Two-Way Satellite Time Transfer to a Moving Platform; Conference paper

摘要

Precision time transfer is a key requirement for many applications. Three methods of time transfer that have typically been used are Stand-alone GPS, GPS Common View, and Two-way Satellite Time Transfer (TWSTT). Only the Stand-alone GPS approach has been regularly been used on a moving platform and this is the least accurate of the three time transfer methods. Analyses show that the standalone method is inadequate to meet the time requirement specified for some applications. Boeing and the US Naval Observatory (USNO) have investigated and tested a Two-way Satellite Time Transfer (TWSTT) method that has the potential of providing adequate time transfer accuracy to aircraft in flight. This approach employs a TWSTT system that communicates via satellite with a time reference center (such as the USNO) and the aircraft to provide accurate absolute time. Equipment used in the TWSTT test consisted of a time transfer modem and a GPS time transfer receiver furnished by the USNO, and a Boeing Connexion Ku-band aircraft transceiver and phased array antennas. The Connexion transceivers provided the satellite communication link between the moving platform and a Geostar-1 satellite that was used to relay information between USNO headquarters and the Boeing Seattle test site. Special test software, including a Kalman filter that processed raw pseudorange and pseudorange rate outputs from the GPS time transfer receiver, was also developed for the test. Data collected during the tests are presented in this paper along with an analysis of the results that have been collected to date. The two-way link that offers the cancellation of all errors in the time transfer channel could be provided by either geostationary or lower orbit altitude satellites.