Some more info on SS2 development

... SpaceShipOne used rubber and laughing gas. Scaled Composites is studying alternatives to rubber that may offer better performance.

Another change in the design of the spaceship is the insertion of a flexible glass-fibre section into its composite structure. This will allow the rocket's oxidiser tank to expand when it is full. All these changes mean that when SpaceShipTwo does begin flight tests, the programme will last at least a year before paying customers can take to the skies.

Work will also begin soon on fitting out another factory to start making more of these craft. Virgin Galactic has ordered five spaceships and two carrier aircraft. The spaceships will take longer to refuel for their next flight than the carrier aircraft do, so—thinking just as an airline would—the firm has concluded it needs more spaceships than carriers. Each spaceship should eventually be capable of making two trips into space every day, and the launch aircraft three or four flights....