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ULA Delta IV Heavy Launches into History with Spectacular Final Mission

Written by: Space Foundation Editorial Team

On April 9, 2024 at 12:53 p.m. EDT, the final United Launch Alliance (ULA) Delta IV Heavy rocket launched a classified payload for the National Reconnaissance Office, NROL-70, marking the end of an era for this remarkable rocket. As one of the most powerful launch vehicles ever built, its propulsion and avionics systems built by L3Harris have played a pivotal role in the success of the Delta IV program.

The retirement of the Delta IV Heavy marks a transition to ULA’s new Vulcan rocket, which successfully completed its inaugural mission earlier this year, signaling the continuous evolution of space exploration technology.

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

At the heart of the Delta IV Heavy are its three Common Booster Cores, each powered by an Aerojet Rocketdyne, and L3Harris Technologies company, RS-68A engine, the most powerful hydrogen-fueled rocket engine ever flown. Known for its reliability and efficiency, the RS-68A has been a workhorse for the Delta IV Heavy, contributing to its success in delivering payloads to a variety of orbits. Together, these three boosters generate over two million pounds of thrust, propelling the rocket through the Earth’s atmosphere and into space. The original variant of the engine, the RS-68, was commercially developed using private company funds.

Each Common Booster Core is also equipped with a complete suite of L3Harris avionics that support communications, range safety, navigation and data acquisition systems.

The second stage of the Delta IV Heavy employs a single Aerojet Rocketdyne RL10 engine; a cryogenic rocket engine also powered with liquid hydrogen and liquid oxygen propellants. This stage, which also includes Aerojet Rocketdyne reaction control system thrusters and pressure tanks, is responsible for fine-tuning the trajectory and placing the payload into its precise orbit. The RL10 engine is renowned for its precision and versatility, making it a crucial component in achieving the high-energy orbital requirements of National Security Space Launch (NSSL) missions.

“For nearly 20 years, our reliable propulsion systems have helped the Delta IV rocket achieve an outstanding record of 100% mission success,” said Jim Maus, general manager of Defense and Commercial Space Launch Systems at Aerojet Rocketdyne. “The Delta IV Heavy has launched a range of payloads, from classified military satellites to spacecraft exploring the mysteries of our solar system.”

After launching 45 Delta IV missions, 16 of those Delta IV Heavy missions, the Delta IV leaves behind a legacy of enabling groundbreaking scientific endeavors and critical national security missions as it makes way for the next generation of launch vehicles.