Virgin Galactic said its first passenger flights will not occur before 2013.
Sir Richard Branson's space tourism venture said it hopes to launch the service in two years time, but even that date is not fixed.
The firm's commercial director, Stephen Attenborough, told the BBC that its customers' safety is paramount.
Test flights are currently underway, with rocket-powered tests scheduled to start next year.
Almost 500 people have bought tickets.
Sir Richard had originally hoped the first commercial spacecraft, SpaceShip Two, would take off as early as 2007. However, Mr Attenborough stressed there never was an official date set for the inaugural launch.
He criticised some press reports, notably an article in the Wall Street Journal, that described the 2013 goal as yet another delay.
This is a programme that can't have a hard-end date as safety is number one priority, Mr Attenborough said.
Our foot is flat on the gas, we have proven technology, we have a spaceport that opened last week, and the test flight programme is well advanced - I don't think you can ask for a lot more from a programme like this. A delay is strange word, and there is no delay.
New pilot
Mr Attenborough also revealed that the venture's chief pilot, David Mackay, has recently been joined by a second pilot.
Keith Colmer, a former Air Force test pilot, was chosen from more than 500 applicants, among them a handful of astronauts.
Sir Richard dedicated the launchpad for the space tourism venture in the New Mexico desert on 18 October.
He plans to take the inaugural flight, accompanied by his children.
Mr Attenborough said that although all of the future tourists were eager to blast off to space, none were pushing for an early flight.
They are willing to put a large amount of money up front because they trust us, because they know we will only take them to space if it's safe to do so, he said.
The 2.5-hour flights will offer five minutes of weightlessness. Tickets cost $200,000 (ã127,000).
