The replacements for NASA's two stuck astronauts launched to the International Space Station on Friday night, paving the way for the pair's return after nine long months.

Butch Wilmore and Sunita Williams need SpaceX to get this relief team to the space station before they can check out. Arrival is set for late Saturday night.

NASA wants overlap between the two crews so Mr.Wilmore and Ms.Williams can fill in the newcomers on happenings aboard the orbiting lab. That would put them on course for an undocking next week and a splashdown off the Florida coast, weather permitting.

The duo will be escorted back by astronauts who flew up on a rescue mission on SpaceX last September alongside two empty seats reserved for Mr.Wilmore and Ms.Williams on the return leg.

Reaching orbit from NASA's Kennedy Space Centre, the newest crew includes NASA 's Anne McClain and Nichole Ayers, both military pilots; and Japan's Takuya Onishi and Russia's Kirill Peskov, both former airline pilots. They will spend the next six months at the space station, considered the normal stint, after springing Wilmore and Willams free.

As test pilots for Boeing's new Starliner capsule, Mr. Wilmore and Ms. Williams expected to be at the ISS for just a week when they launched fro Cape  Canaveral last June. Helium leaks and thruster fails marred their trip, making months of investigation by NASA and Boeing on how to proceed best.