给你一个位置矢量

Given one vector, the position vector.

你可以说，位置矢量在另一个时间或在任何时间，无论如何，位置矢量始终在这个平面上。

You could say the position vector at another time, or at any time, but in fact, what's also true is that the velocity vector is in the plane.

如果你看一下任何时刻运动时的，位置矢量和速度矢量，它们决定了某个平面。

So, if you just look at the position vector, and the velocity vector for any motion at any given time, then together, they determine some plane.

所以，开普勒第二定律说,加速度平行于位置矢量。

OK, so, in fact, what Kepler's second law says is that the acceleration is parallel to the position vector.

姿态确定后， 根据卫星姿态与位置函数的关系，可确定位置矢量的方向数。

First, if attitude is known, the direction number of the position vector of satellite can be determined;