Rob Coppinger has some thoughts on SpaceShipOnePointFive.
I suspect that Alex, and perhaps Sir Richard, are now regretting their decision to not take advantage of the bird in the hand, holding out for the flock in the bush. They probably (in fact, almost certainly) didn't anticipate the development problems they'd have with the propulsion system, though they were warned. I suspect that they (like Burt) drank too much of the hybrid koolaid, and were lulled into complacency by the success and (apparent, though this was an illusion) safety of the SpaceShipOne engine.
As for the comment that a passenger wouldn't have paid the costs of the flights, I don't buy it. They could have charged much more than a couple hundred thousand for the first several, perhaps even few dozen, flights. But we'll never know.
It's not "hybrid" kool-aid unless you mean the idea that hybrids are so simple that you can build them without hiring engineers familar with the art.
Several people that have a lot of experimental rocketry experience are much more afraid of Nitrous hybrids than anything else. A gentleman I've seen using a hand held fire extinguisher on a burning LOX tank is very wary of nitrous hybrids almost to the point of parnoia.
Several people in the amateur experimental rocketry community have had unexplained nitrous hybrid detonations at ignition. The unsupported working theory is that even minor nitrous leaks in the area of rubber based hybrid grains can make a detonable substance. The nitrous somehow permeates into the rubber. then when you light the hybrid it goes bang rather than wooosh...
Paul, the Scaled test that killed people was a cold-flow test over (AFAIK) an unfueled test article. So I'm not sure that your comment is relevant. At least the latter part.
Personally, I was surprised that Rutan didn't use SS1 or a copy of it to refine the aerodynamics and develop a better flight control system. SS1 had excessive dihedral that caused some of the stability problems like the famous corkscrewing flight. An SS1.5 would've preserved the original for the Smithsonian and allowed for a cheaper way to improve the design before going all the way to SS2.
In addition, uncontrollable rolls have occurred at the peak of almost all of the flights. This is due to control ineffectiveness in the thin upper atmosphere and side forces imposed on the aircraft by the feathering mechanism. Rutan admitted poor design (Dornheim, “Spin,” 2004) when describing the causes of the upper atmosphere rolls, “SpaceShipOne has too much dihedral effect, or that sideslip causes too much rolling moment. This makes it too sensitive to side gusts or rudder input, which is exacerbated by the short wingspan with low roll inertia and damping.” In classic fashion, Rutan declined to make improvements to his design (Dornheim, “Spin,” 2004) saying, “the problem has to be lived with in SpaceShipOne.”
Scaled & Virgin could very well have met exactly the same troubles with a SS1.5 as they have with SS2. The SS2 survives on the promise but I'm not sure a SS1.5 would have.
At least that's the way I'm thinking based on the notion that in part the WK2/SS2 plays a role as a flagship product for the Virgin group. I think they made the right call.
Ask any drag racer and they will tell you full and well the potential for Nitrous Oxide detonation. When I used to turn wrenches I worked in the pit on the shop owner's drag truck. He had a 250 HP plate system and a 400 hp fogger system on a 454 punched .30 over.
When NO2 has fuel to munch on it is generally fine. However, when you run into a lean condition from a fuel pump that croaks or a collapsed fuel line then the nitrous detonates rather violently. In fact, I saw a guy with a '71 Mach 1 Mustang blow his intake manifold up and out of a fiberglass hood. Most nitrous systems come with a relay and fuel pressure sensor that closes off a valve to the nitrous bottle if the fuel pressure drops.