Stock material or miscellaneous articles – Composite – Of polyisocyanurate
Patent
1984-11-09
1987-05-05
Herbert, Thomas J.
Stock material or miscellaneous articles
Composite
Of polyisocyanurate
244163, 428457, 428699, 428701, B32B 2706, B32B 1508
Patent
active
046632344
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to new coatings capable of withstanding high thermal stresses such as those to which satellites and spacecraft are subjected, and to a process for the production of these coatings. The present invention relates more particularly to coatings suitable for preventing the formation of cracks in the electrically conducting layer of the second-surface mirrors which form the outer surface of satellites.
PRIOR ART
The equilibrium temperature of a satellite is normally maintained by passive temperature control. This control is effected by applying to the outer surfaces of the satellite materials which are totally reflecting and which must simultaneously possess properties of weak solar absorptance and of strong infrared emittance. The materials satisfying these conditions which are most often used are dielectric materials such as white paints, silica glass or cerium-doped glass whose rear face is coated with silver, "KAPTON" (registered trademark denoting a film of polyimide resin) or "TEFLON" FEP (registered trademark denoting fluorinated ethylene/propylene) whose rear face is also coated with silver or aluminum.
In geostationary orbit, a satellite is exposed not only to solar radiation but also to space plasma, which has the effect of accumulating electrical charges on its outer surface. On insulated surfaces in shadow, potentials of as much as 19 kV, due to the interaction of solar radiation and space plasma on the surface of a satellite, have been recorded, whereas the illuminated surfaces of the same satellite have potentials on the whole of around zero. Such potential differences lead to arc discharges, the effect of which is to degrade the thermo-optical and mechanical properties of the satellite coating, to produce noisy radio-frequency interference emissions and, in certain cases, to cause the on-board electronic equipment to switch from one state to another.
While the accumulation of electrical charges on a spacecraft of satellite can harm the operation of scientific satellites carrying plasma experiments, application satellites could tolerate surface potentials of as much as several hundred volts, provided that discharges can be avoided.
A solution has been proposed to the problems presented by the accumulation of electrical charges on satellites, whether scientific satellites or application satellites; this solution consists in providing a spacecraft with a conducting outer skin having a ground connection to the metal part of the structure of the spacecraft. This solution is based on the principle that the application and interconnection of conducting surface materials makes it possible to avoid charge differences and favors the setting-up of an equalization of the potentials on the surface of the spacecraft.
The development of GEOS, which is a geostationary scientific satellite, demonstrated that this solution is valid; GEOS was the first satellite to have a more than 96% conducting surface.
Several combinations of materials were examined and tested for the purpose of ensuring thermal-control and rendering the outer surface of the satellites conducting. White paints provided with conducting loadings, coatings made of textured silver or quartz, and transparent conducting coatings deposited on the front face of second-surface mirrors, represent examples of such combinations of materials. The second-surface mirrors can be made of silica glass, cerium-doped glass, "KAPTON" or "TEFLON" FEP.
The outer surfaces of a satellite are exposed to the various components of the space environment (particles, ultraviolet radiation, vacuum, thermal conditions). One of the consequences of exposure to this environment is degradation of the physical properties of the dielectric materials applied to the outer skin to ensure heat control. This degradation can cause these materials to change color, which generally results in an increase in the solar absorptance. It is known that such a modification is mainly due to the high-energy electrons and protons encountered in or
REFERENCES:
patent: 3384324 (1968-05-01), O'Sullivan
patent: 4008348 (1977-02-01), Slemp
Agence Spatiale Europeenne
Herbert Thomas J.
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