wumpus

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About wumpus

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  1. wumpus

    Probability Puzzle

    You've nailed it. Unfortunately, word problems have sounded the same since day 1 (I forgot whether it was the Islamic-era work that the name "Algebra" comes from or an earlier mesopotamian work, but the algebra problems in translation sounded exactly like modern "word problems"). I'm not volunteering to fix it. Trying to come up with problems that are appropriate for the class to solve while ignoring the obvious math underneath seems exactly like the classic "don't think of polar bears" problem. The classic counterexample is "what's 2*7+3?". "Don't know."[US specific content follows] "what's two touchdowns and a field goal?" "17."[/US content].
  2. wumpus

    Probability Puzzle

    I'm curious under what possible conditions you could realistically acquire the information such that the odds would hold for 1/3. If each cubscout in a cubscout den had a sibling, would the odds of each sibling being a girl be 2/3? (replace "cubscouts" with "members of GetRidOfSlimygirlS" for co-ed cubscout packs). Presumably the rarity of such events means that the built-in heuristics in our brains simply don't handle the events properly (which means that people can get excited about disease tests for even less rare diseases that aren't close to being sufficiently accurate). I'm not sure where to put the Monty Hall problem. Certainly it is a math oddity (that entire university math departments got wrong), but the really weird thing is that the TV show that inspired it must have run for years, and nobody realized that there was a huge advantage in following a simple strategy. Possibly a few people did, but considering the difficulty Martin Gardner (I think his Scientific American column got the ball rolling) in convincing people that switching doors was optimal I doubt anyone believed them or cared. To be honest, most people have issues with even basic probability issues before you get into weird bayesian interactions. Teach those first, so at least you can understand how it works. True, but the world rarely leaves such things in convenient little phrases that match up to traditional math problems (if it did, science would be much easier). At least in the US, math education has been traditionally lousy at teaching word problems (although I suspect that a group who deals with the rocket equation for fun might be outliers). I can only hope that the math bits of common core are able to fix this. If you can't apply math to the real world (or spend your time doing "pure math" dealing with proofs), then it seems that a great deal of your education has been wasted.
  3. wumpus

    Probability Puzzle

    It would be 50/50 if and only if you could consider them separately. If you said the elder (or younger) was a boy then the other would be 50/50. But since they are lumped together and all you know is that one is a boy you get 1/3. This is basically the Monty Hall paradox. And yes, the wording of where the givens are lends itself to mistakes.
  4. wumpus

    Does anyone ever put fuel in the wings?

    My understanding is the whole point of putting fuel in the wings (IRL anyway) is that it *doesn't* alter the CoM. Since the Center of Lift is presumably somewhere on the wing, draining the wings fuel doesn't change the CoM. The other thing is that since the wings carry the plane, it makes the most structural sense to put the heavy fuel in the wings to avoid any structural issues: of course this leads to weird "wing wheels" in cases like the B-52 as this is only true *after* takeoff.
  5. wumpus

    Moon is a Black Hole

    Just watched the Scott Manley video on this. https://www.youtube.com/watch?v=IM8HvoaKsBU summary follows: SR= schwarzschild radius, i.e. the event horizon 1 to 1.5 SR: any attempt to orbit at this radius is doomed. I'm having issues with the math, but I think you need to burn a delta-v near the speed of light for each time you cross through this zone. Avoid at all costs. 1.5SR technically allows an orbit at the speed of light, but you will either zoom off to infinity or fall into the "doomed zone" listed above. 2.0 SR zero energy radius. Scott didn't begin to explain it. Also unstable for unexplained reasons. 3.0 SR and beyond - stable orbit. Also gets at most 30% time dilation (how much from your orbital speed and how much thanks to gravity, I'm not sure). Scott also mentioned that the numbers above are for non-rotating black holes. The black holes in the movie Interstellar are rotational and require even more math (and are not covered in said video). I suspect that to get your Obereth, you would basically get into an elliptical orbit, then burn at Pe for significant boost (just plan ahead as you will presumably get a lot more than 30% time dilation by doing that). I'm not quite sure why you chose that mass, did it have something to do with the pressures inside the blackhole being right for fusion (which really wouldn't be valid) or the accretion disc (which would)? The Sun's would be a 2.95km, the Earth's would be 1cm, and presumably the Moons would be quite a bit less than 64nm.
  6. wumpus

    Bad science in fiction Hall of Shame

    I'd have to assume that you could set a thermo-nuclear rocket to a sufficiently low setting to allow power generation with closed-loop cooling. But such a design might not be lighter than solar panels, so you would forget it and bring solar panels. A TNR is primarily designed around relatively high power and open-loop cooling, kludging it into acting as a power-generating reactor might be quite a kludge. More likely, the special effects guys knew that the ISS is more or less what any near-term interplanetary spaceship looks like (that's how we know how to build things in space), so they made it "look like ISS" complete with solar panels (and if they have nuclear power anything, make sure the black panels (cooling) are nearly as big (or bigger) than the solar panels).
  7. wumpus

    ISRU

    My comment for fancy gravity tricks is for fuel. You can "beat" the rocket equation by making sure that the fuel doesn't lift fuel. Burn ~1333 m/s from LEO, dock with fuel brought by ions (might take gravity tricks to get it into the right elliptical orbit) and burn 1333m/s, dock with last fuel depot and finally do the escape burn to Mars at 1333m/s. Even going to Jupiter you can cut the 6000m/s to 3000m/s and one or two burns to 3000m/s. This means far less fuel, and if you can get it in place by burning less fuel (because you are using ions an patience), you win. Note that the orbits of the fuel depots tend to determine the trajectory of the available launches, but launch windows do that enough anyway. Humans are doing chemical burns via Hohmann trajectories during launch windows: they are too expensive to go any other way (I'm not expecting torchships anytime soon). Everything else gets the slowboat.
  8. wumpus

    ISRU

    Fancy gravity tricks and schedules are antonyms. Moore's law (and most of the electronics industry) would have been dead 20 years ago without plenty of fancy tricks. If the cost to avoid them is too high, they get used. Ask the general public how they expect to go to Mars and they will show a torchship trajectory. Eventually they might understand a Hohmann transfer. While time may be money, I suspect that most beancounters will be willing to launch a year early (before the Hohmann window) to start the intricate dance that goes to Mars with 10% of the delta-v (and mostly done via ions) that the straightforward Hohmann transfer has. In the end, engineering is all about cost and risk. KSP mostly ignores the risk (especially for players who love the F5 key), but if the "fancy tricks" are low risk you can expect that they will be used.
  9. wumpus

    ISRU

    Energy shouldn't be a problem considering you have solar power that doesn't have to deal with weather or even an atmosphere, although in practice this will mean far less fuel than you would expect for a given amount of power. That story pretty much repeats itself over and over again in lunar ISRU, the shear scale of the ISRU facility needed to provide meager amounts of fuel means you can't build the thing until it is already unneeded. Call way, way in advance for your tanker. You really want to use ions, solar sail, nuclear, or virtually anything but kerolox-similar fuels. Beyond the Moon you probably want to use fancy gravity tricks to get wherever you need to be (assuming you have the time).
  10. wumpus

    What's kerbal money called?

    Kroots just doesn't work as well with a "k" as kredits.
  11. The simulator is pretty deceptive, especially due to build in navigation aids and third person view. Also since KSP has manual control (without guidance help from NASA computers, not even 1960s mainframes) it tends to have extremely forgiving controls and delta-v budgets. I'd recommend Orbital for a better simulator (KSP was originally conceived as a simplified (and probably 2d) Orbital). But yes, it doesn't take long before KSP players have a better grasp of orbital mechanics than any NASA astronaut of 1965 (except Dr. Buzz Aldrin). Here are a list of things needed to unlearn before/while playing with realism overhaul: https://github.com/KSP-RO/RealismOverhaul/wiki/False-KSP-Lessons Orbiter webpage: http://orbit.medphys.ucl.ac.uk/download.html And of course, Scott Manley goes into great detail about this: Can KSP teach rocket science?: https://www.youtube.com/watch?v=ogC6ds81gek&index=9&list=PLYu7z3I8tdEknQK8KQqHA5sc0wbvj2q7z&t=0s KSP doesn't teach nozzles (and gets it backwards): https://www.youtube.com/watch?v=l5l3CHWoHSI&index=8&list=PLYu7z3I8tdEknQK8KQqHA5sc0wbvj2q7z&t=0s KSP doesn't teach rocket ignition: https://www.youtube.com/watch?v=capiUBVd7EU&index=6&list=PLYu7z3I8tdEknQK8KQqHA5sc0wbvj2q7z&t=0s KSP doesn't teach plumbing: https://www.youtube.com/watch?v=4QXZ2RzN_Oo&index=4&list=PLYu7z3I8tdEknQK8KQqHA5sc0wbvj2q7z&t=0s KSP doesn't teach ion thrust: https://www.youtube.com/watch?v=Cb_U_CbQ5sc&index=2&list=PLYu7z3I8tdEknQK8KQqHA5sc0wbvj2q7z&t=0s
  12. If you want a lot of open ocean to the East (or South), nearly all locations are going to be windy.
  13. Isn't Merlin 1D more than 200% of Merlin 1A? I don't think it is 40% to 200%, but I have to wonder how much bigger they have to make the first stage merely to keep the hoverslam possible with the more powerful engines. Don't forget that changing the thrust of solid rockets is far more likely in real life than throttling liquid rockets. You can't change them in flight, but you can manufacture the rocket to give higher/lower thrust as it burns through the fuel. https://en.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_Booster
  14. wumpus

    Future Surface to Orbit travel?

    Iron is the 3rd most common element in the Earth's crust and aluminum is the fourth (and aluminum is way further down as far as the Milky Way is concerned, don't know about the asteroid belt). The main point with aluminum is prying off the oxygen atoms that are inevitably attached. Even if they are attached on the belt, you could presumably send bauxite to high Earth orbit (or possibly much closer to the Sun) for removing the oxygen and producing "frozen electricity". Of course, if we are using nukes to get to the belt, I suspect that we won't care as much about the electricity needed to produce aluminum.
  15. wumpus

    Future Surface to Orbit travel?

    The asteroid belt is almost certainly profitable to send materials back to Earth. One critical element is that it likely requires nuclear power (I still suspect that large mylar reflectors might work as well). No idea if a human makes more economic sense to be present or only robots (which would have to deal with distance lag worse than Mars). Martian colonies are likely to exist to have Martian colonies, and last until they can either become profitable or people get tired of them.