Hawthorne-based commercial launch vehicle startup SpaceX said Monday that it has signed a contract with the Department of Defense, to carry a space satellite into orbit. According to Space Exploration Technologies, which is funded by PayPal founder Elon Musk, the contract calls for the firm to carry an as-of-yet determined payload on its June 2008 flight. SpaceX said the contract was signed with the Department of Defense’s Operationally Responsive Space (ORS) Office. Possible satellites to be launched by the firm include a satellite from the Air Force Research Laboratory, a satellite developed by SpaceDev, Inc., and a experiment developed by Cornell University with the Air Force Office of Scientific Research.