This project uses GIT to manage its source code. Instructions on GIT use can be found at http://git-scm.com/documentation.
The source can be checked out anonymously from GIT with this command (See http://git-scm.com/docs/git-clone):
$ git clone http://www.orekit.org/git/orekit
Only project developers can access the GIT tree via this method (See http://git-scm.com/docs/git-clone).
$ git clone ssh://git@www.orekit.org/orekit.git