VANDENBERG AIR FORCE BASE, Calif. -- With the fairing door off, Orbital Sciences' Glenn Weigle and Brett Gladish maneuver into position to take the GN2 flow reading from NASA's Orbiting Carbon Observatory, or OCO, spacecraft. At left, Jose Castillo and Mark Neuse stand by to replace the fairing door when the OCO operation is complete. The spacecraft sits atop Orbital Sciences' Taurus XL rocket. At right is a portion of the umbilical tower attached to the upper stack. The spacecraft sits atop Orbital Sciences' Taurus XL rocket. At right is a portion of the umbilical tower attached to the upper stack. 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 courtesy of Jim Stowers, Orbital Sciences