[Video] ISS Astronauts Climb Aboard the SpaceX Dragon Capsule

The main purpose of the flight was to demonstrate that the Dragon capsule and the Falcon 9 rocket that delivered it were capable of reaching the station. SpaceX plans to begin regular cargo missions this year. The Dragon capsule is capable of accommodating up to seven astronauts, and the company hopes to begin manned missions within three years.

The station crew wore oxygen masks and protective gear as a precaution when boarding Dragon, but they found the capsule to be clean and free of debris. "It looks great," Pettit said.

SpaceX represents a sea change for the business of spaceflight. NASA has poured nearly $400 million in seed money into SpaceX in hopes of outsourcing its flight operations to private companies. Just a few years ago, SpaceX launches were failing repeatedly. Dustin Curtis has an awesome excerpt from a Wired Magazine interview with SpaceX founder Elon Musk from 2008. "You're still zero for three," Wired's Carl Hoffman said. "You have so far failed to put a rocket into orbit. ... How do you maintain your optimism?"

"Optimism, pessimism, f___ that; we're going to make it happen," Musk replied. "As God is my bloody witness, I'm hell-bent on making it work."

Four years later, astronauts are aboard the first private spacecraft to ever rendezvous with with International Space Station. In yesterday's press conference after the successful berthing, NASA staff were in tears.

Images and video courtesy of NASA