NASA's Orbiting Carbon Observatory, a reflight of the spacecraft by the same name, was mounted atop its Delta 2 rocket booster at Vandenberg Air Force Base in California on Saturday.

The OCO 2 observatory. Credit: NASA/Doug Gruben, 30th Space Wing

Replacing the observatory lost in a 2009 launch failure, OCO No. 2 seeks to understand how the Earth breaths and map global carbon dioxide levels.

The craft was hauled to Space Launch Complex 2 early Saturday morning for hoisting aboard its rocket, the United Launch Alliance Delta 2 that returns to action after a two-year hiatus.

The two stage rocket and its three strap-on solid-fuel boosters will deliver OCO 2 into a polar orbit. The observatory will fly 438 miles high and scan the entire planet from pole to pole once every 16 days.

"Understanding the processes controlling carbon dioxide in our atmosphere will help us predict how fast it will build up in the future. Data from this mission will help scientists reduce uncertainties in forecasts of how much carbon dioxide will be in the atmosphere and improve the accuracy of global climate change predictions," said Michael Gunson, OCO 2 project scientist.

The Orbiting Carbon Observatory was designed to study natural and man-made carbon dioxide emission and absorption to assist scientists assess how the greenhouse gas might be contributing to global warming.

"Knowing what parts of Earth are helping remove carbon from our atmosphere will help us understand whether they will keep doing so in the future," Gunson said.

An artist's concept of OCO 2. Credit: NASA/JPL-Caltech

The craft's single instrument is a three-channel, high-resolution spectrometer fed by a common telescope to measure carbon dioxide and molecular oxygen absorption of sunlight reflected off the same location on Earth's surface. The device works in the near-infrared part of the electromagnetic spectrum, invisible to the human eye.

OCO will observe how the carbon dioxide level varies from place to place as well as the different absorption rates.

"Carbon dioxide in the atmosphere plays a critical role in our planet's energy balance and is a key factor in understanding how our climate is changing," said Michael Freilich, director of NASA’s Earth Science Division in Washington.

"With the OCO 2 mission, NASA will be contributing an important new source of global observations to the scientific challenge of better understanding our Earth and its future."

The mission comes five years after the devastating blow of losing the first OCO when the Taurus rocket launching the craft failed to jettison its nose cone, weighing down the booster and preventing it from reaching orbital speed.

The Delta 2 rocket for OCO 2. Credit: NASA/Randy Beaudoin

Ready to try again, the OCO 2 was trucked to the launch pad overnight from the commercial Astrotech payload processing facility on North Vandenberg where the craft had been fueled and tested. Once at the pad, the satellite was hoisted into the gantry and mated to the Delta 2 rocket's second stage.

Encapsulation within the rocket's 10-foot-diameter composite payload fairing is planned for next week.

Liftoff is slated for 2:56 a.m. PDT on July 1.