Systematic survey of space debris with the MU radar

为甚高频有源相控阵雷达开发了一种特殊的空间碎片观测模式，以便测量雷达截面积随时间的变化。由于使用很长的波长，小碎片的雷达散射截面减小，但天线孔径大，输出功率高，因此，该雷达在空间碎片探测方面的灵敏度与美国空间司令部用于空间碎片例行监测的雷达相当。该模式充分利用了多波束雷达快速波束可调的特点，通过比较重叠波束的回波功率比来精确确定目标的瞬时位置。该模式的高度和角度分辨率分别约为200米和0.1毫米，比雷达的原始分辨率好几十倍。由于简单的低频近似法适用于分析大多数空间碎片对MU雷达信号的散射，因此可以根据观察到的RCS变化幅度来估计每个目标的有效轴比。初步统计研究表明，雷达散射截面较小的碎片比较大的碎片具有更大的雷达散射截面变化，这表明它们可能具有细长的形状，而不是撞击估计中通常假设的球形。假定为椭球形的一系列数值模拟表明，观测到的小碎片的体积估计不到雷达散射截面相同的球体的一半。这些结果可望成为碎片屏蔽设计中的宝贵资料。

A special observation mode for space debris was developed for a VHF active phased-array radar(MU radar)in order to measure the time variation of the radar cross section(RCS). The reduced RCS of small debris due to the use of a very long wavelength is compensated for by the large antenna aperture and the high output power, so that the radar has shown comparable sensitivity in space debris detection to those employed by US SPACECOM for routine monitoring of space debris. The mode makes full use of the fast beam-steerability of the MU radar, so that the instantaneous location of a target can be determined precisely by comparing the echo power ratio of overlapping beams. The height and angular resolutions of this mode are about 200 m and 0.1ﾟ, respectively, which are several tens of times better than the raw resolutions of the radar. Since a simple low-frequency approximation holds for the analysis of scattering of the MU radar signal from most of space debris, it is feasible to estimate the effective axial ratio of each target from the magnitude of observed RCS variations. Preliminary statistical study showed that debris with smaller RCS has larger RCS variations than larger debris, suggesting that they may have elongated shape rather than spherical shape as usually assumed in the impact estimation. A series of numerical simulations assuming an ellipsoidal shape has shown that the volume of small observed debris is estimated to be less than half of that of a sphere with the same RCS. These results are expected to serve as valuable information in the debris shield design.