A Ringside Seat at Saturn

PASADENA, Calif. (7/1/04) -- After years of traveling through the lonely depths of space, the Cassini spacecraft finally reached its destination this summer, surviving a critical insertion into near-perfect orbit around Saturn on July 1. Since then, Cassini has been transmitting remarkable images of the planet's rings and principal moon, Titan. The success of this mission, managed for NASA by Caltech's Jet Propulsion Laboratory (JPL), has given scientists around the world a cause for celebration—including some at Aerospace, who provided technical support during various phases of the program.

Image: JPL/NASA

For example, from approximately 1995 through launch in 1997, Aerospace and Lincoln Laboratory jointly conducted an external independent readiness review of the satellite for NASA. James Gilchrist, Aerospace cochair of the review, said it encompassed the spacecraft design, most of the instruments built by U.S. manufacturers, and the Huygens probe (sponsored by the European Space Agency). Aerospace also conducted the independent review of the Cassini ground operations.

The review lasted more than two years and began with an early independent assessment of the trajectory design, which included an Earth flyby. This trajectory held potential risk because the spacecraft carried about 33 kilograms of radioactive plutonium dioxide to power its thermal generators.

Formal risk assessment was required because of the presence of this nuclear power source onboard the spacecraft, said Sergio Guarro, director of Aerospace's Risk Planning and Assessment office. Guarro developed the risk assessment methodology to support the environmental assessment and launch approval process for the mission. Aerospace assisted with the risk assessment from early phases of the mission planning and development until launch approval. The importance of this work was recognized by NASA with a project award signed by the former administrator, Daniel Goldin.

William Ailor, director of the Aerospace Center for Orbital and Reentry Debris Studies, was chair of the Interagency Nuclear Safety Review Panel's Reentry Subpanel for the Cassini mission. Ailor's group focused on how well the material protecting the radioisotope would perform under reentry velocities approaching 20 kilometers per second—far beyond the reentry velocities from standard Earth orbits, which range closer to 7.5 kilometers per second.

Aerospace participated in launch readiness tests and the Titan IVB launch-vehicle processing and was instrumental in developing procedures to support the design, installation, and test of a modified Solid Rocket Motor Upgrade actuator. Aerospace supported integration of the payload, including special acoustic tests, thermal analysis, electromagnetic compatibility analysis, loads analysis, targeting, and software testing for the first Centaur launched on a Titan IVB.

In 1998 and 1999, at the request of JPL, Aerospace implemented a number of software enhancements to its Satellite Orbit Analysis Program (SOAP) to model the Cassini mission, said David Stodden, senior project engineer in the Software Assurance and Applications Department. Aerospace developed Cassini solid models and trajectories in 2002 and rendered them to help visualize maneuvers and scientific observation opportunities. JPL used SOAP for visualization and analysis of the June 11 Phoebe flyby, and Cassini is using it to visualize pointing and camera fields of view.

Aerospace also supported in October 2003 a review of the Saturn orbit insertion, the climax of Cassini's long journey and the crux of mission success. "These maneuvers were performed very efficiently, so it appears that the spacecraft may have sufficient propellant to conduct an extended mission beyond the planned four years," said David Bearden, Aerospace Systems Director, Jet Propulsion Laboratory Program Office. "Aerospace congratulates JPL on Cassini's successful seven-year journey to Saturn and insertion into orbit, and looks forward to the tremendous scientific return during the coming years," he said.