Cassini Significant Event Report
For Week Ending 03/27/98
The Cassini spacecraft is presently traveling at a speed of approximately 143,000 kilometers/hour (~89,000
mph) relative to the sun and has traveled approximately 439 million kilometers (~273 million miles) since
launch on October 15, 1997.
The most recent Spacecraft status is from the DSN tracking pass on Thursday, 03/26, over Madrid. The
Cassini spacecraft is in an excellent state of health and is executing the C7 sequence nominally, having been
returned to standard sequence-based activities on Thursday, 3/26, following an occurrence of spacecraft
system-safing on Tuesday, 3/24 (see below). 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, 03/20, there were no changes in spacecraft configuration.
On Saturday, 03/21, 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 Sunday, 03/22, and Monday, 03/23, there were no changes in spacecraft configuration.
On Tuesday, March 24, the Cassini spacecraft automatically entered "safing" (i.e., a pre-defined, low-activity
safe operating mode of the spacecraft) while performing a planned spacecraft maintenance activity. The
spacecraft executed the "safing" response exactly as designed. Tuesday's telemetry indicated that safing
resulted from a small variation in information about the spacecraft's orientation (i.e., attitude), that occurred as flight controllers were switching between the spacecraft's two stellar reference units.
On Tuesday, Wednesday and Thursday ground controllers prepared and uplinked the commands needed to
return the spacecraft to its planned operating state. By Thursday afternoon, 3/26, the recovery effort had been
completed, the C7 sequence had been reactivated and the planned activities were again executing on
schedule. No mission impacts occurred as a result of this event. All planned activities for the Venus 1 flyby
remain on schedule.
On Thursday evening, 3/26, the second Probe Checkout was conducted, as planned. This activity occurs
approximately every 6 months. Temperature and power telemetry from the DSN track immediately following
the activity indicated that the activity executed as expected. A series of data playbacks from the SSR which
begin on 3/31 will provide detailed information on the results of the checkout.
Also on Thursday, the spacecraft passed through perihelion, the point in its orbit closest to the sun.
Activities scheduled for the week of 3/27 - 4/02 include: the first 2 (of 7) Probe Checkout data playbacks
(3/31 and 4/1), an SSR pointer reset (4/1), and an SSR FSW partition maintenance activity (4/1).
Over the past week Cassini had 8 scheduled DSN tracks occurring from 03/20 through 3/22 and 3/24
through 3/26. Additional DSN coverage was obtained on Tuesday, Wednesday, and Thursday. In the coming
week there will be 9 DSN passes.
Preparations are continuing for the Launch-plus-14 month initial instrument checkout of the orbiter
instruments. Engineering Change Requests for that important functionality test were approved on Wednesday.
The approved timeline of activities for the Instrument Checkout will pass from the Mission Planning Virtual
Team to the Sequence Virtual Team in the near future.
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.