NASA's commercial crew program is a plan to return to space on American rockets. It docked autonomously under the station astronauts' watchful eyes, instead of relying on the station's robot arm for berthing.
They rushed there from Florida after watching the Dragon rocket into orbit early Saturday from NASA's Kennedy Space Center.
After about five days docked, the crew is expected to place some return equipment inside before closing the hatch.
He congratulated SpaceX in a tweet Sunday morning, noting the Crew Dragon was the first spacecraft to visit the station's forward port since he departed aboard the shuttle Atlantis.
Though NASA and SpaceX were confident it would go seamlessly, it was a reminder that "there's always human life at risk", Patrick Forrester, chief of NASA's astronaut office at Johnson Space Center, said last week.
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This beefed-up, redesigned Dragon is the first American-made, designed-for-crew spacecraft to pull up to the station in eight years.
"Congratulations to all nations, private space firms and individuals who wake up every day driven by the magic of exploration", American astronaut Anne McClain, the third crew member on the station, said at a welcoming ceremony broadcast over NASA TV.
Why it matters: For almost a decade, NASA has been reliant on Russian rockets to put their astronauts into orbit. "We've got NASA "rocking" again," the president wrote.
It just first disconnect and undock from the space station, re-enter the Earth's atmosphere, and lastly, splash back down off the Florida coast.
Transporting people is a more complex task, requiring seats, a pressurized cabin with breathable air, temperature regulation and emergency escape systems.
Since then, NASA and partner astronauts from the European Space Agency, Canada and Japan have been forced to hitch rides to the station aboard Russian Soyuz spacecraft at a current cost of more than $80 million a seat. The US space agency has been paying Russian Federation roughly $81 million for a single seat on the Soyuz spaceship every time it needs to ferry an astronaut to or from the ISS.
Next up, though, should be Boeing, NASA's other commercial crew provider. Though no astronauts were aboard this first demonstration flight, the successful launch is critical in persuading any doubters and paves the way for SpaceX to launch with astronauts as soon as this summer.