CubeSats (Cube Satellites) are a fast-growing area due to their associated low cost and advancements in capabilities. However, with the increasing levels of power and miniaturisation of electrical components, the heat loads within next generation high-powered CubeSats are increasing. This is a challenge for CubeSats since they have limited surface area available to radiate heat to space due to their small size and limited capacity to manage the transient heat loads within a demanding thermal environment.

Phase Change Material (PCM) heat sinks can provide thermal management for CubeSats by absorbing the peak thermal loads and dissipating the waste heat to space during periods of downtime, thereby enabling the use of high-powered electronics. PCMs use latent heat to store thermal energy, typically in the solid to liquid phase transition. The key advantage of PCMs is their large Thermal Energy Storage (TES) capacity over a narrow temperature range, which allow compact and lightweight PCM heat sinks. For CubeSat applications, PCM heat sinks have been predominately investigated with paraffin PCMs, due to their ideal melting range and high latent heat of fusion per unit weight.

However, paraffin PCMs suffer from inherently low thermal conductivity. To ensure adequate heat dissipation from high-powered electronics, heat transfer enhancement techniques are required. With the expansion of metal additive manufacturing processes, this research investigated the viability of enhancing PCM heat transfer with additive structures. Additive manufacturing offers heat transfer enhancement structures not before possible with traditional manufacturing methods, which have the potential to improve PCM heat transfer whilst minimising the weight of the PCM heat sink.

This research firstly analysed the PCM thermal performance of additive structures using numerical modelling. The traditional fin structure for PCM heat transfer was compared to a struct-based additive structure and a sheet-based organic additive structure. The selected structures were compared for a conceptual 50 W PCM heat sink design and a base size analysis was also performed pushing the limits of allowable additive manufacturing minimum feature sizes. The numerical investigation found that the gyroid sheet-based additive structure demonstrated the best overall heat transfer performance for transferring heat to PCM in three directions. In addition, the numerical modelling also confirmed that smaller base sizes improved the performance of PCM heat sinks.

Secondly, the research explored metal additive manufacturing for PCM heat transfer and containment. This research focused on Bound Metal Deposition (BMD), a recently developed metal extrusion method. BMD was chosen for this investigation since copper material for high thermal conductivity heat dissipation was recently released and the metal extrusion technique provided the unique capability of fabricating structures without the need to remove fine metal powders from internal cavities. The research investigated the material properties of BMD copper and the printability of the sheet-based gyroid structure. It was found that BMD provided the ability to print the desired gyroid base sizes with a relatively high thermal conductivity (average 353 W/m·K). However, BMD was unable to provide leakproof PCM containment in a vacuum, because of the toolpath porosity inherent in the manufacturing process.

Finally, a hybrid manufacturing solution was evaluated to overcome the challenges identified with the BMD additive manufacturing technique. To provide leakproof PCM containment, a conventional metal case was combined with the benefit of an optimised BMD copper internal additive structure. A prototype PCM heat sink was developed and tested in a vacuum chamber and demonstrated that effective heat dissipation could be achieved from a high heat load using paraffin PCM. A validation model using the numerical methodology employed in this Thesis was also compared with the testing results and showed good alignment for the temperature response at the heat input.