Virgin Galactic has again pushed back its timeline for launching space-tourism flights from southern New Mexico's Spaceport America.
Virgin owner and British billionaire Richard Branson told David Letterman last week that he hopes to board the first flight early next year. The company previously said it wanted to get the first flight launched by the end of 2014.
The company for years has been pushing back its launch date as it works to overcome challenges developing its rocket motor. When New Mexico first agreed to build the quarter-billion-dollar spaceport with Virgin Galactic as an anchor tenant, officials predicted flights would start in 2011.
Virgin Galactic officials say they are emphasising safety over meeting timelines.
"Customers are eager to fly, but they know we'll fly them when we feel ready," Virgin Galactic CEO George Whitesides said Wednesday. "Obviously we want to do it as quickly as possible, but we don't want to rush it."
Virgin Galactic's plan is to take tourists into space for $250,000 per person. The company says more than 700 people have signed up for the trip.
On Wednesday, Virgin brought the WhiteKnightTwo "mothership" to the spaceport for test flights. The aircraft will take its rocket-powered spaceship up to 15,000 metres for it to launch into space.
Whitesides called the craft's visit it to New Mexico a "critical milestone on our path to operations from Spaceport America." Most of the company's testing and operations are in the Mojave Desert.
"I think you'll see a lot more of these milestones coming over the next several months," he told reporters.