Here is our Angry Birds Space walkthrough video that will help you unlock Centripetal Force (Lagrangian Point) Achievement. You can find info on a Lagrangian Point on Wikipedia.
Update: As of the v1.1.0 (Fry Me to the Moon) update, the Centripetal Force achievement has been fixed and the understanding changed. The concept is no longer to get a bird stuck in a Langrangian Point, but rather to simply pass through one. This is a million times easier. While it doesn’t really need a video, we already have the page created, so why not, eh?
The first level where this achievement is attainable is Pig Bang level 1-5. Simply fire the Red bird above the first planet so that it passes through the overlapping gravitational fields.
If you have a different method for obtaining this that you think is easier feel free to leave a comment below explaining your strategy.