Leveraging microgravity to investigate earth- And space-based centrifugal casting of wax

Abstract

A multi-year research effort aimed at increasing understanding of the centrifugal casting process of wax fuels for hybrid chemical propulsion in multiple thermal and gravitational environments is described. As both radiative and convective heat transfer drive the casting process, the suborbital and orbital microgravity environments are critical to disentangling these contributions to heat transfer away from the fuel. The experimental effort comprises testing on multiple platforms, including the ambient atmosphere of the laboratory, as well as various mobile microgravity platforms. Testing onboard reduced-gravity aircraft facilitates increased understanding of how these types of fluids perform in the microgravity environment, while a suborbital spaceflight and orbital platform under standard atmosphere allow for longer-term observation of natural convection sans buoyancy. An orbital platform subjected to the space environment facilitates understanding of the contribution of radiation to the heat transfer away from the liquid fuel. Each progressive testing environment requires updates to the experimental setup in order to accommodate respective physical and electrical constraints which are described in detail herein. An image analysis routine was developed in order to automate post-processing and determine the solidification front speed for each test. A rotation rate actuation routine is in development which aims to improve the accuracy of the centrifuge control system by leveraging electromagnetic sensing and feeding back rotation rate measurements to the motor driver. Preliminary modeling work was conducted which aims to elucidate the fundamental physics of the centrifugal casting problem; specifically, the impact of rotation rate, material properties, and environmental conditions on the heat transfer and fluid mechanics which constitute the larger casting problem. Both paraffin wax - a solid fuel with two decades of heritage - and the more novel beeswax are considered in this study.