Media playback is unsupported on your device Media caption NTSB acting chairman Christopher Hart outlines the investigation process

The investigation into the Virgin Galactic spacecraft crash in California's Mojave Desert could take about a year, the head of the US transport safety agency has said.

Christopher Hart said Virgin Galactic would be able to conduct further test flights while the investigation took place.

SpaceShipTwo broke up in mid-air during a test flight on Friday.

One of the pilots was killed and the other injured.

Virgin chief Sir Richard Branson says he is "determined to find out what went wrong" and learn from the tragedy.

The US National Transportation Safety Board team had completed its first full day of investigation, Mr Hart said, and would be examining evidence at the scene for four to seven days.

He said the craft's debris was spread over an area measuring five miles from end to end.

He told a news conference the test flight had been "heavily documented" and his team would have to trawl through "extensive data", which was why the full investigation could take "about 12 months or so".

He said there were six cameras on the craft itself, with another three on its launcher, an aircraft called WhiteKnightTwo, although it was unclear whether SpaceShipTwo's cameras had been found.

Image copyright Getty Images Image caption The pilot who died was named as Mike Alsbury

Media playback is unsupported on your device Media caption Virgin Galactic founding astronaut Per Wimmer: "Space is difficult"

The co-pilot who died when SpaceShipTwo disintegrated shortly after take-off was named as 39-year-old Michael Alsbury.

The pilot who survived was identified as Peter Siebold. Scaled Composites, the company both pilots worked for, said Mr Siebold, 43, was "alert and talking with his family and doctors".

Mr Hart said his team were waiting for doctors to allow them to interview Mr Siebold.

The pilots

Image copyright AP Image caption Peter Siebold, left, survived the incident but his co-pilot, Michael Alsbury, died

Michael Alsbury

Aged 39

Married with two children

15 years of flying experience

First flew in SpaceShipTwo in 2010

Flew craft's first rocket-powered run in April 2013

Peter Siebold

Aged 43

Married with two children

Received pilot's licence when just 16

Started working for Scaled Composites in 1996

Had spent 2,000 hours in 35 different fixed-wing aircraft

Will crash set back space tourism?

'A massive setback'

Speaking earlier at the at the Mojave Air and Space Port, where the craft was being developed, Sir Richard said "nobody underestimates the risks involved in space travel".

Virgin Galactic had hoped to launch commercially in 2015. It has already taken more than 700 flight bookings at $250,000 (£156,000) each, with Sir Richard pledging to travel on the first flight.

"It's a horrible day for Virgin Galactic and for commercial space travel. It's a massive setback," Sir Richard told the BBC.

He said the company had to pick itself up, find out what went wrong and see whether they can fix it.

"I'm hopeful we'll be able to overcome the problems," he added.

Media playback is unsupported on your device Media caption Sir Richard Branson: "It's a massive setback"

The spacecraft was flying its first test flight for nine months when it crashed near the town of Bakersfield.

Virgin Galactic said SpaceShipTwo had experienced "a serious anomaly" after it separated from WhiteKnightTwo.

The space craft was using a new type of rocket fuel never before used in flight, although officials said it had undergone extensive ground testing.