on July 1, 2004, and release its piggybacked Huygens probe about six months later for descent through the thick atmosphere of the moon Titan. Cassini-Huygens is a cooperative mission of NASA, the European Space Agency and the Italian Space Agency. JPL, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Office of Space Science, Washington, D.C.

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