15 thoughts on “No Sunk-Cost Fallacy Here”

  1. A tremendous waste of money. Still I guess it is less bad than if they persisted on that path. The jig was also using up space. So it probably was the best decision. People also easily forget that Beal Aerospace ran into the same issues with composites. And that was with much more benign, non-cryogenic, propellants in an expendable.

    I still remember talking about the large BFR composite tank test (was it a year ago?) which, back then, SpaceX claimed to be a success. I pointed out to people that it was, in fact, not a success. Because the tank was not strong enough to meet the design pressure with the proper safety margin. Also, to boot, the test was simply a water burst test. It did not even use a cryogenic propellant. I had more than one person tell me I was wrong back then and that SpaceX clearly had to know better. Oh well.

    So yeah, that tank was clearly not up to scratch. Could they not have figured that one out with subscale tests?

    Still I think if they did fire all the people working on composites they had that was a bit much. For example, for the Dragon V2, I think having composite tanks for the hypergolic fuel would be, in fact, a great idea. There are other places where composites would make sense. But not with cryogenic fuels or at high temperatures I think.

    1. There’s also the problem of building very large structures out of carbon fiber. Sure, Boeing can do it, but according to a conservative estimate by the Seattle Times, their 787 program cost $32 billion dollars, half spent on development and half building the aircraft prior to the first acceptance by an airline. They’re selling plenty of them, but they still cost $150 million each.

      I would venture that Musk realized he couldn’t dramatically bend the cost curve on that, and the BFR has to deal with cycling between cryogenic temperatures and Mach 9 heating. If the lightweight carbon fiber airframe requires to much thermal protection, the weight might not come out much better than stainless, and the turnaround time and cost might end up being too much like the Space Shuttle’s for affordable flight operations.

  3. IANAE, and I am not saying that a composite would be better, but doesn’t stainless become brittle at cryogenic temperatures?

    2. The 300 series stainless steels are great for cryogenic applications. At LOX temps, their tensile strength will more than double and their fracture strength increases, too.

      Musk said he’s using a modified 301 SS. I’ll bet the modifications he’s talking about are in a 1966 NASA Technical Report on improving low-temperature cryogenic notch-toughness of 301 stainless pressure vessels by reducing the amount of sulfur, phosphorus, manganese, silicon, and carbon, while leaving the normal amounts of chromium and nickel.

  4. Designing anything is a path. Sometimes, the only choice is to go back and take a different fork. Sooner is cheaper than later. Only time will tell whether this saved BFR or killed it.

    It’s so easy to fix on one characteristic early and end up at a dead end. It’s also so easy to allow all of the possible choices cause endless delay and paralysis. There are a lot of examples of both in history. Luck helps a lot.

    1. I think it’s a good choice because it makes design and manufacturing much easier and faster, which should allow them to continue with their tight design/fly/upgrade loop.

      I think the other path might’ve left them in a position similar to the SLS, spending year after year explaining why they haven’t flown yet as they struggle with production processes and test articles.

  5. I fully support the switch to stainless, I think it’s wise, and will result in better, cheaper, faster.

    However, it’s not certain stainless will work. So, unless the space was costing significant money, or the needed it for something else, why scrap the composite jigs now? Maybe after a few hop tests, but this just seems a tad hasty to me – burning bridges and all that.

    The composite structure and tankage was actually my #1 reason for being a bit of a skeptic on BFR/Starship.Composite is tricky, especially when cryo is involved. They lost one rocket and payload to that already (if I remember right, the case was unexpected solidification of LOX within the composite COPV skin).

    1. As soon as Elon decided that composites weren’t the way to go, all that tooling became useless and took up valuable factory real estate. There was almost certainly no buyer for it, and he probably couldn’t even donate it to any organization due to the federal guidelines that classify his rockets as ordnance. So he had to scrap it to take the write off.

  7. It was in a tent on the waterfront, probably not prime production space. The more important space it was taking up was in peoples minds. The pile of scrap certainty sends an unmistakable message.

    Probably cheaper than it looked. The big parts, specific to the large tanks are fairly simple. The smaller, much more expensive parts that actually laid down the composite probably aren’t in the pile and are probably in fair demand.

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