NASA says it will modify an existing and proven Delta IV rocket second stage to launch an Orion spacecraft on an unmanned test flight in 2017. A manned flight to lunar orbit is planned for four years after that, the agency said. The Boeing upper stage is \"the only means available to support the immediate in-space propulsion needs\" for the excursions, NASA said in a statement. An internal study of in-space propulsion systems available in the United States, Europe and Japan determined the Delta IV upper stage \"is the only known in-space stage requiring relatively minor modifications\" to meet mission requirements as well as the launch schedule, NASA said. The Delta IV second stage is powered by a single Pratt & Whitney RL-10B2 engine fueled by liquid hydrogen and liquid oxygen. Both Orion missions will be launched from complex 39B at Kennedy Space Center on early versions of NASA\'s new heavy-lift Space Launch System, Florida Today reported.