Prearrival Deployment Analysis of Rovers on Hayabusa2 Asteroid Explorer

This paper documents the prearrival planning strategy and analysis for the deployment of rovers on board the Japanese Hayabusa2 asteroid sample return mission. This will allow for rigorous comparison with postarrival results obtained at a future date. Hayabusa2 will arrive at asteroid Ryugu sometime between June and July of 2018. During its stay, the spacecraft will deploy three MINERVA-II rovers and obtain several surface samples. The autonomous Hayabusa2 descent guidance requires the rovers to avoid some exclusion zone around the target sample site(s). Although the limited current knowledge of the Ryugu system prohibits accurate deployment predictions, a mock shape model allows for a qualitative prearrival deployment analysis. Using a signed distance field shape, constant-density polyhedron gravity, and an impulsive contact model, high-fidelity simulations of the MINERVA-II deployment are performed. Simulations to the Ryugu reference sphere identify general trends in the rover motion and suggest the inclusion of a horizontal prerelease maneuver that minimizes the rover tangential velocity at first impact. These insights are applied to the Ryugu training model, in which appreciably small surface dispersions are observed when including the prerelease maneuver and when deploying to a large crater. These results will adjust the nominal mission operation plan at the asteroid.