A spaceship set to be used as a taxi service for NASA is due to lift off today.
The Falcon 9, built by California's SpaceX, should launch from Cape Canaveral at 11.00 Eastern Time, carrying a dummy payload in its Dragon capsule.
The launch can be viewed via webcast.
"As always, weather will play a significant role in our overall launch schedule," says CEO Elon Musk. "The weather experts at the Cape are giving us a 40 percent chance of 'no go' conditions for both days of our window, citing the potential for cumulus clouds and anvil clouds from thunderstorms."
The 47m-long spacecraft is powered by ten kerosene/liquid oxygen Merlin-1C engines - nine to get it off the ground and the tenth to get it into the right, 250km-high, orbit.
The company's first rocket, the Falcon 1, had three failed launches before finally making it into the sky. Failure today is not unlikely, says Musk, but could still lead to useful data.
"It would be a great day if we reach orbital velocity, but still a good day if the first stage functions correctly, even if the second stage malfunctions. It would be a bad day if something happens on the launch pad itself and we’re not able to gain any flight data," he says.
If the launch is successful, the trip to orbit will last just ten minutes. The spaceship will then orbit for around a year before eventually burning up in the atmosphere.
Falcon 9 has been designed to carry a six-tonne payload, but could be readily-convertible to carry passengers. SpaceX hopes for commissions from NASA - which helped fund the spaceship's development - as well as from satellite operators.
So far, the cost has reached nearly $400 million.