NASA's Orbiting Carbon Observatory-3 (OCO-3) is installed on the International Space Station and continues the data record started by the OCO-2 platform. Launched on May 4, 2019, OCO-3 acquires space-based global measurements of atmospheric carbon dioxide (CO₂) with the precision, resolution, and coverage needed to characterize its sources and sinks (fluxes) on regional scales (≥1000km). Data from OCO-3 help quantify CO₂ variability over seasonal cycles and are also being used to help validate space-based measurement approaches and analysis concepts that could be used for future systematic CO₂ monitoring missions.

From its mounting on the International Space Station, OCO-3 acquires data between approximately 52 degrees north to 52 degrees south latitude—a spatial range that spans roughly from London to Patagonia. Most of Earth’s living things are found within these limits. The orbit enables OCO-3's instrument to collect a denser dataset than OCO-2 over high-carbon regions such as the Amazon rainforest.

The OCO-3 instrument was built using OCO-2’s spare instrument and the appropriate electronics and interfaces to operate on the space station’s Japanese Experiment Module-Exposed Facility (JEM-EF). The OCO-3 instrument consists of three high-resolution spectrometers integrated into a common structure and illuminated by a common telescope. One spectrometer measures how much sunlight oxygen in the atmosphere has absorbed, the other two measure sunlight absorption by CO₂ at two different sets of wavelengths. The ratio of CO₂ to oxygen is used to determine the concentration of atmospheric CO₂.