On 18 March, NASA successfully tested the biggest segment of its Space Launch System (SLS). It will be the primary vehicle of Artemis, the space agency’s programme to return to the Moon during this decade. The test, known as “hot fire”, took place at Stennis Space Center near Bay St. Louis, Mississippi, and provided the necessary data for the team to evaluate in preparation for flight.
The SLS’s core stage — the largest rocket element NASA has ever built — fired its four RS-25 engines for eight minutes and 19 seconds, generating 1.6 million pounds of thrust. A crucial landmark in the Artemis programme’s realisation and, more specifically, ahead of the Artemis I mission: NASA’s goal is to send an uncrewed Orion spacecraft on a test flight around the Moon and back to Earth later this year.
Success arrived two months after NASA had to cut short, on 16 January, the first attempted hot fire (about one minute into the test). Last week’s second attempt saw the engines firing through 499.6 seconds with no early shutdowns, enduring three different power levels and movements that simulate flight steering.
“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 acting NASA Administrator Steve 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.”
733,000 gallons (around three million litres) of propellant filled the tanks in the core stage: super-cold liquid hydrogen and oxygen combined to fuel the four RS-25 engines, generating super-hot water vapour from the exhaust.
It was the culmination of a series of tests called Green Run, which allowed engineers to check for and identify any issues by activating the stage’s components one by one over several months. The eight tests succeeded through a collaborative effort between the SLS programme, the Stennis test team, core stage manufacturer Boeing, and engine manufacturer Aerojet Rocketdyne.
“Green Run is the step-by-step testing and analysis of the new SLS rocket core stage that will send astronauts to the Moon,” said Richard Sheppard, NASA’s SLS Stages Green Run Test Lead. “This testing will reduce risks for, not only the first flight, but also for the Artemis mission that will land astronauts on the Moon in 2024.”
The test presented some historical features. RS-25s are also known as the Space Shuttle main engines: the four tested last week — although refurbished now — flew on different Shuttle’s missions, contributing to the vehicle’s 30 years of activity. Moreover, the giant structure (B-2 Test Stand) holding everything in place during the hot fire was the same NASA used in the 1960s to test the massive Saturn V’s engines: the Apollo programme’s iconic rocket that launched the first humans to the Moon.
After last week’s successful test, the SLS’s core stage will be refurbished and sent to NASA’s Kennedy Space Center, in Florida. There, engineers will assemble it with the rest of the rocket, two solid boosters, and the Orion spacecraft, in preparation for Artemis I.
We’re finally approaching the return of crewed missions to the Moon since 1972’s Apollo 17. The Artemis programme will allow us to look back at our home, back at humankind as a whole once again. It will be an incredibly inspiring moment: another chance to come together and improve as a global community through more concrete actions.