Atomic-Oxygen Effects on a Siloxane-Polyimide Block-Chain Copolymer (BSF-30)

Abstract

Very low Earth orbit (VLEO) offers advantages, such as high-resolution Earth observation, low-cost launches, and reduced risk from orbital debris. However, satellites are rarely deployed in VLEO because of the dense and harsh residual atmosphere, primarily composed of atomic oxygen (AO) and molecular nitrogen (N₂), which collide with ram surfaces at a relative velocity of ∼7.5 km s^–1. Organic polymers that are used for structural, thermal control, and coating materials are susceptible to AO attack. A common approach to mitigate AO-induced damage is to copolymerize or blend the polymer with an inorganic silicon (Si) component, which reacts with AO to form a passivating silica layer on the surface. Still, such organic/inorganic hybrid materials often become rough through initial AO reactions with organic components as the passivating layer forms, increasing satellite drag. As a potential low-drag and AO-resistant material, we investigated BSF-30, a commercial siloxane-polyimide block-chain copolymer film. BSF-30 was exposed to a beam of orbital velocity AO at a fluence of ∼1 × 10²¹ O atoms cm^–2 and was found to have an erosion yield of less than 0.6% of that of Kapton, a commonly used satellite material. The AO-exposed surface of BSF-30 was smooth (S_q ≲ 1 nm) and composed of silica (SiO_x, with x ≈ 2). Molecular beam-surface scattering experiments were conducted on the AO-exposed BSF-30 surface, and the scattering dynamics revealed that the inelastically scattered O atoms were overwhelmingly dominated by quasi-specular scattering with little energy transfer. These results demonstrate that BSF-30 exhibits exceptional resistance to AO attack, while maintaining a smooth surface that promotes low-drag scattering dynamics, indicating great potential for use on the external surfaces of satellites in VLEO.