Benjamin P. P. Mallett

The Hēki technology demonstration payload was launched to the International Space Station (ISS) in September 2025. Hēki is designed to advance the technology readiness level of two novel technologies: a high-temperature superconducting magnet and a ‘flux pump’—an inductive superconducting rectifier which energizes the magnet to field. This paper describes the rigorous pre-launch test and analysis program developed to meet ISS safety requirements and to demonstrate that these new components will survive the environment of launch and operations in space. The tests included structural analyses and random vibration testing to emulate launch conditions, thermal vacuum testing to simulate operations in space, and electromagnetic compatibility testing to verify Hēki can be operated without interfering with neighbouring experiments and electronics. Hēki successfully completed this pre-launch test program without degradation in performance, reducing the risk of failure in flight and marking an important milestone toward commercialization of these technologies for space applications.

The Robinson Research Institute is developing a type of electric propulsion for spacecraft called an applied-field magneto-plasma-dynamic thruster (AF-MPD) that is operating in the 500–1500 W range using argon as the propellant. The applied field module of the thruster is a cryocooler-cooled high-temperature-superconducting (HTS) electromagnet generating a central field exceeding 1 T. Ground-based characterisation of this type of electric thruster is challenging due to the millinewton-range thrust forces from the applied field module and numerous facility effects. This paper reports on the development of a purpose-built pendulum thrust-stand able to measure millinewton thrust whilst subjected to Tesla level magnetic flux densities and the vibrational loads generated by a mechanical cryocooler—required to maintain the HTS magnet at cryogenic temperatures between 55 and 75 K. Measurement data, postprocessing methods and uncertainty calculations are presented for direct AF-MPD thrust-measurements. These demonstrate accuracies of between ±1–2 mN (1 σ ) are achievable in the 100 mN calibration range when operating an AF-MPD thruster weighting 32 kg, with a 1 T central magnetic field and with the thruster exposed to 60 Hz oscillatory accelerations peaking at ±1.47 m s ⁻² , generated by a mechanical cryo-cooler.

In many high-temperature superconducting applications, the advantages of no-insulation (NI) coils, such as self-protecting capability and thermal stability, make them a promising alternative to insulated (INS) coils. Magnetisation loss will be generated when the coil is exposed to time-varying magnetic fields. This loss can vary with the applied field angle, magnitude, and frequency, resulting in parasitic heat loads. In this study, we investigate magnetization loss in NI and INS double-pancake and double-racetrack coils of identical dimensions, experimentally and numerically. Experiments were conducted at 77 K under external AC magnetic fields up to 100 mT, considering various field angles (0°–90°) and frequencies (73–146 Hz). The experimental results are compared with the finite element simulation results of the coils’ three-dimensional models. Interestingly, NI coils exhibit no significant angular dependence of loss within a specific field range; however, beyond this range loss increases with increasing field angles. In contrast, the loss in INS coils consistently increases with decreasing field angles across the entire field range. Coil level shielding of the magnetic field is observed in NI coils under parallel fields which is similar to a bulk superconductor. The losses in INS and NI coils are comparable under a perpendicular magnetic field, which can be attributed to the dominance of superconducting currents, as confirmed by the current and field distributions observed in simulations.

No-insulation (NI) high-temperature superconductor (HTS) coil possess inherent advantages compared with their insulated (INS) counterparts, including enhanced current density, improved mechanical integrity, thermal stability, and self-protecting properties, making them a more appealing technological choice for high-field magnets, rotating machines, and linear propulsion applications. In many such applications, the coils are exposed to time-varying magnetic fields which results in magnetization loss. This loss, which creates a heat load that could significantly impact the cryogenic system, has yet to be well characterized and understood for NI coils. In this study, magnetization loss in a double-pancake, solder-impregnated NI coil wound HTS coated conductor is investigated both experimentally and numerically at 77 K. The amplitude of the applied AC field is varied between 10 and 100 mT with frequency varying from 72 Hz - 145 Hz and field orientation varying between parallel to perpendicular with respect to the normal vector of the conductor surface of the coil. The experimental results showed no frequency dependence and no clear angular dependence with the loss essentially equal between parallel and perpendicular fields, in striking contrast to INS coils. Numerical analysis carried out in a 2D configuration for parallel fields was able to reproduce the relevant experimental data. The current density and magnetic field distributions calculated from the analysis show that the NI coil can completely shield its inner turns, attributed to the effective shielding provided by the radial and screening currents. As such the magnetization loss characteristics of NI coils are better understood as those of an HTS bulk, rather than of a coil.

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.