New Trouble on SLS. Bob Zimmerman, BehindtheBlack.com

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05-09-2017

(Photo:Date Set for Second SLS Booster Qualification Ground Test )

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New Trouble on SLS. Bob Zimmerman, BehindtheBlack.com

Brittle and weak welds on SLS tanks?

May 9, 2017 at 8:39 am Robert Zimmerman

Government in action! The hydrogen tanks that will be used for the first SLS rocket flight were welded using a technique that NASA has since found to be untrustworthy.

Although the weld strength issue stopped welding the qualification and flight articles of the LOX tank before it could start, the issue wasn’t caught until after both LH2 tanks were welded with the modified pin tool last summer. The implications of the two tanks possibly having below design strength welds disrupted the original, post-weld plans.

The LH2 qualification tank, which will be used for structural testing at Marshall Space Flight Center in Huntsville, Alabama, was welded first and after setup and configuration was taken to Building 451 in December of last year both for proof testing of the welds and to qualify the test facility and procedures for subsequent flight tanks. Hydrogen tanks are proof tested by pressurizing them with nitrogen gas while a hydraulic test rig applies loads to the structure. “We wanted to wring out…the control system – 451 was another building that was made bigger to fit the hydrogen tank,” Doering said. “The control system is all new, the reaction fittings are all new, along with all the actuators. We didn’t want to put the flight asset in there to try to use it for the first time, so [using] the qual[ification] article [first] was also trying to wring out the pressurization and the actuation of the control system in 451.”

Originally, the plan included a test case to pressurize the qualification tank to slightly above flight pressure to help as a part of that “pathfinding” work; however, the discovery that the welds may be below design strength forced plans to be reconsidered.“We couldn’t say with any real degree of certainty that these welds would make it to [flight pressure],” Doering said. “In a pneumatic test, pressurizing it like that, it’s like a balloon…there’s a good portion of the community that thinks it will survive, there’s another portion of the community that says you don’t know enough to be able to say that, [and] there’s another portion of the community that says…’no way.’ [emphasis mine]

This is merely the qualification tank, built to find out if the tank design, which appears to be overly complicated to begin with, will work. The flight tank?

Lower pressure isn’t an option for the LH2 flight tank, which must perform at flight pressures both in testing and in flight. The SLS Program developed and is working on multiple, parallel options for consideration that include repairs and/or replacement of the already-welded flight tank. “We’re looking at use as-is – can I get to the point where I’m comfortable using that flight tank?” Doering said. “The answer to that is probably not, just because the analysis tools don’t exist yet to do this.” [emphasis mine]

They are faced with the likely possibility that they will have to repair the tank, which will likely cause the now 2019 launch date for the first unmanned test to be delayed further.

The rumors that NASA is considering making that first test flight a manned one makes me think that they are considering that decision as a cover for these additional delays. “We need more time to make this work as a manned flight,” NASA management will claim, using that extra time to fix the tanks as well. They will also claim they need more money, as they always do.

Meanwhile, NASA is having trouble building rocket tanks, an item that aerospace engineers figured out how to build half a century ago. Way to go, NASA!

http://behindtheblack.com/behind-the-black/points-of-information/brittle-and-weak-welds-on-sls-tanks/

May 11, 12:00 AM
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