Evaluating New Liquid Storable Bipropellants: Safety and Performance Assessments

Abstract

Conventional storable bipropellants make use of hydrazine and its derivatives as fuels and nitrogen tetroxide as an oxidizer. In recent years, the toxicity character of these chemicals pushed the propulsion community towards “green” alternatives. Several candidates have been proposed among existing and newly developed chemicals, highlighting the need for a common and robust selection methodology. This paper aims at reviewing the most important selection criteria in the field of toxicity and discusses how to objectively define a green propellant, considering both the health and environmental hazards caused by the chemicals. Additionally, consistent figures of merit in the field of safety and handling operations and performance are proposed. In particular, operating temperatures, flammability and stability issues are discussed in the framework of physical hazards and storage requirements, while vacuum impulses, adiabatic flame temperature and sooting occurrence of the investigated couples are compared to the UDMH/NTO benchmark case. Hydrogen peroxide and nitrous oxide, and light hydrocarbons, alcohols and kerosene are selected from the open literature as promising green oxidizers and fuels, respectively. The identified methodology highlights merits and limitations of each chemical, as well as the fact that the identification of a universally best suited green couple is quite impractical. On the contrary, the characteristics of each propellant lead to a scenario of several “sub-optimal” couples, each of them opportunely fitting into a specific mission class.

Review and perspectives of “Green” Self-Pressurizing Propellants for In-Space Propulsion and their applicability to Orbital Stages

“…Institutional -EU and international regulations -Management and handling of hydrazine -Re-entry of parts In Europe, the European Chemicals Agency (ECHA) proposed the identification of hydrazine as a Substance of Very High Concern (SVHC) due to its carcinogenic properties, and it is foreseen a possible ban or forced reduced use in the coming years. This event would strongly impact the space sector, hence the research on alternatives is a growing field [6][7][8][9][10][11]. Other countries appropriately acknowledge the dangers associated with the handling of toxic propellants, and numerous regulations are in place to mitigate these risks.…”

“…Properties extracted from NIST website -https://webbook.nist.gov/chemistry6 Description from ECHA website -https://echa.europa.eu…”

Review on Sustainable Development of Space Vehicles

“…Stefania Carlotti, et al, proposes a ranking of suitable figures of merit for novel propellant that aim at substituting hydrazine/NTObased systems [8]. The main goal of the study was to derive a consistent and quantitative set of criteria that could lead to a systematic and simple selection methodology.…”

Test Activities on Hybrid Rocket Engines: Combustion Analyses and Green Storable Oxidizers—A Short Review

“…Thermal decomposition of the oxidizer occurs at temperatures of around 793 K, while a list of the possible catalysts for N 2 O decomposition is given in [100][101][102][103]. Further considerations on N 2 O physical properties are included and referenced in [104].…”