# Gravity Assist

## Gravity Assisted Navigation-How to increase the speed of a spacecraft using the moon’s gravity

A method of increasing speed using the celestial body’s gravity as the spacecraft moves around a moving object is called ‘Gravity Assist Navigation.’
This navigation is also referred to as ‘swing-by’ or ‘slingshot effect.’ They all say the same thing.
When using this to increase the spacecraft’s speed, it is economical because you do not have to use the energy of the spacecraft itself.
Scientists believe that with the help of gravity, space travel is possible with little energy use.

In the movie ‘Armageddon,’ the spacecraft moves around the moon to get enough speed.

## If the moon stops and the spacecraft approaches constant velocity v

The spacecraft draws an elliptical orbit with the moon as the focus.
There is no change in the speed of the spacecraft leaving the moon.
If you look at this scene from a distance, it looks like a tiny spacecraft hits the moon’s surface with full elasticity and bounces back.

## If the moon moves at a constant velocity V

The spacecraft draws sharply close to the moon.
From the moon’s point of view, the spacecraft will appear to be approaching at V+v, and the speed of the returning spacecraft will also appear to be V+v.
When viewed from the outside, the moon’s own speed, V, must be added, so the speed the spacecraft gets is 2V+v.