标题： 跟踪星链卫星在太阳活动周期25上升阶段的再入情况 显示英文标题

标题： Tracking Reentries of Starlink Satellites During the Rising Phase of Solar Cycle 25

摘要： 过去五年低地球轨道（LEO）卫星数量的指数增长，使得可靠监测和再入预测的需求变得尤为迫切，以防止太空碰撞和地面碎片的影响。 然而，LEO卫星在大气层上层飞行，该区域对其轨道施加了显著的大气阻力，缩短了它们的寿命，并在动态事件（如地磁风暴）期间增加了碰撞风险。 这些条件在地磁风暴期间可能会变得更加严重，尤其是在极端事件期间。 在这项工作中，我们使用双线元素（TLE）卫星跟踪数据来研究地磁活动对从2020年到2024年的523颗Starlink卫星再入影响。 这一时期与太阳活动周期25的上升阶段相吻合，而该周期表现出比前一个周期更为强烈的特点。 我们从TLE文件中推导出卫星的高度和速度，并进行了叠加平均分析，这是首次对数百颗相似卫星进行的分析。 即使TLE数据精度有限，我们的结果无可辩驳地表明，卫星在地磁活动增强时再入速度更快。 这可以通过卫星因增加的大气阻力导致的最快轨道衰减速率（以千米/天计）来解释。 我们还发现，预测误差——定义为实际再入时间点与参考高度预测再入时间点之间的差异——随着地磁活动的增加而增大。 因此，我们清楚地表明，当前太阳活动周期的强烈太阳活动已经对Starlink卫星的再入产生了重大影响。 这是卫星轨道阻力研究非常激动人心的时刻，因为LEO中的卫星数量和太阳活动达到了人类历史上前所未有的水平。 显示英文摘要

摘要： The exponential increase of low-Earth orbit (LEO) satellites in the past 5 years has brought into intense focus the need for reliable monitoring and reentry prediction to safeguard from space collisions and ground debris impacts. However, LEO satellites fly within the upper atmosphere region that exerts significant drag forces to their orbits, reducing their lifetimes, and increasing collision risks during dynamic events, like geomagnetic storms. Such conditions can become more severe during geomagnetic storms, particularly during extreme events. In this work, we use two-line element (TLE) satellite tracking data to investigate geomagnetic activity effects on the reentries of 523 Starlink satellites from 2020 to 2024. This period coincides with the rising phase of solar cycle 25, which has shown itself to be more intense than the previous solar cycle. We derive satellite altitudes and velocities from TLE files and perform a superposed epoch analysis, the first with hundreds of similar satellites. Even with limitedly accurate TLE data, our results indisputably show that satellites reenter faster with higher geomagnetic activity. This is explained by the fastest orbital decay rates (in km/day) of the satellites caused by increased drag forces. We also find that prediction errors, defined as the difference between the epochs of actual reentries and predicted reentries at reference altitudes, increase with geomagnetic activity. As a result, we clearly show that the intense solar activity of the current solar cycle has already had significant impacts on Starlink reentries. This is a very exciting time in satellite orbital drag research, since the number of satellites in LEO and solar activity are the highest ever observed in human history.