Based on free-molecule flow in the rarefied dynamics field, the atmospheric drag for the passive jamming, such as balloon and chaff, is investigated. It is derived that the drag coefficient of the balloon would have a value of 2. For the chaff in the case of mirror reflect. The formula of drag for chaff with arbitrary attack angle is derived, and the impact of various factors on drag coefficient is discussed. An approximate formula of drag coefficient is present for the case. of mirror reflect. A typical trajectory is obtained by simulation, and based on this trajectory the figures are presented, which shows drag for balloon and chaff at various at-titudes. Advice on the use of passive jamming is given at last.%借鉴稀薄流体力学领域里自由分子流动的相关知识,对箔条气球等典型的无源干扰在低轨道大气中所受的空气阻力进行了定量分析.对气球,导出了在低轨道大气中完全镜而反射时气球的阻力系数为2的结论;对箔条,首次导出了任意攻角下箔条所受阻力的计算公式,并分析了各种凶素对阻力系数的影响,得到了完全镜面反射时箔条阻力系数的近似公式.利用仿真方法得到了弹道导弹的典犁弹道,基于此弹道,分析了气球和箔条的大气阻力随高度的变化曲线.最后对无源干扰的抛撒高度提出了合理的建议.
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