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Delta IV Heavy Nails Final Flight

NROL-70 lifts off atop the ultimate Delta IV Heavy from SLC-37 at Cape Canaveral Space Force Station, the final flight of the Delta family.
Credit: David Diebold

On April 9th, 2024 at 12:53 PM EST- the final rocket of the Delta family lifted off from SLC-37 at Cape Canaveral Space Force Station, ending a career and lineage with roots as far back as the dawn of the space program. After a scrub due to high winds and technical issues on March 28th, 2024 and a stand down due to gaseous nitrogen pump issues, the vehicle was finally able to get underway – providing a dramatic show for all who were present to witness her. This launch, a classified mission for the National Reconnaissance Office atop a Delta IV Heavy, is a herald of change: a signal that a new and exciting era in modern rocketry is here, and the last vestiges of the dynamic Space Race are winding to a close.

The Delta rocket series, since its maiden launch carrying Echo-1 on May 13, 1960 has been a cornerstone of American space power, and served as an early workhorse in the advancement of spaceflight and technology. With the need for infrastructure in space quickly growing during the 60s, a conversion of the Thor missile served as the basis for America’s smaller launch vehicle, alongside the converted Atlas intercontinental ballistic missile. Since the family’s inception, Delta has completed 389 missions lofting a wide variety of payloads for customers across the globe. The final Delta to fly with direct Thor heritage took to the skies in 2018, launching the ICESAT-2 mission from Vandenberg Air Force Base in California (now Vandenberg Space Force Base). Now, with the launch of NROL-70, the story of the Delta family comes to a close, with the vehicle playing a pivotal role in the advancement of American aerospace excellence. 

Delta IV Heavy powers uphill, its 3 RS-68 main engines burning liquid hydrogen and oxygen. The center core’s throttle difference is clearly visible in this image.
Credit: David Diebold

In the late 1990s, the United States Air Force, recognizing the need to modernize its fleet of launch vehicles, initiated the Evolved Expendable Launch Vehicle (EELV) program. This program aimed to expand the American launcher fleet, with vehicles being tailored to fit the needs of government customers. Boeing and Lockheed Martin, two major aerospace contractors, were selected to develop new families of rockets under this program. Boeing took the lead in developing the Delta IV, a radical new design which ditched the existing Thor derived tankage in favor of a 5 meter, hydrogen and oxygen core stage, known as the Common Booster Core or CBC. Their upper stage, the Delta Cryogenic Second Stage, carried some lineage from the problematic Delta III rocket family, which flew its last flight in 2000. Using the RS-68, a cousin of the Space Shuttle Main Engine, the vehicle was built with the hopes of high flight rate and competitive pricing, two milestones the vehicle would sadly never reach due to its complex infrastructure and a downturn in the global launch market. Delta IV made its first flight in 2002 carrying the commercial Eutelsat 5W payload, flying in the Medium configuration with two solid rocket motors. The first tricore Delta IV Heavy flew on December 21, 2004, carrying a demonstration payload to certify the vehicle for flight. This flight would result in a partial failure, as cavitation in the liquid oxygen propellant lines would force the side boosters to shut down early, placing the payload in a lower than intended orbit. Since this flight, however, the vehicle has enjoyed a 100% success record, and the Delta IV Heavy at one point claimed the title of the world’s most powerful rocket. 

Like the Titan IV before it, the Delta IV family has been instrumental in deploying satellites for the U.S. Department of Defense, National Reconnaissance Office (NRO), and other national security entities. Some of this hardware, including the metallic fairings commonly seen on Delta IV Heavy missions, are leftover from the Titan family of launch vehicles. These missions include reconnaissance satellites, communication satellites for military use, and other critical payloads that support national security and global military operations. Like most NRO missions, details of the payload onboard NROL-70 are classified; however, publicly available documentation and hazard zones suggests that it is an electronic signals intelligence (ELINT) satellite bound for geostationary orbit – where its high power monitoring systems will keep a close watch on global communications for the NRO and its partners across the world from a fixed relative position. 

After igniting excess hydrogen, Delta IV Heavy climbs through its own fireball – scorching its three Common Booster Cores.
Credit: David Diebold

The NRO’s geostationary ELINT satellites are part of a spacecraft family known as MENTOR or Advanced ORION, which entered operation in 1995 with USA-110. Operated by the NRO and developed with input from the Central Intelligence Agency, eight have been launched from Cape Canaveral on Titan IV and Delta IV launch vehicles since 1995. The NROL-70 mission was the 17th Delta IV launch for the NRO, which will switch to using Vulcan, Falcon and other new launch vehicles for future missions. Twelve of these launches have used the Delta IV Heavy configuration, launching from both the East and West coast. 

As well as its eight MENTOR missions, Delta IV has deployed five KH-11 CRYSTAL reconnaissance satellites, three TOPAZ radar-imaging satellites, one QUASAR communications satellite, and one elliptical-orbit ELINT-TRUMPET satellite for the NRO. The names of the NRO’s satellites are classified but many have found their way into the public domain through declassified or leaked documents throughout the program’s history. Delta IV launched several additional Air Force and Space Force payloads throughout its service life, highlighting the vehicle’s strong commitment to Department of Defense operations. These included two Defense Satellite Communications System communications satellites and eight spacecraft for the successor Wideband Global Satcom program; seven GPS navigation satellites; two pairs of Geosynchronous Space Situational Awareness Program space domain awareness satellites and a Defense Meteorological Satellite Program weather spacecraft.

Delta IV Heavy ascends from SLC-37, as seen from off the coast of Cape Canaveral Space Force Station.
Credit: JJ Carola

The Delta IV Heavy configuration supported two notable missions for NASA, the only time it has done so. The first was the launch of EFT-1 on December 5, 2014, a preliminary shakedown test for the Orion Multipurpose Crew Vehicle. The mission was a four-hour, two-orbit test of the Orion crew module featuring a high apogee on the second orbit and concluding with a high-energy reentry at around 8.9 kilometers per second (20,000 mph), simulating lunar return conditions essential for future human missions. The flight was a resounding success and paved the way for the successful launch of Artemis I in November 2022. The second dedicated NASA payload flown by Delta IV Heavy was the Parker Solar Probe, a daring mission to explore the outer corona of the Sun. Launched on August 12, 2018, the spacecraft flew in a unique configuration, utilizing a STAR-48V solid upper stage to propel the spacecraft towards the inner Solar System. After a series of gravity assists, the spacecraft was able to begin its operational mission: passing through elements of the solar atmosphere to study our local star, and becoming the fastest object ever constructed by humanity.

Throughout its operational life, the Delta IV program demonstrated its reliability and versatility, playing a significant role in advancing space exploration, commercial satellite deployment, and national security initiatives. It emerged at a time when the future of space was somewhat uncertain; the wind down in direct aggravation following the Cold War presented something of a vacuum for the future of global aerospace developments. It was from this that vehicles many have come to know today emerged: Atlas V, Delta IV and more. However, facing competition from newer, more cost-effective launch vehicles since the onset of heavy commercialization, Delta IV’s retirement became inevitable in order to keep up with these ever changing times. Recognizing this, United Launch Alliance made the choice to wind down both the Delta and Atlas lines, consolidating the best parts of each vehicle into their new vehicle, Vulcan, which debuted successfully on January 8, 2024. Vulcan, as it stands, will be able to adequately serve the same payload class as Delta IV Heavy, even in a “single stick” configuration – with future upgrades potentially outclassing the baseline vehicle entirely. Speaking after launch, ULA CEO Tory Bruno said: “The Delta rocket played a pivotal role in the evolution of space flight since the 1960s, this final Delta mission signals ULA’s evolution to the new Vulcan rocket, providing even higher performance than our three-core Delta IV Heavy rocket in a single-core rocket to launch heavy-class missions for the nation. We will continue to deliver our superior reliability and unprecedented orbital precision for all our customers across the national security, civil and commercial markets.” 

Vulcan lifts off on its maiden flight on January 8, 2024 carrying the Peregrine Lunar Lander.
Credit: Brandon Berkoff

The final launch of Delta IV Heavy, and the closeout of the rocket family’s production serves as a reminder that the landscape of space is changing rapidly. Space has become ingrained in every aspect of human life on planet Earth, and with the changing needs of the industry at play, the vestiges of space launch from the days of the Cold War are slowly slipping from our grasp. In 2018, the last Thor derived rocket flew. In 2024, the last Delta IV. In 2029, the final Atlas will likely take flight, closing the book on the first families of American rocketry for good. As one story comes to an end, another one is beginning, with a new age of American lifters coming online to support even broader ambitions than those envisioned in the late 1990s. In some ways, it is a return to form, a renewal of the period of optimism that Delta IV emerged in. We are going further now, back to the Moon and beyond as part of the Artemis program, and charting a new path in American aerospace excellence. These new vehicles stand on the shoulders of giants, a crucial legacy of space hardware that goes back to where it all began.

Edited by Beverly Casillas

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