1421620 Inertial navigation system FERRANTI Ltd 11 June 1974 [12 June 1973] 27989/73 Heading G1C In an inertial navigation apparatus, the heading alignment of an inertial platform carried by a vechicle 14, e.g. ship-based aircraft is checked and corrected by means of a base station 10, e.g. the ship, which has equipment for determining the orientation α of a datum line 11 relative to a fixed reference direction, e.g. true north. The vehicle 14 carries a sighting mark and the base-station 10 a mirror 12 in which the sighting mark is visible to an observer in the vehicle 14 when the vehicle 14 is located on a base line 13 defined by the mirror 12. An aiming mark is carried on the vehicle and is movable 80 as to be aligned with the image of the sighting mark in the mirror 12, the aiming marks generating a signal indicative of its position relative to the vehicle axis 15 i.e. dependent upon angle γ. A navigation computor responds to the signals indicative of angle γ, to the angle between axes 11 and 13 which may be zero in the Fig. 1 embodiment, or # in the Fig. 3 embodiment, and angle α. Thus the heading alignment # of the vehicle inertial platform may be checked and corrected since if correct α = # - γ (Fig. 1) or α = # + γ - α (Fig. 3). The computer sends a correction signal to the platform if the equality is absent. The mirror may be a corner reflector.
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