Accession Number : ADP004589

Title :   The Role of a Low Earth Orbiter in Intercontinental Time Synchronization via GPS (Global Positioning System) Satellites,

Corporate Author : JET PROPULSION LAB PASADENA CA

Personal Author(s) : Wu,S. C. ; Ondrasik,V. J.

Report Date : 02 APR 1984

Pagination or Media Count : 18

Abstract : Time synchronization between two sites using differential GPS has been investigated by a number of researchers. When the two sites are widely separated, the common view period of any GPS satellite becomes shorter; low elevation observations are inevitable. This increases the corrupting effects of the atmospheric delay and, at the same time, narrows the window for such time synchronization. This difficulty can be alleviated by synchronization. This difficulty can be alleviated by using a transit site located midway between the two main sites. The main sites can now look at different GPS satellites which are also in view at the transit site. However, a ground transit site may not always be conveniently available, especially across the Pacific Ocean; also, the inclusion of a ground transit site introduces additional errors due to its location error and local atmospheric delay. An alternative is to use a low earth orbiter (LEO) as the transit site. A LEO is superior to a ground transit site in three ways: (1) It covers a large part of the earth in a short period of time and, hence, a single LEO provides worldwide transit services; (2) it is above the troposphere and thus its inclusion does not introduce additional tropospheric delay error; and (3) it provides strong dynamics needed to imrpove GPS satellite positions which are of importance to ultraprecise time synchronization. (Author)

Descriptors :   *SYNCHRONIZATION(ELECTRONICS), *GLOBAL POSITIONING SYSTEM, *DATA TRANSMISSION SYSTEMS, SITES, ORBITS, MATHEMATICAL MODELS, COVARIANCE

Distribution Statement : APPROVED FOR PUBLIC RELEASE