Techniques for determining orbital data

Abstract

Techniques are disclosed for determining orbital data of space borne vehicles including earth satellites such as those of the NAVSTAR Global Positioning System. Each of a set of such satellites transmits signals which include carrier waves which may be suppressed, or only implicity present. The signals are received from the observable satellites concurrently by means of an antenna at each of at least three ground stations forming a network of baselines. The stations are arrayed such that the ratio of the maximum to the minimum baseline length is much greater than one. From the signals received at a station pair forming each baseline a time series of doubly-differenced phase measurement data is formed which is biased by an integer number of cycles of phase. The data series for different satellite and station pairs are processed together to determine the orbits of the satellites and the doubly-differenced phase biases. Unique determination of the integer values of at least some of the biases is facilitated by the above noted spatial arrangement of the stations such that the ratio of the maximum to the minimum baseline length is much greater than one. This integer bias determination enhances the accuracy of the related orbit determination. Unique determination of the integer values of at least some of the doubly-differenced carrier phase biases may also be facilitated by the use of a plurality of carrier frequencies with the ratio of the maximum to the minimum frequency being much greater than one.