Design of a digital self-alignment controller for a ship´s inertial navigation system at sea

Mathematical models are developed for the misalignment equations of a ship´s inertial navigation system (s.i.n.s.) following restart after a complete shutdown at sea. The ships manoeuvres are modelled as stochastic processes and the misalignment is presented as a linearised stochastic process, which can be controlled by the gyro torqueing currents. The misalignment is observed by accelerometers, assuming base motion isolation, augmented by the `ships log¿ (a measure of velocity). The alignment is treatedas a discrete stochastic linear regulator problem, using a Kalman-Bucy filter. Simulation results show that good alignment can be achieved in about an hour, but a time-varying estimator must be incorporated.