Design of spacecraft swarm flybys for planetary moon exploration

Exploration of small bodies brings insight to the origins of the life, the Earth, and the solar system. However, attempting surface missions to small-bodies with inadequate gravity field information is prone to high-risk of failure. Spacecraft flybys can be a viable approach to perform an initial reconnaissance before a surface mission can be deployed. The challenge with flybys is that they are time and coverage limited thus providing only a limited glimpse of the target. These disadvantages can be overcome using a swarm approach. While swarms are important platforms for small-body exploration, their mission design is a complex design problem, and more importantly, there is no end-to-end tool for designing spacecraft swarm missions. This paper presents IDEAS, an end-to-end mission design architecture that designs swarm missions for small body flyby exploration. The IDEAS platform, at its heart, will have three automated design modules corresponding to spacecraft design, swarm design, and trajectory design. In our previous work, we developed the Automated Swarm Designer module of the IDEAS platform to explore uniformly rotating asteroids. The current work will focus on enabling the IDEAS architecture to design visual mapping missions to planetary moons through spacecraft swarm flybys. Specifically, a swarm of spacecraft will be designed to explore a target moon through multiple encounters at different orbital locations using hyperbolic trajectories around the central planet. The objective of the designed swarm is to produce a detailed surface map of the moon with a minimum number of spacecraft. Here, we show that the design of swarm trajectories will result in a boundary value problem, where we have a rendezvous location and an excess velocity asymptote. This boundary value problem will be formulated as a system of non-linear equations which will then be solved using an iterative scheme. The solutions to this will specify a hyperbolic reconnaissance trajectory of a participating spacecraft in the swarm. We then determine the optimal set of these flyby trajectories using an evolutionary search algorithm to meet the required coverage criterion with a minimum number of spacecraft. Finally, the algorithms developed in this work are demonstrated through a theoretical example of designing a reconnaissance mission to the Martian moon Phobos.