The Delta IV Heavy's West Coast work is done.
The powerful United Launch Alliance (ULA) rocket launched a hush-hush satellite for the U.S. National Reconnaissance Office (NRO) from Vandenberg Space Force Base in California today (Sept. 24), the vehicle's last-ever liftoff from the Golden State.
The Delta IV Heavy took flight at 6:25 p.m. EDT (2225 GMT; 3:25 p.m. local time) from Vandenberg's Space Launch Complex-6 on a mission called NROL-91. Very little is known about the spacecraft that went up on NROL-91. That's no surprise; the NRO builds and operates the U.S. fleet of spy satellites, the activities and payloads of which tend to be classified.
The Delta IV Heavy: Powerful launch vehicle (reference)
An NRO mission description outlines NROL-91 only in vague terms, saying it "supports the overall national security mission to provide intelligence data to the United States' senior policy makers, the Intelligence Community and Department of Defense."
We don't even know which orbit the satellite will occupy; that information isn't given in the NRO or ULA descriptions, and ULA ended its webcast about seven minutes after launch today at the NRO's request.
Today's launch was the 14th overall for the Delta IV Heavy, which debuted in 2004. The 233-foot-tall (71 meters) rocket is capable of lofting 62,540 pounds (28,370 kilograms) to low Earth orbit (LEO), more than any other currently operational launcher except SpaceX's Falcon Heavy.
The Falcon Heavy can deliver 140,660 pounds (63,800 kg) to LEO, according to its SpaceX specifications page.
Most Delta IV Heavy missions have carried NRO payloads to orbit, but NASA has employed the powerful booster as well. Delta IV Heavy vehicles launched the space agency's Parker Solar Probe in 2018 and the first flight test of its Orion crew capsule in 2014.
ULA is phasing out the Delta IV Heavy in favor of a new rocket called the Vulcan Centaur, which could debut by the end of 2022. Just two Delta IV Heavy flights remain, both NRO missions that will launch from Cape Canaveral Space Force Station in Florida. Those missions will lift off in 2023 and 2024, if all goes according to plan.
Mike Wall is the author of "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or on Facebook.