NASA has finished welding together the very first fuel tank for America’s humongous Space Launch System (SLS) deep space rocket currently under development. RocketSTEM had an up close look at the liquid hydrogen (LH2) test tank shortly after its birth as well as the first flight tank, within hours of completion of the milestone assembly operation at NASA’s Michoud rocket manufacturing facility located in New Orleans.
“We have just finished welding the first liquid hydrogen qualification tank article … and are in the middle of production welding of the first liquid hydrogen flight hardware tank [for EM-1] in the big Vertical Assembly Center welder,” explained Patrick Whipps, NASA SLS Stages Element Manager during our tour of the massive factory.
“We are literally putting the SLS rocket hardware together here at last. All five elements to put the SLS stages together [at Michoud].”
This first fully welded SLS liquid hydrogen tank is known as a qualification test article. It was assembled using basically the same components and processing procedures as an actual flight tank, said Whipps.
“We just completed the liquid hydrogen qualification tank article and lifted it out of the welding machine and put it into some cradles. We will put it into a newly designed straddle carrier article next week to transport it around safely and reliably for further work.”
Welding of the liquid hydrogen flight tank is moving along well.
“We will be complete with all SLS core stage flight tank welding in the VAC by the end of September,” added Jackie Nesselroad, SLS Boeing manager at Michoud. “It’s coming up very quickly!”
“The welding of the forward dome to barrel 1 on the liquid hydrogen flight tank is complete. And we are doing phased array ultrasonic testing right now.”
SLS is the most powerful booster the world has even seen. Beginning in the 2020’s it will propel NASA astronauts within the agency’s Orion crew capsule on exciting missions of exploration to deep space destinations including potentially the Moon, asteroids and Mars – venturing further out than humans ever have before.
The LH2 qualification test article was welded together using the world’s largest welder – known as the Vertical Assembly Center, or VAC, at Michoud. The state-of-the-art welding giant stands 170 feet tall and 78 feet wide. It complements the world-class welding toolkit being used to assemble various pieces of the SLS core stage including the domes, rings and barrels that have been previously manufactured.
The fuel tank is a giant – measuring approximately 130-feet in length and 27.6 feet (8.4 m) in diameter.
The qual test article is the immediate precursor to the actual first LH2 flight tank now being welded.
Technicians assembled the LH2 tank by feeding the individual metallic components into NASA’s gigantic ‘Welding Wonder’ machine – as it’s affectionately known – at Michoud, thus creating a rigid 13 story tall structure.
The team was also already hard at work fabricating the first liquid hydrogen flight article tank in the VAC, right beside the qualification tank resting on the floor.
Welding of the other big fuel tank, the liquid oxygen (LOX) qualification and flight article tanks will follow quickly inside the impressive ‘Welding Wonder’ machine, Nesselroad explained.
The LH2 and LOX tanks sit on top of one another inside the SLS outer skin.
The SLS core stage – or first stage – is mostly comprised of the liquid hydrogen and liquid oxygen cryogenic fuel storage tanks which store the rocket propellants at super chilled temperatures. Boeing is the prime contractor for the SLS core stage.
To prove that the new welding machines would work as designed, NASA opted “for a three stage assembly philosophy.
Whipps stated that engineers first “welded confidence articles for each of the tank sections” to prove out the welding techniques “and establish a learning curve for the team and test out the software and new weld tools. We learned a lot from the weld confidence articles.”
“On the heels of that followed the qualification weld articles” for tank loads testing. “The qualification articles are as ‘flight-like’ as we can get them. With the expectation that there are still some tweaks coming.”
“And finally that leads into our flight hardware production welding and manufacturing the actual flight unit tanks for launches.”
“All the confidence articles and the LH2 qualification article are complete.”
What’s the next step for the LH2 tank?
The test article tank will be outfitted with special sensors and simulators attached to each end to record reams of important engineering data, thereby extending it to about 185 feet in length.
Thereafter it will loaded onto the Pegasus barge and shipped to NASA’s Marshall Space Flight Center in Huntsville, Alabama, for structural loads testing on one of the new test stands currently under construction. The tests are done to prove that the tanks can withstand the extreme stresses and safely carry astronauts to space.
“We are manufacturing the simulators for each of the SLS elements now for destructive tests – for shipment to Marshall. It will test all the stress modes, and finally to failure to see the process margins,” explained Whipps
The SLS core stage builds on heritage from NASA’s Space Shuttle Program and is based on the Shuttle’s External Tank (ET). All 135 ET flight units were built at Michoud during the 30 year Shuttle program by Lockheed Martin.
“We saved billions of dollars and years of development effort vs. starting from a clean sheet of paper design, by taking aspects of the Shuttle … and created an External Tank type generic structure – with the forward avionics on top and the complex engine section with four engines on the bottom,” Whipps elaborated.
“This is truly an engineering marvel like the External Tank was – with its strength that it had and carrying the weight that it did. If you made our ET the equivalent of a Coke can, our thickness was about 1/5 of a Coke can.”
“It’s a tremendous engineering job. But the ullage pressures in the LOX and LH2 tanks are significantly more and the systems running down the side of the SLS tank are much more sophisticated. Its all significantly more complex with the feed lines than what we did for the ET. But we brought forward the aspects and designs that let us save time and money and that we knew were effective and reliable.”
The SLS core stage is comprised of five major structures: the forward skirt, the liquid oxygen tank (LOX), the intertank, the liquid hydrogen tank (LH2) and the engine section.
The LH2 and LOX tanks feed the cryogenic propellants into the first stage engine propulsion section which is powered by a quartet of RS-25 engines – modified Space Shuttle main engines (SSMEs) – and a pair of enhanced five segment solid rocket boosters (SRBs) also derived from the Shuttles four segment boosters.
The tanks are assembled by joining previously manufactured dome, ring and barrel components together in the Vertical Assembly Center by a process known as friction stir welding. The rings connect and provide stiffness between the domes and barrels.
The LH2 tank is the largest major part of the SLS core stage. It holds 537,000 gallons of super chilled liquid hydrogen. It is comprised of five barrels, two domes, and two rings.
The LOX tank holds 196,000 pounds of liquid oxygen. It is assembled from two barrels, two domes, and two rings and measures over 50 feet long.
The material of construction of the tanks has changed compared to the ET.
“The tanks are constructed of a material called aluminum 2219 alloy,” said Whipps. “It’s a ubiquitously used aerospace alloy with some copper but no lithium, unlike the Shuttle superlightweight ET tanks. This alloy is heavier but does not affect our payload potential.”
“The intertanks are the only non welded structure. They are bolted together and we are manufacturing them also. It’s much heavier and thicker.”
The entire SLS core stage will tower more than 212 feet (64.6 meters) tall and sport a diameter of 27.6 feet (8.4 m).
The total weight of the empty core stage will be 188,000 pounds, and 2.3 million pounds when fully loaded with propellant. The empty ET weighed some 55,000 pounds.
Considering that the entire Shuttle ET was 154-feet long, the 130-foot long LH2 tank alone isn’t much smaller and gives perspective on just how big it really is as the largest rocket fuel tank ever built.
Every fuel tank welded together from now on after this series of confidence and qualification LOX and LH2 tanks will be actual flight article tanks for SLS launches.
What’s ahead for the SLS-2 core stage?
“We start building the second SLS flight tanks in October of this year,” Nesselroad stated.
The maiden test flight of the SLS/Orion is targeted for November 2018 and will be configured in its initial 70-metric-ton (77-ton) Block 1 configuration with a liftoff thrust of 8.4 million pounds – more powerful than the Saturn V moon rocket.
Although the EM-1 flight in 2018 will be uncrewed, NASA plans to launch astronauts on the EM-2 mission slated for between 2021 and 2023.
The exact launch dates fully depend on the budget NASA receives from Congress, who is elected President in the upcoming election, and whether they modify NASA’s objectives.
“If we can keep our focus and keep delivering, and deliver to the schedules, the budgets and the promise of what we’ve got, I think we’ve got a very capable vision that actually moves the nation very far forward in moving human presence into space,” said William Gerstenmaier, associate administrator for the Human Exploration and Operations Mission Directorate at NASA Headquarters in Washington.
“This is a very capable system. It’s not built for just one or two flights. It is actually built for multiple decades of use that will enable us to eventually allow humans to go to Mars in the 2030s.”