NASA tests SLS backup tank to failure


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In preparation for the only planned full scale static fire engine test of the core first stage of the SLS rocket, NASA engineers have successfully completed a tank test to failure on a back-up oxygen tank.

The tank was filled with water to simulate the oxygen, and cracked as expected at the predicted pressure and at the predicted weld. A short 11-second video of the moment of failure test is embedded below the fold.

This test illustrates the methods by which NASA works. Unlike SpaceX, which is doing similar tests at the very beginning of its Starship design stage to best improve their design, NASA does this testing at the very end of construction, to prove that what they have built will work. The former method in the long run is less risky and faster, as SpaceX quickly finds out what works and doesn’t and builds accordingly.

The latter method is more risky because it depends on complex computer models, which can always be wrong. It also is more expensive in that it requires NASA to build its rockets with large margins of error, just in case those models are wrong. Finally, it appears to take longer to build, because of those required large margins of error. Your rocket or spaceship needs almost to be “gold-plated” to make sure it will work, when completed, since you really can’t test it in the design phase and build it more efficiently based on those tests.

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16 comments

  • Col Beausabre

    NASA does this testing at the very end of construction

    “You know this is a government program” – Apollo 13

  • sippin_bourbon

    Both are interesting methods. I am not an design or mechanical engineer by trade, so do not know if there are better methods.

    My own thought would be to test components or assemblies and then out it all together, but I am sure there are flaws with that too.

  • John

    First thought was yeah, water’s just as good as cryogenic oxygen.

    But they applied millions of pounds of force to simulate flight…whoa. SpaceX will probably just fly the tanks to simulate flight.

    The article says this is the last in a three year campaign, so at least some testing has been done previously.

  • MDN

    The key difference between these approaches is that SpaceX EXPECTS failures and uses them to learn fast and early. On the other hand NASA FEARS failure so is endlessly paranoid to even test at all, and therefore over-designs unnecessarily and learns nothing or little until it is too late and certainly too expensive to fix problems.

    Or more succinctly, SpaceX uses the scientific method (experiment, learn, refine, repeat to learn what does work), where NASA uses the modern academic method of endless models and studies untethered to reality trying to divine what should work.

  • Chris Lopes

    Another difference is that Musk actually expects his spacecraft to be used on a regular basis. SLS is just a jobs program, so it might as well take forever to get it flying.

  • Ray Van Dune

    Water is essentially incompressible. Is LOX? Even if LOX is incompressible, gaseous oxygen is NOT. As the liquid oxidizer is consumed during boost, the remainder of the tank volume will be filled with gaseous oxygen and/or whatever other gas is used to sustain pressure within it, and that mixture will NOT be incompressible!

    So NASA chooses to wait until very late in the development cycle to do a supposed real-world physical test, but then adopts an approach that arguably only approximates reality! So what did this test supposedly verify?

  • Ray Van Dune

    Ps. Did anyone else notice the similarity of this test to the “swimming pool” test used to isolate the fault in the fuselage design of the de Havilland Comet airliner? Unfortunately, that test was carried out even later, after many had died!

  • pzatchok

    If you can predict where the fault will happen you should be re-enforcing that spot.

    And it failed within 2% of its expected pressure. But they never said how far over the needed rating that was.

    What if it only hit the bare minimums?

    They also crushed it from top down. Simulating the vertical pressures during lift off.
    What if the tank was close to empty? Wouldn’t it then be weaker like an empty beer can?

  • john hare

    And what about the cryo temps. A comprehensive test should be using liquid nitrogen, shouldn’t it? A couple of hundred degrees difference has bitten SpaceX as I recall, but early enough to be addressed in the next unit.

  • Chris

    What I would expect is that both NASA and SpaceX have excellent design and simulation modeling. They may use different platforms (Say SolidWorks vs ProE) and some customized internal modules may exist but the I expect the design tools are the same. There will also be simulation software within the package or elsewhere that would determine design issues (harmonics ..etc).

    I expect all this is the same between the two. The difference I see As Bob points out is a desire to prototype early and do iterative design on SpaceX’s part. I think their approach is to not have a complete design before proto but to have general minimum requirements (from the system design) and built/test to them. This way they show design flaws early (“fail quickly”), can incorporate design improvements from the test, refine their model from the tests (making the model AND the modeling better), and possibly remove cost where there is over designed areas.
    In this approach there is a bit more work but results can come quickly.

    NASA has a (hopefully) single design test cycle with perhaps some component testing prior to the large system (tank) test. I suspect a hierarchy that requires lots of formal review and larger design teams that preclude a more iterative approach. (Pure conjecture but based on some old prior NASA interaction).

  • Patrick Underwood

    pzatchok,

    Logically, there has to be a weak spot. If you reinforce the current weak spot, all you get is a new weak spot somewhere else. Endless cycle until you have a battleship instead of a rocket. :)

  • Patrick Underwood

    Oh and the tank is gas pressurized for the entire burn, so it can’t collapse when the fuel is low.

    NASA and Boeing really do have competent engineers. It’s execs and politicians you have to watch out for.

  • Ray Van Dune

    And that elaborate test shielding structure that Spacex obviated with the simple expedient of getting far the hell away? Bets on what that cost?

  • Patrick Underwood

    Ray Van Dune, one of my favorite factoids is that NASA spent more to modify a launch pad for a single test of the awful and doomed Ares 1, than SpaceX spent to develop the world-changing Falcon 9 family of boosters.

  • Edward

    Ray Van Dune asked: f”So what did this test supposedly verify?

    It verified what it was supposed to verify. Failure was as expected and at the expected location.

    John hare asked: “And what about the cryo temps

    SpaceX’s recent cryogenic test was to verify the strength at cryogenic temperature and NASA’s test was to test failure location, not necessarily the strength of the material at temperature. Hopefully they did that test before designing the launch vehicle. Water, rather than air, is often used to pressure test pressure vessels in order to prevent shrapnel during a possible or planned failure.

    pzatchok suggested: “If you can predict where the fault will happen you should be re-enforcing that spot.

    Reinforcement may not be desirable. Often, a design wants a built-in failure mode that is safe for, say, crew members. SpaceX had a recent pressurization failure that resulted in the top bulkhead flying off vertically into the air. That could have been disastrous to a manned compartment mounted on top. A sideways rupture would be safer.

    What if it only hit the bare minimums?

    Then it was barely acceptable, but acceptable nonetheless.

    Robert wrote: “This test illustrates the methods by which NASA works. Unlike SpaceX, which is doing similar tests at the very beginning of its Starship design stage to best improve their design, NASA does this testing at the very end of construction, to prove that what they have built will work.

    I see a different difference, that they are at opposite ends of development. NASA is currently verifying the design they built, but SpaceX is testing materials and methods in order to finalize the design what they will build. NASA/Boeing should have done similar design testing prior to this or relied upon previous testing by others in order to determine how to design their launch vehicle.

    Because there are not many people closely watching all the testing and construction that Boeing and NASA do on SLS, as SpaceX fans do to SpaceX, they may have done much more pre-design testing than we know. On the other hand, Congress and NASA became timid of using new technologies on Orion and SLS, so they probably are not using many innovative materials, methods, or technologies. Even the stir welding they used is not so new.

    SpaceX needs all this pre-design testing in order to be innovative. They may be using rapid construction techniques that they may not intend to use for operational spaceflight units. SLS was not so innovative, reverting to 1960s overall methodologies.

  • Diane E Wilson

    SpaceX is also designing and building their production facilities, so that they can build many rockets reliably and quickly. Their tests are tests of their production capability, as much as they are tests of their rocket designs and building techniques. They’ve also done this for their Raptor and Merlin engines, and for their Starlink satellites.

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