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  • 11
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    A genetic algorithms approach for altering the membership functions in fuzzy logic controllers (1992)
    In:  Other Sources
    Details
    Publication Date: 2013-08-29
    Description: Through previous work, a fuzzy control system was developed to perform translational and rotational control of a space vehicle. This problem was then re-examined to determine the effectiveness of genetic algorithms on fine tuning the controller. This paper explains the problems associated with the design of this fuzzy controller and offers a technique for tuning fuzzy logic controllers. A fuzzy logic controller is a rule-based system that uses fuzzy linguistic variables to model human rule-of-thumb approaches to control actions within a given system. This 'fuzzy expert system' features rules that direct the decision process and membership functions that convert the linguistic variables into the precise numeric values used for system control. Defining the fuzzy membership functions is the most time consuming aspect of the controller design. One single change in the membership functions could significantly alter the performance of the controller. This membership function definition can be accomplished by using a trial and error technique to alter the membership functions creating a highly tuned controller. This approach can be time consuming and requires a great deal of knowledge from human experts. In order to shorten development time, an iterative procedure for altering the membership functions to create a tuned set that used a minimal amount of fuel for velocity vector approach and station-keep maneuvers was developed. Genetic algorithms, search techniques used for optimization, were utilized to solve this problem.
    Keywords: THEORETICAL MATHEMATICS
    Type: North American Fuzzy Logic Processing Society (NAFIPS 1992), Volume 2; p 515-523
    Format: text
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  • 12
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    Determining rules for closing customer service centers: A public utility company's fuzzy decision (1992)
    In:  Other Sources
    Details
    Publication Date: 2013-08-29
    Description: In the present work, we consider the general problem of knowledge acquisition under uncertainty. Simply stated, the problem reduces to the following: how can we capture the knowledge of an expert when the expert is unable to clearly formulate how he or she arrives at a decision? A commonly used method is to learn by examples. We observe how the expert solves specific cases and from this infer some rules by which the decision may have been made. Unique to our work is the fuzzy set representation of the conditions or attributes upon which the expert may possibly base his fuzzy decision. From our examples, we infer certain and possible fuzzy rules for closing a customer service center and illustrate the importance of having the decision closely relate to the conditions under consideration.
    Keywords: THEORETICAL MATHEMATICS
    Type: North American Fuzzy Logic Processing Society (NAFIPS 1992), Volume 2; p 398-407
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  • 13
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    Fuzzy logic in autonomous orbital operations (1991)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: Fuzzy logic can be used advantageously in autonomous orbital operations that require the capability of handling imprecise measurements from sensors. Several applications are underway to investigate fuzzy logic approaches and develop guidance and control algorithms for autonomous orbital operations. Translational as well as rotational control of a spacecraft have been demonstrated using space shuttle simulations. An approach to a camera tracking system has been developed to support proximity operations and traffic management around the Space Station Freedom. Pattern recognition and object identification algorithms currently under development will become part of this camera system at an appropriate level in the future. A concept to control environment and life support systems for large Lunar based crew quarters is also under development. Investigations in the area of reinforcement learning, utilizing neural networks, combined with a fuzzy logic controller, are planned as a joint project with the Ames Research Center.
    Keywords: CYBERNETICS
    Type: Proceedings of the Second Joint Technology Workshop on Neural Networks and Fuzzy Logic, Volume 2; p 81-110
    Format: application/pdf
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  • 14
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    Applications of fuzzy logic to control and decision making (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Long range space missions will require high operational efficiency as well as autonomy to enhance the effectivity of performance. Fuzzy logic technology has been shown to be powerful and robust in interpreting imprecise measurements and generating appropriate control decisions for many space operations. Several applications are underway, studying the fuzzy logic approach to solving control and decision making problems. Fuzzy logic algorithms for relative motion and attitude control have been developed and demonstrated for proximity operations. Based on this experience, motion control algorithms that include obstacle avoidance were developed for a Mars Rover prototype for maneuvering during the sample collection process. A concept of an intelligent sensor system that can identify objects and track them continuously and learn from its environment is under development to support traffic management and proximity operations around the Space Station Freedom. For safe and reliable operation of Lunar/Mars based crew quarters, high speed controllers with ability to combine imprecise measurements from several sensors is required. A fuzzy logic approach that uses high speed fuzzy hardware chips is being studied.
    Keywords: COMPUTER PROGRAMMING AND SOFTWARE
    Type: NASA, Washington, Technology 2000, Volume 2; p 67-75
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  • 15
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    Applications of fuzzy sets to rule-based expert system development (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Problems of implementing rule-based expert systems using fuzzy sets are considered. A fuzzy logic software development shell is used that allows inclusion of both crisp and fuzzy rules in decision making and process control problems. Results are given that compare this type of expert system to a human expert in some specific applications. Advantages and disadvantages of such systems are discussed.
    Keywords: NUMERICAL ANALYSIS
    Type: NASA. Goddard Space Flight Center, The 1989 Goddard Conference on Space Applications of Artificial Intelligence; p 385-388
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  • 16
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    Autonomous control procedures for shuttle rendezvous proximity operations (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The results are presented of a study which uses fuzzy sets to model a Space Shuttle pilot's reasoning and actions while performing rendezvous proximity operation maneuvers. In this model fuzzy sets are used to simulate smooth and continuous actions as would be expected from an experienced pilot and to simulate common sense reasoning in the decision process. The present model assumes visual information available to the Shuttle pilot from the Shuttle Crew Optical Alignment Sighting (COAS) device and the overhead window and rendezvous radar sensor information available to him from an onboard display. This model will be used in a flight analysis simulator to perform studies requiring a large number of runs, each of which currently needs an engineer in the loop to supply the piloting decisions. This work has much broader implications in control of robots such as the Flight Telerobotic Servicer, in automated pilot control and attitude control, and in advisory and evaluation functions that could be used for flight data monitoring or for testing of various rule sets in flight preparation.
    Keywords: SPACE TRANSPORTATION
    Type: First Annual Workshop on Space Operations Automation and Robotics (SOAR 87); p 281-286
    Format: application/pdf
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  • 17
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    Learning characteristics of a space-time neural network as a tether skiprope observer (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Software Technology Laboratory at JSC is testing a Space Time Neural Network (STNN) for observing tether oscillations present during retrieval of a tethered satellite. Proper identification of tether oscillations, known as 'skiprope' motion, is vital to safe retrieval of the tethered satellite. Our studies indicate that STNN has certain learning characteristics that must be understood properly to utilize this type of neural network for the tethered satellite problem. We present our findings on the learning characteristics including a learning rate versus momentum performance table.
    Keywords: CYBERNETICS
    Type: North American Fuzzy Logic Processing Society (NAFIPS 1992), Volume 1; p 154-165
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  • 18
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    Learning characteristics of a space-time neural network as a tether skiprope observer (1993)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Software Technology Laboratory at the Johnson Space Center is testing a Space Time Neural Network (STNN) for observing tether oscillations present during retrieval of a tethered satellite. Proper identification of tether oscillations, known as 'skiprope' motion, is vital to safe retrieval of the tethered satellite. Our studies indicate that STNN has certain learning characteristics that must be understood properly to utilize this type of neural network for the tethered satellite problem. We present our findings on the learning characteristics including a learning rate versus momentum performance table.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA, Washington, Technology 2002: The Third National Technology Transfer Conference and Exposition, Volume 2; p 262-273
    Format: application/pdf
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  • 19
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    Automated space vehicle control for rendezvous proximity operations (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Rendezvous during the unmanned space exploration missions, such as a Mars Rover/Sample Return will require a completely automatic system from liftoff to docking. A conceptual design of an automated rendezvous, proximity operations, and docking system is being implemented and validated at the Johnson Space Center (JSC). The emphasis is on the progress of the development and testing of a prototype system for control of the rendezvous vehicle during proximity operations that is currently being developed at JSC. Fuzzy sets are used to model the human capability of common sense reasoning in decision-making tasks and such models are integrated with the expert systems and engineering control system technology to create a system that performs comparably to a manned system.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Telematics and Informatics (ISSN 0736-5853); 5; 3, 19; 179-185
    Format: text
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  • 20
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    Fuzzy logic and neural network technologies (1992)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Applications of fuzzy logic technologies in NASA projects are reviewed to examine their advantages in the development of neural networks for aerospace and commercial expert systems and control. Examples of fuzzy-logic applications include a 6-DOF spacecraft controller, collision-avoidance systems, and reinforcement-learning techniques. The commercial applications examined include a fuzzy autofocusing system, an air conditioning system, and an automobile transmission application. The practical use of fuzzy logic is set in the theoretical context of artificial neural systems (ANSs) to give the background for an overview of ANS research programs at NASA. The research and application programs include the Network Execution and Training Simulator and faster training algorithms such as the Difference Optimized Training Scheme. The networks are well suited for pattern-recognition applications such as predicting sunspots, controlling posture maintenance, and conducting adaptive diagnoses.
    Keywords: CYBERNETICS
    Type: AIAA PAPER 92-0868
    Format: text
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