What does spending a long time in space do to the human body? Most space station missions last six months, with a few reaching a full year. So the extension to Butch and Suni's already overdue stay in space should not be a problem, according to Dr Simeon Barber, from the Open University. "I'm sure that they are already disappointed that they were going to miss Christmas back home with the folks. But this is only another two months on an already quite long mission, and I'm sure if you ask them, I'm sure they would tell you that the space station is where they love to be," he said. A new crew needs to launch before Wilmore and Williams can return and the next mission has been delayed by more than a month, according to the space agency. Nasa's next crew of four for the ISS was supposed to have been launched in February 2025. The capsule carrying that crew was due to be the one bringing Butch and Sunni home, as well as NASA astronauts Nick Hague and Roscosmos cosmonaut Aleksandr Gorbunov as part of the normal crew rotation. But there has been a delay by the private sector firm SpaceX in preparing a brand-new Dragon capsule for the mission. That is now scheduled for flight readiness no earlier than late March. Nasa said it considered using a different SpaceX capsule to fly up the replacement crew to keep the flights on schedule. But it has now decided the best option is to wait for the new capsule to transport the next crew.