![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2017\/01\/2017-01-09-194206-350x230.jpg\")
\u201cOnce we get the tank transported out to 451, of course, we\u2019ve got to do all the mating and integration within the test facility.\u201d<\/p>\nThe first fully-welded Space Launch System (SLS) Core Stage propellant tank was recently moved to its proof testing facility at the Michoud Assembly Facility (MAF), to begin final preparations for the first set of tests to begin. The liquid hydrogen (LH2) qualification tank will be a pathfinder for Core Stage prime contractor Boeing and NASA to begin validating the newly-assembled Core Stage hardware, along with the facilities, testing procedures, and analytical models that will help qualify the design and development of the stage for its first flight.<\/p>\n
Getting set up to test:<\/p>\n
The LH2 qualification tank was rolled from the Final Assembly area of Building 103 to Building 451, a test facility at MAF away from the main assembly area, on December 10. The first of its kind article then began preparations to do the first proof tests of the program.<\/p>\n
\u201cThis is a development program and you know the first out of the chute so there\u2019s a lot of learning going on along the way and a lot of trying to make sure that we absolutely understand every aspect,\u201d Steven Ernst, Boeing\u2019s SLS Cryogenic Tanks and Welded Structures Manager, said in a recent interview with NASASpaceflight.com.<\/p>\n
\u201cOnce we get the tank transported out to 451, of course, we\u2019ve got to do all the mating and integration within the test facility.\u201d<\/p>\n
Both propellant tanks have structural rings welded to the semi-circular domes at either end. The rings incorporate a flange that will eventually be used to mate to the other elements of the Core Stage; for the proof test, these will be used to bolt the hydrogen tank into the test bed.<\/p>\n
\u201cWe attach to the forward flange of the LH2 tank and we attach to the aft flange of the LH2 tank and then we impart some pretty significant loads, both axially and moments on the tank itself through some extremely large hydraulic actuators,\u201d Ernst explained.<\/p>\n
The hydraulic test rig is attached to the aft flange; the forward flange attaches to a feature of the facility called the \u201cbeer can,\u201d which is in part a simulator for the cylindrical intertank section of the Core Stage.<\/p>\n
Building 451 modifications:<\/p>\n
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At a high-level, proof testing of the propellant tanks is done similarly to the heritage Space Shuttle External Tank (ET) that was assembled at MAF for over 30 years.<\/p>\n
LH2 tanks are proof tested pneumatically by filling them with nitrogen gas in Building 451, a test facility at MAF separated from the main assembly area; LOX tanks are proof tested hydrostatically in Cell F in Building 110.<\/p>\n
![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2017\/01\/2017-01-09-194303-350x249.jpg\")
Although the test facilities are in the same locations as the Shuttle ET, modifications were required to accommodate the significantly longer SLS tanks. In particular, with the LH2 tank of Core Stage being almost as long as the whole Shuttle ET by itself, not did Building 451 need to be stretched in length, but much of the inside was overhauled.<\/p>\n
\u201cThe beer can was something we were able to utilize from the ET program, but we had to do a significant amount of modifications to the other end of the test set up,\u201d Ernst explained.<\/p>\n
\u201cWe really had to retrofit Building 451 because as you know [for] the External Tank [there were] applied loads during the pneumatic proof test for the hydrogen tank.<\/p>\n
![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2016\/12\/2016-12-15-233935-350x260.jpg\")
\u201cOn the SLS side we have the same situation, but obviously while we have solid rocket boosters (SRBs) on the side we don\u2019t have an orbiter attached [to the side of the tank], so the load cases are different [and] the loads are somewhat higher.<\/p>\n
\u201cSo we had to gut most of 451 and build a whole new test bed, we call it, with the hydraulic actuators and an aft truss that establishes boundary conditions at the back end of the tank.\u201d<\/p>\n
In contrast to the Shuttle ET, where the orbiter was mounted to the side of the tank and the thrust from its three main engines were significantly off-axis, four of those same engines (now called RS-25s) apply their thrust more symmetrically through the bottom of the SLS Core Stage.<\/p>\n
The thrust loads from the SLS Boosters are carried like the Shuttle SRBs were, through a thrust beam in the intertank that attaches to the top of the boosters at their forward skirts. As with Shuttle, the SLS intertank sits between the two propellant tanks with the LOX tank forward and the LH2 tank aft.<\/p>\n
Proof test pathfinding:<\/p>\n
The LH2 qualification tank is the first article to be tested in the newly renovated facility, and it will play a pathfinding role while it is there. \u201cWe\u2019re going to use this [initial opportunity] to check out the test bed [and] test out the tank,\u201d Ernst said.<\/p>\n
![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2017\/01\/2017-01-09-194338-350x219.jpg\")
\u201cIn the case of this qual tank we have a lot of instrumentation. There are strain gauges in various parts of the tank; during the test we\u2019ll gather all that data, actual data on how the tank is reacting during the different phases of the test, and then we go back and correlate all that actual data with the analysis models, to make sure that all of our models are good \u2013 how the data correlates with our models will really help dictate what the actual proof test scenarios for the flight articles will look like.\u201d<\/p>\n
He noted that a formal test readiness review will be conducted shortly before Boeing begins running a set of test cases on the qualification tank: \u201cGenerally you do that a week to two weeks out and we\u2019ll have an exhaustive review of every aspect of it that will not only include the technical community but program leadership both with our Boeing team as well as with our NASA team,\u201d Ernst said.<\/p>\n
\u201cJust setting up the tank to run that test is no small task. We\u2019ve got to check out our data acquisition system and there\u2019s a lot of \u2018pre-work\u2019 before you actually get into the test and then after you get through running all your test cases, the process in reverse is equally time-consuming.\u201d<\/p>\n
Since this is the first time most of the hardware and procedures will be exercised, the test team will go more slowly at first. \u201cWe\u2019ll run some if you will \u2018mini tests\u2019 to make sure we understand how the system works,\u201d Ernst said.<\/p>\n
\u201cDuring the pneumatic test [of] the LH2 tank, given that we\u2019re putting tremendous amounts of force into the tank and of course we\u2019ve got a tremendous amount of energy contained in the pressurized volume of the tank, we absolutely need to make sure that we understand every single nuance about that system. So we\u2019re going to \u2018sneak up\u2019 to what will be the actual proof test levels.\u201d<\/p>\n
Running the tests:<\/p>\n
The large volume of gaseous nitrogen \u2013 an asphyxiant \u2013 and the energy involved in the high pressures and loads applied to the tank means that for safety reasons the tests will be run from a separate building. \u201cYou\u2019ve got the blast concern if something were to fail and of course you wouldn\u2019t want the release of that much nitrogen in an extremely short amount of time, so the team running and monitoring the test are tucked safely away in a building nearby 451,\u201d Ernst explained.<\/p>\n
![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2017\/01\/2017-01-09-194438-350x235.jpg\")
\u201cIt\u2019s not far, but it\u2019s all protected in the event of a failure to make sure everybody is safe. There\u2019s also a blast zone that will be established during the higher pressure test that people will be kept out of, which is a perimeter that\u2019s some distance away from 451.\u201d<\/p>\n
Ernst also explained that the test cases themselves are fairly quick: \u201cThe tests \u2013 and we have five separate load cases \u2013 the tests themselves aren\u2019t terribly long, but it could be days and days or even weeks to get prepared to actually run the test. In our peak test at the highest pressure, the test itself only lasts around 60 seconds.\u201d<\/p>\n
He also noted that the proof tests will go somewhat beyond what is predicted to occur in flight: \u201cThe combination of the pressure and that in conjunction with the loads that [are] put into the tank test it, at levels above what we would expect to see during flight.\u201d<\/p>\n
LOX tank proof testing:<\/p>\n
Proof testing the SLS LOX tanks will be more similar to how it was done with the Shuttle ET. \u201cWe\u2019re actually reusing the same hydrostatic test cell that ET used,\u201d Ernst said. The LOX tanks will be tested in Cell F of Building 110, just across the way from the Vertical Assembly Center where they will be welded together.<\/p>\n
![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2017\/01\/2017-01-09-194538-350x266.jpg\")
\u201cThe test process for the hydrostatic test of the LOX tank aligns very closely with legacy [Shuttle ET], so we come in with a lot of experience in that cell. In fact, we\u2019re actually relying on help from folks that were involved in the hydrostatic testing on the External Tank program.\u201d<\/p>\n
Although there are more similarities than with the hydrogen tanks, the SLS LOX tank still required changes to the test cell. \u201cThere had to be a number of modifications to the cell because the LOX tank on SLS is a good bit larger than the LOX tank was on External Tank,\u201d Ernst explained.<\/p>\n
\u201cBut we\u2019re using the same cell and, in fact, the majority of the control system is the same because that control system on ET had been upgraded at some point in the latter days of the program, so that\u2019s just in the process of being modified to accommodate the parameters required to test the Core Stage LOX tank.\u201d<\/p>\n
![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2017\/01\/2017-01-09-194629-350x324.jpg\")
Ernst said that the LOX tanks will be mounted vertically in the test cell. \u201cThe bottom end of it, if you will, is really essentially identical to how the External Tank LOX tank was tested because our tank diameters are the same,\u201d he explained.<\/p>\n
\u201cIt\u2019s really more of the delivery system that puts the water in the tank and things like that \u2013 the standpipe that had to be modified to accommodate the [increased length] of the Core Stage LOX tank.\u201d<\/p>\n
Ernst also outlined hydrostatic test itself: \u201cThe LOX tank is filled with demineralized water and there\u2019s a head pressure put on that.<\/p>\n
\u201cBecause of the density of LOX, we have to apply a pretty significant load to the aft of the LOX tank, so it\u2019s different than what we\u2019re doing with the LH2 tank because we\u2019re not actively applying external loads to it. This is really just a \u2018fill it with water\u2019 [test] and basically pressurize that until we get the loads we needed on the aft end of the tank.\u201d<\/p>\n
In contrast to the LH2 tank, the LOX tanks only need to be tested once. \u201cWe\u2019ll do a fill and a drain initially that\u2019s just to check everything out, but for the test itself [we\u2019ll do] just one [test],\u201d Ernst said.<\/p>\n
Post-test steps:<\/p>\n
All propellant tanks will be proof tested after welding is completed; after the proof test cases are done, the tanks will be re-inspected and the state of the welds will be compared.<\/p>\n
![\"\"](\"\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2017\/01\/2017-01-09-194707-350x264.jpg\")
\u201cWhat we will do is called post-proof NDE (non-destructive evaluation),\u201d Jackie Nesselroad, Boeing\u2019s Director of Production Operations at MAF, explained.<\/p>\n
\u201cAs we complete each weld, we inspect them using phased-array ultrasonic testing (PAUT) and we archive those images. And then after we do a proof test we go back and redo the phased-array ultrasonic testing and compare [them]. That comparison is looking for anything that may have propagated between the as-welded versus the as-tested.\u201d<\/p>\n
After the proof test is over, Nesselroad said that in addition to inspections, more instrumentation will be added to the qualification tank for structural testing that will be done at Marshall Space Flight Center in Alabama.<\/p>\n
\u201cWe have some instrumentation that we need to do before we take it into our priming cell and then we\u2019ll be in the process of priming and then we\u2019ll apply spray-on foam in the next cell over.\u201d<\/p>\n
(Images via NASA and L2 SLS and ET Historical).<\/p>\n","protected":false},"excerpt":{"rendered":"
The first fully-welded Space Launch System (SLS) Core Stage propellant tank was recently moved to its proof testing facility at the Michoud Assembly Facility (MAF), to begin final preparations for the first set of tests to begin. The liquid hydrogen (LH2) qualification tank will be a pathfinder for Core Stage prime contractor Boeing and NASA […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":"","_links_to":"","_links_to_target":""},"categories":[2],"tags":[3718,7866,624],"class_list":["post-38884","post","type-post","status-publish","format-standard","hentry","category-news","tag-em-1","tag-maf","tag-sls"],"acf":[],"_links":{"self":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/38884"}],"collection":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/comments?post=38884"}],"version-history":[{"count":0,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/38884\/revisions"}],"wp:attachment":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/media?parent=38884"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/categories?post=38884"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/tags?post=38884"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}