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Delta IV is an active expendable launch system in the Delta rocket family. Delta IV uses rockets designed by Boeing's Integrated Defense Systems division and built in the United Launch Alliance (ULA) facility in Decatur, Alabamamarker. Final assembly is completed at the launch site by ULA. The rockets were designed to launch payloads into orbit for the United States Air Force Evolved Expendable Launch Vehicle (EELV) program and commercial satellite business. Delta IV rockets are available in five versions: Medium, Medium+ (4,2), Medium+ (5,2), Medium+ (5,4), and Heavy, which are tailored to suit specific payload size and weight ranges. Delta IV was primarily designed to satisfy the needs of the U.S. military.

The rockets are assembled at the Horizontal Integration Facility for launches from SLC-37Bmarker at Cape Canaveralmarker, and in a similar facility for launches from SLC-6marker at Vandenberg AFBmarker.

Vehicle description

The first stage of a Delta IV consists of one, or in the Heavy variety three, Common Booster Core(s) (CBC) powered by a Rocketdyne RS-68 engine. Unlike most first-stage rocket engines, which use solid fuel or kerosene, the RS-68 engines burn liquid hydrogen and liquid oxygen.

The RS-68 is the first large, liquid-fueled rocket engine designed in the U.S. since the Space Shuttle Main Engine (SSME) in the 1970s. The primary goal for the RS-68 was to reduce cost versus the SSME. Some sacrifice in chamber pressure and specific impulse was made, hurting efficiency; however, development time, part count, total cost, and assembly labor were reduced to a fraction of the SSME, despite the RS-68's significantly larger size. Typically, the RS-68 runs at 102% rated thrust for the first few minutes of flight, and then throttles down to 58% rated thrust before main engine cutoff. On the Heavy variant, the core CBC's engine throttles down to 58% rated thrust around 50 seconds after liftoff, while the strap-on CBCs remain at 102%. This allows the core CBC to conserve propellant and burn longer. After the strap-on CBCs separate, the core CBC's engine throttles back up to 102% before throttling back down to 58% prior to main engine cutoff.

The RS-68 engine is mounted to the lower thrust structure of the vehicle by a four-legged (quadrapod) thrust frame, and enclosed in a protective composite conical thermal shield. Above the thrust structure is 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 is a cable tunnel to hold electrical and signal lines, and a tube to carry the liquid oxygen to the RS-68 from the tank. The CBC is of a constant, 5-meter, diameter.

The L-3 Communications Redundant Inertial Flight Control Assembly (RIFCA) guidance system used on the Delta IV is common to that carried on the Delta II, although the software is different because of the differences between the Delta II and Delta IV. The RIFCA features six ring laser gyroscopes and accelerometers each, to provide a higher degree of reliability.

The upper stage of the Delta IV is nearly identical to that of the Delta III, however the tanks are either stretched (in 4-meter variants), or have a larger diameter (5-meter variants). The second stage is powered by a Pratt & Whitney RL-10B2 engine, which features an extendable carbon-carbon nozzle to improve specific impulse. Depending on variant, two different interstages are used to mate the first and second stages. A tapering interstage which narrows down from 5-meters to 4-meters in diameter is used on 4-meter variants, where a cylindrical interstage is used on 5-meter variants. Both interstages are built from composites.

To encapsulate the satellite payload, a variety of different payload fairings are available. A stretched Delta III 4-meter composite payload fairing is used on 4-meter variants, where an enlarged, 5-meter composite fairing is used on 5-meter variants. A longer version of the latter is standard on the Heavy variant, and a Boeing-built Titan-IV derived 5-meter, aluminum isogrid payload fairing is also available for the Heavy.

At over 63 meters in length, the Delta IV has been the tallest rocket in active use since its introduction.

The Delta IV entered the space launch market at a period when global capacity was already much higher than demand. Furthermore, as an unproven design it has had difficulty finding a market in commercial launches, and the cost to launch a Delta IV is somewhat higher than that for competing vehicles. In 2003, Boeing pulled the Delta IV from the commercial market, citing low demand and high costs. In 2005, Boeing stated that it may return the Delta IV to commercial service; however as of 2006 no further announcements have been made regarding this. All but one of the first launches have been paid for by the U.S. Government, with a cost of between $140 million and $170 million.

Comparable rockets:Atlas V -Ariane 5 -Chang Zheng 5 -Angara -H-IIB -Proton -Falcon 9


The Delta IV Medium (Delta 9040) is the most basic Delta IV. It features a single CBC and a modified Delta III second stage, with 4-meter liquid hydrogen and liquid oxygen tanks and a 4-meter payload fairing derived from the Delta III fairing. The Delta IV Medium is capable of launching 4,210 kg (9,285 lb) to geosynchronous transfer orbit (GTO).

The Delta IV Medium+ (4,2) (Delta 9240) is similar to the Medium, but uses two Alliant-built 1.5-m (60-in) diameter solid rocket strap-on Graphite-Epoxy Motors (GEM-60s) to increase payload capacity to 5,845 kg (12,890 lb) to GTO.

The Delta IV Medium+ (5,2) (Delta 9250) is similar to the Medium+ (4,2), but has a 5-m–diameter payload fairing for larger payloads and a modified second stage with a 5-meter liquid hydrogen tank and stretched liquid oxygen tank. Because of the extra weight of the larger payload fairing and second stage, the Medium+ (5,2) can launch 4,640 kg (10,230 lb) to GTO, less than the Medium+ (4,2).

The Delta IV Medium+ (5,4) (Delta 9450) is similar to the Medium+ (5,2), but uses four GEM-60s instead of two, enabling it to lift 6,565 kg (14,475 lb) to GTO.

The Delta IV Heavy (Delta 9250H) is similar to the Medium+ (5,2), except that it uses two additional CBCs instead of using GEMs. These are strap-on boosters which are separated earlier in the flight than the center CBC. The Delta IV Heavy also features a stretched 5-meter composite payload fairing. An aluminum trisector (3 part) fairing derived from the Titan IV fairing is also available. This was first used on the DSP-23 flight.

Capacity (separated spacecraft mass) of the Delta IV Heavy:

The Heavy's total mass at launch is approximately 733,000 kg, much less than that of the Space Shuttle (2,040,000 kg).

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 CBC. The Small variant was dropped by 1999. This was probably because the Delta II has a similar payload capability.

Future variants

Delta IV evolution (US Govt)

Possible future upgrades for the Delta IV include adding extra strap-on solid motors to boost capacity, higher-thrust main engines, lighter materials, higher-thrust second stages, more (up to six) strap-on CBCs, and a cryogenic propellant cross feed from strap on boosters to the common core. These modifications could potentially increase the mass of the payload delivered to LEO to 100 tonnes.

At one point NASA had plans to use Delta IV to launch a Crew Exploration Vehicle.But with the change of the CEV from a winged or lifting body spacecraft to an Apollo-like capsule and a new launch vehicle based on Space Shuttle components, the only component from the Delta IV that NASA would adopt is the RS-68 engine that would be used to power the new cryogenically-fueled Ares V rocket.

In 2009 The Aerospace Corporation reported to NASA results of study intended to determine the feasibility of modifying Delta IV to be human-rated for use in NASA human spaceflight missions. According to Aviation Week the study, "found that a Delta IV heavy [...] could meet NASA's requirements for getting humans to low Earth orbit."

The possibility of an extra-heavy variant was indicated in a 2006 RAND Corporation study of national security launch requirements out to 2020, which noted, "...only the Delta IV Heavy has the performance to lift the ten NSS launch requirements that require a heavy-lift capability... the production capacity for Delta IV, with one possible exception, can satisfy the entire projected NSS launch demand. The exception involves the requirement to increase the Delta IV Heavy lift capability to accommodate a single NRO (National Reconnaissance Officemarker) payload. The best solution to this requirement is currently under study."

An upgrade of the Delta IV Heavy, using the higher-performance RS-68A engine, is under development with initial availability in early 2011. This upgrade is planned to provide a roughly 13% improvement in payload capability to GTO. The new RS-68A is also planned to be used throughout the entire Delta IV family, where at 106% thrust it will provide a roughly 7-11% improvement in GTO payload (although this higher power level may require structural changes; running the engine at the current 102% produces a smaller improvement but requires less modification).

Another possible upgrade to the Delta IV family is the creation of new variants by the addition of extra solid motors. One such modification, the Medium+(4,4), would pair the four GEM-60s of the M+(5,4) with the upper stage and fairing of the (4,2). This would theoretically provide a GTO payload of 7,500 kg (16,600 lb) and an LEO payload of 14,800 kg (32,700 lb). This is the simplest variant to implement and is available within 36 months of the first order. Two other possible versions, the Medium+(5,6) and (5,8), would add two or four extra GEM-60s to the (5,4) variant, respectively. These would provide significantly higher performance (up to 9,200 kg/20,200 lb to GTO for the M+(5,8)) but would require more extensive modifications to the vehicle, such as adding the extra attach points and changes to cope with the different flight loads. They would also require pad and infrastructure changes. The Medium+(5,6) and (5,8) can be available within 48 months of the first order.

Launch sites

Delta IV launches occur from either of two rocket launch sites. On the East coast of the United States, Space Launch Complex 37marker (SLC-37) at the Cape Canaveral Air Force Stationmarker. On the West coast, polar-orbit and high-inclination launches use Vandenberg Air Force Basemarker's Space Launch Complex 6marker (SLC-6) pad.

Launch facilities at both sites are similar. At the pad is a Mobile Service Tower (MST), which provides service access to the rocket and protection from the weather. There is a crane at the top of the MST, which allows the payload and GEM-60 solid motors to be attached to the vehicle. The MST is rolled away from the rocket several hours before launch. At Vandenberg, the launch pad also has a Mobile Assembly Shelter (MAS), which completely encloses the vehicle; at CCAFS, the vehicle is partly exposed near its bottom.

Beside the vehicle is a Fixed Umbilical Tower (FUT), which has two (VAFB) or three (CCAFS) swing arms. These arms carry electrical, hydraulic, environmental control, and other support functions to the vehicle through umbilical lines. The swing arms retract at T-0 seconds to prevent them from hitting the vehicle.

Under the vehicle is a Launch Table, with six Tail Service Masts (TSMs), two for each CBC. The Launch Table supports the vehicle on the pad, and the TSMs provide further support and fueling functions for the CBCs. The vehicle is mounted to the Launch Table by a Launch Mate Unit (LMU), which is attached to the vehicle by bolts that sever at launch. Behind the Launch Table is a Fixed Pad Erector (FPE), which uses two long-stroke hydraulic pistons to raise the vehicle to the vertical position after being rolled to the pad from the Horizontal Integration Facility (HIF). Beneath the Launch Table is a flame duct, which deflects the rocket's exhaust away from the rocket or facilities.

The Horizontal Integration Facility (HIF) is situated some distance from the pad. It is a large building that allows the Delta IV CBCs and second stages to be mated and tested before they are moved to the pad. The horizontal rocket assembly of the Delta IV are similar to the ones with the assembly of Soyuz launch vehicles; they are also assembled horizontally, unlike the current Space Shuttles, the past Saturn launch vehicles and the upcoming Ares I and Ares V, where they are assembled and rolled out to the launch pad entirely vertically.

Movement of the Delta IVs among the various facilities at the pad is facilitated by Elevating Platform Transporters (EPTs). These rubber-tired vehicles can be powered by either diesel engines or electric power. Diesel EPTs are used for moving the vehicles from the HIF to the pad, while electric EPTs are used in the HIF, where precision of movement is important.

Vehicle processing

Delta IV 4-Meter Second Stage

The Delta IVs are assembled using a process that Boeing claims reduces cost and expensive on-pad time. The CBCs are built in Boeing's factory in Decatur, Alabamamarker. They are then loaded onto the M/V Delta Mariner, a roll-on/roll-off cargo vessel, and shipped to either launch pad. There, they are offloaded and rolled into a Horizontal Integration Facility (HIF), where they are mated with the second stages, which were shipped separately to the pad on the Delta Mariner. Also, in the HIF, the three CBCs of Heavy variant are mated to each other.

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


Recent history

The United States Air Force (USAF) continues to fund Delta IV engineering, integration and infrastructure 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 $1,656 million to extend the period of performance through the end of FY09. In addition a $557.1 million option was added to cover FY10.

Delta IV launches

List Date: November 24, 2009

Type Serial-no. Startplace Payload Type of payload Orbit Outcome Remarks

Medium+(4,2) 293 CCAFS SLC-37Bmarker Eutelsat W5 Commercial communications satellite GTO Success First Delta IV launch

Medium 296 CCAFS SLC-37B USA-167 (DSCS-3 A3) Military communications satellite GTO Success First Delta IV Medium launch
First USAF EELV mission

Medium 301 CCAFS SLC-37B USA-170 (DSCS-3 B6) Military communications satellite GTO Success

Heavy 310 CCAFS SLC-37B DemoSat / 3CS 1 / 3CS 2 Demonstration payload GSO (planed) Partial failure, only DemoSat reached incorrect orbit First Delta IV Heavy launch

Medium+(4,2) 315 CCAFS SLC-37B GOES 13 (GOES-N) Weather satellite GTO Success First Delta IV launch for NASAmarker

Medium+(4,2) 317 VAFB SLC-6marker NROL-22marker Reconnaissance satellite Molniya Success First Delta IV launch from Vandenberg

Medium 320 VAFB SLC-6 DMSP F17 Military weather satellite SSO Success First Delta IV launch into a LEO/SSO

Heavy 329 CCAFS SLC-37B DSP-23 Missile Warning satellite GSO Success First Delta IV launch contracted by United Launch Alliance
Launch delayed due to damage to launch pad caused by a liquid oxygen leak

Heavy 337 CCAFS SLC-37B USA-202 (NROL-26) Reconnaissance satellite GSO Success

Medium+(4,2) 342 CCAFS SLC-37B GOES 14 (GOES-O) Weather satellite GTO Success
For planned launches, see:

List of Thor and Delta launches #Planned launches

Notable past launches

GOES-N launch on a Medium+ (4,2)
The first payload launched with a Delta IV was the Eutelsat W5 communications satellite. The launch vehicle was a Medium+ (4,2) variant, launched from Cape Canaveralmarker. It carried the communications satellite into geostationary transfer orbit (GTO) on November 20 2002.

Heavy Demo was the first launch of the Heavy variant in Dec. 2004 after significant delays due to bad weather. Due to cavitation in the propellant lines, sensors registered depletion of propellant. The strap-on, and later 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 under-burn, until it ran out of propellant. This flight was a test launch carrying a payload consisting of:
  • 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.

A unique aerial view of NROL-22 launch from SLC-6 (USAF photo/Staff Sgt.
Quinton Russ)

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

DSP-23 was the first launch of a valuable payload aboard a Heavy vehicle. 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 Canaveralmarker occurred at 01:50:00 GMT on 11 November 2007 (20:50 EST, November 10, 2007).

NROL-26 was the first "heavy" EELV launch for the NRO. It carried USA 202, a classified reconnaissance satellite, on a Delta IV Heavy that lifted off 18 January 2009 at 02:47 UTC.

Planned launches

  • Several GPS Block IIF satellites will be launched using Medium+ (4,2) rockets, the first launch scheduled for early 2010.

  • The Air Force has ordered two additional Heavy flights. NROL-32 will launch from Cape Canaveral and NROL-49 will launch from Vandenberg in, "the next few years." NROL-32 is scheduled to launch sometime around 2010.

See also


  1. United Launch Alliance Transaction completed
  2. Delta IV GOES-N Launch Timeline
  3. Delta IV Heavy Demo Launch Timeline
  4. L-3 Space & Navigation's RIFCA Trihex
  5. US Air Force - EELV Fact Sheets
  6. Delta IV Small on
  7. Gunter's Space page - Delta IV
  8. Delta IV Launch Facilities
  9. Delta IV prelaunch assembly
  10. Spaceflight Now | Delta 4-Heavy mission report

External links

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