William W. answered • 12/23/19
Experienced Tutor and Retired Engineer
There are two important things to know related to this problem.
1) The amount of rocket fuel needed is proportional to the force required for the rocket to offset. Simply, if the rocket must escape a huge force of gravity it takes more fuel than if it only needs to escape a small force of gravity.
2) The more massive an object is, the higher the force of gravity it has on an object. So, the earth exerts a larger force on the rocket than the moon because the earth has significantly more mass than the moon.
So, putting those two principles together, the rocket requires more fuel to take off from the earth (and leave it's gravitational influence) than it does to take off from the moon
Arturo O.
I would like to add one more thing to William's fine explanation. Going from the earth to the moon, the rocket is trying to escape the strong gravitational pull of the earth, even as it tries to get drawn by the weak gravitational pull of the moon. From the moon to the earth, the rocket is trying to escape the weak gravitational pull of the moon as it tries to get drawn by the strong gravitational pull of the earth. So you can see the trip is much harder one way than the other. As astrodynamicists would say, it is easier to escape the sphere of influence of the moon as you approach the sphere of influence of the earth, than to escape the sphere of influence of the earth as you approach the sphere of influence of the moon. The harder job requires more fuel consumption to attain the required escape speeds.12/24/19
David W.
... which is why the same rocket takes longer to get to the moon than to get to Earth (Earth's gravity "pulls" it more).12/23/19