Cassini Significant Event Report
For Week Ending 03/13/98
The Cassini spacecraft is presently traveling at a speed of approximately 141,000 kilometers/hour (~88,000
mph) relative to the sun and has traveled approximately 392 million kilometers (~244 million miles) since
launch on October 15, 1997.
The most recent Spacecraft status is from the DSN tracking pass on Thursday, 03/12, over Canberra. The
Cassini spacecraft is in an excellent state of health and is operating nominally, with the C6 sequence executing
onboard. The speed of the spacecraft can be viewed on the "Where is Cassini Now?" web page (http://saturn.jpl.nasa.gov/operations/present-position.cfm)
Inertial attitude control is being maintained using the spacecraft's hydrazine thrusters (RCS system). The
spacecraft continues to fly in a High Gain Antenna-to-Sun attitude. It will maintain the HGA-to-Sun attitude,
except for planned 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. The downlink telemetry rate is
presently 40 bps.
Spacecraft Activity Summary:
On Friday, 03/06, CDS String Reset Counters were re-initialized as part of preparations for a future CDS
Also on Friday, an SSR Partition Repair activity was performed to clear three non-software region double bit
errors (DBEs). Friday's activity cleared two of the three. Results indicated that the spacecraft has experienced
its first "stuck" SSR memory bit, as evidenced by the inability to successfully clear the DBE by writing over it.
The stuck bit is located in an unused section of memory and, as such, does not pose a problem. New DBEs
which occur in the affected SSR submodule can still be cleared with already existing procedures. If the bit had
been located in a portion of memory which contains flight software, the unusable spot would be marked as
such and "skipped over" in the future - a capability designed into both ground and flight software during the
design phase of the Program. (It should be noted that such "stuck" bits were predicted to occur in the Solid
State Recorder, based on pre-Launch radiation effect studies. This expectation is what led to writing the
appropriate ground and flight software pre-Launch to deal with the phenomenon.)
From Saturday, 03/07, through Monday, 03/09, there were no changes in spacecraft configuration.
On Tuesday, 03/10, 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.
On Wednesday, 03/11, the Cruise 6 sequence auto-deregistered, on schedule, when its final command
executed on the spacecraft.
On Thursday, 03/12, AACS Fault Protection Log Maintenance was performed, as scheduled. Also on
Thursday, the C7 sequence was uplinked to the spacecraft.
Events for the week of 03/13 through 03/19 include: turning off of the VIMS Infrared Optics decontamination
heaters (03/15), uplink and execution of the SRU-B Decontamination Mini sequence (03/17 - 03/18), and
SSR FSW Partition Maintenance (03/18). The C7 sequence will begin executing on Sunday, 3/15/98, at 4pm
local Pacific time.
Over the past week Cassini had 8 DSN tracks occurring daily from Friday (03/06) through Thursday
(03/12). In the coming week there will be 9 DSN passes.
Additional information about Cassini-Huygens is online at http://saturn.jpl.nasa.gov.
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.