Interactive 3D Visualization to Support Concurrent Engineering in the Early Space Mission Design Phase
Planning a space mission and designing a spacecraft involves complex interdisciplinary systems engineering. Space mission projects are typically expensive, of long duration and require experts from various domains, such as power, communication, thermal, structure, propulsion and payload. In order to manage the project complexity, the lifecycle of a spacecraft is commonly divided into seven phases as defined by European Space Agency (ESA) in ECSS (European Cooperation for Space Standardization). Phase 0/A refers to the beginning of mission planning, in which the feasibility study is carried out. Over the past ten years, the concurrent engineering (CE) process has been widely adopted for such early space mission design activities. At the German Aerospace Center (DLR) in Bremen, the Concurrent Engineering Facility (CEF) is setup for this purpose. It is a specially designed room that offers the space and technical equipment for a group of discipline experts to collaboratively develop a concept of a proposed space mission. It allows the co-located experts to discuss the various aspects face-to-face, present ideas, draw sketches and build ad hoc groups to discuss sub-topics. It especially allows to overseeing the contributions from all disciplines at a whole and, thus, spotting conflicts or design issues early in the design phase. The ability of spontaneous interactions between the experts can immensely speed up the design phase. Similar facilities have been used at NASA, ESA and other space agencies. Although the CEF and similar facilities allow all discipline experts to work closely together improving communication, the fragmentation of used domain-specific data and specialist tools still induce issues of data exchange and data consistency. To tackle the problem of interdisciplinary data exchange, DLR’s department of Simulations and Software Technology in Braunschweig is developing a software tool called ‘Virtual Satellite’ (VirSat) to support concurrent engineering in the CEF. The tool implements principles of model-based systems engineering (MBSE). Throughout the planning phase, it collects data from all relevant domain experts, exchanges the data between different domains as per requirements and always maintains consistency. It generates a common system level model based on the data from all domains, linking data from all disciplines together, and shares it between all. It provides a common understanding of a system to all domain experts. Based on this system model, VirSat additionally supports data analysis, inter-disciplinary dependency management, data synchronization and graphical modelling of a space system. Although VirSat solves the problem of data sharing, the general issues of inter-domain communication still exist. Different domains have different means of communicating their data. For example, the expert of a payload instrument may not intuitively understand the numbers, graphs and diagrams of the thermal expert. Thus, in technical discussions very often experts do not understand each other in detail, leading to misinterpretation or even failure to notice important constraints. In this paper, we propose to combine and utilize interactive three-dimensional (3D) visualization and Virtual Reality (VR) technologies as a tool to unify some of the different views and parameters seen by the experts from diverse disciplines in CE and to make these more accessible. Complex scenarios can be illustrated and animated using 3D graphics. This is already used by the configuration engineer, for example, or often when presenting simulation results. Interactive 3D visualization lends itself well as a medium for sharing expert knowledge within a group. Complex processes can be explained more easily when parameters can be changed and its effect is shown instantly. VirSat already includes support for interactive 3D visualization, e.g. for space craft configuration and orbit simulation. However, the current implementation is limited to desktop-based display systems only, typically using a PC mouse or keyboard as input devices. However, although a mouse is an intuitive input device which allows precise pointing, every monitor has finger prints. This is because people find it much more intuitive to point with their finger at objects while discussing with others. VR technology can bridge the gap between the users and the visualized content. Motion tracking devices and suitable interaction techniques support the intuitive and natural selection and manipulation of the displayed virtual objects. Using large scale display systems or networked VR environments supports collaboration around visualization within a group of users. Interactive visualization and VR has been used already in later design phases of space missions. However, we argue that it is highly beneficial in the early design phase as well. It enables all domain experts to get an overview of the complete system in one view at an early stage of mission planning. Design flaws or conflicting constraints may be recognized easier. For example, data of mission analysis, spacecraft structure and orbit simulation could be combined in one view. All relevant data is extracted from the shared system model and reconstructed to a VR scenario showing a 3D model of the spacecraft with its internal components moving along the proposed orbit. The engineers could interactively move around the virtual spacecraft; visualize the sun and shadow phase of Earth, as well as results from a thermal simulation mapped onto the 3D model; change parameters and visualize the effect of change in parameter value. Thus, experts from the configuration, orbit, payload and thermal domain can easily explain and discuss together the effects of heat propagation inside the spacecraft and better understand the dependencies of various parameters in the design. Furthermore, the involvement of interactive 3D visualization from the planning phase and its link to the common system model creates a concrete base for later phase design. In later phases, a more detailed design and domain specific simulations can be visualized and maintained in synchronization with the common system model developed in the planning phase. Typical use cases include collaborative design review, maintainability analysis of a spacecraft or astronaut training. For example, VR allows to realistically simulating an on-orbit servicing mission in a safe environment without the need for a physical mock-up, supporting visibility and reachability analysis of spacecraft parts for a servicing robot based on data from the central system model In order to take advantage of the shared system model generated during CE, it is necessary to link the visualization model to the common system model created by VirSat. This is done using model- to-model transformation techniques. The transformation from the system data model to a visualization model can be one-directional when only visualization is required. A bidirectional transformation allows both, visualization of data and inserting design changes back into the system model. The transformation can be automatic based on pre-defined rules. Furthermore, the visualization model can be reduced to the necessary data only. For example, a visualization model used for maintainability analysis in a VR system would include not only the geometric shapes of spacecraft components, but also a set of physics properties in order to simulate collisions, kinematic behavior and visual effects, such as reflections of the sun on object surfaces. In contrast, a visualization model used on a mobile device, such as a tablet, for design review purposes might include basic shapes only, as well as relevant meta data to be displayed in text form.