Cassini Significant Event Report
For Week Ending 04/24/98
The Cassini spacecraft is presently traveling at a speed of approximately 136,000 kilometers/hour (~84,000
mph) relative to the sun and has traveled approximately 531 million kilometers (~329 million miles) since
launch on October 15, 1997.
The Cassini spacecraft has been flying for just over 6 months. Cassini's first planetary gravity assist, a
technique used to increase spacecraft velocity, is approaching; the Venus-1 flyby scheduled for early Sunday
morning, April 26th.
The most recent Spacecraft status is from the DSN tracking pass on Thursday, 04/23, 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, 04/17, the third Periodic Instrument Maintenance activity (PIM) completed execution, as planned.
This activity is carried out every three months by 11 of the 12 Orbiter instruments. All Instrument
representatives reported successful completion of their PIM activities.
Also on Friday, the realtime portion of an SSR Flight Software Partition maintenance activity was performed,
as planned, completing the activity which had begun on Tuesday, April 14.
On Saturday, 4/18, the Attitude and Articulation Control Subsystem's (AACS's) active vector was updated
as part of the preparations for the upcoming Venus-1 gravity assist flyby.
On Sunday, 04/19, and Monday, 04/20, there were no changes to spacecraft configuration.
On Tuesday, 04/21, 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, 04/22, the RPWS/RADAR minisequences for execution and playback were uplinked to the
spacecraft. The RPWS activity is one which will search for lightning in the atmosphere of Venus using the
Radio and Plasma Wave Science instrument. The RADAR activity is an engineering test to verify the ability of
the Cassini RADAR instrument to detect a signal reflected back from a target body (the surface of Venus).
The data collection minisequence's activities will be carried out on Sunday, April 26 around the Venus closest
approach point. The results of Sunday's activities will be returned to Earth in the playback minisequence,
scheduled to occur the following Friday and Saturday nights (May 1 and 2).
On Thursday, 04/23, there were no changes to spacecraft configuration.
Activities scheduled for the week of 4/24 - 4/30 include: Venus Flyby (04/25 thru 04/26), with closest
approach occurring on Sunday morning (04/26), execution of the RPWS and Radar Venus activities (04/26),
Pre-TCM 4 Memory Read Out of Mass Properties (04/27), SSR FSW Partition Maintenance (04/28), and
an SSR Pointer Reset (04/30). Additionally, the first Solar and Earth Occultations will occur (04/26).
Over the past week Cassini had 10 scheduled DSN tracks occurring from 04/10 through 4/16. In the coming
week there will be 16 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.