Space: Robinson Research Institute’s next frontier
Director of the Robinson Research Institute Dr Nick Long explains how his teams' expertise in electromagnetic technologies is taking them to space.
For most of us raised watching moon landings, Star Trek and Star Wars, space technology is synonymous with the highest human aspirations to travel far and fast and explore the unknown. Unsurprisingly then at Robinson Research Institute we’ve grabbed whatever opportunities have presented themselves to take our technologies beyond the earth’s surface.
Space-related research is now a New Zealand government priority. Rocket Lab has demonstrated that New Zealand can develop launch capability for small satellites, supported by local firms. New Zealand has the potential to go well beyond launch services and there are already further activities here in propulsion technologies, tracking services and earth observation. With a worldwide boom in commercial space companies and lower-cost access to space, there is something of the sense of goldrush times in the space sector.
At Robinson we explore electromagnetic and material technologies which can benefit NZ. Our deep expertise is in superconductors, the defining property of which is zero Direct current (DC) resistivity at temperatures below their critical temperature. We are interested in using so-called High Temperature Superconductors, which can operate usefully at temperatures around and below the boiling point of liquid nitrogen, that is 77 K (-196 °C).
The most important property of superconductors from our point of view is the high current density. The current capacity of copper is limited by heat generation due to resistance. For a superconductor there is no heat generation as long as the current is below a value called the critical current. The critical current density can be as high as 1000 times the current density typical of copper. This means we can create very high magnetic fields with lower volume of conductor, therefore there is less weight, and no dissipation of energy. So, this is the primary value proposition for using superconductors in space—we can create lightweight, strong magnets.
Travelling in space doesn’t require much energy, if you are moving in the right direction! This is Newton’s first law of motion. The problem is Newton’s other laws—the second law implies we need energy to slow down and speed up, and the law of gravitation implies energy is needed to get on and off planets safely. In going to for example, Mars and back, it’s really the energy to stop at Mars and get off again which is the problem. If all this energy is carried as chemical energy to burn, then the mass of chemicals required gets very large. In fact, so large that a Mars return trip becomes unfeasible with existing rocket technology.
An alternative to carrying chemical energy is to harvest energy from the sun. Then we can use this energy to accelerate particles at very high speeds, and eject them from the spacecraft, creating thrust in what is called an ion thruster. We have to take the ions (particles) with the spaceship but the impulse obtained per kilogram of material is much, much higher. To accelerate the ions we need a high magnetic field, and that gets us back to our superconductors which we use to create a large magnetic field.
At Robinson we are working on these ion thrusters which can be used on anything from positioning small satellites to powering spacecraft on interplanetary missions. The key is having high magnetic fields to accelerate ions. The superconductors are kept cold by what is essentially a miniaturized refrigerator also powered by the sun. We have a Ministry of Business, Innovation, and Employment-funded programme working with partners at the University of Auckland and University of Canterbury as well as private NZ companies to develop superconductor-enabled ion thrusters.
There are further applications for high magnetic fields in space which sound close to science fiction but are based on known physics.
The problem of stopping at a distant planet or decelerating as a spacecraft enters the earth’s atmosphere is one of the trickiest problems in space flight. Under the right conditions a large magnetic field can interact with the ions in a planet’s atmosphere, just as the northern and southern aurora are charged particles being accelerated in the atmosphere by the earth’s magnetic field. This interaction can create a braking force on a spacecraft which is projecting a large magnetic field, so we can create a kind of magnetic brake to efficiently slow down a spacecraft as it enters the outer atmosphere of a planet. We are working on this problem with a small team at DLR (German space agency) and NZ company Argo Navis.
A vibrant space industry in NZ would have seemed like a long shot a decade ago, but now we would be disappointed if NZ failed to capitalize on the opportunity. One of the most satisfying aspects of our programme is training a new generation of research students in the unique skills needed to build technology for space.