Spacecraft materials in low Earth orbit (LEO) can be subjected to oxidative erosion from both direct and scattered atomic oxygen (AO). Scattered atomic oxygen AO is important for the assessment of the durability of polymers and metals that are not directly exposed to AO but may receive AO through secondary reflection processes, such as when apertures in the spacecraft surface allow LEO AO to enter into the interior of a spacecraft. Materials that receive such scattered AO may be compromised if their function depends on their structural, optical, or surface conductivity properties.
Scattering chamber in experiment tray after retrieval.
The Scattered Atomic Oxygen Characterization Experiment was proposed, designed, constructed, and analyzed by the NASA Glenn Research Center as part of our role as a world leader in understanding AO interactions with materials. The objective of this effort was to measure the scattered angular erosion characteristics of AO that is scattered from typical spacecraft surfaces. To make such measurements, a small AO scattering chamber was placed on the Materials International Space Station Experiment (MISSE) Passive Experiment Carrier 2and exposed to LEO AO for almost 4 years as part of MISSE 1 and 2. The experiment (see the preceding figure) was flown in the Passive Experiment Carrier 2, tray 1, attached to the exterior of the International Space Station Quest Airlock. It consisted of a chamber with an aperture disk lid of Kapton H polyimide coated on the space-exposed surface with a thin, AO-durable, silicon dioxide (SiO2) film. The aperture lid had a small hole in its center to allow AO to enter into the chamber and impact a base disk of aluminum. The AO that scattered from the aluminum base could react with the underside of the aperture lid, which was coated sporadically with microscopic sodium chloride (NaCl) particles.
Section view of scattering chamber.
The erosion of the underside of the Kapton lid was sufficient to be able to use profilometry to measure the height of the buttes that remained after the salt particles were washed off. The erosion pattern indicated that a highly peaked flux of scattered AO occurred at an angle of approximately 45° from the incoming normal incidence on the aluminum base unlike that expected for simple cosine or Lambertian scattering (see the following figure). Thus, very little atomic oxygen actually scattered in a specular direction as one might expect. The atomic oxygen that scattered was measured to have an effective erosion yield of 6.4×10-25 cm3/atom, which was a factor of 0.214 of that for direct impingement on Kapton H polyimide.
Angular distribution of scattered atomic oxygen erosion rate on Kapton H polyimide relative to normal incident erosion rate.
Banks, Bruce A.; de Groh, Kim K.; and Miller, Sharon K.: MISSE Scattered Atomic Oxygen Characterization Experiment. NASA/TM--2006-214355, 2006. http://gltrs.grc.nasa.gov/Citations.aspx?id=23
Find out more about the research of Glenn’s Electro-Physics Branch: http://www.grc.nasa.gov/WWW/epbranch/ephome.htm
Glenn contacts:
Bruce A. Banks, 216-433-2308, Bruce.A.Banks@nasa.gov
Kim K. de Groh, 216-433-2297, Kim.K.deGroh@nasa.gov
Sharon K. Miller, 216-433-2219, Sharon.K.Miller@nasa.gov
Authors:
Bruce A. Banks, Kim K. de Groh, and Sharon K. Miller
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Last updated: December 17, 2007
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