DEVELOPMENT OF HIGH VISCOSITY COATINGS FOR ADVANCED SPACE SHUTTLE APPLICATIONS.

Laboratory studies were conductd to increase the use temperature capability of coatings for Silica Reusable Surface Insulation. The approach for this aspect of improved coating studies under NAS2-9809 is based on increasing the viscosity at the re-entry temperature to more adequately resist the aerodynamic shear forces experienced during entry from Earth orbits. The methods used to increase coating viscosity while maintaining current processing techniques and sintering schedules were: (1) reduction in the concentration of the relatively low viscosity additive, B//2O//3; (2) reduction in the particle size of the constituent powders used in making the coatings; and (3) addition of a relatively high viscosity glass former (GeO//2). In combining all three methods, a coating system was identified that showed apparent higher viscosity than the current coating while satisfying all the current Shuttle Orbiter Coating requirements.