SpaceX's Dragon cargo vessel smells like a new car, said astronauts at the International Space Station after opening the hatches Saturday following the spacecraft's landmark mission to the orbiting lab.

The California-based SpaceX on Friday became the first commercial outfit to send its own unmanned cargo capsule to the ISS, heralding the start of a new era for private spaceflight after the end of the 30-year US shuttle program.

The Dragon capsule delivered about a half ton of supplies and science experiments for the ISS, and aims to return a slightly larger load of gear to Earth on May 31.

Shortly after the hatches between the ISS's Harmony node and the Dragon spacecraft were opened at 5:53 am EDT (0953 GMT), astronauts ventured in for the first time.

"Like the smell of a brand new car," remarked US astronaut Don Pettit, who on Friday was the one who reached out with the station's robotic arm and snared the Dragon as it approached the research outpost.

"Dragon's interior looked good," SpaceX said in a statement.

"The ship is in good shape," said a NASA commentator on the US space agency's television channel.

Now that the doors between the two spacecraft are open, the crew has begun four days of work to unload and restock the world's first commercial resupply vessel with gear to return to Earth.

The Dragon has toted 521 kilograms (1,148 pounds) of cargo for the space lab, including food, supplies, computers, utilities and science experiments. It plans to return a 660-kilogram load to Earth.

"I spent quite a bit of time poking around in here this morning, just looking at the engineering and the layout, and I am very pleased. It looks like it carries about as much cargo as I could put in my pickup truck," Pettit told reporters later in the day.

"It's roomier than a Soyuz," he added, referring to Russia's spaceships that can carry both humans and cargo.

The white Dragon capsule stands 4.4 meters (14.4 feet) high and is 3.66 meters in diameter.

Dragon can carry over 3,310 kilograms split between pressurized cargo in the capsule and unpressurized cargo in the trunk.

"We have already had all six people in here for a real brief period of time," said Pettit.

"There is not enough room in here to hold a barn dance but for transportation of crew up and down through Earth's atmosphere and into space, which is a rather short period of time, there is plenty of room in here for the envisioned crews."

SpaceX's Dragon was built to carry up to seven humans to the ISS. The Soyuz carries three at a time.

The US space shuttle program ended in 2011, leaving only Russia capable of carrying astronauts and cargo to the ISS and back to Earth.

The space agencies of Japan and Europe have supply ships that can ferry cargo to the ISS but cannot return to Earth intact, and those missions are set to end in the coming years.

That means SpaceX and its competitor Orbital Sciences Corporation would likely become the chief cargo servicers of the $100 billion space station, which is set to remain operational until 2020, NASA said.

SpaceX has a $1.6 billion contract with NASA to supply the station over the coming years, and Orbital Sciences has a $1.9 billion contract to do the same. Orbital's first test flight is scheduled for later this year.

SpaceX and a handful of other companies are also competing to replace the crew capability that the United States lost when the shuttle program ended.

SpaceX, owned by Internet entrepreneur Elon Musk, says it aims to begin taking people to the space station by 2015.

In the meantime, the world's astronauts must rely on Russia's Soyuz craft for ISS transport at a cost of $63 million per seat.