Avionics Navigation Systems, 2nd Edition

7 Inertial Navigation

7.1 INTRODUCTION

Inertial navigation is a technique for determining a vehicle's position and velocity by measuring its acceleration and processing the acceleration information in a computer. Compared with other methods of navigation, an inertial navigator has the following advantages:

1. Its indications of position and velocity are instantaneous and continuous. High data rates and bandwidths are easily achieved.
2. It is completely self-contained, since it is based on measurements of acceleration and angular rate made within the vehicle itself. It is nonradiating and nonjammable.
3. Navigation information (including azimuth) is obtainable at all latitudes (including the polar regions), in all weather, without the need for ground stations.
4. The inertial system provides outputs of position, ground speed, azimuth, and vertical. It is the most accurate means of measuring azimuth and vertical on a moving vehicle.

The disadvantages of inertial navigators are the following:

1. The position and velocity information degrades with time. This is true whether the vehicle is moving or stationary.
2. The equipment is expensive ($50,000 to $120,000 for the airborne systems in 1996).
3. Initial alignment is necessary. Alignment is simple on a stationary vehicle at moderate latitudes, but it degrades at latitudes greater than 75° and on moving vehicles.
4. The accuracy of navigation information is somewhat dependent on vehicle maneuvers.

The techniques of inertial navigation evolved from fire-control ...