Development of a Head-End Ignition System for the Sustainer Motor of a Two-Stage Sounding Rocket

The mission objective of Georgia Tech Experimental Rocketry (GTXR), a project team of the Ramblin’ Rocket Club, is to reach the Kármán Line using a two-stage sounding rocket. The second stage motor, known as the sustainer, implements head-end ignition with an igniter that can operate in high-altitude, low-pressure environments. The solid propellant in the motor requires a pressure buildup of 81 psi in order to begin burning. From previous investigations, GTXR found that commercial off-the-shelf (COTS) igniters are at risk of firing from electrostatic discharge, making them unreliable and unsafe. As an alternative, the team developed an ignition system using nichrome wire to combust Fe2O3 and BKNO3 (known as Iron (III) Thermite and BPN), consequently initiating the combustion of propellant cast into the igniter, which generates the required pressure to burn the motor’s grains. To develop the igniter, the team reviewed the properties of the combustibles, iteratively tested the current and pressure thresholds needed for ignition, and sized the igniter for overall vehicle design constraints. Initial testing indicated that a minimum of 5A of current was necessary for ignition and provided a preliminary understanding of the pressure required and generated by the igniter. The findings of this investigation are instrumental in the development of future head-end ignition systems, outlining ideal chemical compositions and the metrics for reliable ignition. Design specifications and further characterization of ignition pressures through vacuum testing are later discussed and analyzed.