Update on green chemical propulsion activities and achievements by the University of Padua and its spin-off T4I

In recent years, there has been a great research interest on green propulsion, both for environmental, cost and ease-of-use considerations, further accelerated by the needs of the NewSpace Economy. Hydrogen peroxide is a green and versatile propellant that is suitable for a lot of different uses in space applications. Following a previous AIDAA publication of 2019, this paper updates the research performed on hydrogen peroxide-based propulsion by the University of Padua and its spin-off T4i with the latest achievements. Starting from the simplest propulsion systems, several monopropellant thrusters have been successfully designed and tested, ranging from a propulsion module of 1 N, to a 10 N and 200 N flight-weight items. The thrusters can operate in blowdown or pressure-regulated mode, and they have been tested for hundreds of seconds of continuous operation and for thousands of pulses. A 450 N liquid bipropellant motor that burns the monopropellant exhausts with diesel fuel has also been developed and tested. The motor uses an unconventional internal vortex flow field to achieve stability, efficiency, and selfcooling of the chamber. The nozzle throat region temperature is kept under control by regenerative cooling channels fed by the peroxide. All thrusters make extensive use of additive manufacturing. The hydrogen peroxide technology has also been applied on hybrid propulsion, which was the initial main expertise of the Padua University propulsion group. Hundreds of tests have been performed at lab-scale, mainly with paraffin wax and polyethylene as fuels, with burning time up to 80 seconds. The motors are able to start, stop and restart multiple times. A cavitating pintle valve has been developed in house in order to control the oxidizer mass flow. With this valve, the hybrid motors are able to throttle the thrust in a range of 1:12.6. A similar valve has been also employed in the integrated monopropellant propulsion system of a lunar drone, composed by a 400 N throttleable engine together with 4 small 14 N on-off attitude control thrusters. Moreover, several dozens of hybrid tests have been performed at 5-10 kN scale up to 50 seconds. Finally, a composite sounding rocket powered by a pressure-regulated 5 kN hybrid rocket has been fully designed and successfully flight tested.