So we are burning up an enormous amount of fuel at every launch just to get the rocket up to what's known as escape velocity.
所以每一次发射我们都要耗费大量的燃料来让火箭达到所谓的“逃逸速度”。
2
But to get the planet's mass, astronomers normally need to follow up with time-consuming radial velocity observations at some ofthe planet's biggest telescopes.
但测量行星的质量,天文学家通常还需要使用地球上最大的天文望远镜,来测算径向速度的耗时。
3
This is just thevelocityofthe source relative to you at that Angle.