Gravity-Independent Locomotion: Dynamics and Position-Based Control of Robots on Asteroid Surfaces

In recent years, the scientific community has had an increased interest in exploring the asteroids of the solar system (JAXA/ISAS, 2003; JHU/APL, 1996; NASA/JPL, 2007). Technological advances have enabled mankind for the first time to take a closer look at these small solar system objects through sensors and instruments of robotic deep space probes. However, most of these space probe missions have focused on the reconnaissance of the asteroids’ surfaces and their compositional analysis from a distance. Little attention has been given to locomotion on their surfaces with a mobile robotic system, due to the challenging gravity conditions found in these small solar system bodies. In small bodies like asteroids, the gravitational fields are substantially weaker than those of Earth or Mars, therefore the likelihood of a robot’s unintentional collision with the surface while attempting a movement is substantially higher. In one of the latest missions, the Japanese Hayabusa spacecraft carried onboard a small robot named MINERVA (Yoshimitsu et al., 2001) to be deployed and used to explore the asteroid surface. The robot was designed with a single reaction wheel, located inside of it, to produce the necessary inertial reaction to move. But with this system the location of the robot when the motion is damped out is very challenging to predict or control. Subsequently, in order to maximize the scientific return from any given mission on an asteroid’s surface, future missions must have the ability to conduct stable mobility and accurate positioning on the rough terrain. In the robotics field, limbed locomotion is broadly recognized as superior in its capability to traverse terrains with irregularities such as obstacles, cliffs and slants. Exotic types of wheeled rovers (Bares et al., 1999; Wilcox & Jones, 2000) can only drive over obstacles of heights that are at best a fraction of the vehicle’s body length. Thus, some terrains are not accessible to wheeled vehicles. Conversely, legged or limbed locomotion has the possibility to provoke minimum reactions on the asteroid surface that could push the robot with sufficient force to reach escape velocity and drift into space. It also facilitates achievement of desired goal configurations that deal with new complex situations, ensuring that a robot’s behavior does not deviate from a stable condition. In this chapter, the focus is on gravity-independent locomotion approaches, technologies and challenges of robotic mobility on asteroids. Recommendations and methods to perform 16