When NASA’s Space Launch System (SLS) is fully integrated, assembled, and completed with testing, it will be the most powerful rocket since Saturn V to bring the Apollo astronauts to the moon. To get there, NASA ran a test campaign known as the Green Run. This 8-stage assessment results in a test fire of all four RS-25 engines in the Core (also known as the “hot fire” test). .
On January 16, NASA made its first attempt at a Green Run Hot Fire test at the Stennis Space Center’s B-2 test stand in Mississippi, which lasted only about a minute. Another attempt was made on Thursday, March 18, with all four engines firing for 8 minutes and 19 seconds. This successful fire test is a crucial milestone for the SLS and brings it one step closer to sending astronauts back to the moon.
On the first attempt, the ground controllers in the Stennis Space Center were able to fire all four RS-25 engines together for the first time. The test ended in 67.2 seconds when the automated safety systems were triggered and the engines shut off. This was the result of an intentionally conservative test parameter to ensure the safety of the core level during the test.
After analyzing the test data, NASA determined that a second, longer hot fire test was required. On their second attempt, the engines managed to fire for 499 seconds, slightly longer than it would take to simulate a take-off (485 to 493 seconds). NASA TV reported again with a live broadcast (see above), which can also be found on the Artemis page in the NASA blogs.
As acting NASA administrator, Steve Jurczyk stated in a press release below:
“The SLS is the most powerful rocket NASA has ever built, and during today’s test, the rocket’s core stage generated more than 1.6 million pounds of thrust in seven seconds. An incredible feat of engineering, the SLS is the only rocket that can propel America’s next generation missions, putting the first woman and the next man on the moon. Today’s successful hot fire test of the core stage of the SLS is an important milestone in NASA’s goal of bringing people back to the surface of the moon – and beyond. “
In addition to validating the engines and the fuel system, various operating conditions were tested during the prolonged hot fire. Specifically, the ground teams set the engine nozzles in specific patterns at 30-second intervals to direct the direct thrust (known as a gimbal test). In the meantime, the crews throttled the engines to 109% power and then back up and down – something they were hoping for in January.
The eight-step Green Run process. Photo credit: NASA / Kevin O’Brien
John Honeycutt, manager for the SLS program at NASA’s Marshall Space Flight Center, stated:
“This lengthy hot-fire test provided the wealth of data we needed to ensure that the SLS core stage can successfully propel any SLS missile. During this test, the team performed new operations with the core phase for the first time, repeated some critical operations, and recorded test data that we can use to verify that the core phase is ready for the first and future SLS flights for NASA’s Artemis program is. “
This final stage of the Green Run campaign will also test the SLS Core Stage’s fuel system, which consists of two fuel tanks that hold more than 2.77 million liters. This consists of liquid hydrogen (LH2) and liquid oxygen (LOX) and is then fed to the engines via a long network of pipes and valves. All of the LH2 / LOX fuel has to be pumped in beforehand and creates an extreme pressure situation within the core stage.
The core stage also has a complex network of flight software and avionics systems that control the missile and enable it to collect flight data at the core stage and monitor its overall health. Along with the stage’s propulsion and hydraulic systems, these were the subject of previous Green Run tests where the avionic sensors were activated throughout the stage (Test 2) and all integrated systems were tested with a simulated start countdown (Test 6).
The core stage will be placed on the B-2 test bench in NASA’s Stennis Center. Photo credit: NASA / SSC
Richard Gilbrech, the director of NASA’s Stennis Center, said:
“Today is a great day for NASA, Stennis, and this nation’s human space exploration program. This final test in the Green Run series is an important milestone in this nation’s return to the moon and the eventual mission to Mars. So many people across the agency and across the country contributed to this core SLS phase, but special credit goes to the mixed team of test operators, engineers and support staff for running the test in an exemplary manner today. “
In order to refuel the core stage in time for the test, the Stennis teams deployed no fewer than 114 tank trucks and six drifters. During the fire test, the teams monitored the structural interfaces of both the core stage and the B-2 test bench. They also supplied the stand with operating power and more than 1.25 million liters of water per minute for the stand’s flame deflector.
After completing this final test, the core phase will now be refurbished and delivered to NASA’s Kennedy Space Center in Florida. This is where the core stage will be assembled with the other parts of the SLS, such as the solid fuel rocket boosters that were recently stacked at Kennedy. The Orion spacecraft will also be integrated and the entire system will be placed on the mobile launch vehicle in the vehicle assembly building in preparation for launch.
NASA Orion spacecraft. Photo credit: NASA
That mission, Artemis I (currently slated for November 2021), will see an unscrewed Orion spacecraft launch from Launch Complex 39-B at the Kennedy Space Center and fly around the moon before returning to Earth. Artemis II, scheduled for August 2023, will be the first crewed SLS and Orion, and four astronauts will perform a similar orbit.
If all goes well, Artemis III and the long-awaited return of mankind to the lunar surface in October 2024 will follow. Combined with the Moon Gate, Artemis Base Camp and other mission elements, SLS and Orion will not only usher in a new era of re-exploring the moon will also facilitate future missions to Mars and beyond.
Further reading: NASA
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