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  • Writer's pictureVedant Parikh

Lab Notes: HETs

Updated: Aug 11, 2023

Lab Notes on Hall Effect Thrusters by Aleksander Garbuz.


Over the past few decades, technology within the space sector has been rising in complexity and capability at an exponential rate. Whether that be new technologies in the field of space mining or the mission to find new types of propulsion, the strive for innovation is at an all-time high (Signé & Dooley, 2023). Researchers at the Imperial Plasma Propulsion Laboratory (IPPL) in London are no exception to this new age “space race”. They are conducting an exciting investigation into the use of different propellants for use in spacecraft. The report aims to compare the use of water vapor and oxygen feed systems for Hall Effect Thrusters.

A Hall Effect Thruster (HET) is a type of Electric Propulsion (EP) technology that has been widely used to propel spacecraft in space. HETs are usually placed in Geostationary Orbits (GEO) and are used for telecommunications and the propulsion system on these devices has changed over time.

As the report writes, around 70% of GEO space missions utilize HETs, and they aimed to optimize the process by introducing water vapor as a new propellant system.

The researchers compared the efficiency of using water vapor as a propellant to oxygen, which is the intended propellant for a water electrolysis Hall Effect Thruster. Results indicated that oxygen is approximately 20% more efficient than water vapor under the same conditions. The highest thrust measurement recorded with water vapor was 20.0 ± 0.2 mN (milli-Newtons of force), with a specific impulse of 2039 ± 20s and an anode efficiency of 12.5 ± 0.3% at the largest discharge power of investigation, 1600 ± 1W. In comparison to the more widely used xenon thrusters – which at 2.2 kW output a thrust of 123 mN, a specific impulse of 1765s, and an efficiency of 48% – the technology has a long way to go before it can meet, or surpass, the current figures (Aerojet, 2003).

Water propulsion presents several benefits, making it an appealing choice for Electric Propulsion (EP) devices and HETs. Besides its low cost and non-toxic nature, water is also easily accessible within the Solar System. This could potentially pave the way for future In-Situ Resource Utilization (ISRU) missions, with the Moon serving as a potential fueling station by extracting water from its surface to be used as a propellant. This strategy could significantly reduce the high cost of transporting propellant from Earth, thereby enhancing future missions and allowing for further exploration.

Additionally, water is environmentally friendly and doesn't compromise the Earth's sustainability. In contrast, xenon, despite being praised as a green propellant, is associated with a high environmental carbon footprint due to the energy-intensive processes involved in its extraction and purification.

This research is contributing to the development of more efficient and environmentally friendly propulsion systems in space. The team writes that they wish to delve deeper into water vapor as a propellant and make a comparative analysis with water electrolysis. Though it remains unsure whether either of these systems will replace the widely used xenon currently used in HETs, it is certain this research is a prime example of the important and innovative research being done in the propulsion sector.

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