Collaborative Development of a Space System Simulation Model
Total Page：16
File Type：pdf, Size：1020Kb
View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Institute of Transport Research:Publications Collaborative Development of a Space System Simulation Model Volker Schaus∗, Karsten Großekatthofer¨ ∗∗, Daniel Ludtke¨ ∗, Andreas Gerndt∗ ∗German Aerospace Center (DLR) Simulation and Software Technology Software for Space Systems and Interactive Visualization Lilienthalplatz 7, 38108 Braunschweig, Germany Email: fvolker.schaus, daniel.luedtke, [email protected] ∗∗Astro- und Feinwerktechnik Adlershof GmbH (AFW) Albert-Einstein-Str. 12, 12489 Berlin Email: [email protected] Abstract—Modeling and simulation is a powerful method temperatures of satellite components. Widespread tools for to evaluate the design of a space system. Simulation models thermal analysis are ESARAD/ESATAN or ThermalDesktop. represent valuable knowledge and require considerable time Such examples can be named for all engineering domains and effort for their development. Means for reuse should be taken into account from the beginning of model creation. This involved in space system design. However, all these sim- paper presents a collaborative model development process, which ulations stay within their domain. Portability and data ex- creates prerequisite information for successful reuse of simulation change between the simulations are major issues and make models. It introduces a knowledge model and proposes reviewed the evaluation of cross-domain dependencies very difficult. documentation at each step in the process. These pieces of Recent initiatives, such as European Space Agency’s (ESA) documentation enable successive reuse at different levels. The modeling process was evaluated by creating a system simulation SimVis project [4] and German Aerospace Center’s (DLR) of the OOV-TET-1 satellite including three satellite subsystems, Virtual Satellite initiative [5] aim to establish overall system dynamics, kinematics, and space environment. Furthermore, the simulations during the early system design phase in order to organization of models and their documentation artifacts is evaluate system performance. crucial in order to search, find, and reuse models across project partners and across projects. The paper suggests a flexible model Within a project, collaboration among the design team is database that suits the special requirements of typical space one of the key factors for a successful design. In this context, projects and large research organizations. collaboration usually stands for teamwork, communication, sharing information, and product data exchange. Over the past Keywords—model development process, model reuse, model decade, concurrent engineering techniques have been put into database, space system simulation practice and special facilities for concurrent design have been established at many sites [6][7][8]. Data exchange and data I. INTRODUCTION consistency issues are addressed by defining a global system Space systems tend to be complex system designs with model that is holding all design parameters. This ensures that many interdependencies between various subsystems, compo- the design team always works with the same common data nents, and the payload. Typically, the development process basis and creates a certain awareness of changes and their lasts several years, involves an interdisciplinary design team, consequences to other domains or the whole system. Recent and follows the well-established Systems Engineering V-model attempts are to use this system model not only in early designs [1] that has been tailored to the space domain [2][3]. but also in subsequent phases, possibly throughout the whole Modeling and simulation has become an inherent part of design process [9][10]. This provides consistency and reuse of the design process. Simulations are mainly used during the design information and removes the existing barriers between domain specific detailed design. Basically, all engineering distinct design phases. disciplines have developed special computer-aided engineering However, teamwork within a project or in a design team tools that are specific to their domain. For example, control is only one aspect of collaboration. For the DLR as a large engineers model the attitude and orbit control system (AOCS) research organization and satellite designer, two more ways of of a spacecraft and use a continuous or discrete simulation collaboration are very important: to validate orbit maneuvers and attitude control performance. One of the standard software packages used in this field is • model sharing and reuse across projects • collaboration across partners MATLAB/Simulink. On the other hand, thermal engineers set up a simulation based on a geometry model, the orbit, the Many projects have similar requirements for simulation exposure to direct sunlight, and internal heat sources that models; therefore reuse is desired to shorten design time and calculates the developing of thermal housekeeping data and should be easily possible. According to Pidd [11], reuse strate- gies require certain features that can be arranged in four cat- used to create simulation models of the satellite bus. It consists egories: abstraction, selection, specialization and integration. of five steps and is based on the waterfall model in software An abstract, high-level description is needed to understand engineering. Each step generates documentation, but not nec- the model quickly. Means of searching are necessary to find essarily a document. Starting with a problem description, the and compare models and select the right artifacts for reuse. requirements are analyzed first. They state what the model This also requires a certain organization of models, such as should do, what precision, accuracy or performance is needed, a model library or database. Modularity and small granularity etc. Typically, requirements are written in natural language is needed to support specialization and to enable the creation and can be organized as a list. The next process is the model of model variants. Interfaces need to be well defined to allow analysis which includes the relevant physics, a mathematical integration. representation, algorithms, and constraints. The common situation, however, is that design time in The third step is the abstract design phase. Here, the model’s projects is limited and next deadlines are pushing for fast interface, its input and output values are defined. It also in- results. In consequence, model development often means di- cludes parameter and quantity definitions and different model rectly building running models as fast as possible. Mostly states, if necessary. Additionally, the internal architecture of models are re-implemented from scratch or based on former the model is defined in this step. The abstract model can be implementations (code scavenging). There are no common seen as a platform independent model in terms of model-driven guidelines for developing and documenting models. In addi- architecture (MDA)[14]. tion, existing models are either saved on shared network drives The fourth step in the process is the implementation step or packaged as model libraries. They are typically developed and implements the model as source code for a given plat- by working groups and the knowledge is often kept within form, e.g. C, or in a simulation software package such as departments, institutes, and companies. Sharing and searching MATLAB/Simulink. In addition, this implementation always for potentially reusable models is not easily possible. depends on the current environment and software version. It is The second item regarding the collaboration across partners a so-called platform specific model, again drawing the parallel addresses the fact that DLR in their satellite projects always to MDA in software engineering. works together with partners, among them many small and Finally, validation is a testing step for the model. Tests can medium-sized enterprises (SME). Typically, large organiza- include unit tests on software level, type tests for correct size, tions have special departments dedicated to modeling and format and physical units of input and output signals, and simulation, which makes the use of simulations cost-effective. expected input/output value pairs. However, SMEs face high cost for software licenses and The whole process identifies two roles or actors: the system trainings in order to provide simulation models. Again, the engineer and the simulation engineer. These two roles pass issues here are model portability and transformations. The idea through the modeling process in close collaboration. The right is that in the future SMEs can provide a model together with hand side of Figure 1 indicates the work distribution between their individual hardware component or subsystem. Such a system engineer and simulation engineer. At the beginning, the model can then be integrated into a bigger simulation set up by majority of the work is the system engineer’s responsibility. a simulation department of a larger organization. This situation is especially true for DLR and Astro- und Feinwerktechnik Adlershof GmbH (AFW) who have worked together on several space projects over the years [12][13]. The collaboration was problem system engineer description continued in a nationally funded research project on reusable simulation engineer model development with other industrial partners outside the requirements requirements space domain. analysis definiton In essence, the research focuses on the desire to harmonize