On-orbit and ground testing of space environment interactions with materials

During the past 12 years, a significant number of different materials have been returned to Earth after extended exposure to space in low Earth orbits. The process steps required to conduct on-orbit exposure experiments and a brief historical outline of materials experiments to date will be described. Examples of material degradation, with emphasis on coatings, will be presented using on-orbit and post-flight photographs of spacecraft hardware and flight test specimens. Results of post-flight testing will be compared with test results from ground-based systems. Oxidation of coatings, darkening of surfaces due to UV-induced chemical bond rearrangement, and displacement of oxygen atoms from pigments due to proton and electron impact, mechanical failure due to thermal cycling, damage due to microscopic particle impact, and multiple bond ruptures due to high-energy charged particles are observed on hardware returned from orbit. A current materials flight experiment that includes a significant number of coating specimens, along with many other materials, is the Materials International Space Station Experiment (MISSE). MISSE is flying today on-board the International Space Station (ISS) and will be discussed as an example of the current infrastructure available for on-orbit testing.