Scientists propose adapting a Mars ISRU system to the changing Mars environment

Human missions to Mars would require a considerable launch automobile to ascend from Mars to rendezvous with a ready Earth return automobile in Mars orbit. For an ascending crew of 6, the present finest estimate of oxygen propellants required for ascent is about 30 metric tons. Producing oxygen for ascent propellants and probably life assist from the indigenous CO₂ on Mars, quite than bringing oxygen to Mars from Earth, is of great profit.

The oxygen manufacturing is achieved by way of a course of identified generically as in situ useful resource utilization (ISRU). For the reason that Mars Oxygen ISRU Experiment (MOXIE) Mission demonstrated operation of a prototype electrolysis system for changing Martian CO₂ to O₂ on Mars with nice success, it’s now applicable to research scaling up this prototype to a full-scale system.

In a analysis paper lately revealed in Area: Science & Know-how, Donald Rapp and Eric Hinterman modeled the efficiency of a full-scale Mars in situ useful resource utilization (ISRU) system to supply 30 metric tons of liquid O₂, operated for 14 months because the Mars atmosphere adjustments diurnally and seasonally.

First, the authors introduce the ISRU system format, necessities, and settings. The simplified format of the ISRU system is proven in Fig. 1. The guts of the system is the stack (or, extra probably, a set of stacks) of electrolysis cells, producing a movement of O₂ out of the anode and a combination of CO, CO₂, and inert gases within the cathode exhaust. Whereas the method operates, a compressor first pulls Mars ambiance into the system and compresses it from Mars strain to stack strain.

A warmth exchanger recuperates some warmth from the exhaust gases to incoming fuel from Mars, and this fuel is preheated to stack temperature earlier than coming into the stack. After the electrolysis within the stack, the effluent from the stack is fed again to the warmth exchanger to prewarm incoming Mars fuel, and the cathode exhaust is vented, whereas the anode exhaust is fed to the liquefier.

Furthermore, it’s essential that the voltage throughout the electrolytic cells of the stack(s) should be higher than the Nernst voltage for the oxygen manufacturing response (0.96 V) and fewer than the Nernst voltage for facet response that deposits carbon (1.13 V). The system is required to be on a 14-month (420-sol) run with a mean oxygen manufacturing price of three.0 kg/h to supply a complete of 30240 kg of oxygen over this era. There are additionally a number of management schemes.

In possibility 1, the electrolysis stacks and the liquefier are operated at fixed movement price 3.0 kg/h, whereas the compressor revolutions per minute (RPM) is managed to be higher when the Mars density is decrease, and vice versa. In management possibility 2a, the RPM is all the time maintained at 3325, and the compressor is identical dimension as in management possibility 1, however the variety of cells within the stacks is diminished.

In management possibility 2b, the RPM is all the time maintained at 3325, and the variety of cells is identical as in management possibility 1, however the dimension of the compressor is diminished. In management possibility 2c, the variety of cells and compressor dimension are the identical dimension as in management possibility 1, however the RPM is all the time maintained at 2705.

Then, the authors study the intrinsic area-specific cell resistance (iASR), present density (J), and movement price in several management choices. The fundamental relationship: V_op = + V_different + (iASR)(J) is used, wherein V_op is the typical working voltage utilized to a cell; is the Nernst potential for O₂ manufacturing, averaged throughout a cell; V_different is a voltage added to stability the equation.

As well as, anode strain = cathode strain = 0.2 bar, utilization = 0.60, and iASR is assumed to start out at 1.00 ohm-cm² and improve to 1.20 ohm-cm² after 420 sols of operation. In management possibility 1, the required cell space to supply 3 kg/h of oxygen is A_T = 83750 cm².

With cells of space 100 cm² every, this requires 840 cells. The span of cell-operating voltages is Max V_op = 1.060, Avg. V_op = 1.048, and Min V_op = 1.036. The RPM varies from 3325 at minimal density, to 2706 at common density, to 2251 at most density. In management possibility 2a, Max V_op = 1.114, Avg. V_op = 1.078, and Min V_op = 1.037.

The utmost common cell voltage is perilously near the Nernst voltage for carbon formation, and contemplating the uncertainties in estimating iASR, this selection is unacceptable. In management possibility 2b, Max V_op = 1.077, Avg. V_op = 1.048, and Min V_op = 1.014. In management possibility 2c, Max V_op = 1.077, Avg. V_op = 1.048, and Min V_op = 1.014, that are basically the identical as for management possibility 2b.

Lastly, authors talk about the outcomes and draw conclusions. As for the stable oxide electrolysis (SOXE) system, the electrochemical energy is 14.6 kW for management possibility 1 and 4.87*FO₂ kW for management possibility 2. The preheat energy is estimated to be ~0.5 kW. The warmth loss is roughly 0.35 kW, though it is dependent upon atmospheric circumstances. The full SOXE energy for any management possibility is the sum of the electrochemical energy, preheating energy, and warmth loss energy.

The runs for the varied management choices yield the outcomes proven in Desk 4. As for the compressor, the adiabatic effectivity is a operate of inefficiencies of its elements, together with motor losses, seal friction, and bearing friction. Desk 5 summarizes energy necessities for compression in numerous management choices. The speed of warmth elimination from the system by the cryocooler is calculated because the cooling required to decrease the temperature of the gaseous oxygen to its boiling level and liquefy it. The result’s proven in Desk 6. Complete energy together with all contributions is concluded in Desk 7. All tables may be seen within the open entry paper.