The All-Terrain Hex-Limbed Extra-Terrestrial Explorer (ATHLETE) is a new mobility platform developed for potential lunar operations. This six limbed rover is designed to traverse quickly over benign terrain by rolling, traverse rough and steep terrain by walking, as well as perform general manipulation of tools and payloads. This flexible robotic platform will provide a mobile base for pressurized lunar habitats allowing for long range surface exploration and crew transport. It will also enable in-situ construction of lunar assets providing astronauts with the ability to assemble, maintain, and service a wide range of cargo.

To explore extremely rough and steep terrain, such as the base of an impact crater, safety lines are required to ensure the stability if the vehicle. For use on steep slopes (> 20 deg) a rappelling winch has been incorporated into a face of the rover as shown below. This winch uses a brushless DC motor with a safety brake and a 16:1 planetary gearbox. At the top of the hill, the ATHELETE vehicle can secure an anchor using a 2 m long auger bit driven into the ground by the tool mechanism. The rappelling line is attached to the auger and as the vehicle descends down the hill a cable spool that is carried on the vehicle is paid out. When the vehicle is stationary, the winch brake is engaged and power is not required on the winch to hold the vehicle. As the vehicle moves, the brake is released and a constant current controller on the winch motor delivers approximately constant tension on the line as additional cable is released. The rappelling line offloads the downslope weight of the vehicle and allows the rover to safely drive and/or walk down steep slopes without additional demand from the wheel or joint actuators.

The ATHELETE vehicle is a complex robot with more degrees of freedom that any other planetary rover. This complexity, however, comes with the benefits of capability and flexibility. The ATHELETE rover can traverse terrain that no other planetary rover can traverse. It can negotiate a step nearly equal to its fully extended limb length and more than three times its wheel diameter. It can act as an exploration rover, a crew transport vehicle, and a construction asset on the lunar surface. This wheel-on-limb rover is highly adaptable and will potentially play a key role in man’s return to the moon.

Taken from a paper by Matthew Heverly & Jaret Matthews
Jet Propulsion Laboratory, California Institute of Technology