ISRU / A future cislunar economy
Producing oxygen near the Moon could let compatible spacecraft refuel there, reducing the oxidizer mass launched from Earth.
3D viewing is unavailable in this browser. Earth and Moon are shown as the two ends of a future cislunar supply network.
Both tanks drain during departure and arrival burns; levels hold during coasting. In lunar orbit, the lander delivers oxygen while receiving hydrogen from the cycler for its descent and next ascent. Earth resupply replaces both the hydrogen burned by the cycler and the hydrogen delivered to the lander. Percentages show each tank’s own capacity, not equal masses or volumes.
2 H₂ + O₂ → 2 H₂O
Complete combustion combines roughly 8 kg of oxygen with 1 kg of hydrogen: oxygen is about 89% of the combined mass. That is the stoichiometric ratio.
This animation assumes an oxygen-rich 9:1 LOX-to-LH₂ mass ratio to illustrate a system supplied with lunar oxygen and imported hydrogen. For every 10 kg of propellant used, 9 kg is LOX and 1 kg is LH₂: 90% oxygen by mass. This is above the stoichiometric ratio, so some oxygen remains unreacted.
LOX / 90% of massLH₂ / 10% of mass
The assumed mixture favors locally supplied oxygen over imported hydrogen. Whether it reduces Earth-launched mass for a given mission depends on engine performance and vehicle sizing. The lander keeps oxygen for its own burns and receives hydrogen through the cycler.
The 9:1 ratio is a scenario assumption, not a validated engine specification. Fuel-rich hydrolox mixtures generally provide higher specific impulse; oxygen-rich operation requires an engine designed for those conditions. Inventories and burn amounts are illustrative, with no specific-impulse or mission mass-budget calculation. Hydrogen delivered to the lander is included in the cycler gauges; the lander’s own burns and boil-off are not modeled. Propulsion background: NASA hydrogen propulsion overview.
Body sizes to scale; distance compressed for viewing.
Click the gold cycler to track · Drag to orbit · Pinch or scroll to zoom · Click a world for its role
Illustrative Earth-centered model. The Moon’s near side faces Earth; Earth’s rotation is smoothed for visibility. Flight times are compressed, and spacecraft, orbital clearances, and docking gaps are enlarged.
O2FR addresses oxygen production. A refueling service would also need equipment to purify, liquefy, store, and transfer the oxygen.
Earth texture: NASA Blue Marble. Moon texture: NASA Scientific Visualization Studio. Propellant context: NASA lunar oxygen refueling research.
Other uses
Beyond refueling, lunar oxygen could support water production and energy storage. These uses would require additional equipment.
Oxygen accounts for eight-ninths of water’s mass. Combining lunar oxygen with imported hydrogen could reduce the reactant mass shipped from Earth. Any savings must be weighed against storage requirements, transport losses, and processing energy.
Source: NASA in-situ resource utilization.
Surplus daytime electricity could split water into hydrogen and oxygen for storage. Recombining them could later generate power and recover the water. PLAZAIC is considering a hydrogen–oxygen turbine generator for this purpose; its efficiency and hardware require validation.
Source: NASA lunar energy storage.
Hydrolox and methalox engines combine oxygen with hydrogen or methane fuel. If production and liquefaction reach sufficient scale, lunar oxygen could supply compatible landers and transfer vehicles.
Source: NASA lunar oxygen refueling research.