All RS-25 engines flew numerous times in space during the shuttle era, which ranged from 1981 to 2011. NASA and Aerojet Rocketdyne modified 16 engines that are remaining from that program and have already completed tests for the first four Artemis missions to prove they are fit for flight. Artemis 1 flew uncrewed in 2022, Artemis 2's astronauts should be announced this spring for a moon-circling mission in 2024, and Artemis 3 is bound for the surface no earlier than 2025