Heliocentric transfer trajectory design for multiple spacecraft using lunar gravity assists

Abstract

This paper presents the methodologies to design the transfer trajectories from Earth nearby to heliocentric orbits. For multiple spacecraft with the same initial condition but aiming to different phases in the heliocentric orbit, several lunar gravity assists are used to divert them into different interplanetary orbits. Firstly, based on the patched-conic approximation, a complete design process for deep-space transfer orbits was proposed for multiple spacecraft performing lunar gravity assist maneuvers. In this design process, it was assumed that each spacecraft had the same initial conditions. The periodic matching method was introduced to design the interplanetary transfer orbit, satisfying the initial and terminal constraints. An iterative method was proposed to search lunar gravity assist parameters that satisfied the hyperbolic excess velocity condition for the escape trajectories. Furthermore, a semi-analytical correction method was proposed to further approximate the precise transfer trajectory. This correction method was found to have a reduced time cost and a better error convergence compared with conventional correction methods.