What bothers me is I often read they are using the planet’s gravity to gain speed. Whatever speed an objet may gain while entering orbit should be lost when exiting it, right ?
So I guess it’s the cinetic energy of the planet that is actually fuelling the spacecraft, isn’t it ?
Yes. If the planet was stationary in space, it wouldn’t work. Approach from ‘behind’ the planet and you get a boost, approach from the ‘front’ and you hit the brakes.
What bothers me is I often read they are using the planet’s gravity to gain speed. Whatever speed an objet may gain while entering orbit should be lost when exiting it, right ? So I guess it’s the cinetic energy of the planet that is actually fuelling the spacecraft, isn’t it ?
Yes. If the planet was stationary in space, it wouldn’t work. Approach from ‘behind’ the planet and you get a boost, approach from the ‘front’ and you hit the brakes.