Galileo Signal Tracking and Acquisition Performance Predictions for a Dynamic Launcher

Jean-Jacques Floch, Francis Soualle, Pier Domenico Resta, S. Belin, and S. Reynaud

Abstract:	This paper deals with the Galileo/GPS Tracking and acquisition performance prediction for a dynamic launcher. This study has been done under a European Space Agency contract: “Study on the use of Galileo for launch vehicles services”, for which EADS Astrium is prime. The contract aims at assessing the potential improvements, from a launcher system point of view (navigation, safety, localization for safeguard…), of using Galileo services in the frame of European launchers (Ariane 5, VEGA, future reusable launch vehicles). One objective is to improve the launchers accuracy in particular for future long duration mission with direct payload jettisoning on GEO orbit for instance. The other main objective is to use the Galileo system to replace the tracking radars of Kourou with potential high recurring cost savings. Using Galileo system for safeguard means a guaranteed availability at the beginning of the launchers flight. This paper more particularly focuses on the possibility to use GNSS signals considering the dynamics of a typical launcher (Ariane 5), and on the advantages of Galileo signals compared to GPS ones. The acquisition will be considered on the launching pad, so no dynamic will be applied. This means that the onboard velocity of the GNSS receiver is 0, and only the velocity for the navigation satellites (GPS or Galileo) has to be taken into account (Commonly ±8 KHz). The available (C/No) will be estimated on the launching pad. The tracking will be considered during the launch and will be submitted to the high dynamic of the launcher. GPS- and Galileo- satellites or augmentation systems transmit different types of navigation signals especially e.g. with respect to signal-modulation, frequency and power. Navigation receivers measure the signal propagation time from the GNSS satellite to the receiver and finally evaluate the receiver position. The respective accuracy depends mainly on the signal, the receiver dynamics and environment and on some major receiver parameters. A major part of the analysis is the numerical tracking simulation. This will be performed for a typical launcher scenario described by respective range-, acceleration-, jerk-, environment and C/N profiles to one representative GPS and one comparable Galileo satellite. The numerical simulation models the navigation receiver with its code- and carrier-tracking loops and allows for assessment of the ranging- and Doppler-error due to receiver noise and loop-feedback delays. They are finally evaluated statistically as code- and carrier-jitter and bias. The code- / carrier-tracking errors of a navigation satellite signal are mainly caused by thermal noise, multi-path, and user dynamics. These errors mainly depend for each signal on the following user receiver characteristics: • Correlator spacing • Integration time • Carrier Phase Locked Loop (PLL) characteristics (filter order, filter bandwidth) • Code Delay Locked Loop (DLL) characteristics (filter order, filter bandwidth) Concerning the optimization of the correlator spacing (first characteristic) the noise-jitter and the maximum multi-path envelope error will be analyzed for different BOC(1,1) bandwidth and also BPSK1. For the three other characteristics (i.e. integration time, carrier PLL characteristics, code DLL characteristics) a compromise has to be found between: • random signal errors caused by the Additive White Gaussian Noise (AWGN) and multi-path channel • code / carrier loop stress due to the user dynamics All the tracking performance predictions will be performed using the numerical simulator tool SiSi (Signal Simulator) developed by EADS Astrium GmbH. Then, these results are used to assess the system performances on several European Launchers with Galileo constellation. Localization performances for the safeguard function and the hybrid Inertial Unit Measurement / Galileo navigation performance will be presented for several schemes of hybridization (loose or tight) with a state of the art Extended Kalman Filter for current and future missions.
Published in:	Proceedings of the 2008 National Technical Meeting of The Institute of Navigation January 28 - 30, 2008 The Catamaran Resort Hotel San Diego, CA
Pages:	636 - 647
Cite this article:	Floch, Jean-Jacques, Soualle, Francis, Resta, Pier Domenico, Belin, S., Reynaud, S., "Galileo Signal Tracking and Acquisition Performance Predictions for a Dynamic Launcher," Proceedings of the 2008 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2008, pp. 636-647.
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