Dynamic neural network-based pulsed plasma thruster (PPT) fault detection and isolation for the attitude control subsystem of formation flying satellites

The main objective of this thesis is to develop a dynamic neural network-based fault detection and isolation (FDI) scheme for the Pulsed Plasma Thrusters (PPTs) that are used in the Attitude Control Subsystem (ACS) of satellites that are tasked to perform a formation flying mission. In order to accomplish these objectives three fault detection and isolation (FDI) approaches based on dynamic neural networks (DNN) are developed: (i) a "Low Level" FDI scheme, (ii) a "High Level" FDI scheme, and (iii) an "Integrated" FDI scheme. Based on data that is collected from the electrical circuit of the PPTs, our proposed "Low Level" FDI scheme can detect and isolate faults in the PPT actuators. Using a Confusion Matrix evaluation system we demonstrate that can achieve a high level of accuracy but the precision level is below expectations and the misclassification rate is expressed as False Healthy and False Faulty parameters is significant. Our proposed "High Level" FDI scheme utilizes data collected from the relative attitudes of the formation flying satellites. According to the simulation results, our proposed FDI scheme can detect the pair of thrusters which is faulty. It represents a promising detection capability, however its isolation capabilities are not adequate. Finally, our proposed "Integrated" FDI scheme takes advantage of the strengths of each of the previous schemes and at same time reduces their individual weaknesses. To demonstrate its capabilities, various fault scenarios were simulated. The results demonstrate a high level of accuracy (99.79%) and precision (99.94%) with a misclassification rate that is quite negligible. Furthermore, our proposed "Integrated" FDI scheme provides additional and interesting information related to the effects of faults in the thrust production levels that would not be available from simply the low and high levels separately

Fault Detection, Isolation and Identification of Formation Flying Satellites using Wavelet-Entropy and Neural Networks

The main objective of this thesis is to develop a fault detection, isolation and identification (FDII) scheme based on Wavelet Entropy (WE) and Artificial Neural Network (ANN) for reaction wheels (RW) that are employed as actuators in the attitude control subsystem (ACS) of a satellites to perform the formation flying (FF) missions. In this thesis two FDII approaches are proposed, i) Spacecraft-level fault diagnosis and ii) Formation-level fault diagnosis. In the "spacecraft-level" fault diagnosis scheme in order to analysis faults, absolute attitude and angular measurements from a satellite are considered as diagnostic signals. In order to detect the fault, the wavelet-entropy technique is employed on diagnostic signals and the sum of the absolute wavelet entropies (SAWE) of the diagnostic signals are obtained and compared with an appropriately selected threshold. If the SAWE passes the threshold the faulty condition is established. In order to isolate the fault in a satellite the angular velocity measurements in a satellite are considered as diagnostic signals and the relative wavelet energy (RWE) of these signals are obtained and compared to a threshold. In our proposed fault identification scheme, the attitude measurements in a satellite are considered and the detail and approximation coefficients of the wavelet signals are obtained and these coefficients are used as inputs to an artificial neural network to identify the type of the fault in a satellite. Using a confusion matrix evaluation system we demonstrate that our spacecraft-level FDII can detect, isolate and identify the high severity faults in a satellite however this scheme cannot detect low severity faults in a satellite. Our proposed "formation-level" FDII scheme utilizes data collected from the relative attitudes and relative angular velocity measurements of the formation flying satellites. In this fault diagnosis scheme, the relative attitude and relative angular velocity measurements in a satellite with respect to each its neighbor's in a formation are considered as diagnostic signals. In order to detect the fault, the relative attitude measurements in a satellite are considered as diagnostic signals. The wavelet-entropy technique is utilized on diagnostic signals and the SAWEs with respect to each satellite's neighbor are obtained. These SAWEs are then compared with an appropriately selected threshold. The faulty satellite is determined if these SAWEs pass the thresholds. In order to isolate the fault in a faulty satellite, the relative angular velocity measurements are considered as diagnostic signals. The RWE of these signals are obtained and compared to a threshold. In our proposed fault identification scheme, the relative attitude measurements in a satellite are considered as diagnostic signals. In this scheme, the RWEs of the diagnostic signals are obtained and used as inputs to an artificial neural network to identify the type of the fault in a satellite. According to the simulation results, our proposed FDII scheme can detect, isolate and identified both low severity and high severity faults in the reaction wheels of satellite

Neural Network-based Fault Diagnosis of Satellites Formation Flight

The main objective of this thesis is to develop a methodology for detecting and isolating faults (i.e. fault diagnosis) in any of multiple reaction wheels that are commonly employed as actuators in a consensus-based virtual structure controlled formation of satellites. In order to accomplish this objective, a two-level fault diagnosis system is developed based on Dynamic Neural Networks (DNNs). In the lower-level of the formation flight system hierarchy, a local fault diagnosis module is available in each individual satellite. In this level, the fault diagnosis system may consist of a dynamic neural network that is trained by using absolute measurements and states of each single satellite. Unfortunately, a local fault diagnosis system may fail to detect the presence of low severity faults. In an individual satellite these low severity faults may not cause any serious complications with the specifications of the overall mission, however they can cause significant impact on the satellite’s attitude or rates in a given precision formation flight of a network of satellites. Consequently, in order to detect these low severity faults a fault detection system is required to be designed and developed at the higher-level or the formation-level of the mission hierarchy. Towards this end, the highly nonlinear dynamics of the formation flight and the reaction wheels are modeled by using dynamic multilayer perceptron neural networks. The proposed formation-level DNNs invoke the extended back propagation learning algorithm and are trained based on sets of input/output data that are collected from the relative attitude determination sensors of the 3-axis attitude control subsystems of the satellites. The DNN parameters are adjusted to minimize certain performance indices (representing the output estimation errors). The capabilities of the proposed DNNs are investigated under various faulty situations, including single and multiple actuator fault scenarios and under high severity and low severity faulty situations. Using a Confusion Matrix evaluation method, it is demonstrated that by using the proposed fault detection and isolation (FDI) scheme, one can achieve a high level of accuracy and precision in detecting faults. The proposed formation-level FDI system has capabilities in efficiently detecting and isolating actuator low severity faults simultaneously

Guidance, Navigation, and Control of Small Satellite Attitude Using Micro-Thrusters

M.S. University of Hawaii at Manoa 2016.Includes bibliographical references.In this study, a new and automated Navigation, Guidance and Control system is designed, analyzed, simulated and tested for small satellites. As is known, this system represents the primary unit of on-board control of a flight vehicle. It consists of a set of system software algorithms and hardware elements, including various sets of sensors and electronics depending on the type of the vehicle. This study is focused on small satellites, which are becoming one of the primary tools for a wide range of low Earth and deep space missions. The Navigation subsystem has been described in terms of its sensors and filtering technique, known as the Extended Kalman Filter. This subsystem provides the estimates of the satellite’s state vector. It is assumed that this vehicle’s Navigation subsystem includes GPS receiver, and accelerometer and gyro, which are considered as Inertial measurement Unit (IMU) component subsystems. The Guidance subsystem provides guidance commands for satellite’s actuators, which are assumed to include a set of micro-thrusters. The Control subsystem provides control commands for increments of torque of actuation. This study deals with the development, design and integration of the Navigation, Guidance and Control (known as GNC) subsystems into a unique framework that can be executed on-board in real time to perform satellite attitude maneuvers. The main focus is on the development of Guidance subsystem functions and algorithms. These functions, in particular, include attitude angles, angular rates and coefficients. The Guidance subsystem provides commanded angular acceleration based on a fourth-order polynomial with respect to time, which was used for lunar-descent trajectory guidance during the Moon landing maneuvers of Apollo Landers. The difference in the utility of this polynomial law in Apollo missions and this work is that in those missions this polynomial was used for trajectory guidance using numerically integrated trajectories as reference solutions. In this work, this polynomial is used to compute attitude guidance commands using a simple PD controller as an analytic reference attitude profile. The novelty of this work is that this polynomial law is formulated and implemented for the first time for real-time and on-board attitude guidance and control using a set of microthrusters as part of the integrated GNC system. Another element of novelty is associated with targeting. A real-time targeting procedure implies on-board computations of the target states and the time remaining to achieve the target state from the current state. In this work, the target state includes Euler angles and their rates. As such, the targeting is considered as an integral and critical part of the guidance function. The guidance command is computed only after computations of the target state and is the explicit function of this state. Therefore, the proposed guidance function is considered as the ob-board target-relative attitude guidance. The performance of the proposed GNC system has been demonstrated by two illustrative examples. In the first example, the satellite is guided to orient itself to its target position. In the second example, the satellite is guided to perform two consecutive rotational maneuvers, detumbling and reorientation, to achieve a desired attitude. The numerical simulation parameters and its results are illustrated by various plots and qualitative analysis of the relationships between the satellite’s state and guidance parameters. The list of references and appendix with necessary formulas and figures are provided

Large space structures and systems in the space station era: A bibliography with indexes (supplement 04)

Bibliographies and abstracts are listed for 1211 reports, articles, and other documents introduced into the NASA scientific and technical information system between 1 Jul. and 30 Dec. 1991. Its purpose is to provide helpful information to the researcher, manager, and designer in technology development and mission design according to system, interactive analysis and design, structural concepts and control systems, electronics, advanced materials, assembly concepts, propulsion, and solar power satellite systems

ESMD Space Grant Faculty Report

The strength of the Exploration Systems Mission Directorate ESMD Faculty Project lies in its ability to meet National Aeronautics Space Administration NASA's Strategic Educational Outcome 1 by developing a sustainable and long-term integration of student involvement at academic institutions with all NASA Centers. This outcome is achieved by a three-fold approach: 1) by collecting Senior Design projects pertaining to Constellation work performed at each of the ten NASA Centers, 2) by engaging students at Minority Serving Institutions in the art of systems engineering and systems design of technologies required for space exploration, and 3) by identifying potential internships at each Center relative to exploration that provide students who are supported by their institutional Space Grant to engage in on-going mission-level and explorative systems designs. The objectives of the ESMD Faculty Project are to: 1. Aid the Centers (both Education Offices and associated technical organizations) in providing relevant opportunities for the ESMD Space Grant Program to support student and faculty in Senior Design projects 2. Enable better matches between the ESMD work required and what the Space Grant Consortia can do to effectively contribute to NASA programs 3. Provide the Space Grant Consortia an opportunity to strengthen relations with the NASA Centers 4. Develop better collective understanding of the U.S. Space Exploration Policy by the Center, Space Grant, faculty, Education Office, and students 5. Enable Space Grant institution faculty to better prepare their students to meet current and future NASA needs 6. Enable the Center Education Offices to strengthen their ties to their technical organizations and Space Grant Consortia 7. Aid KSC in gaining a greater and more detailed understanding of each of the Center activities Senior Design projects are intended to stimulate undergraduate students on current NASA activities related to lunar, Mars, and other planetary missions and to bring out innovative and novel ideas that can be used to complement those currently under development at respective NASA Centers. Additionally, such academic involvement would better the prospects for graduating seniors to pursue graduate studies and to seek careers in the space industry with a strong sense for systems engineering and understanding of design concepts. Internships, on the other hand, are intended to provide hands-on experience to students by engaging them in diverse state-of-the-art technology development, prototype bread-boarding, computer modeling and simulations, hardware and software testing, and other activities that provide students a strong perspective of NASA's vision and mission in enhancing the knowledge of Earth and space planetary sciences. Ten faculty members, each from a Space Grant Consortium-affiliated university, worked at ten NASA Centers for five weeks between June 2 and July 3, 2008. The project objectives listed above were achieved. In addition to collecting data on Senior Design ideas and identifying possible internships that would benefit NASA/ESMD, the faculty fellows promoted and collected data when required for other ESMD-funded programs and helped the Center's Education Office, as,needed.

NASA patent abstracts bibliography: A continuing bibliography. Section 2: Indexes (supplement 44)

A subject index is provided for over 5500 patents and patent applications for the period May 1969 through December 1993. Additional indexes list personal authors, corporate authors, contract numbers, NASA case numbers, U.S. patent class numbers, U.S. patent numbers, and NASA accession numbers

COBE's search for structure in the Big Bang

The launch of Cosmic Background Explorer (COBE) and the definition of Earth Observing System (EOS) are two of the major events at NASA-Goddard. The three experiments contained in COBE (Differential Microwave Radiometer (DMR), Far Infrared Absolute Spectrophotometer (FIRAS), and Diffuse Infrared Background Experiment (DIRBE)) are very important in measuring the big bang. DMR measures the isotropy of the cosmic background (direction of the radiation). FIRAS looks at the spectrum over the whole sky, searching for deviations, and DIRBE operates in the infrared part of the spectrum gathering evidence of the earliest galaxy formation. By special techniques, the radiation coming from the solar system will be distinguished from that of extragalactic origin. Unique graphics will be used to represent the temperature of the emitting material. A cosmic event will be modeled of such importance that it will affect cosmological theory for generations to come. EOS will monitor changes in the Earth's geophysics during a whole solar color cycle

Planetary Science Vision 2050 Workshop : February 27–28 and March 1, 2017, Washington, DC

This workshop is meant to provide NASA’s Planetary Science Division with a very long-range vision of what planetary science may look like in the future.Organizer, Lunar and Planetary Institute ; Conveners, James Green, NASA Planetary Science Division, Doris Daou, NASA Planetary Science Division ; Science Organizing Committee, Stephen Mackwell, Universities Space Research Association [and 14 others]PARTIAL CONTENTS: Exploration Missions to the Kuiper Belt and Oort Cloud--Future Mercury Exploration: Unique Science Opportunities from Our Solar System’s Innermost Planet--A Vision for Ice Giant Exploration--BAOBAB (Big and Outrageously Bold Asteroid Belt) Project--Asteroid Studies: A 35-Year Forecast--Sampling the Solar System: The Next Level of Understanding--A Ground Truth-Based Approach to Future Solar System Origins Research--Isotope Geochemistry for Comparative Planetology of Exoplanets--The Moon as a Laboratory for Biological Contamination Research--“Be Careful What You Wish For:” The Scientific, Practical, and Cultural Implications of Discovering Life in Our Solar System--The Importance of Particle Induced X-Ray Emission (PIXE) Analysis and Imaging to the Search for Life on the Ocean Worlds--Follow the (Outer Solar System) Water: Program Options to Explore Ocean Worlds--Analogies Among Current and Future Life Detection Missions and the Pharmaceutical/ Biomedical Industries--On Neuromorphic Architectures for Efficient, Robust, and Adaptable Autonomy in Life Detection and Other Deep Space Missions

Safety and Reliability - Safe Societies in a Changing World

The contributions cover a wide range of methodologies and application areas for safety and reliability that contribute to safe societies in a changing world. These methodologies and applications include: - foundations of risk and reliability assessment and management - mathematical methods in reliability and safety - risk assessment - risk management - system reliability - uncertainty analysis - digitalization and big data - prognostics and system health management - occupational safety - accident and incident modeling - maintenance modeling and applications - simulation for safety and reliability analysis - dynamic risk and barrier management - organizational factors and safety culture - human factors and human reliability - resilience engineering - structural reliability - natural hazards - security - economic analysis in risk managemen