Space station astronauts floated into the Dragon on Saturday, a day after its heralded arrival as the world's first commercial supply ship.

NASA astronaut Donald Pettit, the first one into the docked capsule, said it reminded him of the cargo capability of his pickup truck back home in Houston.

To protect against possible debris, Pettit wore goggles, a mask and a caver's head light as he slid open the hatch of the newest addition to the International Space Station.

Pettit said the capsule smelled like a brand new car and reminded him of the cargo capability of his pickup truck. He and his crewmates have until the middle of next week to unload Dragon's supplies and refill it with gear for return to Earth.

The complex sailed 400 kilometres above the Tasman Sea, just west of New Zealand, as he and his crewmates made their grand entrance.

The California-based SpaceX — formally Space Exploration Technologies Corp. — is the first private company to send a vessel to the space station.

It's run by Elon Musk, a billionaire who helped create PayPal and founded the electric car company Tesla Motors.

The station's 17.7-metre Canadarm2 robotic arm grappled with Dragon and connected it to the space station on Friday.

Challenging manoeuvre in space

"It is almost the most complicated thing we do with Canadarm2," veteran Canadian astronaut Chris Hadfield told CBC News on Saturday.

"There are several space ships that come up close to the station and then what they do is they just shut off and they float, hoping that before they start drifting away with whatever rates they have that we can reach out and grab them and hold them in space and attach them to the station."

Hadfield, who spoke from the European Space Agency in Cologne, Germany, is set to become the first Canadian commander of the International Space Station.

He heads to Russia on Sunday and will backup for a crew that launches on July 15, replacing Sunita (Sunny) Williams if she is not capable of making the journey.

It's more of a sure thing that Hadfield, 52, will go into space Dec. 5 and orbit the Earth for six months as ISS commander. During that time, he expects his crew to be in charge of receiving two more SpaceX supply runs.

NASA is handing over orbital delivery work to American business in order to focus on bigger and better objectives, such as getting astronauts to asteroids and Mars.

SpaceX contends its Dragons could be carrying space station astronauts up and down within three or four years.