Washington  - Two NASA astronauts didn't let their distance from Earth deter them from voting in the US presidential election Tuesday.

Commander Mike Fincke and Flight Engineer Greg Chamitoff voted from their current home in the International Space Station - 322 kilometres above Earth and orbiting at 28,200 kilometres per hour - and beamed back a message urging others to exercise their franchise.

Voting from space was made possible through a 1997 bill passed by Texas legislators, as nearly all the astronauts live in Houston, a statement from the National Aeronautics and Space Administration said.

NASA's Johnson Space Centre uplinked a secure electronic ballot - an email with the crew member's credentials sent from the county clerk. The astronauts then cast their votes and the completed ballot was downlinked and sent back to the county clerk's office via email.

"Although we're a long way from home as we orbit 200 miles (322 kilometres) above our beautiful planet, we're exercising our constitutional right and privilege," Fincke said in a video message.

"Voting is the most important statement Americans can make in fulfilling a cherished right to select its leaders. If we can vote, so can you."