https://motherboard.vice.com/en_us/article/nepwwg/heres-how-astronauts-space-vote-elections-midterms

There’s almost always an American on the International Space Station (ISS) at any given moment. So what do these astronauts do on election day? Per a Texas state ordinance, astronauts on the ISS have a way to cast their ballots in space.

According to a blog published by the Smithsonian Institute, the astronaut has to tell NASA prior to liftoff that they plan on voting in a particular election. Then, before Election Day, the astronaut gets an encrypted email ballot sent up from the Johnson Space Center Mission Control in Houston, Texas to the International Space Station (ISS). After completing the email ballot, it's sent to the astronaut's County Clerk's Office.