MULTI-LEVEL SOIL SENSING SYSTEMS TO IDENTIFY SAFE TRAFFICABILITY AREAS FOR EXTRA-PLANETARY ROVERS William A. Lewinger (1) , Francisco Comin (1) , Stephen Ransom (2) , Lutz Richter (2) , Said Al-Milli (1) , Conrad Spiteri (1) , Yang Gao (1) , Marcus Matthews (1) , Chakravarthini Saaj (1) (1) University of Surrey, Guildford, Surrey, GU2 7XH, United Kingdom, Email: william.lewinger@surrey.ac.uk (2) LIQUIFER Systems Group GmbH, Vienna, Austria ABSTRACT A handful of robotic exploration rovers have had successful landings and missions on Mars. These missions, however, were not without issues. The Mars Exploration Rovers (MER) Opportunity and Spirit, as examples, had several difficulties in traversing the terrain; and Spirit’s mission ultimately ended due to becoming permanently embedded in loose soil. This paper describes the development of multiple sensor systems on a highly-mobile scout rover with overlapping areas of detection for data correlation and fault redundancy; allowing for collection of both rapid, cursory data while the rover is in motion and highly- detailed soil characteristic information while the rover is stopped. The mission-critical primary rover will also possess its own direct and remote sensing systems for added mission safety. 1. INTRODUCTION The continued interest in extra-terrestrial exploration has led to several robotic missions to Mars. These rovers have provided great insight into the planet, but each has faced difficulty with traversing the Martian surface. Both of the MER rovers, Opportunity and Spirit, each became trapped in the soft, underlying soil [1]. Opportunity was able to be navigated away from its hazardous soil; however, Spirit was not so fortunate and it remains lodged in the soil at the location known as “Troy” [2]. To address these hazardous terrain issues, the Forward Acquisition of Soil and Terrain data for Exploration Rover (FASTER) project (an EU-funded, FP7 multi-partner collaboration) is developing a two-rover team formed by a small scout rover that can survey and assess the trafficability of the surface [3], thereby minimising the risk of becoming immobile for the larger, mission-performing rover. The scout rover is designed with five-spoked, rim- less wheel-legs that allow it to traverse hazardous terrain, such as soft soils and obstructing rocks. In order to assay the soil, the scout is equipped with an array of soil sensor systems (developed by the University of Surrey (1) ): a leg-soil interaction observation system to determine soil bearing ability and detect leg slip; a ground penetrating radar unit to detect duricrusts and subsurface hazards; a dynamic plate to replicate the bearing pressure of a primary rover wheel; and a dynamic cone penetrometer to assay soil properties both at and beneath the surface. These sensor systems have overlapping areas of detection and vary in their deployment and operation times. To maintain rapid traverses, systems that allow the scout rover to remain in motion are used first, while more- detailed systems that require the scout to stop are used when the more rapid systems provide inconclusive information on the safety of the soil. This hierarchical deployment concept provides a high level of safety while also maintaining rover movement whenever possible. The sequential deployment of the sensor systems also minimises the power consumption of the rover, as each system is operated independently and not simultaneously. In addition to the host of sensor systems on the scout rover, the primary rover is also equipped with its own means of trafficability analysis (developed by LIQUIFER Systems Group (2) ). While the primary rover will be equipped with a single sensor system, two systems are being developed as candidates. The first is a wheeled bevameter that will analyse the load bearing and shear properties of the terrain before primary rover. The other is a novel concept called PathBeater and it includes two arms with penetrometer tips that cyclically impact the soil in front of its wheel paths and infers mechanical properties of the soil. Each of these sensor systems is able to provide a trafficability assessment to the navigation system as a numerical confidence value and as a trinary state of: GO, MAYBE, or NO-GO. For the scout rover, sensor system assays that yield a MAYBE initiate the next sensor system in the sequence, for a more-detailed soil analysis. The purpose, function, and development of each of these sensor systems are described in detail throughout the paper. They are currently being developed independently, but will be integrated into the scout and primary rovers in early 2014. Tab. 1, describes the detection and operation features of each of the sensor systems.