Three astronauts arrived Saturday for their mission aboard the International Space Station after Russia's Soyuz MS-13 spacecraft carried them into space from the Baikonur Cosmodrome in Kazakhstan.

The spacecraft has docked to the station's Zvezda service module after a four-orbit, six-hour flight, according to NASA.

NASA astronaut Andrew Morgan, Luca Parmitano of European Space Agency and Alexander Skvortsov of the Russian space agency Roscosmos joined NASA astronauts Nick Hague, Christina Koch and Roscosmos's Alexey Ovchinin on the space lab, restores the station's crew complement to six.

The arrival date is memorable as Saturday is the 50th anniversary that Neil Armstrong and Buzz Aldrin stepped on the Moon in a giant leap for humanity.

The crew will spend more than six months conducting about 250 science investigations. One of those key technology developments will be the arrival and installation of the second docking port for commercial crew spacecraft -- SpaceX's Crew Dragon and Boeing's Starliner, according to NASA.

Parmitano and Skvortsov are scheduled to remain aboard the station with Koch until February 2020, leaving Morgan on station for an extended stay. Hague and Ovchinin are set to return to the Earth on Oct. 3.