First Four Space Launch System Flight Engines Ready To Rumble

The flight preparations for the four engines that will power NASA’s Space Launch System (SLS) on its first integrated flight with Orion are complete and the engines are assembled and ready to be joined to the deep space rocket’s core stage. All five structures that form the massive core stage for the rocket have been built including the engine section where the RS-25 engines will be attached.

“NASA’s priority is to deliver hardware for the first flight of the Space Launch System and Orion spacecraft,” said John Honeycutt, SLS program manager at NASA’s Marshall Space Flight Center in Huntsville, Alabama. “This year, the SLS team has constructed major parts of the rocket, such as the in-space stage, which is already at NASA’s Kennedy Space Center in Florida, the four RS-25 engines, core stage structures, and solid rocket booster segments.”

The SLS has the largest core stage ever built and includes four RS-25 engines, which previously powered NASA’s space shuttle. The RS-25 engines that are being tested and prepared for SLS were proven during the years they were responsible for propelling 135 shuttle missions, and have been upgraded for the first SLS flight. The four that will fly on Exploration Mission-1 supported a total of 21 shuttle missions.

In total, NASA has 16 flight-proven RS-25 engines and two development engines that are being used as “workhorse” engines for testing. These engines have been used to test new controllers – the brains of the engine – which have now been installed on the flight engines. The flight engines will be attached to the core stage to prepare for green run testing – the final test for the four flight engines and the core stage that will occur before the first mission.

“NASA has transformed these phenomenal engines that served so well in the past for a new bold mission — the first integrated launch of SLS and Orion,” said Steve Wofford, the SLS liquid engines manager at Marshall. “For engines needed beyond the first four flights, we are working with our industry partner Aerojet Rockedyne to streamline manufacturing and make future engines more affordable.”

In addition, NASA is investing in new RS-25 engines for future launches built with modern manufacturing techniques. Aerojet Rocketdyne has restarted RS-25 production and the agency has ordered six new RS-25 engines built to be expendable and more affordable to produce for future deep space exploration missions.

The welding completion on the liquid hydrogen tank for SLS marked the last of five parts to be built for the rocket’s core stage. When it is assembled, the core stage will stand taller than a 20-story building and hold more than 700,000 gallons of propellant. The core stage is made up of the liquid hydrogen and liquid oxygen tanks; the engine section where the RS-25 engines will be housed; and the intertank and the forward skirt.

“To make these massive propellant tanks, NASA and our industry partner Boeing have used the largest robotic rocket welding tool to build the thickest pieces ever welded with self-reacting friction stir welding,” said Steve Doering, SLS stages manager at Marshall. “Now, we are moving from manufacturing major structures for the core stage to outfitting them to do their jobs and make the rocket fly.”

The liquid oxygen flight tank recently completed the first hydrostatic test for an SLS tank. The weld strength was tested by filling the tank with 200,000 gallons of water and subjecting it to pressures and forces similar to those it will experience during flight. The liquid hydrogen tank will soon undergo proof testing using gaseous nitrogen. The core stage pathfinder recently arrived at Michoud, and it will be used to help develop and verify handling and transportation procedures before these processes are used on the valuable flight hardware.

“This rocket is happening now,” said Honeycutt. “The Space Launch System team has made great progress and has an exciting year ahead as NASA conducts crucial structural tests at Marshall, assembles the core stage and the four RS-25 engines at Michoud and delivers more hardware to the launch pad at Kennedy.”