Spacecraft External Heat Flow Analysis by z-Buffer Method

Determining the external heat flow from direct sunlight to spacecraft is an important stage in analysis and design of the spacecraft thermal control. The Earth IR and albedo radiation provide the noticeable contribution in total spacecraft heating in case when a spacecraft is operating in Low Earth Orbit. The task gets significantly more complicated in case of complex spacecraft geometrical configuration in presence of mutual shading by spacecraft components. The zonal method is often applied to simplify calculations when visible terrestrial region is subdivided into a finite number of surface area zones. The radiation from each zone is approximated as a parallel beam is irradiated from a point source placed in the zonal center. Direct sunlight is considered to be a parallel beam from the point source as well, therefore it is possible to calculate the total external heating using the same approach. The key point of the approach implementation is to choose an algorithm for calculating the spacecraft external surface projected area facing radiation from each point of the source if there is a possibility of spacecraft components mutual shading. Known algorithms based on ray-tracing could experience a significant loss of performance being applied to complex models, especially containing components of non-regular shape. This paper presents a method for carrying out such calculations on a meshed spacecraft CAD model with its external surface subdivided into a finite number of faces of any kind (triangles, quadrangles or isoparametric faces). The method uses the z-buffer (or depth buffer) technique well-known in the field of computer graphics. Advantages of the method are straightforward implementation, applicability to a geometrical model of any complexity and acceptable performance which is not affected by the nonregularity of geometry.

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