PulCheR (Pulsed Chemical Rocket with Green High Performance Propellants) is a new propulsion concept in which the propellants are fed in the combustion chamber at low pressure and the thrust is generated by means of high frequency pulses, reproducing the defence mechanism of a notable insect: the bombardier beetle. At each pulse, pressurization of the combustion chamber gases takes place due to the decomposition or combustion reaction, and the final pressure is much higher than the one at which the propellants are stored. The weight of the feeding system is significantly reduced because the propellants are fed at low pressure. The feed pressure becomes independent on the chamber pressure and the performance degradation typical of the blow down mode in monopropellant thrusters can be drastically reduced. Finally, pulse mode greatly simplifies the throttling of the thrust.
The PulCheR project aims at demonstrating the feasibility of this new propulsion concept that can substitute today’s propulsion system for accessing space. The new propulsion system can be employed for low orbital flight and beyond, and subsequent re-entry, allowing also for re-usable vehicles. It can be used in satellites or space ships to carry out typical manoeuvres around a planet or during interplanetary missions as North-South / East-West station keeping, low orbit flight, orbital re-phasing, de-orbiting, docking / rendez-vouz, re-entry, attitude control and orbit transfer.
The feasibility of the new propulsion concept has been investigated both in mono and bipropellant configurations at breadboard level through the design, realization and testing of a platform of the overall propulsion system. High performance green propellants have been selected for the experimental campaign in order to further investigate possible candidates for substituting current toxic propellants.
During steady-state tests, high grade hydrogen peroxide (98% by weight) proved to be a very good candidate for substituting hydrazine, even with conventional feeding system, for monopropellant system characterized by short enough mission times and not so severe specific impulse requirements. Moreover, the monopropellant thruster exploiting the PulCheR concept was successfully tested and the feasibility of the new propulsion concept was demonstrated with only some minor concerns regarding the propulsive performance that was able to fulfill the requirements only in some cases.
Even if the selected innovative bipropellant combination of propyne and hydrogen peroxide proved to be not hypergolic, these green propellants showed propulsive performance comparable to the current toxic bipropellant combinations. Further improvements of the ignition system based on a catalytic bed will allow for a possible application of these propellants in future missions. Moreover, in the framework of the project, a wide screening of hypergolic combinations with HTP has been carried out. Some fuels have been identified as hypergolic with HTP after their mixing with metal transition salts and metal hydrides. In particular, impinging tests of MEA+7% NaBH4 with HTP have shown that repeatable and very stable hypergolic ignition is possible, even for long time injections (at least 5 s). Therefore, this combination has been identified as a promising candidate to exploit the PulCheR concept in green bipropellant system.
Finally, even if the effort in the development of innovative materials for combustion chamber (such as SiC/Mo and ZrO2/Mo multilayer system) has resulted in the failure of all the tested samples, the chambers debris showed no melting of the materials, thus confirming the goodness of the selected materials whose manufacturing process and technology still needs to be improved for avoiding microcracks that were probably the main reasons of their failures.
New frontiers of research have been opened by PulCheR for virtually all the propulsion system components, due to the new concepts developed for the thrust generation (pulsed operation) and for the feeding system. Moreover, new avenues of research have been opened also in the field of high performance green propellants, with the identification of effective substitutes for the hydrazine and its by-products as space propellants