Cassini Significant Event Report

For Week Ending 05/08/98

Spacecraft Status:


The Cassini spacecraft is presently traveling at a speed of approximately 145,000 kilometers/hour (~90,000
mph) relative to the sun and has traveled approximately 580 million kilometers (~359 million miles) since
launch on October 15, 1997.


The most recent Spacecraft status is from the DSN tracking pass on Wednesday, 05/06, over Goldstone.
The Cassini spacecraft is in an excellent state of health and is executing the C7 sequence nominally. 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, 05/01, part two of Solid State Recorder (SSR) Flight Software Partition maintenance was
performed. Part one occurred on 04/28 as part of the background sequence. This activity repaired SSR
double bit errors (DBEs) which had occurred in the code-containing portions of the Flight Software partitions
during the preceding period. Friday's real-time command based portion of the activity cleared telemetry flags
and sent down the results of the maintenance activity.


The Reaction Wheel Assembly Exercise also occurred on Friday, as planned.


On Saturday, 05/02, data from the Radio Plasma Wave Subsystem (RPWS) Venus-1 activity was
successfully played back. A separate news release will detail the results of the RPWS experiment.


On Sunday, 05/03, data from the Radar Venus-1 engineering test was successfully played back. Results have
confirmed that the RADAR instrument's electronic components functioned end-to-end, which was the
objective of the test.


Also on Sunday, the Attitude and Articulation Control Subsystem Inertial Vector Propagation (AACS IVP)
vector update was successfully performed. This update is a maintenance activity, performed as needed based
on the geometry of the trajectory.


On Tuesday, 05/05, the Solid State Recorder 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, 05/06, the first portion of the Stellar Reference Unit-A (SRU-A) decontamination activity
was performed. Part one of the activity involves powering a heater attached to the SRU radiator for a period
of time, inducing volatilization of any contaminants which may have accumulated on the radiator since Launch.
The temperature profile followed in the SRU-A decontamination was very similar to that followed by SRU-B
which was decontaminated in mid-March. Part two of the activity will be performed on Friday, May 8, and
will involve collecting a test star image and powering down SRU-A.


Also on Wednesday, the C8 background sequence was successfully uplinked to the spacecraft. The C8
sequence begins on Sunday afternoon, May 10.


On Thursday, 05/07, there were no changes in spacecraft configuration.


Upcoming events:


Activities scheduled for the week of 5/08 - 5/14 include: completion of SRU-A decontamination activity and
turn-off of RPWS instrument (5/08), an SSR Pointer Reset and AACS Attitude Estimator readout (5/11),
and an SSR Pointer Reset and SSR Flight Software Maintenance (5/13). As noted in last week's report, the
Trajectory Correction Maneuver originally scheduled for 5/14 was cancelled due to excellent Navigation
during Venus-1 flyby.


DSN Coverage:


Over the past week Cassini had 9 scheduled DSN tracks, occurring from 05/01 through 5/07. In the coming
week there will be 6 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.


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