As part of the ESA/ESOC study "Linux & Multi Core Processor Technology for Simulators" [7], several concepts concerning performance optimization of SIMULUS based operational simulators were introduced. Starting from the possibility to explore parallelism and distributed execution of computational loads (PDES approach) and continuing with the profiling, analysis and focused optimization of specific simulation models our efforts and ideas converged to a Performance Optimization Framework (POF). The present paper summarizes the way the idea of a Performance Optimization Framework can be applied in future operational simulators.

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Over the past years it has been the standard approach to have two separate simulators for Flight Dynamics (FD) and for the Flight Control Team. Flight Dynamics are developing their FD simulator in order to validate procedures, data products, timelines as well as the performance and functionalities of AOCS related FD applications and systems. It is also used for training of their FD teams. The Mission Data System Section is responsible for the development of operational simulators in order to validate Flight Control Procedures, to verify specific items of the Ground Segment and to train the Flight Control Team. This paper will focus on the reasons behind the separation of these two simulators as well as explain the recent performance improvements which resolve these differences. Indeed, with the evolution of mission requirements and operational simulator technologies, a working group was set up prior to the Gaia simulator development, in order to assess the possibility of satisfying Flight Dynamics requirements using an operational simulator.  At a high level, many requirements of the two simulators are indeed similar. This includes the ability to perform closed loop AOCS simulations and in some cases the ability to incorporate the On-Board Software (OBSW).  Exploitation of the synergies between different simulation environments is consideredone of the means to increase efficiency and reduce ground segment and operational costs.  It has also been observed that the OBSW is becoming more and more complex and that the efforts required for developing a functional model scales with this increasing complexity. Furthermore, this trend is expected to continue in the future.The Gaia operational simulator will be the first simulator to serve both Flight Control and Flight Dynamics needs. As part of its development, improvements to the simulator infrastructure and new interfaces are also required and will be presented. One of these new extensions is the Flight Dynamics Direct Interface (FDS-DIF), which is being developed as a new SMP2 Generic Model. Several challenges, like reaching more than 5 times real-time simulations as well as high fidelity AOCS and space environment modelling, will be faced as part of the Gaia simulator development. This article will cover these issues, the present developments and the future objectives and approaches to achieve the use of operational simulators in the FlightDynamics environment. 2 1. Nomenclature AOCS = Attitude and Orbit Control System DHS = Data Handling System DSM = Data System Manager ESA = European Space Agency ESOC = European Space Agency's Space Operations Centre FCT = Flight Control Team FD = Flight Dynamics FDS = Flight Dynamic Systems FDIR = Fault Detection, Isolation and Recovery FSS = Fine Sun Sensor HW = Hardware ICD = Interface Control Document IO = Input / Output Kbps = Kilo bits per second Mbps = Mega bits per second MIPS = Million instructions per second MCS = Mission Control System MDS = Mission Data System NST = Nitrogen Storage Tank OBSW = On-board software PEM...

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