Significant Event Report for Week Ending 1/23/1998

Cassini Significant Event Report

For Week Ending 01/23/98

MSO Significant Events input for week of Friday 01/16 through Thursday 01/22:

Spacecraft Status:

The Cassini spacecraft is presently travelling at a speed of approximately
116,000 kilometers/hour (~72,000 mph) and has travelled approximately 241
million kilometers (~151 million miles) since launch last October 15.

The most recent Spacecraft status is from the DSN tracking pass on Thursday,
01/22, over Madrid. The Cassini spacecraft is in an excellent state of health
and is operating nominally. The C5 sequence activities concluded Saturday, 01/
17. The C6 sequence is now executing onboard the spacecraft. 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 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. The downlink telemetry rate is presently 40 bps.

Spacecraft Activity Summary:

On Friday, 01/16, 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 Saturday, 01/17, the downlink telemetry rate was decreased from 948 bps to 40
bps.

Also on Saturday, the AACS BAIL Maintenance activity was executed for the first
time. The AACS BAIL software is stored on EEPROMs for the purpose of providing
basic AACS capabilities for use in the recovery from a deep undervoltage
anomaly. The BAIL maintenance, planned every 3 months, is intended to detect
and repair any Single Bit Errors (SBEs) that may have occurred on the EEPROMs in
the preceeding period. The activity will also identify, but not repair, any
Double Bit Errors (DBEs); DBEs would then be repaired by further ground
commanding at a later time. Saturday's activity was successful and, in fact,
determined that no SBEs or DBEs have occurred on the EEPROMs. (This activity is
similar to the SBE scrub/DBE detection done by CDS flight software on the Solid
State Recorders.)

From Sunday, 01/18, through Tuesday 01/20, there were no changes in spacecraft
configuration.

On Wednesday, 01/21, the Periodic Instrument Maintenance activity executed, as
planned. This activity is carried out every three months by 11 of the 12
Orbiter instruments. All participating instruments reported the successful
execution of their maintenance activities.

Also on Wednesday, a maintenance activity was performed on the SSR Flight
Software Partitions. This activity, previously performed by real-time
commanding, has now been incorporated into the stored sequence (presently C6).
The activity is scheduled to occur approximately every two weeks. It will
repair any SSR DBEs which have occurred in the code-containing portions of the
Flight Software partitions during the preceeding period. Telemetry from
Wednesday's activity confirmed that exactly one DBE existed on each SSR and that
they were successfully repaired.

On Thursday, 01/22, the Solid State Recorder (SSR) record and playback pointers
were reset, according to plan.

Upcoming spacecraft events:

Events for the week of 01/23 through 01/29 include: a reset of the SSR pointers
(01/28), the unlatch of the Articulated Reaction Wheel Mechanism (ARWM) (01/29),
and an update of the active vector in the Inertial Vector Table (01/29).

DSN Coverage:

Over the past week, Cassini had 4 track periods, (01/17 crossing over to 01/18)
and (01/21 crossing over to 01/22). In the coming week, there will be 4 DSN
passes, Sunday (01/25), and Tuesday through Thursday (01/27 - 01/29).

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.

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