Outer space 32 Exploration 30 Juvenile literature 29 History 24 Astronautics 18 Space warfare 16 Fiction 13 Space vehicles 13 Astronomy 12 Astronautics, Military 11 Space flight 11 Space weapons 11 Airplanes 8 Congresses 8 Sacred space 8 Space surveillance 8 Astronautics and state 7 Juv. literature 7 Space flight to the moon 7 Aeronautics 6 Astronauts 6 Design and construction 6 Interior decoration 6 Manned space flight 6 Space sciences 6 Thesis 6 Military policy 5 Space exploration 5 Space law 5 Ballistic missile defences 4