Numerical modeling and passive thermal control of external lighting systems for space station freedom

External lighting systems for Space Station Freedom serve a host of functions critical to its mission. Luminaires must be designed not only to provide the appropriate light distribution, but also to passively withstand the extremes in temperature and pressure imposed by the harsh, low-earth orbit environment external to the space station. Thermal considerations are of paramount importance to the design process, and rely on the use of sophisticated numerical models to study the effects of various design parameters on critical (most restrictive) luminaire temperatures. Three generic families of luminaires have been studied, with lamp power ranging from 150 watts for the largest luminaires (video camera family), to 11 watts for the smallest family. Worst hot and cold case environments were imposed using the concept of an equivalent radiation node boundary temperature, and transient finite-difference models were developed to study the effects of geometry and thermal control coating optical properties, with appropriate adjustment for changes anticipated in coating properties during the 30-year design life. Minimum and maximum transient temperatures computed at the critical location during the 90 minute orbit were compared with allowable limits. The results indicate that with the proper choice of optical properties, the luminaires can be passively controlled to within acceptable limits.