New Zealand Team Prepares to Test Electric Propulsion System

2025-02-24 09:06:00
spectrum.ieee.org

Nestled at the foot of a steep, forested hill, 16 kilometers outside Wellington, New Zealand, is a rather unassuming building; one among many on a research campus that was first established in the 1940s. From outside, there’s little to suggest that this is the birthplace of a remarkable piece of technology bound for the International Space Station (ISS) in the coming months.

The building is home to the Paihau-Robinson Research Institute, part of Victoria University of Wellington. And the technology being developed there could one day reduce the space industry’s reliance on chemical rockets.

“Our focus here is applied-field magnetoplasmadynamic [AF-MPD] thrusters. It’s a class of electric propulsion that uses an applied magnetic field to accelerate ions to extremely high speeds,” says Randy Pollock, the chief engineer for space at Paihau-Robinson, during a visit to its labs.

This group isn’t the first to work on AF-MPD thrusters—the technology has been tinkered with since the 1970s—but Pollock and his team have overcome a major hurdle to their application in spacecraft. Rather than use conventional copper electromagnets to create the magnetic field, their magnet is made with high‐temperature superconductors (HTS); a class of materials that have close-to-zero electrical resistance, allowing them to generate strong magnetic fields while consuming minimal power.

How Electric Propulsion Works

In 2023, Paihau-Robinson installed the first version of its superconducting electromagnet onto an existing ion thruster at Nagoya University in Japan. The magnet operates at the “high temperature” (as far as superconductors are concerned) of -198.15 °C (75 kelvins). To reach that temperature, the researchers used a cryocooler—effectively a miniaturized mechanical refrigerator—that had previously been qualified for spaceflight. This did away with the need for a continuous flow of expensive liquid helium.

They successfully fired the thruster over a hundred times, and generated magnetic fields of 1 tesla with less than 1 watt of magnet power. That was a 99 percent reduction in input power compared to a copper electromagnet, while generating a field three times as strong.

Back at the lab in Wellington, the team are now developing their own thruster, which they test inside a car-size vacuum chamber. Atop the chamber is a soft toy kōkako—the mascot for their mission, and its namesake. The kōkako is a species of bird native to New Zealand, instantly recognizable thanks to a rich blue wattle under its beak. “To name these missions, we worked with Professor Rawinia Higgins, who is the deputy vice-chancellor (Māori) at Victoria,” says Betina Pavri, a senior principal engineer at Paihau-Robinson. “Kōkako comes from the fact that the plasma glows a distinctive blue-purple color when the thruster is in operation.”

The HTS magnet, barely visible inside the vacuum chamber, comprises four “double-pancake” coils of superconducting tape. It’s about the size of a dinner plate, and the ion propellant line runs through the hole in the center of it. The cryocooler is just out of view, but it’s the same space-qualified model the team trialed in Japan. The next stage of the project will involve moving to a smaller magnet, approximately the size of a bagel, with the goal of making the system more suited to spaceflight.

Hēki Will Test Kōkako’s Tech

Kōkako is one half of the research effort—the ground-based development of a practical AF-MPD thruster. The other half has been on building a technology demonstrator that will soon be mounted onto the exterior of the ISS via a commercial experiment portal called the NanoRacks External Platform. Pavri describes the demonstrator as “a critically important precursor to the Kōkako thruster,” which is why it’s named Hēki, the word for “egg” in the Māori language.

“As I like to say, we took a position on the chicken-egg question,” says Pollock.

On 7 November, Hēki was packed up and shipped to Houston, where it’ll undergo final tests at Voyager Space’s facilities. (Voyager Space is also the company behind the NanoRacks platform.)

The Hēki demo due to arrive on the ISS later this year carries a depiction of the story of how the Kōkako bird got its blue wattle.Laurie Winkless

Hēki is, in effect, everything needed for Kōkako, excluding the ion line. In the center of the baseplate is a steel bagel—lightweight external shielding for the smaller superconducting magnet. When in operation, this magnet will generate a field of up to 0.5 T, “similar in level to what you would see inside an MRI machine but in a very small space,” explains Pavri.

“To our knowledge, this is the most powerful electromagnet that will have ever flown,” Pollock says. “So, it took a lot of design work to meet the very stringent stray magnetic field requirements of the ISS.”

Sitting just above the shield is a flux pump—another new component built at Paihau-Robinson. It acts as an inductive power supply that gradually builds current in the magnet over several hours. Because it also uses superconductors, the flux pump doesn’t heat up, which helps maintain the magnet’s temperature. It too is new to the space environment. The soda-can-size cryocooler and all of the support electronics for the system sit on the underside of the baseplate—a decision motivated by thermal management needs.

Testing the Magnets in Space

When installed on the ISS—which at the time of publication, will most likely be June—the magnet will be operated remotely, cycling through various field strengths, and testing shutdown scenarios. Pavri describes the overall goal as “a demonstration that these new technologies—the high temperature superconducting magnet and flux pump power supply—can survive and operate reliably in the space environment.”

Zenno, a space startup based in Auckland, New Zealand, says it has been testing a superconducting magnet in orbit since 2023. Zenno has not yet published any data on its experiment.

The Paihau-Robinson team also has a secondary objective for the mission; “an experiment of opportunity,” says Pollock, made possible by its high-field magnet. “People have talked since the sixties about using strong magnetic fields for shielding in space. While Hēki is not the ideal setup for measuring it, I was keen to incorporate sensors to see what effect our magnet might have on the radiation environment.” He sourced two sensors from the Czech Technical University in Prague, installing one directly above the magnet, and the other a short distance away within the enclosure. “As we ramp the field up and down, I believe we’ll see an effect.”

The final view of Hēki before it is packed away is its protective cover. The coated sheet of metal includes a list of the team members who worked on the project, and those who funded its development. But it’s the front that’s most eye-catching. Adorned with the work of contemporary Māori artist Reweti Arapere, the imagery tells the story of how the Kōkako bird got its blue wattle.

“When the astronauts pull this out, we want to not leave any doubt about where this instrument has come from,” says Pollock.

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