SomeGuy12

No. K^2, you may be a well educated guy in physics, but your statement is nonsense. Within the universe we are in, something can't come from nothing, and something must always precede something else happening in time. In terms of what we know, the instant the big bang began something impossible happened. Inconveniently, we don't have any at hand means to resolve this paradox.

If you wanted to put astronauts on the inner moons of Jupiter, what would it take? Wikipedia says it's about 8 rems a day on Ganymede, with a fatal dose at 100, so it doesn't seem very habitable. Some of the radiation belts are just charged particles, which you could in principle shield against with magnets or something, but these accelerated particles emit gamma and x-rays, which you would need a massive quantity of shielding for. What alternative is there besides a spacecraft that is weighed down by carrying a submarine sized (probably more cramped than that) lead lined "vault" for the crew, and then exploration of Ganymede would be done via robots while the crew huddles in their vault or in a cavern deep under the surface. Even if you suppose there might be treatments for the long term damage of radiation exposure (the various leukemias and tumors and stuff), you gotta survive the short term acute exposure as well...

So I was thinking about the optimal "lander" for exploring the various vacuum moons in our solar system. Optimally, you'd have a mothership with a powerful nuclear-electric power generator of some type. Best way seems to be aneutronic fusion where you decelerate helium ions escaping from the reaction for direct power conversion, but if that never ends up being workable, you could use a conventional nuclear reactor to pump hot sodium in a circle and extract energy from the moving sodium directly. Problem is, the reactor is heavy, and then there's all those heat radiators and the radiation shield. There's also no convenient place to put the reactor on a lander - you have to have this big heavy radiation shield as well, and you want part of the shielding to be distance, so the reactor should be on a long boom away from the astronauts. Just doesn't work for a lander design though. So your lander has a "roof" of a microwave receiver array. You have a larger array on the mothership beaming power to it. You use some kind of efficient but also lightweight electric thruster. I read that MPDs are a good way to do it, because the thruster itself is very lightweight and simple, and you only need it to work for about 10 minutes on landing and ascent and then you can rebuild it in the machine shops on the mother-ship. Maybe a few hours of total burn time if you are using the shuttle to ferry materials to and from the surface. You use hydrogen as propellant.

So even the most magical sci fi universe, the wormhole has to be up in orbit at the least, right, so the black hole that is a critical part of it doesn't fall through the floor to the core of the planet. Even if you could somehow "stabilize" those tidal forces with magical technology, you'd want it to be in space in microgravity, and even if humans could traverse it, you'd need a pressure suit possibly. - - - Updated - - - One reasonable theory is that for anything exiting a wormhole, the mass-energy of the object exiting comes from the mass of the black hole on that side of the wormhole link. This means there's no free lunch - you could build an infinite energy generator by setting up 2 wormholes a certain way, but the energy you're gaining is getting subtracted from the mass of the wormhole itself, so eventually you'll run out of mass unless you constantly feed more into it. If wormholes were ever a real thing, of course, they'd be microscopic. You don't need the ability to send anything through - at that level of technology, you'd be able to convert human beings into digital files and send them through in a few seconds via data link. To avoid philsophical issues you could send just a copy of yourself through the wormhole, have it go explore at the other end, then beam back what it learned as a difference file between the copy's memories when it started the journey and the end.

Laser tweezers are one way that works on neutral atoms.

I just want to say : when I saw that SRB separation, I was thinking "man, I bet whoever designed that rocket had to revert to the VAB a few times to get that separation reliable." I always found that designs that depend on stuff like that are never reliable. You'll have to revert to the launchpad every other launch. Better to go for something simpler, just a big pile of liquid fuel boosters above other boosters.

How feasible would it be to do the following? 1. Create antimatter with spontaneous pair production. As I understand it, you just build big honking lasers and crisscross the beams in free space. Matter will spontaneously form if the light intensity is too high where the beams cross, and you then just collect the antiprotons and positrons. This is supposed to theoretically be moderately efficient, though I'm not sure what the practical efficiency limits for this method are. 1% efficiency would be enough to be practical, I think. 2. Trap the antimatter and form it into anti-hydrogen. You just shove the antiprotons and positrons into the same trap, anti-hydrogen forms spontaneously. 3. Force the antihydrogen to fuse. Never touch it with any physical apparatus. The first fusion step is the hardest. 4. Keep on a series a fusion steps until you either reach anti-iron (a long way there), or more practically, you hit something that is a Type 1 superconductor. Lithium works, though 0.0004 K is a bit too touchy. Beryllium, 0.023 K, might be feasible. 5. Now, to store it on the starship, you just need a series of canisters with magnets, even permanent magnets in the walls. The superconductor rejects the magnetic field lines and will levitate in the middle. Just have to keep it cold. 6. You move one of the cannisters down to the main engine. A lasers vaporizes a tiny fleck from the bottom of the superconductor and you use laser tweezers to move the fleck into the engine without touching the walls, ever. This bit might be tricky... 7. The engine uses big honking magnets, and you just dispose of the positrons by dumping them overboard after accelerating them to high velocity, and you combine the anti-lithium with ordinary lithium. The resulting annihilation creates 20% or so pions which your repel with magnets. Rest of the energy you try to let either escape into space or it impinges on the engine. So you want the engine to have lots of gaps for light to escape. It would probably resemble a very thin, light latticework, with the engine on a big cable or long boom to separate it from the spacecraft. Would still need big honking radiator wings. Could this end up being a feasible idea, assuming you had incredible engineering capability (like tens of thousands of geniuses and centuries, or an AI equivalent) and orbital facilities to develop the systems?

K^2 : Yeah. It depends on unknowns about black holes to know if a baby one can actually eat or not. That certainly is the ultimate engine. Ramscoop + black hole is the kind of combo that actually would resemble a ship from science fiction. Probably 1/10 G indefinitely, it might never run out of propellant, at least on intergalactic missions, you'd be able to reach 0.9 C eventually, it would take just a few weeks to get around our solar system, as your engine burns a few kilograms of matter a second. I wonder if you could devise a way to refuel such a monster vehicle from gas giants or a star without shutting down. Eh, you'd probably just drop off smaller shuttles near a gas giant. You'd beam energy to engines on the shuttles (they wouldn't have significant thrust without a laser or microwave beam from the mothership). They'd collect gas on a high atmosphere flight and return. Any old matter would work. And your ship has to be positively massive. Million ton +. More than enough room for an onboard factory able produce from raw elements any component of the ship and a ....ton of weapons and armor. Maybe even a human crew, though I'm not sure what you do about the gamma rays. I think tentatively you have to expect the crew to be cyborgs, possibly former human beings who have been upgraded to be non biological and resistant to radiation. You could pack one of those 1 AU range gamma ray lasers mentioned in another thread. It would be one massive weapon, but it could fire pulses that would put craters in stuff from an AU out. You'd never be able to stop something like this without comparable technology. If space aliens ever showed up on a mission to conquer us, this is what they would have. So, if you wanna speculate about what new physics might find...well...what if you could create the conditions for a really tiny black hole right there in the engine chamber? The black hole would evaporate in microseconds, but you would keep doing it. A "pulsed singularity thruster" or something. That might be a little more practical, and it has the advantage of not requiring you to feed the black hole or move it with your ship, which is really hard to do. (you'd have to electrically charge the black hole by putting it on an imbalanced diet, then move it with magnets or electric fields so it stays in your engine chamber as your ship accelerates)

Or just use a stream of pellets launched via superconducting quench gun. Catch em to speed up. Ramjet to slow down. Done. No antimatter needed. I hear antimatter is kind of energy intensive to make and not all that safe to have onboard a spaceship...

Bussard Ramjet is a great idea. If you think about it, slowing down is actually a much bigger problem than speeding up. To speed up, you just fire a stream of tiny iron pellets at relativistic velocities from a gigantic accelerator anchored in the home star system. Ship contains a decelerator and they pass through a linear track inside the ship. Ship accelerates at several gs until it hits a 0.1 C or so. To slow down, the same accelerator magnets get diassembled by onboard robots on the ship, and the constituent elements are used to manufacture the magnets for a ramscoop. That thing kicks in. Ironically, you might not even run a fusion engine on the hydrogen you collect, simply collecting it is enough to slow down due to conservation of momentum.

No. You just add. How much does a cheap natural gas turbine cost, one without the steam portion for combined cycle. How much does a solar panel cost in 2015? How much does wind cost? How much solar + wind are you going to get for the geographic area, on each day of the year? What is the probability distribution for that solar + wind? Then, taking probably the worst case - the bottom 5% chance of combined solar + wind, you know how much natural gas turbine capacity you need. You would have some of the turbines be the co-generation or combined cycle style, since you would expect those to run most of the time, except when there is exceptional solar + wind output, and the rest be the cheaper straight turbine style. I don't have the data in front of me, but you could probably get a study like this done in a few months with a single grad student. Really, all we have to do is show that nuclear, including all costs such as end of life disposal and liability insurance, including the government's portion, and the interest rate on all the money when you wait 10 years to build the plant, is much more expensive. Assuming this is true, and nuclear is hugely more expensive, then the final step to dismiss Thorium from consideration at all is to show that none of the cost savings with Thorium are significant enough, especially compared to the extra costs of all that reprocessing equipment.

Ok, if I read this, it seems to indicate I'm right, natural gas is cheaper. Nuclear does do pretty well on this chart, but I have read many articles indicating it often goes much higher for actual installations. Yes, Wind has a 30% capacity factor. I meant that you build ~3x as many wind turbines, of course, such that the rated maximum watts is 3 times the average load of a geographic area, such that on an average day, most of your power comes from wind. Well, ok, if you do that, there will be large periods of time where you are making too much wind power and the extra capacity is wasted. So the math to figure out how many wind turbines and solar panels you actually need is quite a bit more complex and depends on empirical data. But the point is, you never assume the wind will go to zero everywhere - that won't happen - so you don't need enough natural gas backup generators to run the entire load at peak conditions on a black swan day where there is zero wind across a thousand mile geographic area. That can happen, but is unlikely, you spec for probable situations. The utility regulators in a particular power market don't expect zero blackouts, that is unrealistic - even a market where you use all nuclear reactors, they could all scram at the same time due to random chance conspiring against each one. They just want the statistical number of hours per year when there are some areas of the grid offline to be low.

Ok, so, to summarize : Thorium reactors have the potential of higher power density per core, cheap, near infinite fuel, and less worry about people making nuclear warheads as a side bonus. They have the disadvantage of requiring a lot of technological development, and the liquid fuel you have mentioned is inherently harder to control than solid rods. It also means you need a number of pieces of machinery to conduct reprocessing on the fuel, and those pieces of machinery will be so hot to give someone a lethal dose in a minute or less, probably too hot to work on with waldos behind glass - you'd probably be forced to use remote cameras. Also, when the machinery breaks, it is really hard to fix and it's high level radioactive waste in itself, kind of negating any reduced waste advantages of thorium. And this means that thorium reactors share the other huge disadvantage of nuclear. Once you fuel one of these puppies and put it into service, you have created a place that contains literal tons of lethal poison that has a tendency to escape containment. This can be dealt with, but it means you must spend large sums of money building a containment facility with many many redundant and expensive layers of protection. You can't pinch pennies anywhere - cheaper equipment, cheaper people, etc, all raise the risk of an accident. I don't see it. What are you guys seeing that I'm not? New nuclear is already more expensive than new wind. Yeah, yeah, "baseload", but new nuclear is also more expensive than new wind and sufficient backup generators to run when the wind dies. Someone upthread thought that wind + solar only works 30% of the time, that's absurd and not based on real numbers (I've seen articles indicating it is much higher because over a large geographic area, the probability is very high there is significant sun or wind in parts of it, at any time, day or night). In any case, the gas backup turbines are cheap, the cheapest form of power at the present, wind and solar is just to reduce your fuel costs to less than half. It's not going to happen. (thorium or even a significant nuclear resurgence). The fundamental problem is that solar and wind and batteries are going to keep getting cheaper, because there are a lot of competitors, and there is room to innovate. If you come up with an innovative new windmill, battery, or solar panel design, and it fails prematurely, all that happens is some warranty claims and unhappy customers. If you think of a way to save money on a nuclear reactor, well, you see the problem. Tepco thought they could save a few million by building a lower protective wall. They also didn't pay for the auxillary steam turbine option package, or a transformer set to power their own plant from their own reactor power, or even 1 extra backup generator located higher up, nothing.

So, you have reduced the risk of a core burn through, but now you have lethally radioactive liquid metal that you have to pipe around, including through a complex series of chemical reaction stations. Among other things, it sounds to me that you could end up with an accident where the metal comes into contact with the water used for the steam turbine loop and flashes it into steam, carrying away bits of the reactor with it. Unlike fuel rods for a conventional reactor, it sounds like the actual lethally radioactive core stuff is kind of evenly mixed instead of normally being trapped in a fuel rod. I'm not using the word "lethal" for dramatic effect - as I understand it, direct line of sight exposure to a moderate quantity of stuff this radioactive is a lethal dose in seconds, similar to the danger of the Elephant's foot at Chernobyl. The EF wasn't pure fuel core either, it was a mixture of melted fuel rod, melted reactor core lining, melted concrete, and the actual fuel. It also doesn't sound trivial to contain if stuff goes badly enough. If that liquid metal flows everywhere and contaminates a damaged reactor building, it's basically the kind of mess that you have to wait 50 years before you can even begin the cleanup. Causing mass death? No, but little flakes of a liquid metal core would probably contaminate surrounding agricultural land enough that you can't use it, causing a loss of that land value. That's a big liability to incur to build one of these. To me, Thorium does not sound like the way. Currently, the cheapest and most practical way is : Build solar panels, wind generators, and natural gas turbines. Is it night and the wind is calm? Burn the natural gas. Is it daytime and there is too much solar power compared to demand? Use the excess solar energy to compress air and store it in caverns under the natural gas generators. Currently, as I understand it, that mix is the cheapest. Existing nuclear reactor designs are already too expensive to even compete, and thorium reactors, while they might ultimately have cost advantages if they run at higher temperatures and need cheaper fuel, would be even more expensive initially. Farther in the future, for spaceflight, if you are using NERVA engines, you wouldn't use thorium either, right? You'd use weapons grade U-235 or pure plutonium for you reactor fuel core, because anything else is adding mass. And, fusion, if we ever did get it working (yeah, yeah, always 50 years away), is more ideal for both spaceflight (lighter reactor designs are possible) and on the ground (no load of tons of fissionables that you have to keep contained)

So, exactly how much cheaper and/or better will thorium reactors be? As I understand it, they are just a form of breeder reactor where the breeding happens inside the core, so you aren't having to constantly cycle out hot fuel, reprocess it while it is hot, and then insert hot replenished fuel rods. That does make breeding a lot more practical. However, as I understand it, the cost of the fuel is still negligible compared to the cost of everything else. So how does a thorium reactor make the economics of nuclear work better for right now?

PB, I personally have had to optimize stuff in assembler for micro controllers just a few weeks ago. I was running on the internal oscillator at x1 multiplier for power consumption reasons, and the compiler's solution was just not adequate. By manually using lots of registers (PICs have 16 which is a lot for a microcontroller) I was able to boost performance considerably. Even then, I used it very sparingly. I had an operation I needed to happen on a hard timing edge, so I pre-loaded registers with the states, and I had a loop that was acquiring data at a high sampling rate that needed to work smoothly. What I'm saying is, before you even touch assembler, have you 1. Optimized your algorithm? 2. Used all the multithreading you can? 3. Identified a core, tiny main loop where all the magic is happening where you think you can boost performance further? Have you tried GCC or Intel's compiler? It often beats Microsoft's compiler on the programming shootouts and it may support ASM. What I did in order to learn assembler quick and dirty was I just found the loops I needed to speed up in the assembler listing file. I looked at how the compiler did it, looking up each instruction. I then copied the compiler's solution to a section of inline C code, and got it to run using the compiler's working solution for that step. I had to email the compiler authors as their inline assembler had errors and could not read it's own listing file format. Once I got the code working again in inline, I make tweaks a little bit at a time, checking the results for correctness, and eventually I was able to pare it down to about 1/4 the instructions, although I used a lot more registers to do it. You can do the same, possibly. Be aware that this means your solution will be machine specific. Those special registers you are having a tough time digging up? They won't be on every chip. Also, if you are doing something complex, with complex logic, you just don't have time to optimize it all in assembler. You would probably be better served by redesigning your algorithm to be more cache friendly, or making it multithread better and just rent access to more cores if you need it. I was using a janky, poorly written compiler to get the speedups I was getting - I bet you can't do better than 50% faster hand optimizing the output of GCC. For that matter, if your algorithm is N-body gravity, which is sounded like above, you should be using a GPU. Orders of magnitude more power. Check the Nvidia example for a basic implementation.

I think my analogy could be described more aptly as "let's research better guns" instead of "let's research the stars". You know, if the year were the time where the plague, arrow wounds, and gunpowder were all unknowns. I would be right. I ain't even saying not to research the stars eventually, I'm saying that it's not the time for it. Knowledge of relativity would not have helped during the industrial revolution. Similarly, yes, for humans to continue to exist they do need to leave the planet, but it's not the next step on the tech ladder. Before worrying about whether some humans can exist 1000 years from now, maybe we should worry about whether we personally can exist in 1000 years. Maybe it's impossible, but it's where the research funding should go.

"Accomplish" what? What is learning more about a dead planet going to help people on earth? Manned mission life support and planning may sound cool, but in what concrete way will it help people on earth, versus researching, oh, I dunno, aging, disease, and death. Until decades, maybe centuries more R&D are done, we will never be able to gather non-negligible quantities of raw materials, make anything really complex in space, or use the sunlight for power, etc. Even communication satellites are becoming increasingly useless as we need more bandwidth than they can possibly provide due to fundamental physics limitations. I know it isn't popular to say this, especially here, but it's the truth. If we want to really accomplish stuff in space, we need to first dump trillions into more close to home topics like medical science, artificial intelligence, molecular manufacturing, and so forth so we have the infrastructure and the means to do it on non-negligible scales. So since space is a waste, might as well rob the government for all you can. That's how Lockheed sees it.

Why would you think they work? The reason people look old or ugly is because of flaws in their genetics that cause their bodies to not repair themselves correctly over time, and/or genetic defects from the start. Vegetables on the skin doesn't change anything.

Please don't post in my thread. Nothing of what you said has any relevance to the discussion. The type of fusion I am describing, you extract electricity directly from the moving charged particles produced by the nuclear reaction. No conversions. Antimatter produces very difficult to deal with products, trashing performance because the products are not electrically charged, so you need a gigantic, massively heavy engine to get any thrust at all. Antimatter may end up being exclusively for interstellar travel, where you need the additional dV and can afford to wait for years. As for it being a long way off - no ..... I'm talking about what engineering can do, not what will be plausibly done in the foreseeable future. Fusion is basically just as long a way off as nuclear thermal. I mean, we could build and fly nuclear thermal rockets probably 2 years from now if there was a pressing need, but they have never been flown and there is no plans to do so in even 50 years.

So, apparently, trialpha has a method to confine the plasma where they accelerate particle beams of more plasma that are then bent inwards by massive magnets to surround the hot core where the fusion reaction takes place. So, essentially, the container holding the incredibly hot fusing plasma is more plasma. They claim this is stable. So what happens if you keep making it larger? If you keep making the reactor larger, the surface area of the plasma container grows slower than the inner core. If the inner core is all fusing fusion fuel, the power output would grow non linearly with the size of the reactor. An engine version of the reactor, there would be a more complex set of magnets and plasma flows that would form an extremely narrow, long opening to outside the spacecraft. This would be tuned just right so only incredibly hot plasma at the temperature of the reaction itself could escape at the same rate that new superheated plasma is forming from further fusion. What would ultimately limit performance? My guess is that light from the reaction and neutrons, as you keep making the engine bigger and bigger and more powerful, would grow proportional to engine power output. Since engine power output grows faster than the surface area of the inner part of the engine, eventually there would be too much neutron impingement and light for the materials to handle and the superconducting magnets would probably quench and the whole thing fails. So you'd want to do aneutronic fusion to minimize the neutrons, since light is much easier to shield against than neutrons. Looking at the readily available fuels, you'd use either hydrogen/boron or hydrogen/lithium. The lithium one is almost double the power output so it would be preferred if you had mastered the technology to make these things. Variations in the design would run "fuel rich" where unreacted hydrogen gets heated up and is allowed to escape the engine with the hot stuff, this would give you more thrust at the expense of ISP. Does anyone know a way to rough out what the power/mass limitations would ultimately be? Even to get a guess? Figuring out the ISP is easier, you just take the velocity of the fusion products and divide by 10. It's about 7% C with Hydrogen-Lithium, so about 2 million. So running at maximum ISP, if your spacecraft were 50% fuel, you'd have a dV of 13594 kps. The limiting factor is acceleration - this kind of performance doesn't help if you have to spend years to burn all your fuel. To get sci-fi levels of thrust, you need megawatts of fusion power per kilogram of engine. "Sci-fi" means around 1 G. I think it might be possible, actually. Plasma acts to protect the engine material from the core producing all that energy, so you don't actually touch it, and you might be able to tweak your reaction to produce less neutrons. You might also have gaps in the engine bell to reduce surface area exposed to light and neutrons. Some rough figuring : assuming the engine is 20% of the mass of your spacecraft, you need 500 megawatts/kilogram of engine expressed in the plasma stream escaping your engine. This sounds a bit much, at 0.1 G it would be 50 megawatts, etc. The best engines on earth can do around 10 kilowatts/kilogram, but jet engines have to touch the fuel mixture they are burning and they have to mechanically spin. The limiting factor isn't magnet mass, because the engine is very large compared to the surface area of the fusion core. It isn't heat radiator mass, because you would use negligibly light droplet radiators. You might even be able to use a series of plasma mirrors to reduce the amount of energy impinging on your solid, physical mirrors that you have to replace if they are damaged. Let's see. Maybe the way to get a rough estimate is to say : ok, 1/3 of the mass of the engine is the part that deals with the heat. How much heat can you shed and/or resist per kilogram? If 1% of the engine's power output reaches the engine components themselves, then to hit 50 megawatts/kilogram you need to shed 1500 kilowatts/kilogram. That may not be possible. You might be able to do 15. So the futuristic engine of the future, when it's blasting out a star-bright plasma exhaust, accelerates the spacecraft at 1 centimeter/second. You gain 864 m/s a day and need 43 years to burn all your fuel, assuming your spacecraft is 50% fuel.

If a few tiny drops of methylmercury, through a glove, is enough to kill, then a few tons of it...wow. I suspect that using a nuclear salt or other open cycle nuclear exhaust rocket would be a lot safer, especially if you stuck the launch pad 20 miles or more from a populated area.

Historically, every rocket project for decades has ended up costing much more than initial estimates. It is not very intelligent of you to trust 1962 figures for a design that was never flown. What you should know, and any real genius would immediately know, is that a review like you describe can only be done for known knowns. When you actually try to do something like a Sea Dragon...or even something vastly simpler...in the real world, you get slammed in the face with all kinds of issues and difficulties and unexpected problems no amount of paper analysis could have found. And these problems drive up the cost, a lot, to overcome them. Finally, the Sea Dragon figures had to be marginal cost per rocket launched. That is not what modern cost numbers are about : rolled into it is money to support the company doing the launches and the R&D and customizations and new engineering work done to update the design.

I think the reason we make high-tech rockets so expensive is because the agencies who launch them lose face - they look bad when their funding comes up for review, they are a less reputable institution - when they fail. "Better, Faster, Cheaper" Supposedly launched 10 missions for the price of one, and succeeded about 50% of the time? That's an enormous boost in productivity, but people are still making jokes about that unit conversion bug that took out a mars probe.

Yeah. This is why I wanted Wedge to actually do the math. It's one thing to say "it's gonna be low". It's another thing to actually find out the mean velocity for, say, hydrogen gas at 4 Kelvin and calculate the ISP for it. There is a point at which ISP is so low you don't really have a maneuvering engine, just a way to waste expensive propellant and be on basically the same course you were before. v = √(3RT/M). T is 4. R is 8.314. M is 1. ISP is about 1. Yeah, you aren't going anywhere.