That will be the first time astronauts will have landed this way since 1975, before the days of the Space Shuttle program.
Following a successful SpaceX Demo-2 mission, NASA and SpaceX hope to use the Crew Dragon to send and return astronauts to the ISS on a regular basis. Historically, NASA subcontracted numerous aerospace companies to build spacecraft, but SpaceX exists in the private sector. Look carefully, and you'll see one on the wrist of Behnken during the pre-launch checks with the signature velcro strap.
The first launch was scheduled for May 27, but poor weather prompted a "launch scrub" which meant that it was forced to go to a secondary time slot of Saturday, May 30 at 12:22 p.m. EDT. If Sunday's launch is also scrapped, there will be a third chance at 12pm (Florida time) on May 31.
As part of the launch, the first stage of the Falcon 9 Block 5 rocket successfully landed on the company's drone ship, appropriately named Of Course I Still Love You.
Around 10 minutes after lift-off, the rocket will separate into a first stage and a second stage.
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Behnken is the joint operations commander for the Demo-2 mission, responsible for activities such as rendezvous, docking and undocking, as well as activities while the spacecraft is docked to the space station. Traveling ~8 km/s (~5 mi/s), Crew Dragon will detach its expendable trunk, perform a several-minute retrograde burn with its Draco thrusters, point its ablative PICA-X heat shield towards its velocity vector, and careen through Earth's atmosphere, reaching spectacularly high temperatures.
Aside from completing the most important U.S. launch in nearly a decade, SpaceX also managed to successfully land Falcon 9 Block 5 booster B1058 on drone ship Of Course I Still Love You (OCISLY), stationed several hundred miles down range in the Atlantic Ocean.
The craft is expected to rendezvous and dock, with the space station on Sunday at 3.30pm United Kingdom time.
Mr Vagner tweeted earlier to say he was waiting for the duo at the space station.