Experimental Study on Silicon Carbide Passivation in High-Enthalpy Oxygen Flows

Kurzfassung

Satellite missions in Very Low Earth Orbit (VLEO), at altitudes below 450 km, face challenges such as rapid orbital decay due to atmospheric drag and material degradation caused by erosion from Atomic Oxygen (AO). To address these challenges, Atmosphere-Breathing Electric Propulsion (ABEP) technology offers a promising solution by utilizing atmospheric particles as propellant to significantly extend mission durations without the need for onboard fuel. This thesis explores the behavior of possible advanced coatings for the intake of ABEP systems, with particular attention to the passivation of sintered Silicon Carbide (SiC) in high-enthalpy oxygen flows. SiC is selected for its high chemical and thermal stability, the material’s potential to form a protective layer of silicon dioxide (SiO2) enhances its properties, mitigating erosion caused by AO. This study analyzes the behavior of SiC in oxygen plasma by exposing it to the inductively driven Plasma Wind Tunnel (PWK3) at the Institute of Space Systems (IRS) of the University of Stuttgart. By varying the exposure time as a parameter, the passivation of SiC is evaluated by measuring its performance under high-enthalpy oxygen exposure. Furthermore, SiO2 coatings were developed on potential intake samples using the PlasmaEnhanced Chemical Vapor Deposition (PECVD) technique, in order to verify the preservation of specular reflection properties necessary for efficient particle collection. SiO2 demonstrated specular properties at surface roughness levels in the Angström range, an essential characteristic for optimizing particle intake efficiency in ABEP systems. Surface analysis, conducted at the German Aerospace Center (DLR) in Stuttgart, employed advanced techniques such as Nomarski Microscopy, White Light Interferometry (WLIM), Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), and Energy-Dispersive X-ray Spectroscopy (EDX). The findings contribute to the advancement of sustainable propulsion technologies for satellites by informing the selection and optimization of materials for ABEP intake systems, thereby enhancing both performance and longevity in the challenging VLEO environment.