One early winter morning, David Crisp watched his dream launch into outer space.

He was at the takeoff for a new NASA satellite he conceived, a mission called the Orbiting Carbon Observatory, which would track carbon dioxide from space. Crisp, a senior research scientist at NASA's Jet Propulsion Laboratory in California, had worked on the project for nine years.

As the rocket carrying the satellite left Southern California's Vandenberg Air Force Base and shot into the sky, the researcher and his science team tracked its path.

"Everything went absolutely perfectly for the first three minutes and 42 seconds," Crisp said. "And then everything went wrong."

The rocket carrying the satellite failed to shed a certain portion that protected the satellite during launch and was too heavy to reach orbit. Crisp and his team watched in horror as their mission crashed into the Pacific Ocean, somewhere near Antarctica. It was Feb. 29, 2009.

"It wasn't my best day," Crisp said. The researcher now discusses the devastating moment with the calm precision of a scientist.

But since he first conceived the project nearly 15 years ago, he and other scientists had been eagerly awaiting the opportunity to use this satellite to track the increasingly vast quantities of carbon dioxide humans were emitting. Such information could be used as a foundation for tracking emissions if a global climate treaty is ever approved.

The launch failure meant that even as the question of where carbon dioxide was coming from and what, exactly, was soaking it up became increasingly important, the instrument that might have answered these questions was somewhere in the bottom of the ocean.

Crisp's NASA supervisors told him not to give up, that the Orbiting Carbon Observatory could get a second chance. It took a while, but eventually the second Orbiting Carbon Observatory—now called OCO-2—was approved and funded. If all goes as planned, it will take to the skies July 1.

Soon after, the observatory will begin its primary task: solving the mystery of the missing carbon.

Where carbon dioxide goes is still an open question
In the years since Crisp originally proposed the carbon observatory, average levels of atmospheric carbon dioxide have gone from about 365 parts per million to almost 400 ppm, unseen in Earth's recent history.

About 40 billion tons of carbon dioxide is released into the atmosphere every year as a result of human activities—around 5.5 tons per person on Earth.

Based on that figure, scientists have estimated that the amount of CO2 in the atmosphere should be increasing by about 1 percent a year.

"It's not," though, Crisp said. It's increasing by half that, or 0.5 percent per year.

So where is the rest of the carbon dioxide going? That's the question OCO-2 tries to answer.

Scientists have discovered that about half of the missing CO2, or a quarter of the total, is going into the ocean. But why that ratio stays constant, with the ocean always absorbing enough each year to equal half of the ever-increasing amount humans release, is still a mystery.

As to what happens to the rest of the missing carbon dioxide, scientists assume it gets taken up by forests and soil. Which forests do the heavy lifting, though, is still an open question.

"Something in the ocean or in the land biosphere is absorbing half of the carbon dioxide we have been emitting," Crisp said.

As the globe warms and more CO2 is pumped into the atmosphere, scientists need to understand just where the carbon is going in order to predict what might change in the future, said Annmarie Eldering, the deputy project scientist for the new carbon observatory mission.

"The role of the tropics is a big question. Some people think the tropics are responsible for taking up all this carbon right now, and other people think it is really the [boreal forests in the] north," she said.

Understanding this could help people make decisions about how to combat climate change, too. If scientists learn that tropical forests take up a majority of carbon dioxide, more actions could be taken to protect or restore them. If in fact it is boreal forests high in the Arctic, priority can go toward their conservation.

The satellite helps in this project by taking very precise measurements of the amount of carbon dioxide in the atmosphere. OCO-2 will collect "at a million points a day," Eldering said. It has to take so many because just 10 to 20 percent of those samples will result in accurate estimates of atmospheric carbon dioxide.

The primary advantage of the space-based measurements is their coverage and resolution.

"We'll create this great, dense complete set of CO2 measurements across the globe," she said.

The scientists will use these measurements to calculate carbon dioxide concentrations in the atmosphere. These are compared with ground-truth measurements from Earth's surface, to make sure they are accurate.

While NASA scientists and others eagerly await OCO-2's launch, an earlier satellite launched in 2009 by a consortium of Japanese partners, including the Japanese Aerospace Exploration Agency (JAXA), the Ministry of the Environment, and the National Institute of Environmental Studies, has given them the opportunity to work with similar, if more limited, data.

The Japanese satellite is called the Greenhouse Gases Observing Satellite, also referred to as GOSAT. Of the up to 10,000 measurements GOSAT sensors can collect each day, around 1,000 of these are cloud-free enough to yield accurate estimates of both carbon dioxide and methane, another powerful greenhouse gas.

Working with the Japanese GOSAT team, the NASA scientists have learned a lot about how to measure greenhouse gases from space.

But as useful as GOSAT has been, it does not provide the information needed to quantify emission sources, or to solve the big question researchers like Crisp, Eldering and other climate scientists are after: identifying the natural processes responsible for absorbing the missing half of the carbon dioxide emitted into the atmosphere.

To do that, scientists need even greater sensitivity, resolution and coverage of the globe.

That's what OCO-2 does. It collects 96 times as many measurements as GOSAT, and each OCO-2 measurement is more sensitive to small changes in carbon dioxide, especially over dark surfaces.

Because of this, the new satellite is expected to provide much more useful data in partially cloudy regions, like those tropical rainforests, and over the ocean or in high northern forests.

"I was a little bit of a fanatic with precision and measurement density," Crisp admits.

An 'incredibly sensitive' measure from space
Although OCO-2's mission is to measure where carbon dioxide is coming from and where it is going, it does not directly measure those two values.

Rather, it uses the intensity of sunlight reflected off Earth's surface to determine the concentration of carbon dioxide molecules in the locations it measures, and then uses models to understand which locales, like cities or power plants, are sources of carbon dioxide, and which, like forests or the ocean, are absorbing it.

Because this method of measurement depends on "seeing" through to the Earth's surface, sometimes clouds or rugged topography like mountains can get in the way. That's why it needs such dense quantity of measurements, to help overcome that problem.

And even though human activities release a lot of carbon dioxide into the atmosphere, in order to detect that from space, the instrument has to be "incredibly sensitive," Crisp said.

For example, to see the carbon footprint of Los Angeles, he said, "we have to detect a 10th of a percent change in the brightness of certain colors of reflected sunlight. That is how well we have to calibrate this instrument."

Which is why, after the satellite launches, it will take a few months to get it into the correct orbit and calibrate its instruments, as scientists work to validating its measurements from space with other stations measuring atmospheric carbon dioxide from the ground.

Bonus measurement captures plant health
In the years between the loss of the original carbon observatory and OCO-2, scientists have also realized the mission has a side benefit—one of its instruments is able to measure whether plants are growing.

The satellite can measure a property called fluorescence, which is a light signal given off by growing plants. It can't be seen by the human eye, but as long as a plant is photosynthesizing, it is also releasing some light, or fluorescing.

This measurement allows researchers to understand how large forests, which take up huge amounts of carbon dioxide and release oxygen, respond to droughts of varying intensity, said Joshua Fisher, a scientist at NASA's Jet Propulsion Laboratory. This measurement can also help farmers see drought in crops.

Many global climate models are predicting that parts of the Amazon rainforest might die as droughts intensify in the future. Since this massive forest takes up a lot of carbon dioxide and releases a lot of oxygen, that is "a bit worrisome," Fisher said.

Originally, this measurement of fluorescence was supposed to be a correction to the other measurements the satellite makes. But then scientists realized it could also be used independently to measure plant health.

Other satellites traditionally used to monitor plant activity often use a measure called greenness, which is just what it sounds like—they see changes in the colors of plants from space. But just like cut flowers in a vase, plants can be green and also be dead, explains Fisher—and scientists often wouldn't know it until too late.

In contrast, the fluorescence signal only comes from growing plants, giving researchers the ability to see if plants are growing or if they are stressed.

In combination with another recently launched NASA satellite, the Global Precipitation Measurement (ClimateWire, Jan 28), and a new soil moisture measuring satellite that will launch later this year, scientists like Fisher will be able to track different kinds of stress on forests, whether they be drought or loss of soil moisture, and use the OCO-2 mission to see how that affects growth and how plants soak up carbon dioxide.

"When you put these missions all together, you really start to describe the entire Earth rather than just one aspect of it," Fisher said.

Completing 'unfinished business'
Since the first mission fell into the ocean, there's been the inevitable question: Will this one make it?

While there is always some risk, Ralph Basilio, the project manager for the second Orbiting Carbon Observatory, said the launch vehicle for this satellite, the Delta II rocket, has a better than 98 percent success rate.

The emotions Basilio experienced when the first observatory fell into the sea he would not wish even on his worst enemy, the scientist said. After the failed launch, he was at a loss.

"An engineer is trained to solve problems. And we didn't have a problem to solve," he said. "We had zero. And that was a very painful moment to us."

The logo for the second Orbiting Carbon Observatory mission looks like a phoenix, rising up to cover the globe. And at a cost of $467.7 million and years in the making, no one wants to see this phoenix burn again anytime soon.

"We're all excited to have this opportunity to launch on July 1," Basilio said. "It's an opportunity again to fill this void that has been with us over the last five years. We want to be able to complete this unfinished business."

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500