NASA's Ares I rocket is on its launch pad at the Kennedy Space Center in Florida, awaiting its first experimental flight, scheduled for Tuesday. ((NASA/Associated Press))

NASA officials say the Ares I-X test rocket is ready for launch Tuesday morning, but weather could scrub the test flight until Wednesday.

NASA weather officer Kathy Winters said there's only a 40 per cent chance that weather will be favourable for a launch during the four-hour window available for 8 a.m. until noon ET Tuesday.

Winters said clouds and rain could push the launch to Wednesday morning.

The director for the Ares I-X test launch, Jeff Spaulding, said the vehicle itself is ready to go.

"I'm very happy to report that we are tracking no problems and the vehicle is in great shape," he said.

The 98-metre Ares rocket is on the launch pad at the Kennedy Space Center in Florida. The test launch will help NASA's engineers determine if the design can withstand the extreme stresses that occur during lift-off.

No astronauts will be on board the rocket. The Ares I-X is the first version of a series of rockets set to carry the U.S. space agency's next-generation Orion spacecraft after the space shuttle fleet is retired in 2010. There are only six scheduled flights left for the shuttles.

The Orion-Ares combination is not due to launch with astronauts on board until 2017 at the earliest. That poses a problem for the U.S. contribution to the International Space Station, which is currently scheduled to be decommissioned in 2015.