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So, for a KSP like game, you want to be able to specify a rendezvous with, say, that comet, and perform a series of burns to set up the intercept. With true N-body gravity, everything affects everything to a degree, and you cannot serially run the simulation beyond the serial processing speed of your GPU. Well, we can't make that intercept perfectly in real life, either. Corrective burns have to be done. So, what you *could* do is the following : Plan the trajectory to reach the intercept position (a closest approach to the target) by using long timesteps and high order symplectic integration over a brief period of realtime. Essentially, you now have a rough trajectory that using a lower precision integration method than your game's real simulation uses (the longer timesteps cut the precision), ends up somewhere roughly where you want to be. If the player approves the flight plan, you would perform corrective burns automatically during the flight if the relative differencee between the planned trajectory and the actual trajectory were tiny enough to correct this way. Another approach is one even you probably haven't heard of, K^2. There is a method to simulate a serial trajectory in parallel, despite trajectories being a series of mathematically dependent states. PM me if you'd like an explanation of how to use the method. Using that method, and given access to a monster GPU, you could run at at full simulation precision at millions of times speedup and predict a trajectory perfectly.

Good stuff Kibble. I see you've read up on Spherical War Cows. One comment : wouldn't it be a good idea for the badguy pwnboat to have it's own lasers to deliver a nice hefty zap on any incoming killer buses?

So why not just go ahead and do it with numerical integration for the N-body, using an octree to group together and average farther away bodies? GPU-gems makes it look so easy.

Well, make the struts thicker. Point is, you could clearly build two saturn 5s and connect them together with a girder between the rockets. While this would be a bad idea, you could probably make the 2 connected rockets hold together well enough to reach orbit. If you can do it with 2, you can do it with any number of Saturn 5s, although there is a problem that impulses could spread across the 2d mesh of rockets and cause some of the rockets to point the wrong way, causing further wobble, til the whole assembly flies apart. This is probably a solvable problem, you could use computer controlled dampers on the interconnects among other things. So even if there is a practical limit on how big a rocket shaped like a saturn 5 can scale to, due to surface area : volume constraints, you could bolt together smaller rockets and call the assembly a bigger rocket.

To handle higher timewarps, you have to start to sacrifice positional accuracy to a larger degree, which you don't want to do with planets. So, at least for Sol, baked solutions exist that work at any time warp like http://en.wikipedia.org/wiki/VSOP_%28planets%29#VSOP87 . To do what you would like, you would need to create an analytical solution for the Kerbin system for all the major planets and moons that was accurate for several thousand years, just like VSOP87. This is essentially a gigantic equation that will tell you where any given body is at any given time, specific to the major planets in Sol. A solution like this is what you're really asking for : you would probably dig up the methods and code used to created VSOP87, then simulate the bodies of KSP over time using a powerful computer and then generate the equations from that empirical data.

By "doesn't scale", I mean just that. You could maybe have 1 planet and a moon considered at the same time, but what about 2 moons? What about 1 moon and 1 asteroid and 1 planet? And so on and so forth. The correct solution is much easier and simpler to program than what you're asking for. As for errors accumulating, actually, if you use symplectic integration, the errors for energy are guaranteed to remain bounded. What that means is, the actual position of the simulated bodies (aka phase angle) will vary over time, but the energy in their orbits will not. That means that stuff won't fall out of orbit, etc. The current method KSP uses does not preserve phase angle, either, so this drawback is not a detriment. (I don't know the exact reason it loses phase angle, but I know that if you put a satellite into perfect geosync it will drift anyway)

Yes. You could even just aim your flashlight like a rocket engine. The problem is that the thrust per energy is very very low. You need some method of generating bat.... insane methods of energy. Essentially you need to be able to release all of the mass-energy present in matter itself. Antimatter drives do this (although they get some of the thrust from other particles than just photons) and black hole drives work this way.

The math for 3 body is much much much harder than the math for 2 body. And it doesn't scale. The correct method to use that will work to N-bodies is described here : http://http.developer.nvidia.com/GPUGems3/gpugems3_ch31.html By using an octree to represent far away clouds of particles, the actual computational load is much less than N^2. It's not even that complicated - the code listings for all the key parts are right there in the article, and I've heard of a half dozen folks who have gotten such a simulation running in their spare time. Also, using proper N-body gravity means it would not be any big deal to have ships running their engines during timewarp so that we don't have to wait all day for ion drive burns.

Taking a shower with heated water doesn't change the basic need for heat generated = heat radiated. Essentially, over time, 100% of the heat generated must be radiated somehow. Firing a laser weapon that is 20% efficient radiates 20% of the energy as laser light, so you need to radiate the other 80% via radiators of some kind. Ditto for the nuclear electric engine case. Since the surface of your spacecraft hull radiates heat at a rate proportional to the T^4 (temperature raised to the fourth power), any parts of your ship that are not high temperature radiators can be ignored as they don't radiate enough heat to matter. This is just the overall theory. In practice, using foreseeable future tech, heat management is an even bigger problem because a lot of the nifty gadgets you need require very low temperatures to work. Sensitive infrared detectors to spot enemy ships - better cool that detector down to reduce thermal noise in the sensor element and also use a cooled shroud to protect it from IR from your own ship. Want a coilgun? All those magnets need to be cold, even if room temp superconductors are possible, superconductors work better when cold. Want a fusion reactor and your design uses magnets? Ditto for the cooling need. Want a free electron laser? About half the laser is superconducting magnets FTW. Are you storing hydrogen slush onboard for use as propellant, since it is frequently the most efficient possible propellant? Better keep that tank at under 20 kelvin.

Your own website describes droplet radiators and links to a droplet radiator calculator. Liquid Tin droplets at 1000 Kelvin allow for a pretty compact radiator. You'd have to turn off the droplet radiator and collect the droplets before making maneuvers not along the plane created by the 2 radiator booms (and have enough thermal mass on the ship to not burn up right away without coolant for a brief period). That might make for an interesting tactical option - obviously, in an emergency you could make your turns and lateral maneuvers without turning off the droplet flow and just eat the coolant loss.

Found this fascinating image on wikipedia : Why are there miles of wiring, using what look like fairly heavy insulation and connectors? What's in the various boxes visible in the image? What about the spherical red tanks? Or the cylindrical ones located higher up? Part of my questioning is, I just wonder what all that stuff is for. The second bit is that I thought with rocket engineering, you would want to save every gram. I see an awful lot of stuff that doesn't look like it is as low mass as it could theoretically be : you could in theory store the same compressed gas volume that's in those red tanks in a smaller number of larger tanks. You could replace what look like analog signal cables bundles with digitizing the sensor data closer to the sensor and use lighter digital bus cables. So I wonder how much performance you lose, although I guess the reasoning is that reliability is a much more important goal than saving a few kilograms on the control and sensor systems.

On your website, you have an example where you analyze "plasma weapons". A super heated stream of material heated by a nuke probably acts like plasma, with the lighter electrons driven off. That means that electrostatic repulsion between the protons would shove the stream apart very rapidly, soon dissipating it to harmless levels. The total energy doesn't matter if by the time it reaches the enemy ship it's so dispersed that 99% or more of the energy doesn't even impact with the target. Anyways, if we had that relationship between angle and Z, it would be straightforward to calculate the energy per area for a target at a given distance, and then determine how destructive it would be. Shame it is classified.

Your site lacks a key calculation : changing the Z-value of the nuclear shape charge payload, what does it do to the angle of the resulting stream of particles? Also, wouldn't a nuclear accelerated particle stream dissipate just like any other stream of particles over distance? I'm not convinced this weapon would have more than a few kilometers of range no matter how powerful the nuclear warhead driving it was.

Q-thrusters might have major drawbacks. Essentially they are trying to manipulate virtual matter that is barely even there. The energy to do this may always be extremely high, and the apparatus very large and massive. If you look at this paper and assume a power density of 1 kilogram per kilowatt for your power plant (possible with theoretical bleeding edge nuclear designs) and that future advances let Q-thrusters weigh 1 kg per kilowatt of power used, and the same power efficiency (0.1 newton per kilowatt), then you arrive at the following numbers (again, I'm assuming that future engineers can do 10 times better in both power generation and Q-thrusters than we can do today): Assume the ship is 1/3 power reactor (including the radiator mass), 1/3 engines, and 1/3 everything else. Then, for 3 kilograms worth of ship, you have 0.1 newtons of thrust from the main engine that is 1/3 of the ship. F=ma, 0.1 = 3*a, a = 0.033333 m/s. That's 0.33% of 1 G acceleration. A quick bit of figuring shows it would take 30 days to reach Mars with this, which is no better than you can do with a top end VASIMR. Sure, that tiny force will add up over time enormously. What I've described here would make interstellar travel practical, and would also make relativistic missiles that wreck planets possible. But you will have trouble dodging incoming fire, it's actually going to take a while to transit to Mars, and your spaceship would probably want to have an orion drive or something for dodging incoming fire. The Q-thrusters would be helpful in that once you are out of propellant you could recover the ship if you're willing to wait long enough, assuming you still have power and at least 1 working Q-thruster. Regarding radiators : no need to dump coolant. That's one of the things that there actually is a clever solution for. Use this drop radiator calculator. Assume you are using liquid tin as the coolant at 1000 kelvin. Let's say we're making 5 gigawatts thermal, and the space along the hull of the ship where the drops fly free is 100 meters long. Then we need just 4 booms each 18 meters long, half sending and half receiving. Calculating the mass of the pumps, compressors, total volume of liquid, and plumbing is beyond the scope of this message board, but even using 1987 assumptions it's less than 1 kg per kilowatt of heat rejected. Dumping coolant is super bad and I think most warships would be designed to never do this even when at maximum power output and taking extraneous heat from enemy laser fire.

Project Pluto isn't a hybrid.

EM is too many orders of magnitude stronger than gravity, so no.

Changing subject : was any research done on some kind of hybrid NERVA-jet-scramjet design? I thought of this when trying to work out a plausible method of exploring an earth-like planet. Suppose, just for the sake of argument, that warp drives like described here work and are even easier to make work than Dr. White and co think. So in the near future (100 years), a manned spacecraft with a warp drive is assembled and launched and they find a planet that has gravity and atmosphere similar to earth's. Assuming no other massive breakthroughs besides the warp drive itself, how would they land on the planet and reach orbit again? Well, landing's easy, just need a heat shield and parachutes/a little rocket dV when the atmosphere is thick enough like on Earth. So you're on the ground, and you'd like to reach orbit again in 1 stage without a runway. So say you have a huge fan, driven by a working fluid cycle that runs through part of the NERVA reactor. You compress oxygen or CO2 and inject it into the reactor instead of hydrogen. (a larger volume of the stuff would be needed). Assuming you can get a TWR larger than 1, your ascent vehicle lifts off and begins to pick up speed. At some time later, you divert air from the compressor fans to a straight ramjet intake that changes geometry in flight to become a scramjet intake... This unholy hybrid of engineering then somehow reconfigures itself during scramjet flight to accept hydrogen as the propellant instead (I guess you gradually transition the internal state of the control rods in the NERVA reactor to the mode that is configured for hydrogen and gradually increase the percentage of hydrogen injected). It uses the stored hydrogen and a nice strong ISP of better than 1000 to reach orbit. At some point during this process you actually jettison the compressor fans and air intakes, they descend on a parachute and could in theory be recovered if you wanted to do this all over again a second time on the same planet. The showstopper problem I can see here is that the internal structural of a NERVA optimized for hydrogen is probably hugely different than one designed to heat some mix of CO2 and oxygen, and in flight transitions might be unfeasible.

I think I've established the benefits. If you can get a railgun muzzle velocity of 20 kps (I can link you to patents that describe how to build one on paper), then here's your tradeoff : Missile case : chemical engine ISP of 400. Good ole rocket equation says to hit 20 kps you need to throw away 94% of the mass. Not to mention tank mass, and you're going to probably want stages. Want a nuclear engine? Then the minimum size of your missile becomes gigantic because nuclear reactions require a critical mass, I was estimating a nuclear engined missile at the size of a Falcon 1. Railgun Case : You essentially launch the kinetic interceptor package at the very top of the missile used in the missile case in the railgun. Kind of like this one, but with radical design changes to tolerate the incredible g forces at launch. In a battle against an enemy vessel who has defenses and the ability to maneuver rapidly with large dV reserves (aka various fission drive variants), you're going to need a sustained barrage of fire to destroy them. If you have a railgun/coilgun, you can haul at least 33 times as many munitions. Also, surprisingly, I think both vessels would be surprisingly hard to kill, despite being spacecraft and very lightweight. Laser weapons that can disable enemy laser weapons but lack the firepower to do significant damage to the enemy hull (essentially, anti-laser lasers) are lighter than offensive laser mounts. Incoming missiles, especially big ones like you advocate for, could be disabled by using small railgun/coilguns to fire golf ball sized hypervelocity slugs. Just 1 hit from a slug at 20 kps will kill any plausible missile. Honestly, it could easily turn out that all the systems we have mentioned aren't all that effective and that the only way to go is something like a fission bomb pumped X-ray laser.

Cicatrix, the wall of text located directly above yours explains the reason why guided/homing missiles are not necessarily the best. Regarding Newton's second law : that is an issue but it is in principle possible to build a railgun aiming system that compensates for that, or to mount your railgun in line with the center of mass of the ship. You can think of the movement of the ship as you fire as adding an unwanted velocity vector to the shot. Subtract that unwanted velocity vector from your intended velocity vector, and you have the new velocity vector you want your railgun system to impart to the projectile. Then have your aiming system calculate an angle and a switching sequence to deliver that vector. The new firing "plan" as it were (a plan would be a series of settings for the railgun weapon system, such as switch timings, how much the capacitors are charged, and of course the angular settings of the servos controlling the barrel) you then have to evaluate again against your dynamics model of your ship to find out what the new unwanted velocity vector is (it's different now since you changed things). You iterate until the shot is "close enough" to hitting the target that rocket motors in the railgun round itself can provide the teensy bit of correction needed for a direct hit.

Even if such a planet existed, in order to reach it, you would need either the technology to : 1. Create an absurdly large starship that will throw away most of it's mass in transit and keep alive a population of humans for decades in an artificial environment OR 2. Create human beings from straight data files of their DNA and files describing the molecular structure of enough biomolecules to "boostrap" your way to a human embryo. Either way, at this tech level, what need do you have for habitable planets? You could build machines that can live natively just anywhere and support human thought, you could build enclosed habitats that recycle everything like a planet, etc etc.

K^2 knows nothing of which he speaks. SSDs are mandatory and you do not own a 2010+ era computer without one. He's right on everything else but the SSD comment. SSDs are now $120 for a 240 gig. You cannot go wrong with an Intel SSD, they have the best reputation and reliability. Samsung SSDs are a close second. TLDR, conventional hard drives have something called a "seek time". That's the time for moving the arm on the mechanical system to a different point on the platter, and then waiting for the platter to revolve to a particular position. It's only about 8 milliseconds, the problem is that some games and some applications depend on thousands of tiny files that end up scattered in different physical locations all over your hard drive. This in turn means that loading applications is several times slower with a hard drive than an SSD. TLDR I didn't read the first TLDR : an SSD makes the largest perceptible difference for day to day computer usage. Nothing says "I just bought a fast new computer" than the feeling of being able to start instantly any application installed to the SSD. If you have to skimp on the processor and video card to afford an SSD, do it.

[quote name=Raukk;1571800 I'd personally prefer Missile volleys' date=' the enemy knows that a few have nukes and the rest are traditional, but intercepting all of them would be hard, also shrapnel could damage or disable point defenses. The downside is the long flight time required to reach the target. A hybrid weapon is possible. It would be a railgun slug that has a small rocket motor. Essentially, it would be a golf ball sized slug, and the rocket motor might be a series of solid rocket propellant "pits" drilled into the slug. Electrical igniters under control of a tiny computer would set off these pits. The slug would use crude sensors to detect a carrier beam coming from the launching ship that would orient it in space and tell it course corrections in flight. The reason to do it this way is that a railgun/coilgun is not itself subject to the rocket equation. It could send the slugs at 10-20 kilometers/second (the slugs heat up when in the armature of a railgun or barrel of a coilgun, so the limit to how fast the slugs can be launched would depend on heating among other problems) without the slugs needing to carry 20 kps worth of delta-v onboard. And that's the other problem : rocket engine designs exist that have large delta v, but those engines are things like orion drives and nuclear salt engines and nuclear electric engines. All those engines are huge : scaling laws means they cannot be miniaturized. So missiles, by necessity, either are something that will run out of fuel quickly while chasing a target running away on orion drive, or they are essentially robot spacecraft the size of a modern day rocket or bigger that you are throwing away. Also, you could shoot down an incoming missile the size of a falcon 1 with a railgun or coilgun slug the size of a golf ball. It hurt's the missiles delta V greatly if it tries to evade. If the missile is incoming at 20 kilometer/second, and you intercept it 500 kilometers away with a railgun/coil/laser beam, then your spacecraft has 25 seconds to get out of the missile's shrapnel cloud. If your spacecraft has an orion drive or nuclear salt thruster able to accelerate at 10 m/s^2, then it could "dodge" by 3 kilometers and avoid the big pieces from the missile's debris cloud. (and a whipple shield could soak up the paint chip sized flecks of missile that would probably be in that debris cloud as well) Of course, you could give the missile point defense cannons to shoot down incoming railgun/coilgun slugs bound for it, but then you could still shoot the missile down (by shoot it down, I mean put a hole in it to disable it's ability to maneuver and/or blow it up, obviously there is no down in space) with laser beams. Of course, then you could stick laser beams on the missile to snipe enemy laser beams... TLDR, the missile ends up being the size of an entire warship, and you are using the strategy Ramming Always Works. Truth in television, indeed.

A maser is just a laser that uses microwave frequency light. Unfortunately, longer wavelengths are fundamentally harder to focus to a small spot at long ranges - this is why one of the posters in this thread was advocating for X-ray lasers, even though X-rays are very difficult to focus at all. What you are saying here is assumption dependent. I somewhat agree with you : if you had a given amount of mass available for weapons on your ship, you would do more DPS, essentially, by putting that mass into railgun/coilguns. The TLDR reason for that is the an FEL has a lot of heavy components, and a semiconductor laser heats itself up, while the superconducting magnets in a coilgun do not. So you'd probably have more kinetic energy in the coilgun/railgun shots per kilogram of weapon mass, and then physical impacts fundamentally do more damage for the same energy delivered. The advantage lasers have is : 1. You cannot intercept incoming laser fire 2. Laser beams travel much faster than practical railgun/coilgun slugs 3. At extreme ranges, lasers can take out lasers due to the weaknesses inherent in dielectric mirrors. The advantage hot gas cannons have is that they do not need huge quantities of electrical power to run, and they are much lighter and smaller than railguns/coilguns (with the drawback that their ammo is heavier). Their drawback is poor muzzle velocity, but they might be useful for intercepting incoming projectiles. TLDR : I suspect there would be legitimate reasons for all of the physically plausible, practical weapon systems in a space warship using near to mid future technology. Of course, once someone works out a way to build 1 million ton x-ray laser cannons that have ranges of 1 AU are more, all bets are off.

I suspect you need to take your model and run it through a CFD solver and have it calculate the lift and drag coefficients numerically. I highly doubt an analytical solution to a complex, arbitrary shape like this exists. I don't think analytical solutions exist even for wings as complex as the ones used on real world aircraft - pretty sure they have to use numerical solvers and wind tunnel tests to determine their actual performance. Let me know if you find a good solver, I've been curious about this myself. Once you have those coefficients, you could then solve for an equivalent airfoil, if one exists, and feed that to orbiter.

All of the things are fairly well known to biology and don't need a lot of expensive space-specific research. At the cellular level, gravity is a negligible force, and most of your questions can be trivially answered with ground experiments or just checking the literature for past research. More useful research would be full up testing - using what we already know about plants, and using what we already know about recycling systems, build an actual life support recycling system and test it on the ground heavily. Then, once the design is reliable in testing on the ground, launch one into space and test it there.