# Falling back to orbit

1. Feb 20, 2004

### wimms

I understand that to get to orbit and stay there, rocket needs only velocity. Its velocity around planet and gravity defines the height of orbit. To change to higher orbit, rocket is firing engines to speedup rocket, to go to lower orbit, rocket fires to slow down.

I assume that engines are fired in back direction of travel. So I had this thought, what is supposed to happen if rocket fires engines towards center of planet? If it standed on surface, it would take off and when engines cut off, would fall back down. So, if rocket would fire engines in direction towards center of planet, so as to climb higher, is this going to happen? And when it stops burner, is it going to "drop" back to its previous orbit? I guess so.

And if opposite, rocket firing into open space so as to "dive" towards center of planet - as long as engines fire, it does. But when engines stop, is its velocity throwing it back up into its previous orbit? Seems kinda funny.

2. Feb 20, 2004

### Janus

Staff Emeritus
Firing the rocket inwards or outwards from the planet would put the rocket in a new, more eccentric, orbit than the one it started in. The new orbit would have a closer perigee and further apogee than the old orbit, and would cross the old orbit at two points. The rocket will not return to its old orbit.