Cassini Significant Event Report

For Week Ending 04/06/01

The most recent spacecraft telemetry was acquired from the Goldstone
tracking station on Tuesday, April 3. The Cassini spacecraft is in an
excellent state of health and is operating normally. The speed of the
spacecraft can be viewed on the
"Present Position"
web page.

Recent spacecraft activities included a Command & Data Subsystem (CDS)
automatic repair of both Solid State Recorders (SSRs), a Reaction Wheel
Assembly (RWA) unload, and a High Water-Mark clear. Instrument activities
included Spica observations and an Imaging Science Subsystem (ISS) dustband
observation with Composite Infrared Spectrometer (CIRS) monitoring, successful
normalization of instrument flight software, an ISS Instrument Expanded
Block (IEB) load and dark frames activity, restart of the Cassini Plasma
Spectrometer (CAPS) actuator sweep, a Radio and Plasma Wave Science (RPWS)
HFR calibration, and start of the RPWS Periodic Instrument Maintenance.
Commands were sent to increase the Cosmic Dust Analyzer (CDA) multiplier
voltage to 3100 volts to better observe the effects on output science
data. This was followed by a CDA CPU reset, release and instrument power
off. Later in the week CDA was temporarily powered on and a diagnostics
mini-sequence successfully run.

The Cassini RADAR was powered on for 23.5 hours of data collection, the
most aggressive set of radiometric observations to date. Flight software
(FSW) was loaded to the RADAR system from the SSR, data were then
collected during raster scans of five microwave sources that are scattered
widely over the celestial sphere, as well as Jupiter and the Sun. Jupiter
and the sources were observed using two orthogonal polarizations,
accomplished by rolling the spacecraft 90 degrees, with 2 raster scans per
polarization. Total data volume was roughly 500 Mbits. Included as part
of this test was execution of a simulated Titan flyby by using all RADAR
instrument modes.

The Radio Science Subsystem (RSS) team performed another series of tests
and a boresight calibration to further prepare for the Gravity Wave
Experiment (GWE) test to be performed in May. This week's test objective
was to characterize the Ka-band Translator behavior. The next opportunity
for testing will be next week when an Operational Interface Test/Mission
Verification Test (OIT/MVT) will be performed over a three day period.

A Simulation Coordination meeting and a Preliminary Sequence Change
Request Approval meeting were held in support of the Cruise 26 development
process. A Project briefing for the Cruise 27 sequence was held this week
where an integrated plan was presented and approved. Detailed
implementation of the plan will now begin.

Several science working groups met this week. The Atmosphere Working
Group (AWG) continued development of an overall discipline strategy for
the Tour, the Rings Working Group (RWG) worked to identify the key Tour
segments and priorities in support of the Cross-Discipline Workshop coming
later this month, and the Surfaces Working Group (SWG) began
identification and prioritization of the non-targeted satellite
opportunities throughout the Saturn Tour.

Two DCMs were held this week. One was for CIMS version 1.1, which
provides streamlined access through the Cassini consolidated web server,
enhanced security, additional output capability for teams' APGEN requests,
and provides the science planning team with enhanced capability to manage
the data for sequences under development. The other DCM was held for MSS
Version D7.5 software. This version provides an update to SEG in support
of the GWE and has now been installed on all appropriate workstations.

The Spacecraft Office has reviewed, approved and released for distribution
Revision D of 699-CAS-3-271 The Cassini Functional Requirement Book -
Spacecraft Intercommunications.

Navigation Ancillary Information Facility (NAIF) personnel have published
an article on the recent NAIF-sponsored Spacecraft, Planet, Instruments,
C-matrix, and Events kernels (SPICE) conference. Cassini Team members
both attended and presented at this event. The article entitled "SPICE
Workshop Brings Enthusiastic Users and Developers Together," is due out in
the April 2001 edition of the Science Information Systems Newsletter
(SISN), and will be available at: .

Additional information about Cassini-Huygens is online at

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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