Most facilities for testing the stability of spacecraft materials under attack by fast atomic oxygen (AO) are based on the generation of hypersonic beams of AO in nozzle sources with the use of continuous electrical discharges or in laser pulse-induced breakdown of the gaseous oxygen. In both cases, the sources of fast AO are simultaneously quite intense sources of vacuum ultraviolet (VUV) radiation. In the present study the intensity of VUV radiation with wavelengths > 115 nm from fast AO source were directly measured in the Central Aerohydrodynamic Institute facility VAT- 103. The intensity of this VUV radiation at the nozzle exit was shown to be almost equal to the intensity of the commercial lamp XeR-2 emitting at 147.0 nm (at its window). This VUV radiation can take part in destruction and erosion of polymer materials simulating the oxydative effects of fast AO. Its contribution to observed mass losses is greatly dependent on the material under test. For polymers consisting of carbon, hydrogen, oxygen and nitrogen the main role in erosion is played by fast AO. The decisive role of VUV radiation is shown in the erosion of fully fluorinated polymers. The mass losses of Teflon and Teflon FEP films in facilities for generation of fast AO are suggested as a means of measuring the VUV radiation dose in these facilities. The main features of mass losses that depend on duration of VUV irradiation are formulated. They are based on the previously proposed model of mass losses from these polymers during VUV photodestruction. The key feature of this model is the limited rate of photofragment evaporation (sublimation) into vacuum.
About 60 samples of various materials exposed to low Earth orbit (LEO) conditions for 997 days on board the orbital space station ‘Mir’ were investigated. The aim was to determine the properties of the contamination layers formed during LEO exposition. The following methods were used: optical and scanning electron microscopy, local x-ray microanalysis, secondary ion mass spectrometry in fast atom bombardment ionization mode, electron spectroscopy for chemical analysis, temperature programmed desorption mass spectrometry, x-ray phase analysis, spectral reflectance, solar absorbance and relative emittance measurements. Two effects were observed for all samples: the formation of contamination deposits and the erosion of the substrate–original surface. The relative contribution of both effects changes depending on the sample type and on exposure conditions. The deposit thickness varies on the sample surface over a very wide range (at least five decimal orders of magnitude), changing from values exceeding 100 μm to values of less than 2 nm (possibly these regions do not contain any deposit at all). The main element of contamination is silicon; the others are potassium and calcium. Evidence of a chemical reaction between the Teflon FEP substrate and the contamination was observed.
A theoretical analysis has been made on the reliability of the simulation of solar radiation effects on polymer films under conditions of the space environment by using various light sources under laboratory conditions. Two main factors are noted that can influence the possible differences in the results of natural and laboratory tests; namely, the differences between the spectral distributions of solar radiation and laboratory light sources and the differences in the intensity of the radiation used in tests. It is found that at least two radiation sources are needed for the simulation of the erosion and the deterioration of the mechanical properties of polymer films. The effect of intensity occurs for polymers that are destroyed by radiation (a typical example is Teflon) and this has as a basis in the limited rate of evaporation of fragments of polymer chains.
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