Update: The crew is now successfully in orbit awaiting to dock with the space station, and Falcon 9's first stage has landed on the drone ship "Of Course I Still Love You".
Original: SpaceX is attempting to launch four astronauts to the International Space Station - using a recycled Falcon 9 rocket and Crew Dragon spacecraft
It's the first time that a Falcon 9 and Crew Dragon will be reused for a crew mission, which makes it a big milestone for affordable space travel.
Launch is scheduled for 09:49 UTC (05:49 ET). You can watch the historic launch attempt below.
The first SpaceX launch for NASA, Crew-1, occurred in November, and the astronauts from that launch are still on board the ISS. The Falcon 9 used today is the same one that was used by Crew-1.
Today, four astronauts will be part of the launch: alongside Shane Kimbrough and Megan McArthur of NASA is Akihiko Hoshide of the Japan Aerospace Exploration Agency, and Thomas Pesquet of the European Space Agency.
Today's Crew-2 launch has an instantaneous launch window, which means if there needs to be a hold for any reason, the launch will have to be postponed for three days until the next available window.
The journey to the ISS will take around 23 hours, and will be similar to the route that the Crew-1 launch took. They're scheduled to dock with the ISS at 09:10 UTC (05:10 ET) on Saturday.
"Once aboard the station, the Crew-2 astronauts will spend a lot of time on science - in areas such as medical technology, human health, and materials to benefit life on Earth," NASA wrote today on a live Facebook update.
"The space station is a unique scientific platform, enabling researchers from all over the world to put their talents to work on innovative experiments. It has instruments that monitor our home planet's global climate, environmental changes, and natural hazards."
After the astronauts said goodbye to their families earlier this morning, they boarded three white Teslas for the launchpad - with license plates reading "recycle", "reuse", and "reduce".