Virgin Galactic owner Sir Richard Branson vowed not to give up on his dream of commercial space travel as investigations continue into a spacecraft crash that killed a pilot and seriously injured another.

Speaking publicly for the first time since the SpaceShipTwo crashed in California’s Mojave Desert during a test flight, Branson admitted the incident was “a massive setback” but that he was “determined” to move forward.

The investigations come as reports emerged that Virgin Galactic ignored warnings that its $500 million rocket was unfit for flight.

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“It is a horrible day for Virgin Galactic, for commercial space travel – it’s a massive setback,” Branson told reporters.

“But we’ve got to pick ourselves up and see whether the problem is fixable, and hopefully move the programme forward.

“I’m hopeful we’ll be able to overcome the problems.”

Authorities in the United States named the pilot killed in the crash as 39-year-old Michael Alsbury.

The pilot who survived is 43-year-old Peter Siebold. He parachuted to the ground and is now in hospital being treated for moderate to major injuries.

Virgin boss Richard Branson says he will push on with his space program. Photo: AAP

A team of investigators from the National Transportation Safety Board (NTSB) arrived at the crash site on Saturday to begin piecing together what led to the accident.

Authorities say the probe into the crash could take up to a year.

The crash was the second disaster to rock the private space industry in the space of a few days, after an Antares rocket carrying supplies to the International Space Station exploded after take-off in Virginia on Tuesday.

Early theories about the causes of the latest crash have focused on the fuel, amid reports the company was repeatedly warned of concerns about its safety.

A rubber-based fuel was previously used.

The Sunday Telegraph disclosed that Branson’s company, as well as US authorities, were warned about safety issues on numerous occasions, as long ago as 2007 when three engineers died in an explosion during testing of a rocket engine on the ground.

Carolynne Campbell, the lead expert on rocket propulsion at the International Association for the Advancement of Space Safety (IAASS), said on Saturday night: “This explosion is not a surprise. None whatsoever, I am sorry to say. It is exactly what I was expecting. It was Russian roulette which test flight blew up.”

Mr Alsbury was a project engineer and test pilot at Scaled Composites, a Northrop Grumman Corp subsidiary that built and designed the spacecraft for Virgin Galactic.

Mr Siebold was piloting SpaceShipTwo on Friday and Mr Alsbury was serving as co-pilot, Scaled Composites said in a statement.

Michael Alsbury, who was killed when a Virgin Galactic spaceship crashed. Photo: Supplied

‘We’ll make absolutely certain that the dream lives on’

Branson met with Virgin Galactic employees and officials from the NTSB, the agency which he said would handle all work and official comment on the investigation.

The billionaire entrepreneur said safety remained his paramount concern.

“We owe it to our test pilots to find out exactly what went wrong, and once we’ve found out what went wrong, if we can overcome it, we’ll make absolutely certain that the dream lives on,” he said.

“We do understand the risks involved, and we’re not going to push on blindly. To do so would be an insult to all those affected by this tragedy.

“We’re going to learn from what went wrong, discover how we can improve safety and performance and then move forward together.

“We’ve been undertaking a comprehensive testing program for many years and safety has always been our number one priority.”

NTSB acting chairman Christopher Hart told reporters investigators were entering unknown territory but hoped to find clues to the accident in data gathered by Virgin Galactic.

“This will be the first time we have been in the lead of a space launch that involved persons on board,” Mr Hart said.

He said it was not immediately known if a black box flight data recorder was installed on the doomed suborbital craft.

“This was a test flight and test flights are typically very well documented in terms of data,” Mr Hart said.

“And we may get some video feed. We may have lots of evidence that will help us with the investigative process.”

Crashed spaceship was using new type of fuel

The Virgin probe will likely focus on SpaceShipTwo’s rocket engine, which 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 the spaceship’s three previous rocket-powered test flights to get better performance.

Law enforcement officials take a closer look at the wreckage. Photo: AAP

“We’ve tested both of these fuel grains a lot,” Virgin Galactic chief executive George Whitesides told Reuters at the time.

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

Virgin Galactic is a US offshoot of the London-based Virgin Group founded by Branson, one of the world’s most famous entrepreneurs whose business empire ranges from airlines to music stores and mobiles phones.

Both crew members of the spaceship were test pilots for Scaled Composites, the Northrop Grumman Corp subsidiary that designed and built the spacecraft for Virgin and lost three other employees in a July 2007 ground test accident.

“While not a NASA mission, the pain of this (new) tragedy will be felt by all the men and women who have devoted their lives to exploration,” US space agency NASA said in a statement.

Setback for space travel

Experts say the accident will delay the advent of commercial space tourism by several years.

Virgin Galactic had hoped to start ferrying wealthy customers to the edge of space in 2015, charging $US250,000 ($A270,490) per person for a ticket on the company’s six-seater vehicle.

Around 500 people, including a slew of celebrities such as Hollywood star Leonardo DiCaprio, had already reserved tickets on the first wave of Virgin Galactic flights.

– with AAP