Imagine! The ground rumbling, your heart pounding with excitement and then you see a wondrous sight, a bright orange rocket rising into the sky. Thanks to the hard work by the NASA, Boeing and Aerojet Rocketdyne teams, we are one step closer to seeing that vision become a reality.

On Nov. 6, 2019 the last of four RS-25 engines were successfully integrated with the first Space Launch System (SLS) rocket at NASA’s Michoud Assembly Facility (MAF). These engines will help send the first Artemis lunar mission to space.

RS-25 core stage integration

Connecting the engines to the core stage was not a simple task. As Bill Muddle, RS-25 field integration engineer, explained, “The back of the SLS rocket is huge, and then you look at the access space you have available to actually install the engines and you realize you can take nothing for granted. You can apply a lot of lessons from the Space Shuttle program, but that is just a baseline; you’ve got to adapt to the unique aspects of SLS.”

During the Space Shuttle program, technicians had access to 360 degrees around the Space Shuttle Main Engines, which have been upgraded and renamed the RS-25 engines. But with SLS, you only have half of that amount, making it a choreographed dance of five technicians working in concert to install each engine and properly align them to ensure that when the vehicle gimbals all four engines, they don’t touch.

“It is easy to forget the sheer size of four engines clustered together,” said Muddle. “I’m fortunate to have seen the last engine leave Kennedy Space Center for upgrades at Aerojet Rocketdyne’s facility located at NASA’s Stennis Space Center, and now I’ve seen the first flight engines for SLS arrive and be installed at the Michoud Assembly Facility. I have a lot of pride in seeing the marriage of these two amazing programs,” added Muddle.

The RS-25 engines for the first flight of SLS have been upgraded since the shuttle to ensure that they can operate in the unique environment of this rocket. For example, all of the engines received new controllers, ensuring that each engine is able to relay real-time performance data to the rocket and is able to regulate thrust and propellant mixtures while the vehicle is making its eight and one-half minute climb into space. The engines have to operate at higher power levels for the SLS compared to the shuttle, and the new rocket delivers propellant to the engines at different pressures and temperatures. Additionally, insulation was added to each engine nozzle to protect and prevent them from overheating during launch. These and dozens of other changes had to be assessed analytically and then verified safe by full-scale engine hot-fire tests.

Now that the SLS team has installed all four engines onto the core stage, they can turn their attention to final integration testing of the vehicle to make sure that the engineers can obtain a good signal from the ground operators to the vehicle and from the vehicle to the engine controllers. Once that is complete, the team will start preparing the first SLS core stage for Green Run testing at NASA’s Stennis Space Center in Mississippi. All four engines will fire during this test.

Once Green Run testing is complete, the core stage will be shipped to Kennedy Space Center in Florida, where it will be joined with the Interim Cryogenic Propulsion Stage, the stage that provides the power to send the Orion spacecraft to the Moon. Here, the entire rocket will be assembled and prepared for launch. Then you will no longer have to imagine the ground rumbling, heart-pounding excitement of a rocket launch – the bright orange rocket will actually be rising into the sky to open a new chapter in the story of human exploration.