Operators fire the RS-25 engine at NASA’s Stennis Space Center on Nov. 15, 2023, up to the 113% power level. The first four Artemis missions are using modified space shuttle main engines that can power up to 109% of their rated level. New RS-25 engines will power up to the 111% level to provide additional thrust, so testing up to the 113% power level provides a margin of operational safety.