NROL launches OSIRIS-REx Solar Dynamics Observatory Solar Orbiter Space Test Program USA-212 Replacement with Vulcan In 2014, geopolitical and U.S. political considerations because of the Russian war with Crimea led to an effort to replace the Russian-supplied RD-180 engine used on the first-stage booster of the Atlas V. Formal study contracts were issued in June 2014 to a number of U.S. rocket-engine suppliers. The results of those studies led to a decision by ULA to develop the new Vulcan Centaur launch vehicle to replace the existing Atlas V and Delta IV. In September 2014, ULA announced a partnership with Blue Origin to develop the BE-4 LOX/methane engine to replace the RD-180 on a new first-stage booster. As the Atlas V core is designed around RP-1 fuel and cannot be retrofitted to use a methane-fueled engine, a new first stage is being developed. This booster will have the same first-stage tankage diameter as the Delta IV and will be powered by two thrust BE-4 engines. The engine was already in its third year of development by Blue Origin, and ULA expected the new stage and engine to start flying no earlier than 2019. Vulcan was initially planned to use the same Centaur upper stage as on Atlas V, and later to upgrade to ACES, however ACES is no longer being pursued, and Centaur V will be used instead. It will also use a variable number of optional solid rocket boosters, called the GEM 63XL, derived from the new solid boosters planned for Atlas V. As of 2017, the Aerojet AR1 rocket engine was under development as a backup plan for Vulcan. , the first Vulcan flight is planned for early 2023. Retirement In August 2021, ULA announced that they are no longer selling launches on the Atlas V and they would fulfill their 29 existing launch contracts. They made a final purchase of the RD-180 motors they needed and the last of those motors were delivered in April 2021. The last launch will occur "some time in the mid-2020s". , 20 launches remain. Photo gallery See also Comparable rockets: Angara Ariane 5 Delta IV Falcon 9 Falcon Heavy GSLV Mk III H-IIA H-IIB Long March 5 Proton Vulcan Centaur Zenit Medium-lift launch vehicle Comparison of orbital launchers families Comparison of orbital launch systems Notes References External links ULA Atlas V data sheets Atlas 500 series cutaway Atlas 400 series cutaway ULA