Metrics and Models for Gravity Tractor Demonstration Missions and Deflections

The gravity tractor is an asteroid deflection technology that uses the mutual gravity between a spacecraft and a small body to perturb the body’s trajectory. We develop low-fidelity and high-fidelity models to track the effects of a gravity tractor on a target body. As a case study, we simulate a demonstration mission to the binary asteroid system (162000) 1990 OS. We derive a predictive metric for gravity tractor effectiveness that directly compares changes made to an asteroid moon’s orbit about its primary to changes made to the heliocentric orbit of a single asteroid. We also introduce the push–pull efficiency parameter, which may be used to evaluate gravity tractor effectiveness in the same way that the momentum enhancement factor is used for the kinetic impactor. We find that the gravity tractor efficiency is independent of the target’s spin state for the cases we examine, being equally effective for tumbling and relaxed targets. For 1990 OS, we find that the push–pull efficiency parameter is maximized when hovering 4.5 volume-equivalent radii from the target center. Additionally, we find control strategies for gravity tractors with chemical propulsion systems that are viable and robust to model-error disturbances up to 50% as strong as the modeled dynamics.