The Space Launch System (SLS) rocket’s core stage for the Artermis I lunar mission has successfully completed its first four Green Run tests.
Green Run is a demanding series of eight tests and early 30 firsts: first loading of the propellant tanks, first flow through the propellant feed systems, first firing of all four engines and first exposure of the stage to the vibrations and temperatures of launch.
On 5th August, NASA engineers completed the fourth of eight planned tests of the 212-foot-tall core stage.
For Test 4, engineers performed the initial functional checkout of the main propulsion system components to verify command and control operability (valve response, timing, etc.) and performed leak checks on the core stage-to-facility umbilical fluid and gas connections.
Engineers were able to conduct the test with gaseous nitrogen and helium, which is more efficient than using liquid hydrogen and oxygen propellants, which are only needed for the actual hot-fire test.
As these gases flowed through systems, special instrumentation monitored for any leaks or poor connections.
“With test gases flowing through this many parts of a complex rocket stage, we expected the test team to encounter some issues,” said Jonathan Looser, who manages the SLS core stage main propulsion system.
“Historically, there’s never been a NASA human-rated launch vehicle flown without one or more full-up tests before flight, and they have all encountered first-time issues.”
“As expected, we found a few with valves and seals and addressed them, and now we’re ready to complete the next four Green Run tests.”
Next up for the Green Run team is Test 5, which will ensure the stage thrust vector control system works correctly, which includes huge components that steer the four RS-25 engines, called actuators, and provides hydraulics to the engine valves.
Test 6 simulates the launch countdown to validate the countdown timeline and sequence of events.
This includes the step-by-step fueling procedures in addition to the previous test steps of powering on the avionics and simulated propellant loading and pressurization.
As one final checkout before the full firing test, Test 7 is called the ‘wet dress rehearsal’, meaning it builds on the simulations in Test 6 and includes fuelling the rocket.
After once again powering on the avionics, hydraulic systems, fail-safe systems and other related systems that have been checked out in the prior six tests, the team will load, control, and drain more than 700,000 gallons of cryogenic propellants.
Only after passing these seven tests will it be time for Test 8, a full countdown and hot fire test for up to eight minutes.
During the test, all four RS-25 engines will be firing at a full, combined 1.6 million pounds of thrust just as they will on the launch pad.
Test 8 will be the final checkout to verify the stage is ready for launch. Afterward, engineers will prepare the stage for its trip to Kennedy Space Center in Florida.