gums: I'm a s/w guy trying to understand the pros and cons of when to unlock.
Not too early
At first sight unlocking just after rocket ignition seems premature and a needless hole in the cheese.
Not too late
I've seen something to the effect that the plane cannot re-enter without functioning feathers. Which gives a
reason for checking that it can unlock before passing the point of no return (wherever that is on the flight path).
To allow the feathers to be rapidly deployed for non-reentry reasons
To quote from another blog:
http://www.orbiter-forum.com/showthread.php?p=486049
...because I wonder if SS2 lost attitude control (pitch/yaw/roll) after engine ignition? That might be one reason
why Alsbury pushed the feathering system to the unlock position. Remember the SS1 1st X-prize flight (16P)
in September 2004? Mike Melvill had to deploy the feathers early after it entered a violent roll late in the engine
burn. Maybe something was wrong early in the engine burn this time and Alsbury decided to arm the system
early in order to get it deploy ASAP after it gets above the atmosphere and engine shuts down?
... or course you might proactively unlock in anticipation of such an eventuality, especially on test flights?