Cape Canaveral | Just over a day after blasting off, a SpaceX crew capsule arrived at the International Space Station on Sunday, delivering the replacements for NASA's two stuck astronauts.

The four newcomers — representing the US, Japan and Russia — will spend the next few days learning the station's ins and outs from Butch Wilmore and Indian-American Sunita Williams.

Then the two will strap into their own SpaceX capsule later this week to close out an unexpected extended mission that began last June.

Wilmore and Williams expected to be gone just a week when they launched on Boeing's first astronaut flight. They hit the nine-month mark earlier this month.

The Boeing Starliner capsule encountered so many problems that NASA insisted it come back empty, leaving its test pilots behind to wait for a SpaceX lift.

Their ride arrived in late September with a downsized crew of two and two empty seats reserved for the leg back. But more delays resulted when their replacements' brand new capsule needed extensive battery repairs. An older capsule took its place, pushing up their return by a couple weeks to mid-March.

Weather permitting, the SpaceX capsule carrying Wilmore, Williams and two other astronauts will undock from the space station no earlier than Wednesday and splash down off Florida's coast.