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Post by AtomHeartDragon on Sept 9, 2018 15:08:53 GMT
60 km/s is what you'd get from a full head-on retrograde collision in circumsolar orbit at 1AU. I would expect most actual collisions to be less energetic.
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Post by Apotheon on Sept 15, 2018 19:05:23 GMT
Lithium:I generally consider anything from the first column of the periodic table and anything but beryllium and magnesium from the second column to be unsuitable for any structural applications as unalloyed metal. Even in space. Tell an engineer that you want to encase air, humans or warm/hot cooling water in lithium or potassium and he will run away screaming and flailing his arms so fast that he won't actually be within earshot any more when you mention any actual coating you intend to use. For some extra fun you can also tell him you intend to use it to pump liquid fluorine too (after he returns). Anyway, it's probably about time I change my radiator lithium for realism. Lithium is out and... calcium is in probably?
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Post by AtomHeartDragon on Sept 15, 2018 19:36:34 GMT
Lithium:I generally consider anything from the first column of the periodic table and anything but beryllium and magnesium from the second column to be unsuitable for any structural applications as unalloyed metal. Even in space. Tell an engineer that you want to encase air, humans or warm/hot cooling water in lithium or potassium and he will run away screaming and flailing his arms so fast that he won't actually be within earshot any more when you mention any actual coating you intend to use. For some extra fun you can also tell him you intend to use it to pump liquid fluorine too (after he returns). Anyway, it's probably about time I change my radiator lithium for realism. Lithium is out and... calcium is in probably? Second column, not magnesium nor beryllium.
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Post by Apotheon on Sept 15, 2018 19:50:11 GMT
Anyway, it's probably about time I change my radiator lithium for realism. Lithium is out and... calcium is in probably? Second column, not magnesium nor beryllium. Oh, you're telling me to pick magnesium? Ok.
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Post by AdmiralObvious on Sept 16, 2018 5:35:50 GMT
Magnesium reacts with a lot of stuff, so it depends on what you're piping through it.
Calcium is also rather "chalky" for lack of a better term, so it might actually disintegrate with the fluid pressure.
I think most of the carbide type of materials are actually used as radiators.
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Post by apophys on Sept 16, 2018 9:15:53 GMT
My questions: - How realistic is CDE propulsion/power? I assume it's possible to re-create real propulsion or power and get accurate results within an order of magnitude, at least within reason, or is it coarse?
- How realistic is Apophys propulsion/power? The stuff is highly optimised and that makes me wonder if it's because he's getting his information straight out of rocket books or just abusing the code?
- How realistic are command modules? The dimensions are kind of arbitrary and the volume apparently comes straight out of NASA research (I've read it), which leaves me only wondering about the mass.
- Also, for command modules, I'm making mine out of polyethylene... sounds awesome... and it's freaking plastic. Can someone reassure me that this doesn't wear out or degrade in any way on the inside or outside from air, vacuum, cosmic and solar radiation, the acids on human skin, or anything such? Apparently, NASA already use some kind of "reinforced polyethylene", is this what we have?
- My propellant tanks are made out of vanadium chromium steel. I've not idea what it's used for IRL, but it's steel and I guess it does what it says on the box?
- My radiators are made out of lithium. Reasonable?
Many CDE stock modules can be clearly pointed out as unrealistic in their details.
My vanilla stuff is purely minmaxed within game limitations, with virtually no concern for realism. My modded stuff is minmaxed while addressing any realism concerns that I'm aware of that the game doesn't take into account. I assume that the game's modeling is reasonably accurate for most of what it does model, but I have no way to verify a lot of things (tell me if you notice anything unrealistic; I'm not perfect). I expect the overall performance values of my modded stuff to be close (order of magnitude or two) to the ultimate limit of possibility for the tech, but still possible. Different technologies than those implemented ingame may make things better in some cases (like electromagnetic pumps instead of mechanical turbopumps). I have no rocket science or materials science education (I'm a math major); I have no access to a rocket scientist IRL, and I'm not taking anything from any real-life source other than material data for the material mods I made. So take it all with a healthy pinch of salt.
Crew requirements are generally considered somewhat excessive. I have done no actual comparisons on the topic of how much volume or mass they take, but I assume you can pack people densely like in an airplane if you really need to (particularly since at least 1/3 will be asleep at any one time, at least out of combat).
Polyethylene degrades when exposed to UV (which should not be the case if you have any armor). Otherwise it has great longevity, as the great Pacific garbage patch shows. Some plastics exposed to vacuum have significant outgassing issues, but iirc high-density polyethylene is not one of them. Borated polyethylene is actually used for radiation shielding in space, iirc. Human skin is oily, not acidic.
VCS is a tool steel, and our VCS is the best such alloy available. As steels go, it is pretty extreme, but it exists. Making it in large plates may not be currently practical. However, the game doesn't allow us to use fibrous materials to reinforce propellant tanks, which would be possible IRL; it would probably improve things over pure VCS if we use UHMWPE fiber. So I think ingame VCS is good enough for modeling purposes.
Lithium is really soft, so don't use that for radiators of any kind if you want realism. Possible but not at all reasonable. Use carbon, aluminum alloys, or a ceramic. Lithium makes a nice liquid coolant for things in the 1000 K range, though.
Realistic micrometeorite armor is a whipple shield: roughly, 1 mm aluminum or other light material spaced out 1 m from a 1 cm-thick bulk armor layer. Stuff the gap with aerogel for better results. Larger debris is best countered with a laser broom.
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Post by AtomHeartDragon on Sept 16, 2018 10:15:45 GMT
Magnesium reacts with a lot of stuff, so it depends on what you're piping through it. Calcium is also rather "chalky" for lack of a better term, so it might actually disintegrate with the fluid pressure. I think most of the carbide type of materials are actually used as radiators. I wouldn't use magnesium for radiators either, but while reactive it's already resistant enough (mostly because of passivation) to be used as structural material even on Earth (and it's both light and quite strong) - you might even make people cans out of it, although any sort of fire on board would even more scary than usual.
Calcium isn't chalky, you're thinking calcium carbonate, but metallic calcium is soft and bloody reactive (not as bloody reactive as, say, potassium, but still - it even reacts with poor man's noble gas - nitrogen). Nope, not the first thing I would think of when thinking of structural metals.
As for ceramics, I tend to use them for all radiators on anything crewed even if their working temperature is low as they are meant to survive nuke flashes and tank lasers at least a little bit - stock Gunship and Laser Frig are textbook examples of how not to do it.
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Post by Apotheon on Sept 17, 2018 16:12:13 GMT
Thanks for the answers! What about RCC/boron nitride?
Actually, after some thought I’ve started to iterate on the central questions in the original post. What I’m REALLY curious about is the following: is there anything that should be added to or change in CDE, which would affect the mass or volume by spaceships by about >5%? My working theory is that it’s only the command module and rocket that significantly affects this. The rocket determines the amount of propellant for a given dV, which determines almost all the mass and volume along with the command module. I.e. for realism, focus on those two modules! The other modules, including power and radiators, have an insignificant mass and volume in civilian ships, any objections to this? It appears to be true if you play with (excessively?) min-maxed modules.
Basically, my theory is that someone interested in writing a book with realistic spaceships could simply determine the dV, determine the mass and volume of the command module, determine the rocket performance (the parts that affect dV) from which the amount of propellant and its mass and volume follows, and based on that, have a +/-5% accurate estimate of what mass and volume it would have and be free to design the spacecraft according to those constraints, while remaining realistic. Power, radiators, and other things, such as communications, don’t make a difference in mass or volume. In other words, if a writer wanted to design a ship that goes to Mars (6 km/s dV) and the writer accepted Apophys rockets performance and CDE's command modules mass and volume as realistic, then it would follow that the ship should have a mass of about 110 tons +/- a few tons, just like I got in the original post, because all things follow from that, unless you add armour/weapons and this would be a realistic rule of thumb.
If I'm correct and mass is quite accurate, then it follows that dV/acceleration is accurate and the ability to move around the solar system is accurate, which means CDE is accurate overall and the conclusions are informative for a future spacewar, if it at all happens in the way we envision it, which would be great. At least before thinking about armour and weapons.
I'm guessing the currently weightless structural support would make a difference... any idea of how big? Just looking at the stuff in my example craft, the struts look like they may mass only a few tons if made of aluminium.
I've looked at a few lists of what's unrealistic about CDE and haven't seen anything else I guess would make a big difference in the appearance, mass, or volume of the ships.
Qswitched may have followed a similar thought process in the creation of CDE. Starting with rockets, propellant tanks, and command modules, which determine most spaceship's properties, and then deciding to add weapons, which also made it necessary to add power and radiators (and radiation shields, before he realized they're completely insignificant if you make them out of Li-6, unless the current modelling is wrong).
Maybe this is why we don't have communications modelled yet. Adding it wouldn't change the mass significantly, hence not change the dV or acceleration, hence not change the travel capabilities or military capabilities of the ships and well... not really affect much at all. Unless communications equipment is especially sensitive to a certain kind of weapon modelled in CDE, for instance if nukes are guaranteed to fry any communications within a million miles, there's no real reason to simulate it.
1. Propulsion suffers from the baseline physical simulations for the materials involved, besides this its fine. 2. Total game-based min-maxing, intermediate physics knowledge is helpful to get a good sense of how thing A might influence property B. But good physics skill aren't required in any way. 3. Seems like a game-balancing thing to me rather than anything else, qswitched can change the mass arbitrary depending on several possible, but valid, assumptions. 4. The command module usually isn't exposed, but you could use some kinds of plastics to do such a thing. 5. Depends on the purpose, there isn't much speaking directly against it when talking about the game. 6. Why exactly? The ISS just uses a multitude of Whipple shields and spall liners, depending on whether or not the game actually realistically simulates the kinetics in the hypervelocity regime you want to go with crystalline materials such as sapphire. But you want civilian armor, so multiple layers of Whipple shield make sense. 7. That really depends on your assumption, realistic according to whom? Actual spacecraft? Also, can you edit the image out of your quote?
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Post by Apotheon on Sept 17, 2018 20:15:29 GMT
I added a few ideas that I'm interested in knowing more about in my above post.
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Post by apophys on Sept 21, 2018 22:22:43 GMT
What I’m REALLY curious about is the following: is there anything that should be added to or change in CDE, which would affect the mass or volume by spaceships by about >5%? My working theory is that it’s only the command module and rocket that significantly affects this. The rocket determines the amount of propellant for a given dV, which determines almost all the mass and volume along with the command module. I.e. for realism, focus on those two modules! The other modules, including power and radiators, have an insignificant mass and volume in civilian ships, any objections to this? It appears to be true if you play with (excessively?) min-maxed modules.
Basically, my theory is that someone interested in writing a book with realistic spaceships could simply determine the dV, determine the mass and volume of the command module, determine the rocket performance (the parts that affect dV) from which the amount of propellant and its mass and volume follows, and based on that, have a +/-5% accurate estimate of what mass and volume it would have and be free to design the spacecraft according to those constraints, while remaining realistic. Power, radiators, and other things, such as communications, don’t make a difference in mass or volume. In other words, if a writer wanted to design a ship that goes to Mars (6 km/s dV) and the writer accepted Apophys rockets performance and CDE's command modules mass and volume as realistic, then it would follow that the ship should have a mass of about 110 tons +/- a few tons, just like I got in the original post, because all things follow from that, unless you add armour/weapons and this would be a realistic rule of thumb. Depends on the main drive type and acceleration profile of your civilian vessel. If you use an MPD or other ion drive (alone or with an NTR secondary), your non-payload dry mass will be dominated by the power system, so any changes to the power system may change that mass a fair bit (for example, Curie point radiators, better pumps, reinforced pipes, thermophotovoltaics, concentrated solar for a heat source rather than a reactor, etc). But unless you're going for maximum speed with basically no payload (like Homecoming speedruns), you can afford to carry more dry mass due to the high exhaust velocity; your payload fraction can be quite high regardless. Payload mass (passengers/cargo/drones) can even exceed propellant mass. If you use NTRs or chemical thrust only, the power system is indeed insignificant if you have no weapons. On the other hand, you have noticeably higher acceleration, and this will require structural reinforcement of your ship, which is currently not modeled at all. That is likely to change dry mass quite a lot if your ship is large, or has very high acceleration. If you consider materials weakening with high temperature, you may need to additionally reinforce things like radiators and reactors. Payload fractions aren't nearly as good as on ion drive ships, so dry mass changes are more visible overall. You can avoid these issues by having very low acceleration (i.e. a small, weak rocket), though that is a design choice. But yes, as for the engine itself, how deeply you minmax its mass & cost has relatively little bearing on the end results, only its exhaust velocity. For any decent engine (like SpaceX's Merlin; that's already good enough), its mass is dwarfed by the crew and payload and structural reinforcement. No, I have no idea how much mass the reinforcement would actually take for normal vessels. Pure aluminum is a very poor choice for structural material, btw.
Seeing how ion drives allow very high payload fractions, and faster possible travel times due to high maximum dV, they are almost certainly the more relevant one.
Radiation modeling is questionable. Reactors should definitely be outputting more than just fast neutrons, and Li-6 is probably not quite that good at neutron shielding (more likely, we'd see LiH or LiBH4, using Li-6 and B-10). Unfortunately, it's hard to say how much effect that will have when fixed up. In particular, distance shielding may be employed, which takes very little mass.
Communication equipment is pretty trivial, and can be hidden from enemy fire, so that isn't really relevant.
Sensor equipment could make a significant mass difference in a war scenario when engagement ranges are long (as they are in the meta), since the sensors necessarily need to be more powerful. Qswitched did not expect lasers to be as useful as they are shown to be (stock reactors and lasers are much, much worse optimized than guns), so engagement ranges were assumed to be short.
Disabling sensors by laser fire is a topic of varied debate. On one hand, they are clearly more fragile than hull. On the other hand, filters can be added in front to reduce the incoming light by an arbitrary amount, which means disabling fragile sensors immediately gives hardened sensors the precise location of the attacker (as well as giving everyone else its location due to diffraction of the laser). On the third tentacle, it may be possible to mask it by using a cloud of reflective chaff. Such concerns are integral to warfare and have the potential to be the defining concern in ship design. This of course means the mass allotted can vary greatly. Fortunately, the aperture of a laser can double as a telescope for a sensor, so a laser-heavy fleet doesn't need quite as much extra mass allotted to sensors.
Sensor modeling would take quite a lot of development effort, so it is reasonable that it hasn't been implemented up to this point (qswitched is just one guy). You can't have ships without thrusters, propellant, power, and crew; you can't have proper warfare in the first place without weapons. Those obviously had to be done first, they aren't bug-free yet, and we still would like more options among them (like neutral particle beams, other laser types, or using guns for thrust).
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Post by Apotheon on Sept 24, 2018 14:15:13 GMT
I also looked into life support... apparently astronauts use about 30 kg (!) of water per day, which dwarfs the other components of life support (air, food, and waste), which total about 5 kg per day. However, water estimates range from 10-30 kg and I believe that's without accounting for recycling... and isn't water super recyclable (99% of the ISS water is apparently recycled)? Even a small 12 crew ship for Mars in 6 months would need 80 tons of life support, which is 50% the mass of my ship and will probably double the final mass of the ship. But if there's high recycling, the life support may only amount to 10 tons, which won't necessitate complete spacecraft redesigns. The underlying assumptions make a frustratingly big difference!
Unfortunately, Atomic Rockets only has about one paragraph on water. Anotherfirefox complained about life support a while ago and whether it makes a big difference (at least in small ships) or not depends on how much water is used (10 kg or 30 kg?), how much is water recyclable, and to a much smaller degree to what extent air or food may be "recyclable".
If we look at the Gunship, it might need anywhere from 50 tons to 450 tons of life support for 6 months of operation. One might probably add +50% to all figures above for systems, storage, spares, and other miscellany.
It's not necessarily an insignificant amount of mass!
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Post by AtomHeartDragon on Sept 24, 2018 15:01:12 GMT
Water is only non-recyclable if you use it for lossy cooling (like in space-suit life support). For a proper crew module you're looking at water being recycled endlessly with nearly no losses.
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Post by Apotheon on Sept 25, 2018 16:15:06 GMT
Water is only non-recyclable if you use it for lossy cooling (like in space-suit life support). For a proper crew module you're looking at water being recycled endlessly with nearly no losses. Hmmm... is air and water theoretically 100% recyclable? According to this research, 2.8 kg per person per day is apparently reasonable for a 6 person 360 day Mars mission, which I guess is the same as the 12 person 180 day Mars mission I'm currently investigating in CDE. It accounts for all kinds of things, including recycling apparently, but still includes significant "air" and "water" mass, because of disposables, such as filters! It's 1.1 kg food, 0.6 kg air, 0.5 kg water, 0.4 kg human accommodations (aka clothes to laypeople), 0.1 kg thermal (regulation, I've no idea what this actually encompasses), and 0.1 kg waste expendables (food packaging, wipes etc) per person/day. 3 kg/person/day seems an appropriate rule of thumb, which may ultimately be decreased to ~1.5 kg.
www.marsjournal.org/contents/2006/0005/files/Hanford2005.pdf
Edit:
After looking over a little more data (and there's a lot of data), I found one study that thought 1.8 kg/person/day is viable by 2024 (written in 2004) with 95% recycling of air and water. Assuming ~100% recycling of air and water and half the amount of food packaging, 1.33 kg/person/day appears possible, which is 1/2 food, 1/10 packaging, and 4/10 other inorganic materials, which appear to be cleaning, hygiene, and waste supplies that calculations weren't given for and I cannot guess at a reasonable optimisation of them. A 20% optimisation would result in a 1.2 final, a 40% optimisation would result in a 1.1 final, and a 60% optimisation would result in 1.0 kg/person/day final. In other words, 1 kg/person/day may be possible, is my conclusion here!
All of these numbers include only "supplies" and exclude the life support systems, weighing in at about 10 tons for 6 people 1000 days.
emits.sso.esa.int/emits-doc/1-5200-RD20-HMM_Technical_Report_Final_Version.pdf
Edit 2:
I forgot one caveat: the above study counts on ~0.67 kg dry food per person/day... originating in energy calculations.
Also, assuming 99% air and water recycling, 25% improved packaging, and no inorganic materials optimisation, which all appears reasonable, we get 1.5 kg person/day. Maybe more reasonable than 1 kg person/day, really...
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Post by Rocket Witch on Sept 26, 2018 17:45:49 GMT
I wonder if that 0.67kg is every day or an average over time, because you don't need to eat every day. The body is adapted to putting up with fasting periods of anything from 3 to 30 days, and if you eat less your metabolism slows to match and actually bothers to recycle and repair old cells etc. and mental acuity actually increases. The trouble with people (and life in general) is access to trace vitamins and minerals rather than energy.
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Post by gedzilla on Sept 26, 2018 19:08:31 GMT
I wonder if that 0.67kg is every day or an average over time, because you don't need to eat every day. The body is adapted to putting up with fasting periods of anything from 3 to 30 days, and if you eat less your metabolism slows to match and actually bothers to recycle and repair old cells etc. and mental acuity actually increases. The trouble with people (and life in general) is access to trace vitamins and minerals rather than energy. Yo rocketwitch, this is off topic, but do u know where all the old regulars went ? These forums used to be bustling with all these familiar users, and now there almost all gone. You, newageofpower, apophys and (maybe) me, are all thats left of the old guard
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