EFFECT OF ACCELERATION SWITCHING DURING INS IN-FLIGHT ALIGNMENT.

Covariance simulation results are presented which show that the application of alternating axial acceleration to inertial navigation systems (INS) during in-flight alignment (IFA) results in an alignment time which is longer than that produced by a constant axial acceleration. Similarly, an S-shaped maneuver, which by its nature requires acceleration sign changes, yields a longer alignment time than that produced by a circular flight path. These results are also obtained analytically when simple IFA models, developed in an earlier work, are used. Using the simple models, it is shown that acceleration sign changes produce a correlation coefficient between the measured INS velocity error and the azimuth misalignment angle which crosses zero. This finding yields an explanation of the phenomenon of increased alignment time when the acceleration changes sign during the IFA.