目标天体极轨道卫星的轨道寿命

星际探测器轨道的特征与探测目的密切相关，对目标天体两级地区进行探测显然采用的是极轨道（或接近极轨道）。对于这类卫星（或称轨道器），如果轨道半长径较大，则会因第三体报骚动国导致轨道偏心率增大，使其近星距减小到等于目标天体的赤道半径而落到该天体上，结束其运动寿命，即使目标天体不存在大气（如月球等）亦会如此。

LIFETIME OF POLAR-ORBIT SATELLITE

The orbital characteristic of interplanetary probes has a direct bearing on the aim of probing.To explore the polar cap of the object body requires polar orbit(or the high inclination orbit).When this kind of satellite (orbiter) is orbiting far from the body being probed,its lifetime is limited.With the effect of the third body attraction perturbation,its eccentricity increases and peri distance decreases to the equatorial radius of the primary body until falling down,and ends its lifetime.If there is no atmosphere around the target body,such as moon,things happen too.