United Launch Alliance — the one that replaced the Russian engine

United Launch Alliance was formed in December 2006 as a 50/50 joint venture between Boeing and Lockheed Martin. The consolidation merged the Atlas V (Lockheed) and Delta IV (Boeing) programmes into a single company and, from that date until 2015, held effective monopoly on United States national-security space launch.

Atlas V, introduced in 2002, has flown over 100 consecutive successful missions. Delta IV Heavy, introduced in 2004, served as the highest-capacity operational US launcher until its retirement in April 2024. In its 18-year history ULA has completed more than 155 orbital launches with a mission-success rate reported at approximately 100 percent.

Every Atlas V first stage from 2002 to 2024 was powered by the RD-180, an oxidiser-rich staged-combustion engine manufactured in Russia by NPO Energomash. In the 2015 National Defense Authorization Act, Congress mandated the phase-out of Russian-made engines for national-security launches.

ULA responded by contracting Blue Origin to develop a US-made alternative: the BE-4, an oxygen-rich staged-combustion engine burning liquid oxygen and liquid methane. Flight-ready BE-4s were delivered to ULA in late 2022. Two BE-4 engines power the Vulcan Centaur first stage.

The first Vulcan Centaur (Certification-1) launched on 8 January 2024 from Cape Canaveral Launch Complex 41, carrying Astrobotic's Peregrine lunar lander on a trans-lunar injection trajectory.

The second flight (Certification-2) launched on 4 October 2024 with a mass simulator. Approximately 37 seconds after launch, the nozzle of one of the two GEM-63XL solid rocket boosters detached. The vehicle compensated for the resulting asymmetric thrust and delivered its payload to the target orbit. Investigation attributed the event to an insulator manufacturing defect.

The Space Force certified Vulcan for National Security Space Launch missions in March 2025. The first NSSL flight, USSF-106, launched on 13 August 2025 carrying the experimental NTS-3 navigation satellite.

On 12 February 2026, Vulcan Centaur launched the USSF-87 mission from SLC-41, carrying the GSSAP 7 and 8 Geosynchronous Space Situational Awareness satellites. During ascent, a second GEM-63XL solid rocket booster nozzle event occurred, comparable to the one observed on Certification-2 in October 2024. The vehicle again corrected in flight and delivered the payloads to their target orbit.

The Space Force temporarily paused National Security Space Launch missions on Vulcan pending investigation of the recurring SRB nozzle behaviour and evaluation of alternative launchers to mitigate schedule risk. As of the time of writing, that pause remains in effect.