Stober, K.J., Wanyiri, J., Sanchez, A., Hooper, M., Mazumder, M., Jiwani, S., Waft, C., Lifson, M., Joseph, C., and Wood, D., "An Investigation of the Centrifugal Casting of Paraffin Wax in the Laboratory and in Microgravity," AIAA 2019-4012, AIAA Propulsion and Energy Forum, Indianapolis, IN, August 2019

Abstract

This paper describes the results of numerous laboratory-based studies as well as an initial
parabolic aircraft microgravity flight studying the relationship between rotation rate and the
ability of the working fluid to form a smooth annulus for the purposes of producing paraffin fuel grains for hybrid rockets. A multi-step research plan is discussed which aims to elucidate the challenges associated with centrifugal casting in the space environment. With the small satellite form factor in mind, a miniaturization of the casting process was successfully carried out which sought to minimize size, power, and cost. A 12V, 2A, Arduino-controlled DC brushed motor proved sufficient for casting 2 in. diameter fuel grains. The miniaturization of the centrifugal casting process is a critical step towards on-demand production of paraffin fuel grains for in-space hybrid propulsion systems and continued efforts are required to further qualify paraffin for this application. 

Three working fluids were used: paraffin wax (approximately C32H66), SAE 5W-30 motor
oil, and dyed water, in order to understand the dependence upon fluid properties. Rotation
rates of 460, 480, and 600 RPM were required to reliably form a smooth annulus in a 1g
environment in water, oil, and liquid paraffin, respectively, for working fluid outside diameters
of 1.75-2 in. A rotation rate of roughly 555 RPM was the lowest tested and consistently yielded a smooth annulus of water with 1.75 in. outside diameter and 3 in. length in the microgravity environment, but further short- and long-term microgravity testing is planned in order to determine the minimum required rotation rate under these conditions.