NASA astronaut Butch Wilmore has officially retired, just months after returning from an unexpectedly extended mission aboard the malfunctioning Boeing Starliner.

The astronauts who were stranded on the International Space Station after a botched flight more than nine months ago are just minutes away from touching down, with the landing expected at 8:57 AM AEDT.

Boeing's Starliner spacecraft has completed its journey back to Earth - but the astronauts it was supposed to be carrying remain behind on the International Space Station.