Australian Space Science Conference 2011
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Sin Ting Angela Lui

Decentralised Decision Making with Hard Constraints for Multi-Wheeled Rovers

Sin Ting Angela Lui
ACFR The University of Sydney

*Salah Sukkarieh
ACFR The University of Sydney

     Full text: Not available
     Last modified: July 29, 2011

Abstract
Recent planetary exploration missions to Mars have predominantly used multi-wheeled rovers. One of the main issues of utilising rovers is that their wheels can be lodged in soft soil, as evidenced by Marsian rovers Spirit and Opportunity. Traditionally, the rover's wheels execute the globally optimal path determined by a central processing unit. Although, this top-down solution minimises the global cost of traversing to the goal, it does not consider the risk each wheel undertakes to execute the action.

The work presented attempts to address this challenge by proposing a decentralised system, where each wheel is an individual processor capable of decision making. Each wheel tries to make traversibility decisions to minimise the risk of it being lodged in soft soil, whilst being confined by hard constraints that represent the fixed location of the roverís wheels. Consequently, these processors must negotiate with one another to converge to a feasible solution. Furthermore, by considering a decentralised system, the system becomes more modular, scalable and there is no single point of failure.

Our approach utilizes Lagrangian multipliers to encapsulate constraints into the problem, then Taylor expansions and the Method of Multipliers to generate a solution which ultimately reaches the destination. Statistical findings with multiple terrain maps demonstrate that although the rover does not take the globally optimal path, the risk of being lodged for the wheels is equal to or less than the globally optimal path.

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