Triple-band GNSS Receiver with E6 HAS corrections for Precise Onboard Orbit Determination in LEO

C. Bastos, R. Fernandes, R. Prata, J.M. Palomo, A. Fernandez, F. Darugna, M. Bardella, M. Sciarratta, S. Casotto, P. Giordano, P. Zoccarato

Abstract:	Small satellites are traditionally in Low Earth Orbits (LEO), which have been elected as their preferred orbits because of launch price. In the last years, the space market evolved from the usual operations/missions to space supported by governments to a new space era with private companies also competing in this arena. As a result, more and more missions have been flown and the costs start to have an impact on the market. Technology improved and nano satellites started to be a reality. In particular, very large or mega constellations of LEO satellites are being proposed to provide affordable wideband connectivity worldwide, where GNSS can position the satellites, which in return can provide assistance and augmentation data and even complementary positioning signals to terrestrial applications. In this sense, a new market opened for GNSS receivers. They started to be even more important in missions like space debris removal and also in scientific missions and in Earth observation missions, where they could be of particular interest in order to guarantee Precise Orbit Determination. High accuracy positioning can be a key feature for the GNSS space receivers nowadays. In order to achieve some degrees of onboard autonomy, real-time Precise Onboard Orbit Determination (P2OD) [RD 1] needs to be become an onboard system capability in the near future, bringing the current ground-based PPP (Precise Point Positioning) and PPP RTK (Precise Point Positioning -Real Time Kinematic) concepts to space users. Here we present a low-cost space GNSS receiver, G3PSTAR, for CubeSats promoted by the European Space Agency (ESA), that is able of providing real-time P2OD, making use of the new open service from Galileo, the High Accuracy Service (HAS). G3PSTAR is based on Deimos dual-frequency GPS / Galileo receiver (L1/E1 and L5/E5a) [RD 2], integrated in a space qualified Software Defined Radio (SDR) hardware platform manufactured by GOMSpace. This platform is based on the Zynq-7000 System-on-Chip (SoC) equipped with an FPGA and a dual-core ARM Cortex-A9 processor. One of these processors is devoted to the GNSS receiver software, while the P2OD navigation software jointly with the system management software runs on the other core. The receiver is being upgraded for triple-band tracking in order to process the precise corrections broadcast on the Galileo E6-B channel. The in-orbit demonstration of G3PSTAR and P2OD is planned for 2022 as part of the experimentation in the ESA/GOMSpace GOMX-5 mission. The P2OD SW tool [RD 3] that is being integrated in G3PSTAR is based on a reduced-dynamics, EKF (Extended Kalman Filter) tool with an extensive force modelling capability and process noise handling that achieves state-of-the-art positioning performances in the presence of high-quality support data. The P2OD tool has been upgraded to handle multi-frequency, multi-constellation GNSS signals using integer ambiguity resolution, including all Galileo standard channels and the GPS extended service channel (L5), and optimized to process data with appropriate real-time interfaces within the G3PSTAR receiver. The G3PSTAR receiver together with the P2OD SW is expected to reach performances at the level of 10 cm 3D position, 0.1 mm/s 3D velocity and 5 ns timing, processing pseudoranges and carrier phases from the Galileo and GPS constellations and making use of the PPP corrections broadcast on the E6 band. A noteworthy feature of the P2OD SW tool is its capability to predict the dynamical state of the LEO satellite with good accuracy over long periods to support on-board operations in case of GNSS data outages. Here we first present the performance results of G3PSTAR receiver in a laboratory environment through the pseudoranges and carrier phases assessment on CubeSat hardware considering a simulated Low Earth Orbit (LEO). Afterwards, results of the analysis of the P2OD software tool running on the SDR platform hosting the G3PSTAR receiver using externally simulated G3PSTAR measurements will also be shown. [RD 1] P. Giordano, et al, “P2OD: Real-time Precise Onboard Orbit Determination for LEO Satellites”, ION GNSS+ 2017 [RD 2] J. M. Palomo et al.: “Space GNSS Receiver for In-Orbit Demonstration of Precise Real-Time On-board Orbit Determination (P2OD) for Cubesat Missions”, NAVITEC 2018, December, 2018, ESTEC, Noordwijk, The Netherlands. [RD 3] S. Casotto, M. Bardella, P. Zoccarato, P. Giordano “Real Time Reduced-Dynamics POD for LEO Satellites from GNSS Measurements”, 8th ESA Workshop on Satellite Navigation Technologies (Navitec 2018) & European Workshop on GNSS Signals and Signal Processing, Noordwijk, 2018
Published in:	Proceedings of the 34th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2021) September 20 - 24, 2021 Union Station Hotel St. Louis, Missouri
Pages:	1053 - 1065
Cite this article:	Bastos, C., Fernandes, R., Prata, R., Palomo, J.M., Fernandez, A., Darugna, F., Bardella, M., Sciarratta, M., Casotto, S., Giordano, P., Zoccarato, P., "Triple-band GNSS Receiver with E6 HAS corrections for Precise Onboard Orbit Determination in LEO," Proceedings of the 34th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2021), St. Louis, Missouri, September 2021, pp. 1053-1065. https://doi.org/10.33012/2021.18041
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