Design Engineering

NASA begins constructing the world’s largest rocket


General Aerospace NASA rocket

The SLS rocket was designed to support missions to the moon starting in 2018 and other deep space destinations.

NASA is currently in the process of building the world’s most powerful rocket, piece-by-piece. The space agency is joining together large elements of the rocket’s 212-foot-tall core stage, the backbone of the SLS rocket at the Michoud Assembly facility in New Orleans.


Engineers just completed welding the liquid hydrogen tank that will provide fuel for the first SLS flight in 2018. Photo coutresy of NASA/Michoud/Steven Seipel

The SLS rocket was designed to support missions to the moon starting in 2018 as well as house large hardware like landers, habitats and supplies needed to travel extensive distances to explore places like Mars and other deep space destinations.

The Mars rocket is powered by a core stage that carries 2.3 million lbs of liquid hydrogen and liquid oxygen to fuel the four RS-25 engines. Engineers have recently finished welding the largest part of the core stage, the 130-foot-tall liquid hydrogen tank that will provide fuel for the first flight.

“Building the core stage is similar to building a house,” said Joan Funk, SLS core stage lead at NASA’s Marshall Space Flight Center in Huntsville, Alabama. After all the foundation elements are in place, engineers will clean and prime each element before beginning the internal integration.


Michoud’s Vertical Assembly Center is welding many of the core stage’s main elements including the forward skirt, the liquid oxygen tank, the liquid hydrogen tank and the engine section. The core stage’s fifth element, the intertank, which is bolted, is also being built at Michoud. Boeing is building the core stage, but to build the stage, the aerospace giant has worked with 442 businesses across America, including 297 small businesses.

After construction, each element within the rocket will undergo extensive testing. Wet structures — elements that hold fuel, or the liquid oxygen and liquid hydrogen tanks — are put through “proof tests” to assure manufacturing quality. The liquid oxygen tank is hydrostatically tested and filled with water; and the liquid hydrogen tank is pneumatically tested.

Once tested, all the structural elements are constructed to enable engineers to assemble the “brains” rocket. In the SLS’s core stage, 45 miles of wire cabling carry power and data from element to element powering flight computers, cameras, sensors, avionics and other electronics housed in the dry structures.

The core stage’s plumbing contains lines that deliver the propellant and oxidizer from the tanks to the engines. Each dry structure also contains purge vent lines and hazardous gas lines designed to eliminate dangerous gases building up in the dry structures prior to launch. Racks, cameras, sensors, vent lines, wire cabling, valves, shelves, couplings, and more fill the core stage’s dry structures to near capacity. After this is complete, the dry structures are ready to be joined to other elements.

NASA SLS rocket

The liquid oxygen tank is the second tank that makes up the core stage, which towers more than 200 feet tall with a diameter of 27.6 feet. Photo coutresy of NASA/Michoud/Steven Seipel

Before this happens, though, insulation is applied. NASA’s thermal protection system give the rocket its signature orange color, but more importantly, it protects the core stage from the extreme temperatures encountered during launch and maintains the fuels’ extremely low temperatures. The liquid hydrogen is chilled to minus 423 degrees Fahrenheit and the liquid oxygen is chilled to minus 297 degrees.

Each section is then stacked vertically, with elements bolted to one another using segmented support rings welded to each element, providing stiffness. The liquid hydrogen tank sits atop the engine section to create the aft section, and the forward skirt and intertank are bolted to the top and bottom of the liquid oxygen tank to create the forward section.

Engineers are responsible for moving the elements into a horizontal position for final assembly. Final wiring, plumbing and insulation are installed after the forward section is joined to the aft to complete the core stage assembly.

The core stage is set to travel to NASA’s Stennis Space Center near Bay St. Louis, Mississippi, where it will undergo testing called a “green run.” A green run, or the first time the engines are assembled into a single configuration with the core stage and fired at nearly full-power, tests the compatibility and functionality of the system to ensure a safe and viable design.

Once testing is complete, the core stage will head to NASA’s Kennedy Space Center in Florida, for its first flight with Orion.


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