> But then again, we live in a world where Boeing has a patent on certain trajectories that use the moon's gravity
Interesting. That particular patent was owned by Hughes Electronics, though, not Boeing [1]. EDIT: Apparently in 2000 Boeing acquired that division of Hughes Electronics [2] but the transfer of ownership of the patent was never recorded in the USPTO.
The patent expired in 2012 because the owner didn't pay the required "maintenance fee," which is a statutory fee that must be paid every few years to keep a patent alive [3]; see the end of the document to which you linked.