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Delta IV

Overview

Delta IV

comparable
function	Orbital launch vehicle
manufacturer	United Launch Alliance
country-origin	United States
cpl	US$164+ million‡R1R‡
height	63-70.7 m
diameter	5.1 m
mass	249500-733400 kg
stages	2
family	Delta (rocket family)

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.[4] 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

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.[45] 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.[46]

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 5 m diameter.[10]

Delta Cryogenic Second Stage

The upper stage of the Delta IV was the Delta Cryogenic Second Stage (DCSS). The DCSS was based on the Delta III upper stage but has increased propellant capacity. Two versions have been produced: a 4 m diameter DCSS that was retired with the Delta IV Medium and a 5 m diameter DCSS that remained in service with the Delta IV Heavy. The 4-meter diameter version lengthened both Delta III propellant tanks, while the 5-meter version had an extended diameter liquid hydrogen tank and a further lengthened liquid oxygen tank. Regardless of the diameter, each DCSS was powered by one RL10B-2 engine, with an extendable carbon-carbon nozzle to improve specific impulse.[47] Two different interstages were used to mate the first stage and DCSS. A tapering interstage that narrowed down from 5 to 4-meter diameter was used to mate the 4-meter DCSS to the CBC, while a cylindrical interstage was used to mate the 5-meter DCSS. Both interstages were built from composites and enclosed the liquid oxygen tank, with the larger liquid hydrogen tank making up part of the vehicle's outer mold line.[48][49]

Launch sites

Delta IV launched from either of two rocket launch complexes. Launches on the East coast of the United States used Space Launch Complex 37 (SLC-37) at the Cape Canaveral Air Force Station. On the West coast, polar-orbit and high-inclination launches used Vandenberg Space Force Base's Space Launch Complex 6 (SLC-6).

Launch facilities at both sites were similar. A Horizontal Integration Facility (HIF) was situated some distance from the pad. Delta IV CBCs and second stages to be mated and tested in the HIF before they were moved to the pad. The partial horizontal rocket assembly of the Delta IV was somewhat similar to the Soyuz launch vehicle, which is completely assembled horizontally. The Space Shuttles, the past Saturn launch vehicles, and the Space Launch System were assembled and rolled out to the launch pad entirely vertically.

Movement of the Delta IVs among the various facilities at the pad was facilitated by rubber-tired Elevating Platform Transporters (EPTs) and various transport jigs. Diesel engine EPTs were used for moving the vehicles from the HIF to the pad, while electric EPTs were used in the HIF, where precision of movement was important.[50]

The basic launchpad structure includes a flame trench to direct the engine plume away from the rocket, lightning protection, and propellant storage.

Vehicle processing

Delta IV CBCs and DCSSs were assembled at ULA's factory in Decatur, Alabama. They were then loaded onto the R/S RocketShip, a roll-on/roll-off cargo vessel, and shipped to either launch pad. There, they were offloaded and rolled into a HIF. For Delta IV Medium launches, the CBC and DCSS were mated in the HIF. For Delta IV Heavy launches, the port and starboard strap-on CBCs were also mated in the HIF.

Various tests were performed, and then the vehicle was rolled horizontally to the pad, where the Fixed Pad Erector (FPE) was used to raise the vehicle to the vertical position. At this time, the GEM 60 solid motors, if any were required, were rolled to the pad and attached to the vehicle. After further testing, the payload (which has already been enclosed in its fairing) was transported to the pad, hoisted into the MST by a crane, and attached to the vehicle. Finally, on launch day, the MST was rolled away from the vehicle, and the vehicle was then ready for launch.[51]

Launch history

The 45 Delta IV launches consist of 3 Delta IV Medium, 36 Medium+, and 16 Heavy.

Delta family launches by decade

List of Thor and Delta launches (2000–2009)
List of Thor and Delta launches (2010–2019)
List of Thor and Delta launches (2020–2024)

Delta IV launches by configuration

List of Delta IV launches (all variants, Medium and Heavy)
List of Delta IV Medium launches
List of Delta IV Heavy launches

Notable launches

The first payload launched with a Delta IV was the Eutelsat W5 communications satellite. A Medium+ (4,2) from Cape Canaveral carried the communications satellite into geostationary transfer orbit (GTO) on November 20, 2002.

Heavy Demo was the first launch of the Delta IV Heavy in December 2004 after significant delays due to bad weather. Due to cavitation in the propellant lines, sensors on all three CBCs registered depletion of propellant. The strap-on CBCs and then core CBC engines shut down prematurely, even though sufficient propellant remained to continue the burn as scheduled. The second stage attempted to compensate for the shutdown and burned until it ran out of propellant. This flight was a test launch carrying a payload of:

NROL-22 was the first Delta IV launched from SLC-6 at Vandenberg Space Force Base (VSFB). It was launched aboard a Medium+ (4,2) in June 2006 carrying a classified satellite for the U.S. National Reconnaissance Office (NRO).

DSP-23 was the first launch of a valuable payload aboard a Delta IV Heavy. This was also the first Delta IV launch contracted by the United Launch Alliance, a joint venture between Boeing and Lockheed Martin. The main payload was the 23rd and final Defense Support Program missile-warning satellite, DSP-23. Launch from Cape Canaveral occurred on November 10, 2007.[94]

NROL-26 was the first Delta IV Heavy EELV launch for the NRO. USA 202, a classified reconnaissance satellite, lifted off January 18, 2009.[95]

NROL-32 was a Delta IV Heavy launch, carrying a satellite for NRO. The payload is speculated to be the largest satellite sent into space. After a delay from October 19, 2010, the rocket lifted off on November 21, 2010.[96]

NROL-49 lifted off from Vandenberg AFB on January 20, 2011.[57] It was the first Delta IV Heavy mission to be launched out of Vandenberg. This mission was for the NRO and its details are classified.[97]

On October 4, 2012, a Delta IV M+ (4,2) experienced an anomaly in the upper stage's RL10B-2 engine which resulted in lower than expected thrust. While the vehicle had sufficient fuel margins to successfully place the payload, a GPS Block IIF satellite USA-239, into its targeted orbit, investigation into the glitch delayed subsequent Delta IV launches and the next Atlas V launch (AV-034) due to commonality between the engines used on both vehicles' upper stages.[98] By December 2012, ULA had determined the cause of the anomaly to be a fuel leak (into the combustion chamber[99]), and Delta IV launches resumed in May 2013. After two more successful launches, further investigation led to the delay of Delta flight 365 with the GPS IIF-5 satellite.[100] Originally scheduled to launch in October 2013, the vehicle lifted off on February 21, 2014.[101]

A Delta IV Heavy launched the Orion spacecraft on an uncrewed test flight, EFT-1, on December 5, 2014.[102] The launch was originally planned for December 4, 2014, but high winds and valve issues caused the launch to be rescheduled for December 5, 2014.[103]

On August 12, 2018, another Delta IV Heavy launched the Parker Solar Probe on a mission to explore or "touch" the outer corona of the Sun.[104]

The second GPS Block III satellite was launched with the final Delta IV Medium+ (4,2) configuration rocket on August 22, 2019.[87]

The final flight from Vandenberg of the Delta IV Heavy launched the NROL-91 mission in September 2022.

The final flight from Cape Canaveral of the Delta IV Heavy and of the Delta rocket family took place in April 2024 carrying the NROL-70 mission.

DemoSat – 6020 kg; an aluminum cylinder filled with 60 brass rods – planned to be carried to GEO; however due to the sensor faults, the satellite did not reach this orbit.
NanoSat-2, carried to low Earth orbit (LEO) – a set of two very small satellites of 24 and 21 kg, nicknamed Sparky and Ralphie – planned to orbit for one day. Given the under-burn, the two most likely did not reach a stable orbit.[93]