The launch of a rocket carrying a national security satellite from Vandenberg Air Force Base that was delayed multiple times this week is expected Friday shortly after 2 p.m. United Launch Alliance issued the following statement regarding the scrub:

(Vandenberg Air Force Base, Calif. Jan. 11, 2018) – The launch of a United Launch Alliance Delta IV carrying the NROL-47 mission was scrubbed today due to an issue with a ground system valve. United Launch Alliance’s CEO and President, Tory Bruno expressed the excitement of seeing the final planned launch of a Delta IV Medium+ (5,2) soar through California’s skies when he tweeted: “Delta is ripping the sky at incredible speed.”

The Delta IV Medium+ (5,2) rocket is part of a family of launch vehicles that are described as follows by the Colorado-based launch service provider:

The Delta IV family of launch vehicles combines design simplicity, manufacturing efficiency, and streamlined mission and vehicle integration to meet customer requirements to launch high-priority U.S. Air Force (USAF), National Reconnaissance Office (NRO), NASA, and commercial payloads to orbit. With operational launch pads on both coasts—Space Launch Complex-37 at Cape Canaveral Air Force Station, Fla., and Space Launch Complex-6 at Vandenberg Air Force Base, Calif.—every Delta IV configuration is available to service the requirements of current and future satellite programs. “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.”

The launch of a a SpaceX Falcon 9 rocket from Vandenberg’s Space Launch Complex-4 on Dec. 22 created a spectacular sight across Southern California skies at dusk, prompting immediate speculation about the mysterious shape of the rocket’s trail – and many, many posts on social media.
A Delta IV launches NROL-47, a classified U.S. military payload, from Vandenberg Air Force Base, California. It is the last single-core Delta IV to launch from Vandenberg.