In space propulsion technology, particularly in plasma thrusters for satellites, boron nitride is playing an increasingly important role. But what are the underlying physical principles, and why is boron nitride so well-suited for use in space? We’ll explore this question in more detail in this blog post.
Plasma propulsion systems—efficient space travel
Unlike chemical rocket engines, which derive their energy from the combustion of propellants, satellites use electric propulsion systems, specifically plasma propulsion. In this process, a gaseous propellant—often xenon or krypton—is ionized, meaning it is split into positively charged cations and free electrons. These ions are accelerated by electric fields, generating a gentle but continuous thrust. Physically, this is based on the Hall effect, which gives the components their name: Hall effect thrusters.
Plasma propulsion is highly attractive for satellite propulsion systems due to its high efficiency. It consumes less fuel than traditional propulsion systems and can provide constant thrust over long periods of time, making it ideal for long-duration missions.
Compared to chemical propulsion systems, a Hall-effect thruster generates only a small amount of thrust. It is therefore not suitable for launches from the Earth’s surface, but is primarily designed for operation in the vacuum of space. For this reason, plasma thrusters are used to position satellites in Earth orbit or to correct their trajectory. They are also used in missions where space probes are sent to other planets, as they offer advantages for interplanetary travel due to their high specific impulse.
Boron nitride in space
The manufacture and maintenance of these Hall-effect thruster systems are challenging and require advanced technologies, as they rely on the precise control of electric and magnetic fields to accelerate the ions. The materials used must also withstand extreme conditions. Hexagonal boron nitride offers the perfect conditions for the high demands of high-performance plasma propulsion systems. Due to its high resistance to thermal and mechanical stress, as well as its chemical inertness, it is ideal for extraterrestrial use. It is often used as an insulating material in critical areas, particularly where components are exposed to high temperatures and severe erosion caused by ionized gases.
One of the greatest challenges in plasma propulsion systems is precisely this erosion of components caused by the bombardment of ionized fuel. The ions can strike the surfaces of the propulsion components at extremely high speeds and wear them down over time. This wear and tear determines the service life of the propulsion system. Here, boron nitride demonstrates the ideal ability to emit secondary electrons at the surface, which is exposed to the cation bombardment of the inert gases. It is precisely this secondary electron emission that is a crucial property, contributing to the stabilization of the plasma drive while simultaneously increasing energy efficiency. Material ablation is minimized, surfaces are protected from excessive damage, and the service life of the systems is thereby extended.
Our HeBoSint® grades combine key physical properties and provide essential functions that significantly extend the service life and operational capability of plasma propulsion systems in space, while simultaneously reducing satellite maintenance costs.
Insulator
As an electrical insulator with outstanding electrical resistivity > 1015 ohm*cm; HeBoSint® prevents short circuits and ensures safe control of the electric field required to accelerate the ions.
Chemical stability
HeBoSint® is stable in the harsh environments that can be encountered in space. It does not react with the propulsion plasma because the material has no open pores and a high relative density. Additionally, it has the ability to emit secondary electrons from its surface to maintain a balanced electron density in the propulsion plasma. This resistance contributes to the longevity and reliability of the propulsion system.
Thermal stability
HeBoSint® has high thermal conductivity, which efficiently dissipates the heat generated during operation in the drive to prevent overheating and potential damage.
HeBoSint® can withstand both high and low temperatures, which is crucial in the vacuum of space.
Mechanical stability
Compared to other materials available on the market, which often contain SiO₂, our material is free of silicon dioxide, which enhances mechanical stability and thermal conductivity while minimizing the risk of cracking.
Conclusion and Outlook
Overall, plasma propulsion systems represent a forward-looking and efficient propulsion technology for satellites in space, playing a key role in many modern space missions.
In the future of spaceflight and satellite technology, the importance of materials such as hexagonal boron nitride will continue to grow. Its excellent resistance to the extreme conditions of space, its low reactivity, and its ability to serve as an electrical insulator make it the material of choice for plasma thrusters.
As technologies such as plasma propulsion continue to be optimized, more efficient and durable satellites can be developed, enabling long-term missions with minimal fuel consumption. Boron nitride is not just another material, but a technological solution that continues to blur the line between science fiction and the reality of space propulsion.
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Excerpt from the source:
Plasma Erosion of Stressed Fused Silica and M26 Borosil, Aaron M. Schinder1, Julian J. Rimoli2, and Mitchell L.R. Walker, Georgia Institute of Technology, Atlanta, AIAAPropulsion and Energy Forum, 2016
Slow crack growth of boron nitrides for electric propulsion components, J. Salem, J. Mackey and H. Kamhawi, NASA Glenn Research Center, Cleveland, Ohio 43nd International Conference and Expo on Advanced Ceramics and Composites, 2019
Plasma-Induced Erosion on Ceramic Wall Structures in Hall-Effect Thrusters, Thomas Burton, Aaron M. Schinder, German Capuano, Julian J. Rimoli, and Mitchell L. R. Walker, Georgia Institute of Technology Atlanta and Gregory B. Thompson University of Alabama, Journal of propulsion and power, 2012
INVESTIGATION OF HALL EFFECT THRUSTER CHANNEL WALL EROSION MECHANISMS, Dissertation, Aaron M. Schinder, 2016