The rocket belonging to hedonist billionaire Sir Richard Branson's space tourism venture exploded in a fireball during a test flight before crashing in the Mojave Desert in California.
A Virgin Galactic spokesman said the rocket "suffered a serious anomaly" after a test flight conducted by partner business Scaled Composites.
Parabolicarc.com, saw SpaceShipTwo's engine sputter when it first came to life during the test flight, after WhiteKnightTwo released it.
"It looked like the engine didn't perform properly," Messier told Space.com's Tariq Malik. "Normally it would burn and it would burn for a certain period of time. It looked like it may have started and then stopped and then started again."
Then, Messier saw the ship break apart. "I didn't see an explosion, but it definitely broke into pieces," he added.
Sir Richard wrote on Twitter: "Thoughts with all @virgingalactic & Scaled, thanks for all your messages of support. I'm flying to Mojave immediately to be with the team."
"We are going to be supporting the investigation as we figure out what happened today. We are going to get through it."
"The future rests in many ways on hard days like this but we believe we owe it to the folks who were flying these vehicles as well as the folks who have been working so hard on them to understand this and to move forward."
He said it was the first time the rocket had been flown using a new fuel formulation.
"It had been proven and tested on the ground many times," he added.
Mr Whitesides said the pilots were employed by Scaled Composites. He added that the injured pilot was "as well as could be expected".
SpaceShipTwo has been under development at Mojave Air and Spaceport .
This venture was not about the advancement of science or for the benefit of humankind. This was a 'for profit' venture.
The pursuit of fame, increased revenues and bottom-line profits by Virgin's hedonistic billionaire figure-head has now led to the premature and terrifying death of one man and crippling injuries and pain of another.