More than 500 people have signed up to travel on SpaceShipTwo, including Ashton Kutcher, star of the TV show Two and a Half Men.

The carbon composite craft is 60 feet long and can carry six passengers and two pilots.

It's designed to launch from a mothership, WhiteKnightTwo, at around 50,000 feet and will use a hybrid rocket motor to ascend to the edge of space.

The ship will travel high enough to give passengers a glimpse of the curvature of the earth.

SpaceShipTwo passengers will have to undergo a week of training to cope with the high g-force during launch and re-entry and how to move around in microgravity.

Training will take place at Spaceport America in New Mexico.

After SpaceShipTwo begins running commercially, Virgin Galactic will launch about one mission per week, with the number of launches gradually increasing over time, Virgin Galactic CEO George Whitesides told ZDNet.

Virgin Galactic has built two SpaceShipTwos — three including this replica — and Whitesides said that the company hopes to build more.

Virgin Galactic recently signed a deal to charter flights for NASA on SpaceShipTwo. The craft is capable of carrying up to 600 experimental payloads per flight for the US space agency.

An important feature of SpaceShipTwo is its ability to remain stable during turbulence when re-entering the Earth's atmosphere. The craft's tail can be rotated upwards by 65 degrees to generate very high drag during re-entry, and create a stable orientation.

The combination of high drag and low weight, due to the very light materials used to construct the vehicle, means that the skin temperature during re-entry stays very low compared to previous manned spacecraft. Thermal protection systems such as heat shields or tiles are not needed.

Following re-entry at around 70,000 feet, the tail returns to its original position and the spaceship becomes a glider for the flight back to the spaceport runway.

The craft has successfully completed a series of glide tests and Whitesides said the company hopes to carry out its first powered flight later this year.

The outer fins, seen here, are horizontal stabilisers for the craft — similar to those used on commercial airliners.

Chairman of Virgin Group Richard Branson and some future SpaceShipTwo passengers will also be attending the Farnborough air show.

SpaceShipOne aerospace engineer Burt Rutan inside the cockpit of SpaceShipTwo during its construction.