Final Flight: What made ULA's Delta IV Heavy stand apart from other rockets?

After making its mark in the history of space exploration, the Delta IV Heavy is set to launch this week on its 16th and final flight.

As United Launch Alliance (ULA) rolls out a Delta IV for the last time, its legacy will live on.

This Thursday, the Delta IV Heavy rocket, which had been dubbed by ULA as ‘the most metal of rockets’, will deliver NROL-70, a National Reconnaissance Office mission, to space. The mission is planned to lift off from Space Launch Complex-37 at Cape Canaveral Space Force Station at 1:40 p.m.

The current forecast shows only a 30 percent change of weather favorable for the farewell flight.

Here's what you need to know about this powerful rocket.

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What was special about the Delta IV Heavy aka "The most metal of rockets"?

FLORIDA TODAY spoke with Dave McFarland, who played a key role in the Delta IV program. McFarland recalled his career of watching Delta IV — especially Delta IV Heavy — lift essential payloads with its great power.

McFarland worked with ULA for almost 47 years and played a key part in assisting with the development of Launch Complex 37 for Delta IV.  He served as the chief engineer for the Delta program before eventually becoming the chief engineer of ULA, following its creation in 2006.

McFarland watched as Delta IV Heavy first took to the skies above the Space Coast two decades ago when it launched on a demo flight in December 2004.

It would be a few years later, in late 2007, that the rocket would begin providing essential launch services for important customers. For the past 17 years, this rocket has successfully delivered payloads for the U.S. Air Force, Space Force, and National Reconnaissance Office (NRO).

The rocket has enjoyed a 100 percent success rate.

Among its flights were two key NASA missions: one which helped prepare for the return to the Moon while the other visited the Sun.

The size and power of the ULA Delta IV Heavy rocket

Unlike the regular Delta IV medium, Delta IV Heavy has three Delta IV core stages together. According to the ULA website, each rocket engine produces up to 702,000 lbs. of thrust. With this performance, one can see why ULA dubbed it "the most metal."

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These engines are not small either. Just one engine weighs around 14,876 lbs and is 204 inches (17 feet) in length.

Powered by liquid hydrogen and liquid oxygen, the Delta IV Heavy appears to set itself on fire just before liftoff as buoyant hydrogen gas, which is used to cool down the rocket before launch, ignites and burns off. The fiery start may look frightening, yet it's part of the process.

Delta IV Heavy rocket payload protected for flight into space

The Delta IV Heavy protects its sensitive payloads in payload fairings. Simply put, it's a shield covering the satellite which will protect it from the rough ride into orbit. Friction from the atmosphere, temperature changes, vibrations and g-forces from launch can easily damage hardware.

These fairing are situated at the very top or the "point" of the rocket. Underneath, the payload sits secured for transport.

This rocket never launched crewed missions ? only satellites and exploratory spacecrafts. It's successor, the Vulcan Centaur, will be able to launch both crewed missions and payload satellites.

Delta IV Medium vs Delta IV Heavy – what's the difference

Compared to the regular Delta IV Medium, the Delta IV Heavy has 2 additional common booster cores; in simple terms ? 2 more rockets attached to the main rocket.

ULA’s Delta IV Heavy delivered 2 key NASA missions

Delta IV transported mostly NRO, US Air Force, and US Space Force payloads, getting them safely to their orbit or destination. However, it has two historic NASA missions to its name.

The Delta IV Heavy rocket is remembered for its transportation of not only the NASA Parker Solar Probe in 2018, but the first orbital test flight of the Orion crew capsule in 2014.

It was following the success of this flight that NASA’s Orion crew capsule flew on NASA’s Space Launch System (SLS) rocket, successfully demonstrating an uncrewed mission around the Moon in 2022. ULA assisted in this flight as well, as the organization designed the upper stage of the SLS rocket.

The Orion spacecraft is slated to take Artemis II astronauts around the Moon in late 2025.

The future of ULA spaceflight – Vulcan Centaur, NASA’s SLS, Boeing’s Starliner, and beyond

ULA continues to support NASA with its monster SLS rocket, providing development of the rocket’s upper stage, which stems from the design of the Delta IV.

While ULA's Atlas V rocket, which will ferry the first Boeing’s Starliner missions, nears retirement, ULA continues to focus on its Vulcan Centaur rocket. This rocket will replace both the Delta IV and Atlas V, providing the ability to carry both payload and crewed missions.

Introducing the Vulcan: ULA Vulcan rocket launches without delay on history-making maiden flight from Cape Canaveral

Atlas V currently has sixteen flights left until retirement. These missions will be a mix of U.S. Space Force payload deliveries and commercial crew flights.

Why is Delta IV being retired?

Vulcan Centaur, ULA’s newest rocket, had a successful test flight in January of 2024. The Vulcan will replace the Delta, and soon the Atlas, family of rockets.

The Vulcan Centaur rocket is less expensive and ULA says it will allow for more flexibility in power, giving the option to add on 2, 4, or 6 solid rocket boosters. According to McFarland, ULA is currently testing methods and aiming for reusability in the future, which will lower costs further.

What Delta IV Heavy did for the U.S.

The missions that Delta IV Heavy carried were not all related to science; many were for navigation and U.S. security. As McFarland recalled the GPS satellites and national security missions the Delta program delivered, he said, “Delta has changed the world for the better, and I will always be extremely proud of my small piece (in it).”

McFarland referred to the retirement of the Delta rocket family as "bittersweet."

“We are well on our way of making Vulcan the 'go to’ vehicle for the foreseeable future,” said McFarland.

It will be a Vulcan Centaur which will fly Dream Chaser, a cargo spaceplane from Sierra Space, to the ISS. The flight date has yet to be announced, but the FLORIDA TODAY space team will provide updates as they become available.

Brooke Edwards is a Space Reporter for Florida Today. Contact her at [email protected]

This article originally appeared on Florida Today: Delta IV Heavy: ULA's fiery rocket making its final flight