Green Run

Green Run refers to a series of critical integrated system tests conducted on rocket engines, particularly large and complex engines like those used in NASA's Space Launch System (SLS). The purpose of a Green Run test is to fire the engine or the complete engine stage for an extended duration, simulating a flight-like scenario, to verify its design, performance, and operational capabilities before its first actual launch.

The term "Green Run" implies that the testing is being done on a newly assembled or significantly modified piece of hardware, effectively its "first run." These tests are essential for identifying any potential issues, validating engineering models, and ensuring the engine or stage is safe and ready for its intended mission. The tests involve a comprehensive assessment of all systems, including propulsion, avionics, hydraulics, and structures, under extreme conditions. Success in a Green Run test is a major milestone in the development and certification process for rocket engines and launch vehicles.