IntroductionT HE concerted synergistic interaction between high-velocity oxygen atoms and vacuum ultraviolet (VUV) radiation has been found to contribute significantly to materials degradation in low-Earth-orbiting spacecraft. In particular, organic polymers used as electrical insulation materials and as thermal control blankets show the most significant degradation due to these environmental effects.The existence of this synergistic effect has been proven under laboratory conditions 1>2 and inferred from the degradation observed in samples of silverized FEP (fluorinated ethylene propylene) Teflon (®E.I. Du Pont de Nemours Inc.) thermal blanketing materials recovered from the Solar Maximum Mission satellite and, 3 ' 4 more recently, from the Long Duration Exposure Facility (LDEF) satellite. To date, the detailed chemical origin of this synergistic effect has not yet been fully elucidated.We report here preliminary results of a micrographic investigation of FEP thermal blanket samples recovered from the LDEF satellite. From this investigation and from laboratory experiments, we are able to propose a possible mechanism for the synergistic effect by identifying the role VUV radiation plays in enhancing the atomic oxygen reactivity of FEP.
ExperimentalSamples of silverized FEP (Teflon) thermal blankets recovered from two specific areas of the LDEF satellite were analyzed. A sample was taken from row 2 on the trailing edge (P0004) of the spacecraft, which received predominantly VUV exposure (9346 equivalent solar hours) with very little atomic oxygen fluence (4.7 x 10 9 atoms/cm 2 ), and a sample was taken from row 8 (a position -40 deg off ram), which received both
The solar constant was directly measured from an altitude of about 82 kilometers-apparently the first such determination. The total solar intensity was 136.1 milliwatts per square centimeter, or 1.952 calories per square centimeter, per minute-about 2.5 percent less than Johnson's derived value. Energy in the ultraviolet and visible regions (for lambda less than 607 nanometers) was 7.0 percent less than that obtained by integration over Johnson'Scurve; for integral flux of lambda greater than 607 nanometers there was almost perfect agreement. Seven supporting series of measurements from lower altitudes agreed extremely well with these results after correction for atmospheric extinction.
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