Sure: intuition, not anything in that paragraph besides the simple fact that the vehicle destroyed itself during rocket powered flight. You've got a hybrid mot

Sure: intuition, not anything in that paragraph besides the simple fact that the vehicle destroyed itself during rocket powered flight. You've got a hybrid motor, it's flown a number of times. You have a program that has been going for years but still hasn't got the motor design finalized due to unknown (to us) problems. Failure modes that could destroy the vehicle include things like pressurized oxidizer tank failure, burn-through of the nozzle, burn-through of the main combustion pressure vessel, blocking of the nozzle by unburned solid fuel chunks causing over-pressure failure, and the like. The last one seems most likely, since it's likelihood is modified by modifications to the fuel (which is what they are probably changing, as opposed to the nitrous system or structure or nozzle). Obviously no one knows for sure yet. I'd love to see civilian spaceflight become a reality, so this is an unfortunate setback. I hope Virgin will be able to take the time to get it right. I hope they will look back at this accident the same way the Apollo program viewed the Apollo 1 fire, as a much needed chance to fix a lot of potential issues that needed fixing that were thought to have contributed in a fundamental way to the lack of subsequent in-flight failures.