electronic system that continuously monitors the position and acceleration of a vehicle, usually a submarine or a missile, and thus provides navigational data or control without need for communicating with a base station. The basic components of an inertial guidance system are gyroscopes, accelerometers, and a computer. The gyroscopes provide fixed reference directions, and accelerometers measure changes in the velocity of the system. The computer processes information on changes in direction and acceleration of the vehicle and feeds its results to the vehicle's navigation system. A typical inertial guidance system, such as might be used on board a missile, uses three gyroscopes and three accelerometers. The three gimbal-mounted gyroscopes establish a reference frame in terms of the vehicle's roll, pitch, and yaw for the orientation of the three accelerometers. The accelerometers measure velocity changes in each of these three directions. The computer performs two separate integrations on the data it receives from the inertial guidance system. First, it integrates the acceleration data to get the current velocity of the vehicle; then, it integrates the computed velocity to determine the current position. This information is compared continuously to the desired (predetermined and programmed) course. Minute errors in the measuring capabilities of the accelerometers or in the balance of the gyroscopes can introduce large errors into the information that the inertial guidance system provides. These instruments must, therefore, be constructed and maintained to strict tolerances.

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