They will travel to the International Space Station
Weather permitting the space craft will launch at just before 1am Irish time from the Kennedy Space Centre in Florida.
In May, Space X launched four Nasa astronauts on a historic mission to the Space Station... which was fundamentally a test flight.
However today's scheduled flight is the first time Crew Dragon, SpaceX’s human-rated capsule, will be flown for an operational "shift-change" mission at the space station.
NASA administrator Jim Bridenstine said it's a big leap in the commercialisation of space flight:
'We are taking another big leap in this transformation and how we do human spaceflight. And, and what we're talking about here is the commercialization of space where NASA is one customer of many customers.'
