On a bittersweet day in in the annals of spaceflight, the United Launch Alliance (ULA) said goodbye to one of its most powerful and storied rockets. With an ontime launch at 12:53 PM EDT on April 9, the Delta IV Heavy rocket soared into the skies for its final mission, carrying a classified payload for the National Reconnaissance Office (NRO), designated NROL-70.

“It is a bittersweet moment for us. It is such an amazing piece of technology — 23 stories tall, half a million gallons of propellant, two and a quarter million pounds of thrust and the most metal of all rockets, setting itself on fire before it goes to space.”

Tory Bruno, chief executive officer of United Launch Alliance – March 26th

The Delta IV Heavy, known for its immense power and capability, has been a cornerstone in the United States’ space launch capabilities for over two decades. Its final launch was a bittersweet moment, symbolizing both the culmination of its storied career and the dawn of a new era in launch technology led by ULA’s next-generation Vulcan rocket, which successfully completed its inaugural mission earlier this year.

Delta Family of Rockets Also Retiring

The Delta family of rockets also came to an end after over sixty years of service. In service from 1960 to 2024, the versatile range of American rocket-powered expendable launch systems that provided space launch capability for the United States, and it launched many memorable missions including early communications satellites like Echo 1A, TIROS-2 and TIROS-3 weather satellites in the 1960s, NASA’s rovers Spirit and Opportunity, the Phoenix Mars Lander, all operational GPS missions through the constellation of 21 GPS II-R missions for the Air Force, and commercial missions for Iridium, Globalstar and three DigitalGlobe satellites. Japan also launched license-built derivatives (N-I, N-II, and H-I) from 1975 to 1992.

ULA’s Future is With Vulcan, Its New Rocket

Regarding the move to Vulcan boosters for future launches, ULA CEO Tory Bruno said “This is a great mission to think about that transition, because national security space missions is our core and the unique set of missions there require a high-energy launch vehicle. We designed Vulcan specifically for that.”

The rocket’s second stage, powered by an Aerojet Rocketdyne RL10 engine, was instrumental in the precise delivery of payloads into their designated orbits. The RL10’s precision and versatility were crucial in meeting the demanding requirements of National Security Space Launch (NSSL) missions.

Reflections On Delta IV Heavy’s Legacy

Kristin Houston, the President of Space Propulsion and Power Systems at Aerojet Rocketdyne, reflected on the Delta IV Heavy’s legacy, stating, “The Delta IV has been reliably delivering our nation’s most important payloads to the most challenging orbits for more than two decades.”

Houston expressed a mix of farewell to the iconic launch vehicle and anticipation for the future, affirming, “While we bid farewell to this impressive launch vehicle that has made such significant contributions to the scientific and national security goals of the United States, L3Harris looks forward to providing propulsion and avionics systems to support ULA’s Vulcan rocket for many years to come.”

Jim Maus, general manager of Defense and Commercial Space Launch Systems at Aerojet Rocketdyne, lauded the Delta IV Heavy’s flawless performance record, stating, “For nearly 20 years, our reliable propulsion systems have helped the Delta IV rocket achieve an outstanding record of 100% mission success.” He highlighted the diversity of missions the Delta IV Heavy supported, ranging from classified military satellites to spacecraft destined to unravel the mysteries of our solar system.

Central to the Delta IV Heavy’s success were its three Common Booster Cores, each powered by an RS-68A engine developed by Aerojet Rocketdyne, an L3Harris Technologies company. The RS-68A, heralded as the most powerful hydrogen-fueled rocket engine ever flown, was a key contributor to the rocket’s impressive track record. The engines, alongside a suite of sophisticated avionics provided by L3 Harris, enabled the Delta IV Heavy to deliver payloads to a variety of orbits, generating over two million pounds of thrust to breach the Earth’s atmosphere.

As the Delta IV Heavy embarks on its retirement, its legacy is cemented. Having successfully completed 45 Delta IV missions, including 16 aboard the Delta IV Heavy configuration, the rocket leaves behind a legacy of innovation, reliability, and contribution to both scientific exploration and national security. As the commercial spaceflight industry looks to the future with the ULA’s Vulcan rocket, the Delta IV Heavy’s pioneering spirit and contributions will not be forgotten.

_{Note: Story by Mark Stone of Florida Media Now with additions by Charles Boyer.}