**Abstract**

Concepts are presented for "green" (with reduced hazards) replacements for monopropellant hydrazine propulsion systems and for hypergolic bipropellant systems while maintaining similar performance. At the onset of the "green propulsion" age, "green" alternatives to hydrazine propulsion have been emerging. The introduction rate of these into space systems is very slow due to the conservatism of the space propulsion industry. The concept presented here for monopropellant hydrazine systems offers gradual conversion to "green propellants" by dual capability of conventional hydrazine systems and ammonium dinitramide (ADN)-based systems. An initial risk reduction program has been carried out for materializing the concept. It includes proof of concept of dual use of all propulsion system parts. Materials compatibility and actual operation have been demonstrated. For bipropellants, we present the emerging "green" hypergolic system based on kerosene and peroxide, similar in performance to MMH/N2O4. Results of the proof-of-concept and development model systems are presented. The experimental results of various engine types demonstrate the capability to operate in both pulse and steady-state modes and the ability to produce different thrust levels. The fuel and oxidizer show very robust hypergolicity and short ignition delay times, as well as characteristic velocity efficiency exceeding 98%.

**Keywords:** green propulsion, hypergolic, space propulsion, rocket, thruster, H2O2, kerosene, hydrazines
