Transfer Alignment Design Using a Gyro-free Inertial Navigation System

The initial value of the inertial navigation system of a launched vehicle can be obtained through the transfer alighnment. If the rotational rate of a moving vehicle exceeds the range of the gyroscope measurements, the angular velocity cannot be measured. Use of the gyroscope with complex structure, large size, more power consumption, and high cost may be avoided. These problems can be resolved by adopting a gyro-free inertial navigation system (GF-INS), which comprises only accelerometers. In the transfer alignment, the slave INS can be configured using a GF-INS. This paper proposes a new type of GF-INS-based transfer alignment design. The configuration of the proposed transfer alignment is presented and an error model of the GF-INS for the Kalman filter is derived. The observability of the proposed method is investigated for a gyro-free inertial measurement unit (GF-IMU) with a cubic structure at level flight with constant velocity and turn maneuver motions. Employing the same GF-IMU undergoing the same motions, the performance of the proposed transfer alignment is also evaluated. As the angular velocity can be measured additionally to the velocity and attitude, angular velocity matchings are also considered in the observability analysis and performance evaluation. It is found that the velocity and attitude measurements should be combined in the matchings of the GF-INS to improve the accuracy of the state estimates.