United Launch Alliance will try again Wednesday to put NASA's long-awaited Orbiting Carbon Observatory into orbit around Earth for a two-year mission, following a last-minute launch scrub early Tuesday.
A water deluge system at Space Launch Complex 2 at California's Vandenberg Air Force Base failed to activate as planned, triggering the delay.
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The system helps protect the pad from high temperatures and potentially damaging acoustic vibrations during launch.
Technicians later traced the problem to a failed valve, NASA said in a statement.
United Launch Alliance will try again at 2:56 a.m. PDT/5:56 a.m. EDT on Wednesday to get its Delta 2 rocket off the pad.
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The rocket has just a 30-second launch window to hit its intended orbit. The OCO observatory is to become the lead satellite in a train of remote sending spacecraft in polar orbit around Earth.
OCO is designed to make very detailed, global measurements of concentrations of carbon dioxide in the atmosphere, a greenhouse gas tied to global warming.
OCO is a replacement for a nearly identical spacecraft that was destroyed in a 2009 launch accident.