Launch and Early Operations of the NASA Orbiting Carbon Observatory – 2 Mission (OCO-2)
OCO-2 is a near duplicate of the Orbiting Carbon Observatory (OCO), which was NASA's first satellite designed to measure atmospheric carbon dioxide (CO2) with the precision, resolution, and coverage needed to identify its sources and sinks on regional scales. The OCO mission was lost in February 2009 when its launch vehicle malfunctioned and failed to reach orbit. NASA was directed to build a replacement for OCO 2010 and the OCO-2 project was initiated. OCO-2 was delivered to Vandenberg Air Force Base for integration with a Delta-II 7320 launch vehicle in late April, 2014, in preparation for a launch in early July. The OCO-2 launch proceeded smoothly. After a near-perfect 56-minute flight, the observatory was initially deployed in a sun synchronous orbit with a semi-major axis near 692 km, about 13 km below the 705 km Afternoon Constellation (A-Train). During its first week in space, the spacecraft checkout activities were successfully completed. The on-board propulsion system was then used to execute a series of maneuvers to adjust the orbit's altitude and inclination and the observatory's phase to insert OCO-2 at the head of the A-Train on 3 August 2014, following the CloudSat orbit track.
OCO-2 carries and points a single instrument that incorporates 3, high-spectral resolution imaging grating spectrometers, designed to measure the absorption of reflected sunlight by the 0.760-micron molecular oxygen (O2) A-Band and the CO2 bands centered near 1.61 and 2.06 microns. Spatially-coincident observations in the 3 channels are combined into “soundings” and analyzed with a “full-physics” remote sensing retrieval algorithm to yield spatially-resolved estimates of the column-averaged CO2 dry air mole fraction, XCO2. The instrument's optical bench and focal plane arrays remained warm during the launch and orbit raising maneuvers to minimize contamination, but will be cooled to their operating temperatures once OCO-2 is in the A-Train. If all goes as planned, “first light” will be recorded on 6 August 2014. Over the following 60 days, a rigorous series of geometric, radiometric, and spectroscopic calibration observations will be collected and analyzed to characterize the observatory and instrument on-orbit performance. Routine science observations are also expected to begin over this period, with the instrument returning about one million soundings each day over the sunlit hemisphere. Ten to twenty percent of these soundings are expected to be sufficiently cloud free to yield precise, full-column estimates of XCO2, surface pressure, and chlorophyll fluorescence.
Routine science observations will be collected continuously at 24 Hz along a narrow (< 10.6 km) path, either at the local nadir, or in the direction of the “glint spot”, where sunlight is specularly reflected from Earth's surface. Nadir observations are expected to yield the highest spatial resolution and the most cloud-free scenes in partially cloudy regions. Glint observations are expected to yield much more signal over ocean or ice covered surfaces, which are quite dark at short wave infrared wavelengths. OCO-2 will also target Total Carbon Column Observing Network (TCCON) stations as often as once each day, and collect thousands of soundings as it flies overhead for use in XCO2 validation. Calibrated, geo-located radiance spectra will start being delivered to the NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) for distribution to science community before the end of 2014. Validated estimates of XCO2 will start being delivered to the GES DISC during the first quarter of 2015.