This story was updated on May 22 at 12:15 a.m. EDT.
CAPE CANAVERAL, Fla. — A privately built rocket carrying the first commercial spacecraft ever to visit the International Space Station has begun fueling for its planned early-morning launch into orbit on Tuesday (May 22).
The Falcon 9 rocket built by the commercial spaceflight company SpaceX is making its second attempt to launch the company's robotic Dragon space capsule, with blastoff set for 3:44 a.m. EDT (0744 GMT) from the Cape Canaveral Air Force Station here. The Falcon 9 booster is now being filled with liquid oxygen and kerosene fuel to power its nine engines.
"Fueling has begun," NASA spokesman Mike Curie told SPACE.com. "There are no constraints, and weather looks good."
Weather forecasts predict an optimistic 80 percent chance of clear skies for this second try at launch. [Quiz: How Well Do You Know SpaceX's Dragon?]
The unmanned 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 in the last half-second. Over the weekend, SpaceX engineers 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 the Hawthorne, Calif.-based SpaceX, said Monday.
Dragon 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.) 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.
For this debut mission, the Dragon spacecraft is packed 1,200 pounds of cargo, including 162 meals for the station crew, science experiments designed by middle and high school students, and a supply of commemorative mission patches and pins.
If Dragon lifts off Tuesday, it is expected to approach the space station on Thursday (May 24), and then be attached to the orbiting lab 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 ocean.