Plasma-deposited protective coatings for spacecraft applications

Abstract

T HE design of spacecraft structures is driven by environmental factors that affect their functional performance. Although a great deal of work is being directed toward the solution of the problem of degradation of polymeric and other materials by atomic oxygen in low Earth orbit (LEO),'-~ this is only one of the many environmental factors that can affect the physical and functional performance of spacecraft. Other factors include thermal cycling, vacuum, radiation (both charged particles and energetic photons), debris, and micrometeoroid impacts. Also, man-made environmental factors such as electromagnetic interference (EMI) must be considered. Therefore, coatings that may be proposed for exterior surfaces of spacecraft must be able to withstand all of the effects of the space environment, although the relative importance of each effect will be dependent on the orbit and application of any particular hardware. In particular, evaluation of atomic oxygen resistant coatings must include the performance in the presence of other factors, perferably taken together. All spacecraft are affected by atomic oxygen degradation. Those spacecraft in LEO are most prone to long-term attack, but even short times spent in a parking orbit for a geostationary spacecraft can result in exterior surface damage. When organic materials are exposed to the highly oxidizing 0 atoms, especially at the elevated velocities of spacecraft, the observed result has been rapid erosion (loss of mass) and surface roughening. This, in turn, leads to irreversible degradation of the physical characteristics (optical, thermal, electrical, and mechanical) for which the surface or structural members were designed.