Workers prepare NASA's Orbiting Carbon Observatory or OCO upper stack for attachment to Orbital Sciences' Taurus XL rocket's Stage 0.

On Launch Complex 576-E at Vandenberg Air Force Base in California, workers prepare NASA's Orbiting Carbon Observatory, or OCO, upper stack for attachment to Orbital Sciences' Taurus XL rocket's Stage 0. The upper stack consists of Stages 1, 2 and 3 of the Taurus as well as the encapsulated OCO spacecraft. Orbital Sciences workers put the non-flight environmental shield over the fairing prior to erection. A portion of the umbilical tower (above it) is attached to the upper stack. 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