Cookbook: a practical, recipe based collection of patterns, procedures, and best practices for executable systems engineering for the Thirty Meter Telescope,"
Abstract. The most ambitious projects of the European Southern Observatory's (ESO) is the construction of the European Extremely Large Telescope (E-ELT) which will be by far the world's largest optical and near-infrared telescope, and. will provide images 15 times sharper than those from the Hubble Space Telescope. Such a project poses continuous challenges to systems engineering due to its complexity in terms of requirements, operational modes, long operational lifetime, interfaces, and number of components. Since 2008 the Telescope Control System (TCS) team has adopted a number of Model Based Systems Engineering (MBSE) practices in order to cope with the various challenges ahead. This paper provides an overview of the different approaches we took during this time -which ones worked, and which did not.
Large telescopes pose a continuous challenge to systems engineering due to their complexity in terms of requirements, operational modes, long duty lifetime, interfaces and number of components. A multitude of decisions must be taken throughout the life cycle of a new system, and a prime means of coping with complexity and uncertainty is using models as one decision aid. The potential of descriptive models based on the OMG Systems Modeling Language (OMG SysML™) is examined in different areas: building a comprehensive model serves as the basis for subsequent activities of soliciting and review for requirements, analysis and design alike. Furthermore a model is an effective communication instrument against misinterpretation pitfalls which are typical of cross disciplinary activities when using natural language only or free-format diagrams. Modeling the essential characteristics of the system, like interfaces, system structure and its behavior, are important system level issues which are addressed. Also shown is how to use a model as an analysis tool to describe the relationships among disturbances, opto-mechanical effects and control decisions and to refine the control use cases. Considerations on the scalability of the model structure and organization, its impact on the development process, the relation to document-centric structures, style and usage guidelines and the required tool chain are presented.
Model Based Systems Engineering (MBSE) is an emerging field of systems engineering for which the System Modeling Language (SysML) is a key enabler for descriptive, prescriptive and predictive models. This paper surveys some of the capabilities, expectations and peculiarities of tools-assisted MBSE experienced in real-life astronomical projects. The examples range in depth and scope across a wide spectrum of applications (for example documentation, requirements, analysis, trade studies) and purposes (addressing a particular development need, or accompanying a project throughout many -if not all -its lifecycle phases, fostering reuse and minimizing ambiguity). From the beginnings of the Active Phasing Experiment, through VLT instrumentation, VLTI infrastructure, Telescope Control System for the E-ELT, until Wavefront Control for the E-ELT, we show how stepwise refinements of tools, processes and methods have provided tangible benefits to customary system engineering activities like requirement flow-down, design trade studies, interfaces definition, and validation, by means of a variety of approaches (like Model Checking, Simulation, Model Transformation) and methodologies (like OOSEM, State Analysis)
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