Cassini Significant Event Report

For Week Ending 02/20/98

Spacecraft Status:


The Cassini spacecraft is presently traveling at a speed relative to the sun of approximately 131,000
kilometers/hour (~82,000 mph) and has traveled approximately 324 million kilometers (~202 million miles)
since launch last October 15.


The most recent Spacecraft status is from the DSN tracking pass on Thursday, 02/19, over Madrid. 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.


The spacecraft passed through Inferior Conjunction on February 9, with a minimum Sun-Earth-Spacecraft
angle of 4.2 degrees. Because the spacecraft is held in a HGA-to-Sun attitude while in the inner solar system,
the angle from the Earth to the spacecraft's LGA falls farther off the LGA boresight for the several weeks
surrounding this geometric condition. During this period, the Deep Space Net transmitters and the spacecraft
telecom subsystem are configured as necessary to direct signal strength either into Ranging for Navigation or
telemetry for spacecraft health monitoring. The need for this additional management of spacecraft
configuration ended on February 18.


Spacecraft Activity Summary:


From Friday, 02/13 through Tuesday, 02/17, the spacecraft was in the ranging- only (i.e. telemetry off)
configuration with the exception of Saturday, 02/14, when telemetry was turned on for several hours to
acquire a track of data to monitor spacecraft health.


On Sunday, 02/15, 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, updates to spacecraft mass value and RCS thruster parameters were sent to the spacecraft.
These activities were performed as part of standard preparations for Trajectory Correction Maneuver #2,
scheduled for February 25th.


On Thursday, 02/19, there were no changes in spacecraft configuration.


Upcoming spacecraft events:


Events for the week of 02/20 through 02/26 include: a reset of the SSR pointers (02/20), uplink of the TCM
#2 mini-sequence and a reset of the SSR pointers (02/24), execution and playback of the TCM #2
mini-sequence (02/25).


DSN Coverage:


Over the past week Cassini had 11 DSN tracks occurring daily from Friday (02/13), through Thursday
(02/19). One of these was for telemetry-only and eight were for ranging-only. The final two passes of the past
week had both ranging and telemetry, as the geometry of the Inferior Conjunction period is now behind us. In
the coming week, in support of TCM-2, there will be 14 DSN passes.


Letters of Agreement:


Agreements on funding levels and major tasks for each of the 24 scientific investigations, including Program
support for those investigations, have been or are being prepared. Agreement has now been reached and
Letters of Agreement signed for 19 of the 24 investigations. The newest three include the Cosmic Dust
Analyzer, the Cassini RADAR, and the Huygens Surface Science Package investigations.



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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Jet Propulsion Laboratory

California Institute of
Technology


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Administration


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Telephone (818) 354-5011





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