Fused Granular Fabrication of CF/PEEK-PEI hybrid joints for demise of satellite structures

Abstract

The exponential increase in satellite launches has heightened the risk of space debris, necessitating innovative solutions to mitigate this threat. The German Aerospace Center (DLR) Institute of Structures and Design has been working on a novel approach to satellite design developing Demisable Joints which promote structural disaggregation during high-altitude atmospheric re-entry. This innovative concept enables exposure of satellite subcomponents to prolonged and intensified plasma flows, significantly enhancing the probability of their total burn-up and thereby reducing space debris accumulation. The proposed design concept envisages replacing conventional bolt joint elements with additive manufactured hybrid joints. These joints incorporate a temperature-activated ejection mechanism, as proposed for both thin plates and sandwich panels. Building upon previous studies that concentrated on thermal design and melting mechanisms for activation, this work explores the manufacturing of these hybrid joints using high-temperature Fused Granular Fabrication (FGF). The hybrid joints are composed of carbon fiber-reinforced polyether ether ketone (CF/PEEK) and polyetherimide (PEI), exploiting the lower glass transition temperature of PEI to trigger a release mechanism. Upon reaching the critical temperature, the PEI component softens, activating a spring-loaded system that ejects the joint and releases the attached satellite components. The present study focuses on manufacturing hybrid CF/PEEK-PEI structures to derive mechanical characteristic values essential for the design of the Demisable Joints. Hybrid test specimens were manufactured using high-temperature FGF. Mechanical tests were carried out to quantify the mechanical properties of the fusion bonded boundary layer between CF/PEEK and PEI, and vice versa. To investigate the interfacial boundary layers between the joining materials, as well as potential porosity, advanced microscopy techniques were utilized. The results obtained form a basis for the mechanical design of the Demisable Joints and assess the suitability for launch and orbit loads. This approach not only aligns with sustainable space exploration strategies but also represents a significant innovation in additive manufactured satellite components. Further investigations will build on these results and focus on optimizing the joint design with the objective of demonstrating a flight experiment with in-orbit validation of the activation mechanism.