Final SLS Green Run test goes the distance

The core stage for the first flight of NASA’s Space Launch System rocket is seen in the B-2 Test Stand during a second hot fire test at NASA’s Stennis Space Center near Bay St. Louis, Mississippi. The four RS-25 engines fired for the full duration of 8 minutes during the test and generated 1.6 million pounds of thrust. Credit: NASA/Robert Markowitz

NASA successfully completed the critical and long-awaited hot fire test of the core stage engines for the agency’s Space Launch System (SLS) human-rated mega Moon rocket Thursday afternoon, March 18, on a test stand in Mississippi. The rocket stage will now be shipped to the Kennedy Space Center, paving the path for the launch of the uncrewed Artemis-1 moon mission later this year or early next year followed by future Artemis missions with astronauts to orbit and land on the surface.

During the engine test dubbed the ‘Green Run’ the SLS core stage fired its four RS-25 engines for the full duration test period planned for a whopping 8 minutes and 19 seconds, nearly 500 seconds, and generated 1.6 million pounds of thrust with a huge billowing cloud of steam and smoke upon ignition Thursday at  4:37 p.m. EDT (3:37 p.m. CDT; 2037 GMT)  at NASA’s Stennis Space Center B-2 test stand near Bay St. Louis, Mississippi and scored an “A+”, NASA officials said afterward.

“Everything we’ve seen in the test today looked nominal, so I would say that the core stage got an A-plus today,” said John Honeycutt, the SLS program manager at NASA’s Marshall Space Flight Center in Huntsville, Alabama, at the post-test media briefing.

The full-duration eight-minute-long Green Run test was finally completed on the second try following a premature shutdown after just over one minute on the first try earlier this year.

A successful completion to the long-awaited and absolutely critical Green Run hot fire test of all RS-25 four core stage engines simultaneously firing is essential for NASA to move forward with confidence with Project Artemis missions aimed at returning US astronauts to the moon and landing the first woman and next man as soon as late 2024.

Standing 212 feet tall (65-meter), the SLS core stage is the largest rocket element NASA has ever built. SLS will be the most powerful rocket the world has ever seen when it launches, producing up to 8.8 million pounds of liftoff thrust fueled by more than 700,000 gallons of cryogenic liquid oxygen and liquid hydrogen propellants

“What a great day, and a great test,” said NASA Acting Administrator Steve Jurczyk at the post-test media briefing. “This is a major milestone advancing our goals for Artemis.  I’m almost speechless at how well things went today.”

Engineers designed the eight-part Green Run test campaign to gradually bring the SLS core stage to life for the first time, culminating with the hot fire. The team will use data from the tests to validate the core stage design for flight.

“The SLS is the most powerful rocket NASA has ever built, and during today’s test, the core stage of the rocket generated more than 1.6 million pounds of thrust within seven seconds. The SLS is an incredible feat of engineering and the only rocket capable of powering America’s next-generation missions that will place the first woman and the next man on the Moon,” said Jurczyk.

“Today’s successful hot fire test of the core stage for the SLS is an important milestone in NASA’s goal to return humans to the lunar surface – and beyond.”

The Green Run test was carried live on NASA TV. Jump ahead to the 51-minute mark in the video to watch the full duration firing of the core stage’s four engines.

The four RS-25 core stage engines were built and provided by Aerojet-Rocketdyne and are recycled and upgraded Space Shuttle main engines.

The March 18 hot fire test was conducted because the first test on Jan. 16 in the B-2 test stand at NASA’s Stennis Space Center only lasted about 67 seconds vs. the planned full duration test run of about 8 minutes or approximately 485 seconds – the time it takes to achieve orbit.

NASA and prime contractor Boeing officials determined that the premature engine shutdown was “triggered by test parameters that were intentionally conservative to ensure the safety of the core stage during the test” involving a hydraulic system parameter.

Standing 212 feet tall, the SLS core stage is the largest rocket element NASA has ever built and SLS is the most powerful rocket the world had ever seen when it fires producing up to 8.8 million pounds of liftoff thrust fuel by over 700,000 gallons of cryogenic propellants liquid oxygen and liquid hydrogen.

The Green Run test series involves eight major tests and is a comprehensive assessment of the rocket’s core stage prior to launching Artemis missions.

This infographic explains the objectives of the Space Launch System rocket’s core stage Green Run test series. Credit: NASA

The NASA/Boeing/Aerojet Rocketdyne team opted to conduct the second hot fire test with a full duration of 8 minutes vs. just the 1 minute obtained in the first test in order to collect important data.

The longer duration hot fire tested a variety of operational conditions, including moving the four engines in specific patterns to direct thrust and powering the engines up to 109% power, throttling down and back up, as they will during flight, said officials.

Prior to and after the first test NASA and Boeing officials said they needed the test to run a minimum of about 250 seconds to obtain sufficient data to proceed ahead with the Artemis 1 mission.

Inspections of the core stage after the Jan 16 hot fire test revealed it to be “in excellent condition” with no significant repairs required

“This longer hot fire test provided the wealth of data we needed to ensure the SLS core stage can power every SLS rocket successfully,” said Honeycutt. “During this test, the team conducted new operations with the core stage for the first time, repeated some critical operations, and recorded test data that will help us verify the core stage is ready for the first and future SLS flights for NASA’s Artemis program.”

The next steps are for the core stage to be refurbished, then shipped to NASA’s Kennedy Space Center in Florida. There it will be assembled with the solid rocket boosters already stacked on the mobile launcher platform inside the Vehicle Assembly Building at Kennedy in preparation for Artemis I.

It should be ready for shipping on the Pegasus barge by mid to late April.

Meanwhile, teams at KSC have completed stacking of the pair of solid rocket boosters for Artemis 1 as well as finished assembly of the Orion crew vehicle.

In High Bay 3 of the Vehicle Assembly Building at NASA’s Kennedy Space Center in Florida, stacking of the pair of solid rocket booster on the mobile launcher for SLS has been completed. When the core stage arrives, it will join the boosters on the mobile launcher, followed by the interim cryogenic propulsion stage and Orion spacecraft. Credit: NASA/Isaac Watson
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