Robotic rovers equipped with articulated rocker-bogie suspension have aroused great interest after the explorations on Mars; this interest has also shifted to different types of terrestrial applications such as in the agriculture, military, and rescue fields. The suspension can be designed so that, when the rover is on flat and horizontal ground, the weight is evenly distributed among the wheels; in this way, all wheels have the same traction capability and offer the same rolling resistance. As the operating conditions vary due to sloping ground, uneven ground surface, or different payload position, the weight distribution can undergo considerable variations. This type of suspension is statically determined with respect to weight, but it is indeterminate with respect to traction forces; the traction control system aims to avoid the wheels slippage. In this paper, the traction contribution that each wheel can provide, to overcome a step obstacle, is shown. Furthermore, the possibility of regulating the distribution of vertical loads among the wheels adopting a torsion spring, with adjustable preload, arranged between rocker and bogie, is evaluated. A suitable spring preload facilitates the initial phase of the obstacle overcoming if the rover advances with the bogie forward. Numerical simulations show that to increase the possibility of overcoming an obstacle it is sufficient for the spring preload to reduce the vertical load on the front wheel; in any case, a higher load variation would not be advisable as it could involves an excessive load difference among the wheels.

The Aurora programme is the European Space Agency programme of planetary exploration focused primarily on Mars. Although the long-term goals of Aurora are uncertain, the early phases of the Aurora programme are based on a number of robotic explorer missions – the first of these is the ExoMars rover mission currently scheduled for launch in 2013 (originally 2011). The ExoMars rover – developed during a Phase A study – is a 240 kg Mars rover supporting a 40 kg payload (called Pasteur) of scientific instruments specifically designed for astrobiological prospecting to search for evidence of extant or extinct life. In other words, ExoMars represents a new approach to experimental astrobiology in which scientific instruments are robotically deployed at extraterrestrial environments of astrobiological interest. Presented is an outline of the design of the rover, its robotic technology, its instrument complement and aspects of the design decisions made. ExoMars represents a highly challenging mission, both programmatically and technologically. Some comparisons are made with the highly successful Mars Exploration Rovers, Spirit and Opportunity.