Microreactor development for Martian in situ propellant production

Prediction of the electron kinetics relevant for CO2 splitting using in situ propellant production technology: Effect of the gas composition

Electron kinetics plays an essential role in CO2 splitting in non-equilibrium plasmas. Indigenous resources, particularly CO2 rich in the Martian atmosphere, are utilized as the feedstock for the technology of in situ propellant production (ISPP) in Mars missions. To obtain electron kinetics including electron energy distribution function (EEDF) and transport coefficients, a Boltzmann analysis is adopted. In view of ISPP in the upper Martian atmosphere, the complicated variation of the gas composition with the altitude in both dayside and nightside is considered. The composition of gas mixture is derived from the previous measurement data through site survey and numerical models. According to the results of calculation, altitude affects the behavior of EEDFs and transport coefficients in both dayside and nightside. The rapid drop in CO2 content and the rise in O content with altitude lead to a broader EEDF. The reduction of the critical breakdown electric field strength with the increasing altitude is ascribed to the combined effects of the decline of the attachment coefficient and enhancement of the ionization coefficient. The electron energy loss mechanism is presented for the analysis of energy efficiency. At low mean electron energy, electron energy is mostly transferred to vibrational levels of CO2. With the increasing electron energy, more energy-demanding processes, like ionization and electronic excitation, become essential pathways of energy loss.