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Lunar Rover Optimization Platform for Wheel Traction Studies/Robotic Mobility in Extreme Terrain
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Assessing Impact of Joint Actuator Failure on Lunar Rover Mobility
Wheeled rovers are critical to exploration of the lunar surface, and loss of mobility actuators can have mission-ending consequences. NASA’s upcoming Volatiles Investigating Polar Exploration Rover (VIPER) has a four-wheeled active suspension, which gives it flexible extreme terrain mobility at the cost of an increased number of mobility actuators and potentially a higher mobility cost due to actuator loss than might occur on a similar six-wheeled rover. Impact varies greatly by both the affected joint and its failure state, and that in some cases modification of driving strategy may be able to partially mitigate mobility impact.
Athlete: A Mobility and Manipulation System for the Moon
A robotic vehicle called ATHLETE - the All-Terrain Hex-Limbed, Extra-Terrestrial Explorer is described, along with initial results of Field tests of two prototype vehicles. This vehicle concept is capable of efficient rolling mobility on moderate terrain and walking mobility on extreme terrain. Each limb has a quick-disconnect tool adapter so that it can perform general purpose handling, assembly, maintenance, and servicing tasks using any or all of the limbs.
Methods for Improving Long-Range Wireless Communication Between Extreme Terrain Vehicles
Axel is an extreme terrain, two-wheeled rover designed to traverse rocky surface and sub-surface landscapes in order to conduct remote science experiments in hard-to-reach locations. The rover's design meets many requirements for a mobile research platform capable of reaching water seeps on Martian cliff sides. Axel was developed by the Mobility and Robotic Systems section at the Caltech Jet Propulsion Laboratory. Unique design criteria associated with extreme terrain mobility led to a unique rover solution, consisting of a central module, which provides long-term energy storage and space for large-scale science payloads, and two detachable Axels that can detach and explore extreme terrain locations that are inaccessible to conventional rovers. The envisioned mission could involve a four-wheeled configuration of Axel called 'DuAxel' that is able to traverse the benign, flattened terrain of a landing site and approach the edge of the targeted crater or cave where it would deploy anchoring legs and detach one of the Axel rovers [1]. A tether provides a secure link between the Axel rover and the central module, acting as an anchor to allow Axel to descend along steep crater walls to collect data from the scientifically relevant sites along the water seeps or crater ledges. After completing its scientific mission Axel would hoist itself up to the central module and dock autonomously (using its on-board stereo cameras), allowing the once-again recombined DuAxel to travel to another location to repeat data collection.
Compact Robotic Vehicle
Radio-controlled microrover features light weight and agility. Miniature robotic vehicle, called Go-For, implements new fork-wheeled mobility concept to traverse extremely rough terrain. Weighs 4 kg and is 0.4 m long, climbs over obstacles as large as 60 percent of its length. Mobility concept applied to much larger vehicles. Demonstrates such applications as exploration of planetary surfaces, military surveillance, and assessing hazardous situations. Video camera on vehicle sends images to control station, where human supervisor chooses sequence of paths to traverse to reach locations of interest. For planetary exploration, spectrometer and seisometer on vehicle sends scientific data to control station, and onboard tools collect soil and rock samples. Terrestrial version equipped similarly to take samples in chemically and/or biologically contaminated areas.
Towards Articulated Mobility and Efficient Docking for the DuAxel Tethered Robot System
Sites of increasing interest for planetary science,such as craters, cold traps, and vents lie in terrains that are inaccessible to state-of-the-art rovers. The Jet Propulsion Laboratory, in collaboration with Caltech, is actively developing a tethered mobile robot, Axel, for traversing and exploring extremely steep terrain, such as Recurring Slope Lineae on Mars and vertical pits on the Moon. However, on Mars, where landing-site uncertainty is high due to the presence of an atmosphere, Axel may need to traverse several kilometers from its lander untethered due to a finite tether carrying capacity (⇠300m). This paper proposes a novel design for a hybrid mobility system that allows a pair of Axel rovers to dock, lock, and drive long distances as a four-wheeled, articulated steering vehicle. The design improves upon prior efforts to achieve DuAxel mobility by leveraging two actuated docking mechanisms attached on opposite ends of a central module to enable ‘sit/stand’ functionality; the prior DuAxel system was limited to skid steering, which was inefficient due to Axel’s grouser-style, high-friction wheels. In the proposed system, the ‘sit’ configuration is achieved by aligning each dock parallel to the surface, allowing one Axel to detach and explore while the other remains docked and serves as a backup. While ‘sitting’, the central module rests on the ground and is outfitted with shovel-style wedges for passive anchoring to sandy terrain (an optional drill can be integrated for anchoring to rock). In order to ‘stand’, the exploring Axel reattaches, locks, and both docks are rotated until Axel’s tether caster arm is upright and the central module is lifted off the ground. Once upright, each Axel rotates about a pivot point for articulated, all-wheel steering, which is accomplished by applying differential wheel torques. The main contributions of this paper are i) a detailed systems design of the docking mechanism and central module, ii) kinematic modeling of articulated mobility and ‘sit/stand’ docking functionality, and iii) initial testing in a relevant environment to characterize the mobility of the proposed system.
On the Design of the Axel and DuAxel Rovers for Extreme Terrain Exploration
The solar system's most scientifically tantalizing terrain remains out of reach for traditional planetary rovers, which are typically limited to driving on slopes below 30 degrees. This paper details the design of a novel robotic explorer that would open access to these previously inaccessible locales, such as Martian crater walls where evidence of salty water was recently detected, Lunar polar craters where evidence of water ice was detected, and Lunar and Martian lava tubes for future habitability. The Axel rover is a two-wheeled robot capable of rappelling down steep (even vertical) slopes supported by a tether. The DuAxel rover is comprised of two Axel vehicles docked to a central module. Unrestricted by tether length, this four-wheeled system would be capable of driving long distances from a safe landing zone to the extreme terrain of interest. Once in the vicinity of terrain in which the tether would be required, one of the Axel rovers could undock from the central chassis and rappel downslope. The other Axel and central chassis would remain topside to act as an anchor and to provide line of site to Earth (for communications) and the Sun (for energy). As the detached Axel descends into the area of interest, it would receive power and relays data through conductors in its tether. Each Axel would carry a suite of instruments in a bay that would be tucked inside the wheels. Because of the novel configuration of Axel's major degrees of freedom, these instruments could be precisely pointed at targets at any desired downslope spatial separation. These instruments could then be deployed into close proximately to the ground by means of a simple mechanism, allowing for detailed study of the strata on the slope. Axel could accommodate a host of instruments, including a microscopic imager, infra-red spectrometers, thermal probes, and sample collection devices. This paper will describe the design of both the latest generation of Axel and DuAxel systems and their instrument/sampling mechanisms. Results from recent field trials at a rock quarry in California and a Martian analog site in the desert of Arizona will be described.
Autonomous Off-road Navigation over Extreme Terrains with Perceptually-challenging Conditions
We propose a framework for resilient autonomous navigation in perceptuallychallenging unknown environments with mobility-stressing elements such asuneven surfaces with rocks and boulders, steep slopes, negative obstacles like cliffsand holes, and narrow passages. Environments are GPS-denied and perceptuallydegradedwith variable lighting from dark to lit and obscurants (dust, fog, smoke).Lack of prior maps and degraded communication eliminates the possibility of prioror off-board computation or operator intervention. This necessitates real-time onboardcomputation using noisy sensor data. To address these challenges, we proposea resilient architecture that exploits redundancy and heterogeneity in sensing modalities.Further resilience is achieved by triggering recovery behaviors upon failure.We propose a fast settling algorithm to generate robust multi-fidelity traversabilityestimates in real-time. The proposed approach was deployed on multiple physicalsystems including skid-steer and tracked robots, high-speed RC car and legged robotsand as a part of Team CoSTAR’s effort to theDARPASubterranean Challenge, wherethe team won 2nd and 1st place in the Tunnel and Urban Circuit, respectively.
On the Design of the Axel and DuAxel Rovers for Extreme Terrain Exploration
No abstract available
The LEMUR 3 Limbed Climbing Robot
This paper introduces a new four-limbed robot, LEMUR 3, that has demonstrated climbing on cliff faces and smooth glass. Each limb on the robot consists of seven identical actuators in a serial chain. Each limb terminates in a single axis force sensor that allows various end effectors to be mounted and connected to the robot’s power and communication system. Microspine grippers were used for climbing the rocky surface and gecko adhesive grippers were used for the glass solar panels. All other hardware and much of the software was common for the two demonstrations. The robot’s mechanical, electrical, and software systems, various gripping devices, and field demonstrations are described. Limbed mobility is of interest to JPL and NASA because of its potential to access extreme terrain, including that on Mars and in microgravity environments.
Benefit of "Push-pull" Locomotion for Planetary Rover Mobility
As NASAs exploration missions on planetary terrains become more aggressive, a focus on alternative modes of locomotion for rovers is necessary. In addition to climbing steep slopes, the terrain in these extreme environments is often unknown and can be extremely hard to traverse, increasing the likelihood of a vehicle or robot becoming damaged or immobilized. The conventional driving mode in which all wheels are either driven or free-rolling is very efficient on flat hard ground, but does not always provide enough traction to propel the vehicle through soft or steep terrain. This paper presents an alternative mode of travel and investigates the fundamental differences between these locomotion modes. The methods of push-pull locomotion discussed can be used with articulated wheeled vehicles and are identified as walking or inchinginch-worming. In both cases, the braked non-rolling wheels provide increased thrust. An in-depth study of how soil reacts under a rolling wheel vs. a braked wheel was performed by visually observing the motion of particles beneath the surface. This novel technique consists of driving or dragging a wheel in a soil bin against a transparent wall while high resolution, high-rate photographs are taken. Optical flow software was then used to determine shearing patterns in the soil. Different failure modes were observed for the rolling and braked wheel cases. A quantitative comparison of inching vs. conventional driving was also performed on a full-scale vehicle through a series of drawbar pull tests in the Lunar terrain strength simulant, GRC-1. The effect of tire stiffness was also compared; typically compliant tires provide better traction when driving in soft soil, however its been observed that rigid wheels may provide better thrust when non-rolling. Initial tests indicate up to a possible 40 increase in pull force capability at high slip when inching vs. rolling.
ATHLETE: A Cargo-Handling Vehicle for Solar System Exploration
As part of the NASA Exploration Technology Development Program, the Jet Propulsion Laboratory is developing a vehicle called ATHLETE: the All-Terrain Hex-Limbed Extra-Terrestrial Explorer. Each vehicle is based on six wheels at the ends of six multi-degree-of-freedom limbs. 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 or other extreme terrain. Since the vehicle has this alternative mode of traversing through or at least out of extreme terrain, the wheels and wheel actuators can be sized for nominal terrain. There are substantial mass savings in the wheel 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. A side benefit of this approach is that each limb has sufficient degrees-of-freedom to use as a general-purpose manipulator (hence the name "limb" instead of "leg"). Our 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 power-take-off from the wheel actuates the tools, so that they can take advantage of the 1+ horsepower motor in each wheel to enable drilling, gripping or other power-tool functions. Architectural studies have indicated that one useful role for ATHLETE in planetary (moon or Mars) exploration is to "walk" cargo off the payload deck of a lander and transport it across the surface. Recent architectural approaches are focused on the concept that the lander descent stage will use liquid hydrogen as a propellant. This is the highest performance chemical fuel, but it requires very large tanks. A natural geometry for the lander is to have a single throttleable rocket engine on the centerline at the bottom, and to have the propellant tanks arranged as compactly as possible around and above that engine, with nearly-straight structural load paths that carry the heavy LO2 tanks as well as the ascent stage or cargo on a top deck. (The requirement for exactly one descent engine stems from the need to avoid symmetry planes in the exhaust plume that can entrain surface particles and loft them up into the system at hypervelocity.) This geometry is especially attractive since abort considerations drive the ascent stage to have as much open space around it as possible, in case the ascent stage needs to fire away from an out-of-control descent stage. These considerations lead to a configuration where the cargo deck of the lander is relatively high off the ground (over 6 meters in current concepts, using a 10-meter diameter launch shroud). These considerations have led some observers to presume that there is a "lander offloading problem". ATHLETE has been demonstrated as a solution to this problem, walking cargo off the high deck. This paper describes the applicability of the ATHLETE concept to exploration of the moon, Mars and even to Near- Earth Objects. Recent field test results for long-range traverse are described, along with plans for testing in the simulated microgravity environment of a NEO.
ATHLETE: A Limbed Vehicle for Solar System Exploration
As part of the Human-Robot Systems project funded by NASA, the Jet Propulsion Laboratory has developed a vehicle called ATHLETE: the All-Terrain Hex-Limbed Extra-Terrestrial Explorer. Each vehicle is based on six wheels at the ends of six multi-degree-of-freedom limbs. 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 or other extreme terrain. Since the vehicle has this alternative mode of traversing through or at least out of extreme terrain, the wheels and wheel actuators can be sized for nominal terrain. There are substantial mass savings in the wheel 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. A side benefit of this approach is that each limb has sufficient degrees-of-freedom to use as a general-purpose manipulator (hence the name "limb" instead of "leg"). Our 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.
ATHLETE: a Cargo and Habitat Transporter for the Moon
As part of the NASA Exploration Technology Development Program, the Jet Propulsion Laboratory is developing a vehicle called ATHLETE: the All-Terrain Hex-Limbed Extra-Terrestrial Explorer. The vehicle concept is based on six wheels at the ends of six multi-degree-of-freedom limbs. 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 or other extreme terrain. Since the vehicle has this alternative mode of traversing through (or at least out of) extreme terrain, the wheels and wheel actuators can be sized only for nominal 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 percent lighter than a conventional mobility chassis for planetary exploration. A side benefit of this approach is that each limb has sufficient degrees-of-freedom for use as a general-purpose manipulator (hence the name "limb" instead of "leg"). Our 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-plus-horsepower motor in each wheel to enable drilling, gripping or other power-tool functions.
A High Voltage Tethered Power System for Planetary Surface Applications
In the pursuit of human and robotic expansion of theLunar surface and other planetary bodies, power conversionand transmission over long distances has emerged as a distinctneed. The ability to transmit power over kilometers at highefficiency enables human settlement, in-situ resource utilization,and extreme terrain robotic exploration, through the ability toreach previously unreachable places. The critical buildingblocks of such a system are being developed by the TetheredPower System for Lunar Mobility and Power Transmission(TYMPO) project, a NASA project aimed at reaching flightreadiness by 2024. This paper presents an architectural andrequirements overview of the TYMPO project, along withtechnology discussions on the GaN-based multilevel DCXconverters, dual fiber optics and power-line communicationssystem, and high-voltage tether. Finally, a set of proposed futuremissions will be presented, mapping the capabilities of theTYMPO system to missions that may soon explore planetarysurfaces throughout the solar system.
NASA Tech Briefs, August 2009
Topics covered include: Aligning a Receiving Antenna Array to Reduce Interference; Collecting Ground Samples for Balloon-Borne Instruments; Tethered Pyrotechnic Apparatus for Acquiring a Ground Sample; Enhanced Video-Oculography System; Joint Carrier-Phase Synchronization and LDPC Decoding; Dual-Polarization, Sideband-Separating, Balanced Receiver for 1.5 THz Modular Battery Charge Controller; Efficient Multiplexer FPGA Block Structures Based on G4FETs; VLSI Microsystem for Rapid Bioinformatic Pattern Recognition; Low-Noise Amplifier for 100 to 180 GHz; Improved Fabrication of Ceramic Matrix Composite/Foam Core Integrated Structures; Inert Welding/Brazing Gas Filters and Dryers; Fabricating Copper Nanotubes by Electrodeposition; Reducing Aerodynamic Drag on Empty Open Cargo Vehicles; Rotary Percussive Auto-Gopher for Deep Drilling and Sampling; More About Reconfigurable Exploratory Robotic Vehicles; Thermostatic Valves Containing Silicone-Oil Actuators; Improving Heat Flux Performance of Flat Surface in Spray-Cooling Systems; Treating Fibrous Insulation to Reduce Thermal Conductivity; Silica-Aerogel Composites Opacified with La(sub0.7)Sr(sub0.3)MnO3; Cyclic Oxidation Behavior of CuCrAl Cold-Sprayed Coatings for Reusable Launch Vehicles; Ceramic Fiber Structures for Cryogenic Load-Bearing Applications; Elastomer Reinforced with Carbon Nanotubes; Biologically Inspired Purification and Dispersion of SWCNTs; A Technique for Adjusting Eigenfrequencies of WGM Resonators; Low-Pressure, Field-Ionizing Mass Spectrometer; Modifying Operating Cycles to Increase Stability in a LITS; Chamber for Simulating Martian and Terrestrial Environments; Algorithm for Detecting a Bright Spot in an Image; Extreme Programming: Maestro Style; Adaptive Behavior for Mobile Robots; Protocol for Communication Networking for Formation Flying; Planning Complex Sequences Using Compressed Representations; and Self-Supervised Learning of Terrain Traversability from Proprioceptive Sensors.
ATHLETE: Lunar Cargo Unloading from a High Deck
As part of the NASA Exploration Technology Development Program, the Jet Propulsion Laboratory is developing a vehicle called ATHLETE: the All-Terrain Hex-Limbed Extra-Terrestrial Explorer. Each vehicle is based on six wheels at the ends of six multi-degree-of freedom limbs. 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 or other extreme terrain. Since the vehicle has this alternative mode of traversing through or at least out of extreme terrain, the wheels and wheel actuators can be sized for nominal terrain. There are substantial mass savings in the wheel and wheel actuators associated with designing for nominal instead of extreme terrain. These mass savings are at least 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 lighter than a conventional all-terrain mobility chassis. A side benefit of this approach is that each limb has sufficient degrees-of freedom to be used as a general-purpose manipulator (hence the name "limb" instead of "leg"). Our 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 power-take-off from the wheel actuates the tools, so that they can take advantage of the 1+ horsepower motor in each wheel to enable drilling, gripping or other power-tool functions.