|This article contains information regarding a rocket that is scheduled to launch in the next 4 days.
Details may change as the countdown and ascent progress. Launch details: United Launch Alliance will use a Delta IV M+(5,4) to launch WGS-5, a military communication satellite for the United States Air Force. Launch will occur from SLC-37B at Cape Canaveral. • Live countdown clock • Webcast
Delta IV Medium launch carrying DSCS III-B6
|Function||Orbital launch vehicle|
United Launch Alliance
|Country of origin||United States|
|Height||63 - 72 m (206-235 ft)|
|Diameter||5 m (16.4 ft)|
|Mass||249,500-733,400 kg (550,000-1,616,800 lb)|
|Payload to LEO||8,600-22,560 kg (18,900-49,740 lb)|
|3,900-12,980 kg (8,500-28,620 lb)|
|Launch sites||SLC-37B, Cape Canaveral
SLC-6, Vandenberg AFB
Medium+ (4,2): 9
Medium+ (5,2): 1
Medium+ (5,4): 2
Medium+ (4,2): 9
Medium+ (5,2): 1
Medium+ (5,4): 2
|Partial failures||1 (Heavy)|
|First flight||Medium: 11 March 2003
Medium+ (4,2): 20 November 2002
Medium+ (5,2): 3 April 2012
Medium+ (5,4): 6 December 2009
Heavy: 21 December 2004
|Boosters (Medium+ Variants) - GEM 60|
|No. boosters||Medium: 0; M+4,2: 2; M+5: 2 or 4|
|Thrust||826.6 kN (185,817 lbf)|
|Specific impulse||275 sec|
|Burn time||90 seconds|
|Boosters (Heavy) - CBC|
|Thrust||3,312.8 kN (744,737 lbf)|
|Specific impulse||410 sec|
|Burn time||249 seconds|
|First stage - CBC|
|Thrust||3,312.8 kN (744,737 lbf)|
|Specific impulse||410 sec|
|Burn time||259 seconds|
|Second stage - DCSS|
|Thrust||110 kN (24,740 lbf)|
|Specific impulse||462 sec|
|Burn time||850 - 1,125 seconds|
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, Alabama. 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 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[update] 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.
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[update]. In addition a $557.1 million option was added to cover FY10.
2012 upper stage anomaly 
An anomalous event in the use of the Delta IV launch system occurred October 4, 2012, when a leak developed above the narrow throat portion of the thrust chamber in the RL10B-2 engine within the Delta's upper stage. However, due to the low mass of the payload and the excess fuel load coupled with the fault tolerant guidance software which recalculated and fired the engine longer than planned, the payload was placed in the intended orbit.
The investigation into the anomaly led to a delay in subsequent Delta IV launches and the next Atlas V launch (AV-034) due to commonality between the engines used on both vehicles' upper stages. The root cause of the leak had not been determined by March 2013. The rocket has been cleared for launch on May 10, 2013.
Vehicle description 
Delta IV first stage 
The first stage of a Delta IV consists of one, or in the Heavy variety three, Common Booster Cores (CBC) powered by a Rocketdyne RS-68 engine. Unlike many first-stage rocket engines, which use solid fuel or kerosene, the RS-68 engines burn liquid hydrogen and liquid oxygen.
In 2002 the RS-68 became 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 main 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 main CBC to conserve propellant and burn longer. After the strap-on CBCs separate, the main 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 feedline to carry the liquid oxygen to the RS-68 from the tank. The CBC is of a constant, 5-meter, diameter.
Delta Cryogenic Second Stage 
The upper stage of the Delta IV, or DCSS, is based on the Delta III upper stage, but with increased propellant capacity. The 4-meter version uses lengthened propellant tanks, while the 5-meter version has a 5-meter diameter liquid hydrogen tank and a further lengthened liquid oxygen tank. 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.
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.
Payload encapsulation 
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 first launch in 2002; it is taller than the Ariane 4, Titan IV, Atlas V, Ariane 5, Long March 5, Proton rocket, Energia, LGM-118 Peacekeeper, and Space Shuttle.
Delta IV Small 
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.
Delta IV Medium 
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.
Delta IV Heavy 
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:
- geosynchronous transfer orbit (GTO) 13,130 kg (28,950 lb), more than any other currently available launch vehicle.
- geosynchronous orbit (GEO) 6,275 kg
- escape orbit 9,306 kg
- C3 performance of 30 km²s−2: 5,228 kg
- C3 performance of 60 km²s−2: 2,521 kg
The Heavy's total mass at launch is approximately 733,000 kg, much less than that of the Space Shuttle (2,040,000 kg).
Future variants 
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 planned to use Delta IV to launch a Crew Exploration Vehicle. But with the CEV changed from a winged spacecraft to an Apollo-like capsule with the Ares I launch vehicle, based on Space Shuttle components. After the change only the Delta IV's RS-68 engine was considered by NASA for the new cryogenically fueled Ares V rocket. A Delta IV Heavy rocket launch is planned for the Orion Multi-Purpose Crew Vehicle on an unmanned test flight, known as EFT-1, for the spring of 2014.
In 2009 The Aerospace Corporation reported on NASA results of a study 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 Office) 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, was successfully flight tested in a launch on June 29, 2012. This upgrade provides 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 37 (SLC-37) at the Cape Canaveral Air Force Station. On the West coast, polar-orbit and high-inclination launches use Vandenberg Air Force Base's Space Launch Complex 6 (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 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 
The Delta IVs are assembled using a process that reduces cost and expensive on-pad time. The CBCs are assembled in the company's factory in Decatur, Alabama. 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.
Delta IV launches 
|Type||Serial-no.||Startplace||Payload||Type of payload||Orbit||Outcome||Remarks|
|Medium+(4,2)||293||CCAFS SLC-37B||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 (planned)||Partial failure|
|Medium+(4,2)||315||CCAFS SLC-37B||GOES 13 (GOES-N)||Weather satellite||GTO||Success|
|Medium+(4,2)||317||VAFB SLC-6||USA-184 (NROL-22)||Reconnaissance satellite||Molniya||Success||First Delta IV launch from Vandenberg|
|Medium||320||VAFB SLC-6||USA-192 (DMSP F17)||Military weather satellite||SSO||Success||First Delta IV launch into a LEO/SSO|
|Heavy||329||CCAFS SLC-37B||USA-197 (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|
|Medium+(5,4)||346||CCAFS SLC-37B||USA-211 (WGS-3)||Military communications satellite||GTO||Success||First Delta IV Medium+ (5,4) launch|
|Medium+(4,2)||348||CCAFS SLC-37B||GOES 15 (GOES-P)||Weather satellite||GTO||Success|
|Medium+(4,2)||349||CCAFS SLC-37B||USA-213 (GPS IIF SV-1)||Navigation Satellite||MEO||Success|
|Heavy||351||CCAFS SLC-37B||USA-223 (NROL-32)||Reconnaissance satellite||GSO||Success|
|Heavy||352||VAFB SLC-6||USA-224 (NROL-49)||Reconnaissance satellite||LEO||Success||First Delta IV Heavy launch from Vandenberg|
|Medium+(4,2)||353||CCAFS SLC-37B||USA-227 (NROL-27)||Reconnaissance satellite||GTO||Success|
|Medium+(4,2)||355||CCAFS SLC-37B||USA-231 (GPS IIF SV-2)||Navigation Satellite||MEO||Success|
|Medium+(5,4)||358||CCAFS SLC-37B||USA-233 (WGS-4)||Military communications satellite||GTO||Success|
|Medium+(5,2)||359||VAFB SLC-6||USA-234 (NROL-25)||Reconnaissance satellite||LEO||Success||First flight in the Medium+(5,2) version|
|Heavy||360||CCAFS SLC-37B||USA-237 (NROL-15)||Reconnaissance satellite||GSO||Success||First flight of the RS-68A engine|
|Medium+(4,2)||361||CCAFS SLC-37B||USA-239 (GPS IIF SV-3)||Navigation Satellite||MEO||Success||Minor upper stage anomaly|
List Date: October 7, 2012
List of Thor and Delta launches (2010–2019)
Notable past launches 
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 Canaveral. 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 December 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 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.
NROL-22 was the first Delta IV launched from SLC-6 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 Office (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 Canaveral occurred on November 10, 2007.
NROL-32 was a "heavy" launch, carrying a satellite for NRO. The payload is speculated to be the largest satellite sent into space. The rocket lifted off on November 21, 2010; the launch was delayed from October 19.
NROL-49 lifted off from Vandenberg AFB on January 20, 2011. 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.
Planned launches 
- Several GPS Block IIF satellites will be launched using Medium+ (4,2) rockets (as well as Atlas V 401 rockets). The first of these was launched in May 2010.
- Debut unmanned test flight of the Orion Multi-Purpose Crew Vehicle, known as EFT-1, that will launch aboard a Delta IV Heavy rocket in mid-2014.
See also 
- Comparison of orbital launchers families
- Comparison of orbital launch systems
- Advanced Common Evolved Stage
- Expendable launch system
- List of launch vehicles
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|Wikimedia Commons has media related to: Delta (rocket)|
- Delta IV Launch Vehicle page on United Launch Alliance site
- Boeing's Delta IV Rocket page
- Delta IV information on Gunter's Space Page
- Comparison of Delta IV Heavy with Space Shuttle
- First Vandenberg Delta IV Heavy launch video via EducatedEarth.
- Bates, Jason. Boeing's Delta IV Heavy Gets Ready for its Close-Up, Space News, 2004-12-06.
- Rocketdyne Space Page
- Delta IV page on Astronautix.com