Robustness Assessment of Deployable Gossamer Structural Space Systems

Kurzfassung

The growing interest of science and industry in space, especially for commercial use in communications, climate and earth observation, as well as space exploration, is leading to the demand for increasingly efficient and lighter technical systems. For economic use, weight savings and the associated development of alternative and advanced designs are necessary, such as deployable, ultralight weight structural systems, so-called Gossamer structures that enable a wide variety of space applications to be realized. To this end, the thesis will investigate one of the most important aspects of deployable ultra-lightweight structural space systems, their robustness. This is investigated on different levels of complexity and finally quantified for the Gossamer structural space system as a whole. Although such structural systems are characterized by their very large outer dimensions, with a filigree design featuring very thin walls, and have a superior mass-area or mass-length ratio, thus offering great advantages in terms of economy and mission technology, they are at the same time more susceptible to disturbances, variation and imperfections, compared to traditional designs. The analysis of robustness, understood as a quantifiable metric, as well as the integration of robustness considerations and corresponding methods, can identify and determine these vulnerabilities and reduce them already during the development and design process by countermeasures. As a result, a structural system with minimized vulnerabilities and increased structural performance in the form of robustness can be achieved. In order to provide a first overview a general classification of existing Gossamer structural space systems and existing approaches for robustness assessment and quantification are analyzed. However, very different approaches are reported in the various fields of technology and engineering, with some highly theoretical and some only partially transferable. For this reason, a new methodology is developed and discussed in this thesis, which considers the characteristics of two-dimensional deployable Gossamer structural space systems and allows for a technical assessment of individual subsystem and overall system robustness. This is mainly shown by the example of the DLR solar sail demonstrator Gossamer-1. With the focus on quantification, it is essential to determine influencing variables and parameters, such as disturbances and deviations, which characterize the robustness of such structural systems. In practical experiments geometrical changes, such as shape and form deviations, caused by the manufacturing process, tooling and long-term stowage, changes in material properties due to environmental influences in space, as well as load changes due to interaction of components are investigated. Based on this, the here presented thesis investigates the effects of the determined influences on the robustness of deployable fiber composite booms and its subsystem, in mechanical bending tests as well as in numerical calculations. The resulting robustness parameters are subsequently used to quantify subsystem and overall system robustness facilitating the here developed method. Consequently, this thesis enables direct comparability and assessment of ultra-light weight Gossamer structural space systems based on their robustness as quantified metric.