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Surface Motion and Speed Limits on Small Bodies

Daniel Scheeres
Delivered As: 
Abstract Text: 

Motion of robotic vehicles (or humans) on small body surfaces such as asteroids and comets, or on Phobos and Deimos, are subject to a unique dynamical environment that must be accounted for in their design and operation. Given basic models of shape, density and spin state one can derive limits for motion on and about these bodies. For example, every surface has speed limits at which a body can move before it achieves ballistic flight. Should it exceed these limits (which can be very modest) it is subject to a global and uncontrolled motion across the body, potentially leading to a chaotic motion about the body that can deposit the vehicle at a random location or even eject the body into an escape orbit. Thus, the design and operation of mobile rovers or other agents on a small body must be developed with these constraints in mind.

We present research results from our SSERVI-supported studies for theoretical and practical limits on surface mobility to ensure that a body retains control of its motion, and explore the implications of exceeding these limits for global transport across the small body surface. Our theoretical evaluations are tested with detailed simulations that accurately capture the interaction of a rigid body with the asteroid surface. Our specific study for this meeting will focus on motion on a few different classes of bodies: the Martian moon Phobos, the small rubble pile asteroid Itokawa, the 1998 KW4 binary system for motion on both the primary and secondary, and motion on a larger asteroid such as Eros. For each of these bodies we can develop specific limits on a vehicle’s speed to ensure that it remains captured at the body, that it remains in contact with the surface, or that it follows a predictable ballistic arc that will not lead to uncontrolled global motion.

From these simulations and studies we can define important design and operation principles for ensuring controlled motion across a small body surface. The simulation tools we have developed also have applications beyond the design and operation of active rovers, and can be used to understand the reconfiguration and fission of asteroids comprised of irregular components resting on each other. Preliminary results of these studies will also be given.

Melchiorre Masali (Università di Torino, Department of Human and Animal Biology)
SSERVI Identifier: 

Recognizing that science and human exploration are mutually enabling, NASA created the Solar System Exploration Research Virtual Institute (SSERVI) to address basic and applied scientific questions fundamental to understanding the Moon, Near Earth Asteroids, the Martian moons Phobos and Deimos, and the near space environments of these target bodies. As a virtual institute, SSERVI funds investigators at a broad range of domestic institutions, bringing them together along with international partners via virtual technology to enable new scientific efforts."