The pilots were flying the place for Virgin Galactic, whose SpaceShipTwo rocket plane was meant to carry tourists on short but expensive trips to space.
The doomed flight - the 35th by SpaceShipTwo - marked the first time the spaceship had flown on a new kind of plastic-based rocket fuel mixture.
A team of federal investigators launched a probe of the causes of Friday's accident, which dealt a devastating setback to the cause of commercial space tourism.
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.
Speaking to reporters after arriving in the California facility that had served as the hub of Virgin Galactic's space program, Branson 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," a grim-faced Branson told reporters.
"We do understand the risks involved, and we're not going to push on blindly.
"Safety has always been our number one priority," he added before heading off to rally grieving Virgin Galactic staff at the Mojave Air and Space Port.
The surviving pilot, Peter Siebold, is now "alert and talking with his family and doctors", plane designer and builder Scaled Composites said in a statement.
It named the dead pilot as 39-year-old Michael Alsbury, a father of two.
National Transportation Safety Board acting chairman Christopher Hart told reporters investigators 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," Hart said.
It was not immediately known if a black box flight data recorder was installed on the doomed suborbital craft, though Hart stressed that test flights are usually documented with significant amounts of data.
Branson headed to California within hours of the crash, which saw the company's suborbital SpaceShipTwo break apart and hurtle to the ground shortly after it had detached from a mothership at an altitude of around 13,700 metres during a test flight.
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.
