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.
 

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.