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K^2

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Everything posted by K^2

  1. GREEN FLAME! But yeah, there is honestly no reason to invent anything new. If you need all the ISP you can get, you are probably going to go with cryogenics anyhow. And if you are looking for something you can store, your considerations are probably closer to these of cost and safety, and then you can't do better than RP-1. Oxidizer, there are more options with, but again, it's hard to beat N2O4 for relative safety and ease of use. Chemical exotics are just not worth consideration after nearly a century of rocketry. We ought to be looking strictly beyond chemical energy now.
  2. It's a type of silicone rubber. So it's going to depend on curing agent and amount of carbon and hydrogen present. I think you'll have to do tests, as shynung says.
  3. I still say it's better to go with something relatively inert, like silicone, than hunting for something with halogens in it. Edit: It really shouldn't react by itself. It might add a bit to fuel as it disintegrates, but not significantly. That said, I have never tried mixing silicone with an oxidizer. And you do have to be careful with curing agents. Some of these will readily ignite with oxidizer. But there are plenty that will not.
  4. No idea about other countries, but here in the States, I might need a HAM license. Tidal orientation-keeping isn't an option, because the sat is going to be spinning as required per experiment.
  5. I can guarantee you that PVA + KNO3 will burn. In fact, you can make a solid fuel rocket out of just these.
  6. With solid/hybrid motors, your combustion chamber is surrounded by your solid fuel (or oxidizer, as case may be). If walls of your combustion chamber got hit, that means your fuel burnt through. Avoid that by making sure liquid runs out first. All the walls have to do is hold the fuel (or oxidizer) together against the pressure in the chamber. They do not need to be very heat-resistant. Indeed, hobby rocket motors are made out of cardboard. Of course, you might have to deal with more pressure, so maybe some sort of plastic would be good. But something non-brittle, so that you don't get with sharp edges on shrapnel when it does explode. Nozzle does have to withstand high temperatures, but here the situation is opposite. Temperatures are too high. If you build your engine right, metal nozzle will simply burn through, and you'll loose pressure causing your engine to fizzle out. Or, you know, spray liquid fuel all over the place and light up whatever's near. One or the other. Best material for nozzle is carbon. That stuff sublimates at 3900K, which is way, way higher than any metal. And it cools itself as it does so. It's also pretty easy to work with. It's not cheap, but you shouldn't need anything bigger than a five pence in diameter, and maybe a few mm to 1cm thick.
  7. Using cheapest materials isn't always the greatest idea in rocketry. I do understand trying to be thrifty with the stuff, though. Just be careful. And if you do end up causing trouble and anyone asks, you got all your advice on 4chan. P.S. And by the way, the most important advice in this thread was given on the previous page. Do not use metal parts. That stuff will explode. There will be shrapnel. In rocketry and explosives, safety rules are written in blood.
  8. If you go to ATV page on Wikipedia, in the panel on the right you can find, "Main engine: 4 × 490N, Aerojet (GenCorp) Model R-4D-11." For a total of 1.96 kN of thrust.
  9. I hope you mean kN. I think you are going to have to be more precise. What do you need ATV thrust for? Are you coming up with a problem for a project, or solving one? If you are solving a problem for ATV thrust, you should probably solve the problem. Edit: But this info is available on Wikipedia, so I'm a little confused about you asking it here.
  10. Anything that's solid needs to be bound into a soft matrix/binder. It's how you avoid cracks. Take a look at composition of shuttle boosters. From Wikipedia: "a polymer (such as PBAN or HTPB, serving as a binder that holds the mixture together and acting as secondary fuel, 12.04%)." It's the "secondary fuel" that you'll have a problem with when building a solid fuel hybrid. But not every possible binder is reactive. I think I'd start by researching silicone options. It has some organics, so it does have some reactivity, but that's basically just going to allow it to disintegrate as oxidizer is consumed. It shouldn't be capable of self reacting under any conditions, I don't think. At least, with "reasonable" oxidizers, like KNO.
  11. Oh, absolutely. Paying for a torquer would be a criminal waste of whatever money people end up entrusting us. This isn't an MRI spectrometer, where mag field has to be perfect. As for ground station, we might be able to just do radio bursts with higher power. But I really am going to take a look at how feasible a ground array is going to be.
  12. Yeah, if you buy any significant quantity of ammonium nitrate, expect a visit from well dressed men with no sense of humor. There isn't really a specific reason why you can't make solid oxidizer hybrid, but there are additional challenges. Just like with solid motors, you usually want some sort of a matrix to bind your oxidizer into. Otherwise, you might end up with cracks, and the only way that can go is boom. With conventional hybrid, matrix is part of your fuel. Problem solved. With solid ox, if it starts reacting with matrix, you won't be having a good day. Unless you plan for it. But then you aren't even running a liquid-solid hybrid. You are running a liquid-solid-solid hybrid hybrid. I have no idea what British Law would say on the topic, but the judge is liable to fine you for a headache he's going to get, at least. I'd stick with conventional hybrid and explore liquid ox options you have. There is way more out there than just NOX, LOX, and peroxide.
  13. Newt, Mbobrik is trying to convince us to use directional antenna and rotate the sat towards target on Earth. I'm not convinced, at the moment, that it is a great idea. For reasons of reliability, complexity, added weight, and power generation and consumption. I'm not all together certain that it wouldn't affect the experiment, either.
  14. Warp to a remote location, accelerate to near light speed away from Earth (using reaction drive, not warp), warp back to Earth, decelerate. As you can see, it's practically impossible even if you have FTL. P.S. Essentially, it's the same reason FTL + wormholes give you time travel. The extreme acceleration you need to pull this off causes extreme space-time curvature from perspective of the pilot. (Gravity indistinguishable from acceleration, etc.)
  15. Geometry gives you energy density. There's a formula. (See: Einstein Field Equations.) Alcubierre Metric has ring-shaped energy density distribution. It's not something you can change. If you take a different energy density distribution, you'll have a different metric with different geometry. It can still be a warp metric. But it won't be Alcubierre Metric.
  16. Do you actually know what "symplectic integrator" means? I have no idea how you've managed to pick up that term and not understand something about potentials. In the context of gravitational interaction, and without getting into details of symplectic geometry, symplectic integrator would be the one that keeps energy within roughly the correct value. It can change due to numerical errors, but these errors don't explode over time. For example, if you are simulating a spring, Forward Euler is not symplectic. But then pretty much any second order method is. Which is why nearly every half-decent game simulation is done using Velocity Verlets. It's enough to prevent your collisions from "exploding" the system. Gravity has no symplectic method. Any integration method will end up with energy being lost or generated in the system. And that very quickly causes the system to diverge from true solution in chaotic and unpredictable way. There is no fix for it. You can keep padding your numerical accuracy and reducing the step size, using implicit methods for every step, but you will eventually have to give up. The reason we can do better with planets is because we use classical perturbation theory to improve our computations. These are analytical methods that let you take into account the most significant deviations from Kepler. So when we get down to numerical integration, we aren't computing the trajectory, but just small deviations from it. If you have skill to actually write a numerical integrator, I suggest you try this. JPL's Horizons will let you get NASA's solutions for trajectories of major bodies in Solar System. You can get it to dump literal XYZ coordinates with respect to your chosen origin. (I recommend using Solar System's barycenter, because you'll be in accelerated frame otherwise.) Grab the data for the Sun, all planets, major moons, and anything else you might consider a significant source of gravity. Then get trajectory of some comet or asteroid. (67P/Churyumov–Gerasimenko, for example?) Try to take its initial position and velocity, then use your favorite integration method, and see how close you get to the actual trajectory. Don't forget to compare kinetic energy at different points. After you have tried this, I think we'll end up having a completely different conversation about N-body dynamics.
  17. And there is no symplectic method for 1/R potential. So you are down to implicit integration over collocation points, or some variation on that, which tends to be extremely time consuming. It also can't be broken into parallel computations, because you are solving a non-linear optimization problem at each point. Or we'd all be doing that.
  18. Ah. Yeah, that might actually be cheaper and easier to make than a mechanical tracking station. Definitely worth considering. Very high chances of it seizing up. I'd try to come up with something that's either more reliable or has redundancy.
  19. Also, while not a huge problem with 3 bodies, a general N-body 1/R potential problem is a numerical nightmare. Don't trust any game-oriented literature on the subject. You can run a plausible-looking galaxy with millions of stars using GPU, but you wouldn't be able to simulate trajectory of a comet well enough to say for sure if it will hit your planet within a few years with just a handful of significant sources of gravity in the system. And for a KSP-like game, ability to predict precisely where you'll end up is the key.
  20. Both are bad. Spin rate must stay constant for experiment. Mechanical rotation is problematic in space. Consider, e.g., problem of bearing lubrication kn vacuum. Any ways, the only reasonable way to reorient the axis is precession. Phase array is only viable in microwave, and even then, very limited with 10cm. UHF array is practically useless at this scale. I would also lean towards omni, and consider precession as plan b.
  21. One of the things I'd like to have on board of the sat is at least one optical gyro for spin rate/orientation control. So it will be measuring speed of light about a hundred times a second. Or rather, it will measure a quantity that depends on spin rate and the speed of light. But if we grab accelerometer data to establish spin rate independently, it does give us a speed of light measurement. Problem is, it'd be imprecise measurement due to accelerometer measurements being of limited quality. Which is the reason for having optical gyros in the first place. By assuming the known value for speed of light, we can get very precise rate of spin measurement instead. Just thought you might find it interesting.
  22. Sound doesn't travel in vacuum. LEO isn't perfect vacuum, but satellite orbits are far above the altitude at which any discussion of sound is sensible on relevant scales. For all intents and purposes, molecules/atoms up there are ballistic projectiles.
  23. I seem to recall Duma working on a law that would limit export of RD-180 anyhow. This is a good move. It will force military to invest into a replacement before Russia refuses to supply these engines.
  24. I've just realized, as I was writing it all down, that centrifugal potential breaks the cylindrical symmetry in the rotating frame. So it probably needs to be planar, after all. At least, I see no obvious way of separating this crocodile of an equation.
  25. Indeed. In order to get on-the-rails solution, you must first find constants of motion. There are 6 for a general orbit. In 2-body problem, these are trivially related to the 6 orbital elements. Furthermore, Energy and Angular Momentum account for 3 of the 6, which leaves a time and two angle references as your other 3. A 3-body restricted problem is not conservative. So energy is not a constant of motion. Neither is reference time. When you can't use time as a coordinate, you know you are in trouble. If the two massive bodies are further restricted to a circular orbit, then you can go into a rotating frame of reference, where energy is conserved. But you still have only one component of angular momentum. So that leaves two constants of motion and two coordinates to disentangle. If orbits are not circular, then you are completely screwed. I'm not entirely sure why planar motion is a requirement. Intuitively, it feels like cylindrical symmetry here should let you generalize to any restricted 3-body where the two massive bodies are on a fixed circular orbit with respect to each other. I'm going to play with Hamilton-Jacobi for this setup in cylindrical coordinates and see if I can come up with anything half-useful. Edit: Took a look at your link. It looks to me like 2D case is considered for simplicity. Same methodology should be applicable for general 3D motion. It's just going to be way scarier. But this would suggest that at least something like Kerbin-Mun system could be done as restricted 3-body on rails, giving these two their own, combined SOI. (Minmus would still need its own SOI.)
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