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Post by apophys on Jan 23, 2019 19:36:53 GMT
My instinct is to keep it liquid @ 1000 K (with proper thermal insulation) rather than deal with solids. Mechanically pumping liquid over 1600 K is current tech, with ceramics.
Consider using it as a phase-change heat sink for cooling weaponry, because of its very high heat of fusion: ~ 2.85 MJ/kg.
Consider also that LiH & LiH2 are top-tier neutron radiation shielding materials IRL.
Finally, notice that F 2 + LiH is the best-performing chemical rocket in the modded game.
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Post by apophys on Jan 22, 2019 5:29:36 GMT
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Post by apophys on Jan 21, 2019 23:32:55 GMT
The only way to get a truly recoil-less gun is to throw stuff equally in the opposite direction of the projectile.
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Post by apophys on Jan 13, 2019 19:00:28 GMT
Why are "guest" accounts even allowed to post here?! Because sometimes we have one of those hilariously broken auto-translated messages for the amusement of all? (Not sure either) It hasn't been a problem until very recently. The past spam attacks always used registered accounts.
Whereas guest posting was useful for some people.
Sadly, I'm not sure what, if anything, can be done to save guest posting now that spammers have discovered it.
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Post by apophys on Jan 4, 2019 18:48:08 GMT
Welcome, jfmoyen ! Trial & error is basically it. Just do a rough burn plan at some point of the orbit, and see how far out of phase you are. Try at a different nearby point; see if you're closer or farther, and you should get a good idea of where you actually need to burn from. When you get a decent enough trajectory, you can fine-tune the phasing with the radial (green) knob. For Uranian Cargo Run, the ideal transfer timing is around 1 day 13 hours from the start (you'll need to escape Miranda first though, or you'll crash into it). My ending maneuver illustrates another case where you need trial & error for phasing. I'm doing an Oberth capture at Titania (disturbingly close to the surface... ), and want to use just enough dV that one orbit will put the craft in phase with the target when I burn again for it. There's no tool I know of that can make this easier, but it's not really that bad. Btw, this run is my lowest dV use on the stage, at 2.95 km/s.
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Post by apophys on Jan 4, 2019 13:34:05 GMT
Keeping vacuum between parts people need to to regularly move between is an awful idea. Not only it will require suiting up every time leading to inefficiency and cutting corners, but it will also cause air losses every time system is cycled. It's much better to just deal with some extra power requirement and waste heat, possibly using it to drive ventilation as well, it's even better to just sidestep all problems by spinning up the whole ship.
To me, it seems most sane for everyone who might leave the rotating hab on a daily basis (of which there shouldn't be many) to be in skin-tight mechanical counterpressure suits at all times, meaning all you need to do is put on your helmet and wait for the airlock to cycle. Clothing can be worn on top if desired.
I don't see the need to pressurize the main ship to begin with, other than a compact, heavily protected central module (used for combat or bad solar storms). Too much pressurized surface area invites tiny leaks that go unnoticed for months; air is a fire hazard, it lets shockwaves travel, etc. The rotating hab is made for humans to live and work in; it might as well get used for that purpose to the exclusion of the rest, as much as feasible.
My other reason for considering a connection in vacuum is to be able to have practically no friction, using magnetic bearings. For combat situations, after evacuating everyone from the hab to the ship, this allows using the hab as high-RPM flywheel energy storage for weaponry (you've got all that mass there; might as well get your money's worth out of it).
For purely civilian ships, the energy savings should be worth it if the airlock is not used much (really, how often does one need to leave the hab while in transit?... ).
Spinning the whole ship works, and is the simple answer. But it causes issues with precisely pointing spinal weaponry. Spinning down the ship for combat wastes dV (more mass than airlock losses, I bet), unless you happen to have a really heavy flywheel somewhere...
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Post by apophys on Jan 4, 2019 9:42:14 GMT
Since the highest RPM that can be comfortably adjusted to is 6 RPM (giving 1 G at 25 m radius), with 2-4 RPM normal, the rim speed near the axis is necessarily low, and you can simply step off (no need for a train). This means you don't need your connecting hallway exactly at the axle, but can work with a toroidal crossing passage around it. www.artificial-gravity.com/sw/SpinCalc/Sketch by me in MS Paint: Green: spinal weapon, as well as propellant lines. Purple: non-rotating ceiling Red: rotating floor (held with bearings), & spokes to edge Blue: non-rotating "floor" (Mind the gap! ) Yellow: ladder/elevator access from edge It's possible to add an intermediate-speed ring on each side for an even gentler transition. IMO, it would be simplest to do this hallway joint in vacuum, to avoid the generated wind that AtomHeartDragon mentions (and also to allow the rotating section to stick out far from the ship in some designs, to get 1 G with very low RPM). Note that no fluids can be piped between the ship & the hab with this construction, only brought across in tanks. So they will need separate plumbing systems (and separate air if the joint is in vacuum).
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Post by apophys on Dec 31, 2018 5:10:03 GMT
I'm guessing diamond anvil manufactured meta stable metallic hydrogen is too speculative for your liking? Too explosive also.
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Post by apophys on Dec 31, 2018 3:34:25 GMT
Couldn't you build a double hulled tank for storing H2, with something like a mercury vacuum pump or some other extremely low pressure pump process recollecting the leaking H2 from the outer hull? Yeah, that's necessary when you want to store the H 2 for months/years without noticeable losses. Not great for tank mass ratios though (which already suck for H 2 due to its density), & increases complexity, adding a mechanical point of failure. I tried building an MPD-equipped ship as light as practically possible - got this, seems pretty nice: Pro tips: Maximally-lengthened polyethylene crew modules are lightest. Boron nitride or amorphous carbon make the best reactor radiators. Surface with tungsten for realism (lowest vapor pressure). Use diamond or VCS tanks, maximally lengthened. If they become hard to fit, use bundles of small tanks (like 5x 100t) instead of 1 big one. These changes shave 20 tons of dry mass from the craft, giving +10 km/s dV.
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Post by apophys on Dec 30, 2018 16:36:59 GMT
With custom MPDs and reactors the main issue seems to be pumping gigawatts into at most dinner plate sized thrusters - I do expect this kind of power density to cause... interesting engineering problems CDE's equations for MPDTs aren't really equipped to deal with (even stock MPDTs are way beyond any existing applications AFAIK). That is rather relevant. How effective MPDs can be expected from applying tech currently in development? I intend to have as starting point technology we know can be built. "The device has been operated with currents up to 300 kA and power levels up to 200 MWe. These values are among the highest levels reached in an magnetoplasmadynamic thruster."
"A time-dependent, two-dimensional, axisymmetric magnetohydrodynamics code is employed to model, validate and extend the experimentally-limited performance characteristics of a gigawatt-level plasma source that utilized magnetoplasmadynamic (MPD) acceleration for gas energy deposition. [...] They also allow examination of the device as a very high power MPD thruster operating at power levels in excess of 180 MW."
You can build such things. Note that you need enough active cooling of the waste heat, or you're limited to very short pulses (not modeled in CoaDE, sadly).
"The MPDT has a unique place among electric thrusters in its ability to process megawatts of electrical power in a small, simple, compact device and produce thrust densities (thrust per unit exhaust area) of O(105) N/m2. However, this major advantage of the MPDT has also been the disadvantage to its development. Since high efficiencies (greater than 30%) are only reached at high power levels (exceeding 200 kW), MPDTs require power levels that are an order of magnitude higher than what is currently available on spacecraft in order to be competitive with other propulsion options. Therefore, research on MPDTs was largely sidelined, in favor of thrusters that have higher efficiencies at lower power levels."
CoaDE's MPD modeling seems to be quite good, since I have seen this effect when designing them. Thus why my lowest-power standard MPDs are 10 MW for most propellants, or 1 MW for HD.
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Post by apophys on Dec 30, 2018 11:12:12 GMT
I want to try out some orbital transits between planets. [...] I thought maybe I could make a suitable mission using Level Editor. I tried to, but when I open a mission, I seem unable to edit it. Maybe the default missions are read-only? Do I have to somehow make my own campaign? Yes, default levels are read-only. The simplest is to use a custom campaign with one level in it. I made one for you just now, with the important bodies up to Jupiter: UserLevels.txt (1.83 KB)Put this in C:\Users\YourName\AppData\Roaming\CDE Merge the content if you already have custom levels. (Be sure not to use Notepad, because it screws formatting. Wordpad is fine.) Propellant is cargo like any other raw material, imo (which is probably what most cargo trade will be). Fast ships would only be needed for human passengers or expensive priority cargo. In each case, you'll want MPDs (or other high-exhaust-velocity drives), just with different mass ratios on the craft. Slow transit would use very high payload fractions (large majority of the craft's wet mass being payload), and save propellant using slow but efficient orbital transfers (like bi-elliptic). Rapid transit would carry plenty of propellant and burn a few hundred km/s dV on fast near-brachistochrone transfers. What exactly the fuel is will limit where it can come from which will kind of define the logistical infrastructure, as will how optimistic the science of the engines you use. [...] Solar sails or Laser sails are probably the best bet by far for using today's tech to go interstellar. I like CO 2 or O 2 for ion drive propellant. CO 2 is easily siphoned from Venus or sublimated out of icy asteroids/comets. O 2 is a waste product of refining metal from rock, and can be processed from CO 2. H 2O or CH 4 are commonly considered due to their decent performance in thermal drives (but I don't see those as very relevant for interplanetary travel, only for surface liftoff to orbit... or for space combat). H 2 is very annoying to store (supercold, low density, & leaks out through walls), making the mass ratio of tanks terrible. For going interstellar, relying on only the sun for your sail is too weak & slow. Laser sails are good, though. Riding a neutral particle beam might be even better, due to the superior efficiency achievable. Combining the two may be possible, to improve focus over long distances (see PROCSIMA). I like air-breathing laser thermal for that purpose, because it's easily scalable, very cheap to operate once you've got the infrastructure, and the infrastructure can be multipurpose (asteroid sampling/defense, laser sail, interstellar comms, military, etc). I meant the stock ships - I suppose one can build a ship that has huge number of reactors - it probably requires custom modules? I dunno, when I tried to build a faster going MPD ship I did not have much success. Also question would then arise how feasible would really be to build a ship with a terawatt of reactor power. The important statistic is not the total power of reactors, but the specific power of the full system. That is: the electricity generated, divided by the mass of reactors + radiators. Yes, custom modules are needed, since stock reactors are horribly heavy and output heat at low temps (requiring oversized radiators). IMO, they are by far the worst-optimized stock parts ingame. You can do perfectly fine on merely 1 GW. More is always better due to the dead mass of the crew module, which doesn't scale up along with the power system. I searched for some kind of guide for better MPD, but found none and I don't have time to spare for experimenting. The wiki is woefully incomplete & a bit outdated, but: coade.wikia.com/wiki/Magnetoplasmadynamic_Thruster (written by me, btw) Or you can use the MPDs in my thread. I've got neon, CO 2, O 2, D 2O, CH 4, HD, & RP-1 from 10 MW to 100 GW. These particular fission reactors are using a lot of osmium, and they are designed with power to weight ratio prioritized over cost, but that's really not unreasonable. Actually, I prioritize low cost over low mass, within reason. Other people have made lighter but more expensive reactors than mine, e.g. Ianthe on Discord. Osmium + tungsten is just a bit better than tungsten rhenium + tungsten (if you ignore expansion stress by using multiple stages), which is what we use IRL for high-temperature thermocouples.
One major reason osmium isn't used much is that it creates osmium tetroxide (OsO 4) when exposed to air. Osmium tetroxide easily vaporizes and is extremely toxic. So you can't leave osmium metal exposed to our atmosphere. Not a problem in space, though.
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Post by apophys on Dec 26, 2018 3:20:16 GMT
It's great to see new faces. Welcome! I've spent most of my game time in the module editor, because stock modules are very unsatisfying with the tools at hand. Other people primarily build ships and test them in combat against each other (and for these I provide my standard modules). People enjoy different things; try stuff out. The mods for the game are mostly: - real materials not currently in the game - materials that simulate something with best guesses (like fusion or bulk graphene) - other solar systems - textures IIRC, back when I cleared Vesta Overkill, I had manually unlocked module editing, built a laserstar with custom modules, & overwhelmed the level from 1 Mm range with a fleet of them.
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Post by apophys on Oct 19, 2018 0:44:03 GMT
Try gadolinium for the stator and calcium for the forcer. Ugh. Structural Calcium again.
I use & recommend zirconium carbide for the forcer. The forcer's melting point is relevant for the outlet temp of the launcher.
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Post by apophys on Oct 10, 2018 5:42:11 GMT
You might need moar power. Try my standard 10 TW neon MPD (1.06 Mm/s exhaust velocity), with 1 TW modded reactors. Or try fusion mods, but making that realistic takes a lot more effort.
(Though in reality, we're most likely to go interstellar using beamed power, like PROCSIMA
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Post by apophys on Oct 8, 2018 1:46:11 GMT
Stock? About 1990 or so.
Customized vanilla or reasonably modded modules? Definitely sometime before 2050 if we actually try (though estimation is hard, and we may not actually try).
Extreme modded modules (abusing graphene, carbyne, & fusion)? Unknown, possibly never.
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