The privately-owned SpaceX prepares for a first rocket flight on Friday, a key test in developing commercial launchers capable of servicing the orbiting International Space Station.
President Barack Obama hopes the private sector will fill the gap in supplying the ISS between the time the Space Shuttle fleet is decommissioned later this year and the next generation of space vehicles comes into service.
SpaceX's Falcon 9 rocket is scheduled to liftoff from Cape Canaveral, Florida, sometime in a four-hour window starting at 11 am (between 1500 GMT and 1900 GMT). If that fails, the company would attempt again Saturday during the same time frame.
"Regardless of the outcome, this first launch attempt represents a key milestone for both SpaceX and the commercial spaceflight industry," the company said in a statement.
The launch comes as Obama seeks to convince a reluctant Congress of the merits of his decision in February to cancel the Constellation program -- designed to return US to the moon by 2020 -- which effectively killed the Ares 1 rocket.
US astronauts in the meantime will have to hitch rides on Russian spacecraft to the orbiting space station until a replacement is developed.
Obama has proposed spending six billion dollars over five years to help the private sector develop reliable and affordable launchers to transport cargo and US astronauts to the ISS.
During the transition period, the United States depend on Russian Soyuz to access the ISS.
Obama visited the SpaceX installations in Cape Canaveral during an April visit to the Kennedy Space Center.
SpaceX leaders emphasized that the Friday event is just a first of a series of test flights.
"Since this is a test launch, our primary goal is to collect as much data as possible," SpaceX said.
"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," the company said.
If all goes according to plan, ten minutes after its launch the 55 meter (180 foot) long rocket, as tall as an 18-story building, will place the Dragon capsule into orbit.
NASA has already signed contracts with SpaceX, a start-up launched in 2002 by Elon Musk, who made his fortune with the creation and eventual sale of online pay system PayPal.
The contracts, signed in late 2008 and worth 3.1 billion dollars, are to deliver cargo to the ISS between 2011 and 2016.
NASA has also signed contracts with another company, Orbital Sciences Corp. Its Taurus II rocket is set to for its first flight in 2011.
SpaceX and other upstarts would be up against industry giants Boeing and Lockheed Martin, which together operate United Launch Alliance (ULA), whose stable includes Atlas V and Delta 4 rockets that have logged considerable flight hours.
"Symbolically that is very important for the new strategy that Obama has proposed," said John Logsdon, a space expert and former head of the Space Policy Institute at George Washington University.
Nevertheless Falcon 9 "has to prove itself as a cargo carrier before any serious consideration of putting people on board," he told AFP, noting the long track record of the Atlas V and the Delta 4.
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