Santa Barbara
25-01-2004, 08:36
Military Spacecraft Design 101
This is what I think is for most a fairly detailed, mostly realistic process to build a generic futuristic space warships. It's an alternative to the old standby, the 'pull numbers out of ass' method (which has it's own virtues sometimes...)
Building An Imaginary Space Ship In Ten Easy Steps!
1. Come up with the idea of a ship type, at least a general one. It's nice to have a system here, not necessarily of coming up with acronyms for ships but a concept of their purpose. Check out these US naval ship designations (http://www.navweaps.com/index_tech/index_ships_list.htm) for some inspiration.
A good thing to note is how many varieties of ship types, or even of ships within a single class, there are. It can be a noncombatant, or a main warship/capital ship/fleet ship/whatever. Then it can have specializations, such as missile or some other class of weapons (as in missile frigate) or speed ("fast" cruiser/whatever). You can be creative here. Militaries are always coming up with new names for things.
Anyway, so let's say I choose a 'light frigate', by which I mean a small warship with light armaments and usually specializing in some area of warfare such as anti-surface, anti submarinal, anti-orbital, anti-interplanetary, etc. Or some kind of weapon. I like it actually specializing in laser, hence "light" frigate in that sense as well. Just to be confusing.
2.Sketch. Draw. Model. Render. Get an overall feel for the outer look of the ship. You can just google it if you want, but bear in mind thousands of other NSers got their pics that way too, and originality and creativity is more respected (and fun!).
Also note, unless you're designing a ship that can fly in atmospheres (or oceans), having a streamlined elegant curved look is not needed for spaceflight, and in fact is probably less space-efficient than using simple shapes like spheres and cuboids.
Bear in mind that:
+with normal, reaction drives (fusion, fission, ion, thermoelectric, chemical...) a ship burning at full speed will have a force of gravity towards the "back" of the ship at the speed it is accelerating.
+This means if you accelerate at 1 g, that's about 10 meters per second, per second, and you would feel Earth-like gravity towards the rear of the vehicle.
+If 10 g, that means if you're standing perpendicular to the direction of thrust, and you're not restrained and protected somehow, you're going to FLY "downward" towards the back of the ship. Splat!
And in fact, there is no way I know of (without inventing some scientific principle or something) to protect a human going at 12 g or above for very long. Frankly, I LIKE this limit, because it gives a grand strategy aspect of travelling between nearby planets in time, very old school. But if you go magic tech and your ships and their passengers can withstand accelerations of 1,00,000 times g, you miss out on that (and you're a spacewanker, if not strictly speaking a godmodder).
3. Some other things to consider is the scale of your ship. Do you really need it to be 15,506,030,059 kilometers long? What are you compensating for? At any rate, be prepared to explain what every kilometer of that ship is FOR, or if you just like the extra size because it's more impressive seeming. Militaries don't like to build things that are too large for their own good... and governments don't like to arbitrarily shell out funding for just any half-brained deathstar design.
Scaling Tips
Look at the heights of your rooms and houses, think of how much space between decks you'd need as a max or minimum. Do measurements in metric SI units, it's MUCH easier in the end (and what I use, and I'm not converting here). Look at actual naval ship lengths and widths.
Think about your propulsion system and it's particular requirements. Does it need fuel? Does it have a nasty exhaust? Is it magical and can go whoosh as it flies by the camera, with John Williams music blaring annoyingly and a feeling of impending archetypal-characiturization<sp>?
The engine generally goes at the "back" of the ship. There is nothing 'below' or 'behind' the engine, except whatever it ejects as reaction mass (the exhaust).
Unless, again, it's a magic tech drive and it just sorta 'warps' space ahead of it instead of crudely throwing stuff out the back. In that case, you could theoretically put the engine anywhere you wanted.
NASA suggested as a minimum for a voyage (I forgot which one) of 17 cubic meters living space per person. I like 3 meters between decks as a general rule, with some bigger or smaller depending on equipment and stuff. That way I can get a feel for how big the decks will be if, for example, the ship is shaped like a brick or tower.
So for example if you had 1000 meters (1 km) of deck length devoted solely to crew quarters, that could be 330+ decks! Again, reconsider any 104,506,000 kilometer long spaceships you wanted. Then you can actually figure out the 'floor plan' of a basic deck, see how many people you could fit on a standard, generic 'crew living quarters' deck. At least, you could figure out the volume of the deck, and divide it by 17 to see how many people NASA thinks you could house there (assuming perfect efficiency). More on this later, though. [/i]
For now get dimensions, and things like volume. Don't be afraid to use basic geometry. For our light frigate, it is 20 x 20 x 60 total volume, 24,000 cubic meters.
+(Deck plans, if you got em. Now is the time to do it rather than later, if you're going to do it. I suggest doing a bit of research on this, and leave lots of space for other things that you don't know yet. Don't make it ridiculous, like people stacked up like piles of wood in the passenger section (unless that's really how you're shipping them). Or don't have nothing but weapons and no power or anything else.)
4. Mass, volume, breakdown
+Consider that in modern US naval vessels, ships overall mass/volume breaks down like this:
40-45 percent Structure (presumably including armor)
20-25 percent Power Plant
15-30 percent Auxiliary machinery and equipment
6-14 percent Weapons systems
+Now, for a spaceship, this won't exactly be the same. Spaceships don't need a certain amount of seaworthy, curved hull and superstructure coming out of only one side. A whole spaceship could be "superstructure." Or it could be a tin can of a thin coating, leaving much more room for power, weapons, fuel, cargo or whatever. Think about the needs of your ship.
For my light frigate, I decide that it will have a thin but sturdy 500 mm outer hull, with even thinner but solidly built 100mm decks. That's actually quite a bit. Here's how I calculate the VOLUME of the outer hull- subtraction.
Dimensions of rectangular light frigate, including armor/outer hull: 20m x 20m x 60m = 24,000 m^3
Dimensions of rectangular light frigate, minus outer hull width: 19 x 19 x 59 = 21299
Subtract and get 2701 cubic meters of hull/armor material.
+Now why is this useful? Because we're going to decide what that hull material is, and how heavy it is, and how much it costs! You'll quickly find that building a ship out of silver will be cost prohibitive, so it's good and adds the nice touch of realism if cost of that fancy-shmancy hull of yours proves to be a limit.
5. Hull and armor
+Looking up some materials, I find that titanium-aluminum alloy takes up 4.9 tonnes for every cubic meter. Not bad, says I, nice and thick and that's what the ladies like. SO, for the light frigate's hull and armor, using titanium alloy will require 13,234.9 tons of the stuff! That's just for the armor!
+In comparison, modern naval destroyers tend to range in total mass from 8 to 16 thousand (or so) tons displacement. But, this will be a lot thicker armored than a modern naval destroyer, that's for sure. (You can get into the various qualities of armor and energy effects and such, I'm not going to right here. Except to remember that you'll want a mixture of ceramic and metals for two main types of attacks. Basically.)
6. Decks
+Now I'm imagining the decks like giant single plates laid on top of one another somehow. I said the decks would be 100mm each. Looking at the 60 meter length (or 'height' if you look at it like a tower) hull, minus the outer armor 59 meter, and with an average of 3 meters between decks that's 19.6 decks maximum-- that would assume zero thickness decks, however. So let's assume more like 16 decks, that's 1.6 meters total. And the decks would be 19 x 19 wide, so for deck material volume we have 577.6 cubic meters!
+Looking up some materials again, I find that ordinary rolled steel has 7.85 tons per cubic meter. So that's 4534.16 tons of steel for the decks. You can repeat this for the 'walls' if you like, but I'm not going to-- there's a limit to how much work I'm gonna do, hey.
+So, we have 17769.06 tons of mass just for the outer armor and the deck floors. I'm going to guess about 3000 more tons for other parts of the structure for a total of 20769.06 tons. That's the ship's weight-- assuming no atmosphere, crew, weapons, equipment, fuel, engine, cargo, ammunition, power plant. You'll have to add these things yourself.
7. Engines are a big subject which I'll go into more later. But most of them require fuel. Many use hydrogen as a propellant because it is cheap and abundant and efficient, although it's not very dense in gas or liquid form and requires lots of volume. In every engine, you'll find some sort of trade-off-- there is no absolutely perfect engine for all things, and if you have one in your story universe, you're being boring. Perfection is boring. Anyway, the trade off is usually between performance and efficiency; that is acceleration, thrust, exhaust type and signature, etc, and how many miles it gets to the gallon. The best engines are good in both categories, but not usually as good as the ones that specialize.
8. Putting it together, kinda.
+So keep in mind fuel, cargo, weapons. You can go for the whole thing. For example, I use 2nd Generation Santa Barbaran modules and I decide on having:
Engines - 10 x dense plasma focus systems, 100 cubic meters and 40 tons total.
Power - 1 x advanced fission plant, 5000 cubic meters, 1200 tons total.
Hull/Armor - titanium-alloy, 2701 cubic meters, 13,234.9 tons total.
+Remembering that the total volume of the design we sketched is 24,000 cubic meters. This means we have 16199 cubic meters more to work with. Fuel seems important if we want to move. However, I don't want to get into ISP, kilograms of propellant per newton of thrust and all that. I'm willing to fudge a little, as long as I have a reasonable figure devoted to fuel. Otherwise I'm not really going to get into rocket physics, hey.
+But I remember that hydrogen is 70 kilograms per cubic meter (stored as a gas, which is what I'll do here just for simplicity's sake). Also coming to the arbitrary figure that about half the ship can be engines and fuel (sounds good, no? I mean it's a spaceship engine, not a rowboat motor, dammit!), so figure on 1000 tons (1000000 kilograms) of fuel. That's 14285.7 cubic meters of space. That's almost everything left on the ship!
+Okay, well let's go with it just to make it challenging. Another route could be to require less fuel, or have a more dense fuel (I use this, but I have a very particular method of storage which I won't go into here). But going with it, we find we have 1913.3 cubic meters of space left.
+Let's see, if we devote that to just crew living space (at the NASA suggested limit, which is probably too small and cramped), that's enough for about 112 crew members. Of course, they would require life support systems, waste management, weapons, consoles, equipment, etc etc. Let's go with a very low crew (it's a light frigate after all) of 20. We'll give them cramped quarters, and have 340 cubic meters more gone.
+Now for weapons, I go back to my 2nd Generation modules again and pick out a St George Heavy Neutral Particle Beam Weapon, designed by Whispering Voices. I can really only have one, because the power plant provides 2.3 gigawatts, and the St. George requires 1.42 GW of power when operating. The volume is pretty minimal as it's just a long particle accelerator. It weighs 23.64 tons overall and requires 13 crew to keep operational (though of course only one or less to 'shoot' it). (Overall, a powerful weapon for a ship this size, since firing it takes up most of it's power (possibly giving power problems for general electricity or propulsion during firing) and the St George happens to be 80 meters long, running from the very back to 20 meters extended in front of the Light Frigate.)
+Then I assume the rest of the volume and mass goes to various equipment, sensors, etc.
(And, because I've chosen a beam weapon I don't have to figure out ammunition, ammunition firing rates and costs of ammunition, all of which are things I do have to deal with in my other ships. (And a major pain I say!))
So in the end, it appears we have:
Engines - 10 x DPF systems, 100 cubic meters and 40 tons total
Power - 1 x advanced fission plant, 5000 cubic meters, 1200 tons total
Hull/Armor - titanium alloy, 2701 cubic meters, 13,234.9 tons total
Fuel - 14,285.7 cubic meters hydrogen propellant, 1000 tons total
Crew - 20 crew, 340 cubic meters living space
Weapons - 1 x St George Heavy NPBW, 23.64 tons total
Everything else: 1573.3 cubic meters
+Giving a total of 24,000 cubic meters.
Now, using the known mass, that's a total of 15498.54 tons. Sounds about right, however that would assume "everything else" has no mass. For "everything else" I assume an AVERAGE density of 1.5 tons per cubic meter, meaning the equipment and stuff as well as the vacant air and such. That's 2359.95 tons more.
+Total mass of ship with fuel: 17858.49 tons.
9. Performance
Okay, so now we know the size and weight of the Light Frigate. We also know how many crew it has, and how dense and thick the armor is, and even how likely it is that you could shoot a pistol round through the floor (not bloody likely). What else is there to know?
+Acceleration. The formula is, Acceleration is equal to Force divided by Mass. We already know the Mass, and we know we want to accelerate at at least 10 meters per second per second (1 g) so we can escape Earth's velocity, and no more than 120 meters per second per second (since we have no anti-squashing technology). And, because of the 2nd Generation Santa Barbaran module tables, we know how much the DPF engines can give in terms of maximum thrust. Each one gives 400,000,000 Newtons of Thrust (better even than a chemical rocket, and way more efficient.) With ten of them, that's 4,000,000,000 N. Plug it into the formula, uh oh Algebra!
A=4000000000/17858490
That's 223.98 meters/second/second of acceleration, or 22.4 g. That's more than we can use, however in low-thrust, high efficiency it will be more acceptable. (Nice thing about those DPFs!)
+In all this, I neglected one important thing: THRUSTERS. It's easy to forget these. You need a bunch, and they can't be 'neglible' because they have to be able to, if your ship is a combat vessel, rotate the whole thing around quickly, and so they need lots of thrust. But they also need high efficiency since they'll be operating almost all the time. And, they'll probably use fuel too. As it is, the Light Frigate has only thrust vectoring to rely on, and I suppose ion engines. So it has pretty crappy maneuverability, unless I want to spread the engines around and have each one act like a thruster/engine. That means recalculating everything, so I don't!
+I'm sure you won't neglect to find out what your weapons are like. For example, the St George NPBW has a 90 second recharge. Because it's not a laser or any other form of light, it travels at slower speeds and so has a relatively short range. Also, the particles will not work well in atmosphere, but that's okay since the Light Frigate is shaped like a brick anyway. You might also want to figure out things like Rate of Fire (especially with missiles and projectile weapons), range, etc.
10. Cost
+Wait, you thought it was all free? Of course not! I of course have my materials charts and my 2nd Generation Modules charts, which have all the costs of everything too. But if you don't have them, and you don't, here's some starting points when calculating costs.
Modern aircraft cost about $2640 per kilogram to construct.
Modern armored vehicles, $55 per kilogram
Modern ships, $154 per kilogram
Conventional modern ammunition, $8500 per ton
Missile munitions, $600,000 per ton
Modern jet/tank fuel, about $1000 per ton
Rolled steel, $2450 per ton
Titanium aluminum alloy, $102,000 per ton
Tungsten, $97,000 per ton
+For my general war and material and ship design costs, I assume raw materials (especially things like uranium and other exotic materials) costs come down, and that finished products costs go up. This is because mining and transportation efficiency has gotten better, and because cutting edge gear such as spaceships and military technology is only going to get more complicated and costly. For example, aircraft costs have been increasing FOUR times every TEN years, for the past 80 years.
So I calculate the construction of the Light Frigate.
Engines - 10 x DPF systems = $18 billion
Power - 1 x advanced fission plant = $0.9 billion
Hull/Armor - titanium alloy 13,234.9 tons = $1.35 billion
Weapons - 1 x St George Heavy NPBW = $1.2 billion
Total of $21.45 billion.
+However, I figure that the construction company, launching, all the miscellaneous gear (and very expensive gear, like sensors, computers, fire control, etc etc etc), and the price the maker stacks on to make a profit in this thing, will all add another 50 percent. For more efficient construction (let's say you produce it yourself, eliminating the middle man cost) you can change that to maybe 25 percent. For more lavish sensors (etc) stack on more than 50 percent as you see fit.
My total construction price for this will be: $32,175,000,000
+Then if you're really down with things, you'll have costs for fuel and supplies, full reloads of ammunition, annual operational cost (including the crew wages), etc. However I'm not going to go into all that, except to suggest an annual operating cost about 1/10th the construction cost of the ship. That means for me, a further 3.2 billion dollars will be taken from my annual military budget, to operate one more Light Frigate.
So our (my) finished Light Frigate is here:
Example Class Light Frigate
Length: 60 meters
Width: 20 meters
Height: 20 meters
Crew: 20 (7 Pilots/Officers, 13 Main Weapons techs)
Decks: 16
Combat Mass: 17858.49 tons
Armor/Hull: 500mm titanium alloy
Main Weapon: 1 x St George Heavy NPBW
Engines: 10 x DPF-400
Max Acceleration: 22 g
Max Acceleration, Crew Tolerated: 12 g
Replacement Cost: $32.175 billion
Annual Operating Cost: $3.2 billion
Formulas and Science and Stuff
THRUST:
Everything moves, and to move you produce thrust. Thrust is measured in Newtons, and is also for the purposes of my calculations Force. Force equals mass times acceleration. F=ma, A=F/m, M=F/a.
ACCELERATION:
Acceleration is how much velocity you change, over time. In short, it's how fast you get to 60 after stepping on the pedal, and how much whiplash your neck is going to suffer as a result. In the case of combat spaceships, too much acceleration turns your body into jelly. Acceleration equals force divided by mass.
1 Newton propels 1 Kilogram of mass at an Acceleration of 1 m/s/s.
ISP and EFFICIENCY:
Without getting into rocket science, of which I know nothing, ISP is a measure of how many seconds one kilogram of fuel produces one newton of thrust. In short, it's efficiency. A high ISP means good gas mileage, low ISP means bad gas mileage. For example, a chemical rocket has a really high thrust (producing a lot of acceleration) but a low efficiency (with just a few hundred seconds ISP). On the other hand, ion engines have really high efficiency (as much as 40,000 I think) but terrible rate of acceleration (a thrust-to-weight ratio much less than one. Don't even THINK about having high performance ion engines, there's a physical limit to how much thrust ions can produce!)
DENSITY equals MASS divided by VOLUME.
MASS equals DENSITY times VOLUME.
VOLUME equals MASS divided by DENSITY
These are useful if you happen to know the volume (or can reasonably guess the volume) requirements or availability of something, and know the density of a material and want to find the mass, etc.
VOLUME:
Don't forget, geometry is your friend. A sphere's volume is 4 pi times the radius squared. A cuboid or rectangular is the length times width times height. A cylinder is pi times the height times radius squared. Etc.
SI UNITS:
Obviously I use meters, kilometers, kilograms and metric tons, newtons, joules, seconds, etc. Here's some reference points:
Speed of sound in air: 340 m/s
Speed of light in vacuum: 299,790 km/s
CONVERSIONS:
1 meter = 3.2808 feet
1 kilometer = 0.6214 miles
1 square kilometer = 247.0983 acres
1 kilogram = 2.2046 pounds
1 megaWatt = 1341.0219 horsepower
1 Joule = N x m
1 Joule = 1 kg*(m^2/s^2)
1 mJ/s = 1 mW
ENERGY AND STUFF:
Kinetic Energy is the energy of an object in motion. Technically, any weapon involving an object in motion slamming into a target (or indirectly slamming shrapnel/fragments into a target) is a "kinetic weapon." The damage is done by imparting energy and heat to the target. It takes certain amounts of heat and/or energy to destroy/penetrate/vaporize various types of armor materials. It's good to figure out these things if you really want to know for sure how much energy a weapon will roughly have to deal to defeat your armor.
Kinetic Energy = 1/2 (mass)(velocity)(velocity)
KE=1/2 (m[v^2])
Kinetic Energy of a .44 calibre, 15.55g bullet fired at 426 m/s: 1410 Joules (1.41 kilojoules)
1 "Megaton" of energy (1,000,000 tons TNT): 4,186,800,000,000,000 Joules (4.1868 petajoules, or 4,186,800,000 megajoules)
US current annual energy consumption: 100,000,000,000,000,000,000 Joules (100 exajoules, or 100,000 petajoules)
Some Tips And Stuff
Alright, if you're still reading this after all this I'm very impressed. Good work, I hope you learned something. Maybe you learned that you'd rather just by a generic cardboard Enterprise/Star Destroyer/Whatever. Maybe you learned something about building imaginary spacecrafts. I hope so, because that's a really useful tool in life!
+Notes on tech: Obviously, if you go much beyond plausible, foreseeable future reality and start inventing scientific principles left and right, you will not be limited by such things as thrust or acceleration or fuel.
But try to balance things out by making sure your ultra-uber tech is not cheaper than shit (by mass OR volume!). FTL engine? Fine, but just make sure it doesn't let your ship travel ANYWHERE, INSTANTLY, ALWAYS. Make sure it costs a pretty penny (it IS a highly advanced piece of machinery, no? So why price it like a refrigerator?) and make sure you can't make more than your economy and budget can spare.
Magic energy shields? Okay, but they better not make the ship invincible in combat, and they better have some sort of clearly defined limits (recharge time, cost, whatever).
Plasma bolts? Okay, explain to me how you can make a bunch of highly energized plasma hold together, stay hot, AND be launched gun-like. Or maybe you don't have them in bolts, but just spray plasma out over a very short distance. More plausible, that.
Railguns? Fine, but I hope you bring along spare rails-- the plasma and friction wears railguns out VERY quickly. There is no known way to make large railguns (linear electromagnetic accelerators) that fire large projectiles very fast without destroying themselves in the process. Coilguns are more plausible as a weapon.
+Of course it vastly helps if you know the mass, crew requirements, power requirements, dimensions etc of your various weapons, ammunition, etc. It also helps if you can find densities and material properties of various types of steel and armor and whatever. When making up numbers, as you inevitably have to do, try not to go overboard and invent "ubermaterials" that can withstand the Universe exploding, or evade any kind of detection.
+While on the subject of detection, there are literally dozens of different methods, TODAY, of detecting objects and energy and everything else in space. As time goes on, we will have even more ways (neutrino detectors, anyone?). While it's possible you may develop ways to reduce emissions and be less detectable, it's not very believable that you can find a way to technologically defeat ALL detection methods and have 'stealth' ships all the time. Invisible ships, much like invulnerable ones, tend to be a no-no 'round these parts.
+Notes on Magic Things: I find things get boring very quickly when EVERYONES tech comes from ass-space and no attention is paid to reality at all. Almost as boring as people who like to play that way, find the 'hard sci fi' approach! So, I think like everything a balance is required. I myself make most of my technology a LITTLE more efficient and advanced overall, using basically known-things, with 2 or 3 "black boxes" that I can't explain whatsoever. For example, I use electromagnetic weapons, magnetically confined fusion electric power, and alloys of known materials. But I also have Menelmacari gravitics here and there-- it is very expensive and limited in uses. I have a Quantum Computer running amok sometimes. I am not slavishly "hard sci fi," I just like working within the limits and boundaries of the genre. In the end, I think if it makes sense to the RP, can be explained in character, and is believable to the people you are playing with and the people reading, then go for it.
+Notes on the Budget: Remember, no matter what your military budget is, you CAN'T simply divide the total budget by the price of a particular weapon or spaceship to see how many you can afford. I have a guide around to doing the military budget, but the end result is you will probably have less than 1 percent of your annual military budget to use on things like buying vessels. And I doubt you can spend more than 10 percent of your annual military budget operating your existing vessels. Remember these things, because mis-doing the military budget is one of the easiest and most common ways to accidentally godmod! If you're unsure of how much you spend, save your UN Defense Rankings and let me know, and I'll see if I can help you figure it out.
This is what I think is for most a fairly detailed, mostly realistic process to build a generic futuristic space warships. It's an alternative to the old standby, the 'pull numbers out of ass' method (which has it's own virtues sometimes...)
Building An Imaginary Space Ship In Ten Easy Steps!
1. Come up with the idea of a ship type, at least a general one. It's nice to have a system here, not necessarily of coming up with acronyms for ships but a concept of their purpose. Check out these US naval ship designations (http://www.navweaps.com/index_tech/index_ships_list.htm) for some inspiration.
A good thing to note is how many varieties of ship types, or even of ships within a single class, there are. It can be a noncombatant, or a main warship/capital ship/fleet ship/whatever. Then it can have specializations, such as missile or some other class of weapons (as in missile frigate) or speed ("fast" cruiser/whatever). You can be creative here. Militaries are always coming up with new names for things.
Anyway, so let's say I choose a 'light frigate', by which I mean a small warship with light armaments and usually specializing in some area of warfare such as anti-surface, anti submarinal, anti-orbital, anti-interplanetary, etc. Or some kind of weapon. I like it actually specializing in laser, hence "light" frigate in that sense as well. Just to be confusing.
2.Sketch. Draw. Model. Render. Get an overall feel for the outer look of the ship. You can just google it if you want, but bear in mind thousands of other NSers got their pics that way too, and originality and creativity is more respected (and fun!).
Also note, unless you're designing a ship that can fly in atmospheres (or oceans), having a streamlined elegant curved look is not needed for spaceflight, and in fact is probably less space-efficient than using simple shapes like spheres and cuboids.
Bear in mind that:
+with normal, reaction drives (fusion, fission, ion, thermoelectric, chemical...) a ship burning at full speed will have a force of gravity towards the "back" of the ship at the speed it is accelerating.
+This means if you accelerate at 1 g, that's about 10 meters per second, per second, and you would feel Earth-like gravity towards the rear of the vehicle.
+If 10 g, that means if you're standing perpendicular to the direction of thrust, and you're not restrained and protected somehow, you're going to FLY "downward" towards the back of the ship. Splat!
And in fact, there is no way I know of (without inventing some scientific principle or something) to protect a human going at 12 g or above for very long. Frankly, I LIKE this limit, because it gives a grand strategy aspect of travelling between nearby planets in time, very old school. But if you go magic tech and your ships and their passengers can withstand accelerations of 1,00,000 times g, you miss out on that (and you're a spacewanker, if not strictly speaking a godmodder).
3. Some other things to consider is the scale of your ship. Do you really need it to be 15,506,030,059 kilometers long? What are you compensating for? At any rate, be prepared to explain what every kilometer of that ship is FOR, or if you just like the extra size because it's more impressive seeming. Militaries don't like to build things that are too large for their own good... and governments don't like to arbitrarily shell out funding for just any half-brained deathstar design.
Scaling Tips
Look at the heights of your rooms and houses, think of how much space between decks you'd need as a max or minimum. Do measurements in metric SI units, it's MUCH easier in the end (and what I use, and I'm not converting here). Look at actual naval ship lengths and widths.
Think about your propulsion system and it's particular requirements. Does it need fuel? Does it have a nasty exhaust? Is it magical and can go whoosh as it flies by the camera, with John Williams music blaring annoyingly and a feeling of impending archetypal-characiturization<sp>?
The engine generally goes at the "back" of the ship. There is nothing 'below' or 'behind' the engine, except whatever it ejects as reaction mass (the exhaust).
Unless, again, it's a magic tech drive and it just sorta 'warps' space ahead of it instead of crudely throwing stuff out the back. In that case, you could theoretically put the engine anywhere you wanted.
NASA suggested as a minimum for a voyage (I forgot which one) of 17 cubic meters living space per person. I like 3 meters between decks as a general rule, with some bigger or smaller depending on equipment and stuff. That way I can get a feel for how big the decks will be if, for example, the ship is shaped like a brick or tower.
So for example if you had 1000 meters (1 km) of deck length devoted solely to crew quarters, that could be 330+ decks! Again, reconsider any 104,506,000 kilometer long spaceships you wanted. Then you can actually figure out the 'floor plan' of a basic deck, see how many people you could fit on a standard, generic 'crew living quarters' deck. At least, you could figure out the volume of the deck, and divide it by 17 to see how many people NASA thinks you could house there (assuming perfect efficiency). More on this later, though. [/i]
For now get dimensions, and things like volume. Don't be afraid to use basic geometry. For our light frigate, it is 20 x 20 x 60 total volume, 24,000 cubic meters.
+(Deck plans, if you got em. Now is the time to do it rather than later, if you're going to do it. I suggest doing a bit of research on this, and leave lots of space for other things that you don't know yet. Don't make it ridiculous, like people stacked up like piles of wood in the passenger section (unless that's really how you're shipping them). Or don't have nothing but weapons and no power or anything else.)
4. Mass, volume, breakdown
+Consider that in modern US naval vessels, ships overall mass/volume breaks down like this:
40-45 percent Structure (presumably including armor)
20-25 percent Power Plant
15-30 percent Auxiliary machinery and equipment
6-14 percent Weapons systems
+Now, for a spaceship, this won't exactly be the same. Spaceships don't need a certain amount of seaworthy, curved hull and superstructure coming out of only one side. A whole spaceship could be "superstructure." Or it could be a tin can of a thin coating, leaving much more room for power, weapons, fuel, cargo or whatever. Think about the needs of your ship.
For my light frigate, I decide that it will have a thin but sturdy 500 mm outer hull, with even thinner but solidly built 100mm decks. That's actually quite a bit. Here's how I calculate the VOLUME of the outer hull- subtraction.
Dimensions of rectangular light frigate, including armor/outer hull: 20m x 20m x 60m = 24,000 m^3
Dimensions of rectangular light frigate, minus outer hull width: 19 x 19 x 59 = 21299
Subtract and get 2701 cubic meters of hull/armor material.
+Now why is this useful? Because we're going to decide what that hull material is, and how heavy it is, and how much it costs! You'll quickly find that building a ship out of silver will be cost prohibitive, so it's good and adds the nice touch of realism if cost of that fancy-shmancy hull of yours proves to be a limit.
5. Hull and armor
+Looking up some materials, I find that titanium-aluminum alloy takes up 4.9 tonnes for every cubic meter. Not bad, says I, nice and thick and that's what the ladies like. SO, for the light frigate's hull and armor, using titanium alloy will require 13,234.9 tons of the stuff! That's just for the armor!
+In comparison, modern naval destroyers tend to range in total mass from 8 to 16 thousand (or so) tons displacement. But, this will be a lot thicker armored than a modern naval destroyer, that's for sure. (You can get into the various qualities of armor and energy effects and such, I'm not going to right here. Except to remember that you'll want a mixture of ceramic and metals for two main types of attacks. Basically.)
6. Decks
+Now I'm imagining the decks like giant single plates laid on top of one another somehow. I said the decks would be 100mm each. Looking at the 60 meter length (or 'height' if you look at it like a tower) hull, minus the outer armor 59 meter, and with an average of 3 meters between decks that's 19.6 decks maximum-- that would assume zero thickness decks, however. So let's assume more like 16 decks, that's 1.6 meters total. And the decks would be 19 x 19 wide, so for deck material volume we have 577.6 cubic meters!
+Looking up some materials again, I find that ordinary rolled steel has 7.85 tons per cubic meter. So that's 4534.16 tons of steel for the decks. You can repeat this for the 'walls' if you like, but I'm not going to-- there's a limit to how much work I'm gonna do, hey.
+So, we have 17769.06 tons of mass just for the outer armor and the deck floors. I'm going to guess about 3000 more tons for other parts of the structure for a total of 20769.06 tons. That's the ship's weight-- assuming no atmosphere, crew, weapons, equipment, fuel, engine, cargo, ammunition, power plant. You'll have to add these things yourself.
7. Engines are a big subject which I'll go into more later. But most of them require fuel. Many use hydrogen as a propellant because it is cheap and abundant and efficient, although it's not very dense in gas or liquid form and requires lots of volume. In every engine, you'll find some sort of trade-off-- there is no absolutely perfect engine for all things, and if you have one in your story universe, you're being boring. Perfection is boring. Anyway, the trade off is usually between performance and efficiency; that is acceleration, thrust, exhaust type and signature, etc, and how many miles it gets to the gallon. The best engines are good in both categories, but not usually as good as the ones that specialize.
8. Putting it together, kinda.
+So keep in mind fuel, cargo, weapons. You can go for the whole thing. For example, I use 2nd Generation Santa Barbaran modules and I decide on having:
Engines - 10 x dense plasma focus systems, 100 cubic meters and 40 tons total.
Power - 1 x advanced fission plant, 5000 cubic meters, 1200 tons total.
Hull/Armor - titanium-alloy, 2701 cubic meters, 13,234.9 tons total.
+Remembering that the total volume of the design we sketched is 24,000 cubic meters. This means we have 16199 cubic meters more to work with. Fuel seems important if we want to move. However, I don't want to get into ISP, kilograms of propellant per newton of thrust and all that. I'm willing to fudge a little, as long as I have a reasonable figure devoted to fuel. Otherwise I'm not really going to get into rocket physics, hey.
+But I remember that hydrogen is 70 kilograms per cubic meter (stored as a gas, which is what I'll do here just for simplicity's sake). Also coming to the arbitrary figure that about half the ship can be engines and fuel (sounds good, no? I mean it's a spaceship engine, not a rowboat motor, dammit!), so figure on 1000 tons (1000000 kilograms) of fuel. That's 14285.7 cubic meters of space. That's almost everything left on the ship!
+Okay, well let's go with it just to make it challenging. Another route could be to require less fuel, or have a more dense fuel (I use this, but I have a very particular method of storage which I won't go into here). But going with it, we find we have 1913.3 cubic meters of space left.
+Let's see, if we devote that to just crew living space (at the NASA suggested limit, which is probably too small and cramped), that's enough for about 112 crew members. Of course, they would require life support systems, waste management, weapons, consoles, equipment, etc etc. Let's go with a very low crew (it's a light frigate after all) of 20. We'll give them cramped quarters, and have 340 cubic meters more gone.
+Now for weapons, I go back to my 2nd Generation modules again and pick out a St George Heavy Neutral Particle Beam Weapon, designed by Whispering Voices. I can really only have one, because the power plant provides 2.3 gigawatts, and the St. George requires 1.42 GW of power when operating. The volume is pretty minimal as it's just a long particle accelerator. It weighs 23.64 tons overall and requires 13 crew to keep operational (though of course only one or less to 'shoot' it). (Overall, a powerful weapon for a ship this size, since firing it takes up most of it's power (possibly giving power problems for general electricity or propulsion during firing) and the St George happens to be 80 meters long, running from the very back to 20 meters extended in front of the Light Frigate.)
+Then I assume the rest of the volume and mass goes to various equipment, sensors, etc.
(And, because I've chosen a beam weapon I don't have to figure out ammunition, ammunition firing rates and costs of ammunition, all of which are things I do have to deal with in my other ships. (And a major pain I say!))
So in the end, it appears we have:
Engines - 10 x DPF systems, 100 cubic meters and 40 tons total
Power - 1 x advanced fission plant, 5000 cubic meters, 1200 tons total
Hull/Armor - titanium alloy, 2701 cubic meters, 13,234.9 tons total
Fuel - 14,285.7 cubic meters hydrogen propellant, 1000 tons total
Crew - 20 crew, 340 cubic meters living space
Weapons - 1 x St George Heavy NPBW, 23.64 tons total
Everything else: 1573.3 cubic meters
+Giving a total of 24,000 cubic meters.
Now, using the known mass, that's a total of 15498.54 tons. Sounds about right, however that would assume "everything else" has no mass. For "everything else" I assume an AVERAGE density of 1.5 tons per cubic meter, meaning the equipment and stuff as well as the vacant air and such. That's 2359.95 tons more.
+Total mass of ship with fuel: 17858.49 tons.
9. Performance
Okay, so now we know the size and weight of the Light Frigate. We also know how many crew it has, and how dense and thick the armor is, and even how likely it is that you could shoot a pistol round through the floor (not bloody likely). What else is there to know?
+Acceleration. The formula is, Acceleration is equal to Force divided by Mass. We already know the Mass, and we know we want to accelerate at at least 10 meters per second per second (1 g) so we can escape Earth's velocity, and no more than 120 meters per second per second (since we have no anti-squashing technology). And, because of the 2nd Generation Santa Barbaran module tables, we know how much the DPF engines can give in terms of maximum thrust. Each one gives 400,000,000 Newtons of Thrust (better even than a chemical rocket, and way more efficient.) With ten of them, that's 4,000,000,000 N. Plug it into the formula, uh oh Algebra!
A=4000000000/17858490
That's 223.98 meters/second/second of acceleration, or 22.4 g. That's more than we can use, however in low-thrust, high efficiency it will be more acceptable. (Nice thing about those DPFs!)
+In all this, I neglected one important thing: THRUSTERS. It's easy to forget these. You need a bunch, and they can't be 'neglible' because they have to be able to, if your ship is a combat vessel, rotate the whole thing around quickly, and so they need lots of thrust. But they also need high efficiency since they'll be operating almost all the time. And, they'll probably use fuel too. As it is, the Light Frigate has only thrust vectoring to rely on, and I suppose ion engines. So it has pretty crappy maneuverability, unless I want to spread the engines around and have each one act like a thruster/engine. That means recalculating everything, so I don't!
+I'm sure you won't neglect to find out what your weapons are like. For example, the St George NPBW has a 90 second recharge. Because it's not a laser or any other form of light, it travels at slower speeds and so has a relatively short range. Also, the particles will not work well in atmosphere, but that's okay since the Light Frigate is shaped like a brick anyway. You might also want to figure out things like Rate of Fire (especially with missiles and projectile weapons), range, etc.
10. Cost
+Wait, you thought it was all free? Of course not! I of course have my materials charts and my 2nd Generation Modules charts, which have all the costs of everything too. But if you don't have them, and you don't, here's some starting points when calculating costs.
Modern aircraft cost about $2640 per kilogram to construct.
Modern armored vehicles, $55 per kilogram
Modern ships, $154 per kilogram
Conventional modern ammunition, $8500 per ton
Missile munitions, $600,000 per ton
Modern jet/tank fuel, about $1000 per ton
Rolled steel, $2450 per ton
Titanium aluminum alloy, $102,000 per ton
Tungsten, $97,000 per ton
+For my general war and material and ship design costs, I assume raw materials (especially things like uranium and other exotic materials) costs come down, and that finished products costs go up. This is because mining and transportation efficiency has gotten better, and because cutting edge gear such as spaceships and military technology is only going to get more complicated and costly. For example, aircraft costs have been increasing FOUR times every TEN years, for the past 80 years.
So I calculate the construction of the Light Frigate.
Engines - 10 x DPF systems = $18 billion
Power - 1 x advanced fission plant = $0.9 billion
Hull/Armor - titanium alloy 13,234.9 tons = $1.35 billion
Weapons - 1 x St George Heavy NPBW = $1.2 billion
Total of $21.45 billion.
+However, I figure that the construction company, launching, all the miscellaneous gear (and very expensive gear, like sensors, computers, fire control, etc etc etc), and the price the maker stacks on to make a profit in this thing, will all add another 50 percent. For more efficient construction (let's say you produce it yourself, eliminating the middle man cost) you can change that to maybe 25 percent. For more lavish sensors (etc) stack on more than 50 percent as you see fit.
My total construction price for this will be: $32,175,000,000
+Then if you're really down with things, you'll have costs for fuel and supplies, full reloads of ammunition, annual operational cost (including the crew wages), etc. However I'm not going to go into all that, except to suggest an annual operating cost about 1/10th the construction cost of the ship. That means for me, a further 3.2 billion dollars will be taken from my annual military budget, to operate one more Light Frigate.
So our (my) finished Light Frigate is here:
Example Class Light Frigate
Length: 60 meters
Width: 20 meters
Height: 20 meters
Crew: 20 (7 Pilots/Officers, 13 Main Weapons techs)
Decks: 16
Combat Mass: 17858.49 tons
Armor/Hull: 500mm titanium alloy
Main Weapon: 1 x St George Heavy NPBW
Engines: 10 x DPF-400
Max Acceleration: 22 g
Max Acceleration, Crew Tolerated: 12 g
Replacement Cost: $32.175 billion
Annual Operating Cost: $3.2 billion
Formulas and Science and Stuff
THRUST:
Everything moves, and to move you produce thrust. Thrust is measured in Newtons, and is also for the purposes of my calculations Force. Force equals mass times acceleration. F=ma, A=F/m, M=F/a.
ACCELERATION:
Acceleration is how much velocity you change, over time. In short, it's how fast you get to 60 after stepping on the pedal, and how much whiplash your neck is going to suffer as a result. In the case of combat spaceships, too much acceleration turns your body into jelly. Acceleration equals force divided by mass.
1 Newton propels 1 Kilogram of mass at an Acceleration of 1 m/s/s.
ISP and EFFICIENCY:
Without getting into rocket science, of which I know nothing, ISP is a measure of how many seconds one kilogram of fuel produces one newton of thrust. In short, it's efficiency. A high ISP means good gas mileage, low ISP means bad gas mileage. For example, a chemical rocket has a really high thrust (producing a lot of acceleration) but a low efficiency (with just a few hundred seconds ISP). On the other hand, ion engines have really high efficiency (as much as 40,000 I think) but terrible rate of acceleration (a thrust-to-weight ratio much less than one. Don't even THINK about having high performance ion engines, there's a physical limit to how much thrust ions can produce!)
DENSITY equals MASS divided by VOLUME.
MASS equals DENSITY times VOLUME.
VOLUME equals MASS divided by DENSITY
These are useful if you happen to know the volume (or can reasonably guess the volume) requirements or availability of something, and know the density of a material and want to find the mass, etc.
VOLUME:
Don't forget, geometry is your friend. A sphere's volume is 4 pi times the radius squared. A cuboid or rectangular is the length times width times height. A cylinder is pi times the height times radius squared. Etc.
SI UNITS:
Obviously I use meters, kilometers, kilograms and metric tons, newtons, joules, seconds, etc. Here's some reference points:
Speed of sound in air: 340 m/s
Speed of light in vacuum: 299,790 km/s
CONVERSIONS:
1 meter = 3.2808 feet
1 kilometer = 0.6214 miles
1 square kilometer = 247.0983 acres
1 kilogram = 2.2046 pounds
1 megaWatt = 1341.0219 horsepower
1 Joule = N x m
1 Joule = 1 kg*(m^2/s^2)
1 mJ/s = 1 mW
ENERGY AND STUFF:
Kinetic Energy is the energy of an object in motion. Technically, any weapon involving an object in motion slamming into a target (or indirectly slamming shrapnel/fragments into a target) is a "kinetic weapon." The damage is done by imparting energy and heat to the target. It takes certain amounts of heat and/or energy to destroy/penetrate/vaporize various types of armor materials. It's good to figure out these things if you really want to know for sure how much energy a weapon will roughly have to deal to defeat your armor.
Kinetic Energy = 1/2 (mass)(velocity)(velocity)
KE=1/2 (m[v^2])
Kinetic Energy of a .44 calibre, 15.55g bullet fired at 426 m/s: 1410 Joules (1.41 kilojoules)
1 "Megaton" of energy (1,000,000 tons TNT): 4,186,800,000,000,000 Joules (4.1868 petajoules, or 4,186,800,000 megajoules)
US current annual energy consumption: 100,000,000,000,000,000,000 Joules (100 exajoules, or 100,000 petajoules)
Some Tips And Stuff
Alright, if you're still reading this after all this I'm very impressed. Good work, I hope you learned something. Maybe you learned that you'd rather just by a generic cardboard Enterprise/Star Destroyer/Whatever. Maybe you learned something about building imaginary spacecrafts. I hope so, because that's a really useful tool in life!
+Notes on tech: Obviously, if you go much beyond plausible, foreseeable future reality and start inventing scientific principles left and right, you will not be limited by such things as thrust or acceleration or fuel.
But try to balance things out by making sure your ultra-uber tech is not cheaper than shit (by mass OR volume!). FTL engine? Fine, but just make sure it doesn't let your ship travel ANYWHERE, INSTANTLY, ALWAYS. Make sure it costs a pretty penny (it IS a highly advanced piece of machinery, no? So why price it like a refrigerator?) and make sure you can't make more than your economy and budget can spare.
Magic energy shields? Okay, but they better not make the ship invincible in combat, and they better have some sort of clearly defined limits (recharge time, cost, whatever).
Plasma bolts? Okay, explain to me how you can make a bunch of highly energized plasma hold together, stay hot, AND be launched gun-like. Or maybe you don't have them in bolts, but just spray plasma out over a very short distance. More plausible, that.
Railguns? Fine, but I hope you bring along spare rails-- the plasma and friction wears railguns out VERY quickly. There is no known way to make large railguns (linear electromagnetic accelerators) that fire large projectiles very fast without destroying themselves in the process. Coilguns are more plausible as a weapon.
+Of course it vastly helps if you know the mass, crew requirements, power requirements, dimensions etc of your various weapons, ammunition, etc. It also helps if you can find densities and material properties of various types of steel and armor and whatever. When making up numbers, as you inevitably have to do, try not to go overboard and invent "ubermaterials" that can withstand the Universe exploding, or evade any kind of detection.
+While on the subject of detection, there are literally dozens of different methods, TODAY, of detecting objects and energy and everything else in space. As time goes on, we will have even more ways (neutrino detectors, anyone?). While it's possible you may develop ways to reduce emissions and be less detectable, it's not very believable that you can find a way to technologically defeat ALL detection methods and have 'stealth' ships all the time. Invisible ships, much like invulnerable ones, tend to be a no-no 'round these parts.
+Notes on Magic Things: I find things get boring very quickly when EVERYONES tech comes from ass-space and no attention is paid to reality at all. Almost as boring as people who like to play that way, find the 'hard sci fi' approach! So, I think like everything a balance is required. I myself make most of my technology a LITTLE more efficient and advanced overall, using basically known-things, with 2 or 3 "black boxes" that I can't explain whatsoever. For example, I use electromagnetic weapons, magnetically confined fusion electric power, and alloys of known materials. But I also have Menelmacari gravitics here and there-- it is very expensive and limited in uses. I have a Quantum Computer running amok sometimes. I am not slavishly "hard sci fi," I just like working within the limits and boundaries of the genre. In the end, I think if it makes sense to the RP, can be explained in character, and is believable to the people you are playing with and the people reading, then go for it.
+Notes on the Budget: Remember, no matter what your military budget is, you CAN'T simply divide the total budget by the price of a particular weapon or spaceship to see how many you can afford. I have a guide around to doing the military budget, but the end result is you will probably have less than 1 percent of your annual military budget to use on things like buying vessels. And I doubt you can spend more than 10 percent of your annual military budget operating your existing vessels. Remember these things, because mis-doing the military budget is one of the easiest and most common ways to accidentally godmod! If you're unsure of how much you spend, save your UN Defense Rankings and let me know, and I'll see if I can help you figure it out.