News | February 12, 1998
Significant Event Report for Week Ending 2/13/1998
Cassini Significant Event Report
For Week Ending 02/13/98
MSO Significant Events input for week of Friday, 02/06 through Thursday, 02/12:
The Cassini spacecraft is presently traveling at a speed relative to the sun of approximately 127,000
kilometers/hour (~80,000 mph) and has traveled approximately 302 million kilometers (~188 million miles)
since launch last October 15.
The most recent Spacecraft status is from the DSN tracking pass on Thursday, 02/12, over Goldstone. 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 will end on February 18.
Spacecraft Activity Summary:
On Friday, 02/06, and Saturday, 02/07, the spacecraft was in the ranging-only (i.e. telemetry off)
On Sunday, 02/08, telemetry was turned on to acquire a track of data to monitor spacecraft health. Telemetry
was turned off again prior to the end of the DSN track. This configuration change is being scheduled
approximately twice per week during the ranging-only period surrounding Inferior Conjunction.
On Monday, 02/09, 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 Tuesday, 02/10, and Wednesday, 02/11, there were no changes in spacecraft configuration.
On Thursday, 02/12, a Read-out was conducted of Propulsion Module Subsystem (PMS) Mass Properties.
This activity was performed as part of standard preparations for Trajectory Correction Maneuver #2,
scheduled for February 25th.
Upcoming spacecraft events:
Events for the week of 02/13 through 02/19 include: a reset of the SSR pointers (02/15), and SSR Flight
Software Partition Maintenance (02/18).
Over the past week Cassini had 7 DSN track periods (02/06, 02/08, 02/09, and 4 periods occurring 02/10 -
01/12). Two of the track periods were for telemetry; the others for ranging (Navigation). In the coming week
there will be 11 DSN passes occurring daily from Friday (02/13), through Thursday (02/19). One of these
will be for telemetry-only and eight will be for ranging-only. The final two passes of the coming week will have
both ranging and telemetry, as the geometry of the Inferior Conjunction period will be behind us.
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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