Development of the Cassini spacecraft propulsion subsystem

Abstract

The Cassini Spacecraft will be launched on an expedition to Saturn in October 1997. The mission is an eleven-year operation; the first seven years traveling to Saturn via a combination of propulsive burns and VenusVenus-Earth-Jupiter gravity-assist, and the remaining four years orbiting Saturn while exploring the planet, its moons, rings, and nearby icy satellites. The propulsion module subsystem provides thrust and torque to the spacecraft. Larger Delta-V maneuvers are conducted with a primary (with redundant backup) pressure-regulated 445-N engine, which burns nitrogen tetroxide (NTO) and monomethylhydrazine (MMH). Total propellant capacity is 3000 kg. Saturn Orbit Insertion (SOI) is accomplished with a 170minute (maximum duration) continuous firing of the bipropellant engine. Attitude control of the spacecraft is maintained by 1-N thrusters (arranged in two redundant pairs per each of four clusters), which operate in a blowdown mode, with the monopropellant tank (containing 132 kg of hydrazine) recharged once from a dedicated helium pressurant tank. A significant development program was implemented to provide design verification of major assemblies, and to extend the performance capabilities of heritage components. The flight hardware is currently in the final integration and test phase prior to shipment to JPL for integration with the spacecraft. Introduction Historical Background Cassini has its roots in the Saturnian system exploration studies that began in 1989 with the CRAF/Cassini Program. That Program involved two separate spacecraft — the CRAF (Comet Rendezvous and Asteroid Flyby), originally targeted for a 1995 launch to flyby an asteroid and eventually rendezvous with a comet; and Cassini, slated for a 1996 launch to explore Saturn and its many satellites and rings. Although going through major changes since its inception, Cassini remains an international cooperative effort of NASA, which is producing the main orbiter spacecraft (S/C); the European Space Agency (ESA), which is providing the Huygens Probe; and the Italian Space Agency (ASI), responsible for the S/C radio antenna and portions of three scientific experiments. The mission is being managed by NASA's Jet Propulsion Laboratory (JPL), where the orbiter is being designed, built and tested. In keeping with the international flavor of CRAF/Cassini from its inception, the earliest S/C Propulsion Subsystem was to be built by the Federal Republic of Germany (FRG). Technically, the Germans were contributing one propulsion subsystem for the CRAF Mission and a spare subsystem that was * Member AIAA * Senior Member AIAA Copyright © 1996 Lockheed Martin Astronautics. Published by The American Institute of Aeronautics and Astronautics, Inc. with Permission