Improving ground-based plasma thruster tests for space-based applications

Relying on accelerated plasma to produce a thrust, Hall effect thrusters (HETs) are efficient electric propulsion (EP) systems for long-duration space missions, like space stations, satellites, and deep space travel. HETs have been used since the 1970s and will be included in components of NASA’s Artemis program.

But conditions in space can be different from laboratory-based test conditions for EP devices, and it is difficult to properly extrapolate the plasma variables to real operating conditions to fully predict the in-space performance. To bridge this gap, Theo Zivre and Kentaro Hara implemented a data assimilation technique commonly used in fields like atmospheric science to better understand how zero background pressure in space affects HET operations.

“While traditional approaches typically extrapolate the measured thrust directly, our method estimates how the plasma state variables evolve with background pressure, extrapolate those states to the zero-pressure limit, and then reconstruct the corresponding thruster metrics, like thrust and discharge current,” said Zivre.

The technique they used, called the extended Kalman filter, feeds real thrust and plasma discharge data into a model. The real data all comes from different pressures, so the model continuously updates its plasma density and velocity to get a better estimation. Eventually, it can extrapolate down to zero pressure to predict the HET’s behavior in space.

“Combining physics-based models with real measurements gives us a new way to capture complex plasma behavior and address long-standing challenges in ground testing of HETs,” said Zivre.

Zivre and Hara plan to further refine their model to account for other effects that differ between the laboratory and space, such as the plasma interacting with experiment vacuum chamber walls and sputtered materials reentering the plasma.

Source: “Estimation of in-space thruster performance of a Hall effect thruster through extrapolation of plasma states using extended Kalman filter,” by T. Zivre and K. Hara, Journal of Applied Physics (2025). The article can be accessed at https://doi.org/10.1063/5.0284774 .

This paper is part of the Impact of Vacuum Facilities on Plasma Thruster Operation Collection, learn more here .