Watch: ULA will launch its Delta IV rocket for one of the last times

Watch the penultimate launch of Delta IV

The NROL-68 mission was originally due to lift off today, June 21, but an issue with a ground-system valve on the Delta IV rocket caused a delay. The launch of NROL-68 can be viewed live via the embedded video below.

Though we know very little about the payload going to orbit aboard Delta IV Heavy, the mission insignia, which features two dragons and the moon, offers vague clues.

In a short mission description, NRO officials wrote that "the baby dragon illustrates the birth of a new satellite system, while the moon with the mother dragon silhouette represent protection of the Five Eyes community, the nation, and its allies."

Five Eyes refers to an alliance between the intelligence agencies of the US, UK, Australia, Canada, and New Zealand.

"The passage along the bottom, Nusquam Celare, is Latin for 'Nowhere to Hide,'" the NRO statement added. "The baby dragon may be science fiction, but NROL-68's impact on national security is real!"

ULA readies Vulcan Centaur

NROL-68 will be the 15th Delta IV Heavy launch ever and it will be ULA's first mission of 2023. The 235-foot-tall (71.6 meters) rocket generates 2.1 million lbs of thrust at liftoff.

Part of the reason Delta IV will now be phased out is that its Heavy configuration is far behind the competition when it comes to sheer power: SpaceX's Falcon Heavy produces 5 million lbs of thrust; NASA's Space Launch System (SLS) produces 9.5 million lbs; and Starship emits a massive 17 million lbs at liftoff, making it the most powerful rocket to ever fly.

ULA still has Atlas V missions booked through 2029, though. Most of these are part of Amazon's "largest commercial procurement of launch vehicles in history" for its Starlink-rival internet satellite service, called Project Kuiper. Atlas V is also booked to send astronauts to the ISS aboard Boeing's Starliner capsule, though the first crewed mission of the spacecraft is delayed indefinitely due to major issues discovered ahead of a scheduled launch.

ULA's next-generation Vulcan Centaur rocket, meanwhile, recently passed a key engine test, though the company hasn't announced a rough launch window, stating recently that "we will fly when we believe it is safe to launch."