MOJAVE, Calif. - Billionaire Virgin Galactic founder Richard Branson vowed Saturday to find out what caused the crash of his prototype space tourism craft that killed one of two test pilots, adding that while he remains committed to civilian space travel "we are not going to push on blindly."

In grim remarks at the Mojave Air and Space Port, where the craft known as SpaceShipTwo was under development, Branson gave no details of Friday's accident and deferred to the National Transportation Safety Board, whose team had just arrived.

"We are determined to find out what went wrong," he said, asserting that safety has always been the top priority of the program that envisions taking wealthy tourists six at a time to the edge of space for a brief experience of weightlessness and a view of Earth below.

"Yesterday, we fell short," he said. "We'll now comprehensively assess the results of the crash and are determined to learn from this and move forward."

He also criticized early speculation about crash causes. "To be honest, I find it slightly irresponsible that people who know nothing about what they're saying can be saying things before the NTSB makes their comments."

The pilot killed in the test flight was identified Saturday as Michael Tyner Alsbury, 39, of nearby Tehachapi. The surviving pilot is Peter Siebold, 43, who parachuted to safety and was hospitalized.

Both worked for Scaled Composites, the company developing the spaceship for Virgin Galactic. Scaled Composite said Alsbury was the co-pilot for the test flight. Siebold, who was piloting SpaceShipTwo, "is alert and talking with his family and doctors," the company said in a statement

More than a dozen investigators in a range of specialties were forming teams to examine the crash site, collect data and interview witnesses, NTSB Acting Chairman Christopher A. Hart told a press conference at Mojave Air and Space Port.

"This will be the first time we have been in the lead of a space launch (accident) that involved persons onboard," said Hart, noting that the NTSB did participate in investigations of the Challenger and Columbia space shuttle disasters.

Hart said he did not immediately know the answers to such questions as whether the spaceship had flight recorders or the altitude of the accident, but noted that test flights are usually well-documented.

Virgin Galactic - owned by Branson's Virgin Group and Aabar Investments PJS of Abu Dhabi - plans to fly passengers to altitudes more than 62 miles above Earth. The company sells seats on each prospective journey for $250,000.

The company says that "future astronauts," as it calls customers, include Stephen Hawking, Justin Bieber, Ashton Kutcher and Russell Brand. The company reports receiving $90 million from about 700 prospective passengers.

On Saturday, Branson said none of that money has been spent and that anyone who wanted a refund could get it. However, he said, no one has asked, and instead someone signed up on the day of the accident in a show of support.

At 60 feet long, SpaceShipTwo featured two large windows for each of up to six passengers, one on the side and one overhead. Branson once envisioned operating flights by 2007. Last month, he talked about the first flight being next spring with his son.

Friday's flight marked the 55th for SpaceShipTwo, which was intended to be the first of a fleet of craft. This was only the fourth flight to include a brief rocket firing. The rocket fires after the spacecraft is released from the underside of a larger carrying plane. During other flights, the craft either was not released from its mother ship or functioned as a glider after release.