Self-Transforming Robotic Planetary Explorers Final Report
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NASA Institute for Advanced Concepts Phase I Study of Self-Transforming Robotic Planetary Explorers Final Report Reporting Period: 11/98 - 5/99 Steven Dubowsky, PI Field and Space Laboratory Department of Mechanical Engineering Massachusetts Institute of Technology Abstract The exploration and development of the planets and moons of the solar system in the next 10 to 40 years are stated goals of NASA and the international space science community. These missions will require robot scouts to lead the way, exploring, mapping and constructing facilities. The fixed configuration planetary robots of today will not be able to meet the demands of these missions forecast for the coming millenium. This Phase I study explorered preliminary feasibility issues in preparation for future studies related to the concept of self-transforming robotic planetary explorers to meet the needs of future missions. A self-transforming system would be able to change its configuration to overcome a wide range of physical obstacles and perform a wide range of tasks. In order to achieve self-transforming robots for planetary exploration, conventional complex and heavy physical components, such as gears, motors and bearings, must be replaced by a new family of elements. We propose light weight, compliant elements with embedded actuation are proposed. The actuation would be binary in nature, simplifying the control architecture. The physical system would allow the robot to make both geometric and topological configuration changes. We have examined configuration planning through the implementation of genetic algorithms. This Phase I research developed concepts and technologies that will be relevant to the needs of NASA in the 10- 40 year period. This program has focused on the preliminary study of the underlying, fundamental physics and feasibility of self-transforming robotic planetary explorers. Program Overview The exploration and development of the planets and moons of the solar system in the next 10 to 40 years are stated goals of NASA and the international space science community, including Human Exploration and Development of Space – HEDS [NASA, 1999] and similar programs [NASDA, 1999]. These missions will require robot scouts to lead the way, exploring, mapping and constructing facilities. Current planetary rovers (Sojourner) [Bickler, 1992] and those under development are relatively conventional fixed configuration vehicles carrying a simple mechanical manipulator [Schenker, 1997]. This technology, while well conceived for current and near-term science objectives, will not meet the demands of missions forecast for the coming millennium. Present technology would not be able to explore rough terrain, such as cliff sides, deep ravines and craters, where the most interesting scientific samples and information are probably located. Nor will they be able to perform even the simplest assembly or construction tasks. New robot technology concepts are required to meet the needs of future planetary exploration and development programs. This research program has begun the study of the concept of self-transforming robotic planetary explorers to meet the needs of future missions. A self-transforming system would be able to change its configuration to overcome a wide range of physical obstacles and perform a wide range of tasks. It would also replace the heavy and complex conventional physical components, such as gears, motors, bearings, cables and connectors, with elements that use compliant members with embedded actuators, sensors, and information and power networks, called Articulated Binary Elements, or ABEs. This would result in more reliable and robust systems that are also easier to control than conventional systems. The development of future robotic systems presents a number of important technical challenges, such as in the areas of sensor technologies, communications and artificial intelligence. This research has focussed on the problems associated with the design of the physical system and its control. Further, the charge of the NIAC program is to develop technology and concepts that are relevant to the needs of NASA in the 10 to 40 year period. Clearly, this 6 month study has not been able to begin to address all the technical issues relevant to the problem in this time frame. Page 2 It has focussed instead on studying the underlying fundamental physics of self-transforming robotic systems. The approach has been to develop the concept of a self-transforming robotic planetary explorer, called the STX, that could be used in exploration missions in 10 to 15 years. The STX is a hybrid system composed of a combination of conventional system components and ABEs. The addition of small-scale binary actuation (2-4 binary states) to enhance conventional fixed configuration robots with some limited configuration change has also been pursued. The projection into 30 to 40 years would be a system of very large-scale binary actuation (VLSBA; 103 to 104 binary states) which can also deliver the changing topology necessary for truly effective planetary robots. The study has identified some of the key enabling technologies required for the successful implementation of the STX and future work will assess the feasibility of the approach, its potential and its fundamental limitations. Future study would also attempt, consistent with the NIAC charge, to project this technical approach into the 30 to 40 year timeframe. Review of the State of the Art In order to understand the inherent need for self-transforming robotic planetary explorers, it is necessary to understand the current state of the art in planetary exploration. Current planetary exploration is conducted with fixed configuration rovers capable of traversing benign terrain, performing specific surveying and small sample collection. They are composed of discrete mechanical and electrical components such as gears, motors, bearings, encoders, and sensors. A model Mars rover, based on the Jet Propulsion Laboratory’s Light Weight Survivable Rover (LSR shown in Figure 1) has been designed and built in the Field and Space Robotics Laboratory at Massachusetts Institute of Technology (FSRL Mod 2 shown in Figure 2.) Figure 1 LSR (Left) and Sojourner (right) (Schenker, P., et al.) Page 3 Figure 2 FSRL Mod 2 Rover, view of discrete components Force Torque IF Encoder IF PC/104 Stack Arm RAM Amplifiers Motherboard Harddrive Wireless Modem Body Central Frame Figure 3 Block Diagram of Electrical Components of Mod 2 Rover The FSRL rover has been used to study such things as local path planning, soil tire interaction, and the implementation of a smart traction control scheme using fuzzy logic (Hacot 1998, Burn 1998), see Appendix B. It is based on a PC/104 computer, uses several different I/O modules, and is powered by nickel cadmium batteries. The system controls 12 motors via pulse width modulation, reads four encoders and six tachometers, and uses a six axis force-torque sensor. (Figure 3 shows a block layout for the interaction of the individual components and subsystems.) This descriptive list, which is representative of the numbers and kinds of discrete elements in any rover, begins to show some of the limitations of current rover technology. The focus of initial work with telerobotics has been related to building highly robust systems capable of receiving and implementing basic commands received from Earth-based control. To Page 4 this end, current technologies suffice. Figure 2 demonstrates the complexity of systems composed of these components of current technology. Particularly confounding is the necessity for so many wires. While the size of individual electronic components will decrease progressively as integration and miniaturization processes improve, the size of the electronics as a whole will likely increase as more demanding tasks are slated for planetary rovers. And with this increase in the number of discrete components will come an increase in number of wires necessary for controlling the system. Even with these evolutionary advances in planetary robotics, a natural limit to the types of tasks capable of being performed by rovers exists. This limit results from the fact that regardless of how small the components become, they are still individual, discrete components in a fixed configuration system. The tasks they are capable of performing will always be limited by the number and nature of the discrete implements they are able to carry. Exit velocity and the cost of propulsion will limit these implements by weight criteria. It becomes clear that any hope of thorough planetary exploration will depend upon the development of robots that are capable of taking a limited number of elements and reconfiguring them in an efficient and useful manner. In the next 10 to 40 years, it is possible to imagine robots that will be able to explore and help prepare the way for human exploration and even habitation. In order to accomplish these goals, planetary robots will have to be able to scout, mine, conduct science experiments, construct ground facilities and aid human planetary explorers and settlers. These tasks necessitate robots that are extremely flexible and adaptive to varying terrain, environments and duties. This requirement of adaptability calls to mind the “robot” from the movie Terminator 2; a transforming metal system that can assume the shape required to accomplish its task and Odo, a shape shifter from Deep Space Nine. Science fiction aside, there is validity in the idea of moving from a paradigm of fixed