NEW OBSERVATIONAL TECHNIQUES AND PRECISE ORBIT DETERMINATION OF ARTIFICIAL-SATELLITES

Modern observational techniques using ground-based and space-based ins trumentation have enabled the measurement of the distance between the instrument and satellite to better than one centimeter. Such high prec ision instrumentation has fostered applications with centimeter-level requirements for satellite position knowledge. The determination of th e satellite position to such accuracy requires a comparable modeling o f the forces experienced by the satellite, especially when classical o rbit determination methods are used. Geodetic satellites, such as Lage os, in conjunction with high precision ground-based laser ranging, hav e been used to improve for modeling of forces experienced by the satel lite. Space-based techniques, such as Global Positioning System (GPS), offer alternatives, including kinematic techniques which require no m odeling of the satellite forces, or only rudimentary models. This pape r will describe the various techniques and illustrate the accuracies a chieved with current satellites, such as TOPEX/POSEIDON, GPS/MET and t he expectations for some future satellites.