Cassini Significant Event Report

For Week Ending 04/10/98

Spacecraft Status:


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 485 million kilometers (~300 million miles) since
launch on October 15, 1997.


The most recent Spacecraft status is from the DSN tracking pass on Thursday, 04/09, over Canberra. 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 except during the Probe Checkout #2 data playback over specially requested 70m passes.


Spacecraft Activity Summary:


Orbiter:


On Friday , 04/03, the third of seven sequenced data playbacks occurred for Huygens Probe Checkout #2.
The Probe checkout activity occurs approximately every 6 months. The series of data playbacks from the
SSR will provide detailed information on the results of the checkout.


On Saturday, 04/04, the fourth data playback occurred for Probe Checkout #2.


On Sunday, 04/05, the fifth data playback occurred for Probe Checkout #2.


On Monday, 04/06, 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.
Additionally, the sixth data playback occurred for Probe Checkout #2.


On Tuesday, 04/07, the seventh data playback occurred for Probe Checkout #2.


On Wednesday, 04/08, a partition copy maintenance activity was performed to fix two double bit errors that
are not in code-containing portions of the SSR Flight Software Partitions.


Also on Wednesday, a mini-sequence to perform an eighth data playback for Probe Checkout #2 was
uplinked. This playback was requested by the Huygens Probe Operations Centre to assist in the ongoing
evaluation of the drop in the Probe Umbilical AGC measurements. The playback occurred on Thursday,
04/09, and returns the 10 seconds out of each minute of recorded Probe telemetry for that part of the
Checkout data that has not already been played back.


Huygens Probe:


ESA has formed a team to examine the umbilical AGC data reported last week. The team
will meet on 4/16.


Upcoming events:


Activities scheduled for the week of 4/10 - 4/16 include: Periodic Engineering Maintenance (4/10), an SSR
pointer reset (4/11), SSR Flight Software Partition Maintenance (4/14), an SSR pointer reset (4/16), and
Periodic Instrument Maintenance (4/16 into 4/17).


DSN Coverage:


Over the past week Cassini had 13 scheduled DSN tracks occurring from 04/03 through 4/09. 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.


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