Artist rendition of NASA's OCO-2 orbiting above the Earth. Image Credit: NASA

Last month, NASA's Orbiting Carbon Observatory-2 (OCO-2) lifted off from California's Vandenberg Air Force Base atop a United Launch Alliance (ULA) Delta II rocket. OCO-2 has now parked in its designated spot, at the head of the "A-Train" (the name given to the international collaborative effort designed to measure atmospheric carbon dioxide levels). This makes it the first successful spacecraft designed to exclusively study atmospheric carbon dioxide. The spacecraft recently "opened its eyes" and collected its first bits of data, confirming the health of the science instrument on board.

OCO-2 will supply scientists with the most detailed images of global carbon dioxide sources and sinks (the latter being regions where the gas is naturally removed from the atmosphere). This detailed picture will assist researchers in understanding the evolution of both CO2 sources and sinks. The vehicle's orbiting altitude is 438 miles (705 kilometers) above the Earth. In order to reach this orbit, the observatory had to go through a series of post launch steps. Mission control established communications with the vehicle, then stabilized its orientation, and finally deployed the solar arrays, supplying the spacecraft with power. A final systems check indicated OCO-2 was functioning normally.

In order to assume its position as the lead observatory in the international Afternoon Constellation (the previously mentioned "A-Train"), OCO-2 performed a series of propulsive burns. The A-Train is considered to be a multi-satellite "super observatory", and is designed to analyze specific conditions in the Earth's atmosphere and surface environments. Collectively, the many satellites record near simultaneous weather, climate, oceanic ,and land measurements. OCO-2 is the leader of the pack, followed by the Japanese GCOM-W1 satellite, then NASA's Aqua, CALIPSO, CloudSat, and Aura spacecraft at 16-minute intervals.

OCO-2 is equipped with a three-spectrometer science instrument. Prior to use and to ensure the maximum sensitivity, both the instrument and the detectors needed to be cooled to operating temperatures. In order to focus the instrument and to limit the amount of heat radiating from it, the spectrometer needed to be cooled to around 21 degrees Fahrenheit (-6 degrees Celsius), and the detectors to around -243 degrees Fahrenheit (-153 degrees Celsius).

Spectra data recorded by OCO-2. Image Credit: NASA/JPL-Caltech

Once these temperatures had been reached, the team set out to test the spectrometer to see if it functioned to the same levels it did prior to launch. On August 6, as the vehicle soared above Papua New Guinea, OCO-2 collected its "first light". The data collected was transferred from the orbiting observatory to a ground station in Alaska, then to NASA's Goddard Space Flight Center for decoding, and finally on to NASA's Jet Propulsion Laboratory. This data was evidence that OCO-2 and the ground stations were properly functioning.

OCO-2 records up to one million science observations each day. As it orbits the Earth, OCO-2 collects sunlight. Each spectrometer collects one frame of light three times each second, for a total of 9,000 frames each orbit. The individual frames are then divided into eight chemical signatures, or spectra. The spectra measure the molecular oxygen or carbon dioxide levels over corresponding ground "footprints". The spectra are then converted into an image. Appearing as car codes, the bands of light are separated by sharp, dark lines. These lines are indicative of either the molecular oxygen or the carbon dioxide absorption.

"The initial data from OCO-2 appear exactly as expected -- the spectral lines are well resolved, sharp and deep," said OCO-2 chief architect and calibration lead Randy Pollock of JPL. "We still have a lot of work to do to go from having a working instrument to having a well-calibrated and scientifically useful instrument, but this was an important milestone on this journey."

Over the next few weeks, the team will continue to test the instrument, conducting a series of calibration techniques. The team expects to share spectra data with the science community before the end of this year and estimates carbon dioxide levels will be distributed early next year.


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