Hybrid Demisable Joint Concept for High-Altitude Break-Up of Primary Satellite Structures (Masterarbeit)

Kurzfassung

The increasing number of rocket launches and the emergence of satellite constellations such as SpaceX’s Starlink and OneWeb have once again highlighted the need for effective management of man-made objects in orbit. This includes addressing the growing issue of space debris, which arises from not only the launch of new spacecraft but also collisions in congested orbits like GEO, LEO, and polar orbits, as well as anti-satellite weapon tests and other mission-related debris. To prevent a cascading effect known as the Kessler syndrome, comprehensive measures for space debris mitigation, guided by the policies of major space agencies like ESA and NASA since the late 1990s, must be implemented. ESA, together with its national partners, is actively developing both active and passive approaches for debris reduction and restriction through its CleanSpace initiative. One passive measure, known as Design for Demise (D4D), aims to ensure the complete or partial ablation of space system hardware during uncontrolled atmospheric re-entry after the end of life phase. To minimize the risk for humans and property posed by surviving satellite parts, it is crucial to induce a high-altitude break-up of the primary structure, maximizing the heat load on components that are challenging to eliminate. At DLR Institute of Structures and Design, concepts have recently been proposed to address this challenge by utilizing additively manufactured patches and inserts within the D4D philosophy. These concepts are further reinforced by passive ejection mechanisms, such as embedded preloaded springs and programmable materials. In the course of this work, a summary of the relevant theory is provided, followed by a description of the state-of-the-art technologies relevant for the thesis. Previous investigations into D4D techniques, aimed at elevating the breakup altitude of satellites, are discussed, and innovative concepts for hybrid-material demisable joints are derived to address challenges identified in earlier studies. Based on ESA’s Sentinel-6 mission as reference, designs are formulated originating from the conceived concepts, and adaptable for use in common primary structural joints of most satellites. Following this, a thorough characterization of components constructed from thermoplastic materials such as PEI and CF15-PEI is undertaken, and requirements for an Shape Memory Alloy (SMA) spring actuator are established. An iterative mechanical design process, incorporating simulations and testing, is employed to demonstrate the structural joints’ capability to withstand various loads experienced during launch. Subsequent re-entry simulations are performed to evaluate the system-level demise behavior. Within the re-entry analysis, the impact of the disintegration of specific primary structural panels, triggered by demisable joints, on the overall demise behavior is assessed. Various configurations are defined and compared to a baseline setup with the aim of identifying the optimal utilization of demisable joints to increase breakup altitude and reduce the debris casualty area. With a strategic replacement of classical joints, a maximal reduction in Debris Casualty Area (DCA) of around 30% compared to the baseline configuration was determined, while achieving separation altitudes of up to 115 km. Following the re-entry analysis, data generated is used for thermal transient simulations of detailed joint assemblies to evaluate their heating behavior and validate simulated separation altitudes. The findings suggest a slight delay in separation altitude, with the overall results proving to be suffienctly accurate. In the final phase, physical prototypes of the designs are fabricated and tested at DLR facilities to showcase functionality and assess the performance of the passive mechanism.