A Throttling Solid Propellant Rocket Motor with Adaptive Thrust Control

This proposal addresses a Phase II program to demonstrate the validity of combining two techniques for solid rocket motor control: a moveable pintle for thrust control and an aerospike plug nozzle for nozzle efficiency over a 15:1 turn-down range. The goal of this program is demonstration of a solid propellant motor which can be throttled multiple times between full boost thrust and near-extinguishment, while maintaining near-optimal nozzle efficiency over this throttling range. The use of moveable pintles to control flow rate and grain burn rate for thrust control, are well developed, but nozzle efficiency suffers at low thrust due to boundary-layer separation in conventional bell or conical nozzles. Plug nozzles have long been recognized for their ability to compensate for a wide variation in altitude, or nozzle pressure ratio, which provides improved nozzle efficiency in a throttled solid motor. Results during GHKN's Phase I program to evaluate the feasibility of this approach indicate that the aeropintle design will meet the oveall program requirement. The nozzle/aeropintle contours will be optimized by CFD analysis and cold flow testing prior to design, fabrication and hot fire testing of a variable thrust solid motor using the aeropintle nozzle configuration.