In this paper the preliminary design of multiple gravity-assist trajectories is formulated as a global optimization problem. An analysis of the structure of the solution space reveals a strong multimodality, which is strictly dependent on the complexity of the model. On the other hand it is shown how an oversimplification could prevent finding potentially interesting solutions. A trajectory model, which represents a compromise between model completeness and optimization problem complexity is then presented. The exploration of the resulting solution space is performed through a novel global search approach, which hybridizes an evolutionary based algorithm with a systematic branching strategy. This approach allows an efficient exploration of complex solution domains by automatically balancing local convergence and global search. A number of difficult multiple gravity-assist trajectory design cases demonstrates the effectiveness of the proposed methodology.

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Preliminary design of multiple gravity-assist trajectories

On the Preliminary Design of Multiple Gravity-Assist Trajectories

The Mariner 10 mission to Venus and Mercury

The navigation aspects of the Mariner Venus/Mercury 1973 mission are presented. Principal emphasis is on the maneuver strategy employed, propellant costs and the results of the navigation performance relating to the accomplishment of the mission objectives including an extended mission for a second Mercury encounter. Key error sources and mission constraints are discussed. Of particular interest is the impact of in-flight adaptation of the pre-launch maneuver strategy (due to spacecraft anomalies) on propellant cost and the delivery achieved at the first Mercury encounter. The maneuver strategy and propellant cost for the extended mission are shown to be heavily influenced by the delivery achieved at the first Mercury encounter and the science objectives at the second Mercury encounter.

Navigation results of the Mariner Venus/Mercury 1973 mission

A major accomplishment of the mission analysis performed for Mariner 10 was the selection of a trajectory which optimized science return from the mission. The analysis utilized simple, unweighted 'science value functions' which allowed the relative values of each candidate trajectory, for each of the seven science experiments, to be calculated. A total relative value for each trajectory was determined by a simple averaging process and sensitivities were revealed by multiplying individual values. This showed a clear scientific preference for launching in early November and was used to support deferral of the launch from early October to November 3, 1973.

D. L. Shirley

Papers

Mariner 10 mission analysis - Application of a black art