Watch a huge Delta IV Heavy rocket launch a US spy satellite on its final West Coast flight live today

A United Launch Alliance (ULA) Delta IV Heavy rocket will launch a U.S. spy satellite on its final flight from California on Saturday (Sept. 24), and you can watch it live.

The powerful Delta IV Heavy is scheduled to lift off from Vandenberg Space Force Base in California Saturday at 5:53 p.m. EDT (2153 GMT; 2:53 local time), on a mission for the U.S. National Reconnaissance Office (NRO) called NROL-91. Watch it live here, courtesy of ULA, or directly via the company.

The NRO builds and operates the nation's fleet of spy satellites. The activities and payloads of those spacecraft tend to be classified, and the NROL-91 mission is no exception; little is known about the satellite that it will loft.

Related: The Delta IV Heavy: Powerful launch vehicle

The last Delta IV Heavy rocket to launch from the West Coast is seen inside its vertical assembly building at Vandenberg Space Force Base in California for a Sept. 24, 2022 launch.  (Image credit: United Launch Alliance)

"We're on track to launch another national capability into space. This will be our sixth national security launch this year. We've worked alongside ULA to prepare this Delta IV Heavy, and in just a few days, we will see the fruits of our labor," Brig. Gen. Stephen Purdy,  Space Force program executive officer for assured access to space, said in an emailed statement Thursday (Sept. 22).

"These launches place critical capabilities into orbit for our nation and our allies in a time of increasing risks and threats," Purdy added. "Every member of our launch team understands what's at stake and works with both care and efficiency to prepare for what’s going to be a tremendous launch."

Saturday's launch will be the final Delta IV Heavy liftoff from California. ULA is phasing out the burly rocket in favor of a new vehicle called Vulcan Centaur, which could debut before the end of 2022, company representatives have said.

There are two Delta IV Heavy missions left after Saturday's flight. Both will launch from Florida's Space Coast, 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.  

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Mike Wall
Senior Space Writer

Michael Wall is a Senior Space Writer with and joined the team in 2010. He primarily covers exoplanets, spaceflight and military space, but has been known to dabble in the space art beat. His book about the search for alien life, "Out There," was published on Nov. 13, 2018. Before becoming a science writer, Michael worked as a herpetologist and wildlife biologist. He has a Ph.D. in evolutionary biology from the University of Sydney, Australia, a bachelor's degree from the University of Arizona, and a graduate certificate in science writing from the University of California, Santa Cruz. To find out what his latest project is, you can follow Michael on Twitter.