(CNN)-- Virgin Group founder Richard Branson said Saturday that invesigators will find out what caused the Virgin Galactic's SpaceShipTwo to break apart during a test flight over the Mojave Desert Friday, killing one pilot and injuring another.
"We are determined to find out what went wrong," he said at a press conference.
Branson said everybody knows commercial space travel is "an incredibly hard project."
"This is the biggest test program ever carried out in commercial aviation history to ensure that this never happens to the public," he said. "The bravery of test pilots cannot be overstated. Nobody underestimates the risks involved in space travel."
The company, he said, will not "push on blindly."
"To do so would be an insult to all those affected by this tragedy," he said. "We're going to learn from what went wrong, discover how we can improve safety and performance and then move forward together."
When asked about the future of Virgin Galactic, Branson said the company's goal is still putting people safely into space.
"I think millions of people in the world would love one day to have the chance to go to space, and this is the start of a long program," he said.
Still, he said, the company will gladly give refunds to anybody who had already purchased a flight.
Chris Hart, acting chairman of the National Transportation Safety Board, said Saturday that test flights like the SpaceShipTwo flight are usually well-documented.
"We may have lots of evidence that will help us with the investigative process," he said. "That will make our job simpler and make it able to find out not only what happened but also more importantly why it happened."
Nothing seemed abnormal before incident
The first sign there was a problem with Virgin Galactic's SpaceShipTwo came at about 45,000 feet, just two minutes after the spaceplane separated from the jet-powered aircraft that carried it aloft.
It wasn't something overt with SpaceShipTwo, said Stuart Witt, the chief executive of Mojave Air & Space Port in California, where it was launched and monitored. It was what didn't happen next during the test flight, he said. Witt did not offer details, but appeared to indicate the spaceplane did not follow its previous test-flight patterns.
Nothing seemed abnormal during the takeoff or flight prior to the spaceplane's failure, Witt told reporters.
Virgin Galactic conducted "extensive ground testing of all parts of the spaceship," Branson said earlier.
"We've always known that the road to space is extremely difficult -- and that every new transportation system has to deal with bad days early in their history," Branson said in a statement as he was en route to the firm's Mojave site.
The pilot who is hospitalized parachuted to the ground, Virgin Galactic said.
"Our thoughts and prayers are with the families of all those affected by this tragic accident," the company said in a statement.
The two pilots worked for Scaled Composites, its president, Kevin Mickey, said. He declined to publicly identify the pilots or detail their experience.
Questions raised about new fuel mixture
"Space is hard, and today was a tough day. We are going to be supporting the investigation as we figure out what happened today, and we are going to get through it," Virgin Galactic CEO George Whitesides said.
"The future rests in many ways on hard, hard days like this."
For years, Virgin Galactic has planned to sell trips in which SpaceShipTwo transports passengers about 62 miles above Earth -- the beginning of outer space -- and lets them experience a few minutes of weightlessness before returning to ground.
The incident occurred shortly after SpaceShipTwo separated from WhiteKnightTwo, the vehicle designed to carry it aloft, the Federal Aviation Administration said. The jet-powered WhiteKnightTwo returned safely to the Mojave Air & Space Port, Witt said.
Said Branson: "This was the latest part of an extensive test flight program, and the 55th time SpaceShipTwo had flown. It was WhiteKnightTwo's 173rd flight and the 35th time SpaceShipTwo had flown freely."
Questions are being raised about a new fuel mixture used after Mickey said it had been ground-tested a number of times, but Friday's flight was the first time it was used in a test flight.
The National Transportation Safety Board is leading the investigation with FAA support, under a voluntary cooperative agreement between the agencies.
NASA administrator Charles Bolden offered his condolences to the family of the pilot killed in the test flight failure.
"While not a NASA mission, the pain of this tragedy will be felt by all the men and women who have devoted their lives to exploration," Bolden said. "Spaceflight is incredibly difficult, and we commend the passion of all in the space community who take on risk to push the boundaries of human achievement." Celebrities have signed up for flights
It's unclear what the failure of the spaceplane will mean for the program. Virgin Galactic planned to send paying customers on SpaceShipTwo as early as next year.
Virgin has sold more than 700 tickets, each costing more than $250,000, for future flights. Several celebrities have already signed up, including Justin Bieber, Ashton Kutcher, Leonardo DiCaprio and Stephen Hawking.
With composite lightweight materials, "feathered" rudders capable of turning 90 degrees and a hybrid rocket engine, SpaceShipTwo is as safe as modern technology can make it. As designer and aviator Burt Rutan put it in 2008, "This vehicle is designed to go into the atmosphere in the worst case straight in or upside down and it'll correct."
Details of Friday's test flight plan were not immediately known. But in previous test flights, SpaceShipTwo has been loaded on the jet-powered WhiteKnightTwo, which can take the spaceplane to about 50,000 feet before the spaceplane is released to fly free.
At that altitude, SpaceShipTwo would then fire its RocketMotorTwo, a hybrid rocket engine powered by both solid and liquid fuel.
SpaceShipTwo would reach supersonic speeds on its way to its intended altitude of about 62 miles above the Earth. At that point, people onboard would get about five minutes of weightlessness before the bonds of Earth retract with 6 G's of force.
The spaceplane would then glide back through the atmosphere to landing.
Friday's is the second incident in a week involving the commercial space industry.
On Tuesday, an unmanned Antares rocket exploded just after takeoff off the coast of Virginia. Controllers deliberately destroyed the craft after it became apparent there was a problem, a spokesman for Orbital Sciences Corp. said Thursday.
CNN's Mayra Cuevas, Paul Vercammen, Michael Martinez, Mike Ahlers, Rosalina Nieves, Sonya Hamasaki, Shelby Lin Erdman and Todd Leopold contributed to this report.
™ & © 2014 Cable News Network, Inc., a Time Warner Company. All rights reserved.