| Popis: |
This paper investigates the effectiveness of pre-compensating the beam wander effect (tip-tilt distortion) experienced by an uplink optical signal, from a ground station to a satellite, based on the tip-tilt information of the downlink signal (from the satellite to the ground). A test campaign was carried out in May 2018 at the Optical Ground Station (OGS) of the European Space Agency (ESA), to perform measurements of double stars featuring angular separations representative of the point-ahead angle of GEO/LEO satellites. The purpose of gathering these measurements is to investigate the relationship between double stars angular separation and their differential tip-tilt distortion. This analysis evaluates the influence of the point-ahead angle of the satellite, on the tip-tilt correlation between the uplink and the downlink signals. This paper describes the algorithm used to determine the tip-tilt error due to anisoplanatism, and presents the preliminary results that were extracted from the measurements. Then, it is shown how to estimate the jitter of the telescope from the common motion of two independent stars as seen in the focal plane of the telescope. Finally, the paper provides a methodology to determine the maximum transmitter aperture diameter of a ground-based laser communication terminal, in case tip-tilt pre-compensation is applied to the uplink signal based on the received satellite signal. |
