Washington, May 31 2020 - Marking the beginning of a new era in the US space programme, the SpaceX Crew Dragon spacecraft carrying NASA astronauts Robert Behnken and Douglas Hurley successfully docked with the International Space Station (ISS) on Sunday.

"Docking confirmed - Crew Dragon has arrived at the @space_station," SpaceX tweeted.

Aboard the space station, Expedition 63 Commander and NASA astronaut Chris Cassidy and Russian cosmonauts Anatoly Ivanishin and Ivan Vagner welcomed Behnken and Hurley aboard the orbiting laboratory.

The two NASA astronauts made history on Saturday as they became the first Americans to launch on a US rocket from American soil to the space station in nearly a decade.

The spacecraft lifted off on a reusable SpaceX Falcon 9 rocket from Launch Complex 39A at NASA's Kennedy Space Centre in Florida.

This is the first-ever crewed mission for SpaceX. This was also the first crewed launch from the US after the government retired the space shuttle programme in 2011.

The US space agency on Sunday said the mission is an important step to expand human exploration to deeper space missions.

"Today, a new era in human spaceflight begins as we once again launched American astronauts on American rockets from American soil on their way to the International Space Station, our national lab orbiting Earth," said NASA Administrator Jim Bridenstine.

"The launch of this commercial space system designed for humans is a phenomenal demonstration of American excellence and is an important step on our path to expand human exploration to the Moon and Mars," he added in a statement.

The successful launch left SpaceX Founder Musk almost in tears.

"I'm really quite overcome with emotion on this day, so it's kind of hard to talk, frankly. It's been 18 years working towards this goal, so it's hard to believe that it's happened," Musk said during a post-launch press conference.

"This is something that I think humanity should be excited about proud of occurring on this day," he added.

Known as NASA's SpaceX Demo-2, the mission is an end-to-end test flight to validate the SpaceX crew transportation system, including launch, in-orbit, docking and landing operations.

Behnken and Hurley will work with SpaceX mission control to verify the spacecraft is performing as intended by testing the environmental control system, the displays and control system, and by manoeuvring the thrusters, among other things.

The Demo-2 mission is the final major test before NASA's Commercial Crew Programme certifies Crew Dragon for operational, long-duration missions to the space station.

For operational missions, Crew Dragon will be able to launch as many as four crew members at a time and carry more than 220 pounds of cargo, allowing for an increased number crew members aboard the space station and increasing the time dedicated to research in the unique microgravity environment, as well as returning more science back to Earth.

The first operational Crew Dragon mission, called Crew-1, could launch to the space station as early as August 30, Space.com reported. The Crew Dragon being used for this flight test can stay in orbit about 110 days, and the specific mission duration will be determined once on station based on the readiness of the next commercial crew launch.

The operational Crew Dragon spacecraft will be capable of staying in orbit for at least 210 days as a NASA requirement.

At the conclusion of the mission, Behnken and Hurley will board Crew Dragon, which will then autonomously undock, depart the space station, and re-enter Earth's atmosphere. Upon splashdown off Florida's Atlantic coast, the crew will be picked up by the SpaceX recovery ship and returned to the dock at Cape Canaveral.

NASA selected SpaceX and Boeing to design, build, test and operate safe, reliable and cost-effective human transportation systems to low-Earth orbit as part of its Commercial Crew Programme to reduce the agency's dependence on Russia's Soyuz capsule for transportation of astronauts to the space station.

"This is a dream come true for me and everyone at SpaceX," said Musk.