@msnbc: A SpaceX crew arrived at the International Space Station, delivering the replacements for two NASA astronauts. Butch Wilmore and Suni Williams are expected to head back home no earlier than Wednesday, closing out their unexpected extended mission that began in June. Wilmore and Williams expected to be gone just a week when they launched on Boeing’s first astronaut flight and hit the nine-month mark earlier this month. NBC's Marissa Parra explains. #astronauts #nasa #space