The two astronauts have been on at the International Space Station since last June after the ship they arrived in experienced helium leaks and thruster issues, requiring a new ship for the ride back to Earth.

The mission, initially set for a March 14 launch, would have marked the return of astronauts Butch Wilmore and Sunita Williams from the International Space Station (ISS). NASA had recently accelerated their return by two weeks following pressure from President Donald Trump, who urged the agency to expedite their homecoming.

NASA was due to launch a SpaceX rocket from Florida carrying a replacement crew for the International Space Station in a mission that would set up the return to Earth of US astronauts Butch Wilmore and Suni Williams - stuck in space for nine months after a trip on Boeing's faulty Starliner.