Materials Issues in the Space Environment
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Judith C. Yang and Kim K. de Groh, Guest Editors Abstract To explore higher, farther, and faster, scientists and engineers have developed advanced materials for manned spacecraft and satellites for a range of sophisticated applications in transportation, global positioning, exploration, and communication. Materials used in space are exposed to vacuum, intense ultraviolet radiation from the sun, and ionizing radiation that results in material damage as well as charging (electrostatic discharge effects), micrometeoroids and debris impacts, and thermal cycling (typically from −175 to 160°C). In terms of materials degradation in space, the low Earth orbit (LEO), where LEO is defined as 200–1000 km above the Earth’s surface, is a particularly challenging synergistic environment, since atomic oxygen (AO) is present along with all other environmental elements. Hence, this special issue focuses primarily on the materials issues experienced in LEO by space environmental exposure, such as on the exterior of the International Space Station and the Hubble Space Telescope, and the challenges and opportunities of ground-based laboratory sources to mimic LEO. The combination and comparison of both in-flight and groundbased experiments are needed for the development of predictive understanding of the materials degradation and AO passivation mechanisms in LEO. Such insights are essential for the development of advanced materials and coatings to ensure the longterm durability and performance of vehicles employed in space.
Introduction and Background Space exploration began with gazing at the stars; as early as 3000 BC, Babylonian astronomers made methodical observations of the skies. The telescope was invented in ~1600 AD, and Galileo Galilei introduced the telescope to the study of astronomy in 1609; the developments and utilization of the telescope have had a tremendously profound impact on our understanding of the universe. However, it was not until the last century that we accomplished the spectacular achievement of sending engineered spacecrafts and humans into space. The first successful orbital launch was of the Soviet unmanned Sputnik (“Satellite I”) mission on October 4, 1957, which weighed about 83 kg and orbited Earth at a height of ~250 km. By 1960, the first communications and weather satellites were launched. By 1969, Neil Armstrong became the first human to
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step on the moon. As space programs developed during the past 50 years, the focus has shifted from single-use space vehicles to re-usable and long-term vehicles, such as the Space Shuttle and the International Space Station (ISS)—both of which are substantial engineering achievements—that must withstand long-term exposure to the harsh space environment. The orbits in space are classified as geostationary Earth orbit (GEO), which is a geosynchronous orbit 36,000 km directly above the equator, and medium Earth orbit (MEO), which is between GEO and the low Earth orbit (LEO), where LEO is defined as 200–1000 km above the Earth’s surface. Each orbit is used for di
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