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The two test pilots planned on being away just a week or so when they blasted off June 5 on Boeing’s first astronaut flight to the International Space Station. Their mission grew from eight days to eight months after NASA decided to send the company’s problem-plagued Starliner capsule back empty in September.

Now the pair won’t return until the end of March or even April because of a delay in launching their replacements, according to NASA.

A fresh crew needs to launch before Wilmore and Williams can return and the next mission has been bumped more than a month, according to the space agency.

NASA's next crew of four was supposed to launch in February, followed by Wilmore and Williams' return home by the end of that month alongside two other astronauts. But SpaceX needs more time to prepare the brand new capsule for liftoff. That launch is now scheduled for no earlier than late March.

NASA said it considered using a different SpaceX capsule to fly up the replacement crew in order to keep the flights on schedule. But it decided the best option was to wait for the new capsule to transport the next crew.

NASA prefers to have overlapping crews at the space station for a smoother transition, according to officials.

Most space station missions last six months, with a few reaching a full year.

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