A High Sensitive GNSS Receiver for High Altitude Space Missions

Abstract

Global Navigation Satellite System (GNSS) receiver were designed to provide positioning and timing service for terrestrial users. For recent decades, it has been gradually used in low earth orbit (LEO) space missions, such as LEO satellites and spacecraft. However, there is a big challenge for GNSS receiver to use in high earth orbit (HEO) or lunar mission. Because the altitude of HEO or moon spacecraft is higher than that of GNSS satellites whose antenna points to the Earth to serve the terrestrial earth users, the GNSS receiver for HEO or lunar mission has to receive the signal from the spillover around the earth of the main lobe or from the transmitting antenna side lobes. The power of the first side lobe signal is 20 dB lower than the main lobes signal. It is difficult for a traditional GNSS receiver to track the side lobe signal and provide positioning service. In order to solve this problem, we are developing a High Sensitive GNSS Receiver (HiSGR) which can be used by a halo orbiter at Earth-Moon L2 point. This HiSGR employs the parallel code search (PCS) algorithm to speed up the acquisition process and the full bit method is used to improve sensitivity. In order to track the weak GNSS signal, an EKF is used for each satellite tracking channel to replacing the traditional loop filter. The GPS performance for the halo orbiter is analyzed and the HiSGR has experienced extensive tests to demonstrate the promising performance. It is shown that the acquisition and track sensitivity of HiSGR can reach 15 dB-Hz, which can meet the requirement of a spacecraft in the halo orbit and can be used on the Earth-Moon L2 point.