Throttleable Solid Propellants Through Embedded Shape Memory Alloy and Resistance Wires

ABSTRACT Solid propellants are used in propulsion systems for their high performance, feasibility to manufacture, long shelf life, and ease of storage and handling; however, they are limited by the inability to actively control the burning rate. The overall burning rate of solid propellant is predetermined based on geometry (surface area) and operating conditions such as initial temperature and pressure. In this article, we propose two methods to tailor the rate of pressurization ( dP / dt ) of solid composite ammonium perchlorate/hydroxyl‐terminated polybutadiene (AP/HTPB) propellants using embedded shape memory alloy (SMA) and Nichrome wires through Ohmic heating. First, Nitinol wires, coiled into a spring, are demonstrated to increase the burning surface area upon expanding inside of the solid propellant. The result of this geometry modification was shown to increase the dP / dt by over 180%, thereby throttling the propellant sample. Second, Nichrome wire was embedded in the samples to demonstrate that varying the heat flux (between 24.4 and 153.6 kW/m 2 ) also affects the rate of pressurization under heated conditions. Preheating the solid propellant in this manner increased the rate of pressurization from 69 to 110 MPa/s. This concept is useful for many applications such as in electro‐explosive devices (EEDs) or actuators where it is desired to have the resulting gas expansion rate tailored.