ATHLETE: A Mobility and Manipulation System for the Moon

1. ATHLETE: A Mobility and Manipulation System for the Moon Brian Wilcox ATHLETE Principal Investigator Jet Propulsion Laboratory IEEE International Conference on Robotics and Automation 14 April 2007

2. ATHLETE: the All-Terrain, Hex-Limbed Extra-Terrestrial Explorer • Two fully-functional prototype vehicles were built in 2005 as part of NASA “Technology Maturation Program” • Each vehicle is ~850 kg, hexagonal frame 2.75 m across, ~300 kg max payload, top speed of ~10 km/h (2.8 m/s), power budget ~5000W, max limb tip speed at full extension of about 0.2 m/s

3. What is ATHLETE? • 6 Wheels-on-Legs. • Quick-disconnect tool adapter on each 6-DOF leg. • Wheels sized for power-efficient mobility on moderate (“2-σ”) terrain. • Brakes sized for walking on extreme (“3- or 4-σ”) terrain.

4. A Wheel-on-Leg Vehicle: ATHLETE • Absorbs landing energy, provides mobility and manipulation (using quick-disconnect tools to perform self-maintenance, regolith handling, drilling, as well as generalized assembly, maintenance, and servicing). • CBE is that ATHLETE legs can be built for ~5% of landed mass (vs. 2.8% for Apollo landing legs). Wheels designed for “2-sigma” terrain (e.g. 5 PSI ground pressure, combined rim thrust at stall = weight of vehicle, 40% of weight at 1 m/s cruise). • 2.75 m, 850 kg ATHLETE test-bed vehicles developed under ICP-TMP program, continuing as part of Intercenter robotics program led by Chris Culbert of JSC.

5. Tool Use on ATHLETE • “Dozer Blade” allows scooping top layer of regolith for use in radiation protection, landing ejecta removal, or ISRU collection. • Auger-bit can be drilled 1-3 m into surface for ISRU assay, science, blast hole drilling, etc.

6. ATHLETE at Intercenter Field test at Meteor Crater, Sep 3-15, 2006

7. Rappelling on Slopes

8. Mobility on the Lunar Surface Access Module? • Propulsive landing will “sandblast” nearby objects (e.g. as Apollo 12 did to Surveyor) large fractions of a mile away – so habitats and payloads need surface mobility to reach the outpost. • Unloading stationary landers or ferrying them a mile or more to where they are needed represents a logistical challenge and a waste of precious EVA/IVA and/or robotic resources (recall the Fisher-Price studies of EVA logistics for Space Station). • Wheels-on-legs permit power-efficient rolling on “2-σ” terrain and “walking” on “3-4 σ” extreme terrain, as well as use of limbs as manipulators for any assembly, maintenance, or repair function. • Once you have short-range mobility, you can have long-range mobility almost “for free”.

9. Phase 2 JPL Concept Overview – Side-mounted Ascent Stage: the “Mobilander”

10. Functionality for Outpost Buildup • ATHLETE mobile base allows LSAM habitats to self-align for mating of “bellows” passages to make up outpost. • ATHLETE mobile base allows outpost to be put on an “unimproved” foundation, providing self-leveling and accommodation for settling of regolith and even moonquakes. • Use of tools, grippers, etc. on ATHLETE legs used as manipulators allows self-maintenance of LSAM habitat modules; use of dexterous manipulators (e.g. Robonaut) will allow assembly of important systems such as the radiation protection “tent”.

11. Other Advantages of Mobile LSAM • Every lander becomes a long-range pressurized rover – every 2 or 3 landers can support (multi-fault-tolerant) long-range crewed expeditions using adaptive suspension to explore ~1000 km in 14 days. • Regolith-covered radiation tents can be erected to make “cabin in the woods” refuges for sites that may be visited more than once. • Landers could have built-in “glove boxes” and “sample airlocks” on the bottom to allow sample collection without EVA. These could be within reach of core drills and other sampling tools used by the ATHLETE legs. • If all crewed landers are identical, each can be cannibalized to keep the others running. In particular, modular ATHLETE legs with quick-release bolt-pattern & electrical connector interfaces can be cannibalized from some landers (e.g. some legs that are part of the permanent outpost) to keep other vehicles running.

12. Radiation Shielding • Will need 1-3 m of regolith shielding using tent-like structure. • First MobiLanders that arrive at the outpost site can begin construction • Illustrated in next several slides • Use L or U shape for larger Outpost • Need to set up solar arrays and radiators outside the tent (robotic or first crew TBD)

24. Robonaut on ATHLETE for Self-Maintenance

25. Robonaut on ATHLETE for Self-Maintenance

26. LaRC Concept for CraneMounted on ATHLETE

27. Where we are, Where we want to be... • Today we can: • perform continuous weight redistribution and body reposing at almost 1 km/h • rappel on steep slopes • Work in progress: • detect anomalous forces on a wheel, autonomously make decision to put some or all of its weight on other wheels, and lift and advance selected wheel in a lightly-loaded “terrain following” mode • fully autonomous walking on extreme terrain (walking algorithms being developed by NASA Ames Research Center)

28. Summary and Conclusions • Adding “2-sigma” wheels and actively-articulated legs to lander adds little extra mass beyond Apollo-style crushable legs, and less mass increase than needed for payload separation interfaces. • 6-DOF legs with quick-disconnect tool adapters allow generalized assembly, maintenance, and servicing functions. • Long-range mobility and self-maintenance allows Sortie assets to coalesce into Outpost with few or no extra launches. • Simple force-redistribution and body reposing algorithms are very effective in providing good, power-efficient mobility on moderate terrain. • Six (or more) smaller wheels and motors on limbs can have less mass (and cost) than three or four larger wheels and motors without limbs, since the “walk out” contingency option means they don’t need to satisfy all the worst-case requirements. • ATHLETE provides a rich environment in which to study the adaptive-suspension problem, autonomous walking, general-purpose manipulation and other challenging problems.