UPDATE | Branson vows to find out cause of spacecraft crash

MOJAVE, Calif. (AP) — Billionaire Virgin Galactic founder Richard Branson today vowed to find out what caused the crash of his prototype space tourism rocket, killing one crew member and injuring another.

But he sounded a cautious note about any move to quickly push the project forward.

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."

Branson added, however, that "we are not going to push on blindly."

He also criticized early speculation. "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 as Michael Tyner Alsbury, 39, of nearby Tehachapi, who worked for Scaled Composites, the company developing the spaceship for Virgin Galactic.

The surviving pilot was identified as Peter Siebold, 43. Siebold was to undergo surgery today.