Contributing » History » Version 4
Orekit is free software, which means you can use the source code as you wish, without charge, in your applications, and that you can improve it and have your improvements included in the next mainstream release.
If you are interested in participating in the development effort, subscribe to the mailing lists and step up to discuss it. The larger the community is, the better Orekit will be. The main rule is that everything intended to be included in Orekit core must be distributed under the Apache License Version 2.0.