Hmm I have some homebrew stuff I can share here.... It's not deck plans, but more of a way to integrate ship combat into the game a little. Yeah, the core book says don't do it, but A: one character invested in pilot, and B: physical transport exists. Therefore C: Someone will try and use a ship in combat. Dropbox link: https://dl.dropboxusercontent.com/u/17358196/Ships.ods it's not perfect, and probably has a ton of holes, but I think it'll work till something better comes along. As much as possible is based on the little bit of info on ships that there is (mostly the weapon damage multipliers). Travel times are pretty much BS.

Quote:

I really liked Adam Jury’s attitude on the maps, specifically the lack of a size legend. “The ship is the size you need to have an awesome game!”

I just want detailed measurements on *everything*, dammit! I'm just that sort of nerd. :) Yeah, EP tends to be loose about this sort of thing. And I'm not even saying that's a bad thing: not every RPer get excited about statting a vehicle using the trig and logarithmic functions you find in a GURPS vehicle builder, haha. Really, my approach to narrative quantification has disadvantages of its own: the "clomping foot of nerdism". I totally see myself in that :/

ThatWhichNeverWas wrote:

. . .There simply aren't enough values for advanced tech - How big does the fuel/propellant tank for a Metal-Hydrogen engine have to be?. . .

That depends upon the maximum Δv you want the ship to be able to obtain. According to Atomic Rockets the projected exhaust velocity for Metallic Hydrogen is 17,000 m/s. Other pages tell you how to convert that to specific impulse and how to use specific impulse to calculate your Δv. Now you're right in that it doesn't actually tell you how big that tank will be but it does mention things such as the fact that the storage has to handle millions of atmospheres of pressure. With that information I could fabricate some rough numbers if I had to. I could do something such as assume that the walls of the container will need to be 30cm thick with the approximate density of iron. If we assume a ship with a mass similar to the space shuttle's orbiter vehicle while carrying a payload we are looking at around 100 metric tons. If we want a maximum Δv of 10 km/s then 44.53% of the mass needs to be metallic hydrogen. If we assume a density of .8 grams per cubic cm then we need a sphere 2.37m in radius. A 30 cm thick shell with the density of iron would weigh close to 189 tons which tells us that our fuel tank is too heavy (since the tank and fuel are 233% of the total mass of the ship). So this means we will need to re-evaluate some of our starting hypotheses. Either we have to have a bigger ship if we assume the tank has to remain 30 cm thick with the density of iron (the cube-square rule means that eventually we will reach a point where it is possible), we need to make the walls of the tank thinner (because we are using stronger materials) and/or we need to reduce the density of the walls (we could reasonably have a density anywhere from 2-4.5 if we assume some form of carbon titanium composite). All of which is a lengthy way of saying that while Atomic Rockets won't give you simple formulas for a ship for Eclipse Phase it will give you a lot of data that can be used to devise a framework.

2300AD is probably the longest running (in its various forms) and most supported "hard sci fi" setting with no artificial gravity, but it has a real shortage of deck plans. I think the best source for this stuff is probably in Jovian Chronicles, if you can find the old books. It is not always done deck by deck, but they usually give you modular layouts that you can potato-head into your own ships. different areas (engineering, flight deck, living) are denoted, even if not room-by-room plans. Some feature re-configurable habitat rings with modules that adjust their layout depending on if they are under thrust or under spin grav. I can't think of any better published material, though there are a few websites with old home brew stuff that I have in an old bookmark file somewhere. And their might be something like this back in the ancient history of the Diaspora G+ community, where people shared and collected links for these sorts of deckplans. There is even a previous thread here on these forums, but I cant remember what is in it. Maybe someone with a little time and search-foo can dredge it up.

Lazarus wrote:

That depends upon the maximum Δv you want the ship to be able to obtain. According to Atomic Rockets the projected exhaust velocity for Metallic Hydrogen is 17,000 m/s. Other pages tell you how to convert that to specific impulse and how to use specific impulse to calculate your Δv. Now you're right in that it doesn't actually tell you how big that tank will be but it does mention things such as the fact that the storage has to handle millions of atmospheres of pressure.

You're right till here but going farther is hard. EP's metallic hydrogen is metastable through the use of electromagnetics, and if atomic rockets has numbers for magnetic containment vessels then I can't find them. I tried using numbers from ITER, but they don't really apply thanks to the lack of shielding and the presence of room-temperature superconductors, so we have to use Handwavium. An interesting side note is that the propulsion bus of an EP metallic hydrogen ship is going to be a lot shorter than you'd expect.

Lazarus wrote:

A 30 cm thick shell with the density of iron would weigh close to 189 tons which tells us that our fuel tank is too heavy (since the tank and fuel are 233% of the total mass of the ship).

The math is a lot easier to handle if you start with what you need for the Scenario (The payload and structural mass), use the Tsiolkovsky rocket equation to get the propellant/fuel mass for that, and then go from there.

ThatWhichNeverWas wrote:

. . . You're right till here but going farther is hard. EP's metallic hydrogen is metastable through the use of electromagnetics, and if atomic rockets has numbers for magnetic containment vessels then I can't find them. . .

Actually, I don't recall seeing that metallic hydrogen works that way in EP. I'm not saying that you're wrong, simply that I was working from a different perspective. Now you're correct, Atomic Rockets doesn't have any figures for the mass of a theoretical magnetic containment vessel, but then it didn't have the requirement that the containment vessel needs to be 6" thick with the density of iron. That was a figure I made up. In a similar vein I could come up with some pseudo-plausible figures based on the size and weight of coils of conductive wire.

Quote:

The math is a lot easier to handle if you start with what you need for the Scenario (The payload and structural mass), use the Tsiolkovsky rocket equation to get the propellant/fuel mass for that, and then go from there.

Actually, that was what I did. I assumed a complete payload and remass total of 100 tons, a specific impulse of 1732, and a target Δv of 10 km/s. That gave the percentage of total mass that had to be metallic hydrogen (44.53%). I had to estimate the density of metallic hydrogen from a couple of publications since people aren't completely sure but that gave me a volume which I was then able to turn into a weight for the vessel holding the remass (by expanding the dimensions of the metallic hydrogen mass).

doesn't the metallic hydrogen require an oxidizers? I recal the books mentioning Red Oxygen somwhere

The PDF's pretty good but I wish the Author'd listed his sources. My only issues are the same ones I have with Automic Rockets, and arise from inconcistencies / incompatabilities with the Setting - for example, Every Gram Counts only applies to a limited degree in a setting with Commercial Shipping.

Lazarus wrote:

Actually, I don't recall seeing that metallic hydrogen works that way in EP. I'm not saying that you're wrong, simply that I was working from a different perspective. Now you're correct, Atomic Rockets doesn't have any figures for the mass of a theoretical magnetic containment vessel, but then it didn't have the requirement that the containment vessel needs to be 6" thick with the density of iron. That was a figure I made up. In a similar vein I could come up with some pseudo-plausible figures based on the size and weight of coils of conductive wire.

It's mentioned in the description of Propulsion Systems in the core book: "Although naturally unstable, it can be stabilized with carefully controlled electrical and magnetic fields, and these field generators are an integral part of every metallic hydrogen fuel tank." In my headcannon Metallic Hydrogen is a Type 2 Superconductor and is stabilized via Flux Pinning, but that's just me. Actually now that you mention it, would it make sense to have a thread with semi-standardised values for EP tech, and how it effects design? I kinda like the idea of having a single page with all the numbers/considerations in one place.

Just quickly touching base - I've gotten most of my basic design notes together, and am formatting them to be readable by People. I've also got basic values for MH engines, and am currently looking at Hydrogen-Remass storage, particularly Metal-Hydrides. I also have basic hull-plating, but getting absorption values for x-ray shielding is proving to be annoying.

The thrust to weight ratios I'm proposing for the plasma and fusion engines are what I would call 'abstract' ratios. In the case of HOx, AM, and MH engines there is no need for a separate power plant for the production of thrust. The AM and MH engines require power for the containment of fuel but in both cases the production of thrust doesn't come from energy being injected into the remass. In the case of both plasma and fusion engines, however, energy is used to excite the remass (I'm assuming the fusion reaction is not self sustaining). That means that part of the weight in their thrust/weight ratios is the power plant that sustains the reactions.

Are you referring to this specific post? http://eclipsephase.com/comment/10887#comment-10887

The only problem with those figures is they don't tell you things like how much of the weight is engine, how much is power plant, etc.. They don't even really tell you how much is fuel although you can reverse engineer that without too much difficulty since they tell you the delta-v of the ship. Metal hydrogen is a solid but that doesn't mean you need to push the entire body of fuel around to the motor. The fuel in the SRBs of the space shuttle doesn't move at all. Of course there's also the fact that those can't be refueled and they can't be started and stopped. One possible design for a metal hydrogen motor would be to have fuel be in some sort of standardized plates. Since there is an electromagnetic field stabilizing the hydrogen you could lower the field over certain plates and allow them to begin converting into gaseous hydrogen. Depending on how much you lower the field would vary how rapidly the plates convert. You might go from back to front or you might go from the center of the column out (similar to how solid rockets burn).

ThatWhichNeverWas wrote:

. . .This is one place I disagree, and it's honestly the cause of most of my problems – when I look at the properties of the materials which are in common use in EP construction the numbers are... well, let's just say that the values I actually calculate look like I made them up. Carbon Nanotubes are the prime offender as even small amounts of them in a composite can give pretty ridiculous performance improvements – for example, depending on which sources I use I get Specific Stiffness values running from 1000 to over 20,000 Mm^2/s^2.

Yeah. I've actually considered CNTs myself. I came to a realization a while back that most likely an awful lot of the things that we assume are fabricated from metal (guns, synthmorph frames, vehicle hulls, etc.) are quite likely made out of things such as CNT composites. This wasn't so much for performance reasons but because carbon is going to be much easier to get a hold of then metals. If you would like to provide your figures I for one would love to see them. I'm pretty good with a lot of the physics but I'm not as good with the specifics of material sciences. The only thing I would suggest is that you take into account that there's going to be more than simply structural strength involved with some of the materials. As an example you can probably produce a CNT composite interior wall that is more than strong enough at only a few millimeters of thickness but if it is going to transmit sound straight through it then people are not going to be happy with it. You're also not going to be able to run wiring or tubes for carrying materials through such a thin wall. Filling it with an aerogel is a lightweight solution that deals with the noise but it still adds mass and such a solution is probably not viable since it makes retrofitting parts way more difficult. One possible idea is dual layers with each consisting of structural substrate and a layer of baffling/insulation/shielding such as an aerogel separated by an airgap (not completely separated as there would be anchors running from one structural surface to the other to keep them spaced appropriately but the majority of the space between the surfaces is an airgap).

Quote:

I'm really not a fan of those numbers. Even from a pure storytelling point of view, the dimensions are aggravatingly small; an MH-LLOTV is a 16m*25m squat cone! What am I supposed to do with that? It may be useful for aerobraking or Warships, but for everything else it's just impractical. I realize I'm overreacting, but both the GM and Engineer in me are grinding their teeth.

The main thing I would use those figures for is to double check proposed solutions. The stats for the LLOTV don't really produce a vehicle you would have your party adventure in but that's because the LLOTV (large lander and orbit transfer vehicle) isn't much more than a vehicle for moving cargo from a transport ship to the surface of a planet. It's sort of the spaceship equivalent of one of the large trash barges you see move up and down the Hudson, although in this case it transports useful cargo rather than garbage. It probably has a relatively tiny bridge, a fairly specialized engine, and a small amount of fuel/remass and absolutely no living quarters. It is entirely possible it doesn't even have sanitary facilities as operators are expected to hold it for the few hours they are on the ship or else use their vacuum suit's facilities. Any adventures you have concerning one probably deal with things like stowing away on one, hiding something on one, or robbing one.

Quote:

An odd thing about MH engines is that they should arguably be able to scale their mass-flow rate to a nigh-arbitrary degree because for all intents and purposes metallic hydrogen is a compressed gas, so the thrust/weight ratio can be pretty much whatever you need.

No. I'm going to disagree with you here. It's not really a compressed gas. The energy comes from the metallic hydrogen sublimating to its gaseous form as the fields are turned down, so it's kind of like a dry ice rocket. That pressure has a very definite upper limit as beyond that the metallic hydrogen simply wouldn't sublimate. In theory you might be able to squeeze a little more energy out of it if the solid itself is held under pressure but it would be extremely complicated and the amount of energy would be relatively small compared to what you are already getting. In all likelihood the mass of the extra equipment required to harvest this energy would probably be greater than the benefit (I realized this when I was working up an alternate concept of using metallic hydrogen to power a plasma or fusion drive. Yes, the extra pressure would, in theory, enable a higher specific thrust but it would be a relatively small amount compared to the Isp of the plasma and fusion engines and the extra mass would bite into that. In the end you might still wind up with a small benefit but it wouldn't be worth the additional complications that would make repair and maintenance much more costly)

Quote:

Quick clarifier: should I put what I've got here, or make a new thread?

I'm all for adding it here. If things get too messy with multiple proposals strung throughout the thread one of us can eventually recompile it into a new thread, but for now it would probably complicate matters more to have the separate ideas in multiple threads.

[center][b][u]Basic Shipbuilding Design Assumptions – Part 1.[/u][/b][/center] - [u]1. Fusion Power and Molecular Construction.[/u] Fusion means that power is available in abundance. Molecular construction means that items that would be infeasible because of their complexity are easy to get. On the other hand, items which make use of rare elements are harder to get. What this means is that systems that are power hungry or complex are more desirable than simple ones which use up more resources – a simple example is that magnetic bearings and magnetic levitation are more desirable to use than actual bearings or lubricants. If something in the real world wouldn't be practical because of manufacturing difficulty, then it is absolutely used in EP. - [u]2. Altered Carbon.[/u] Carbon is amazing, it's allotropes more so. In EP we have mass-produced synthetic diamond nanotubes and all sorts of fullerines. Individually these have incredible potential which magnifies exponentially when they are used in compounds materials – and if you can mass produce both you can have compounds which consist purely of both. For convenience, I'll refer to all diamond/fullerine composites as NRSD (Nanotube-Reinforced Synthetic Diamond) As a rule of thumb, any structure made out of NRSD will weigh from two to twenty times less than if it was made out of steel, or up to ten times less than one of Carbon Fibre, depending on the exact purpose of the structure, with the largest difference in purely tensile structural members. - [u]3. Room temperature superconductors.[/u] Assuming the performance of the Room Temperature Superconductors available in EP is roughly equivalent to those currently used with a higher operating temperature, then the effect they have on technology cannot be understated. Not only can power be transferred with effectively no loss, incredibly high magnetic fields can be created generated with small devices without huge cooling systems to support them, drastically reducing their operating costs. Electrodynamic Bearings and Maglev systems can be created anywhere, making them almost perfectly efficient, and any device that employs Magnetic Confinement can be significantly smaller due to the reduced coolant requirements. - [u]4. Power Storage.[/u] Working from the values given in the Corebook gear section, Superconducting batteries can provide a Specific Energy of 35-46 MJ/kg and and Energy Density of 14-19 MJ/L, depending on quality and manufacturer - this is approximately 1000 times higher than what we can achieve today. We can use this to give a general density of ~2.45g/cm^3 for pure superconductor structures. - [u]5. Life support.[/u] Using Makers and recycling, life support is almost a closed system; food and water can be recycled nigh indefinitely, with oxygen/CO2 being the only significant exception. Looking at Vacusits, life support packs and the GEV, we can see that an almost perfect recycling system is small/light enough to be man-portable and we can reasonably assume that larger versions are even more efficient, so the volume/mass of the life support system is going to be defined by the amount of reserves being carried. I think that food and water would be transported together as feedstock, with a mass/volume of 30kg/25L per person per day of reserves, minimum one. Oxygen is harder to calculate but NASA's value of 0.8kg/PersonDay seems reasonable, stored either as water ice or compressed in NRSD pressure tanks, both with a volume of about 0.9L/PersonDay. Given this relatively low mass/volume ratio, it's fair to assume that the amount of oxygen held in reserve is going to be relatively large. - [u]6. Ship Size and Classification.[/u] The primary factor influencing a ship's design is it's range, or more precisely it's "travel time". The longer the ship is away from shelter/port at a time, the more radiation it's exposed to, the more self-sufficient it must be and the greater the crew's requirements for mental health. (H+) - Ships that will be underway for less than a few days (H+) have low requirements – these are xLOTVs, Fighters, Orbital Tugs and the like. These ships aren't intended for independence, so they only need basic hull plating and no dedicated reactors – their requirements can be met purely through nuclear and superconducting battery storage. These ships will usually use MH engines due to their simplicity and low incidental mass cost. (W+) - The next level is those that have a range up to weeks. These will have more room for the crew and dedicated reactors for power, using plasma or fusion propulsion. They'll also have proper armor and a Parasol (see below). (M+) - Ships that can go up to months at a time begin to resemble small habitats, with serious plating and power/fuel capabilities. These are your destroyers and scum barges. (Y+) - Above this level ships are pretty much indistinguishable from full-blown habitats, capable of indefinite survival given sufficient raw materials. - [u]7. Armor.[/u] I've had some trouble finding numbers for the radiological environment of space, so I've abstracted from the best ones I found. In (my) EP, ships are first assembled as clusters of NRSD pressure vessels which become the cabins and storage spaces, which are then wrapped in a secondary hull of mass-produced, modular armor "tiles" separated by a vacuum-gap, each of which is easily manufactured and replaceable. W+ and larger ships will pretty much always have the capability of manufacturing/recycling tiles onboard. The first line of defence ships have is a magnetic shield to deflect charged particles generated by superconductors embedded in the tiles. These generate a field strong enough to deflect almost all incoming charged particles whilst creating another to negate the field within the ship proper. These weigh 5.4kg/m2 of armour. The main structure of the plate is a foam of diamond microspheres filled with compressed polyethylene with a standard mass of 50kg/m2. This mass is sufficient to make Neutron radiation largely meaningless – any source capable of delivering a meaningful dose through it will incinerate the ship entirely. The killer is ray shielding. There are AFAIK no ways to artificially enhance a shield's X-ray cross-section, you simply have to pile on the mass with high Z materials (i.e. Lead) providing the most bang for your buck. H+ ships can get away without any significant shielding, but W+ and larger should have a coat about 3cm thick to reduce the ambient to acceptable levels, massing at about 341kg/m2. Higher fluxes from solar weather or hostile weapons require a depth of 5+ cm with mass of 568kg/m2 , but it's possible to cheat. The thing about Solar X-Rays and Xasers is that the vast majority of the time they come from a single direction – the Sun and the hostile ship/fleet respectively. Accordingly, you usually only need to have a single axis of the ship armoured to that level, ideally the axis with the smallest cross section. Most of the time this will be the Prow. Ships with this "Parasol" shadow shield can orientate themselves between burns so that their thickest armour faces the largest radiation source, turning the whole ship into a faux stormshelter. This may take more mass than an actual storm shelter, but is infinitely more convenient. H+ ships intended for extended independent use may have a partial of full Parasol to allow it to act as a de-facto shelter. Finally, the plates have conduits allowing them to connect to the ship's coolant network. In short: Basic Hull plating is about 350kg/m2, Normal is 695kg/m2 and Parasol/Combat armour is 925kg/m2 and higher. - [u]8. Every Gram Counts.[/u] Common wisdom is to absolutely reduce the amount of mass a given ship will have because increasing it's deltaV requires exponentially larger amounts of fuel. However, this is slightly dampened in EP, partially due to the presence of fuel depots and fuel refineries, but mostly because it's become an economic venture: rather than shifting as much as possible within budget, the goal is to make the greatest profit on a mission with a set deltaV. Assume we have a Unit-Payload consisting of an amount of cargo and the fuel to ship it to it's destination, and a drive unit of arbitrary mass to get it there. We know this is profitable, so we can ship another Payload for the same or slightly lower profit... or we can attach the second Payload to the first and ship them together. The deltaV doesn't change so the mass requirement is roughly the same, but we no longer have the cost of the second drive unit, so the shipment is actually more profitable. As a general rule, large ships are more desirable because the ratio of profitable cargo to the rest of the ship drops the larger the ship gets. This is balanced by the ever decreasing profitability of the cargo, but plotted together on a graph we are given a curve of profitability to Payload, with the maximum profit occurring before the maximum is reached. This means that any ship is going to have a generous budget of extraneous mass which they can carry and still be "worthwhile", proportional to the mass of the ship and the profitability of the cargo. - [u]9. Metallic Hydrogen Engines.[/u] Metallic Hydrogen engines are incredibly versatile, requiring no mass beyond their storage to be used and capable of extremely high thrust/weight values depending on how the tank is configured. Simple versions are nothing more than a storage tank, which forms a simple magnetic nozzle when the hydrogen is released. More advanced systems may use separate storage tanks, passing grains of MH to the tank which serves as the engine. W+ and higher ships will usually use more efficient plasma/fusion drives, but many will use MH for combined attitude control and point defence. Unfortunately I haven't been able to find anything on RL metallic hydrogen storage, so this is all derived from what I “want” it to be capable of. Using a Exhaust velocity of 16km/s, the ratio of Remass to Remass Storage cannot exceed 1/R, at the maximum possible deltaV the drive can produce, as deltaV above that amount converges to infinity. In my head it's reasonable for a ship to be able to get from any planet in the solar system to any other. The mission table from Atomic Rockets gives a maximum value of 33159m/s to get from Mercury to Jupiter. 1/R for this value is ~0.126. In order to make the math simpler and give a buffer we can reduce this to 0.12, which gives a maximum deltaV of 33924m/s. To be continued (when I get time) :D

ThatWhichNeverWas wrote:

. . . The energy Metallic Hydrogen provides is released when it is removed from containment – and that's it. There are no reaction chambers or extraneous features necessary because it's all implicit in the mass of the tank - you just have to “open the valve”. This means that if you want to get more thrust you just need to push it out of containment quicker, increasing the Mass Flow, with the only limitation being the forces the tank can withstand.

No. Your ultimate limitation is the pressure at which metallic hydrogen will remain metallic. When you reach that pressure the metallic hydrogen will stop sublimating into gaseous hydrogen which in turn will stop the pressure from increasing. Beyond that the only way to increase the pressure would be to heat the gas and according to the 2D phase diagrams I'm looking at you would need to heat it to around 10,000 Kelvin before you begin to see an appreciable increase in pressure. While that is certainly within the realm of possibility you are now looking at a hybrid system where you need to have a power plant generating a great amount of heat and you are no longer simply 'opening a valve'.

ThatWhichNeverWas wrote:

. . .Metallic Hydrogen engines are incredibly versatile, requiring no mass beyond their storage to be used and capable of extremely high thrust/weight values depending on how the tank is configured. Simple versions are nothing more than a storage tank, which forms a simple magnetic nozzle when the hydrogen is released. . .

No mass beyond their storage tank and their nozzle, and the weight of that storage tank is not insignificant. If it were to operate solely by maintaining pressure it would need to withstand something in the neighborhood of 15,000,000 psi which would probably require massive walls. In EP, however, we are told that people use magnetic fields to keep metallic hydrogen metastable. While this removes the massive walls you probably needed it does still require weight in the form of magnetic field generators as well as the power plant that generates the energy to generate the fields, and that is probably not insignificant. Based off the 3 G figure estimated in EP as the capability of a metallic hydrogen engine I came up with an extremely rough approximation of a 45:1 power to weight ratio for your 'standard' setup. That means that with an 'average' size tank and an 'average' nozzle setup 1/15th of the mass of the ship is taken up with fuel, nozzles, the physical components of the storage tank (walls, magnetic field generators, etc.) and the portion of the power plant necessary to power the coils.

iirc ine one the books there is a trade flow diagram Also there are the bounties promised by the reliably unreliable pandora gates

If I remember right up to Nickel it shouldn't be so hard to get. At least on Jupiter moons and in the Belt. Don't remember about Saturn. Elements heavier than Nickel start to get progressively more rare and hard to mine unless they are in some asteroid. With Io probably being the main source of them which gives many opportunities for games (volcanoes everywhere).

Zoolimar wrote:

[u]1. Fusion Power and Molecular Construction.[/u] What about dependence on ship origins and intended purpose? Mars and Jupiter probably don't care that much about using rare materials or metals in construction.

Ship origins and purpose don't apply at this level, and rarity only to a limited degree. Yes, Military vessels are more likely to use technologies employing "rare" materials, but those materials will be as energy rich as possible to minimize the amount of the material used.

Zoolimar wrote:

Additionally there is a good reason real world militaries ascribe to a KISS principle. Magnetic bearings and similar designs are a good thing for a vessel not intended for combat but any ship that is supposed to be hit by laser and proton beams probably won't be that happy about them due to possible charges messing with generators.

Simple is relative. Physical bearings means you're dealing with wear and tear, lubricants, potential shrapnel, the possibility of misalignment, and so on. Magnetic bearings are for all intents and purposes solid state. And if a ship is getting charges in the interior from weapons fire, they have [i]much[/i] more important things to worry about. Like the crew's flesh boiling.

Zoolimar wrote:

What about boron carbide/boron nitride as armour and protection against radiation? It's also possible to use small fuel tanks with hydrogen as shielding and armour - before combat you will remove air from ship crew quarters to tanks so there will be no risk of reaction with oxygen. I think I also seen somewhere a solution with hydrogen being "dissolved" in fullerene. Not as mass effective as liquid but much more effective as armour. So you can combine part of the fuel tanks as a multi-purpose system.

Boron X-ide is fine against low energy particles, but doesn't do jack against high energy stuff. If you want to protect against high energy neutrons then you need a high atomic number material, and anything thick enough to block them is going to stop slow neutrons dead. The problem with using your fuel tanks as shielding is that... well... you'll be using the fuel, so your protection decreases over time. Hydrogen tanks also leak and can be punctured, creating a ever-so-handy stream of gas to destabilise the ship and prevent repairs. Using a hydrogen-rich solid prevents these issues, and PE is the most hydrogen-rich solid I could find. It's also really easy to work with.

Lazarus wrote:

No. Your ultimate limitation is the pressure at which metallic hydrogen will remain metallic. When you reach that pressure the metallic hydrogen will stop sublimating into gaseous hydrogen which in turn will stop the pressure from increasing.

Presumably the pressure required to contain Metastable Metallic Hydrogen is significantly less than that required to contain Metallic Hydrogen mehanically, because otherwise why bother. From this it's safe to assume that the tank would rupture long before the hydrogen stops sublimating.

Lazarus wrote:

No mass beyond their storage tank and their nozzle, and the weight of that storage tank is not insignificant. ... That means that with an 'average' size tank and an 'average' nozzle setup 1/15th of the mass of the ship is taken up with fuel, nozzles, the physical components of the storage tank (walls, magnetic field generators, etc.) and the portion of the power plant necessary to power the coils.

I'm not sure what you're getting at here. - I've been trying to get some figures together for fusion reactor mass, and failing utterly. Think it would make sense simply to use Atomic Rockets values for Fusion/Plasma/AM drives?

For EP, I would assume there there no real such thing as rarity. There arent any natural materiel that are rare. EP isn't post scarcity, so even though there is de facto infinite of any element you want, you're limited by infrastructure to extract it, and process it. So... I guess there is rarity but not from quantity but of logistics.

actually with our current tech level ball bearings are more reliable and longer life than magnetic bearings

Zoolimar wrote:

. . .Than what about using same metallic hydrogen as storage for fusion fuel and shielding ?

Metallic hydrogen requires a magnetic field to keep it metastable. If the field were to turn off your fuel tanks would quite literally explode. Metallic hydrogen is stored inside tanks, even though it is metallic. While the tanks probably aren't strong enough to keep the hydrogen compressed (the pressures necessary to keep metallic hydrogen metallic without the magnetic field McGuffin are massive) they are probably strong enough to prevent an explosion by venting excessive pressure outside the ship.