Restricting partially and temporally the initial propellant burning surfaces with thin HTPB inhibitors realized a new method of controlling the chamber pressure rise rate at ignition. The merits of the method are to be manufactured easily, to hardly affect the whole motor thrust pattern, and low in cost. The ground firing tests with sub-scale motors have verified the method to be reliable and flexible.
The principal concept of a "staged ignition system" is to replace the ignitor main charge by an "ignition cavity" perforated at the fwd.-end of the motor propellant grain. This 'ignition cavity' generates the combustion gas required for igniting the remaining portion of the grain. It has been employed in the designs of two ISAS' solid motors now under development and has contributed to simplification of the ignition systems.