Advanced Transfer Alignment for Inertial Navigators (A-Train)

William Graham and Kevin Shortelle

Abstract:	Airborne transfer alignment refers to the process of initializing a weapon-grade IMU prior to launch using data provided by the aircraft’s INS. Traditional transfer alignment procedures require the aircraft to execute lengthy horizontal-plane (s-turn) maneuvers lasting several minutes. During the maneuvers, INS and IMU velocity-match data are processed by a Kalman filter algorithm which recursively estimates and corrects IMU attitude and inertial sensor errors. Although capable of attaining milliradian alignment accuracy, lengthy traditional alignment procedures are not generally consistent with the requirements of quick-reaction weapon systems. This paper presents an advanced transfer alignment procedure developed to significantly reduce the alignment maneuver and timeline requirements for an air-launched weapon. An 18-state KaIman filter is designed to recursively process INS and IMU velocity-match and attitude-match data at a 12.5 Hz rate. The aircraft is required only to perform a brief 20-deg wing-rock maneuver during alignment. Laboratory and flight tests on an AH-64A Apache aircraft indicate that the A-TRAIN filter is capable of aligning the IMU to within 1 mrad of truth within 5 sec.
Published in:	Proceedings of the 1995 National Technical Meeting of The Institute of Navigation January 18 - 20, 1995 Disneyland Hotel Anaheim, CA
Pages:	113 - 124
Cite this article:	Graham, William, Shortelle, Kevin, "Advanced Transfer Alignment for Inertial Navigators (A-Train)," Proceedings of the 1995 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 1995, pp. 113-124.
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