If Dragon continues to operate as planned, it will fly to within about 30 feet of the $100 billion station on Friday and shut down its maneuvering thrusters so the station crew can snare it with a robotic crane and hook it onto a docking port.

Dragon took a test drive past the station early on Thursday, coming as close as about 1.5 miles as the two vessels soared around the planet at 17,500 miles per hour.

Astronauts aboard the station showed they could command Dragon by ordering the capsule to turn on and off its strobe light.

"“It went very, very smoothly," NASA flight director Holly Ridings told reporters after the test.

“"We've been training and practicing for many years, but doing it for the first time with two dynamic spacecraft flying very close together you always want to make sure that you're going to be able to work as you trained," she said.

"“It's a big confidence boost," added mission director John Couluris, with California-based Space Exploration Technologies, or SpaceX.

"“It's exciting to be an American and part of putting an American spacecraft into orbit. We're very proud right now," he said.

With the retirement of the space shuttles last year, the United States is dependent on station partners Europe, Japan and especially Russia to reach the orbiting laboratory, which flies about 240 miles above Earth.

Rather than building a government-owned and operated replacement for the shuttle, the Obama administration is supporting private industry efforts to develop cargo ships and space taxis so NASA can buy flight services instead, a far cheaper alternative.

If SpaceX's Dragon continues to operate as planned, the company will be cleared to begin working off its 12-flight, $1.6 billion NASA contract to fly cargo to and from the station. A second freighter owned by Orbital Sciences Corp is expected to debut later this year.

NASA is incubating similar partnerships to develop passenger spaceships, which would break the U.S. reliance on Russia for crew flight services that cost about $400 million a year.

Dragon blasted off aboard a SpaceX Falcon 9 rocket from Cape Canaveral Air Force Station in Florida on Tuesday.

If all goes as planned, station flight engineers Don Pettit and Andre Kuipers will use the station's 58-foot (17.7-metre) robot arm to pluck Dragon from orbit shortly after 8 a.m. EDT (1200 GMT) on Friday and attach it to a berthing port on the station's Harmony connecting node about three hours later.

“"It is a test flight so I don't want to jinx myself and say what I can expect (on Friday) and then see something different," Couluris said. "“We fly by the mantra of 'Train like you fly and then fly like you train,' and so far the mission has been proceeding just like a regular simulation."

Dragon is carrying about 1,200 pounds (544 kg) of food, water, clothing and supplies for the station crew.

The capsule will be repacked with equipment to come back to Earth, leaving the space station on May 31 and splashing down in the Pacific Ocean off the coast of Southern California later that day.

(Editing by Jane Sutton, Vicki Allen and Eric Beech)

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