The thrust of a solid rocket motor (SRM) mainly depends on the combustion chamber pressure, nozzle geometry and propellant characteristics. The most commonly used method for a prescribed thrust profile design relies only on propellant grain geometry. This method is limited and does not comply with all the needs and requirements of rocket motors. Real time thrust modulation can significantly extend mission versatility and performance of SRM based missiles. One group of methods for real time thrust modulation is based on modification of the nozzle throat area, either directly by moving parts, or effectively by aerodynamic means. Another group of methods for thrust modulation deals with modification of the propellant grain burn rate by different means. Reducing the throat area, or increasing the burn rate, increases the pressure and thrust of the motor, and vice versa.
This work includes a literature survey, description of requirements, review of concepts, design and experimentation of an electromechanical system for real time thrust modulation of a SRM. The design is based on a movable pintle against a fixed nozzle. The system is integrated with an existing generic rocket motor employing a propellant with a relatively high pressure exponent (0.5). The propellant is free of metal particles in order to limit the maximum chamber temperature to 3000K and avoid extensive erosion and particle accumulation on critical surfaces. The system components are thermally insulated in order to withstand the harsh conditions of the motor operation for a sufficient amount of time. The components exposed to the most challenging conditions of the nozzle area are made of materials such as molybdenum and tungsten. System operation and thrust modulation are demonstrated successfully.
