Design for demise applied to spacecraft structural panels and experiments for ClearSpace One platform

With growing awareness of the vulnerability of the near-Earth space region and the anticipated surge in satellite objects, efforts are underway to assess and implement various mitigation strategies. These aim to minimize the impact of space activities and establish a secure and sustainable space environment. However, challenges from knowledge uncertainties and technology gaps hinder our immediate capacity to act, particularly in adopting a design-for-demise (D4D) approach. D4D seeks to modify spacecraft design processes for the safest possible destructive reentry, employing strategies like material substitution, specific geometries, or dedicated subsystems.Initiated under a Network Partnering Initiative by the Swiss Federal Institute of Technology in Lausanne (EPFL) and the European Space Agency (ESA), this project focuses on designing and experimentally evaluating novel composite components to enhance spacecraft demisability. A comparative analysis with baseline critical systems focuses on achieving higher altitude break-up while preserving mission-relevant properties. The project primarily explores a dual strategy, involving material substitution in a benchmark system comprising an external sandwich panel and its fasteners.The first aspect examines a novel short carbon fiber reinforced polyetheretherketone (CF/PEEK) bolted joint design as a substitute for critical titanium or steel alloys. The second involves evaluating a hybrid reinforcement, combining carbon and demisable flax fibers, to replace aluminum panel skins or critical full carbon composite skins. Additionally, the integration of a thermally conductive and reactive metallic matrix filler composed of aluminum-magnesium alloy micro-powder is investigated.Demisability assessments is performed at material and lab scale component levels. This encompasses measuring material mechanical properties under static loading at room temperature and dynamic loading over a temperature range to identify their softening point. Static and dynamic reentry simulation tests, including a laboratory-scale high-temperature creep test and a plasma wind tunnel test, assess thermo-mechanico-physical property changes over uncontrolled reentry conditions and composite degradation.Results indicate the promising potential of an optimal ply-by-ply carbon-flax hybrid/epoxy reinforcement for the skin, offering a 180% ablation rate improvement starting at a lower temperature compared to CFRP. Meanwhile, the addition of the AlMg filler enhances matrix pyrolysis rate by over 10%, reducing its onset by 40°C. Joint studies reveal that stainless-steel bolts exhibit no effective demise under testing up to 800°C, whereas CF/PEEK bolts start to demise before reaching ~400°C, with superior specific tensile and shear strength within typical space mission temperature ranges.This research project represents a significant milestone in identifying and developing optimal demisable composite structures. The focus on novel material combinations through dedicated test campaigns underscores the commitment to preparing findings for space applications. The direct experiment-to-model approach not only contributes to a better understanding of composite material demise but also effectively reduces uncertainties. The ultimate goal of enhancing the safety of future space debris reentry is clearly articulated, laying an essential foundation for achieving this objective.