NASA recently completed welding on a new component of their revolutionary Space Launch System (SLS), bringing the rocket one step closer to the stars. The new component is called a liquid oxygen tank confidence article. Standing over 200 feet with a diameter of 17.6 feet, the tank is used to store cryogenic liquid hydrogen and liquid oxygen. Completed at the Michoud Assembly Facility, the tank provides the first glimpse of what the SLS’s core stage will eventually look like.
However, the newly-completed tank will not be the final model. In fact, it is a replica made in advance of the final product. The replica will be put through rigorous testing in order to ensure everything functions as planned. One of the tests that will be conducted will look for signs of “geysering” in the tank’s fuel system. Geysering occurs when heat seeps into the liquid oxygen feed system, causing the liquid to boil. This boiling of the liquid results in very large gas bubbles that are quickly expelled. According to Chad Bryant, a Propulsion Manager for NASA’s Marshall Space Flight Center, “this rapid expulsion of boiling liquid can momentarily displace large volumes of heavy liquid that crash back down, causing a damaging hammer effect on the system.” Bryant emphases that testing for geysering is incredibly important. “One of the largest risks with a liquid oxygen feed system of this scale is the potential of creating a geyser,” said Bryant. A replica is also used to develop safer and more effective assembly procedures before the rocket can be trusted to ferry humans. Furthermore, the confidence article tank will be used to develop an application process for the rocket’s thermal protection system, a kind of foam insulation that gives the tank its orange color.
All welding for the SLS core stage, including confidence article tanks and eventually flight hardware, is scheduled to be finished this summer in preparation for the first flight of NASA’s Orion spacecraft in 2018. The craft will take an unmanned flight for its maiden voyage. However, as the SLS evolves, it will go from its initial 70-metric-ton lift capacity to an eventual 130, allowing for missions even further into our solar system. NASA is developing the Orion spacecraft with an eye towards taking a four man crew all the way to Mars, making it the first spacecraft capable of carrying humans into deep space since the Apollo missions over 40 years ago. Currently, the feasibility of such a long trip is still in question until the rocket is completed. Especially with a recent audit at NASA revealing that the SLS launch control software, which includes past NASA launch software, is behind schedule and significantly over budget. As of this time, however, no announcement has been made regarding the scheduling of the rocket’s first launch.
The completed confidence article, consisting of a dome and two barrels, verifies weld procedures are working as planned and tooling-to-hardware interfaces are correct. It also gives the weld team experience in bringing all aspects of hardware, tooling and software together to create a tank. Once a confidence article is completed, the structural qualification article is welded, which closely replicates flight hardware and processing procedures. The structural qualification article will be rigorously tested as part of the design verification process for the core stage. The Vertical Assembly Center is the largest spacecraft welding tool in the world and is part of six state-of-the-art tools designed to weld the core stage of SLS. More than 50 pieces of flight and qualification hardware for the core stage liquid oxygen and liquid hydrogen tanks have been completed and are ready for welding in the Vertical Assembly Center at Michoud. –NASA
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