SpaceShipTwo is designed to be carried to 51,000 feet by its mother ship, then launched to attain a final altitude of 65 miles above the Earth's surface. The rocket fuel is a combination of nitrous oxide and a rubber-based solid fuel. Each flight is to last about 2.5 hours, including about five minutes of zero-gravity. SpaceShipTwo accommodates up to six passengers and two pilots. Tickets are priced at $200,000, and Virgin Galactic reports it has sold around 300.