Planetary Rover Mobility Performance on Soft and Uneven Terrain

Rovers on Mars or Moon for planetary exploration are obtainig increased importance within the spaceflight nations. To achieve full mission success, driveability and mobility in all kind of complex motion scenarios has to be guaranteed. Here, proper modeling and understanding of the complex wheel-soil interaction, i.e. the terramechanics for flexible and hard wheels interacting with hard, soft and loose soil, is a major driver for supporting reliably rover design and to assist in testing of the flight model. The physical contact models are integrated within a multibody system approach, and the performance of the rover mobility will be shown for various worst case driving scenarios on hard and soft soil

A novel Terramechanics testbed setup for planetary Rover wheel-soil Interaction

For planetary rovers, demonstration of the overall mobility performance on soft soil is a demand to guarantee for mission success. Since several years, DLR’s Institute of Robotics and Mechatronics is strongly engaged in planetary mobile system developments. For the very important wheel-soil interaction a 3D-MBS tool for modeling and simulation of the overall terramechanics behavior, making use of Bekker’s well-known terramechnical equations, has been developed. Currently, major applications are followed within ESA’s Exomars mission. For the purpose of verification and validation of the 3D-MBS tool intensive hand in hand rover testing in a lab environment is necessary. Therefore, a new facility for planetary locomotion systems including a large testbed and a novel, high-precision bevameter to characterize the soil on which the tests are to be carried out is presented. For precise rover pose estimation inside the testbed a high-level position tracking system is used, and for proper soil surface determination on an in-house developed digital elevation mapping system is relied on. For the Bekker parameter determination, a portable and lightweight bevameter equipped with a state-of-the-art sensor technology is designed. Different design concepts are analysed open minded without any orientation on existing bevameter designs. This leads to a tripod design with electromechanical actuators and sensors integrated in a real-time computing environment to develop own control algorithms. Besides soil testing and soil preparation influence detection, the bevameter is mainly used for identifying soil parameters of the testbed. Finally, for correlation purposes, these parameters are taken as inputs to the 3D-MBS tool for simulating the drive manoeuvres performed inside the testbed. Results obtained from bevameter testing are presented together with the testbed setup design

Modelling of planetary rovers by means of a dynamical system approach with respect to mobility requirements

The term of terramechanics is somewhat deceptive when used in conjunction with planetary exploration rovers but the field of application is comparable to off-road vehicles on earth. In contrast to classical off-road vehicle design the challenge of vehicle design for extraterrestrical exploration requires immense research effort due to the demand for mobility and the absence of engagement possibilities with the vehicle. Therefore autonomous vehicles with optimised mobility performance are needed for future missions and hence tools for design, layout and multiobjective optimisations are needed to fullfil mission requirements without having the possibility to conduct hardware tests in the later working environment. The definition of vehicle performance in rough and soft soil terrain can be distinguished by the terms of trafficability, manoeuvrability and terrainability. Trafficability, which is a robot's ability to traverse soft soils or hard ground without loss of traction, is the main subject of investigation for the presented multibody system (MBS) simulation approach

Multibody System Modelling and Simulation of Plenetary Rover Mobility on Soft Terrain

For planetary rovers often very unconventional suspensions and tyre designs are investigated. With the possibility of Multibody System (MBS) simulation one has the unique opportunity to investigate a wide range of potential configurations and terrains and, moreover, the importance of the dynamical effects can be efficiently taken into account. The main goal is to reduce the amount of costly prototypes and give assistance in field experiments. A great advantage is the integration of the Multibody Sytem simulation and the very complex typre-soil interaction into the vehicle's conceptual design process. This ranges from kinematic investigations for gradeability, maximum step crossing and side slope driving up to investigations of trye-soil interaction with respect to tyre sinkage and rolling resistance. In this paper the focus lies on the simulation of longitudinal slip of tyres on soft soil which is important to bear in mind when considering driven wheels and furthermore, slip sinkage behaviour

Development of a Mobility Drive Unit for Low Gravity Planetary Body Exploration

The 10 kg asteroid lander package MASCOT (mobile asteroid surface scout), developed by DLR, is a contribution to the JAXA Hayabusa-II mission, intended to be launched in 2014. MASCOT will provide in-situ surface science at several sites on the C-type asteroid 1999 JU3. An innovative hopping mechanism, developed at the Robotics and Mechatronics Center (RMC) in Oberpfaffenhofen, allows the lander to upright to nominal position for measurements as well as to relocate by hopping. The mechanism concept considers the uncertain and harsh environment conditions on the asteroid surface by using the impulse of an eccentric mass with all rotating parts completely inside the MASCOT structure. The paper gives an overview of the major development activities which lead to a new promising powerful and scalable drive system for low gravity planetary body exploration