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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 ‘Hēki 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 Hēki 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.

The “Hēki magnet mission” is a collaboration between the Paihau-Robinson Research Institute (Wellington, New Zealand) and Nanoracks (Houston, Texas, USA), aiming to deploy a high-temperature superconducting magnet aboard the International Space Station to demonstrate the operation of miniaturised cryocoolers, HTS magnets, and flux pumps in space. This paper focuses on the quench tolerance of non-insulated (NI) HTS magnets within the context of the Hēki mission. NI HTS coils can enhance quench resistance and tolerance because the absence of turn-to-turn insulation allows current sharing during quench events, improving thermal stability and reducing the risk of hot spots. Simulations under typical space conditions demonstrate that NI magnets can manage quench events without complex protection circuits, which is advantageous for the simplicity and reliability required in space applications. These findings support the feasibility of employing NI HTS technology in future spacecraft propulsion systems.

Magnets using high-temperature superconducting (HTS) tapes have been proposed for use in several space-borne applications. In particular they are well suited for use in applied-field magnetoplasmadynamic (MPD) thrusters for satellites as they can achieve a high magnetic field intensity in a suitable volume and mass range and can be cooled by commercial-off-the-shelf space-heritage Sterling cryocoolers. However, the stray fields produced by such magnets can be problematic, in that they can generate undesirable torque through interaction with the Earth's magnetic field and can interfere with other on-board systems and electronics. We present the design and initial mass optimization of a passive DC magnetic shield for a small HTS magnet that could fit within a 12U cubesat but will in the first instance be tested on board the International Space Station (ISS) in 2025. The magnet has a 62 mm diameter clear bore, compatible with a small MPD thruster, and will generate the target central field of at least 300 mT. The stray field from this magnet would be 1.7 mT at a distance of 220 mm from the center of the magnet and a magnetic shield is required to reduce this to 0.3 mT to comply with ISS specifications. We describe active and passive shield options, and choose ultimately to construct a passive shield from magnetic low-carbon steel and confirm that this is able to achieve the required stray-field level.