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This paper describes the architecture and implementation of a distributed simulation of NASA's Orion spacecraft and Ares launch vehicle in a mission to the International Space Station. The simulation is part of the Integrated Mission Simulation (IMSim) project which aims at research and development collaboration among NASA centers. As mission systems are complex, a distributed simulation allows participating centers to build specific simulation models utilizing specialized technologies at each center. Interactions among the simulation models are defined according to mission operation concepts. Traditionally, simulation of space vehicles has been performed as disjoint collections of simulations. However, the traditional approach does not address integration and interaction among the separate simulations. To simulate a system of systems, distributed simulation technologies provide promising solutions. Evaluations from a previous middleware trade study showed that the IEEE 1516 High Level Architecture (HLA) standard is a suitable candidate for IMSim. In this paper, we describe the use of HLA for the Orion to ISS mission. As of July

An assessment of a draft AIAA standard for flight dynamics model exchange, ANSI/AIAA S-119-2011, was conducted on behalf of NASA by a team from the NASA Engineering and Safety Center. The assessment included adding the capability of importing standard models into real-time simulation facilities at several NASA Centers as well as into analysis simulation tools. All participants were successful at importing two example models into their respective simulation frameworks by using existing software libraries or by writing new import tools. Deficiencies in the libraries and format documentation were identified and fixed; suggestions for improvements to the standard were provided to the AIAA. An innovative tool to generate C code directly from such a model was developed. Performance of the software libraries compared favorably with compiled code. As a result of this assessment, several NASA Centers can now import standard models directly into their simulations. NASA is considering adopting the now-published S-119 standard as an internal recommended practice.