The shuttle decoupled from the ISS at 23.10 Swedish time on Tuesday, and started its journey back to earth.
The space station crew had earlier gathered to say farewell. Astronauts Michael Lopez Alegria and Sunita Williams and cosmonaut Mikhail Tyurin will remain on the ISS.
The shuttle is expected to arrive back on earth on Friday evening, Swedish time.
Until then, the shuttle’s heat protection shield will be inspected, and several small satellites will be released on the journey down. The crew will also assemble the seats that are to be used for landing, according to Sven Grahn at the Swedish Space Corporation.
The shuttle will land either at the Kennedy Space Center in Florida, the Edwards Air Force Base in California or the White Sands Base in New Mexico. Exactly where will depend on the weather.
“Right now there seem to be a few problems with low clouds and rain in Florida and high winds in California,” said Grahn.