Cassini Significant Event Report
For Week Ending 05/01/98
The Cassini spacecraft is presently traveling at a speed of approximately 147,000 kilometers/hour (~91,000
mph) relative to the sun and has traveled approximately 555 million kilometers (~344 million miles) since
launch on October 15, 1997. Cassini's first planetary gravity assist, a technique used to increase spacecraft
velocity, occurred early Sunday morning, April 26th. Cassini is now traveling approximately 11,000 kph
(7,000 mph) faster than it was a week ago. The Venus-1 flyby was a tremendous success. Post-flyby
Navigation tracking has indicated that the spacecraft is precisely on the desired trajectory. This information
has allowed the Program to cancel the next trajectory correction maneuver, which had been planned for May
14, as it is no longer needed.
The most recent Spacecraft status is from the DSN tracking pass on Tuesday, 04/28, over Canberra. There
have been two additional no-telemetry passes on Wednesday 04/29 and Thursday 04/30. 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, 04/24, there were no changes to spacecraft configuration.
On Saturday, 04/25, 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 Sunday, 04/26, the Venus-1 flyby and associated activities took place, with Venus closest approach
occurring at 6:44am PDT. The Radio & Plasma Wave Science (RPWS) instrument conducted a several-hour
search for signals which could indicate the occurrence of lightning in the Venusian atmosphere. The Radar
instrument conducted an engineering test near closest approach to attempt to acquire its first "bounce" from a
target body - a closed-loop test very difficult to accomplish on the ground. Finally, during the portion of flyby
when the spacecraft flew behind Venus (as seen from the Earth), some of NASA's Deep Space Network
equipment was employed to conduct an atmospheric occultation experiment to obtain data which can be used
by the Radio Science team. Results of the RPWS and Radar activities are going to be played back from the
Cassini Solid State Recorders (SSRs) this coming Saturday (5/2) and Sunday (5/3), respectively.
On Monday, 04/27, as part of the onboard sequence, Cassini executed a Memory Readout of Mass
Properties in preparation for TCM#4. As it turns out, TCM#4 will not be needed and has since been
cancelled (see above).
On Tuesday, 04/28, a maintenance activity was performed on the SSR Flight Software Partitions. This activity
repairs any SSR double bit errors (DBEs) which have occurred in the code-containing portions of the Flight
Software partitions during the preceding period. The real-time command based portion of the activity, which
clears telemetry flags and reads out the results of the maintenance activity, is scheduled for this Friday, 5/1.
On Wednesday, 04/29, there were no changes to spacecraft configuration.
On Thursday, 04/30, the Solid State Recorder (SSR) record and playback pointers were reset, according to
Activities scheduled for the week of 5/01 - 5/07 include: Reaction Wheel Assembly Exercise, and AACS
Fault Protection Log Maintenance (05/01), playback of RPWS Venus-1 Mini sequence data (05/02),
playback of Radar Venus-1 Mini sequence data (05/03), AACS Inertial Vector Propagation (IVP) Update
Part#1 (05/03),AACS IVP Update Part#2 (05/04), SSR Pointer Reset (05/05), and SRU-A
Over the past week Cassini had 17 scheduled DSN tracks, occurring from 04/24 through 4/30, to support
the Venus-1 flyby. In the coming week there will be 9 DSN passes.
Huygens Probe Status:
No report this week. POP 98-1 Review was held on April 30, 1998 at NASA Headquarters.
The Cassini Outreach Program held a workshop for teachers on Saturday, April 25, in conjunction with the
spacecraft's Venus 1 flyby the next day. Approximately 105 teachers attended and heard presentations on
Cassini, swingby dynamics, Cassini's power system, the current state of knowledge regarding Venus'
atmosphere and surface, and Cassini educator materials including the teacher guide, web page, and "Ways of
Seeing" CD-ROM. Survey forms returned by the attendees were very favorable.
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.