The Problems With The Last Dragon Flight

…weren’t as bad as originally reported. I found this interesting, though:

As for the engine shutdown issue, data analysis has yet to result in any definitive conclusions. Although the analysis will continue, the observation that this particular engine had undergone a comparatively high degree of pre-flight testing, may ultimately lead to the conclusion that the shut down was related to the accumulating fatigue of an engine firing more than its nominal mission requirements. If this turns out to be the case; it would prove to be both somewhat ironic, as well as easily addressed by limiting cumulative firings for flight engines. Ongoing analysis has likely pushed the likely date of the next Dragon flight to ISS into the early March time frame.

Wouldn’t “limiting cumulative firings for flight engines” have interesting and problematic implications for reusability?

If this is really a problem, sounds like they’ll have to have a more robust engine design (or perhaps downgrade performance) for reusable versions. And of course, it’s possible that the new engine to start being used next year will resolve whatever the issue is.

16 thoughts on “The Problems With The Last Dragon Flight

  1. George Turner

    Well, that would also be good news because it means they could run the heck out of a few engines, until they fail, and then find the flaw. Any chance it could be related to fuel residue building up in the coolant passages during repeated firings, or to thermal fatigue?

  2. ken anthony

    SpaceX seems to be agreeable to licensing out some of their technology. Even if they go with a new engine they may still want to do some destructive testing on whatever version they sell or license. Seeing those bells glow makes you wonder what kind of fatigue they suffer?

    1. George Turner

      Well, it would also make sense to just use up the last of the Merlin 1C’s, not flying any that have had the extra testing that the failed engine did, and focusing a test campaign on the 1D. For re-usability they’ll want an engine that can withstand a lot of cycling.

    2. Godzilla

      IIRC Orbital tried to purchase Merlin engines from SpaceX and failed. So I am not sure how open they would be to licensing.

      1. ken anthony

        Either they didn’t make a good enough offer or SpaceX isn’t making them fast enough for their own expected usage. Countering Elon’s willingness to license (only read re: Dragon) is his desire to keep his competitive advantage.

        Perhaps after Raptor (will it be methane?) he’d be more willing to make the Merlin available.

  3. Josh Reiter

    Well it could be not so much the length of time but the amount of fiddling with it. I’d imagine in testing your taking apart messing around and putting back together things a lot more because well your testing it. You are trying to come close to the margins of breaking it in some sense; gotta find those margins. I guess in terms of length of time it would maybe be more like, this unit was ‘tested’ the equivalent of one normal production units lifetime within a matter of weeks.

    1. ken anthony

      Generally, you want to isolate and test in the actual environment, which you can’t really do here. Isolate can mean all up… So you run the engine for more than the longest as you expect to and do that repeatedly until the thing breaks. Then you look at the thing that broke, including using a penetrating dye to show up flaws you wouldn’t normally be able to see.

      My dad used to do that for an aerospace company that made golf club heads. They would test each finished head nondestructively for flaws. He was an A&P licensed mechanic, but did some odd things when not supervising jet engine manufacturing. It was a big joke for him that when he first worked at Lockheed on the Tristar coming from Boeing (remember the I-5 sign that said, ‘will the last person to leave Seattle please turn out the lights’) he was a ‘cabin furniture.’

      Or you run just a part like a pump until it breaks.

      That might actually be a good use for a Bigelow habitat as an orbital engine test facility. Not that they would fire the engines there (although two opposing they could) but that they would recover engines that have gone to orbit and test them.

      1. ken anthony

        One time my dad signed off on a presumed drug smugglers plane which landed on a dirt road near our house in the high desert (near Mojave, windiest place I ever lived. We would watch continuous dust devils in the valley below.) They’d damaged it on landing and it required someone with an A&P license to sign off on the work.

      2. Frank Glover

        It occurred to me long ago that once it’s practical enough to get there. the surface of the Moon could be an effective test range for various kinds of engines, in the more realistic vacuum and deep-space conditions.

        Not to mention isolation, where advanced nuclear-thermal might be involved…

        1. ken anthony

          Testing nuclear engines on the moon would solve the Fermi paradox for us. If anybody is out there they would realize we haven’t grown enough as a species and would establish the quarantine.

  4. MfK

    The engines on the last Falcon 9 flight were Merlin 1Cs. Those are going to be replaced by the Merlin 1D, a significantly different engine. Perhaps the life issues are being addressed in the 1D.

  5. Vladislaw

    I thought a disposable engine is maximized for weight and the few actual firings it will go through? The more firing the more you have to beef it up. I thought Musk had mentioned that the engines for resuable rockets will be strengthened a lot more and able to do repeated firings?

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