Related by context. Frequent words. (Click for all words.) 68 zero gravity 67 weightlessness 56 weightless 50 spaceflight 48 suborbital 48 spacecraft 47 lunar surface 47 CloudSat 47 cosmic radiation 47 experiments 46 microscale 46 cosmonauts 46 spacesuit 46 regolith 46 orbital 46 LASP 46 Earth orbit 46 Martian surface 46 astronaut 46 International Space Station 45 robotic arm 45 physiology 45 ionosphere 45 NASA Goddard 45 spacecrafts 45 physiological 45 orbiter 45 Space Station 45 hypersonic 44 astronauts 44 outer space 44 Martian soil 44 sub orbital 44 suborbital flight 44 LCROSS 44 astronautics 43 atmospheric chemistry 43 GLAST 43 microsatellite 43 NASA 43 lander 43 thruster 43 lunar lander 43 Orion spacecraft 43 spaceflights 43 scramjet 43 Deep Impact mission 43 Mars 42 Ares IX 42 muscle atrophy 42 laboratory experiments 42 astrobiology 42 payloads 42 biomimetic 42 biomolecular 42 GOCE 42 outer planets 42 Martian atmosphere 42 cosmic ray 41 rocket propulsion 41 Orion capsule 41 orbiting spacecraft 41 Space Shuttle 41 lunar module 41 spacesuits 41 rovers 41 lunar missions 41 thrusters 41 jet propulsion 41 Space Agency 41 Bob Thirsk 41 Mars Rover 41 Huygens 41 chemical reactions 41 Shenzhou VI 41 Mars rover 41 simulate 40 geosynchronous orbit 40 Kaleri 40 lunar exploration 40 planetary exploration 40 propellant 40 Space Shuttle Endeavour 40 lunar orbit 40 Sensing Satellite 40 Centennial Challenges 40 Mars lander 40 NASA Langley 40 AFRL 40 Soyuz 40 cometary 40 NASA Ames 40 polar regions 39 Apollo astronauts 39 Applied Physics Laboratory 39 martian 39 JAXA 39 physics 39 Space Shuttle Discovery 39 Astronauts 39 LRO