Accession Number : ADP009111

Title :   Time Transfer Using Geostationary Satellites: Implementation of Kalman Filter,

Corporate Author : NATIONAL AERONAUTICS AND SPACE ADMINISTRATION GREENBELT MD GODDARD SPACE FLIG HT CENTER

Personal Author(s) : Meyer, F.

Report Date : 02 DEC 1993

Pagination or Media Count : 9

Abstract : Since 1988, various experiments 1, 2, 3, 4 have shown that the TV signals transmitted by direct TV satellites may easily be used to perform time transfers at the level of a few tens of nanoseconds, the main source of error being the uncertainty on the satellite position. We first present the two methods used in our experiment to reduce the effects of the satellite residual motion : the first one consists in estimating the longitude variations of the satellite and then using this information to improve other measurements. This allows to reduce the uncertainty to values between 9 and 50 nanoseconds according to the position of the involved stations. In the second method we deter-mine the satellite position by using the data collected by three calibrated stations. Time transfer between each of these stations and a fourth one has been shown to be achievable at the precision level of ten nanoseconds. A new approach based on the use of a Kalman filter is proposed in order to take account the dynamics of the geostationary satellite. The precisions on orbital elements and clock differences and rates determination given by the first simulated applications of the Kalman filter are presented and compared to those obtained by the other methods.

Descriptors :   *SYNCHRONIZATION(ELECTRONICS), *VIDEO SIGNALS, *RADIO LINKS, CLOCKS, DETERMINATION, ERRORS, LONGITUDE, MEASUREMENT, MOTION, PRECISION, RATES, TIME, UNCERTAINTY, VARIATIONS, FRANCE, KALMAN FILTERING, CALIBRATION, COMMUNICATION SATELLITES, COMMUNICATION SATELLITES.

Subject Categories : Radiofrequency Wave Propagation

Distribution Statement : APPROVED FOR PUBLIC RELEASE