Research On In-flight Alignment Technique Of High-precision Strapdown Inertial Navigtation System

Strapdown inertial navigation systems (SINS), which have high reliability and low cost, have been chosen for more andmore tactical guidance weapons, and at the same time，these guidance weapons have begun to using aircraft as theirlaunch platform for improving tactical agility. Inertial navigation systems (INS), which are the core navigation apparatusof tactical guidance weapons, must be aligned befor launching, and therefore the in-flight alignment of SINS has been animportant subject in inertial navigation techniqure filed. In-flight alignment of hign precision SINS is reaserched in thisthesis.Based on the calculating equations of SINS, a transfer alignment error equation is founded, wherein instrument error,flexture movement, installation error, and rod effection in operating enviorment of master INS and slave INS areconsidered. In-flight alignment method of ring laser gyro strapdown inertial navigation system (RLG SINS) and fiberoptic gyro strapdown inertial navigation system (FOG SINS) are both researched in this thesis.Ring laser gyro has advantages of high scale factor stability and linearity, low sensitivity of acceleration, short startup time,and high turn-on repeatablity, therefore the main purpose of the alignment of RLG SINS is to estimate the three angularmisalignment, while gyro drift and scale factor error are both ignored. Location match, velocity match, and velocity pluseattitude match scheme are studied for RLG SINS in-flight alignment. Mathematical simulation is operated as well, andthe result shows that the velocity pluse attitude method has advantages of short alignment time and low maneuverrequirement, which is an ideal in-flight alignment method of RLG SINS.Fiber optic gyro, which has important status in inertial technique area, has potential predominance on both precision andcost. However, the drift stability of FOG is lower than that of RLG, especially in temperature-change environment.Therefore, unlike the RLG SINS, the gyro drift measurement of FOG SINS must be considered during in-flightalignment. Because of the impaction of flexture movement of aircraft wings and the output noise of the inertialinstruments, the location match, the velocity match, and the velocity pluse attitude match scheme are not fit for the gyrodrift measurement task. Accordingly, a new-style transfer alignment method named ‘piece-wise velocity match transferalignment method’ is brought out. In this method, two level straight skyways are set for measuring the three anglemisalignment and the two level gyro drift, a third skyway is set for measuring the azimuth gyro drift. Mathmeticalsimulation and flight test result shows that the ‘piece-wise velocity match transfer alignment method’ is a reliable andperfect in-flight alignment scheme for FOG SINS.