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 the many critical Cassini milestones met this month was the 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 (PPS), which governs the flow of electricity through seven miles of cabling that will link all of Cassini's systems, and the command and data subsystem (CDS) which acts essentially as Cassini's brain, controlling all spacecraft functions.

While the Cassini spacecraft is assembled 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 that which 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 3,100 kilograms (6,800 pounds) 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 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.

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.

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