The Delta IV Heavy is United Launch Alliance’s (ULA’s) rocket for US military operations.

Launching from both Florida and California, ULA plans to retire the rocket in 2024 in favor of the Vulcan rocket, which is capable of doing everything Delta IV Heavy can -- and more -- for one-third the price tag.

The Delta IV Heavy is the most powerful and final variant of the Delta IV family. With a per-flight base cost of at least $350 million USD, the rocket’s price tag is quite a bit more than any other rocket in its class.

Stats

Height: 72 m (236 ft)

Diameter: 5 m (16 ft)

Width: 15 m (49 ft)

Mass: 733,000 kg (1,616,000 lb)

Stages: 2+

Developed in the mid- to late-1990s by Boeing as part of the U.S. government's initiative to create an Evolved Expendable Launch Vehicle (EELV) program for national security missions, the rocket traces parts of its lineage to the Thor-Delta launch vehicle that debuted in 1960.

The two companies that developed EELV rockets -- Lockheed Martin with Atlas V and Boeing with Delta IV -- merged those specific assets in 2006 under a new company, ULA.

Despite a stellar success record of 100% per the payload customer's point of view, the Delta IV's price tag prohibited it from competing successfully on the commercial market.

Image: ULA

Space Launch Complex SLC-37B at Cape Canaveral Space Force Station is a historic launch pad that served as the primary site for the Delta Four family of rockets. It was built as part of the modern redevelopment of the original Complex 37 area, which had first supported the Saturn One and Saturn One B program in the nineteen sixties. After decades of inactivity the site was rebuilt for Delta Four operations and became active again in the early two thousands.

The pad features a large fixed service structure and a mobile service tower that was used to assemble and protect the rocket vertically. The mobile tower could roll back before launch, revealing the vehicle for final checks and countdown operations. The design supported all Delta Four configurations including the heavy variant, which was among the most powerful rockets in the world during its years of service.

SLC-37B became best known for hosting national security missions, weather satellites, and scientific spacecraft launched by United Launch Alliance. The site was also notable for its dramatic heavy rocket launches, which produced intense sound pressure and towering flames that became a familiar sight to observers on the Space Coast.

With the retirement of the Delta Four program, SLC-37B has completed its active role and is now entering a major transition period. SpaceX is preparing the complex for future Starship operations, which require new ground systems, updated commodity handling, and redesigned safety zones based on years of data collected from Falcon and Starship testing. As part of bringing Starship to Florida, SpaceX and government partners have been refining modern clear areas and hazard models that allow safe operations with minimal impact on other launch providers. These updates rely on extensive testing of methane and oxygen systems, real world flight data, and close coordination with the Space Force, NASA, and the FAA.

As Starship moves toward regular operations at the Cape, SLC-37B is expected to become a fully modernized facility that supports rapid and reliable launch activity. The pad will be adapted to integrate advanced safety planning, smaller and more efficient air and sea clear zones, and procedures designed to fit within the busy environment of Cape Canaveral. These changes position SLC-37B to play a new role on the Space Coast, transforming it from a legacy Delta Four site into an active platform for the next generation of heavy lift vehicles.

SLC-37A sits nearby but has never been developed into a full launch pad in the modern era. During the Saturn program it served as a companion area for support structures, but it was never rebuilt for Delta operations and remained inactive through the return of the complex in the two thousands. Today it is considered an unused part of the larger Complex 37 footprint, and its future role will depend on how SpaceX and the Space Force choose to expand or redesign the Starship facilities in the coming years.

Photo courtesy of SpaceX.