From NASANews@luna.osf.hq.nasa.govThu Feb  1 07:44:42 1996
Date: Mon, 29 Jan 1996 16:28:47 -0500
From: NASA HQ Public Affairs Office <NASANews@luna.osf.hq.nasa.gov>
To: press-release-com@mercury.hq.nasa.gov
Subject: Key Components Installed on Saturn-Bound Spacecraft

Douglas Isbell
Headquarters, Washington, DC                 January 29, 1996
(Phone: 202/358-1753)

Mary Beth Murrill      
Jet Propulsion Laboratory, Pasadena, CA
(Phone:  818/354-5011)

RELEASE:  96-16

KEY COMPONENTS INSTALLED ON SATURN-BOUND SPACECRAFT

        Computer brains, an electronic inner ear and the 
spacecraft equivalent of a cardiovascular system have been 
successfully installed into NASA's Cassini spacecraft bound 
for a launch to Saturn in 1997.

        Engineers and technicians at the Jet Propulsion 
Laboratory (JPL), Pasadena, CA, this month completed 
installation of this key flight hardware on the Cassini 
spacecraft framework in JPL's spacecraft assembly facility 
clean room.

        Also included among many critical Cassini milestones 
met this month was a successful 200-minute engine firing of 
the spacecraft's main rocket engine last week, and successful 
completion of launch-like vibration testing for Cassini's 
Huygens probe.  This conical payload of science instruments, 
provided by the European Space Agency (ESA), will be deployed 
from the orbiter and parachute to the surface of Saturn's moon 
Titan, in a manner similar to the recent successful mission of 
the Galileo atmospheric probe into Jupiter.

        "The Cassini team has done an excellent job of keeping 
the program on track to complete the orbiter and probe on 
schedule and within budget," said Richard J. Spehalski, Cassini
program manager at JPL, which manages the effort for NASA.  "Our
challenge in 1996 will be to maintain our momentum as all the
spacecraft elements come together."

        Last week, Cassini's attitude and articulation control 
subsystem (AACS) was integrated. The AACS allows the 
spacecraft to maintain its bearings in space.  It joined the 
already-installed power and pyro subsystem, which governs the 
flow of electricity through seven miles of cable that will 
link all of Cassini's systems, and the command and data 
subsystem, which acts essentially as Cassini's brain, 
controlling all spacecraft functions.  

        While Cassini engineers and technicians assemble the 
spacecraft in the clean room, engineers and technicians in an 
adjacent shirtsleeve environment are remotely controlling the 
new subsystems in tests that run each through the commands and 
phenomena they will experience in flight.

        This complex computer-based ground system largely 
resembles the one that will be used to control Cassini once in 
flight, and it allows the Cassini team to identify problems 
and make changes needed in the flight operations system well 
ahead of launch.

        Last week also marked the successful completion of a 
critical 200-minute test firing of one of the two spacecraft 
rocket engines, demonstrating the capability of the main 
engine assembly including the successful operation of JPL-
developed engine gimbal actuators -- sophisticated devices that
fine-tune the motion and pointing of the spacecraft's two engines. 

        The engine gimbal actuators, based upon the design of 
unique actuators used on the orbiter spacecraft for the Viking 
missions to Mars in the mid-1970s, come into play during 
spacecraft course corrections and in the critical braking 
maneuver that Cassini must perform when it arrives at Saturn 
in July 2004.  

	There, Cassini must fire one of its engines for about 90 
minutes to brake into orbit around the ringed planet.  The two 
redundant engines are mounted side-by-side at the base of the 
Saturn orbiter, and the engine that fires must be pointed so 
that the rocket thrust is directed through the spacecraft's 
center of gravity. The engine gimbal actuators, responding to 
commands from the attitude and articulation control subsystem, 
will make constant minute adjustments in the engine's position 
to compensate for the shifting weight of more than 6,800 
pounds (3,100 kilograms) of propellant.

        Important tests of Cassini's multiple-frequency radio 
system were also successfully completed this month at JPL.  In 
addition, ESA, assembling the Huygens probe in Otterbrun, 
Germany, received hardware for U.S.-provided Titan science 
instruments -- a qualification model of the gas 
chromatograph/mass spectrometer from NASA's Goddard Space 
Flight Center, Greenbelt, MD, and the flight model of the 
descent imager/spectral radiometer from the University of Arizona.

        Integration of Cassini components will continue 
through October this year, readying the spacecraft for dynamic 
and other testing in the space-like environment of the solar-
thermal vacuum chamber at JPL.  The spacecraft will be shipped 
to Cape Canaveral, FL,  in late April 1997 for an October 1997
launch.

        Cassini is a joint mission of NASA, ESA and the 
Italian Space Agency (ASI). The main Cassini spacecraft will 
orbit Saturn to provide four years of close-up data on the 
moons, rings, planet and Saturn's magnetic and charged 
particle environment.  The Huygens Titan probe is provided by 
ESA, and Cassini's sophisticated radio antenna is provided by 
ASI.  JPL manages the overall mission for NASA.

                          -end-

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