Have you ever wondered why we don’t have electrical passenger aircraft? Why don’t we use fusion, the clean and safe energy production happening in the Sun, to power our houses and industry? Why despite years of development haven’t we established a human presence outside of low-earth orbit?The answer is, in short, the lack of suitable materials.
Can superconductors, materials that exhibit zero resistivity be an answer? If we eliminate the resistive losses in our wires, we could build machines that are energy dense and enable outstandingly efficient devices. Superconducting machines could be small enough to propel a passenger aircraft, enable fusion reactors with magnetic fields strong enough to produce energy, space thrusters to go beyond what is known, shields that could protect our astronauts from deadly space radiation and the list goes on and on…
Short History of Superconductors
The superconducting machines could truly change the world. However, don’t buy your tickets for the deep space mission yet. Superconductors were discovered almost 100 years ago and only recently started to step into the industry. The problem with superconductors is the extreme temperature required to reach and sustain the superconducting state. The material must be cooled down almost to absolute zero (-273 C) which for years had been achievable only in specialised laboratories. The breakthrough came in the 1980s when a new family of compounds, based on copper oxides (cuprates) were discovered. These were enthusiastically called “high-temperature superconductors”. Quite a misleading name as the superconducting state is achieved at 77 K (-196 C). The temperature, however, was high enough to enable the use of widely available and cheap cryogens such as liquid nitrogen. Everyone was expecting the industrial application of superconductors to be around the corner. However, as the material is a ceramic it has two unfavourable features; it is a good insulator outside of the superconducting state and it is difficult to work with. As a result, even a small increase in temperature will change a superconductor to a resistor destroying the device. The second problem is that these materials are brittle and therefore difficult to form into a wire. In fact, only recently has the industrial process matured enough to reach a state in which superconducting
cables can be mass-produced.
Figure 1 Superconducting tape
The world of today needs superconducting machines like never before. Major problems like climate change and growing energy consumption cannot be solved with our current technology. However, these devices are still in the early development stages and have not proven themselves in operational conditions. The change will not come in the form of a revolution, but rather an evolution through the research and development of new, more complex superconducting prototypes.
What about Aero(space)?
The dream of an efficient way of crossing enormous distances of outer space has been with us for decades. Can we make it a reality with the use of energy-dense materials like superconductors?
Superconducting devices for space applications will share the same design philosophies, with cooling continuing to pose a significant challenge. You may say that the space is cold, at –
270 C, which is an ideal temperature for superconductors and closes the topic, but not so fast… Space is pretty much empty, and a vacuum is a perfect insulator. In fact, our artificial
satellites tend to overheat as the heat generated on board and delivered from the Sun cannot leave the system. To add on top of these issues, the presence of cryogenic fluids, like liquid nitrogen, complicates satellite design. Sloshing fluid can destabilise the satellite and extra care must be taken to ensure no leakages nor vaporisation occurs. One solution can come with a combination of passive shielding and miniature mechanical coolers . Particularly, the latter technology has significantly advanced in recent years and several missions  showed that it is possible to manage cryogenic conditions in an earth-orbit environment. For the first time in history, we can think about building superconducting space devices, which open a whole range of new possibilities.
Figure 2 Superconducting magnetoplasmadynamic thruster in action (photo: Chris Acheson and Ryota Nakano, used with permission)
First and foremost, we can build superconducting electrical thrusters. These thrusters can be used to carry payloads to new ambitious destinations, with a fraction of the propellant required by chemical rockets. Thrusters, minuscule in size with the use of strong magnetic fields will be able to accelerate the propellant to 10 000s m/s. Such cutting-edge technology is currently under development in China, Japan, Russia, Germany and New Zealand.
The future of superconducting materials is not only in propulsion. Many different utilisations have been proposed including radiation shields, energy storage and magnetic sails; each of them has the potential to change how we see space exploration and await further development. Firstly, we need to show that we can operate our superconductors in space conditions. An important milestone for superconducting space devices will come in 2025  when the first superconducting magnet will go to space and show its functionality on board the International Space Station. This demonstration will show the functionality of the materials as well as the whole magnet assembly in the space environment. Could it be the start of a new era in space engineering, catalysed by the utilisation of high-temperature superconductors?
- Ross, R.G., Boyle, R.F. (2003). NASA Space Cryocooler Programs—An Overview. In: Ross, R.G. (eds) Cryocoolers 12. Springer, Boston, MA., https://www2.jpl.nasa.gov/adv_tech/coolers/Cool_ppr/C12-2002%20NASA%20Overview.pdf
- Berg, Jared, (NASA Kennedy Space Center Cocoa Beach, FL, United States), KSC-2013-107, https://ntrs.nasa.gov/api/citations/20130013661/downloads/20130013661.pdf
- “Partnership to launch ground-breaking superconducting magnet in space”, Wellington Faculty of Engineering https://www.wgtn.ac.nz/engineering/news/partnership-to-launch-ground-breaking-superconducting-magnet-in-space