Ballard said NASA designed a program that allows election officials to upload the ballot, encrypt it and create three different passwords for it. Only the two Texas county clerks involved - one astronaut lives in Harris County and another lives in Brezoria County - and the astronauts have the keys to break the encryption.

The clerks send the digital ballot files to NASA's Johnson Space Center Mission Control Center, which then sends them to the space station. The clerks then email the astronauts directly with their credentials and passwords. The astronauts then send the encrypted ballot back to the clerks through Mission Control.

"Nobody can get into the ballot," said Ballard. "I know because I've tested it. I tested it extensively. You have to have the password to get into the ballot."

A U.S. astronaut onboard the Russian Space Station first voted from space in 1997. Four different astronauts have voted from space before this year. 

According to NASA, the passage of a 1997 Texas state bill sets up a technical procedure for astronauts -- nearly all of whom live in Houston -- to vote from space.