[island911]

Yeah, the hybrid solid rocket engine was the most intriguing thing about SpaceShipOne.

Have you heard any insider analysis of the failure? Seems unusually quiet on that front.

In the meantime... Looking at the engines... compared to the X15

1943 began the development of the first rocket motor of the X15 -they used 2 of these reaction motors for one X-15. Reaction Motors XLR11 - Wikipedia, the free encyclopedia

Replaced in 1960 with one XLR99

This 1960 engine, it appears, puts out 95% thrust of SS2 engine, but can sustain burn time of 150 seconds, vs the needed 60 seconds burn of the SS2 engine.

Looking at those rough thrust numbers and the relative sizes of the SS2 vs the X-15 (like a shuttle-cock vs a dart), and seeing the altitude records of the X-15... I dunno... maybe that SS2 is a lot slippery (at Mach >1) than it appears.