Lift-off for Nasa’s ‘CO2 hunter’

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Nasa has launched its first mission dedicated to measuring carbon dioxide (CO2) from space.

The Orbiting Carbon Observatory (OCO) will help pinpoint the key locations on our planet’s surface where the gas is being emitted and absorbed.

CO2’s increased concentration in the atmosphere will lead to global climate change, say the major institutions and agencies that study Earth sciences.

The OCO data is intended to help forecast that change more accurately.

Currently, carbon dioxide is regularly sampled at about a hundred sites around the world. The new satellite will be taking roughly 30,000 readings on each orbit.

“We need to make a measurement that is about three times more precise than has ever been made for a trace gas in the Earth’s atmosphere,” said Dr David Crisp, OCO’s principal investigator.

“We regularly measure ozone in the Earth’s atmosphere to about 1%. We need to make a measurement of CO2 to about three-tenths of 1% to start answering the questions that face scientists.”

Colour clues

The $270m mission was launched by the smallest ground-launched rocket currently in use by the US space agency.

The Taurus XL vehicle left the Vandenberg Air Force Base in California at 0951 GMT, Tuesday.

It lofted OCO into a near-polar orbit at an altitude of 705km (438 miles). The spacecraft will circle the planet once every 98.8 minutes, passing over the entire globe in the course of 16 days.

Nasa stresses the mission is an experimental one; it first has to establish that the measurement approach it has adopted is a robust one.

OCO carries a spectrometer that analyses the sunlight reflected off the Earth’s surface. By splitting that light into its component colours, it will be able to see the part of the spectrum absorbed by carbon dioxide molecules.

By measuring oxygen’s presence in the atmosphere also, OCO should be able to arrive at a concentration figure for CO2. The instrument is sensitive to carbon dioxide in the lower reaches of the atmosphere.

“We’ll be pumping down about 50 gigabits of data every day,” said Dr Crisp.

“We’re a very small spacecraft - we’d be a very cosy telephone booth - but we’ll pump down data at such a high rate I often joke we’ll melt the snow around the base of the down-link station.”