On April 29th Virgin Galactic, a private space firm, lit the engine on SpaceShipTwo, its air-launched suborbital rocketplane, for the first time. Unlike other companies such as SpaceX, which has contracts to launch satellites and resupply the International Space Station, Virgin is focusing on the tourist trade. For $200,000 a seat, customers will get a joyride just over the 100km-high (62-mile) Karman Line, which marks the boundary of space. After six minutes of weightlessness, SpaceShipTwo will ferry its passengers back to a landing strip in the Mojave desert. The successful test-firing is a milestone for a firm repeatedly hit by delays: passenger flights were originally scheduled to begin in 2007.