Virgin Galactic founder Richard Branson, speaking to reporters in Mojave, Calif., salutes the bravery of his company's test pilots, Nov. 1, 2014.
Virgin Galactic founder Richard Branson, speaking to reporters in Mojave, Calif., salutes the bravery of his company's test pilots, Nov. 1, 2014.

British billionaire Richard Branson said Saturday that he was determined to find out what went wrong with his space tourism aircraft that crashed, killing one pilot and seriously injuring the other, but he also expressed a desire to press on with the dream of commercial space flight.

Branson said at a news conference in Mojave, California, that safety has always been the top priority of the program.

He would not discuss details of Friday's accident, which U.S. transportation officials are in the early stages of investigating, but he said that "we owe it to our pilots to find out exactly what went wrong. If we can overcome it, we will make absolutely certain that the dream lives on."

The Virgin Galactic commercial spaceship, SpaceShipTwo, crashed after it was released from a plane during a test flight over the Mojave Desert.

Pilot Michael Alsbury, 39, was found dead in the aircraft, Kern County Sheriff Donny Youngblood said.

Alsbury, who a sheriff's spokesman said was from Tehachapi, California, was a project engineer and test pilot at Scaled Composites, a Northrop Grumman Corp. subsidiary that built and designed the spacecraft for Virgin Galactic.

Alsbury was flying for the ninth time aboard SpaceShipTwo, including serving as the co-pilot on the vehicle's first rocket-powered test flight on April 29, 2013, according to his biography on the company's website.

The injured pilot, identified by the sheriff's office as Peter Siebold, 43, parachuted from the plane and was hospitalized for severe injuries, officials said.

The Virgin probe will most likely focus on SpaceShipTwo's engine, which on Friday was flying with a new type of fuel for the first time, experts said.

The solid plastic-type propellant is ignited by nitrous oxide, commonly known as laughing gas.

Virgin Galactic announced in May that it was replacing the rubber-based propellant used during previous test flights to get better performance.

"We've tested both of these fuel grains a lot,'' Virgin Galactic Chief Executive George Whitesides said at the time.

Before Friday's flight, SpaceShipTwo's last powered test flight was in January, though the rocket and its new propellant had passed multiple ground tests.

Virgin Galactic, which was founded by Branson, plans to sell trips on SpaceShipTwo to the edge of space. Passengers would have a few minutes of weightlessness before returning to Earth.

The accident was the second suffered by a private U.S. space company in recent days. On Tuesday, an unmanned commercial rocket that was supposed to send a cargo ship to the International Space Station exploded seconds after liftoff from a NASA launch pad in Virginia.

Friday's accident also marked the fourth fatality in Scaled's SpaceShipTwo development effort. In 2007, a fuel tank exploded, killing three Scaled employees.

Some information for this report comes from Reuters.