Design of a Superconducting Magnet for Space Propulsion on the International Space Station

Applied-field magnetoplasmadynamic (AF-MPD) thrusters are a form of high-power in-space electric propulsion for satellites and spacecraft, offering high-efficiency and high-specific impulse. These thrusters utilise electric fields and strong external magnetic fields to accelerate plasma to high velocities. The use of high-temperature superconducting (HTS) applied field modules significantly reduces the mass, power, and volume required for AF-MPD thrusters, paving the way for their use in space. To validate this key enabling technology, a team led by Paihau-Robinson Research Institute is collaborating with Nanoracks LLC to send an HTS magnet to the International Space Station (ISS). Named the 'Heki mission', an HTS magnet will be installed onto the Nanoracks External Platform (NREP) for this technology demonstration, with the goal to validate and de-risk the use of HTS magnets and flux pumps in space. This is an important step toward the in-space use and commercialisation of HTS-powered thrusters. This article provides details of the Heki mission, with a focus on the design philosophy and modelling. The HTS magnet has a 50 mm diameter warm bore to accommodate the future integration with a thruster and comprises four double-pancake HTS coils for a target 0.3-0.5 T central field. A thermal model was formulated and used to inform the conduction-cooled cryogenic design, using a miniaturised cryocooler to operate the magnet at 75 K, consuming less than 100 W of power. Additionally, magnetic shielding was an extremely important aspect of the design, to align with safety criteria of the ISS. Magnetic models were formulated and used to minimise stray field, while simultaneously optimising for weight.