Outer space -- Exploration Astrophysics 3 Astronautics -- Technological innovations -- United States 2 Planets -- Exploration 2 Aeronautics, Commercial -- United States 1 Aeronautics, Commercial -- United States -- Planning 1 Astronautics 1 more ... Astronautics in astronomy -- Research -- United States 1 Atmosphere -- Research 1 Atmosphere, Upper 1 Atmospheric pressure -- Physiological effect 1 Dark matter (Astronomy) 1 Heliosphere (Astrophysics) 1 Microbial metabolism 1 Microorganisms -- Physiology 1 Moon -- Exploration 1 National Research Council (U.S.). -- Committee on Planetary and Lunar Exploration 1 Outer space -- Exploration -- Protection 1 Outer space -- Research 1 Planets -- Exploration -- Protection 1 Planets -- Water 1 Reduced gravity environments 1 Research in reduced gravity environments 1 Solar activity 1 Space environment 1 Space sciences 1 Space security 1 United States. -- National Aeronautics and Space Administration 1 United States. -- National Aeronautics and Space Administration -- Research 1 less ...