Mars Oxygen ISRU Experiment (MOXIE)
NASA is preparing for human exploration of Mars, and the MOXIE investigation on the Mars 2020 mission aims to address key knowledge gaps, including:
- demonstration of In-Situ Resource Utilization (ISRU) technologies to enable propellant and consumable oxygen production from the Martian atmosphere, and
- characterization of atmospheric dust size and morphology to understand its effects on the operation of surface systems.
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 shows the MOXIE functional block diagram. The CO2 Acquisition and Compression (CAC) system pulls Martian atmosphere from outside the Rover through a filter and pressurizes it to ~1 atmosphere. The pressurized CO2 gas is then regulated and 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 SOXE operates at 800° C, requiring a sophisticated thermal isolation system, including input gas preheating and exhaust gas cooling. There are O2 exhaust and CO2/CO exhaust streams, which are then analyzed to verify O2 production rate and purity and for process control. The electrical current through the SOXE is a direct result of the oxide 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 control for the two process steps, CAC and O2 generation, is performed by the MOXIE electronics (ELX). Process telemetry is reported to the Rover for downlink.