It was initially scheduled to launch on January 10 and later January 11, but was delayed twice due to weather conditions and technical issues. NROL-47 is NRO's 50th launch since 1996.
The top secret NRO missions are generally classified - so it is unclear what specifically the satellite will be doing on its orbit around earth.
With more than a century of combined heritage, United Launch Alliance is the nation's most experienced and reliable launch service provider. As per Space.com, the National Reconnaissance Office (NRO), which builds and manages the spy satellites of the USA, will operate the new classified NROL-47 satellite.
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The launch will happen at Space Launch Complex-6, which sits about 140 miles west of downtown Los Angeles.
UPDATE (4:45 p.m.): Thursday's scheduled Delta IV launch from Vandenberg Air Force Base has been called off. The Delta IV M+(5,2) and Delta IV M+(5,4) have two and four SRMs, respectively, and 5-m-diameter PLF. They burned for about 90 seconds and provided more than 560,000 pounds of thrust.
The GEM 60s provided additional thrust to the lone Aerojet Rocketdyne RS-68A engine located in the Delta IV's first stage. It was also the 36th flight of the Delta IV rocket since its inaugural launch in 2002. The RS-68A engine provided an estimated 702,000 pounds of thrust during the initial phase of the flight.
ULA said: "The ULA #DeltaIV #NROL47" launch for the @NatReconOfc was scrubbed today due to an issue with a ground system valve. "We are proud to provide this national defense capability, and every Team V member involved has tirelessly worked to ensure the launch is safe and successful".