Fibonacci, the September version of Principia, is available, with orbit analysis and bug fixes. Download it here.

For the convenience of Chinese users, downloads from 腾讯微云: Principia Fibonacci, Trappist-1 for Principia.

Principia is a mod for Kerbal Space Program (KSP) which implements N-body and extended body gravitation. Instead of being within the sphere of influence of a single celestial body at any point in time, your vessels are influenced by all the celestials. This makes it possible to implement missions that are more complex and more realistic than in the stock game, especially if used in conjunction with a mod like RealSolarSystem which has real-life celestials.

N-body gravitation is more complex than the toy physics of the stock game. Therefore, before using the mod we recommend that you read the concepts document which explains the most important parts of Principia. In particular, you should learn about the plotting frame and flight planning.

You might also want to go through our tutorial which shows how to go to the Mun with Principia in an energy-efficient manner. We also have a guide explaining how to use the support for rendezvous.

The FAQ explain how to install, how to report bugs and documents the known issues and limitations.

The change log gives a fairly detailed description of the new features in each release.

Principia is released on every new moon with whatever features and bug fixes are ready at the time. This ensures relatively timely improvements and bug fixes.

Download the binary (Ubuntu, macOS, and Windows) here for 1.5.1, 1.6.1 and 1.7.x. Download the “Trappist-1 for Principia” mini-mod here. Or, if you don't trust our binary, build the mod from the Fibonacci release.