Engineers Complete Test Campaign by Breaking SLS Rocket Tank... on Purpose

FMEA at its finest

Published: Monday, August 17, 2020 - 12:02

On June 24, 2020, engineers completed the Space Launch System (SLS) rocket’s structural testing campaign for the Artemis lunar missions by testing the liquid oxygen structural test article to find its point of failure.

“The Space Launch System and Marshall test team have done a tremendous job of accomplishing this test program, marking a major milestone not only for the SLS program but also for the Artemis program,” says John Honeycutt, the SLS program manager. “From building the test stands, support equipment, and test articles, to conducting the tests and analyzing the data, it is remarkable work that will help send astronauts to the moon.”

For the final test, the liquid oxygen tank test article—measuring 70 ft tall and 28 ft in diameter—was bolted into a massive 185,000-lb steel ring at the base of Marshall’s Test Stand 4697. Hydraulic cylinders were then calibrated and positioned all along the tank to apply millions of pounds of crippling force from all sides while engineers measured and recorded the effects of the launch and flight forces. The liquid oxygen tank circumferentially failed in the weld location as engineers predicted and at the approximate load levels expected, proving flight readiness and providing critical data for the tank’s designers. This final test on the liquid oxygen structural test article met all the program milestones.

Engineers completed almost 200 tests on the Space Launch System (SLS) rocket by breaking the liquid oxygen tank test article. This test was the last in a three-year structural campaign to ensure the rocket’s structure was designed to endure the rigors of space flight. The tests were essential for safely sending astronauts to space on the Artemis missions to the moon. First, engineers used computer modeling to design the rocket’s major structures to specific factors of safety. Then, they anchored those models with testing to see if the model’s predictions were correct. More than 20 SLS structural tests showed that the liquid oxygen tank would survive the forces predicted to occur during launch and flight. The June 24, 2020, tests pushed the tank beyond its limits to see how much force it would take to break the tank’s structure. This image shows water gushing out of the tank as it failed. The resulted circumferential buckling of the structure occurred within 2 percent of the predicted failure value. The test results will provide rocket designers with valuable information for making the SLS tanks lighter and for informing the designs of other government and commercial rockets. Credit: NASA/David Olive

The successful completion of SLS structural qualification testing at NASA’s Marshall Space Flight Center in Huntsville, Alabama, wraps up the largest test campaign at the center since tests conducted for the Space Shuttle program more than 30 years ago. During the test campaign, five structural test articles underwent 199 separate test cases, and more than 421 gigabytes of data were collected to add to computer models used to design the rocket. The final test marks the achievement of all SLS structural testing requirements prior to the Artemis I mission—the first in a series of increasingly complex missions that will enable human exploration to the moon and Mars.

Earlier this year, NASA and engineers from Boeing, the core stage prime contractor, completed 24 baseline tests that simulated actual flight conditions on the liquid oxygen structural test article. For all the tests, thousands of sensors measure stress, pressure, and temperature, while high-speed cameras and microphones sought to identify any buckling or cracking in the tank’s cylindrical wall. The data gathered from these baseline tests helped qualify the SLS core stage structures and integrated upper stage for flight.

The Marshall team has been conducting structural qualification testing on the rocket since May 2017, with an integrated test of the upper part of the rocket stacked together—including the interim cryogenic propulsion stage, the Orion stage adapter, and the launch-vehicle stage adapter. That was followed by testing of the four largest structures that compose the core stage—the engine section, the intertank, the liquid hydrogen tank, and the liquid oxygen tank. Each of these tests provided additional data to computer models that predict how the structures will perform under the harsh conditions of launch and flight.

“The Marshall test lab team has worked closely with the Space Launch System program to test the rocket’s structures from the top to bottom,” says Ralph Carruth, Marshall’s test lab director. “After watching the test stands being built, working alongside SLS and Boeing engineers to establish testing procedures, and conducting and gathering results of five structural qualifying tests, we are proud to contribute data that show these structures can withstand the rigors of flight.”

With the conclusion of testing, designers now have data that may be helpful in optimizing SLS hardware. SLS will have the power to send astronauts forward to the moon and ultimately to Mars. Testing the new, complex pieces of hardware is critical to the success not only of the first flight test of SLS and NASA’s Orion spacecraft, but also to all future missions.

“This year is a landmark year for core stage testing for the Artemis missions,” says Julie Bassler, the SLS stages manager. “We have successfully completed our core-stage major structural tests at Marshall Space Flight Center and are making progress on Green Run testing of the Artemis I core stage at Stennis Space Center that will simulate launch. All these tests are not only valuable for the first Artemis mission but also validate the new integrated design of the SLS core stage structure, propulsion, and avionics systems, and ensures its readiness for future flights.”

To complete the structural qualification test campaign for NASA's Space Launch System (SLS) rocket, the liquid oxygen structural test article was pushed beyond its limits until it broke, and water gushed from the tank. The tank is a test article that is part of the SLS core stage that will produce 2 million lb of thrust to help launch the rocket. The tank was bolted into a massive steel ring at the base of Marshall’s Test Stand 4697. Hydraulic cylinders were then calibrated and positioned along the tank to apply millions of pounds of crippling force from all sides while engineers measured and recorded the effects of the launch and flight forces. For the test on June 24, 2020, water used to simulate the liquid oxygen flows out of the tank after it ruptures. The structural test campaign was conducted on the rocket to ensure the SLS rocket’s structure can endure the rigors of launch and safely send astronauts to the moon on the Artemis missions. Credit: NASA/David Olive

Teams at Stennis Space Center near Bay St. Louis, Mississippi, are making progress on Green Run testing of the assembled SLS core stage for the Artemis I mission. At NASA’s Michoud Assembly Facility in New Orleans, Boeing, the core stage prime contractor, has manufactured all the main core stage structures for the Artemis II mission and started work on Artemis III structures. The 212 ft-tall core stage is the largest, most complex rocket stage NASA has built since the Saturn V stages that powered the Apollo missions to the moon. Aerojet Rocketdyne has assembled engines for the Artemis II mission and is in the process of assembling Artemis III engines.

Northrop Grumman recently delivered booster segments to the NASA’s Kennedy Space Center in Florida where they are being prepared for launch. All 10 of the segments for the second Artemis mission are cast, and Northrop Grumman is now working on the boosters for Artemis III. With the arrival of the boosters to Kennedy, the only remaining pieces of hardware for the Artemis I flight test to be delivered are the launch-vehicle stage adapter, which connects the rocket to the Orion spacecraft and will arrive this summer, and the SLS core stage, which will be transported to Kennedy by barge after the Green Run hot fire test at Stennis later this year.

The SLS rocket, Orion spacecraft, Gateway, and human landing system are part of NASA’s backbone for deep space exploration. The Artemis program is the next step in human space exploration. It’s part of America’s broader Moon to Mars exploration approach in which astronauts will explore the moon and gain experience there to enable humanity’s next giant leap, sending humans to Mars.

First published July 10, 2020, on engineering.com.

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