WASHINGTON -- NASA's first spacecraft dedicated to studying carbon dioxide, the leading human-produced greenhouse gas driving changes in Earth's climate, has arrived at Vandenberg Air Force Base, Calif., to begin final launch preparations.

The Orbiting Carbon Observatory arrived Nov. 11 at its launch site on California's central coast after completing a cross-country trip by truck from its manufacturer, Orbital Sciences Corp. in Dulles, Va. The spacecraft left Orbital on Nov. 8. After final tests, the spacecraft will be integrated onto an Orbital Sciences Taurus rocket in preparation for its planned January 2009 launch.

The observatory will help solve some of the lingering mysteries in our understanding of Earth's carbon cycle and its primary atmospheric component, carbon dioxide, a chemical compound that is produced both naturally and through human activities. Each year, humans release more than 30 billion tons of carbon dioxide into the atmosphere through the burning of fossil fuels. As much as 5.5 billion tons of additional carbon dioxide are released each year by biomass burning, forest fires and land-use practices such as "slash-and-burn" agriculture. These activities have increased atmospheric carbon dioxide levels by almost 20 percent during the past 50 years.

Greenhouse gases like carbon dioxide trap the sun's heat within Earth's atmosphere, warming it and keeping it at habitable temperatures. However, scientists have concluded that increases in carbon dioxide resulting from human activities have thrown Earth's natural carbon cycle out of balance, increasing global temperatures and changing the planet's climate.

While scientists have a good understanding of carbon dioxide emissions resulting from burning fossil fuels, their understanding of carbon dioxide from other human-produced and natural sources is relatively poor. They know from ground measurements that only 40 to 50 percent of the carbon humans emit remains in Earth's atmosphere; the other 50 to 60 percent, they believe, is absorbed by Earth's ocean and land plants.

Scientists do not know, however, precisely where the absorbed carbon dioxide from human emissions is stored, what natural processes are absorbing it or whether those processes will continue to work to limit increases in atmospheric carbon dioxide in the future as they do now. The observatory's space-based measurements of atmospheric carbon dioxide will have the precision, resolution and coverage needed to provide the first complete picture of both human and natural sources of carbon dioxide emissions. It will show the places where they are absorbed, known as "sinks," at regional scales everywhere on Earth. Its data will reduce uncertainties in forecasts of how much carbon dioxide is in the atmosphere and improve the accuracy of global climate change predictions.

The observatory's science instrument features three first-of-a-kind high-resolution spectrometers that spread reflected sunlight into its various colors. By analyzing these spectra, scientists can detect what gases are in Earth's atmosphere and determine their amounts. The spectrometers are specifically tuned to measure the amount of reflected sunlight absorbed by carbon dioxide and molecular oxygen. These measurements will be analyzed to yield monthly estimates of atmospheric carbon dioxide over 621-square-mile regions of Earth's surface to an accuracy of 0.3 to 0.5 percent. Scientists will analyze these data using global atmospheric chemical transport models, similar to those used to predict the weather, to locate carbon dioxide sources and sinks.

The observatory will launch into a 438-mile near-polar, sun-synchronous orbit inclined 98.2 degrees to Earth's equator, mapping the globe once every 16 days. The mission is designed to last two years. It will fly in formation with the five other NASA missions that are part of the "A-Train" or afternoon constellation of Earth Observing System satellites that cross the equator each day shortly after noon. This coordinated flight formation will enable researchers to correlate the observatory's data with data from the other NASA spacecraft, including nearly simultaneous carbon dioxide measurements from the Atmospheric Infrared Sounder instrument on NASA's Aqua satellite.

The Orbiting Carbon Observatory is a NASA Earth System Science Pathfinder Program mission managed by NASA's Jet Propulsion Laboratory in Pasadena, Calif., for NASA's Science Mission Directorate in Washington. Orbital Sciences provides mission operations under JPL's leadership. Hamilton Sundstrand in Pomona, Calif., designed and built the observatory's science instrument. NASA's Launch Services Program at NASA's Kennedy Space Center in Florida is responsible for launch management.

For more information about the Orbiting Carbon Observatory, visit:

http://oco.jpl.nasa.gov