Sep 262017

This… this struck many a nerve. Back in my aerospace engineering days, I had a *lot* of meetings that went more or less like this.

The end result, both in the video and in reality, is for the engineer to just give up and say “yeah, sure, I can do the crazy incomprehensible thing you think you want.” Work from that point forward then becomes an effort not to produce the impossible thing, but to plan out in advance how you’re going to blame who for what.

There were times when I was told to design a component that would only be physically possible in a reality with four physical dimensions. There were *many* times when I had to actually invent something (not just design, but invent, as in come up with a new propellant combination and propellant geometry that had apparently never been tried before, with all the tests and undoubtedly failures and revisions that would require) and I had to tell management in advance how much it would cost and how many man hours it would take, to within a few percent accuracy. There were times when I was told to replace an electrical conductor with a non-conductor, but to make sure that it maintained its conductance. Told to make a rocket motor that performed as well as a standard one, weighed the same, cost the same, but didn’t have a hot exhaust plume. And so on. And every time I made an objection I was told I was being “negative” or was told “that’s your job” or “make it work.”

This also works as an allegory for “a rational man among the social justice warriors.”


 Posted by at 3:15 pm
  • becida

    Wow! I can’t imagine that… I’d have been looking for a new job.

    • Scottlowther

      Shit, that was the *good* company. The first one had a boss that made us pressure test condemned aluminum fire extinguisher bottles to well over the rated pressure, and screamed at us when we took some basic precautions that “There are no safety concerns!” The last company decided that the best possible role for a design engineer was as accountant. So… the company that set irrational design tasks? Best case scenario at the time.

      • Adam

        Where were you an accountant?

        • Scottlowther

          About ten miles from here.

      • markus baur

        “if there are no safety concern, please keep standing right there and hold the extinguisher, while i retire behind that blast shield.”

  • “…a rocket motor that performed as well as a standard one, weighed the same, cost the same, but didn’t have a hot exhaust plume.”

    That third bit…is…ummm….wait…how…whut?

    • Scottlowther

      A cool rocket exhaust is a perfectly cromulent thing for, say, the military to want. If the exhaust is 500 degrees rather than 2,500, then it doesn’t make near as big of a target for IR seekers and trackers. So it would be a wonderful thing to have in an ICBM or an AAM or basically *any* kind of missile that you’d rather just snuck up and whopped the enemy upside the head.

      And a cool exhaust *is* possible. The same sort of thing happens all the time in turbojets and especially turbofans; you take the insanely hot combustion product and mix it with air (or some other working fluid) and you get a cooler gas flow.

      It’s *possible.* It’s just not what you’d call terribly *practical.* You have to mix a *lot* of some cool gas or fluid with the exhaust. To first order, if you mix a 1:1 ratio of rocket exhaust with, say, water, you cut the temperature of the exhaust in half. But half of “insanely hot” is still “damn hot.” And carrying several times the mass of your propellant in water is a damned fine way to make your missile immobile. Swapping out water for liquid nitrogen or even liquid helium is not a spectacular improver of the situation.

      You’d think this sort of situation would be simple to explain, simple to understand. But then you get ht with “just add a heat exchanger.” Or the customer dreams up the notion of a regeneratively cooled throat and you have to explain that most large liquid rockets *already* do that with liquid friggen hydrogen cooling the throats and nozzles, and *they* hardly have cool exhausts.

      It’s fine when a non-technical customer wants something that just ain’t practical. It’s hair pulling when they refuse to listen to you when you explain why they can’t have it. Often times management knows full well that X ain’t happenin’,but they still enthusiastically nod and say “we can do that.” The company gets paid to do the work, often enough, not to make the product.

      • Peter Hanely

        Years ago I figured that, in principle, a rocket exhausting into a hard enough vacuum with a high enough expansion ratio could have a very cold exhaust plume. In practice it needs a huge and heavy exhaust nozzle for very little performance improvement.

        • Scottlowther

          A very long time ago (20? 30? years? goddam I’m old) Analog magazine had a story about a deep-space ship that used, IIRC, a nuclear thermal engine of some kind but which had a *vast* expansion bell made of some thermal superconductor, with the end result that the exceedingly cold hydrogen exhaust cooled the nozzle enough to, IIRC, hide the whole ship in IR.

          The math on that… I don’t think she works, but it sounds nifty.

          • Ian Bruene
          • publiusr

            That’s where a lot of size comes in. Eats up the performance–but for a colony sleeper ship… Use the engine as a dome once you get to an asteroid in the next star system or whatever.

            I’ve often wondered what an engine could be used for once no longer needed for propulsion. I like pressure-feds for HLLVs,But upper stages to carry with you need a turbo-pump.

            Putting a good turbo-pump placed in one of the tiger stripes of Enceladus might be a good way to generate power–and maybe the best place for something like HYPACC

      • Herp McDerp

        But what if you reverse the polarity?

        • Scottlowther

          We tried that once. Sucked all the aluminum powder in the plant into the motor case. Which was cool, but having to explain to the EPA how we’d accidentally compressed a hundred tons of metal into a half-cubic-meter chunk of degenerate matter… ugh.

          • markus baur

            sell it to the army as a new type of armour plate

      • publiusr

        A cool rocket exhaust.

        The only thing I could come up with would be a hollow–very thick walled cone.

        The wall of the cone IS the liquid hydrogen tank. The engine would be just under the point of the cone–with a LOX dome above it.

        This would almost be a tractor rocket like Goddard’s early design, with the true nozzle itself hidden behind a cone of tankage on all sides.

        By the time the gases emerge from view–they’ve had time to lose some heat…

        Deep space design only.

  • Peter Hanely

    I remember that video. Good example of the power of a credentialed idiot among uncritical fools. But engineers are supposed to look at a situation critically.