Horizon-Based Satellite Navigation Systems

The earth´s horizon provides an important and conspicuous basis for the development of self-contained systems for earth-satellite navigation. The present paper investigates horizonbased navigational systems in which the requirement for vehicular yaw stabilization is not imposed. This permits the development of a variety of navigational techniques which generally fall within one of the following divisions: star matching, stellar almucantar transits, limb occultations, surface almucantar transits and map matching. By measuring time directly the raw data is immediately available for digital processing. Error contributing factors such as the aspherical shape of the earth and the seasonal and latitudinal variation of the atmospheric density profile can be largely eliminated by introducing suitable corrections. Furthermore, heavy reliance can be placed on the digital computer for star identification and for the introduction of these various correction terms. As a result, these techniques have the virtue of requiring only the simplest of navigational equipment. They yield earth-satellite position fixes with potential accuracies in the range from 1 to 10 miles.