In space, no one can hear you scream. The clanging air conditioners, thumping compressors, overworked pumps and whining motors create so much noise that they drown out most of what an astronaut utters. Spacemen cannot sleep or even hear commands as a result of this interplanetary cacophony. ‘What?’ is the most common word spoken on the International Space Station. ‘It is not a healthy situation,’ admitted Mike Engle, the orbiting laboratory’s acoustics integration manager. ‘Apart from astronauts losing precious sleep, there is now a real danger that one of them will mishear a colleague’s instruction and press an incorrect button – and that could have very unfortunate consequences.’