30 thoughts on “Static Fire”

  1. Last night I spent about five minutes doing some really rough comparisons of Raptor exhaust static ram pressure versus older solids or rockets like the Titan II. Due to the higher ISP, the exhaust velocity should be very much higher, and is likely producing forces well beyond what concrete blast defectors encountered back in the 50’s and 60’s. From reading some the period reports, the reason the military used concrete, and then covered it with various refractory mixes common in metal foundries, was because it was cheap, cheap, cheap.

    I didn’t spend time trying to figure up the Raptor’s exhaust pressure, temperature, and molecular weight to firm up any comparisons, since I’m sure SpaceX is working the problem, and if I kept Googling I’d probably find all the relevant equations in an old NASA technical report. Of course placing an extremely heavy, crude spring scale under the pad would produce the answer, too.

    1. Just curious to consider whether water in large quantities would help or make this situation worse. I know it supplies acoustical suppression for Falcon 9. What about in this scenario? Hard to imagine how you could get cheaper than that.

      1. My guess:
        One issue with water suppression is that it works great when you have plenty of water. The thing about Starship is Musk wants to land and return from other planets with it. What then to do about water suppression for return? You will need less engine, but what if you didn’t need water suppression at all?

        1. Good point. So maybe they need to try various rocky surfaces? They won’t have this luxury on the moon for example. Does crushed concrete make for a good simulated regolith? Excellent topic I hadn’t thought of before…. Details, details….

          2. The landing rockets planned for the Lunar Starship are something like Super Dracos situated about 1/2 way up the Fuselage.

      2. Water at Boca might be difficult since they are only a few feet above sea level. The civil engineering to make it work would be immense and the current test stands would have to be rebuilt – runoff there would flood the entire area. Maybe more practical as part of the OLM under construction – it’s going to be well over 50 feet tall from the looks of the legs they’ve built already.

        Even so would they use sea water or fresh? Maybe tap into the Rio Grande? EPA would likely get involved.

        1. Definitely makes more sense for Super Heavy. The P2P scenarios have it launching from a sea based platform. But of course there are the land-locked cities and doubtful in every case they are going to make a lake to accommodate SpaceX.

    2. The Raptor exhaust is pretty benign. The mother of all flame deflectors was for the Saturn V, which had to handle 26,000 pounds/second of exhaust at about 9,300 feet/second. They resurfaced it with fireclay after every launch. It didn’t provide the worst environment, however. That was the province of the Shuttle SRBs, which spewed out 23,140 pounds/sec of corrosive, abrasive, and much hotter exhaust at about 7,800 feet/second. Lots of water, and a resurfaced flame deflector every launch.

      1. When you’ve got a huge overall budget and a very low flight rate, the concrete/refractory approach makes sense, as the up-front cost is very low compared to anything else.

        But the resurfacing is certainly a major issue if you’re planning for an extremely high flight rate. Refractories typically take a couple weeks to fully cure. Re-pairing refractory coatings after a single use would generally be a non-starter in industry or commercial use, due to labor cost and down-time.

        I’d suggest a wall of stainless steel water cooled pipes, perhaps brazed or welded together like an RL-10 engine, though something more like a loose mesh of water-cooled pipes might be better at damping the acoustics and shock waves.

          2. Willy Ley’s old book on Peenemunde says operational V2 crews created a launch pad by pouring liquid oygen on the ground. Then they’d sit the launch ring and and cone on that.

  2. A question for all the rocketry and aerospace veterans here: When you watch the various live streams of these tests, do you frequently mute the audio commentary so you don’t have to roll your eyes or fight the urge to bang your head into your desk? I find myself doing that a lot.

      1. He at least has done some research. I just checked the LabPadre live feed. The audio commentators missed the static fire because they were busy reading super-chats. Finally, as the dust cleared, they realized that the engine and fired, and said “Well that wasn’t very nice.”

        During a previous test fire I listened to the NASA spaceflight commentators discussing whether the “blue glow” of the venting was Cherenkov radiation, which then generated more audio commentary debunking the idea, which nobody else had advanced, that the Raptor engines use plutonium, before one commentator read the live chat to find out the blue glow was just the back lighting from Hoppy. And it often is much worse than that.

        1. To be fair though, they don’t know when it will happen and they can’t just sit there not saying anything. I’ve enjoyed Everyday Astronaut’s streams but in the test fire today, he was overly excited after it happened. I get that people are enthusiastic about stuff but I don’t quite empathize with it. To me, it was rather boring and anti-climatic but I did enjoy the talking and Q&A before and after.

          Funny part was how his audience trolled him into saying Mike Hunt and him not getting it for quite some time.

          I’ve been looking for more YouTube type of resources, since digital print hasn’t been keeping up, and there are more popping up. A while back, I suggested to the Space Show that they get in on it but the host wasn’t very receptive. Kinda sucks because I think he would do a good job.

    2. Somewhere in the audio commentary in Rand’s link above they said that if you pay for your stream you get a link to a video feed without the running commentary.

    3. The worse for me is still “NASA Spaceflight”. But yeah, the commentary is piss poor. I suspect it is hard to find people willing to watch what is going on in Boca Chica Texas. If not for SpaceX, nobody would want to know what is going on in Boca Chica Texas. I’d need a few drinks to have anything interesting to say about Boca Chica Texas. Alas, SpaceX doesn’t provide clear time lines for tests, and I’m glad they don’t. But without time lines, it is hard for media to follow, which I don’t mind at all, because I can mute.

    4. Yes.

      The commentators are annoying but I believe they are unpaid volunteers and the site still has to pay the bills. From reading the chats, the typical comment is by a dorky teenager and mods / commentators constantly have to both police stupid comments and acknowledge the donors.

    5. I know what you mean. I don’t watch any of the livestreams. First, because, even as a retiree, watching the equivalent of paint drying for hours in the hopes of catching a few seconds of interesting stuff doesn’t appeal. Even I have better things to do with my time. Second, the commentaries are usually beyond dumb. Third, anything really worth looking at will be quickly clipped and posted and can be looked at in a short form not long after it occurs anyway.

      I am particularly struck by the contrast between, say, nasaspaceflight.com’s excellent, commentary-free 10 – 15 minute daily digest videos of all Boca Chica doings with witty captions added – based on raw footage by the peerless and tireless BocaChicaGal Mary – and the ear-bleedingly unlistenable and endless livestreams done by the same organization. Jekyll and Hyde.

  4. Just looking at pics, the Saturn 5 pad had an elevated platform with gas ducting underneath something that looks 20 feet thick shielding the rocket from debris. Starship’s pad looks like it has no shielding for bouncing concrete chunks knocked loose during firing.

    1. The Saturn V pads were built with a bigger rocket in mind. Tne elevated platform is due to the nature of Florida barrier island soil (there’s no bedrock). It’s charitable to call the flame trench “gas ducting.” It’s concrete over brick and there’s no shielding protecting the rocket from liberated debris. You can look up video of an incident where a Shuttle liberated loose bricks that flew up in the air. The water spray on launch pads (see “rainbirds”) is for sound suppression.

      Musk is steadfastly doing the minimum necessary, and adds more when the previous minimum was not enough. His plan for the KSC Starship pad included steel pipes with water flowing inside them to carry off heat (and thus expended exhaust energy). He just stated (you can look it up on twitter) he now intends to do the same at Boca Chica.

  5. The static fire does not appear to have been an abort, just very brief, which is the usual for Starship static fires. (Though I can sure see how it looked like an abort).

    There’s a guy on twitter who occasionally leaks SpaceX insider info. He’s rumored to be pretty well connected at SpaceX. 🙂

    “Elon Musk
    Good Starship SN8 static fire! Aiming for first 15km / ~50k ft altitude flight next week. Goals are to test 3 engine ascent, body flaps, transition from main to header tanks & landing flip.
    3:59 PM – 24 Nov 2020”

    2. There was an abort earlier in the day – I assume that’s what Rand reported about. Several hours later came the actual SF.

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