A review of optical diagnostic methods for space electric propulsion

Abstract Space electric propulsion (EP) systems are significantly more efficient than their chemical counterparts and are increasingly favored for a wide range of space missions. Despite over a century of EP research, the expanding mission envelope and growing understanding of complex discharge phenomena continue to drive the development of new diagnostic techniques. Among these, non-intrusive optical diagnostics have gained considerable prominence, which include approaches ranging from theoretical modeling and data-driven analysis to spectroscopy, plasma imaging, tomography, laser-induced fluorescence, Thomson scattering, and refractometry. Given the growing body of literature and the specialized expertise required for the various approaches, this review consolidates the existing literature on optical diagnostics for EP systems. We categorize the techniques based on their capabilities and describe the necessary apparatus or models required for their implementation. Our goal is to provide EP researchers with a comprehensive reference of optical diagnostic tools, highlight recent trends, and discuss future directions for advancing optical diagnostics in support of both fundamental studies and applied EP development. Additionally, this review also offers insights into recent progress in EP research viewed through the lens of modern optical diagnostics.