ULA concludes six decades of Delta rocket flights with final Delta 4 Heavy mission

A ULA Delta 4 Heavy rocket lifts off from Space Launch Complex 37 on Tuesday, April 9, 2024. This was the 16th and final launch of a Delta 4 Heavy rocket. Image: Adam Bernstein/Spaceflight Now

The second time was the charm for the finale of the Delta family of rockets. Following an issue with a gaseous nitrogen pipeline beyond the control of United Launch Alliance (ULA) that caused the March 28 scrub the second launch attempt on April 9 proved successful.

Liftoff of the Delta 4 Heavy rocket from Space Launch Complex 37 (SLC-37) at Cape Canaveral Space Force Station occurred at 12:53 p.m. EDT (1653 UTC). The “most metal of all rockets” as described by ULA President and CEO Tory Bruno rocketed away from the pad at the start of the launch window, carrying a payload for the National Reconnaissance Office (NRO).

In the final four minutes prior to liftoff last go around, there were two issues that cropped up, according to Bruno. The first was a violation of ground wind limits, which forced the initial hold. That was coupled with an issue that came up with a gaseous nitrogen pump.

The pipeline system that services active launchpads both at the Kennedy Space Center as well as at CCSFS is owned by NASA and is managed by prime contractor, Air Liquide. 

In response to questions from Spaceflight Now regarding the extent of the issue and the measures taken to resolve it, Air Liquide provided the following statement:

“Air Liquide is committed to providing a safe and reliable supply of industrial gases to the U.S. space industry, as it has successfully been doing for more than 60 years.  Air Liquide confirms that a pump failure occurred on March 28 at its nitrogen plant supplying NASA’s Space Launch System (SLS).  Air Liquide worked diligently with NASA to understand the circumstances and resolve the situation and is prepared onsite to support the rescheduled launch of the Delta IV Heavy rocket.”

In a follow-up with NASA regarding the steps taken, the agency said that it “is aware that Air Liquide has taken action to resolve the pump issues at their nitrogen plant,” adding that “We appreciate their efforts in this matter.”

“As always, NASA Kennedy continues to monitor the pipeline and other infrastructure of key launch commodities on Kennedy property and will take any other steps that may be needed to ensure successful delivery of these important resources,” NASA said in a statement.

The 45th Weather Squadron also forecast much better conditions for launch with this second go-around. Its launch day forecast showed 90 percent odds of favorable weather during the launch window with the potential for cumulus clouds as the only watch item.

The NRO’s rocket

The NROL-70 mission will carry a spacecraft for the National Reconnaissance Office (NRO) up to orbit. Because it is a classified payload, little is publicly known about the satellite and its capabilities.

During a prelaunch press briefing in late March, Dr. Chris Scolese, the director of the NRO, noted that the NROL-70 payload will help boost needed capabilities on the ground without going into detail.

“It will provide exquisite capability that is needed by a lot of people and organizations, clearly, the policymakers, the warfighter and others, so that they can know what’s going on on the Earth,” Scolese said.

Out of the 16 missions that the Delta 4 Heavy rocket flew, 12 of them were in support of NRO missions. Bruno quipped during the briefing that it was “your rocket,” gesturing to Scalese.

“This will be the 16th flight. All but four of those have been for the NRO because of its unique capabilities,” Bruno said. “And so, we are looking forward to a successful mission and a great retirement of an amazing vehicle.”

The three-core vehicle will be replaced in its capabilities by ULA’s Vulcan rocket. It flew its first certification mission with the launch of Astrobotic’s Peregrine lunar lander in January and is preparing to fly for a second certification mission with Sierra Space’s Dream Chaser spaceplane onboard.

In response to reports that they may pursue a different path to certification, with either a different payload or just one mission, Bruno rebuked that, stating that ULA has “not asked for our cert plan to be amended from two flights to one” and that they have “no intention of doing so.”

Over the course of five order years for National Security Space Launch (NSSL) as part of Phase 2 of awards, 26 out of a total of 48 missions were awarded to ULA with 25 of those bound for flights using Vulcan. The first mission up to bat for the new launch vehicle will be USSF-106. Out of the nine NRO missions awarded, seven will launch using Vulcan.

The finale of the Delta family of rockets also comes as ULA is preparing to launch its first astronaut crew to low Earth orbit with the forthcoming Boeing Starliner Crew Flight Test. That spacecraft is preparing to roll out to ULA’s other launch pad at Space Launch Complex 41 (SLC-41) next week.

At Space Launch Complex-37, the Mobile Service Tower has retracted to the launch position about a football field's length away from the #DeltaIVHeavy rocket for today's #TheDeltaFinale liftoff of #NROL70. https://t.co/0ZAppUgxBy pic.twitter.com/BVNIu8o2aS

— ULA (@ulalaunch) April 9, 2024