The All-Terrain Hex-Limbed Extra-Terrestrial Explorer (ATHLETE) vehicle concept is based on six wheels at the ends of six multi-degree-of-freedom limbs. ATHLETE uses its wheels for efficient driving over stable, gently rolling terrain. Because each limb has enough degrees of freedom for use as a general-purpose leg, the wheels can be locked and used as feet to walk out of excessively soft, obstacle rich, or other extreme terrain. ATHLETE is envisioned as a heavy-lift utility vehicle to support human exploration of the lunar or Martian surface, useful for unloading bulky cargo from stationary landers and transporting it long distances over varied terrain.
To demonstrate this concept, several prototype vehicles have been developed for testing at JPL. The 1st generation ATHLETE prototype, built in 2005, consists of 6, six-degree-of-freedom limbs mounted to the corners of a hexagonal ring 2.75m (9 ft) wide. These vehicles have a maximum standing height of just over 2m (6.5 ft), weigh approximately 850 kg (1875 lb) and can carry a maximum payload of 300 kg (660 lb) in Earth gravity. Two identical prototypes were constructed in 2005, and one of these is still operational in 2010.
The 2nd generation ATHLETE prototype was constructed in 2009 and is implemented as a coordinated system of two Tri-ATHLETEs, fully independent three-limbed robots. This innovation allows a straightforward cargo handling strategy: two Tri-ATHLETEs dock to opposite sides of a cargo pallet, forming a six-limbed symmetrical vehicle, work together to move and emplace the cargo, then undock and depart. This strategy provides all the advantages of the six-limbed concept for cargo or habitat transport with the additional benefits of flexibility and modularity. The 2nd generation prototype is designed to demonstrate cargo handling at ½ the anticipated lunar scale. The robot stands to a maximum height of just over 4m (13 ft) and has a payload capacity of 450 kg (990 lb) in Earth gravity.
A side benefit of the wheel-on-limb approach is that each limb has sufficient degrees-of-freedom for use as a general-purpose manipulator (hence the name "limb" instead of "leg"). The prototype ATHLETE vehicles have quick-disconnect tool adapters on the limbs that allow tools to be drawn out of a "tool belt" and maneuvered by the limb. A rotating power-take-off from the wheel actuates the tools, so that they can take advantage of the 1+ horsepower (745+ watt) motor in each wheel to enable drilling, gripping or other power-tool functions.
Since the vehicle has an alternative mode of traversing through (or at least out of) extreme terrain, the wheels and wheel actuators can be sized for nominal, rather than worst-case terrain. There are substantial mass savings in the wheels and wheel actuators associated with designing for nominal instead of extreme terrain. These mass savings are comparable-to or larger-than the extra mass associated with the articulated limbs. As a result, the entire mobility system, including wheels and limbs, can be about 25% lighter than a conventional mobility chassis for planetary exploration.
This work was performed at the Jet Propulsion Laboratory (JPL), California Institute of Technology, under contract with NASA. ATHLETE is being developed by JPL as part of the Human-Robot Systems (HRS) Project managed by Robert Ambrose of the Johnson Space Center (JSC). HRS is one of several projects funded by the NASA Exploration Technology Development Program (ETDP) that is developing new technology in support of human exploration.