Photodegradation in the space environment

Spacecraft operating in low Earth orbit (LEO) are exposed to an extremely harsh environment. One component of this environment is atomic oxygen, which is produced by dissociation of molecular oxygen by UV radiation from the sun (cf section 7.2). Due to the high velocity required to maintain 

In the Geosynchronous Earth Orbit (GEO) two other space environmental hazards, energetic charged particles and UV (vacuum and far) radiation, play important roles. The charged particles, electrons and protons have energies of 0.4-4MeV and each has a flux of 10 cm s Over a lifetime of 30 years, materials in the GEO environment will have absorbed a dose of 10 rads 

In order to study the effects of space environment on different materials, including polymers [326, 450, 1326, 2314], NASA s Office of Aeronautics and Space Technology launched, in 1984, the Long Duration Exposure Facility (LDEF) unmanned, free-ffying spacecraft (Fig. 9.9) for long term (69 months) exposure to the space environment [1198, 1632]. 

The materials examined were high and low density polyethylene, silvered fluorinated ethylene propylene teflon blanket material, polysulphone matrix resin/graphite fibre reinforced composites, poly(methyl methacrylate) and silicones [326, 450,1326, 2314]. Long term exposed polymeric samples show loss of surface integrity and surface erosion. The radiation combines with atomic oxygen to initiate chain scission and crosslinking, both of which greatly affect the polymers structural properties. 

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