Material Stability and Durability Testing Using the Extreme Space Environment in Low Earth Orbit

The extreme environment of space provides an ideal domain for testing the stability and durability of materials for use in multiple applications both in space and on Earth. Materials exposed to the harsh space environment in low Earth orbit (LEO) are subject to atomic oxygen (AO) erosion, ultraviolet (UV) radiation, ionizing radiation, vacuum, thermal cycling, and temperature extremes. Depending on the material, each of these factors can lead to significant material degradation. For materials used in space applications, space exposure testing is critical for evaluating the performance of the material. For materials designed for Earth applications, long-term space exposure provides a mechanism for accelerated material degradation testing, where the impact of space-exposure can be correlated to degradation via Earth-based testing to identify failure modes and evaluate the lifespan of the material.<br/>The International Space Station (ISS) National Laboratory offers an ideal platform for long-term exposure to the extreme space environment in LEO, particularly because power, data, and imaging can be provided <i>in-situ</i> and samples can be returned to Earth for postflight analysis and comparison to ground samples. Some materials that have been investigated using ISS external platforms include silicon-, organic-, copper-zinc-tin-sulfide (CZTS), and perovskite-based 3D photovoltaic cells; methylammonium lead tribromide (MAPbBr₃) and methylammonium lead triiodide (MAPbI₃) perovskites; Beta Barium Metaborate (BBO) lenses; biomaterials; polymers; ceramics; and metals. In addition, several electronic, photonic, and other devices have been tested in the harsh space environment outside the ISS.<br/>In this work, we will introduce the damage mechanisms present in the extreme space environment. We will discuss how the magnitude of each damage mechanism is affected by sample orientation: nadir (Earth-facing), zenith (space-facing/opposite of nadir), ram (direction of travel), and wake (opposite of ram). We will present case studies of materials and devices for both space- and Earth-based applications that were investigated using ISS external platforms, including the performance of 3D photovoltaic cells, perovskites, and polymers. We will also discuss translational lessons learned from space-exposure experiments that inform and direct terrestrial research and materials science. Finally, we will present opportunities for future space-exposure experiments and access to ISS facilities through the ISS National Lab.