I have been reading lately that there has been serious concern about the liquid-solid hybrid engine used in Spaceship 2. In 2007 there was a nitrous oxide explosion that killed three people.
On 26 July 2007, during the early rocket testing phase, an explosion occurred during a propellant flow test at the Mojave Air and Space Port. The test included filling the oxidizer tank with 4,500 kg (10,000 pounds) of nitrous oxide, followed by a 15-second cold flow injector test. Although the tests did not ignite the gas, three employees were killed and three injured, two critically and one seriously, by flying shrapnel.
parabolicarc.com is a pretty good source of information on New Space. Here are some tweets:
Parabolicarc.com @spacecom Oct 31
I had deep concerns over both the new plastic/nitrous oxide engine and so did other sources familiar with the testing. #SpaceShipTwo
The concerns were three fold. One, that it wasn't being tested sufficiently on the ground before it was flown. #SpaceShipTwo
Second: that modifications required to ship to accommodate the new engine introduced additional complexity and failure modes. #SpaceShipTwo
Third, handful of test flights they were doing with new #SpaceShipTwo engine before putting Richard and Sam Branson aboard were insufficient
Let me stress2 things: one, we don't know what happened yet, so I'm not making a snap judgment about what caused the accident #SpaceShipTwo
Second, these concerns about the new engine were not mine alone. Folks much smarter and knowledgble than me were worried. #SpaceShipTwo
I predict you will be hearing a lot more about these concerns and the problems they were having in the days and weeks ahead #SpaceShipTwo
Scaled's Kevin Mickey called the engine change "a minor nuance". He rushed out of the press conference once it was over.
Mickey claimed "minor nuance" engine change thoroughly tested on ground. Tried to ask for details, but presser ended quickly & Mickey left.
Ken Brown was taking photos through the entire incident. Tracked one large piece of debris down to the lakebed. #SpaceShipTwo
I heard Ken say, "They're in trouble." And then "They're tumbling. Ken's pictures will be very crucial to understanding it. #SpaceShipTwo
Just talked to Ken Brown. Pictures show Engine fired fine, then there's a white plume. He thinks the nitrous oxide tank blew. #SpaceShipTwo
I am a huge supporter of commercial space, most especially Space X. But I think that accidents like this give the whole sector a bad name. Virgin Galactic/SC have been building this ship for 10 years, and they still don't have a viable engine. That is not a good sign.
Contrast that with Space X, which in about the same amount of time has built the Falcon 9, which has a string of 13 straight successes (touch wood). It seems to me that not all space companies are created equal.