SomeGuy123

It's pretty much a trope of space opera that smaller space fighters are faster*. This is generally true in Earth's atmosphere, because fast aircraft are extremely expensive and drag slows them down the larger they are. But if you had a fusion engine, the bigger the engine is, the larger the internal core volume where the conditions permit fusion, and the smaller the mass ratio of magnets and other equipment relative to the power output of the engine. Since a fusion exhaust engine just lets the hot plasma escape directly, as power output rises the mass of the equipment that handles the waste heat and so forth rises more slowly, because most of the heat and light reflects off other plasma and not off the engine walls. Allegedly, other effects related to fusion I don't know about make the power output scale with something like the fifth power of the radius of the reactor core. Anyways, at some point the scaling would stop because the engine core would be so hot that the engine walls would ablate away faster than you could practically repair or cool them. But that power level might require a truly gigantic engine. Something massing thousands of tons. Something so big and complex that after you add the warship's other systems - armor, weaponry, defense systems, sensors, propellant tanks - you might as well have a crew onboard because the mass of their accommodations isn't significant. Also, there would be so many onboard systems to repair, and a trillion dollar asset like this would be best utilized if humans are onboard to optimize the decision making. Engines like I'm describing would still not be capable of all that much acceleration - maybe 1/100 of a G? It wouldn't be much, even with a power output measurable in terawatts. So crew would have no trouble with the forces. Space fighters, psh. Capital ships all the way. *By faster I mean more acceleration at high ISP. This means the warship with the bigger, more efficient engine is much harder to hit with missiles because it can choose to run away if too many missiles for it to shoot them all down are launched at it. Since the missiles have to be small to be cost effective, their engines have to be inefficient, so even if they have higher peak acceleration, at longer ranges they will run out of fuel before they ever reach their target, assuming the target is running away at maximum burn. Fusion engines have enough ISP to burn for days. The warship with the better engine also gets to decide the terms of it's encounters and can run down ships with smaller engines at will.

Is there a way to discuss this conceptually without a screenful of greek letters? Ok, so the throttle back part I think I understand. At a certain speed, the forces from air resistance are larger than the forces from gravity. So you throttle back before you exceed that speed, specific to actual drag coefficient and air resistance in the case of an actual rocket. Or is that not it? Every unit of time, you're losing upward velocity component due to gravity. So you want to reach orbit as fast as feasible to eliminate that. Every unit of time, you're losing velocity as long as you stay in the atmosphere. So you want to ascend as fast as possible to escape it. But if you reach a speed where you actually are losing more from air resistance than the derivative of the change of gravity...ok yeah I guess we do need some greek letters here. The other part I can't quite grasp is why you want to cant over soon after you leave the tower. Don't you want to escape the atmosphere first and then burn sideways?

I suppose. Part 2 of my "story" is that the surviving humans, who live in various space stations and underground vaults, are each ruled by an autocratic or corrupt government that stalls recovery. You know, the usual, some dictator dude makes sure all the resources that might have gone to developing solutions to the problems they face goes instead to more champagne and parties for himself. So the "space stations" and "underground vaults" are these ramshackle things that barely hold together, and since minimal resources go to education, the people running it are mostly technicians who can barely hold it together at all. Naturally, the protagonist is someone with a real engineering degree who's been cryogenically frozen for the past ~100-200 years. He gets awoken by Plot Events and he's someone who has to Fix Things. He has "forgotten more than he knows" which is why the Player of the video game can make mistakes and come up with fairly sad and not all that clever designs and yet it's of course better than anything the NPCs have stock. Hey. It's not gonna win a Hugo award for story but it's self consistent and could make for a fun game or a fun light read.

It could be that there is nothing wrong with it other than a lack of market size and money. Private aviation prop planes now cost a quarter million dollars new and they mostly still use engines with manual fuel/air mixture controls. The actual engines are these air cooled rotary things that look like something out of an old movie. I agree, the ski looks like a no-brainer.

I think having the star be the problem is just a bad direction to go in. It's not much of an apocalypse if it's predictable for millions of years, more than enough time to do something. My "salt the earth with cobalt bombs" proposal could happen, start to finish, in about an hour, from the moment the order is given to the moment all the nukes have exploded.

Yeah, but those fans/thermal turbojets are heavy. You have insanely awesome rocket performance on the one hand and now you have to bolt on some clunky fans that weigh you down. Not elegant, although if that's what you gotta do. On the bright side, it makes a videogame - KSP or others - that has this kind of OP engine at least a little more interesting in that the overpowered engine can't be used everywhere.

Well, the whole idea of an engine like this is that you have an ISP of something like 1 million. Today's rocket engines have an ISP 2500 times lower. So you have 6.25 million!!! times as much energy per unit of thrust in your exhaust plume. The only way this even works at all is almost all that energy never reaches the walls of your engine, and your engine is absolutely gigantic, with the star-hot core located far from the cooler gas at the edges. The whole concept behind Orion drives which apparently pass basic math tests of feasibility says you can do this, orion drives, the fusion bomb detonation temperature is many many times what the pusher plate can take. Anyways, 6.25 million is a big number. I don't think you could go safely near a planet of any sort with a torch beam like that (assuming you actually could build an engine with enough thrust to matter at all)

I had a similar idea. Game needs to be an environment where everything is basically wrecked beyond most recognition and there are a handful of survivors living in a small number of armed, factional groups. This is because it's possible to actually show in a feasible game. You could allow players to explore the whole Earth - but the nuke craters and rogue nanotech have erased most signs of human presence and smeared out the geography. Major cities are just "ruined urban biome" where only fragments of road and building foundations remain. The small number of human survivor groups live in camps or space stations or small settlements, with a small enough number of NPCs that you can actually model and show them all, and make the whole station/settlement an explorable place, and they only have 1 leader with a simple government and a simple set of programmatic rules they use to deal with the player. "halt, turn over your stolen goods, or "this is contraband. I'm charging you a fine, citizen, and taking all the contraband". "here's the town message board where various chores that NPCs want doing are listed". You know the drill. Anyways, I figured it needed to be multiple causes. "War never changes". Some jerks salted the earth with cobalt and other long life radioisotopes, creating lots of hot zones, other jerks released killbots that lie in wait like land mines for anything that moves, yet more jerks released a cloud of nanotech disassembly machines that try to oxidize biological materials. (and more machines are being made by these self replicating plants, so all humans have to seal themselves away in clean environments or wear space suits outside - even a single breath of dirty air has enough nanomachines to be fatal) Radioactive salting (some gigantic gigaton class nukes with plates of cobalt metal in the casing) and killbots (think the modern Atlas robot, upgraded, and lying in wait for you with a machinegun) are realistic. The nanomachines would be these nanoscale things made of diamond that combines organics with oxygen, essentially combusting them, and collect enough energy from the reaction to run themselves. They get the oxygen by trapping it from the atmosphere. The machines cannot build anything or self replicate or destroy anything that is not from a list of common organic substances.

Suppose you had a fusion (or a really, really hot plasma stream from gas core fission) exhaust on your spacecraft. Magnets and stuff keep any of that plasma from touching the walls of your engine, and the outer plasma protects you from the radiant light of the inner plasma. Anyways, as you come in for a landing, won't the plasma plume reflect off the surface of the world you are landing on and send hot gas and debris against things like your engine mounts and other delicate structures that aren't able to tolerate it?

The other side of the coin is that human pilots make certain common mistakes. You can prevent these common mistakes with a computer in the way, at the expense of making it more difficult to recover from rare mistakes. Analogous to how an automatic transmission sometimes picks the wrong gear, but prevents you from grinding the gears or stalling your engine. Anyways, by blocking common mistakes, you may prevent more accidents than you cause by making it harder to save an aircraft when a rare edge case happens. There are so many confounding factors, and lost aircraft are so rare, that I don't know if in the end there is any statistically significant safety difference between Airbus and Boeing as a result of this philosophical difference, but considering doing it this way is not a bad idea. It's a valid engineering tradeoff. In the long run, as you keep making the software better and covering more of those rare edge cases, you would expect that you would come out way ahead, because human pilots are a lot harder to make universally reliable than software.

That thing isn't economical. You can make the bomb "just" 5 or 10 times bigger and get 300-500 kilotons instead of less than 1 kiloton (the portable version is that weak) That's what I mean. The W-79 is estimated to weigh 700-800 pounds with a yield of 350 kilotons. If the backpack nuke weighs 100 lbs, that's 8 times the weight for 350 times the yield. (if it only weighs 50 lbs, it's still a 16 time mass increase for 350 times the yield)

The actual reasons have to do with liability, a limited market, the high cost of electronics properly hardened for aviation use, and a fear that such a control system might have hidden "edge cases" that cause fatal and expensive crashes. For a quadcopter I've built one by purchasing a frame, the 4 motors, and an arduino and xbox controller RF module. I also have an IMU, compass, a laser rangefinder, and a GPS module. I had full auto flight, basically. Think "videogame helicopter controls". You could start the vehicle and just hold down the "up" arrow on one stick on the xbox controller. It would keep itself level and adjust the internal "set point" for autopilot height. The user did not directly or indirectly control the rotors. If you released the controls, the quadcopter would attempt to remain exactly where it was, subject to a bit of drift because GPS drifts. If you held down a direction key, the whole quadcopter would tilt and begin to fly in that direction, with the autopilot code what is actually still flying the aircraft, as it would only tilt over so far, keeping itself in stable flight. Anyways, this is what "semi-automatic" helicopter controls would be like. I'm well aware it would cost tens of millions of dollars to design the equivalent system intended for a manned, full scale turbine helicopter. My little hobbyist system had a few edge cases I never fixed and all the electronics were just hand soldered exposed circuit boards on top of the copter. You would have to use aviation grade connectors and shielded boxes and extremely expensive sensors and you'd need so much of them that it would weigh down the helicopter and reduce it's payload by 100kg or more. (it's all the sensors and wiring and motor drivers and servos) And you'd need a very rigorous formal development and testing regimen. But the long of the short of it is you could "hover" such a helicopter simply by releasing the controls. Fly in a given direction by holding down a "direction yoke". Don't worry about pushing the yoke down too far - the helicopter will never exit a stable flight region as it's autopilot is aware of where the boundaries are at all times. Get in trouble, and you just release the controls, and the autopilot will restore the aircraft to a stable hover, assuming the actual rotors and engines and servos still work, recovering itself from all possible spins and other bad events. (this is where the "edge case" fear comes in - there are high end quadcopter algorithms that can basically recover from anything, even deliberately removing a rotor, and the algorithms learn in realtime, but it's really hard to prove that there are absolutely no situations you have not thought of) It would have things like belly cameras pointed straight down so you could land by just using the direction yokes so the helipad logo appears centered in the camera view, then hold down the "down" yoke to descend for a landing. (the 8 controls would be Translation : Forward/Reverse/Left/Right/Up Down, rotation left and right.) There would also be a "throttle" lever so you could just push the throttle forward and the helicopter would fly itself "forwards" at a relation % of the throttle (so 100% throttle means "fly forward as fast as possible given current conditions"). Like everything else, this throttle lever has nothing to do with what the engine is doing - you're just commanding the autopilot to fly forward, and it decides how much engine power to use.

Neat. And once you are talking about "hypothetical physics", you could posit that whatever magic you are invoking to release the energy stored in ordinary matter only works against the dense central core of a planet. You cannot make the upper crust or atmosphere explode, whatever you are doing requires a big central mass as a target. This would explain both why the Death Star has to be this big, and why you don't invest smaller resources to make mere atmosphere burning superweapons. If the Empire could make weapons that can set the atmosphere of a planet on fire that are 1/100 the size of a death star, they would. This is true in IRL - you cannot make a hand grenade sized nuclear bomb because of critical mass requirements. The smallest nuke you can possibly made is pretty heavy, and a slight increase in size means a huge increase in output levels, so it makes economic and practical sense to make your nukes all a certain size, which in turn means you need a jet aircraft or a big missile to deliver them. No nuclear bullets fired from a handgun.

Source? I believe you, I'd like to see the numbers because I wonder 1. What does power level do to this? Would a futuristic fusion drive with a huge ISP and enormous energy level be many times worse? 2. Just how many tons of shielding do you need. Is it enough to reduce the neutron dose to "fatal dose takes 1 year"? That would mean 24 halvings of the neutron flux. Simple google searches won't tell me how much shielding you need to do that. 3. Geometry wise, your shadow shield must be at least the diameter of the engine, right? It cannot be smaller than that, because if you do a ray diagram, you end up with a small cone that gets smaller with distance from engine. If the shadow shield is slightly larger than the engine diameter (if the engine is a cylinder, this is a disk bolted on top), your ray diagram creates a large shadow, growing bigger with distance. 4. I read that hydrogen is one of the best forms of radiation shielding. Conveniently, it also is what you use for propellant. Why not skip the heavy shielding materials and have hydrogen tanks. This also lets you use the remaining hydrogen as propellant if you get desperate or would rather get the ship back home even if it kills the crew.

Could it be worth it if you used a NERV the way we do in KSP, as a workhorse engine for an interplanetary vessel? If you get to use a single NERV that is relatively low mass compared to the total propellant it processes, and it essentially increases the efficiency of every kilogram of propellant by about 2.5 times (1000-1200 ISP instead of 400), it works out, right? Basically you'd build the interplanetary vessel by launching a heavy lift rocket like the S5 dozens of times, gradually adding and bolting together the crew module, science payload, lander, many many propellant tanks that keep themselves cold and the H2 in them in a slush state, and then you'd launch the NERV as a series of separate subcritical pieces. I guess the unfueled reactor would be a piece, then the fuel would be packed into separate modules that you'd somehow install in orbit. Be tricky to come up with a way to pack the fuel so you don't have to haul a bunch of dead weight in packaging but can prevent it from hitting critical mass. As a side note : does anyone have any specific information on if H2, kept in a slush state (where there is solid H2 frozen around the cooling tubes and it is in equilibrium with a liquid phase inside the same tank) will leak through the metal walls of a storage tank? I know gaseous H2 will, but the liquid phase has drastically lower velocities, so...

So the catch is they have to fire up the rocket before the LOX in the tank warms to the boiling point of LOX. Once it gets that hot, any more LOX you add will just warm up to that temperature as well and you have to continually vent the lox vapor..but... OH...the BUBBLES. See, if there's a vent at the top of the tank, you can just keep adding LOX to keep the "fluid level" a millimeter below the top. But the fluid will also be full of bubbles of gas, in the process of rising to the top like bubbles of steam do in water. Might be slower in LOX, dunno, I haven't handled it but it's a lot colder albeit with weaker intermolecular bonds. Anyways, you cannot get rid of the bubbles so you permanently lose tank capacity. So the drawbacks of this method is you have to fill the rocket really fast, you need to launch soon after filling, and if you have a launch hold, you have to pump out the LOX tanks back into a holding tank in your cryogenic tank farm and rechill it back to this supercooled temperature.

Question about the super chilled propellant. Water boils at 100 C. So if the rocket were full of water at 100 C, some of the water would be in the vapor phase, creating this bubble of steam at the top of the propellant tank. Since the propellant tanks on a rocket are made as thin and light as possible, the tank can withstand very little internal pressure, so you have to continually vent the bubble of steam and you cannot pressurize the tank enough to force the steam back into the vapor phase. But if you loaded the rocket with 50 C "super chilled" water, there wouldn't be any steam phase, and you could fill the tank to the brim. A more full tank means you effectively get more mileage out of the dead weight metal you have to make your tanks out of, raising your payload fraction. Is this what they are doing, except with liquid oxygen?

Nobody would build a physical dyson sphere. Why would they? Why not just convert all the solid matter in a solar system to either free flying solar arrays or robots and computers and whatever else a civilization at this level wants to play with.

Decent sci fi shows that have high budgets don't grow on trees. I don't actually know of any other show other than this one. What's higher in your schedule? Also, having read the books, I know that a great many intelligent and unexpected plot twists are in store for us. Despite the early episodes, violence and space battles is not the main plot driver. There's events that happen 4 books later I can see them foreshadowing in these early episodes. Hope the show does well so it can make it to that point.

Right. Even if you ignore thermal equilibrium, the Epstein...those numbers above assume it's a real engine with the ability to basically contain a fusion bomb, for hours of burn time, and it's 95% efficient. That's basically as described by the author. The flare that would leave..one thing in the latest book they got right is that from a human perspective, seeing a ship in the distance using one of these engines, you see a gigantic plume of glowing gas. At the very top of the massive drive cone is a tiny object you might miss. That's the ship. One would think that every time somebody fires one of these things off, thousands of separate sensors in the solar system would get triggered without fail, automatically recording the course of the spacecraft in question. And you would reasonably assume all the major factions - Earth, Mars, the Belters - would have vast surveillance networks. It wouldn't be very expensive - as I said, firing a drive like this, with a plume power measured in terawatts, is going to be really easy to see. So if you have a stealth warship, that's cute, but one would reasonably expect that everyone would know about it's every move as you just can't hide your flare.

Nobody wants to discuss fusion drive performance or water recycling? Bueller? Anyone?

Also, even if the Kraken is pushing on em, they probably still obey conservation of energy. Technically, "hovering" in midair must consume a vast amount of energy because you're actually producing as much work as the mass of the vehicle falling over 1 second times mgh. At least, I think so... And one could reasonably expect that even if it works, the force per joule should be a whole lot less than a rotor turning in the atmosphere. TLDR, it's not going to be possible to fly at all without a ridiculous power source.

That I can say is a problem that's solvable. It's possible to make safeguards that won't lose data until the end of the universe, and to make the replication systems only capable of producing identical children, all the way down to the bonding of individual atoms. There are issues with this in that if the machines can't really adapt themselves they might fail after a while.

Just stop arguing with Jouni. He's a grad student somewhere who knows only a tiny sliver of math he doesn't understand, and he seems to think he can apply this to the universe, even when it disagrees with centuries of findings by every other scientist. I think he's being willfully ignorant as well, because he never "updates" his arguments even when we tell him about factual disagreements with his theories.

1. Why are they running out of water on Ceres? They show a big recycling plant in episode 2, and isn't a space habitat a closed system? It doesn't have to be a closed system but it seems like a no-brainer to make it one. My only thought is that something is consuming water permanently, which segues to 2. What kind of performance could Epstein Drives theoretically have if they are just a way to make fusion easy and high thrust? (as in, they still obey conservation of momentum) My thought is that the logical reaction would be lithium-7 + protons. They would then inject oxygen into the fusion plasma stream when they want more thrust. This would therefore make the primary propellant they use water. A quick perusal of this table here says 8.5% of the speed of light is the exhaust velocity. My thought is the Epstein must be using aneutronic fusion, that the secret behind it is that it shapes plasma so well that there are these plasma mirrors inside, where sheets of hot plasma reflect the incredible heat of a star away from the components of the drive. These plasma mirrors aren't going to be very effective against neutrons, but they would reflect away light and charged particles, allowing you to reach insane internal fusion reaction rates relative to the mass of the drive. This also agrees with plot points in the show - the drive has so much hot fusing plasma inside that if a software failure causes the bottle to fail, it blows up the ship it is attached to. It's basically the core of a fusion bomb continually reacting. So for every proton, you get 2 helium atoms. Total atomic mass 8. Oxygen has an atomic mass of 16. So you're tripling your total mass. Assuming even division of the kinetic energy, and some energy is lost and the Epstein is only 95% efficient (it has to be extremely efficient or the whole ship using it is going to vaporize) x = 1/2 * m * .95(8.5%c)^2 x = 1/2 * 3m * (V)^2 .5m(8.5c)^2 = 1.5m(V)^2 0.33333 *.95 (8.5c)^2 = V^2 0.562(8.5c) = V V = 4.777%C ISP = 1 459 845 Now we're hauling ass. If your space awesomesauce wtf sci-fi Mars warship (that is "stealth" as well, of course, cuz special black paint prevents the star like flare from your engine from being detected) is half propellant (gotta have room for the railguns, armor, and really posh looking interior!) you can do a 10 m/s burn for 275 hours! It depends on planetary positioning but it appears that this is about 11.4 days at full thrust, you could build a ship that could do a Mars to Jupiter run at 10m/s^2 the whole trip. This is also why in theory, if you just posit that the Epstein drive internally basically uses magic - it's made of indestructible adamantium with internal mirrors that reflect 100% of all incoming energy away from the drive - you could do multiple gravity burns, for days even, if you had a ship that is all engine and propellant tanks. (there are rich people racing ships in the novels that can do this) One thing of note : if you're using proton-lithium or proton-boron fusion, the main mass of fuel is actually the lithium or boron. The water consumption is nothing. You'd be consuming the ship's mass in boron or lithium to do a high gravity trip between planets. I'm not sure how much lithium or boron there really is in our solar system, at least in minable forms, to be throwing it away like this. Something like the Epstein might be possible, albeit it might have to be extremely large. If you think about it, the larger a fusion reaction chamber is, the more the outer plasma protects the walls of the chamber from being heated by the energy produced by the inner core. Logically you could just keep making the reactor bigger and bigger and bigger. You could never use the energy produced directly - converted to electric power, you'd be producing as much energy as it takes to convert your whole ship to vapor every second - but you could allow it to escape, shaping the thrust plume with magnets indirectly and using yet more layers of plasma to protect you. Of course, good luck with stealth. The absurdity of even attempting to stealth something that probably makes a plasma plume brighter than the inner planets as seen from earth...