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Materials under the adverse environment in space
Abstract
Materials degradation is an important long-term issue for spacecraft orbiting in low earth orbit (LEO). The spacecraft materials in LEO are vulnerable to the synergistic damaging effects of atomic oxygen (AO), ultraviolet radiation (UV), thermal cycling, high vacuum, and micrometeoroid and debris impact, etc. The interaction of AO with spacecraft materials results in mass loss (or gain) and changes in surface morphology and optical, mechanical and thermal properties. Moreover, contamination of optical and thermal control surfaces on spacecraft in LEO has been an ever-present problem as a result of the interaction of AO with volatile species from silicones and hydrocarbons onboard spacecraft. Simulation of materials exposure to AO in LEO is achieved using an Electron Cyclotron Resonance (ECR) oxygen plasma chamber. Materials studied include CV-1144-O silicone, an AO protective coating; iridium (Ir), a candidate substrate for space contamination studies; and zinc selenide (ZnSe), a proposed AO protective, infrared (IR) antireflection coating for electrochromic emissivity modulation devices. Spectroscopic Ellipsometry (SE) is employed to study these materials under AO irradiation, ex situ and/or in situ. Optical constants are determined over the spectral range from vacuum UV (VUV) through the middle IR. Trends of development, rates of oxidation/etching, and changes in surface morphology, optical properties and composition are studied. AO-treated CV-1144-O film thickness and refractive index (as a function of depth into the material) are quantified. In addition, SE is used to map thickness and uniformity. Major resonant absorption peaks in the IR region are identified. Extremely smooth thin films of Ir are deposited by dc magnetron sputtering, and their surface morphologies and microstructures are examined using Atomic Force Microscopy (AFM), x-ray diffraction, and EDX. The as-determined film optical constants are expected to be the best available for Ir bulk metals. The Herzinger-Johs model is used to fit for ZnSe thin film optical constants. Six critical points are identified, with E2 and E0 ′ being reported by SE for the first time. Theoretical electrochromic device performance is evaluated with and without a ZnSe top layer.
Subject Area
Materials science|Chemical engineering|Electrical engineering
Recommended Citation
Yan, Li, "Materials under the adverse environment in space" (2003). ETD collection for University of Nebraska-Lincoln. AAI3116615.
https://digitalcommons.unl.edu/dissertations/AAI3116615