A Parametric study and experimental testing of lunar-wheel suspension on dynamic terrainability

Abstract

The development of a flexible metallic wheel proved to be one of the most challenging and time-consuming aspects of the Lunar Roving Vehicle of the Apollo missions (V. Asnani, D. Delap, and C. Creager. 2009. Journal of Terramechanics, 46: 89 103). The design was realized through an iterative trial and error design process, driven primarily by manufacturability and physical testing. Although the wire-mesh-compliant wheel design was identified as the best choice for the Lunar Roving Vehicle, mission scenarios have evolved and future lunar vehicles are bound to have to meet different functional requirements and more severe life and operational constraints. For example, these vehicles will have to travel farther on the lunar surface, explore permanently shadowed craters, and perform a variety of tasks such as transporting sensitive payloads and excavatiing regolith, and allow for both unmanned and manned operation. This work focuses on optimizing the suspension design parameters of a flexible, compliant wheel for maximizing the dynamic terrainability performance of a lunar rover. The suspension design parameters are identified, independently of the explicit wheel configuration. The terrainability of the rover is defined here as the rover's ability to negotiate terrain irregularities. Terrainability is quantified by the objective functions describing road holding and rider comfort. These objective functions ensure that the rover payload is isolated from vehicle terrain-induced vibrations, and that the wheels maintain ground contact during higher speed traversals. A simplified vehicle model is used for the dynamics analysis of the terrain vehicle system with the terrain modeled as a random stationary ergodic process characterized by a power spectral density function. A sensitivity analysis is performed to identify conflicting objectives, and a recommendation on optimal wheel suspension design variables is made. Finally, experimental testing of reduced-scale wheels with different suspension properties is conducted on three irregular terrain types and results confirm the theoretical predictions. Ultimately, the results of this research will be used in a system-level analysis of the wheel design parameters on vehicle performance to guide the structural optimization of the compliant wheel for lunar surface exploration vehicles. Resume ´. Le developpement d'une roue en metal flexible s'est averel'un des aspects les plus problematiques et onereux en termes de temps lors du developpement du Lunar Roving Vehicle pour les missions d'Apollo (V. Asnani, D. Delap, and C. Creager. 2009. Journal of Terramechanics, 46: 89 103). Le concept a er eau moyen d'une procedure iterative de conception basee sur des essais et des erreurs developpee principalement apartir de tests de fabricabiliteet physiques. Bien que le concept de roue souple fabriquee d'un treillis metallique ait eteidentifiecomme etant le meilleur choix pour le « Lunar Roving Vehicle », les scenarios des missions ont eet les vehicules lunaires futurs devraient vraisemblablement remplir des besoins fonctionnels differents et affronter des contraintes de vie et operationnelles