Since October 2010 and after successfully completing the requisite reviews, the OCO-2 mission has been in implementation to meet the new launch date. OCO-2 will be based on the previously launched Orbiting Carbon Observatory (OCO) satellite and will carry a single instrument, consisting of three high-resolution grating spectrometers (instruments that measure properties of light within the electromagnetic spectrum). This instrument will obtain the most precise measurements of atmospheric CO2 ever made from space. The spacecraft, developed by Orbital Sciences Corp., will be based upon the LeoStar-2 architecture, which was also used on the successful Earth orbiting SORCE and GALEX missions. OCO-2 will fly in a near-polar orbit, thus enabling it to observe most of the Earth's surface at least once every sixteen days.
Since the abundance of CO2 in the atmosphere varies with the time of day and season, OCO-2 measurements will record changes in CO2 over yearly and seasonal cycles within each year. To remove the effect of changes in CO2 abundances each day and discriminate between seasonal variations and long term changes, OCO-2 will acquire measurements in the sun-synchronous orbit. This means that OCO-2 will measure carbon dioxide over a given point on Earth’s surface at the same local mean solar time.
The Observatory will fly with a series of other Earth orbiting satellites, known as the Earth Observing System Afternoon Constellation or the A-train. These satellites all cross the equator at approximately noontime, a few minutes apart from each other. This coordinated flight formation will enable researchers to correlate OCO-2 data with data acquired by other instruments onboard Earth observing spacecrafts, such as the Atmospheric Infrared Sounder (AIRS) instrument, which flies on the Earth Observing System Aqua platform and the Tropospheric Emission Spectrometer (TES), which flies on the Earth Observing System Aura.
To provide the mission with additional flexibility, the Observatory will acquire data in three different measurement modes. In Nadir Mode, the instrument views the ground directly below the spacecraft. In Glint Mode, the instrument tracks near the location where sunlight is directly reflected on the Earth's surface. Glint Mode enhances the instrument's ability to acquire highly accurate measurements, particularly over the ocean. In Target Mode, the instrument views a specified surface target continuously as the satellite passes overhead. Target Mode provides the capability to collect a large number of measurements over sites where alternative ground-based and airborne-instruments also measure atmospheric CO2. The OCO-2 Science Team will compare Target Mode measurements with those acquired by ground-based (e.g., from the Total Carbon Column Observing Network (TCCON)) and airborne-instruments to calibrate the OCO-2 instrument and validate mission data.