Aerospace Navigation Systems

Alexander V. Nebylov, Joseph Watson, Alexander V. Nebylov, Joseph Watson

• Publisher: Wiley
• Year: 2016
• Print ISBN: 9781119163077
• eBook ISBN: 9781119163046
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Mechanical Engineering
• Index: Technology & Engineering

Compiled by leading authorities, Aerospace Navigation Systems is a compendium of chapters that present modern aircraft and spacecraft navigation methods based on up-to-date inertial, satellite, map matching and other guidance techniques. Ranging from the practical to the theoretical, this book covers navigational applications over a wide range of aerospace vehicles including aircraft, spacecraft and drones, both remotely controlled and operating as autonomous vehicles.  It provides a comprehensive background of fundamental theory, the utilisation of newly-developed techniques, incorporates the most complex and advanced types of technical innovation currently available and presents a vision for future developments. Satellite Navigation Systems (SNS), long range navigation systems, short range navigation systems and navigational displays are introduced, and many other detailed topics include Radio Navigation Systems (RNS), Inertial Navigation Systems (INS), Homing Systems, Map Matching and other correlated-extremalsystems, and both  optimal and sub-optimal filtering in integrated navigation systems.

1
Inertial Navigation Systems

Michael S. Braasch

School of Electrical Engineering and Computer Science, Avionics Engineering Center, Ohio University, Athens, OH, USA

1.1 Introduction

Inertial Navigation Systems (INSs) are modern, technologically sophisticated implementations of the age-old concept of dead reckoning. The basic philosophy is to begin with a knowledge of initial position, keep track of speed and direction, and thus be able to determine position continually as time progresses. As the name implies, the fundamental principle involved is the property of inertia. Specifically, a body at rest tends to stay at rest and a body in motion tends to stay in motion unless acted upon by an external force.

From Newton’s second law of motion, the well-known relation can be derived:

(1.1)

where “

” is a force vector, “m” is mass, and “

” is the acceleration vector. Conceptually, it is then possible to measure force and subsequently determine acceleration. This may then be integrated to determine velocity, which in turn may be integrated to determine position.

Each accelerometer described in chapter 5 of the companion volume, Aerospace Sensors (Konovalov, 2013), can determine a measure of linear acceleration in a single dimension, from which it follows that multiple accelerometers are needed to determine motion in the general three-dimensional case. However, in addition, it is necessary to determine the direction in which the accelerometers are pointing, which is not a trivial exercise considering that an aircraft can rotate around three axes. If the accelerometers are hard-mounted to the vehicle (as is typically the case), then theoretically they can be oriented in any direction. Double integration of their outputs is useless if this time-varying orientation is not properly taken into account.

The determination of orientation (also known as attitude determination) is accomplished through processing of data from the gyroscopes described in chapter 6 on Aerospace Sensors (Branets et al., 2013). These devices measure either angular rate and/or angular displacement. So-called navigation-grade gyros can measure angular rate with accuracies on the order of 0.01°/h. Such sensors are needed to determine attitude to permit velocity and position determination in a given reference frame.

There are two main types of INSs: gimbaled and strapdown (Lawrence, 1998). In a gimbaled system, the accelerometers are mounted on a platform that is rotationally isolated from the vehicle. This platform is maintained in a local-level orientation so that there are two accelerometers in the horizontal plane for providing the data needed to compute horizontal velocity and position. In a strapdown system, the accelerometers are hard-mounted to the vehicle itself. Gimbaled systems are mechanically complex but do not require intensive computational capability. Strapdown systems are mechanically simple but require more intensive computations to deal with the time-varying orientation of the vehicle. Throughout the remainder of this chapter, strapdown operation will be assumed because modern processors are in no way challenged by the computational requirements. Furthermore, the simplified mechanical design (along with modern optical gyros) yields systems with Mean Time Between Failures (MTBFs) measured in tens of thousands of operational hours (versus ...

Table of contents

• Cover
• Title Page
• Table of Contents
• The Editors
• Acknowledgments
• List of Contributors
• Preface
• 1 Inertial Navigation Systems
• 2 Satellite Navigation Systems
• 3 Radio Systems for Long-Range Navigation
• 4 Radio Systems for Short-Range Navigation
• 5 Radio Technical Landing Systems
• 6 Correlated-Extremal Systems and Sensors
• 7 Homing Devices
• 8 Optimal and Suboptimal Filtering in Integrated Navigation Systems
• 9 Navigational Displays
• 10 Unmanned Aerospace Vehicle Navigation
• Index
• End User License Agreement