Private rocket maker SpaceX aimed for a Tuesday liftoff after fixing the engine problem that caused a launch abort over the weekend, stalling the world's first commercial space station supply flight.
Forecasters put the odds of good weather at 80 percent for the test flight. Launch time was 3:44 a.m. with a split-second window.
The California-based Space Exploration Technologies Corp., better known as SpaceX, is the first private business to attempt to launch a vessel to the International Space Station. The Dragon capsule atop the Falcon 9 rocket is filled with 1,000 pounds of food and other provisions.
All nine of the Falcon's engines ignited during the first launch attempt Saturday. But with just a half-second remaining before liftoff, on-board computers shut everything down because of high pressure in the combustion chamber of engine No. 5.
The problem was traced to a faulty valve. Engineers put in a new valve and declared the rocket ready to fly.
SpaceX is run by billionaire Elon Musk, the co-founder of PayPal. His company is in the lead of the NASA-sponsored competition to hand over space station cargo runs — and eventually astronaut ferry trips — to private business.
Musk said his Dragon capsules could be carrying astronauts to orbit in about four years. Until a private spacecraft is ready to fly, NASA astronauts will continue to ride Russian rockets to the space station.
The switch from government to commercial spaceflights is the cornerstone of President Barack Obama's exploration plan. The administration wants NASA spending its limited resources on missions beyond low-Earth orbit.
If launched Tuesday, the Dragon will reach the space station Thursday and undergo a series of practice maneuvers from more than a mile out. Then on Friday, the capsule will fly within reach of the station's 58-foot robot arm, which will snare it and berth it to the orbiting lab.
The arm will be operated by two of the six space station residents: American Donald Pettit and Andre Kuipers, who is Dutch.
"Ready to monitor the approaching Dragon spacecraft in bright sunlight and complete darkness," Kuipers said via Twitter on Monday. He posted a picture of the two crewmen awaiting the capsule. "Sunglasses, headlamp, reading glasses. Now for the launch."
The Dragon will spend a week at the space station before being cut loose and parachuting into the Pacific with experiments and equipment. None of the other visiting supply ships — from Russia, Europe and Japan — are designed to return intact.