K^2

With Teflon, I don't even know if you'd qualify it as a fuel or oxidizer. I think it's going to depend on what you use as your liquid component. But good point. I was thinking of substances that are typically used as an oxidizer, while there are plenty of options that are simply too unstable or too hazardous to be considered. I think, by now, I can mention Sand Won't Save You This Time without linking to it. Not that it'd work as solid in a hybrid, just as illustration to things that would make a good oxidizer, but just no.

The biggest problem with solid oxidizers that I'm aware of is that all of the good solid oxidizer options I know are brittle. This is why solid rocket boosters have granules of oxidizer in poly matrix. Hybrid rockets tend to have a very similar matrix, but with no oxidizer embedded. This still works, because you still have a material resistant to cracking. But if you were to take a typical oxidizer and try to build a hybrid with a liquid fuel, under typical rocket engine mechanical stress, the solid portion is going to develop cracks, at which point, the whole thing goes kablamo. In contrast, everything you'd use as a matrix to resolve this is either a fuel or wasted weight. Making a hybrid with oxidizer in poly matrix would probably work, but then it's going to combust even if you turn off the fuel flow, which defeats the purpose. Even just throttling back a little is going to cost you performance. At this point, you might as well just go pure solid. On the other hand, non-fuel matrix would be extra weight you have to carry. I'm pretty sure you could make a silicone matrix solid oxy that you could pipe fuel through and get combustion. It would technically be a solid oxy hybrid. But ISP is going to be absolutely terrible because of how much extra weight you are carrying that you aren't using as either fuel or oxidizer.

Oxidizer is the heavier part of the propellant. You need four times the oxygen as you need methane by mass. Even if atmosphere was pure methane, it'd still be easier to build an airbreather rocket on Earth than on Titan, and we haven't even done that. The actual concentration of methane on Titan is less than 2% in atmosphere, which is bellow the flammability limit. Even if you add oxygen, it simply won't burn. To build an engine, you'll need a precooler and a centrifuge compressor stage to condense and separate methane from nitrogen, then send nitrogen to a high bypass fan and use methane-rich fraction to power the engine. This is pretty complex. And while this might work for something like a jet engine, it'd make for a terrible rocket. On the other hand, it might just about make sense to simply land the ascent stage with empty fuel tank and use a condenser to extract methane from atmo to fill it up before ascent. It's not a huge saving overall, but the 10%-20% weight reduction you may squeeze out of it is not bad, and might be worth the complexity and additional point of failure. The reason I'm suggesting condensing methane is because a) it's already really close to dew, and b) you'll get much higher purity that way than trying to pump stuff from lakes. It will be easier to build a condenser than a proper filtration system with a pump, and might actually take less energy to fill the tanks.

It's the anomaly (angle) between ascending node (place where orbit crosses ecliptic or equivalent plane for parent body) and the periapsis, which is the lowest point in ship's/satellite's orbit. It is one of the six orbital elements that specify orbit and position of the craft. Basically, it's one of the things you need to know to define orientation of the orbit in 3-dimensional space.

If you have a reasonably recent nVidia graphics card, try Shadowplay. It lets you record or stream your games with very little overhead. Most other solutions will hurt performance. Otherwise, my second recomendation would be Open Broadcast Software. Once you have video, almost any video editor will be able to save GIFs. But if you just want a couple of short loops converted, there are online services that will do it for you. The support for WebM is also growing, so you might want to consider it as alternative to GIF.

Optical rectenas are expected to be manufactured by far simpler process. Relevant scales are hundreds of nanometers, not tens. A polymer substrate also makes things easier. We are still talking optical lithography, not 3d printing, but clean room requirements are not going to be Intel-strict. We are talking your local university's prototype cleanroom, or even just a hood to keep the dust out. Unlike a CPU or display, a single grain of dust is not going to take out an entire array. So production on Mars is not out of the question. In fact, so long as timelines work out, that is what I would expect ITS to ultimately rely on for their growing power needs on the Red Planet.

You mean a GeV? Also, didn't they change definition of amu to something like 1/12th of 12C?

Works with Vive (and I'm assuming Oculus) via Virtual Desktop. Open up the cockpit you want in a window, not quite full screen size. Set cardboard mode at the bottom left. Then enable SBS direct in VD (F10).

They actually go into quite lengthy details on why not use H2. In fact, ITS simply cannot work in its current form with H2 fuel. Neither the booster nor the interplanetary stage for slightly different reasons. I encourage you to actually watch Musk's presentation and pay attention to these parts. If it still doesn't make sense after presentation, I can expand on it by filling the gaps. And cost becomes significant even at 10x prices, which is the minimum increase we are looking at for kerosene if space industry becomes the sole user. It's likely to be higher. Currently, Falcon 9 v1.1 takes about $300k worth of RP-1 to fuel up. That's ~$7.50/gallon, which is a bit pricey for kerosene, but you have to keep in mind that it has to be even cleaner than Jet-A, which is about $5/gallon. At 10x the price, we'll be looking at $3M of the launch cost coming from fuel, and that's at current cost of approximately $62M per launch. So we are looking at price of fuel going from 0.5% to 5% of the launch cost, and 9v1.1 is not reusable. For a reusable craft, that fraction becomes significantly higher. Musk's plan for ITS booster is to make it work like an airliner, where fuel is approximately 50% of the cost over the life time of the unit. At this point, if you can shave 10% off the cost of your fuel, you go for it. And if we really abandon fossil fuels on Earth, the difference between synthetic methane and synthetic RP-1 is going to be way higher than 10%. Of course, that's a very big if. More likely, we'll still have significant kerosene production worldwide by the time ITS is scheduled to start flights. But again, it's not Elon Musk's stance. He is trying to push for a world where this is not the case, and everything the two companies do reflect it. Of course, all of this is just an additional PR twist. The bigger reasons are purely practical. Methane is a great compromise between heavy hydrocarbons and hydrogen fuel. And FFSC design of Raptor absolutely requires methane as fuel. Hydrogen would have worked perfectly fine for Raptor, but as I've mentioned above, there are other reasons not to go with that. As for efficiency, once you take into account the additional weight of the tank you need for hydrogen, Methane is actually almost as good. The only place where you really have to go with hydrogen is SSTOs. For everything else, hydrocarbons a good enough option. That's why Russians are still flying RP-1, and that's why even SpaceX's Falcon rockets are fueled with RP-1. And as you yourself point out, Musk is definitely not a stupid person.

To clarify, what we sometimes incorrectly refer to as an explosion in conventional rocket engine is still formally a combustion. The wave front propagates at subsonic speeds, matched by the speed of the fuel and oxidizer inflow. This means that pressure at which combustion happens is entirely determined by the pressure at which the fuel and oxidizer are fed and which combustion chamber can withstand. Detonation wave travels at supersonic speeds. For conventional rocket engine, detonation is bad news and usually leads to RUD of the engine and the rest of the rocket. On the plus side, however, the pressure is generated entirely by the dynamics of the gas, and can be dramatically higher than anything you can achieve in a conventional rocket, leading to higher overall efficiency. If you can build an engine that is designed to withstand detonation, you can potentially build a lighter engine with better ISP. But this involves extremely hard engineering and mathematical problems.

Well, no, not with current fuel prices. But you have to also keep in mind that Elon Musk is a founder and CEO of yet another high-tech company, Tesla Motors. A company founded on a principle that fossil fuels have had their time, and we can and should be moving on to better things. The future that Tesla Motors envisions has no need for massive global scale oil extraction and refining. A world where kerosene is actually a very expensive fuel. Whether you think we can get there within the time frame set for ITS or not is beside the point. Fact remains that SpaceX acting as if kerlox is a good idea in the long run would be undermining that. So SpaceX is building the ITS as if kerosene is something that might need to be synthesized whether you are on Mars or Earth. And if you are going to synthesize your fuel, methane is by far the cheaper of the two. If SpaceX ends up using the same production pipeline for methane on Earth as it's planning to use on Mars, it can also be killing two more birds with that stone. First, they get to test all of their systems extensively, and see first hand all the little things that can go wrong so that they can make sure this doesn't cause problems on Mars. Second, provided that they manage to source all their energy from renewables or nuclear, they get to claim to have environmentally friendly rockets. After all, net carbon footprint of an ITS launch is actually going to be negative in that case. All the carbon for fuel is extracted from atmospheric CO2, and only some of it is burned in the atmosphere, so they'd be ferrying CO2 off the planet in a way. Of course, for the time being, it's way cheaper to extract methane from natural gas, so they might not bother for the boosters. But I bet the fact that they can claim they could was at least a small factor.

Pulsejets are inherently limited to a low chamber pressure, which means low efficiency. You can't cheat thermodynamics. You can submit and build a proper engine. Scramjet as a first stage isn't a terrible idea, but then you are forced to use a booster and the actual duration in flight during which it will be useful isn't great. A much better idea is an air-augmented rocket.

If you have to involve a moving picture in your explanation, you might be picturing it completely wrong.. Space-time is static. It just looks like it's expanding to us because we're in it, and it happens to be smaller on the side we call "the past". On the more concrete side of it, while it's entirely possible to construct geometry that has time acting like minor circumference of a torus, not just any geometry is valid. Space-time geometry has to be a solution to Einstein Field Equations, and we know something about matter content in the visible universe at least. Since our observation is that the universe is not only expanding, but undergoes accelerated expansion, this would imply that the "sides" of the torus have been "blown out", and the size of the universe tends to infinity on the "upper" half of the torus. In which case, the "lower" half might as well not exist. More importantly, as I've indicated at the top, there is no actual movement. "Upper" and "lower" halves of the torus are absolutely identical. There is no reason why universe would be expanding in one half and collapsing in another. In fact, our choice of time direction is entirely driven by the expansion itself. Which means that inhabitants of both the upper and lower halves would describe their universe as expanding. This would be true even if the size was finite, but it would also have very interesting implications for how the universe ends. On the net, though, it absolutely doesn't matter. Since expansion is accelerated, we can concern ourselves with just the portion of universe we happen to be in and treat it as if it's the only thing that exists. For all practical purposes, it is.

The turbo pump unit is also going to be heavier, as well as all of the plumbing. And we know that at very least there will be the short bell and full bell versions of Raptor. But I think they are going to try to keep variety to a minimum and try to leverage economy of scale for these. That's why it's Raptors all the way down. Scot Manley did some videos that are relevant to the Raptor and some of the discussions that took place earlier in the thread. It won't be anything new for people who already did their homework on liquid fuel rockets, but for anyone wondering about the different sizes of nozzle bells or turbo pump configurations, this could be a very simple way to learn about it. Nozzles Full Flow Staged Combustion

The answer is always no, of course, but it's an even bigger no in this case. Quenching takes superconductor to normal phase, which means it becomes a resistor. In turn, that means it's guaranteed to dump all of its energy as heat. There is absolutely no way to recover that with capacitors, magical or otherwise, since heat is generated in the former superconductor itself. It is possible to use superconductors to convert between mechanical and electrical energy almost flawlessly. But that still doesn't give you a way to generate extra energy. Nothing does. Such is the fundamental symmetry of our space-time. Not that it can't be fun and/or educational to figure out why such things don't work.

You do realize that proteins, and anything else that relies on hydrogen bonds, are going to be frozen solid at 90K, right? Fortunately, the only reason we need hydrogen bonds for our life is because weaker bonds can't withstand 300K. On Titan, they don't need to. If cryogenic life exists anywhere in the universe, its basic molecules aren't going to be proteins. They will be much simpler hydrocarbons with no functional groups that would result in strong polarization. The energy scale you are looking for at 90K is van der Waals interactions. There are a number of functional groups that would allow hydrocarbon chains to behave similar to proteins, but at much lower temperatures and with no polar bonds involved. The perfect solvent for these molecules is, indeed, methane. There are limitations, certainly. Flexibility is much less of an issue for proteins at 300K. Getting hydrocarbon chains to fold at all at 90K is going to require a lot of compromises. That means, you are going to lose a lot of complexity. At the same time, I'm not expecting marvels of intracellular engineering like the kinesins or the ATP synthase. We are talking about the most basic life. Something that can metabolize acetylene to power self-replication and construction of the simplest of barriers between itself and the environment. That doesn't take nearly as complex of biomolecules as complex life requires. If it did, life would probably never be able to evolve in the first place. I have no doubt that life on Titan is possible. Given unlimited time and resources, even with our understanding of biochemistry, we could engineer something that would qualify. The only question is whether it's capable of emerging naturally. Given much, much slower rates of all chemical processes and reduced variety of options that could possibly work, age of the universe might not be sufficient time for this to have happened anywhere. Then again, all other chemical barriers are lower, and variety of molecules isn't as high to begin with, so maybe it's not all that difficult. I have no idea. I'm pretty sure nobody else can say for certain as well. Given that Titan is practically in our backyard, on cosmic scale, we really ought to just check.

This seems relevant.

Different type is a much stronger indicator. Any life we find on Mars or in subsurface oceans of outer moons can have common origin with terrestrial life. We find rocks from Mars on Earth all the time. life could have easily first evolved there. Or it could have evolved on Earth and one of comet impacts would have spread it through Solar System. We've had life long enough for this to have happened several times over. If life we find happens to have same origin as life on Earth, we are back to sample of one. No matter how rare life is in the universe, we are guaranteed to live in a star system that has life, because we are a life form. So the basic fact of finding life elsewhere in the Solar System tells us nothing. But if we can prove that it has evolved independently, then we can make a statement about how common life is likely to be in the universe. And while water-based life could still prove to be different enough that we could distinguish it as separate origin, even that would take decades of research to exclude a very early diversion. Methane-based life, however, could not have come from the same ancestor as water-based life. So finding life in surface lakes of Titan would automatically give us two distinct origins. Not that I'm going to complain about discovery of any sort of life on any other body in this Solar System. It'd still be a great discovery and we are bound to learn much invaluable information. If I can stretch my earlier lottery analogy, finding life anywhere in the Solar System would be winning a lottery, but finding it on Titan would be getting the big jackpot.

Gravitational waves work exactly the same way as photon drive for propulsion. They also follow the relation E = pc. And because in these quantities, E of the craft actually contributes to the mass, while radiation itself has no mass, you still have to expend mass to propel yourself. The most efficient method being consuming matter and anti-matter. Whether you use the energy to produce gamma radiation or gravitational wave is absolutely irrelevant. You get the same thrust. This is because the conservation laws apply to absolutely all forms of propulsion, or indeed, interaction in general. If you take a system that's uniform in spatial dimension, such as vastness of empty space, linear momentum is conserved. To accelerate a body, you must expel something with opposite momentum, which, in turn, requires craft to consume mass one way or another. It's a fundamental problem with all forms of propulsion, including OP's proposal. This does break down if you break down the symmetry. If you are orbiting a planet, there are tricks you can pull. But you need to be working with the scale comparable to scale of the problem. Various forms of tether propulsion rely on this. Which is why the test a propulsion method must pass is whether or not it can work in empty space. If it is, it must expend reaction mass or equivalent in radiation. No exceptions.

Statistics and entropy. Given life on Earth, I can say with confidence that there is life on Earth. Given life on Earth and on Titan, I can construct a probability distribution that is very heavily slanted towards some form of life being present in nearly every star system. If it was otherwise, finding two planets with life in the same star system would be extremely unlikely. And the type of planet or life form is irrelevant. We just have to be able to exclude common origin via panspermia. And no, this doesn't tell us that life on Titan-like worlds is likely. That would be true if all we had was a completely random star system and we found life on it on a Titan-like world. No, the crucial statistical quirk here is that there are two distinct origins for two distinct life forms in one star system. Rest is cold statistics. Fermi Paradox is better viewed as proof by counterexample. (I'm simplifying a bit, but I don't want to get bogged down in details.) Suppose life is common in the universe. Suppose, it is natural for complex life to evolve from simple life. Suppose, complex life tends to evolve towards intelligence. Suppose, intelligent life tends to evolve into a space-faring civilization. Then we ought to have encountered some indications of one in our neighborhood. We have not, therefore, one of our assumptions is false. The condition preventing that assumption from being fulfilled is referred to as the Great Filter. The big question is, which one is it? We are pretty confident about simple life to complex given a good environment, and there are going to be a decent number of planets with the right environment based on latest data. Finding life on Titan would also cross out the first one. So either intelligent life isn't common, or civilizations don't make it very far past discovering radio and space flight. If it's former, we might not have anything to worry about. If it's the later, we are heading for some catastrophe more likely than not. Right now, our best bet on great filter being behind us is if life is not all that common to begin with. That would mean Earth is special, either due to circumstance or by lucky draw. Life on Titan shoots it down, dramatically increasing the odds of great filter still being ahead. And that's something we really, really need to know.

Correct. However, observations on gravitational lensing and rotation speed agree. Which means that while luminous matter does not add up to the total masses of galaxies we've observed, whatever adds to it still behaves like normal matter. At least, in all of the ways that are relevant to discussion of gravity. This means that we are either missing something in our models of star systems (e.g. MACHO hypothesis) or there are particles we have not discovered that contribute to the mass (e.g. WIMP hypothesis - aren't scientists great at naming things?). What this tells me is that while we are definitely lacking some information about dark matter, there is no indication that it behaves in any way differently from ordinary matter. Again, with respect to gravity. So we're completely in the clear with General Relativity (which is the branch of Field Theory containing conservation laws) and might or might not be missing some matter fields in the Quantum Field Theory. At the worst, there are a few particles that aren't part of the Standard Model yet, and the underlying physics is intact. Naturally, I can't insist on this as a certainty, but there is zero indication of the opposite from experimental data. Dark Energy is more interesting. It's still in the clear with General Relativity, which is why I insist that it still gives us no reason to suspect any problems with conservation laws, but it definitely points to us missing something in Quantum Field Theory. Still, as of yet, there is no reason to suspect that it's something absolutely fundamental which would make us question the principles that go into Field Theory. Just the Standard Model specifically. And that still leaves conservation laws way, way in the clear. Honestly, though, neither makes me as uncomfortable as the largest error in physics, and even that seems to stem either form Standard Model, or our understanding of divergences in QFT. Either way, still no reason to suspect any problems with underlying theory.

I'm not going to insist on it as "one true philosophy" for space exploration. But there are two factors here, philosophical and practical. Discovery of life on Titan makes it an almost certainty that extraterrestrial life is abundant in the Universe. The philosophical implications are "We are likely not alone." There either are, were, or will be other sentient beings among the stars. One may argue that it already seems likely, but with a datum of one, which is effectively zero due to anthropic principle, we can't really draw any conclusions. Having two points of data, we can make a strong statement about this. Second is practical. If life is found on Titan, Fermi Paradox suddenly becomes that much more important. It tells us with extreme confidence that origin of life isn't the Great Filter. This still doesn't say with certainty if the filter is ahead of us or behind, but it just shot down a likely candidate for the past, and it's a red flag at the very least. When survival of the species is on the line, knowing this information as early as possible could be crucial for us avoiding whatever calamity we might be heading for. There are other reasons why space exploration is matter of species survival in the long term, but exploration of Titan would still further these goals. As such, I conclude that exploration and discovery of life on Titan would be the most important scientific achievement of Human kind to that point. Whereas exploration of Titan with no discovery of life would simply be an important step in space exploration in general. And centuries down the line, hopefully, we'll make bigger and more important discoveries to which Titan was but a stepping stone.

Dark energy is a pressure term in the stress-energy. It's completely conservative. And dark matter is just matter. It's not radiating, so we can't tell what it is, but otherwise, it's just matter. It follows ordinary, Newtonian physics as far as all the forces go. So yeah, all of these things fall under umbrella of Field Theory. Other than the fact that we still have not pin-pointed the sources for these, there is nothing special about them whatsoever. That's why scientists talk about them with such confidence despite having not actually seen any.

To be mathematically precise, we are 99.9999999999% certain that they are valid in Quantum Mechanics. This is precision to which modern field theory is tested with experiments. To put it into perspective, odds that there will be another sunrise tomorrow are nowhere near as certain. You have better odds to win a lottery, yes, even without buying a ticket, and then get struck by lightning on the clear day while on your way to pick up the winnings than for conservation laws to fail. There is a higher probability that there is a lost island somewhere in the pacific with real life unicorn than for symmetry relations being a fluke. There are caveats. There are ways to achieve propulsion with no exhaust and without violation of conservation laws. But these are very fine details. If you see a device that is claimed to be capable of operation in an empty vacuum of space, it is safe to simply say it's baloney. Whether it is mechanical or employs QM trickery makes no difference. Later just makes it harder to spot the specific flaw in logic, but conservation laws are only stronger in Field Theory. The only cases where some slack can be cut is if device claims to operate only in orbit. But even then, typical energy densities required for known configurations are comparable to warp drives. In other words, the grain of salt should be rather considerable in diameter. As for educational value of lettings posts like this be, valid point, however, we always have exactly the same explanation. Maybe we should have a pinned topic on conservation and thermodynamics laws that mods can link to and lock the offending thread. There is no reason to have the same material repeated over and over again. I mean, I might have used leprechauns instead of unicorns last time I explained this, but otherwise, there has been no significant breakthroughs in field theory for the past fifty years that would even suggest that there is flexibility on these laws. If anything, we managed to gain stronger and stronger confirmation. We already have a thread on EM Drive. I'm happy with that. We don't need one every time a new person shows up with zero understanding of even classical mechanics claiming to have invented an amazing device that violates all known laws of physics. Yes, I'm saying all laws, because every single principle can be derived from conservation laws as a consequence of underlying symmetries. The EM Drive, at least, is interesting in that the flaw isn't obvious. But the moment someone says "springs" or "magnets", or worse, both, we really don't need to hear the rest. A boilerplate response thread is all we need.

You are decades late for this "theory". There is an entire set of topologies of the universe that admits matter and antimatter on the opposite sides of the expanding universe. This hypothesis is one of the explanations for matter/antimatter imbalance. Of course, there is no danger of it collapsing, since expansion is accelerated. And this has nothing to do with multiverses. It's all part of one universe.