This is the author pre-publication version. This paper does not include the changes arising from the revision, formatting and publishing process. The final paper that should be used for referencing is: S. Ramasamy, M. Sangam, R. Sabatini, A. Gardi, “Flight Management System for Unmanned Reusable Space Vehicle Atmospheric and Re-entry Trajectory Optimisation”, Applied Mechanics and Materials, vol. 629, pp. 304-309, Trans Tech Publications, 2014. DOI: 10.4028/www.scientific.net/AMM.629.304 Flight Management System for Unmanned Reusable Space Vehicle Atmospheric and Re-entry Trajectory Optimisation Subramanian Ramasamy 1 , Manoj Sangam 2 , Roberto Sabatini 3,a* and Alessandro Gardi 4 1,3,4 School of Aerospace, Mechanical and Manufacturing Engineering, RMIT University, Melbourne, VIC 3000, Australia 2 Department of Aerospace Engineering, Cranfield University, Cranfield, MK43 0AL, United Kingdom a roberto.sabatini@rmit.edu.au Keywords: flight management system, unmanned reusable space vehicle, trajectory optimisation, re-entry trajectory planning Abstract. The design and trajectory computation algorithms of an innovative Flight Management System (FMS) for Unmanned Reusable Space Vehicle (URSV) are presented. The proposed FMS features a number of functionalities in common with modern aircraft FMS that enable flight planning in non-segregated airspace, as well as specific features for optimal trajectory generation and space segment monitoring of the flight mission. The general avionics architecture of the URSV is presented and the specific FMS algorithms are developed to cope with the flight vehicle optimal trajectory planning and monitoring. Simulation case studies are performed in a realistic operational scenario resulting in the rapid generation of feasible trajectories, ensuring no violation of the defined mission and vehicle dynamics constraints. Additionally, an error budget analysis is performed on the longitudinal profile trajectories to evaluate the performance of the URSV. Introduction Unmanned platforms are being increasingly adopted for both atmospheric and space applications, despite the access to the civil airspace remains currently restricted to segregated areas. Similar to the manned aircraft versions, Flight Management System (FMS) for unmanned platforms is the core avionics component to introduce extensive automation algorithms for a number of Navigation, Guidance and Control (NGC) tasks. In this paper we propose an innovative FMS design, which incorporates both conventional aircraft FMS capabilities [1 – 3] and spacecraft re- entry trajectory generation algorithms, enabling non-segregated operations of an Unmanned Reusable Space Vehicles (URSV) in the civilian airspace. The Space Shuttle’s entry guidance system [4] is used as a reference for re-entry trajectory planning. Guidance systems based on angle of attack (α) and bank angle (μ) modulations [5], on the quasi-equilibrium glide condition [6] and on the tracking of aerodynamic acceleration [7] have been developed. An improved methodology for re-entry trajectory planning based on creation of a drag acceleration profile as a function of energy has been developed [8] and is used as a baseline. Avionic Systems Architecture The avionic systems conceived for the URSV include an FMS, a Communications System (CS), a Flight Control System (FCS), a Mission Management System (MMS) for strategic/space orbital management, a Remote Piloting Management System (RPMS), which manages data exchanged via the CS to the remote Human Machine Interface and Interaction (HMI 2 ) station, an Obstacle Avoidance System (OAS) and a Rendezvous and Docking System (RVDS). The FCS translates the FMS/RPMS/OAS guidance or manual steering command inputs to actuators commands. Fig. 1 illustrates the functional architecture of the spacecraft avionic systems including the FMS subsystems listed in Table 1.