Technicians prepare to roll the mobile service tower away from the United Launch Alliance Delta II rocket at Space Launch Complex 2.

Technicians prepare to roll the mobile service tower away from the United Launch Alliance Delta II rocket carrying NASA's Orbiting Carbon Observatory-2, or OCO-2, at Space Launch Complex 2 on Vandenberg Air Force Base in California.

Launch of OCO-2 is scheduled for 5:56 a.m. EDT on July 2 following the repair of the pad's water suppression system, which failed on the first launch attempt July 1. OCO-2 is NASA’s first mission dedicated to studying atmospheric carbon dioxide, the leading human-produced greenhouse gas driving changes in Earth’s climate. OCO-2 will provide a new tool for understanding the human and natural sources of carbon dioxide emissions and the natural "sinks" that absorb carbon dioxide and help control its buildup. The observatory will measure the global geographic distribution of these sources and sinks and study their changes over time. To learn more about OCO-2, visit http://www.nasa.gov/oco2. Photo credit: NASA/Kim Shiflett