The four upgraded RS-25 space shuttle engines that will power NASA’s first Space Launch System rocket have come to life at the agency’s Stennis Space Center in Mississippi.

The Aerojet Rocketdyne engines, attached to the first Boeing-built SLS core stage, moved back and forth in response to tests of the thrust vector control (TVC) system’s ability to steer them. Engineers also fully verified the sequence of commands for ignition and engine cutoff.

The multiday test, completed September 13, was the fifth of eight major tests that make up a series called Green Run, which includes nearly 30 firsts: first loading of the propellant tanks, first flow through the propellant feed systems, first exposure of the stage to the vibrations and temperatures of launch; and ultimately, first firing of all four engines for up to eight minutes.

“For Test 5, we fully verified the integration between the RS-25 engines, the main propulsion system in the engine section, and the thrust vector control system,” said Boeing SLS Green Run Director Mark Nappi. “This was the most dynamic test performed to date, with the vehicle operating with full hydraulic pressure (3000 psi), main-propulsion engine pneumatic supply (4500 psi He) and physical movement of the RS-25s through their maximum allowable thrust vector angles.”

Each test builds on the prior test and is longer than the previous one, adding new hardware activations to those already completed. Green Run Test 6 will simulate the launch countdown to validate the timeline and sequence of events. This includes simulating the step-by-step fueling procedures in addition to the previous demonstrations of powering on the avionics and simulated propellant loading and pressurization.

As one final checkout before the full firing test, Test 7 is called “wet dress rehearsal.” The team will load, control, and drain more than 700,000 gallons (roughly 2.6 million liters) of cryogenic propellants.

Test 8, anticipated later this year, will be a full countdown and hot-fire for up to eight minutes. All four RS-25 engines will fire at a full, combined 1.6 million pounds (over 700,000 kilograms) of thrust, just as they will on the launch pad. Thrust increases as the rocket ascends and the atmosphere thins, ultimately reaching the “vacuum” level of more than 2 million pounds (roughly 900,000 kilograms) of thrust.

After that, Boeing engineers and technicians will refurbish the stage and prepare it to be delivered to Kennedy Space Center in Florida. There, it will be joined with waiting components – including the Orion human-rated spacecraft and the Boeing-United Launch Alliance Interim Cryogenic Upper Stage – ahead of launch on NASA’s uncrewed Artemis I launch in late 2021.

NASA’s Space Launch System will launch missions powered by four Aerojet Rocketdyne RS-25 engines, reliable engines used for more than 135 space shuttle missions. The engines have been upgraded with new controllers and other features for SLS.

NASA photo