Hēki: A High Temperature Superconductor Technology Demonstration Mission to the International Space Station

High-temperature superconducting (HTS) electromagnets have been identified as a key enabling technology for many new applications in space such as radiation shielding, electric propulsion, and science instruments. Despite their potential benefits, to date there have been no public examples of HTS electromagnets operating in space. A consortium led by Paihau-Robinson Research Institute intends to fly a technology demonstration mission called Hēki to the International Space Station (ISS) for operation in 2025.Hēki’s primary magnet consists of four double-pancake HTS coils with warm bore of 52 mm and targets a 0.3-0.5 T central field. It will be conduction-cooled to its 75 K operating temperature using a mechanical cryocooler. During the cool down of the magnet, power will be limited to 100 W, while steady state operation is expected to be less. Most of this power is consumed by the cryocooler. The magnet itself will be energized by a superconducting power supply called a flux pump which draws very little power as it builds the magnet current to 12-18 A over several hours.An important element of the experiment is the inclusion of two TimePix radiation sensors – one near the location of the highest curvature of the magnetic field and another near the magnetic field minimum. These will be monitored as a function of the magnetic field and provide an in-space demonstration of the influence of strong HTS fields on radiation.Another significant challenge is the management of the stray magnetic field. We plan to demonstrate a mass-optimized magnet shield that will ensure that the high magnetic field generated by the HTS solenoid does not interfere with key parts of our own experiment (e.g. the cryocooler’s compressor) or violate the stray field requirements for externally mounted hardware on the ISS. Paihau-Robinson Research Institute has partnered with Nanoracks LLC to host our experiment on the Nanoracks External Platform (NREP).The Hēki mission is a part of a larger project to mature the technology of a type of electric propulsion called applied-field magnetoplasmadynamic (AF-MPD) thrusters. While these systems have been demonstrated on the ground for over 50 years, the technology to produce the very high magnetic fields was not compatible with operation in space due to the need for bulky and power hungry magnets. Recent advances in HTS materials, cryocoolers and flux pumps have encouraged a new look at this technology.The HTS magnet thruster under development has been dubbed ‘Kōkako’, after a native New Zealand bird with a blue wattle reminiscent of the blue glow emitted by the operating plasma thruster. Since the HTS technology demonstration is an important preliminary step to the creation of the Kōkako thruster, it has been dubbed the ‘Hēki mission’, hēki being the word for egg in te reo Maori, the language of the indigenous people of Aotearoa/New Zealand.