The design, development and initial testing of a hypervelocity atomic oxygen source for space simulation

Abstract

Atomic Oxygen is the dominant atmospheric specie at low earth orbit altitudes for spacecraft orbiting the earth. This altitude range of atomic oxygen dominance extends from 120 km to 900 km. Other species such as helium, molecular oxygen and nitrogen make up the bulk of the rest with the densities corresponding to high to ultrahigh vacuum levels. Spacecraft orbiting at this altitude need to travel at a velocity of 8 km/sec to maintain orbit and therefore spacecraft encounter a high fluence of impinging rarefied atmosphere in a short time period. This gas-surface interaction has several effects which affect the space vehicle. They include aerodynamic drag, surface reaction and surface glow. The need to model these effects on spacecraft surfaces has resulted in the design, development and construction of an advanced facility to simulate these L.E.O. atmospheric effects. This facility utilizing an arc heated source can produce high energy species of the common atmospheric species at a velocity of up to 4.5 km/sec with fluxes comparable to orbit. This particular type of source is unique in Europe with two similar types reported in the U.S.A. Considerable effort was expended in optimizing the source for atomic oxygen production via beam characterization and stagnation condition measurement. This has enabled the radial and axial temperature profiles in the source to be deduced, thus providing a clearer idea of the processes in the source and therefore benefits future users of this technique. In addition, alternative routes of producing atomic oxygen were pursued via nitrous oxide and nitrous oxide/nitrogen seeding. Extensive work on developing reliable beam characterization equipment resulted in the comparison of two methods of beam analysis. This involved the development of a new method of beam mass/energy analysis, which has several advantages over current instruments. Conclusions are made on the suitability of mass spectroscopic detection of reactive specie beams. Finally, atomic oxygen degradation tests were pursued on a variety of surfaces including the polyimide Kapton-H. It was concluded from these tests that Kapton-H erosion has a form of energy dependence, with an energy threshold to erosion of approximately 0.5 eV. The erosion rate above this energy rises rapidly to rates comparable to those of orbit. The Southampton results agree reasonably with the very few results on Kapton-H in this energy range. This has important implications on spacecraft material design.

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