Story highlights A lever on SpaceShipTwo was moved earlier than it should have

But the NTSB says the cause of the accident is still unclear

A memorial fund is set up for Michael Tyner Alsbury

The co-pilot "is alert and talking with his family and doctors"

A lock-unlock lever on the doomed Virgin Galactic SpaceShipTwo was moved earlier than it should have been, the National Transportation Safety Board said Sunday night.

But the agency's acting chairman stressed it was unclear whether pilot error, mechanical problems or a host of other possibilities caused the spacecraft to disintegrate in the air.

"We are still a long way from finding a cause. We are months and months away," NTSB Acting Chairman Christopher Hart said.

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And despite a debris field spanning 5 miles, investigators have found almost all the parts of the spacecraft needed for the investigation, Hart said.

The accident killed co-pilot Michael Tyner Alsbury, 39. A memorial fund has been set up for him.

Co-pilot alert and talking

The surviving co-pilot is "alert" and speaking, the company that partnered with Virgin on the test flight program said Sunday.

"Peter Siebold, the director of flight operations at Scaled Composites, was piloting SpaceShipTwo. He is alert and talking with his family and doctors," the company said in a statement.

"We remain focused on supporting the families of the two pilots and all of our employees, as well as the agencies investigating the accident."

NTSB investigators have yet to interview Siebold.

"We have not because doctors did not recommend we do an interview at this stage," Hart said.

Inflight breakup?

SpaceShipTwo disintegrated Friday, just two minutes after the space plane separated from the jet-powered aircraft that carried it aloft.

At the time, it was about 45,000 feet above, and about 20 miles northeast, of Mojave, California.

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While the NTSB hasn't determined what broke the test aircraft apart, "when wreckage is dispersed like that, it indicates the likelihood of in-flight breakup," Hart said.

A team of 13 to 15 investigators from the National Transportation Safety Board will be on site in the Mojave Desert for about a week. But analyzing the data from the test aircraft will take much longer.

'We're going to learn'

Virgin Group founder Richard Branson said Sunday he didn't personally know Alsbury, but had the privilege of knowing Siebold.

"Mike was a dear friend and inspiring colleague to the many, many friends he left behind. My heart goes out to his parents, his wife and children, his sister and the rest of his family and friends," he said about Alsbury.

He wished Siebold a speedy recovery.

On Saturday, Branson said that the company is "determined to find out what went wrong."

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.

Years of flight experience

The two test pilots had both had a great deal of flight experience.

Alsbury worked at Scaled Composites and logged more than 1,600 hours as test pilot and test engineer in Scaled aircraft.

Siebold had worked for Scaled Composites since 1996 and had 17 years and more than 2,000 hours of flight experience.

Both had degrees in aeronautical engineering from California Polytechnic State University.

As for the program itself, SpaceShipTwo had flown 55 times, 35 times on its own, Branson said in a statement. WhiteKnightTwo, the jet-powered "mothership" charged with transporting SpaceShipTwo to altitude, has flown 173 times, Branson said.

"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. "Space is hard -- but worth it. We will persevere and move forward together."

Future of the program

For years, Virgin Galactic has planned to sell trips in which SpaceShipTwo would transport passengers about 62 miles above Earth -- the beginning of outer space -- and let them experience a few minutes of weightlessness before returning to the ground.

It's unclear what the failure of the space plane will mean for the program. Virgin Galactic planned to send paying customers on SpaceShipTwo as early as next year.

The company released a statement late Sunday.

"At Virgin Galactic, we are dedicated to opening the space frontier, while keeping safety as our 'North Star'. This has guided every decision we have made over the past decade, and any suggestion to the contrary is categorically untrue," it said.

"Now is not the time for speculation. Now is the time to focus on all those affected by this tragic accident and to work with the experts at the NTSB, to get to the bottom of what happened on that tragic day, and to learn from it so that we can move forward safely with this important mission."

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.