设探月卫星的质量为m0，万有引力常量为G，根据万有引力定律有
| GMm |
| r2 |
| 4π2 |
| T |
| Gmm0 | ||
|
| 4π2 |
| T1 |
式中，T1是探月卫星绕月球转动的周期．
由①②式得(
| T1 |
| T |
| M |
| m |
| r1 |
| r |
设卫星的微波信号被遮挡的时间为t，则由于卫星绕月球做匀速圆周运动，应有
| t |
| T1 |
| α−β |
| π |
式中，α=∠CO′A，β=∠CO′B．
由几何关系得 rcosα=R-R1⑤r1cosβ=R1⑥
由③④⑤⑥式得t=
| T |
| π |
|
| R−R1 |
| r |
| R1 |
| r1 |
| GMm |
| r2 |
| 4π2 |
| T |
| Gmm0 | ||
|
| 4π2 |
| T1 |
| T1 |
| T |
| M |
| m |
| r1 |
| r |
| t |
| T1 |
| α−β |
| π |
| T |
| π |
|
| R−R1 |
| r |
| R1 |
| r1 |