A Russian Soyuz rocket is to blast off from Kazakhstan’s Baikonur cosmodrome to bring a three-member crew to the International Space Station (ISS).
Among them is US billionaire Charles Simonyi, aged 60, who is the first space tourist to make the trip twice.
The software tycoon, who paid $35m (£24m) for the trip, will be the last tourist for the foreseeable future.
During his 13-day mission, he will help with research projects and take part in live broadcasts with schools.
Mr Padalka and Mr Barratt will form part of a new six-member crew aboard the ISS.
Until now only three astronauts lived on the station at any one time.
