Todd Litwin

Athlete: A cargo handling and manipulation robot 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.

Mars microrover navigation: performance evaluation and enhancement

In 1996, NASA will launch the Mars Pathfinder spacecraft, which will carry an 11 kg rover to explore the immediate vicinity of the lander. To assess the capabilities of the rover, as well as to set priorities for future rover research, it is essential to evaluate the performance of its autonomous navigation system as a function of terrain characteristics. Unfortunately, very little of this kind of evaluation has been done, for either planetary rovers or terrestrial applications. To fill this gap, we have constructed a new microrover testbed consisting of the Rocky 3.2 vehicle and an indoor test arena with overhead cameras for automatic, real-time tracking of the true rover position and heading. We create Mars analog terrains in this arena by randomly distributing rocks according to an exponential model of Mars rock size frequency created from Viking lander imagery. To date, we have recorded detailed logs from over 85 navigation trials in this testbed. In this paper, we outline current plans for Mars exploration over the next decade, summarize the design of the lander and rover for the 1996 Pathfinder mission, and introduce a decomposition of rover navigation into four major functions: goal designation, rover localization, hazard detection, and path selection. We then describe the Pathfinder approach to each function, present results to date of evaluating the performance of each function, and outline our approach to enhancing performance for future missions. The results show key limitations in the quality of rover localization, the speed of hazard detection, and the ability of behavior control algorithms for path selection to negotiate the rock frequencies likely to be encountered on Mars. We believe that the facilities, methodologies, and to some extent the specific performance results presented here will provide valuable examples for efforts to evaluate robotic vehicle performance in other applications.

Obstacle detection for unmanned ground vehicles: a progress report

To detect obstacles during off-road autonomous navigation, unmanned ground vehicles (UGVs) must sense terrain geometry and composition (terrain type) under day, night, and low-visibility conditions. To sense terrain geometry, we have developed a real-time stereo vision system that uses a Datacube MV-200 and a 68040 CPU board to produce 256/spl times/240-pixel range images in about 0.6 seconds/frame. To sense terrain type, we used the same computing hardware with red and near infrared imagery to classify 256/spl times/240-pixel frames into vegetation and non-vegetation regions at a rate of five to ten frames/second. This paper reviews the rationale behind the choice of these sensors, describes their recent evolution and on-going development, and summarizes their use in demonstrations of autonomous UGV navigation over the past five years.

Robotic vehicles for planetary exploration

Future missions to the moon, Mars, or other planetary surfaces will use planetary rovers for exploration or other tasks. Operation of these rovers as unmanned robotic vehicles with some form of remote or semi-autonomous control is desirable to reduce the cost and increase the capability and safety of many types of missions. However, the long time delays and relatively low bandwidths associated with radio communications between planets precludes a total “telepresence” approach to controlling the vehicle. A program to develop planetary rover technology has been initiated at the Jet Propulsion Laboratory (JPL) under sponsorship of the National Aeronautics and Space Administration (NASA). Developmental systems with the necessary sensing, computing, power, and mobility resources to demonstrate realistic forms of control for various missions have been developed and initial testing has been completed. These testbed systems, the associated navigation techniques currently used and planned for implementation, and long-term mission strategies employing them are described.

Sensing and perception research for space telerobotics at JPL

A useful space telerobot for on-orbit assembly, maintenance, and repair tasks must have a sensing and perception subsystem which can provide the locations, orientations, and velocities of all relevant objects in the work environment. This function must be accomplished with sufficient speed and accuracy to permit effective grappling and manipulation. Appropriate symbolic names must be attached to each object for use by higher-level planning algorithms. Sensor data and inferences must be presented to the remote human operator in a way that is both comprehensible in ensuring safe autonomous operation and useful for direct teleoperation. Research at JPL toward these objectives is described.

Mobile robot localization by remote viewing of a colored cylinder

To visually determine the position and orientation of a mobile robot from a fixed location in its vicinity, the authors have employed a cylindrical target which has different colors in each of its four quadrants. By judicious selection of the colors, segmentation of imagery from the fixed location can determine the size and centroid of the cylinder, as well as the visible color quadrants. Both the cylinder size in monocular images, and the centroid disparity in stereo pairs, are shown to provide a measure of distance. The angle of the cylinder is determined by analyzing which color quadrants are visible and to what degree. Implementation and experimental testing of this technique shows that it provides accurate localization data to within one or two pixels of error.

Real-Time Model-Based Vision System For Object Acquisition And Tracking

A useful space telerobot for on-orbit assembly, maintenance, and repair tasks must have a sensing and perception subsystem which can provide the locations, orientations, and velocities of all relevant objects in the work environment. This function must be accomplished with sufficient speed and accuracy to permit effective grappling and manipulation. Appropriate symbolic names must be attached to each object for use by higher-level planning algorithms. Sensor data and inferences must be presented to the remote human operator in a way that is both comprehensible in ensuring safe autonomous operation and useful for direct teleoperation. Research at JPL toward these objectives is described.

Modular Additive Construction Using Native Materials

Using modular construction equipment and additive manufacturing (3D printing) techniques for binding, mission support structures could be prepared on remote planetary surfaces using native regolith. Material mass contributes significantly toward the cost of deep space missions, whether human or robotic, due to the resources needed to lift each kilogram of equipment out of Earth’s gravity well. Proposing the modular Freeform Additive Construction System (FACS) concept, using the reconfigurable All-Terrain Hex-Limbed Extra-Terrestrial Explorer (ATHLETE) robotic mobility platform, a variety of walls, berms, vaults, domes, paving, and thick radiation shielding could be prepared in advance of crews and mission assets to help reduce the material needed to be brought from Earth. This paper discusses the current ATHLETE technology, and describes how flexible mission elements could be derived using a combination of three dimensional additive construction and in-situ manufacturing technologies using native regolith.

Operation and performance of the Mars Exploration Rover imaging system on the Martian surface

The imaging system on the Mars Exploration Rovers has successfully operated on the surface of Mars for over one Earth year. The acquisition of hundreds of panoramas and tens of thousands of stereo pairs has enabled the rovers to explore Mars at a level of detail unprecedented in the history of space exploration. In addition to providing scientific value, the images also play a key role in the daily tactical operation of the rovers. The mobile nature of the MER surface mission requires extensive use of the imaging system for traverse planning, rover localization, remote sensing instrument targeting, and robotic arm placement. Each of these activity types requires a different set of data compression rates, surface coverage, and image acquisition strategies. An overview of the surface imaging activities is provided, along with a summary of the image data acquired to date.

General 3D acquisition and tracking of dot targets on a Mars rover prototype

In June and July 2003 two Mars Exploration Rovers were launched to the Red Planet. Back on Earth, engineering-model rovers were driven on a mock Mars landscape in a large indoor sandbox. Characterizing their complete 6-DOF motion was accomplished by automatically acquiring dot targets mounted on their clattered, upper surfaces from any position and orientation within the sandbox using a system of 12 ceiling-mounted cameras. A least-squares, n-camera, triangulation technique was used to attain typical 3D accuracies of 1-2 cm within the 22m /spl times/ 9m test area.