Author Topic: SLS Core Stage team recovering from consequences of weld pin change  (Read 8193 times)

Offline MP99

Is the SLS tank significantly thicker than the ET, or is it just an unprecedented thickness for friction stir welding?

https://www.nasaspaceflight.com/2013/02/sls-new-buckling-standards-drops-super-light-alloy/

This is my only article written for NSF, but seems to be relevant here.

Shuttle's ET went through revisions to lighten it, once to the Light Weight Tank, then to Super Light Weight Tank.

SLWT introduced Al-Li alloys, orthogrid structures, and (IIRC) friction stir welding.

SLS has reverted back to Al alloys because Al-Li suffers from brittleness​ when formed into cylindrical sections (limiting its thickness) and is a pain to weld. They gave up on Al-Li for some parts of SLWT over time.

Thicker Al panels could be used on SLS because they took the stresses of being formed better, and thicker panels result in deeper stiffening ribs. Since these are stronger, a thick Al panel ends up being lighter than a thin Al-Li panel once it's beefed up to cope with SLS's loads.

But, that thickness seems to be contributing to these FSW issues.

Although Al-Li tanks would be thinner, the hassles of welding it might just have landed them with similar problems, anyway.

Basically, engineering trades aren't necessarily as simple as they first seem.

Cheers, Martin

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Offline Steven Pietrobon

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SLWT introduced Al-Li alloys, orthogrid structures, and (IIRC) friction stir welding.

They didn't use friction stir welding on SLWT. The SLWT was first flown in 1998, way before friction stir welding became common. They used variable polarity plasma arc welding.

https://app.aws.org/wj/may/chienar.htm

"The early shuttle tanks were welded using gas tungsten arc welding. Hibbard said, "In the early 1980s, we developed with NASA Marshall the variable polarity plasma arc (VPPA) welding process." That process creates a keyhole in the metal and the molten metal then solidifies at the back of the hole as the torch progresses. "We used those processes for the 2195, plus a hybrid process where the plasma arc alternates current and does some cathodic cleaning at the torch," he said."
Akin's Laws of Spacecraft Design #1:  Engineering is done with numbers.  Analysis without numbers is only an opinion.

Offline rsnellenberger

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Friction stir welding was used for SLWT beginning with ET-134, flown on STS-130.

https://www.nasa.gov/centers/marshall/news/news/releases/2010/10-010.html

Online AnalogMan

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Friction stir welding was used for SLWT beginning with ET-134, flown on STS-130.

https://www.nasa.gov/centers/marshall/news/news/releases/2010/10-010.html

Small correction (as noted in the linked press release) - the first SLWT to fly with FSW was ET-132 flown on STS-128.  It only had two barrel sections of the LH2 tank welded this way (out of four total).  ET-134 was the first with all LO2 and LH2 tank longitudinal joins of the barrel sections welded by FSW.

Incidentally the first FSW pathfinder LH2 barrel section was produced in October 1998 using SLWT panels.
« Last Edit: 05/24/2017 03:39 PM by AnalogMan »

Offline psloss

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