The development of an optimized filtering algorithm for tracking Ariane launchers

Abstract

This paper describes the method used to select and implement a filtering algorithm for tracking Ariane launchers. The algorithm provides the best compromise between filtering out noise and allowing launcher deviations to be detected quickly, while being reliable and robust for operational use. A third-order polynomial filter was selected, for which the time constant varied as a function of the time since launch. This work led to the development of a working prototype through which real tracking data from previous launches was played. Theoretical worst-case deviating trajectories were derived for critical points along the trajectories, and were also fed through the prototype to investigate the reaction-time of the filter to launcher deviations. The team used this prototype to carry out numerical analysis to parameterise the filter for several typical launcher types and trajectories, in order to optimise the filter performance. Following the development of the prototype, the algorithm was implemented by an independent team using safety-related development techniques, without which it could not be recommended for operational use. The paper describes these techniques, and the extensive testing carried out on the algorithm using recorded tracking data from real launches and theoretical deviating trajectories. It then describes the sophisticated analysis methods used to verify its performance was as good as, or better than, the prototype. The main contribution of this paper is to describe the INTRODUCTION work we have done : The SCTV project is part of CNES's CSG2000 1} to select a filtering algorithm which balances the programme to modernise the Ariane launch facilities conflicting requirements for : for Ariane 4 and 5. It is one of four major implementation projects to improve and update the • noise filtering, system which the flight safety officers use to ensure . responsiveness to launcher deviationS) the safety of proposed launcher trajectories, and to monitor the trajectory within predefined safety limits • efficiency in terms of processing during flight. The system gives the officers the requirements; information they need to determine when to destroy „,. . , , v . , , . , .. , . , . r i u j j , j • 2) to implement it in such a way that it can be relied the launcher it it should deviate dangerously from its , .. , . . ,,. , , „, . . „ . . on for operational use. nominal flight path. The system is installed at the launch site in Kourou, French Guyana. This launch site belongs to the Centre National d'Etudes Spatiales SYSTEM OVERVIEW (CNES) and is used by ESA to launch ARIANE The simplified system block diagram overleaf shows rockets. me principal data flows involved in one of the The system uses radar measurements and on-board trajectography chains. External measurements of the telemetry to determine the launcher trajectory, and a position and velocity of Ariane are acquired by three novel filtering algorithm to detect dangerous radars (BR1, BR2 and AD2). This data is passed by situations quickly. The project team carried out an the radar interface equipment (EIRs) to the extensive study to select the most appropriate trajectography computers (only data flows to TR1 are algorithm and to optimise the parameters for running )Here the trajectory data are filtered to it. This study analysed the data from several launches provide a prediction of the launcher position and to characterise the noise in the data, and to determine velocity. This prediction is primarily used to monitor the optimum way to filter the noise, whilst the launcher trajectory against safety limits in the SSV maintaining a quick response to a real launcher sub-system, and it is also used to send tracking deviation information to the acquisition systems. 705 Copyright© 1997, American Institute of Aeronautics and Astronautics, Inc. A Simplified System Block Diagram RCTDL (Responsable Centre de Traitemem des Donn6es de Localisation)