See the mighty Delta IV Heavy rocket's final West Coast launch in these stunning photos

So long, and thanks for all the classified satellites.

The mighty United Launch Alliance (ULA) Delta IV Heavy rocket launched from Vandenberg Space Force Base in California for the final time on Saturday (Sept. 24). The mission, known as NROL-91, blasted off at 6:25 p.m. EDT (2225 GMT; 3:25 p.m. local time) from Vandenberg's Space Launch Complex-6.

The Delta IV Heavy's final West Coast launch saw the rocket place a classified satellite into an unknown orbit on behalf of the U.S. National Reconnaissance Office (NRO), an agency within the Department of Defense tasked with operating spy satellites and disseminating the intelligence they gather throughout the U.S. military and intelligence communities. 

Related: Delta IV Heavy: Powerful launch vehicle

The 217-foot-tall (66.2 meters) ULA Delta IV Heavy has been in service since its first flight in 2004. The rocket was built by McDonnell-Douglas (which was later acquired by Boeing) and can launch to geosynchronous transfer orbit payloads weighing between 11,060 and 15,470 pounds (5,020 and 7,020 kilograms).

Most of the rocket's 14 total flights launched classified payloads for the NRO, but NASA has also used the Delta IV Heavy to boost scientific missions into space. The space agency's Parker Solar Probe was launched atop the rocket in 2018, while the Artemis program's Orion crew capsule took its first test flight in 2014 after being launched from a Delta IV Heavy.

ULA has a new massive rocket on the horizon to replace the Delta IV Heavy, called the Vulcan Centaur. The company hopes the behemoth will make its first flight later this year with a mission that will see the ashes of late "Star Trek" creator Gene Roddenberry and "Trek" actors Majel Barrett Roddenberry and James "Scotty" Doohan launched into space.

The ULA Delta IV Heavy will launch two more missions, both of which are likewise on behalf of the NRO, from Florida's Space Coast. Those two launches will occur in 2023 and 2024, respectively, if all goes according to plan.

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Brett Tingley
Editor, Space.com

Brett is a science and technology journalist who is curious about emerging concepts in spaceflight and aerospace, alternative launch concepts, anti-satellite technologies, and uncrewed systems. Brett's work has appeared on The War Zone at TheDrive.com, Popular Science, the History Channel, Science Discovery, and more. Brett has English degrees from Clemson University and the University of North Carolina at Charlotte. In his free time, Brett is a working musician, a hobbyist electronics engineer and cosplayer, an avid LEGO fan, and enjoys hiking and camping throughout the Appalachian Mountains with his wife and two children.