The US National Aeronautics and Space Administration (Nasa) has successfully conducted a second ‘hot fire’ test of the core stage of its new Space Launch System (SLS) rocket. The SLS core stage, the prime contractor for which is Boeing, is powered by four Aerojet Rocketdyne RS-25 rocket engines.

“The SLS is the most powerful rocket Nasa has ever built, and during [this second] test the core stage of the rocket generated more than 1.6-million pounds (7 117 kN) of thrust within seven seconds,” highlighted Nasa acting administrator Steve Jurczyk. “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. [This] 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 first hot fire test had taken place on January 16, but had lasted only one minute. Nasa and industry engineers carefully studied all the data from the test, which resulted in the agency determining that a second such test could be executed with minimal risk to the core stage, which, with attached (and already tested) rocket boosters, will launch the uncrewed Artemis I mission.

The second hot fire lasted for eight minutes and 19 seconds, which is the time the core stage will be run during a Moon mission launch. During the test, the engines were powered up to 109% thrust, and throttled up and down, and moved in predetermined patterns to direct their thrust, all these actions replicating what will happen during an actual launch. Every minute during the test, almost 1.25-million litres of water were directed on to the test stand’s flame deflector.

“The longer hot fire test provided the wealth of data we needed to ensure the SLS core stage can power every SLS rocket successfully,” reported Nasa Marshall Space Flight Centre SLS programme manager John 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 the Nasa Artemis programme.”

The hot fires were the last and culminating tests in a series known to Nasa as a Green Run. Conducted in the B-2 test stand at Nasa’s Stennis Space Centre, the SLS core stage Green Run was divided into eight phases. The phases before the first hot fire were concerned with testing the core stage’s avionics, hydraulic and propulsion systems and their integrated functionality and performance.

The SLS core stage has two propellant tanks and, together, when full, they hold nearly 2.8-million litres of extremely cold liquid hydrogen and liquid oxygen, which, in combination, fuel the RS-25 engines. Filling these propellant tanks required 114 tanker trucks and six dedicated propellant barges.

“This final test in the Green Run series represents a major milestone for this nation’s return to the Moon and eventual mission to Mars,” affirmed Nasa Stennis Space Centre director Richard Gilbrech. “So many people across the agency and the nation contributed to this SLS core stage, but special recognition is due to the blended team of test operators, engineers, and support personnel for an exemplary effort in conducting the test [last week].”

With the conclusion of the Green Run test series, the SLS core stage will now be refurbished. It will then be transported to the Nasa Kennedy Space Centre and there reassembled on the mobile launcher platform inside the Vehicle Assembly Building, between the already assembled solid rocket boosters. The Orion spacecraft will then be placed on top, followed, in due course, by the launch of the complete assembly as the Artemis I mission. The SLS is the only rocket capable of sending an Orion spacecraft, with astronauts and supplies, to the Moon in a single mission.