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Everything posted by jf0

  1. Of course only English speaking countries use amber, it's an English word! But really only in traffic light standards or when talking about petrified tree sap! Where I am from the law *specifically* states that yellow (or amber) traffic light means you must stop unless it is unsafe to do so. So If a policeman sees you passing a yellow and judges that it was in fact safe to stop, they could potentially give you a fine for disobeying a traffic light.
  2. Well we usually assume under 'normal' conditions that we have the axiom of choice. This allows us to prove there are unmeasurable sets (and to make the pieces for banach-tarski balls). The point of the video is that your everyday intuition about measure (length, area volume etc) and 'continuum' type sets (real numbers, euclidean space etc) can't be combined without causing conflict (some sets might change their volume if you rotate or translate them for example). Axiom of choice lets you explicitly narrow down some examples (like banach-tarski). without it you can't say such things happen. It's like saying about any maths video "ahh but they didn't mention the axiom of the empty set" - the point is we make the mathematics as we think it should be, and we have tried to come up with axioms that we can reduce everything to. Not the otherway around! So we could have the axiom of choice because it makes possible banach-tarski (that's not actually why we decide to have it, just an example). Mr banach consipres with mr tarski and come up with this mathematically interesting thing. They find there is no way to reduce its description to combinations of the existing axioms, so they add choice. You can talk about the interesting mathematical thing still without ever talking about choice - it is interesting not just because of it's relation to the axiom of choice!
  3. With latest version, I have a ship with a 1.25 fairing closed on top, I went to launch pad, and before launch opened the settings menu with esc, adjusted the music volume and returned to the game, and the fairing had dissapeared. I tried again and it is 100% repeatable. The fairing wont dissapear just through entering the settings menu, it *only happens after changing the music volume*. I'm sorry if this sounds like the ramblings of a mad man but it is repeatable. Any ideas?
  4. I started a complete fresh game in a newly downloaded 1.2, every thing works fine. I rarely use any mods, and all I wanted was real plume. I added real plume, ow I can't right click anything in EVA, can't right click about half of anything any other time, after eva and entering the pod once the hatch becomes permentantly 'obstructed', the staging ui in the VAB goes insane regularly. Anyone else have similar issues, any idea how to fix? I just want stock plus real plume, that's it!
  5. I am from Australia and my native language is English. I can emphatically say that a couple is almost always taken to be a small, perhaps indefinite, amount of more than 1. "I'll have to think about it for a couple of minutes" "He saw me a couple of times." Almost never does it mean 'exactly two' except in the context of a married couple for example. in regular conversation it would usually be taken to be 2, 3 or 4. In the context of "a couple of minutes" even 15 would not be unreasonable. I now live in a country where the native language is not English, and those here that speak English as a second language also use it in this way; a small indefinite number more than one. If some one said to me "can I have a couple of days off work?" I would ask "how many?" without hesitation.
  6. The paper claims Isp from 225 upto 260, but it also contains several editing errors and liberal use of the trademark 'TM' symbol, which to me gives it the appearance of nonsense (but thats just me....)
  7. Well, apparently the cargo bay is 4.6 x 18m (I'll assume that means 4.6 x 4.6 x 18m), so it has a volume of 380000 L. Going by the capacity and volume of the external tank which is about 553000L of LOX + 1500000 L LH2, with masses of 629000kg and 106000kg, the combined 'density' of LH2 and LOX propellent in the correct ratio is about 0.36 kg/L, so lets say you could get about 133000kg of propellent in the cargo bay. according to this http://bado-shanai.net/Speculative%20Engineering/SESpShMainEngine.htm the ssme uses 466.3 kg/s of propellent, so with three engines firing it would burn for about 95 seconds. Apparently according to this http://www.braeunig.us/space/specs/orbiter.htm the dry mass of the obiter is 84t (lighter than I thought...) so this would give a delta v of about 4200m/s, and a starting thrust to weight ratio of about 2.94 ... so actually I reckon it would get well beyond the end of the runway, even with these approximate numbers... That being said, I seriously doubt it would be structurally capable of holding 133t of propellent in the cargo bay!
  8. The irrationality has nothing to do with the decimal (or any other) representation. It is to do with the fact that it is not equal to any rational number. You define rational numbers without even talking about 'base' anything.
  9. I'm no expert on parachutes, but I would guess they wouldn't give a soft enough landing on solid terrain. But you could always add some kind of squishy inflatable landing bag. But maybe by this point it is getting just as complicated as doing a powered landing with the rocket.
  10. This page http://orbitalaspirations.blogspot.it/2011/10/japanese-lambda-4s-launcher.html says: "... is, to date, the smallest ground based launch vehicle to place a satellite into orbit..." If that is true, I feel like it would be very very difficult and unlikely that a "hobbyist" beat this, even tehough it is 1970s tech. according to this also http://www.isas.jaxa.jp/e/enterp/rockets/vehicles/l-4s/ you can see the mass at ignition and burn out for each stage, the mass ratio and specific impulse, for those interested. I would make a guess that solid rockets are used as they significantly simpler to build, cheaper and smaller. It's interesting at times on these forums people ask questions such as 'why would you use a solid rocket when x is 4 times as efficient!'. In reality, you can build 'anything' if money and time is no concern. But engineering is not about building 'the best', it is about finding a way to make something that meets the requirements, within the constraints. The most important constraints are: money, time, resources. The actual capability of current technology is rarely a real problem! Eg why did ww2 give so many leaps foward in technology? It is not because the war made people smarter, it is because it made governments pour money into the problem to make it go faster, so they could beat the enemy. There are always trade offs in engineering. I would still say that it is far far far beyond a 'hobbyist' project, you would need at least a significant team of people and money to do such a thing.
  11. "Hydrogen can be stored in a metallic state" in the same sense that you can supply the worlds electricity by running hamsters in wheels, or that I can make an integrated circuit at home using a microwave oven, or I could get rich recovering gold from seawater as a hobby. In principle, yes, hydrogen is thought to have a metallic phase ... at several hundred gigapascals of pressure.
  12. Under 10t is feasible, this one took 26kg to orbit https://en.wikipedia.org/wiki/Lambda_4S
  13. The specific impulse will be very low because the specific heat of water is much much lower that the heat of combustion of, say, kerosene. Hot liquid water can hold something like 5J/g/K of energy (so cooling it from say 300 C to 0C as it expands in the nozzel could give you, say, 1500J per gram of water . The heat of combustion of kerosene is about 50000 J per gram! Very rough numbers but good enough to make a rough estimate: heat capacity changes with temperature... and ok not considering the mass of oxygen to burn the kero, but lets say chop it in half, kerosense/oxygen still gives nearly 20 times the energy per gram of fuel, and you dont need to store it pressurised at an extreme high temperature! (liquid oxygen is cold, but not unmanagably cold, super heated waterr would probably be more difficult) So in short: we want rocket fuels to hold as much energy as possible per unit mass, and an engineering tradeoff with ease of handling etc. thermal energy stored in water is nowhere near as good as run-of-the-mill chemical propellants!
  14. It's Spanish not Portuguese! The video description says (the speech in the video is just someone reading this text): "Scientists manage to capture an image of Schrodinger's Cat An international group of physicists have shown for the first time images taken with a camera without using a real object. Experts say that the idea can be useful in medicine. In their experiment, the scientists from Viena and New York used a laser and a stencil of a cat. The scientists did not choose the stencil of the cat by chance (however it could have been any other object), But because this aludes to Schrodinger's paradox. Shrodinger's paradox helps to explain the complexities of quantum mechanics. The Austrian physicist Erwin Schrodinger presented in 1935 an experiment about an imaginary cat trapped in a box, that could be both dead and alive at the same time, to demonstrate quantum entanglement of particles. The experiment by Anton Zeilinger and Gabriela Barreto Lemos is based on the same idead and they were able to 'take photos of Shrodingers quantum cat' in the process, following an according to an article published in Nature. The scientists made a circuit across which they shot pairs of yellow and red photons and with different wavelengths (after coming from a divided green photon). The yellow photons were sent toward the sillouette of the cat while the red photons toward the camera. By the phenomenon of quantum entanglement, the red photons formed an image of the cat thanks to their entanglement with their paired yellow photons. The device with which the experiment was performed can be found in use in medical applications. According to the scientists, images of damaged tissues can be created. The investigators have filed a patent application." I think using Schrodingers cat to describe this experiment is not right, but done to illustrate it to a general audience. And yes it is peer reviewed! There is a paper in Nature and here is some discussion http://www.nature.com/news/entangled-photons-make-a-picture-from-a-paradox-1.15781 and here is the paper http://www.nature.com/nature/journal/v512/n7515/full/nature13586.html
  15. This all comes about because of the idea that KSP 'is a game not a simulator', so I imagine it went something like this: Oh we think a real sized Earth/Kerbin would be too difficult/not fun/whatever for a game, so we'll make it 1/6th the size. But for simplicity, we'll keep gravity at 9.8m/s^2. Now there is a problem: that 'simplicity' implies that kerbin is super dense. Oh no matter we'll just make fuel heavier, part heavier too. Oh now our eninge isp and thrust numbers cant match up to real life, so we need to change those too. But now something else is broken, so we need to deviate there from reality too. In short, a change of one 'small' thing right at the start (who knows what, size of kerbin or something else) led to some chain reaction that means every other thing needs to be adjusted in this artificial universe to try to make other things correlate to how they would behave in the real universe. Unfortunately that doesn't make sense and it means they will always be going around in circles readjusting and deviating further from reality or reasonable numbers because in some places they have decided some things should be like they are in reality, yet in others they should be different. Basically you cannot really have everything both ways, because it is inconsistent, but they are trying hard to it seems...
  16. Of course you can, and in fact isn't that what I said: The OPs point was, I think, a frame where all other frames are at rest. This does not exist because surely given any coordinate system you can always easily find 'another' that is in relative motion. also a side note: also we should start being more specific about the correct use and meaning of 'coordinate system', 'object', 'point', 'reference frame'...
  17. Surely not: if I come up with a coordinate system that is stationary relative to me, I can come up with infinitely many that are in motion relative to it. Ok sure; if you have a coordinate system that you call 'at rest' you can come up with infinitly many that have no realtive motion to it (simple example just shift the origin by any amount...), relativity or not. But that does not mean every thing is at rest relative to it, you can still come up also with infinitely many that are in motion relative to it ... maybe you meant something else could you explain?
  18. Imagine a pump where the arrow is, imagine the second tank is missing at first. The fuel exiting the pump pushes back on the pump with the same force the pump is pushing on the fuel (this is really just like how rockets produce force anyway, so we know that works...) so in this case there is definitely a force. When the second tank is there, initially the same force pushes back to the left on the full tank. When the liquid hits the opposite wall of the empty tank,or diffuses into any liquid already in the tank, it creates an equal force to the right, so in 'steady state' there is no net force, but initially there will be a force. What I was trying to explain in my last post was: now imagine a hole in the right-hand side of the right-hand tank: some of the pumped liquid will simply 'go straight through', some will hit the walls of the right-hand tank/or mix with fuel aready in the tank. Then in this case the force is not perfectly balanced - some momentum is carried by the fuel leaving the system. In asparagus staging we aren't just pumping from one full tank to an empty one, we are pumping from one tank into another and simultaneously draining fuel from the other. The actual forces produced would depend on the geometry of the tanks and the piping and exactly how the flow of liquid occurs in the tanks. In asparagus staging (or any rocket for that matter), it is not a closed system (fuel leaves the tanks and out the rocket nozzel!), so momentum/forces does not necessarily need to be conserved/balanced.
  19. For the angular momentum of the rocket plus fuel. If you had a circular pipe filled with fuel with a pump on it, floating in space and you turned the pump on so the fuel started circulating in the pipe, the whole contraption will start rotating in the opposite direction. Conservation of angular momentum is correct, but an even more obvious way to look at it is that the pump pushes on the fuel, and the fuel pushes back on the pump with the same force. If you had two fuel tanks say arranged 180 degrees apart around a rocket and you simply pumped fuel from one to another, fuel leving one tank would push on that tank/pump and give an opposite push when it slowed down as it fills the second tank, so the net force on the rocket/tanks/pump arrangement is zero. But I think things would be different if the fuel did not all decellerate in the second tank, as would happen in asparagus staging, there is still a net flow out of the second tank. The flow does not completely decellerate or diffuse in the second tank so there is some net force on the rocket. This thing wont spin, provided the flow through the two spirals is the same because one is on the opposite direction to the other. If only one spiral carried fuel, I think there would be a net torque. But I think it would depend very strongly on how diffused the flow of fuel becomes into the second tank. Imagine simply chopping off the second tank and letting the fuel out the end of one spiral: I think we all agree it would spin then. Now imagine the second tank starts empty (hollow sphere with a nozzle on the bottom) If all the jet of fuel from the spiral went through the middle of the tank out the nozzle with out hitting the walls of the tank, I think we can still agree the thing would spin. Now what if the second tank has fuel in it? How much does the fuel flow from the top tank become diffused as it enters the bottom? Bottom line is in principle, yes asparagus staging (pumping fuel around) will cause a force on the rocket. But it could probably be eliminated by diffusing the flow into the second tank, or more likely gimbaling engines...
  20. A simple idea, no influence on game play except a little enjoyment: I'd love to be able to place flags, (or even other signs, text etc?) on my rockets in any position. Mainly I thought of this because 1) many parts that seem like they should have a flag, don't (all the fuel tanks for example) and almost without fail, the flag placement on the command pods is in a weird position: eg the 3-kerbal pod say you want to put 2 or 4 things symmetrically around it: in almost every postiion they interfere with something, the hatch, the windows, and of course the flag. If I could place the flag in any position on the surface that I wanted, I'd feel a little better .
  21. For the boost into orbit, not at all. Computers fly a combination of preprogrammed trajectory and real time calculations. All major maneuvers and burns would be pre-planned and calculated, and even contingencies for use in an emergency. Even unplanned maneuvers would be calculated by computer. I'd say usually, the astronauts punch numbers into a computer which does the work. Softwier is right about the role of astronauts in apollo, but almost all of the actual 'flying' is done by computer. During the lunar landing, the computer controlled the de-orbit burn and attitude using its inertial navigation system and radar to detect altitude. It guided the lem to a preprogrammed area and then the astronauts took partial control, in 'steering' to guide to a suitable landing place. But even during this step the computer controlled the throttle, gimbal, attitude, rcs, everything using the astronauts input to calculate the control needed. I don't know about docking, i think in apollo it was fairly manual (but i think the computer still had direct control of the rcs and used the astronauts control input and current state of the craft to control attitude and translation. And of course most things would have a manual override (except probably some things during boost to orbit...) but it would not be the 'normal' operation, in a perfect mission everything would go as it had been planned.
  22. This. This. This. add apoapsis, periapsis, time to each, etc to the staging view, fix the 'stage only' fuel calculation in the resources tab (I have never seen it give me the correct amount of fuel when I click the 'stage only button') and change the little roll/pitch/yaw input indicators under staging to show the roll/pitch/yaw RATES not the current vaule of the input! (This is really completely useless, I almost feel like it happened by mistake some one seeing a picture of a space craft control panel and seeing these little needle displays and not realising they actually should show angular rates rather than the current control input...)
  23. I always thought this would be good, but definitely a configurable option. The way I imagined it is something like this: all parts, perhaps in the r&d menu or in the VAB would have a slider. When full, the part is very expensive, but very reliable, with minimum rare faliures that are not critical (example an engine could lose 50% of its thrust or shut down early, or a battery could lose some capacity/whatever)/ With the slider at minimum, the part is cheap BUT has a higher rate of faliure, and the faliures are more severe (structural faliure, explosion, gimbal stuck at full angle etc). This could give an interesting dimension to career: make money more critical and difficult to get, you need to balance your trade off between reliablility (manned missions, critical parts like engines on your booster need to be relaiable, but maybe things like the landing light not so much), and being able to afford your missions. It could also drastically change the way you build manned ships: you might need to consider redundancy, you'll need to plan your missions and every burn you are going to make and know exactly what is the point of adding a certain part, rather than just "I'll put this stuff incase I need it, I'll work it out when I get there...". You could extend this furthur: as you use a part more often, it becomes more reliable, and if you recover a part you get a bonus to the reliablitity increase. You could also tie it into part availability: at the moment you can launch one rocket every five minutes with 20 mainsails and 10 nuke engines and 50 solid rockets if you want. In real life there is a limit to how fast they can be built. If you 'order' a more reliable part, its availability could decrease because it takes more care to build. I really like the idea of a 'space race' career mode too. there are so many opportunities to develop career mode and the gam in general, I think that now because the game has been out for a while, people are 'bored' of just launching rockets and really want new elements to the game, I know I do at least...
  24. In light of the facts: 1) All rocket engines currently use fuel and oxidiser in the same ratio and all rocket tanks hold it in this ratio 2) There is only one type of fuel and oxidiser (and I think it has been said before that adding different kinds is out of the question) 3) Jets and the nuke use only liquid fuel 4) There is no tank in the stock that can hold only oxidiser 5) all 'rocket proellant' tanks (with a couple of bizzare excepetions) have the same full to empty mass ratio 5) fuel and oxidiser have the same density - therefor the center of mass of a single tank never changes (in real life oxidiser and fuel are in seperate compartments that empty at different rates, so the center of mass will shift: in fact the way the game treats it now, fuel and oxidiser are seemingly stored mixed together in the tanks! :confused:) There is absolutely no reason what-so-ever to have seperate fuel and oxidiser resources. There should just be one, 'rocket fuel' (along with liquid/jet fuel and mono-propellant). If different engines used different ratios, or there was a tank that held only oxidiser, or they were they were different densities, then it would make some sense or have some function. What I think would be interesting is have different engines use different ratios, and fuel and oxidiser have different densities. Tanks would have a fixed volume and could be filled with any combination of fuel resources you want upto that volume (this is what would happen in real life anyway). But I'm certain this will [I]never[/I] happen in stock, so why not just scrap seperate fuel/oxidiser and have 'rocket fuel', 'jet fuel', 'monopropellant' etc?
  25. In real life most rocket propellants are liquids (or solids) which don't compress much, even under very high pressure. The reason liquid propellants are good is because they are dense without storing under pressure. High pressure means you need stronger and heavier tanks. This is why liquid oxygen,for example, is used in rockets rather than compressed oxygen gas. The density of some liquid propellants can be increased a tiny bit by (furthur) cooling and pressurising, but nowhere near doubling the density (which is what you get by clipping two tanks into each other)
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