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sevenperforce

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Everything posted by sevenperforce

  1. I don't know. Possible that since it is an expander cycle, they want to maximize the surface area to maximize the power output of the cycle. The more heat they can acquire, the higher chamber pressure they can achieve. That's particularly important with methalox, after all, since methane has a lower heat capacity than hydrogen. It's a 3D-printed engine, I believe, so that makes designing the cooling channels for maximum heat takeup a little easier than it otherwise would be. I'm guessing it's a pure dual closed expander cycle without a split. But who can tell for sure? Interestingly enough one of their patents contemplates first-stage recovery using ducted lift fans located perpendicularly up the sides of the first stage.
  2. Dilithium crystals don't provide enough lithiums to counteract flux capacitor depression. The only true solution is the trilithium crystal. 50% more lithium and 100% as much crystal.
  3. I didn't see a thread yet for this, so I figured why not go ahead and talk about it? Spanish smallsat launch startup with a dual-regeneratively-cooled methalox aerospike engine. Or, more accurate, a "spike" engine; there's no truncation of the nozzle. Here's one of the hot fires: Some of their corporate material suggests a two-stage reusable rocket: This cutaway seems to confirm an annular chamber: I do love a dual-expander cycle methalox design, if that's what they're doing here. Won't have a TWR ratio as good as staged combustion but there's still something very pure about it.
  4. One of the issues with a prepared landing surface is that you can end up making the problem worse if you’re not careful. As long as your landing site is sufficiently flat, your landing engine plume is **probably** only going to spew dust everywhere; there’s a risk of excavating larger pieces of debris but there’s also no guarantee there are any such pieces of debris to be excavated. In preparing a pad, you’ve gotta be 100% certain that your preparation will result in a surface that’s truly impermeable to an exhaust plume, because otherwise you have basically just created a giant layer of potential shrapnel.
  5. Little shade being thrown here: The focus on dexterity and mobility is definitely making me feel some kind of a way. (Come on, Iron Man suit!)
  6. Interesting that they're using TEA-TEB for a hydrolox engine. Ordinarily you can just use an augmented spark igniter because hydrogen ignites so easily. I wonder if they're going with a hypergolic starter because it ends up being simply lighter for a bunch of different engines, or if they're doing a hypergolic start now but something else in the future. It was interesting to me that the Ars Technica article didn't talk about it being an aerospike. It may not be exactly an aerospike after all. Higher than some RL-10 variants -- that's quite the boast! It sounds less like a proper aerospike and more like a bimodal engine that operates as an aerospike at low throttle but as a fully-expanded vacuum engine at high throttle. The patent may prove instructive: In other words: at low throttle for landing, there is induced flow separation at the inflection point 68, making the entire engine act as a conventional aerospike. However, at high throttle, the inflection point 68 acts like a secondary throat and is the origination point for the bulk of expansion, allowing the entire cavity to serve as an expansion nozzle without any aerospike effects required. As envisioned by FIG. 8, it is even possible that no outer expansion surface 66 is required at all, allowing the inflection point and the nozzle throat to be one and the same. It also appears that the inflection point 68 may also be the gas bellows seal at the gimbal joint.
  7. Dunno. That would require higher performance rockets probably as you don’t have the Earth’s turn to assist you on the way up. Proton and Shuttle did just fine launching ISS modules into inclined equatorial LEO, not sure if they have the same payload capability to any polar orbits. As others have pointed out, there are really no countries with launch sites at higher latitudes than Baikonur, so there's really no need for a higher inclination. Also keep in mind that for everyone else, a higher inclination means a shorter launch window. A perfectly polar orbit means an instantaneous launch window for everywhere other than the poles. So that's annoying. I've seen research that shows sintered regolith construction to be pretty promising. No binder needed.
  8. So, magic. The answer, FWIW, is that you can give a chemical rocket engine almost arbitrarily high T/W. A Merlin 1D at full thrust pushes a T/W ratio of around 180 which is certainly more than you'd need for any conceivable application. It's actually one of the most overpowered possible designs. It will be a relativistic projectile within a few hours. Solid-propellant rockets are chemical rockets. Yep, this should work. You can have explosives in a semiliquid form that are pumped into a very wide cylindrical chamber, then have the doors open. Ignite it as you switch the linear accelerator on. T/W ratio is arbitrarily high.
  9. True. However, there are situations where engines are more fault-tolerant than wings; for example, fewer weather constraints. There were numerous shuttle missions where re-entry and landing had to be delayed due to inclement weather at the landing site. In contrast, propulsive landings (at least of the SpaceX variety) couldn’t care less what the weather is like. If Shuttle had possessed the ability to abort or divert landings via onboard jet engines as originally imagined, this would have been ameliorated a little. Yeah, the propulsively-landed horizontally-flown spaceship of science fiction is super cool but it is really only needed on an undeveloped world. So far we have not really had reasons to bring significant downmass. If we had a colony on another planet with an atmosphere similar to Earth’s, that would be a meaningful consideration, but that doesn’t appear to be on the horizon in this solar system. Even Shuttle had oversized wings for ordinary landing because of crossrange reqs. The Air Force wanted to be able to do polar dogleg launches with a landing at the launch site after a single orbit, so it needed insane amounts of glide. Without those requirements I believe the Shuttle would have been closer to a pure lifting body design.
  10. They must be very concerned about OLM debris and engine-to-engine fragging. Putting each of the Merlin engines inside a frag shield proved to be a very good move for Falcon 9.
  11. Well we could also suppose that rockets are powered by unicorn farts, but that wouldn't be any closer to reality than whatever this is. ~16 were most certainly not built into the contract from the beginning. The "~16 launches" bit was part of an attack ad from Blue Origin. Rather, as Elon points out in the tweet you quote, the total tank capacity of Starship is 1200 tonnes, so with 150 tonnes of propellant delivered per fully-reusable launch, that's a max of 8 launches. Elon further notes that they may be able to lighten the lander vehicle enough that it could make the trip to the moon on as little as half a tank, necessitating fewer prop launches. However, these would still be fully-reusable launches. NONE of this has anything to do with Starship tankers flying expendable. But even if it did, it still wouldn't be a reason to suggest that there was something amiss about the contract price. NASA is paying for a service, not a series of launches. If SpaceX decides to reconfigure its launch system to include expendable tankers in order to do the whole thing in fewer launches, that's up to them to pay for (or reap the benefits of); NASA doesn't care. NASA only cares about the whole system meeting certain safety requirements. Which is why it's so puzzling that you keep trying to estimate the mass of an expendable Starship, when Elon already stated it. By this I suppose you mean an SSTO expendable Starship. If that's the case, then no, not so much once you add sea level engines. And SpaceX doesn't want to operationally throw away engines. Gross mass is all well and good, but the bottom line is money. SpaceX wants to deliver a certain amount of payload (usually propellant) to orbit. They will endeavor to do so at the lowest possible cost. Throwing away engines to save on propellant only makes sense if propellant is very expensive or upper-stage recovery is too long a pole. It was not, and even if it had been, that wouldn't be meaningful. If SpaceX can do it cheaper than expected, more power to them.
  12. I was able to pull together a basic B-2 clone that didn't use any reaction wheels and relied on split aileron differential drag for yaw control, but I had to use a KAL for it so it responds to manual input only.
  13. Do they, tho? I was under the impression that, while e.g. the "Big-S" wing parts indeed have variable thickness, they're still symmetric and thus have zero camber (and thus work equally well even if placed upside down). Let me do a quick test and see. Yep. Those rear wings are rotated 180 degrees and they have the exact same positive or negative lift as the front ones all the way.
  14. Why are you doing all these random estimates and guesstimates when Elon has already said how much an expendable Starship would mass? 40 tonnes dry, 1200 kg of propellants. As an SSTO, though, you'd need to add six more engines, so tack on 10 tonnes more. So 50 tonnes dry. ~16 vs ~4 is a totally different question than anything related to SSTO applications, so that's immaterial.
  15. I think MOAR BOOSTERS are needed. Specifically on the near side of the vehicle.
  16. Now, if you could mount the boosters on either side of the orbiter and send it up in parallel launch style, that could work.
  17. Yeah, and even weirder he conceptualized launching it on a pair of Falcon 9s: Putting in SuperDracos for aux is nice and all but it's not like they're going to be a meaningful contributor during abort. Eight SuperDracos together produce only a quarter the thrust of a single sea level Raptor 2. Could be useful for moon landings though.
  18. That's how most of the flying wings I've built in KSP fly, but in real life you have to be able to have full control in an engine-out scenario, which is where you run into problems. A more workable solution is differential drag via split ailerons. Rather than just having a single aileron control surface at the tip of each wing, you have two overlapping ones, and so you can either deflect them up or down in a pair (to control roll) or you can deflect them in opposite directions to induce drag. By making the tip of one wing more draggy than the other, you turn the plane toward that wing in the yaw axis.
  19. I beg to differ. Flying Wing Starboost88 Beautiful! Of course I mean in real life. But yes. I'm trying to think whether there is any better orientation to come up with in terms of engines than the one in the NASA study. Excited to see what you come up with!
  20. Unrelated to the launch, I'm surprised I never saw this anywhere on this thread. It's a cool concept from a couple of years ago. Full concept art gallery is here.
  21. So not only magic Isp but magic engines. Because either those engines rotate or are duplicated and still don't overdo the mass issues of SSTO. And of course all those SF vehicles somehow don't abuse the landing pad (Kirk landed his Klingon Bird of Prey in a 20th century park, Stormtroopers stood nearby the Millennium Falcon when we first saw it take off) even with a TWR>>1. On the other hand, Arthur C. Clarke was right about the definition of "magic" and such things might well be possible well before the 2200s. Oh yes, magic indeed. Of course, the slower the exhaust is moving, the less dangerous it is to be in the vicinity. And fortunately the ground has a bunch of thick air around it which tends to be useful for such things. I've always wanted to come up with a realizable way that you could have air intakes with extremely high bypass in one direction and progressively lower bypass in the other direction so that you wouldn't need variable geometry for an airbreather. Just rotate the nacelle based on speed and altitude.
  22. Oh, that's very cool! One of the specifics about the bi-directional flying wing idea is that it's supposed to NOT be symmetric in different flight modes. But yeah, very nice job.
  23. Looks like they used an Einstein doll for the zero-g indicator. And nose cone deployment started! All systems go.
  24. Entry burn start. Nice pretty Eye of Sauron. I love seeing that hard-over body lift turn into the wind at the end of the entry burn. SECO -- we have Endurance in orbit! Landing burn, and down! Very shaky coming in, though. And a nice clean separation from the second stage. Endurance is flying free.
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