Space-borne pseudo-range reconstruction and its performance analysis in dynamic orbit determination

The Global Positioning System (GPS) is nowadays widely used for navigation of spacecraft in low Earth orbit (LEO). Both real-time positioning information (navigation solutions) and raw GPS measurements (pseudo-range, carrier-phase, Doppler shift and signal-to-noise ratio) are usually transmitted to ground control centres for post-processing. However, for certain LEO missions, only navigation solutions are available due to the limited capability of space-borne GPS receivers. In this case, navigation solutions are commonly used as pseudo-observations in dynamic orbit determination (referred to as dynamic filtering) to obtain a smooth and continuous orbit; however, the achievable orbit accuracy is limited since broadcast ephemeris data from the GPS navigation messages are used and the more accurate GPS orbit and clock information are only available in post-processing. In this study, a method of reconstructing space-borne pseudo-range measurements from real-time positioning information is developed, thus, the more accurate GPS orbit and clock products from the International GNSS Service (IGS) are able to be used in dynamic orbit determination. Real GPS data from the TerraSAR-X mission are used to validate this approach and its performance in dynamic orbit determination is assessed as well. Results show that the orbit accuracy of navigation solutions can be significantly improved from 15m to 5m after a dynamic filtering process is performed. A remarkably better orbit accuracy of about 0.5m is achieved in dynamic orbit determination using the reconstructed pseudo-range measurements and IGS rapid orbit and clock products; both the requirements of 24-h timeframe and an orbit accuracy of 2m for generating proper SAR images are well satisfied.