OCO-2. Credit: Jet Propulsion Laboratory

SAN FRANCISCO — The spacecraft NASA plans to launch July 1 to replace the carbon dioxide measurement spacecraft lost in a 2009 rocket failure is not markedly different from its predecessor, but the questions the mission seeks to answer have changed dramatically.

In 2009, when NASA launched the first Orbiting Carbon Observatory (OCO), researchers could identify the primary sources in the United States, Europe and Japan responsible for the majority of the world’s man-made carbon dioxide emissions because those nations monitor power plants and fuel sales. Five years later, more than half of the atmospheric carbon dioxide stems from emissions in the developing world, primarily China and India, whose governments have been unable to track the rapid increases in carbon dioxide emissions, said David Crisp, OCO-2 science team leader and principal investigator at the Jet Propulsion Laboratory in Pasadena, California.

At the same time, atmospheric carbon dioxide levels have continued to climb. In 2009, measurements from Hawaii’s Mauna Loa Observatory indicated an average monthly value of 387 carbon dioxide molecules for every million gas molecules in Earth’s atmosphere. In 2013, monthly average atmospheric carbon dioxide levels at this site reached 396 parts per million. 

In spite of that increase, Earth’s oceans, forests and other terrestrial ecosystems continue to absorb approximately half of the carbon dioxide emitted. 

“Why is it that regardless of how much faster we put carbon dioxide into the atmosphere, the ocean and the land biomass has been able to keep absorbing half of it?” Crisp asked. 

Researchers also want to know how Earth is responding to increases in carbon dioxide emissions. 

“On one hand, if increasing temperatures reduce atmospheric moisture, does that reduce the ability of the world’s forests to take up carbon dioxide?” asked Michael Gunson, OCO-2 project scientist. Or, he said, will the fact that increased levels of atmospheric carbon dioxide are lengthening the growing seasons for some types of vegetation help to sustain the ability of the world’s forests to take carbon dioxide out of the atmosphere?

The OCO-2 mission seeks to answer those questions by making 1 million daily measurements of carbon dioxide and oxygen molecules in Earth’s atmosphere based on the way those molecules absorb sunlight. Researchers plan to use those data to identify the locations on Earth where human and natural sources produce carbon dioxide, determine which oceans, forests or other ecosystems absorb carbon dioxide, and observe changes over time.

Today, most data on atmospheric carbon dioxide concentrations come from about 150 ground stations, clustered primarily in the United States, Europe, Australia and Japan. Although clouds will interfere with many of OCO-2’s measurements, the mission still is expected to generate far more data on carbon dioxide emissions than are currently available. The OCO-2 team expects to obtain valuable information from at least 10 percent of the spacecraft instrument’s 1 million daily measurements, said Ralph Basilio, OCO-2 project manager.

The OCO-2 spacecraft, built by Orbital Sciences Corp. and equipped with a three-channel grating spectrometer built by JPL, is scheduled for launch July 1 on a United Launch Alliance Delta 2 rocket from Vandenberg Air Force Base in California into a sun-synchronous, near-polar orbit. The OCO-2 instrument is similar to the one developed by Hamilton Sundstrand of Pomona, California, and JPL for the first OCO mission, which was destroyed in February 2009 when the payload fairing on an Orbital Sciences Taurus XL rocket failed to separate.

Immediately after the launch failure, the OCO team began working with the Japan Aerospace Exploration Agency to analyze data drawn from the Greenhouse Gases Observing Satellite (GOSAT), a mission launched in January 2009 to measure atmospheric carbon dioxide and methane. “That partnership has allowed us to mitigate technical risks and plan to deliver OCO-2 data sooner than we had originally envisioned on OCO,” Basilio said.

After launch into a transfer orbit, OCO-2 will use its onboard thrusters to move into the constellation of international Earth observing satellites, known as the A-train. Then, the instrument needs to be cooled before the OCO-2 team can begin learning to make measurements, retrieve and analyze data. In February or March of 2015, OCO-2 is scheduled to begin delivering carbon dioxide measurements to the global research community. “By that time we should be putting verified, validated data into the archive so it can be distributed to the entire world,” Crisp said. 

In addition to pinpointing carbon dioxide sources and absorbers of the greenhouse gas, researchers are eager to use OCO-2 data to study solar-induced fluorescence, the minuscule amount of light emitted by plants at near-infrared wavelengths during photosynthesis. In 2011, researchers at JPL and NASA’s Goddard Space Flight Center in Greenbelt, Maryland, used GOSAT data to produce the first maps of global plant health based on measurements of fluorescence. That research will be bolstered by OCO-2 data because one of its instrument channels is tuned to the wavelength to identify solar-induced fluorescence because engineers wanted to ensure that this light source would not interfere with carbon dioxide measurements.

“By better understanding an error source, we were able to find additional geophysical data we can publish from this mission,” Basilio said.

If OCO-2 proves to be a valuable data source, its success is likely to improve the outlook for OCO-3, a mission designed to use spare parts from OCO-2 to build an additional carbon dioxide measurement instrument and install it on the exterior of the international space station, NASA officials said. 

The OCO-3 mission is “on hold,” Betsy Edwards, OCO-2 program executive at NASA headquarters, said during a June 12 press briefing. “We hope to get back to OCO-3, but right now the budget doesn’t allow for us to do that.”