Axel and DuAxel rovers for the sustainable exploration of extreme terrains

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. © 2012 Wiley Periodicals, Inc.