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.
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.[6][7]
During the Delta IV's development,a small variant was considered. This would have featured the Delta II second stage,an optional ThiokolStar 48B third stage,and the Delta II payload fairing,all atop a single Common Booster Core (CBC).[8] The Small variant was dropped by 1999.[9][10]
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.[12]
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.[13] 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.[14]
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.[15]
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.[16]
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.[17] Lift capacity was increased by developing the higher-performance RS-68A engine,[18] which first flew on June 29,2012.[19] 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,[20] 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.[21] The Delta IV Heavy required non-standard CBCs for the core and boosters.[22]
Masses include a Payload Attach Fitting (240kg to 1,221kg depending on payload).[2]
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.[25]
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 7,500kg (16,500lb),a LEO payload of 14,800kg (32,600lb),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 9,200kg (20,300lb) 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.[28]
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.[29]
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 0.3 meters (1ft) larger.[30]:1–5 It is powered by two BE-4 methane-fueled engines developed by Blue Origin.[31][32] 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.[31][32]
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 27,200 kilograms (60,000lb) to low Earth orbit (LEO),[33] surpassing the Atlas V's maximum of 18,850kg (41,560lb)[34] and approaching the Delta IV Heavy's 28,790kg (63,470lb) capacity.[35]
The Vulcan Centaur was originally projected to enter service in 2023,[36][37] but its first launch took place on January 8,2024.[38] 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,[39][40] and the final Delta IV Heavy launch was on April 9,2024,with the NROL-70 mission.[41]
Delta IV Medium
The Delta IV Medium (also referred to as single stick)[42][43] was offered in four configurations:Medium,Medium+ (4,2),Medium+ (5,2),and Medium+ (5,4).[39]
The Delta IV Medium (Delta 9040) was the baseline configuration. It featured a single Common Booster Core (CBC) and a 4-meter (13ft)Delta Cryogenic Second Stage (DCSS),derived from the Delta III design but with enlarged propellant tanks. Because the CBC was 5 meters (16ft) 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 4,200 kilograms (9,300lb) into geostationary transfer orbit (GTO). From Cape Canaveral,GTO is 1,804 meters per second (5,920ft/s) short of geostationary orbit (GEO). Performance figures exclude the mass of the payload fairing and payload attach fittings.[7]
The Delta IV Medium+ (4,2) (Delta 9240) used the same CBC and 4-meter (13ft) DCSS as the Medium,but added two Orbital ATK-built GEM 60 solid rocket boosters (SRBs),increasing payload capacity to GTO to 6,150 kilograms (13,560lb).[7]
The Delta IV Medium+ (5,2) (Delta 9250) retained the two GEM 60 SRBs of the Medium+ (4,2),but used a larger 5-meter (16ft) DCSS and a 5-meter (16ft) payload fairing,allowing it to accommodate larger payloads.[44] Due to the added mass of the larger fairing and second stage,payload to GTO was reduced to 5,072 kilograms (11,182lb).[7]
The Delta IV Medium+ (5,4) (Delta 9450) used the same 5-meter (16ft) DCSS and payload fairing of the Medium+ (5,2),but used four GEM 60 SRBs instead of two,increasing payload capacity to GTO to 6,882 kilograms (15,172lb).[7]
The Delta IV Heavy (Delta 9250H) combined a 5-meter (16ft) 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.[25][44] With the extended fairing,the vehicle stood over 203 feet (62m).
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 aluminumisogrid (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 of a constant 5m (16ft) diameter.[11]
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 4m (13ft) diameter DCSS that was retired with the Delta IV Medium and a 5m (16ft) diameter DCSS that remains in service with the Delta IV Heavy. The 4 m diameter version lengthened both Delta III propellant tanks,while the 5-meter version has 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 m to 4 m diameter was used to mate the 4 m DCSS to the CBC,while a cylindrical interstage was used to mate the 5 m 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
First Delta IV Heavy with three CBCs prior to launch
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.[50] 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.[citation needed]
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. In the case of Delta IV,the vehicle was completed on the launch pad inside a building. This Mobile Service Tower (MST) provides service access to the rocket and protection from the weather and was rolled away from the rocket on launch day. A crane at the top of the MST lifts the encapsulated payload to the vehicle and also attached the GEM 60 solid motors for Delta IV Medium launches. The MST was rolled away from the rocket several hours before launch. At Vandenberg,the launch pad also had a Mobile Assembly Shelter (MAS),which completely enclosed the vehicle;at CCAFS,the vehicle was partly exposed near its bottom.[50]
Beside the vehicle was a Fixed Umbilical Tower (FUT),which has two (VSFB) or three (CCAFS) swing arms. These arms carry telemetry signals,electrical power,hydraulic fluid,environmental control air flow,and other support functions to the vehicle through umbilical lines. The swing arms retract at T-0 seconds once the vehicle was committed to launch.[50]
Under the vehicle was 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 was mounted to the Launch Table by a Launch Mate Unit (LMU),which was attached to the vehicle by bolts that sever at launch. Behind the Launch Table was a Fixed Pad Erector (FPE),which used two long-stroke hydraulic pistons to raise the vehicle to the vertical position after being rolled to the pad from the HIF. Beneath the Launch Table was a flame duct,which deflects the rocket's exhaust away from the rocket or facilities.[50]
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.[51]
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]
GOES-N launch on a Medium+ (4,2)A unique aerial view of NROL-22 launch from SLC-6
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.[citation needed]
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:
DemoSat– 6020kg;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 21kg,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]
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-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.
↑ Whitesides, Loretta Hidalgo (July 9, 2008). "Why NASA Isn't Trying to Human-Rate the Atlas V or Delta IV Rockets". Wired. "You could launch a smaller human vehicle on a current expendable rocket [...] In fact, before the Columbia disaster NASA teams were working on an Orbital Space Plane (OSP) designed to do just that".
1 2 de Selding, Peter B. (March 16, 2016). "ULA intends to lower its costs, and raise its cool, to compete with SpaceX". SpaceNews. Archived from the original on March 17, 2016. Retrieved March 19, 2016. Methane rocket has a lower density so we have a 5.4 meter design outside diameter, while drop back to the Atlas V size for the kerosene AR1 version.
↑ Schaub, Michael B. "Mission Set Database". NASA GSFC/Honeywell TSI. Archived from the original on March 20, 2009. Retrieved October 13, 2008. This article incorporates text from this source, which is in the public domain.
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