Apollo, Ansari and the Hobbling Effects of Giant Leaps

From the astonishingly prescient article, which was written shortly _before_ today's disaster:

  The Achille’s Heel
  ...
  But, there was a deeper, more fundamental problem that
  Rutan wasn’t even aware of, one that has bedeviled the 
  program to this day.
  ...
  Rutan steered away from liquid engines; he viewed them 
  as being overly complicated and possessing too many failure
  modes. Instead, he developed a novel hybrid motor that used
  nitrous oxide (laughing gas) to burn a large chunk of
  rubber fuel. SpaceShipOne was the first time a hybrid 
  engine had been used in human spaceflight.
  ...
  Rutan came out of SpaceShipOne’s short flight test program 
  believing the hybrid engine was simple and safe, and that
  it could be easily scaled up for the much larger 
  SpaceShipTwo. He was wrong on both counts.

  The first belief was shattered on a hot summer afternoon of
  July 26, 2007. Scaled engineers were conducting a cold flow
  of nitrous oxide that did not involve igniting any fuel.
  Three seconds into the 15-second test the nitrous tank
  burst, resulting in a massive explosion that destroyed the
  test stand and killed three engineers. Three others were
  injured.
  
  Explosions are not unusual in engine development. However,
  it is rare that anyone dies in them. Safety procedures call
  for the evacuation of personnel to a safe area before any
  tests begin. That was not done in this case; the dead and
  injured were part of a group of 11 people standing near the
  test stand.

  Following the accident, Rutan and Scaled Composites claimed
  ignorance. “The body of knowledge about nitrous oxide (N2O)
  used as a rocket motor oxidizer did not indicate to us even
  the possibility of such an event,” Scaled said in a press 
  release. The media and Scaled supporters have largely 
  parroted this explanation.

  A team of experts experienced in working with nitrous oxide
  reviewed the accident and disputed the claim. “This would
  seem to indicate either a lack of due-diligence in 
  researching the hazards surrounding N2O (negligence) or a
  wilful disregard of the truth,” they concluded.

  Whatever Scaled’s culpability, there is no dispute the
  accident delayed the program significantly. Work on 
  SpaceShipTwo was put on hold while engineers investigated
  the cause of the explosion. Hybrid engine tests would be 
  delayed for nearly two years.

  Once engine tests began again in April 2009, engineers 
  would discover that Rutan’s other assumption was wrong. The
  hybrid engine just didn’t scale very well. The larger the
  engine became, the more vibrations and oscillations it
  produced. As engineers struggled to find a solution, Scaled
  Composites and Virgin Galactic quietly began work on
  alternative motor designs.

  The failure of the hybrid to scale led to another problem. 
  SpaceShipTwo had already been designed and built. The
  dimensions of the ship, the size of the passenger and crew
  cabin, the center of gravity…all those were already set.
  So, engineers now had to fit an engine within those
  parameters that could still get the vehicle into space.

  This is the reverse of how rocket planes are typically
  designed. Engineers figure out the engine first and then
  build the ship around what it can do. Rutan – a novice in
  rocket propulsion who had hit a home run with SpaceShipOne
  – got the process backward, resulting in years of delays. 
  This failure would cause numerous headaches.

  The rubber hybrid engine did get a workout in three flight
  tests, but the vibrations and oscillations it produced were
  so severe the motor couldn’t be fired for more than 20
  seconds. The engine was sufficient to get SpaceShipTwo
  through the sound barrier, but it couldn’t get the vehicle
  anywhere near space.

  It was not until May 2014 – after spending nearly a decade
  on the program, and a reported $150 million on engine 
  development – Virgin Galactic announced it would be 
  switching to a different type of hybrid engine, one powered
  by nitrous oxide and plastic. They are hoping for much
  better performance in flight.

  By then, Rutan was gone, long since retired to a spread in
  Idaho. It was for others to make the new engine work and
  fix the mistake he had made.
  ... 
  Flush with success and not knowing what he didn’t know, 
  Rutan bet the future on a poor propulsion system that he 
  never took the time to fully test, much less understand. 
  His failure to grasp the nature of technology he selected 
  cost three men their lives.

Wow, he wrote that yesterday. Seems especially prescient given that he's on the ground in Mojave today.