On NASA research paper nitrous oxide (N₂O) / propane (C₃H₈) (NOP) / acetylene (C₂H₂) (NOA) rocket engines are analyzed. (https://tfaws.nasa.gov/TFAWS06/Proceedings/Aerothermal-Propulsion/Papers/TFAWS06-1026_Paper_Herdy.pdf) Here are some remarks from the paper:
Most propellants commonly used today have relatively low vapor pressure (lower than the rocket chamber pressure) and consequently have to be pressurized. This is accomplished in one of several ways. Turbo pumps are used for launch vehicle applications. The pumps are driven using onboard propellant and form part of the thermodynamic cycle for the system. For space applications, expulsion systems are used to pressurize the propellant and drive it out of the propellant system. Expulsion systems use high pressure gas (either helium or nitrogen) to pressurize the liquid propellant.
In contrast to these systems the NOP/NOA propellants are self-pressurizing due to their relatively high vapor pressures (higher than the rocket chamber pressure). Consequently, they do not require separate expulsion systems and the entire tank volume can be used to store propellant. The vapor pressure of nitrous oxide is approximately 750 psi and that of propane is 125 psia at ambient temperature.
The non-toxic nature of the NOP/NOA propellants will serve to reduce operating costs due to the handling issues associated with the hypergolic propellants currently in use for space applications. The NOP/NOA propellants are benign and not highly reactive. They remain so until the nitrous oxide is catalytically decomposed and combined with the fuel. Exhaust products consist mainly of nitrogen, water, and carbon dioxide. The NOP/NOA propellants are storable over long periods of time without degradation. Inadvertent decomposition is one of the main technical obstacles for hydrogen peroxide use in space propulsion systems.
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