Operational satellite simulators are used in space missions to provide validation of Ground Systems and the Operational Procedures before and after launch of satellite. They may simulate the satellite, taking into account the space environment and the ground stations, providing an accurate and realistic modeling of their interfaces. The simulators must be sufficiently realistic to allow the operators to run flight procedures as if they were interfacing to the real satellite. Furthermore, they allow encountering unknown scenarios that cannot be tested before launch. The advantages of developing simulators include the ability to: (i) validate operational procedures, (ii) train operators before launch and (iii) validate the Satellite Control System (SCS) and the Telemetry and Telecommand database (Williams, 2004). The high cost and the compression of the development timescale of a realistic satellite simulator motivated the definition of a set of functional requirements based on standardized space services, which is presented in this paper. In order to improve as much as possible reusability and consequently decrease cost in development, the use of standards were intensively adopted specially for the satellite independent functions, namely, data handling and communication among ground and on-board systems. Functions related to the on-board data handling computer and its communication with the ground systems were based on the ECSS-E-70-41A (2003) standard, which focusing on telemetry and telecommand packet utilization definition. The protocol supporting the ground and on-board system communication, at several layers, were based on the Consultative Committee for Space Data Systems (CCSDS) recommendations. This paper presents the results of modeling a set of generic satellite simulator functional requirements into the UML use case artifact. The satellite and ground station functions are as much general as possible, as they were based on practical publications of related works (Saraf, 2001) and in space service standard (ECSS, 2003). For a new mission definition, the satellite simulator use cases model provided a generic basis with which a specific simulator design could be instantiated. The breakdown and the functions choices allow its reuse for future micro-satellite and small satellite programs in different missions. The paper presents the most common functional requirements of a satellite simulator described in the use case notation of UML. The breakdown of the software into modules, the main functions and the advantages of using use cases to specify this kind of software and the way the use cases helped the development team in the future satellite simulators at INPE are also discussed. References: European Cooperation for Space Standardization (ECSS). ECSS-E-70-41A: Space engineering: ground systems and operations telemetry and telecommand packet utilization Netherlands, 2003. Saraf, S.; Adourian, C.; Melanson, P.; Tafazoli, M. Use of an operations simulator for small satellites. In: 15th Annual AIAA/USU Conference on Small Satellite., 2001, Utah, Canadá. Disponível na biblioteca digital URLib: . Acesso em: 17 fev. 2005. Williams, A.; Seymour, M.A. Radarsat-2 Software simulator: benefits of an early delivery. In: 8th International Conference on Space Operations, 2004, Montreal, Canadá. Proceedings... 1 CD-ROM.
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