SAN FRANCISCO — Suborbital space tourism venture Virgin Galactic hopes to begin powered test flights of its SpaceShipTwo rocket vehicle next year, representing a delay from previously disclosed plans to begin those tests in 2011, company officials said.

George Whitesides, Virgin Galactic’s chief executive, said the tests could begin during the first half of the year. “I think we need to see how things go over the next few months before we determine which quarter,” he said via email.

Meanwhile, Scott Ostrem, chief engineer at the Spaceship Company, prime contractor on SpaceShipTwo and its WhiteKnightTwo carrier aircraft, briefly addressed a problem that occurred during a Sept. 16 glide test of the suborbital rocket. The problem followed a clean release of SpaceShipTwo by its carrier aircraft.

“We pitched down a little too steeply on that flight and experienced a tail stall,” Ostrem said Oct. 19 at the International Symposium for Personal and Commercial Spaceflight in Las Cruces, N.M. He added that SpaceShipTwo’s pilot managed to stabilize the craft at an altitude of between 6,000 and 9,000 meters and bring it in for a safe runway landing.

It was the 16th glide test of SpaceShipTwo, dubbed VSS Enterprise. WhiteKnightTwo, christened VMS Eve, took off from the Mojave Air and Space Port in Mojave, Calif., where the Spaceship Company, a joint venture of Virgin Galactic and Scaled Composites, is based.

Virgin Galactic, bankrolled by airline and record entrepreneur Sir Richard Branson, will begin commercial operations at an as-yet-unspecified date out of Spaceport America north of Las Cruces. SpaceShipTwo is designed to haul six paying customers and two pilots on suborbital space journeys.

The company dedicated its Terminal Hangar Facility at the spaceport Oct. 17. During dedication ceremonies, the Terminal Hangar was named “Virgin Galactic Gateway to Space” by Branson.

Meanwhile, Virgin Galactic announced Oct. 27 the selection of U.S. Air Force test pilot Keith Colmer as the first astronaut-pilot to join the company’s flight team. In a press release, the company said Colmer was one of more than 500 applicants for the job.

Colmer will join Chief Pilot David Mackay to begin flight training and testing, leading to operational missions to space with Virgin Galactic’s revolutionary vehicles, WhiteKnightTwo and SpaceShipTwo,” the press release said. “Additional selections will be made |as the company nears commercial operations.”

Leonard David has been reporting on space activities for nearly 50 years. He is the 2010 winner of the prestigious National Space Club Press Award and recently co-authored with Apollo 11’s Buzz Aldrin the book “Mission to Mars — My Vision for Space...