Improvements In Trajectory Optimization For Messenger: The First Mercury Orbiter Mission

MESSENGER (MErcury Surface, Space, ENvironment, GEochemistry, and Ranging), the seventh NASA Discovery Program mission, will utilize a carefully planned sequence of Venus and Mercury gravity assist flybys to deliver the 3-axis-stabilized, dual-mode-propulsion spacecraft into Mercury orbit. During spring 2000 a methodical search of newly identified Venus-Venus transfer trajectories yielded two new minimum-AV ballistic trajectories to Mercury within MESSENGER's highly-constrained mission requirements. Both minimum-AV launch opportunities in March and May 2004 not only satisfy a wide array of science goals, but also meet engineering, operational, programmatic, and cost constraints. These new baseline and backup trajectories provide substantial improvements for several mission-critical aspects of MESSENGER's five-year journey to Mercury over the lowest-AV trajectories known at the start of Phase B studies. Some of these performance improvements were noted as key factors in NASA's June 2001 confirmation for Phase C/D funding.