The atmospheric drug must be fully taken into account for accuracy orbit determining of space-craft below 500 km. In this paper, a computer graphical approach based on the fundamental idea of shadow map is proposed to accurately calculate the cross section area of spacecraft. Firstly, the complex geometry surface of spacecraft is represented in the form of triangle grids, and the relative motion among spacecraft components is considered. Secondly, the shadow map algorithm is employed to project the spacecraft model onto a shadow plane, and then the cross section area can be found out by analysis the amount of shadow pixels in the shadow graph. The simulation and experiments are given to validate the proposed method and the results indicate that this method can deal with complex spacecrafts whose components have relative motion.%航天器轨道低于500 km时大气阻力影响显著,该阻力与航天器迎风面的面积成正比.对于复杂外形的航天器, 其迎风面积常常进行近似处理, 会对阻力分析结果带来一定误差. 针对航天器迎风面积对大气阻力的影响, 提出一种复杂航天器迎风面积的精确计算方法. 该方法同时考虑航天器几何外形和部件运动, 根据活动部件的实际运动状态对复杂外形和结构进行精细三维建模; 利用图形学中的实时阴影生成方法产生航天器在投影面的阴影图像, 进一步分析得到航天器的迎风面积. 该方法易于实现, 能处理复杂外形航天器及其活动部件的运动, 具有较好的通用性. 将文中方法应用到我国航天测控任务中, 证明了该方法的有效性.
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