Four veteran Space Shuttle Main Engines will benchmark the performance of the rookie Space Launch System (SLS) Core Stage in the final two critical tests of NASA’s Green Run campaign. After loading the stage with propellant for the first time and demonstrating in a countdown that it can satisfy engine start criteria, the final test will be a full-duration firing of the Core Stage that is tentatively scheduled for late-October.

Last fired nearly a decade ago, the four Aerojet Rocketdyne RS-25 flight engines in the stage are going through some of their final pre-firing checkouts in the new SLS environment. After another brush with tropical weather, Green Run testing resumed this week with the fifth of eight Green Run test cases, where Core Stage hydraulic systems will be used with previously tested avionics and propulsion systems to verify they are ready to support the stage’s first fueling and firing.