The Dragon mission would be the first time a privately owned and operated vessel visits the space station, a $100 billion research laboratory owned by the United States, Russia, Europe, Japan and Canada that orbits about 240 miles above Earth.

NASA is counting on Space Exploration Technologies, also known as SpaceX, and a second company, Orbital Sciences Corp., to keep the space station stocked with supplies and science experiments following the retirement of the space shuttles last year. The companies' combined contracts for cargo deliveries are worth $3.8 billion.

"In order for space station to be successful, these systems have to be there for us," space station program manager Mike Suffredini said at news conference following a NASA review of the upcoming SpaceX mission.

"We're really rooting for the teams to come through," added NASA Associate Administrator Bill Gerstenmaier.

So far, NASA has invested $381 million in the SpaceX rocket and cargo capsule, with the company and investors contributing about another $700 million, SpaceX founder and Chief Executive Elon Musk said.

The Falcon 9 rocket and Dragon capsule also are in the running to serve as a space taxi for astronauts. The United States hopes to break Russia's monopoly on flying crews to the station, a service that cost more than $60 million per person, by 2016 under a related NASA program.

"This is a test flight and we may not succeed on getting all the way to the space station," Musk said. "I think we've got a pretty good shot, but it's important to acknowledge that a lot can go wrong. This is pretty tricky."

If the launch is successful, the Dragon capsule would conduct a series of maneuvers and tests in orbit before NASA clears it for approach and berthing at the station, which is targeted for May 3. It would remain attached to the outpost for several weeks before flying back to Earth and splashing down in the Pacific Ocean for recovery.

The capsule will carry 1,149 pounds (521 kg) of food and non-critical equipment and supplies to the station. It is expected to return 1,455 pounds (660 kg) of cargo back to Earth, a capability that far exceeds what the Russian Soyuz capsules can hold.

The European and Japanese ships that also fly cargo to the station incinerate in the atmosphere after making deliveries and do not return to Earth.

NASA plans a final review of the Dragon mission on April 23 to verify SpaceX flight software. The Falcon 9 rocket is scheduled for launch at 12:22 p.m. EDT (1622 GMT) on April 30, with a backup launch opportunity on May 3.

(Editing by Jane Sutton and Sandra Maler)

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