Originally Posted by
silverstrata
From what I understand, the solid-gasseous rubber/polymer engine was suffering from surges or stuttering, especially at start up or shut down.
One reason for using a hybrid is that this doesn't lead to an explosion. I.e. the engine is more tolerant to propellant cracks. All these motors seem to suffer from surges.
Unless the surges were so severe that it had an effect on other parts of the motor causing the flame to reach the liquid fuel it doesn't explain what happened.