Aboard the space station, NASA astronaut Anne McClain, David Saint-Jacques of the Canadian Space Agency, and Russian cosmonaut and Expedition 58 commander Oleg Kononenko opened the hatch between the Crew Dragon and the orbital laboratory at 8:07 a.m. EST.
The spacecraft attached to ISS via "soft capture" at 5:51 a.m.
The US government is also eager to have the ability to fly to the ISS without buying seats on Russian Soyuz capsules.Early Saturday, NASA's Twitter feed and blog posts were filled with images of SpaceX's Falcon 9 rocket carrying Crew Dragon vertical on the launch pad.
The new capsule blasted off aboard the Falcon 9 rocket built by SpaceX - run by billionaire Elon Musk -49 am (0749 GMT) from the Kennedy Space Center at Cape Canaveral, Florida, lighting up the coastline. That mission is now scheduled for launch no earlier than July, with both NASA and SpaceX expecting it will launch before the end of the year.
It was the first time humans have entered a Crew Dragon while in space and the first time anything has passed through that hatch since the Space Shuttle Atlantis docked to the ISS' forward end in 2011.
Crew Dragon will remain connected to the space station for five days, and will depart on Friday.
Believe it or not, the US Saturday launched a spaceship that can carry astronauts to outer space.
Ever since NASA retired the space shuttle in 2011, the USA has been hitching rides to and from the space station aboard Russian Soyuz spacecraft. "It's different", said Mark Geyer, director of the Johnson Space Center, where United States astronauts are based.
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In retrospect, the bilateral meetings in Beijing prior to last week's talks in Washington were "critically important", he said. Beijing has reportedly proposed a significant increase in its imports of U.S. energy and agricultural exports.
As a result, NASA and SpaceX modified the mission design to constrain the thermal environment and ensure the thrusters would be ready for flight.
The Demo-1 mission, SpaceX's inaugural flight with NASA's Commercial Crew Program, will provide the teams an end-to-end flight test to ensure the spacecraft and systems operate as designed before launching with astronauts.
The company has been sending an earlier version of its capsule to the ISS for a number of years, but in those instances the space station's robotic arm has helped the smaller vehicle successfully dock.
While Saturday's SpaceX test mission is a crucial step in the oft-delayed project, there are questions about whether NASA can achieve its 2019 flight goal of manned flight.
Dragon crew capsules will splashdown in the Atlantic not far from Kennedy.
The Commercial Crew Program is a very big deal for NASA. Both companies are focused on test missions, including abort system demonstrations and crew flight tests, ahead of regularly flying crew missions to the space station.
"Roscosmos congratulates NASA on the successful docking of the new ship and emphasizes that flight safety must be immaculate", the space agency tweeted according to Google Translate.