Contact dynamics of internally-actuated platforms for the exploration of small solar system bodies

Directed in-situ science and exploration on the surface of small Solar System bodies requires controlled mobility. In the microgravity environment of small bodies such as asteroids, comets or small moons, the low gravitational and frictional forces at the surface make typical wheeled rovers ine?ective. Through a joint collaboration, the Jet Propulsion Laboratory together with Stanford University have been studying microgravity mobility approaches using hopping/tumbling platforms. They have developed an internally-actuated spacecraft/rover hybrid platform, known as "Hedgehog," that uses flywheels and brakes to impart mobility. This paper presents a model of the platform's mobility, analyzing its three main states of motion (pivoting, slipping and hopping) and the contact dynamics between the platform's spikes and various regolith simulants. To experimentally validate the model, an Atwood machine (pulley and counterbalance) was used to emulate microgravity. Experiments were performed with a range of torques on both rigid and granular surfaces while a high-speed camera tracked the platform's motion. Using parameters measured during the experiments, the platform was simulated numerically and its motion compared. Within the limits of the experimental setup, the model is consistent with observations; it indicates the ability to perform controlled forward motions in microgravity on a range of rigid and granular regolith simulants.