MOXIE for Scientists
(Mars Oxygen ISRU Experiment)

NASA is preparing for human exploration of Mars, and the MOXIE investigation on the Mars 2020 mission addresses a key knowledge gap by demonstrating In-Situ Resource Utilization (ISRU) technologies to enable oxygen production from the Martian atmosphere.

MOXIE collects CO2 from the Martian atmosphere, then electrochemically splits the CO2 molecules into O2 and CO. The O2 is then analyzed for purity before being vented back out to the Mars atmosphere along with the CO and other exhaust products.

MOXIE Functional Block Diagram
Figure 1. MOXIE Functional Block Diagram. Credit: NASA/JPL-Caltech/MIT
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Figure 1 shows the MOXIE functional block diagram. A scroll compressor pulls Martian atmosphere from outside the rover through a filter and pressurizes it to about half an atmosphere. The pressurized CO2 gas is then fed to the Solid OXide Electrolyzer (SOXE), where it is electrochemically split at the cathode to produce pure O2 at the anode, a process equivalent to running a fuel cell in reverse. The byproducts are carbon monoxide (CO) and unused CO2. Electrochemical constraints limit the fraction of the CO2 that can actually be converted without producing waste carbon, which would destroy the instrument.

The SOXE operates at 1,472 degrees Fahrenheit (800 degrees Celsius), requiring a sophisticated thermal isolation system, including input gas preheating and exhaust gas cooling. The O2 stream is analyzed to verify O2 production rate and purity, and the CO2/CO exhaust stream is analyzed for process control. The electrical current through the SOXE is a direct result of the oxygen ions transported across the electrolyte, and provides an independent measurement of O2 production rate.

Based on conversion efficiency calculated from flow rates and composition measurements, SOXE control parameters such as CO2 input flow rate, temperature, and applied voltage are used to optimize O2 production under Mars environmental conditions. The cooled exhausts are then filtered to satisfy planetary protection requirements and vented from the rover. Process telemetry is reported to the rover for downlink.