Just a couple of hours go, in a series of four tweets, Virgin Galactic announced the loss of SpaceShipTwo due to an in-flight incident.
Reports indicate that at least two people were aboard; one person was killed on impact, another suffering a major injury. SpaceShipTwo flies with two pilots - it is unknown whether any other people were on-board.
SpaceShipTwo is the sub-orbital vehicle that is intended to fly to the very edge of space (around 100km high) where paying passengers are able to clearly see the curvature of the Earth and to experience weightlessness. To date over 800 have paid in full, or made a deposit on such a flight.
According to reports, this was the first flight since January and was intended to test an alternative plastic-type of fuel grain for the hybrid rocket motor.
Image: KDVR FOX31 Denver
Far from a short-term program, Virgin Galactic noted in their twitter feed that this was SpaceShipTwo's 55th flight, and WhiteKnightTwo's 173rd.
Update: NASA Administrator Charles Bolden has said, "On behalf of the entire NASA family, I offer our deepest condolences to the family and loved ones of the pilot lost in today's accident involving Virgin Galactic's SpaceShipTwo, and we are praying for a speedy recovery of the other pilot.
"While not a NASA mission, the pain of this tragedy will be felt by all the men and women who have devoted their lives to exploration. Space flight is incredibly difficult, and we commend the passion of all in the space community who take on risk to push the boundaries of human achievement."
(also, edited for minor error - thanks TachyonRider)