Why do astronauts say houston?

When an astronaut says "Houston", they are addressing a room rather than a place: the Mission Control Center, and specifically the flight director and the capsule communicator sitting in it. Radio discipline in spaceflight borrows from aviation, where every station has a short unambiguous identifier. Mission control took the name of its host city, exactly as an air traffic facility takes the name of its airport.

The centre moved there for political and practical reasons. The Manned Spacecraft Center, renamed the Lyndon B. Johnson Space Center in 1973, was established near Houston in the early 1960s, and from the Gemini programme onwards it ran crewed missions from the moment the vehicle left the pad. Mercury flights had been controlled from Cape Canaveral in Florida, which is why the earliest American crews did not use the word at all.

The division of labour still holds. Countdown and liftoff are directed from the launch control centre at Kennedy Space Center in Florida, and a handover to Houston occurs shortly after the vehicle clears the tower. From then on, every orbital manoeuvre, spacewalk and re-entry is run from Texas.

Apollo 13 fixed the word in popular culture. The crew's actual transmission after the oxygen tank failure was closer to "OK, Houston, we've had a problem here", spoken first by Jack Swigert and repeated by Jim Lovell; the familiar present tense version comes from the 1995 film. Today the habit persists among international crews too: a Japanese or European astronaut aboard the International Space Station still calls Houston, even though control of the European and Russian segments is shared with centres in Germany and Moscow.