Determining low-Earth-orbit satellite orbits with software-defined radio phased-array observations.

In recent years the need for Low Earth Orbit (LEO) satellite ground station are increased because of the explosion of small satellites such as Cubesat. Most of these ground stations have mechanical rotators for directing antennas toward satellites and depend on Two-line Element (TLE) orbit parameters which are provided by NORAD for tracking satellite positions. We propose and implement an approach that can help satellite ground stations working autonomously without access to NORAD TLE. Radio signals that are transmitted by the satellites themselves can be observed from Earth by a phased array technique. The radio receiver was designed and built with software-defined-radio technology that made it simple and flexible so that the phased array that is used for satellite tracking may also be used for satellite communication without hardware redesign. Orbit determination was implemented using a least squares fitting algorithm. The experimental results from tracking a real satellite showed that the idea is feasible. The satellite motion was predicted accurately when new observations were updated regularly. In case of loss of observations, the propagation result was still less than 100 kilometers error (equivalent to 0.2% of the orbit circumference) after one week from the last observation.