Cassini Significant Event Report
For Week Ending 02/27/98
The Cassini spacecraft is presently traveling at a speed relative to the sun of approximately 135,000
kilometers/hour (~83,000 mph) and has traveled approximately 343 million kilometers (~213 million miles)
since launch on October 15, 1997.
The most recent Spacecraft status is from the DSN tracking pass on Thursday, 02/26, over Canberra. 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.
Spacecraft Activity Summary:
On Friday, 02/20, 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 Saturday, 02/21, Sunday, 02/22, and Monday, 02/23, there were no changes in spacecraft configuration.
On Monday, 02/23, the mini-sequence containing Cassini's second Trajectory Correction Maneuver was
approved for uplink to the spacecraft.
On Tuesday, 02/24, the TCM2 mini-sequence was uplinked to the spacecraft. Also on Tuesday, the SSR
record and playback pointers were reset, per plan, in preparation for the TCM.
On Wednesday, 02/25, Cassini's second Trajectory Correction Maneuver (TCM) was performed at
approximately Noon, PST. Because the magnitude of the needed trajectory correction was very small, the
TCM2 maneuver was conducted using the spacecraft's hydrazine thrusters, rather than one of its main
engines. Realtime data gave preliminary indications of a good burn; this result was confirmed later Wednesday
afternoon using high-resolution telemetry played back from the SSR. The total change in spacecraft velocity
(delta-V magnitude) was approximately 0.18 meters/sec, as planned. All spacecraft and ground components
performed superbly. The TCM2 maneuver puts the spacecraft on target for its final adjustment (TCM3,
scheduled for early April) prior to the 26 April flyby of Venus.
On Thursday, 02/26, there were no changes to spacecraft configuration.
Events for the week of 02/27 through 03/05 include: a reset of the SSR pointers (03/03), SSR Flight
Software Partition Maintenance (03/04), and an adjustment of the PCA Panel HTR thresholds and unmasking
of the 158bps telemetry mode (03/05).
Over the past week Cassini had 14 DSN tracks occurring daily from Friday (02/20), through Thursday
(02/26). In the coming week there will be 8 DSN passes.
Nicole Rappaport has left the Science Office to take up duties on the Genesis Project at JPL. She will remain,
however, as a Team Member on RSS. Two new people have been hired to work in the area of "science
system engineering." Both have PhDs in the fields related to planetary science. Kevin Grazier received his PhD
from UCLA, and Stuart Stephens received his PhD degree at Caltech.
A presentation about the Cassini Mission (including the safety of the Earth swingby) was made by Reed
Wilcox at the annual meeting of the United Nations Committee on the Peaceful Uses of Outer Space Scientific
and Technical Subcommittee (UNCOPUOS/STSC) in Vienna, Austria. During the meeting the STSC
adopted a joint US/UK/Russia work plan that provides for a five year effort to develop a technical foundation
for future UNCOPUOS deliberations on space nuclear power sources. The French delegation stated that
within the scope of the work plan, consideration should be given to NPS safety issues (e.g., the possibility of
releases) on surfaces of the moon and other planets. This concern could lead to public discussions of the
controlled disposal of the Cassini RTGs later in the mission.
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.