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This paper discusses the design, control, and experimentation of internally‐actuated rovers for the exploration of low‐gravity (micro‐g to milli‐g) planetary bodies, such as asteroids, comets, or small moons. The rover is actuated by spinning three internal flywheels, which allows all subsystems to be packaged in one sealed enclosure and enables the platform to be minimalistic, thereby reducing its cost. By controlling the spin rate of the flywheels, the rover can achieve large surface coverage by attitude‐controlled hops, fine mobility by tumbling, and coarse instrument pointing by changing the orientation relative to the ground. We first discuss the dynamics of such rovers, their control, and key design features (e.g., flywheel shape and orientation, geometry of external spikes, and system engineering aspects). We then discuss the design and control of a first‐of‐a‐kind test bed that enables the accurate emulation of a microgravity environment for mobility experiments, which consists of a three‐degree‐of‐freedom gimbal attached to an actively controlled gantry crane. Finally, we present experimental results on the test bed that provide key insights for rover control and validate our theoretical analysis.

We present in detail some of the challenges in developing reusable robotic software. We base that on our experience in developing the CLARAty robotics software, which is a generic object-oriented framework used for the integration of new algorithms in the areas of motion control, vision, manipulation, locomotion, navigation, localization, planning and execution. CLARAty was adapted to a number of heterogeneous robots with different mechanisms and hardware control architectures. In this paper, we also describe how we addressed some of these challenges in the development of the CLARAty software.

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Some of the most appealing science targets for future exploration missions in our solar system lie in terrains that are inaccessible to state‐of‐the‐art rover technology. This paper discusses the challenges and constraints of designing a robotic explorer for these “extreme'' terrains and then examines the trade‐offs among different mobility architectures. To address many of these challenges, we have developed the Axel family of rovers. The Axel rover is a two‐wheeled tethered robot capable of rappelling down steep slopes and traversing rocky terrain. The DuAxel rover, which is a four‐wheeled vehicle formed from two Axel rovers, provides untethered mobility to get to extreme terrains. We describe the basic design principles of these rovers and review our efforts to implement the key features of the Axel concept. Limitations found during experiments with prior Axel rover prototypes led to the design of a third‐generation Axel rover. We describe the features of this new rover and then present a thermal analysis conducted to assess the feasibility of exploring lunar cold traps, which are expected to have a temperature range of 40 to 70 K. We conclude the paper with results showcasing Axel and DuAxel's extreme‐terrain performance as evaluated during two recent field tests in a steeply sloped Southern California rock quarry and at a location in Arizona that closely resembles rugged Martian terrain. We also summarize lessons learned during the Axel development program. © 2012 Wiley Periodicals, Inc.

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