Modeling and Simulation of In-Orbit Centrifugal Casting of a Paraffin Wax Grain Inside a 3U CubeSat

The work conducted by the authors, and described herein, investigates the possibility of performing centrifugal casting of paraffin into annular shapes while the spacecraft is orbiting the Earth. The adopted strategy involves the use, at the beginning-of-life, of the wax as a thermal insulator and, at the end-of-life, recast it as a fuel to allow a controlled re-entry of the satellite. The experiments currently conducted by the Space Enabled Research Group at 1g conditions have been characterized by the use of paraffin wax and beeswax as working fluids, with rotation rates ranging from 50-1500 rpm, and an initial temperature of 75-100 °C. All data relative to the paraffin wax has been derived experimentally by the Space Enabled Research Group. The polymer considered in this work has the formula of C32H66. The workflow is conceived such that the wax will be melted and conveyed into the combustion chamber, which will be spun by a DC motor, allowing the wax to be shaped into a hollow cylinder. Future extensions of this research effort will involve the design of a proper thermal bus capable of melting and conveying the wax inside the combustion chamber. This work is developed under the assumption that the wax is already inside the combustion chamber, and the simulations conducted take into account the grain formation phase and the re-entry trajectory design. The model developed to deliver the needed results is based on the propagation of a quasi-ISS orbit under the two-body problem assumption, including all relevant perturbations. The orbital dynamics is, then, coupled with the true attitude, measured by on-board sensors (a magnetometer and a Sun sensor are considered). At last, these two are coupled with a multi-node thermal model used for a transient thermal analysis, taking into account direct solar radiation, Earth albedo and infrared radiation, as well as internal power dissipation due to on-board electronics. It is shown that the stability of the spacecraft can be maintained with minimum effort, especially thanks to the low inertia of the rotating device. Also, with a passive thermal control based upon the use of a Multi Layer Insulator, the wax endures the eclipse-sunlight cycles and is kept below its melting temperature. The deorbit of the spacecraft can also be accomplished by considering the theoretical performances of the paraffin wax-based engine with one burn only, which is designed to lower the altitude of the spacecraft enough to induce atmospheric re-entry.