F-16 flight tests of a rapid transfer alignment procedure

Abstract

This paper presents the results of an effort directed at developing and flight-testing an innovative rapid transfer alignment algorithm for inertially-guided air-launched munitions. The algorithm, referred to as RAP (Rapid Alignment Prototype), employs a 17-state Kalman filter designed to accurately align a weapon-grade Inertial Measurement Unit (IMU) relative to an aircraft-grade Inertial Navigation System (INS) within five seconds. The alignment procedure requires the pilot to execute only a brief wing-rock maneuver. No time-consuming heading changes or lengthy s-turns are required. The RAP Kalman filter achieves the rapid convergence time by recursively processing both velocity-match and attitude-match measurements at a 12.5 Hz rate to estimate and correct IMU velocity, attitude, and inertial sensor errors. Following laboratory and van testing at Eglin AFB, a series of F-16 flight tests were conducted. Flight test results demonstrated that the RAP filter achieved sub-milliradian alignment accuracy in less than 10 seconds. As further confirmation of alignment accuracy, IMU position error statistics were computed over a 100-sec post-alignment captive-carry trajectory. Test results indicated that the mean radial position error after 100-sec of unaided navigation was roughly 70 ft with an associated CEP of 61 ft. RAP's unprecedented alignment accuracy and reduced launch timeline provide a rapid-response capability for time-critical targets such as mobile launchers and troop emplacements.