OCO-3

While OCO-2 is a free-flying satellite in a polar sun-synchronous orbit, OCO-3 was installed on the International Space Station's Japanese Experiment Module in May 2019, giving it a different orbital coverage pattern. OCO-3 also features a unique pointing mirror assembly that enables it to collect Snapshot Area Maps of specific targets like cities and power plants.

OCO-3 is mounted on the Japanese Experiment Module—Exposed Facility (JEM-EF) on the exterior of the ISS. Because the ISS orbits at approximately 51.6 degrees inclination, OCO-3 observes nearly the entire sunlit Earth but lacks the full polar coverage that OCO-2 achieves in its sun-synchronous polar orbit.

OCO-3 uses three high-resolution grating spectrometers to measure sunlight absorbed by carbon dioxide molecules in specific infrared wavelength bands near 1.61 and 2.06 micrometers. By analyzing the absorption spectra, scientists can determine the column-averaged CO2 concentration in the atmosphere below the ISS, identifying both sources and sinks of carbon.

OCO-3's pointing mirror assembly and Snapshot Area Map mode were specifically designed to target localized emission sources such as major cities and industrial regions, a capability that OCO-2's fixed pointing system cannot match. While it cannot resolve individual smokestacks, its data has been used to map elevated CO2 plumes over metropolitan areas like Los Angeles and Tokyo.