The rocket is said to be carrying a spy satellite for the United States government.
The top secret NRO missions are generally classified - so it is unclear what specifically the satellite will be doing on its orbit around earth.
A Delta IV rocket is scheduled for launch Thursday afternoon from Vandenberg Air Force Base on the California coast.
It was initially scheduled to launch on January 10 and later January 11, but was delayed twice due to weather conditions and technical issues. "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".
Because of the secretive nature of the mission, not much is known about the NROL-47 payload.
If you see a rocket in the sky tonight, don't panic it's supposed to be there.
This satellite was launched aboard a Delta IV Medium (5,2) configuration Evolved Expendable Launch Vehicle. It performs launch services for the USA government at Vandenberg and Cape Canaveral Air Force Station in Cape Canaveral, Florida. The common booster core was powered by an RS-68A liquid hydrogen/liquid oxygen engine.
The launch provider United Launch Alliance (ULA) subsequently delayed it by 24 hours.
The launch, NROL-47, will mark ULA's 27th mission for the National Reconnaissance Office.
Col. Greg Wood, 30th Space Wing vice commander, was the space launch commander. "Aerojet Rocketdyne employees across the country work hard to ensure 100 percent mission success, and our role in yet another launch for the National Reconnaissance Office demonstrates the trust and confidence in our propulsion". The NRO publicized the launch with generic tweets, saying the mission was the first of two planned by the agency this year.