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Second static test firing of DoubleSShot rocket motor failed big (again)

Second static test firing of DoubleSShot rocket motor failed big (again). CATO of the rocket motor.

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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 ?