Virgin Galactic's space tourism rocket SpaceShipTwo may fly free in its first glide test later this year, the company said.
The six-passenger spaceship has been carried aloft three times attached to the wing of its special jet-powered mothership, including a July 15 flight with two pilots aboard for the first time.
That flight, conducted by spaceship-builder Scaled Composites over California's Mojave Desert, allowed the crew to evaluate all systems and functions in the air, said Stephen Attenborough, an executive with Sir Richard Branson's Virgin Galactic in London.
"Scaled are now evaluating the data from this recent captive-carry flight before we know when the first SS2 independent glide flight will be but there's a reasonable possibility that we could see it happen in the fall (autumn)," Mr Attenborough said.
Virgin Galactic also released the first photographs of SpaceShipTwo with its wings and tail structures in the "feathered" position, a unique and critically important element of the system created by legendary aviation designer Burt Rutan.
SpaceShipTwo will be carried by the mothership to an altitude of up to 50,000 feet, then released before its rocket engine ignites for a high-speed ascent into space, where passengers will experience a few minutes of weightlessness.
The spaceship's twin tails and portions of the wings will then rotate about 65 degrees upwards to create high drag, slowing re-entry into the atmosphere and preventing a buildup of heat on the ship's skin.
At an altitude of about 70,000 feet, the tails will rotate back down to a conventional aircraft configuration for the glide back to a runway landing.
The photographs were taken as SpaceShipTwo was being prepared for its third captive-carry flight.
"Nobody's ever seen SpaceShipTwo with the wings feathered before," Mr Attenborough said. "It's another sign of progress and quite an interesting view of the spaceship."
The mothership, a four-engine jet dubbed WhiteKnightTwo, carries the spaceship on the centre of its wing between two fuselages.
The aircraft has made 33 flights and its testing is "substantially complete", Mr Attenborough said.
He said that although both companies were pleased with the flight tests, "no corners will be cut in order to achieve arbitrary deadlines".
Virgin Galactic has said the test programme is expected to run through next year before commercial operations begin. Some 300 clients have paid for a £131,500 ticket or placed a deposit, according to the company.