TiN-alloy coatings for temperature control of space vessels

The problem of combining the temperature control of a space vehicle with th e mechanical and chemical stability of the surface is addressed. With the a bsorption of solar radiation and the emission of thermal radiation consider ed the static and dominant factors that determine the equilibrium temperatu re of a spherical object, a simple model is formulated. Realistic variation s of the two material-dependent parameters, solar absorptance alpha and hem ispherical emittance epsilon, permit a large change in the equilibrium temp erature, from less than -50 to more than +150 degrees C. It is pointed out that for a generalized gray surface, i.e., one made from a material whose r eflectance emittance has the same value within the visible and the thermal wavelength regions, the equilibrium temperature is approximate to 5 degrees C, independent of the numerical value of the reflectance. With the require ment for electrical conductivity also taken into account, TiN alloys are id entified as candidate materials. Measurements and calculations of some of t hem indicate that this group may contain a material that fulfills all the r equirements. The experimental reflectance spectrum is used in estimating th e equilibrium temperature for different TiN alloys; one Ti-Al-N-alloy with a gradient content of Al is found to have the lowest equilibrium temperatur e, 66 degrees C. (C) 1999 Optical Society of America OCIS codes: 120.6810, 160.0160, 310.1620, 350.6050.