New approach to coarse alignment

Two different methods for coarse alignment are discussed. One of them (direct method) utilizes both accelerometers and gyros output for continuously tracking attitude estimation while the other (gyrocompassing) utilizes gyro outputs for continuously tracking attitude system and accelerometers for attitude estimation. The standard approach is gyrocompassing in spite of the fact that it is not always the most accurate. The rule for selecting an appropriate algorithm is obtained. Our approach is based on DCM instead of Euler angles estimation, a fact which allows us to solve the nonlinear problem