Method for determining the orientation of a moving platform

摘要

An improved method for continuously determining the orientation of a moving user platform at a selected time fix. A Global Positioning System (GPS) is used to carry out the method and is made up of a plurality of twenty-four (24) earth-orbiting satellites wherein each satellite continuously transmits a pair of distinctively encoded RF signals. The GPS system is also provided with a computerized GPS receiver apparatus for use on a moving platform. The receiver apparatus is generally comprised of a rotatable antenna, a single channel multi-track geodetic receiver, a receiver microprocessor, and an orientation computer with a display. The receiver processor selects an optimum group of four satellites to be tracked. The orientation computer during antenna rotation selects a series of four equidistant points about the antenna periphery for receiving signals from each tracked satellite. The signals are transformed by the computer so as to provide a graphic data display output in near real time of the biased range (Doppler phase measurement) of each optimum-tracked satellite in relation to the moving platform. The biased range data of each graphic display for an optimum-tracked satellite is represented by a series of relatively spaced biased range data lines wherein any point on each line represents the biased range of the satellite in near real time. A common time fix is selected for the graphic data so that the change-in-range of each optimum-tracked satellite is analytically obtained with respect to at least one pair of diametrically opposed points of the series of four equidistant points of the antenna. The change-in-range is a function of predetermined equations so that the orientation of the rotating antenna and thus that of the platform is determined in terms of pitch, roll and yaw. By reason of the improved method for continuously determining orientation of a moving platform in relation to the earth, the method assists in accurately setting, e.g., a platform fire control system whether the platform is on or above the earth's surface.