X-33 hydrogen tank adhesive joint failures

Composite hydrogen tank originally designed for 2.0 safety factor. Manufacturing defects (potentially 3-4 inches in size) led program to recalculate as 1.05 safety factor to justify proceeding to test rather than scrapping $225M-$250M vessels. Failed in test at Huntsville. Used as exemplar of "political games" with safety factors.

The X-33 spaceplane — I didn't bring the piece but in some of the other lectures you'll see it. That's one of mine. It's a piece of composite material. They originally designed it for a 2.0 safety factor. It turns out they had a manufacturing problem and they knew they had some flaws that were not half an inch in size, they could have been three or four inches in size. So they sharpen their pencils, because they have these $225 million vessels, or maybe it was $250 million vessels — I just remember the 15 million number. They didn't want to declare them junk. That would not be politically a good move. They sharpen their pencils and said, oh well, we don't have a factor of two safety, we have a factor of 1.05 safety, so we can put them in test. This is for the liquid hydrogen tank for the X-33 spaceplane. And as long as we pass the test, it'll be fine and we can fly the darn thing. Unfortunately they put them in test, and it probably wasn't 1.05, maybe it was 0.95. They failed in tests in Huntsville, Alabama. So people will play games with safety factors. That's an example of a political game: oh yeah, we still got a safety factor. I've never known anyone who designed something with a 1.05 safety factor.

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A piece of the X-33 hydrogen tank is shown as an example of a $12,000/lb fabricated structural material. Used as the high-end anchor of the price-per-pound argument that becomes §8. No failure discussion here.

[Tom shows images of structural applications.] When we're talking about structural materials, we're talking about things like ships, reactors. All-composite aircraft — this is the first large all-composite aircraft, the V-22 Osprey. The Marine helicopter, about 60 million a pop, is all graphite carbon fiber composite. Could not fly without that material. Try to make something heavy like aluminum — too heavy. So they have to use a very expensive material. This was the X-33 space plane. This is a piece of the X-33 hydrogen tank, fabricated for twelve thousand dollars a pound. It's not very heavy but that's the price.

Half-size shuttle-replacement prototype. Adhesively bonded hydrogen tanks at $250M each, factor-of-safety reduced from 2.0 to 1.05 to meet schedule. Held during cryogenic test, failed on warm-up. $1.3B program cancellation.

[Tom holds up a piece of composite material.] I passed around a piece from this. This was an artist's rendition of the X-33 space plane that was supposed to be a half-size prototype that was going to go into space to replace the proven design that was going to replace the space shuttle. The fuel had to be lightweight — it was hydrogen and oxygen tanks. You had to design it so the tanks actually are the structure. You can't afford to build a structure to give strength and then put some fuel tanks on. The fuel tanks actually have to provide the strength for the structure in order to meet the weight requirements of this engine. It failed because — actually, the reason I have that little piece is, the hydrogen tanks were built in the same hangar at the Lockheed Martin Skunk Works in Palmdale, California where they built the first stealth fighter. It's not that big — the size of about two basketball courts. They had the all-composite stealth fighter in there, and then the space was available and they were going to build the X-33 space plane. They built the hydrogen tanks at a cost of $250 million a tank.

Two adhesively-bonded Nomex/carbon-fiber composite liquid hydrogen tanks built at $50 million apiece, ~4,000 pounds each, ~$12,000/lb fabrication cost. "Except it didn't [work]. But that's another story." Physical sample passed around class.

We also couldn't use ceramics because it was hard to join them. We can join them now — if you're willing to pay the price. [Tom holds up a piece of the X-33 space plane hydrogen tank.] Here's a piece of the X-33 space plane. This is all composite — Nomex, which is the same thing as Kevlar but from a different manufacturer than DuPont. You can buy this foam Nomex, which is like Kevlar — fire-resistant. The suits for firemen are made of Nomex; you pay $300 for a jacket rather than $100 because it won't burn very well in a fire. Carbon fiber composites, adhesively bonded. They built this structure on a fast track. It has a foamed adhesive joint through here. They built two of these. That was supposed to be the liquid hydrogen tank for the X-33 space plane. They built them at about $50 million apiece, and they weighed about 4,000 pounds — so it cost about $12,000 a pound to fabricate. What I'm holding is less than an ounce; it's not even $1,000 worth of product.