Boron nitride is playing an increasingly important role in space propulsion technology, especially in plasma propulsion systems for satellites. But what is the physics behind it and why is boron nitride so suitable for use in space? We address this question in more detail in this blog post.
In contrast to chemical rocket propulsion systems, which generate their energy by burning fuel, satellites use electric propulsion systems, in particular plasma propulsion systems. A gaseous propellant, often xenon or krypton, is ionized, i.e. separated into positive cations and free electrons. These ions are accelerated by electric fields, generating a gentle but continuous thrust. Physically, the principle behind this is the Hall effect, which gives the components their name - Hall-effect thrusters.
Plasma propulsion is very attractive for satellite propulsion technology due to its high efficiency. It consumes less fuel than traditional propulsion systems and can deliver constant thrust over long periods of time, making it ideal for long-term missions.
Compared to chemical propulsion, a Hall-effect thruster generates only a small amount of thrust. It is therefore not suitable for launches from the Earth's surface, but primarily for operation in the vacuum of space. Plasma thrusters are therefore used to position satellites in Earth orbit or to correct their orbit. They are also used in missions in which space probes are sent to other planets, as they offer advantages for interplanetary travel due to their high specific impulse.
The manufacture and maintenance of these Hall-effect thruster systems are demanding and require advanced technologies, as they rely on precise control of electric and magnetic fields to accelerate the ions. The materials used must also be able to withstand the extreme conditions. Hexagonal boron nitride offers the perfect conditions for the high requirements in high-performance plasma drives. Due to its high resistance to thermal and mechanical stresses and its chemical inertness, it is ideal for extraterrestrial use. It is often used as an insulation material in critical areas, especially where components are exposed to high temperatures and severe erosion from ionized gases.
One of the biggest challenges with plasma drives is precisely this erosion of the components caused by the bombardment of the ionized propellant. The ions can hit the surfaces of the drive components at extremely high speeds and erode them over time. This wear determines the service life of the drive. Boron nitride has the ideal ability to emit secondary electrons on the surface, which is exposed to the cation bombardment of the inert gases. It is precisely this secondary electron emission that is a decisive property and contributes to the stabilization of the plasma drive and at the same time increases energy efficiency. Material erosion is minimized, surfaces are protected from excessive damage and the service life of the systems is extended as a result.
Our HeBoSint® grades combine the physically significant properties and provide the essential functions that significantly extend the service life and operational capability of plasma propulsion systems in space while reducing satellite maintenance costs.
As an electrical insulator with an outstanding specific electrical resistance of >1015 Ohm*cm, HeBoSint® prevents short circuits and ensures safe control of the electrical field required to accelerate the ions.
HeBoSint® is stable against aggressive environments that can occur in space travel. It does not react with the propulsion plasma as the material has no open pores and a high relative density. It also has a balanced ability to emit secondary electrons from the surface to keep the electron density in the propulsion plasma in the required range. This resistance contributes to the longevity and reliability of the actuator.
HeBoSint® has a high thermal conductivity that efficiently dissipates the heat generated in the actuator during operation to prevent overheating and possible damage. HeBoSint® can withstand high and low temperatures, which is crucial in the vacuum of space.
Compared to other grades available on the market, which often have a SiO2 content, our material is free of silicon oxide, which increases mechanical stability and thermal conductivity and minimizes the risk of cracking.
Overall, plasma propulsion in space travel is a forward-looking and efficient propulsion technology for satellites in space, which plays a key role in many modern space missions.
In the future of space travel 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 a material of choice for plasma propulsion.
By further optimizing technologies such as plasma propulsion, 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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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
