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Flow animation is illustrative: speeds, amounts and the share of CO₂ converted are not to scale.
Martian air, mostly CO₂
Oxygen ions
O₂
Cathode exhaust
How do you make oxygen on Mars?
MOXIE, inside NASA's Perseverance rover, made 122 g of oxygen from Martian air: collect the air, compress and heat it, separate the oxygen, measure it.
Drawn outside the rover so you can see it.
Your device asks for less motion, so the gas stands still until you scroll.
What the sources say
An experiment inside NASA’s Mars 2020 Perseverance rover, MOXIE has successfully produced oxygen from the carbon dioxide that comprises ~95% of the martian atmosphere.
The scandia-stabilized zirconia ceramic electrolyte selectively passes oxygen ions to the anode, where the ions recombine into O 2 , which is measured for quantity and purity before being released to the Mars atmosphere.
An experiment inside NASA’s Mars 2020 Perseverance rover, MOXIE has successfully produced oxygen from the carbon dioxide that comprises ~95% of the martian atmosphere.
Early oven tests suggested this as an optimal compromise between efficient operation and the risk of damaging heat-sensitive materials.
Volume and power limits ruled out an oven in the rover, so two heater plates, top and bottom, do the heating. The centre cells run up to 10 °C cooler.
What the paper says
Initial tests of the SOXE, performed in an oven, suggested that an operating temperature of 800°C is an optimal compromise between efficient operation and the risk of damaging heat-sensitive materials.
Inside the Perseverance rover, however, volume and power constraints precluded an oven, so, instead, MOXIE’s SOXE is heated by two heater plates at the top and bottom of the electrolysis stacks with insulation partially covering its sides.
This configuration results in thermal gradients of up to 10°C between the cooler cells in the center of the stack and the warmer cells nearer the heaters.
Solid oxide electrolysis (SOXE) happens here: 10 cells wired in series, with a centre tap so they can be controlled as two five-cell halves, top and bottom.
Manifolds are shared by all 10 layers, and thin Inconel leads connect the stack to the voltage control circuitry.
What the paper says
The SOXE uses a stack of 10 electrolysis cells, electrically wired in series with a center tap such that they can be controlled as two five-cell stacks, referred to as top (T) and bottom (B).
sends it through a solid oxide electrolysis (SOXE) assembly, where CO 2 flows over a nickel-based catalyzed cathode and decomposes into oxygen ions and CO.
FM OC12 was designed to estimate the resistance ( R L ) of the thin Inconel leads connecting the MOXIE voltage control circuitry to the stack of electrolysis cells that comprise the SOXE.
CO₂ flows over a nickel-based catalyzed cathode and decomposes into oxygen ions and CO, carbon monoxide.
What the paper says
sends it through a solid oxide electrolysis (SOXE) assembly, where CO 2 flows over a nickel-based catalyzed cathode and decomposes into oxygen ions and CO.
The scandia-stabilized zirconia ceramic electrolyte selectively passes the oxygen ions to the anode.
What the paper says
The scandia-stabilized zirconia ceramic electrolyte selectively passes oxygen ions to the anode, where the ions recombine into O 2 , which is measured for quantity and purity before being released to the Mars atmosphere.
The scandia-stabilized zirconia ceramic electrolyte selectively passes oxygen ions to the anode, where the ions recombine into O 2 , which is measured for quantity and purity before being released to the Mars atmosphere.
Another reaction, 2CO → 2C + O₂, would form carbon. So in the main segment of a generic run the estimated electrolysis voltage is kept at least 0.1 V below the Nernst potential for carbon formation.
O₂ reaction can startCarbon formation can start
Main segment: estimated voltage at least 0.1 V below · schematic, not to scale
Cooler cells have a higher resistance and a smaller safe voltage zone, so they are at greater risk of coking.
What the paper says
sets the current to as high a value as possible for this maximum gas intake while keeping the estimated electrolysis voltage at least 0.1 V below the Nernst potential for carbon formation.
Oxygen leaves from the anode side. The cathode exhaust is a mixture of CO₂, CO and inert gases, mainly argon and nitrogen.
What the paper says
The scandia-stabilized zirconia ceramic electrolyte selectively passes oxygen ions to the anode, where the ions recombine into O 2 , which is measured for quantity and purity before being released to the Mars atmosphere.
The oxygen is measured for quantity and purity before it is released to the Mars atmosphere.
Purity is judged by an infrared sensor watching for trace CO₂ in the anode exhaust, one of four gas-specific sensors.
What the paper says
The scandia-stabilized zirconia ceramic electrolyte selectively passes oxygen ions to the anode, where the ions recombine into O 2 , which is measured for quantity and purity before being released to the Mars atmosphere.
Purity is determined by a commercial nondispersive infrared (NDIR) CO 2 sensor that monitors trace CO 2 (0 to 5%) in the anode exhaust. This is one of four gas-specific sensors.
To reduce mass, volume, and complexity, the cathode and anode flow channels are equipped with passive viscous flow control devices rather than true pressure regulators.
The reference segment starts with a 16-min “equilibration” step with 2-A electrolysis current (6 g/hour of oxygen), during which time, the internal operating temperature stabilizes.
This is followed by 3.5-min steps at 1.6 A and 1.2 A (4.8 and 3.6 g/hour of oxygen, respectively), providing a voltage-current ( V - I ) sweep to determine the internal resistance of the SOXE
sets the current to as high a value as possible for this maximum gas intake while keeping the estimated electrolysis voltage at least 0.1 V below the Nernst potential for carbon formation.
At the end of a run, the compressor speed and electrolysis current are reset for 5 min to the values used in the reference segment to compare the system behavior at the beginning and at the end of the run.
Previous laboratory tests have demonstrated that it is the cooling and heating between cycles rather than the start-up and shutdown of the oxygen production process that causes this degradation, suggesting that it is likely associated with differential thermal stress.
Initial tests of the SOXE, performed in an oven, suggested that an operating temperature of 800°C is an optimal compromise between efficient operation and the risk of damaging heat-sensitive materials.
of oxygen in total, by the 16th and final run on 7 August 2023.
This record's summary, from the NASA/JPL release it cites. That 16th run made 9.8 g, as the same release says.
What the record says
First production was on 20 April 2021 (about 5 grams); by its 16th and final run on 7 August 2023 it had produced 122 grams in total,
This record, Record summary
Since Perseverance landed on Mars in 2021, MOXIE has generated a total of 122 grams of oxygen
This record, NASA/JPL release of 6 September 2023, quoted in source [1]
On its 16th run, on Aug. 7, the instrument made 9.8 grams of oxygen.
This record, NASA/JPL release of 6 September 2023, quoted in source [2]
About 50 g in seven runs through 2021
At night and by day, MOXIE met its requirements for oxygen generation rate and purity.
Grams of oxygen per run, from the run table in the paper.
Oxygen made in each run of 2021, from the run table in the paper
Run
Date
Day or night
Oxygen (g)
Running total (g)
FM OC9
20 April 2021
Night
5.4
5.4
FM OC10
12 May 2021
Night
6.9
12.3
FM OC11
1 June 2021
Day
6.9
19.2
FM OC12
27 July 2021
Night
8.9
28.1
FM OC13
17 August 2021
Night
8.1
36.2
FM OC14
24 October 2021
Night
6.9
43.1
FM OC15
29 November 2021
Day
6.8
49.9
Reducing the stack's wear from cycle to cycle was a primary development focus, and operation on Mars so far indicated it was highly successful.
The rover's energy limits did not allow testing over the thousands of hours of continuous operation that a human mission will require.
What the paper says
In seven oxygen production runs through 2021, MOXIE successfully produced ~50 g of oxygen and definitively demonstrated that it meets requirements for oxygen generation rate and purity despite design compromises demanded by severe constraints on mass, power, volume, and cost.
Reduction in cycle-to-cycle SOXE degradation was a primary development focus, and operation so far on Mars indicates that the outcome was highly successful.
the energy constraints of Perseverance do not allow testing of longevity over the thousands of hours of continuous operation that will be required in support of a human mission,
Flow animation is illustrative: speeds, amounts and the share of CO₂ converted are not to scale.
About this view
Illustrative layout, not NASA's drawing. Positions, sizes, shapes and orientation inside the published 23.9 × 23.9 × 30.9 cm chassis dimensions are schematic, and the schematic inlet port and outlets extend beyond them. The 10 cells in two halves, and the heater plates above and below the stack, follow the paper. The paper's Figure 1 and NASA/JPL's Components of MOXIE (Illustration) show the real arrangement; this model is not traced from them. MOXIE sits inside the rover; it is drawn outside so you can see it.
What the paper says
The inlet filter, sensor and flow control panel, and electronics are not shown. The dimensions of the MOXIE chassis are 23.9 cm by 23.9 cm by 30.9 cm.
The SOXE uses a stack of 10 electrolysis cells, electrically wired in series with a center tap such that they can be controlled as two five-cell stacks, referred to as top (T) and bottom (B).
Inside the Perseverance rover, however, volume and power constraints precluded an oven, so, instead, MOXIE’s SOXE is heated by two heater plates at the top and bottom of the electrolysis stacks with insulation partially covering its sides.
An experiment inside NASA’s Mars 2020 Perseverance rover, MOXIE has successfully produced oxygen from the carbon dioxide that comprises ~95% of the martian atmosphere.
The particles and the glow are schematic. The number of particles means nothing and no particle turns into another. Speeds, amounts and the share of CO₂ converted are not to scale, and neither are the layer thicknesses in the cut cell. The glow is not a temperature scale: the paper gives thermal gradients of up to 10 °C between the cooler cells in the centre and the warmer cells nearer the heaters, and the drawing exaggerates that.
What the paper says
This configuration results in thermal gradients of up to 10°C between the cooler cells in the center of the stack and the warmer cells nearer the heaters.
Decoration. The Martian sky, hills, rocks and dust are decorative, and so are the cooling fins, bolts, filter pleats, sensor blocks and heater pattern on the model. The panels that fly away are a way of showing the inside.
The totals cover different time spans. The paper covers seven oxygen runs to the end of 2021, about 50 g in all (49.9 g in its table); the record gives 122 g up to the 16th and final run on 7 August 2023.
What the sources say
In seven oxygen production runs through 2021, MOXIE successfully produced ~50 g of oxygen and definitively demonstrated that it meets requirements for oxygen generation rate and purity despite design compromises demanded by severe constraints on mass, power, volume, and cost.
Inside the Perseverance rover, however, volume and power constraints precluded an oven, so, instead, MOXIE’s SOXE is heated by two heater plates at the top and bottom of the electrolysis stacks with insulation partially covering its sides.
sends it through a solid oxide electrolysis (SOXE) assembly, where CO 2 flows over a nickel-based catalyzed cathode and decomposes into oxygen ions and CO.
The SOXE uses a stack of 10 electrolysis cells, electrically wired in series with a center tap such that they can be controlled as two five-cell stacks, referred to as top (T) and bottom (B).
The scandia-stabilized zirconia ceramic electrolyte selectively passes oxygen ions to the anode, where the ions recombine into O 2 , which is measured for quantity and purity before being released to the Mars atmosphere.
An experiment inside NASA’s Mars 2020 Perseverance rover, MOXIE has successfully produced oxygen from the carbon dioxide that comprises ~95% of the martian atmosphere.
