Final launch of Delta IV Heavy rocket scrubbed late in countdown

an orange and white rocket stands on the launch pad under cloudy gray skies
United Launch Alliance's last Delta IV Heavy rocket stands on the pad ahead of a planned March 28, 2024 liftoff. The attempt was scrubbed with less than 4 minutes left on the countdown clock. (Image credit: ULA)

We'll have to wait a few more days to see the swan song of United Launch Alliance's (ULA) powerful Delta IV Heavy rocket.

The Delta IV Heavy was supposed to launch for the final time on March 28, sending a U.S. spy satellite skyward from Cape Canaveral Space Force Station in Florida. But the attempt was scrubbed with just under four minutes left in the countdown "due to an issue with the gaseous nitrogen pipeline which provides pneumatic pressure to the launch vehicle systems," ULA wrote in an update on March 28.

ULA is now targeting April 9 at 12:53 p.m. EDT (1653 GMT) for the liftoff. You can watch the action live here at, courtesy of ULA.

Related: United Launch Alliance to launch final Delta Heavy IV rocket. Here's how to watch live

The coming launch will be the 16th and final Delta IV Heavy mission, as well as the last for the Delta rocket family, which has been flying for more than six decades.

The Delta IV Heavy's successor, ULA's Vulcan Centaur, is already up and running. The new rocket aced its first mission this past January, successfully lofting the private Peregrine moon lander (although Peregrine suffered problems after deploying into space and failed to reach the moon as planned).

A United Launch Alliance (ULA) Delta IV Heavy rocket is raised vertically at the Space Launch Complex-37 pad in preparation to launch the NROL-70 mission for the National Reconnaissance Office. (Image credit: United Launch Alliance)

The final Delta IV Heavy mission, called NROL-70, will launch a classified payload for the U.S. National Reconnaissance Office. The NRO builds and operates the nation's fleet of spy satellites and rarely divulges many details about their capabilities and activities.

Thus, unsurprisingly, ULA's NROL-70 mission description is vague, as the team only stated that the launch will "strengthen the NRO's ability to provide a wide range of timely intelligence information to national decision makers, warfighters and intelligence analysts to protect the nation’s vital interests and support humanitarian efforts worldwide."

Editor's note: This story was updated at 3:30 p.m. ET on April 3 with the new target launch date of April 9.

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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.