VANDENBERG AIR FORCE BASE, Calif. -- On Launch Complex 576-E at Vandenberg Air Force Base in California, NASA's Orbiting Carbon Observatory, or OCO, upper stack is prepared to be raised to vertical. The upper stack, consists of Stages 1, 2 and 3 of Orbital Sciences' Taurus XL rocket as well as the encapsulated OCO spacecraft. Once vertical, the upper stack will be lifted and attached to the Taurus Stage 0, at left. OCO is scheduled for launch aboard the Taurus Feb. 24 from Vandenberg. The spacecraft will collect precise global measurements of carbon dioxide (CO2) in the Earth's atmosphere. Scientists will analyze OCO data to improve our understanding of the natural processes and human activities that regulate the abundance and distribution of this important greenhouse gas. Photo credit: NASA/Dan Liberotti, VAFB KSC-2009-1715