Sputter Deposited, Electrically Conductive, Oxidation Resistant Coatings
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SHARON K. RUTLEDGE NASA Lewis Research Center,
21000 Brookpark Rd.,
Cleveland, OH.
44135
ABSTRACT Significant polymer weight loss has been observed due to environmental ashing by atomic oxygen at low earth orbital (LEO) altitudes. Static charging during deployment and charging caused by the space plasma in LEO polar orbits may cause electromagnetic interference (EMI) problems on insulating polymer materials that are integral to such applications as high voltage solar arrays. Simultaneous ion beam sputter deposited coatings of indium-tin-oxide (ITO) with polytetrafluoroethylene (PTFE), carbon, air, or methane were investigated as potential solutions to these problems. The purpose of this research was to improve the flexibility of ITO coatings with these additives and to study the effect the addition of these materials had not only on the flexibility of ITO sputter deposited thin films but also on the conductivity and optical properties.
INTRODUCTION Spacecraft materials must be environmentally durable without adversely affecting systems operations. Insulating polymer surfaces may fail to meet both of these requirements due to degradation by ram atomic oxygen in the low Earth orbital (LEO) environment and by surface charging caused by environmental or triboelectric phenomena. Atomic oxygen is the most predominate environmental species from an altitude of 180 km (97 n mi) to 650 km (351 n mi).[1] Energetic ram impingement of this species with material surfaces and the subsequent oxidation of these surfaces is believed to be the cause of degradation observed on early shuttle flights.[2] Observed degradation consisted of optical property changes caused by surface texturing and material loss.[2,3,4] Observed loss rates for materials such as polyimide (Kapton ) and some paints are large enough to cause some concern for the life of these materials in applications such as space station. [5,61 (see Table I) These materials need to be protected from degradation by atomic oxygen if they are to be used with reliability for space applications in LEO. There are two main types of surface charging that are of concern. One of these is charging in polar orbits. Charging events in LEO polar orbits are short lived but similar in nature to those that occur in geosynchronous orbit (GEO).[7] Arcing from the surface to the space plasma as a result of charging could lead to electromagnetic interference (EMI) problems and to material degradation as a result of pinhole formation in protective coatings. The second type of charging is triboelectric or static charging which may be present during unfolding or unrolling of surfaces such as solar array blankets. If there is no mechanism for draining charge from these surfaces, static charge could build up or propagate during deployment. This could cause arcing from the surface to the space plasma resulting in problems similar to those experienced during charging in polar orbits. One solution to these problems which would allow a material such as a solar array blanket to maintain most of its bu
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