制约卫星轨道寿命的另一种机制(续)

对于制约低轨人造地球卫星轨道寿命的耗散机制，人们已有足够的重视，但在深空探测中，另一种制约低轨卫星轨道寿命的引力机制同样应予重视，前文讨论了高轨卫星的情况，在第三体引力作用下，有可能导致卫星轨道偏心率产生变幅较大的长周期变化。特别是极轨卫星，其轨道偏心率在一定的时间内可增大到使其近星距rp=a(1-e)≈Re（Re是中心天体的赤道半径），从而落到中心天体上，结束其轨道寿命，目前对低轨卫星作了详尽的理论分析，研究表明，与高轨卫星有类似结果，但其力学机制却不相同，低轨卫星的轨道寿命与第三体引力无关。它取决于中心天体非球形引力位中的扁率项（即J2项）与其他带谐项之间的相对大小，这不仅是一个纯理论结果，也有实际背景，在太阳系中慢自传天体（月球和金星等）的低轨卫星就存在这一问题，还给出了有关判据，并以计算实例作了验证。

Another Mechanism of Restriction on the Orbital Lifetime of Satellites (Continued)

Dissipative effect on the orbital lifetime of LEO has been discussed widely and deeply. But, in deep-space research, another effect from attraction mechanism on low-orbit satellites is important as well. For high altitude satellites, the gravitational perturbation due to the third body means that its orbital eccentricity will so increase that it will eventually fall down onto the primary. This paper focuses on the low-orbit satellites. Though the result is similar to the high altitude ones, the mechanism is totally different. Lifetime of low orbiters depends on the ratio of oblateness to the zonal harmonic, while that of high orbiters depends on the attraction of the third body. Under the background of the solar system, both the theoretical analysis and numerical examples are given .