Trajectory-based generic chassis control framework for the MMX-Rover

Abstract

Martian Moons eXploration (MMX) is a joint project of the French, German and Japanese space agencies Centre national d'etudes spatiales (CNES), German Aerospace Center (DLR) and Japan Aerospace Exploration Agency (JAXA) for an exploration mission to the moons of Mars, i.e. Phobos and Deimos. CNES and DLR are providing a rover payload to the mother spacecraft of JAXA which is designated to be the first rover to drive in milli-g-environment. Locomotion in milli-g-environment on potentially hazardous terrain with steep slopes and high sinkage raises increased demands on the locomotion subsystem and control algorithms. The MMX-Rover chassis control algorithms (CCA) are embedded as part of the MMX-Rover locomotion software partition in a three layer architecture between the Command and Control Software and the hardware-related Basic Software. This paper proposes a trajectory-based generic chassis control framework as extended chassis control variant for the MMX-Rover. The rover locomotion possibilities are formulated upon a generic rover motion interface to derive analytical solutions for the specialized MMX-Rover locomotion modes. The resulting algebraic chassis control algorithms (A-CCA) are mathematically formulated in detail. A connection to meta-modelling for kinematic locomotion functions is established. The generic chassis control framework can be used to formulate the onboard control algorithms as minimal application code or generic application code. The decision between the minimal or generic code formulation variant practically influences the control software architecture and implementation. The generic chassis control framework is used as a practical analysis and verification tool to ensure the qualification of a geometrically inspired and kinematically simplified control algorithm variant (G-CCA) as flight software candidate. In particular, the algebraic equations originating from the generic chassis control framework are compared to the geometric control algorithms regarding their functional scope, kinematic formulation and practical software implementation. Results for the analysis and verification of G-CCA are shown and their qualification in terms of the locomotion functional coverage and rover motion behavior discussed. The generic chassis control framework contributes to ensure and enhance the functioning and quality of the control algorithms in the MMX-Rover mission context.