Titles:

• Simulated Space Vacuum Ultraviolet (VUV) Exposure Testing for Polymer Films  January 2002
   
• Steady State Vacuum Ultraviolet Exposure Facility With Automated Calibration Capability  May 2000
   
• Apparatus to Measure the Reflectivity of Silver and Rhodium Mirrors at Elevated Temperatures  August 1996
   
• Alignment and Initial Operation of an Advanced Solar Simulator  January 1996
   
• Low Earth Orbital Atomic Oxygen Environmental Simulation Facility for Space Materials Evaluation  May 1993

Dever, J. A., Pietromica, A. J., Stueber, T. J., Sechkar, E. A., and Messer, R. A., “Simulated Space Vacuum Ultraviolet (VUV) Exposure Testing for Polymer Films,” prepared for the 39th Aerospace Sciences Meeting and Exhibit, Reno, Nevada, January 2002.

Vacuum ultraviolet (VUV) radiation of wavelengths between 115 and 200 nm produced by the sun in the space environment can cause degradation to polymer films producing changes in optical, mechanical, and chemical properties. These effects are particularly important for thin polymer films being considered for ultra-lightweight space structures, because, for most polymers, VUV radiation is absorbed in a thin surface layer. NASA Glenn Research Center has developed facilities and methods for long-term ground testing of polymer films to evaluate space environmental VUV radiation effects. VUV exposure can also be used as part of sequential simulated space environmental exposures to determine combined damaging effects. This paper will describe the effects of VUV on polymer films and the necessity for ground testing. Testing practices used at Glenn Research Center for VUV exposure testing will be described including characterization of the VUV radiation source used, calibration procedures traceable to the National Institute of Standards and Technology (NIST), and testing techniques for VUV exposure of polymer surfaces.

NASA Glenn Research Center at Lewis Field designed and developed a steady state vacuum ultraviolet automated (SSVUVa) facility with in situ VUV intensity calibration capability. The automated feature enables a constant accelerated VUV radiation exposure over long periods of testing without breaking vacuum. This test facility is designed to simultaneously accommodate four isolated radiation exposure tests within the SSVUVa vacuum chamber. Computer-control of the facility for long term continuous operation also provides control and recording of thermocouple temperatures, periodic recording of VUV lamp intensity, and monitoring of vacuum facility status. This paper discusses the design and capabilities of the SSVUVa facility.
 

Solar thermal power and propulsion systems are being considered for spacecraft where sunlight is directed into the aperture of a heat receiver by first reflecting the sunlight off a large primary concentrator and then passing it through a much smaller secondary concentrator. Selection of materials and coatings for secondary concentrators is of importance owing to the high energy throughput of such optical systems. This paper addresses an apparatus to measure the reflectivity of mirror materials at the elevated temperatures expected for secondary concentrator applications.
 

A solar simulator utilizing nine 30 kW xenon arc lamps was built to provide radiant power for testing a solar dynamic space power system in a thermal vacuum environment. The advanced solar simulator meets requirements specific to the solar dynamic system including: (1) a subtense angle of 1°, (2) the ability to vary solar simulator intensity up to 1.7 kW/m², (3) a beam diameter of 4.8 meters, and (4) uniformity of illumination on the order of ±10%. The flexibility of the solar simulator design allows for other potential uses of the facility, the alignment procedures used to deliver radiant power to the solar dynamic system, and a summary of the performance of the as-built solar simulator.

Simulation of low Earth orbit atomic oxygen for accelerated exposure in ground-based facilities is necessary for the durability evaluation of space power system component materials for Space Station Freedom (SSF) and future missions. A facility developed at the National Aeronautics and Space Administration's (NASA) Lewis (now Glenn) Research Center provided accelerated rates of exposure to a directed or scattered oxygen beam, vacuum ultraviolet (VUV) radiation, and offers in-situ optical characterization. The facility utilizes an electron-cyclotron resonance (ECR) plasma source to generate a low energy oxygen beam. Total hemispherical spectral reflectance of samples can be measured in situ over the wavelength range of 250 to 2500 nm. Deuterium lamps provide VUV radiation intensity levels in the 115 to 200 nm range of three to five equivalent suns. Retarding potential analysis show distributed ion energies below 30 electron volts (eV) for the operating conditions most suited for high flux, low energy testing. Peak ion energies are below the sputter threshold energy (~ 30 eV) of the protective coatings on polymers that are evaluated in the facility, thus allowing long duration exposure without sputter erosion. Neutral species are expected to be at the thermal energies of approximately .04 eV to .1 eV. The maximum effective flux level based on polyimide Kapton mass loss is 4.4x1016 atoms/cm²•s, thus providing a highly accelerated testing capability.
 

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Last Updated: 04/06/2008