Nasa's rocket roll-out complete

The US space agency's Ares 1-X test rocket has reached its launch pad at Florida's Kennedy Space Center. The launcher's journey from its assembly building to the pad took nearly eight hours.

The super-slim, 100m-tall launcher is a demonstrator for the vehicle Nasa plans to use in the next decade to take its new astronaut crewship into orbit. The Ares I-X is expected to make an unmanned, two-minute flight at the end of the month.

This is designed to check out basic design concepts and gather engineering data. However, the project's long-term future is uncertain and could conceivably be cancelled in the coming months. US President Barack Obama convened an expert panel back in May to review American human spaceflight plans and priorities.

Led by former Lockheed Martin CEO Norm Augustine, the advisory group has suggested a range of options for getting astronauts into space - most of which do not require the new stick-like Ares launcher.

The Ares 1-X started its move from the giant Vehicle Assembly Building (VAB) at the Kennedy Space Center at around 0639 BST (0139 EDT) on Tuesday. It was carried atop a huge crawler-transporter vehicle during the 6.7km (4.2 miles) journey to launch pad 39B.

The rocket is now positioned on the pad and engineers are establishing mechanical and electrical connections. Later today, a vehicle stabilisation system - to steady the rocket against high winds - and a rotating service structure will be deployed.

The $350m (£213m; 234m euro) test launch is scheduled to take place from the Florida spaceport no earlier than the 27th of the month. The 1-X will climb about 40km (25 miles) into the sky during the powered phase of its flight, continuously measuring vehicle aerodynamics, controls and performance of the rocket's first stage.

The demonstrator will help verify design assumptions so that when the Ares 1 proper is built, the engineers can be confident it will fly as expected. "It's a tall rocket; it's been over three decades since anyone has built a rocket this tall. That was the Saturn V," explained Trent Smith, the vehicle processing engineer for the Ares 1-X.

"We have over 700 sensors on this rocket; and the whole point of Ares 1-X is to understand how does a rocket this shape, this weight, this tall actually fly," he told BBC News.

The top half of the 1-X is a dummy. What would be an upper-stage, with a crew capsule and its emergency escape mechanism are simulators made to the correct shape and weight.

Once the first stage has been extinguished and has separated from the top of the 1-X, all the elements will come back to Earth.

The first-stage booster will parachute into the Atlantic Ocean where it will be recovered for inspection by engineers. The simulation elements of the vehicle will be destroyed on impact with the water.

The US space agency is scheduled to retire its space shuttles next year, and has begun the development of a new human space launch "architecture" called Constellation.

The architecture calls for two new rockets: the Ares 1 to launch crew, and a new heavy-lift rocket known as Ares 5 that could put into orbit the equipment needed by a manned capsule to travel to the Moon and beyond.

However, all the systems are under review, and many commentators expect the Ares development plans to be heavily modified or even cancelled.

If it is allowed to proceed, a manned Ares 1 is not expected to fly before 2016.