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The Cassini mission to Saturn employs a Saturn orbiter and a Titan probe to conduct an intensive investigation of the Saturnian system. The Cassini orbiter flies series of orbits incorporating flybys of the Saturnian satellites called the “satellite tour”. During the tour, the gravitational fields of the satellites are used to modify and control the orbit, targeting from one satellite flyby to the next. The tour trajectory must also be designed to maximize opportunites for science observations, subject to mission-imposed constraints. Tour design studies have been conducted for Cassini to identify trades and strategies for achieving these sometimes conflicting goals. Concepts, strategies, and techniques previously developed for the Galileo mission to Jupiter have been modified, and new ones have been developed, to meet the requirements of the Cassini mission.

The Cassini mission to Saturn will start a second phase in the exploration of the Saturnian system, after the historical Voyager flybys of Saturn in 1980 and 1981. The Cassini primary mission is scheduled to be launched in October 1997 by the Titan IV/Centaur. Cassini uses four planetary gravity-assist flybys to gain the energy necessary to reach Saturn in July 2004. This arrival date at Saturn provides a unique opportunity for a flyby of Saturn's outer satellite Phoebe on the final approach. This paper provides an overview of the processes involved in the interplanetary trajectory design and analysis of the Cassini mission to Saturn.

The ESA Huygens probe is part of the NASA/ESA Cassini mission to the Saturnian system, and will make a 2–2.5 h exploratory descent to the surface of Titan. Huygens is designed to enter and brake in Titan's atmosphere in order to parachute a fully instrumented robotic laboratory. The main scientific measurements will be performed during the parachute descent, but some will also be performed during atmospheric entry; in addition, the probe resources are sized to allow measurements after it has impacted Titan's surface for at least a few minutes. This paper describes the control design and optimisation of the Huygens mission, based on an open-loop concept which is one of the keys to minimizing the mission risks induced by the uncertainties in the external environment.