Test and Evaluation of Cu-Enhanced, 3-D Printed ABS Hybrid Rocket Fuels

This paper presents preliminary results from a development project whereby modern 3-D printing techniques are used to fabricate sample ABS fuel grains with increasing levels of copper-metallization up to 6% Cu-mass concentrations. Homogeneously mixing a high conductivity metal such as Cu into the ABS fuel provides an efficient heat transfer mechanism, and allows radiant heat from the flame zone to be transferred deep into the fuel material. This process significantly increases the pyrolytic efficiency and regression rate of the fuels. Fabrication and manufacturing methods are described, and results of hot fire tests are presented. The top-level conclusion is that Cu-infusion of the printed fuels measurably increases the fuel regression rate, allowing for a higher thrust level with no increase in the required volume. The Cu-infusion has negligible impact on the propellant characteristic velocity and the overall system specific impulse. The increased burn rate and overall increase in solid-fuel density resulting from Cu-infusion allows a measurable increase in the propellant impulse-density. This increase in volumetric efficiency is potentially significant for small spacecraft applications where available space has a premium value. Follow-on methods that infuse lower-molecular weight and higher thermal conductivity materials like graphene and carbon-nanotubes are proposed.