SpaceX’s Crew Dragon unmanned craft successfully docked with the International Space Station on Sunday, a key milestone for chief executive officer Elon Musk, his team and the American space agency.

The rendezvous with the orbiting lab marks the first time that Crew Dragon, designed to eventually carry astronauts, has ever flown and raises the stakes for rival Boeing Co., which also has a contract with NASA as part of what is known as the agency’s "Commercial Crew" program.

No astronauts or humans were on board the maiden flight, which completed the initial link to the ISS about 5:51 a.m. Eastern time. The only passenger is Ripley, a female mannequin whose name is a nod to the character in the popular "Alien" movies.

"In addition to 400 pounds of supplies and equipment, Crew Dragon is carrying Ripley, an anthropomorphic test device outfitted with sensors to gather important data about what an astronaut flying aboard the spacecraft would experience throughout the mission," said NASA in a blog post Saturday.

Live coverage of the rendezvous and docking aired on NASA television and the agency’s website, with the next highlight due at about 8:30 a.m. Eastern with the hatch opening. It’s been a big weekend for commercial spaceflight. Tourists flocked to the Kennedy Space Center in Florida to watch the launch of the Falcon 9 rocket at 2:49 a.m. Saturday. President Donald Trump congratulated SpaceX in a tweet Saturday afternoon.

The inaugural flight, known as Demo-1, is an important mission designed to test the end-to-end capabilities of the new system, NASA said. It paves the way for Demo-2, a test flight with a crew to carry NASA astronauts Bob Behnken and Doug Hurley to the ISS. That flight is currently slated for July.

Crew Dragon will remain connected to the space station for five days, and will depart on Friday. The mission will not be complete until the spacecraft safely departs from the station and deploys parachutes as part of its splashdown in the Atlantic Ocean.

In 2014, NASA awarded SpaceX and Boeing combined contracts worth as much as US$6.8 billion to fly U.S. astronauts to the space station. The agency chose two companies for the unique public-private partnership to assure safe, reliable and cost-effective access to space while avoiding the perils of one provider having a monopoly. The U.S. government is also eager tohave the ability to fly to the ISS without buying seats on Russian Soyuz capsules.