Initial alignment method for a strapdown inertial navigation system on a swing base

The problem of strapdown inertial navigation system (INS) initial alignment is considered. It is assumed that this system does not move relative to the Earth, but its body frame can perform uncontrolled angular motions. The basic mathematical models of the mentioned problem are described. These models are based on a special approximation procedure applied to accelerometer measurements. These measurements are projected onto the axes of the “frozen” INS instrument reference at the initial time instant of the alignment.