Volker Schaus

Decision Support Tool for Concurrent Engineering in Space Mission Design

The concurrent engineering (CE) approach has been successfully applied to the early design phase of space missions. During CE sessions, a software support is needed to allow multidisciplinary design data exchange. At the moment, a spreadsheet-based solution enhanced with macros is used at the German Aerospace Center (DLR) to create a system model of a space mission during the early design phase. Now there is an increasing demand to take advantage of this system model and provide data analysis features which improve the decision making during CE sessions. Since the current approach is limited for such analysis, DLR has started developing a new tool called Virtual Satellite. It offers extended software support required by the Concurrent Engineering Facility of DLR in Bremen. On top of the previous spreadsheet functionalities, it provides means for online data analysis and system modeling. The results of these data analyses are presented to the discipline experts using different views which help in performing an early design optimization. In this paper, the impact of these views on the decision making during the AEGIS space mission study is presented as a proof of concept.

A Continuous Verification Process in Concurrent Engineering

This paper presents how a continuous mission verification process similar than in software engineering can be applied in early spacecraft design and Concurrent Engineering. Following the Model-based Systems Engineering paradigm, all engineers contribute to one single centralized data model of the system. The data model is enriched with some extra information to create an executable representation of the spacecraft and its mission. That executable scenario allows for verifications against requirements that have been formalized using appropriate techniques from the field of formal verification. The paper focuses on a current approach of integrating this verification mechanism into our Concurrent Engineering environment. In an example study, we explain how basic mission requirements are created at the beginning of the spacecraft design. After each iteration and change, the integrated verification will be executed. This instantly highlights the effects of the modification and points out potential problems in the design. Using the continuous verification process alongside the Concurrent Engineering process helps to mature both, the requirements and the design itself.

Collaborative Development of a Space System Simulation Model

Modeling and simulation is a powerful method to evaluate the design of a space system. Simulation models represent valuable knowledge and require considerable time and effort for their development. Means for reuse should be taken into account from the beginning of model creation. This paper presents a collaborative model development process, which creates prerequisite information for successful reuse of simulation models. It introduces a knowledge model and proposes reviewed documentation at each step in the process. These pieces of documentation enable successive reuse at different levels. The modeling process was evaluated by creating a system simulation of the OOV-TET-1 satellite including three satellite subsystems, dynamics, kinematics, and space environment. Furthermore, the organization of models and their documentation artifacts is crucial in order to search, find, and reuse models across project partners and across projects. The paper suggests a flexible model database that suits the special requirements of typical space projects and large research organizations.

Using timed automata to check space mission feasibility in the early design phases

According to the model-based systems engineering paradigm, all engineers contribute to a single centralized data model of the system. The German Aerospace Center (DLR) develops a software tool Virtual Satellite which enables the engineers to store, exchange and alter their corresponding subsystem data on base of a distributed system model and thus contribute to the overall mission design during concurrent engineering (CE) sessions. Each engineer has their own scope of responsibilities, e.g. satellite trajectory, communication, or thermal analysis. Tracking implications of design changes on the whole system and feasibility aspects of the design is not trivial. Having an automated feasibility checking mechanism as a part of CE which would run iteratively after each design change provides a useful feedback mechanism for engineers and for the spacecraft client. For the purpose of mission feasibility checking a domain specific language (DSL) has been implemented using the Xtext Java framework. The extended parametric data model defined in the DSL serves as an executable representation of the spacecraft mission. The idea to use such an executable model to create a preliminary mission plan and hence confirm missions feasibility during conceptual study has already been introduced by Schaus et al. at the DLR. However, the vector of values of system variables was assumed to be equivalent with the currently active component, implying that component activities are mutually exclusive. This led to over-constraining of the execution model. Our work argues that concurrency considerations are critical from the earliest design phases. Since satellite is coupled with its environment and concurrency is an intrinsic property of the physical nature, considering concurrency allows for more realistic mission plans. The contributions of this paper are the introduction of concurrency considerations at the early space mission design phases and the use of timed automata tool (UPPAAL) for the mission feasibility check during concurrent engineering sessions. As a result, with almost no overhead, the planned mission can be analyzed in a more realistic way. Furthermore, the run-times of the feasibility check amount to 10-100 milliseconds or less, which is also a significant improvement with respect to the previous work. This allows for more precision and fine granular modeling, and is a promising basis for model refinements in the consecutive mission design phases.

A formal method for early spacecraft design verification

In the early design phase of a spacecraft, various aspects of the system under development are described and modeled using parameters such as masses, power consumption or data rates. In particular power and data parameters are special since their values can change depending on the spacecrafts operational mode. These mode-dependent parameters can be easily verified to static requirements like a maximumdata rate. Such quick verifications allow the engineers to check the design after every change they apply. In contrast, requirements concerning the mission lifetime such as the amount of downlinked data during the whole mission, demands a more complex procedure. We propose an executable model together with a simulation framework to evaluate complex mission scenarios. In conjunction with a formalized specification of mission requirements it allows a quick verification by means of formal methods.

Evolution of the European Concurrent Design Tool for Space-based System-of-Systems Studies

One major element in Concurrent Design is the central data model. It allows the various disciplines to share the latest information and to make immediate use of them within their domain specific tools and models. As a successor of the Integrated Design Model, in 2014 the European Space Agency (ESA) released the Open Concurrent Design Tool (OCDT), which aims to be the reference and standard model for European entities performing space system studies during early as well as later phases. This tool, including its web-based server and user interface supporting elements (such as MS Excel Add-ins), is developed in a way that it is not only limited to space system and mission design, but can be used also in other fields such as System-of-Systems (SoS) architecture definition and evaluation, which is becoming an emerging topic for European and international collaborations. Instead of just looking at the technical aspects of a system, SoS-studies provide an opportunity to analyze how to share resources and assets amongst institutions, organizations or nations more efficiently and how to provide integrated and more advanced services. However, due to the different nature and rules of SoS, the OCDT requires certain adaptations regarding domain specific tool interfaces, dedicated data libraries, as well as a SoS-specific data flow and representations to the users. Several studies were performed on ESA’s side in advance, to prepare an initial set of requirements for such an evolution of the tools and processes which eventually led to a project called “Development and Validation of a Generic Systems‐of‐Systems Concurrent Engineering Model (CESoS)”. It has been established by ESA and awarded to a consortium which has experience in Concurrent Design, software development and system architecture definitions.