The privately-owned American firm SpaceX readied Friday for the first test flight of its Falcon 9 rocket, seen as a key step in developing commercial launchers to put people into space.
SpaceX was early Friday awaiting the final go ahead from its engineers, with live images of the take-off from the Cape Canaveral base in Florida due to be shown on its website.
Lift-off is supposed to happen some time in a four-hour window between 1500 GMT and 1900 GMT. If the launch does not go ahead, SpaceX may try again on Saturday.
"Weather will be an issue today," SpaceX said of the launch, which is being keenly watched by the space industry.
President Barack Obama hopes the private sector will help fill the gap after the space shuttle fleet is grounded this year, and before a new generation of spacecraft is developed.
"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.
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 International Space Station.
During the transition period, the United States will depend on Russian Soyuz rockets for access to the ISS.
If all goes according to plan, 10 minutes after its launch the 55-meter (180 foot) long Falcon 9 rocket, as tall as an 18-story building, will place the Dragon capsule into orbit.
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