Aerospace Sensor Systems and Applications PDF
Preview Aerospace Sensor Systems and Applications
Aerospace Sensor Systems and Applications Springer New York Berlin Heidelberg Barcelona Budapest Hong Kong London Milan Paris Singapore Tokyo Shmuel Merhav Aerospace Sensor Systems and Applications With 193 Figures , Springer Shmuel Merhav Department of Aerospace Engineering Technion Israel Institute of Technology Haifa, 32000 Israel Library of Congress Cataloging-in-Publication Data Merhav, Shmuel. Aerospace sensor systems and applications / Shmuel Merhav. p. cm. Includes bibliographical references and index. ISBN-13: 978-1-4612-8465-9 e-ISBN-13: 978-1-4612-3996-3 001: 10.1007/978-1-4612-3996-3 1. Avionics. 2. Detectors. 3. Aeronautical instruments. 4. Space vehicles-Guidance systems. I. Title. TL695.M47 1996 629.135-dc20 95-51161 Printed on acid-free paper. © 1996 Springer-Verlag New York, Inc. Softcover reprint of the hardcover I st edition 1996 All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer-Verlag New York, Inc., 175 Fifth Avenue, New York, NY 10010, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereaf ter developed is forbidden. The use of general descriptive names, trade names, trademarks, etc., in this publication, even if the former are not especially identified, is not to be taken as a sign that such names, as understood by the Trade Marks and Merchandise Marks Act, may accordingly be used freely by anyone. Production managed by Hal Henglein; manufacturing supervised by Joe Quatela. Camera-ready copy supplied by the author. 9 8 7 6 5 4 3 2 To Naomi Preface This book is about aerospace sensors, their principles of operation, and their typical advantages, shortcomings, and vulnerabilities. They are described in the framework of the subsystems where they function and in accordance with the flight mission they are designed to serve. The book is intended for students at the advanced undergraduate or graduate level and for research engineers who need to acquire this kind of knowledge. An effort has been made to explain, within a uniform framework of mathematical modeling, the physics upon which a certain sensor concept is based, its construction, its dynamics, and its error sources and their corresponding mathematical models. Equipped with such knowledge and understanding, the student or research engineer should be able to get involved in research and development activities of guidance, control, and navigation systems and to contribute to the initiation of novel ideas in the aerospace sensor field. As a designer and systems engineer, he should be able to correctly interpret the various items in a technical data list and thus to interact intelligently with manufacturers' representatives and other members of an R&D team. Much of the text has evolved from undergraduate and graduate courses given by the author during the past seventeen years at the Department of Aerospace Engineering at the Technion- Israel Institute of Technology and from his earlier research and development experience in flight control, guidance, navigation, and avionics at the Ministry of Defense Central Research Institute. An effort has been made to create a text that is as self -contained as possible. The professional background, of potential students for the sensor systems area may be aerospace, mechanical, or electrical engineering. Accordingly, the different levels of students' prior knowledge may require different approaches in introducing this interdisciplinary material. In order to minimize this potential difficulty, Chapters 1 and 2 are introductory. Using elementary linear systems theory and random processes, Chapter 1 introduces the principal types of aerospace sensors in generic form. Their common properties are explained in regard to their dynamic response to "legitimate" inputs, environmental interferences, and noise, which in Chapter 1 is not yet statistically defined. Chapter 2 is an introduction to random processes that provides the basis for statistical sensor error modeling and for the operations of filtering and estimation. In many cases, these have become integral functions of the sensor system. The material covered in Chapter 2 also paves the way to the operations of smoothing and prediction and to the mutual aiding of sensors by means of complementary and Kalman filtering. The present time is a period of transition in the field of sensor technology. In addition to classical sensors like the vertical, directional, and rate gyros viii PREFACE or analog accelerometers. all of which date back to the beginning of the century. new developments in the past thirty years have yielded optical "gyros" and quartz or silicon vibrating beam accelerometers. These are gradually gaining more ground in modem sensor systems. Sooner or later. these technologies are bound to replace the traditional ones. It appears. however. that they will coexist side by side for quite a few years to come. The reason for this is that apart from the continuing stringent sensor requirements for high performance aircraft and spacecraft. where cost is relatively immaterial. there is a growing need for low-cost sensors in remotely piloted vehicles (RPVs) and tactical missiles. In these. the traditional sensors often "do the job" at a reasonable cost while the modem technologies. such as quartz or silicon have not yet sufficiently matured or are still too costly. For this reason. Chapter 3 is devoted in part to traditional analog accelerometers and Chapter 4 to electromechanical gyros. Although a vast literature on these topics is available. they are presented here in a manner that is particularly useful for the system engineering level. Combining skeleton 3-D drawings of all the functional parts and components along with the corresponding notations of variables and parameters facilitates the formulation of the mathematical models that provide the responses to the "legitimate" inputs and to noise and environmental interferences. An important class of errors due to imperfections in electromechanical sensors. such as anisoelasticity. vibro-pendulosity. coning. sculling. and anisoinertia. is due to the interaction of vehicular vibrations with the mechanical imperfections. These have been a major issue. especially since the advent of strapdown technology where the sensors are fully exposed to external vibrations. These errors are not treated in this book for the following reasons: (i) They have been amply treated in numerous texts on inertial navigation. such as G.R. Macomber and M. Fernandez (Inertial Guidance Engineering. 1962). and more recently P. Savage (Strapdown Inertial Navigation Notes. 1990). (ii) With the recent maturing of laser gyros and their accelerating application in inertial navigation and flight control. these effects are rapidly becoming less relevant. (iii) In low-cost flight control and guidance applications. their effect is small in comparison with other error sources. Only a modest selection of the most important rotation and force sensors is discussed. Among them are the traditional vertical (VG). directional (DG). and rate gyros (RG). the floated rate integrating gyro (RIG). and the dry tuned rotor gyro (DTG). The gas bearing and electrostatically supported gyro (ESG) are also described as outstanding engineering achievements. Chapter 5 presents a number of important applications of gyroscopic technology. Among them are the two-axis gyro stabilized platform. which is a common payload in remotely piloted vehicles (RPVs) and guided missiles. the spinning wheel seeker heads for infrared homing missiles. ground-based optical seeker heads used in beam riding missile guidance. and the gyro-stabilized three-axis platform for INS and models for its error propagation for different sensor noise statistics. Chapter 6 introduces Coriolis angular rate sensors that use rotating or vibrating accelerometers to provide measurement of inertial angular rate. sometimes along with specific force sensing implemented by quartz or silicon technology. Due to their miniature dimensions. Coriolis inertial sensors are PREFACE ix already applied in low-cost flight control systems and are regarded as strong contenders in inertial navigation, at least for tactical applications. Chapters 7 and 8 are devoted to laser gyros. In Chapter 7, the passive interferometric fiber-optic gyro (IFOG) is presented. Its mathematical model is developed on the basis of the Sagnac effect. Performance limits due to shot noise and other effects are also discussed. The need for its implementation as a force balance sensor is explained. Recent results demonstrating INS grade performance achieved by the leading industries in the field are presented in evidence of their establishment as principal flight control and high-grade navigation sensor technologies. Chapter 8 is devoted to the active ring laser gyros (RLG). Their principle of operation and analytical model as an extremely linear and precise open-loop sensor are presented as an almost ideal incremental rotation sensor, which perfectly and naturally interfaces with digital signal processors and navigation computers. The most recent successful achievements in zero lock RLGs are also presented. Chapter 9 is devoted to mutual aiding of sensors which is also known as measurement fusion. The methodology is a special form of Kalman filtering basically configured by the complementary filter constraint. The application is almost exclusively to linear systems, although its effectiveness in nonlinear problems is also demonstrated. In this Chapter, examples are shown that range from applications of simple linear time invariant systems to nonlinear time-varying systems requiring extended Kalman filtering. The power of the concept is demonstrated by the exceptionally good performance which can be achieved by quite crude low-cost sensors if they are aided by other sensors that have complementary properties. Throughout the text, the emphasis in the presentation has been to provide physical insight, not necessarily formalism and rigor. The material is enhanced by examples, problems, and numerous illustrations. In them, label fonts are in italics if they refer to variables or parameters and in Helvetica if they refer to components or parts. Sections that are either highly specialized or are not essential to the principal topics are marked by the symbol €B. Their omission should not hamper the understanding and digestion of the main material presented. Acknowledgments It is a pleasure to express my appreciation and thanks for the support of colleagues. friends. and organizations throughout the preparation of this manuscript. I thank Professor Dan DeBra of Stanford University. Professor Bernard Friedland of New Jersey Institute of Technology, and Professor W.M. Hollister of MIT for advocating the prospectus. and for their encouragement and enlightening discussions. My thanks also go to Dr. P.K. Menon. who read part of an early version of the manuscript. for his constructive comments and suggestions while. during a sabbatical leave. we shared an office at NASA Ames Research Center in California. I have been fortunate to be associated with Sundstrand Data Control in Redmond. WA (now AlliedSignal) in the research and development effort of novel Coriolis multi-sensor concepts and to get to know the Instrument Division Chief. Norman Klein. to whom I am indebted for his support for my cooperation with such gifted research scientists as Rex Peters. Rand Hulsing. and Brian Norling. who provided valuable technical information and enlightened me with numerous insights which are usually unavailable in the open literature. I am indebted to Mr. Gershon Engel of the Israel Aircraft Precision Instrument Industries for providing me with detailed and valuable material on dynamically tuned gyros. and Professor Shaoul Ezekiel of MIT who brought me up to date on interferometric optical gyros. I am also indebted to Professor I. Bar-Itzhack of the Technion Aerospace Department. who acquainted me with some of the subtleties and intricacies in analytical platform algorithms. and to Professor M. Guelman and Dr. J. Oshman. who read parts of the manuscript and whose comments are greatly appreciated. Last. but not least. I am indebted to my former graduate students. particularly to Dr. Jacob Reiner. Dr. M. Velger. and Mr. M. Koifman. whose work is reflected in some specialized sections of this book. Shmuel Merhav Haifa. Israel Contents Preface vii Acknowledgments xi Introduction and historical background 1 1. Principles and Elements of Measurement Systems 5 1.0 Introduction 5 1.1 Elements in open-loop instruments 5 Instruments, sensors, and systems 5 Basic sensor elements 6 Auxiliary junctions and elements 6 Equilibrium 7 Definitions of sensor junctions 8 1.2 Measures and units 9 Basic measures 9 Units and standards 9 Reference values 9 1.3 Passive and active instruments 10 Contact and remote sensing 10 Tapping of energy sources 10 Input impedance 11 1.4 Characteristics. resolution, and dynamic range 11 Domain and range 11 Linearity, resolution, and dynamic range 12 Bias, dead zone, and saturation 13 Hysteresis 13 I.S Errors due to dynamics. nonlinearity, and noise System and measurement equations 15 Classification of errors 16 1.6 Environmental interference 19 Error model formulation 19 Additive and scaling errors 20
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