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The Orbiting Carbon Observatory (OCO) was a NASA Earth System Science Pathfinder Project (ESSP) mission designed to make precise, time-dependent global measurements of atmospheric carbon dioxide (CO2) from an Earth orbiting satellite. Unfortunately, on February 24, 2009, due to a launch vehicle payload fairing anomaly, OCO failed to reach orbit.

However, in December 2009, the Congressional Conference committee directed NASA to allocate no less than $50M for the 2010 fiscal year (FY10) for the initial costs associated with an OCO replacement. Released on February 1st, 2010, the President's Budget provided adequate funding to support the launch of an OCO re-flight mission (now known as OCO-2). The OCO-2 mission underwent critical design review (CDR) in August 2010 and key design point-C (KDP-C) in September 2010. On October 2010, it began the implementation phase.

On July 16, 2012, NASA announced that it had awarded launch services contracts for three United Launch Alliance Delta 2 rockets. A little over 5 years after the OCO launch failure, OCO-2 launched from Vandenburg Air Force Base on Wednesday, July 2, 2014. Originally flown on a Taurus XL, OCO-2 flew on a Boeing Delta II 7320-10C. The Delta II is one of the most successful launch vehicles ever flown with well over 100 successful launches.

OCO-2 was built based on the original Orbiting Carbon Observatory mission to minimize cost, schedule and performance impacts. OCO-2 is designed to have a nominal mission time frame of at least two years, but the spacecraft could continue to fly well beyond its prime mission. OCO-2's primary science objective is still to substantially increase our understanding of how carbon dioxide sources and sinks are geographically distributed on regional scales and how their efficiency changes over time.

As of December 22, 2015, OCO-3 was given the green light to move forward as the next installment in the OCO legacy that has and continues to build on using innovative technologies to continue NASA's space borne study of carbon dioxide. Initially, the OCO-3 Project was not included in the President’s Proposed Budget for FY2018 when it was released in February 2017. However, funding for the project was restored in March 2018 with the Enacted Budget for FY2018. At his first NASA town hall, NASA Administrator Jim Bridenstine mentioned OCO-3 and said, “… It’s not been cut. In fact, it’s going to be on orbit very, very soon.”

OCO-3 is a NASA-directed mission on the International Space Station (ISS). The primary mission objective is to collect the space-based measurements needed to quantify variations in the column averaged atmospheric carbon dioxide (CO2) dry air mole fraction, XCO2, with the precision, resolution, and coverage needed to improve our understanding of surface CO2 sources and sinks (fluxes) on regional scales (≥1000 km). The precision requirement is identical to that of OCO-2. Operations on ISS allows latitude coverage from 51 deg N to 51 deg S.

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