Jovus

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About Jovus

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  1. Hello @ferram4, I went back to college to get a PhD in Physics in large part because of your work, and eventually settled into CFD. Way back when I first became aware of FAR I was impressed, and it ignited a love for aerodynamics (specifically around rockets and re-entry) that I had never had before. Now that I'm much more familiar with the problems involved and the methods used to solve them, I'm even more impressed. Flabbergasted, is the word, that you've made an acceptable-accuracy aerodynamic calculator for almost arbitrary shapes that works in real time on a home computer to any accuracy while that same computer is also running everything else KSP does. Kudos to you. Greatest kudos.
  2. Oi. Yes, it is. Density was used to find the radius of the 'disk' (cylinder). So the radius is off by a factor of 103, which means acceleration due to gravity on the surface of the sphere is off by a factor of 106, and centrifugal force is off by a factor of 103; but still, the disk won't fly apart under the force of its own rotation.
  3. Well, yeah, the hypothetical is absurd. It would definitely condense into a sphere; that's in fact what actually happened according to our current models. (Though it may take a good long while on a human time-frame.) However, I should point out that the whole point about centrifugal force being lower than gravitational force was to see whether this construction would immediately fly apart at the rim, which it wouldn't due purely to mechanical forces of the object itself. (In 'reality', of course, perturbations from the other celestial bodies would take care of it pretty quickly.) As to the moment of inertia: no, you want the moment of inertia around the z-axis. Moment of inertia is relative to the axis of rotation, and the axis of rotation for this disk is through the z-axis (that is, I took it as rotating like a top or the disk in a gyroscope, instead of like a coin spun on a table). As for the rest, I was explicitly not treating of anything other than the barest, simplest-order mechanics. You can if you like. I admit there would be other effects; I just don't care enough about the question to work them out.
  4. Now continued. First, found a couple stupids. We assume the density of the Earth, and therefore the volume of the Earth, is unchanged. Modeling the Earth as a perfect sphere of uniform density (close enough for our purposes), we find: VEarth = (4/3)*π*Rearth3= (4/3)*π*(6.371 x 106 m)3 = 1.083 x 1021 m3 Now we can say Vdisk = VEarth = 1.083 x 1021 m3 = 2πhRdisk2 , or Rdisk = sqrt((1.083 x 1021 m3)/2π(10m)) = 4.152 x 109 m which is a lot more reasonable. so the force on a mass m at the surface of the disk (on the outer edge, not on one of the faces) is Fgrav = GMm/Rdisk2 = m*(2.3 x 10-5 m/s2) So our new 'g' (acceleration by gravity at or near the surface) is 2.3 x 10-5 m/s2 Putting that into perspective, gPluto = 0.62 m/s² and gGilly = 0.049 m/s2, though I find those numbers suspect. (The Pluto-Charon system has a barycentre outside itself, so gPluto necessarily depends heavily on where you are on the planet, and Gilly is lumpy and small, so the same can be said of it.) Since the Earth didn't lose any mass in the transition, angular momentum should be conserved. Since the disk is spinning through the same axis, and it's also a prinicpal axis of the disk, the calculations for moment of inertia are simple: LEarth = IEarth * ωEarth Ldisk = Idisk * ωdisk LEarth = Ldisk so IEarth * ωEarth = Idisk * ωdisk Moment of inertia of a sphere is 0.4*mr2, so IEarth = (0.4)*(5.972 × 1024 kg)*(6.371 x 106 m)2 = 9.696 x 1037 kg*m2 Moment of inertia of a disk is 0.5*mr2, so Idisk = (0.5)*(5.972 × 1024 kg)*((6.371 x 106 m)2 = 5.148 x 1048 kg*m2 TEarth = 1 day = 86400 sec, so ωEarth = 2π/86400sec = 7.272 x 10-5 rev/sec IEarth * ωEarth = Idisk * ωdisk so ωdisk = (IEarth/Idisk) * ωEarth = ((9.696 x 1037 kg*m2)/(5.148 x 1048 kg*m2)) * (7.272 x 10-5 rev/sec) = 1.370 x 10-10 rev/sec Which means that a day on the disk is roughly twice as long. (hah! That's very wrong. But 'twice' is revealing to the way astrophysicists think, so I'm leaving that in.) Tdisk = 2π/ωdisk = 2π/(1.370 x 10-10 rev/sec) = 4.587 x 1010 sec, or 5.31 x 105 Earth days. Now then, the force from gravity at the rim of the disk as shown above is m*(2.3 x 10-5 m/s2) (where m is the mass of a particle on the rim), but centrifugal force on a spinning object is -m*ω x (ω x r). The cross-products, on a disk spinning through the centre around the z axis, resolve to radial out, and Fcent = -m*ωdisk2*Rdisk = m*(1.370 x 10-10 rev/sec)2*(4.152 x 109 m) = m*7.790 x 10-11 Compared to Fgrav = m*(2.3 x 10-5 m/s2), we can say that this object wouldn't spin itself apart. So much for simple mechanics. I'll leave worrying about interactions with other bodies, weather, effect on life, thermodynamic effect of injecting enough energy to accomplish this feat, etc. to other minds.
  5. Just for funsies:( Gravitational force at the surface of the Earth (in 'disk' configuration): GMm/r^2 M = 5.972 × 1024 kg Now then, the average density of the Earth remains unchanged at 5.51 g/cm³ or 5.51 x 10-9 kg/m3 (because I said so) Assuming the disk is a smooth disk with h = 10m, that makes Vdisk = 2 πhRdisk = 3.29 m3, so Rdisk = 5.237 x 1014 m2 G = 6.67408 × 10-11 m3 kg-1 s-2 so F (on a mass at the 'rim' of the Earth) = m*(1.45m/s2) Or 1.45m/s2) is our new 'g' To be continued when I get home/feel like it
  6. Also, maps of the near side were better, so it was a lot easier to choose and aim at good-looking landing spots.
  7. Nope. Wouldn't fit in my freezer, and the warranty doesn't last that long anyway.
  8. The recent historical answer has been spy satellites. Some of thos suckers are really big.
  9. Jovus

    KSP Acquired by Take-Two Interactive

    Also, I could easily see DLC covering areas of the game that people want but that have been off the table for a while now, all without changing anything truly core to the game and without harming craft intersharing by releasing new parts. For example: New Planets and moons (we finally get that second gas giant) Storyline content (either sandbox puzzle-clues leading to some culmination like the original story idea for KSP, or even something more scripted to fit an actual 'campaign' Factions to work with/compete against Some kind of multiplayer support
  10. Jovus

    KSP Acquired by Take-Two Interactive

    I for one look forward with cautious optimism to the future. There are companies who specifically purchase IP in order to ruin it, but that exclusively happens when that IP is in competition with something else the acquiring company offers. That's definitely not the case with KSP. It's possible that Take 2 will somehow flub the KSP market, but I don't think they'll set out to do so. Big companies aren't evil by virtue of being either big or companies. They sometimes make decisions you might disagree with, because they prize different things (revenue, for example), but it's not like Take 2 is staffed by a secret cabal of sith wizards who extract continual youth from the tears of gamers. And the funny thing about caring about revenue for a product is that Pareto optimization is automatically psuedo-democratic. Maybe with fresh collaboration efforts, someone will finally have the bravery to fix some of the established warts in KSP, like the career system. Probably not, but a man can dream.
  11. Jovus

    KSP Caveman Evolved Challenge

    ...you know what, sure, I'll give this a go. Though don't be surprised if I just drop off the radar. I've got an RP-0 save that needs my attention, and, you know, real life keeps interrupting. Important mods: [x] Science! BetterBurnTime Docking Port Aligment Indicator Interstellar Fuel Switch. This might get moved to ModularFuelTanks. I have this because I want to be able to use the NERVA, eventually. Kerbal Engineer. I'm aware this makes things way, way easier. Kerbal Inventory System. I never use this, and maybe this save will force me to finally do something with it. PreciseNode - I might drop this. Procedural Fairings TAC Life Support Universal Storage - I've never used this before, and it looks interesting. I also have a number of other QoL/visual mods, but nothing that should change gameplay. This will also be one of the very few times I play the game without Kerbal Construction Time. We'll see how that works out; maybe KCT has been holding me back and contributing to my KSP fatigue. Settings screenshots: Hopefully I'll get a chance to fly later today or tomorrow.
  12. Jovus

    Realism Overhaul Discussion Thread

    You beat me to this post by about ten seconds.
  13. Jovus

    Realism Overhaul Discussion Thread

    Thanks. I was hoping for some specific link hinting for a resolution to the problem; I know where to find Heat Pumps. I'll look about and see if I find something. (I'm not upset or snarking at you; just explaining that I didn't intend to use you as my personal LMGTFY)
  14. Jovus

    Realism Overhaul Discussion Thread

    You happen to have a link? Last I checked the HeatPump thread (yesterday morning) there was still a problem with timewarp over 1000x, which for me personally isn't worth the trouble. I suppose I could just bash together an MM cfg to remove all boiloff from cryogenic tanks. Also, thanks guys for answering my question above.
  15. Jovus

    Realism Overhaul Discussion Thread

    I'm one of those masochistic guys who likes to build planes in RSS/RO and try to get them to space, not because it's a good idea, but because I want to, damnit. I was surprised to find in 1.2.2 that the runway now has huge gaps that like to catch my gear and toss my plane into the air. I vaguely remember some blog post about Squad trying to fix something with PQS modeling, so I suspect this is a stock bug that just gets hugely magnified by the real scale, but I figured I'd ask: does anyone know a fix, patch, or workaround for this issue? T'anks.