An official investigation into the deadly crash of a Virgin Galactic spacecraft over California last October has found a co-pilot unlocked a braking system too early.

National Transportation Safety Board (NTSB) investigators said no safeguards had been built into the system to overcome the error.

The co-pilot died when the spaceship broke apart over the Mojave Desert during the powered test flight.

The pilot was seriously injured.

The NTSB found that co-pilot Michael Alsbury, who died, prematurely unlocked the so-called feathering system, which slows the spacecraft's descent during re-entry.

The system is meant to be unlocked while SpaceShipTwo is travelling at around Mach 1.4, just before it reaches the peak of its flight path.

The manoeuvre makes the wings flick up at an angle, creating atmospheric drag to slow down the rocket plane as it re-enters Earth's atmosphere.

But in this case, the feathering occurred while SpaceShipTwo was still accelerating, generating too much force for the craft to handle.

NTSB chairman Christopher Hart said the agency had established "with a high degree of certainty the events that resulted in the breakup".

Virgin Galactic, part of British billionaire Richard Branson's Virgin Group, is now building another spacecraft.

The company says it has added an inhibitor to prevent premature unlocking during SpaceShipTwo's future flights.

Virgin Galactic aims to become the world's first commercial "spaceline".

It is offering to send customers willing to pay up to $250,000 (£160,000) for a short journey into zero gravity and a glimpse of the planet from the edge of space.

After launching from New Mexico, it is envisaged that each spaceship will take six passengers on a journey of between two and three hours just over 62 miles (100km) from Earth.

Richard Branson has said he hopes eventually to build a hotel in space