Ferranti: Light-Weight Inertial Platforms

An ideal inertial navigation system should present an accurate indication of the position and the velocity of a vehicle at every point on its journey. For civil aviation, maritime and land uses this provides a task of enormous technological complexity, but it is in military aircraft and aerospace applications that the demands made on a system reach their peak. Great accuracy, light weight, fast response and the ability to cope with extreme operating conditions (including aircraft manoeuvres) all contribute to this. Two types of components, the accelerometers and the gyroscopes, provide the sensors by which motion is detected. The principle behind their operation is that matter resists changes in its motion — that it has inertia. In its simplest aspect, the accelerometer measures vehicle acceleration, integrating once to give a measure of velocity and twice to give a measure of distance travelled. The direction along which the accelerometer measures must be kept fixed in space or else allowance must be continuously made for its changing direction. This is achieved by the gyroscopes which provide a stable attitude-reference.