A Russian Soyuz rocket rolled out to a launch pad in Kazakhstan early Thursday in preparation for liftoff Saturday with a Russian commander, Italian flight engineer and U.S. astronaut heading for the International Space Station.

NASA has purchased two seats on Russian Soyuz capsules launching later this year and in early 2018 to expand the crew on the U.S. segment of the International Space Station from three to four, and reserved options to fly astronauts on Soyuz spacecraft in 2019 if commercial rides are not available in time.

Two days after launch from Kazakhstan, a Russian Soyuz ferry ship glided to a smooth docking with the International Space Station Saturday, bringing a veteran cosmonaut, a Frenchman making his first flight and NASA’s most experienced female astronaut to the lab complex.