Aerospace Sensor Systems and Applications

473 Pages·1996·10.08 MB·English

by  Shmuel Merhav (auth.)

Aerospace Sensor Systems
and Applications
Springer
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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