Those gravitational fields are the crux of the game - there are many asteroids and planets scattered about, each of which has its own unique gravitational field, velocity and rate of spin. You may be tasked with orbiting a particular planet, so you have to approach carefully, then alter your velocity and direction as you "feel" the gravitational field increase on your approach. There are nine missions in the game. Some take quite a few replays to nail down but some are a little easier.
There's an extra level, "Playground", which lets you loose in a very complicated area and tasks you with picking up objects, orbiting various bodies and docking with some very tricky space ships.
New Orbit
From: Blackish
For: iOS, Android
Review courtesy of Fatso