The Delta IV medium rocket will carry a national security payload designed, built and operated by the NRO, the agency said.
That Falcon 9 rocket launch delivered 10 satellites into low-Earth orbit for Iridium, a communications company.
The original launch, scheduled for Wednesday, was scrubbed due to high winds. "My honest thanks to the entire ULA team and our mission partners at the NRO and U.S. Air Force who made this, our 27th NRO launch, possible". NROL-47 will join the Future Imagery Architecture (FIA) satellite constellation, which flies under the code name Topaz.
"This was an incredibly important launch for the 30th Space Wing and our mission partners", said Wood.
If you see a rocket in the sky tonight, don't panic it's supposed to be there.
The launch of the new classified reconnaissance satellite has been much anticipated - as it has been delayed several times. While it's no longer a secret, it does still use its systems to collect information and "Play a crucial role in providing global communications, precision navigation, early warning of missile launches and potential military aggression, signals intelligence, and near real-time imagery to US forces to support the war on terrorism and other continuing operations", according to the NRO site. The common booster core was powered by an RS-68A liquid hydrogen/liquid oxygen engine. "The forecast shows a 90% chance of favourable weather conditions for launch".
United Launch Alliance, headquartered in Denver, is a joint venture of Lockheed Martin and the Boeing Co.
The mission was due to take place at Space Launch Complex-6 - around 140 miles from downtown Los Angeles in California.
The launch was delayed twice earlier this week.
"We are proud to provide this national defence capability and every Team V member involved has tirelessly worked to ensure the launch is safe and successful". "This will be the first of two launches scheduled for NRO in 2018".