# Delta IV Heavy

The Delta IV Heavy (Delta 9250H) was an expendable heavy-lift launch vehicle, the largest type of the Delta IV family. It had the highest capacity of any operational launch vehicle in the world after the retirement of the Space Shuttle in 2011 until the Falcon Heavy debuted in 2018, and it was the world's third highest-capacity launch vehicle in operation at the time of its retirement in 2024. It was manufactured by United Launch Alliance (ULA) and was first launched in 2004. Delta IV Heavy was the last operating member of the Delta IV family, and its final flight was on 9 April 2024. It is succeeded by the Vulcan Centaur rocket.
The Delta IV Heavy first stage consisted of a central Common Booster Core (CBC), with two additional CBCs as liquid rocket boosters instead of the GEM-60 solid rocket motors used by the Delta IV Medium+ versions. At lift-off, all three rocket engines would operate at full thrust, and 44 seconds later the central engine would throttle down to 55% to conserve fuel until the other two engines separate. The latter engines burn out at 242 seconds after launch and are separated as the central engine throttles back up to full thrust. The central engine burns out 86 seconds later, and the second stage completed the ascent to orbit.
The launch vehicle used three RS-68 engines, one in the central core and one in each booster. On the last seconds of countdown, the liquid hydrogen fuel would flow through the engines and upwards along the booster body, and after the ignition that hydrogen inflamed, creating the characteristic fireball and charred look of the booster.

## History

The Delta IV line of rockets were developed by Boeing. The program was later transferred to United Launch Alliance. The Delta IV Heavy was the most powerful member of the line, which also includes the smaller Delta IV Medium. The Delta IV Heavy can lift 28,370 kg (62,550 lb) to low Earth orbit and 13,810 kg (30,450 lb) to geostationary transfer orbit (GTO). It was an all liquid-fueled launch vehicle, consisting of an upper stage, one main booster and two strap-on boosters.
The first launch of the Delta IV Heavy on 21 December 2004 carried a boilerplate payload and was a partial failure. Cavitation in the liquid-oxygen propellant lines caused shutdown of both boosters eight seconds early, and the core engine nine seconds early; this resulted in a lower staging velocity for which the second stage was unable to compensate. The payload was left in a lower than intended orbit.
Its first operational payload was the DSP-23 satellite, successfully launched in 2007; it was then used to launch a further five visual and electronic reconnaissance satellites for the National Reconnaissance Office (NRO) through 2013. In December 2014, the Delta IV Heavy was used to launch an uncrewed test flight of the Orion spacecraft, designated Exploration Flight Test-1 (EFT-1). After several delays, the mission was successfully launched at 12:05 UTC on 5 December 2014.
On 12 August 2018, the Delta IV Heavy with an additional Star 48BV third stage was used to launch the Parker Solar Probe into an elliptical heliocentric orbit. In May 2023, the final Delta IV Heavy core and boosters finished construction, officially ending Delta IV production and making way for the Vulcan launch vehicle. The final Delta IV heavy would launch on April 9, 2024.
Delta IV's final flight was initially scheduled for March 29, 2024 for the National Reconnaissance Office; its actual launch date was April 9, 2024 after a postponement.

## Capabilities

Capacity of the Delta IV Heavy:
* Low Earth orbit (LEO), 200 km × 28.7°: 28,790 kg (63,470 lb)
* Low Earth orbit (ISS), 407 km × 51.6°: 25,980 kg (57,280 lb)
* Geosynchronous transfer orbit (GTO): 14,220 kg (31,350 lb)
* Geosynchronous orbit (GEO): 6,750 kg (14,880 lb)
* Lunar transfer orbit (LTO): 10,000 kg (22,000 lb)
* Mars transfer orbit: 8,000 kg (18,000 lb)
The Delta IV Heavy's total mass at launch was approximately 733,000 kg (1,616,000 lb) and produce around 952,000 kg (2,099,000 lb) of thrust to power the rocket skyward at liftoff.

## Launch history

| Flight | Date | Payload | Mass | Launch site | Outcome |
| 1 | 21 December 2004 | DemoSat, Sparkie / 3CS-1 and Ralphie / 3CS-2 | ≈6,000 kg (13,000 lb) | Cape Canaveral, SLC-37B | Partial failure |
| 2 | 11 November 2007 | DSP-23 | 5,250 kg (11,570 lb) | Cape Canaveral, SLC-37B | Success |
| 3 | 18 January 2009 | Orion 6 / Mentor 4 (USA-202 / NROL-26) | Classified | Cape Canaveral, SLC-37B | Success |
| 4 | 21 November 2010 | Orion 7 / Mentor 5 (USA-223 / NROL-32) | Classified | Cape Canaveral, SLC-37B | Success |
| 5 | 20 January 2011 | KH-11 Kennen 15 (USA-224 / NROL-49) | <17,000 kg (37,000 lb) | Vandenberg, SLC-6 | Success |
| 6 | 29 June 2012 | Orion 8 / Mentor 6 (USA-237 / NROL-15) | Classified | Cape Canaveral, SLC-37B | Success |
| 7 | 26 August 2013 | KH-11 Kennen 16 (USA-245 / NROL-65) | <17,000 kg (37,000 lb) | Vandenberg, SLC-6 | Success |
| 8 | 5 December 2014 | Orion Exploration Flight Test-1 (EFT-1) | 21,000 kg (46,000 lb) | Cape Canaveral, SLC-37B | Success |
| 9 | 11 June 2016 | Orion 9 / Mentor 7 (USA-268 / NROL-37) | Classified | Cape Canaveral, SLC-37B | Success |
| 10 | 12 August 2018 | Parker Solar Probe | 685 kg (1,510 lb) | Cape Canaveral, SLC-37B | Success |
| 11 | 19 January 2019 | NROL-71 | Classified | Vandenberg, SLC-6 | Success |
| 12 | 11 December 2020 | Orion 10 / Mentor 8 (USA-268/ NROL-44) | Classified | Cape Canaveral, SLC-37B | Success |
| 13 | 26 April 2021 | KH-11 Kennen 17 (NROL-82) | Classified | Vandenberg, SLC-6 | Success |
| 14 | 24 September 2022 | KH-11 Kennen 18 (NROL-91) | Classified | Vandenberg, SLC-6 | Success |
| 15 | 22 June 2023 | Orion 11 / Mentor 9 (NROL-68) | Classified | Cape Canaveral, SLC-37B | Success |
| 16 | 9 April 2024 | Orion 12 / Mentor 10 (NROL-70) | Classified | CCSFS, SLC-37B | Success |
* ↑ Common Booster Cores underperformed, lower orbit than planned
* ↑ The officially reported mass of 21,000 kg includes the Launch Abort System (LAS) which did not reach orbit, but excludes the residual mass of the upper stage, which did reach orbit.
* ↑ Star 48BV upper stage

## Comparable vehicles

Current:
* Long March 5 (geostationary transfer orbit)
* Long March 5B (low Earth orbit)
* Long March 7A (geostationary transfer orbit)
* Falcon Heavy
* Proton-M
* Vulcan Centaur
* Angara A5
* Ariane 6
* New Glenn
Retired or cancelled:
* Ariane 5 (retired)
* Atlas V Heavy (proposed, never developed)
* Saturn IB (retired)
* Titan III (retired)
* Titan IV (retired)