sevenperforce

Our Milky Way galaxy has multiple dwarf galaxies and stellar clusters orbiting it. The size of a galaxy is dependent on the size of its central black hole. We don’t yet know why there seems to be a big jump in supermassive black hole sizes.

Z-pinch uses a chemically-induced magnetic flux collapse to trigger a fusion pulse. It’s ideal in a vacuum but it can be done anywhere, really. There are no actual magnets involved. There is no pure fusion . . . anything. There are no pure fusion bombs. If there was a way to directly harness pure fusion fuel then you could make it into a rocket engine but at no point would you ever remotely consider a pusher-plate design. I don’t know why you think a pusher plate design has special SSTO capabilities. Pound for pound, for a given a fuel type, a pusher plate will always be the least efficient design. If you want more payload, just build a bigger rocket. If you want to write a science fiction story in which a pusher plate design is common place, for whatever reason, just make it so. Say that fissile material is extremely accessible and so everyone has nukes laying around. Say whatever you want. But know that the only possible universe where you would ever consider using a pusher plate is the universe where it is the absolute last resort. They won’t be. By basic rocket science definition, the propellant consumption and TWR of a rocket engine will always be better than a vehicle which uses the same fuel in a pusher plate design. A Project Orion design is wildly inefficient and has abysmal TWR and abysmal specific impulse for the type of energy it is harnessing. The only reason anyone would ever consider using pusher plates is if they have an energy source like nuclear bombs, which are so wildly energetic that you can afford to waste 90% of the energy but have a minimum size. Nooooooo. If you have pure fusion ANYTHING it will be better than a pusher plate.

Chemical rockets have very high TWR so if all you need is getting off the ground, they are your drug of choice. The pistons are able to handle close proximity nuclear explosions. That’s because the Orion concept is 100% not useful as a shuttle. It’s for lifting very massively heavy things into a trajectory that requires ridiculous dV. Conveniently, nuclear explosions are known to generate a great deal of heat. I would be much more concerned about landing somewhere without a convenient source of refueling. I don’t know of any place where I can casually pick up a few hundred nuclear weapons. Well I don’t advise trying to hold a fusion reaction in a jar. I don’t advise holding any rocket fuel combustion in a jar. That is an inefficient path to propulsion. If you want propulsion, put a hole on one end of the jar and then it will produce thrust.

Modern solid high explosives can be up to around double the specific energy of TNT. For a HE-based pulse pusher plate propulsion system, you would want an explosive with maximal specific energy. For the highest specific energy, you’ll probably want a mixture of ammonium perchlorate and powdered aluminum. You’ll also need something to bind it together into a putty of some kind, like polybutadiene acrylic acid acrylonitrile prepolymer, which also burns well with ammonium perchlorate and increases specific energy. One advantage of this high explosive mixture is that you can make very small “pulse” units and therefore extract more of their energy by detonating them against a conical pusher plate. In fact, if you really want to extract the maximum energy, you can detonate them inside a sphere with an opening on one end so that all of the gases from the explosion flow out of that opening in a straight line. If you’re very very clever you can make the pulse units very small — only a few molecules each — and detonate many of them continuously in a giant cylinder with a hole on one end. The first all-up launch of the Saturn V knocked ceiling tiles loose at a distance of three miles, if I recall correctly. You don’t want to be anywhere near any rocket of any kind while it is launching. The neutron activation radiation range of a pure fusion reaction is measured in centimeters.

It is not. A pure fusion reaction produces no heavy nucleotides. A fusion-based rocket will produce no radiation pollution at the launch site. Not sure why flipping is at all necessary. Pure fusion reactions are not difficult to contain; they are difficult to sustain. So pulse-based fusion engines are a good idea, like the Z-pinch. However, all these designs can be scaled down to minimal size. A pusher-plate approach is ridiculously inefficient and unnecessary.

Ah, yes, I thought it was in there. For non-English speakers, “funny business” colloquially would encompass anything that feels like cheating or abusing the rules to unbalance the challenge. So, the reason the RS-68 on the DIVH is throttled down is to reduce prop consumption in the center core so that the side boosters run out of propellant faster and can be dropped at empty while the center core still has propellant. But in this challenge you can’t drop tanks, only engines, so there would be no reason to throttle down the center engine preferentially; if you need lower thrust you can either downthrottle all the engines or you can start dropping unnecessary engines.

This is a hybrid... high explosives are merely to gain some altitude without buring VTOL rocket propellant. That is absolutely the worst possible use of reaction mass. Rocket propellant in a rocket engine is specifically designed to exit precisely opposite the intended thrust vector with maximal efficiency. Rocket engines are a marvel of engineering. They are ridiculously efficient for what they do. Blowing up high explosives against a pressure plate "merely to gain some altitude without buring [sic] . . . propellant" is like trying to propel a racecar by stuffing hand grenades in the tailpipe to avoid burning fuel. A racecar has a perfectly good engine capable of burning perfectly good fuel at maximal efficiency; there is absolutely no reason to waste dry mass on hand-grenade starters. Any science fiction situation where pure fusion can be harnessed to energize reaction mass, you will be able to downscale to produce a pure fusion throttleable engine. The only reason the Orion idea ever existed is because fission bombs require a minimum pulse thanks to the critical mass rule.

I thought I said this before (apparently I didn't) but in the spirit of the challenge, no in-flight thrust limiter adjustments. If you wanna burn a NERV at 1% thrust, that's fine, but you can't change the thrust limiter later on. That's fairly true to life because real-world engines can't actually throttle that aggressively anyway so if you're going to build a sustainer architecture you'll probably use something that's altitude-compensating; if you're including a vacuum-only engine you'll just use ordinary staging. I think you'll find that the NERV and the Dawn engines burn so little fuel anyway that burning them at full throttle from the ground up isn't that significant of a fuel waste. My 6.55 km/s test run burned two NERVs all the way from sea level to orbit. Since we are using a vertical ascent and gravity turn anyway, a decent TWR off the pad (which is essential to SSTO architectures anyway) will get you high quickly enough that the NERVs will be useful very soon. An all-LF design!! Very impressive. I honestly didn't expect anyone to start with an all LF design but it does make intuitive sense. I think you could save significant weight by using fewer heavy shock cone intakes. I believe just one shock cone intake should be enough to power four RAPIERs all the way up. All visual mods are fine. I just don't want someone with an unbalanced physics mod messing it up for everyone else. Why did you use a fairing? I strongly -- STRONGLY -- suspect that just topping it with the Mk1 pod and the nose cone will have less weight and less aero incidence than the fairing.

Loved those photos and whatever visual mods you have. This doesn't have to be an Atlas LV-3B clone; you can make it as big or as small as you want, with as many or as few engines as you want. It's going to be to your advantage to drop engines, though. The goal is to reach LKO with as much remaining dV as possible.

Visual mods and part mods that don't impact physics are fine. Mod tanks are fine as long as they have the same mass ratio as stock tanks. I don't think part clipping will be a significant issue simply because this is a vertical launch with a gravity turn and so aero exploits won't be particularly significant. Mod engines are fine as long as their TWR and specific impulse is in line with stock engines. You're correct, the answer there is no; SRBs and Twin Boars would allow essentially ordinary staging and so that wouldn't work. You're welcome to use the Twin Boar or SRBs, of course, but they would have to go all the way to LKO. I suppose you could use the Twin Boar without any fuel onboard at launch, but that would be a waste since there are better engines. I was able to reach LKO on a fairly inefficient trajectory with 6,550 m/s of dV off a 240-tonne launch vehicle but I'm sure improvements are possible. I worry that players may just start building larger and larger vehicles; I may eventually have to put in a launch mass limit or weight classes. Also, it may be possible to hack the hell out of this challenge by spamming lots of xenon. If xenon makes the challenge trivial then I may have to ban Dawn engines altogether, or at least add a rule that nerfs them a little. So don't try that, haha. The spirit of the challenge is that you're supposed to light all the engines at launch like Atlas LV-3B or Saturn S-ID Super Atlas and drop them as they are not needed.

Most of us are likely familiar with the staging approach used by the Mercury Atlas LV-3B, where three engines were lit at launch but two were dropped during the ascent on a jettisonable skirt: Some of us are also probably familiar with the proposed Saturn S-1D SSTO, which would have repurposed a Saturn V first stage, with a modified thrust structure and jettisonable skirt, as an stage-and-a-half taxi to LEO carrying an Apollo crew capsule: Your mission, should you choose to accept it, is to build a vertically-launched SSTO which reaches low Kerbin orbit with the maximum possible dV. All engines must fire at liftoff; no thrust limiter funny business. You can drop engines, but you cannot drop tanks. You can use any engines you like, including engines from the DLC. Airbreathing engines are fine if you want to try using them, but you still need to use a typical vertical takeoff and gravity turn. Fins for control are okay, but wings and aerodynamic lift are not allowed. To keep everything equal, your payload is a single Kerbal in a Mk1 command pod. Recovery is not necessary. You just need to be able to reach LKO with the maximum amount of remaining dV *and* all of the tanks you launched with. There are a lot of ways to tackle this challenge and I'm not sure what a straightforward path would be, so feel free to experiment.

Launching humans without LAS is a non-starter. Starship Tankers + Starship HLS could readily do a Moon landing with a Crew Dragon, if Crew Dragon was given a lunar-return-capable heat shield.

I must have missed a step; what is this? A Raptor 2? An RVac?

Just slapped all five of my kids’ names on it.

Liability for refusal to deal is only triggered when the purpose and effect of the refusal is to totally foreclose a competitor from the market. For example, if SpaceX was the only launch provider, then refusing to allow Starliner capsules or Kuiper satellites to fly on Falcon 9 in an effort to protect Crew Dragon and Starlink would be an actionable refusal to deal. But since there are other launch providers theoretically available, refusal would not be not a market foreclosure and thus would not be considered an act of monopolization under §2.

Having just taken (and, miraculously, passed) antitrust law, I would tend to think that because SpaceX has already gone to such lengths to be vertically integrated, they wouldn't be liable under §2 for failure to deal unless they did something nefarious to Starliner or Boeing.

Giving this a touch more thought: what about dispensing with the zinc-air “battery” concept altogether and just going straight to a metal-oxide hydrogen generator? Sodium metal will react quite spontaneously and exothermically with water to produce sodium hydroxide and hydrogen gas. The same reaction happens for any of the alkali metals. The potential energy of the sodium+water reaction is 141 kJ/mol, and burning the resultant hydrogen in an air-hydrogen fuel cell gets you another 241.8 kj/mol. Given the 60% efficiency of a hydrogen fuel cell, the sodium metal + water + hydrogen pathway yields a specific energy off the fuel cell alone of 491 Wh/kg, nearly double that of the best lithium-ion batteries. Assuming you can in some way use a portion of the sodium+water reaction energy (let’s say 20% to give a Carnot buffer), that goes up to 914 Wh/kg. The zinc-water reaction is not nearly so exothermic or rapid, but it still produces up to 538 Wh/kg. Zinc oxide has the tremendous advantage of being thermally reduced back to zinc metal and oxygen gas. The reaction of sodium hydroxide with more pure sodium will produce sodium oxide and steam, and sodium oxide (like zinc oxide) can be thermally reduced back into sodium metal and oxygen gas. So there should be an alloy of zinc, sodium, and/or other metals which would react rapidly with water to produce hydrogen to operate a fuel cell and yet still be thermally reducible in a simple reprocessing unit. So your car could run on water and you’d just need to swap out your metal fuel core once a week at the gas station. Or, in the case of an electric plane, swap out the metal fuel core between flights.

COME ON IRON MAN SUIT

“I have a giant shock-absorbing landing pad. Better not land on it.” My guess is that the weight of a zeolite bed and pressurization system would be prohibitive at scale. There’s really no weight at all added by introducing electrolysis; the battery already requires an aqueous catalyst. That’s interesting. I’ve seen amateur cells set up where the oxygen-gathering side used steel wool but I suppose carbon’s affinity for oxygen makes it a better choice. But if increasing oxygen partial pressure doesn’t affect uptake at all then this is DOA.

We are pulling in the oxygen from the ambient air.

I’ve had a little extra free time on my hands lately, and instead of spending it on duteous pursuits as I ought, I’ve spent an inordinate amount of time watching YouTube DIY videos where enterprising souls are trying to make iron man suits, repulsors, lightsabers, and the like. It’s very entertaining. Some of these videos set me on a rabbit trail concerning battery specific energy and specific power. As we likely all know, one of the challenges in trying to get electric planes and electric flying cars is the competition against the terrific specific energy of hydrocarbons. The weight of the batteries required to generate enough power for sustained flight is just about prohibitive, and incremental advances in lithium-ion technology are unlikely to change that any time soon. One promising alternative to lithium-ion batteries is the zinc-air battery, where zinc reacts with air using a catalyst to produce zinc oxide and electrical energy. Because the air is one ion source, it has a very good specific energy (5-6 times greater than lithium-ion) and reasonably good specific power (about 30-50%). They do have some odd side effects, though. For example, because zinc oxide is heavier than zinc, the batteries get heavier as they discharge; for another thing they are tricky to recharge over many cycles and usually must have their zinc “fuel” reprocessed rather than simply being plugged into the wall. Now, if there was a way to catalyze a faster uptake of oxygen atoms by zinc air battery, then presumably you could increase specific power. If you could quadruple specific power, then zinc air batteries would dramatically outperform lithium ion batteries, perhaps to the point that they would become a viable alternative to hydrocarbons. It is worth noting that zinc air batteries are much cheaper, much safer, and much more environmentally friendly than lithium ion batteries. But how exactly would one quadruple the reaction rate of a battery? Here’s where it gets interesting. I freely confess I am no chemist, so this could be absolute BS, but it seems to me that if zinc and air reacts together at rate R, and air is only 21% oxygen, then zinc and pure oxygen should react together at 4-5R. If the reaction rate is 4 to 5 times faster, then presumably the specific power would also be significantly higher. Bringing canisters of pure oxygen along doesn’t seem like the greatest idea, though, for a number of reasons. So we will have to get our oxygen somewhere else. Remember all those silly “water fueled car” hoaxes that pop up from time to time? They purport to use electrolysis from a vehicle alternator to split water into hydrogen and oxygen, increasing vehicle gas mileage. Of course this is nonsense; whatever negligible power is added by burning trace amounts of oxygen and hydrogen in the engine is outweighed by power lost to the alternator to split the water in the first place. There is no free lunch. But we don’t need a free lunch. We are looking for something different. What if we bring along water and use electrolysis from the zinc-air battery to split the water into hydrogen and oxygen, then feed that oxygen back into the zinc air battery to increase the rate of the reaction? As an added bonus, electrolysis is a self-pressurizing reaction, meaning we can feed the pure oxygen into the zinc air battery at pressures that would otherwise require a heavy turbine or compressor, thus further increasing the reaction rate. Of course, since the discharge of the zinc air battery is now being tapped to provide current for our electrolysis, the actual output of our battery has gone down, not up. It seems this exercise has been a waste. But is it? No. Because the system is producing some thing else: pure hydrogen. Pure hydrogen can be fed into a hydrogen fuel cell which reacts with ordinary air to recuperate roughly 60% of that lost energy, and hydrogen fuel cells have a specific power in order of magnitude higher than lithium ion batteries. There’s no free lunch happening here, of course. This system would simply take advantage of the fact that the reaction between hydrogen and air happens much, much more quickly than the reaction between zinc and air, and so it’s an acceptable trade to lose some specific energy in order to feed pure pressurized oxygen to the zinc-air battery. This only works if doing so will linearly increase the reaction rate. That is where my chemistry knowledge fails. Operationally, you would merely need to refill your tanks with water between trips/flights, and swamp out a zinc coil for reprocessing every couple of weeks. A reprocessing system wouldn’t be very large at all and could run off of ordinary grid electricity.

I built a fully-functional VTOL Quinjet from the MCU:

I decided to try my hand at the Avengers Quinjet, but I couldn't decide which version to do. There's the early one with the large in-wing rotor that can tilt: There's an intermediate version with lift fans hidden in an intake underneath fixed wings: And then there are several late-stage versions which don't appear to have any lift fans at all: After some thought, I decided to try and replicate the mid-to-late-stage Quinjet from the end of Black Widow because I didn't really want to bother too much with rotors, so here you go! There's really minimal part clipping. The Dawn engines are really just for show; they don't provide anything like a usable amount of thrust. You don't need infinite fuel or infinite electricity to fly it but I turned on infinite electricity just because it keeps the Dawns from flaming out. This quinjet has thirteen Juno engines for forward thrust and two Wheesleys for vertical lift inside of a 1.25-meter payload bay. All of them are controlled with independent action groups. When the Quinjet is fully loaded with fuel, the Wheesleys don't have quite enough thrust for VTOL, so I added two clusters of Twitch engines inside the payload bay: I turned off the gimbal on all of the Twitch engines and inside tied them to a couple of KAL-1000 controllers, one for roll and one for pitch. The throttle on the Twitch engines is bound to the main throttle, allowing me to easily manage hover, but the KAL-1000s can reduce the thrust limiter by up to 80% to control roll and pitch for stability. There's not a lot of oxidizer on board because sustained hover really wasn't the point; you really only need 2-3 seconds of thrust from the Twitch engines to get off the ground and then you can turn them off and fire up the Junos: It has ridiculously low wing loading (not by design, just a consequence of trying to match the appearance of the movies) so stall speed is stupidly low, like 34 m/s or something. At the same time the center of lift is just barely behind the center of mass so while it is stable in level flight it is also ridiculously maneuverable. It can go from level flight at 200 m/s to a pitch-up, roll, and turn to 180 degrees in mere seconds by trading speed for lift. Unfortunately it is not what I would describe as terribly fast. There's a LOT of drag and the Junos just don't have that much power. If it can hit Mach 0.7 in level flight it's doing well. It can land vertically with or without using the Twitch engines, although it is much more controllable with the Twitches or with a puff of RCS. Landing without the Twitches takes some finesse, as you basically have to cut the Junos, glide to your stall speed, then pitch up and fire up the Wheesleys at the exact same time: If you leave the brakes off and allow a forward roll, the STOL works ridiculously well. I could probably do a STOL from on top of the VAB easily: With the Twitch engines and the KAL controllers, the hover mode is an absolute DREAM.

They won’t try to catch Superheavy the first time; they’re dropping the first one in the Gulf so they’ll use that to assess landing accuracy.

Some energy in the system is lost to heat because of the inherent resistance of the conductor (whether the conductor is a sacrificial armature which pushes the projectile, as @Spacescifi notes, or if the projectile itself is the conductor). That's just Ohm's Power Law. But by far the bulk of the heat in the system is the result of frictional losses, which act in largely similar ways on both the conductor and the rail itself, since the materials must both be conductive. The laws of thermodynamics tend to frown on any attempts to force heat to flow from something cooler into something warmer, which is what you'd need to do in order to use the projectile as a heat sink for the system. However, that doesn't mean it's a lost cause. There are many ways to cool things, after all. For rocket engines, you can use radiative cooling (requires the vacuum of space and a large surface area), regenerative cooling (requires a fuel you can use as a coolant), or ablative cooling. Ablative cooling sucks for rocket engines, generally, but it's used to great effect on spacecraft heat shields. An ablator carries away heat by being vaporized and carrying that vaporization heat with it. So, one way to make a railgun work would be to use a conductive projectile, but place a layer of an ablative, conductive material on either side. Then, use rails that are slightly narrower at the exit than they are at the entrance. Thus as the projectile travels down the barrel, the ablative coating is gradually vaporized by the combination of Ohmic heating and friction. As long as the ablative coating vaporizes at a much lower temperature than the rails, the rails themselves will remain undamaged. The process causes the overall size of the projectile+coating to shrink, which is why the bore of the railgun narrows toward the exit. This way the heat is carried away not by the projectile, but by what the projectile leaves behind. With a little extra design work, you could even shape the rear of the projectile such that the escaping vaporization gases expand against it like an aerospike engine, adding to its velocity. Bonus if the reduced stresses on the rails mean that you can use the rails themselves as a supercapacitor, rather than needing a separate capacitor bank to fire. Air is not an ideal dielectric for a capacitor by any means, but perhaps it would still be doable.