The Navstar Global Positioning System Control Segment Performance During the First Year

Abstract

This paper reports the preliminary performance of the Navstar Global Positioning System Control Segment (CS) during the period July 1977 through July 1978. During this period, three navigation satellites were launched and were tracked and uploaded by the CS. An overview of the CS is presented as well as a summary of the present system status. User performance, total system performance, and CS performance are discussed, and methods for determining the latter are described. Performance measures including first measurement residuals and predicted pseudorange error for NTS 2 and first measurement statistics, predicted User Range Error, ephemeris prediction error, and predicted clock error for the NDS satellites are presented. The preliminary performance results presented are very good considering the early stage of multi-satellite tracking. Projecting the two satellite performance to four satellites, the CS contribution to user navigation error is 12.8-20.5 meters at 2 hours. This error consists of ephemeris and clock prediction errors of approximately 3.5 and 4.5 meters, respectively.