Teams at NASA's Stennis Space Center near Bay St. Louis, Mississippi, test-fired RS-25 engine No. 10001 on Oct. 21, 2026, NASA reported. The hot fire lasted almost eight-and-a-half minutes (500 seconds), matching the burn time of RS-25 engines during a launch of the agency's Space Launch System rocket, and reached a 111% power level.

According to NASA, four RS-25 engines produce up to 2 million pounds of combined thrust to help launch the SLS rocket on each Artemis mission. All RS-25 engines are proven flightworthy at Stennis before use. The tested engine is a developmental unit that will not be used in flight, but the agency said the run gave NASA and its prime engine contractor, L3Harris Technologies, the ability to capture critical data to improve engine performance and reliability.

The image accompanying the announcement was credited to NASA/Danny Nowlin.