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Vulcan Centaur is a heavy-lift launch vehicle developed and operated by United Launch Alliance (ULA). It is a two-stage-to-orbit launch vehicle consisting of the Vulcan first stage and the Centaur second stage. Replacing ULA's Atlas V and Delta IV rockets, the Vulcan Centaur is principally designed to meet the needs of the National Security Space Launch (NSSL) program, which supports U.S. intelligence agencies and the Defense Department, but ULA believes it will also be able to price missions low enough to attract commercial launches.
ULA began development of the new launch vehicle in 2014, primarily to compete with SpaceX’s Falcon 9 and to comply with a Congressional mandate to phase out the use of the Russian-made RD-180 engine that powered the Atlas V. The first launch of the Vulcan Centaur was initially scheduled for 2019 but faced multiple delays due to developmental challenges with its new BE-4 first-stage engine and the Centaur second-stage.
The Vulcan Centaur had a near perfect first launch on January 8, 2024, carrying the Peregrine lunar lander, the first mission of NASA's Commercial Lunar Payload Services program. Its second launch, a NSSL certification flight, took place on October 4, 2024, which achieved an acceptable orbital insertion, despite the nozzle on one of the GEM-63XL solid rocket boosters falling off which led to reduced, asymmetrical thrust. Following a five-month review of the launches, the Space Force certified the Vulcan for NSSL missions in March 2025.
The Vulcan's first stage shares a common heritage with the Delta IV's Common Booster Core. It is built in the same Decatur, Alabama factory using much of the same manufacturing equipment, but is about larger in diameter. The most significant change in the first stage is its use of liquid methane (liquefied natural gas) as fuel in two BE-4 engines developed by Blue Origin. Compared to the liquid hydrogen used on the Delta IV, methane is denser and has a higher boiling point, allowing for smaller, lighter fuel tanks. It also burns cleaner than the kerosene used in the Atlas V, reducing hydrocarbon buildup in engines, which would facilitate refurbishment under the proposed SMART reuse system.
The rocket's second stage, the Centaur V, is an upgraded version of the Centaur III used on the Atlas V offering enhanced performance. It is powered by two RL10 engines from Aerojet Rocketdyne, fueled by liquid hydrogen.
To further enhance payload capacity, the Vulcan Centaur can be equipped with up to six GEM 63XL SRBs (solid rocket boosters) from Northrop Grumman—a lengthened version of the GEM 63 SRBs used on the Atlas V.
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 a single core and six GEM boosters, the Vulcan Centaur can lift to low Earth orbit (LEO), surpassing the Atlas V's maximum of with a single core and five GEM boosters, and approaching the capacity of the three-core Delta IV Heavy.
Beyond Gravity provides additional components, including the interstage adapter, payload fairing, and payload attachment fitting, which secures the payload and fairings to the second stage until commanded to release. The company also supplies a heat shield to protect equipment.
Designed to meet the National Security Space Launch (NSSL) program's requirements, the Vulcan Centaur is also designed to be capable of achieving human-rating certification, enabling it to carry crewed spacecraft such as the Boeing Starliner or Sierra Nevada Dream Chaser.
In September 2018, ULA announced that it had picked the BE-4 engine from Blue Origin and fueled by liquid oxygen (LOX) and liquid methane (CH4) to replace the RD-180 on a new first-stage booster. The engine was already in its third year of development, and ULA said it expected the new stage and engine to start flying as soon as 2019. Two of the -thrust BE-4 engines were to be used on a new launch vehicle booster.
A month later, ULA restructured company processes and its workforce to reduce costs. The company said that the successor to Atlas V would blend existing Atlas V and Delta IV with a goal of halving the cost of the Atlas V rocket.
By March 2016, the United States Air Force (USAF) had committed up to $202 million for Vulcan development. ULA had not yet estimated the total cost of development but CEO Tory Bruno said that "new rockets typically cost $2 billion, including $1 billion for the main engine". In March 2018, Bruno said the Vulcan-Centaur had been "75% privately funded" up to that point. In October 2018, following a request for proposals and technical evaluation, ULA was awarded $967 million to develop a prototype Vulcan launch system as part of the National Security Space Launch program.
In August 2019, the parts of Vulcan's mobile launcher platform (MLP) were transported to the Spaceflight Processing Operations Center (SPOC) near SLC-40 and SLC-41, Cape Canaveral, Florida. The MLP was fabricated in eight sections and moves at on rail bogies, standing tall. In February 2021, ULA shipped the first completed Vulcan core booster to Florida for pathfinder tests ahead of the Vulcan's debut launch. Testing continued proceeded with the pathfinder booster throughout that year.
In August 2019, ULA said Vulcan Centaur would first fly in early 2021, carrying Astrobotic Technology's Peregrine lander. By December 2020, the launch had been delayed to 2022 because of technical problems with the BE-4 main engine. In June 2021, Astrobotic said Peregrine would not be ready on time due to the COVID-19 pandemic, delaying the mission and Vulcan Centaur's first launch; further Peregrine delays put the launch of Vulcan into 2023. In March 2023, a Centaur V test stage failed during a test sequence. To fix the problem, ULA changed the structure of the stage and built a new Centaur for Vulcan Centaur's maiden flight. In October 2023, ULA announced they aimed to launch Vulcan Centaur by year's end.
A failure in the Peregrine's propulsion system shortly after separation prevented it from landing on the Moon; Astrobotic said the Vulcan Centaur rocket performed without problems.
On August 14, 2019, ULA won a commercial competition when it was announced the second Vulcan certification flight would be named SNC Demo-1, the first of seven Dream Chaser CRS-2 flights under NASA's Commercial Resupply Services program. They will use the four-SRB VC4 configuration. The SNC Demo-1 was scheduled for launch no earlier than April 2024.
After Vulcan Centaur's second certification mission, the rocket will be qualified for use on U.S. military missions. , Vulcan was to launch ULA's awarded 60% share of National Security Space Launch payloads from 2022 to 2027, but delays occurred. The Space Force's USSF-51 launch in late 2022 was the first national security classified mission, but in May 2021 the spacecraft was reassigned to an Atlas V to "mitigate schedule risk associated with Vulcan Centaur non-recurring design validation". For similar reasons, the Kuiper Systems prototype flight was moved to an Atlas V rocket.
After Vulcan's first launch in January 2024, developmental delays with the Dream Chaser led ULA to contemplate replacing it with a mass simulator so Vulcan could move ahead with the certification required by its Air Force contract. Bloomberg News reported in May 2024 that United Launch Alliance was accruing financial penalties due to delays in the military launch contracts. On May 10, Air Force Assistant Secretary Frank Calvelli wrote to Boeing and Lockheed executives. "I am growing concerned with ULA's ability to scale manufacturing of its Vulcan rocket and scale its launch cadence to meet our needs", Calvelli wrote in the letter, a copy of which was obtained by the Washington Post. "Currently there is military satellite capability sitting on the ground due to Vulcan delays." In June 2024, Bruno announced that Vulcan would make its second flight in September with a mass simulator with some "experiments and demonstrations" to help develop future technology for the Centaur upper stage.
Vulcan Centaur lifted off on the second of two flights needed to certify the rocket for future NSSL missions at 11:25 UTC on October 4, 2024. Approximately 37 seconds into the launch, the nozzle on one of the solid rocket boosters (SRB) fell off resulting in a shower of debris in the exhaust plume. Although the SRB continued to function for its full 90-second burn, the anomaly led to reduced, asymmetrical thrust. This caused the rocket to slightly tilt before the guidance system and main engines successfully corrected and extended their burn by roughly 20 seconds to compensate. Despite the anomaly, the rocket achieved an acceptable orbital insertion.
The nozzle anomaly added to the already extensive process required to certify the Vulcan for NSSL missions. Following a five-month review, the Space Force certified the Vulcan on March 26, 2025.
Despite achieving certification, military officials have expressed sharp dissatisfaction with Vulcan's performance during its protracted development. In written testimony to the House Armed Services Committee in May 2025, Major General Stephen G. Purdy, said that the program had performed "unsatisfactorily" in the previous year. He noted that the slow transition from the retired Atlas and Delta vehicles to Vulcan had delayed four national security launches, hindering the completion of Space Force objectives. Purdy said that, moving forward, United Launch Alliance must "repair trust" and demonstrate greater accountability.
Starting in late 2025, ULA plans to upgrade the Centaur upper stage with the RL10E engine which will have a fixed nozzle extension and offer slightly increased thrust and specific impulse, offering minor improvements to payload capacities.
These capabilities reflect NSSL requirements, plus room for growth.
A Vulcan Centaur with six solid rocket boosters can put into low Earth orbit, nearly as much as the three-core Delta IV Heavy.
Since 2015, ULA has spoken of several technologies that would improve the Vulcan launch vehicle's capabilities. These include first-stage improvements to make the most expensive components potentially reusable and second-stage improvements to allow the rocket to operate for months in Earth-orbit cislunar space.
However, ULA said in 2021 that it is working to add more value to upper stages by having them perform tasks such as operating as space tugs. CEO Tory Bruno says ULA is working on upper stages with hundreds of times the endurance of those currently in use.
On August 28, 2025, in an infographic by ULA posted by Tory Bruno, a variant of Centaur V was referred as "ACES", this time standing for "Advanced Centaur Endurance Stage". Few details were provided about this updated ACES concept, other than a mention of "Smart Propulsion", which was not further explained
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