Robust rapid transfer alignment with an INS/GPS reference

Paul D. Groves, Genevieve G. Wilson, and Christopher J. Mather

Abstract:	Transfer alignment is the process of aligning and calibrating a guided weapon INS using data from the host aircraft INS. An all-purpose rapid transfer alignment algorithm set has been developed in-house by QinetiQ (formerly DERA). Rapid transfer alignment algorithms differ from their conventional counterparts in that attitude data from the host aircraft is used for the main alignment process in addition to velocity data. Previous work has shown how enhancements to a basic rapid transfer alignment algorithm can improve accuracy, particularly where lower grade inertial sensors are used. This paper presents the results of further studies, showing how transfer alignment robustness may be maximised. To optimise conventional transfer alignment performance, it is necessary to align for a certain duration and for the host aircraft to perform a manoeuvre between weapon initialisation and launch. Simulation studies show that this also applies to rapid transfer alignment, but that the manoeuvre requirements are less stringent than for conventional techniques. A problem with basic rapid alignment, where the weapon is mounted on a wing pylon of a fixed-wing aircraft, is that roll manoeuvres, such as wing rocks, can destabilise the Kalman filter, disrupting the estimation of attitude errors. This is verified by simulation and two different solutions are demonstrated. Weapon navigation accuracy may be significantly improved by using the aircraft INS/GPS navigation solution as the reference for transfer alignment as opposed to a pure inertial reference. However, where GPS is re-acquired after an outage of several minutes, a transient occurs in the INS/GPS solution which can disrupt transfer alignment. Transient detection and handling techniques have therefore been added to the QinetiQ transfer alignment algorithm set. Where the transfer alignment algorithm is provided with a pure INS reference in addition to the INS/GPS reference or with aircraft INS corrections, transients may be handled directly. Otherwise, Kalman filter based integrity monitoring techniques must be used. Both approaches are verified by simulation.
Published in:	Proceedings of the 2002 National Technical Meeting of The Institute of Navigation January 28 - 30, 2002 The Catamaran Resort Hotel San Diego, CA
Pages:	301 - 311
Cite this article:	Groves, Paul D., Wilson, Genevieve G., Mather, Christopher J., "Robust rapid transfer alignment with an INS/GPS reference," Proceedings of the 2002 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2002, pp. 301-311.
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