The test pilots of SpaceShipTwo were soaring more than eight miles above the Mojave Desert when they signaled to mission control that their experimental rocket motor was ready to fire.

All signals from the space plane indicated the test flight was proceeding as planned, according to sources familiar with the flight. But seconds after the two pilots shouted “Yahoo!,” ground crews lost connection with the rivers of data pouring from the craft’s advanced instruments.

Mission control called for the pilots to abort their flight, said observers speaking on the condition of anonymity because of the sensitive subject. But the space plane had already shattered with an explosive jolt, sending its cockpit and fuselage raining down over five miles of the desert’s sagebrush and sand and killing one pilot.

The investigation into Virgin Galactic’s spaceship disaster hinges closely on those crucial few seconds on Friday.

The strands of technical data beamed from the test flight’s computers to ground crews could provide a level of detail rarely seen in fatal accidents. And the memories of the surviving pilot, now recovering in a hospital, could prove key to unlocking what went wrong.

But the probe will be an unprecedented endeavor for the National Transportation Safety Board, the federal agency that reviews plane crashes, traffic accidents and train derailments. It will be the first time the NTSB has led an investigation of a space launch with people on board. However, the agency did assist in the probes of the crashes of the space shuttles Challenger and Columbia.

About 15 investigators are combing through the wreckage and corralling data connected to the explosion. They will be gathering evidence in the barrens surrounding the Mojave Air and Space Port for nearly a week, said Christopher Hart, acting chairman of the NTSB. A final report could take up to year.

Every move of the flight was recorded by a battery of cameras, including six mounted on the space plane and three on its carrier plane, the White­KnightTwo. Footage could also come from a radar-equipped chase plane that was following the carrier, as well as from a long-range camera at nearby Edwards Air Force Base.

Hart added that onboard aircraft performance data could provide a closer view of the craft’s inner workings. The NTSB said it had recovered a number of crucial elements from the wreckage, including two propellant tanks, but Hart could not say which cameras had been found.

Engineers began carefully scouting for clues in the high-speed photos taken of the explosion. Experts said it appeared to break apart a few seconds after detaching from the belly of the WhiteKnightTwo, while pushing for a vertical ascent near supersonic speeds.

More crucial evidence could come from Pete Siebold, the 43-year-old pilot who parachuted to safety after the blast. Siebold suffered a shoulder injury and underwent surgery but was alert and talking with his family and doctors Saturday, according to Scaled Composites, the firm that created the rocket plane.

His co-pilot, Mike Alsbury, was found dead in the rocket plane’s wreckage. A 39-year-old father of two young children, he had worked for 13 years as a test pilot and engineer for Scaled Composites, logging more than 1,600 hours of flight time in research aircraft, the company said.

Alsbury, who had helped in flight testing of nine manned aircraft, co-piloted SpaceShip­Two last year when it climbed to 56,000 feet and broke the sound barrier during its first successful powered flight. He last co-piloted the space plane during an unpowered “cold flow” test flight in late August, during which nitrous oxide was vented through the engine but not ignited, according to Scaled Composites’ public test logs.

Friday’s flight was SpaceShip­Two’s 55th, its 35th “free” flight and its fourth powered flight, propelled on its own. But it was the first flight powered by a new plastic-based fuel mix. Its traditional fuel had been a hybrid of a rubber compound and nitrous oxide.

Virgin and Scaled have said all parts of the spaceship underwent “extensive ground testing,” including test firings using the new fuel.

Some engineers suspect the new fuel could be to blame for the disaster. But others have questioned whether it was the result of a structural failure, possibly due to the high aerodynamic force needed to approach suborbital flight.

“If you look at the debris on the ground, you can clearly see that the nitrous tank is intact and the motor case is there,” said Tim Pickens, an engineer who worked on rockets for SpaceShipOne and Virgin Galactic. “That could not possibly be the case if the rocket itself was to blame.”

Hart said a preliminary assessment showed that the spacecraft's engine landed intact.

SpaceShipTwo has been a darling of “New Space,” the embryonic industry of start-up companies that seek not only to defy the planet’s gravity but also the decades-long dominance of spaceflight by aerospace companies such as Boeing and Lockheed Martin. More than 700 people have paid up to $250,000 each to reserve flights on the space plane, during which they would see the Earth’s curvature and the darkness of the universe and experience a few minutes of weightlessness.

The investigation could have deep consequences for the future of commercial space. The Federal Aviation Administration was restricted from regulating private spaceflight as part of the Commercial Space Launch Amendments Act, passed in 2004 in the upbeat days after SpaceShipOne’s success. Experts said the moratorium, which was extended in recent years until October 2015, could come under fire from a renewed call for regulation of the commercial space industry.

Virgin and Scaled said they are helping gather evidence and cooperating in the investigation.

“We aren’t going to push on blindly. To do so would be an insult to all those affected by this tragedy,” said Richard Branson, Virgin's billionaire founder. "We are going to learn from what went wrong, discover how we can improve safety and performance and then move forwards together.”

Virgin Galactic’s chief executive, George Whitesides, said Sunday that the company still plans to complete work on a second rocket plane by year's end. The firm has spent $500 million so far on its space-tourism work.