SpaceX successfully launched a private supply ship to the International Space Station (ISS) early this morning, marking the first flight by a private company after NASA retired its space shuttle program last year.

"The significance of this day cannot be overstated," said NASA Administrator Charles Bolden. "It's a great day for America. It's actually a great day for the world because there are people who thought that we had gone away, and today says, 'No, we're not going away at all.'"

The Dragon flight represents a new era in space travel, with private companies building spacecraft to transport supplies - and eventually people - to the ISS. NASA awarded California-based SpaceX a $396 million contract to create the spacecraft and also gave $266 million to Virginia-based Orbital Sciences Corp.

If the flights continue to succeed, private American companies could be ferrying American astronauts into space within five years. NASA is investing $800 million in the concept, given incrementally as companies reach certain milestones.

"Every launch into space is a thrilling event, but this one is especially exciting," said John Holdren, President Barack Obama's chief science adviser. "This expanded role for the private sector will free up more of NASA's resources to do what NASA does best - tackle the most demanding technological challenges in space, including those of human space flight beyond low Earth orbit."

The space transport company originally scheduled the launch for take-off last Saturday, but a half-second before liftoff, onboard computers detected high combustion chamber pressure in one of its engines and aborted the launch. Later, engineers discovered that a faulty valve caused the problem and worked into the evening to replace it.

NASA retired the shuttle last July after 30 years to focus on deep space exploration, forcing American astronauts to depend on foreign spacecraft. But setbacks in the past year, including the crash of a Russian supply ship last August and the postponement of a manned flight due to technical difficulties, raised questions over the Russian space program's dependability.

"For sure it has raised jitters," Rene Pischel, head of the Moscow branch of the European Space Agency, told Reuters after the supply ship crash. "You have this sequence of failures.... That of course makes everybody very cautious."

Even though today's launch succeeded, Dragon's real test comes Thursday. With the risk of a collision damaging the space station, NASA has required a day of practice maneuvers before allowing the craft to dock. Once landed, the capsule's cargo - a half-ton of food and other pantry items - will be unloaded. After two weeks, the capsule will return with old space station equipment and experiments, landing in the Pacific Ocean off the coast of Southern California.

Two more Dragon supply missions are planned for this year. Orbital Sciences Corp. is also planning for a launch by the year's end.

While acknowledging challenges ahead, SpaceX CEO Elon Musk savored Tuesday's triumph:"I would really count today as a success, no matter what happens the rest of the mission."

The Associated Press contributed to this report