Photos: Atlas 5 on the pad awaiting liftoff on NROL-52

The United Launch Alliance Atlas 5 rocket, standing 197 feet tall and and weighing 1.2 million pounds, unleashes 2.4 million pounds of thrust from its main engine and four solid-fuel boosters at 6:42 p.m. EST (2342 GMT) Saturday to launch the GOES-R weather observer for NASA and NOAA from Cape Canaveral, Florida.

Two U.S. military satellite launches planned for this fall from Cape Canaveral are being delayed to 2018 due to separate factors, the Air Force says.

Taking a U.S. national security satellite payload into space is the primary objective of the 70th Atlas 5 booster that will be launched Wednesday.