jf0

Members
  • Content Count

    32
  • Joined

  • Last visited

Community Reputation

12 Good

About jf0

  • Rank
    Bottle Rocketeer

Recent Profile Visitors

The recent visitors block is disabled and is not being shown to other users.

  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...