The space propulsion market has experienced steady growth in recent years, driven by increasing demand for solutions that enhance satellite autonomy, versatility, economy, payload capacity, and readiness to fly. Key trends, initiated 25 years ago with CubeSats, include system miniaturization and modularization. These trends highlight the need for simple, small, high-performing solutions characterized by streamlined procedures and rapid maneuvers, which are required to optimize mission costs and lead times. Traditional chemical and electric space propulsion technologies, such as those based on hydrazine and its derivatives or Hall-Effect Thrusters, are being surpassed by cheaper, more powerful, and leaner systems that emphasize sustainable and safer green propellants, according to the current and future global policy initiatives.

This paper presents an extensive and critical overview of innovative propulsion system solutions, already existing or currently under development, which meet these criteria. It analyzes commonalities and differences among space propulsion technologies in terms of mission goals, satellite size, architectures, and performance parameters, as well as key points of departure from traditional systems. It investigates solutions utilizing green propellants, focusing on those based on water, especially water electrolysis propulsion technology.

This overview aims to provide a comprehensive definition of stakeholder expectations in the current space propulsion scenario, serving as input to the design process of an innovative water electrolysis propulsion system.