Second static test firing of DoubleSShot rocket motor failed big (again). CATO of the rocket motor.
We think it was a crack in the propellant grain. Increased burning surface led to over pressuring. Chamber pressure were monitored as well as thurst. The GoPro (which I donated) did not servive.
Yes, a crack would do exactly that.
Still too much internal pressure, so I would surmise that still there is either:
(1) Too much burning surface area at the same time,
(2) Too small an opening in the nozzle throat. (I presume this was designed for a certain chamber pressure?)
(3) The casing needs to be stronger steel (which would add more weight.)
I would think #1 is the best thing to change.
You could either not use the star shaped burning surface and try a smooth surface,
or make the propellant stack shorter and let there be another stage to fire after the first stage burns down.
Were you monitoring internal chamber pressure?
i assume the gopro did not survive . why do you think it failed ?