Send robot to moon. Robot #1: locate he-3! he-3 robot finds he-3 on moon! Send 2 more robots to moon. Robot #2: build he-3 reactor! reactor robot starts to

Send robot to moon. Robot #1: locate he-3! he-3 robot finds he-3 on moon! Send 2 more robots to moon. Robot #2: build he-3 reactor! reactor robot starts to build reactor .. Robot #3: build little factory for making: robots! robot-building robot builds robot-building factory .. reactor robot is finished! Just Plug In! robot-building robot is finished! Plugged In! ROBOTS in SPACE!! (Edit: to answer this - "the fuel is not the expensive part of nuclear reactors", yes the most expensive part of all this is doing it on Earth.)