Which is mine.

The fact that the roll problem seems to get worse as the burn progresses could be a result of:

1. higher acceleration as the vehicle gets lighter
2. less atmosphere as altitude increases, with correspondingly less aerodynamic control
3. increasing thrust asymmetries as the nozzle erodes

I’m guessing that it’s a combination of all of the above and that the vehicle doesn’t have enough RCS control authority to muscle past the (unplanned) thrust asymmetries. The pilot is probably fighting to keep the nose pointed forward, and as Brett Buck suggested, yaw and pitch moments are getting coupled into roll.

If so, this is a problem that could be solved with a better engine nozzle design, thrust vector control on the main propulsion (a more expensive fix), more powerful RCS jets, or all of the above.

As I said previously, though, this shouldn’t necessarily prevent them from winning the prize, as is.

says it was caused by a “known deficiency”:

The unplanned corkscrew maneuver Wednesday was characterized as a “spin-stabilized” roll. Rutan said there