CAPE CANAVERAL, Fla. â€"  The private rocket company SpaceX is officially "go" to make a second try at launching its unmanned Dragon capsule early Tuesday, May 22, from Florida's Space Coast.

The spacecraft was due to make its maiden trip to the International Space Station Saturday, May 19, but a rocket engine glitch forced a launch abort at the last second. Over the weekend, SpaceX engineers investigated the problem and discovered a faulty check valve was to blame for the abnormally high chamber pressure in the engine that caused the abort.

"Since then they replaced that check valve with a new unit and have tested all the other engines for similar problems and believe they are good to go," Mike Horkachuck, NASA project executive for SpaceX, said today (May 21).

Dragon is now due to lift off atop SpaceX's Falcon 9 rocket from Launch Complex 40 at the Cape Canaveral Air Force Station at 3:44 a.m. EDT (0744 GMT). Weather forecasters have upgraded the outlook to an optimistic 80 percent chance of clear skies for the launch. [Quiz: How Well Do You Know SpaceX's Dragon?]

'They replaced that check valve ... and believe they are good to go.'

- Mike Horkachuck, NASA project executive for SpaceX

The vehicle is making its final test flight under a NASA program aimed at developing commercial U.S. spacecraft to fill in for the cargo-delivering capabilities of the retired space shuttles, which flew their final missions last year. SpaceX (Space Exploration Technologies Corp. of Hawthorne, Calif.) has a $1.6 billion contract to fly 12 delivery missions to the space station following a successful test flight to the orbiting lab.

"Space Exploration Technologies (SpaceX) will attempt to launch a Falcon 9 rocket carrying a Dragon spacecraft to orbit in an exciting start to the mission that will make SpaceX the first commercial company in history to try to send a spacecraft to the International Space Station," company officials said in a statement Monday.

If Dragon lifts off Tuesday, it plans to near the space station on Thursday (May 24), and rendezvous and berth there to deliver supplies on Friday.

The space capsule, while robotic, is not able to dock itself at the International Space Station. Instead, the spacecraft will pull up close to the station so that astronauts inside the orbiting lab can use a robotic arm to latch onto the vehicle and attach it to an available docking port.

After several weeks linked to the space station, the Dragon capsule is expected to depart the outpost and splash down in the Pacific Ocean a few hundred miles west of the Southern California coast. A recovery ship will retrieve the capsule from the the ocean.