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SpaceX fires Falcon's rocket engines

SpaceX conducts a test firing of a Falcon 9 rocket's engines.

SpaceX conducted a successful test firing of a Falcon 9 rocket's engines on its Cape Canaveral launch pad, one week before its precedent-setting launch to the International Space Station. But it took more than one try.

The initial countdown was halted just 47 seconds before the nine engines were scheduled to start up. SpaceX fixed what it called a "limit that was improperly set" on the flight computer and quickly set up another countdown. The second countdown proceeded smoothly, and the rocket's nine engines fizzed to life for two seconds as expected, at 4:15 p.m. ET today.

"Woohoo, rocket hold-down firing completed and all looks good!!" SpaceX's millionaire founder, Elon Musk, reported in a Twitter update. Meanwhile, company spokeswoman Kirstin Brost Grantham said "engineers will now review data as we continue preparations for the upcoming launch."

This was a full dress rehearsal for SpaceX's second official demonstration flight for NASA. The first demo flight, back in December 2010, sent a gumdrop-shaped Dragon space capsule into orbit for the first time. The second flight, scheduled to lift off as early as May 7, could see the Dragon go all the way to the space station.

The company has received more than $375 million so far from the space agency for the development of the Falcon 9 and the Dragon. SpaceX and another company, Orbital Sciences Corp., are getting the money to help NASA fill the gap in payload transportation capability left by last year's retirement of the space shuttle fleet.

In addition, SpaceX is receiving tens of millions of dollars from NASA under a separate program to make the Falcon/Dragon launch system suitable for carrying astronauts as well as cargo. Musk founded the California-based company in 2002 with the long-range aim of flying people to Mars.

The Falcon 9 didn't fly anywhere during today's test at Cape Canaveral Air Force Station's Launch Complex 40 in Florida, but if SpaceX and NASA stick to the current timeline, the rocket will send the robotically controlled Dragon capsule into orbit on May 7. A couple of days later, the spacecraft will catch up with the space station and go through a sequence of rendezvous maneuvers.

If the Dragon performs those maneuvers correctly, NASA would give the go-ahead for the Dragon to approach a station docking port. The station's robotic arm would grab onto it and bring it in for berthing. There'll be some cargo riding aboard the Dragon — water, clothing, scientific gear and the like — and the astronauts would take a couple of weeks to take on those payloads and load up the Dragon with Earth-bound cargo. Then the Dragon would be unberthed and sent back down to a Pacific splashdown, marking the successful end of the first flight of a private-sector spaceship to the International Space Station..

There are a lot of "ifs" on that list of contingencies. This launch has been delayed repeatedly due to software glitches, and if a snag like the one that occurred today happened to crop up on May 7, liftoff would have to be postponed for three days. To reach the space station, the Falcon has to lift off right on the dot. The orbital mechanics will not allow for same-day do-overs. But that's OK. Last month, SpaceX President Gwynne Shotwell said "we may have to have a couple of attempts, but we're certainly looking forward to getting that flight off."

If the Falcon 9 and the Dragon pass their tests, that would put SpaceX in a position to ship supplies to the space station in earnest, under the terms of a $1.6 billion NASA contract.

Will SpaceX get 'er done? Feel free to weigh in with your comments below.

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Last updated 4:27 p.m. ET.

Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter or adding Cosmic Log's Google+ page to your circle. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for other worlds.