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

The RS-25 is the staged-combustion engine that powers the SLS core stage. Each unit must demonstrate its thermal and structural behaviour on the stand before being accepted for flight, and the test duration deliberately replicates the operating window the engine will experience from liftoff to core-stage separation. The 111% power level corresponds to the liftoff regime, above the nominal design cruise level, subjecting the combustion chamber and turbopump to the most demanding conditions of the mission.

Acceptance testing at Stennis is the final quality-control barrier before an engine is mated to the rocket. Serial number 10001 belongs to the new batch of RS-25 engines built specifically for flights after Artemis I, with manufacturing changes intended to reduce cost and production time compared with units reused from the shuttle programme. NASA has not yet announced which specific Artemis mission this unit has been assigned to.

The SLS programme continues to accumulate stand hours as the agency prepares the Artemis II and Artemis III missions, intended to carry astronauts back to lunar orbit and to the lunar surface. Each long-duration test provides data on component lifetime and on the repeatability of performance between units, two of the factors that will determine the rocket's launch rate in the coming years.