MOXIE- Mars Oxygen In-Situ Resource Utilization Experiment
NASA launched the Perseverance rover on the 30th of July 2020 and made its landing on the 18th of February 2021. It was manufactured by the Jet Propulsion Laboratory (JPL short) and has 7 primary payload instruments, nineteen cameras, and two microphones [1].
The most important instrument on the rover was Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE for short). It is an experiment contained in the Perseverance rover. Its main job is [3] to produce oxygen from Mars’s highly concentrated CO2 atmosphere. It is about 17,7 kilograms and consumes 300 Watts. It was thought that it will produce 10 grams of Oxygen per hour. An operation time of 1 hour of oxygen production per experiment will be scheduled intermittently over the duration of the mission. Oxygen is not only for humans. Oxygen will be used for rockets’ propellant.
MOXIE works by taking CO2 from the atmosphere and compressing the air. It vents the non-condensable molecules. It is electrochemically split into O2 and CO with Solid Oxide Electrolysis. The whole electrochemical system is called a Solid Oxide Electrolyzer (SOXE for short). SOXE is the most complicated instrument in all MOXIE. It operates at 800oC with a thermal isolation system, input gas preheating, and exhaust gas cooling. In Figure 3, the [4] working principle of MOXIE can be seen.
MOXIE implemented the first test on April 20 [5]. In the first test, MOXIE’s oxygen production was about 5 grams equivalent to 10 minutes’ worth of breathable oxygen. This was for ensuring MOXIE is intact and worked after landing.
Oxygen-producing runs will occur in three phases. In the first phase, MOXIE will be checked out and characterize the instrument’s condition and function. In the second phase, MOXIE will run at different times of day and seasons. In the third phase, NASA will try new operating modes [5].
Michael Hecht who is the principal investigator at the MOXIE project published a great article about the day of MOXIE [2]. They published the first peer-reviewed article which gives information about the progress. They have performed 11 runs until August 2022. August 2022, is the peak of Mars’s winter which means higher pressures, high air density and, high CO2 concentration. This also means higher O2 production in theory. MOXIE was designed to produce 10 grams of O2/ hour however at the last run, they pushed to 10,5 grams O2 /hour [2]. However, there is a long way towards making 2 to 3 kilograms per hour needed to lift the human crew into Mars orbit.
Efficiency is the most important aspect of MOXIE. Efficiency must be increased in order to produce 2 to 3 kilograms O2 per hour. Efficiency can be increased with power usage. Right now, MOXIE uses %10 of the total energy to produce oxygen. %90 of energy goes to running a compressor, electronics, and heat loss from our 800 oC electrolysis unit [2].
Right now, one peer-reviewed article published [6]. MOXIE has produced 7 times between landing and the end of 2021. In Figure 5, the times of different experiments and air density can be seen. Actual O2 production rates do not exactly correlate with air density. However, it seems that there is optimal air density for O2 production is between 0,017 and 0,018 kg/m3 of air.
Nernst potential (VN) is the voltage that must be given to start an electrolysis reaction. To produce oxygen, MOXIE must be in voltage above of oxygen producing reaction VN (2CO2 → 2CO + O2) and below of carbon formation reaction VN (2CO → 2C + O2). In Figure 5, Nernst potentials of reactions and safe voltage zone can be seen.
Although MOXIE leaped a big step by producing oxygen in the Mars atmosphere, there is a long way towards self-sustainable oxygen production enough for Human habitation. An important subject is the substantial thermal stress caused by the occasional and intermittent nature of MOXIE. This creates substantial thermal stress on materials which increases the degradation and efficiency in the future. Also, constraints of Perseverance do not allow to test the longevity of MOXIE. MOXIE also does not respond to external conditions such as an HVAC system in a factory. If MOXIE was able to change its compressor pressure, and temperature, it can increase its efficiency. Although there are downsides to MOXIE, it taught us SOXE technology can be applied in the Mars atmosphere. And most important thing is that MOXIE showed that upscaled MOXIE can take crews from Mars surface to Mars orbit.
References
[1]
Wikipedia, “Perseverance (rover),” Wikipedia, 2022. [Online]. Available: https://en.wikipedia.org/wiki/Perseverance_(rover). [Accessed 18 12 2022].
[2]
NASA, “2020 MISSION PERSEVERANCE ROVER,” NASA Science, 31 08 2022. [Online]. Available: https://mars.nasa.gov/mars2020/mission/status/401/a-day-full-of-moxie/. [Accessed 25 12 2022].
[3]
NASA, “NASA MARS,” NASA, 2022. [Online]. Available: https://mars.nasa.gov/mars2020/spacecraft/instruments/moxie/. [Accessed 18 12 2022].
[4]
NASA, “NASA MARS,” NASA, 2022. [Online]. Available: https://mars.nasa.gov/mars2020/spacecraft/instruments/moxie/for-scientists/#:~:text=MOXIE%20collects%20CO2%20from,CO%20and%20other%20exhaust%20products.&text=Figure%201%20shows%20the%20MOXIE%20functional%20block%20diagram.. [Accessed 18 12 2022].
[5]
NASA, “NASA,” 2022. [Online]. Available: https://www.nasa.gov/press-release/nasa-s-perseverance-mars-rover-extracts-first-oxygen-from-red-planet. [Accessed 22 12 2022].
[6]
J. A. Hoffman, M. H. Hecht, P. Steen , H. Okkels, F. E. Meyen, K. J. Horn, S. Hariharan, M. Nasr, E. D. Hinterman, A. M. Liu, J. B. McClean, A. M. Aboobaker, J. G. SooHoo, J. J. Hartvigsen and D. Rapp, “Mars Oxygen ISRU Experiment (MOXIE) — Preparing for human Mars exploration,” Science Advances, vol. 8, no. 35, 2022.
