Astronaut Shane Kimbrough, the only US citizen off the planet on election day, has cast his vote from the International Space Station.
Kimbrough, who arrived on board the ISS in mid-October, exercised his right to vote from the space platform orbiting the Earth at 27,000km/h.
"An electronic and secure ballot is sent to the member of the ISS crew from the clerk in his county. (The astronaut) fills in the form and returns it electronically. It's all secure. It is all private," NASA said in a brief statement.
The voting procedure was first established in 1997, and astronauts who will be away from Earth on election day must request their ballots one year before launch.
Most astronauts reside in Houston, where one of the main U. space centres is located and their votes are thus counted in Texas.
