Two-Way Satellite Time and Frequency Transfer Experiment via IGSO Satellite

In order to study the instability introduced by path non-reciprocity due to satellite motion in an earth fixed frame in Two-Way Satellite Time and Frequency Transfer (TWSTFT), we do TWSTFT experiment between National Time Service Center (NTSC) and Urumchi Observatory (UO) via APSTAR-1 inclined geosynchronous satellite orbit (IGSO) satellite for the first time. The satellite is with the inclination of 2.2 degree and it can moves up to plusmn1600 km in the direction of perpendicular to equator plane, while SINOSAT-1 geostationary (GEO) satellite moves only up to about 30 km in that direction. To improve the quality of observation, the PN-code with chip rate of 20 MChip/s is chosen in SATRE modem in TWSTFT. Each observation period includes 3 hours: APSTAR-1 satellite is observed with the two TWSTFT stations in the first hour, and SINOSAT-1 satellite is observed with the same stations in the second hour, and nothing is done in the third hour. We repeat the periodic observation for about two months in winter in 2006. Our analysis is as follows, for a given satellite, we first calculate the ionosphere delay with IGS TEC map data and deduce it from TWSTFT result, for our TWSTFT comparison is with C-band. Then we calculate and deduce Sagnac effect. After that, the variation of difference between the TWSTFT result via SINOSAT-1 satellite and that via APSTAR-1 satellite mainly represents the influence introduced by APSTAR-1 satellite motion in the earth fixed frame. Experiment result and analysis indicate that the path non-reciprocity due to satellite movement in the earth fixed frame in TWSTFT between NTSC and UO via APSTAR-1 satellite varies in an approximate sinusoidal pattern everyday, and the amplitude of the daily variation is about a few tenths of a nanosecond. The experiment is helpful for studying TWSTFT via non-geostationary satellite.