Popis: |
During the past two NASA Mars rover missions – Mars Pathfinder (1997) and MER (2003-4) – the rovers have been required to negotiate notoriously difficult terrain. The vehicles in each of these missions belong to different weight categories, microand minirovers, respectively. They have been limited to a range much below their pre-determined daily travel due to the inefficiency of their mobility system to negotiate the terrain most efficiently. We are currently engaged in a study for the ExoMars mission, the first Aurora flagship mission. We are currently assessing 4-5 different mobility systems that may be deployed on the ExoMars rover. It is known that the mobility system for unmanned robotics planetary exploration vehicles is the backbone of robotic planetary exploration. The study here assesses the suitability of various mobility systems – wheeled, tracked, and legged – that can be deployed on either microor mini-rovers. Dr. M. G. Bekker did much of the work for off-road locomotion in the 1950s. The theory deals with computing the mobility and locomotion performance parameters of terrestrial vehicles on a variety of terrain. He calculated performance in terms of the vehicle’s Drawbar Pull, which is defined as the difference between soil thrust and motion resistance. Resistance to motion comprises of a number of component resistances – rolling, compaction, bulldozing, wheel flexure, and slippage. Soil thrust is provided by the traction of the vehicle on the given soil. We have suitably modified his theory to make it applicable to planetary exploration rovers, which are much lighter than the vehicles used to formulate the original theory. The Rover Mobility Performance Evaluation Tool (RMPET) has been developed during this study to evaluate the performance of wheeled, tracked, and legged rovers using Bekker theory. The software provides an option for assessing the performance of vehicles on a variety of soil conditions, including Martian and Lunar soil simulants, a number of terrestrial soils and user-defined soil compositions. We plan to discuss this software and its application of Bekker Theory to land locomotion and mobility system design. These techniques will allow accurate theoretical performance analyses of the impacts of different soils and surfaces, either terrestrial or extraterrestrial, on a wheeled, tracked, or legged robot. |