现在约有2万间太空垃圾在地球低轨道运行，其中大部分是航天器的分离部分或者碰撞残骸。

Some 20,000 pieces of rubbish are currently being monitored in low-Earth orbit, the majority of which are discarded bits of spacecraft or debris from collisions.

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推导了基于NASA标准解体模型的碎片分离速度概率密度函数，建立了计算航天器与单颗碎片碰撞概率的时间积分算法。

Space debris delta-velocity probability density function was deduced by NASA's standard breakup model, and time integral algorithm of collision probability between spacecraft and any debris was built.

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