Delta IV was a group of five expendable launch systems in the Delta rocket family. It flew 45 missions from 2002 to 2024. Originally designed by Boeing's Defense, Space and Security division for the Evolved Expendable Launch Vehicle (EELV) program, the Delta IV became a United Launch Alliance (ULA) product in 2006. The Delta IV was primarily a launch vehicle for military payloads for the United States Air Force (USAF), but was also used to launch a number of United States government non-military payloads and a single commercial satellite.
The Delta IV had two main versions, which allowed the family to cover a range of payload sizes and masses: Medium, which had four configurations, and Heavy. The final flight of a Medium configuration occurred in 2019. The final flight of Heavy was in April 2024.
Delta IV vehicles were built in the ULA facility in Decatur, Alabama. Final assembly was completed at the launch site by ULA: at the horizontal integration facility for launches from SLC-37B at Cape Canaveral in Florida and in a similar facility for launches from SLC-6 at Vandenberg in California.
History The latest evolutionary development of the Delta rocket family, the Delta IV was introduced to meet the requirements of the USAF's EELV program, now known as National Security Space Launch (NSSL) program. While the Delta IV retains the name of the Delta family of rockets, major changes were incorporated, the most significant being the switch from kerosene to liquid hydrogen fuel with new tankage and a new engine required.
During the Delta IV's development, a small variant was considered. This would have featured the Delta II second stage, an optional Thiokol Star 48B third stage, and the Delta II payload fairing, all atop a single Common Booster Core (CBC)."Delta IV Small" Astronautix.com The Small variant was dropped by 1999.Gunter's Space page - Delta IV
In 2002, the Delta IV was first launched, with the RS-68 becoming the first large liquid-propellant rocket engine designed in the United States since the Space Shuttle main engine (SSME) in the 1970s.
The L3 Technologies Redundant Inertial Flight Control Assembly (RIFCA) guidance system originally used on the Delta IV was common to that carried on the Delta II, although the software was different because of the differences between the Delta II and Delta IV. The RIFCA featured six ring laser gyroscopes and six accelerometers, to provide a higher degree of reliability."L-3 Space & Navigation's RIFCA Trihex"
Boeing initially intended to market Delta IV commercial launch services. However, the Delta IV entered the space launch market when global capacity was already much higher than demand. Furthermore, as an unproven design it had difficulty finding a market in commercial launches, and Delta IV launch costs were higher than comparable vehicles of the same era. In 2003, Boeing pulled the Delta IV from the commercial market, citing low demand and high costs. In 2005, Boeing stated that it sought to return the Delta IV to commercial service. Ultimately, with the exception of the first launch, which carried the Eutelsat W5 commercial communications satellite, all Delta IV launches were paid for by the US government.
As of 2009, the USAF funded Delta IV EELV engineering, integration, and infrastructure work through contracts with Boeing Launch Services (BLS). On August 8, 2008, the USAF Space and Missile Systems Center increased the "cost plus award fee" contract with BLS for US$1.656 billion to extend the period of performance through the September 30, 2008 (FY09). In addition, a US$557.1 million option was added to cover FY10.
In February 2010, naturalized citizen Dongfan Chung, an engineer working with Boeing, became the first person convicted under the Economic Espionage Act of 1996. Chung passed on classified information on designs including the Delta IV rocket to China and was sentenced to 15 years.
RS-68A booster engine upgrade The possibility of a higher performance Delta IV was first proposed in a 2006 RAND Corporation study of national security launch requirements out to 2020. A single National Reconnaissance Office (NRO) payload required an increase in the lift capability of the Delta IV Heavy. Lift capacity was increased by developing the higher-performance RS-68A engine, which first flew on June 29, 2012. ULA phased out the baseline RS-68 engine with the launch of Delta flight 371 on March 25, 2015. All following launches used the RS-68A, and the engine's higher thrust allowed the use of a single standardized CBC design for all Delta IV Medium and M+ versions. This upgrade reduced cost and increased flexibility, since any standardized CBC could be configured for zero, two, or four solid-propellant rocket boosters. However, the new CBC led to a slight performance loss for most medium configurations. The Delta IV Heavy required non-standard CBCs for the core and boosters. VersionFairingCBCsSRBsWith original RS-68 After RS68A upgradePayload to LEOPayload to GTOLaunchesPayload to LEOPayload to GTOLaunches Medium 4 m 1 08,800 kg4,540 kg38,510 kg4,440 kg0 M+ (4,2) 4 m 1 211,920 kg6,270 kg1312,000 kg6,390 kg2 M+ (5,2) 5 m 1 210,580 kg5,430 kg110,220 kg5,490 kg2 M+ (5,4) 5 m 1 413,450 kg7,430 kg412,820 kg7,300 kg4 Heavy 5 m 3 022,980 kg13,400 kg725,980 kg14,220 kg9
Masses include a Payload Attach Fitting (240 kg to 1,221 kg depending on payload). Proposed upgrades that were not implemented Possible future upgrades for the Delta IV included adding extra strap-on solid motors, higher-thrust main engines, lighter materials, higher-thrust second stages, more (up to eight) strap-on CBCs, and a cryogenic propellant cross feed from strap on boosters to the common core.
At one point, NASA planned to use Delta IV or Atlas V to launch the proposed Orbital Space Plane, which eventually became the Crew Exploration Vehicle and then the Orion. Orion was intended to fly on the Ares I launch vehicle, then the Space Launch System after Ares I was cancelled.
In 2009, The Aerospace Corporation reported on NASA results of a study to determine the feasibility of modifying Delta IV to be crew-rated for use in NASA human spaceflight missions. According to Aviation Week & Space Technology the study, "found that a Delta IV heavy [...] could meet NASA's requirements for getting humans to low Earth orbit".
A proposed upgrade to the Delta IV family was the addition of extra solid motors. The Medium+ (4,4) would have used existing mount points to pair the four GEM 60s of the M+ (5,4) with the upper stage and fairing of the (4,2). An M+ (4,4) would have had a GTO payload of , a LEO payload of , and could have been available within 36 months of the first order. It was also considered to add extra GEM 60s to the M+ (5,4), which would have required adding extra attachment points, structural changes to cope with the different flight loads, and launch pad and infrastructure changes. The Medium+ (5,6) and (5,8) would have flown with six and eight SRBs respectively, for a maximum of up to to GTO with the M+ (5,8). The Medium+ (5,6) and (5,8) could have been available within 48 months of the first order.
Retirement and replacement ULA was formed in December 2006 as a joint venture between Boeing and Lockheed Martin Space, inheriting the Atlas rocket family from Lockheed Martin and the Delta rocket family from Boeing. The Atlas V offered better performance than the Delta IV Medium at a lower cost, and in March 2015 ULA announced plans to retire the Delta IV Medium by 2018.
In 2014, ULA also began development of the Vulcan Centaur to replace both the Atlas and Delta families. The Vulcan's first stage shares design heritage with the Delta IV's Common Booster Core and is manufactured in the same Decatur, Alabama, facility using much of the same equipment, but with a diameter about larger. It is powered by two BE-4 methane-fueled engines developed by Blue Origin. Compared with the liquid hydrogen used on the Delta IV, methane is denser and has a higher boiling point, allowing for smaller and lighter fuel tanks.
A single-core Vulcan Centaur with six SRBs delivers heavy-lift capabilities comparable to the larger and more expensive three-core Delta IV Heavy. With this configuration, the Vulcan Centaur can lift to low Earth orbit (LEO), surpassing the Atlas V's maximum of and approaching the Delta IV Heavy's capacity.
The Vulcan Centaur was originally projected to enter service in 2023, but its first launch took place on January 8, 2024. The final Delta IV Medium launch (in a M+ 4,2 configuration) occurred on August 22, 2019, carrying a GPS III-2 satellite, USA-293, and the final Delta IV Heavy launch was on April 9, 2024, with the NROL-70 mission.
Delta IV Medium
The Delta IV Medium (also referred to as single stick) was offered in four configurations: Medium, Medium+ (4,2), Medium+ (5,2), and Medium+ (5,4).
The Delta IV Medium (Delta 9040) was the baseline configuration. It featured a single Common Booster Core (CBC) and a Delta Cryogenic Second Stage (DCSS), derived from the Delta III design but with enlarged propellant tanks. Because the CBC was in diameter, a tapered interstage was used to transition to the smaller second stage. The vehicle reused the Delta III payload fairing and was capable of placing into geostationary transfer orbit (GTO). From Cape Canaveral, GTO is short of geostationary orbit (GEO). Performance figures exclude the mass of the payload fairing and payload attach fittings.
The Delta IV Medium+ (4,2) (Delta 9240) used the same CBC and DCSS as the Medium, but added two Orbital ATK-built GEM 60 solid rocket boosters (SRBs), increasing payload capacity to GTO to .
The Delta IV Medium+ (5,2) (Delta 9250) retained the two GEM 60 SRBs of the Medium+ (4,2), but used a larger DCSS and a payload fairing, allowing it to accommodate larger payloads. Due to the added mass of the larger fairing and second stage, payload to GTO was reduced to .
The Delta IV Medium+ (5,4) (Delta 9450) used the same DCSS and payload fairing of the Medium+ (5,2), but used four GEM 60 SRBs instead of two, increasing payload capacity to GTO to .
Delta IV Heavy
The Delta IV Heavy (Delta 9250H) combined a Delta Cryogenic Second Stage with two additional Common Booster Cores (CBCs) strapped to the central core. The side CBCs separated earlier in flight than the center core. Starting in 2007, a longer composite fairing became standard, with optional aluminum isogrid or trisector fairings also available. With the extended fairing, the vehicle stood over tall.
Vehicle description
Common Booster Core
Each Delta IV consists of at least one Common Booster Core (CBC). Each CBC was powered by one Aerojet Rocketdyne RS-68 engine, which burns liquid hydrogen and liquid oxygen.
On flights of the Medium, the RS-68 ran at 102% rated thrust for the first few minutes of flight, and then throttled down to 58% rated thrust before main engine cutoff. On the Heavy, the main CBC's engine throttles down to 58% rated thrust around 50 seconds after liftoff, while the strap-on CBCs remain at 102%. This conserves propellant and allows the main CBC to burn after booster separation. After the strap-on CBCs separate, the main CBC's engine again throttles up to 102% before throttling back down to 58% prior to main engine cutoff.
The RS-68 engine was mounted to the lower thrust structure of the CBC by a four-legged (quadrapod) thrust frame and enclosed in a protective composite conical thermal shield. Above the thrust structure was an aluminum isogrid (a grid pattern machined out of the inside of the tank to reduce weight) liquid hydrogen tank, followed by a composite cylinder called the centerbody, an aluminum isogrid liquid oxygen tank, and a forward skirt. Along the back of the CBC was a cable tunnel to hold electrical and signal lines, and a feedline to carry the liquid oxygen to the RS-68 from the tank. The CBC was a constant diameter.