2 research outputs found
Materials International Space Station Experiment (MISSE): Overview, Accomplishments and Future Needs
Materials and devices used on the exterior of spacecraft in low Earth orbit (LEO) are subjected to environmental threats that can cause degradation in material properties, possibly threatening spacecraft mission success. These threats include: atomic oxygen (AO), ultraviolet and x-ray radiation, charged particle radiation, temperature extremes and thermal cycling, micrometeoroid and debris impacts, and contamination. Space environmental threats vary greatly based on spacecraft materials, thicknesses and stress levels, and the mission environment and duration. For more than a decade the Materials International Space Station Experiment (MISSE) has enabled the study of the long duration environmental durability of spacecraft materials in the LEO environment. The overall objective of MISSE is to test the stability and durability of materials and devices in the space environment in order to gain valuable knowledge on the performance of materials in space, as well as to enable lifetime predictions of new materials that may be used in future space flight. MISSE is a series of materials flight experiments, which are attached to the exterior of the International Space Station (ISS). Individual experiments were loaded onto suitcase-like trays, called Passive Experiment Containers (PECs). The PECs were transported to the ISS in the Space Shuttle cargo bay and attached to, and removed from, the ISS during extravehicular activities (EVAs). The PECs were retrieved after one or more years of space exposure and returned to Earth enabling post-flight experiment evaluation. MISSE is a multi-organization project with participants from the National Aeronautics and Space Administration (NASA), the Department of Defense (DoD), industry and academia. MISSE has provided a platform for environmental durability studies for thousands of samples and numerous devices, and it has produced many tangible impacts. Ten PECs (and one smaller tray) have been flown, representing MISSE 1 through MISSE 8, yielding long-duration space environmental performance and durability data that enable material validation, processing recertification and space qualification; improved predictions of materials and component lifetimes in space; model verification and development; and correlation factors between space-exposure and ground-facilities enabling more accurate in-space performance predictions based on ground-laboratory testing. A few of the many experiment results and observations, and their impacts, are provided. Those highlighted include examples on improved understanding of atomic oxygen scattering mechanisms, LEO coating durability results, and polymer erosion yields and their impacts on spacecraft design. The MISSE 2 Atomic Oxygen Scattering Chamber Experiment discovered that the peak flux of scattered AO was determined to be 45 deg from normal incidence, not the model predicted cosine dependence. In addition, the erosion yield (E(sub y)) of Kapton H for AO scattered off oxidized-Al is 22% of the E(sub y) of direct AO impingement. These results were used to help determine the degradation mechanism of a cesium iodide detector within the Hubble Space Telescope Cosmic Origins Spectrograph Experiment. The MISSE 6 Indium Tin Oxide (ITO) Degradation Experiment measured surface electrical resistance of ram and wake ITO coated samples. The data confirmed that ITO is a stable AO protective coating, and the results validated the durability of ITO conductive coatings for solar arrays for the Atmosphere-Space Transition 2 Explorer program. The MISSE 2, 6 and 7 Polymer Experiments have provided LEO AO Ey data on over 120 polymer and composites samples. The flight E(sub y) values were found to range from 3.05 x 10(exp -26) cu cm/atom for the AO resistant polymer CORIN to 9.14 x 10(exp -26) cu cm/atom for polyoxymethylene (POM). In addition, flying the same polymers on different missions has advanced the understanding of the AO E(sub y) dependency on solar exposure for polymers containing fluorine. The MISSE polymer results are highly requested and have impacted spacecraft design for WorldView-2 & -3, the Global Precipitation Measurement-Microwave Imager, and other spacecraft. The flight data has enabled the development of an Atomic Oxygen Erosion Predictive Tool that allows the erosion prediction of new and non-flown polymers. The data has also been used to develop a new NASA Technical Standards Handbook "Spacecraft Polymers Atomic Oxygen Durability Handbook." Many intangible benefits have also been derived from MISSE. For example, over 40 students have collaborated on Glenn's MISSE experiments, which have resulted in greater than $80K in student scholarships and awards in national and international science fairs. Students have also given presentations and won poster competition awards at international space conferences
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Advancements in null corrector design and certification
The dissertation addresses advancements in null corrector design. The Rayces zero-index concept is validated and used to design null correctors in single pass. By using a doublet field lens in the standard Offner null corrector, the overall length and size of the null corrector are reduced. The Multi-Object Double Spectrograph (MODS) blue corrector study outlines the process associated with designing and producing a null corrector. A novel ghost image analysis technique is used to evaluate candidate MODS blue null corrector designs. Tolerance analysis is performed and manufacturing specifications are defined for the MODS blue null corrector. Several off-axis null corrector designs are investigated as potential solutions to test 8.4 m off-axis elements of a 25 m diameter parabola. The dissertation also addresses advancements in null corrector certification. Truncated-series solutions for diamond turned mirrors and computer generated hologram certifiers for aspheric surfaces that can be modeled in lens design code are derived. The truncated-series solutions are general and can be applied to most aspheric surfaces with only simple changes in coefficients. These equations are implemented in lens design code via the user defined surface (UDS). The process of implementing a UDS is outlined in the dissertation. Once a UDS is identified, a two-step design process is used to create the certifier. First, the corresponding Shack surface of the aspheric surface or surfaces under test must be defined. Second, a point source illuminates the mirrored Shack surface and a certifier is placed at, in, or outside the center of curvature of the Shack surface. Because the rays go back to a point source after reflection from the Shack surface, a standard merit function that minimizes RMS spot radius can be used to find the coefficients. Certifier surface solutions are presented at the center of curvature and inside the center of curvature of the Shack surface for a broad range of aspheric optics. The solution for a certifier outside of the center of curvature of a parabola's Shack surface is also provided