sevenperforce

Makes perfect sense. I will note for what it’s worth that the word you’re looking for is “ordnance” not “ordinance”. The former means artillery or other ranged weaponry; the latter means a law or regulation.

Make sense. As far as we know, antimatter has positive inertial and gravitational mass, but you could very easily envision a fictional universe where it does not. And so in this fictional universe, applying some sort of current or field to antimatter contained in a self-sustaining inertial magnetic loop creates a “dark matter interaction field” which produces apparently-reactionless thrust by pushing against dark matter particles. Then the reason for gee-limiting the drive is trivial: the antimatter containment loop won’t remain stable if it is pushed to over 3 gees. As a corollary, any non-negligible acceleration applied to the antimatter containment loop by an outside force will make it fail, so ships can’t carry missiles with these drives. The point is that ships would not be able to carry missiles. I mean it seems like your idea would give all missiles infinite range, allowing them to pursue ships infinitely and become relativistic kill vehicles capable of taking out planets, but if you’re interpreting your rule to do something different from what you said your rule would do then I suppose it could do something different.

Did you read my post? I literally said that if you don’t want missiles to be able to outrun ships, simply say that missiles can’t use the fancy reactionless drives that the ships use. So the missiles can use conventional rocket propulsion to accelerate at high speeds over short distances, but they cannot catch up to the constant gradual acceleration of the spaceships over long distances.

I have a much simpler solution. If your spaceships have fancy reactionless drives that can accelerate the spaceships at up to three gees indefinitely, and you want missiles to be able to catch up to them, then just don’t give the missiles fancy reactionless drives. Make up a reason. Say that the reactionless drives are very bulky, or perhaps they are too expensive to use in missiles, or say that a human is required to operate them. Or, maybe best of all, say that the reason the drives are limited to three gees is that they are very sensitive to acceleration and so as a corollary one drive cannot ever be transported by another drive or it will become unstable and explode. This would also mean that a spaceship with one of these drives cannot carry shuttles with reactionless drives, so the shuttles need to have ordinary engines. All that is much simpler than trying to invent physical answers for things that already break physics.

If a vehicle driven by nuclear pulses via pressure plate had a less massive pressure plate then it would have a pressure plate that was less massive. I’m not really sure what that is supposed to suggest. Decreasing structural mass is always good for rocket design, of course; every kilogram of reduced structural mass is an extra kilogram of payload. But that doesn’t seem to have any connection to high-acceleration solid rocket boosters. A lot of these questions generate tautological answers. What happens if you decrease the structural mass of a rocket? Well, if you decrease the structural mass of the rocket, then you get more payload, regardless of what kind of rocket it is or what propulsion system it uses. What happens if you had a spaceship that could accelerate at three gees for three hours? Well, you would have a spaceship that could accelerate for three hours at three gees. What if you had a special drive that could turn off gravity? Well, I suppose you wouldn’t have to worry about gravity. I’m not trying to discourage you from learning about these things; I’m just very confused because you don’t seem to be. The United States government found the Nike Sprint missile to be very practical, until they decided it wasn’t.

The Hercules X-265 first-stage booster wasn’t magic, but it was unique; it used zirconium in addition to aluminum as fuel and the base was smokeless gunpowder mixed with nitroglycerin. It had extremely high burn rates as a result. But with high burn rates comes low burn times and low total dV. That’s why the Sprint needed two stages, after all. The high acceleration was required due to the low intercept window for re-entering Soviet warheads. The high acceleration was, in every other respect, a bug rather than a feature. A high-acceleration solid booster is a terrible idea for creating an SSTO.

It doesn't quench combustion; it just kills thrust. The blow-out panels on US cold war solid-fueled ballistic missiles allowed the pressure in the chamber to vent. Without pressure in the chamber, the choke at the nozzle throat dies and all meaningful thrust stops. And since burn rate in a solid rocket is a function of chamber pressure, this also reduces the propellant burn rate by orders of magnitude. I don't know whether the blow-out panels created any retrothrust or not. https://what-if.xkcd.com/24/ And the payload small enough. And even the answer given assumes multiple stages and presumably no structural mass other than the container for the estes rocket engine (which would certainly be more than the payload even if you were just gluing the motors together, thus requiring an even bigger rocket...). Well if you COULD make structural mass fraction arbitrarily low, then you could get to orbit with virtually any propellant. But obviously the lower your specific impulse drops, the sillier your mass fractions need to become. For an Estes model rocket engine that has roughly 100 s of specific impulse, you can reach orbit (~9 km/s) with a mass fraction of 0.01%. Sadly, model rocket motors typically have a structural mass fraction on the order of 50% in the casing and nozzle alone. I will also note that this makes no sense whatsoever. Air turns to plasma in front of a high-hypersonic vehicle because of compression drag. If you are trying to "deflect" drag plasma to create thrust, then you are attempting to create a perpetual motion machine, because whatever energy you can extract from the plasma was put into the plasma by robbing your vehicle of kinetic energy via drag in the first place. That won't work. If you propose having magnetohydrodynamic fields capable of accelerating the air plasma, so that you actually add energy to it, then that's great and all, but you're going to carry an energy source with you.

This is wildly, wildly wrong. I'll take your last point first. Scaling a rocket up improves the mass ratio only if you take advantage of the square-cube law. Simply making a vehicle longer is a linear change, which won't improve the mass ratio at all; in practice, you'll end up needing additional stiffeners when you increase the fineness, so that makes the mass ratio slightly worse. Also, sanity check. Superheavy has 33 engines on it. Raptor 1 was around 2 tonnes; Raptor 2 is around 1.6 tonnes. A single-stage Superheavy would need fewer engines -- let's say 25 -- but that's still 40 tonnes in engine mass alone. Compare that to the ~13.5 tonnes of engines you were (inaccurately) claiming on the stripped-down expendable starship. Since structural mass is independent of the engines mass, using your own numbers would yield 145.5 tonnes which is already significantly higher than the dry mass you supposed. And you CAN'T simply scale up the Starship's mass ratio linearly to get here, because Superheavy is MUCH heavier than Starship. It has to be; it is carrying dramatically higher loads. The dry mass of Superheavy is generally believed to be on the order of 200-220 tonnes. Let's take that lower number (since we're not using quite as many engines). So an expendable Superheavy launched without payload, using sea level engine vacuum ISP, has 10.15 km/s of dV. Enough to make orbit empty, sure. Enough to carry meaningful payload, accounting for the added mass of a fairing, etc.? No. Silverbird estimates the payload of this configuration at 232-428 kg. Your math here is wrong. 358 s * g = 3511 m/s. Not a huge difference, but a difference. PICA-X is not immediately reusable, so that doesn't even begin to work. But while we're at it, where is this TPS supposed to go?? Superheavy is a lawn dart. All of its weight is on the back end. It will plummet back into the atmosphere tail-first and all those Raptor 2s will immediately turn to slag. And how is it supposed to land? You haven't reserved any propellant for a landing burn. Is it going to land horizontally? If so, you haven't reserved any structural mass for wings (or an explanation of how to get the center of mass forward enough to allow a horizontal landing). None of this makes any sense. No, your math and your foundational assumptions are wrong. The reserve propellant for a boostback burn does not even come CLOSE to being significant in comparison to the advantage of staging.

Hybrid rocket motors are chemical. Delta-V is a measure of the total velocity change associated with any single stage; it is not a function of propellant type. A better propellant type with a better engine cycle will have a higher specific impulse and therefore a higher dV for a given mass ratio, but that's something else entirely. Solid fueled boosters can absolutely be cut off. The ones the US created for ballistic missiles often had blow-out panels near the top to immediately kill the pressure in the combustion chamber and quench thrust instantly. Nothing about hybrid rockets or orion nuclear pulse propulsion lends itself in any way to that conclusion. Anything with a T/W ratio greater than 1 can be an SSTO if you can get structural mass fraction low enough or specific impulse high enough. Slight caveat to 1) -- an SSTO can be as light or as heavy as you want; the issue is that it needs to have a low structural mass fraction. I know that's what you were getting at, but...yeah.

I built a HTOL SSTO which can trivially deliver 5.2 tonnes of payload to LKO and return to the KSC: And it's got two long Mk2 cargo bays worth of volume, so it's not difficult (at all) to utilize all the payload capacity on each launch. Construction of an ISRU single-stage-to-anywhere in 5.2-tonne modules will take a minute, but it's entirely doable. The Dart engine is also mounted on a docking port so it can be removed and transferred to the orbiter at the final stage of assembly. However, I do not think it is possible to get off Eve with only a single Dart. EDIT: Turns out I had gravity set to 48% due to some earlier testing I had begun and then forgotten about, so this DEFINITELY is not nearly as powerful as I thought. However I'm sure I can still manage.

I got swag

If you keep the combustion localized that will be the bulk of the waste heat. One idea for creating a pulsed detonation engine would be to have numerous small combustion chambers where the detonation in one chamber provides direct thrust but also rotates the turbine which compresses and initiates the next detonation, and so forth all around. Like a weird cross between a reciprocating engine and a turbine engine and a ramjet.

I think the heat is vented via the repulsors, no? Like, the atmosphere you’re compressing and igniting is what carries the heat away.

Either will work but mechanical counterpressure is harder to get correct

Cold fusion. A real-world analogue would use primarily electrohydromagnetic systems so it wouldn't be an issue. None of this makes sense. High-hertz detonation engines can absolutely be scaled up for an airbreathing spaceplane but that has nothing to do with anything.

Ironman has to be, hands-down, the coolest character in the MCU, at least as far as technology and engineering is concerned. In particular, the way his suits function and fit together just feel intrinsically real and believable. And of course, we have real-world 3D-printed titanium suits lightweight enough to walk around in, like the one Adam Savage built: Not only is it actually bulletproof, but it can actually fly, with the right attachments: The crazy "arc reactor" power source and the associated repulsors, of course, are what make the suit function in-universe. The in-universe explanation is that the repulsors produce a "muon beam", and we know they require palladium, so it is likely that they are supposed to be a cold fusion reactor which creates a stream of muons which can be "tuned" to decay at a given location, allowing them to dump their energy wherever it is wanted. This way the reaction mass is the surrounding air which is simply supercharged with a decaying muon stream. Of course, cold fusion doesn't exist and palladium-catalyzed cold fusion wouldn't produce muon beams anyway, but that's beside the point. People have done a lot of DIY adaptations of Ironman's repulsors, including lasers and even oxyhydrogen blasters. But, based on the way they look in the movies, I wonder if they could be replicated more closely with some sort of pulsejet or even pulse detonation engine. If we take a close look at the way the repulsors are depicted in the first film, a few things pop out: In the first gif, Tony is assuring Pepper that it's just a flight stabilizer and it's completely harmless. He hits the activation switch, and a few moments later, the repulsor starts to glow and the air in front of it becomes distorted, as if it is producing an invisible beam of heat. A moment later, you can see a flash along his forearm and then the repulsor erupts with a massive pulse of energy and thrust. That same flash along his forearm is some sort of energy transfer coming from the arc reactor in his chest, as seen in the second gif. So we have a mechanism of some kind in the hand which builds up energy and then is fed a little bit of whatever is coming out of the arc reactor; once it reaches the mechanism in the hand it produces a concussive/thrust beam. It feels very much like a buildup and combustion/detonation inside of a pulsejet or pulse detonation engine. The major advantages of a pulse detonation engine are that they can be miniaturized and that the detonation itself provides the necessary compression, obviating the need for a compressor or other fan in an airbreathing engine. This is precisely what a real-world ironman suit would need, given that there is no room for any visible compressor fans (and such fans are extremely heavy). I wonder how difficult it would be, really, to fit something like that into a mechanism like this.

You need pressure on the chest or you won't be able to exhale properly.

Yep. Pulses are required when you have an energy source you can't control. Pulsed propulsion is not a solution to things like heating, weight, efficiency, thrust, etc. In a detonation wave, the supersonic combustion process itself serves to compress the fuel, meaning that (a) you don't need a heavy compressor and (b) it can operate at any speed from a standstill up to Mach 5 or beyond. And a notional PDE would have up to 1000 pulses per second, making it effectively continuous from an engineering standpoint. I've always thought Iron Man's repulsors looked like some sort of pulsed detonation gadget.

Yeah all my kids got those too.

Something something heat something pusher plate something melt? Antimatter is a PARTICULARLY bad way to build a pulsed rocket, because the only way to pulse antimatter is to have antimatter pellets in little containment vessels that can be “switched off” and go boom. Even the most advanced conceivable antimatter containment vessels mass orders of magnitude more than the mass of antimatter they can contain. As with anything else impacted by the square-cube law, you’re going to do better with a larger vessel than a small one. So you’re just torpedoing your specific energy right out of the gate by using pulse units instead of having a large containment vessel that slowly releases the antimatter into the combustion chamber. Another thing @Spacescifi seems to consistently ignore: neither fission explosions nor fusion explosions nor antimatter explosions are a source of propulsion. They are all a source of energy. Energy alone does not produce thrust; you need to put that energy into a reaction mass (commonly termed propellant) or you don’t move. Every rocket has a source of energy and a source of reaction mass. Sometimes they are the same; sometimes they are not. Even in classic Project Orion, exploding the thermonuclear warhead doesn’t do anything to the pressure plate. It’s just an extremely bright flash of light, nothing more. The only reason you get any effect on the pressure plate is because the warhead has a bunch of tungsten on one side that is vaporized by the flash of light and flung at the pressure plate at ridiculous speeds; the tungsten vapor bouncing off the plate is what provides the impulse. Project Orion is just a very inefficient nuclear thermal rocket which uses tungsten vapor as its propellant and thermonuclear explosions as its energy source. In this sense it is no different from a NERVA which uses liquid hydrogen as its propellant and a nuclear reactor as its energy source, or an ion thruster which uses xenon as its propellant and solar panels as its energy source. Even the RS-25 SSME engine doesn’t technically use the same energy source and propellant. The RS-25 burns liquid oxygen and liquid hydrogen together, but it injects additional liquid hydrogen as additional propellant along with the steam produced by the hydrolox reaction. By adding extra liquid hydrogen, the molecular weight of the exhaust goes down and so the specific impulse goes up. All that to say, the fundamental concept of a pulsed antimatter engine is TERRIBLE. Antimatter is the perfect energy source. It requires no ignition. It reacts with literally everything. It can be most easily manipulated and controlled in small quantities. So if you have a way to contain and release antimatter, then fire that stuff into whatever propellant you choose and enjoy arbitrarily high specific impulse.

A quick observation: a plug nozzle is still a “bell” nozzle; it has simply been turned inside-out. A plug nozzle will be less efficient (both in terms of specific impulse and T/W) than an equivalently-sized bell nozzle at any given pressure. Its advantage is that it can be more efficient at a broader pressure range, so it is a good sustainer design.

No, because laser beams are not created by focusing light with mirrors. In the business world it is common to hear people discuss “laser focus” which always makes me chuckle. I suppose people assume that a handheld laser pointer consists of a tiny flashlight and a complex array of mirrors that turns the diffuse flashlight rays into a parallel stream of light. But that is not the case at all. The light coming out of a laser pointer did not originate from a tiny flashlight or other conventional light source. What do mercury lamps, lightning bugs, an old-fashioned TVs have in common? One thing: fluorescence. Numerous elements and chemicals have the ability to absorb energy (in the form of heat, electricity, chemical reactions, or high-frequency light) and then radiate it out as low-frequency light. Even your skin has this capability. Lasers do use mirrors, but they use mirrors to trap light, not focus it. Lasers consist of a fluorescent material which is placed in a mirrored cavity such that only a specific wavelength of fluorescent light can escape. The material is then “pumped” full of energy from an outside source, producing a perfectly parallel beam of escaping fluorescent light. Now, you could certainly use mirrors to focus sunlight to provide the “pumping” mechanism for a laser. But the laser itself needs to be made of some fluorescent gain medium material.

Anything above .22LR will certainly penetrate, but I don’t imagine a tracer or incendiary would make much of a difference compared to standard ball ammunition. It’s not as if the tanks are filled with an explosive mixture, after all; both oxygen and methane are quite safe as long as they aren’t mixed with each other. Obviously if the round punctured the common bulkhead or the downcomer it would be a different matter. As others have pointed out, the size of a bullet hole puncture is pretty insignificant compared to the size of Starship and the amount of propellant on board. Bernoulli’s equations tell us that to a first order, the flow rate at a 2-bar differential through a 5.56-mm hole is on the order of 1.1 gallons per minute. Won’t be missed. The more likely failure mode from a ballistic impact, imo, would be pressure-driven tensile failure propagation from the puncture point. I don’t know enough about metallurgy to hazard a guess about whether 304 stainless (or whatever alloy they’re using) is resistant to failure propagation.

People underestimate the size of SSMEs. Just one weighs four times as much as the entire (empty) Electron first stage.

And let's also note that the 16-tonne engine compartment would exceed the lift capacity of the Chinook itself. Certainly a far, far greater load than any skyhook recovery ever attempted.