Outer space 32 Exploration 30 History 20 Juvenile literature 20 Space warfare 16 Astronautics 14 Space vehicles 13 Space flight 11 Space weapons 11 Fiction 10 Airplanes 8 Sacred space 8 Space surveillance 8 Juv. literature 7 Space flight to the moon 7 Astronautics, Military 6 Astronomy 6 Congresses 6 Manned space flight 6 Space sciences 6 Astronauts 5 Design and construction 5 Space exploration 5 Space law 5 Aeronautics 4 Ballistic missile defences 4 Space in economics 4 Space shuttles 4 Thesis 4 Aerodynamics 3