Inertial Instrument Error Characterization

Abstract

ABSTRACT: Dependence of inertial instrument errors on forces and rotations acting on a strapdown IMU is well-known. With the same motions affecting many error sources it is obviously inaccurate to ignore these interactions. Although this fact is likewise well known, the implications need to be confronted industry-wide. This will improve both compensation of degradations and specifications for amounts remaining after imperfect calibration. Importance of the issues raised herein arises from the need for free-inertial coast capability when GPS and other updates are unavailable. After path changes – or even different modes of vibration – drift patterns that were “learned” pre-outage then become inapplicable, thus needing to be “unlearned.” Self-evident as that may seem, there is substantial literature endorsing extended coast periods with simplified drift models for use in congested airspace (in or near terminal phase). That endorsement would vanish after a simple test (not a simulation) comparing GPS vs free-inertial coast for a half Schuler period starting with a 90 deg or 180 deg turn.