Kalman filter mechanization for INS airstart

A strapdown mechanization and associated Kalman filter were developed to provide both ground align and airstart capabilities for inertial navigation systems using Doppler velocity and position fixes, while not requiring an initial heading estimate. This is accomplished by use of a Doppler velocity sensor and a position source such as the global positioning system (GPS) manual fly-over update or target sighting systems. Filter transition from coarse to fine align mode is accomplished without disrupting the estimation of the inertial instrument or aiding sensor errors, by defining the azimuth error state as wander angle error, and using a simple, but effective, manipulation of the filter covariance matrix