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 6, known as SLC-6, at Vandenberg Air Force Base, California, is currently used to launch ULA’s Delta IV Heavy rocket.

The pad was originally built starting March 12th, 1966 for human launches of the Air Force’s Manned Orbiting Laboratory program and would have launched Titan III rockets with a modified Gemini Program capsule for 40 day human polar missions.

The Manned Orbiting Laboratory program was canceled in 1969 and all work on the pad stopped.  Three years later, plans began to finish the pad and convert what was built for use by NAS’s upcoming Space Shuttle Program under an Air Force mandate that the Shuttles launch human polar orbit missions for national security.

A Shuttle pad was nearly fully built prior to the Challenger Disaster of January 28th, 1986.  The investigation resulting from the deaths of Challenger’s seven crewmembers revealed major safety issues at the Vandenberg Shuttle launch site, which would have endangered the lives of Shuttle crews and the lives of the launch and processing teams.

The idea of launching the Shuttle from anywhere other than the Kennedy Space Center in Florida ended, and the Air Force canceled Vandenberg Shuttle launch plans.

SLC-6 again was a pad without any rocket to launch.

The first launch from SLC-6 eventually happened on August 15th, 1995 with Lockheed-Martin Launch Vehicle I (soon to be renamed Athena I).  One more Athena I launched from the pad in 1997 and two Athena IIs lifted off from here in 1999.

Boeing then signed an exclusive lease of the pad for the Delta IV family of rockets being developed for the Air Force’s Evolved Expendable Launch Vehicle (EELV) program to assure the U.S. government access to space.

The first Delta IV from SLC-6 was assembled on the launch site in late-2003 and remained on the pad for nearly three years as technical issues with the pad and rocket were identified and fixed.  The mission finally launched on June 27th, 2006.

To date, only 12 missions have launched from SLC-6, and only two remain -- one in October 2020 and a final one in 2022.

ULA is retiring the Delta IV rocket family and replacing it with Vulcan, which will launch from a different pad for its Vandenberg operations.

Presently, no plans exist for SLC-6’s future use once ULA is finished with the pad in 2022.