Boeing's troubled Starliner capsule that left two NASA astronauts on the International Space Station last year may need to fly a third uncrewed test flight before it carries astronauts again, agency officials said as the spacecraft's first crew had to return to Earth on a SpaceX capsule this week.

Both NASA and Boeing are pressing ahead with efforts to certify the Starliner capsule to join SpaceX's reusable Crew Dragon capsule for regularly scheduled crew launches to the ISS, agency officials noted following the safe Crew-9 splashdown.