4. Green Monopropellants: State-of-the-Art

Recent trends in research and development on in-space propulsion have advanced the use of the “green propellants” on an ample scale, mainly eyeing environmental sustainability and especially addressing the handling safety concerns. Small satellites, in particular micro and nanosatellites, have advanced from passive orbiting to having the ability to perform active orbital operations with considerable responsiveness, which tends to call for relatively high-thrust impulsive capabilities. Deep space exploration spacecraft of small size with high ΔV requirements, either intended for Lunar exploration or beyond, necessitate the use of storable propellants to support these relatively high-thrust capabilities, as was seen in several CubeSat missions recently (i.e., 2021 onwards) launched to, or intended for, such missions. Hence, onboard propulsion systems sufficing such requirements, while maintaining the now inevitable environmental sustainability standards, are more sought than before. Green propellants for micro propulsion take a major role and a specific attention in small-sized spacecraft design because of their evident potential in replacing conventional propellants. Green propellants demonstrated comparable, or even higher, performance and above all much less safety concerns in handling, storage, and transportability. Safer-to-handle green propellants reduce a significant financial burden for small and medium-sized enterprises, academic institutions, and innovators who are involved in R&D activities in the field of propulsion systems and space systems development.